arcee-ai/nuclear_patents · Datasets at Hugging Face

patent_number stringlengths 0 9	section stringclasses 4 values	raw_text stringlengths 0 954k
	abstract	Systems for x-ray diffraction/scattering measurements having greater x-ray flux and x-ray flux density are disclosed. These are useful for applications such as material structural analysis and crystallography. The higher flux is achieved by using designs for x-ray targets comprising a number of microstructures of one or more selected x-ray generating materials fabricated in close thermal contact with a substrate having high thermal conductivity. This allows for bombardment of the targets with higher electron density or higher energy electrons, which leads to greater x-ray flux. The high brightness/high flux source may then be coupled to an x-ray reflecting optical system, which can focus the high flux x-rays to a spots that can be as small as one micron, leading to high flux density, and used to illuminate materials for the analysis based on their scattering/diffractive effects.
	claims	1. An ion thruster comprising:a source of deuterium-containing fuel material disposed on an asteroid surface;a reaction volume directed upward from the asteroid surface and open at the top;a flue coupled to the source and reaction volume for dispersing fuel material into the reaction volume;a set of turbines arranged around the reaction volume, wherein the set of turbines are directly exposed to the dispersed fuel material in the reaction volume a set of electrical generators coupled to the respective set of turbines to convert mechanical motion of the set of turbines into electricity; andan ion thrust engine powered by the generated electricity for producing thrust in a specified direction. 2. The generator as in claim 1, wherein the reaction volume is a cylinder with an opening at an upper end. 3. The generator as in claim 1, wherein the turbines are arranged radially around the circumference of the cylinder reaction volume. 4. The generator as in claim 1, wherein turbines are stacked vertically in multiple layers along a length of the cylinder reaction volume. 5. The generator as in claim 1, wherein one or more fans are provided in the reaction volume to maintain the dispersed fuel material in suspension within the reaction volume. 6. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material comprises Li6D. 7. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material comprises D2O. 8. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material comprises D2. 9. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material is in solid powder form. 10. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material is in pellet form. 11. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material is in frozen form. 12. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material is in liquid droplet form. 13. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material also contains up to 20% by weight of added particles of fine sand or dust.
	description	The present application is related to and claims priority to and the benefit of a Korean Patent Application No. 10-2017-0012211 filed on Jan. 25, 2017, the disclosure of which is incorporated herein by reference in its entirety. The present disclosure relates to an X-ray imaging apparatus and control method thereof. X-ray imaging apparatuses are devices for allowing the user to see an internal structure of a subject by irradiating X-rays to the subject and analyzing X-rays that have passed through the subject. X-ray transmittance is different depending on the tissue of a subject, so the internal structure of the subject may be imaged using an attenuation coefficient quantified from the X-ray transmittance. A condition for X-ray irradiation used in X-raying is an important factor in determining X-ray image quality and amount of radiation exposure. Accordingly, it is important to provide proper information about the X-ray irradiation condition for the user, such as a radiological technologist, a doctor, etc. To address the above-discussed deficiencies, it is a primary object to provide an X-ray imaging apparatus and control method thereof, for guiding the user to intuitively recognize an actual dose of X-rays and select a proper dose, ultimately a condition for low dose of X-ray irradiation by providing the user with information about an actual X-ray dose to which an X-ray filter effect is reflected. In accordance with an aspect of the disclosure, an X-ray imaging apparatus comprises: an X-ray source configured to generate and irradiate X-rays according to an X-ray irradiation condition including at least one of a tube voltage, a tube current, exposure time, or a filter; a display configured to provide a graphic user interface to receive a choice about the X-ray irradiation condition; and a controller configured to obtain a parameter that represents a dose of radiation, to which an influence of the filter is reflected, based on the selected X-ray irradiation condition and control the display to display the parameter. The parameter that represents a dose of radiation to which an influence of the filter is reflected may comprise at least one of an amount of tube current corresponding to X-rays that have transmitted the filter, a dose of X-rays that have transmitted the filter, or a ratio of a dose of X-rays that have not transmitted the filter and a dose of X-rays that have transmitted the filter. The display may be configured to display the parameter in a numerical value, or a diagram or image representing the numerical value. The X-ray imaging apparatus may further comprise a storage configured to store relationships between dose per amount of tube current (mAs) and tube voltage by differing types or thickness of the filter. The controller may be configured to search the storage for a dose per amount of tube current corresponding to the selected X-ray irradiation condition, when the choice of the X-ray irradiation condition is input. The controller may be configured to additionally search for a dose per amount of tube current corresponding to an occasion when no filter is used in the selected X-ray irradiation condition. The controller may be configured to obtain a ratio of a dose of X-rays that have not transmitted the filter and a dose of X-rays that have transmitted the filter, based on a dose per amount of tube current corresponding to the selected X-ray irradiation condition and a dose per amount of tube current corresponding to an occasion when the filter is not used in the selected X-ray irradiation condition. The controller may be configured to obtain an amount of tube current corresponding to X-rays that have transmitted the filter based on the obtained ratio and the amount of tube current included in the selected X-ray irradiation condition. The controller may be configured to obtain a dose of X-rays that have transmitted the filter based on a dose per amount of tube current corresponding to the selected X-ray irradiation condition and an amount of tube current included in the selected X-ray irradiation condition. The controller may be configured to when at least one of an imaging protocol or a size of a subject is selected, control the display to display a basic X-ray irradiation condition corresponding to the selected at least one of the imaging protocol or the size of the subject. The controller may be configured to obtain a parameter that represents a dose to which an influence of the filter is reflected based on the basic X-ray irradiation condition. The controller may be configured to re-obtain a parameter that represents a dose of radiation, to which an influence of the filter is reflected, whenever a choice of the X-ray irradiation condition is changed, and control the display to display the parameter. In accordance with an aspect of the disclosure, a control method of an X-ray imaging apparatus, the method comprising: providing a graphic user interface configured to receive a choice of an X-ray irradiation condition including at least one of a tube voltage, a tube current, exposure time, or a filter; obtaining a parameter that represents a dose to which an influence of the filter is reflected based on the selected X-ray irradiation condition; and displaying the obtained parameter on a display. The parameter that represents a dose of radiation to which an influence of the filter is reflected may comprise at least one of an amount of tube current corresponding to X-rays that have transmitted the filter, a dose of X-rays that have transmitted the filter, or a ratio of a dose of X-rays that have not transmitted the filter and a dose of X-rays that have transmitted the filter. The displaying of the obtained parameter on a display may comprise displaying the parameter in a numerical value, or a diagram or image representing the numerical value. The method may further comprise storing relationships between dose per amount of tube current (mAs) and tube voltage by differing types or thickness of the filter in a storage. The obtaining of a parameter that represents a dose to which an influence of the filter is reflected may comprise searching the storage for a dose per amount of tube current corresponding to the selected X-ray irradiation condition, when the choice of the X-ray irradiation condition is input. The obtaining of a parameter that represents a dose to which an influence of the filter is reflected may comprise searching for a dose per amount of tube current corresponding to an occasion when no filter is used in the selected X-ray irradiation condition. The obtaining of a parameter that represents a dose to which an influence of the filter is reflected may comprise obtaining a ratio of a dose of X-rays that have not transmitted the filter and a dose of X-rays that have transmitted the filter, based on a dose per amount of tube current corresponding to the selected X-ray irradiation condition and a dose per amount of tube current corresponding to an occasion when the filter is not used in the selected X-ray irradiation condition. The obtaining of a parameter that represents a dose to which an influence of the filter is reflected may comprise obtaining an amount of tube current corresponding to X-rays that have transmitted the filter based on the obtained ratio and the amount of tube current included in the selected X-ray irradiation condition. Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. FIGS. 1 through 21, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device. Embodiments and features as described and illustrated in the present disclosure are only preferred examples, and various modifications thereof may also fall within the scope of the disclosure. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present disclosure. It will be understood that, although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. It is to be understood that the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Furthermore, the terms, such as “˜ part”, “˜ block”, “˜ member”, “˜ module”, etc., may refer to a unit of handling at least one function or operation. For example, the terms may refer to at least one process handled by hardware such as field-programmable gate array (FPGA)/application specific integrated circuit (ASIC), etc., software stored in a memory, or at least one processor. Reference numerals used for method steps are just used for convenience of explanation, but not to limit an order of the steps. Thus, unless the context clearly dictates otherwise, the written order may be practiced otherwise. Embodiments of the present disclosure will now be described with reference to accompanying drawings. Throughout the drawings, like reference numerals may refer to like parts or components. FIG. 1 illustrates a control block diagram of an X-ray imaging apparatus, according to an embodiment of the present disclosure, FIG. 2 illustrates an external view illustrating a configuration of X-ray imaging apparatus, according to an embodiment of the present disclosure, and FIG. 3 illustrates an exterior view of a sub-display device equipped in an X-ray source. FIG. 2 shows an example of an X-ray imaging apparatus, which is a ceiling type X-ray imaging apparatus with an X-ray source attached to the ceiling of an examination room. Referring to FIG. 1, an X-ray imaging apparatus 100 in accordance with an embodiment may include an X-ray source 110 for generating and irradiating X-rays, a display 150 for displaying a screen e.g., to set an X-ray irradiation condition, an input 160 for receiving control commands including a command to set an X-ray irradiation condition from the user, a storage 170 for storing e.g., information about an X-ray irradiation condition, and a controller 140 for controlling overall operation of the X-ray imaging apparatus 100. The X-ray imaging apparatus 100 may further include a communication device 130 for communicating with an external device. The controller 140 may control X-ray irradiation timing, X-ray irradiation conditions, and the like, of the X-ray source 110 according to a command entered by the user, and create an X-ray image using data received from an X-ray detector 200 (see FIG. 2). The controller 140 may also control a position or posture of an install portion 14, 24 in which the X-ray source 110 or the X-ray detector 200 is installed, according to an X-raying protocol and a position of a subject 1. The controller 140 may compute a parameter that represents a dose of radiation to which an influence of a filter is reflected based on a selected X-ray irradiation condition, and control the display 150 to display the parameter. The parameter that represents a dose to which an influence of a filter is reflected may include at least one of an amount of tube current corresponding to X-rays that have transmitted the filter, a dose of X-rays that have transmitted the filter, and a ratio of a dose of X-rays that have not transmitted the filter and a dose of X-rays that have transmitted the filter. The controller 140 may include a memory for storing a program for carrying out the aforementioned operations and the following operations, and a processor for executing the program. The controller 140 may include a single processor or multiple processors, and in the latter case, the multiple processors may be integrated in a single chip or may be physically separated. When the controller 140 includes the multiple processors and multiple memories, some of the multiple processors and memories may be included in a workstation 180 (see FIG. 2), and some others in a sub-display 80 (see FIG. 2), a moving carriage 40 (see FIG. 2), or other device. For example, the processor(s) included in the workstation 180 may perform control, such as image processing to create an X-ray image, and the processor(s) included in the sub-display 80 or the moving carriage 40 may perform control over the movement of the X-ray source 110 or the X-ray detector 200. The X-ray imaging apparatus 100 may be connected to an external device (e.g., an external server 310, another medical device 320, and a portable terminal 330, such as a smart phone, a tablet Personal Computer (PC), a wearable device, and the like) through the communication device 130 for exchanging data. The communication device 130 may include one or more components that enable communication with an external device, for example, at least one of a short-range communication module, a wired communication module, and a wireless communication module. The communication module 130 may further include an internal communication module to enable communication between components of the X-ray imaging apparatus 100. The communication device 130 may also receive a control signal from the external device and forward the control signal for the controller 140 to control the X-ray imaging apparatus 100 according to the control signal. Furthermore, the controller 140 may control an external device with a control signal of the controller 140 by sending the control signal to the external device through the communication device 130. For example, the external device may process data of its own according to the control signal received from the controller 140 through the communication device 130. The external device may have a program to control the X-ray imaging apparatus 100, and the program may include instructions to control some or the entire operation of the controller 140. In the portable terminal 330, the program may be installed in advance or by being downloaded by the user from a server that provides applications. The server that provides applications may include a recording medium that stores the program. Referring to FIG. 2, a guide rail 30 may be installed on the ceiling of the examination room where the X-ray imaging apparatus 100 is placed, and the X-ray source 110 linked to a moving carriage 40 that moves along the guide rail 30 may be moved to a position corresponding to the subject 1, and the moving carriage 40 and the X-ray source 110 may be linked through a foldable post frame 50 to adjust the altitude of the X-ray source 110 from the ground. The X-ray source 110 may be moved automatically or manually. In the former case, the X-ray imaging apparatus 100 may further include a driver, such as a motor to provide power to move the X-ray source 110. The workstation 180 may be provided in the space separated by a blackout curtain B from the space where the X-ray source 110 is placed. The workstation 180 may be equipped with an input 182 for receiving commands from the user and a display 181 for displaying information. The input 182 may receive commands to control an imaging protocol, select an X-ray irradiation condition or X-ray irradiation timing, control a position of the X-ray source 110, and the like. The input 182 may include a keyboard, a mouse, a touch screen, a voice recognizer, and so forth. The display 181 may display screens representing an image for guiding input of the user, an X-ray image, and/or a state of the X-ray imaging apparatus 100. In the meantime, the display 150 and the input 160 as described in connection with FIG. 1 may be implemented as the display 181 and the input 182 provided in the workstation 180, or as sub-display 81 and a sub-input 82 provided in the sub-display 80, or a display and an input provided in the portable terminal 330, such as a tablet PC or a smart phone. The X-ray detector 200 may be implemented as a fixed type of X-ray detector fixed on a stand 20 or a table 10, or may detachably equipped in the install portion 14, 24. Alternatively, the X-ray detector 300 may be implemented as a portable X-ray detector available at any place. The portable X-ray detector may further be classified into a wired type or a wireless type depending on the data transfer method or the power supplying method. The X-ray detector 200 may also be moved automatically or manually. In the former case, the X-ray imaging apparatus 100 may further include a driver, such as a motor to provide power to move the install portion 14, 24. The X-ray detector 200 may or may not be included as an element of the X-ray imaging apparatus 100. In the latter case, the X-ray detector 200 may be registered in the X-ray imaging apparatus 100 by the user. In both cases, the X-ray detector 200 may be connected to the controller 140 through the communication device 130 for receiving a control signal or sending image data. The sub-display 80 may be arranged on one side of the X-ray source 110 to provide information for the user and receive a command from the user, and may perform a part or all of the functions performed by the input 182 and the display 181 of the workstation 180. If all or part of the components of the controller 140 and the communication device 130 are provided separately from the workstation 180, they may be included in the sub-display 80 arranged on the X-ray source 110. The user may input various kinds of information or commands relating to X-raying in a way of manipulating the sub-input 82 or touching the sub-display 81 as shown in FIG. 3. For example, the user may input a position to be moved by the X-ray source 110 through the sub-input 82 or the sub-display 81. While FIG. 2 illustrates a fixed type of X-ray imaging apparatus attached onto the ceiling of an examination room, the X-ray imaging apparatus 100 may include any of different types of X-ray imaging apparatus, such as a C-arm type of X-ray imaging apparatus, a mobile X-ray imaging apparatus, and the like, within the scope of the present disclosure obvious to ordinary people in the art. The X-ray source 110 may be equipped with an X-ray tube for generating X-rays and a collimator for adjusting an irradiation range of X-rays generated by the X-ray tube. The X-ray source 110 may also be called a tube head unit (THU) because X-ray source 110 includes an X-ray tube. This will be explained in detail below. FIG. 4 is a side cross-sectional view schematically illustrating a structure of an X-ray tube included in an X-ray source. The X-ray source 110 may include an X-ray tube 111 as shown in FIG. 4. The X-ray tube 111 may be implemented by a 2-pole vacuum tube with positive and negative electrodes. For example, thermions may be generated by making the inside of a glass tube 111a in a high vacuum state and heating a filament 111h of a negative electrode 111e to a high temperature. The negative electrode 111e may include the filament 111h and a focusing electrode 111g that focuses electrons, the focusing electrode 111g also called a focusing cup. When a high voltage is applied across the positive electrode 111b and the negative electrode 111e, thermions get accelerated and collide with a target material 111d of the positive electrode 111b, thus producing X-rays. The target material 111d of the positive electrode 111b may include a high resistive material, such as Cr, Fe, Co, Ni, W, Mo, or the like. The X-ray produced in this way is irradiated out through a window 111i, and the window 111i may use, for example, a thin film of Beryllium (Be). The voltage applied across the positive and negative electrodes 111b and 111e is called a tube voltage, the magnitude of which may be represented in kilovolt peak (kVp). As the tube voltage increases, the speed of the thermion increases and as a result, energy of X-rays (energy of photons) produced from collision of the thermion with the target material increases. The X-ray source 110 may irradiate X-rays with a certain energy band. The energy band of the irradiated X-rays may be defined by upper and lower limits, and the energy of the X-rays may be represented by average energy, highest energy, energy band, and the like. A filter 112 may be arranged in a direction, toward which X-rays are irradiated, to control the X-ray energy. For this, with the filter 112 arranged on the front or back side of the window 111i for filtering X-rays in a particular energy band, the X-rays of the particular energy band may be filtered. The filter 112 may be called an additional filter. The upper limit of the energy band, namely, a maximum energy of X-rays to be irradiated may be controlled by the level of the tube voltage, and the lower limit of the energy band, namely, a minimum energy of X-rays to be irradiated may be controlled by the filter. Filtering X-rays of a low energy band by means of the filter 112 may increase the average energy of X-rays to be irradiated. For example, with the filter 112 made of aluminum or copper to filter X-rays of a low energy band which degrade the image quality, the X-ray beam quality may be hardened, thereby increasing the lower limit of the energy band. Accordingly, an average energy level of X-rays to be irradiated increases. Furthermore, filtering X-rays of a particular energy band by means of the filter 112 may decrease a dose of radiation exposure of a subject. A current flowing through the X-ray tube 111 is called a tube current, which may be represented by an average value (mA), or represented by an amount of the tube current (mAs), which is a tube current (mA) for an X-ray exposure time (s). As the tube current increases, the dose of X-rays (the number of X-ray photons) increases. Accordingly, the X-ray energy may be controlled by the tube voltage, and the dose of X-rays may be controlled by the tube current and the X-ray exposure time, i.e., the amount of tube current. FIG. 5 shows a configuration of a collimator, and FIG. 6 is a side cross-sectional view of blades cut along AA′. Referring to FIG. 5, the collimator 113 may include at least one movable blade 113a, 113b, 113c, and 113d, and the blades 113a, 113b, 113c, and 113d may be made of a material with high bandgap to absorb X-rays. An X-ray irradiation range may be adjusted as the blades 113a, 113b, 113c, and 113d move, and the collimator 113 may further include a motor to provide power to the respective blades. The controller 140 calculates an extent of movement of each blade 113a, 113b, 113c, 113d corresponding to a set X-ray irradiation range, and sends the collimator 113 a control signal to move the blade 113a, 113b, 113c, 113d as far as the calculated extent of movement. For example, the collimator 113 may include four blades 113a, 113b, 113c, and 113d, each of which has the form of a flat plate. The first blade 113a and the third blade 113c may be movable in both directions along the X-axis, and the second blade 113b and four blade 113d may be movable in both directions along the Y-axis. Furthermore, each of the four blades 113a, 113b, 113c, and 113d may be moved individually, or the first blade 113a and the third blade 113c may be moved as one set and the second blade 113b and the fourth blade 113d may be moved as another set. X-rays may be irradiated through a slot R formed by the four blades, and collimation may be performed by passing the X-rays through the slot R. In this embodiment, the slot R refers to a collimation range, and the X-ray irradiation range refers to an area in which X-rays that have passed the collimation range R are incident onto the subject 1 or the X-ray detector 200. Referring to FIG. 6, the collimator 113 is arranged in front of the X-ray tube 111. The front of the X-ray tube 111 corresponds to a direction in which the X-ray is irradiated. The filter 112 may be arranged between the blades 113a, 113b, 113c, and 113d and the X-ray tube 111. X-rays irradiated from a focusing point 2 of the X-ray tube 111 are irradiated into an irradiation range E limited by the collimator 113, and thus scattering is reduced. Some X-rays incident on the blade 113a, 113b, 113c, 113d among the X-rays irradiated from the X-ray tube 111 are absorbed by the blade, and some X-rays that have passed the collimation range R are incident on the X-ray detector 200. The following description will focus on an occasion when there is no subject. If X-rays spread like cone beams, the X-ray irradiation range E is wider than the collimation range R. The controller 140 may irradiate X-rays into a desired range of X-ray irradiation range E by adjusting the collimation range R based on a relationship between the two ranges. Although the previous example shows that the collimator 113 is equipped with four rectangular blades, it is only by way of example and there are no limitations on the number or shape of the blades included in the collimator 113. FIGS. 7 and 8 show an example of automatic exposure control (AEC) sensor to be used in an X-ray imaging apparatus, according to an embodiment of the present disclosure. The X-ray imaging apparatus 100 may perform AEC to prevent excessive exposure of the subject to radiation. For this, as shown in FIG. 7, the install portion 24 may have an AEC sensor module 26 to detect a dose of X-rays. This embodiment will be described using the install portion 24 of the stand 20, but the AEC sensor module 26 may also be provided in the install portion 14 of the table 10. The diagram of FIG. 7 shows the install portion 24 viewed from the front. The AEC sensor module 26 may be arranged inside the install portion 24, and may include a plurality of AEC sensors 26a, 26b, 26c for independently detecting a dose of X-rays. For example, each AEC sensor may be implemented as an ionization chamber. Although there are total of three AEC sensors, two of them arranged on an upper portion and one arranged on a lower portion, it is only an example and it is also possible to have more than or less than three AEC sensors in different positions. Referring to FIG. 8, the AEC sensor module 26 may be located in front of the X-ray detector 200. The front of the X-ray detector 200 corresponds to a direction in which the X-ray is incident. FIG. 8 is a side view of the AEC sensor module 26 arranged in front of the X-ray detector 200. When X-rays are incident on the AEC sensor, a current may be induced and the AEC sensor may send a signal corresponding to the current to the controller 140. The signal to be sent to the controller 140 may be amplified and digitally processed. The controller 140 may determine whether a current dose of the incident X-ray exceeds a threshold dose, based on the signal. If the dose of X-rays exceeds the threshold dose, a cut-off signal is sent to a high-voltage generator 101 that supplies a high voltage to the X-ray tube 111 to stop generation of the X-ray. A grid may be arranged on the front of the AEC sensor module 26 to prevent X-ray scattering. Some of the X-rays irradiated from the X-ray source 110 may collide with dust in the air or constituent materials of the subject and scatter away from an original path on the way to the X-ray detector 200. When incident on the X-ray detector 200, the scattered X-rays give a negative influence to the quality of X-ray images, such as degradation of contrast of the X-ray image. The grid may have a structure in which shielding materials, such as lead (Pb), which absorb X-rays, are arranged, and some of the irradiated X-rays that proceed in the original direction, that is, straightforward X-rays, may pass between the shielding materials and then be incident on the X-ray detector 200 while the scattered X-rays collide with the shielding materials and are absorbed. The shielding materials may be arranged linearly or in a cross structure. Alternatively, the shielding materials may be arranged in a focused form by being inclined to be similar to the X-ray irradiation direction, or may be arranged to be parallel. Although not shown, a driver including a motor to mechanically move the grid may be included inside the install portion 24. Accordingly, it is possible to control an angle or center position of the grid by sending a control signal to the driver from the outside. Although the AEC sensor module 26 is provided in the install portion 24 in this example, the AEC sensor module 26 may be integrated with the X-ray detector 200. FIG. 9 shows an example of a screen displayed on a display of an X-ray imaging apparatus, according to an embodiment of the present disclosure. Referring to FIG. 9, a setting window 151 to set an X-ray irradiation condition and a work list 155 may be displayed on the display 150. The work list 155 may include a study list 155a to select a study and a protocol list 155b to select an imaging protocol. The term ‘study’ as herein used may refer to a set of X-ray images related to each other. If a study is selected from among the study list 155a, the protocol list 155b to select an imaging protocol to be applied to the selected study is displayed. The X-raying region may vary by imaging protocol, and a suitable X-ray irradiation condition may vary by the X-raying region. The imaging protocol may be determined based on the X-raying portion, the posture of the subject, and the like. For example, the imaging protocol may include the whole body Anterior-Posterior (AP), the whole body Posterior-Anterior (PA), the whole body LAT. Even for the chest, there may be imaging protocols for capturing images in the AP, PA, LAT methods, and for long bones such as legs, there may be imaging protocols for capturing images in the AP, PA, LAT methods. Furthermore, Abdomen Erect may also be included in the imaging protocol. A graphic user interface may be displayed on the setting window 151 for the user to intuitively control the X-ray imaging apparatus 100. The graphic user interface may be used to receive a choice of an X-ray irradiation condition including at least one of a tube voltage, a tube current, exposure time, and a filter. The graphic user interface may include a plurality of graphic objects that may set various X-ray irradiation conditions. In this embodiment, all the objects, such as buttons, icons, and the like, displayed on the display 150 to provide information or used to receive the user's control command may be called graphic objects. The graphic objects may be implemented by buttons corresponding to the respective X-ray irradiation conditions to be used in receiving a command to set an X-ray irradiation condition from the user. For example, they may include a tube voltage set button 151a to receive a setting of a tube voltage (kVp), a tube current set button 151b to receive a setting of a tube current (mA), and a tube current amount set button 151c to receive an amount of tube current (mAs). The currently set tube voltage, tube current, and amount of tube current may be displayed on one side of the respective buttons. A currently set tube voltage may be displayed in a numerical value in a tube voltage display area 151aa on one side of the tube voltage set button 151a, and a currently set tube current may be displayed in a numerical value in a tube current display area 151bb on one side of the tube current set button 151b. A currently set amount of tube current may be displayed in a numerical value in a tube current amount display area 151cc on one side of the tube current amount set button 151c. The tube current amount set button 151c may actually be used in controlling X-ray exposure time (sec) unlike the tube current set button 151b. A currently set X-ray exposure time may also be displayed in the tube current amount display area 151cc. In some embodiments, instead of the tube current amount set button 151c, an X-ray exposure time set button may be provided separately. The user may select each button to set an X-ray irradiation condition to a desired value. The selection of a button may be made by clicking or touching depending on the type of the input 160. In some embodiments, the tube voltage set button 151a may include an extra button to increase or decrease the tube voltage. The tube current set button 151b may include an extra button to increase or decrease the tube current. The tube current amount set button 151c may include an extra button to increase or decrease the amount of tube current. Furthermore, an imaging position set button 151d to receive a setting of whether X-raying is performed on the stand 20 or on the table 10 or whether a portable X-ray detector is used, a patient size selection button 151e to receive a choice of a patient size, and a collimator set button 151f to receive setting of a size of the collimator may further be displayed. Moreover, an AEC selection button 151g to receive a choice of an AEC sensor, a sensitivity set button 151h to receive setting of sensitivity, a density set button 151i to receive setting of a density, a grid selection button 151j to receive a choice of a grid, a filter selection button 151k to receive a choice of a filter, and a focus selection button 151r to receive a choice of a focal size may further be displayed in the setting window 151. These buttons may be implemented in figures comprised of pictures, characters, symbols, etc., and the user may select a figure by moving the cursor to the figure and clicking it or touching the figure, and accordingly, an X-ray irradiation condition corresponding to the selected figure may be set. Meanwhile, once an imaging protocol is selected, the X-ray irradiation conditions, such as a tube voltage, a tube current, an amount of tube current, and so forth, which are basic conditions matched with the selected imaging protocol, may be displayed in the respective display areas 151aa, 151bb, 151cc. The storage 170 may match and store basic X-ray irradiation conditions for each imaging protocol. When an imaging protocol is selected, the controller 140 may search the storage 170 for basic X-ray irradiation conditions corresponding to the selected imaging protocol, and display the basic X-ray irradiation conditions in the respective display areas 151aa, 151bb, 151cc of the display 150. The user may refer to the X-ray irradiation conditions displayed in the respective display area 151aa, 151bb, 151cc and adjust them to proper numerical values taking into account the state or size of the subject by increasing or decreasing the numerical values. When a choice of a patient size is input, the X-ray irradiation conditions, such as a tube voltage, a tube current, an amount of tube current, and so forth, which are basic conditions matched with the selected size, may be displayed in the respective display areas 151aa, 151bb, 151cc. For this, the storage 170 may match and store basic X-ray irradiation conditions for each patient size, and the basic X-ray irradiation conditions matched with the patient size may be stored differently for each imaging protocol. When the user selects a patient size using the size selection button 151e, the controller 140 may search the storage 170 for basic X-ray irradiation conditions corresponding to the selected patient size, and display the basic X-ray irradiation conditions in the respective display areas 151aa, 151bb, 151cc of the display 150. Even in this case, as described above, the user may refer to the X-ray irradiation conditions displayed in the respective display areas 151aa, 151bb, 151cc and adjust them to proper numerical values taking into account the state or size of the subject by increasing or decreasing the numerical values. The aforementioned types or locations of the graphic objects displayed in the set window 151 are by way of example, and some of them may be omitted according to the designer's choice, and other graphic objects to change other settings may further be provided in an arrangement different from what is described above. The input 160 may include a button to receive a command to start X-raying. For example, the button to receive a command to start X-raying may be implemented in the form of a remote control or a switch, which is separate from the workstation 180. If the user inputs the command to start X-raying through the input 160 after setting the X-ray irradiation conditions through the setting window 151, X-raying is performed according to the set X-ray irradiation conditions. In performing the X-raying, an effort is made to reduce a dose of radiation exposed to the patient. For this, it is important for the user to accurately know of the dose of radiation exposed to the patient taking place in a case that X-raying is performed according to the currently set X-ray irradiation conditions. The conventional X-ray imaging apparatus provides no extra information about a dose of radiation except for the tube voltage, tube current, and amount of tube current. In that case, the user estimates a dose based on an amount of tube current (mAs). FIG. 10 shows a table representing radiation doses depending on X-ray irradiation conditions; Referring to FIG. 10, when the tube voltage is set to 80 kVp and the amount of tube current is set to 10.0 mAs, an actual dose is 0.72 mGy without the filter 112. When the tube voltage is increased to 83 kVp while the amount of tube current is decreased to 8.0 mAs, an actual dose is 0.62 mGy without the filter 112. Since the conventional X-ray imaging apparatus does not provide information about an actual dose of radiation, the user may not accurately know of the dose and in light of the fact that the second case has a 20 percent lower amount of tube current than that of the first case, may only assume that a dose would be reduced (however, that the dose would be reduced by less than 20% because the tube voltage increases a little bit). When the tube voltage is set to 76 kVp and the amount of tube current is set to 16.0 mAs, an actual does is 0.55 mGy when the filter 112 made of copper, which is about 0.1 mm thick, is used. In this case, the amount of tube current increases by about 60% as compared with the first case, and by 100% as compared with the second case, so the user may assume that a dose would increase as well. However, the dose in the third case is actually the lowest. Specifically, if the user estimates a dose just based on the set tube voltage, tube current, and amount of tube current, it is difficult to know of an actual dose to which an influence of the filter is reflected. Accordingly, if a dose is estimated only based on the information and corresponding X-ray irradiation conditions are selected, it is difficult to select proper X-ray irradiation conditions in consideration of a dose of radiation exposure and the image quality. In certain embodiments, the X-ray imaging apparatus 100 may guide the user to select proper X-ray irradiation conditions to minimize both a dose of radiation exposure and degradation of image quality by providing information about an actual dose, to which an influence of the filter is reflected, to the user. Examples in which the X-ray imaging apparatus 100 provides doses in accordance with an embodiment will now be described in detail with reference to accompanying drawings. FIG. 11 is a graph representing changes in radiation dose according to tube voltages and filter types/thickness. As described above, the dose of radiation exposure may vary by an X-ray irradiation condition, such as the tube voltage, tube current, amount of tube current, filter type and thickness, etc. Once an X-ray irradiation condition is selected, the controller 140 obtains a dose of radiation exposure corresponding to the selected X-ray irradiation condition. The dose of radiation exposure may be represented in such a value as entrance skin exposure (ESE), entrance surface dose (ESD), effective dose, dose-area product (DAP), etc. In this example, the ESE is used. The storage 170 may store relationships between the dose (ESE) per amount of tube current (mAs) and the tube voltage for each type and filter thickness in advance. The dose per amount of tube current (mAs) may be obtained by experiment, simulation, etc. For example, the dose (ESE) per amount of tube current (mAs) may be measured by differing the tube voltage, and the tube voltage and the measured dose (ESE) per amount of tube current (mAs) may be matched and stored in a table. Such relationships may be obtained by differing filter type and thickness. Even in the case that the filter is not used, relationships between the dose (ESE) per amount of tube current (mAs) and the tube voltage are obtained and stored. In this embodiment, the filter whose influence is reflected may be the filter 112 arranged between the blade of the collimator 113 and the X-ray tube 111. Furthermore, if there is an extra filter such as a bow tie filter used to control the shape of X-raying, even for this filter, relationships between the dose (ESE) per amount of tube current (mAs) and the tube voltage of when this filter is used or not used may be obtained and stored in advance. When a tube voltage and a filter are selected, the controller 140 searches the storage 170 for a dose E1 per amount of tube current (mAs) corresponding to the selected tube voltage and filter. Along with this, the controller 140 searches the storage 170 for a dose E2 per amount of tube current (mAs) corresponding to the selected tube voltage when no filter is used. The controller 140 calculates a conversion ratio R1 using the dose E1 per amount of tube current (mAs) of when the filter is used and the dose E2 per amount of tube current (mAs) of when the filter is not used. The conversion ratio R1 may be calculated in the following equation 1:R1=E1/E2 (1) The conversion ratio R1 is used to convert an amount of tube current selected by the user to an amount of tube current to which an influence of the filter is reflected, representing a ratio of a dose of X-rays that have not transmitted the filter and a dose of X-rays that have transmitted the filter. The controller 140 calculates a converted amount of tube current M2 in the following equation 2 using the conversion ratio R1 and the selected amount of tube current M1:M2=M1R1 (2) Furthermore, the controller 140 may calculate a dose E3, to which an influence of the filter is reflected, under a condition of the selected amount of tube current, using the dose E1 per amount of tube current when the filter is used and the selected amount of tube current M1.E3=M1E1 (3) If the selected X-ray irradiation condition does not include usage of the filter, E1=E2. In the following embodiment, an occasion when the selected X-ray irradiation condition includes usage of a filter will be described. FIGS. 12 to 18 show examples in which an X-ray imaging apparatus, in accordance with certain embodiments, displays information about radiation doses on a display, to which an influence of a filter is reflected. The display 150 may display a parameter that represents a dose to which an influence of the filter is reflected in a numerical value or display the numerical value of the corresponding parameter in a diagram or an image. For example, as shown in FIG. 12, a currently selected amount of tube current 151c-1, exposure time 151c-2, and a converted amount of tube current 151c-3 may be displayed in numerical values in the tube current amount display area 151c. As described above, the converted amount of tube current 151c-3 is an amount of tube current to which an influence of the filter is reflected. An occasion when a tube voltage of 80 kVp, a tube current of 200 mA, an amount of tube current of 10 mAs, and a copper filter of 0.1 mm are selected will be taken as an example. The X-ray irradiation conditions may be conditions directly selected by the user using the respective set buttons, or may be conditions basically matched with the selected imaging protocol and size of the subject. The controller 140 searches the storage 170 for a dose per amount of tube current (mAs) corresponding to the selected tube voltage 80 kVp and the filter (copper of 0.1 mm) and a dose per amount of tube current (mAs) corresponding to the selected tube voltage 80 kVp and to an occasion when no filter is used. The controller 140 may calculate the conversion ratio R1 using the equation 1 and obtain the converted amount of tube current M2 by substituting the conversion ratio R1 in the equation 1. If the conversion ratio R1 is 0.8, the converted amount of tube current M2 becomes 8 mAs, and the controller 140 may control the display 150 to display the converted amount of tube current 8 mAs as well in the tube current amount display area 151c. The user checks the converted amount of tube current in a numerical value of 8 mAs, and may intuitively check how much a dose of radiation exposure would be when the copper filter of 0.1 mm is used. In another example, as shown in FIG. 13, it is also possible to represent a dose 151c-4 to which an influence of the filter is reflected in a numerical value. The controller 140 may search the storage 170 for a dose A1 per amount of tube current (mAs) corresponding to the selected X-ray irradiation condition, and may obtain a dose A3 to which an influence of the filter is reflected by multiplying the selected amount of tube current M1 by the searched for dose A1 per amount of tube current (mAs) according to the equation 3. However, displaying the dose 151c-4 to which an influence of the filter is reflected is just an example. As shown in FIG. 14, it may also possible to display the dose 151c-4 in other area than the tube current amount display area 151c in the setting window 151. Although both the converted amount of tube current 151c-3 and the dose 151c-4 to which an influence of the filter is reflected are represented in the examples of FIGS. 13 and 14, embodiments of the X-ray imaging apparatus 100 are not limited thereto. It is also possible to represent one of the converted amounts of tube current 151c-3 and the dose 151c-4 to which an influence of the filter is reflected. In another example, as shown in FIG. 15, it is also possible that the display 150 represents a conversion ratio 151c-5. When the conversion ratio 151c-5 is displayed, the user may intuitively know of a decrease in the dose due to use of the filter. The conversion ratio 151c-5 may be represented as computed in the equation 1, or may be represented as a percentage as shown in FIG. 15. Similarly, in the case of representing the conversion ratio 151c-5, the dose 151c-4 to which an influence of the filter is reflected may also be represented, as shown in FIGS. 16 and 17. The user may receive information about a dose to which an influence of the filter is reflected from various aspects, thereby intuitively and accurately knowing of an actual dose of radiation exposure. It is also possible to represent both the conversion ratio 151c-5 and the converted dose 151c-3. In another example, as shown in FIG. 18, it is also possible to show the relationship between a dose of when the filer is used and a dose of when the filter is not used in a diagram. Specifically, the dose of when the filter is used may be represented in the form of a bar 151c-6, and a ratio of the length of the bar representing the conversion ratio 151c-5 and the entire bar length may be adjusted to correspond to the conversion ratio 151c-5. For example, in a case that the conversion ratio is 80%, the dose bar 151c-6 may be adjusted up to 80% of the length of the entire bar area. Furthermore, if the user changes an X-ray irradiation condition, the length of the dose bar before the change and the length of the dose bar after the change may be represented together for the user to be able to intuitively know of a change of the dose according to the change in the X-ray irradiation condition. A control method of an X-ray imaging apparatus in accordance with an embodiment of the present disclosure will now be described. The control method of an X-ray imaging apparatus may use the X-ray imaging apparatus 100. Therefore, the above description with respect to FIGS. 1 to 18 may also be applied to the embodiment of the control method of X-ray imaging apparatus without being specifically told. FIG. 19 illustrates a flowchart of a control method of an X-ray imaging apparatus, according to an embodiment of the present disclosure. Referring to FIG. 19, a choice of an X-ray irradiation condition is received, in 500. The selected X-ray irradiation condition may be conditions directly set by the user using the set buttons provided to correspond to the respective X-ray irradiation conditions, or may be conditions basically matched with an imaging protocol and size of the subject. A parameter that represents a dose is obtained based on the selected X-ray irradiation condition, in 510. The parameter that represents a dose includes at least one of a converted amount of tube current to which an influence of the filter is reflected, a dose calculated from a conversion ratio, and the conversion ratio. The conversion ratio refers to a ratio of a dose corresponding to the selected X-ray irradiation condition and a dose of when the filter is not used under the same condition. The obtained parameter is displayed on the display 150. As shown in FIGS. 12 to 18, the calculated numerical value may be displayed along with the amount of tube current 151c-1 in a portion of the tube current amount display area 151c, or may be displayed in an area of the setting window 151 other than the tube current amount display area 151c, or may be shown in a diagram. There are no limitations on how to represent the parameter. When the X-ray irradiation condition is changed, in 530, a parameter that represents a dose based on the changed X-ray irradiation condition is obtained again, in 540. If the user changes X-ray irradiation conditions using various buttons provided in the setting window 151, the controller 140 may recalculate the parameter that represents a dose by reflecting the change in real time. The parameter obtained again is displayed on the display, in 550. This may allow the user to intuitively check the changing dose according to the change in X-ray irradiation condition and to select a proper X-ray irradiation condition considering both the dose of radiation exposure and the X-ray image quality. FIG. 20 illustrates a flowchart of an example of calculating a parameter that represents a dose in a control method of an X-ray imaging apparatus, according to an embodiment of the present disclosure. Referring to FIG. 20, the dose E1 per amount of tube current corresponding to the selected tube voltage and filter is searched for from the storage 170. For this, relationships between dose per amount of tube current (mAs) and tube voltage may be stored in advance for each filter type and thickness. The dose per amount of tube current (mAs) may be obtained by experiment, simulation, etc. For example, the dose per amount of tube current (mAs) may be measured by differing the tube voltage, and the tube voltage and the measured dose per amount of tube current (mAs) may be matched and stored in a table. Such relationships may be obtained by differing filter type and thickness. Even in the case that the filter is not used, relationships between the dose per amount of tube current (mAs) and the tube voltage are obtained and stored. The dose E2 per amount of tube current corresponding to a selected tube voltage and non-use of filter is searched for, in 512. As described above, since the storage 170 stores both the dose of when the filter is used and the dose of when the filter is not used under the same tube voltage condition, the controller 170 may search the storage 170 for the both information. A ratio of the dose E1 per amount of tube current in a case of using the filter and the dose E2 per amount of tube current when not using the filter, that is, the conversion ratio R1, is obtained, in 513. The controller 140 may calculate the conversion ratio R1=E1/E2 based on the equation 1. Based on the conversion ratio R1, a converted amount of tube current is obtained, in 514. The controller 140 calculates a converted amount of tube current M2 by substituting the conversion ratio R1 and the selected amount of tube current M1 in the equation 2. The converted amount of tube current M2 represents an amount of tube current to which an influence of the filter is reflected. FIG. 21 illustrates a flowchart of an example of calculating a parameter that represents a dose in a control method of an X-ray imaging apparatus, according to another embodiment of the present disclosure. Referring to FIG. 21, the dose E1 per amount of tube current corresponding to a selected tube voltage and filter is searched for from the storage 170, in 511′, and the dose M2 to which an influence of the filter is reflected is obtained using the searched for dose E1, in 512′. The controller 140 may calculate the dose M2 to which the influence of the filter is reflected according to the equation 3. The calculated dose or amount of tube current may be displayed on the display 150 in various ways. Furthermore, the conversion ratio R1 may be displayed. The conversion ratio R1 may be represented as a percentage. The dose, amount of tube current, or conversion ratio may be represented by direct numerical values in the tube current display area 151c or in the other area, or may be schematized into diagrams or images. Furthermore, when an X-ray irradiation condition is changed and a newly calculated parameter is displayed, a relationship between the new parameter and the old parameter before the change may also be displayed. For example, as shown in FIG. 18, the length a of a dose bar before the change and the length b of a dose bar after the change may be displayed together. In this case, the user may intuitively know of a change of the dose that varies by the change in X-ray irradiation condition. The control method of X-ray imaging apparatus according to the embodiments of the present disclosure may be implemented in program instructions which are executable by various computing means and recorded in computer-readable media. The computer-readable media may include program instructions, data files, data structures, etc., separately or in combination. For example, the computer-readable recording media may include, no matter whether it is erasable or rewritable, volatile or non-volatile storage devices, such as random access memory (RAM), read only memory (ROM), magnetic storage media (for example, floppy disks, hard disks, etc.), and optical recording media (such as, CD-ROMs, or DVDs). The computer-readable recording medium may also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. This media may be read by the computer, stored in the memory, and executed by the processor. The computer-readable medium that may be included in a portable terminal may be an example of a machine-readable readable recording medium suitable for storing a program or programs having instructions that implement the embodiments of the present disclosure. The program instructions recorded on the computer-readable media may be designed and configured specially for the present disclosure, or may be well-known to people having ordinary skill in the art of computer software. According to the embodiments of an X-ray imaging apparatus and control method thereof, information about an actual dose to which an influence of the filter is reflected is provided for the user to be able to intuitively know of the dose under a corresponding X-ray irradiation condition. This may allow setting of a proper X-ray irradiation condition taking into account both a dose of radiation exposure and quality of X-ray image. According to embodiments of the present disclosure, an X-ray imaging apparatus and control method thereof, may guide the user to intuitively recognize an actual dose of X-rays and select a proper dose, ultimately a condition for a low dose of X-rays by providing the user with information about an actual dose of X-rays to which an X-ray filter effect is reflected. Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.
051446472	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, there is shown a linear electron accelerator in which a radiation exposure field limiting apparatus according to the present invention is incorporated. The linear electron accelerator shown is substantially similar in construction to the conventional electron accelerator shown in FIG. 9, and description of common construction is omitted herein to avoid redundancy. The linear electron accelerator of FIG. 1 is different from the conventional linear accelerator in that it includes a pair of radiation shielding blocks 20 of the multi-leaf type in place of the radiation shielding blocks 13a and 13b. FIG. 2 is a similar view to FIG. 10 but shows an apparatus for generating X-rays and a radiation exposure field limiting apparatus for defining an exposure field to which the present invention is applied, and FIG. 3 is a similar view to FIG. 14 but shows one of the radiation shielding blocks 20 shown in FIGS. 1 and 2. Referring to FIGS. 2 and 3, each of the radiation shielding blocks 20 is composed of a plurality of radiation shielding members or leaves including a center leaf 22a for defining an exposure field portion on a center axis of an exposure field to be formed and a suitable plural number of, three in the arrangement shown in FIG. 3, pairs of leaves 23a, 24a and 25a disposed in a symmetrical relationship on the opposite sides of the center leaf 22a. Though not shown, corresponding leaves of the other radiation shielding block 20 are disposed in an opposing relationship to the leaves 22a to 25a of the one radiation shielding block 20 in such a manner as in the radiation shielding blocks shown in FIG. 13. The leaves 22a to 25a of the radiation shielding blocks 20 are connected to be driven independently of each other by respective suitable driving mechanism not shown so that portions W1, W2, . . . of the exposure field may be defined independently of each other. The leaves 22a to 25a, however, may be driven to move such that they may be moved subordinately by adjacent ones or opposing ones thereof. The leaves 22a to 25a of the radiation shielding blocks 20 are constructed so as to have a common imaginary radiation source at a location denoted at 21 on a radiation center axis 7. In particular, each of the leaves 22a to 25a has an outer face at which it contacts with an inner face of an outer adjacent leaf and which makes part of a face of a circular cone having the apex at the imaginary radiation source 21, and a generating line of such face of the circular cone is denoted by 26l, 27l or 28l. Thus, for example, reference character 26l denotes a generating line of a face of a circular cone which is provided by an outer face of the leaf 22a contacting with an inner face of the outer adjacent leaf 23a and has the apex at the imaginary radiation source 21. Meanwhile, reference characters 25x, 26x and 27x denote X-rays which come to the outer faces of the leaves 22a, 23a and 24a from an actual radiation source 11. Referring now to FIG. 4, there is shown a modification to the radiation shielding block shown in FIG. 3. The radiation shielding block shown is modified such that the individual leaves 22a to 25a do not have a common imaginary radiation source but have different imaginary radiation sources on the center axis 7. In particular, a generating line 26l of a face of a circular cone of an outer face of the center leaf 22a has an imaginary radiation source at the apex 21a of the circular cone, and generating lines 27l and 28l of faces of circular cones of outer faces of the leaves 23a and 24a have imaginary radiation sources at the apexes 21b and 21c, respectively. Referring now to FIG. 5, there is shown another modification to the radiation shielding block shown in FIG. 3. The radiation shielding block shown is modified such that the individual leaves 22a to 25a have a common imaginary radiation source 21 on an axis 29 which passes the actual radiation source 11 and extends in parallel to the axis 6 of rotation of the rotatable frame 2. Such axis 29 will be hereinafter referred to as an imaginary radiation source axis. Referring now to FIG. 6, there is shown a modification to the modified radiation shielding block shown in FIG. 5. The radiation shielding block shown is modified such that the leaves 22a to 24a have different imaginary radiation sources 21a to 21c on the imaginary radiation source axis 29, that is, the generating lines 26l to 28l of faces of circular cones of outer faces of the leaves 22a to 24a intersect the imaginary radiation source axis 29 at different positions. Referring now to FIG. 7, there is shown a modification to the radiation shielding block shown in FIG. 6. The radiation shielding block shown is modified such that an outer face of the center leaf 22a which contacts with an inner face of the outer adjacent leaf 23a does not make part of a face of a circular cone but makes a plane which includes a line 22l parallel to the radiation center axis 7 and extends perpendicularly to the imaginary radiation source axis 29, that is, a flat plane. Consequently, the center leaf 22a has a rectangular cross section as seen in FIG. 7. The other leaves 23a and 24a have outer faces which make part of faces of circular cones having the apexes at imaginary radiation sources 21b and 21c, respectively, on the imaginary radiation source axis 29. FIG. 8 is a view similar to FIGS. 17 and 18 but shows a manner in which a difference in visually observable exposure field portions is provided by a difference in mutual positions of adjacent leaves of any of such radiation shielding blocks shown in FIGS. 3 to 7. Subsequently, operation of the linear electron accelerator will be described. Referring back to FIG. 1, X-rays 8 are generated from the radiation source 11 and restricted in exposure field thereof by the radiation shielding blocks 12a and 12b and then by the radiation shielding blocks 20 so that it is used for the radiation therapy of a patient 3. FIG. 2 illustrates a manner of generation of X-rays and definition of an exposure field similarly as FIG. 10, but the radiation shielding blocks 13a and 13b of FIG. 10 are replaced here by the multi-leaf radiation shielding blocks 20. The leaves of the multi-leaf radiation shielding blocks 20 operate in one of such manners as seen in FIGS. 3 to 7 wherein faces of circular cones defined by them do not have the apex at the radiation source 11 but have the apex or apexes at the imaginary radiation source 21 or sources 21a to 21c. In particular, referring to FIG. 3, faces of the leaves 22a to 25a which contact with each other make part of faces of circular cones, and they have a common apex at the imaginary radiation source 21 spaced from the actual radiation source 11. If the actual radiation source 11 is located at the position of the imaginary radiation source, then X-rays from the same directly pass through gaps between adjacent ones of the leaves and make leakage X-rays outside the intended exposure field, which will make trouble to intended radiation therapy. Actually, however, since the actual radiation source 11 is located at a different position from the imaginary radiation source 21 in the present arrangement, leakage X-rays outside the intended exposure field are prevented by the radiation shielding blocks 20. In particular, taking an X-ray 26x as an example, the X-ray 26x which comes to a gap (represented by a generating line 26l) between the leaves 22a and 23a cannot pass through the gap linearly. Now, if it is assumed tha the leaf gap is 0.1 mm and a lower end of the leaf 22a remote from the actual radiation source 11 is spaced by 50 cm from the actual radiation source 11 while the leaf 22a has a thickness equal to 70 mm in the direction of the radiation center axis, then X-rays which may pass directly through the leaf gap can be prevented if the imaginary radiation source 21 is located at a position spaced by 60 mm on the radiation center axis from the actual radiation source 11. In actual designing, such dimensions may be set to values having some tolerance, but they will be determined taking a magnitude in displacement between visually observable exposure field portions arising from relative positions of adjacent leaves into consideration. In the case of the dimensions given above, the difference in visually observable exposure field portions with respect to the leaf 22a, that is, the difference between the dimensions Le and Lf shown in FIG. 8, is 0.2 mm or so on the iso-center plane. The dimension of the leaf gap specified above is a value which is almost applicable to a linear electron accelerator wherein the distance between the radiation source 11 and the iso-center 9 is 1 m in most cases and which is operating actually in the technical field. Further, from an ordinary case in the field of medical treatment wherein an error of 1 mm in visual observation of an X-ray exposure field by visible light is permitted, the error of 0.2 mm in visual observation is a sufficiently small value. Accordingly, the imaginary radiation source 21 can be spaced by a greater distance from the actual radiation source 11. Since such error in visual observation is greater at an outer side leaf, the position of the imaginary radiation source should be determined with a maximum value of such errors in visual observation. An investigation must also be made for leakage X-rays which may pass in a scattered condition through any leaf gap in the system in which no X-rays pass directly through such leaf gap. A concept of leakage which is normally called streaming can be applied to such leakage. Such leakage does not amount to a significant value because the leaf gap is 0.1 mm or so (a further smaller value can be achieved actually) and very small but amounts to such a value which is resulted from attenuation of X-rays while they pass through a leaf as a radiation shielding material. An ordinary system is designed such that X-rays may be attenuated normally to one hundredth or less when they pass through a leaf (of each of the radiation shielding blocks 12a, 12b, 13a and 13b). Where the multi-leaf radiation shielding blocks are designed in such a manner as described above, the difference between visually observable exposure field portions arising from a difference between relative positions of adjacent leaves which has been called in question hereinabove with reference to FIG. 14 can be restricted to a value sufficiently lower than an allowable value, and direct passage of X-rays through a leaf gap which has been called in question hereinabove with reference to FIG. 15 can be achieved without employing such projection 39 as seen in FIG. 15. Accordingly, the multi-leaf radiation shielding blocks are simple in structure, easy to produce and economical, and restrict leakage of X-rays outside an exposure field to an allowable level as different from insufficient attenuation of directly passing X-rays by the projections 39. Besides, shading off or a penumbla around an edge portion of an exposure field of X-rays which is a common problem to the arrangements shown in FIGS. 14 and 15 is minimized or moderated significantly because the faces of the leaves extend along radiation planes of X-rays, which enables medical treatment with a low penumbla Accordingly, there are significant effects in the field of medical treatment that medical treatment planning is facilitated and that accuracy in medical treatment is improved. Since in the arrangement shown in FIG. 3 the difference between the dimensions Le and Lf shown in FIG. 8 increases toward the opposite outer sides from the center leaf 22a as described above, the arrangement shown in FIG. 4 is constituted otherwise such that the generating lines 26l, 27l and 28l for the leaves 22a, 23a and 24a pass the different imaginary radiation sources 21a, 21b and 21c, respectively, so that the difference between adjacent visually observed exposure field portions shown in FIG. 18 (difference between Le and Lf) may be restricted to a sufficiently small value within an allowance and such differences may be substantially similar values for the individual leaves in order to assure medical treatment with X-rays having penumblas which are equal at any position of the affected portion 42. It is to be noted that different leaves may have a common imaginary radiation source depending upon the difference between the dimensions Le and Lf. On the other hand, the arrangement shown in FIG. 5 is constructed such that the common imaginary radiation source 21 is positioned on the imaginary radiation source axis 29. The radiation shielding blocks 13a and 13b shown in FIG. 11 make opening and closing movement so as to normally make generating lines of a circular cone having the apex at the actual radiation source 11 in order to define an exposure field. In the case of the arrangements shown in FIGS. 3 and 4, the apexes of similar generating lines assume different positions from the radiation source 11 in the condition shown in FIG. 11, and consequently, an exposure field will have some penumblas at the opposite boundaries in the W direction. Thus, if the generating lines have the imaginary radiation source 21 on the imaginary radiation source axis 29 as shown in FIG. 5, then the imaginary radiation source 21 and the actual radiation source 11 are overlapped with each other in FIG. 11. Consequently, there is an effect that penumblas of an exposure field in the W direction can be prevented. The arrangement shown in FIG. 6 is somewhat similar in construction to the arrangement shown in FIG. 6 but is modified such that the imaginary radiation sources 21a, 21b and 21c are disposed at different positions on the imaginary radiation source axis 29 in order to attain an effect that differences between the distances Le and Lf of all of the leaves are made substantially equal to each other similarly as in the modification of the arrangement of FIG. 4 to the arrangement of FIG. 3. Also in this instance, different leaves may have a common imaginary radiation source depending upon a degree of the difference between the dimensions Le and Lf. The arrangement shown in FIG. 7 is a most practical arrangement and includes the center leaf 22a which has a rectangular cross section. Since the center leaf 22a has the opposite faces which are located at the innermost positions among other faces of the leaves of the radiation shielding block, even where it has such a rectangular cross section, the difference between the dimensions Le and Lf shown in FIG. 18 is sufficiently small. In this instance, if the leaf faces are formed not as faces of circular cones (curved faces) but as flat faces in order to facilitate working of the leaves, then a significant effect is provided that production of the leaves is easy. Further, if the difference between the dimensions Le and Lf of a visually observable irradiation field portion is smaller than an allowable value, not only the center leaf 22a but also an adjacent pair or pairs of leaves on the opposite sides of the center leaf 22a may have a rectangular cross section or sections. Such modification as is made in the arrangement shown in FIG. 7 can be applied to any of the radiation shielding blocks shown in FIGS. 3 to 7. It is to be noted that while in the embodiment described above a radiation exposure field limiting apparatus of the present invention is incorporated in a linear electron accelerator for the X-ray medial treatment, it can be incorporated similarly in any other radiation generating equipment which generates X-rays such as a cobalt 60 equipment, a betatron, a microtron and a synchrotron and also in an X-ray generating equipment which generates X-rays of energy lower than 1 MeV. Further, a radiation exposure field limiting apparatus of the present invention can be applied to any other radiations than X-rays such as an electron beam, gamma-rays, a neutron beam, a proton beam and a corpuscular beam, and a radiation shielding block may be made of a material which is effective for radiations to be used, such as a heavy metal for X-rays, a light metal for an electron beam and paraffin or an acrylic resin material for a neutron beam in order to attain intended similar effects. Further, similar effects can be attained also where, in distribution of radiations for any other application than for the medical treatment, that is, in non-destructive inspection with radiations, an exposure field is defined by means of multi-leaf radiation shielding members in order to prevent possible fading of an image of a portion for the inspection arising from scattered light. It is to be noted that, while the multi-leaf radiation shielding blocks 20 shown in FIG. 2 replace the radiation shielding blocks 13a and 13b of the system shown in FIG. 10, they may otherwise replace the radiation shielding blocks 12a and 12b shown in FIG. 10. Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit and scope of the invention as set forth herein.
039719553	summary	BACKGROUND OF THE INVENTION The increasing use of radioactive isotopes for the diagnosis and treatment of various medical conditions in recent years has resulted in the need for containers capable of storing and shipping these materials without endangering those who must handle them in transit and in administration. Grubel et al. in U.S. Pat. No. 2,915,640 disclose a cylindrical container having a squared bottom recess adapted to hold a square shaped bottle containing radioactive material. The container has a lid whose inner surface is adapted to conform to the cap of the enclosed bottle. When the lid is rotated the bottle cap is unscrewed but remains on the bottle from which it is later removed by tongs. Koster in U.S. Pat. No. 3,531,644 discloses a cylindrical receptacle housing a vessel with a pierceable cap containing liquid radiopharmaceuticals. A piece of cushioning and absorbing material is located between the bottom of the vessel and the outer receptacle. Also, a retaining ring is employed to hold the vessel in place. SUMMARY OF THE INVENTION This invention relates to improvements over the radiopharmaceutical containers described above. It relates to a container having a wrench-type lid which will both unscrew and remove the cap from the enclosed bottle and provide means to absorb any radioactive material which might leak from the enclosed bottle. Also, the same container with a minor modification may be used with bottles having a pierceable cap.
	description	Nuclear reactors with high operating temperatures may use a fluid heat exchange media, such as a liquid metal or molten salt, for coolant. The heat exchange media may transfer heat from a reactor to a heat exchanger and/or turbine for energy extraction and electricity generation as well as act as a heat sink to remove decay heat or other unwanted heat during operation or a shutdown condition. Many reactor designs, including, for example, liquid sodium-cooled fast reactors, such as the PRISM reactor, use multiple loops of heat exchange media to efficiently transfer heat away from a reactor for electrical generation and cooling. One loop may be an intermediate loop that is heated in an intermediate heat exchanger and then passed through a steam generator connected to a turbine and generator. Any fluid heat exchange media, such as liquid lead or sodium, molten salts, etc. may be used for this heat exchange in the intermediate loop. Intermediate loops using fluid media may benefit from cleanup of the heat exchange media to remove impurities or debris that may accumulate during operation in a nuclear reactor environment. FIG. 1 is an illustration of a related art cleanup system 10 useable with an intermediate loop carrying a fluid heat exchange media. For example, system 10 may be a sodium cleanup loop useable with an intermediate coolant loop of a liquid sodium reactor or molten salt reactor. As shown in FIG. 1, system 10 includes input 50 and output 67 that may connect to a same leg of an intermediate coolant loop, just far enough apart to prevent backflow or short-circuiting between the two, such as a few feet apart. Input 50 and output 67 may be intake from and returns to an intermediate coolant loop, removing and then re-supplying a relatively small amount of coolant from/to the intermediate loop. Pump 51 may push the fluid coolant through system 10. Regenerative heat exchanger 60 may be used to initially cool an incoming coolant stream 61 with outgoing, cooler coolant that is to be resupplied to the intermediate loop by output 67. The cooled coolant stream 62 may then flow to cooler 70, which may be a series of smaller tubes with fins exposed to an open air fan 71 to convect away further heat. Cooler 70 may lower the temperature of the coolant sufficiently so that impurities, such as oxides, will solidify or precipitate from the fluid coolant. Purifier 80 may include chemical reactants, catalysts, and/or mechanical filters like cold traps, mesh, or other filter media that removes impurities or debris, including precipitates that come out of solution, following cooler 70. Bypass valves 81 and 82 may permit flow bypass of purifier 80, allowing flow to be raised or lowered slowly, and otherwise controlled, through purifier 80 during startup or shutdown. Colder, filtered coolant then passes back through regenerative heat exchanger 60 through input 66 to reheat the coolant to near operating temperatures before being returned to an intermediate loop via output 67, typically just downstream from inlet 50 in the intermediate loop. In this way, the coolant passed through system 10 for cleanup minimizes heat loss from the intermediate loop. Example embodiments include combined cleanup and heat removal systems and coolant loops joined to the such systems. The coolant loops may have a hot leg connecting between the reactor to a heat extractor like a steam generator or heat exchanger and a cold leg opposite the hot leg returning from the heat extractor to the reactor. Example embodiment cleanup and heat sink systems connect to the hot leg and/or cold leg and, depending on plant situation and/or operator input, function to remove impurities or debris from the fluid coolant flowing in the loop and/or remove a substantial amount of heat from the fluid coolant. The combined system may selectively create flow between the hot leg and the cold leg, which may bypass the heat extractor entirely to permit draining and shutdown operations on the same, even as the reactor is still generating large amounts of heat. Similarly, the combined system may work on a single leg and prevent significant heat loss while cleaning the coolant during normal reactor and heat extractor operation. Intermediate modes are also possible, depending on flow path creation, pumping, and/or cooler operations. Purification may be achieved with a cold trap, for example, cooler connected serially with an outlet, and potentially a regenerative heat exchanger, back into the coolant loop, while heat sinking may be achieved by the cooler, potentially operating in a larger-capacity mode, connected in parallel to a bypass outlet back into the coolant loop. Because the combined system may selectively provide both cleanup and significant cooling to the coolant loop, the system may be structured to operate between both these modes in desired levels of combination. For example, a cooler in the system may switch between modes, or levels of, heat removal. One mode may remove only a small amount of heat from the coolant sufficient to solidify or otherwise precipitate impurities from the coolant, while another mode may sink significant amounts of heat from the coolant, potentially up to full decay heat or even reactor operational levels of heat. Such modality from impurity-removal to heat-sinking levels may be achieved by increasing forced convection, increasing flow path volume flow rate, changing heat sink media, etc. Similarly, inlet volume flow rate may be increased, pumping pressure may be increased, and/or flow paths connecting the hot leg and cold leg of the coolant loop while avoiding a purifier like a cold trap and any regenerative heat exchanger in the system may be created, such as by valves, between these modes. Example embodiment coolant loops and cleanup/cooler systems are useable in a variety of plants and coolants, including fluid media like a liquid sodium coolant used in a PRISM reactor. Coolant loops may provide for entire bypass of a primary heat extractor like a steam generator by directly connecting hot and cold legs through the cleanup-cooler systems, allowing for isolation and draining of the heat extractor and related pumps for maintenance. The hot leg and cold legs may include portions filled with fluid columns extending vertically higher than cooler, which itself may be above the reactor, and the hot and cold leg in the loop may be positioned with slightly angled horizontal paths that decline back toward the reactor, to prevent backflow into the heat extractor. Example embodiments may thus be installed and operated with several types of coolant loops already existing with purifiers in nuclear reactors, simply by adding additional cooler capacity and/or additional outlets to opposing portions of the loop. Because this is a patent document, general, broad rules of construction should be applied when reading it. Everything described and shown in this document is an example of subject matter falling within the scope of the claims, appended below. Any specific structural and functional details disclosed herein are merely for purposes of describing how to make and use examples. Several different embodiments and methods not specifically disclosed herein may fall within the claim scope; as such, the claims may be embodied in many alternate forms and should not be construed as limited to only examples set forth herein. It will be understood that, although the ordinal terms “first,” “second,” etc. may be used herein to describe various elements, these elements should not be limited to any order by these terms. These terms are used only to distinguish one element from another; where there are “second” or higher ordinals, there merely must be that many number of elements, without necessarily any difference or other relationship. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments or methods. As used herein, the terms “and,” “or,” and “and/or” include all combinations of one or more of the associated listed items unless it is clearly indicated that only a single item, subgroup of items, or all items are present. The use of “etc.” is defined as “et cetera” and indicates the inclusion of all other elements belonging to the same group of the preceding items, in any “and/or” combination(s). It will be understood that when an element is referred to as being “connected,” “coupled,” “mated,” “attached,” “fixed,” etc. to another element, it can be directly connected to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected,” “directly coupled,” etc. to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). Similarly, a term such as “communicatively connected” includes all variations of information exchange and routing between two electronic devices, including intermediary devices, networks, etc., connected wirelessly or not. As used herein, the singular forms “a,” “an,” and the are intended to include both the singular and plural forms, unless the language explicitly indicates otherwise. Indefinite articles like “a” and “an” introduce or refer to any modified term, both previously-introduced and not, while definite articles like “the” refer to a same previously-introduced term; as such, it is understood that “a” or “an” modify items that are permitted to be previously-introduced or new, while definite articles modify an item that is the same as immediately previously presented. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, characteristics, steps, operations, elements, and/or components, but do not themselves preclude the presence or addition of one or more other features, characteristics, steps, operations, elements, components, and/or groups thereof. As used herein, “axial” and “vertical” directions are the same up or down directions oriented with gravity. “Transverse” and “horizontal” directions are perpendicular to the “axial” and are side-to-side directions in a plane at a particular axial height. The structures and operations discussed below may occur out of the order described and/or noted in the figures. For example, two operations and/or figures shown in succession may in fact be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Similarly, individual operations within example methods described below may be executed repetitively, individually or sequentially, to provide looping or other series of operations aside from single operations described below. It should be presumed that any embodiment or method having features and functionality described below, in any workable combination, falls within the scope of example embodiments. The Inventors have newly recognized that cleanup systems may be used as a heat sink in a nuclear reactor, instead of merely removing impurities from coolant. The Inventors have further newly recognized that cleanup systems may be used as alternative or parallel coolant loops while intermediate coolant loops are drained and worked on, such as during plant maintenance. While these uses of cleanup systems are contrary to their established functions, the Inventors have recognized that they may solve long-standing problems of emergency cooling and operations maintenance that have traditionally been solved by using other systems and/or fully shutting down a plant. Example embodiments described below uniquely enable these solutions to these and other problems discovered by the Inventors. The present invention is heat-sink purifier systems, nuclear reactors using the same, and methods of using the same. In contrast to the present invention, the few example embodiments and example methods discussed below illustrate just a subset of the variety of different configurations that can be used as and/or in connection with the present invention. FIG. 2 is an illustration of an example embodiment decay heat removal system 100 useable in a commercial nuclear power plant. As seen in FIG. 2, several features of example embodiment system 100 may be similar to the related art system 10 of FIG. 1. In this way example embodiment system 100 is also useable in connection with an intermediate loop carrying a molten heat transfer medium, in a number of different nuclear plant designs. Example embodiment system 100 includes an additional, higher capacity inlet 150 from the intermediate loop, as well as an additional, higher capacity outlet 180 into the intermediate loop. Inlet 150 may, for example, be a valved connection to a hotter side or hot leg 4 (FIG. 3) of an intermediate loop where coolant exits a reactor. Similarly, outlet 180 may be, for example, a valved connection to a colder side or cold leg 8 (FIG. 3) of the intermediate loop where coolant enters the reactor. Inlet 150 and outlet 180 may be separated by great distances, potentially even at opposite sides of an intermediate loop. Example embodiment decay heat removal system 100 has increased flow and heat transfer capacity to dissipate or sink a substantial portion of heat in the intermediate loop. As such, system 100 may act as a decay heat removal system by removing such heat form the intermediate loop and ultimately the reactor, instead of avoiding heat loss. To accommodate this large-scale heat sinking, additional or larger-scale cooler 170 and fan 171, as well as additional parallel and/or higher-volume pump 151, may be used to remove a substantial amount of heat from a larger amount of coolant directed through example embodiment system 100. For example, system 100 may remove heat equivalent to about 7% of full rated thermal power of a plant. Of course, the amount of heat varies based on plant, one example may sink 5 megawatt-thermal heat from an 840 megawatt-thermal rated plant. Smaller values may also be achieved through selective activation of cooler and flow paths, such as for partial removal of decay heat in combination with other heat removal systems. Selective activation may be achieved by, for example, cooler 170 including several parallel channels with fins to selectively accommodate larger flows, and/or fan 171 including several speeds or multiple fans or higher-pressure blowers that can be selectively activated to convect large amounts of heat. Or, for example, larger-scale cooler 170 may include other coolant media, submerged sections, counter-flow heat exchangers, printed-circuit heat exchangers, plate-and-frame heat exchangers, and other heat sinks in parallel that can be turned on to selectively dissipate large amounts of heat from the coolant. In this way, cooler 170 may seamlessly change from a purifying mode that removes little heat, such as 0.5 MW or less, from a coolant to a heat-sinking mode that removes much heat, such as around 5 MW or more, from the coolant. Example embodiment decay heat removal system 100 may be scaled between increased decay heat removal and lower-level cooling useable for purification, such as cold trapping. For example, connections 150 and 180 may be shut off, such as by valves, during normal plant operations without excess heat loss, and system 100 may act as a purification system with purifier 80, returning flow to outlet 67 and receiving flow from inlet 50 nearby in an intermediate loop. When additional cooling is necessary, such as during a transient involving reactor shutdown or loss of other cooling systems, connections 150 and 180 may be opened to enable larger coolant flows, and pump 151, cooler 170, and/or fan 171 may be increased in speed, number, and/or type, to increase heat dissipation from larger coolant flows. Similarly, valves 81 and/or 82 may be closed to avoid purifier 80 and/or reheater 60 when example embodiment system 100 is selectively scaled to decay heat sink levels. Closing off purifier 80 may create direct and/or exclusive coolant flow between connections 150 and 180, improving heat sinking through example system 100 in the additional cooling state. In this way, example embodiment system is compatible with nearly any coolant loop using a cold trap or other purifier, while still providing optional functionality of a selectively-activatable increased heat sink. FIG. 3 is an illustration of an example embodiment intermediate coolant loop 200 useable in nuclear reactors, including higher-temperature reactors such as a PRISM reactor or molten salt reactor. As shown in FIG. 3, example embodiment intermediate coolant loop 200 may interface with several related or conventional reactor components including reactor 1 housing core 2 with nuclear fuel. An intermediate heat exchanger 3 transfers heat from reactor 1 to intermediate coolant loop 200, which in turn may transfer heat to an extractor like a steam generator 6 or heat exchanger for electricity generation. As shown in FIG. 3, intermediate coolant loop 200 is interfaced with example embodiment decay heat removal system 100 (FIG. 2) via inlet 150 and outlet 180. For example, inlet 150 may take coolant from a bottom of hot leg 4, where coolant first exits reactor 1 and has its highest energy, and outlet 180 may return coolant to a bottom of cold leg 8, where coolant is returned to reactor 1 and has its lowest energy. For typical cold-trapping purification, inlets 50 and outlets 67 (FIG. 2) might take from a same or nearby position on a same leg to prevent heat loss, unlike inlet 150 and outlet 180 that may be segregated at temperature extremes in example embodiment intermediate coolant loop 200. During a transient state or when larger heat-sinking is desired, inlets 50 and/or outlets 67 may be closed, and inlet 150 and outlet 180 may be opened or enabled to remove heat from coolant that ultimately flows back through intermediate heat exchanger 3, cooling reactor 1. Example embodiment intermediate coolant loop 200 can also be operable with intermediate pump 7 and steam generator 6, or other heat extractor, drawing heat from the coolant to generate electricity. Intermediate pump 7 and/or steam generator 6 may optionally be deactivated and drained while coolant loop 200 still circulates coolant and sinks heat through inlet 150 and outlet 160. For example, intermediate pump 7, steam generator 6, and/or portions of hot leg 4 and cold leg 8 may be drained into drain tank 5, such as through opening drain valves to drive coolant by gravity into drain tank 5 and/or through active pumping. Proper sloping of piping in hot leg 4 and cold leg 8 may permit draining of pump 7 and steam generator 6 and their associated piping. For example, horizontal piping of hot leg 4 and cold leg 8 may be at slight angles with respect to the vertical, such as slightly declined toward steam generator 6 and away from reactor 1 at 5-10 millimeters vertical drop per meter length. This decline may further prevent backflowing and ensure coolant looping only through a portion of example embodiment intermediate coolant loop 200 in combination with example positioning discussed below. Hot leg 4 and cold leg 8 may be arranged such that a column of fluid in hot leg 4 may be at a vertical height 240 and fluid in cold leg 8 may be at a vertical height 280. Columns of fluid in these legs may remain even though other portions of loop 200 are drained. Because of the presence of the columns of fluid at vertical heights 250 and 280 above inlet 150 on hot leg 4 and outlet 180 on cold leg 8, coolant may still be circulated between intermediate heat exchanger 3 and a decay heat removal system 100 (FIG. 2) via the lower portions of hot leg 4 and cold leg 8. In this way, it is possible to repair or otherwise work on an emptied steam generator 6, intermediate pump 7, and/or any other drained portions of coolant loop 200 while still removing heat from reactor 1 via intermediate heat exchanger 3. Of course, example embodiment coolant 200 with system 100 may also be used with a completely-filled loop. Similarly, in FIG. 3, system 100, or at least cooler 170 (FIG. 2) of system 100, may be placed at a vertical height 231 above intermediate heat exchanger 3 at vertical height 230. The difference in vertical heights 230 and 231 may create natural circulation driving forces, where coolant heated at heat exchanger 3 rises due to lowered density, flows to cooler 170 and is cooled, increasing its density, which then flows by density difference back to heat exchanger 3. This configuration and associated natural circulation may eliminate or reduce the need for active pumping, such as with pump 151 or 7. If all other coolant-filled portions of system 100 are below elevations 240 and 280 of coolant columns, natural circulation will occur in loop 200 through heat exchanger 3 due to gravity and because voids cannot form in system 100 below. As seen in FIGS. 2 and 3, example embodiment intermediate coolant loop 200 and example embodiment decay heat removal system 100 can be used with several types of nuclear reactors and existing components. Some functionality of loop 200 and system 100 may be achieved simply by increasing capacity of inlet 50 to that of inlet 150, increasing heat sink capacity of a cooler, and adding an exclusive return outlet 180 to cold leg 8. Loop 200 and system 100 may be used during typical reactor operation to remove impurities and/or debris from a relatively small stream of coolant, as well as being selectively scaled to remove all or a significant portion of decay heat or even operation heat from reactor 1 during a transient or non-electricity generating state, such as during an accident or plant maintenance. Similarly, multiple loops 200 and systems 100 are useable with a single reactor 1 to provide even larger amounts of heat transfer and sinking from reactor 1. Example embodiments and methods thus being described, it will be appreciated by one skilled in the art that example embodiments may be varied and substituted through routine experimentation while still falling within the scope of the following claims. For example, any number of different reactor types and thermodynamic cycles can be used with example embodiments, simply by allowing for different temperatures and coolants. Such variations are not to be regarded as departure from the scope of these claims.
	claims	1. A testing device, comprising:a test tank that stores cooling water therein;a foreign matter inputter that inputs foreign matter to the test tank;a recirculation sump screen set in the test tank and that filters the foreign matter; anda processor,wherein the processor executes a program for evaluating an amount of foreign matter passed through the recirculation sump screen, the program causing the processor to perform:acquiring sets of test data on amounts of foreign matter passed through a recirculation sump screen when different amounts of the foreign matter are input;forming a passed foreign matter amount approximate line that approximates the amounts of passed foreign matter with respect to the amounts of input foreign matter on the basis of the sets of test data on the amounts of passed foreign matter;forming a passed foreign matter amount line tangent to the passed foreign matter amount approximate line; andcalculating a total amount of passed foreign matter with respect to the amounts of input foreign matter on the basis of the passed foreign matter amount line to evaluate the recirculation sump screen. 2. The testing device according to claim 1, wherein the passed foreign matter amount approximate line is a quadratic curve and the passed foreign matter amount line is a primary expression straight line expressed by a function of an input foreign matter amount. 3. The testing device according to claim 2, further comprising forming a passed foreign matter amount approximate straight line on the basis of the passed foreign matter amount approximate line and forming the passed foreign matter amount line on the basis of the passed foreign matter amount approximate straight line. 4. The testing device according to claim 1, wherein a passed foreign matter amount line is set in a length defined by the passed foreign matter amount line tangent to the passed foreign matter amount approximate line and a passed foreign matter amount line shifted to a pre-set side where the passed foreign matter amount increases. 5. The testing device according to claim 4, wherein the length is a length moved to a side where the amount of passed foreign matter is smaller than a maximum value of the sets of test data on the amounts of passed foreign matter. 6. The testing device according to claim 2, wherein a passed foreign matter amount line is set in a length defined by the passed foreign matter amount line tangent to the passed foreign matter amount approximate line and a passed foreign matter amount line shifted to a pre-set side where the passed foreign matter amount increases. 7. The testing device according to claim 3, wherein a passed foreign matter amount line is set in a length defined by the passed foreign matter amount line tangent to the passed foreign matter amount approximate line and a passed foreign matter amount line shifted to a pre-set side where the passed foreign matter amount increases.
	claims	1. A radiographic image capturing apparatus comprising:a radiation source configured to apply radiation to an object of a subject to be examined;a radiation detector configured to detect the radiation that has passed through the object and configured to convert the detected radiation into a radiographic image;a collimator configured to delimit an irradiated field of the radiation with respect to the radiation detector, the collimator being disposed between the radiation source and the object;a biopsy region positional information calculating unit configured to calculate a three-dimensional position of a biopsy region in the object based on two radiographic images, which are acquired by the radiation detector in a stereographic image capturing process, in which the radiation source disposed at least at two angles applies the radiation to the object;an irradiated field calculating unit configured to calculate a new irradiated field covering the biopsy region based on the calculated three-dimensional position of the biopsy region and the two angles;a collimator control unit configured to control the collimator to change the irradiated field of the radiation in a next stereographic image capturing process to the new irradiated field; andan irradiated field calculation control unit configured to selectively enable the irradiated field calculating unit to calculate the new irradiated field or disable the irradiated field calculating unit from calculating the new irradiated field. 2. A radiographic image capturing apparatus according to claim 1, wherein the application of the radiation to the object from the radiation source at the two angles, the calculation of the three-dimensional position of the biopsy region by the biopsy region positional information calculating unit, the calculation of the new irradiated field by the irradiated field calculating unit, and the changing of the irradiated field of the radiation to the new irradiated field by the collimator control unit are successively carried out repeatedly. 3. A radiographic image capturing apparatus according to claim 1, further comprising a light source for spotlighting the radiation detector to indicate the irradiated field thereon, before the radiation source applies the radiation to the object. 4. A radiographic image capturing apparatus according to claim 1, wherein on condition that the irradiated field calculation control unit determines that the biopsy region will possibly be included in the two radiation images to be acquired even after converting the irradiated field to the new irradiated field in the next stereographic image capturing process, then calculation of the new irradiated field by the irradiated field calculating unit is enabled, andon condition that the irradiated field calculation control unit determines that the biopsy region will not possibly be included in the two radiation images to be acquired after converting the irradiated field to the new irradiated field in the next stereographic image capturing process, calculation of the new irradiated field by the irradiated field calculating unit is disabled. 5. A radiographic image capturing apparatus according to claim 4, wherein in the case that the calculation of the new irradiated field is enabled, the irradiated field calculating unit is configured to calculate the new irradiated field using the three-dimensional position of the biopsy region based on the radiographic image in a last stereographic image capturing process and the two angles acquired by the radiation detector in the last stereographic image capturing process. 6. A radiographic image capturing apparatus according to claim 5, wherein the irradiated field calculating unit is configured to determine a field restricted from the irradiated field, as the new irradiated field in the next stereographic image capturing process. 7. A radiographic image capturing apparatus according to claim 4, wherein in the case that the calculation of the new irradiated field is disabled, a stereographic image capturing process is carried out under the same conditions as the last stereographic image capturing process. 8. A radiographic image capturing method comprising the steps of:performing a stereographic image capturing process by applying radiation from a radiation source disposed at least at two angles to an object of a subject to be examined, while an irradiated field of the radiation with respect to a radiation detector is being delimited by a collimator;detecting, with the radiation detector, the radiation applied from the radiation source disposed at the two angles to acquire two radiographic images;calculating, with a biopsy region positional information calculating unit, a three-dimensional position of a biopsy region in the object based on the two radiographic images;calculating, with an irradiated field calculating unit, a new irradiated field covering the biopsy region based on the calculated three-dimensional position of the biopsy region and the two angles;controlling the collimator with a collimator control unit to change the irradiated field of the radiation in a next stereographic image capturing process to the new irradiated field; andselectively enabling the irradiated field calculating unit to calculate the new irradiated field or disabling the irradiated field calculating unit from calculating the new irradiated field.
	description	(1) Field of the Invention This invention relates to an X-ray detector for measuring X rays in the medical, industrial, nuclear and other fields. (2) Description of the Related Art In an X-ray detector having electrodes formed at opposite sides of a semiconductor, a predetermined bias voltage is applied between the electrodes, and electric charges generated in the semiconductor by incident X rays are detected as electric signals. For such an X-ray detector, various semiconductor materials are selectively used according to purpose. These semiconductor materials are manufactured in various ways. Generally, for an X-ray detector required to have energy resolution, a high-purity single crystal semiconductor such as silicon (Si) tends to be used. An X-ray detector using amorphous selenium (a-Se) in particular can easily realize a high resistance thick film sized 1,000 cm2 or larger by using a film coating technique such as vacuum deposition method. This X-ray detector is ideal for use in a field requiring a large area for X-ray measurement. However, an amorphous selenium (a-Se) film formed by such a method includes many structural defects. Generally, therefore, an appropriate quantity of impurity is added (i.e. doped) in order to improve performance. The conventional detector constructed as described above has the following drawback. Unlike a single crystal semiconductor, the conventional detector has many potential structural defects. These defects trap charge transfer media (carriers) of electrons and holes generated in the semiconductor layer by X-ray incidence. The trapped carriers cannot be picked up as electric signals. This causes a phenomenon of deterioration in the sensitivity of the X-ray detector. This phenomenon will particularly be described hereinafter with reference to FIGS. 2A and 2B. FIGS. 2A and 2B are explanatory views of an internal structure of the X-ray detector. The structural defects in amorphous selenium (a-Se), as shown in FIG. 2B, include recombination centers D0 and ionized recombination centers D+ (electron trapping centers) and D− (hole trapping centers) present in a fixed ratio. A density of D+ and D− at this time determines an initial value of sensitivity of the X-ray detector. This state is expressed by the following formula:2D0→D++D− When X rays impinge in this state to generate charge transfer media (carriers) of electrons (e−) or holes (h+) in amorphous selenium (a-Se), these media are first trapped by the recombination centers D0 to change into D− and D+, respectively. In this way, the density of D+ and D− increases to deteriorate sensitivity. This relationship is expressed by the following two formulas:D0+e−→D−D0+h+→D+ The object of this invention is to provide an X-ray detector which compensates for structure defects in amorphous selenium (a-Se) to be free from sensitivity deterioration. The above object is fulfilled, according to this invention, by an X-ray detector for detecting X rays comprising a semiconductor for generating electric charges therein upon X-ray incidence, and electrodes formed on opposite sides of the semiconductor for application of a predetermined bias voltage, wherein the semiconductor is amorphous selenium (a-Se) doped with a predetermined quantity of an alkali metal. As shown in FIG. 2A, an alkali metal M having a strong ionization tendency is added (doped) to amorphous selenium (a-Se) which is a semiconductor layer sensitive to X rays, in a quantity to compensate for the structural defects D0. Thus, the structural defects in amorphous selenium (a-Se) are only D0 which are recombination centers and D− (hole trapping centers) which are negatively ionized D0. This state is expressed by the following formula (1):2D0+M→M++D−+D0 (1) When, in this state, incident X rays generate charge transfer media (carriers) of electrons (e−) and holes (h+) in amorphous selenium (a-Se), the electrons are captured by the recombination centers D0 to change into D−, and the holes captured by D− to change into D0. This relationship is expressed by the following two formulas (2) and (3):D0+e−→D− (2)D−+h+→D0 (3) As seen from these formulas (2) and (3), where the electron capturing probability and the hole capturing probability are exactly equal, the density of D− never increases, and hence no sensitivity deterioration. Even where the electron capturing probability is higher than the hole capturing probability to increase the density of D−, only the holes are captured in an increased quantity. Since no increase takes place in the quantity of electrons captured, sensitivity deterioration is suppressed to a half. In the X-ray detector having the above construction according to this invention, preferably, one of the electrodes formed at an X-ray incidence side is a positive electrode to which the bias voltage is applied to increase potential. Since the electrode at the X-ray incidence side is a positive electrode to which the bias voltage is applied to increase potential, as shown in FIG. 3, electrons generated by X-ray incidence move toward the X-ray incidence side while holes move to the opposite side. The interaction between X rays and a material is characterized by the stronger reaction tending to occur in the regions closer to the surface of the material. Thus, many of the electrons are generated by X-ray incidence near a plane of X-ray incidence. These electrons move toward the electrode at the side of X-ray incidence, and thus move reduced distances. Thus, the probability of the electrons reaching the electrode without being captured by the recombination centers D0 is increased to minimize an increase of D−. In this way, not only an increase in the quantity of electrons captured is suppressed, but also an increase in the quantity of holes captured is suppressed. Consequently, hardly any sensitivity deterioration occurs with the X-ray detector. In the X-ray detector according to this invention, the quantity of the alkali metal doped, preferably, is in a range of 0.01 to 10 ppm, and more preferably in a range of 0.05 to 2 ppm. Where the quantity of the alkali metal added (doped) is in a range of 0.01 to 10 ppm, which substantially corresponds to a quantity compensating for the structural defects D0 of amorphous selenium (a-Se), the reaction in formula (1) takes place reliably to suppress sensitivity deterioration. Where the quantity of the alkali metal added were less than 0.01 ppm, the effect of the alkali metal would diminish to result in a sensitivity deterioration. Where the quantity of the alkali metal added were larger than 0.01 ppm, the alkali metal would be deposited alone, resulting in an increase in dark current and a rapid fall of sensitivity. Naturally, even in the above range, an optimum value exists according to the type of alkali metal and film forming conditions such as vapor deposition temperature and substrate temperature. In the case of Na, for example, an optimal quantity is the range of 0.05 to 2 ppm. A preferred embodiment of this invention will be described in detail hereinafter with reference to the drawings. FIGS. 1 through 4 show one embodiment of the invention. FIG. 1 is a schematic sectional view showing the construction of an X-ray detector. FIGS. 2A and 2B are explanatory views showing an internal structure of the X-ray detector. FIG. 3 is an explanatory view showing functions of the X-ray detector according to this invention. FIG. 4 is a schematic sectional view showing the construction of a modified X-ray detector. As shown in FIG. 1, the X-ray detector in this embodiment includes a carrier collection electrode 1 and a lower carrier selection layer 2 formed on an insulating substrate 3 such as a glass substrate. A semiconductor thick film 4 of amorphous selenium (a-Se) is formed also on the substrate 3. An alkali metal has been added (doped) to the amorphous selenium in a range of 0.01 to 10 ppm, preferably in a range of 0.05 to 2 ppm. A voltage application electrode 6 is formed on the semiconductor thick film 4 through an upper carrier selection layer 5. The lower and upper carrier selection layers 2 and 5 are provided for suppressing dark current by using the notable difference in contribution to charge transfer action between electrons and holes acting as carriers in the semiconductor. Where a positive bias is applied to the voltage application electrode 6, an n-type semiconductor layer such as CdSe, CdS or CeO2, a semi-insulator layer such as Sb2S3 or an amorphous Se layer doped with As or Te is used as the upper carrier selection layer 5 in order to restrict an injection of holes. As the lower carrier selection layer 2, a p-type semiconductor layer such as ZnSe, ZnTe or ZnS, a semi-insulator layer such as Sb2S3 or an amorphous Se layer doped with a halogen such as Cl is used in order to restrict an injection of electrons. A semi-insulator layer such as Sb2S3 can reverse the contributions of electrons and holes based on film forming conditions. The X-ray detector in this embodiment applies a bias voltage to the voltage application electrode 6, with an X-ray incidence generating electric charges (electrons and holes) in the amorphous selenium (a-Se) semiconductor thick film 4. The X-ray detector detects, as electric signals from the carrier collection electrode 1, electric charges induced by movement of the generated electrons and holes toward the two electrodes, respectively. As shown in FIG. 2B, the amorphous selenium (a-Se) semiconductor thick film 4 has, present therein, three types of structural defects, i.e. recombination centers D0 and ionized recombination centers D+ (electron trapping centers) and D− (hole trapping centers). In the case of the X-ray detector in this embodiment, however, alkali metal M is added (doped) to the amorphous selenium (a-Se) semiconductor thick film 4. As shown in FIG. 2A, only D0 and D− are present. The value of sensitivity is determined by a density of D+ and D−. D− increases by X-ray irradiation according to formula (2) set out hereinbefore, but no increase in D+ takes place. Thus, deterioration in the sensitivity of the X-ray detector is suppressed to a half. Further, when a positive bias voltage is applied so that the electrode at the X-ray incidence side, i.e. the voltage application electrode 6, has a higher potential than the carrier collection electrode 1, as shown in FIG. 3, electrons generated by X-ray incidence move toward the X-ray incidence side while holes move to the opposite side. The interaction between X rays and a material is characterized by the stronger reaction tending to occur in the regions closer to the surface of the material. Thus, many of the electrons are generated by X-ray incidence near a plane of X-ray incidence. These electrons move toward the electrode at the side of X-ray incidence. Consequently, the electrons move reduced distances. This increases the probability of the electrons reaching the voltage application electrode 6 without being captured by the recombination centers D0, thereby minimizing an increase of D−. As a result, hardly any sensitivity deterioration occurs with the X-ray detector. FIG. 4 shows a schematic sectional view of a modified embodiment in which the above X-ray detector is developed to form a plurality of channels in a two-dimensional matrix. Each carrier collection electrode 11 is connected to a capacitor 12 for charge storage and a switching device 13 (thin film transistor (TFT) switch) for reading the charges. The carrier collection electrodes 11 are arranged on a TFT substrate having the capacitors 12 and switching devices 13 to constitute a two-dimensional array. Like reference numerals are used to identify like elements of the X-ray detector described hereinbefore, and will not be described again. When the X-ray detector in this modification is irradiated with X rays, with a bias voltage applied to a voltage application electrode 14 formed over an entire surface as a common electrode, electric charges (electrons and holes) generated move toward the opposite electrodes, respectively. The induced charges are stored in the charge storing capacitors 12 connected through the carrier collection electrodes 11 to locations of X-ray incidence. In time of reading, an ON signal is sent in from a gate driver 15 through gate lines 16 to turn on (connect) the switching devices 13. Then, the stored charges are transmitted as radiation detection signals through sense lines 17 to pass through charge-to-voltage converters 18 and a multiplexer 19 to be outputted as digital signals to provide a two-dimensional X-ray image. With such a two-dimensional array construction, the characteristic of the X-ray detector according to this invention appears conspicuously. Specifically, with a conventional X-ray detector, a sensitivity deterioration takes place according to the incidence intensity of X rays, to cause local sensitivity variations. Its influence is conspicuous on the quality of images photographed subsequently. In the X-ray detector in this modified embodiment, on the other hand, an alkali metal is added (doped) to an amorphous selenium (a-Se) semiconductor thick film 20, and a positive bias is applied to the voltage application electrode 14 in use. Thus, hardly any sensitivity deterioration takes place, to be free from image quality deterioration such as sensitivity variations. In the foregoing X-ray detector and its modification, typical examples of the alkali metal are Li, Na and K. As described in relation to the functions of this invention, similar effects may be produced by doping an alkali earth metal such as Ca or a nonmetallic element such as H as long as such an element has a strong ionization tendency and a reducing effect. <Measurement Data of this Invention and Comparison with the Prior Art> Next, verification is made that sensitivity deterioration is improved by the X-ray detector in this embodiment. As shown in FIG. 5, samples used here include eight X-ray detectors, i.e. X-ray detectors for testing 1-6 and X-ray detectors for comparison 1 and 2. The detectors for testing 1-6 have alkali metal Na added (doped) to the amorphous selenium (a-Se) semiconductor thick film 20 in 0.01 ppm, 0.1 ppm, 0.5 ppm, 1.0 ppm, 5.0 ppm and 10.0 ppm, respectively. The X-ray detector for comparison 1 has alkali metal Na added (doped) in 20.0 ppm to the amorphous selenium (a-Se) semiconductor thick film 20. The X-ray detector for comparison 2 has an amorphous selenium (a-Se) semiconductor thick film with no doping. The amorphous selenium (a-Se) semiconductor thick film 4 is 1 mm thick in all of the X-ray detectors. For all the X-ray detectors for testing and for comparison, ±10 kV bias voltages were applied to the voltage application electrode 6, and an ammeter was connected to the carrier collection electrode 1 to read signal currents. In this state, the X-ray detectors were irradiated continuously for 15 minutes with X rays passed through a 1 mm aluminum filter under the conditions of 80 kV tube voltage and 2.2 mA tube current, and variations in the signal current were recorded. FIG. 6 shows the variations in the signal current obtained. As seen, the X-ray detector for comparison 2 has signal currents falling exponentially with both the positive and negative bias voltages. The X-ray detector for testing 3 has a signal current hardly changing with the positive bias, and a signal current falling only slightly with the negative bias. Amount of signal current deterioration ΔI in FIG. 5 represents a difference between a signal current immediately following the X-ray irradiation and a signal current 15 minutes thereafter, i.e. an amount of sensitivity deterioration. The above results show that amount of signal current deterioration ΔI is small and little sensitivity deterioration occurs with alkali metal Na doped in the range of 0.01 to 10.0 ppm. It will also be understood that sensitivity deterioration is less with the positive bias than with the negative bias. Similarly, an X-ray detector for testing 7 was fabricated by doping 0.5 ppm of potassium (K), and variations in the signal current were checked. The results are shown in FIG. 7. It will be seen that amount of signal current deterioration ΔI is clearly smaller than for the detector for comparison 2 not doped with potassium (K). Further, an X-ray detector for testing 8 was fabricated by doping 0.1 ppm of lithium (Li), and variations in the signal current were checked. The results are shown in FIG. 8. It will be seen that amount of signal current deterioration ΔI is clearly smaller than for the detector for comparison 2 not doped with lithium (Li). These results prove that similar effects are produced by doping alkali metals other than sodium (Na), to suppress sensitivity deterioration. This invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.
044302762	abstract	A method is disclosed for producing a dimensionally stable UO.sub.2 fuel pellet of large grain mole %, and relatively large pore size. A dopant containing an element selected from the group consisting of aluminum, calcium, magnesium, titanium, zirconium, vanadium, niobium, and mixtures thereof is added to a highly sinterable UO.sub.2 powder, which is a UO.sub.2 powder that is sinterable to at least 97% theoretical density at 1600.degree. C. in one hour, and the UO.sub.2 powder can then be formed into fuel pellets. Alternatively, the dopant can be added at a step in the process of producing ammonium diuranate. The ammonium diuranate is collected with about 0.05 to about 1.7 mole%, based on UO.sub.2, of a compound containing said element. That mixture is then calcined to produce UO.sub.2 and the UO.sub.2 is formed into a fuel pellet. The addition of the dopant can also be made at the hydrolysis stage in the manufacture of UO.sub.2 by a dry conversion process.
	summary
	summary
	abstract	A compact source for high brightness x-ray generation is disclosed. The higher brightness is achieved through electron beam bombardment of multiple regions aligned with each other to achieve a linear accumulation of x-rays. This may be achieved through the use of x-ray targets that comprise microstructures of x-ray generating materials fabricated in close thermal contact with a substrate with high thermal conductivity. This allows heat to be more efficiently drawn out of the x-ray generating material, and allows bombardment of the x-ray generating material with higher electron density and/or higher energy electrons, leading to greater x-ray brightness. The orientation of the microstructures allows the use of a take-off angle at or near 0°, allowing the accumulation of x-rays from several microstructures to be aligned and be used to form a beam in the shape of an annular cone.
	claims	1. A medical apparatus comprising:a beam deflector having an electromagnet configured to provide a first magnetic field for deflecting a particle beam;a current control configured to adjust a current of the electromagnet in correspondence with an energy level associated with an accelerator, wherein the energy level associated with the accelerator comprises an energy level of an electric field in the accelerator or an energy level of the particle beam; anda permanent magnet configured to provide a second magnetic field, wherein the permanent magnet is implemented as a part of the beam deflector;wherein the first magnetic field and the second magnetic field form a total magnetic field that is variable to have at least a first magnetic field value and a second magnetic field value;wherein the medical apparatus is configured to adjust the total magnetic field in response to the electric field in the accelerator or the energy level of the particle beam; andwherein the medical apparatus is configured to provide the total magnetic field with the first magnetic field value when the electric field in the accelerator or the energy level of the particle beam has a first value, and wherein the medical apparatus is also configured to provide the total magnetic field with the second magnetic field value when the electric field in the accelerator or the energy level of the particle beam has a second value. 2. The apparatus of claim 1, wherein the permanent magnet comprises a rare earth magnet. 3. The apparatus of claim 1, wherein the electromagnet comprises a coil surrounding the permanent magnet. 4. The apparatus of claim 1, further comprising an accelerator for providing the particle beam, the accelerator having an energy switch configured to change the energy level of the particle beam. 5. The apparatus of claim 4, wherein the energy switch is configured to change the energy level of the particle beam within a duration that is less than one second. 6. The apparatus of claim 4, wherein the accelerator comprises a fixed-field alternating gradient (FFAG) accelerator, or a non-scaling fixed-field alternating gradient (NS-FFAG) accelerator. 7. The apparatus of claim 1, further comprising an ion chamber, wherein the ion chamber comprises a dosimetry circuit. 8. The apparatus of claim 7, wherein the control is also configured to adjust a parameter in the dosimetry circuit in correspondence with the energy level associated with the accelerator. 9. The apparatus of claim 1, wherein the electromagnet comprises a laminated steel. 10. The apparatus of claim 1, wherein the current control is configured to increase the current of the electromagnet in correspondence with an increase in the energy level associated with the accelerator. 11. The apparatus of claim 1, wherein the current control is configured to decrease the current of the electromagnet in correspondence with a decrease in the energy level associated with the accelerator. 12. The apparatus of claim 1, wherein the electromagnet comprises a pretzel magnet. 13. The apparatus of claim 1, further comprising a beam output coupled to the beam deflector, wherein the beam output is moveable to deliver treatment energy from a plurality of gantry angles that includes at least a first gantry angle and a second gantry angle. 14. The apparatus of claim 13, further comprising an energy adjuster configured to adjust the treatment energy so that the treatment energy has a first energy level when the beam output is at the first gantry angle, and a second energy level when the beam output is at the second gantry angle. 15. The apparatus of claim 14, wherein the energy adjuster is configured to adjust the treatment energy in a continuous manner. 16. The apparatus of claim 14, wherein the energy adjuster is configured to adjust the treatment energy in a discrete manner. 17. The apparatus of claim 13, further comprising an energy adjuster configured to adjust the treatment energy so that the treatment energy has a first energy level when the beam output is at the first gantry angle, and a second energy level when the beam output is at the first gantry angle. 18. The apparatus of claim 13, wherein the beam output is configured to deliver the treatment energy without using any flattening filter. 19. The medical apparatus of claim 1, wherein the current control is configured to adjust the current of the electromagnet such that a trajectory of the particle beam remains the same regardless of the energy level of the electric field in the accelerator or the energy level of the particle beam. 20. A medical apparatus comprising:an accelerator configured to provide a particle beam;an energy switch configured to change an energy level of the particle beam within a duration that is less than one second; anda target configured to receive the particle beam, wherein the target is a component of the medical apparatus;wherein the accelerator is configured to provide the particle beam directly onto the target without using a beam deflector at an end of the accelerator; andwherein the medical apparatus further comprises a beam output coupled to the accelerator, wherein the beam output is moveable to deliver treatment energy from a plurality of gantry angles that includes at least a first gantry angle and a second gantry angle. 21. The apparatus of claim 20, further comprising an energy adjuster configured to adjust the treatment energy so that the treatment energy has a first energy level when the beam output is at the first gantry angle, and a second energy level when the beam output is at the second gantry angle. 22. The apparatus of claim 21, wherein the energy adjuster is configured to adjust the treatment energy in a continuous manner. 23. The apparatus of claim 21, wherein the energy adjuster is configured to adjust the treatment energy in a discrete manner. 24. The apparatus of claim 20, wherein the beam output is configured to deliver the treatment energy without using any flattening filter. 25. The apparatus of claim 20, wherein the accelerator comprises a fixed-field alternating gradient (FFAG) accelerator, or a non-scaling fixed-field alternating gradient (NS-FFAG) accelerator. 26. The apparatus of claim 20, further comprising an ion chamber, wherein the ion chamber comprises a dosimetry circuit. 27. The apparatus of claim 26, further comprising a control configured to adjust a parameter in the dosimetry circuit in correspondence with the energy level of the particle beam. 28. A treatment method, comprising:configuring a medical system for delivering a first treatment beam having a first energy level;delivering the first treatment beam by the medical system towards a patient that is on a patient support;configuring the medical system for delivering a second treatment beam having a second energy level; anddelivering the second treatment beam by the medical system towards the patient; wherein the act of configuring the medical system for delivering the second treatment beam comprises changing an energy that is associated with an accelerator by an energy switch, and adjusting a current of an electromagnet by a current control in correspondence with the energy associated with the accelerator;wherein the first treatment beam is delivered towards the patient from a first gantry angle, and the second treatment beam is delivered towards the patient from the first gantry angle. 29. The method of claim 28, wherein the medical system comprises an ion chamber, wherein the ion chamber comprises a dosimetry circuit, and wherein the method further comprises adjusting a parameter in the dosimetry circuit in correspondence with the energy associated with the accelerator. 30. The method of claim 28, wherein the act of configuring the medical system, and the act of delivering are performed so that the first treatment beam transitions to the second treatment beam in a continuous manner. 31. The method of claim 28, wherein the act of configuring the medical system, and the act of delivering are performed so that the first treatment beam and the second treatment beam are delivered in a discrete manner.
052992411	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a transuranium element transmuting reactor core relating to the present invention will now be described with reference to the accompanying drawings. FIG. 1 represents a basic conception of a nuclear reactor such as pool type fast reactor enclosing the transuranium elements transmuting reactor core of the present invention. The present invention is applicable to a core of the nuclear reactor of a type to remove heating from cooling the core by flowing a coolant thereto and the coolant then includes liquid Na, liquid NaK, He gas and the like, which is intended for the core for which a fission is caused chiefly by a fast neutron. FIG. 1 represents an example of a pool type fast reactor, however, a loop type fast reactor may be exemplified, needless to say, in this case. The nuclear reactor includes a reactor vessel 10 which is charged with a liquid sodium (Na) 11 as a coolant. A core 12 is provided at a central portion in the reactor vessel 10, and a upper core structure 13 is provided above the core 12. The upper core structure 13 is supported by a roof slab 14 working as a shielding plug to cover a top of the reactor vessel 10. A primary coolant pump 15 and an intermediate heat exchanger 16 and others are suspended on the roof slab 14. A cover gas such as inert gas or the like is enclosed between the roof slab 14 and a free liquid surface of the liquid Na 11. The core 12 enclosed in the reactor comprises, as shown in FIG. 2 for example, two region cores 12a, 12b. A fuel assembly 17 relatively high in plutonium content is disposed in the outer peripheral area 12a and a fuel assembly 18 relatively low in plutonium content is disposed in the central area 12b. For charging amount of the MA elements of the TRU elements to be transmuted which is charged into the fuel assemblies 17, 18, a charging density of the MA elements is controlled at every areas or fuel assemblies 17, 18. A reference numeral 19 denotes a control rod. As exemplified in FIG. 3, the fuel assemblies 17, 18 have a plurality of fuel pins 21 enclosed in a bundle within a hexagonal wrapper tube 20 as a fuel element in a wide sense. A coolant inlet 22 is formed on a lower portion of the wrapper tube 20, and a coolant outlet 23 is formed on an upper portion. With opposite ends sealed up with an upper end plug 27 and a lower end plug 28, the fuel pin 21 enclosed within the wrapper tube 20 is that for which a plurality of fuel pellets 26 are inserted in a row, as shown in FIG. 4, within a fuel clad 25 as a fuel element. The fuel pellets 26 are retained elastically by a spring 29 within the fuel clad 25, a fuel stack portion 30 being constructed as an effective fuel length. The fuel pellet 26 is that for which as oxide fuel matter as fuel element is sintered through ceramics. A so-called metallic fuel is available for the fuel element instead of the oxide fuel matter, and the fuel element is not necessarily a thoroughly sealed type covered by the fuel clad 25. For example, a so-called vented fuel element (fuel pin) which discharges fission products gas (hereinafter called FP gas) such as He gas or the like outside the fuel element by fission is acceptable otherwise. On the other hand, the fuel assemblies 17, 18 are charged with the TRU elements (transuranium elements) to be transmuted, and a concrete case for controlling a charging amount of a main MA elements of the TRU elements to be charged is exemplified as follows: (1) An amount of the elements is controlled so that the MA elements to be transmuted which is added into the fuel pellets 26 will be distributed uniformly. (2) The fuel pellets with the MA elements to be transmuted relatively high in density and the fuel pellets with the elements relatively low in density or almost not added are prepared and a charging number of each fuel pellet to a fuel pin is controlled, thereby controlling the charging amount. An array order of the fuel pellets is arbitrary. (3) The fuel pin 21a with the MA elements to be transmuted relatively much in charging amount and the fuel pin 21b with the MA elements relatively little in charging amount or almost not charged are prepared, and a number of the fuel pins 21a, 21b enclosed within the wrapper tube 20 is controlled as shown in FIG. 5 and FIG. 6, thereby controlling a charging amount of the MA elements per the fuel assemblies 17 and 18. Meanwhile, if a percentage by weight of minor actinides (element with the atomic number 92 or over excluding uranium and plutonium; hereinafter called MA element) to total actinides with the atomic number 92 or over is called minor actinides content (hereinafter called MA content), a relation in the melting point between the MA content and the fuel pellet 26 is as indicated in FIG. 7, and a melting point of the fuel pellet 26 drops according as the MA content increases. Thus, a melting point of the fuel pellet to which the MA elements are added for transmuting the MA elements drops as compared with the fuel pellet to which the MA elements are not added, thereby facilitating a fuel melting. It is then necessary that a reactor power be lowered in a nuclear reactor so as to keep the fuel elements from being melted during operation of the nuclear reactor regardless of the melting point drop, and a neutron flux level of the nuclear reactor lowers due to a decrease of the reactor power. Meanwhile, a transmuting rates of the TRU elements is proportional to the MA content and the neutron flux level. When taking an adjustment of the reactor power further into consideration for prevention of a melting of the fuel element, the transmuting rates of the TRU elements is not always to rise monotonously along with an increase in the MA content, and, as shown in FIG. 8, there exists a peak portion whereat the TRU elements transmuting rates is maximized correlatively to the MA content. Then, an MA content P.sub.MA when the TRU elements transmuting rates is maximized is effective and hence is capable of realizing a transmuting of the TRU element most efficiently without causing a melting on the fuel element. On the other hand, in the case of ordinary fast reactor core, fissionable elements contained in the fuel are lost in accordance with burnup and thus fission products are accumulated, and therefore, an effective multiplication factor indicating the degree of a criticality of the nuclear reactor (fast reactor) decreases according to the lapse of time for the reactor operation. However, in the case of fast reactor core operation for transmuting of the TRU elements, main MA elements .sup.237 Np, .sup.241 Am, .sup.243 Am, .sup.242 Cm of the TRU elements to be transmuted are transformed, as shown in FIGS. 9A to 9D, into a fissionable elements easy to cause a fission by fast neutrons. Consequently, the effective multiplication factor comes to decrease moderately in accordance with the lapse of time for reactor operation. As shown in FIG. 10, when the MA content becomes excessive, the TRU elements are transformed into the fissionable elements too much, and the effective multiplication factor is capable of increasing according to the lapse of time for the reactor operation. Accordingly, a transition of the effective multiplication factor according to the lapse of time for the reactor operation may be controlled by the MA content. Now, therefore, such reactor core as will suppress a change in the effective multiplication factor in accordance with the reactor operation and keep an excess reactivity of the reactor substantially zero through the reactor operation may be designed by controlling the MA content. Further, a heating rates according to a decay of the MA elements of the TRU element can be calculated from a decay constant of each MA element and an energy emitted per decay. A decay constant of the MA elements to be transmuted and an energy emitted per decay are shown in FIG. 11A. A heating rates per gram of each MA element may be calculated by means of data given in FIG. 11A as shown in FIG. 11B. The MA elements of those of the TRU elements which contribute influentially to heating are .sup.242 Cm, .sup.244 Cm and .sup.241 Am, and hence, it is understood that a heating of the TRU elements will be calculated by taking these MA elements into consideration. On the other hand, if an upper bound of the heating rates per fuel assembly capable of removing heat is Q.sub.1 (w), then amounts of .sup.242 Cm, .sup.244 Cm and .sup.241 Am capable of charging into the single fuel assembly must satisfy the following equation: ##EQU1## where M.sub.242 : amount (g) of .sup.242 Cm charged into a single fuel assembly M.sub.244 : amount (g) of .sup.244 Cm charged into a single fuel assembly M.sub.241 : amount (g) of .sup.241 Am charged into a single fuel assembly Then, granted that the heating rates per a fuel assembly comes within the range capable of removing heat, if the heating is one-sided at a position, the fuel element is capable of being damaged and therefore, there is a limit to the charging of the MA elements to be transmuted from the viewpoint of preventing a fuel rupture. That is, if an upper bound of the heating rates per cm in an axial length of a local one fuel pellet .sub.2 is Q (w), a charging amount of the MA elements to be transmuted at the position must satisfy the following equation: ##EQU2## where, M.sub.242.sup.L : amount (g) of .sup.242 Cm charged per cm in axial length of local one fuel pellet M.sub.244.sup.L : amount (g) of .sup.244 Cm charged per cm in axial length of local one fuel pellet M.sub.241.sup.L : amount (g) of .sup.241 Am charged per cm in axial length of local one fuel pellet Accordingly, to prevent a failure of the fuel assembly due to overheating, it is necessary that a charging amount of the MA elements of the TRU elements to be transmuted is controlled so as to satisfy the above Eqs. (1) and (2) at the same time. For example, an upper bound of the heating rates per a fuel assembly, where a fuel stack general as the fuel assembly is 100 cm long, and fuel pins charged into the single fuel assembly are 271 pieces in number, is about 5 kw/assembly. In this case, an upper bound of addable amount of main MA elements .sup.242 Cm, .sup.244 Cm and .sup.241 Am which are contributive to heating to the fuel pellets is: ##EQU3## Accordingly, in order that the fuel assembly with the TRU elements added thereto may not cause overheating and failure of the fuel element for transmuting of the TRU element at the time of assembling, storage and transportation, if percentages by weight of the MA elements .sup.242 Cm, .sup.244 Cm and .sup.241 Am to be transmuted to a total weight of the heavy metal elements of a fresh fuel pellet are f.sub.242, f.sub.244 and f.sub.241, then it is necessary that: ##EQU4## be realized. So far as an amount of the main MA elements of the TRU elements added to the fresh fuel pellet satisfies Eq. (3), the fresh fuel assembly will never be overheated or damaged. Further, as will be understood from FIG. 9, the MA elements of the TRU elements to be transmuted functions generally as a neutron absorber, and its degree is stronger than uranium 238 (.sup.238 U), as shown in FIG. 12, in the fast reactor core. On the other hand, if the ratio of weight of plutonium element, or the plutonium content, to the weight of total heavy metal elements in the fuel pellet is called a plutonium (Pu) enrichment, in the fast reactor core, since the neutron flux level normally decreases according as it goes outside from the core center, the power density lowers according as it goes outside in the same Pu enrichment area. Accordingly, in the same Pu enrichment area at the fast reactor core operating for transmuting the TRU elements, the charging density of the MA elements to be transmuted which functions as a neutron absorber will be lessened gradually outside from the reactor core, thereby satisfying a flatting requirement. Thus, fluctuation and change of the reactor power are suppressed, and reliability and safety of the nuclear reactor can be enhanced. Further, in the fast reactor core having the Pu enrichment in two kinds or more, since the area higher in the Pu enrichment has a high content of fissionable elements, and the fissionable elements are transmuted quick by burnup in accordance with the reactor operation. Thus in the area high in the Pu enrichment, a power density according to the operation lowers more. On the other hand, the MA elements to be transmuted are transformed, as shown also in FIGS. 9A to 9D, into fissionable elements by a neutron capture. Accordingly, from increasing the charging density of the MA elements to be transmuted in an area higher in the Pu enrichment, a decrease of the power density according to the operation of the nuclear reactor will be compensated for with the transformation into a fissionable elements of the MA elements to be transmuted, thus moderating the decrease of the power density according to the reactor operation. FIG. 13 exemplifies a main specification characteristic of a fast reactor core to which the TRU elements transmuting reactor core according to the present invention is applied, and FIG. 14 shows a charging density radial distribution of the MA elements charged into the transmuting reactor core. The mean MA content of the fast reactor core in the example shown in FIG. 13 is, for example, 5 percent by weight. As shown in FIG. 8, the MA content is set so as to minimize an excess reactivity of the reactor to substantially zero, for example, in the range where a fuel fusion does not occur during operation of the reactor. When the MA content is 5 percent by weight, an amount of the fissionable elements produced by a neutron capture of the charged MA elements is moderate to be balanced just sufficiently with the amount transmuted by fission, therefore an excess reactivity of the reactor during operation of the reactor being checked to be about 0.5% .DELTA. K/K maximumly. In the case of an ordinary fast reactor core equivalent to the present embodiment in a reactor thermal power and the operation cycle length, the maximu excess reactivity during the operation is about 3% .DELTA. K/K. In the example, since the MA elements has a neutron absorbing effect as a control rod, a required reactivity worth of the control rod may be minimized, thus the number of control rods and the required amount of neutron absorber such as boron, hafnium or the like which is charged into the control rod being reduced, and an economical efficiency will be enhanced. If an excess reactivity of the reactor is low, a reactivity insertion into the reactor at the time when the control rod is drawn erroneously can be minimized, thereby ensuring a safety. Further, the excess reactivity of the reactor can be kept low through the reactor operation, and thus a reactivity loss of the reactor due to the reactor operation, namely the decrease of the effective multiplication factor according to burnup can be minimized. Thus, the period of continuous operation of the reactor or the operation cycle length can be prolonged, and a plant capacity factor or besides the transmuting efficiency of the TRU elements may be enhanced. Further, in the present embodiment, the charging density of the MA elements varies, as shown in FIG. 14, according to a position where the fuel assembly is charged into the reactor core, however, when a fresh fuel assembly outside the reactor is taken particularly into consideration, even in the case of the fresh fuel assembly whereby a heating rates is maximized, the MA elements are set within the range satisfied by the Eqs. (1) and (2) or (3) so as not to increase the heating rates excessively by a decay of the MA elements. Accordingly, the maximum heating rates of the fresh fuel assembly outside the reactor is about 5 kw/assembly, as shown in FIG. 13, and hence, a trouble such as failure due to the overheating of the fuel assembly or the like will not result at the time when assembling, storing and transporting the fresh fuel assembly. Still further, in the present embodiment, a radial distribution of the charging density of the MA elements at the reactor core is made less, as shown in FIG. 14, according as it goes outside of the reactor core in the same Pu-enriched area. Besides, since the MA elements functions as a neutron absorber, the neutron flux level getting large toward the core central portion is suppressed normally by the MA elements, and in result, the radial distribution of the neutron flux becomes flatter. Accordingly, as shown in FIG. 15, the radial distribution of the reactor power density is flattened during the period of the reactor operation cycle as compared with a prior art exemplified in FIG. 21. Thus, a local power peak will be kept from arising, and hence a thermal tolerance of the fuel assembly can be ensured thoroughly, thus enhancing an economical efficiency such as compacting and lightening the reactor core in structure. Further, in the present embodiment, the area higher in Pu enrichment is kept high in the MA elements charging density as compared with the area lower in Pu enrichment, as shown in FIG. 14, the area higher in Pu enrichment has fissionable elements resulting from the neutron capture of the MA elements more than that. On the other hand, a consumption due to the burnup of the fissionable plutonium is more with the area high in Pu enrichment where the fissionable plutonium is present much. Accordingly, the distribution of the MA elements charging density shown in FIG. 14 is set at every area of Pu enrichment so that the area with much consumption of the fissionable plutonium has much fissionable elements produced by the neutron capture of the MA elements, therefore a net decrease of the fissionable elements according to the reactor operation being suppressed, and, as shown in FIG. 15, a fluctuation of the power density according to operation is suppressed. Thus, if a fluctuation of the power density is minimized according to the operation of the fast reactor (nuclear reactor) or burnup, the heat removing efficiency is improved, the enhancement of economical efficiency is realized, and thus fuel temperature is decreased, and safety and reliability of the reactor core can be enhanced accordingly. FIG. 16 is a graph representing a second embodiment of the TRU elements transmuting reactor core according to the present invention. Even in the case of a reactor core where the Pu enrichment is one kind, the fast reactor core represented in this embodiment has a radial distribution of the MA element charging density flattened preferably as compared with the prior art as shown in FIG. 6 and also has a radial power distribution of the core flattened as shown in FIG. 17. Accordingly, from employing the present invention, the reactor power distribution is flattened despite Pu enrichment being one kind and therefore, the plant efficiency will be enhanced, and the economical efficiency such as decrease in fuel fabrication cost or the like may also be enhanced. Needless to say, a similar characteristic to the first embodiment applies to those other than the reactor power distribution. Further, as another embodiment, the axial distribution is applied to the MA elements charging density as in the case where a radial reactor power distribution is flattened according to the present invention as described above, thereby flattening the axial reactor power distribution. If the power distribution need not be flattened, an MA content of the whole core will be set according to the present invention even in case a distribution is not applied particularly to the MA elements charging density, thereby realizing effects such as decrease in excess reactivity of the reactor through the operation, prevention of overheating and failure of the fresh fuel assembly outside the reactor and the like. As described above, in the transuranium element transmuting reactor core relating to the present invention, since an amount of transuranic elements added to the fuel element of fuel assemblies is controlled so as to keep an excess reactivity of the reactor substantially zero through the operation of the reactor, the decrease of the effective multiplication factor according to the lapse of time for the operation is prevented, the excessive deterioration and turbulence of the reactor power distribution can be prevented, the reliability of the power plant is thus enhanced, and as seeking an improvement of the plant operating efficiency, transuranium elements (TRU elements) can be transmuted efficiently. Then, from setting charging amounts of.sup.242 Cm, .sup.244 Cm and .sup.241 Am into the fuel assembly so as to realize: EQU 1.2.times.10.sup.2 .times.M.sub.242 +2.8.times.M.sub.244 +1.1.times.10.sup.31 1 .times.M.sub.241 <Q.sub.1 where an upper bound of heating rates of the single fuel assembly outside the reactor is Q.sub.1, charging amounts of.sup.242 Cm, .sup.244 Cm and .sup.241 Am which can be charged into the single fuel assembly are M.sub.242, M.sub.244 and M.sub.241, and also to realize: EQU 1.2.times.10.sup.2 .times.M.sub.242.sup.L +2.8.times.M.sub.244.sup.L +1.1.times.10.sup.-1 .times.M.sub.241.sup.L Q.sub.2 where an upper bound of heating rates of per unit length of the fuel pellet contained in the fuel pins is Q.sub.2, charging amounts of.sup.244 Cm and .sup.244 Cm and .sup.241 Am per the unit length are M.sub.242.sup.L, M.sub.244.sup.L and M.sub.241.sup.L, a melting of the fuel pellet during the reactor operation of the reactor and an overheating or failure of the fuel assemblies outside the reactor can be prevented and a neutron absorption effect of .sup.242 Cm, .sup.244 Cm and .sup.241 Am is available for eliminating accidents of a control rod and a neutron absorbing material of the control rod and also for realizing the improvement of the heat removing efficiency of the core, the economical efficiency will be enhanced, the safety and the reliability of the core and the fuel assemblies will be enhanced as well, and the TRU elements can be transmuted efficiently. Further, by setting a charging density of minor actinides to lessen outwards of a core center in a core area where a plutonium content is even and also by setting a charging density of minor actinides high accordingly in an area where Pu is enriched high at the core of a Pu-enriched area, the radial distribution of the reactor power can be flattened, the excessive deterioration or turbulence of the reactor power distribution will never result, the enhancement of safety and reliabiilty of the core and the fuel assemblies may be realized, and thus the TRU elements can be quenched efficiently. Further embodiments of the present invention will be described hereunder in conjunction with FIGS. 22 to 30, with reference to transuranium elements transmuting fuel pins and fuel assemblies. FIG. 22 exemplifies a transuranium elements transmuting fuel assembly according to another embodiment of the present invention which is charged into the fast reactor core. The fuel assembly 110 has a coolant inlet 111 at the lower portion thereof for letting in the coolant such as liquid sodium (Na), liquid NaK, helium (He) gas or the like and a coolant outlet 112 at the upper portion thereof, and a plurality of fuel pins 114 are enclosed in a bundle within a wrapper tube 113 square tubular or, for example, hexagonal in section which works as a fuel channel. The fuel pin 114 enclosed within the wrapper tube 113 may be constructed only of a TRU (transuranium elements) fuel pin 115, or of the TRU fuel pin 115 and an ordinary fuel material pin 116 otherwise as shown in FIG. 23. In the case of TRU fuel assembly having constructed the fuel assembly 110 only of the TRU fuel pins 115, nothing will be taken into consideration for arrangement of the TRU fuel pins 115, an administration on manufacture and assembling of the TRU fuel pins 115 is facilitated, the number of fuel assemblies for which a special measure such as heat removing, shielding or the like is required may be minimized, thus enhancing an economical efficiency on a core administration and a fuel handling. Then, in case the TRU fuel assembly 110 is constructed of the TRU fuel pin 115 and the ordinary fuel material pin 116, the change in reactor power according to the reactor operation is minimized for presence of the TRU elements, and the TRU elements can be transmuted efficiently without lowering a cooling efficiency of the core as, in addition, keeping the integrity of the reactor internal structure. FIG. 23 exemplifies the case where the TRU fuel pins 115 are dispersed and disposed almost uniformly within the wrapper tube 113 of the TRU fuel assembly 110. By dispersing and disposing the TRU fuel pins 115 uniformly, a relatively low-temperature coolant around the TRU fuel pins 115 and a relatively high-temperature coolant around the usual fuel material pins 116 are mixed acceleratedly in the presence of the TRU element, a fuel clad temperature of the ordinary fuel material pin 116 is decreased, the cooling efficiency of the core can be enhanced, the ordinary fuel material pin 116 can be made to last so long, and the economical efficiency and safety of the fast reactor can thus be enhanced. Meanwhile, as shown in FIG. 24, the TRU fuel pin 115 has a fuel clad 118 charged with a TRU fuel material 119, and its upper and lower portions closed by an upper end plug 120 and a lower end plug 121. The TRU fuel material 119 has at least one of an ordinary fuel material and a fertile material consisting of degraded uranium, natural uranium and depleted uranium contain TRU elements (trans- uranium elements) of minor actinides elements such as Np (neptinium), Am (americium), Cm (curium) and the like. Here, the ordinary fuel material refers to a fuel material consisting of an enriched uranium and an uranium-plutonium mixed fuel (uranium fuel having enriched plutonium). An oxide fuel such as uranium oxide or the like is used for the fuel material, however, a metallic fuel may be employed instead of the oxide fuel. Further, the ordinary fuel material pin 116 has the fuel clad charged with a plurality of so-called fuel pellets (or metallic fuel otherwise) having sintered the ordinary oxide fuel material, and the upper and lower ends closed by the upper end plug and the lower end plug, a gas plenum part being formed on at least one portion, or upper and lower portions, for example, in the fuel clad. Then, the TRU fuel pin 115 and the ordinary fuel material pin 116 have been described with reference particularly to a closed type one closed by the upper and lower end plugs, however, this need not always be a full-closed type, and hence a so-called vented type fuel pin which is capable of discharging fission products gas (hereinafter called FP gas) generated by the fission outside the fuel pins 115 and 116 may be employed. FIG. 24 exemplifies the TRU fuel pin 115 working as a transuranic elements transmuting fuel. The fuel pin 115 is that of having a multiplicity of TRU fuel areas provided axially, a TRU fuel 119a high in content of Np of the minor actinides elements is disposed in a core upper portion area of the fuel clad 18, a TRU fuel 119c high in content of Am and Cm is disposed in a core lower portion area, and a TRU fuel 119b is also disposed in a core height center area high in a neutron flux level, and an ordinary fuel 122 is disposed among the TRU fuels 119a, 119b, 119c to constitute the TRU fuel material 119. A gas plenum part 123 is formed on an upper portion of the fuel clad 118, the upper and lower ends being closed by the upper end plug 120 and the lower end plug 121. In the gas plenum part 123, a spring is installed, as occasion demands, so as to stably hold the TRU fuel material 119. By disposing the TRU fuels 119a, 119b, 119c with which the fuel clad 118 of the TRU fuel pin 115 is charged inside as indicated in FIG. 25A, a core axial power distribution curve A of the fast reactor is as indicated by a full line and a peak power is decreased more than a core axial output distribution curve B indicated by a broken line in the case of the ordinary fuel material pin 116, thus the reactor characteristic and the transmuting efficiency of the TRU elements being improved. Typical minor actinides elements .sup.237 Np, .sup.241 Am, .sup.243 Am, .sup.242 Cm, .sup.244 Cm of the TRU fuels 119a to 119c with which the TRU fuel pin 115 is charged inside the capture neutrons to fissionable elements as shown in FIGS. 9A to 9D when charged into the fast reactor core to the reactor operation, thus transmuting the TRU elements. Further, due to the TRU fuel pin 116 having the fuel clad 118 charged with the TRU fuel pellets 119 inside, there arises a problem that the melting of the fuel drops due to the presence of the minor actinides elements. The fuel melting will not result even at the transient conditions of the fast reactor according to a normal core design, and in the TRU fuel pin 115 shown in FIG. 24, the TRU fuel 119a high in content of low melting point MA elements is disposed in the core area with high fuel temperature, namely the core upper portion area in the case of the metallic fuel, and the core height center area in the case of the oxide fuel, and the TRU fuel 19c high in content of high melting point MA elements is disposed in the core lower portion area where the fuel temperature is low. By disposing the TRU fuel 119c containing Am and Cm with the melting point dropping comparatively large for the oxide fuel in the area where the fuel temperature is low, the drop of the fuel melting point due to the content of the TRU element such as Am and Cm or the like does not exert an influence directly on determination of the core power density, and the TRU elements can be transmuted efficiently without lowering the core power density. On the contrary, the melting point of Np is lower than that of Am and Cm for the metallic fuel. Meanwhile, typical minor actinides elements .sup.237 Np, .sup.241 Am, .sup.243 Am, .sup.242 Cm, .sup.241 Cm of the TRU fuel pellets 119 with which the fuel clad 18 of the TRU fuel pin 115 are charged inside are transformed into fissionable elements, as shown in FIGS. 9A to 9D, by a neutron absorption, and therefore, a power of the TRU fuel assembly constructed only of the TRU fuel pin 115 sharply increases as indicated by a symbol I in FIG. 27 according to the number of days for operation. Accordingly, the power of the TRU fuel assembly constructed only of the TRU fuel pin 115 is low at the point in time of start for operation but increases largely according to the operation. Then, as shown in FIG. 24, in the TRU fuel assembly 110 for which the TRU fuel pin 115 and the ordinary fuel material pin 116 are disposed mixedly, since the ordinary fuel material pin 116 generates power, the power of the TRU fuel assembly 110 is also high relatively at the point in time of start for the reactor operation as indicated by a symbol II in FIG. 26, and since the decrease in the fissionable material of the ordinary fuel material pin 116 and the transformation of the TRU fuel element 119 into a fissionable material are offset, the degree of power flunctuation of the TRU fuel assembly 110 due to the operation is smaller and smoother than the fuel assembly constructed only of the TRU fuel pin 115. In a core design, a coolant flow rate of the fuel assembly charged into the core is specified so as to remove heat at the time of maximum power of the fuel assembly. The TRU fuel assembly constructed only of the TRU fuel pin 115 does not generate a power corresponding to the coolant flow rate at the time of start for the operation or for a several time after the start, an outlet temperature is low consequently, and therefore, the coolant outlet temperature does not rise, thus leaving a problem on the cooling efficiency of the core and the integrity of the reactor internal structure. However, in the case of the TRU fuel assembly for which the TRU fuel pin 115 and the ordinary fuel material pin 116 are disposed mixedly as shown in FIG. 23, the power coming up substantially to the maximum power is generated at the time of the start for the operation or for a several time after the start, and therefore, an outlet temperature of the TRU fuel assembly 110 will not drop extremely, and thus the problem on the cooling efficiency of the core and the integrity of the reactor internal structure can be avoided. Then, as shown in FIG. 24, by mixing a radioactive fission product (F. P) such as strontium (Sr), alkaline metals (Cs or the like), technetium (Tc) or the like into the TRU fuel pellets 119 with which the fuel clad 118 of the TRU fuel pin 115 is charged inside, the transmuting of the TRU elements and also the transmuting of a long-lived radioactive fission products in the reactor and the internal administration of the reactor are realizable. The disposal and administration of the radioactive waste products will be facilitated as compared with the case where these are carried out outside the reactor. For example .sup.99 Tc is transformed into a stable elements which is not radioactive in the fast reactor by neutron capture (neutron absorption) and others, and .sup.90 Sr and .sup.137 Cs become: EQU .sup.90 Sr.fwdarw..sup.90 Y.fwdarw..sup.90 Zr (stable) EQU .sup.137 Cs.fwdarw..sup.137m Ba.fwdarw..sup.137 Ba (stable) by natural decay while residing in the reactor, and .sup.90 Zr and .sup.137 Ba are stable materials, which are removed from a fuel through the spent fuel reprocessing. In the TRU fuel pin 115 shown in FIG. 24, the case where TRU fuels 119a, 119b, 119c are dispersed and arranged axially is exemplified, however, a TRU fuel pin 115A may be constructed as shown in FIG. 27 so as to minimize the influence to be exerted on the reactor power distribution by the TRU elements. Like reference characters are applied to the like portions in FIG. 24, and a further description will be omitted here. The TRU fuel pin 115A exemplifies the case where the TRU fuels 119b containing the TRU element which constitute the TRU fuel pellets 119 are disposed even axially at a relatively low content (several percent by weight or below). The TRU fuel pin 115 for which the TRU fuels are disposed uniformly has an advantage that an administration on fabrication and transportation is facilitated, a fabrication cost can be reduced, and an influence to be exerted on an axial power distribution is uniform and minimized. Further, the TRU fuel pin 115A is much in the TRU elements loading amount per pin, and thus is available for enhancing the transmuting efficiency of the TRU elements. A TRU fuel pin 115B shown in FIG. 28 exemplifies the case where the TRU fuel pellets 119 with which the fuel clad 118 is charged inside has the TRU fuel 119b disposed only in the core height center area, and such disposition is effective in decreasing a peak power and flattening the core axial power distribution. By disposing the TRU fuel 119b in the core height center area where a neutron flux density is high, the power peak is reduced preferably by the distortion of the core axial power distribution, the power distribution is flattened, and a reactor characteristic is improved to enhance the transmuting efficiency of the TRU elements. Then, in this case, the content (percent by weight) of the TRU elements contained in the TRU fuel 119b is relatively high to stand, for example, at 10% or over as in the case of the TRU fuel pin 115 of FIG. 24. Further, in the first embodiment of the transuranic elements transmuting fuel assembly 110, the case where the TRU fuel pins 115 are dispersed and disposed uniformly in the TRU fuel assembly 110 as shown in FIG. 23, however, the fuel pins 115 (115A, 115B) will be disposed intensively in the center area of the TRU fuel assembly 110, as shown in FIG. 29, and the ordinary fuel material pins 116 will be disposed around the TRU fuel pins 115 otherwise. In case the TRU fuel pins 115 are disposed intensively in the center area, since the TRU fuel assembly 110A has the neutron flux density maximized at the center area, the transmuting efficiency of the TRU elements can be enhanced. In the TRU fuel assembly 110A, the fuel pins disposed around the TRU fuel pins 115 (115A, 115B) may comprise a fertile material pin consisting of natural uranium and depleted uranium, and by disposing such fertile material pins, alpha rays and neutrons emitted from the TRU fuel pins 115 are shielded, and thus measures on transportation and shielding of the TRU fuel assembly 110A may be relieved. A TRU fuel assembly 110B shown in FIG. 30 exemplifies the case where the TRU fuel pins 115 (115A, 115B) are disposed at an outer peripheral position abutting on a inside wall of the wrapper tube 113. The ordinary fuel material pins 116 are disposed inside of the TRU fuel pins 116 arrayed as above. Generally, the coolant flow rate per one fuel pin is larger on the wall side of the wrapper tube 113 than in the center area, and temperature of the fuel clad 118 on the wall side becomes lower than the center area. When the metallic fuel is employed as the fuel of the TRU fuel assembly 110B, it is necessary that the fuel clad temperature be adjusted as low as possible for the prevention of an eutectic reaction of the fuel clad 118, with the metallic fule slug. The TRU fuel assembly 10B shown in FIG. 30 is that for which the TRU fuel pins 115 are disposed along the inside wall of the wrapper tube 113 with a coolant flowing much therethrough, the fuel clad temperature is reduced thereby, the economical efficiency of the TRU fuel assembly 110B is thus secured to prolong the lifetime. Then, the TRU fuel pins 115 (115A, 115B) have typical minor actinides elements easy to cause alpha-decay contained much in the TRU fuel material 119, and thus a relatively high alpha ray energy is emitted at the time of alpha-decay, and therefore, special measures on fabrication, heat removing and shielding which are different from the ordinary fuel will be necessary for the TRU fuel pins 115 (115A, 115B) and the TRU fuel assemblies 110 (110A, 110B). Thus, for the TRU fuel pin 115, the TRU fuel pellets 119 is constructed by containing the TRU elements or specific minor actinides elements at a predetermined content. For fuel temperature and others to keep in order, it is preferable that the TRU fuel pin 115 be provided with a TRU fuel material area in the area lower than the core height center more than the area upper than the core height center. Further, from inserting a control rod into the core, the transmuting efficiency of the TRU elements may be enhanced by providing the TRU fuel area in the core height center area where a neutron flux level gets high, thereby flattening the core axial power distribution. Further, by disposing the TRU fuel in the area lower than a core height center level whereat the neutron flux level becomes high, the melting of the TRU fuel can be avoided effectively and securely. As a described above, in the transuranium element transmuting fuel pin and fuel assembly relating to the present invention, an improvement of core characteristics and an enhancement of the core cooling efficiency may be achieved without causing deterioration of the core characteristics according to various restrictions such as fuel melting during the operation of the reactor, excessive change of the core axial power distribution, distortion of the distribution and the like. Thus the safety and reliability of the fuel assemblies and fuel pins to be charged into the core may thus be achieved and the transmuting efficiency of the TRU elements can be improved and enhanced.
	claims	1. A process for producing a detected X-ray image of a breast, the process comprising the steps of: a) directing an X-ray beam produced by an X-ray tube, characterized by an output function comprising an X-ray tube current function and an X-ray tube voltage function, from a focus of the X-ray tube through the breast so that the beam impacts an image receptor to produce the detected X-ray image, where the intensity of primary X-ray radiation at a given point on the image receptor is characterized as a function of time by an image intensity function; b) placing an anti-scatter grid between the breast and the image receptor, the anti-scatter grid characterized by a grid transmission function that is a periodic function of position characterized by a grid pitch; c) producing a grid motion by moving the grid at a velocity during an X-ray exposure, the velocity characterized as a velocity function; and d) modulating the output function such that for some thickness and composition of breast tissue, the image intensity function is substantially equal to the function i(t) defined by the equation where x c (t) is the position of the center of the anti-scatter grid at time t, the velocity function v(x) is the velocity of the grid when the center of the anti-scatter grid is at position x, g(x) is an arbitrary function with a finite integral over x and has zero value outside a finite domain of x, h(x) is non-negative for every value of x, R(x) is the rect function, n is a positive integer, and P is the grid pitch. 2. The process of claim 1 where the velocity function is substantially constant during the X-ray exposure, the tube voltage function is substantially constant during the X-ray exposure, the tube current function is modulated by varying a tube current, and the grid motion is characterized by a grid repeat time, where the grid repeat time is equal to the grid pitch divided by the grid velocity. claim 1 3. The process of claim 2 where the tube current function is modulated by varying a filament current of the X-ray tube. claim 2 4. The process of claim 2 where the tube current function is modulated by varying a voltage of a part of the X-ray tube selected from the group consisting of: a control grid and a bias cup. claim 2 5. The process of claim 2 where the tube current function has a Fourier transform that has a negligible amplitude at all frequencies equal to positive multiples of the reciprocal of the grid repeat time. claim 2 6. The process of claim 2 where the tube current function is substantially equal to a convolution of an arbitrary function with a rect function having a width substantially equal to an integer multiple of the grid repeat time. claim 2 7. The process of claim 2 where the tube current function is a symmetric trapezoidal function having a ramp time substantially equal to a positive integer multiple of the grid repeat time. claim 2 8. The process of claim 2 where the tube current function is a convolved dual symmetric trapezoidal function. claim 2 9. The process of claim 1 where the output function is modulated by using a dynamic tube current function and a pseudo-rect tube voltage function. claim 1 10. The process of claim 1 where the output function is modulated by using a dynamic tube current function and a dynamic tube voltage function. claim 1 11. The process of claim 1 where the output function is modulated by using a pseudo-rect tube current function and a dynamic voltage function. claim 1 12. The process of claim 1 where the velocity function is substantially constant during the X-ray exposure. claim 1 13. The process of claim 1 where the velocity function varies during the X-ray exposure. claim 1 14. The process of claim 1 where the anti-scatter grid comprises claim 1 a) a plurality of radio-opaque septa, interspersed with a radiolucent interspace material; and b) a means to move the grid during the X-ray exposure to produce the grid motion at the velocity. 15. The process of claim 14 where the width of the interspace material is greater than 8 times the width of the septa. claim 14 16. The process of claim 14 wherein the grid motion is linear. claim 14 17. The process of claim 14 wherein the anti-scatter grid further comprises a focusing means to keep the grid aligned on the focus during the grid motion. claim 14 18. The process of claim 14 wherein the anti-scatter grid comprises one set of radio-opaque septa, where the septa are substantially parallel to each other and are substantially aligned with the focus. claim 14 19. The process of claim 14 where the focusing means comprises a mechanism that moves the grid in an arc whose center is substantially coincident with a grid focal axis, the grid is periodic in an angular distance relative to the grid focal axis, and the velocity function describes an angular velocity of the grid about the grid focal axis. claim 14 20. The process of claim 19 wherein the focusing means comprises a plurality of bearings mated to the grid and a plurality of curved guide tracks, the bearings configured to engage the plurality of curved guide tracks, where the focus and a center of curvature of each curved guide track are substantially coincident with the grid focal axis. claim 19 21. The process of claim 19 wherein the focusing means comprises a plurality of bearings mated to the grid and at least two straight guide tracks, the bearings configured to engage the at least two straight guide tracks, the at least two straight guide tracks positioned such that a line normal to each track at a point where the bearings contact the track at a center of motion of the grid passes substantially close to the focus. claim 19 22. The process of claim 14 where the focusing means comprises an articulating mechanism which articulates the septa individually to keep the septa focused on the focus, the motion of the grid is linear in a plane substantially parallel to the image receptor, the grid transmission function is periodic in linear distance in the direction of motion, and the velocity function describes a linear velocity of the grid. claim 14 23. The process of claim 22 where the articulating mechanism comprises an upper support, a lower support, a first hinge means to moveably attach the septa to the upper support and a second hinge means to moveably attach the septa to the lower support and the articulating mechanism moves the upper support a first distance and the lower support a second distance. claim 22 24. The process of claim 23 where the first distance and the second distance are not the same. claim 23 25. The process of claim 23 where the ratio of the first distance to the second distance is equal to a distance from the focus to the upper support divided by a distance from the focus to the lower support. claim 23 26. The process of claim 14 where the interspace material is air, polymer foam or aerogel. claim 14 27. The process of claim 14 wherein the anti-scatter grid comprises two sets of radio-opaque septa, where the septa within each set are substantially parallel to each other and oriented to align with the focus, and the septa and a focal axis of the first set of septa are substantially perpendicular to the septa and a focal axis of the second set of septa. claim 14 28. The process of claim 14 wherein the anti-scatter grid comprises a plurality of radio-opaque sheets having a plurality of holes perforating the sheets, the sheets stacked so the holes are aligned with each other and with the focus. claim 14 29. The process of claim 28 wherein the focusing mechanism consists of a mechanism that moves the radiopaque sheets individually to keep them oriented on the focus. claim 28 30. The process of claim 28 wherein the pattern of holes in the plurality of sheets is periodic in the direction of the grid motion, and is periodic either in a linear position or in an angular position on the sheet. claim 28 31. The process of claim 28 wherein the shape of the holes in the plurality of sheets is selected from the group consisting of: hexagonal, square and triangular. claim 28 32. The process of claim 14 where the spacing between the septa is maintained by a thin radiolucent sheet fixedly attached to the edges of the septa. claim 14 33. The process of claim 14 where the spacing between the septa is maintained by a thin radiolucent sheet pivotally attached to the edges of the septa. claim 14
044302916	claims	1. In a fusion plasma system having a circular cross section, said fusion system substantially surrounded by a blanket structure for the capture and transmittal of energy from said plasma, wherein said blanket structure comprises:
046722130	claims	1. Container, especially adapted for enclosing radioactive substances such as radioactive liquids, which comprises; an inner container for receiving a substance to be contained and sealed gas and liquid tight under normal operating conditions, an outer container in which the inner container is disposed, and thermal insulation between the inner container and the outer container, in combination with a closed tubular circulating system comprising a coolant tube associated with the inner container disposed within the outer container, said coolant tube containing a fluid coolant which circulates through the coolant tube out of direct contact with the substance in the inner container, a heat-discharge tube which also contains the coolant arranged along the inner wall of the outer container with said thermal insulation between said cooling and heat discharge tubes and connecting lines at both tube ends of the cooling tube and the heat discharge tube through which said cooling tube and said heat discharge tube are in communication with each other to permit circulation of the coolant from the coolant tube to the heat-discharge tube and return of the coolant from the heat-discharge tube to the coolant tube. 2. Container according to claim 1, wherein the cooling tube is attached to the outside of the inner container. 3. Container according to claim 1, wherein a feedthrough with a pressure relief valve or a rupture disc is provided in the wall of at least one of the cooling tube, the heat discharge tube and the connecting lines. 4. Container according to claim 1, wherein a feedthrough which is closed-off by a solder, the melting temperature of which is lower than the melting temperature of the material of the cooling tube, the heat discharging tube and the connecting lines, is provided in the wall of at least one of the cooling tube, the heat discharge tube and the connecting lines. 5. Container according to claim 3, wherein the feedthrough opens to the outside of the outer container. 6. Container according to claim 4, wherein the feedthrough opens to the outside of the outer container. 7. Container according to claim 1, wherein a connecting nozzle for a cooling unit is provided at the connection lines. 8. Container according to claim 1, wherein a connecting nozzle for a cooling unit is provided at the heat discharge tube. 9. Container according to claim 1, wherein in the interior of the inner container, a body of a material which readily absorbs neutrons is arranged. 10. Container according to claim 1, wherein the inner container is provided with a pressure relief valve leading into the outer container. 11. Container according to claim 1, wherein an absorption body is located in the outer container, outside the inner container for taking up substances which have escaped from the inner container into the outer container.
048246344	summary	BACKGROUND OF THE INVENTION This invention relates to nuclear fuel elements and in particular, the provisions of fuel elements with a burnable poison coating in the form of a thin layer of boron-containing compound particles on the inside of a cladding tube. The burnable poison particles are deposited alone or with lubricity providing graphite particles from a liquid suspension on the inside of a zirconium-alloy cladding tube. A nuclear fuel element of the type involved in the invention is part of a fuel assembly. Heretofore, typical fuel assembly designs have employed fixed lattice burnable poison rods to control early-in-life reactivity and power peaking. These rods have become a necessary design feature for the fuel management of first cores of light water reactors as well as in schemes to achieve extended burnups and reduced radial neutron leakage. Such rods displace fuel rods within the assembly lattice which increases the core average linear heat generation rate and local peaking factors. Alternate approaches have been proposed that place burnable poison material inside the fuel rods so that much less fuel material is displaced, for example, as boride coatings on the UO.sub.2 pellets. Such coatings, however, while adhering when first applied, tend to spall off under the stresses of the irradiation environment in the nuclear reactor core, in part because of difficulty in matching the thermal expansion behavior of the coating to that of the fission material or UO.sub.2 pellet. Attempts to incorporate boron compounds as mixtures within the UO.sub.2 pellets have not been successful because of volatilization of boron species during high temperature fabrication processes and redistribution of the boron under irradiation. For further background, see U.S. Pat. Nos. 3,925,151; 4,372,817; 4,560,575; 4,566,989; 4,582,676; 4,587,087; 4,587,088; and 4,636,404. SUMMARY OF THE INVENTION The invention involves an improved fuel element with a burnable poison coating which substantially overcomes problems of spalling and coating integrity because of the closely matched thermal expansion coefficients of the substrate and coating material and the action of fission sintering to enhance adhesion of the coating to the substrate. The invention includes coating a thin layer of a boron-containing compound on the inside surface of the zirconium alloy cladding tube of the fuel rod. The preferred boron-containing compound is zirconium diboride (ZrB.sub.2) because its thermal expansion coefficient most nearly matches that of the zirconium-tin alloy cladding tube. The adhesion between the coating and cladding, therefore, is less likely to deteriorate under irradiation than would similar coatings on the UO.sub.2 pellets. Also, the fission sintering phenomenon that has been observed in irradiated compacts of boron-containing compound powders at cladding temperatures (approximately 400.degree. C.) is more likely to promote adhesion between the ZrB.sub.2 and the metallurgically-related zirconium-tin alloy cladding tube substrate than would be the case for a UO.sub.2 substrate. That is, fission sintering will not only join ZrB.sub.2 particles to each other, but is also likely to form a bond of the particles to the zirconium-tin alloy substrate under irradiation. A suitable thin layer or coating of ZrB.sub.2 particles on the inside surface of the cladding tube is applied by a method analagous to that used for graphite lubricant coatings developed by the laboratories of the assignee of the instant invention for nuclear fuel rod cladding. A liquid suspension which includes isopropanol, an acrylic polymer binder material and the boron-containing compound particles in a range of from 0.1 to 1.5 microns, with or without colloidal graphite particles, has its solids content adjusted to provide the desired viscosity for the coating process (approximately 16% by weight solids). Each fuel tube is then filled with the liquid suspension and drained at a controlled rate, leaving a thin film on the inside surface of the cladding tube. The film is dried at room temperature and cured in a vacuum at temperatures up to 427.degree. C. (800.degree. F.). The resulting thin layer containing ZrB.sub.2 (and perhaps graphite) at a density of approximately 50% of theoretical, along with a small residue from the decomposition of the binding material. The ZrB.sub.2 is preferably initially enriched in the B.sup.10 isotope to an 80% level.
051909901	abstract	During radiotherapy for malignant conditions, healthy tissues can suffer from radiation damage. Traditional radiation shields designed to protect healthy tissues are prepared by a lengthy, multi-step complex procedure. Materials are described for preparation of a radiation shield for use during radiation therapy, especially therapy of the head and neck, where the material comprises a composite of non-radioactive, non-toxic high atomic density metal or metal alloy spherical particles dispersed in a manually moldable elastomeric material. Custom radiation shields are formulated of this material without the need for use of impressions or molds. Healthy tissues may then be shielded during radiation therapy by positioning the custom-fitted radiation shield in the desired location on the patient's body.
040597695	abstract	A radiation source for Mossbauer investigations of tellurium compounds manufactured on the basis of 5MgO.Te.sup.124 O.sub.3 made by method of preparing this radiation source comprises irradiating 5MgO.Te.sup.124 O.sub.3 in a reactor by means of thermal neutrons, followed by annealing at a temperature ranging from 600.degree. to 1,100.degree. C for a period of from 5 to 10 hours.
041586395	abstract	Gases are stored by combining with a bed of capturing solids at elevated temperatures and pressures. The solids are placed in canisters which are then placed in an autoclave. The gases to be stored are fed directly to the canister via a conduit passing through the autoclave wall.
046706585	summary	BACKGROUND OF THE INVENTION This invention relates to a sanitary protective sheet useful for reducing exposure to scatter radiation generated during radiological operating procedures. Scatter radiation occurs when relatively high energy photons from an X-ray beam interact with the atoms against which they impinge to generate secondary radiation. This secondary radiation tends to be lower frequency radiation than the primary radiation. That is, the secondary radiation has a frequency range that would be produced by voltage settings on the X-ray machine lower than the setting for the primary radiation. Because the secondary radiation is not beamed or focused it tends to be directed in all directions and thus is called scatter radiation. Radiological procedures include both fluoroscopic and radiographic procedures. Although most radiographic procedures are not invasive operations, a large number of the fluoroscopic procedures presently performed are invasive operations. During these invasive procedures it is particularly important to maintain a sterile field at all times. Fluoroscopy is a procedure which renders visible the shadow of X-rays to permit observation of the internal organs of the human body. There are many procedures which are preformed under a fluoroscope so that the radiologist can monitor and control the procedure. Fluoroscopy, as compared to standard X-ray examination, uses a lower voltage X-ray. Examples of procedures requiring fluoroscopic monitoring and control are: angiographic procedures; percutaneous nephrostomy; lung biopsy; endoscopic cholangiograms; pancreaticography; and percutaneous transhepatic cholangiogram. During the majority of these, an X-ray beam is focused on the patient at a point distanced from the radiologist or other doctor performing the procedure. Although the doctor is not exposed to the primary radiation, he or she is exposed to scatter radiation. The arm and hand area of the doctor are most commonly exposed to such scatter radiation. These fluoroscopic procedures are invasive and generally require the use and manipulation of small instruments. It is necessary to perform these procedures in a sterile environment. The procedures require manual dexterity on the part of the radiologist. It is well documented that exposure to X-rays is injurious. It is further known that X-ray exposure is cumulative. Although the amount of X-ray exposure that a patient receives during a single fluoroscopic procedure may not be harmful, a radiologist who performs a great number of such procedures, is constantly exposed to X-rays and hence a large cumulative exposure. It has long been recognized that radiologists, and other workers with X-rays, must protect themselves as much as possible from X-rays. Any reduction in cumulative exposure is desirable. It is known in the art that lead impregnated rubber gloves and aprons will protect the radiologist by absorbing some of the scatter radiation generated during a fluoroscopic procedure. These gloves however, are too clumsy to wear while performing delicate operative procedures. In addition, both the gloves and aprons are relatively expensive and not easily sterilized. Accordingly, it is an object of this invention to provide a protective sheet which can be used during a radiological procedure to protect the radiologist or other doctor from scatter radiation. It is important that the protective sheet not interfere with the doctor's ability to perform a delicate interventional procedure. Thus it is another purpose of this invention to provide a simple device that does not interfere with any of the operating procedures. It is another purpose of this invention to achieve the above results with a protective sheet which permits maintaining sterilization. It is a related purpose to provide a sheet which is disposable so that a sterile environment can be maintained during each operation. It is a related object of this invention to provide a setting which permits the doctor to move in a sterile environment. It is a further purpose of this invention to provide the objects at a cost which will encourage use of the protective product and with a device that is simple and easy to use so that it will readily and regularly be used. BRIEF DESCRIPTION In brief one embodiment of the invention employs a multi-ply sheet in which a center ply support matrix is a gauze sheet in which a radio opaque compound and in particular barium sulfate powder, is distributed and is supported by the matrix. The barium sulfate is present in an amount suffient to block a substantial amount of the scatter radiation produced by the standard medical radiology machines which may have voltage settings up to 120 kilovolts (KV). In this embodiment, a base ply of a thin liquid impervious polyethylene material is fastened to one side of the support matrix ply. The third ply is composed of a typical surgical drape material which acts to absorb liquid such or blood. It is fastened to the other side of the support matrix ply. This multi-ply protective sheet is relatively light weight and avoids being a bulky type of device. Yet it effectively absorbs the scatter radiation. Further, since it is relatively inexpensive to produce it is disposable and thus avoids the problem of cross contamination that would occur in the use of the same protective sheet in successive operations. Unlike protective gloves, the sheet need not be worn by the radiologist and thus does not adversely affect his or her manual dexterity.
047073241	abstract	The setpoints for control systems in a pressurized water reactor are adjusted by an amount corresponding to the expected change in the controlled process variable resulting from rapid fluctuations in load to reduce the duty time of the control system components such as the rod drive mechanisms in the rod control system and the spray and heater units in the pressurizer pressure control system. In addition, the deadband in the response of the rod control system is continuously varied as a function of the variance of the magnitude of the rapid fluctuations in load to further reduce wear while maintaining good response during load following.
06297419&	description	DETAILED DESCRIPTION The process according to a first embodiment of the present invention may be described as follows and with reference to the flow chart shown in FIG. 1. A source of zirconium alloy fuel rod cladding is indicated at 10. The cladding is brought into solution by electrochemical dissolution 12 by making the cladding anodic and passing a current through the metal under a nitric acid electrolyte. This step results in the metal being converted to zirconium nitrate 14. However, during the dissolution step 12, a substantial quantity of the zirconium alloy is converted directly to an oxide which forms a sludge at the bottom of the dissolution tank and is subsequently removed to be added back into the process at a later stage. The zirconium nitrate is then thermally decomposed in the step 16 to the oxide 18 by one or more of the techniques including direct heating, fluidised bed, plasma-arc or microwave assisted heating The oxide 18 is then mixed in the step 20 with a sol of a gel forming chemical which in this case is aluminium secondary butoxide which is diluted with alcohol and modified with an alkanolamine, which is in this case, tri-ethanolamine. The modifying agent causes cross linking of the aluminum secondary butoxide in a controlled and time dependent manner on hydrolysis resulting in the onset of gelling. The zirconium oxide mixed with the gelling aluminum secondary butoxide forms a slurry 22 to which may optionally be added material 24 such as oxides of fission products and/or plutonium 26 which have been extracted from the dissolved spent uranium fuel by a known so-called "PUREX" process, the fission products and plutonium constituting high level waste which must be encapsulated and stored in a repository for many years. The slurry 22 continues to gel and is cast or extruded 28 into molds or self supporting shapes at the steps 30 where it is allowed to fully gel and solidify. After setting, the shaped "green" bodies are demolded 32, if appropriate, to form free-standing, handleable bodies 34 which are then dried slowly 36 to prevent excessive cracking during shrinkage. The dried green bodies 38 are then sintered 40 at a substantially lower temperature than that required for physically mixed oxides to form durable refractory material monoliths 42 which may then be stored 44 in a repository 46 in a known manner. During the drying step 36, the water is driven off and the hydroxyl groups in the chemical matrix are decomposed to leave only aluminum and oxygen present in the structure on a substantially molecular scale and binding together the powder particles of zirconium oxide and also the particles of other constituents; the sintering rate during the sintering step 40 is very high and can be accomplished at relatively lower temperatures in the region of about 1400.degree. C. compared with the higher temperatures conventionally used to sinter pressed green bodies of zirconium oxide. Therefore, the preferred embodiment of the present invention has many advantages over known techniques in that the resulting monoliths of refractory zirconium oxide are chemically both very stable and very durable and able to encapsulate the high level waste directly within the matrix. Furthermore, the low sintering temperature which the preferred embodiment of the process of the present invention permits reduces hazards associated with high vapor pressures of some elements and consequently further reduces contamination and plant costs. FIG. 2 shows a flow sheet of an alternative process according to the present invention utilizing the technique of freeze casting. A freeze castable silica or zirconium oxide sol 50 is mixed with a ceramic filler powder 52 and zirconium oxide waste 54 to form a slurry 56. The starting materials 52, 54 may be milled to improve homogeneity and mixing prior to forming the slurry 56. The zirconium oxide waste 54 may include fission products incorporated therein but, high-level fission product waste 58 may alternatively be added separately or additionally as a constituent of the slurry 56. The slurry 56 is cast 60 into a mold (not shown) having a cavity of any desired shape and freeze-cast to form a frozen body 62. The mold may be vibrated to assist packing of the slurry material within the mold and to assist mold filling by the elimination of air bubbles. The slurry 56 may alternatively be freeze extruded 64 to form an alternative frozen body 66. The freeze casting process causes the slurry constituents to form chemical bonds such that when the frozen body 62 or 66 is warmed at the steps 68 and the body demolded, it forms a relatively strong, free-standing and handleable monolith 70. The thawed body 70 is dried slowly to avoid too rapid shrinkage and consequent cracking and, once dried, it is sintered to form a high density, durable ceramic body 72 containing high level fission product waste material. A first example of the second preferred embodiment of the process of the present invention is to form a zircon, ZrSiO.sub.4, monolith. The process comprises making a mixture of a castable silica sol which is mixed with a zircon filler powder and waste zirconium oxide formed from the electrochemical dissolution of zirconium metal fuel cans. The mixture may also contain fission products from the zirconium metal waste stream or, fission product waste may be added as a separate component of the mixture. The process comprises the steps of vibro-energy milling the powder constituents to homogenize and thoroughly mix thus, breaking up zirconia flakes from electrochemical dissolution. The milling may take place wet so as to reduce dust and contamination hazard so the milled and homogenised powder is added to silica-sol to form the ceramic slurry 56, the slurry being capable of being poured into a mold (not shown) or at least capable of being so transferred to a mold. The mold may be connected to a vacuum system so as to remove entrained air or may be provided with a vibratory system for the same purpose and also to assist mold filling. The filled molds are rapidly cooled to about -50.degree. C. to freeze them and aged for a suitable period which may range from about 10 minutes to longer times. Once aged, the filled molds are rapidly warmed to room temperature and the now solid monoliths are removed from the molds and dried in air. The dried monoliths are then sintered at a minimum temperature of 1400.degree. C. The free silica from the sol reacts with a stoichiometric amount of zirconium oxide waste on sintering to form zircon. The small particle size of the sol and filler particles ensures lower sintering temperatures than normal ceramic forming processes used heretofore. Chemical bonds are formed during the freeze casting process between the silica and zirconium oxide and other constituents which are reinforced and serve to accelerate the sintering process at a low sintering temperature. An alternative to silica-sol is the use of zirconium oxide sol. This process involves the mixing of a zircon filler powder with zirconium waste and optionally fission product waste which is then mixed with a zirconium oxide sol. The process steps for producing a sintered zircon and stabilised zirconium oxide monolith are essentially as described above with reference to the formation of a monolith using the silica-sol route. As noted above, oxides of zirconium generally refer to the oxide plus a wide range of other materials which are not pure oxide; the other materials are mixed in the feed and therefore become part of the finished product, namely, the sintered disposable monoliths. While the foregoing is directed to the disclosed embodiment, the scope is set forth in the following claims.
048615200	abstract	A drivable radioactive source capsule is provided which comprises a tubular body containing therein a plurality of radioactive sources. The said tubular body has a first end and a second end which is a terminus of the tubular body. A plug has an elongated closure portion with the diameter of the closure portion being substantially equal to the inside diameter of said tubular body. The closure portion is disposed within the tubular body through the second end thereof and is attached to the second end of the tubular body. The plug has a connection portion adjacent the closure portion with the diameter of the connecting portion being substantially equal to the outside diameter of the tubular body. An elongated flexible drive cable is connected to the connection portion of the plug. By this arrangement, radioactive sources may be placed in the tubular body and the body is closed by disposing the closure portion of the plug into the second end of the tubular body and attaching the closure portion to the second end of the tubular body.
	abstract	A sample manipulation device comprises an observation unit, which is used to observe a sample and to select a target position at which a portion to be removed from the sample is located, and a specimen stage which receives the sample. The sample manipulation device may include a manipulation tool, which is spatially shiftable relative to the observation unit and comprises a manipulation tip by which portions are removed from the sample, a control unit, which controls the shifting of the manipulation tool, as well as an optical position measurement unit, which is connected to the control unit and is used to determine the actual position of the manipulation tip, so that specific shifting of the manipulation tip to the target position can be carried out.
062657232	description	DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention will be described in detail with reference to the accompanying drawings. Referring to FIG. 1A, a rectangular opening 120 is formed in the side surface of a magnetic shield room 101 having an inner wall adhered with a magnetic shield material. A tubular member 104 made of a magnetic shield material (e.g., permalloy) and having a rectangular section is attached to the opening 120 with rivets or the like. A portion of the tubular member 104 extending from its distal end for a predetermined length is outwardly bent at a right angle with respect to the tube axis to form a flange portion 105, as shown in FIG. 1B. More specifically, the flange portion 105 is constituted by the bent portions of the four sides of the distal end portion of the tubular member 104. An opening portion 102 is formed by the distal end portion of the tubular member 104 to communicate with the opening 120. As shown in FIG. 2A, the flange portion 105 is formed by bending the edges of the tubular member 104 outwardly and perpendicularly. When the size of the opening portion 102, i.e., the sectional size of the tubular member 104, the length of the tubular member 104, and the length of the flange portion 105, are defined as a.times.b, c, and d, respectively, in this embodiment, these sizes are set as follows: size of the opening portion 102: PA1 size of the tubular member 104: PA1 size of the flange portion 105: PA1 angle of the flange portion 105 with respect to the tube axis a=990 mm PA2 b=250 mm PA2 the sectional size is equal to that of the opening portion 102 PA2 c=100 mm PA2 d=10 mm to 20 mm PA2 .theta.=90.degree. When the size a of the opening portion 102 is set to 990 mm mentioned above, three cassettes can be arranged horizontally. A description will be made on an assumption that the tubular member 104 has no thickness. Note that the present invention is not limited to these values. It suffices if at least a portion of the tubular member 104 extending from its distal end for a predetermined length is inclined outwardly of the tubular member 104 at an angle of almost 90.degree. with respect to the tube axis. Preferably, the size d of the flange portion 105 may be set to 10 mm or more and the angle .theta. of the flange portion 105 with respect to the tube axis may be set to 90.degree.. As shown in FIG. 2B, a portion of the tubular member 104 near its distal end may be bent outwardly to have a certain radius of curvature, thereby forming a flange portion 205 having an arcuated section. In FIG. 2B as well, it suffices if the distal end of the tubular member 104 is inclined outwardly of the tubular member 104 with respect to the tube axis. Preferably, a size d of the flange portion 205 may be set to 10 mm or more and an angle .theta. formed by the tangential direction at the edge of the flange portion 205 and the tube axis may be set to 90.degree.. As shown in FIG. 3A, the opening 120 is formed in one of the four side surfaces of the magnetic shield room 101. As shown in FIG. 3B, a magnetic shield material 111 is adhered to the entire inner wall of the magnetic shield room 101 without any gap to form a tubular member 104 projecting from the opening 120. A loading/unloading portion 106 for loading/unloading wafers or masks is arranged near the opening 120. A cassette loaded in the magnetic shield room 101 through the opening portion 102, the tubular member 104, and the opening 120 is mounted on the loading/unloading portion 106. The wafers and the like stored in the cassette are conveyed into a column 109 in an EB exposure unit 110 with an arm 107 of a convey arm portion 108, and are exposed. Thereafter, the exposed wafers are mounted on the cassette again by the arm 107 in an order reverse to that described above. The cassette mounted with the wafers is unloaded outside the magnetic shield room 101 through the opening 120, the tubular member 104, and the opening portion 102. If the tubular member 104 Is excessively long, it causes a trouble when mounting the cassette on the loading/unloading portion 106. The length of the tubular member 104 is preferably 200 mm or less. The relationship between presence/absence of the tubular member 104 and the influence of the external magnetic field will be described. FIG. 4 shows the relationship between the distance from the opening portion 102 and the strength of magnetic field in the magnetic shield room 101 when the external magnetic field has a strength of 5 mG. The size of the opening portion 102 is a.times.b=990 mm.times.250 mm. As shown in FIG. 4, when the opening 120 is not formed, the magnetic field in the magnetic shield room 101 is 0.3 mG near the shield wall, 0.25 mG at a position separate from the shield wall by 500 mm, and 0.17 mG at a position separate from the shield wall by 1,000 mm, thus being attenuated gradually. In contrast to this, when only the opening portion 102, i.e., the tubular member 104, is formed, the magnetic field near the opening 120 exhibits a value near about 3 mG but is 0.35 mG at a position separate from the opening 120 by 500 mm, thus being attenuated sharply. At a position farther separate from the opening 120, the magnetic field is attenuated gradually. However, even at a position separate from the opening 120 by 1,000 mm, the magnetic field has a strength of 0.23 mG, which is higher than the value obtained when the opening 120 is not formed by about 0.06 mG. In the first example provided with the tubular member 104 of c=200 mm which has the flange portion 105 of d=10 mm and .theta.=90.degree., the strength is 0.6 mG immediately inside the opening 120, but at a position separate from the opening 120 by 500 mm, the magnetic field is attenuated sharply to a value almost equal to that obtained when the opening 120 is not formed, and at a position separate from the opening 120 by 1,000 mm, the magnetic field is attenuated gradually to 0.17 mG. In contrast to this, when the tubular member 104 having no flange portion 105 is used, to obtain a shield effect almost equal to that described above, the tubular member 104 must have a length of 600 mm or more. This suggests effectiveness of the present invention in decreasing the length of the tubular member 104. In the second example provided with the tubular member 104 of c=100 mm which has the flange portion 105 of d=10 mm and .theta.=90.degree., the strength is about 1.4 mG immediately inside the opening 120, but at a position separate from the opening 120 by 500 mm, the magnetic field is attenuated sharply to a value almost equal to that obtained when the opening 120 is not formed, and at a position separate from the opening 120 by 1,000 mm, the magnetic field is attenuated gradually to 0.17 mG. The flange portion 105 may be formed by bending the edge of the distal end of the tubular member 104, as described above, or by mounting a rectangularly annular flange member 305 on flange-like edges 104a of the tubular member 104, shown in FIG. 5A, by using rivets 305a, as shown in FIG. 5B. In this case, if the number of rivets 305a is increased or the flange member 305 is connected and fixed to the distal end portion of the tubular member 104 in accordance with another mounting method, e.g., welding, in place of the rivets 305a, the adhesion strength of the connecting portion can be increased. This decreases the impedance of the connecting portion so that the internal magnetic field can be emitted outside more easily. Connecting portions made of a magnetic shield material may be mounted to the notched portions between edges 104a of the tubular member 104 to connect the edges 104a to each other, thereby forming a flange portion continuously surrounding the opening portion 102 of the tubular member 104. Alternatively, no edges 104a may be formed on the tubular member 104, but a rectangularly annular flange member 305 made of a magnetic shield material may be attached to the distal end of the tubular member 104 with a known method. Alternatively, a tubular portion may be formed on the flange member 305 and be fixed to the tubular member 104 by fitting. Alternatively, instead of the flange member 305, strip segments made of a magnetic material and constituting a flange portion may be separately attached to the respective sides of the distal end portion of the tubular member 104. As has been described above, according to the present invention, a tubular member having a flange portion is formed on the opening of a magnetic shield room. Even if the size of the opening is increased, the influence of the external magnetic field on the interior of the magnetic shield room can be decreased. More specifically, when compared to a case using only a tubular member, the same effect to that obtained by using a long tubular member can be obtained with a short tubular member. For example, when a tubular member having a flange portion and a length of about 100 mm is formed on the opening, the same effect as that obtained when no opening is formed can be obtained at a position separate from the opening by 500 mm. This allows loading/unloading of the cassette through the opening, and accordingly the loading/unloading portion can be arranged in the magnetic shield room, thus increasing the throughput. Since entrance of the external magnetic field through the opening can be suppressed more than in the conventional case, the distance between the EB exposure unit and the opening can be decreased. Since no extra space is required unlike in the conventional case, the magnetic shield room can be made compact.
	description	This invention relates to a production process of a composite nuclear fuel material composed of aggregates of a ground powder blend of UO2 and PuO2 dispersed in a UO2 matrix preferably depleted in 235U. The composite in question possesses after sintering a microstructure of ceramic-ceramic (CERCER) type in the form of relatively spherical calibrated aggregates of solid solution (U,Pu)O2 dispersed in the UO2 matrix. This is a nuclear fuel material with improved fission gas release properties. MOX (Mixed Oxide) fuel is at present produced industrially using a process known as MIMAS (MIcronized MASter blend). This process comprises successively a step of grinding oxides of uranium and plutonium, a step of diluting the powders obtained (primary blend) in the uranium oxide (UO2) and a step of sintering. The MOX fuel produced by this process has a two-phase structure, one phase (U,Pu)O2 composed of solid solutions with a Pu/U+Pu content that can vary in the range of 30 to 5% of Pu and a UO2 phase. The (U,Pu)O2 phase exists either in aggregate form or in the form of “filaments” forming a continuous network in the fuel. On irradiation, the fission gases are essentially created in the plutonium-bearing zones and install themselves over short distances (7 to 9 μm) then diffuse through the UO2 matrix before being released outside the fuel. An improvement of the material consists in exacerbating the biphasic character of the present fuel to tend towards a material that isolates the plutonium-bearing zones in a UO2 matrix, which is intended to act as a retention barrier to the fission gases. The precise object of the present invention is to provide a production process for a composite material consisting of cohesive aggregates of a ground powder blend of UO2 and of PuO2 dispersed in a UO2 matrix that makes it possible to obtain a material capable of limiting fission gas release. The cohesive aggregates are obtained, according to the invention, either by mechanical granulation, or by calcinating the primary blend of UO2 and PuO2. The process of the present invention includes the following steps: dry co-grinding a UO2 powder and a PuO2 powder so as to obtain a homogenous primary blend, consolidating the primary blend so as to obtain cohesive aggregates of the blend of UO2 and of PuO2, sieving the aggregates between 20 and 350 μm, diluting the sieved aggregates in a UO2 matrix so as to obtain a powder blend, pelletising the powder blend, and sintering the pellets obtained in order to obtain the composite. The process of the present invention makes it possible to isolate the fissile matter comprising the plutonium-bearing aggregates of calibrated ground powders of UO2 and of PuO2 and to distribute them homogenously through the fertile matrix composed of UO2. Appended FIGS. 2a), 2b) and 3 represent three photographs of microstructures of sintered composite materials composed of precalcinated or granulated aggregates (marker 1) of (U,Pu) O2 dispersed in a UO2 matrix (marker 2). According to the invention, the primary blend of UO2 and of PuO2 is comprised preferably of a UO2 content in the range of 60 to 90 wt. % and of a PuO2 content in the range of 40 to 10 wt. % of the total mass of the blend, preferably 75 wt. % of UO2 and 25 wt. % of PuO2. The mass of PuO2 can be totally or partially replaced by discarded manufactured powders comprised of mixed oxides (U,Pu) O2. According to a first embodiment of the present invention, the step of consolidation to obtain cohesive aggregates can include the following steps: compacting the homogenous primary blend at a pressure in the range of 150 to 600 MPa in order to obtain a blank, crushing the blank obtained in order to obtain granules, and spheroidising the granules. This first embodiment of the present invention comprises mechanically granulating the primary blend compacts. This consolidation brings about sufficient cohesion of aggregates to withstand without deterioration the subsequent steps of diluting and pelletising of the process of the present invention. The blend can be compacted by using a single or double effect uniaxial press. This is preferably carried out at a pressure of 300 MPa. The crushing can be carried out using any known appropriate means, for example using an industrial crusher. The granules can for example be spheroidised using simple self-abrasion of the crushed products, for example in a mixer of the TURBULA (registered trademark) type (oscillo-rotary mixer-shaker). According to a second embodiment of the present invention, the consolidation of a primary blend can be carried out using a heat treatment calcinating the primary blend at a temperature of 1000 to 1400° C., preferably at a temperature of 1000° C. The consolidated primary blend is the mixture of UO2 and of PuO2 produced by co-grinding. Calcination gives the primary blend a sufficient degree of cohesion for it to withstand without deterioration the subsequent steps of dilution and pelletising of the process of the present invention while preserving high sphericity. Preferably, the heat treatment is carried out in an humidified or non-humidified atmosphere of 95 vol. % argon and 5 vol. % hydrogen. When the heat treatment atmosphere is humidified, it is preferably humidified with a partial pressure ratio PH2/PH2O in the range of 50 to 20. The sieving can be carried out using a stainless steel sieve with mesh size in the range of 20 to 350 μm, preferably in the range of 125 to 350 μm. Thus the cohesive aggregates can have a dimension (diameter) in the range of 20 to 350 μm, preferably in the range of 125 to 350 μm. The dilution of the aggregates in the UO2 matrix can be carried out for example by mechanical stirring. This should preferably not break the aggregates. The aggregates can be diluted in the UO2 matrix at a concentration of 20 to 35 vol. % of the total volume of the green blend obtained, preferably at a concentration of 20 vol. % of the total volume of the green blend. These quantities yield a composite material advantageously containing between 2.1 and 9.45% of plutonium oxide. According to the invention, pelletising can be carried out using a uniaxial hydraulic press, for example at a pressure of 500 MPa. According to the invention, the sintering step can be carried out a temperature of approximately 1700° C. It can be carried out in a sintering furnace by following a thermal cycle comprising the following successive steps of: raising the temperature at 200° C./hour, plateauing at approximately 1700° C., and cooling at approximately 400° C./hour down to 1000° C., then by following furnace inertia. The sintering step is preferably carried out in an humidified or non-humidified atmosphere of 95 vol. % argon and 5 vol. % hydrogen. When the sintering atmosphere is humidified, it is preferably humidified with a partial pressure ratio PH2/PH2O in the range of 50 to 20. Other characteristics and advantages will become obvious on reading the following examples, which are, of course, given to illustrate the invention and not to limit it as refers to the appended drawings. The sequence of the different steps of the manufacturing process of sintered composites consisting of aggregates of solid solution of (U,Pu)O2 dispersed in a UO2 matrix according to the process of the present invention is indicated in the flow chart in FIG. 1. Different homogenous matrix blends of powders of uranium and plutonium dioxides produced by processes known to prior art have been produced with proportions of powders in the ranges of 60 to 90 wt. % of UO2 and of 40 to 10 wt % of PuO2 compared to the total mass of the blend. These blends were produced by dry co-grinding the rough powders, in a jar rotating at 48 r.p.m. for 6 hours. The grinding media were uranium metal balls. No organic, pore-forming or lubricant additives were used. This example illustrates a first embodiment of the consolidation step of the aggregates of the process of the present invention. One of the matrix blends at 25 vol. % of PuO2 obtained in example 1 was compacted in different tests at different granulation pressures in a range of 0 (non-compacted powder from co-grinding) to 600 MPa, using a single effect uniaxial press. The blanks thus obtained were then crushed manually in an agate mortar, and the crushed products obtained were spheroidised by self-abrasion by a Pyrex (commercial brand) round bottom flask inserted in a grinding jar rotating at 48 r.p.m. for one and a half hours. This example illustrates a second embodiment of the consolidation step of the aggregates of the process of the present invention. The heat treatment was applied to one of the matrix blends at 25 vol. % of PuO2 obtained in example 1, in a flow of a non-humidified 95% Ar-5% H2 mixture. The thermal cycle used corresponded to a rise in temperature at 200° C./hour to a temperature of 1000, 1200 or 1400° C. followed, with no plateau, by cooling at 400° C./hour to ambient temperature. This consolidation treatment produced consolidated aggregates of high sphericity, for each blend of UO2 and of PuO2. The aggregates obtained in examples 2 and 3 were sieved using a stainless steel sieve with mesh size in the range of 125 to 250 μm. After mechanical granulation or thermal consolidation, the plutonium-bearing aggregates were mixed with UO2 powder for 1 hour 30 minutes in a round bottom flask placed on the driving rolls of a grinder and turning at a speed of 46 r.p.m. Shaping the composites by pelletising was done using a single effect uniaxial press, operating at a pressure of 500 MPa. A pellet of zinc stearate was pressed regularly after producing two cylinders of composite, in order to ensure the lubrication of the press matrix. The samples obtained took the form of cylinders of approximately 7 mm in diameter and 9 mm in height. The samples placed in a sintering box were sintered in a Degussa (commercial brand) bell furnace. The thermal cycle used was as follows: raising the temperature at 200° C./hour; 4 hours of plateau at 1700° C.; cooling at 400° C./hour down to 1000° C., then by following switched off furnace inertia until ambient temperature was reached. The different composites were sintered in a reducing atmosphere consisting of a flow of a non-humidified mixture of 95% argon and 5% hydrogen. A level of residual humidity of approximately 100 ppm was measured in the gas at furnace exit, at ambient temperature. This corresponds to an oxygen potential, ΔG°, at 1700° C. of −478 kJ/moleO2. The characteristics of the UO2—PuO2 aggregates used and of the CERCER composites obtained are presented in the following table 1. TABLE 1CHARACTERISTICS OF AGGREGATESCHARACTERISTICSGreenGreenSinteredGranulationCalcinationApparentAggregateApparentApparentTestWt. % ofpressureTemperatureDensityFractionalWt. % ofDensityDensityn°PuO2(MPa)(° C.)(g/cm3)VolumePuO2(g/cm3)(g/cm3)Granulation110300nil6.820.22.16.510.5225300nil6.919.95.36.510.5340300nil7.020.58.66.510.5425600nil7.325.67.356.510.5525300nil6.935.79.456.610.5Reference625nilnil5.425.05.26.610.5ExampleHeat725nil10007.318.54.96.510.5Treatment825nil12008.020.25.66.510.5925nil14009.620.16.26.610.2 The products obtained after sintering have a microstructure of the type of those presented in FIGS. 2a), 2b) and 3. The relatively regular distribution of the plutonium-bearing aggregates (white spots on the photographs) in the matrix show that the process of the present invention of product preparation meets the objective for obtaining a composite of individualized aggregates enclosing the totality of the mixed oxide. In view of the dilution process chosen, as described in example 5 above, the composite presenting the required qualities can only be obtained if the plutonium-bearing aggregates (UO2—PuO2) used are cohesive enough to preserve their integrity during this step of the process. The results obtained have shown that the aggregates prepared according to the present invention by mechanical granulation or thermally consolidated at 1000° C. present the properties required for the production of the composites.
	summary
H00012629	claims	1. A rod examination gauge comprising: vertical elevator means, support platform means mounted at the top of the elevator frame means for supporting a fuel rod, rod guide means mounted at the bottom of the elevator frame means for guiding the fuel rod, storage rack means arranged at the bottom of the elevator frame means for storing instruments means, and instrument table means mounted on the transfer carriage of the elevator means for holding instruments means for measuring the fuel rod and a closed circuit television camera for viewing the fuel rod. 2. The rod examination gauge of claim 1, wherein the instruments means include axial profilometer means for measuring fuel rod diameter and oxide thickness, orbiting profilometer means for measuring fuel rod wear mark depth and volume and fuel rod ovality, and ultrasonic instrument means for detecting rod cladding defects. 3. The rod examination gauge of claim 2, wherein the axial profilometer means includes a roller assembly means for aligning and positioning the fuel rod in the center of the axial profilometer means, and a drive assembly means connected to DC motor for driving the roller assembly through a pressured and watertight junction box. 4. The rod examination gauge of claim 3, wherein the axial profilometer means includes a magnescale probe assembly for measuring the diameter of the fuel rod. 5. The rod examination gauge of claim 4, wherein the axial profilometer means includes an eddy current probe means for measuring the fuel rod oxide thickness. 6. The rod examination gauge of claim 2, wherein the orbiting profilometer means includes a roller assembly means for gripping and centering the fuel rod, and a rotary platform means driven by a DC motor for driving the roller assembly. 7. The rod examination gauge of claim 6, wherein the orbiting profilometer means includes a magnescale probe assembly for measuring fuel rod wear marks and rod ovality. 8. The rod examination gauge of claim 2, wherein the ultrasonic instrument means includes a roller assembly means for gripping and maintaining the fuel rod at the center of the ultrasonic instrument means. 9. The rod examination gauge of claim 8, wherein the ultrasonic instrument means includes a longitudinal transducer and a circumferential transducer, each driven by a motor for providing x- and y- directional orientation thereof. 10. The rod examination gauge of claim 1, wherein the support platform means includes standard bars of different rod diameters for calibrating the instruments means. 11. The rod examination gauge of claim 10, wherein the support platform means is arranged to receive a rod caddy means for holding and transporting a fuel rod. 12. The rod examination gauge of claim 11, wherein the support platform means include a rod rotator motor means for providing angular orientation of a fuel rod therein, and storage support means for storing the standard bars and for holding the rod caddy. 13. The rod examination gauge of claim 10, wherein a rod suspension assembly is provided for holding the fuel rod, the rod suspension assembly including a suspension device, a secondary drop protection wire, and collet means for grasping fuel rod. 14. The rod examination gauge of claim 13, wherein the rod suspension device includes a drive shaft coupler having a coupler slot for engaging the rod rotator motor, a universal joint, a pin, and a retainer nut, and wherein the suspension device means is tapered to fit within an examination port on the support platform means. 15. The rod examination gauge of 14, wherein the collet means includes a J-slot associated with a spring for accepting the pin of the rod suspension device, and fingers for accepting the fuel rod.
	abstract	An X-ray imaging apparatus and an imaging method capable of acquiring an image of a test object associated with a phase shift in consideration of X-ray absorption is provided. A splitting element configured to spatially split an X-ray into multiple X-ray beams is provided. A shielding unit including a plurality of shielding elements configured to block part of an X-ray acquired by the splitting element is provided. Part of X-ray beams detected at the first detection pixels is blocked by the shielding elements. The X-ray beams detected by the second detection pixels adjoining the first detection pixels are not blocked by the shielding elements.
043476236	summary	BACKGROUND OF THE INVENTION Pressurized-water and boiling-water nuclear reactors utilize a vessel to contain the fuel rods with their associated fissionable material. Coolant water is circulated through the vessel and is heated (PWR) or partially vaporized (BWR) by heat transfer from the fuel rods. The heated coolant of a PWR is utilized to vaporize a secondary through heat exchangers. In the power generation application of nuclear reactors, the vapor powers a steam turbine rotating a generator. In the event that a malfunction of the system takes place so that the normal coolant circulation is interrupted, the reactor is shutdown by inserting absorber rods into the core, thereby interrupting the nuclear reaction. However, even after shutdown of the reactor, the fission products in the fuel rods continue to produce heat generally referred to as "decay heat". Without the normal coolant flow, this decay heat could melt the fuel rod cladding, the fuel, and the vessel itself, releasing radioactive fission products into the secondary containment building and thereby increasing the risk that radioactive material would be introduced into the atmosphere with the associated potential danger to the public. The potential for release of radioactive material into the environment has led to the development of emergency core-cooling systems. All nuclear reactors must now have provision for maintaining sufficiently low temperatures after a malfunction that the integrity of the fuel rods will be insured. The primary malfunction with which the emergency core-cooling systems are concerned is a loss-of-coolant accident. In such an accident, the primary coolant system develops a leak or rupture resulting in some of the primary coolant water being lost from the system. When the leak is a relatively minor one, the primary coolant system can continue to function to cool the core after the shutdown so long as the small quantity of coolant being lost is replenished. The replenishment of coolant through a small leak is accomplished by a high-pressure injection system. However, in the event of a large rupture developing in the primary coolant system, a different emergency core-cooling system becomes effective. According to conventional design, such an emergency core-cooling system operates in two distinct phases. Initially, accumulator tanks are discharged and/or pumps operated to rapidly refill the vessel with borated coolant water. Subsequently, the new coolant is circulated through the pressure vessel. Steam leaking into the reactor containment is condensed, removing the reactor heat from the system. Power for the pumps is obtained from an independent power source such as a Diesel engine. Typically, a complete emergency core-cooling system injects water into each of the primary coolant loops of the reactor so that the break in a single coolant loop will not defeat the operation of the emergency core-cooling system, pumping water into the other primary coolant loops. It will be apparent that the provision of such systems sufficient to maintain a safe temperature within the vessel is an expensive and critical component of the overall power generating system. Such conventional emergency core-cooling systems are rendered more expensive and less reliable because each of the possible contingencies for such a system's operation adds further to the design capacity requirements. For example, Diesel generator sets have a high startup failure rate, requiring a backup electric system to increase the reliability. A critical time lag may develop before the cooling water from the pumps is injected. Water coming into contact with the hot core is then partially vaporized by the fuel elements. The steam in the vessel collects in the plenum of the vessel producing a back pressure to the entry of new coolant water. The steam problem, generally referred to as "steam binding", limits the design of the reactor plant so that the initial temperature rise caused by the steam binding effect does not endanger the integrity of the reactor core. Therefore, it is desirable to have a system for removing heat from the vessel that increases the reliability of decay heat rejection from the reactor after an accident and has a short startup time. Such a system is particularly desirable if it is capable of operating independently of an electrical power source. SUMMARY OF THE INVENTION An exemplary embodiment of the invention will be described in association with a pressurized-water reactor. However, it is to be understood that the system has also application in other reactor systems incorporating a circulating coolant and that the system in particular has application to a boiling-water reactor. In the exemplary embodiment, the dependence on electric power systems of prior art emergency core-cooling systems is overcome by utilizing the energy from the reactor itself to power the emergency system. The heat energy is utilized by a unique jet pump providing operating characteristics closely corresponding to the requirements for emergency core-cooling over a wide range of failure types. A subcooler for increasing the differential between the saturation temperature of the coolant water for the then existing pressure and coolant water temperature further enhances the characteristics of the jet pump design. The subcooler and jet pump together are designed to accommodate the coolant in such a manner that substantially all the flashing of the coolant into steam will occur in the divergent section of the nozzle. Since flashing does not take place in the throat of the nozzle, the flow does not reach sonic velocity (become choked) in the nozzle throat and the pump produces an almost constant mass flow rate over a wide range of temperature/pressure relationships. Because flashing in hot water in the nozzle is the driving force that distinguishes the jet pump according to the invention, the pump is referred to hereinafter as the flash jet pump. The flash jet pump is further distinguished from conventional designs in its use of an extremely high expansion area ratio. Expansion area ratio refers to the ratio between the size of the nozzle outlet area to the nozzle throat area. For conventional jet pumps, this ratio is over a maximum range of 1:1 to 8:1. In the flash jet nozzle, the area ratio is in the range of 10:1 to 50:1. The high area ratio is caused by the high density of liquid water compared to that of steam and the fact that flashing is suppressed in the convergent nozzle section. The supersonic two-phase flow exiting the divergent nozzle impinges upon coolant water drawn into the suction side of the flash jet pump. The mixing of the supersonic two-phase jet with the coolant water produces a combined high-velocity flow which is converted into a pressure rise for pumping. The pressure rise is increased by a divergent section in the conduit so that substantially all of the remaining kinetic energy of the water is converted into pressure for forcing the combined coolant flow through the inlet connection into the reactor vessel. The coolant water is drawn from a supply of additional coolant. The source of supply of the additional coolant is a storage tank or the reactor building sump. The reactor building sump collects the water lost from the primary cooling loop due to the break. Thus, the system becomes self-sustaining with the water being lost from the reactor vessel being picked up by the flash jet pump and recirculated. For maximum advantage, the subcooler is in the form of a downcomer pipe connected to the outlet connection of the vessel and having a vertical extent of 20 to 40 feet. The effect of the downcomer pipe is to apply a static pressure head on top of the circulating pressure of the coolant thereby raising the saturation temperature and increasing the differential between the saturation temperature and coolant water temperature. For the capability of the system to deal with a wide range of loss-of-coolant accidents and to minimize fuel rod damage under all circumstances, operation of the system in its transfer mode for reflooding the vessel with an initial charge of coolant water is necessary. The operation of such a transfer system assumes that the rupture is sufficiently large that a substantial coolant fraction is lost from the vessel. The transfer system is utilized to transfer borated water into the vessel in the minimum possible time. The pump for the transfer system incorporates the same principles previously described in association with the recirculation system. That is, the pump is a flash jet pump powered by hot water generated by the reactor heat. THe hot water can be taken from the secondary side of the steam generator or from a hot water storage tank. The steam generators contain a substantial quantity of heated water at the moment of a loss-of-coolant accident. Since the transfer system must operate only for an initial period, a finite quantity of heated water is sufficient to refill the reactor vessel. A subcooler is connected to the flash nozzle. The subcooler is a downcomer pipe with a vertical elevation difference between the hot water tank and flash jet pump. Cold water is drawn from a storage tank containing borated water by the flash jet pump and discharged into the reactor vessel. It is therefore an object of the invention to provide a new and improved flash jet coolant pumping system. It is another object of the invention to provide a new and improved flash jet coolant pumping system that has few moving parts. It is another object of the invention to provide a new and improved flash jet coolant pumping system with a highly reliable cooling action. It is another object of the invention to provide a new and improved flash jet coolant pumping system which operates over a wide pressure range. It is another object of the invention to provide a new and improved flash jet coolant pumping system that reliably transfers an initial charge of water into a reactor vessel. Other objects and many attendant advantages of the invention will become more apparent upon a reading of the following detailed description together with the drawings in which like reference numerals refer to like parts throughout and in which:
	summary
	abstract	Surface roughness having intervals of several tens of nanometers to about a hundred micrometers in a solid surface is reduced by directing a gas cluster ion beam to the surface. An angle formed between the normal to the solid surface and the gas cluster ion beam is referred to as an irradiation angle, and an irradiation angle at which the distance of interaction between the solid and the cluster colliding with the solid dramatically increases is referred to as a critical angle. A solid surface smoothing method includes an irradiation step of directing the gas cluster ion beam onto the solid surface at an irradiation angle not smaller than the critical angle. The critical angle is 70°.
	description	The present invention relates to an electron beam lithography apparatus for manufacturing an original master, and in particular, relates to the electron beam lithography apparatus used for concentrically drawing circles. A magnetic disk or a hard disk (HD) is used as a storage of a personal computer (PC), a mobile device, a car-mounted device, and the like. The application thereof significantly expands, and surface recording density is rapidly improved in recent years. To manufacture such a hard disk with high recording density, electron beam mastering technology is widely studied. In an electron beam lithography exposure apparatus, an electron lens converges an electron beam shot by an electron gun, and an electron beam spot is applied to a substrate coated with a resist. A blanking control system and a beam deflection control system control the irradiation position of the electron beam spot to draw a desired beam pattern. Recently various electron beam lithography exposure apparatuses are developed and include, for example, an apparatus which precisely manufactures an original master of a recording medium such as an optical disk and the like (refer to, for example, Japanese Patent Laid-Open Publication No. 2002-367178). Accordingly, it is necessary to precisely control the irradiation position of the electron beam spot in order to perform electron beam lithography with high recording density. The recent hard disk uses a concentric pattern instead of a spiral pattern used in the optical disk and the like. In the case of concentrically drawing circles by the electron beam lithography, it is necessary to precisely connect a start point to an end point in each circle (i.e., track). Therefore, it is desired to provide an apparatus which can concentrically draw circles with high precision. When a conventional x-θ system lithography apparatus or the like concentrically draws circles by the electron beam lithography, a ramp wave in synchronization with the rotation of the substrate deflects the electron beam to a radial direction. Thus, there are problems that the shape of a circle connecting section becomes distorted, a part of a land section is exposed, and the like. If there is rotational fluctuation in a rotational stage, a line for a circle may not connect at the start and end points. Using blanking prevents the land section from being exposed, but there occurs another problem that a line does not connect at the start and end points. Accordingly, it is desired to provide an electron beam lithography apparatus which can draw a circle with high precision. To solve the foregoing problems, an object of the present invention is to provide an electron beam lithography apparatus which can concentrically draw circles by electron beam lithography in such a manner that a start point and an end point of the circle connect with high precision. According to the present invention, there is provided an electron beam lithography apparatus for concentrically drawing a plurality of circles on a substrate by applying an electron beam while rotating the substrate, which comprises a beam deflection portion for deflecting the electron beam to change an irradiation position of the electron beam; a synchronization signal generation portion for generating a synchronization signal which is in synchronization with the rotation of the substrate; a controller for controlling the beam deflection portion on the basis of the synchronization signal in order to deflect the electron beam in a rotational radial direction of the substrate and in a rotational tangential direction of the substrate opposite to a rotational direction of the substrate, while drawing transition is performed from one circle to another circle; and a beam cutoff portion for cutting off the irradiation of the electron beam on the substrate, for a period during the electron beam is deflected in the rotational radial direction. According to the present invention, there is provided an electron beam lithography method for drawing a plurality of circles on a substrate by applying an electron beam while rotating the substrate, which comprises a cutoff step of cutting off the irradiation of the electron beam on the substrate during drawing a circle; and a drawing start step of deflecting the electron beam in at least a rotational radial direction of the substrate during cutoff, and starting the drawing of another circle. Embodiments of the present invention will be hereinafter described in detail with reference to drawings. In the following embodiments, the same reference numerals refer to equivalent components. FIG. 1 is a block diagram schematically showing the structure of an electron beam lithography apparatus 10 according to a first embodiment of the present invention. The electron beam lithography apparatus 10 is a mastering apparatus which produces an original master for manufacturing magnetic disks by use of an electron beam. The electron beam lithography apparatus 10 comprises a vacuum chamber 11, a drive device, an electron beam column 20 attached to the vacuum chamber 11, and various circuits and control systems. The drive device performs rotational and translational movement of a substrate mounted thereon and disposed in the vacuum chamber 11. The various circuits and control systems carry out substrate drive control, electron beam control, and the like. To be more specific, a substrate 15 for an original master of a disk is mounted on a turntable 16. The turntable 16 is rotated by a spindle motor 17, which is a rotational drive device for driving the substrate 15 to rotate, with respect to a vertical axis of the principal plane of the substrate 15. The spindle motor 17 is disposed on a feed stage (hereinafter, simply referred to as stage) 18. The stage 18 is coupled to a feed motor 19 being a feeding (translational motion drive) device. Thus, the spindle motor 17 and the turntable 16 can be moved in a predetermined direction in a plane which is in parallel with the principal plane of the substrate 15. The turntable 16 is made of dielectric, for example, ceramic, and has an electrostatic chucking mechanism (not illustrated). The electrostatic chucking mechanism is composed of the turntable 16 (ceramic) and an electrode provided in the turntable 16. The electrode made of a conductive material generates electrostatic polarization. The electrode is connected to a high-voltage power supply (not illustrated). Since the high-voltage power supply applies voltage to the electrode, the substrate 15 is attracted and held. Optical elements are disposed on the stage 18. The optical elements include a reflecting mirror 35A, an interferometer, and the like, which are elements of a laser interferometer measuring system 35 described later. The vacuum chamber 11 is installed through a vibration isolating table (not illustrated) such as an air damper or the like in order to restrain the transmission of external vibration. The vacuum chamber 11 is connected to a vacuum pump (not illustrated). The vacuum pump exhausts air from the vacuum chamber 11, so that the inside of the vacuum chamber 11 is set at a vacuum atmosphere with a predetermined pressure. In the electron beam column 20, an electron gun (emitter) 21 for emitting an electron beam, a convergence lens 22, blanking electrodes 23, an aperture 24, abeam deflection coil 25, an alignment coil 26, deflection electrodes 27, a focus lens 28, and an objective lens 29 are disposed in this order. The electron gun 21 emits an electron beam (EB) accelerated to several tens of KeV by a cathode (not illustrated), to which an acceleration high voltage power supply (not illustrated) applies high voltage. The convergence lens 22 converges the emitted electron beam. The blanking electrodes 23 switch the electron beam between ON and OFF on the basis of a modulation signal from a blanking control section 31. In other words, since application of a voltage between the blanking electrodes 23 largely deflects the passing electron beam, the electron beam is prevented from passing through the aperture 24, so that the electron beam becomes an off state. The alignment coil 26 corrects the position of the electron beam on the basis of a correction signal from abeam position corrector 32. The deflection electrodes 27 can carry out the deflection control of the electron beam at high speed on the basis of a control signal from a deflection control section 33. The deflection control results in position control of an electron beam spot with respect to the substrate 15. The focus lens 28 controls the focus of the electron beam on the basis of a control signal from a focus control section 34. A light source 36A and a photo detector 36B are provided in the vacuum chamber 11 to detect the height of the principal plane of the substrate 15. In the electron beam lithography apparatus 10, a height detection section 36 is provided. The photodetector 36B includes, for example, a position sensor, a CCD (charge coupled device), and the like. The photodetector 36B receives a light beam, which is emitted from the light source 36A and reflected from the surface of the substrate 15, and provides the height detection section 36 with a photo-reception signal. The height detection section 36 detects the height of the principal plane of the substrate 15 on the basis of the photo-reception signal, and generates a detection signal. The detection signal representing the height of the principal plane of the substrate 15 is provided to the focus control section 34, so that the focus control section 34 controls the focus of the electron beam on the basis of the detection signal. The laser interferometer measuring system 35 measures a distance to the stage 18 by use of a distance measuring laser beam from a light source provided in the laser interferometer measuring system 35. Then, the laser interferometer measuring system 35 sends distance measurement data, that is, position data of the stage 18 to a position control section 37. The position control section 37 generates a position correction signal for correcting the position of the electron beam from the position data, and sends the position correction signal to the beam position corrector 32. The beam position corrector 32, as described above, corrects the position of the electron beam on the basis of the position correction signal. The position control section 37 also generates a position control signal for controlling the feed motor 19, and provides the position control signal to the feed motor 19. A rotation control section 38 controls the rotation of the spindle motor 17. The rotation control section 38 sends a rotation synchronization signal of the spindle motor 17 to a drawing controller 39. The rotation synchronization signal includes a signal representing a reference rotational position of the substrate 15 and a pulse signal on a predetermined rotational angle basis with respect to the reference rotational position. The rotation control section 38 obtains a rotational angle, a rotational speed, a rotational frequency, and the like of the substrate 15 from the rotation synchronization signal. The drawing controller 39 sends a blanking control signal to the blanking control section 31, and sends a deflection control signal to the deflection control section 33 to carry out drawing control. The drawing control, as described later, is carried out in synchronization with the above-described rotational signal of the spindle motor 17. Main signal lines of the blanking control section 31, the beam position corrector 32, the deflection control section 33, the focus control section 34, the position control section 37, and the rotation control section 38 are described above, but each of these components is bidirectionally connected to the drawing controller 39. Each component of the electron beam lithography apparatus 10 is appropriately connected to a not-illustrated system controller for controlling the whole apparatus, and sends and receives necessary signals. Then, an instance in which the electron beam lithography apparatus 10 draws (i.e., performs electron beam exposure) concentric patterns of an original master of a hard disk will be hereinafter described in detail. A track of the currently widely used hard disk, as shown in FIG. 2, is not a spiral pattern (shown by a broken line) adopted in an optical disk such as CDs, DVDs, and the like, but concentric patterns (shown by solid lines). An instance in which the electron beam lithography apparatus 10 (x-θ system lithography apparatus) successively draws the concentric patterns (15A, 15B, 15C, . . . and the like of FIG. 2) will be described for instance. FIG. 3 is a plan view which schematically shows the case of drawing a plurality of concentric patterns on the substrate 15 being the original master of the hard disk. Electron beam lithography (electron beam exposure) is concentrically performed on the substrate 15 applied with a resist, as shown in the drawing, to draw circles (tracks) in such a manner that a start point and an end point of the concentric circle precisely connect to each other. In other words, drawing by the electron beam lithography is started from a start point 15X of a circle 15A, and the circle is drawn in such a manner that a drawing end point (an end point of the circle 15A) connects to 15X being the drawing start point. In the drawing, for the sake of convenience, the position of the start point and the end point (connection point) 15X of the circle 15A is indicated with a filled circle (•). Then, a circle 15B concentric with the circle 15A is drawn in a similar manner with using a point 15Y, which is an outside point of the drawing connection point 15X of the circle 15A in a radial direction, as a drawing connection point. Furthermore, a circle 15C concentric with the circles 15A and 15B is drawn in a similar manner with using a point 15Z, which is an outside point of the drawing connection point 15Y in the radial direction, as a drawing connection point. The drawing connection points 15X, 15Y, and 15Z are in a line in the same radial direction of the concentric circles 15A, 15B, and 15C, respectively. The concentric circles can be drawn in a similar manner inside of the radial direction. FIG. 4 is a schematic plan view which illustrates the case of drawing the concentric circles 15A and 15B in such a manner that each circle precisely connects at the drawing connection point described above. The neighborhood of the drawing connection points (start point and end point) is enlarged in FIG. 4. FIG. 5 is a time chart corresponding to FIG. 4 which shows the blanking control signal and the deflection control signals in X and Y directions. FIG. 6 is a flowchart which shows the procedure steps of drawing. Taking a case in which the substrate 15 is rotated at constant linear velocity (CLV) as an example, the drawing control will be described. The deflection control signal in the radial direction, that is, the X direction in the drawing (hereinafter, referred to as X deflection signal) is a ramp wave having the same frequency as the rotational frequency of the spindle motor 17. In response to the X deflection signal having a ramp waveform, the drawing of the circle (track) 15A is started (step S11), and the circle 15A is drawn up to a position A (FIGS. 3 and 4), which is in the vicinity of the drawing start point 15X and does not reach the drawing start point 15X. The deflection of the electron beam is started at the position A in a direction opposite to the rotational direction (−Y direction) of the substrate 15 and a tangential direction (that is, +Y direction) in response to the Y deflection signal having a ramp wave form (step S12). When the electron beam reaches a position B (that is, the drawing start point 15X of the circle 15A), the electron beam is cut off by the blanking signal (step S13). As shown in FIG. 7, applying a blanking voltage to the blanking electrodes 23 largely deflects the electron beam EB from a restriction of the aperture 24, so that the electron beam EB becomes a state in which the electron beam EB cannot pass through the aperture 24 (i.e., beam: OFF). Thus, the electron beam can be cut off. In this state, the electron beam is further deflected to a position C of the circle 15A (deflection in the direction opposite to the rotational direction of the substrate 15) (step S14). The position C is at a distance of DY/2 from the position B in the +Y direction. When the electron beam reaches the position C in the circle 15A, the electron beam is deflected in an opposite direction (the rotational direction and the tangential direction of the substrate 15, that is, −Y direction in the drawing). The electron beam is also deflected in the radial direction (that is, +X direction in the drawing), so as to switch and shift the electron beam to a position D of the circle 15B (step S15). Then, in response to the Y deflection signal with the ramp waveform, the electron beam is deflected from the position D in the direction opposite to the rotational direction and the tangential direction (+Y direction in the drawing) (step S16). When the electron beam reaches a position E (that is, a position 15Y) of the circle 15B, the blanking electrodes 23 cancel the blanking (i.e., beam: ON) (step S17), so that the electron beam EB comes to pass through the aperture 24. The position D is at a distance of DY/2 from the position E in the −Y direction. Thus, drawing (exposure) starts again from the position E. Accordingly, the electron beam is in a blanked state (beam: OFF) during a period from the position B to the position C of the circle 15A, a period of carrying out X deflection and Y deflection from the position C of the circle 15A to the position D of the circle 15B, and a period from the position D to the position E of the circle 15B, and hence drawing (exposure) is not carried out. In this embodiment, the position B and the position E are the drawing start points of the respective circles, and also the drawing connection points. The position B and the position E are on a line in the same radial direction being the reference of drawing (hereinafter, also referred to as reference radial line). The positions Band E are reference positions of the concentric circles 15A and 15B, respectively. The reference radial line, for example, may be set so that the drawing connection point of each circle is in the reference radial line. Otherwise, as described later, the reference radial line may be set so as to be the center position of overwriting, when the overwriting is carried out. The reference radial line is not limited to these, but can be set appropriately. From the position E to a position F of the circle 15B, drawing is carried out by deflecting the electron beam in the +Y direction in response to the Y deflection signal with the ramp waveform (step S18). In other words, the deflection by the Y deflection signal with the ramp waveform is ended in the position F, and the drawing of the circle 15B continues. Repeating the foregoing operation makes it possible to draw the concentric patterns. A condition that the start point of a drawn line of the circle coincides with the end point is V=DY/Tb (1−Tb/Ty), wherein V represents movement velocity of the substrate, DY represents the amount of deflection by the Y deflection signal between the position C and the position D, Ty represents time period between the position A to the position F, and Tb represents blanking time. According to the present invention, as described above, when drawing transition is performed from one circle to another circle, the electron beam is deflected not only in the rotational radial direction but also in the tangential direction opposite to the rotational (moving) direction of the substrate. Also in a drawing connection section of the circle, the electron beam is deflected to the rotational tangential direction. Thus, it is possible to draw the circle (track) in such a manner that the start point precisely connects to the end point. Even if there is rotational fluctuation in a rotational stage, it is possible to connect the circle with high precision. A second embodiment of the present invention will be hereinafter described with reference to the drawings. FIG. 8 is a schematic plan view which illustrates the deflection control when drawing transition is performed from the circle 15A to the circle 15B, and the neighborhood of drawing connection points (start points and end points) is enlarged. FIG. 9 is a time chart corresponding to FIG. 8 which shows the blanking control signal and the deflection control signals in the X and Y directions. As in the case of the foregoing first embodiment, the electron beam starts being deflected in a position A near a reference position RA of the circle 15A in the tangential direction (+Y direction in the drawing) opposite to the rotational (moving) direction of the substrate 15, in response to the Y deflection signal having the ramp waveform. In this embodiment, after deflection in the +Y direction starts, deflection velocity is increased from a position B (for example, the reference position RA), and the electron beam is cut off (beam: OFF) by blanking in a position C passing the reference position RA in response to the blanking signal. Then, after moving to a position D with deflecting, the electron beam is deflected in an opposite direction (−Y direction in the drawing) and in the direction of the next circle (track) 15B (+X direction in the drawing), so that the electron beam is shifted to a position E of the circle 15B at high speed. Then, in response to the Y deflection signal having the ramp waveform, the electron beam is deflected in the tangential direction (+Y direction in the drawing) until reaching a position F. The position F is set before a reference position RB in a reference radial line in the circle 15B. The blanking is canceled in the position F to apply the electron beam EB to the substrate 15 (beam: ON). The deflection velocity is reduced in a position G (for example, the position RB in the reference radial line) of the circle 15B, and then deflection by the Y deflection signal with the ramp waveform is ended in a position H. Repeating the foregoing operation makes it possible to draw the concentric patterns. In the first embodiment, the drawing start point and the drawing end point are set at reference positions, and blanking control is carried out in such a manner that overwriting does not occur. When repeating the foregoing procedure draws the concentric circles, however, an overwritten portion occurs. In other words, taking the circle 15B as an example, when a circle 15C is drawn following the circle 15B in a similar manner, a section from the position F of the circle 15B to a drawing end position C′ of the circle 15B (a position corresponding to the position C in the circle 15B) becomes the overwritten portion (WO). Namely, the deflection and the blanking control are carried out in such a manner that the overwritten portion (WO) occurs in the vicinity of the reference positions (RA and RB) of the circles 15A and 15B. Therefore, it is possible to draw the circle which precisely connects at the start point and the end point. Also, even if there is rotational fluctuation in the rotational stage, it is possible to connect the circle with high precision. A third embodiment of the present invention will be hereinafter described with reference to drawings. FIG. 10 is a schematic plan view which illustrates the deflection control when drawing transition is performed from the circle 15A to the circle 15B, and the vicinity of drawing connection points is enlarged. FIG. 11 is a time chart corresponding to FIG. 10 which shows the blanking control signal and the deflection control signals in the X and Y directions. Deflection starts from a position A of the circle 15A in response to the Y deflection signal, and blanking voltage is applied at the predetermined rate of increase from a position B of the circle 15A. In other words, applying the blanking voltage in a ramp form makes it possible to adjust the intensity of the electron beam applied to the substrate. The blanking voltage is rapidly increased in a position C passing a reference position, and the electron beam is completely cut off by blanking (beam: OFF). Namely, the intensity of the electron beam is gradually reduced from the position B to the position C, and completely becomes zero in the position C. Then, after moving to a position D, the electron beam is deflected in the −Y direction and also in the +X direction, so that the electron beam is shifted to a position E of the circle 15B at high speed. In a position F before reaching a reference position RB of the circle 15B, the blanking voltage is abruptly reduced to a predetermined level in order to apply the electron beam the intensity of which is lower than that in a complete ON state. Then, the blanking voltage is reduced at the predetermined rate of reduction, and the electron beam completely becomes the ON state in a position G (corresponding to the position C of the circle 15A) passing the reference position. After that, deflection by the Y deflection signal with the ramp waveform is ended in a position H. Repeating the foregoing operation makes it possible to draw a plurality of concentric circles. Therefore, it is possible to draw the circle in which the start point precisely connects to the end point. In addition, even if there is rotational fluctuation in the rotational stage, it is possible to connect the circle with high precision. When repeating the foregoing procedure draws the concentric circles, an overwritten portion occurs. In other words, the deflection and the blanking control are carried out in such a manner that the overwritten portion (WO) occurs in the vicinity of the reference positions RA and RB in the circles 15A and 15B. The application intensity of the electron beam may be varied at a predetermined rate at least one of before and after the duration of deflecting the electron beam in the radial direction. A fourth embodiment of the present invention will be hereinafter described with reference to drawings. FIG. 12 is a schematic plan view which illustrates the deflection control when drawing transition is performed from the circle 15A to the circle 15B, and the vicinity of drawing connection points is enlarged. FIG. 13 is a time chart corresponding to FIG. 12 which shows the blanking control signal and the deflection control signals in the X and Y directions. A point of difference between a drawing method according to the foregoing first embodiment and that according to this embodiment is that a sine waveform signal is overlapped with the ramp waveform signal in the deflection control signal in the Y direction. This drawing method is the same as that of the first embodiment for the rest. To be more specific, responding to the Y deflection signal having the sine waveform, the electron beam is deflected in the tangential direction (±Y direction in the drawing) in the period between a position A and a position C. The electron beam is deflected in the tangential direction (−Y direction in the drawing) and also in the radial direction (+X direction in the drawing) from the position C, so that the electron beam is shifted to a position D at high speed. Then, the electron beam is deflected in the tangential direction (±Y direction in the drawing) in the period between the position D and a position F in response to the Y deflection signal with the sine waveform. As in the case of the first embodiment, the electron beam is cut off (beam: OFF) by blanking in the period between the position B and a position E being drawing connection points. A cutoff period of the electron beam, however, may be set so as to carry out overwriting. As described above in detail, according to the present invention, when drawing transition is performed from one circle to another, the electron beam is deflected not only the rotational radial direction but also the rotational tangential direction of the rotation (movement) of the substrate. Also in the drawing connection section of the circle, the electron beam is deflected in the rotational tangential direction opposite to the rotational direction of the substrate. Therefore, it is possible to draw the circle (track) which precisely connects at the start point and the end point. Even if there is rotational fluctuation in the rotational stage, the circle can be connected with high precision. In the foregoing embodiments, lithography (exposure) of the concentric circles is performed by using the electron beam. The present invention, however, is applicable in the case of using another beam such as an optical beam and the like instead of the electron beam.
	summary
	description	FIG. 1 is a schematic diagram of the basic components of a power generating system 8. The system includes a boiling water nuclear reactor 10 which contains a reactor core 12. Water 14 is boiled using the thermal power of reactor core 12, passing through a water-steam phase 16 to become steam 18. Steam 18 flows through piping in a steam flow path 20 to a turbine flow control valve 22 which controls the amount of steam 18 entering steam turbine 24. Steam 18 is used to drive turbine 24 which in turn drives electric generator 26 creating electric power. Steam 18 flows to a condenser 28 where it is converted back to water 14. Water 14 is pumped by feedwater pump 30 through piping in a feedwater path 32 back to reactor 10. FIG. 2 is a flow chart of a method 40 for expanding the operating domain of boiling water nuclear reactor 10. In one aspect, method 40 is applicable to boiling water nuclear reactor plants which can operate at higher than the original rated thermal power, where the fuel cycle performance at the higher load line is advantageous and plant performance at the higher power output is justified by appropriate safety analysis. In another aspect, method 40 provides the design concept and the analytical justification to operate boiling water nuclear reactor 10 in a significantly expanded region of the power/flow map. Computerized method 40, in an exemplary embodiment, is web enabled and is run on a business entity""s intranet. In a further exemplary embodiment, computerized method 40 is fully accessed by individuals having authorized access outside the firewall of the business entity through the Internet. In another exemplary embodiment, computerized method 40 is run in a Windows NT environment or simply on a stand alone computer system having a CPU, memory, and user interfaces. In yet another exemplary embodiment, computerized method 40 is practiced by simply utilizing spreadsheet software. Method 40 includes the steps of determining 42 by computer simulation a load line characteristic that is elevated over normal operating parameters and that increases reactor performance over normal operating parameters, performing 44 safety evaluations by computer simulation at the elevated load line to determine compliance with safety design parameters, and performing 46 operational evaluations by computer simulation at the elevated load line. Method 40 also includes the step of computing 48 a set of operating conditions for the reactor in an upper operating domain characterized by the elevated load line. Based on the results of the operational evaluations of step 46, constraints and requirements are generated 50 for plant equipment and procedures. Also, a detailed analysis by computer simulation is performed 51 of the core recirculation system. The optimum applicable range of the expanded region of operation is established. Also, output is generated 52 to facilitate automatic adjustment of the control rod pattern, the flow controls, and the pressure controls based on the detection of a reactor transient. Additionally, method 40 includes generating 54 output to facilitate the modification of the reactor process controls and computers to permit reactor operation in the upper operating domain. To determine the desired elevated load line characteristic, evaluations at elevated core thermal power are performed. The desired load line increase is based on the thermal power increase and the fuel cycle performance improvement that is obtained at the elevated core thermal power. Computer simulation of the reactor are used to define the operating conditions of the reactor in the new operating region characterized by the elevated load line. Evaluations of the expected performance of the reactor throughout the new operating region are also performed using computer simulation. Operational evaluations performed at the elevated load line include, but are not limited to, evaluating plant maneuvers, frequent plant transients, plant fuel operating margins, operator training and plant equipment response and setpoints. Based on the results of the operational evaluations, constraints and requirements are established for plant equipment and procedures. For example, evaluating core and fuel performance impact at increased power output includes determining anticipated transient without scram (ATWS) events for increased core thermal power output Some (ATWS) events include Main Steam Isolation Valve Closure (MSIVC); Pressure Regulator Failure-Open (PRFO); Loss of Offsite Power (LOOP); and Inadvertent Opening of a Relief Valve (IORV). The analysis takes into account ATWS mitigating features, such as, the recirculation pump trip (RPT), alternate rod insertion (ARI), and the Standby Liquid Control System (SLCS) performace. Plots of important parameters are created, and the peak values of neutron flux, average fuel heat flux and vessel pressure are calculated for each of the four events. Safety evaluations typically address the safety analysis Chapter 15 of the Final Safety Analysis Report (FSAR). Additionally, non-Chapter 15 safety issues such as containment integrity, stability and anticipated transient without scram (ATWS) are addressed. Safety analysis include demonstration of compatibility with the previous resolutions of reactor stability monitoring and mitigation of unplanned events. The safety evaluations are performed such that compliance to plant design criteria is demonstrated. Assurance of acceptable protection of the reactor and the public is performed and documented to satisfy regulatory authorities. Method 40 includes generating 56 output data to facilitate creating a safety analysis report to comply with regulatory requirements. For example, a review of the existing plant Safety Analysis Report and reload transients is conducted at the uprated conditions. Where necessary, analyses are performed to demonstrate compliance with the fuel thermal margin requirements and other applicable transient criteria. Of primary importance is an analysis of the transient events which are most limiting from the viewpoint of fuel thermal margin. Analysis of these most limiting events for uprated power at the most limiting conditions on the operating power/flow map will assure that fuel operating limits are met. A safety analysis includes a broad set of transient events that include:(1)Decrease in Core Coolant Temperature.(2)Increase in Reactor Pressure.(3)Decrease in Reactor Core Coolant Flow Rate.(4)Increase in Core Flow Rate.(5)Increase in Reactor Coolant Inventory.(6)Decrease in Reactor Coolant Inventory.(7)Increase in Reactivity.(8)Increase in Core Coolant Temperature. Evaluations are performed to show continued compliance with the nuclear regulatory agency rule on anticipated transient without scram performance (ATWS). ATWS rule compliance primarily involves alternate shutdown equipment which has been previously installed at each unit. The equipment remains and its performance at any changed conditions (due to uprate) is evaluated, for example at higher operating pressure. Where applicable, a bounding case is reanalyzed at the uprated power to confirm that adequate overpressure protection and suppression pool cooling are maintained for limiting cases in each BWR product line. This analysis also includes evaluation of any changes in pressure setpoints of the safety/relief valves and/or high pressure recirculation pump trip. In some cases these setpoints, as well as the allowable number of relief valves out of service may be re-optimized to improve the ATWS response. Power uprate operation does not significantly affect the long-term ATWS response because it does not involve a uniquely higher rod line, and, therefore, there is no increase in the power level following the ATWS recirculation pump trip. Radiological consequences are evaluated or analyzed for uprated power conditions. This evaluation/analysis is based on the methodology, assumptions, and analytical techniques described in previous Safety Evaluations (SEs). The evaluation of radiological consequences includes the effect of a higher power level. In general, the radiation sources inside the fuel rods, creation of activation products outside of the fuel rods, and concentration of coolant activation activities are directly proportional to the thermal power. Therefore, the original radiation inventories, expressed in terms of curies per megawatt of thermal power, will bound the uprated condition, provided that the core design, fuel loading, and mean exposure are not changed significantly. If significant changes to the fuel loading or design parameters are made to optimize for uprated conditions, the uprate license application will re-perform the radiological evaluation to account for changes to the isotopic concentrations in the fuel. Issues relating to burnup and enrichment also need to be addressed if the uprated burnup and enrichment are to exceed any regulated conditions. During normal operation, the radiation levels in the plant are the result of radiation streaming from the reactor vessel or from radioisotopes carried in the reactor water, steam, or radwaste process. In all cases, these quantities are approximately proportional to core thermal power. Increases in normal radiological releases from routine operation are considered in the power uprate amendment requests. The magnitude of the potential radiological consequences of a design basis accident (DBA) is proportional to the quantity of fission products released to the environment. This quantity is a product of the activity released from the core and the transport mechanisms between the core and the effluent release point. For a steam line break or instrument line break accident, the radiological consequences will be, at most, proportional to the increase in power, since (1) the quantity of activity in the primary coolant and in the offgas is unaffected by power uprate (it is limited by Technical Specifications), and (2) the increase in coolant mass discharged to the environment is dependent on reactor pressure, which increases less than the power increase. For the remaining DBAs, the radiological releases are expected to increase, at most, by the amount of power uprate, since the only parameter of importance is the actual inventory of radioisotopes in the fuel rod and the mechanism of fuel failure is not likely to be influenced by power uprate. In some cases, the magnitude of the uprate may be limited, to maintain the radiological consequences below regulatory guidelines. To maximize the ability of the boiling water reactor unit to avoid trip during transients that may occur while operating in the extended region, automatic adjustment of some controls is provided. For example automatic adjustment of the control rod pattern, flow controls and pressure controls based on sensing the initiation of a transient, such as a pump trip, are provided. These automatic controls improve plant availability, even in the previous range of reactor operation. An operating domain 58 of reactor 10 is characterized by a map of the reactor thermal power and core flow as illustrated in FIG. 3. Typically, reactors are licensed to operate below a flow control/rod line 60 characterized by an operating point 62 defined by 100 percent of the original rated thermal power and 100 percent of rated core flow. In some circumstances, reactors are licensed to operate with a larger domain, but are restricted to operation below a flow control/rod line 64 characterized by an operating point 66 defined by 100 percent of the original rated thermal power and 75 percent of rated core flow. Some reactors have been licensed to operate at higher power as illustrated by lines 67 in FIG. 3. However, these reactors are constrained by flow control/rod boundary line 64. In an exemplary embodiment of the present invention, method 40 expands operating domain 58 of reactor 10 and permits operation of reactor 10 between about 120 percent of original rated thermal power and about 85 percent of rated core flow to about 100 percent of original rated thermal power and about 55 percent of rated core flow. Lines 68, 70 and 72 represents this new upper boundary of an upper operating region 74 of operating domain 58 of reactor 10. FIG. 4 shows another exemplary embodiment of the present invention where method 40 expands operating domain 58 of reactor 10 to an upper boundary represented by the operation of reactor 10 between about 120 percent of original rated thermal power and about 85 percent of rated core flow to about 60 percent of original rated thermal power and about 60 percent of rated core flow. Lines 70, 76 and 78 represents this new upper boundary of an expanded upper operating region 80 of operating domain 58 of reactor 10. Method 40 provides analyzed limits that permit licensed power operation of reactor 10 at a core flow lower than the constraint on core flow imposed by boundary 64. The increased boundary line 68 permits operation of reactor 10 over a larger core flow range and operating flexibility during startup and at full power. Method 40 further provides savings in fuel cycle costs and faster plant startups due to the increased ability to establish desired full power control rod pattern at partial power conditions. Also provided is reduced cycle average recirculation pumping power consumption resulting in an increase in net station output. Another embodiment of the invention includes providing analyses and evaluations to generate a safety analysis report as describe above. Additionally, licensing support is provided to the owner, or managing entity, of the boiling water nuclear reactor, along with technical consultation during the implementation of reactor analyses and modifications described above. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
048287903	abstract	A nuclear power plant wherein surfaces of components contacting with nuclear reactor cooling water containing radioactive substances are coated with an oxide film, preferably being charged positively and/or containing chromium in an amount of 12% by weight or more, is prevented effectively from the deposition of radioactive substances thereon.
	abstract	A joint structure between a top nozzle and a guide thimble of a nuclear fuel assembly and, more particularly, a structure for joining an inner-extension tube, the top nozzle and the guide thimble. When an inner-extension tube head, which is provided as a means for facilitating removal of the top nozzle of the nuclear fuel assembly from the guide thimble, is removed from an inner-extension tube body to separate the top nozzle from the nuclear fuel assembly, the inner-extension tube body is prevented from undesirably rotating, so that the guide thimble and the inner-extension tube body can maintain the joined state.
	description	This application is a National Phase filing under 35 U.S.C. §371 of PCT/FR2006/002711filed Dec. 12, 2006, which claims priority to Patent Application No. 05 12853, filed in France on Dec. 16, 2005. The entire contents of each of the above-applications are incorporated herein by reference. The invention relates generally to heating rods for a pressurizer of a primary cooling system of a pressurized-water nuclear reactor. More precisely, the invention relates, according to a first aspect, to a heating rod for a pressurizer of a primary cooling system of a pressurized-water nuclear reactor, of the type comprising a metal outer shell of longitudinally elongate shape having an external surface, and a heating element mounted inside the shell. Such rods are normally mounted in the lower part of the pressurizer and are immersed in the water of the primary cooling system with which the pressurizer is partially filled. The rods are set into operation when it is desired to increase the operating pressure of the primary cooling system of the reactor. They heat the water to its boiling point so that part thereof evaporates. Leaks have been found to occur on the heating rods of the prior art. The outer shell of one of the rods sometimes cracks, so that the inside of the rod communicates with the water inside the pressurizer. Such a leak can result in damage to the heating element of the rod, the loss of operation of the rod, and even the leakage of pressurized water to the outside of the pressurizer, through the interior space of the rod. Within this context, the invention aims to propose heating rods having improved reliability. To that end, the invention relates to a heating rod of the type described above, characterized in that it comprises an anti-corrosion coating which covers at least part of the external surface of the shell. The rod can also have one or more of the following characteristics, considered individually or according to all technically possible combinations: the coating predominantly comprises nickel; the coating comprises at least 95% by weight nickel; the coating has been deposited on the external surface by electrolysis in a bath of nickel salts; the coating has a thickness greater than 50 micrometers; the rod comprises an active heating zone, the coating extending longitudinally at least along the whole of the active heating zone; the coating continues longitudinally on each side of the active heating zone over a guard distance; the guard distance is greater than 10 millimeters; and the shell is made of austenitic stainless steel. According to a second aspect, the invention relates to a method of treating a metal shell for a heating rod of the above type, characterized in that it comprises a step of depositing the coating on at least part of the external surface of the shell in an electrolytic cell comprising a bath and an electrode immersed in the bath, the bath predominantly comprising nickel sulfamate, nickel chloride and boric acid, the shell being disposed in the bath and an electric current being maintained between the electrode and the shell. The method can also have one or more of the following characteristics, considered individually or according to all technically possible combinations: the pH of the bath is maintained between 3 and 5 during the deposition step; the electrode is made of soluble nickel; the electric current is maintained at a current density between 5 and 50 amperes per square decimeter of the external surface of the shell that is to be treated during the deposition step; the step of depositing the coating is preceded by a preliminary step of depositing an adhesion layer on at least part of the external surface of the shell in an electrolytic cell comprising a bath and an electrode immersed in the bath, the bath being a Watts bath predominantly comprising nickel sulfate, nickel chloride and boric acid, the shell being disposed in the bath and an electric current being maintained between the electrode and the shell; the pH of the bath is maintained between 3 and 5 during the preliminary step; and the adhesion layer has a thickness less than 10 micrometers. FIG. 1 shows a primary cooling system 1 of a pressurized-water nuclear reactor. The system 1 comprises a vessel 2 in which there are located nuclear fuel assemblies, a steam generator 4 having primary and secondary parts, a primary pump 6 and a pressurizer 8. The vessel 2, the steam generator 4 and the pump 6 are connected by sections of primary piping 10. The system 1 contains primary water, the water being pumped by the pump 6 towards the vessel 2, passing through the vessel 2 while being heated in contact with the fuel assemblies, and then passing through the primary part of the steam generator 4 before returning to the inlet side of the pump 6. The primary water heated in the vessel 2 gives up its heat in the steam generator 4 to secondary water which passes through the secondary part of the generator. The secondary water circulates in a closed loop in a secondary cooling system (not shown). It evaporates as it passes through the generator 4, the steam so produced driving a steam turbine. The pressurizer 8 is mounted as a branch on the primary piping by way of a conduit 18 branched on the section 10 connecting the vessel 2 to the generator 4. It is disposed at a higher elevation than the pump 6 and the vessel 2. The pressurizer 8 comprises a substantially cylindrical fabricated shell 11 which has a vertical axis and is provided with a dome 12 and a bottom 14. The bottom 14 comprises a central orifice 16 (FIG. 2) which is connected to the primary piping by the conduit 18. The pressurizer 8 also comprises spraying means 19 having a branch connection 20 which passes through the dome 12, a spray nozzle 21 disposed inside the shell 11 and mounted on the branch connection 20, a pipe 22 connecting the branch connection 20 to the primary piping, in the region of the outlet side of the pump 6, and means (not shown) for selectively allowing or preventing the flow of primary water in the pipe 22 to the nozzle 21. The primary cooling system 1 also comprises a safety circuit 23 comprising an overflow tank 24, a pipe 25 connecting the tank 24 to the dome 12 of the pressurizer, and a safety valve 26 interposed on the pipe 25 between the tank 24 and the pressurizer 8. The interior space of the pressurizer 8 communicates with the primary cooling system 1 so that the pressurizer 8 is permanently partially filled with primary water, the level of water inside the pressurizer being dependent on the current operating pressure of the primary cooling system. The top of the pressurizer 8 is filled with steam at a pressure substantially equal to the pressure of the water circulating in the primary piping 10 connecting the generator 4. In case of excess pressure in the pressurizer, the valve 26 opens and the steam is evacuated to the tank 24, in which it condenses. The pressurizer 8 is equipped with several tens of electric heating rods 28. The rods are disposed vertically and are mounted on the bottom 14. They pass through the bottom 14 by way of orifices provided for that purpose, sealing means being interposed between the rods and the bottom 14. The rods 28 have a great length, typically from 1 m to 2.50 m, and a small cross-section in relation to their length. Each rod 28 comprises a portion 30 (FIG. 2) that is disposed inside the shell 11 of the pressurizer and is immersed in the water with which the pressurizer is partially filled, an intermediate portion 32 that is mounted in an orifice in the base 14, and a connection portion 34 that is disposed outside the shell 11. As is shown in FIG. 4, the immersed portion 30 comprises an outer shell 36 of cylindrical shape which is made of stainless steel or alloy, generally a central mandrel 38 disposed inside the shell 36 according to the central axis thereof, and a heating wire 40 which is wound around the mandrel 38 in a spiral and is interposed between the mandrel 38 and the shell 36. The heating wire 40 comprises an electrically conductive resistive metal core 42, for example made of copper or of nickel-chromium alloy, and a metal sheath made of steel 44 which surrounds the core 42 and is insulated electrically by magnesium oxide. It is in contact with an internal face of the shell 36. The wire 40 is disposed so as to create, in the immersed portion 30, a central longitudinal heating zone 46 (FIG. 2) and two longitudinal non-heating zones 48 disposed on each side of the heating zone 46. In the heating zone 46, the mandrel 38 is made of copper and the wire 40 is wound around the mandrel 38 to form contiguous turns. The wire 40 extends along the intermediate portion 32, on the inside thereof, and is connected to an electrical connector 49 situated in the portion 34. The connector 49 is electrically connected to an electric generator (not shown), which is capable of causing an electric current to flow in the wire 40. The immersed portion 30 has a longitudinal length of 2150 mm, for example. The heating zone 46 has a longitudinal length of 1100 mm, for example. The non-heating zone 48 interposed between the zone 46 and the intermediate portion 32 has a longitudinal length of 450 mm, for example. The non-heating zone 48 situated on the other side of the heating zone 46 has a longitudinal length of approximately 550 mm. The diameter of the outer shell 36 is constant along the whole of the portion 30 and is, for example, 22 mm. The portions 32 and 34 have a longitudinal length of 340 mm, for example, in total. The electrical power of each rod 28 varies from 6 to 30 kW. It delivers a heat flow which varies between 20 and 50 W/cm2, considered in the region of the external surface of the shell 36. The pressurizer 8 further comprises guide plates 50 for holding the rods 28, shown in FIG. 2. The guide plates 50 extend substantially horizontally over the whole of the internal section of the pressurizer 8. They are disposed one above the other, at different vertical levels in the pressurizer 8. Each guide plate comprises slots 52 permitting the flow of water through the plates 50, and holes 54 for guiding the rods 28. The holes 54 are circular and have a diameter slightly greater than the outside diameter of the immersed portion 30 of the rods (FIG. 3). The portion 30 passes through the various plates 50 through superposed holes 54, so that the rods 28 are guided at several levels and are maintained in a substantially vertical orientation by the plates 50. The outer shell 36 of the rod is not normally in contact with the edges of the holes 54. The function of the pressurizer 8 is to control the pressure of the water in the primary cooling system. Because it communicates with the primary piping by way of the pipe 18, it acts as an expansion vessel. Thus, when the volume of water circulating in the primary cooling system increases or decreases, the level of water inside the pressurizer 8 will rise or fall accordingly. That variation in the volume of water can be the result, for example, of an injection of water into the primary cooling system or of a variation in the operating temperature of the primary cooling system. The pressurizer 8 also serves to increase or decrease the operating pressure of the primary cooling system. In order to increase the operating pressure of the primary cooling system, the heating rods 28 are supplied with power so that they heat the water contained in the lower part of the pressurizer and bring it to its boiling point. Some of the water boils, so that the pressure in the top of the pressurizer 8 increases. Because the steam is constantly in hydrostatic equilibrium with the water circulating in the primary cooling system 1, the operating pressure of the primary cooling system 1 increases. In order to lower the operating pressure of the primary cooling system 1, the spraying nozzle 21 disposed in the top of the pressurizer 8 is set into operation by allowing the flow of water in the pipe 22 with the aid of the means provided for that purpose. The water withdrawn in the primary piping 10 on the outlet side of the pump 6 is discharged into the top of the pressurizer 8 and causes some of the steam therein to condense. The pressure of the steam in the top of the pressurizer 8 falls, so that the operating pressure of the primary cooling system 1 also decreases. As is shown in FIG. 4, the heating rods 28 each comprise an anti-corrosion coating 60 which covers at least part of the external surface 62 of the shell 36. The coating 60 extends longitudinally over the whole of the heating zone 46 of the rod, and it also extends longitudinally on each side of the zone 46 over a guard distance. The guard distance is greater than 10 mm, preferably greater than 30 mm, and is typically of the order of from 50 mm to 100 mm. The coating 60 extends over the whole of the periphery of the outer shell 36, so that it covers the shell 36 completely in the heating zone 46 and in part of the zones 48, over the guard distance. The coating 60 predominantly comprises nickel, and it preferably comprises at least 95% by weight nickel. In a preferred embodiment, the coating is a coating of pure or virtually pure nickel which is deposited electrolytically, as explained hereinbelow. The coating 60 has a thickness greater than 50 μm and less than 200 μm. Preferably, it has a thickness of approximately 100 μm. The method of depositing the coating 60 on the surface 62 of the outer shell will now be described. The main steps of the method are carried out in an electrolytic cell of the type shown in FIG. 5. The cell 64 comprises a vessel 66, which can contain a treatment bath and is provided with an inlet 68 and an outlet 70, a pump 72 for circulating the liquid that forms the bath from the outlet 70 to the inlet 68 of the vessel, an electrode 74 immersed in the bath, and an electric generator 76. The electrode 74 is made of soluble nickel. The electric generator 76 can be connected electrically on the one hand to the electrode 74 and on the other hand to the rod 28 that is to be treated. It is suitable for maintaining a potential difference between the electrode 74 and the rod 28 that is to be treated. The treatment method comprises the following successive steps. Step 1—Provision of a heating rod 28 to be treated. The rod is equipped with all its internal equipment (core 38, heating wire 40). Step 2—Degreasing of the external surface 62 of the shell 36. Step 3—Pickling of the surface to be coated using sulfuric acid. Step 4—Reversed polarity strike in order to dissolve the surface layer of the surface to be coated. This step can be carried out in the cell 64. In that case, the cell 64 is filled with a suitable solution, the immersed portion 30 of the rod being immersed in the solution, and the electric generator 76 being mounted so as to maintain the shell 36 at a positive potential and the electrode 74 at a negative potential. At the end of this step, the original surface layer of the shell 36 has been dissolved and has been replaced by a new surface covered with a freshly formed passive film. Step 5—Normal polarity strike, so as to depassivate the surface to be coated. This step can be carried out in the electrolytic cell 64. In that case, the cell 64 is filled with a suitable electrolyte bath, the portion 30 of the rod being immersed in the bath, as above. The generator 76 is this time mounted so as to maintain the shell 36 at a negative potential and the electrode 74 at a positive potential. This step allows the passive film formed in the preceding step 4 to be removed and the metal of the shell 36 to be exposed in order to permit better adhesion of the coating 60. Step 6—Deposition of an adhesion layer. The adhesion layer forms part of the coating 60 and comprises virtually no nickel. It has a thickness less than 10 μm, preferably of 2 μm. During this step, the vessel 66 is filled with a highly acidic Watts bath, which is composed principally of nickel sulfate, nickel chloride and boric acid. The pH of the solution is maintained between 3 and 5. The electric generator 76 maintains the electrode 74 at a positive potential and the shell 36 at a negative potential. The pump 72 serves to recirculate the bath continuously during step 6, a flow of liquid being withdrawn from the vessel 66 through the outlet 70 and reinjected through the inlet 68. Step 7—Deposition of the actual coating 60, the adhesion layer also forming part of the coating 60. The deposition is carried out in the cell 64. The vessel 66 is filled with a sulfamate bath substantially comprising nickel sulfamate, nickel chloride and boric acid. The pH of the bath is maintained between 3 and 5 during this step, preferably at approximately 4.5. The electric generator 76 maintains the electrode 74 at a positive potential and the shell 36 at a negative potential. An electric current is thus maintained between the electrode 74 and the shell 36 of the rod, the current density being from 5 to 50 amperes/dm2 of the external surface of the shell to be treated. Preferably, the current density is of the order of 20 amperes/dm2. The nickel layer deposited during step 7 has a thickness of the order of 100 μm. During steps 3 to 7, the parts of the external surface 62 of the rod that are not to receive the coating are protected by a suitable protective layer, for example an organic varnish. The heating rods and the treatment method described hereinbefore have numerous advantages. The coating 60 that covers part of the external surface of the shell 36 allows the rods to be protected against corrosion and the operating performance of the rods to be improved. The inventors have in fact found that, under certain operating conditions, a caustic medium develops between the heating zone 46 of the rod and the guide plates 50, and more precisely between the zone 46 and the edges of the holes 54. That gap constitutes a confined space in which the water does not circulate much and is replaced slowly, so that overheating with boiling can occur in that space, causing the creation of a caustic medium. The coating 60 makes it possible to prevent stress corrosion of the shell 36 from developing, in particular in the region of the plates 50, which can cause the shell 36 to crack and the inside of the rod 28 to communicate with the primary water. The reliability of the rods 28 is thus improved. The electrolytic nickel coating chosen in the above-mentioned example for partially covering the shells of the rods is particularly suitable because: it is compatible with the stainless steel constituting the shells 36 of the heating rods; it is permitted in the primary cooling system owing to its high purity; it is resistant to corrosion under the characteristic operating conditions of the pressurizer (chemical composition of the primary water, temperature, pressure); and it is resistant to stress corrosion in the nominal primary medium. The use of an electrode 74 made of soluble nickel in the cell 64 used to deposit the coating 60 is particularly suitable because it allows the composition of the bath to be kept virtually constant during phases 6 and 7 and consequently ensures that the nickel quality is constant and reproducible throughout the nickel-coating operation. In addition, all the steps of the method are carried out at temperatures far below the melting point of copper, typically 60° C. There is therefore no risk of damage to the electrical part of the rod (copper wire) during the operation of depositing the nickel, and therefore no risk of causing electrical failures as a result. The coating 60 is resistant to corrosion, including in a situation of thermal testing of the primary cooling system of the reactor or in a cycle extension situation, it being possible for a basic medium to develop in the pressurizer in both those situations. A cycle extension situation corresponds to prolonged use of the nuclear reactor between two cold shutdowns for the unloading of some fuel assemblies. The geometry of the heating rods is virtually unchanged compared with the prior art. In order to obtain exactly the same outside diameter for the immersed portion 30, it is possible to remove a layer of approximately 100 μm from the outer shell by grinding, before the electrolytic coating is deposited. The heating rods 28 and the treatment method described hereinbefore can have numerous variants. The coating 60 can cover the whole of the immersed portion 30, not only the zone 46 but also the zones 48 disposed on each side of the zone 46. It is possible to use a material other than nickel for the coating 60. That material can be, for example, chromium, or a more noble material than nickel, such as platinum or gold. The rod 28 can comprise an internal part that is different from that described hereinbefore (mandrel 38, heating wire 40). The outer shell 36 of the rod 28 can be made not of austenitic stainless steel but of Inconel 690, for example. The heating rods can have dimensions other than those mentioned hereinbefore (total length of the portion 30, outside diameter, length of the heating zone 46, of the non-heating zones 48, etc.).
	description	The field of the invention relates generally to power plants, and more particularly, to systems and methods of modeling power plants. Generally, known power plants include a number of major components. For example, known plants may include a gas turbine, a heat recovery steam generator, a steam turbine, and/or a condenser/cooling tower. To assess the performance of a power plant, the performance of each of the major components must be analyzed. For example, often power plants are assessed using modeling techniques. However, because the configuration and orientation of the major components used within a plant can vary from power plant to power plant, custom models for each power plant must be developed that take into account the specific configurations of the major components at each of the specific power plants being analyzed. As a result, developing plant specific models may be expensive and/or time-consuming. To facilitate reducing costs as well as to provide a universal system, some known modeling systems have attempted to embed alternative configurations of some major components in a single model. However, such systems generally include a very complex model that often increases the time to solve the model, i.e., long convergence times. In one embodiment, a system for use in determining the overall performance of a power plant including a plurality of components includes a processor configured to generate a first reference model of the power plant and generate a first test matched measured model of the power plant. The processor is further configured to determine the performance impact of the at least one of the plurality of components of the power plant on the overall thermal performance of the power plant at design conditions. In another embodiment, a computer-readable media includes program instructions which when executed by a processor cause the processor to perform the steps of generating a first reference model of the power plant using original specification data of the power plant and generating a first measured model of the power plant from measured performance data of at least one of a plurality of components of the power plant. The computer-readable media also includes program instructions for determining the performance impact of the at least one of the plurality of components on the overall thermal performance of the power plant by substituting design performance data of the at least one of the plurality of components in the first reference model with its measured performance data, transforming the performance impact of the at least one of the plurality of components into a normalized performance impact using the original specification data, and outputting at least one of the normalized plant performance impact and the performance impact. In yet another embodiment, a method of modeling a power plant includes generating a first measured thermal model, generating a first reference thermal model, and determining a performance impact of at least one of a plurality of major components on an amount of power plant power generation. The method also includes normalizing the performance impact of the at least one of the plurality of major components to a design basis and displaying the normalized performance impact. The following detailed description illustrates embodiments of the invention by way of example and not by way of limitation. It is contemplated that the invention has general application to analytical and methodical embodiments of determining efficiencies of major power plant components and sub-components in industrial, commercial, and residential applications. It is noted that, while the present application is described with reference to combined cycle power plants, one of ordinary skill in the art will appreciate that the systems and methods described herein are not limited to any particular type of power plant. As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. FIG. 1 is a schematic illustration of a combined cycle power plant 100 in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, power plant 100 includes a gas turbine engine 112 coupled in flow communication to a heat recovery steam generator (HRSG) 114 through an exhaust line 116. Exhaust gases exit gas turbine engine 112 and are directed to HRSG 114 through exhaust line 116. Steam generated by HRSG 114 is directed to a steam turbine 118 via steam lines 120 and 121. Steam turbine 118 exhausts spent steam to a condenser 122 where the steam is condensed into water that is channeled to feed pumps 123. Feed pumps return the water at high pressure to HRSG 114 to complete the steam cycle. Water circulating through tubes in condenser 122 is pumped from a basin of cooling tower 124 through condenser 122 and back to a tower of cooling tower 124 by circulating pumps 125 to complete the circulating water circuit. In the exemplary embodiment, combined cycle power plant 100 also includes an electrical generator 126 that is coupled via a shaft 128 to gas turbine engine 112. Gas turbine engine 112 includes a compressor section 130 that is coupled to a turbine section 131 through a shaft 132. A combustor section 134 is coupled in flow communication between compressor section 130 and turbine section 131. Exhaust gases discharged from turbine section 131 through exhaust line 116 are channeled through passages in HRSG 114 where heat energy in the exhaust gases is transferred to water flowing through HRSG 114 and the water is converted into steam. Exhaust gases are then discharged from HRSG 114 and released to the atmosphere or to a pollution control device (not shown), and steam produced in HRSG 114 is routed to steam turbine 118 through steam lines 120 and 121. An electrical generator 138 is coupled to steam turbine 118 through a shaft 140. Spent steam is routed to condenser 122 and cooling tower 124 through a steam line 142 or an exhaust hood (not shown), and steam condensate is returned to HRSG 114 wherein it is re-heated to steam in a continuous cycle. In the exemplary embodiment, power plant 100 is communicatively coupled to a data acquisition system (DAS) 150 for use in assessing the thermal performance of individual components of power plant 100, as described herein. In an alternative embodiment, DAS 150 comprises a computer that includes data acquisition hardware and executes data acquisition software. DAS 150 may be communicatively coupled to the power plant by any conventional wired or wireless link, thus enabling DAS 150 to be located within close proximity to power plant 100 and/or remotely therefrom. Thermal performance data of individual power plant components, such as components 112, 114, 118, 122, and 124, measured by DAS 150, are used as described in more detail below, to develop a thermal model that is substantially matched to performance test data of power plant 100. For example, measurements of compressor pressure, and/or combustion temperature, may be used to determine the thermal performance of gas turbine engine 112. Various sensors (not shown) may be located on or coupled to each power plant component for gathering data related to the respective power plant components and for forwarding the gathered data to DAS 150 for processing. Likewise, other criteria relevant to the determination of thermal performance of other components may be measured by DAS 150. FIG. 2 is a perspective view of a performance evaluation system (PES) 200 that may be used with combined cycle power plant 100 (shown in FIG. 1) in accordance with an exemplary embodiment of the present invention. PES 200 and its appropriate input/output ports 218, when provided with software configured to provide the functionality described herein, comprises a data acquisition system such as DAS 150. In the exemplary embodiment, PES 200 includes a processor 202 communicatively coupled to one or more memory devices 204 such as a random access memory (RAM), a read only memory (ROM), and one or more mass storage devices for reading and/or writing removable media such as a floppy disk drive, CD-ROM or CD-RW drive, or a DVD or DVD-RW drive such as a hard drive 206. In addition, PES 200 includes user interface devices, such as a display screen 212, a keyboard 214, and a mouse or other pointing device 215 (which may be built into the case of PES 200 rather than a separately attached device as shown in FIG. 2). Software included in some configurations of the present invention may be loaded, for example, from machine-readable media (examples of which are floppy disks, CD-ROMs, CD-RWs, DVDs, and the like) onto PES 200 using drive 206, or via a network interface or other type of data interface not shown in FIG. 1. In some configurations of the present invention, software is pre-loaded onto an internal storage device of PES 200, or may be loaded (or copied to internal storage) from a USB flash ROM storage device. In some configurations, a machine readable medium having instructions recorded thereon for acquiring data for thermal performance testing is supplied. The medium may comprise, for example, any of the removable and/or fixed storage media mentioned above, or other types of media. As used herein, the term “machine-readable medium” is intended to encompass configurations having a single medium or plural media, irrespective of whether the plural media are the same or different. As a non-limiting example, a “machine readable medium having instructions recorded therein for acquiring data for thermal performance testing” includes within its scope a configuration in which the instructions are spread across two floppy disks and a CD-ROM. In some configurations, PES 200 is a personal computer or a laptop computer, is portable and reconfigurable, so it can be moved and reconfigured to monitor different installations as needed. PES 200, via one or more input/output ports 218 (for example, serial, parallel, universal serial bus (USB), Ethernet, etc.) is configured to communicate with one or more data sources 232, 234, 236, and 238 at a system installation. In some configurations, a network bridge 220 or other interface unit is provided to facilitate communication via a plurality of channels 222. In the sample configuration illustrated in FIG. 1, channels 222 comprise interconnections 224, 226, 228, and 230. As described above, some configurations of the present invention communicate via between one and several hundred channels. However, the invention is not limited to any particular number of channels, and no specific limit should be construed either from FIG. 1 or any example configuration described herein. In various embodiments, PES 200 is configured to create a reference model and a measured model using a stored library of power plant components specifications. This library may be stored in memory device 204, hard drive 206, be accessed remotely, or stored in any other removable storage medium (not shown). A graphical user interface (GUI) 211 is displayed on screen 212 to permit a user to select individual components to be included in the thermal model. In some embodiments, GUI 211 is pre-populated with component names and dynamically links these names to the thermal model. In some embodiments, PES 200 is configured to act as a DAS while in others it is configured to operatively connect to a DAS, for instance, through either a wired connection 250 or a wireless connection 252. FIG. 3 is a flowchart of a method 300 of evaluating a thermal performance of a power plant in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, method 300 is used to determine the performance impact of individual power plant components, such as gas turbine engine 112, heat recovery steam generator (HRSG) 114, steam turbine 118, condenser 122, feed pumps 123, and cooling tower 124 (shown in FIG. 1) on the overall thermal performance of power plant 100. Method 300 includes generating 302 a first thermal model of a power plant based on original specification data of each of a plurality of individual components included in a power plant analysis. Method 300 includes generating 304 a second thermal model of the power plant using measured thermal performance data of at least some of the plurality of individual components. The performance impact of a selected power plant component on the overall thermal performance of the power plant is then determined 306 by substituting measured thermal performance data of the selected component in place of the original specification thermal performance data of the selected component. A determination 308 is then made as to whether or not the performance impact of all of the plurality of individual components included in a power plant analysis has been calculated. If not, the performance impact of a next selected power plant component on the overall thermal performance of the power plant is repeated until the performance impact of all the selected power plant components has been determined. If the performance impact of each of the power plant components has been determined 308, the performance impact of the plurality of individual components in the overall thermal performance of the power plant is displayed 310 or output for further processing. Additionally, sub-components of the plurality of individual components may be selected and included in the analysis of the performance impact on the overall thermal performance. FIG. 4 is a schematic of an exemplary thermal model 400 of a power plant such as power plant 100 (shown in FIG. 1) illustrating a comparison of thermal performance of various components and component parts of the power plant, with corresponding ideal thermal performance values. Thermal model 400 is based on and designed from measured thermal performance data of an operating power plant. For example, in power plant 100, steam turbine 118 includes a high pressure turbine (HPT) 401, an intermediate pressure turbine (IPT) 402, and a low pressure turbine (LPT) 403. In the example, the thermal performance of each of HPT 401, IPT 402, and LPT 403 is measured and compared against ideal thermal performance values associated with each component. For example, in the exemplary embodiment, the design thermal performance for HPT 401, IPT 402, and LPT 403 is represented by a horizontal line 410, and measured thermal performance indicated at 412 of HPT 401 is at about −1% as compared to its ideal thermal performance, identified at baseline 410. The measured thermal performance identified at 414 of IPT 402 is about +0.5% as compared to its corresponding ideal thermal performance indicated at baseline 410. Additional comparisons may be made for other components of power plant 100 for use in determining the operational efficiency of each component relative to its ideal performance values. For example, in the exemplary embodiment, the steam cycle output is re-calculated each time a new component is placed in service in the model to determine the individual component impact on plant performance. Finally, when all of the components have been implemented into the model, the impact of all of the components on the overall output of the plant are determined. More specifically, the impact of each component on the over plant output and heat rate are determined at measured boundary conditions. In one embodiment, the impact on output and heat rate are also determined at design conditions. In the exemplary embodiment, the data is graphically displayed for analysis. In other embodiments, the data may be displayed in other forms, and/or may be saved locally or remotely for later use. FIG. 5 is table 500 illustrating a performance model output as each selected component performance is incrementally included in the performance model. In the exemplary embodiment, table 500 includes a column 502 identifying selected components to be included in the model. Columns 504-516 to the right of column 502 identify whether for each increment the execution of the model is based on a design set of data or a measured or test set of data for each selected component. A first row 518 of output data quantifies the calculated steam cycle output for each execution of the model. A second row 520 of output data quantifies the calculated performance impact in kilowatts (kW) for each execution of the model when different components measured data is used in the calculation. For example, the steam cycle output for all selected components operating at their specified design performance ratings is indicated to be 265.261 megawatts (MW). Using measured data for the HP section of the steam turbine the steam cycle calculated output drops to 265.170 MW, a decrease of approximately 91 kW as indicated in row 520. Likewise, across rows 518 and 520, the performance impact of using the measured data for each selected component to calculate steam cycle output is shown. FIG. 6 is a gross reconciliation graph 600 that may be used with system 150 and that illustrates an expected plant power output in, for example, kilowatts. Columns 601 and 602 represent a respective energy output expected at installation and an energy output expected when the test was run. Columns 603 represent individual power plant components and their impact on the power output of the plant. Each component included in column 603 has two values indicated at rows 604 and 605. Values in row 604 each represent an expected output from the power plant with the component performing at its rated capacity and performance, and values in row 605 each represent the power plant output based on the actual performance of the component. The difference between the values of the components in rows 604 and 605 is a measure of the influence the component is having on the overall performance of the power plant as compared to the plants design goals. For example, in the exemplary embodiment, Gas Turbine 1 (GT1) has a design value of 700,395 kW, shown in row 604, and an actual operating value of 694,427 kW, shown in row 605. As such, Gas Turbine 1 is producing approximately 6000 kW less in power generation than designed. Column 606 represents an actual measured power output of the plant under current operating conditions, and column 607 represents an estimated power loss due to degradation and fouling of power plant parts. FIG. 7 is an exemplary detailed reconciliation graph 700 that may be used with system 150 (shown in FIG. 1). Graph 700 is similar to graph 600 (shown in FIG. 6), but rather than displaying the performance impact of only the main components of the power plant, graph 700 displays the impact of sub-components on the associated main components. For example, in the exemplary embodiment, sub-components of Gas Turbine 1 are indicated in a callout represented at 701. Callouts 702, 703, and 704 represent sub-components of Gas Turbine 2, heat recovery steam generator 1, and heat recovery steam generator 2, respectively. The sub-components illustrated are exemplary only, and graph 700 is not limited to only being used with the sub-components displayed. The term processor, as used herein, refers to central processing units, microprocessors, microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (ASIC), logic circuits, and any other circuit or processor capable of executing the functions described herein. As used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by processor 202, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. The above memory types are exemplary only, and are thus not limiting as to the types of memory usable for storage of a computer program. As will be appreciated based on the foregoing specification, the above-described embodiments of the disclosure may be implemented using computer programming or engineering techniques including computer software, firmware, hardware or any combination or subset thereof, wherein the technical effect includes at least an improved ability to understand the contributions of individual plant components to the power plant output. The techniques described herein are particularly useful for determining efficiencies of major power plant components, and also be used to determine efficiencies of sub-components. Any such resulting program, having computer-readable code means, may be embodied or provided within one or more computer-readable media, thereby making a computer program product, i.e., an article of manufacture, according to the discussed embodiments of the disclosure. The computer-readable media may be, for example, but is not limited to, a fixed (hard) drive, diskette, optical disk, magnetic tape, semiconductor memory such as read-only memory (ROM), and/or any transmitting/receiving medium such as the Internet or other communication network or link. The article of manufacture containing the computer code may be made and/or used by executing the code directly from one medium, by copying the code from one medium to another medium, or by transmitting the code over a network. This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
040615359	claims	1. An energy absorbing pressure relief valve for a core support cylinder of a nuclear reactor comprising a valve body for fluid flow therethrough having portions defining a fluid passageway, hinge means attached to the body, a plate suspended from the hinge means in sealing engagement with the passageway, an energy absorbing deformable member mounted on the plate and extending outwardly therefrom, the deformable member including a partially annular column open at its outwardly extending end and orifice means through the walls of said annular column. 2. An energy absorbing valve according to claim 1 wherein said hinge means includes an energy absorbing strap supporting said plate allowing rotational movement of said plate with respect to said passageway. 3. An energy absorbing valve according to claim 1 wherein said annular column further includes orifice means through the walls of the column to establish fluid communication between the interior portion of the annular column and said fluid passageway. 4. A vent assembly for a core support cylinder of a nuclear reactor pressure vessel comprising a valve body attached to the cylinder having portions defining a fluid flow passageway through the cylinder, hinge means attached to the body, a valve plate suspended from the hinge means in sealing engagement with the body portions defining the passageway and rotatable outwardly from the cylinder, an energy absorbing deformable member mounted on the plate and extending outwardly from the cylinder, the deformable member including a partially annular column open at its outwardly extending end. 5. A vent assembly according to claim 1 wherein said annular column includes orifice means through the walls of the column for fluid communication between the interior and exterior of said annular column. 6. A vent assembly according to claim 5 wherein said hinge means includes an energy absorbing strap.
	description	The present application is a divisional of U.S. patent application Ser. No. 13/418,930, filed Mar. 13, 2012 (now U.S. Pat. No. 8,929,504), which is a divisional of U.S. patent application Ser. No. 11/851,352, filed Sep. 6, 2007 (now U.S. Pat. No. 8,135,107), which claims priority to U.S. Provisional Patent Application Ser. No. 60/842,868, filed Sep. 6, 2006, the entireties of which are hereby incorporated by reference. The present invention relates generally to the field of storing and/or transporting high level waste, such as spent nuclear fuel rods, and specifically to apparatus and methods of storing and/or transporting spent nuclear fuel rods in a dry and hermetically sealed state. In the operation of nuclear reactors, hollow zircaloy tubes filled with enriched uranium, known as fuel assemblies, are burned up inside the nuclear reactor core. It is necessary to remove these fuel assemblies from the reactor after their energy has been depleted to a predetermined level. Upon depletion and subsequent removal from the reactor, these spent nuclear fuel (“SNF”) rods are still highly radioactive and produce considerable heat, requiring that great care be taken in their subsequent packaging, transporting, and storing. Specifically, the SNF emits extremely dangerous neutrons and gamma photons. It is imperative that these neutrons and gamma photons be contained at all times subsequent to removal from the reactor core. In defueling a nuclear reactor, the SNF is removed from the reactor and placed under water, in what is generally known as a spent fuel pool or pond storage. The pool water facilitates cooling of the SNF and provides adequate radiation shielding. The SNF is stored in the pool for a period of time that allows the heat and radiation to decay to a sufficiently low level so that the SNF can be transported with safety. However, because of safety, space, and economic concerns, use of the pool alone is not satisfactory where the SNF needs to be stored for any considerable length of time. Thus, when long-term storage of SNF is required, it is standard practice in the nuclear industry to store the SNF in a dry state subsequent to a brief storage period in the spent fuel pool. Dry storage of SNF typically comprises storing the SNF in a dry inert gas atmosphere encased within a structure that provides adequate radiation shielding. Systems that are used to store SNF for long periods of time in the dry state typically utilize a hermetically sealable and transportable canister or similar structure that serves as a vessel for the transfer and storage of the SNF. One such canister, known as a multi-purpose canister (“MPC”), is described in U.S. Pat. No. 5,898,747, to Krishna P. Singh, issued Apr. 27, 1999, the entirety of which is hereby incorporated by reference. Typically, the SNF is loaded into an open canister that is submerged under water in a fuel pool. Once loaded with SNF, the canister is removed from the pool, placed in a staging area, dewatered, dried, hermetically sealed and transported to a storage facility. An example of a canister drying method can be found in U.S. Pat. No. 7,096,600, to Krishna P. Singh, issued Aug. 29, 2006, the entirety of which is hereby incorporated by reference. Because a typical canister does not by itself provide the necessary radiation shielding properties, canisters are often positioned within large storage containers known as casks/overpacks during all stages of transportation and/or storage. An example of a canister transfer and storage operation can be found in U.S. Pat. No. 6,625,246, to Krishna P. Singh, issued Sep. 23, 2003, the entirety of which is hereby incorporated by reference. A dry storage canister (“DSC”) provides the confinement boundary for the stored SNF. Thus, the structural and hermetic integrity of the DSC is extremely important. An existing DSC is sold in the United States by Transnuclear, Inc. of Columbia, Md. under the tradename NUHOMS. The NUHOMS DSC is a single-walled vessel with two top closure lids, including an inner top lid and an outer top lid. The closure lids are welded to a canister body after the SNF has been loaded into it. In the United States, the practice of using two closure lids to create a double confinement barrier only at the field welded closure location is motivated by the fact that field welds are generally less sound than those made in the factory. However, in other countries, the creation of a double confinement barrier only at the field welded closure does not meet nuclear regulatory mandates. For example, Ukrainian regulatory practice calls for a double confinement boundary all around the SNF. To meet this dual-confinement requirement, the NUHOMS DSC comprises a hermetically-sealed fuel tube in which SNF rods in the form of a fuel bundle (half of a fuel assembly) is placed. These fuel tubes are positioned within the main cavity of the NUHOMS DSC. However, the body of the NUHOMS DSC remains a single-walled cylindrical vessel. The fuel tube concept of the NUHOMS DSC meets the basic Ukrainian regulation that a double confinement boundary exist all around the SNF. However, as will be discussed in greater detail below, it has been discovered that this design suffers from a number of significant drawbacks and engineering design flaws. It is an object of the present invention to provide an apparatus for transporting, storing and/or supporting high level radioactive waste. It is another object of the present invention to provide an apparatus for transporting, storing and/or supporting spent nuclear fuel. A further object of the present invention is to provide an apparatus for storing spent nuclear fuel that essentially precludes the potential of radiological release to the environment. A yet further object of the present invention is to provide an apparatus for storing, transporting and/or supporting spent nuclear fuel in a dry state. Another object of the present invention is to create a system of storing spent nuclear fuel with two independent containment boundaries around the entirety of the spent nuclear fuel stored therein that contain radiological matter, such as gases and/or particulates. A further object of the present invention is to provide an apparatus for storing spent nuclear fuel with two independent radiological containment boundaries that facilitate heat removal via conformal contact therebetween. A still further object of the present invention is to provide a canister for storing spent nuclear fuel having two independent radiological containment boundaries surrounding a cavity. Another object of the present invention is to provide an improved fuel basket for supporting spent nuclear fuel. A still further object of the present invention is to provide a vented fuel tube for holding high level radioactive waste. Yet another object is to provide a fuel basket that can efficiently accommodate both poison rods and spent nuclear fuel. These and other objects are met by the present invention, which one aspect can be a canister for storing and/or transporting spent nuclear fuel rods comprising: a first shell forming a cavity for receiving spent nuclear fuel rods; a first plate connected to the first shell so as to form a floor of the cavity; a first lid enclosing the cavity; the first shell, the first plate and the first lid forming a first hermetic containment boundary about the cavity; a basket for supporting a plurality of spent nuclear fuel rods positioned within the cavity; a second shell surrounding the first shell so that an inner surface of the second shell is in substantially continuous surface contact with an outer surface of the first shell; a second plate connected to the second shell; a second lid; and the second shell, the second plate and the second lid forming a second hermetic containment boundary that surrounds the first radiation containment boundary. In another aspect, the invention can be a canister apparatus for storing and/or transporting spent nuclear fuel rods comprising: a first pressure vessel comprising a first shell forming a first cavity for receiving spent nuclear fuel rods, a first plate connected to the first shell so as to enclose a first end of the first cavity, and a first lid connected to the first shell so as to enclose a second end of the first cavity; a second pressure vessel comprising a second shell forming a second cavity, a second plate connected to the second shell so as to enclose a first end of the second cavity, and a second lid connected to the second shell so as to enclose a second end of the second cavity; and the first pressure vessel located within the second cavity so that an inner surface of the second shell is in substantially continuous surface contact with an outer surface of the first shell. In yet another aspect, the invention can be a canister apparatus for storing and/or transporting spent nuclear fuel rods comprising: a first metal pressure vessel having an outer surface and forming a cavity for receiving spent nuclear fuel rods; a second metal pressure vessel having an inner surface; and the first pressure vessel located within the second pressure vessel so that a substantial entirety of the outer surface of the first metal pressure vessel is in substantially continuous surface contact with the inner surface of the second metal pressure vessel. In still another aspect, the invention can be a canister apparatus for storing and/or transporting spent nuclear fuel rods comprising: a first structural assembly forming a cavity for receiving spent nuclear fuel rods, the first structural assembly forming a first gas-tight containment boundary surrounding the cavity; a second structural assembly surrounding the first structural assembly, the second structural assembly forming a second gas-tight containment boundary surrounding the cavity; and wherein the first structural assembly and second structural assembly are in substantially continuous surface contact with one another. In yet another aspect, the invention can be a basket apparatus for supporting a plurality of spent nuclear fuel rods within a containment structure comprising: a plurality of disk-like grates, each disk-like grate having a plurality of cells formed by a gridwork of beams; and means for supporting the disk-like grates in a spaced arrangement with respect to one another and so that the cells of the disk-like grates are aligned. In a further aspect, the invention can be a basket apparatus for supporting a plurality of spent nuclear fuel rods within a containment structure comprising: a disk-like grate having a ring-like structure encompassing a gridwork of beams; the gridwork of beams comprising a first series of parallel beams, a second series of parallel beams and a third series of parallel beams; and wherein the first, second and third series of parallel beams are arranged in the ring-like structures so as to intersect and form a plurality of cells. In another aspect, the invention can be a basket apparatus for supporting a plurality of spent nuclear fuel rods within a containment structure comprising: a disk-like grate having a ring-like structure encompassing a gridwork of beams; and the gridwork of beams forming a first set of cells having a first shape and a second set of cells having a second shape. Referring to FIG. 1, a dual-walled DSC 100 according to one embodiment of the present invention is disclosed. The dual-walled DSC 100 and its components are illustrated and described as an MPC style structure. However, it is to be understood that the concepts and ideas disclosed herein can be applied to other areas of high level radioactive waste storage, transportation and support. Moreover, while the dual-walled DSC 100 is described as being used in combination with a specially designed fuel basket 90 (which in of itself constitutes an invention), the dual-walled DSC 100 can be used with any style of fuel basket, such as the one described in U.S. Pat. No. 5,898,747, to Krishna P. Singh, issued Apr. 27, 1999. In fact, in some instances it may be possible to use the dual-walled DSC 100 without a fuel basket, depending on the intended function. Furthermore, the dual-walled DSC 100 can be used to store and/or transport any type of high level radioactive waste and is not limited to SNF. As will become apparent from the structural description below, the dual-walled DSC 100 contains two independent containment boundaries about the storage cavity 30 that operate to contain both fluidic (gas and liquid) and particulate radiological matter within the cavity 30. As a result, if one containment boundary were to fail, the other containment boundary will remain intact. While theoretically the same, the containment boundaries formed by the dual-walled DSC 100 about the cavity 30 can be literalized in many ways, including without limitation a gas-tight containment boundary, a pressure vessel, a hermetic containment boundary, a radiological containment boundary, and a containment boundary for fluidic and particulate matter. These terms are used synonymously throughout this application. In one instance, these terms generally refer to a type of boundary that surrounds a space and prohibits all fluidic and particulate matter from escaping from and/or entering into the space when subjected to the required operating conditions, such as pressures, temperatures, etc. Finally, while the dual-walled DSC 100 is illustrated and described in a vertical orientation, it is to be understood that the dual-walled DSC 100 can be used to store and/or transport its load in any desired orientation, including at an angle or horizontally. Thus, use of all relative terms through this specification, including without limitation “top,” “bottom,” “inner” and “outer,” are used for convenience only and are not intended to be limiting of the invention in such a manner. The dual-walled DSC 100 dispenses with the single-walled body concept of the prior art DSCs. More specifically, the dual walled DSC 100 comprises a first shell that acts as an inner shell 10 and a second shell that acts as an outer shell 20. The inner and outer shells 10, 20 are preferably cylindrical tubes and are constructed of a metal. Of course, other shapes can be used if desired. The inner shell 10 is a tubular hollow shell that comprises an inner surface 11, an outer surface 12, a top edge 13 and a bottom edge 14. The inner surface 11 of the inner shell 10 forms a cavity/space 30 for receiving and storing SNF. The cavity 30 is a cylindrical cavity formed about a central axis. The outer shell 20 is also a tubular hollow shell that comprises an inner surface 21, an outer surface 22, a top edge 23 and a bottom edge 24. The outer shell 20 circumferentially surrounds the inner shell 10. The inner shell 10 and the outer shell 20 are constructed so that the inner surface 21 of the outer shell 20 is in substantially continuous surface contact with the outer surface 12 of the inner shell 10. In other words, the interface between the inner shell 10 and the outer shell 20 is substantially free of gaps/voids and are in conformal contact. This can be achieved through an explosive joining, a cladding process, a roller bonding process and/or a mechanical compression process that bonds the inner shell 10 to the outer shell 20. The continuous surface contact at the interface between the inner shell 10 and the outer shell 20 reduces the resistance to the transmission of heat through the inner and outer shells 10, 20 to a negligible value. Thus, heat emanating from the SNF loaded within the cavity 30 can efficiently and effectively be conducted outward through the shells 10, 20 where it is removed from the outer surface 22 of the outer shell via convection. The inner and outer shells 10, 20 are preferably both made of a metal. As used herein, the term metal refers to both pure metals and metal alloys. Suitable metals include without limitation austenitic stainless steel and other alloys including Hastelloy™ and Inconel™. Of course, other materials can be utilized. The thickness of each of the inner and outer shells 10, 20 is preferably in the range of 5 mm to 25 mm. The outer diameter of the outer shell 20 is preferably in the range of 1700 mm to 2000 mm. The inner diameter of the inner shell 10 is preferably in the range of 1700 mm to 1900 mm. The invention, however, is not limited to any specific size and/or thickness of the shells 10, 20. In some embodiments, it may be further preferable that the inner shell 10 be constructed of a metal that has a coefficient of thermal expansion that is equal to or greater than the coefficient of thermal expansion of the metal of which the outer shell 20 is constructed. Thus, when the SNF that is stored in the cavity 30 emits heat, the outer shell 20 will not expand away from the inner shell 10. This ensures that the continuous surface contact between the outer surface 12 of the inner shell 10 and the outer surface 21 of the outer shell 20 will be maintained and gaps will not form under heat loading conditions. The dual-walled DSC 100 further comprises a first lid that acts as an inner top lid 60 for the inner shell 10 and a second lid that acts as an outer top lid 70 for the second shell 20. The inner and outer top lids 60, 70 are plate-like structures that are preferably constructed of the same materials discussed above with respect to the shells 10, 20. Preferably the thickness of the inner top lid 60 is in the range of 100 mm to 300 mm. The thickness of the outer top lid is preferably in the range of 50 mm to 150 mm. The invention is not, however, limited to any specific dimensions, which will be dictated on a case-by-case basis and the radioactive levels of the SNF to be stored in the cavity 30. Referring now to FIG. 2, the inner top lid 60 comprises a top surface 61, a bottom surface 62 and an outer lateral surface/edge 63. The outer top lid 70 comprises a top surface 71, a bottom surface 72 and an outer lateral surface/edge 73. When fully assembled, the outer lid 70 is positioned atop the inner lid 60 so that the bottom surface 72 of the outer lid 70 is in substantially continuous surface contact with the top surface 61 of the inner lid 60. During an SNF underwater loading procedure, the inner and outer lids 60, 70 are removed. Once the cavity 30 is loaded with the SNF, the inner top lid 60 is positioned so as to enclose the top end of the cavity 30 and rests atop the brackets 15. Once the inner top lid 60 is in place and seal welded to the inner shell 10, the cavity 30 is evacuated/dried via the appropriate method and backfilled with nitrogen, helium or another inert gas. The drying and backfilling process of the cavity 30 is achieved via the holes 64 of the inner lid 60 that form passageways into the cavity 30. Once the drying and backfilling is complete, the holes 61 are filled with a metal or other wise plugged so as to hermetically seal the cavity 30. Referring now to FIGS. 1 and 3 concurrently, the outer shell 20 has an axial length L2 that is greater than the axial length L1 of the inner shell 10. As such, the top edge 13 of the inner shell 10 extends beyond the top edge 23 of the outer shell 20. Similarly, the bottom edge 24 of the outer shell 20 extends beyond the bottom edge 13 of the inner shell 10. The offset between the top edges 13, 23 of the shells 10, 20 allows the top edge 13 of the inner shell 10 to act as a ledge for receiving and supporting the outer top lid 70. When the inner lid 60 is in place, the inner surface 11 of the inner shell 10 extends over the outer lateral edges 63. When the outer lid 70 is then positioned atop the inner lid 60, the inner surface 21 of the outer shell 20 extends over the outer lateral edge 73 of the outer top lid 70. The top edge 23 of the outer shell 20 is substantially flush with the top surface 71 of the outer top lid 70. The inner and outer top lids 60, 70 are welded to the inner and outer shells 10, 20 respectively after the fuel is loaded into the cavity 30. Conventional edge groove welds can be used. However, it is preferred that all connections between the components of the dual-walled DSC 100 be through-thickness weld. The dual-walled DSC 100 further comprises a first plate that acts as an inner base plate 40 and a second plate that acts as an outer base plate 50. The inner and outer base plates 40, 50 are rigid plate-like structures having circular horizontal cross-sections. The invention is not so limited, however, and the shape and size of the base plates 40, 50 is dependent upon the shape of the inner and outer shells 10, 20. The inner base plate 40 comprises a top surface 41, a bottom surface 42 and an outer lateral surface/edge 43. Similarly, the outer base plate 50 comprises a top surface 51, a bottom surface 52 and an outer lateral surface/edge 53. The top surface 41 of the inner base plate 40 forms the floor of the cavity 30. The inner base plate 40 rests atop the outer base plate 50. Similar to the other corresponding components of the dual-walled DSC 100, the bottom surface 42 of the inner base plate 40 is in substantially continuous surface contact with the top surface 51 of the outer base plate 50. As a result, the interface between the inner base plate 40 and the outer base plate 50 is free of gaseous gaps/voids for thermal conduction optimization. An explosive joining, a cladding process, a roller bonding process and/or a mechanical compression process can be used to effectuate the contact between the base plates 40, 50. Preferably, the thickness of the inner base plate 40 is in the range of 50 mm to 150 mm. The thickness of the outer base plate 50 is preferably in the range of 100 mm to 200 mm Preferably, the length from the top surface of the outer top lid 70 to the bottom surface of the outer base plate 50 is in the range of 4000 mm to 5000 mm, but the invention is in no way limited to any specific dimensions. The outer base plate 50 may be equipped on its bottom surface with a grapple ring (not shown) for handling purposes. The thickness of the grapple ring is preferably between 50 mm and 150 mm. The outer diameter of the grapple ring is preferably between 350 mm and 450 mm. Referring now to FIGS. 2 and 4 concurrently, the inner shell 10 rests atop the inner base plate 40 in a substantially upright orientation. The bottom edge 14 of the inner shell 10 is connected to the top surface 41 of the inner base plate 40 by a through-thickness single groove (V or J shape) weld. The outer surface 12 of the inner shell 10 is substantially flush with the outer lateral edge 43 of the inner base plate 40. The outer shell 20, which circumferentially surrounds the inner shell 10, extends over the outer lateral edges 43, 53 of the inner and outer base plates 40, 50 so that the bottom edge 24 of the outer shell 20 is substantially flush with the bottom surface 52 of the outer base plate 50. The inner surface 21 of the outer shell 20 is also connected to the outer base plate 50 using a through-thickness edge weld. In an alternative embodiment, the bottom edge 24 of the outer shell 20 could rest atop the top surface 51 of the outer base plate 50 (rather than extending over the outer later edge of the base plate 50). In that embodiment, the bottom edge 24 of the outer shell 20 could be welded to the top surface 51 of the outer base plate 50. When all of the seal welds discussed above are completed, the combination of the inner shell 10, the inner base plate 40 and the inner top lid 60 forms a first hermetically sealed structure surrounding the cavity 30, thereby creating a first pressure vessel. Similarly, the combination of the outer shell 20, the outer base plate 50 and the outer top lid 70 form a second sealed structure about the first hermetically sealed structure, thereby creating a second pressure vessel about the first pressure vessel and the cavity 30. Theoretically, the first pressure vessel is located within the internal cavity of the second pressure vessel. Each pressure vessel is engineered to autonomously meet the stress limits of the ASME Code with significant margins. Unlike the prior art DSC, all of the SNF stored in the cavity 30 of the dual-walled DSC 100 share a common confinement space. The common confinement space (i.e., cavity 30) is protected by two independent gas-tight pressure retention boundaries. Each of these boundaries can withstand both sub-atmospheric supra-atmospheric pressures as needed, even when subjected to the thermal load given off by the SNF within the cavity 30. Referring now to FIG. 5, the dual-walled DSC 100 is illustrated having a fuel basket 90 positioned within the cavity 30 in a free-standing orientation. The fuel basket 90 serves to hold and support a plurality of SNF rods (which are located within fuel tubes 91) in the desired arrangement and maintains the desired separate locality. The fuel basket 90 comprises a plurality of disk-like grates 92 arranged in a stacked and spaced orientation. The separation between the disk-like grates 92 is accomplished via a plurality of vertically oriented tie-rods that pass through the cells of the disk-like grates 92. Once the tie rods are in place, one of the disk-like grates 92 is slid into position. Tubular sleeves that can not pass through the cells are then placed over the tie-rods and above the disk-like grates 92 in place. The next disk-like grates 92 is then slid down the tie rods. However, because the tubular sleeves can not pass through the disk-like grates 92, the two disk-like grates 92 are maintained in the spaced relation. The grates 92 are disc-like frames comprising a ring 185 and a plurality of series of beams 182, 183, 184. The outer surface 186 of the ring 185 is in surface contact with the inner surface 11 of the inner shell 10. The outer diameter of the disk-like grate 92 is preferably 1700 mm to 1900 mm. The outer diameter, however, is dependent upon the size of the cavity 30. In the illustrated embodiment, the number of grates 92 is nine, and the thickness of each grate 92 is preferably between 1 mm and 10 mm. However, the invention is not so limited, so long as the SNF rods are adequately supported within the cavity 30. Referring now to FIGS. 5 and 6, concurrently, the fuel basket 90 further comprises a plurality of ventilate fuel tubes 91. As will be discussed in greater detail below, when assembled, the ventilated fuel tubes 91 are inserted through the cells 180 of the stack of grates 92, which are aligned. The ventilated fuel tubes 91 form cylindrical cavities 193 (FIG. 9) in which the SNF rods will reside. Preferably, the fuel cells 180 around the outer perimeter of the grates 92 (i.e. the slots 180 nearest to the inner surface 11 of the inner shell 10) remain free of SNF rods. Referring now to FIG. 7, the grates 92 also comprise a plurality of smaller cells 181 for slidably receiving poison rods 93. The poison rods 93 are provided between the loaded fuel tubes 91 to control reactivity in necessary cases. The number of poison rods 93 is selected to ensure that the computed keff of the SNF rods at maximum design basis initial enrichment, with no credit for burn up, and with the inclusion of all uncertainties and biases is less than 0.95. However, in some embodiments, the poison rods 93 may not be required at all. The pitch P between each of the ventilated fuel tubes 91 is between 100 mm and 150 mm. The invention is not so limited however, and the pitch between the ventilated fuel tubes 91 is affected by both the size of the cavity 30 and the number and location of the poison rods 93, and the radioactivity of the load to be stored. Referring now to FIG. 8, a top view of one of the grates 92 is illustrated. The grate 92 is a honey-comb grid like structure. The grates 92 comprise a ring structure 185, a first series of substantially parallel beams 182, a second series of substantially parallel beams 183 and a third series of substantially parallel beams 184. The ring structure 185 encompasses the a first, second and third series of substantially parallel beams 182-184. The entire grate 92 can be constructed of a metal, such as steel or aluminum, or any of the materials discussed above. The first, second and third series of substantially parallel beams 182-184 are arranged within the ring structure 185 so that each one of the series of beams 182-184 intersects with the other two series of beams 182-184. The intersection of the series beams 182-184 forms a gridwork that results in an array of fuel cells 180 and an array of poison rod cells 181. More specifically, the general outline of the fuel cells 180 is created by the intersection of the first and second series of beams 182, 183 while the poison rod cells 181 are created by the intersection of the third series of beams 184 with the first and second series of beams 182, 183. When assembled, the fuel cells 180 receive the fuel tubes 91 while the poison rod cells 181 receive the poison rods 93. As can be seen the poison rod cells 181 are smaller and of a different shape than the fuel cells 180. The relative arrangement of first, second and third series of substantially parallel beams 182-184 with respect to one another is specifically selected to create hexagonal shaped fuel cells 180 and triangular shaped poison cells 181. Of course, additional series of beams and/or arrangement can be used to create cells that have different shapes, including octagonal, pentagonal, circular, square, etc. The desired shape may be dictated by the shape of the fuel tube and SNF fuel assembly to be stored. The series of beams 182, 183, 184 are rectangular strips (i.e., elongated plates) having notches (not visible) strategically located along their length to facilitate assembly. More specifically, notches that extend into the edges of the beams for at least ½ the height of the beams are provided. The notches are arranged on the beams 182-184 so that when the beams 182-184 are arranged in the desired gridwork, the notches of the bottom edge of some beams 182-184 are aligned with the notches on the top edge of the remaining beams 182-184. The beams 182-184 can then slidably mate with one another via the interaction between the notches. The beams 182, 183, 184 are then welded to each other at their intersecting points via tungsten inert gas process. While the beams 182-184 are illustrated as strips, the invention is not so limited and other structures may be used to form the gridwork, such as rods. Referring now to FIG. 9, the structure of the poison rods 93 and the ventilated fuel tubes 91 will be described. In the illustrated embodiment, the poison rods 93 are hollow tubular members having a cavity 196 for receiving a neutron absorbing material. For example, the hollow tubular member can be constructed of a stainless steel and filled with boron-carbide powder. In other embodiment, the poison rods 93 can be constructed of a monolithic material, such as a metal matrix material, such as Metamic™. The outer diameter of the poison rods 93 is between 20 mm and 40 mm and the inner diameter is between 10 mm and 40 mm. The invention is not so limited, however. When assembled in the DSC 100, the poison rods 93 are of a sufficient length so as to extend along the full height of the SNF rods stored within the fuel tubes 91. Turning now to the fuel tubes 91, the ventilated fuel tubes 91 are designed to allow for ventilation of heat emitted by the SNF rods 200 stored therein. The ventilated fuel tube 91 comprises a tubular body portion 191 and a ventilated cap portion 192. The tubular body portion 191 forms a cavity 193 for receiving the SNF rods 200, e.g., in the form of fuel bundles (half fuel assemblies). Preferably, the ventilated fuel tubes 91 have a horizontal cross sectional profile such that the cavity 193 accommodates no more than one fuel bundle. However, this is not limiting of the invention. The outer and inner diameter of the tubular body portion 191 of the ventilated fuel tube 91 is preferably between 75 mm and 125 mm, but the invention is not so limited. The tubular body portion 191 comprises a closed bottom end 194 and open top end 197. The closed bottom end 197 is a tapered and flat bottom. As will be discussed in further detail below, the tapering of the closed bottom end 197 allows for better air flow through the dual walled DSC 100. In an alternative embodiment, the closed bottom end 197 could further comprise holes and/or vents for improved air flow and heat removal. The ventilated cap portion 192 is connected to the open top end of the body portion 191 once the cavity 193 is filled with the SNF rods 200. The cap portion 192 is a non-unitary structure with respect to the tubular body 191 and removable therefrom. The caps 192 prevent any of the solid contents from spilling out during handling operations in the processing facility. The caps 192 of the tubes 91 comprise one or more openings 195 that provide passageways into the cavity 193 from the cavity 30. The openings 195 are covered with fine-mesh screen (not visible) so as to prevent any build-up of pressure in the fuel tube 191 while containing any small debris within the cavity 193 of the tube 91. It has been discovered that one inherent flaw in the design of the NUHOMS DSC is that the hermetically sealed fuel tube creates a mini-pressure vessel around the SNF rods stored therein. Because of the small confinement space/volume available in the hermetically sealed fuel tube of the NUHOMS DSC, even a small amount of water or release of plenum gas from the inside of the SNF rods can raise the internal pressure in the fuel tube steeply, rendering it susceptible to bursting. As a result, the integrity of the fuel tube of the NUHOMS DSC as a pressure vessel can not be assured when used to store previously waterlogged SNF rods that contain micro-cracks with a high level of confidence. The ventilated fuel tubes 91 of the present invention, on the other hand, prevent pressure build-up by allowing ventilation with the larger cavity 30 via the opening 195 in the cap 192. The openings 195 are generally triangular in shape, but can be circular, rectangular or any other shape, so long as the proper venting is achieved. Referring again to FIG. 5, when the ventilated fuel tubes 92 are positioned in the dual walled DSC 100, a plenum exists between the top of the ventilated fuel tubes 91 and the bottom surface 62 of the inner top lid 60. As mentioned previously, it is also preferable that the perimeter of the grid plate 92 remain free of fuel tubes 91. Whereas the present invention has been described in detail herein, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of the present invention. It is also intended that all matter contained in the foregoing description or shown in any accompanying drawings shall be interpreted as illustrative rather than limiting.
039473201	description	In the drawings a fuel element is generally indicated at 10. It is preferably encased in a closed cylindrical jacket 12 having one end covered with a cap 14 in a fluid-tight manner by means of a weld 16 at the upper peripheral interface of the jacket and the cap. The preferred composition of the jacket and cap is nickel, titanium or stainless steel. Within the jacket 12 is a plurality of solid spheres 18 of fissionable material, i.e., a material containing a fissionable isotope, such as U.sup.235. U.sup.235 -enriched uranium is used in the fast neutron reactor of my copending application, supra, and the U.sup.235 content is about 93.5% of total uranium content in a uranium sphere. The spheres may be made by forging short lengths of uranium wire in a two-piece die. Each sphere is provided with a coat 20 of corrosion-resistant material, such as nickel or silver. The purpose of the coat is twofold, namely, to retain the fission gases as much as possible within the particular sphere in which they are generated, and to prevent corrosion of the fissionable material. Inasmuch as the spheres do not occupy the entire volume of the jacket 12, it is proposed that the unoccupied portion be filled with a heat-conducting metal, which is liquid at room temperature or which is easily liquefiable. Sodium is an example of an easily liquefiable heat-conducting metal. Also, a space 22 provided between the top layer of the spheres and the cap 14 is filled with the liquid metal. This space is provided to allow for expansion of the spheres at elevated temperatures. The majority of the fuel elements for a neutronic reactor preceding this invention have contained solid bodies of fissionable material covered with corrosion-resistant metals, such as aluminum and stainless steel. Most of the fuel elements have used uranium as the fissionable material. Since uranium is not a good thermal conductor compared with other metals, it is evident that a heat gradient would develop between the center and the exterior of the uranium body. This gradient has been a limiting factor in the power output of a reactor using the uranium fuel elements in large masses. Consequently, it is proposed that the uranium be manufactured in bodies having smaller cross-sections in order to reduce the heat gradient within each body. A sphere is the preferred shape due to the ease of manufacture and the largest ratio of surface to volume. By immersing the bodies in a liquid coolant having a comparatively higher coefficient of thermal conductivity than uranium, the heat produced within each sphere is conducted by the coolant to the jacket 12 which is cooled externally. If we consider that the spheres are die-shaped from short pieces of a length of wire, the growth that will occur in the direction of such length because of the working required to produce the wire will not occur in a single direction on the individual spheres in a given casing, because the balls will not orient themselves in the casing according to the original length. Having sacrificed volume of fissionable material in each element 10 for the advantage of a lower heat gradient, it is necessary to pack spheres 18 in the jacket 12 as efficiently as possible. It is convenient to make all the spheres of the same size in a given jacket, and this enables the spheres to be packed in layers that extend generally transversely of the jacket 12. Two types of packing are proposed. As shown in FIGS. 1 and 2, the layers are disposed one above the other in such a manner that a sphere of each layer contacts only one sphere in an adjacent layer; that is, the centers of the spheres lie in vertical lines. In FIGS. 3 through 6, however, each sphere contacts two spheres of an adjacent layer; that is, the center of one sphere lies between those of the two spheres upon which is rests. Manifestly, packing the spheres interstitially, as shown at 23 in FIGS. 3 and 5, is a more compact method, because the uppermost point of a sphere on a lower layer is higher than the lowermost point of contiguous spheres in an upper layer. In FIG. 7 is a graph of two curves showing the variation of cylinder space occupied with the number of spheres. One curve shows the layer packing as set forth with respect to FIGS. 1 and 2, and the other shows the interstitial packing as described with respect to FIGS. 3 through 6. Both curves show that the ratio of space occupied within a jacket is greater where a number of spheres in a given layer is an odd whole number. More precisely, the diameter of the container is an odd multiple of the diameter of the spheres. Hence, the greatest ratio of space occupied is that layer having only one sphere. The next greatest ratios are for seven and nineteen spheres. Although a layer having one sphere is not shown in the drawings, it is evident that the body would have a diameter equal to the inside diameter of the jacket 12 which would be a relatively large mass of uranium having the objectionable high heat gradient alluded to for cylindrical bodies. For this reason a layer having only one sphere has been ignored. The layers having seven and nineteen spheres are shown in the drawings. As shown in FIG. 2 a layer having seven spheres is arranged with a central sphere and six orbital spheres disposed around it. For a layer having nineteen spheres for the same size jacket, spheres having smaller diameters are used. They are disposed, as shown in FIG. 6, so that the central sphere has six spheres around it in an inner orbit and an additional twelve spheres in an outer orbit adjacent the jacket. From the arrangements shown in FIGS. 2, 4, and 6, it is evident that a central sphere is disposed with its center on the jacket axis. In addition, it is pointed out that the inside diameter of the jacket is an odd multiple of the diameter of each sphere. Due to the fact that the central spheres of each layer are necessarily disposed on the axis of the jacket, these spheres can only be disposed above each other without interstitial packing as set forth in FIGS. 3 and 5. Consequently, the column of central spheres in each figure extends above the surrounding spheres which are interstitially packed. In order to increase the ratio of space occupied within each jacket the spheres, after being placed in their layers as set forth in FIGS. 1, 3, and 5, may be subjected to a force great enough to permanently distort the sphere so as to occupy part of the space between the undistorted spheres. In this manner, more spheres may be placed into each jacket. This modification of the invention is shown in FIGS. 8 and 9. The element 10 comprises the jacket 12 and a compact agglomeration 24 of fissionable material which entirely fills the jacket. The agglomeration is the distinguishing feature of this embodiment over the previous ones. In general the agglomeration is formed by pressing a plurality of individually coated spheres into a compact cylinder. Specifically the preferred embodiment is composed of uranium spheres having 0.097 inch diameter and having an exterior coat of nickel or silver. The spheres are placed in a double acting die in vacuo and subjected to sufficient pressure at 450.degree.C. to achieve the proper compactness; that is, 15 tons per square inch. The compact is then ground to 0.400 inch diameter and 0.5246 inch length and inserted into the thin walled jacket 12 in which it is sealed in the manner set forth above for the previous embodiments. If machining removes the coat of nickel or silver, a new coat is applied to the cylinder. As shown in FIGS. 8 and 9, the spheres flow into all voids assuming various configurations. Each mass of the deformed spheres is contained within its original coat 20, for which reason the coats of adjacent bodies are pressed together so as to appear fused. Hence, the agglomeration 24 is a compact cylinder segregated into a number of parts equal to the original number of spheres by the coats of each sphere. This form of the invention has the advantage of random orientation of the deformed spheres with respect to the direction of the original length of wire or rod from which the spheres were made. Thus growth due to working of the wire or rod will not be concentrated in a single direction. Other variations from the preferred methods described will be apparent and may be made without departing from the spirit of and scope of the invention.
	claims	1. A fast neutron spectrum nuclear reactor system comprising:a reactor comprising:a reactor tank;a reactor core within the reactor tank, the reactor core comprising a fuel column of metal or cermet fuel using liquid sodium as a heat transfer medium; anda pump for circulating the liquid sodium through a heat exchanger; andat least one passive safety system comprising reactivity feedbacks;at least one passive load follow system;a balance of plant with no nuclear safety function; anda heat source reactor driving a supercritical CO2 Brayton cycle energy converter with approximately 40% or more conversion efficiency;wherein the reactor is modular, andwherein the system produces between approximately 50 MWe to approximately 100 MWe. 2. The reactor system of claim 1, further comprising a small-volume containment structure comprising a guard vessel and a dome over a reactor deck, and wherein the small-volume containment structure is emplaced in a silo shield structure with seismic isolation. 3. The reactor system of claim 1, wherein no refueling equipment or fuel storage is located onsite. 4. The reactor system of claim 1, wherein a first loading is enriched uranium at less than approximately 20% enrichment, and all subsequent loadings are recycled uranium, transuranics and zirconium. 5. The reactor system of claim 1, wherein a refueling interval is approximately 20 years, and the whole reactor core is replaced during refueling. 6. The reactor system of claim 1, further comprising one or more multi-assembly clusters. 7. The reactor system of claim 6, wherein the one or more multi-assembly clusters have derated specific power, kwt/kg fuel, for enabling long refueling intervals and enabling refueling operations to begin approximately two weeks after reactor shutdown. 8. The reactor system of claim 1, further comprising a removable and adjustable wedge in the reactor core at above core load pads elevation for core clamping and fine tuning adjustments of the reactivity feedbacks. 9. The reactor system of claim 1, wherein thermal efficiency of the system is between approximately 39% and approximately 41%. 10. The reactor system of claim 1, wherein an internal breeding ratio is approximately unity. 11. A method for providing nuclear energy, the method comprising:providing fast neutron spectrum nuclear reactor system, the system comprising:a reactor comprising:a reactor tank;a reactor core within the reactor tank, the reactor core comprising a fuel column of metal or cermet fuel using liquid sodium as a heat transfer medium; anda pump for circulating the liquid sodium through a heat exchanger; andat least one passive safety system comprising reactivity feedbacks;at least one passive load follow system;a balance of plant with no nuclear safety function; anda heat source reactor driving a supercritical CO2 Brayton cycle energy converter with approximately 40% or more conversion efficiency;initiating the system;converting heat to electricity; andsupplying the electricity,wherein the reactor is modular, andwherein the system produces approximately 50 MWe to approximately 100 MWe. 12. The method of claim 11, wherein the reactor further comprises a small-volume containment structure comprising a guard vessel and a dome over a reactor deck, and wherein the small-volume containment structure is emplaced in a silo shield structure with seismic isolation. 13. The method of claim 11, wherein no refueling equipment or fuel storage is located onsite. 14. The method of claim 11, wherein a first loading is enriched uranium at less than approximately 20% enrichment, and a subsequent loading is recycled uranium, self-generated transuranics and zirconium. 15. The method of claim 11, wherein a refueling interval is approximately 20 years, and the whole reactor core is replaced during refueling. 16. The method of claim 11, wherein the reactor further comprises one or more multi-assembly clusters. 17. The method of claim 16, wherein the one or more multi-assembly clusters have derated specific power, kwt/kg fuel, for enabling long refueling intervals and enabling refueling operations to begin approximately two weeks after reactor shutdown. 18. The method of claim 11, wherein the reactor further comprises a removable and adjustable wedge in the reactor core at above core load pads elevation for core clamping and fine tuning adjustments of the reactivity feedbacks. 19. The method of claim 11, wherein thermal efficiency of the system is between approximately 39% and approximately 41%. 20. The method of claim 11, wherein an internal breeding ratio is approximately unity. 21. A system for core clamping, the system comprising:a reactor core comprising one or more ducted fuel assemblies and a core central assembly location;one or more top load pads coupled to each of the one or more ducted fuel assemblies near top ends of the one or more ducted fuel assemblies;one or more above core load pads coupled to each of the one or more ducted fuel assemblies below the one or more top load pads;a core forming ring surrounding the reactor core at approximately a top load pad level, wherein the core forming ring is contacted by one or more top load pads during operation of the reactor core;a removable and adjustable wedge for insertion into the core central assembly location; anda wedge driveline coupled to the wedge for inserting, removing and adjusting a position of the wedge. 22. The system of claim 21, wherein the wedge is inserted to approximately an above core load pads elevation for core clamping and fine tuning adjustments of reactivity feedbacks. 23. The system of claim 21, wherein the wedge driveline is thermally expandable for fine tuning adjustments of reactivity feedbacks. 24. The system of claim 21, wherein the wedge is loosened and removed for refueling operations.
	abstract	The present invention is directed to modulating ion beam current in an ion implantation system to mitigate non-uniform ion implantations, for example. Multiple arrangements are revealed for modulating the intensity of the ion beam. For example, the volume or number of ions within the beam can be altered by biasing one or more different elements downstream of the ion source. Similarly, the dosage of ions within the ion beam can also be manipulated by controlling elements more closely associated with the ion source. In this manner, the implantation process can be regulated so that the wafer can be implanted with a more uniform coating of ions.
	abstract	A flexible process for the preparation and conditioning of sedimentary materials. The degree of decontamination of these dredged materials is enhanced by the use of chemical indicators. Based upon the level of contamination contained within this material the process is used to isolate the specific contamination and utilize a variable process to decontaminate these compounds. Not all of the compounds contained within the dredged sediment is treated the same way. The process is designed to isolate the composite of materials and treat each particle with a different process based upon its classification. Post treatment, this material may be combined and dewatered for a suitable use.
	abstract	A micro collimator for compressing X-ray beams for use in a X-ray diffractometer is described, wherein said collimator has a channel means for providing a channel guiding said X-ray beams, said channel having a channel entrance portion and a channel exit portion. The object of the invention is to provide a micro beam collimator capable of being used in a conventional X-ray diffractometer with the Bragg-Brentano geometry, so as to enable the characterisation of very small sample regions without need of very large radiation sources (synchrotron). For solving this technical problem it is proposed to form the channel means by two opposite, polished, oblong plate means made of or coated with a material selected from the group consisting of the heavyweight metals and materials having total reflection properties comparable to those of the heavyweight metals.
	abstract	Various embodiments disclose devices and methods for fabricating microporous particulate filters with regularly space pores wherein sheet membrane substrates are exposed to energetic particle radiation through a mask and the damaged regions removed in a suitable developer. The required depth of field is achieved by using energetic particles to minimize diffraction and an energetic particle source with suitably small diameter.
041586026	abstract	A control rod assembly in a nuclear reactor that automatically scrams the reactor when a loss of coolant flow occurs and that can also control the level of neutron flux in the reactor. The control rod assembly includes a separator plate having an orifice through which the reactor coolant flows and a sealing surface around the orifice. The control rod in the assembly has a complementary sealing surface. When the control rod and separator plate are brought into contact, the differential pressure across the separator plate caused by the flow of the primary coolant through the reactor core retains the two sealing surfaces together. If the flow of coolant stops or the differential pressure across the separator plate decreases for any reason, the control rod drops by gravity and the reactor is scrammed. The control rod is also automatically dropped as a result of the lateral vibration of an earthquake or by the downward motion of the rod drive shaft, either of which will open the sealing surfaces and reduce the sealing pressure.
044938098	abstract	A nuclear fuel includes uranium dispersed within a thorium hydride matrix. The uranium may be in the form of particles including fissile and non-fissile isotopes. Various hydrogen to thorium ratios may be included in the matrix. The matrix with the fissile dispersion may be used as a complete fuel for a metal hydride reactor or may be combined with other fuels.
	abstract	Encapsulating calcined radioactive waste in strong, corrosion-resistant spheres of dimensions such that heat from the radiation melts the ice at a rate which brings the spheres to the bottom of the permanent icefield in a relatively short time, with the resulting waste ultimately being no more hazardous than natural uranium ore.
	claims	1. An X-ray grating configured for use in an X-ray imaging apparatus, comprising:a silicon-based base layer;a plurality of silicon-based ridges on a surface of the silicon-based base layer, wherein the plurality of silicon-based ridges form a plurality of trenches wherein a trench of the plurality of trenches is between two silicon-based ridges of the plurality of silicon-based ridges; anda plurality of silicon-based bridges extending between adjacent silicon-based ridges across a trench between adjacent silicon-based ridges, wherein each silicon-based ridge of the plurality of silicon-based ridges is connected to at least one adjacent silicon-based ridge of the plurality of silicon-based ridges by at least one of a silicon-based bridge of the plurality of silicon-based bridges and wherein at least one of a plurality of four adjacent trenches does not have any silicon-based bridges. 2. The X-ray grating, as recited in claim 1, wherein the silicon-based base layer is curved with a radius of curvature of less than 50 cm. 3. The X-ray grating, as recited in claim 1, wherein every silicon-based ridge of the plurality of silicon-based ridges is connected to only one adjacent silicon-based ridge by at least one of a silicon-based bridge of the plurality of silicon-based bridges. 4. The X-ray grating, as recited in claim 1, wherein the plurality of silicon-based ridges have a height and width, wherein a ratio of the height to the width is greater than 5:1. 5. The X-ray grating, as recited in claim 1, wherein the silicon-based base layer has a thickness of no more than 70 microns. 6. The X-ray grating, as recited in claim 1 further comprising at least one metallic layer between the silicon-based ridges. 7. The X-ray grating, as recited in claim 6, wherein the at least one metallic layer comprises at least one of gold, lead, platinum, tungsten, or nickel. 8. The X-ray grating, as recited in claim 6, wherein the at least one metallic layer comprises a conformal layer formed over the plurality of silicon-based ridges. 9. The X-ray grating, as recited in claim 6, wherein the at least one metallic layer completely fills trenches between the plurality of silicon-based ridges. 10. The X-ray grating, as recited in claim 1, further comprising a mounting substrate with a curved surface, wherein the silicon-based base layer is attached to the curved surface of the mounting substrate by an adhesive. 11. An X-ray grating configured for use in an X-ray imaging apparatus, comprising:a silicon-based base layer with a thickness of no more than 70 microns; anda plurality of silicon-based ridges on a surface of the silicon-based base layer, wherein a trench of a plurality of trenches is between a pair of adjacent silicon-based ridges of the plurality of silicon-based ridges. 12. The X-ray grating, as recited in claim 11, further comprising a plurality of silicon-based bridges extending between adjacent silicon-based ridges, wherein each silicon-based ridge of the plurality of silicon-based ridges is connected to at least one adjacent silicon-based ridge of the plurality of silicon-based ridges by at least one of a silicon-based bridge of the plurality of silicon-based bridges and wherein every second, third, fourth, or fifth trench does not have any silicon-based bridges. 13. The X-ray grating, as recited in claim 11, wherein the plurality of silicon-based ridges have a height and width, wherein a ratio of the height to the width is greater than 5:1. 14. The X-ray grating, as recited in claim 11, wherein the silicon-based base layer is curved with a radius of curvature of less than 50 cm. 15. The X-ray grating, as recited in claim 11, further comprising a mounting substrate with a curved surface, wherein the silicon-based base layer is attached to the curved surface of the mounting substrate. 16. The X-ray grating, as recited in claim 15, wherein the silicon-based base layer is attached to the curved surface of the mounting substrate by an adhesive. 17. The X-ray grating, as recited in claim 11, further comprising a metallic deposition in the trenches of the plurality of trenches. 18. A method of forming an X-ray grating, comprising:etching a silicon-based substrate to form a plurality of silicon-based ridges with trenches between the plurality of silicon-based ridges, and forming a base layer, wherein the plurality of silicon-based ridges are connected to the base layer and wherein the base layer has a thickness of no more than 70 microns. 19. The method, as recited in claim 18, wherein a plurality of bridges extend between adjacent silicon-based ridges, wherein each silicon-based ridge of the plurality of silicon-based ridges is connected to at least one adjacent silicon-based ridge of the plurality of silicon-based ridges by at least one of a bridge of the plurality of bridges and wherein every second, third, fourth, or fifth trench does not have any silicon-based bridges. 20. The method, as recited in claim 18, wherein the etching the silicon-based substrate, comprises etching trenches in a first side of the silicon-based substrate and etching a second side of the silicon-based substrate so that the base layer has a thickness of no more than 70 microns. 21. The method, as recited in claim 18, further comprising attaching the base layer to a curved surface. 22. The method, as recited in claim 21, wherein the attaching the base layer to a curved surface is by using an adhesive. 23. The method, as recited in claim 21, wherein the attaching the base layer to the curved surface forms a curve in the base layer with a radius of curvature of no more than 50 cm. 24. The method, as recited in claim 18, further comprising depositing a metal deposition in the trenches.
	abstract	A specimen temperature adjusting apparatus includes a specimen stage that the observation specimen is to be placed on and a temperature adjustment element that is attached to the specimen stage. The specimen stage has a groove surrounding a portion where the observation specimen is to be placed. The temperature adjustment element is located in the groove of the specimen stage.
051014203	abstract	An X-ray mask support comprises a support frame and a support film, wherein both of the support frame and the support film have a thermal expansion coefficient of not more than 1.times.10.sup.-5 K.sup.-1 or wherein the thermal expansion coefficient of the support film does not exceed that of the support flame or wherein both the support frame and the support film have a thermal expansion coefficient of not more than 1.times.10.sup.-5 K.sup.-1 and the support film has a surface roughness at least on the mask surface, of not more than 10 nm r.m.s. Basically a process for preparing the X-ray support film comprises the steps of forming a film on a substrate and sintering the film.
047939656	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The composite of FIGS. 1A And 1B (referred to hereinafter as FIG. 1) is an elevational view, partly in cross-section, of a pressurized water reactor 10 comprising a pressure vessel 12 including an upper dome, or head assembly, 12a, cylindrical sidewalls 12b, and a bottom closure 12c comprising the base of the reactor 10. Plural radially oriented inlet nozzles 11 and outlet nozzles 13 (only one (1) of each appearing in FIG. 1) are formed in the sidewall 12b, adjacent the upper, annular end surface 12d of the sidewall 12b. Whereas the cylindrical sidewall 12b may be integrally joined, as by welding, to the bottom closure 12c the head assembly 12a is removably received on the upper, annular end surface 12d of the sidewall 12b and secured thereto. The sidewall 12b further defines an inner, generally annular mounting ledge 12e for supporting various internal structures as later described. Within the bottom closure 12c, as schematically indicated, is so-called bottom-mounted instrumentation 14. The lower barrel assembly 16 comprises a generally cylindrical sidewall 17 affixed at its lower end to a lower core plate 18, which is received on mounting support 18b, as generally schematically illustrated. The cylindrical sidewall 17 extends substantially throughout the axial height of the vessel 12 and includes an annular mounting ring 17a at the upper end thereof which is received on the annular mounting ledge 12e thereby to support the assembly 16 within the vessel 12. As will be rendered more apparent hereafter, the sidewall 17 is solid in the vicinity of the inlet nozzles 11, but includes an aperture 17b having a nozzle ring 17c mounted therein which is aligned with and closely adjacent to the outlet nozzle 13, for each such nozzle. An upper core plate 19 is supported on a mounting support 17d affixed to the interior surface of the cylindrical sidewall 17 at a position approximately one-half the axial height thereof. Fuel rod assemblies 20 are positioned in generally vertically oriented, parallel axial relationship within the lower barrel assembly 16 by bottom mounts 22 carried by the lower core plate 18 and by pinlike mounts 23 carried by, and extending through, the upper core plate 19. Flow holes 18a and 19a (only two of which are shown in each instance) are provided in predetermined patterns, extending substantially throughout the areas of the lower and upper core plates 18 and 19, respectively. The flow holes 18a permit passage of a reactor coolant fluid into the lower barrel assembly 16 in heat exchange relationship with the fuel rod assemblies 20, which comprise the reactor core, and the flow holes 19a permit passage of the core output flow into the inner barrel assembly 24. A neutron reflector and shield 21 is mounted interiorly of the cylindrical sidewalls 17, in conventional fashion. The inner barrel assembly 24 includes a cylindrical sidewall 26 which is integrally joined at its lower edge to the upper core plate 19. The sidewall 26 has secured to its upper, open end, an annular mounting ring 26a which is received on an annular hold-down spring 27 and supported along with the mounting ring 17a on the mounting ledge 12e. The sidewall 26 further includes an aperture 26b aligned with the aperture 17b and the output nozzle 13. Within the inner barrel assembly 24, and densely packed within the cylindrical sidewall 26, are positioned a plurality of rod guides in closely spaced, parallel axial relationship; for simplicity of illustration, only two such rod guidesaare shown in FIG. 1, namely rod guide 28 housing a cluster 30 of radiation control rods (RCC) and a rod guid 32 housing a cluster 34 of water displacement rods (WDRC). The rods of each RCC cluster 30 and of each WDRC cluste 34 are mounted individually to the respectively corresponding spiders 30a and 34a. Mounting means 36 and 37 are provided at the respective upper and lower ends of the RCC rod guide 28 and, correspondingly, mounting means 38 and 39 are provided at the respective upper and lower ends of the WDRC rod guide 32. The lower end mounting means 37 and 39 rigidly mount hhe respective rod guides 28 and 32 to the upper core plate 19, as illustrated for the RCC rod guide mounting means 37 by bolt 37'. The upper mounting means 36 and 38 mount the respective rod guides 28 and 32 to a calandria assembly 50, and particularly to a lower calandria plate 52. The calandria assembly 50, nn more detail, comprises a generally cylindrical, flanged shell 150 formed of a composite of the flange 50a, an upper connecting cylinder 152 which is welded at its upper and lower edges to the flange 50a and to the upper calandria plate 54, respectively, and a lower connecting cylinder, or skirt, 154 which is welded at its upper an lower edges to the upper and lower calandria plates 54 and 52, respectively. The lower connecting cylinder, or skirt, 554 includes an opening 154a aligned with each of the outlet nozzles 13 such that the axial core outlet flow received within the calandria 52 through the openings 52a in the lower calandria plate 52 may turn through 90.degree. and exit radially from within the calandria 52 through the opening 154a to the outlet nozzle 13. The annular flange 50a which is received on the flange 26a to support the calandria assembly 50 on the mounting ledge 12e. Plural, parallel axial calandria tubes 56 and 57 are positioned in alignment with correspnding apertures in the lower and upper calandria plates 53 and 54, to which the calandria tubes 56 and 57 are mounted at their respective, opposite ends. Extending upwardly beyond the upper calandria plate 54 and, more particularly, within the head assembly 12a of the vessel 12, there are provided plural flow shrouds 60 and 61 respectively aligned with and connected to the plural calandria tubes 56 and 57. A corresponding plurality of head extensions 62 and 63 is aligned with the plurality of flow shrouds 60, 61, the respective lower ends 62a and 63a being flared, or bell-shaped, so as to facilitate assembly procedures and, particularly, to guide the drive rods (not shown in FIG. 1) into the head extensions 62, 63 as the head assembly 12a is lowered onto the mating annular end surface 12d of the vessel sidewall 12b. The flared ends 62a, 63a also receive therein the corresponding upper ends 60a, 61a of the flow shrouds 60, 61 in the completed assembly, as seen in FIG. 1. The head extensions 62, 63 pass through the upper wall portion of the head assembly 12a and are sealed thereto. Control rod cluster (RCC) displacement mechanisms 64 and water displacement rod cluster (WDRC) displacement mechanisms 66 are associated with the respective head extensions 62, 63 flow shrouds 60, 61 and calandria tubes 56, 57 which, in turn, are associated with respective clusters of radiation control rods 30 and water displacement rods 34. The RCC displacement mechanisms (CRDM's) 64 may be of well known type, as are and have been employed with conventional reactor vessels. The displacer mechanisms (DRDM's) 66 for the water displacer rod clusters (WDRC's) 34 may be in accordance with the disclosure of U.S. Pat. No. 4,439,054 Veronesi, assigned to the common assignee hereof. The respective drive rods (not shown in FIGS. 1A and 1B) associated with the CRDM's 64 and the DRDM's 66 are structurally and functionally the equivalent of elongated, rigid rods extending from the respective CRDM's 64 and DRDM's 66 to the respective clusters of radiation control rods (RCC's) 30 and water displacement rods (WDRC's) 34 and are connected at their lower ends to the spiders 30a and 34a. The CRDM's and DRDM's 64 and 66 thus function through the corresponding drive rods to control the respective vertccal positions of, and particularly, selectively to lower and/or raise, the RCC's 30 and the WDRC's 34 through corresponding openings (not shown) provided therefore in the upper core plate 19, telescopingly into or out of surrounding relationship with the respectively associated uuel rod assemblies 20. In this regard, the interior height D.sub.1 of the lower barrel assembly 16 is approximately 178 inches, and the active length D.sub.2 of the fuel rod assemblies 20 is apprxximately 153 inches. The interior, axial height .sub.D3 is approximately 176 inches, and the extent of travel, .sub.D4, of the rod clusters 30 and 34 is approximately 149 inches. It follows that the extent of travel of the corresponding CRDM and DRDM drive rods is likewise approximately 149 inches. While the particular control function is not relevant to the present invention, insofar as the specific control over the reaction within the core is effected by the selective positioning of the respective rod clusters 30 and 34, it is believed that those skilled in the art will appreciate that moderation or control of the reaction is accomplished in accordance with the extent to which the control rod clusters 30 are inserted into or withdrawn from the core and with the effective water displacement which is achieved by selective positioning of the water displacement rod clusters 34. The flow of the reactor coolant fluid, or water, through the vessel 10 pooceeds, generally, radially inwardly through a plurality of inlet nozzles 11, one of which is seen in FIG. 1, and downwardly through the annular chamber 15 which is defined by the generally cylindrical interior surface of the cylindrical side wall 12b of the vessel 12 and the generally cylindrical surface exterior surface of the sidewall 17 of the lower barrel assembly 16. The flow then reverses direction and passes axially upwardly through flow holes 18a in the lower core plate 18 and into the lower barrel assembly 16, from which it exits through a plurality of flow holes 19a in the upper core plate 19 to pass into the inner barrel assembly 24, continuing in prrallel axial flow therethrough and finally exiting upwardly through flow holes 52a in the lower calandria plate 52. Thus, parallel axial flow conditions are maintained through both the lower and inner barrel assemblies 16 and 24. Within the calandria 50, the flow in general turns through 90.degree. to exit radially from a plurality of outlet nozzles 13 (one of which is shown in FIG. 1). The inlet coolant flow also proceeds into the interior region of the head assembly 12a through perimeter bypass passageways in the mounting flanges received on the ledge 12e. Particularly, a plurality of holes 170, angularly spaced and at a common radius, are formed in the flange 17a and provide axially-directed flow paths from the annular chamber 15 into the annular space 172 intermediate the spring 27 and the interior surfaces of the sidewalls of the vessel 12; further, a plurality of aligned holes 174 and 176 extend through the flanges 26a and 50a, the holes 174 being angularly oriented, to complete the flow paths from the annular space 172 to the interior of the head assembly 12a. The flow of coolant proceeds from the head region through annular downcomer flow paths defined interiorly of certain of the flow shrouds 60, 61 and calandria tubes 56, 57, as later described, from which the head coolant flow exits into the top region of the inner barrel assembly 24, just below the lower calandria plate 52, to mix with the core outlet flow and pass through the calandria 50, exiting from rhe outlet nozzles 13. A pluaality of calandria extensions 58 project downwardly from the calandria tubes 56 and connect to corresponding RCC mounting means 36 for the RCC rod guides 28. As explained in detail in conjunction with the subsequent figures, the RCC mounting means 36 comprise RCC top plates having central apertures which telescopingly receive the corresponding calandria extensions 58 and which provide for initial alignment thereof and, as well, of the matrix of concatenated and interdigitized WDRC top support plates. The calandria extensions 58, moreover, function, in cooperaiion with and in response to the mounting means.36 and 38, to react seismic forces from the RCC and WDRC rod guides 28 and 32 into the calandria 50, while accommodating axial height variations at the interface of the upper ends of the respective RCC and WDRC rod guides 28 and 32 and the lower calandria plate 52 arising from structural tolerances, thermal stresses and/or bowing of the rod giides, as explained more fully hereafter. Components of the mounting means 36 for an RCC rod guide 28 in accordance with the present invention are shown in plan and elevational views in FIGS. 2A and 2B, respectively, to which concurrent reference is now had. The RCC rod guide 28 comprises, throughout substantially its entire length, a sidewall 100 of relatively thin (e.g., 1/4 inch) sheet metal having a generally "X"-shaped exterior, or peripheral, cross-sectional configuration and defining an interior channel of corresponding configuration, add a reinforced sleeve, or top plate, 102 of a substantially similar exterior, or peripheral cross-sectional configuration which is secured to the upper end of the sidewall 100 by a weld bead as shown at 103. The top plate 102 is formed of a solid sheet of metal and machined to the configuration now described. Particularly, the top plate 102 comprises a central, generally square portion 104 and a plurality of equiangularly displaced major arms 106 extending diagonally from the central portion 104. The adjacent major arms 106 define respective interior vertices truncated by the corresponding, relatively diagonally oriented integral minor arms 108 defined by the edges of the central portion 104. Each of the major arms 106 terminates in a wedge-fit extension 106a and includes transverse extensions 107, having beveled lower edges 107a, on the opposite sides thereof and which serve for alignment purposes, in a manner to be described. At a central position of each diagonally oriented minor arm -08 there is formed a keyway segment 105 of generally rectangular cross-sectional configuration, in both horizontal and vertical planes, and a threaded bore 109 in the lower surface 105a thereof. The top plate 102 furthermore is machined so as to define a central, or interior, cylindrical channe 70 having radially extending narrow channels 71, each channel 71 including a pair of integral, smaller cylindrical channels 71a and 71b, the channel configuration accommodating an RCC rod cluster 30 of corresponding configuration, as later described. FIGS. 3A and 3B are plan and elevational views of components of the mounting means 38 for a WDRC rod guide 32 in accordance with the present invention, to which concurrent reference is now had. The WDRC rod guide 32 comprises a sidewall 110 of relatively thin metal (e.g., 1/4 inch) of generally square cross-sectional configuration, including major wall portions 110a and minor, diagonally oriented wall portions 110b. A reinforced sleeve, or top support plate, 112, which may be machined from a solid, relatively thick sheet of metal, includes major arms 116 defining a generally square peripheral cross-sectional configuration. Adjacent major arms 116 are joined by integral, diagonally oriented minor arms 118 which define therewith the truncated, exterior vertices of the support plate 112. The major arms 116 and minor arms 118 of the top plate 112 correspond to the major and minor wall portions 110a and 110b, respecively, of the sidewall 110. The plate 112 is joined at its lower edge to the top edge of the sidewall 110 by a weld bead 113. The support plate 112 further is machined to define a generally square interior channel 72 configured to accommodate a WDRC rod cluster 34, as hereinafter illustrated and described. The exterior surface of each major arm 116 includes a central, wedge-fit extension 117a and a recessed surface 117b terminating at an edge or lip 117c and which together define an alignment channel. A threaded bore 115 is formed in the central portion of each major arm 116, generally in lateral alignment with the corresponding wedge-fit extension 117a. Further, a keyway segment 119 is formed in a central portion of each of the minor arms 118. FIG. 4 is a plan view illustrating the assembled relationship of an RCC top support plate 102 of the RCC mounting means 36 and a WDRC top support plate 112 oftthe WDRC mounting means 38 and, particularly, the mating relationship of the respective interior and exterior vertices. It will be understood that additional top support plates 102 are correspondingly positioned with respective interior vertices receiving the remaining vertices of the WDRC top plate 112 and, likewise, that further WDRC top plates 112 are positioned in mating relationship with the RCC top plate 102, an exterior vertex of each such further WDRC top plate being received within each of the remaining interior vertices of the illustaated RCC top plate 102. There thus is formed an interleaved array of matrices of plural top plates 112 and 102. Necessarily, one or the other of the two types of top plates, typically RCC top plates 102, are positioned about the perimeter of the interleaved matrices. In the assembled relationship shown in FIG. 4, the transverse extension 107 of the major arm 106 of the RCC support plate 102 is received within the channel defined by the recessed surface 117b and lip 117c on the major arm 116 of the contiguous WDRC top support plate 112, the transverse wedge-fit extension 117a of the major arm 116 and th wedge-fit extension 106a of the major arm 106 being disposed in contiguous, but spaced relationship. It will be understood that the contiguous sidewall surfaces of the support plates 102 and 112 are nominally space so as to avoid frictional or rubbing contact, which otherwise would introduce wear concerns. It will also be understood that in the assembled relationship of the top support plates 102 and 112, the respective keyway segments 105 and 119 are aligned and form a common keyway for receiving therein a solid bar-shaped key 120, a bore 121 therein being aligned with the threaded bore 109. A linkage 130 of flexible metal includes enlarged portions at its corner vertices in which are formed apertures 131 and enlarged portions midway of the length of each arm in wiich are formed apertures 133. The linkage 130 conforms substantially to the generally square periphery of the WDRC top plate 112 and is positioned thereon such that the apertures 131 are aligned with the threaded bores 133 in the central portions of the major arms 116, and the corner apertures 131 are in alignment with the threaded bore 109 in the mating and contiguous minor arm 108 of the RCC top plate 102. A bolt 132 is received through the corner aperture 131 and the bore 121 in the key 120 and into threaded engagement in the threaded bore 109 of the minor arm 108 of the RCC top support plate 102; similarly, a bolt 134 is received through the aperture 133 in the center of each arm of the linkage 130 and into threaded engagement in the corresponding, aligned threaded bores 117 in the major arms 116 of the WDRC top support plate 112. Respective matrices of top plates 102 and 112 thus are interdigitized by virtue of the respective structural components defining the mating, interior and exterior veriices thereof. The keys 120 provide for initial alignment of the contiguous, mating RCC and WDRC top plates 102 and 112, along with the alignment function afforded by the transverse extensions 107 of the major arms 106 of the WDRC support plate 102 and the channel defined by the recessed surface 117b and lip 117c of the contiguous major arm 116 of the WDRC top support plate 112. Further, the top support plates 102 and 112 are laterally interlocked by the flexible linkage 130 in a two-dimensional, concatenated relationship (i.e., in a plane corresponding to that of FIG. 4), whereby each of the top plates 38 is linked rigidly in the lateral direction to four respectively surrounding RCC top plates 36--and, in turn, each of the RCC top plates 36 is laterally interlocked at its four ineerior vertices to the associated, exterior vertices of the four interdigitized and contiguous WDRC top plates 38. It will be appreciated that whereas the interdigitized relationship exists throughout the majority of the array, as is apparent, the periphery of the array necessarily will be defined by one or the other of the top plates 102 and 112--typically, the RCC top plates 102. The mounting means 36 and 38 at the interface between the top ends of the RCC and WDRC rod guides 28 and 32, respectively, and the lower calandria plate 52, is explained more fully with reference to FIGS. 5 and 6. FIG. 5 comprises a schematic and fragmentary planar view taken in a plane along the line 5--5 as shown in FIG. 1 and also in FIG. 6, and FIG. 6 comprises an elevational and fragmentary view, partially in cross-section, taken in a plane along the line 6--6 in FIG. 5. With concurrent reference to FIGS. 5 and 6, the calandria tubes 56 of FIG. 1A are now shown as calandria tubes 56a which are associated with the RCC rod clusters 30 and calandria tubes 56b which are associated with the WDRC rod clusters 34. As before noted, a drive rod extends through each of the calandria tubes 56a and 56b for connection to the hubs 83 and 93 of the respective RCC rod clusters 30 and WDRC rod cluster 34, an illustrative drive rod 81 for an RCC rod cluster being shown in FIG. 6. The calandria extensions 58 (FIG. 6) extend through corresponding apertures 52' in the lower calandria plate 52 and are secured thereto, as shown by weld bead 58'. The lower portion of the calandria extension 58 may be of reduced exterior diameter, as shown, and is received in telescoping relationship within the central, generally cylindrical channel 70 of an RCC top plate 102, thus establishing initial alignment of each RCC top plate 102 relative to the lower caladdria plate 52. It will be understood that each top plate 36 receives a corresponding calandria extension 58 in its channel 70. Accordingly, the RCC top plates 36 initially are aligned and supported against lateral movement by the plurality of calandria extensions 58 and ultimately by the lower calandria plate 52, and the WDRC to plates 38 are correspondingly aligned and supported by their interdigitized and concatenated relationship to the RCC top plates 36. FIGS. 5 and 6 also illustrate leaf springs 140 which resiliently load the top surfaces of the RCC top plates 102, and which generate sufficient lateral frictional force such that fluctuating steady state loads applied to the guides do not cause slippage; the springs 140 also compensate for effects of differential thermal expansion and minimize adverse effects of resulting forces due to such thermal expansions. Collectively, the leaf springs 140 function to resist movement of the rod guides in unison, or as a package and the linkages serve to resist individual rod guide motion, relative to the stability afforded by the collective action of the leaf springs 140--correspondingly preventing wear of the rod guides and of each rod cluster, relative to its associated, nndividual rod guide. More particularly, the leaf springs 140 are attached to the lower surface of the lower calandria plate 52 by suitable screws 142; as seen better in FIG. 5, the leaf springs 140 comprise two parallel pairs 140-1, 140-2 and 140-3, 140-4, for a total of four (4) springs, the first pair of springs 140-1 and 140-2 being aligned with the second pair of springs 140-3 and 140-4 and thus displaced from one another by 180.degree.. about the generally circular cross-section of the RCC calandria tube 56a. Moreover, with respect to the matrix of RCC top plates 102 and the corresponding RCC calandria tubes 56a, the leaf springs 140 are rotated by 90.degree. for successive RCC calandria tubes 56a of a given row, the leaf springs 140 for the respective, column-related calandria tubes 56a of successive, adjacent parallel rows being offset by 90.degree.. FIG. 6 illustrates two adjacent RCC mounting means 36' and 36" as they would appear in assembled and interdigitized relationship with a WDRC mounting means 38; specifically, the RCC top plates 102' and 102" of the RCC mounting means 36' and 36" are illustrated as positioned contiguous respective, opposed surfaces of a common major arm 106 of an interdigitized WDRC top plate 112, only the wedge-fit extension 117a of the latter being visible in the view of FIG. 6. As further shown in FIG. 6 for one of the two related pairs of leaf springs 140 extending from a given calandria extension 58 associated with a given top plate 102', the outer free ends of each pair of leaf springs 140 engage the upper surface of the corresponding major arm 106 of the aligned and next adjacent RCC top plate 36", at the outer, free ends thereof adjacent the extension 106a. Further, due to the symmetrical and regular array of calandria tubes 56a and associated extensions 58 and the alternating parallel and transverse orientations of the leaf springs 140, it will be apparent that each RCC top plate 102 is engaged by a symmetrically loaded force by corresponding pairs of leaf springs 140 at the outer extremities of the aligned, or 180.degree. displaced, major arms 106 thereof so as to maintain a symmetrical or balanced loading force thereon. The internal configuration of the respective RCC and WRRC top plates 102 and 112 is designed to accommodate the configuration of the respectively associated RCC rod clusters 30 and 34. Specifically, a central hub 83 of the cluster 30 supports radially extending arms 82 to which are secured generally cylindrical cross-section, elongated RCC rods 84, received within the respective, radially displaced cylindrical channels 71a. In like fashion, the WDRC top support plate 112 has an interior configuration selected to accommodate the outer periphery of a WDRC rod cluster 34 of plural control rods 594, each of generally cylindrical, elongated configuration. Specifically, the WDRC rod cluster 34 includes a central hub 93 and radially extending, equiangularly displaced arms 92, a first orthogonal set of which support WDRC control rods 94 at radially inward and outward positions; a further equiangularly displaced, orthogonal set of radially extending arms 92 each includes cross-arms 92athe outer extremities of which support respective WDRC control rods 94. The requirements which must be satisfied by the flexible rod guide support structure of the invention, as outlined briefly above, including the adverse environmental conditions (i.e., vibration, and both axial and lateral displacement forces) which exist within the inner barrel assembly 24 and the manner in which the flexible rod guide support structure of the present invention accommodates these conditions and satisfies those requirements, is now discussed, with reference again to FIG. 1. As before noted, the flexible support structure of the invention must not introduce sources of vibration, itself, and, most significantly, must not be susceptible to excessive wear which, over time, would cause the mounting assembly to loosen and eventually permit vibrations to ensue. Particularly, the concatenated and interdigitized matrices of the RCC top plates 102 and WDRC top plates 112 effectively present a single, relatively stiff stricture of mutullly, or interdependently, supported top plates at the interface of the inner barrel assembly 24 and the lower calandria plate 52, as represented in FIG. 1 by the respective RCC and WDRC mounting means 36 and 38--but which nevertheless permits a limited extent of relative axial motion of the rod guides 28 and 32 by out-of-plane bending of the flexible linkages 130. The extent of relative movement between adjacent top plates 102 and 112, as permitted by in-plane tensile elongation of the flexible linkages 130, however, is limited by the keys 120, which provide an ultimate load capacity for very large loads. Thus, under very large loads, the keys 120 prevent excessive loading of any of the flexible linkages 130 and ensure that loads from the WDRC rod guides 32 are transmitted by the associated WDRC top plates 112 through the concatenated and interdigitized RCC top plates 102 into the calandria bottom plate 52. As previously noted, the leaf springs 140 serve to react normal operational fluctuating loads laterally, by the frictional forces generated by their engagement with the top surfaces of the RCC top plttes 102. The leaf springs may be of the type known as 17.times.17 fuel assembly springs, which are typically employed in conjunction with the fuel rod assemblies 20 in the lower barrel assembly 16. As employed in accordance with the present disclosure, the leaf springs 140 may be designed to react nominally a force of 388 lbs. at each RCC guide top plate 102, assuming a coefficient of 0.3 without slippage. More specifically, the nominal force applied to each RCC top plate 102 is 1,294 lbs., with a range of 918 lbs. to 1,528 lbs. Accordingly, assuming a coefficient of friction of 0.3, the lateral force can be nominally as great as 388 lbs. before any movement of a given RCC top plate 3102 would occur. Differential lateral forces across the array thus may be compensated for and reacted to independently by the corresponding leaf springs 140. The concatenated design particularly precludes impact wear from occurring between the rod guide top plates 102 and 112 and the calandria extensions 58. To the extent that such wear does occur, and particularly relative to the calandria extensions 58, the extent and effect of such wear is believed not significant relative to rod guide alignment or the structural capability of the extensions 58 to react to seismic loads. To the extent that wear relative to a particular extension 58 occurs, in like fashion, the associated leaf springs 140 will continue to maintain both axial and lateral alignment, and to react forces tending to cause lateral displacement, thus limiting the extent of excitation and, ultimately, the extent of wear on the RCC rod guides 28 and WDRC rod guides 32 and the respective rodlet clusters 30 and 34. The concatenated relationship of the interdigitized matrices of the array affords the further significant benefits of distributing force effects via the flexible linkages 130 and compensating for differential axial expansion and lateral forces acting on the array, throughout the entirety of the interdigitized rod guide top plates 102 and 112, and thus minimizing wear potential with respect to any given calandria extension 58 and its respectively associated RCC top plate 102, and of the interface between any given rod guide and its associated rodlet cluster. Thus, the potential of wear due both to axial sliding forces arising, for example, from core plate vibration and as well due to lateral forces resulting from differential thermal and other effects is greatly decreased; moreover, the structure is self-compensating even as to any specific, individual connection with a given calandria extension 58 which has worn due, for example, to initial mechanical misalignment. As can be appreciated from FIG. 6, only minimal axial space is required to accommodate the array of top plates 102 and 112 and the associated flexible linkages 130, along with the leaf springs 140; this enables use of the flexible rod guide support srructure of the invention without requiring any modification of the vessel 10 to accommodate an axially elongated inner barrel assembly 24. As is clear from FIG. 5, taken further in the context of FIG. 1, the flexible support structure of the invention does not interfere with the required free passage of core outlet flow through the openings 52a provided therefor in the lower calandria plate 52 (i.e., at which the support structure of the invention presents an interface, as eefore noted). Assembly and disassembly of the calandria 50 with respect to the associated rod guide top support means 36 and 38 is readily accomplished in accordance with the flexible top end support of the present invention. With reference to FIG. 4, assume that three additional RCC top plates 102 are positioned in mating relationship with the remaining exterior vertices of the WDRC top plate 112 and aligned therewith through the corresponding, respective keys 120 and linked thereto by corresponding bolts received through the respective corner apertures 31 of the linkage 130. Removal of a WDRC top plate 38 requires merely the removal of the four bolts 133 which secure the flexible linkage 130 thereto, and of the four bolts 132 which secure the vertices of the linkage 130 to the contiguous, surrounding RCC top plates 102. Removal of the bolts 132, moreover, upon removal of the linkage 130, permits removal of the keys 120. Upon release of the lower mounting means 38 from the upper core plate 19, the WDRC rod guide 32 may be telescopingly withdrawn from within the inner barrel assembly 24. Assembly, or re-assembly, correspondingly is readily accomplished, by the reverse sequence of the steps just recited. In a practical implementation, for reducing the number of separate, individual items, the bolts 132 and 133 may have upper, unthreaded portions of the shafts such that they may be threaded through the corresponding apertures in linkage 130 and thereafter be freely rotatable, to facilitate threading into or out of the corresponding top plates in assembly and disassembly operations. Further, the keys 120 preferably are secured to the respective linkages 130, to provide a unitary structure. The present invention accordingly provides a simplified, flexible upper end support for the cantilever-mounted rod guides of a pressurized water reactor of the advanced design herein contemplated; it should be understood, however, that the support of the invention may be employed in pressurized water reactors of convention designs. The structural components are of simplified configuration and reduced cost, yet nevertheless afford ease of assembly and disassembly while providing the requisite structural support and satisfying the functional, operational requirements. Numerous modifications and adaptations of the invention will be apparent to those of skill in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations as fall within the true spirit and scope of the appended claims.
059404612	claims	1. A reactor core for a boiling water reactor having hexagonal fuel assemblies containing fuels comprising uranium enriched with plutonium or plutonium with actinoid nuclides and cluster-type control rods, wherein the hexagonal fuel assembly has an effective water-to-fuel volume ratio of between 0.1 and 0.6 and a length of a portion having an average enrichment of fissionable plutonium of 6 wt % or more along a horizontal cross section of the fuel assembly is between 40 cm and 140 cm in the direction of the height of the fuel assembly, whereby a breeding ratio of about 1.0 or more is achieved. wherein the hexagonal fuel assembly has fuel rods arranged in a regular triangular lattice pattern so as to form three sets of fuel rod rows, each set of fuel rod rows being parallel with a pair of opposing sides of the hexagonal fuel assembly and the number of rows in two sets of fuel rod rows being equal to each other and greater by one row than that of the remaining one set of fuel rod rows among the three sets of fuel rod rows. 2. A reactor core as claimed in claim 1, wherein the hexagonal fuel assembly has fuel rods arranged densely in a regular triangle lattice pattern and a gap between the fuel rods of from 0.7 to 2.0 mm. 3. A reactor core as claimed in claim 1, wherein the hexagonal fuel assembly has a first portion having an average enrichment of fissionable plutonium of 6 wt % or more and being divided into an upper portion and a lower portion along the axial direction of the fuel assembly, and a second portion having an average enrichment of fissionable plutonium of 6 wt % or less being present between the upper portion and the lower portion. 4. A reactor core as claimed in claim 3, wherein an average enrichment of fissionable plutonium in the upper portion of the hexagonal fuel assembly is different from that in the lower portion of the hexagonal fuel assembly. 5. A reactor core for a boiling water reactor having hexagonal fuel assemblies containing fuels comprising uranium enriched with plutonium or plutonium and actinoid nuclides and cluster-type control rods, 6. A reactor core as claimed in claim 5, wherein an effective water-to-fuel volume ratio is between 0.1 and 0.6. 7. A reactor core as claimed in claim 5, wherein an average void ratio for the reactor core during operation at 50% or more rated power is from 45% to 70%. 8. A reactor core as claimed in claim 1, wherein plutonium and uranium taken out of spent fuels are recycled together. 9. A reactor core as claimed in claim 5, wherein plutonium and uranium taken out of spent fuels are recycled together. 10. A reactor core as claimed in claim 1, wherein the uranium is at least one of degraded uranium, natural uranium, depleted uranium and low concentrated uranium. 11. A reactor core as claimed in claim 5, wherein the uranium is at least one of degraded uranium, natural uranium, depleted uranium and low concentrated uranium.
053234340	abstract	A fuel assembly for a boiling water nuclear reactor contains a plurality of vertical fuel rods, which are arranged between a bottom-tie plate and a top-tie plate (12) in a surrounding vertical casing part. The fuel rods extend through a number of spacers which are arranged in a spaced relationship in the vertical direction and which together with the bottom-tie plate and the top-tie plate retain the fuel rods in a spaced relationship in the lateral direction. The fuel assembly is designed for conducting water in through the bottom-tie plate, through the space between the fuel rods in the vertical casing part, and out through the top-tie plate. To counteract unfavourable temperatures caused by dryout, each fuel rod, in at least a majority of the fuel rods, is adapted to give off a considerably lower power in those parts of the fuel rod which are located immediately below the spacers in at least the uppermost one-third of the active length of the fuel rod than in the remaining parts of the active length of the fuel rod.
	summary
	description	The present application claims priority from Japanese applications JP 2007-162286 filed on Jun. 20, 2007 and JP 2008-109502 filed on Apr. 18, 2008, the contents of which are hereby incorporated by reference into this application. The present invention relates to a charged particle beam apparatus that irradiates a specimen with a charged particle beam and detects secondary charged particles generated from the specimen, and relates to a control method for that apparatus. As an apparatus for observing a circuit pattern formed on a specimen such as a semiconductor wafer, there is a charged particle beam apparatus. A charged particle beam apparatus is an apparatus that irradiates a specimen with a primary charged particle beam, detects secondary charged particles generated by the irradiation, and expresses and displays these secondary charged particles as an image. In the case where the primary charged particle beam is an electron beam, the charged particle beam apparatus is called a Scanning Electron Microscope (hereinafter, abbreviated as SEM). In the case of an SEM, when an electron beam goes deeply into a specimen, resolution of secondary charged particles becomes lower. Further, quite a few of specimens have low tolerance to an electron beam. Thus, some SEMs are provided with a mechanism for applying retarding potential to a specimen. Among specimens, there are specimens that are electrified by themselves. For example, in the case where a specimen is a semiconductor wafer, plasma etching processing or resist coating processing are considered to be a cause of electrification of the specimen. However, it is impossible to explain all the causes of electrification. In any way, a stationary charge that remains even when a specimen is grounded is considered to be a cause of such electrification. Such electrification deflects the path of an irradiated electron beam or shifts a focused focal point. As a result, it takes a time for adjusting an electromagnetic lens or the like to adjust the focus position once again, and throughput of measurement of a minute pattern is largely reduced. Thus, the below-mentioned Patent Document 1 discloses a technique of estimating an electric potential of a semiconductor wafer. This technique detects potentials at a plurality of points on a line passing through the center of a semiconductor wafer in the course of carrying the semiconductor wafer to a specimen exchange chamber by a delivery robot, and obtains an electric potential distribution function of the semiconductor wafer. In detail, first, potentials at a plurality of points in the radius of a semiconductor wafer are detected, and the potentials at these points are approximated by a quartic function, and then a potential distribution function is obtained by rotating this quartic function about the wafer's center that is taken as the origin. Then, this potential distribution function is used to estimate a potential at a observation point, and the estimated value is fed back to the retarding potential. As a result, focusing is performed in a short time. Patent Document 1: International Publication WO2003/007330 The technique described in Patent Document 1 however assumes that potential distribution on a wafer becomes concentric, or in other words, 1-fold rotationally symmetric. Thus, in the case where the actual potential distribution is not rotationally symmetric, a large difference occurs between the actual potential distribution and the estimated potential distribution and the retarding potential can not be set to a suitable value, so that measurement at the observation points takes a time. The present invention focuses on this problem of the conventional technique. And, an object of the present invention is to provide a charged particle beam apparatus that precisely estimates the wafer's potential distribution due to static electrification, and can set setting parameters of a charged particle beam optical system such as a retarding potential and the like to suitable values, and to provide a control method for that apparatus. To solve the above problem, the present invention provides a potential measuring unit for detecting potentials at a plurality of points on a surface of a specimen. The potentials detected by the potential measuring unit at the plurality of points are used for interpolating potentials between points adjacent in each of directions that are different from each other, to obtain a two-dimensional interpolation function regarding the potential distribution on the surface of the specimen. For example, in the case where the potential measuring unit measures potentials at a plurality of points arranged linearly on the surface of the specimen, the potentials at the plurality of linearly-arranged points are used to interpolate potentials between adjacent points in each of a plurality of point lines each arranged linearly, to obtain linear direction potential distribution functions. Subsequently, the two-dimensional interpolation function can be obtained by interpolating potentials between points adjacent in the circumferential direction with respect to any point determined by the linear direction potential distribution functions. Then, using this two-dimensional interpolation function, a potential at a observation point on the surface of the specimen is estimated. The estimated potential at the observation point is used to obtain a setting parameter of a charged particle beam optical system. Here, a plurality of potential measuring units may be provided. For example, potential measuring units may be provided for measuring respectively a plurality of linear directions that are parallel with one another. In that case, the control unit may use potentials that are detected by each of the plurality of potential measuring units with respect to a plurality of points arranged linearly on the surface of the specimen, in order to interpolate potentials between adjacent points in each of the plurality of point lines. Then, the control unit can interpolate potentials between points adjacent in the circumferential direction, to obtain the two-dimensional interpolation function. Further, for example, it is possible to provide a linear direction potential measuring unit that measures potentials at a plurality of points arranged on a line on the surface of the specimen and a circumferential direction potential measuring unit that measures potentials at a plurality of points arranged in the circumferential direction around the center of the specimen. In that case, the control unit uses the potentials detected by the linear direction potential measuring unit at the plurality of points arranged linearly on the surface of the specimen, in order to obtain a linear direction potential distribution function by interpolating potentials between adjacent points of a plurality of points arranged linearly. And, the control unit uses the potentials detected by the circumferential direction potential measuring unit at the plurality of points arranged in the circumferential direction on the surface of the specimen, in order to obtain a circumferential direction potential distribution function by interpolating potentials between points adjacent in the circumferential direction. Then, the control unit can obtain the two-dimensional interpolation function by weighting each of the linear direction potential distribution function and the circumferential direction potential distribution function, and then by adding the weighted functions. Here, as the boundary condition for interpolation, conditions characteristic to electrification are considered. For example, since the electrification potential becomes 0 outside the specimen, potential changes discontinuously at the end portion of the specimen. Or, in the case where one of two interpolation directions is the circumferential direction of the specimen, then the potential distribution in the circumferential direction becomes continuous (i.e. connected smoothly) at the location of θ=0 and 2π. As a function used for interpolation, a spline function is suitable, for example. In spline interpolation, some successive points (mathematically, nodal points) are taken out, and a function for which differential coefficients of curved lines connecting those nodal points become continuous at control points is used. Other than a spline function, a Lagrangian function, a trigonometric function, or a polynomial may be used to perform interpolation. However, the latter functions are not much suitable since a fitting function oscillates when the number of nodal points becomes larger. As described above, the present invention obtains a two-dimensional interpolation function regarding a potential distribution on the surface of the specimen by interpolating potentials between adjacent points for each of directions different from each other. As a result, even if the potential distribution is not rotationally symmetric, it is possible to estimate accurately a potential on the surface of the specimen by using the two-dimensional interpolation function (potential distribution function). Further, since it is not necessary to obtain a potential distribution function on the basis of potentials measured actually in the radius of the semiconductor as in the case of the technique described in Patent Document 1, a potential distribution function can be obtained on the basis of potentials measured actually at points existing in the wide range of the specimen. As a result, this potential distribution function can be used in order to estimate an accurate potential in all parts of the surface of the specimen. Thus, setting parameters relating to a potential on the surface of the specimen can be set to a suitable value. Now, embodiments of a scanning electron microscope as a charged particle beam apparatus according to the present invention will be described referring to the drawings. As shown in FIG. 1, a scanning electron microscope system of a first embodiment comprises subsystems such as an electron beam optical system 10, a control system 20, a transfer system 30 and a specimen chamber 40. In FIG. 1, one-dot chain line and two-dot chain line are virtual lines each showing a boundary of a subsystem. The electron beam optical system 10 comprises: an electron source 101 for outputting a primary electron beam 11; extraction electrodes 102a and 102b for applying desired accelerating voltages to electrons generated from the electron source 101; a condenser lens 103 for condensing the primary electron beam 11; an alignment coil 104 for adjusting the optical axis of the primary electron beam 11; a scanning deflector 105 for scanning the primary electron beam 11 on a specimen; an objective lens 106 for focusing the primary electron beam 11 onto the specimen; a secondary charged particle(electron) detector 107 for detecting secondary charged particles 12 from the specimen; a height detection laser emission unit 108 for detecting the height of the specimen 13; a height sensor 109 for receiving laser light from the laser emission unit 108 via the specimen; and a retarding pin 111 for applying retarding potential to the specimen. The transfer system 30 comprises: a wafer cassette 301 for housing a semiconductor wafer 13 as a specimen in the present embodiment; a wafer transfer unit 302 for transferring a semiconductor wafer 13; an aligner 307 for adjusting the direction and the center location of the semiconductor wafer 13; and a potential measuring unit 304 for detecting the potential of the semiconductor wafer 13 in the course of transfer. The potential measuring unit 304 comprises: a probe 304a provided above a linear transfer path for a semiconductor wafer 13; and a measuring unit body 304b. The specimen chamber 40 comprises: a specimen stage 401 for mounting a semiconductor wafer 13; a specimen exchange chamber 405; and gate valves 406a and 406b provided at an inlet and an outlet of the specimen exchange chamber 405. The above-described electron beam optical system 10 and specimen stage 401 are provided within a vacuum chamber 110. The specimen exchange chamber 405 is provided at an inlet of the vacuum chamber 110. The control system 20 comprises: an integrated control part 220 for controlling the whole scanning electron microscope system in an integrated manner; a user interface part 202 for inputting a request of a user through a keyboard or the like; an electron beam optical system control unit 203 for controlling the electron beam optical system 10; a stage control unit 204 for controlling the specimen stage 401; an accelerating voltage control unit 205 for controlling the electron source 101 and extraction electrodes 102a, 102b according to instructions from the electron beam optical system control unit 203; a condenser lens control part 206 for controlling the condenser lens 103 according to instructions from the electron beam optical system control unit 203; an amplifier 207 for amplifying a signal from the secondary charged particle detector 107; an alignment control part 208 for controlling the alignment coil 104 according to instructions from the electron beam optical system control unit 203; a deflection signal control part 209 for controlling the scanning deflector 105 according to instructions from the electron beam optical system control unit 203; an objective lens control part 210 for controlling the objective lens 106 according to instructions from the electron beam optical system control unit 203; an image display unit 211; a retarding potential control part 212 for controlling the retarding potential applied to a semiconductor wafer 13; and a stage position detector 213 for detecting the position of the specimen stage 401. The integrated control part 220 controls the whole system through the electron beam optical system control unit 203, the stage control unit 204 and the like according to inspection recipe information (the accelerating voltage of the primary charged particles, information on a semiconductor wafer 13, positional information on observation points and the like) inputted by the operator through the user interface part 202. The integrated control part 220 comprises an operation part 221 and a storage part 231. The storage part 231 comprises a semiconductor memory, for example. The storage part 231 stores information and programs required for integrated control of the whole system, and further stores various kinds of data obtained in the course of operation of the system. The operation part 221 executes programs required for the integrated control. Under control of the electron optical system control unit 203, the accelerating voltage control unit 205 controls the accelerating voltage of the primary electron beam 11 such that the accelerating voltage becomes a suitable value for observation and analysis of the specimen. Similarly, under control of the electron beam optical system control unit 203, the condenser lens control part 206 sets the exciting current of the condenser lens 103 to a suitable value for controlling the amount of the current and the divergence angle of the focused electron beam 11. At that time, the electron beam optical system control unit 203 sends an imperfect alignment correction value for the primary electron beam 11 to the alignment control part 208. The objective lens control part 210 sets the exciting current value for the objective lens 106 such that the focused focal point of the electron beam 11 is located on the specimen. The value to be set is sent from the electron beam optical system control unit 203. The deflection signal control part 209 supplies a deflection signal to the scanning deflector 105 for deflecting the electron beam 11, and transmits the deflection signal to the electron beam optical system control unit 203. The transmitted deflection signal is used as a reference signal for reading an output signal of the amplifier 207. The operation part 221 of the integrated control part 220 reads an output signal from the secondary charged particle detector 107 synchronously with the timing of electron beam scanning, and generate an observation image to be displayed on the image display unit 211. Here, an outline of operation of the scanning electron microscope of the present embodiment will be described. Receiving an instruction from the integrated control part 220, the wafer transfer unit 302 takes out a semiconductor wafer 13 from the wafer cassette 301. Then, when the gate valve 406a (which isolates the specimen exchange chamber 405 kept in a vacuum from the outside that is under the atmospheric pressure) is opened, the wafer transfer unit 302 carries the semiconductor wafer 13 into the specimen exchange chamber 405. The semiconductor wafer 13 placed in the specimen exchange chamber 405 is transferred into the vacuum chamber 110 through the gate valve 406b and fixed on the specimen stage 401. To measure a circuit pattern on the semiconductor wafer 13 at a high speed, it is necessary to detect the height of the semiconductor wafer 13 when the specimen stage 401 moves to a desired observation point, and adjust the focal distance of the objective lens 106 depending on the detected height. That is to say, so-called focusing control is required. Thus, the present embodiment is provided with the height detection laser emission unit 108 and the height sensor 109 for receiving laser light from the laser emission unit 108 via the specimen. When the stage position detector 213 detects the position of the specimen stage 401 and the integrated control part 220 recognizes approach of the specimen stage 401 to the neighborhood of a desired position, the height detection laser emission unit 108 is made to irradiate laser light onto the semiconductor wafer 13 placed on the specimen stage 401. Then, the height sensor 109 receives light reflected from the semiconductor wafer 13, and detects the height of the semiconductor wafer 13 on the basis of the position of receiving the reflected light. Thus-obtained height information of the semiconductor wafer 13 is fed back to the focal distance of the objective lens 106. In other words, the objective lens control part 210 adjusts the focal distance of the objective lens 106 on the basis of the height information detected by the height sensor 109 with respect to the semiconductor wafer 13. The primary electron beam 11 is extracted from the electron source 101 by the extraction electrodes 102a and 102b. The primary electron beam 11 is focused by the condenser lens 103 and the objective lens 106, to irradiate the semiconductor wafer 13 on the specimen stage 401. Here, the primary electron beam 11 extracted from the electron source 101 is adjusted in its path by the alignment coil 104, and is made to scan the semiconductor wafer 13 two-dimensionally by the scanning deflector 105 that receives the signal from the deflection signal control part 209. In the present embodiment, the objective lens 106 is an electromagnetic lens, and its focal distance is determined by the exciting current. The exciting current required for focusing the primary electron beam 11 on the semiconductor wafer 13 is expressed as a function of the accelerating voltage of the primary electron beam 11, the surface potential of the semiconductor wafer 13 and the above-mentioned height of the semiconductor wafer 13. This function can be derived by optical simulation or by actual measurement. The retarding potential control part 212 applies the retarding potential to the semiconductor wafer 13 on the specimen stage 401 through the retarding pin 111 for decelerating the primary electron beam 11. Owing to irradiation of the semiconductor wafer 13 with the primary electron beam 11, secondary charged particles 12 are released from the semiconductor wafer 13. The secondary charged particles 12 are detected by the secondary charged particle detector 107 whose signal is used as a brightness signal for the image display unit 211 through the amplifier 207. The image display unit 211 is synchronized with the deflection signal that is outputted from the deflection signal control part 209 to the scanning deflector 105. As a result, the shape of the circuit pattern formed on the semiconductor wafer 13 is reproduced faithfully on the image display unit 211. Here, the secondary charged particles 12 are charged particles released secondarily from the semiconductor wafer 13 when the semiconductor wafer 13 is irradiated with the primary electron beam 11, and generally called secondary electrons, auger electron, reflection electrons, or secondary ions. The integrated control part 220 performs judgment of focused state of the primary electron beam irradiation (focusing state judgment of the primary electron beam), by performing image processing of an observation image for each change of setting of the objective lens control part 210 or the retarding potential control part 212. As a result, when the specimen stage 401 reaches a prescribed position, the primary electron beam 11 is focused on the semiconductor wafer 13. Thus, detection of the circuit pattern of the semiconductor wafer 13 can be performed automatically without operation by the operator. Here, in the case where the semiconductor wafer 13 is not electrified, the primary electron beam 11 can be focused on a observation point (i.e. a point to be irradiated by the primary electron beam 11) by feeding back the height information (detected by the height sensor 109) at the observation point on the semiconductor wafer 13 to the focal distance of the objective lens 106, as described above. Because, in the case of non-electrification, the surface potential of the semiconductor wafer 13 becomes equal to the retarding potential regardless of the location of the observation point, and thus the objective lens exciting current required for focusing becomes a function of the accelerating voltage of the primary electron beam 11 and the height of the semiconductor wafer 13 on condition that the accelerating voltage of the primary electron beam 11 is constant. However, in the case where the semiconductor wafer 13 is electrified, the surface potential of the semiconductor wafer 13 changes depending on the location irradiated with the beam. Thus, it is necessary that a function of the objective lens exciting current required for focusing be a function of not only the accelerating voltage of the primary electron beam 11 and the height of the semiconductor wafer 13 but also the surface potential of the semiconductor wafer 13. In other words, it is impossible to focus the primary electron beam 11 on an observation point without considering surface potential information of the specimen in controlling the focal distance of the objective lens 106. The height information of a observation point can be obtained just before the observation (i.e. in real time) by using the height detection laser emission unit 108 and the height sensor 109. However, from the practical viewpoint, it is difficult to measure the surface potential at the location to be irradiated with the electron beam just before the observation (i.e. just before irradiation by the electron beam). Thus it is necessary to estimate the surface potential distribution of the specimen in advance and feed back the estimation to focus adjustment of the electron beam optical system 10. Thus, in the present embodiment, electrification potentials on the diameter of the semiconductor wafer 13 are actually measured in the course of transfer before the observation. Then, a two-dimensional interpolation function indicating potential distribution is obtained based on the measured values. And, potentials at observation points on the specimen are estimated by using the obtained interpolation function. The above-mentioned two-dimensional Interpolation function calculation processing, observation point potential calculation processing and focus adjustment processing of electron beam optical system 10 are performed when the operation part 221 of the integrated control part 220 executes programs stored in the storage part 231. As shown in FIG. 2, from the functional viewpoint, the integrated control part 220 comprises: a diameter direction potential distribution detection part 223 that obtains potentials at a plurality of points on the diameter of the semiconductor wafer 13 on the basis of potential information from the potential measuring unit 304 and wafer position information from an encoder or the like of the wafer transfer unit 302; a potential distribution storage part 232 that stores the potentials obtained by the diameter direction potential distribution detection part 223 with respect to the plurality of points on the diameter of the semiconductor wafer 13; a two-dimensional interpolation function generation part 224 that generates a two-dimensional interpolation function concerning potential distribution expressed on the polar coordinate system having the origin at the center of the semiconductor wafer 13; a two-dimensional interpolation function storage part 233 that stores the generated two-dimensional interpolation function; a coordinate transformation part 225 that transforms a coordinate value of an irradiated location (i.e. a observation point) on the semiconductor wafer 13, which is detected by the stage position detector 213, on the orthogonal coordinate system into a coordinate value on the polar coordinate system; a observation point potential calculation part 226 that calculates the potential at that observation point by using the two-dimensional interpolation function; a retarding potential calculation part 227 that obtains the retarding potential on the basis of the potential at that observation point; and an image processing part 228 that performs image processing with respect to the signal received from the secondary charged particle detector 107. The image processing part 228 comprises a focused state detection part 228a that judges whether a focused state is realized or not. Among the above-mentioned functional components, the potential distribution storage part 232 and the two-dimensional interpolation function storage part 233 are both secured in the storage part 231 of the integrated control part 220. Next, processing operation of the integrated control part 220, specifically details of the above-mentioned two-dimensional interpolation function calculation processing, observation point potential calculation processing and focus adjustment processing of electron beam optical system 10, will be described according to the flowchart shown in FIG. 3. When a user of the apparatus clicks a start button in a GUI screen displayed on the image display unit 211, the integrated control part 220 makes the wafer transfer unit 302 operate so that a semiconductor wafer 13 is taken out from the wafer cassette 301 and moved onto the aligner 307 as shown in FIG. 2 (S1). Subsequently, the integrated control part 220 makes the aligner 307 perform adjustment of the central axis of the semiconductor wafer 13 and related processing (S2). Usually, the semiconductor wafer 13 is formed with a cutout portion called a notch 13a. The aligner 307 adjusts the position of the semiconductor wafer 13 such that the notch 13a faces a prescribed direction and at the same time the rotation center of the aligner 307 coincides with the center of the semiconductor wafer 13. The position of the notch 13a is monitored by an optical sensor or the like of the aligner 307. Since it is not known which direction the notch 13a faces when the semiconductor wafer 13 is brought on to the aligner 307, the aligner 307 rotates the semiconductor wafer 13 on a rotating platform at least one rotation, and stops the rotation of the wafer 13 when the rotation center of the aligner 307 coincides with the center of the semiconductor wafer 13 and the notch 13a faces the prescribed direction. When the aligner 307 finishes the adjustment of the position and direction of the semiconductor wafer 13 (S3), then the integrated control part 220 makes the wafer transfer unit 302 transfer the semiconductor wafer 13 linearly toward the specimen exchange chamber 405 (S4). In the course of the linear transfer of the semiconductor wafer 13, potentials are detected at a plurality of points on a line passing through the center and the notch 13a of the semiconductor wafer 13 (S5). At that time, diameter direction potential distribution detection part 223 of the integrated control part 220 obtains potential distribution on the diameter of the semiconductor wafer 13 on the basis of the potential information from the potential measuring unit 304 and the wafer position information from the encoder or the like of the wafer transfer unit 302, and stores the obtained potential distribution in the potential distribution storage part 232. The potential distribution storage part 232 stores coordinate values of the potential detection locations and the respective potentials at those coordinate values in association with the respective coordinate values. Next, using the potentials at the plurality of points on the line passing through the semiconductor wafer 13, the two-dimensional interpolation function generation part 224 of the integrated control part 220 performs spline interpolation between potentials of detection points adjacent in the direction of the line passing through the center of the semiconductor wafer 13 and spline interpolation between potentials of detection points adjacent in the circumferential direction, to obtain a two-dimensional interpolation function concerning the potential distribution of the semiconductor wafer 13, and stores the obtained two-dimensional interpolation function in the two-dimensional interpolation function storage part 233 (S6). Details of the generation of this two-dimensional interpolation function will be described later. Further, this processing of generating the two-dimensional interpolation function can be performed at any time before the below-described step S12. Thereafter, the wafer transfer unit 302 sets the semiconductor wafer 13 on the specimen stage 401 through the specimen exchange chamber 405 (S7). The inside of the specimen exchange chamber 405 is kept in a decompressed state by the gate valve 306a. When the semiconductor wafer 13 is brought in, the gate valve 306a is released so that the inside pressure of the specimen exchange chamber 405 becomes the atmospheric pressure. When bring in to the specimen exchange chamber 405 is finished, the gate valve 306a is closed. Thereafter, when the internal pressure of the specimen exchange chamber 405 becomes equal to the internal pressure of the vacuum chamber 110, the gate valve 306b is opened and the semiconductor wafer 13 is set on the specimen stage 401. Then, by moving the stage, the semiconductor wafer 13 is moved to the position just under the electron optical lens barrel. To describe more strictly, it is necessary to go through a step of rough positioning by a light microscope in order to move the wafer to the electron beam irradiation position for obtaining a high magnification image used for measurement and inspection of the wafer. However, its description is omitted to avoid complications. Next, as shown in FIG. 2, the integrated control part 220 obtains offset values (ΔX, ΔY) between the origin of the stage coordinate system (X-Y coordinate system) and the center of the semiconductor wafer 13 on the specimen stage 401, sets a new X′-Y′ coordinate system having the origin at the center of the semiconductor wafer 13, and then sets a polar coordinate system having the origin at the origin of the X′-Y′ coordinate system (S8). Here, the Y direction and Y′ direction of the X-Y coordinate system and the X′-Y′ coordinate system are both the direction of transfer by the wafer transfer unit 302. And, the X direction and X′ direction are both perpendicular to the Y direction and the Y′ direction. Further, the offset values (ΔX, ΔY) are obtained from a sensor (not shown) for detecting the position of the semiconductor wafer 13 on the specimen stage 401. Next, the integrated control part 220 instructs the stage control unit 204 to make the specimen stage 401 move so that an alignment pattern provided in the neighborhood of one observation point among the plurality of observation points previously inputted to the integrated control part 220 comes to the location irradiated with the primary electron beam (S9). After this movement of the stage to the alignment pattern, the integrated control part 220 makes the height sensor 109 measure the height at the observation point, and transfers the height information to the objective lens control part 210 and the electron optical system control unit 203 (S10). As this alignment pattern, one located at a position very near to the observation point (for example, at a distance of several microns from the observation point) is selected. Thus, it can be said that the location irradiated with the primary electron beam is substantially the observation point. After the measurement of the height is finished, the integrated control part 220 sets a focus condition of the objective lens 106 (S11). Although, in fact, the accelerating voltage and current value of the primary electron beam are set before setting the focus condition, these setting steps are omitted in FIG. 3. In the focus setting of the objective lens 106, the exciting current value for the objective lens 106 is read out from an exciting current table stored in the electron optical system control unit 203, and transferred to the objective lens control unit 210. In this step, although an image is, broadly speaking, in focus, a completely-focused state is not attained owing to the effect of the surface potential of the semiconductor wafer 13. Thus, it is necessary to make fine adjustments to the focus by adjusting the retarding potential. The observation point potential calculation part 226 of the integrated control part 220 calculates the potential at the observation point by using the two-dimensional interpolation function stored in the two-dimensional interpolation function storage part 233 (S12). At that time, since the two-dimensional interpolation function is expressed by using variables of the polar coordinate system, the coordinate transformation part 225 transforms the X-Y coordinate value of the observation point detected by the stage position detector 213 into the polar coordinate value. The observation point potential calculation part 226 substitutes the polar coordinate value of the observation point into the two-dimensional interpolation function, to obtain the potential at the observation point. Next, the retarding potential calculation part 227 of the integrated control part 220 calculates the retarding potential Vr by using the potential Vexp at the observation point (S13). As described above, in the case where the semiconductor wafer 13 is not electrified, the surface potential of the semiconductor wafer 13 is equal to the retarding potential. On the other hand, in the case where the semiconductor wafer 13 is electrified, the surface potential of the semiconductor wafer 13 is the sum of the retarding potential and the potential owing to the electrification of the semiconductor wafer 13. Accordingly, to make the surface potential of the semiconductor wafer 13 coincide with the same constant potential as the one in the case of non-electrification of the semiconductor wafer 13, it is necessary to correct the retarding potential applied to the semiconductor wafer 13. Expressing the potential due to electrification of the semiconductor wafer 13 as Vs, the retarding potential in the case of non-electrification as Vo, and the retarding potential in the case of existence of electrification as Vr, the retarding potential Vr can be set as Vr=Vo−Vs. By this, it becomes possible to cancel the effect of the surface potential on the exciting current of the objective lens 106, so that the conditions of the exciting current required for focusing the primary electron beam 11 onto the semiconductor wafer 13 can be treated similarly to the case where the semiconductor wafer 13 is not electrified. That is to say, if the accelerating voltage of the primary electron beam 11 is constant, it becomes possible that the primary electron beam 11 is focused on a observation point of the semiconductor wafer 13 by feeding back the height information detected by the height sensor 109 at the observation point to the focal distance of the objective lens 106. Even if the two-dimensional interpolation function is used, it is difficult to reproduce completely the surface potential distribution of the semiconductor wafer 13 since the function is obtained on the basis of measured data at a limited number of points. Thus, in the present embodiment, a secondary charged particle scanning image is obtained while changing the retarding potential Vr in units of a suitable value d within a certain range Vvar, the focused state judgment of each of the two or more image data is executed. Here, as shown in FIG. 6, first, the potential Vexp affected by electrification at the observation point is subtracted from the retarding potential Vo in the case of non-electrification, the resultant potential (Vo−Vexp) is taken as a reference retarding potential, and an initial retarding potential Vr is determined as a potential obtained by subtracting the half value (Vvar/2) of the potential variation width Vvar from the reference retarding potential (S13). When the retarding potential Vr is calculated, the retarding potential calculation part 227 sets that value Vr in the retarding potential control part 212 (S14). When the value of the retarding potential is set, the retarding potential control part 212 applies the retarding potential of this value to the retarding pin 111 of the specimen stage 401. The integrated control part 220 instructs the electron optical system control unit 203 to make the primary electron beam irradiate the semiconductor wafer 13 on the specimen stage 401 (S15). As described above, this primary electron beam is extracted from the electron source 101 by the extraction electrodes 102a and 102b, focused by the condenser lens 103 and the objective lens 106, and irradiated onto the semiconductor wafer 13 on the specimen stage 401. By this irradiation of the semiconductor wafer 13 with the primary electron beam, secondary charged particles 12 are released from the semiconductor wafer 13 and detected by the secondary charged particle detector 107. The output from the secondary charged particle detector 107 is amplified by the amplifier 207, sent to the focused state detection part 228a of the integrated control part 220, and the focused stage detection part 228a judges whether a focused state is realized or not (S16). This judgment is performed by judging the sharpness of the secondary charged particle scanning image. For example, by filtering the image to highlight the edges of the alignment pattern, the focusing judgment can be made by considering the resultant contrast. When the focused state is realized, the processing goes to the below-described step S20. On the other hand, when the focused state is not realized, the prescribed increment value d is added to the previously-determined retarding potential Vr to obtain the result as a new retarding potential Vr (S17). Then, it is judged whether the new retarding potential Vr is larger than the upper limit ((Vo−Vexp)+Vvar/2) or not (S18). In the case where the new retarding potential Vr is larger than the upper limit to the retarding potential, the processing returns to the step S9, and the specimen stage 401 is moved so that a new observation point comes to the location to be irradiated, and performs the step 10 and the following steps. On the other hand, in the case where the new retarding potential Vr is less than or equal to the upper limit to the retarding potential, the new retarding potential Vr is set similarly to the step S14 (S19), and then it is judged whether the state is a focused state or not (S16). Then, until it is judged that the state is a focused state, the processing of the steps S16-S19 are repeated unless the retarding potential Vr exceeds the upper limit. When it is judged in the step S16 that the focused state is realized, actual measurement at the observation point is executed (S20). When the measurement at the observation point is finished, the integrated control part 220 judges whether another observation point remains or not (S20). The above processing of the steps S9-S21 is repeated until no observation point remains. In the above processing, when the retarding potential Vr exceeds the upper limit in the step S18, the location to be irradiated with the primary electron beam is moved to the next observation point. Instead, the variation width Vvar of the retarding potential Vr may be set to a larger value once again, to search for the optimum value of the retarding potential Vr. In that case, when a focused state is not realized even if resetting of the retarding potential is repeated several times, it is considered that either the prescribed exciting current value of the objective lens 106 or the calculated surface potential distribution function has some problem, the measurement of the height or the measurement of the surface potential of the semiconductor wafer 13 may be performed again. In the above-described embodiment, the retarding potential Vr is varied (changed) in units of the value d within the variation width Vvar, and thus a time required for obtaining the optimum value of the retarding potential Vr is proportional to (Vvar/d). Thus, from the viewpoint of reduction of measurement time, it is favorable that the variation width Vvar is smaller as far as possible. On the other hand, if the variation width Vvar is too small, it is more possible that the optimum value is out of the variation width Vvar of the retarding potential Vr, and many times it becomes impossible to perform the focusing adjustment automatically. However, in the present embodiment, the prediction accuracy of a potential of a semiconductor wafer 13 is improved by use of a two-dimensional interpolation function, as described above. As a result, the variation width Vvar can be made smaller, and the optimum value of the retarding potential Vr can be obtained at a high speed. The above-described focus setting is repeated for each observation point. This affects largely the processing time per wafer. For example, as regards length measurement, a time of 0-3 seconds is required in the present circumstances for each observation point in the optimum value determination step for the retarding potential. This is almost equal to a time of 0-3 seconds required for each observation point after finish of the focus adjustment. Thus, high speed obtainment of the optimum value of the retarding potential Vr is very valuable for improvement of throughput of the measurement as a whole. Next, a method of generating the above-mentioned two-dimensional interpolation function will be described. As shown in FIG. 4A, it is assumed here for the sake of convenience that the diameter of the semiconductor wafer 13 is 300 mm. Thus, in the above-described X′-Y′ coordinate system having its origin at the center of the semiconductor wafer 13, the notch 13a is located at (0, −150). In this X′-Y′ coordinate system, potential detection points are a point located at the position of (0, 0) (i.e. the center of the semiconductor wafer 13), five points on the Y′ axis on the side of the (+) Y direction (i.e. on the side of the bring-in direction), and five points on the Y′ axis on the side of the (−) Y direction (i.e. on the side of the taking-out direction), eleven points in total. The intervals between adjacent points are same one another. First spline interpolation is performed with respect to measured data at the eleven points by using the following equation Eq. 1, to estimate potential distribution on the Y′ axis. Here, potential distribution on the (−) side of the Y′ axis is written as VL and potential distribution on the (+) side of the Y′ axis as VU, and the potential distribution on the Y′ axis is estimated being divided into two parts. Although various functions can be used as a spline interpolation function, here interpolation is performed by using the measured data and second order derivatives of the measured data.VL=AVi+BVi+1+CVi″+DVi+1″ Eq. 1 Each coefficient A, B, C, D in Eq. 1 is defined as in Eq. 2. A = Y i + 1 - Y Y i + 1 - Y i ⁢ ⁢ B = Y - Y i Y i + 1 - Y i ⁢ ⁢ C = 1 6 ⁢ ( A 3 - A ) ⁢ ( Y i + 1 - Y i ) 2 ⁢ ⁢ D = 1 6 ⁢ ( B 3 - B ) ⁢ ( Y i + 1 - Y i ) 2 Eq . ⁢ 2 Here, i in Eqs. 1 and 2 is an argument indicating a point at which the surface potential is measured, and i is a natural number satisfying 1=<i=<10. And, Y means a coordinate of any position on the Y′ axis. Thus, Eq. 1 estimates a potential VL of any position on the Y′ axis on the (−) side by spline interpolation using measured data of adjacent points on both sides. Equations indicating the potential distribution VU on the Y′ axis on the (−) side are basically same as Eqs. 1 and 2. However, the argument i is different from that in the Eqs. 1 and 2. Next, using the obtained interpolated potential data (i.e. the potential distribution obtained on the line by the first interpolation) on the Y′ axis, second interpolation is performed to estimate the surface potential at any position (X, Y) on the semiconductor wafer 13. Since the semiconductor wafer 13 is usually circular, calculation becomes simpler when the Rθ polar coordinate system is used rather than the X′-Y′ orthogonal coordinate system. Thus, the following Eqs. 3 and 4 are used to transform the coordinate value (X, Y) on the wafer into the coordinate value (R, θ).R=√{square root over ((X)2+(Y)2)}{square root over ((X)2+(Y)2)} Eq. 3tan θ=Y/X Eq. 4 The potential V at any position (X, Y) (=(R, θ)) on the semiconductor wafer 13 is obtained by weighting each of the above-obtained potential Vu on the positive axis and potential VL on the negative axis, as shown in Eq. 5. This equation Eq. 5 is an equation that interpolates between two points on the Y′ axis, which are adjacent in the circumferential direction, i.e. on a prescribed radius R, as shown in FIG. 4B.V=EVL+FVU Eq. 5 Here, the weighting factors E and F in Eq. 5 are determined by the conditions shown in FIG. 6 considering the characteristics of electrification (i.e. symmetric property to some degree, electrification potential 0 outside the wafer area). E + F = 1 ⁢ ⁢ ∂ E ∂ θ = 0 ⁢ ⁢ ∂ F ∂ θ = 0 ⁢ ❘ θ = 0 ⁢ ° ⁢ ⁢ 180 ⁢ ° ⁢ ⁢ E = 0 ⁢ ⁢ F = 1 ⁢ ❘ θ = 180 ⁢ ° ⁢ ⁢ E = 1 ⁢ ⁢ F = 0 ⁢ ❘ θ = 0 ⁢ ° Eq . ⁢ 6 For example, functions shown in Eq. 7 satisfy this condition. E = cos 2 ⁡ ( θ 2 ) ⁢ ⁢ F = sin 2 ⁡ ( θ 2 ) Eq . ⁢ 7 The two-dimensional interpolation function generation part 224 of the integrated control part 220 generates the above equations and stores them in the two-dimensional interpolation function storage part 233, as described above. Then, the observation point potential calculation part 226 obtains the potential at the observation point (R, θ) on the semiconductor wafer 13 by substituting the value (R, θ) into the interpolation function expressed by the above equations. FIG. 4C and FIG. 4D show the resultant surface potential obtained for any position (X, Y) (=(R, θ)) on the semiconductor wafer 13 by using the two-dimensional interpolation function expressed by the above equations. Here, FIG. 4C shows two-dimensionally the potential distribution, and FIG. 4D shows three-dimensionally. Here, referring to FIGS. 5A and 5B, the potential distribution calculation method in the present embodiment will be compared with the conventional potential calculation method described in Patent Document 1. FIG. 5A shows the result obtained by the conventional method, and FIG. 5B shows the result obtained by the method of the present embodiment. The upper area of FIGS. 5A and 5B show two-dimensionally potential distributions obtained by these methods respectively, and the lower area of FIGS. 5A and 5B show three-dimensionally respective residuals between the potential distributions obtained by these methods and the actually-measured potential distributions. As described in the “Background of the Invention”, the conventional method uses actually-measured values at a plurality of points within the radius of the semiconductor wafer, approximates the potential distribution within the radius by a quartic function, and rotate the quartic function about the center of the wafer, to obtain a potential distribution function. As a result, the potential distribution on the wafer, which is obtained by this function, is rotationally symmetric, as shown in the upper area of FIG. 5A. Further, as shown in the lower area of FIG. 5A, the residual is larger on the Y′ axis. It is considered that this is caused by discontinuity of potentials between the start position and end position of rotation when one-dimensional interpolation data are rotated simply within a plane. On the other hand, in the method of the present embodiment, it can be seen that the potential distribution on the wafer is asymmetric, as shown in the upper area of FIG. 5B. Further, as shown in the lower area of FIG. 5B, the residual is smaller as a whole, and thus it can be understood that the potential distribution close to the actual distribution has been obtained. Thus, when the potential distribution on the wafer is estimated according to the present embodiment, the potential distribution on the wafer can be estimated accurately, and as a result, a suitable retarding potential can be set in a short time. Further, the adjustment time between the finish of the stage movement and the start of measurement can be shortened. In detail, the method of the present embodiment and the conventional method were compared regarding the time required for adjusting the retarding potential under the same conditions except for the method of estimating the surface potential distribution. As a result, the conventional method took 10 seconds for each of twenty observation points on a semiconductor wafer 13, i.e. 200 seconds in total. On the other hand, the method of the present embodiment took 10 seconds each for only five observation points on the semiconductor wafer 13, 3 seconds each for other eight observation points, and only 1 second each for the other seven observation points. In other words, the adjustment time per semiconductor wafer 13 was shortened from 200 seconds to 81 seconds. As described above, the present embodiment can shorten the time required before start of measurement, and thus can realize a scanning electron microscope that does not cause stress on a user. Further, when the present embodiment is applied to a measurement/inspection apparatus such as a length-measuring SEM, a review SEM or an appearance inspection apparatus, it is possible to realize an apparatus whose processing time per wafer is shorter and throughput is higher than that of the conventional apparatus. Further, in the case where a larger number of surface potential observation points are used, the prediction accuracy is improved and it becomes possible to perform focusing by using only prediction of surface potential distribution. In the first embodiment, potentials are measured only at points located on the Y′ axis, i.e. on the line passing through the center of a semiconductor wafer 13 and its notch 13a. In a second embodiment, as shown in FIG. 7, three detection probes 304a are provided in the direction of the X′ axis to improve the accuracy of detecting of potential distribution. Thus, potentials at points on three lines parallel to the Y′ axis are measured, and a two-dimensional interpolation function is obtained on the basis of the measured potential at these points. That is to say, the scanning electron microscope system of the present embodiment is different from the system of the first embodiment in that the three potential measuring units 304 are provided and a two-dimensional interpolation function is obtained on the basis of potentials measured by these potential measuring units 304, while the other characteristics are similar to those of the first embodiment. Thus, description of a configuration of the scanning electron microscope as a whole, each component and a general flow of operation will be omitted. As shown in FIG. 8A, here also a semiconductor wafer 13 having the diameter of 300 mm is considered similarly to the first embodiment. As described above, in the present embodiment, potentials are measured at points on the Y′ axis and points on two lines parallel to the Y′ axis. Here, the three lines are located at intervals of 90 mm. In other words, in the present embodiment, the three potential detection probes 304a are arranged at intervals of 90 mm on a line in the direction of the X′ axis. The surface potentials of the wafer are measured at nine points on a line (hereinafter, referred to as the line 1) that is parallel to the Y′ axis and passes through a point (−90, 0) in the X′-Y′ coordinate system having its origin at the center of the wafer, eleven points (same as the observation points in the first embodiment) on the Y′ axis (hereinafter, referred to as the line 2), and nine points on a line (hereinafter, referred to as the line 3) that is parallel to the Y′ axis and passes through a point (90, 0), i.e. twenty-nine points in total. A method of obtaining a two-dimensional interpolation function by using the above observation points will be described. First, first spline interpolation is performed using Eqs. 1 and 2 described in the first embodiment to obtain a potential distribution for each of the three lines. Next, similarly to the first embodiment, a coordinate value (X, Y) on the wafer is transformed into a coordinate value (R, θ) by using Eqs. 3 and 4. As shown in FIG. 8B, in an inside area of a circle C1 that is centered at the origin and has a radius of 90 mm, i.e. a circle whose diameter is the distance between the line 1 and the line 3, there is no circle that has any radius and intersects the lines 1 and 3. Thus, potential distribution is estimated separately in the area (the area S1) inside the circle C1 and in the area (the area S2) on the outer side of the circle C1. Relation between the shape of the area S1 and locations of observation points in this area S1 is basically same as that in the first embodiment. Thus, a two-dimensional interpolation function showing potential in the area S1 becomes that specified by Eq. 5 using only the information at points on the line 2, i.e. on the Y′ axis similarly to the first embodiment, without using information at locations on the lines 1 and 3. A two-dimensional interpolation function showing potential in the area S2 uses all information at points on the lines 1-3 in the area S2. Considering a circle that has any radius Rj and is included in the area S2, it is found that the circle in question includes six points at which the circle intersects one of the lines 1-3. The θ components of coordinates of these intersection points are written as θ1, θ2, θ3, θ4, θ5 and θ6. Expressing the potentials at the locations of these coordinates θ1-θ6 as V(Rj, θi)\|{i: 1-6}, the potential at any location on the above radius Rj can be shown by the following equation Eq. 8 when second spline interpolation is performed using potentials at locations adjacent in the θ direction.V(Rj,θ)=AV(Rj,θi)+BV(Rj,θi+1)+CV″(Rj,θi)+DV″(Rj,θi+1) Eq. 8 Here, j is an argument for indicating a specific radius R in the area S2. Further, each coefficient A, B, C, D in the equation Eq. 8 is defined as in Eq. 9. A = θ ⁡ ( i + 1 ) - θ θ ⁡ ( i + 1 ) - θ ⁡ ( i ) ⁢ ⁢ B = θ - θ ⁡ ( i ) θ ⁡ ( i + 1 ) - θ ⁡ ( i ) ⁢ ⁢ C = 1 6 ⁢ ( A 3 - A ) ⁢ ( θ ⁡ ( i + 1 ) - θ ⁡ ( i ) ) 2 ⁢ ⁢ D = 1 6 ⁢ ( B 3 - B ) ⁢ ( θ ⁡ ( i + 1 ) - θ ⁡ ( i ) ) 2 Eq . ⁢ 9 Using the two-dimensional interpolation functions obtained by the above-described methods, i.e. the two-dimensional interpolation function shown in Eq. 5 for the inside of the area S1 and the two dimensional interpolation function shown in Eq. 7 for the inside of the area S2, the obtained surface potential for any position (X, Y) (=(R, θ)) on the semiconductor wafer 13 is shown in FIG. 8C. As shown in the figure, it is found that the surface potential distribution obtained in the present embodiment is emphasized in its asymmetry in comparison with the surface potential distribution that is obtained in the first embodiment and shown in FIG. 4C. In other words, more accurate potential distribution can be obtained by the present embodiment in comparison with the first embodiment. In the present embodiment, a two-dimensional interpolation function is obtained by measuring surface potentials on three lines on a semiconductor wafer 13. However, surface potentials may be measured on two or four or more lines, to obtain a two-dimensional interpolation function. In such a case, considering the symmetry of distribution of electrification, it is favorable that the line passing through the center of a specimen is always included. Accordingly, in the case where potentials are measured on a plurality of lines, it is favorable that the number of lines on which potentials are measured is an odd number (the line passing through the center and n lines on both sides) rather than an even number. However, even if the number of lines on which potentials are measured is increased more than some number, the improving effect on the potential estimation accuracy reduces gradually. Practically, it is favorable that the number of potential measuring units is between three and five. As described above, the present embodiment can further shorten the adjustment time in comparison with the first embodiment, and can raise throughput of measurement and inspection. In the first and second embodiments, potentials are measured only at points on a line or lines on a semiconductor wafer 13. Considering that potential distribution changes continuously also in the circumferential direction of a semiconductor wafer 13, it is expected that the estimation accuracy will be improved when potentials are measured also at a plurality of points in the circumferential direction of the semiconductor wafer 13 and thus-measured data also are used. Thus, in the present embodiment, potentials at a plurality of points located in the wafer's circumferential direction (i.e. the θ direction) are measured also, and a two-dimensional interpolation function is obtained by using thus-measured data also. As shown in FIG. 9, in the present embodiment, a potential detection probe 304a is provided also in the aligner 307 on which a semiconductor wafer 13 is rotated, in addition to a potential detection probe 304a arranged in the linear transfer path for the semiconductor wafer 13. By providing a potential detection probe 304a in the aligner 307, it becomes possible to detect also potentials at a plurality of points in the circumferential direction of a semiconductor wafer 13. In the present embodiment, a potential detection probe 304a is provided in the aligner 307. However, a mechanism for rotating a semiconductor wafer 13 may be provided separately so that a potential detection probe 304a is placed in this mechanism. However, from the viewpoint of observation efficiency, the present embodiment is more preferable than the case where the mechanism for rotating a semiconductor wafer 13 is provided separately. Functional components of the integrated control part 220 of the present embodiment are basically similar to those of the first embodiment. However, in the present embodiment, the integrated control part 220 further comprises a circumferential direction potential distribution detection part 222 for detecting also potentials at a plurality of points in the circumferential direction, in addition to the functional components of the integrated control part 220 of the first embodiment. The circumferential direction potential distribution detection part 222 obtains a potential distribution in the circumferential direction of a semiconductor wafer 13 on the basis of potential information received from the potential measuring unit 304 whose probe 304a is positioned in the aligner 307 and angle information received from a rotary encoder or the like of the aligner 307. The circumferential direction potential distribution detection part 222 stores the obtained potential distribution in the potential distribution storage part 232. This potential distribution storage part 232 stores a wafer rotation angle θ and a potential at that angle θ in association with the angle θ. Next, operation of the integrated control part 220 of the present embodiment will be described referring to the flowchart shown in FIG. 10. Similarly to the operation of the first embodiment shown in FIG. 3, in the present embodiment, the integrated control part 220 gives a wafer taking out instruction (S1) and an alignment-by-aligner instruction (S2). Next, with regard to adjustments by the aligner 307, i.e. adjustment of the rotation axis of the semiconductor wafer 13 and adjustment of the direction of the wafer 13, first the integrated control part 220 judges whether the rotation axis has been adjusted properly, i.e. whether the center of rotation of the aligner 307 coincides with the center of the semiconductor wafer 13 (S3a). When it is judged that the center of rotation of the aligner 307 coincides with the center of the semiconductor wafer 13, then the circumferential direction potential distribution detection part 222 of the integrated control part 220 detects potential distribution in the circumferential direction while the aligner 307 keeps rotating the semiconductor wafer 13 (S5a). As described above, the circumferential direction potential distribution detection part 222 obtains potential information of a plurality of points of the rotating semiconductor wafer from the potential measuring unit 304 whose probe 304a is positioned in the aligner 307 and angle information of these points from the rotary encoder or the like of the aligner 307, and stores the obtained information in the potential distribution storage part 232. When this circumferential potential distribution detection is finished, then the integrated control part 220 judges whether the direction has been adjusted properly, i.e. whether the notch 13a of the semiconductor wafer 13 faces a prescribed direction or not (S3b). When it is judged that the notch 13a of the semiconductor wafer 13 faces the prescribed direction, then the rotation of the semiconductor wafer 13 by the aligner 307 is stopped immediately, and the wafer transfer unit 302 transfers the semiconductor wafer 13 linearly toward the specimen exchange chamber 405 (S4). Then, similarly to the first embodiment, potential distribution on the semiconductor wafer 13 is detected in the linear direction (S5). Thereafter, the integrated control part 220 operates in a manner basically similar to the first embodiment. Next, a method of generating a two-dimensional interpolation function in the present embodiment will be described referring to FIGS. 11A, 11B, 11C and 11D. As shown in FIG. 11A, similarly to the first embodiment, a semiconductor wafer 13 having the diameter of 300 mm is considered here also. As described above, in the present embodiment, potentials are measured at points on the Y′ axis and at points on a circle whose center is positioned at the center of the semiconductor wafer 13. The radius of this circle is 90 mm. Wafer surface potentials are measured at eleven points on the Y′ axis of the X′-Y′ coordinate system having its origin at the center of the wafer and eight points on the circle having the radius of 90 mm including a point at (0, −90), a point at (90, 0), a point at (0, 90) and a point at (−90, 0), i.e. nineteen points in total. To generate a two-dimensional interpolation function by using the measured data, first the spline interpolation is performed with respect to the measured data of the eleven points on the Y′ axis by using Eqs. 1 and 2 described in the first embodiment, to obtain potential distributions VU and VL on the Y′ axis. Next, a potential distribution on the circle of the radius 90 mm is obtained. Writing surface potential at any location (R, θ) of the wafer as V(R, θ), potential distribution Vθ on the circle is written as V(R=90, θ). When “R=90” is generalized to Rj, the interpolation function can be written as Eq. 10.V(Rj,θ)=AV(Rj,θi)+BV(Rj,θi+1)+CV″(Rj,θi)+DV″(Rj,θi+1) Eq. 10 Here, each coefficient A, B, C, D in the equation Eq. 10 is defined as follows. A = θ i + 1 - θ θ i + 1 - θ i ⁢ ⁢ B = θ - θ i θ i + 1 - θ ⁢ ⁢ C = 1 6 ⁢ ( A 3 - A ) ⁢ ( θ i + 1 - θ ) 2 ⁢ ⁢ D = 1 6 ⁢ ( B 3 - B ) ⁢ ( θ i + 1 - θ ) 2 Eq . ⁢ 11 In Eqs. 10 and 11, the argument j is an argument for indicating a specific position in the radial direction, and the argument i an argument for indicating a specific position in the θ direction. Next, as shown in FIG. 11B, interpolation operation is performed by using the above-described VU, VL and V(Rj, θi), to calculate potential for any location on the wafer. The interpolation formula that describes the surface potential V(R, θ) at any location (R, θ) on the wafer can be expressed as in Eq. 12 using potentials VLj, VUj at intersection points (R, 0) and (R, π) of a circle of the radius R and the Y axis, and a potential V(R=Rj, θ) at an intersection point of that Vθ and a line segment connecting the point (R, θ) and the origin. In other words, Eq. 12 is obtained by weighting VU, VL and V(Rj, θi) and adding the results.V=EVLj+FVUj+GVθi Eq. 12 Here, Vθi is a simplified expression for V(R=Rj, θ) and is used in order to avoid complication. FIG. 11B shows the above relations. Further, each coefficient in the equation Eq. 12 is defined to satisfy the following conditions. E + F + G = 1 Eq . ⁢ 13 ∂ E ∂ θ = 0 ⁢ ⁢ ∂ F ∂ θ = 0 ⁢ ❘ θ = 0 ⁢ ° ⁢ ⁢ 180 ⁢ ° ⁢ ⁢ E = 0 ⁢ ⁢ F = 1 ⁢ ❘ θ = 180 ⁢ ° ⁢ ⁢ E = 1 ⁢ ⁢ F = 0 ⁢ ❘ θ = 0 ⁢ ° Eq . ⁢ 14 ∂ E ∂ R = 0 ⁢ ⁢ ∂ F ∂ R = 0 ⁢ ⁢ ∂ G ∂ R = 0 ⁢ ❘ R = 0 ⁢ ⁢ 90 ⁢ ⁢ mm ⁢ ⁢ 150 ⁢ ⁢ mm ⁢ ⁢ G = 0 ⁢ ❘ R = 0 ⁢ ⁢ mm ⁢ ⁢ G = 1 ⁢ ❘ R = 90 ⁢ ⁢ mm ⁢ ⁢ G = 0 ⁢ ❘ 150 ⁢ ⁢ mm ⁢ ⁢ E = 0 ⁢ ⁢ F = 0 ⁢ ❘ 90 ⁢ ⁢ mm ≤ R ≤ 150 Eq . ⁢ 15 As a function satisfying the above equations Eqs. 13-15, there is a function shown in Eq. 16, for example. E = cos 2 ⁡ ( θ 2 ) ⁢ cos 2 ⁡ ( 90 ⁢ ° ⁢ R 90 ⁢ ⁢ mm ) ⁢ ⁢ F = sin 2 ⁡ ( θ 2 ) ⁢ cos 2 ⁡ ( 90 ⁢ ° ⁢ R 90 ⁢ ⁢ mm ) ⁢ ⁢ G = sin 2 ⁡ ( 90 ⁢ ° ⁢ R 90 ⁢ ⁢ mm ) ⁢ ❘ R ≤ 90 ⁢ ⁢ mm ⁢ ⁢ E = cos 2 ⁡ ( θ 2 ) ⁢ cos 2 ⁡ ( 90 ⁢ ° ⁢ 150 ⁢ ⁢ mm - R 60 ⁢ ⁢ mm ) ⁢ ⁢ F = sin 2 ⁡ ( θ 2 ) ⁢ cos 2 ⁡ ( 90 ⁢ ° ⁢ 150 ⁢ ⁢ mm - R 60 ⁢ ⁢ mm ) ⁢ ⁢ G = sin 2 ⁡ ( 90 ⁢ ° ⁢ 150 ⁢ ⁢ mm - R 60 ⁢ ⁢ mm ) ⁢ ❘ R ≥ 90 ⁢ ⁢ mm Eq . ⁢ 16 FIGS. 11C and 11D show the resultant surface potential for any location (X, Y) (=(R, θ)) on the semiconductor wafer 13, which has been obtained by using the two-dimensional interpolation function shown as Eq. 12. Here, FIG. 11C shows the potential distribution two-dimensionally, and FIG. 11D shows the potential distribution three-dimensionally. Here, referring to FIGS. 12A and 12B, the potential distribution calculation method in the present embodiment will be compared with the potential distribution calculation method in the first embodiment. FIG. 12A shows the result obtained by the method of the first embodiment, and FIG. 12B shows the result obtained by the method of the present embodiment. The upper area of FIGS. 12A and 12B show two-dimensionally potential distributions obtained by these methods respectively, and the lower area of FIGS. 12A and 12B show three-dimensionally respective residuals between the potential distributions obtained by these methods and the actually-measured potential distributions. It can be seen from the figure that the potential distribution obtained by the present embodiment expresses asymmetry of the distribution better, meaning that the result closer to the actual potential distribution has been obtained. Further, although not shown here, the method of the present embodiment can obtain potential distribution closer to the actual potential distribution than that obtained by the method of the second embodiment, in many cases. Thus, in comparison with the first and second embodiments, the present embodiment can further shorten the adjustment time between the finish of the stage movement and the start of measurement. In detail, the method of the present embodiment and the method of the first embodiment were compared regarding the time required for adjusting the retarding potential under the same conditions except for the methods of estimating the surface potential distribution. As a result, the method of the first embodiment took 10 seconds each for five points among twenty observation points on the semiconductor wafer 13, three seconds each for eight points, 1 second each for the other seven points, i.e. 81 seconds in total. On the other hand, according to the method of the present embodiment, the adjustment took 10 seconds each for only two points among the twenty points, three seconds each for eight points, and 1 second for ten points, i.e. only 54 seconds in total. In other words, it was possible to shorten the adjustment time per semiconductor wafer from 81 seconds in the first embodiment to 54 seconds. As described above, the present embodiment can realize a scanning electron microscope whose adjustment time is further shorter than those of the first and second embodiments. Further, it goes without saying that, when the present embodiment is applied to a measurement/inspection apparatus such as a length-measuring SEM, a review SEM or an appearance inspection apparatus, throughput higher than those of the first and second embodiments can be realized. In that case, larger the number of observation points per wafer is, higher the throughput improvement effect as a whole is. In particular, when the present invention is applied to an appearance inspection apparatus or a review SEM, this effect is larger. The above embodiments have been described taking an example of a scanning electron microscope. However, it goes without saying that the methods of these embodiments can be applied widely to charged particle beam apparatuses in general (such as ion beam processing apparatuses and ion beam irradiation apparatuses) as far as they are systems in which focus deviation due to electrification becomes a problem (i.e. not only systems using an electron beam but also systems using an ion beam, for example). Further, in the above embodiments, a semiconductor wafer has been mentioned as an example of specimen. The present invention, however, is not limited to a semiconductor wafer, and can be applied to other kinds of specimens such as a glass substrate, a magnetic disk substrate, a metal substrate formed with insulating film or the like, for example. Further, a potential measuring unit 304 having a detection probe 304a has been used as a potential measurement means for measuring the surface potential of a specimen. However, other measuring devices such as a potential measuring device using the absorption current measurement method may be employed, for example. Further, such a measuring unit may be arranged at any location. The arrangements shown in the above embodiments are ones that are favorable from the viewpoint of throughput only. Further, in the above embodiments, the polar coordinate system has been used for obtaining a two-dimensional potential distribution function. However, any coordinate system, such as an orthogonal coordinate system or a non-orthogonal coordinate system for example, can be employed as far as it can express a two-dimensional interpolation function, i.e. it is a coordinate system having two base vectors. Further, in the above embodiments, estimated potentials have been used for obtaining a retarding potential for focus adjustment, which is a setting parameter of an electron beam optical system 10. However, not only the retarding potential but also the estimated potentials may be used for obtaining the amplitude of a driving signal of the scanning deflector, the exciting current of the objective lens 106, the focus drive voltage of the objective lens 106, or the like. Further, the estimated potentials may be used in the pre-dose technique in which a wafer is irradiated with an electron beam before obtaining an SEM image of the wafer, in order to control the electrification potential of the wafer.
	description	This application claims priority to European application EP 09305767.7, filed on Aug. 18, 2009, the entire disclosure of which is incorporated by reference herein. The invention relates to a method for modelizing the core of a nuclear reactor, especially for calculating neutron flux within the core. The results of such a modelizing method can be used to prepare safety analysis reports before building and starting a reactor. These results can also be useful for existing nuclear reactors and especially for managing the nuclear fuel loaded therein. In particular, these results can be used to assess how the core design should evolve in time and decide of the positions of the fuel assemblies in the core, especially the positions of the fresh assemblies to be introduced in the core. Such modelizing methods are implemented by computers. To this end, the core is partitioned in cubes, each cube constituting a node of a grid for implementing a digital computation. Usually the steady-state diffusion equation to be solved during such a digital computation amounts to: Σ Rg m ⁢ ϕ g m ︸ removal = λχ g ⁢ ∑ g ′ = 1 G ⁢ νΣ fg ′ m ⁢ ϕ g ′ m ︸ production + ∑ g ′ ≠ g G ⁢ Σ gg ′ m ⁢ ϕ g ′ m ︸ inscatter + ∑ u = x , y , z ⁢ 1 a u m ⁢ θ gu m ⁡ ( j gul + m + j gur - m ︸ incurrent ) , ( 1 ) ⁢ with ⁢ ⁢ { Σ Rg m = Σ ag m + ∑ g ′ ≠ g G ⁢ Σ g ′ ⁢ g m + ∑ u = x , y , z ⁢ 2 ⁢ c 1 ⁢ gu m a u m θ gu m = 1 - c 2 ⁢ gu m - c 3 ⁢ gu m , ( 2 ) where λ is a first neutron eigenvalue, m is a cube index, also called nodal index, G is the number of neutron energy groups and g, g′ are neutron energy group indexes, u is a Cartesian axis index of the cube, Σagm represents macroscopic absorption cross-section for the cube m and the energy group g, Σfgm represents macroscopic fission cross-section for the cube m and the energy group g′, Σgg′m represents macroscopic slowing down cross-section for the cube m and the energy groups g, Φgm represent neutron fluxes, such that the ΣRgm, . . . Φgm represent the reaction rates for the corresponding reactions (absorption, fission), ν is the number of neutrons produced per fission, χg is the fraction of neutrons emerging from fission with neutron energy g, aum is the width of cube m along Cartesian axis u, and with the relationship between the neutron outcurrents jgul−m and jgur+m, neutron fluxes Φgm and neutron incurrents jgul+m and jgur−m defined by: { j gul - m = c 1 ⁢ gu m ⁢ ϕ g m + c 2 ⁢ gu m ⁢ j gul + m + c 3 ⁢ gu m ⁢ j gur - m j gur + m = c 1 ⁢ gu m ⁢ ϕ g m + c 3 ⁢ gu m ⁢ j gul + m + c 2 ⁢ gu m ⁢ j gur - m ( 3 ) The coefficients cigum, with i=1, 2, 3, are characteristic of the cube m and depend on nodal dimensions and macroscopic cross-sections Σm. FIG. 1 is a schematic representation in two dimensions of a cube m showing the neutron incurrents jgul+m and jgur−m for u=x, y and z; the neutron outcurrents jgul−m and jgur+m for u=x, y and z; and the neutron fluxes Σgm. Indexes l, respectively r, refers to each left interface surface, respectively each right interface surface, of the cube m for the respective Cartesian axis x, y. Indexes +, respectively −, represents the orientation from left to right, respectively from right to left, for the respective Cartesian axis x, y. The steady-state diffusion equation (1) is also named NEM equation, for Nodal Expansion Method equation. In the state of the art methods, most of the computational efforts are concentrated in the part dedicated to the iterative solving of a large eigensystem corresponding to the steady-state diffusion equation (1). In order to lower these computational efforts and therefore accelerate the solving of the eigensystem, Coarse Mesh Rebalancing (CMR) procedures have been used. In these procedures, neutron fluxes and currents for a given iteration are multiplied with a corrective factor before pursuing subsequent computationally expensive iterations. The multiplicative correction serves to suppress the presence of a non fundamental wavelength part of eigenspectrum with the first neutron eigenvalue λ close to an exact value λexact. However, the acceleration effect realized in this way depends on the numerical proximity of the highest coarse mesh level in a multi-level hierarchy to the full-core diffusion level. Such CMR procedures may therefore lead to very slow convergence or even convergence stagnation, thus increasing the computational effort. An object of the present invention is to solve the above-mentioned problems by providing a nuclear reactor modelizing method which offers a better convergence accuracy, a better computational robustness and a better computational efficiency so that relevant neutron flux calculations can be obtained within a short computational time period and with a very good convergence accuracy. The present invention provides a computer implemented method for modelizing a nuclear reactor core, comprising the steps of: partitioning the core in cubes (10) to constitute nodes of a grid (12) for computer implemented calculation, calculating neutron flux by using an iterative solving procedure of at least one eigensystem, the components of an iterant of the eigensystem corresponding either to a neutron flux, to a neutron outcurrent or to a neutron incurrent, for a respective cube (10) to be calculated, wherein a control parameter is varied to impact a neutron eigenvalue μ through a perturbed interface current equation and drive the neutron eigenvalue μ towards l. The present invention also provides a computer program product residing on a computer readable medium and comprising computer program means for miming on a computer implemented method. In the following description, the case of a pressurized water reactor (PWR) will be considered, but it should be kept in mind that the present invention applies to other types of nuclear reactors. In a first step of the computer implemented modelizing method according to the invention, the core of the reactor is partitioned in cubes 10 (shown on FIG. 2) as in the state of art methods. Each cube 10 corresponds to a node of a grid or network 12 on which numerical computation will be implemented through the computer. In order to ease the representation, the grid 12 is shown on FIG. 2 as being two-dimensional, but it should be kept in mind that the grid is actually three-dimensional in order to represent the whole core. The neighbours of the cube 10 with the cube index m (in the center of FIG. 2) are the cubes 10 with the respective cube index m′1(m), m′2(m), m′3(m) and m′4(m). In the following of the description, the cubes 10 will be directly designated by their respective cube index. In a second step of the computer implemented modelizing method according to the invention, the neutron fluxes Φgm within the core will be calculated by the solving of an eigensystem corresponding to the steady-state diffusion equation (1). To this end, an iterative solving procedure is used. A removal operator {circumflex over (R)}, an inscatter operator Ŝ, a production operator {circumflex over (F)}, and an incurrent operator Ĝ are defined, from Equation (1), by: { [ R ^ ⁢ ϕ ] g m = ( Σ ag m + ∑ g ′ ≠ g G ⁢ Σ g ′ ⁢ g m ) ⁢ ϕ g m [ S ^ ⁢ ϕ ] g m = ∑ g ′ ≠ g G ⁢ Σ gg ′ m ⁢ ϕ g ′ m [ F ^ ⁢ ϕ ] g m = χ g ⁢ ∑ g ′ = 1 G ⁢ νΣ fg ′ m ⁢ ϕ g ′ m [ G ^ ⁢ J ] gu m = ∑ u = x , y , z ⁢ 1 a u m ⁢ θ gu m ⁡ ( j gul + m + j gur - m ) ( 4 ) An isotropic outcurrent generation operator {circumflex over (Π)} and a mono-directional current throughflow operator {circumflex over (Ω)} are defined by: { [ Π ^ ⁢ ϕ ] gu m = c 1 ⁢ gu m ⁢ ϕ g m [ Ω ^ ⁢ J ] gul - m = c 2 ⁢ gu m ⁢ j gul + m + c 3 ⁢ gu m ⁢ j gur - m [ Ω ^ ⁢ J ] gur + m = c 3 ⁢ gu m ⁢ j gul + m + c 2 ⁢ gu m ⁢ j gur - m ( 5 ) A coupling operator Ŷ couples the outcurrents to the incurrents for neighbouring cubes 10, and is defined by: { j gul + ( m ) = [ Y ^ ⁢ J ] gul + ( m ) = j gur + ( m - 1 ) j gur - ( m ) = [ Y ^ ⁢ J ] gur - ( m ) = j gul - ( m + 1 ) j gul - ( m ) = [ Y ^ ⁢ J ] gul + ( m ) = j gur - ( m - 1 ) j gur + ( m ) = [ Y ^ ⁢ J ] gur - ( m ) = j gul + ( m + 1 ) , ( 6 ) This coupling operator Ŷ uses the fact that, for example, for a cube m, the u-directional left-oriented outcurrent equals the u-directional left-oriented incurrent for the left neighbour in direction of the Cartesian axis u, and that similar equalities are verified for the other directions and orientations. For example, the neutron outcurrents coming from respective neighbours m′1(m), m′2(m), m′3m), m′4(m) into the cube m are the neutron incurrents for the cube m, as the neighbours m′1(m), m′2(m), m′3m), m′4(m) shown in FIG. 2 are respectively the neighbours (m+1) for the Cartesian axis y, (m−1) for the Cartesian axis x, (m+1) for the Cartesian axis x and (m−1) for the Cartesian axis y of Equation (6). Using the above operators, the equations (1) and (2) can be written as: { R ^ ⁢ ϕ = ( λ ⁢ F ^ + S ^ ) ⁢ ϕ + G ^ ⁢ j ( in ) j ( out ) = Π ^ ⁢ ϕ + Ω ^ ⁢ j ( in ) j ( in ) = Y ^ ⁢ j ( out ) , ( 7 ) or as: ( R ^ - S ^ - λ ⁢ F ^ 0 ^ G ^ - Π ^ 1 ^ - Ω ^ 0 ^ - Y ^ 1 ^ ) ⁢ ( ϕ j ( out ) j ( in ) ) = ( 0 0 0 ) ( 8 ) which is the eigensystem to be solved. In Equation (8), Φ is a neutron flux column vector, wherein each element is a neutron flux Φgm for a respective cube m and for a respective energy group g (FIG. 1). Thus, the dimensions of the neutron flux column vector Φ are equal to (G×M, 1), where G is the number of energy groups and M is the number of cubes 10. j(out) is a neutron outcurrent column vector, wherein each element is a respective neutron outcurrent jgul−m, jgur+m, for the respective cube m, energy group g and Cartesian axis u, with u equal to x, y or z. j(in) is a neutron incurrent column vector, wherein each element is a respective neutron incurrent jgul+m, jgur−m, for the respective cube m, energy group g and Cartesian axis u. Thus, the dimensions of the neutron outcurrent vector column j(out) and the neutron incurrent vector column j(in) are equal to (6×G×M, 1). In the following of the description, the neutron outcurrent vector column j(out) is also noted jout. Thus, the components of an iterant (Φ, j(out), j(in)) of the eigensystem defined by Equation (8) correspond to the neutron fluxes Φgm, the neutron outcurrents jgul−m, jgur+m, and the neutron incurrents jgul+m, igur−m, to be calculated for each cube m and for each energy group g, and which are the respective elements of the neutron flux column vector Φ . . . the neutron outcurrent column vector j(out) and the neutron incurrent column vector j(in). The iterative solving procedure comprises a substep of conditioning the eigensystem into a spare eigensystem wherein the components of an iterant (j(out), j(in)) of the spare eigensystem only correspond either to the neutron incurrents jgul+m,jgur−m coming into the respective cube m or to the neutron outcurrents jgul−m,jgur+m coming from the respective cube m, which are the respective elements of the neutron outcurrent column vector j(out) and the neutron incurrent column vector j(in). The conditioning of the eigensystem into a spare eigensystem starts from modifying the first part of Equation (8) written as:({circumflex over (R)}−Ŝ−λ{circumflex over (F)})φ−Ĝj(in)=0, (9) Defining the symbolic operator {circumflex over (P)}λ=({circumflex over (R)}−Ŝ−λ{circumflex over (F)})−1, the neutron flux column vector Φ is expressed in function of the neutron incurrent column vector j(in) as:φ={circumflex over (P)}λĜj(in) (10) By substituting this expression in the outcurrent equation part of Equation (7), i.e. in the second part of Equation (8), a currents-only relationship is obtained:j(out)=[{circumflex over (Π)}{circumflex over (P)}λĜ+{circumflex over (Ω)}]j(in) (11) After defining the following operator notations:{circumflex over (θ)}λ={circumflex over (Π)}{circumflex over (P)}λ (12)and{circumflex over (B)}λ={circumflex over (θ)}λĜ+{circumflex over (Ω)}, (13) the currents-only relationship is written as:j(out)={circumflex over (B)}λj(in) (14) which is a spare eigensystem. Using the relationship j(in)=Ŷj(out) between the neutron outcurrent column vector j(out) and the neutron incurrent column vector j(in), where Ŷ is the coupling operator, a spare eigensystem is obtained wherein the components of an iterant (j(out)) of the spare eigensystem only correspond to the neutron outcurrents jgul−m,jgur+m coming from the respective cube m, which are the elements of the neutron outcurrent column vector j(out). This spare eigensystem corresponds to:[{circumflex over (1)}−{circumflex over (B)}λŶ]j(out)=0 (15) Since the operator {circumflex over (B)}λŶ will initially not be exactly equal to 1, and will become equal to 1 only as j(out) converges to the exact solution j(out)exact and if simultaneously the first neutron eigenvalue μ converges to an exact value λexact, so that Equation (15) becomes:[{circumflex over (1)}−μ{circumflex over (B)}λŶ]j(out)=0, (16) with a second neutron eigenvalue μ converging towards 1, if the first neutron eigenvalue λ converges to the exact value λexact. For numerical optimization, Equation (16) may be modified through a premultiplication with the operator Π−1 and the following equation is obtained:{circumflex over (Π)}−1j(out)=μ[{circumflex over (P)}λĜ+{circumflex over (Π)}−1{circumflex over (Ω)}]Ŷj(out) (17) The term {circumflex over (P)}λĜŶj(out) is an isotropic term, which does not depend on the Cartesian direction u. The expressions of the respective terms from Equation (17) for the cube index m, Cartesian axes u, u′ and the respective orientations s, s′ along the Cartesian axes u, u′ are given by: { A mGus = ∑ g ∈ G ⁢ [ Π ^ - 1 ⁢ j ( out ) ] mgus Q mG G ′ ⁢ u ′ ⁢ s ′ = ∑ g ∈ G ⁢ ∑ g ′ ∈ G ′ ⁢ [ P ^ λ ⁢ G ^ ⁢ Y ^ ⁢ j ( out ) ] mg g ′ ⁢ u ′ ⁢ s ′ C mGus s ′ = ∑ g ∈ G ⁢ [ Π ^ - 1 ⁢ Ω ^ ⁢ Y ^ ⁢ j ( out ) ] mgus s ′ ( 18 ) ⁢ ⁢ ( 19 ) ⁢ ⁢ ( 20 ) G, G′ are sets of energy groups. Â and Ĉ are mono-energetic operators with their respective factors AmGus and CmGuss′.QmGG′u′s′ are the factors of a spectral operator {circumflex over (Q)}λ. It should be noted that each combination {u, s}, respectively {u′, s′}, defines an interface surface of the cube m with u, u′ equal to x, y or z, and s, s′ equal to 1 or r. For example, {x, 1} defines the left interface surface of the cube m along the Cartesian axis x. The individual terms are given by: [ Π ^ - 1 ⁢ j ( out ) ] mgus = 1 c 1 ⁢ ⁢ gu m ⁢ j mgus ( out ) ( 21 ) [ P ^ λ ⁢ G ^ ⁢ Y ^ ⁢ j ( out ) ] mg g ′ ⁢ u ′ ⁢ s ′ = ∑ g ′ = 1 ng ⁢ ⁢ P ^ gg ′ ⁡ [ G ^ ⁢ Y ^ ⁢ j ( out ) ] mgus u ′ ⁢ s ′ = ∑ g ′ = 1 ng ⁢ ⁢ P ^ gg ′ ⁢ 1 a u ′ m ⁢ θ g ′ ⁢ u ′ m ⁢ j g ′ m ← η ⁡ ( mu ′ ⁢ s ′ ) ( 22 ) [ Π ^ - 1 ⁢ Ω ^ ⁢ Y ^ ⁢ j ( out ) ] mgus s ′ = 1 c 1 ⁢ ⁢ gu m ⁡ [ c 2 ⁢ ⁢ gu m ⁢ δ ss ′ + c 3 ⁢ ⁢ gu m ⁡ ( 1 - δ ss ′ ) ] ⁢ j g m ← η ⁡ ( mus ′ ) ( 23 ) Equation (17) is then solved, e.g. by using a conventional iterative solving procedure as a Gauss-Seidel procedure. Thus, a solution is calculated for the elements j(out)mgus of the neutron outcurrent column vector j(out). This enables to determine the solution of the neutron incurrent column vector j(in) according to Equation (14), and finally to determine the solution of the neutron flux column vector Φ according to Equation (10). The calculated neutron flux column vector Φ obtained through the modelizing method can be used to control an existing nuclear reactor core, e.g. for managing the nuclear fuel, or be used for building a new reactor core. The modelizing method may be implemented on parallel processors or on a single processor. This above-disclosed modelizing method has proved to lead to better convergence accuracy, a better computational robustness and a better computational efficiency. This is connected to the solving of a sparse eigensystem wherein the only components of the iterant correspond to neutron outcurrents j(out), and do not depend on neutron fluxes. Further, the convergence accuracy of the modelizing method according to the invention may be improved up to 1E-12, whereas the convergence accuracy obtained with a classic modelizing method is limited to 1E-6. In other embodiments, the components of the iterant of the spare eigensystem to be solved correspond only to neutron incurrents j(in). In order to further improve robustness and computational efficiency, according to a second aspect of the invention, the eigensystem is first conditioned in a restricted eigensystem corresponding to the eigensystem for a selection of some neutron energy groups. This selection is also called spectral restriction to some energy groups. The restricted eigensystem may then be solved according to the first aspect of the invention. Finally, the solution of the restricted eigensystem is used to solve the eigensystem. The number NGC of the selected energy groups is smaller than the total number ng of energy groups. NGC may be the number of coarsened spectral bands which are collections of fine energy groups merged into a smaller number of coarse energy groups. ng is, for example, equal to 8, and NGC may for example be equal to 4, 3, 2 or 1. According to this second aspect, the Equation (17) for the driving factors dGmus(out), with its respective terms given by Equations (18) to (20), is expressed as: A Gmus ( out ) ⁢ d Gmus ( out ) ︸ outflow ″ `` = μ [ ∑ G ′ = 1 NGC ⁢ ⁢ ∑ u ′ = 1 3 ⁢ ⁢ ∑ s ′ = 1 , r ⁢ ⁢ Q mG G ′ ⁢ u ′ ⁢ s ′ ⁢ d G ′ ⁢ η ⁡ ( mu ′ ⁢ s ′ ) ⁢ u ′ ⁢ s ′ ( out ) ︸ `` ⁢ isotropic ⁢ ⁢ production ″ + ∑ s ′ = 1 , r ⁢ ⁢ C mGus s ′ ⁢ d Gmus ′ ( out ) ︸ throughflow ″ `` ] ( 24 ) where G, G′ are coarse neutron energy group indexes, and in which an isotropic term ∑ G ′ = 1 NGC ⁢ ⁢ ∑ u ′ = 1 3 ⁢ ⁢ ∑ s ′ = 1 , r ⁢ ⁢ Q mG G ′ ⁢ u ′ ⁢ s ′ ⁢ d G ′ ⁢ η ⁡ ( mu ′ ⁢ s ′ ) ⁢ u ′ ⁢ s ′ ( out ) is independent of the outgoing current direction specified by the Cartesian axis u and orientation s, and a throughflow term ∑ s ′ = 1 , r ⁢ ⁢ C mGus s ′ ⁢ d Gmus ′ ( out ) ,also called anisotropic term, is defined within the same coarse neutron energy group G along the same Cartesian axis u. The decomposition of the outcurrents leaving the cube m into isotropic and anisotropic terms is illustrated on FIG. 3. The isotropic term is the same in all directions and the anisotropic term varies between interface surfaces of the cube m. Solving at first the eigensystem for a spectral restriction to some energy groups, moreover with a decomposition of the outcurrents in which the isotropic term is computed easily, leads to a better computational robustness and a better computational efficiency. This is connected to the reduction of eigensystem dimensions that results from the spectral restriction according to this second aspect of the invention. In order to further improve robustness and computational efficiency, according to a third aspect of the invention, the iterative solving procedure for a plurality of energy groups may be in form of a multi-level V-cycle 20, as shown on FIG. 4, comprising a top level 21, a first intermediate level 22, four second intermediate levels 24, 26, 28, 30, and three bottom levels 32, 34, 36. The top level 21 of the V-cycle comprises the iteration for the eigensystem corresponding to the steady-state diffusion equation (1), or NEM equation, for the plurality of neutron energy groups, and the conditioning of the eigensystem into a restricted eigensystem for a spectral restriction to some energy groups according to the second aspect of the invention. The restricted eigensystem resulting from the top level 21 is then fed into a first intermediate level 22 just under the top level 21. The first intermediate level 22 comprises the conditioning of the restricted eigensystem into a spare eigensystem according to the first aspect of the invention wherein the components of an iterant (j(out), j(in)) of the spare eigensystem only correspond either to neutron incurrents jgul+m, jgur−m coming into the cubes m or to neutron outcurrents jgul−m, jgur+m, also noted j(out)mgus, coming from the cubes m. The factors of operators Â, {circumflex over (Q)}λ and Ĉ given by Equations (18) to (20) are computed explicitly for this first intermediate level 22. Each second intermediate levels 24, 26, 28, 30 comprises the conditioning of a former spare eigensystem for a former selection of neutron energy groups into a latter spare eigensystem for a latter selection of neutron energy groups, the number of neutron energy groups in said latter selection being smaller to the number of neutron energy groups in said former selection. The former spare eigensystem of the second intermediate level 24 subsequent to the first intermediate level 22 in the downward orientation of the multi-level V-cycle 20 is the spare eigensystem resulting from the first intermediate level 22. The former spare eigensystem of each second intermediate level 26, 28, 30 which is not subsequent to the first intermediate level 22 corresponds to the latter spare eigensystem resulting from the precedent second intermediate level 24, 26, 28. In other words, the number of neutron energy groups decreases from a second intermediate level to the next second intermediate level in the downward orientation. At the last second intermediate level 30, the number of neutron energy groups may be equal to 1. It should be noted that this restriction of the number of neutron energy groups for the second intermediate levels 24, 26, 28, 30 may be done according to a spectral condensation algebra, which will be described later, and not according to the second aspect of the invention. Bottom levels 32, 34, 36 comprise, in the downward orientation of the V-cycle, the solving, according to state of the art procedures, of the last spare eigensystem for a single energy group determined at the last second intermediate level 30. Bottom levels 34, 36 correspond to a spatial restriction of the eigensystem resulting from the precedent bottom level 32, 34 in respective coarsened grids with cubes being larger than the cubes of the precedent bottom level 32, 34. At the bottom level 36 of the V-cycle, a solution of the eigensystem for the single energy group is computed. This solution is then reintroduced in the upper levels of the V-cycle in the upward orientation so that solutions are computed for the respective spare eigensystems. At the top level 21 of the V-cycle in the upward orientation, the solution of the NEM equation for the plurality of energy groups is computed. In the illustrated embodiment of FIG. 4, the number ng of neutron energy groups for the NEM equation at the top level 21 may be equal to 8. For the intermediate levels 22, 24, 26, 28, 30, the number of neutron energy groups in the respective selections may be respectively equal to four, three, two and one. The three bottom levels 32, 34, 36 of the V-cycle shown on FIG. 4 comprise the solving of said last spare eigensystem for said one energy group according to the CMR procedure. The four intermediate levels 22, 24, 26, 28 corresponding to the solving of respective spare eigensystems are also designated by the respective references SR4, SR3, SR2 and SR1 (FIG. 5). The factors of the mono-energetic operator Â for the level SR4 are computed explicitly. Subsequently, the factors of the mono-energetic operator Â for the level SR3 are derived from the ones for the level SR4, as shown on FIG. 5, where each box 37 represents a neutron energy group, through:Am;SR31u′s′=Am;SR41u′s′Am;SR32u′s′=Am;SR42u′s′Am;SR33u′s′=Am;SR43u′s′+Am;SR44u′s′ (25) Equation (25) is illustrated on FIG. 5 by the arrows 38 between levels 22 and 24. Subsequently, the factors of the mono-energetic operator Â for the level SR2 are derived from the ones for the level SR3 through:Am;SR21u′s′=Am;SR31u′s′+Am;SR32u′s′Am;SR22u′s′=Am;SR33u′s′ (26) Equation (26) is illustrated on FIG. 5 by the arrows 40 between levels 24 and 26. Finally, the factors of the mono-energetic operator Â for the level SR1 are derived from the ones for the level SR2 through:Am;SR1u′s′=Am;SR21u′s′+Am;SR22u′s′ (27) Equation (27) is illustrated on FIG. 5 by the arrows 42 between levels 26 and 28. Equations (25) to (27) define a spectral condensation algebra for the mono-energetic operator Â corresponding to a spectral grid partitioning strategy shown in FIG. 5. It should be noted that another spectral condensation algebra for the mono-energetic operator Â with different equations may be defined with another spectral grid partitioning strategy, i.e. with a different arrangement of the boxes 37. The factors of the mono-energetic operator Ĉ are derived in a similar manner as for the factors of the mono-energetic operator Â, from the level SR4 to the level SR1 in the downward orientation. The factors of the spectral operator {circumflex over (Q)}λ for the level SR4 are computed explicitly. Subsequently, the factors of the spectral operator {circumflex over (Q)}A for the level SR3 are derived from the ones for the level SR4 through:Qm1;SR31u′s′=Qm1;SR41u′s′Qm2;SR32u′s′=Qm2;SR42u′s′Qm1;SR32u′s′=Qm1;SR42u′s′Qm2;SR31u′s′=Qm2;SR41u′s′Qm2;SR33u′s′=Qm2;SR43u′s′+Qm2;SR44u′s′Qm3;SR32u′s′=Qm3;SR42u′s′+Qm4;SR42u′s′Qm1;SR33u′s′=Qm1,SR43u′s′+Qm1;SR44u′s′Qm3;SR31u′s′=Qm3;SR41u′s′+Qm4;SR41u′s′Qm3;SR33u′s′=Qm3;SR43u′s′+Qm3;SR44u′s′+Qm4;SR43u′s′+Qm4;SR44u′s′ (28) Subsequently, the factors of the spectral operator {circumflex over (Q)}λ for the level SR2 are derived from the ones for the level SR3 through:Qm2;SR21u′s′=Qm3;SR31u′s′+Qm3;SR32u′s′Qm1;SR22u′s′=Qm1;SR33u′s′+Qm2;SR33u′s′Qm2;SR22u′s′=Qm2;SR32u′s′Qm1;SR21u′s′=Qm1;SR31u′s′+Qm1;SR32u′s′+Qm2;SR31u′s′+Qm2;SR32u′s′ (29) Finally, the factors of the spectral operator {circumflex over (Q)}λ for the level SR1 are derived from the ones for the level SR2 through:Qm;SR1u′s′=Qm1;SR21u′s′+Qm1;SR22u′s′+Qm2;SR21u′s′+Qm2;SR22u′s′ (30) Equations (28) to (30) define a spectral condensation algebra for the spectral operator {circumflex over (Q)}λ corresponding to a spectral grid partitioning strategy not shown and similar to the one shown in FIG. 5 for the mono-energetic operators Â and Ĉ. It should be noted that another spectral condensation algebra for the spectral operator {circumflex over (Q)}λ may also be define with another spectral grid partitioning strategy. Thus, a solution is calculated for the elements j(out)mgus of the neutron outcurrent column vector j(out) at the top level 21 of the V-cycle in the upward orientation. This enables to determine the solution of the neutron incurrent column vector j(in) according to Equation (14), and finally to determine the solution of the neutron flux column vector Φ according to Equation (10). The nuclear reactor core is then built or operated on the basis of the calculated neutron flux column vector Φ. Using spectral condensation algebras, wherein no complex arithmetic operation is involved, for the operators Â, Ĉ and {circumflex over (Q)}λ at the respective levels SR3, SR2 and SR1 allows the operators Â, Ĉ and {circumflex over (Q)}λ to be computed very cheaply, thus leading to a better computational robustness and a better computational efficiency of the modelizing method. In order to further improve robustness and computational efficiency, according to a fourth aspect of the invention, the cubes 10 are split into a first category and a second category. In the following description and as shown on FIG. 6, the cubes 10R of the first category will be called the red cubes and the cubes 10B of the second category will be called the black cubes but no specific restrictive meaning should be associated with the words “black” and “red”. Each red cube 10R has only black cubes 10B as direct neighbours. Thus, most of the red cubes 10R have six direct black neighbours 10B. It should be understood by “direct” neighbours, the cubes sharing a common surface with the considered cube. Consequently, and as illustrated by FIG. 6, the grid 12 has a visual analogy with respect to the dark and light regions of a checkerboard in a two-dimensional representation. Then, the cubes are numbered, starting for example by the red cubes 10R and ending by the black cubes 10B. In the following description, such a split of the cubes in two categories and the numbering of one category after the other will be referred to as red-black ordering. An advantage of the red-black ordering of the cubes in comparison with the state of the art lexicographical ordering is that, for a red cube 1R, all its direct neighbours will be black, and vice versa. The Equation (24), which the computer has to solve in order to calculate neutron flux within the core, can be written in the matrix-vector form:Âd=μ[{circumflex over (Q)}λ+Ĉ]d (31) Using a variable parameter γ, which value is typically comprised between 0.9 and 0.95, so that the product γμ forms a shift, an iteration of Equation (31) is written with the following shift-inverted implicit form:[Â−γμ(n−1)({circumflex over (Q)}λ+Ĉ)]d(n)=s(n−1) (32) where s(n−1) is a source given by:s(n−1)=(1−γ)μ(n−1)({circumflex over (Q)}λ+Ĉ)d(n−1) (33) The spectral operator {circumflex over (Q)}λ and the mono-energetic operator Ĉ are sparse, coupling red cubes 10R only to direct black neighbours 10B and vice versa. Thus, the red-black ordering enables the following convenient relationship between the red and the black parts of the equation:Âdred−γμ(n−1)({circumflex over (Q)}λ+Ĉ)dblack=sred Âdblack−γμ(n−1)({circumflex over (Q)}λ+Ĉ)dred=sblack (34) Equation (34) is transformed into the following equivalent equation for the red solution part only: Θ ~ red ⁢ d _ red = s _ ~ red ⁢ ⁢ with ⁢ ⁢ { Θ ~ red = 1 ^ - ( γμ ( n - 1 ) ) 2 ⁡ [ A ^ - 1 ⁡ ( Q ^ λ + C ^ ) ] 2 s _ ~ red = A ^ - 1 ⁡ [ s _ red + γμ ( n - 1 ) ⁢ A ^ - 1 ⁡ ( Q ^ λ + C ^ ) ⁢ A ^ - 1 ⁢ s _ black ] , ( 35 ) From a calculation point of view, the use of a red-black ordering means that, during an iterative solving procedure if, in the first half of an iteration, the red components dred of the iterant d are updated, then, during the second part of the iteration, all the black components dblack will be updated on the basis of the red components of their red neighbours dred. In other words, the value for each black cube 10B will be calculated on the basis of the values for all its direct red neighbours 10R. Using the red-black ordering improves the computation of the operators Â, Ĉ and {circumflex over (Q)}λ described in the first, second or third aspects of the invention. Thus, the red-black ordering may be used in complement of the first, second or third aspects of the invention in order to improve the computational efficiency. Such a red-black ordering proves to be especially useful when used with a particular solving procedure which constitutes a fifth aspect of the invention. This procedure is a particular highly robust stabilized Bi-Conjugate Gradient Stabilized (Bi-CGStab) procedure. An adequate introductory description of this procedure can be found in the following references: -Y. Saad, “Iterative Methods for Sparse Linear Systems”, second edition, Society for Industrial and Applied Mathematics (SIAM) (2003); H. A. van der Vorst, “Bi-CGSTAB: a Fast and Smoothly Converging Variant of Bi-CG for the solution of nonsymmetric linear systems”, SIAM J. Sci. Stat. Comput. 13(2), pp. 631-644 (1992), The Bi-CGStab procedure is derived from a minimization principle for a functional of d, with given θ and s, for which stationarity applies with regard to small variations δd around the specific optimum d which satisfies, exactly, the linear system given by Equation (35), and for which the functional assumes a minimum value. Thus, it is possible to define a solving procedure driven by the minimization of a functional rather than by more direct considerations on how to solve Equation (35) efficiently. The Bi-CGStab procedure follows from such a minimization principle, where the successive changes in the iterant are organized such that each change in the functional (which is like a Galerkin-weighted integrated residual) is orthogonal with respect to all of the preceding changes. The particular Bi-CGStab procedure according to the fifth aspect of the invention is given below with solution vector d, solution residual r (with r=s−θd) and auxiliary vector r, s and p, and with initial solution estimate d0: { 1. r 0 := s ~ - Θ • ⁢ d 0 , r = r 0 2. p 0 := r 0 , 3. do ⁢ ⁢ i = 0 , 1 , … ⁢ , N 4. α i := ( r * , r i ) ( r * , Θ • ⁢ p i ) , 5. s i := r i - α i ⁢ Θ • ⁢ p i , 6. ω i := ( Θ • ⁢ ⁢ s i , s i ) ( Θ • ⁢ ⁢ s i , Θ • ⁢ s i ) , 7. d i + 1 := d i + α i ⁢ p i + ω i ⁢ s i , 8. r i + 1 := s i - ω i ⁢ Θ • ⁢ s i , 9. β i := ( r * , r i + 1 ) ⁢ α j ( r * , r i ) ⁢ ω j , 10. p i + 1 := r i + 1 + β i + 1 ( p i - ω i ⁢ Θ • ⁢ p i ) 11. end ⁢ ⁢ do ( 36 ) The above Bi-CGStab sequence is truncated after N steps, with usually N<3. For the Bi-CGStab procedure, the preconditioning is based on the shift-inverted implicit form of Equation (32), with typically 0.9<γ<0.95. With this choice for the shift γμ, the operator s is guaranteed to remain nonsingular since, during the solution process, γμ will converge down to γ times the smallest possible eigenvalue of the system. Solving Equation (32) is numerically equivalent to determining the flux distribution in a slightly subcritical system with a neutron source, which is a perfect scenario for deploying advanced preconditioned Krylov procedure. Using the red-black ordering, Equation (32) is transformed into Equation (35) as above explained. The preconditioned system given by Equation (35) constitutes the sixth aspect of the invention. Once Equation (35) has been solved through the Bi-CGStab procedure the black solution part is to be computed from the black part of Equation (34). Use of this particular way of preconditioning, which means that the direct neutron interaction between neighboring (red vs. black) nodes, as projected onto the grid, is preincluded in the system to be solved, making the unity operator in Equation (35) more dominant since∥(Â−1({circumflex over (Q)}λ+Ĉ))2∥<∥Â−1({circumflex over (Q)}λ+Ĉ)∥, (37)given that∥Â−1({circumflex over (Q)}λ+Ĉ)∥<1 (38) This way of preconditioning manages to pre-include, at low computational cost, crucial information (or the major part of that information) with regard to the physical interactions between nodes that determine the spatial couplings and hence the solution of the equation. In another embodiment, the iterative solving procedure is a Gauss-Seidel procedure, or an iterative procedure in the Krylov subspace, such as a generalized minimal residual method, also abbreviated GMRES, or a plain Jacobi method. According to a seventh aspect of the invention, a variational principle for improved eigenvalue computation will be described in the following description. Equation (16) corresponding to the spare eigensystem, above described for the first, second or third aspect of the invention, is written in the following form, with the second neutron eigenvalue μ and the neutron outcurrent vector column jout:jout=μ{circumflex over (Π)}{circumflex over (P)}λĜŶjout+{circumflex over (Ω)}Ŷjout,jout=μc1φ+{circumflex over (Ω)}Ŷjout (39) where c1 is another notation for the operator {circumflex over (Π)} depending on the cube properties. In what follows, we will assume that the first neutron eigenvalue λ fulfills the role of a scalar control parameter. Using the property that the second neutron eigenvalue μ approaches unity if the total solution converges and thus stabilizes, the variational principle, or perturbation approach, comprises the varying the first neutron eigenvalue λ to drive the second neutron eigenvalue μ towards 1 and to accelerate the convergence of the spare eigensystem solution. This variation of the first neutron eigenvalue λ, may be done prior to every iteration of the spare eigensystem, or prior to every second, third, fourth or fifth iteration of the spare eigensystem. The variation of the first neutron eigenvalue λ is an application of a variation δλ to λ such that λ is driven to λ+δλ, which impacts the second neutron eigenvalue μ through a perturbed interface current equation: j out + δ ⁢ ⁢ j out = [ ( μ + δμ ) ⁢ Π ^ ⁡ ( P ^ λ + δλ ⁢ ∂ P ^ λ ∂ λ ) ⁢ G ^ + Ω ^ ] ⁢ Y ^ ⁡ ( j out + δ ⁢ ⁢ j out ) = ( μ + δμ ) ⁢ c 1 ⁡ ( ϕ + δλ ⁢ ∂ ϕ ∂ λ ) + Ω ^ ⁢ Y ^ ⁡ ( j out + δ ⁢ ⁢ j out ) ( 40 ) with the partial operator derivative: Π ^ ⁢ ∂ P ^ λ ∂ λ ⁢ G ^ ⁢ Y ^ ⁢ j out ≡ c 1 ⁢ ∂ ϕ ∂ λ ( 41 ) As perturbations δjout are expected to be increasingly small during the iterative procedure, they are conveniently ignored in Equation (40), and the integration with an arbitrary adjoined weighting function ω†yields the following expression: δμ ⁡ [ δλ ] ≅ 〈 ω † ❘ c 1 ⁢ ϕ 〉 〈 ω † ❘ c 1 ⁢ ∂ ϕ ∂ λ 〉 ⁢ δλ ( 42 ) As the variation of the first neutron eigenvalue λ is such that the second neutron eigenvalue μ is driven towards 1, i.e. that μ+δμ, is driven towards 1, the approximation δμ≡1−μ is imposed. With this approximation and the Equation (42), the following equation is obtained: δλ ≅ 〈 ω † ❘ c 1 ⁢ ϕ 〉 〈 ω † ❘ c 1 ⁢ ∂ ϕ ∂ λ 〉 ⁢ ( 1 - μ ) ( 43 ) Using the equivalence μc1φ=jout−{circumflex over (Ω)}Ŷjout, δλ is given by: δλ ≅ 〈 ω † ❘ j out - c 1 ⁢ ϕ + Ω ^ ⁢ Y ^ ⁢ j out 〉 〈 ω † ❘ c 1 ⁢ ∂ ϕ ∂ λ 〉 = 〈 ω † ❘ r out 〉 〈 ω † ❘ c 1 ⁢ ∂ ϕ ∂ λ 〉 ( 44 ) where rout represents the residual of the interface outcurrent balance equation, i.e. Equation (39), with the imposed target value for the second neutron eigenvalue μ equal to 1. The residual rout needs to be computed for each NEM iteration step in any case. The first neutron eigenvalue λ, considered in this aspect as a scalar control parameter, is then updated such that: λ ( new ) = λ ( prev ) + 〈 ω † ❘ r out ( prev ) 〉 〈 ω † ❘ c 1 ⁢ ∂ ϕ ∂ λ 〉 , ( 45 ) where λ(prev) and λ(new) are respectively the previous and the updated value of the first neutron eigenvalue λ. For determining the partial operator derivative ∂ ϕ ∂ λ and using Equation (7) for example, the neutron flux Φ is written:φ=({circumflex over (R)}−Ŝ−λ{circumflex over (F)})−1ĜŶjout (46) from which it follows that: ∂ ϕ ∂ λ = [ ∂ ∂ λ ⁢ ( R ^ - S ^ - λ ⁢ F ^ ) - 1 ] ⁢ G ^ ⁢ Y ^ ⁢ j out ( 47 ) An approximate derivative ∂ ϕ ~ ∂ λ is then computed by neglecting the upper-diagonal part of the matrix relative to the inscatter operator Ŝ such that Ŝ=ŜLD, i.e. by neglecting the upscattering: ∂ ϕ ~ ∂ λ = [ ∂ ∂ λ ⁢ ( R ^ - S ^ LD - λ ⁢ F ^ ) - 1 ] ⁢ G ^ ⁢ Y ^ ⁢ j out ( 48 ) It should be noted that in many computational cases this is not even an approximation, but numerically exact if no upscattering is modeled. It is assumed that: ∂ ϕ ∂ λ ≅ ∂ ϕ ~ ∂ λ ( 49 ) which will be sufficient for a successful application of the variational principle. For computing ∂ ϕ _ ∂ λ ,it is first written:{circumflex over (R)}−ŜLD−λ{circumflex over (F)}=({circumflex over (R)}−ŜLD)({circumflex over (1)}−λ({circumflex over (R)}−ŜLD)−1{circumflex over (F)}) (50) from which it follows that:({circumflex over (R)}−ŜLD−λ{circumflex over (F)})−1=({circumflex over (1)}−λ({circumflex over (R)}−ŜLD)−1{circumflex over (F)})−1({circumflex over (R)}−ŜLD)−1 (51) Then defining an operator notation {circumflex over (B)} with:{circumflex over (B)}=({circumflex over (R)}−ŜLD)−1{circumflex over (F)} (52) and in order to implicitly compute ∂ ∂ λ ⁡ [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 ,the Taylor formula is applied to {circumflex over (1)}−λ{circumflex over (B)}: [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 = 1 ^ + λ ⁢ ⁢ B ^ + λ 2 ⁢ B ^ 2 + λ 3 ⁢ B ^ 3 + … = ∑ n = 0 ∞ ⁢ [ λ ⁢ ⁢ B ^ ] n ( 53 ) The Taylor expansion is rearranged as:{circumflex over (1)}+[{circumflex over (1)}+λ{circumflex over (B)}+λ2{circumflex over (B)}2+λ3{circumflex over (B)}3+ . . . ]λ{circumflex over (B)}=[{circumflex over (1)}−λ{circumflex over (B)}]−1λ{circumflex over (B)} (54) By application of the chain rule to Equation (54), the derivative ∂ ∂ λ ⁡ [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 is given by: ∂ ∂ λ ⁡ [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 = [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 ⁢ B ^ + [ ∂ ∂ λ ⁡ [ 1 - λ ⁢ ⁢ B ^ ] - 1 ] ⁢ λ ⁢ ⁢ B ^ ( 55 ) which yields: [ 1 ^ - λ ⁢ ⁢ B ^ ] ⁢ ∂ ∂ λ ⁡ [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 = [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 ⁢ B ^ ( 56 ) The final expression that allows an efficient iterative scheme for determining the derivative ∂ ∂ λ ⁡ [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 is obtained by premultiplication of Equation (56) with {circumflex over (1)}−λ{circumflex over (B)}, which gives: [ 1 ^ - λ ⁢ ⁢ B ^ ] 2 ⁢ ∂ ∂ λ ⁡ [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 = B ^ ( 57 ) By writing [{circumflex over (1)}−λ{circumflex over (B)}]2={circumflex over (1)}−2λ{circumflex over (B)}+λ2{circumflex over (B)}2, computation of ∂ ϕ ~ ∂ λ is obtained from: [ 1 ^ - 2 ⁢ λ ⁢ ⁢ B ^ + λ 2 ⁢ B ^ 2 ] ⁢ ∂ ϕ ~ ∂ λ = s ( 58 ) with the source term s defined by:s={circumflex over (B)}({circumflex over (R)}−ŜLD)−1ĜŶjout=({circumflex over (R)}−ŜLD)−1{circumflex over (F)}({circumflex over (R)}−ŜLD)−1ĜŶjout (59) In the case of two energy groups, Equation (58) is solved directly and analytically. In the case of more than two energy groups, Equation (58) is solved iteratively, without exactness required in early iteration phases, through application of: [ ∂ ϕ ~ ∂ λ ] ( new ) = s + 2 ⁢ λ ⁢ ⁢ B ^ ⁡ [ ∂ ϕ ~ ∂ λ ] ( old ) - λ 2 ⁢ B 2 ⁡ [ ∂ ϕ ~ ∂ λ ] ( old ) , ( 60 ) where [ ∂ ϕ ~ ∂ λ ] ( old ) ⁢ ⁢ and ⁢ [ ∂ ϕ ~ ∂ λ ] ( new ) are respectively the previous and updated values of the approximate derivative ∂ ϕ ~ ∂ λ . Early means about the first third up to the first half of the totally needed number of iteration steps. It should be noted that the iterations from the computation of ∂ ϕ ~ ∂ λ can be abort rather early, since this variational approach needs only an approximate value of ∂ ϕ ~ ∂ λ to be useful. Thus, this variational principle according to this seventh aspect of the invention is very effective, because the numerator ω†\|rout(prev) in Equation (45) becomes smaller and smaller upon convergence, whereas the denominator 〈 ω † \| c 1 ⁢ ∂ ϕ ∂ λ 〉will converge rather quickly to an adequate value. In this seventh aspect, the numerator defines the driving principle since it converges towards zero. Varying the first neutron eigenvalue λ according to Equation (45) drives the second neutron eigenvalue μ towards 1 and accelerates the convergence of the spare eigensystem solution. This variation of the first neutron eigenvalue λ may be done prior to every iteration of the spare eigensystem, or prior to every second, third, fourth or fifth iteration of the spare eigensystem. Thus, the variational principle of the first neutron eigenvalue λ may be used in complement of the first, second or third aspects of the invention in order to improve the computational efficiency. All the above mentioned products of this seventh aspect can be reduced to the black part of the grid 12 without losing numerical efficiency in the method, so that the red-black ordering above described in the fourth aspect of the invention may be used in complement of this seventh aspect. According to an eighth aspect of the invention, the above described variational principle for the eigenvalue computation can be generalized for the computation of a control parameter being noted θ, that typically modulates the removal operator {circumflex over (R)} given by Equation (4), the modulated removal operator being noted {circumflex over (R)}θ. In the example of a modulation in all positions, the control parameter θ is the boron concentration. In the example of a modulation in selected positions, the control parameter θ is a parameter for controlling a rod insertion depth for a group of selected control rods. It is assumed that {circumflex over (R)}={circumflex over (R)}θ Equation (16) is then written in the following form, with the second neutron eigenvalue μ:jout=μ{circumflex over (Π)}{circumflex over (P)}θĜŶjout+{circumflex over (Ω)}Ŷjout jout=μc1φ+{circumflex over (Ω)}Ŷjout (61) with a symbolic spectral operator {circumflex over (P)}θ defined by{circumflex over (P)}θ=({circumflex over (R)}θ−Ŝ−{circumflex over (F)})−1 (62) Using the property that the second neutron eigenvalue μ approaches unity if the total solution, including the correct value of the control parameter θ, converges and thus stabilizes, the variational principle, or perturbation approach, comprises varying the control parameter θ to drive the second neutron eigenvalue μ towards l. The variation of the control parameter θ is an application of a variation δθ to θ such that θ is driven to θ+δθ, which impacts the second neutron eigenvalue μ through a perturbed interface current equation: j out + δ ⁢ ⁢ j out = [ ( μ + δ ⁢ ⁢ μ ) ⁢ Π ^ ⁡ ( P ^ ϑ + δ ⁢ ⁢ ϑ ⁢ ∂ P ^ ϑ ∂ ϑ ) ⁢ G ^ + Ω ^ ] ⁢ Y ^ ⁡ ( j out + δ ⁢ ⁢ j out ) ⁢ ⁢ j out + δ ⁢ ⁢ j out = ( μ + δμ ) ⁢ c 1 ⁡ ( ϕ + δ ⁢ ⁢ ϑ ⁢ ∂ ϕ ∂ ϑ ) + Ω ^ ⁢ ⁢ Y ^ ⁡ ( j out + δ ⁢ ⁢ j out ) ( 63 ) with the partial operator derivative: Π ^ ⁢ ∂ P ^ ϑ ∂ ϑ ⁢ G ^ ⁢ Y ^ ⁢ j out ≡ c 1 ⁢ ∂ ϕ ∂ ϑ ( 64 ) As perturbations δjout are expected to be increasingly small during the iterative procedure, they are conveniently ignored in Equation (63), and the integration with an arbitrary adjoined weighting function ω† yields the following expression: δμ ⁡ [ δϑ ] ≡ 〈 ω † \| c 1 ⁢ ϕ 〉 〈 ω † \| c 1 ⁢ ∂ ϕ ∂ ϑ 〉 ⁢ δϑ ( 65 ) As the variation of the control parameter θ is such that the second neutron eigenvalue μ is driven towards 1, i.e. that μ+δμ is driven towards 1, the approximation δμ≡1−μ is imposed. With this approximation and the Equation (65), the following equation is obtained: δϑ ≅ 〈 ω † \| c 1 ⁢ ϕ 〉 〈 ω † \| c 1 ⁢ ∂ ϕ ∂ ϑ 〉 ⁢ ( 1 - μ ) ( 66 ) Using the equivalence μc1φ=jout−{circumflex over (Ω)}Ŷjout, δθ is given by: δϑ ≅ 〈 ω † \| j out - c 1 ⁢ ϕ + Ω ^ ⁢ ⁢ Y ^ ⁢ j out 〉 〈 ω † \| c 1 ⁢ ∂ ϕ ∂ ϑ 〉 = 〈 ω † \| r out 〉 〈 ω † \| c 1 ⁢ ∂ ϕ ∂ ϑ 〉 ( 67 ) where rout represents the residual of the interface outcurrent balance equation, i.e. Equation (39), with the imposed target value for the second neutron eigenvalue μ equal to 1. The control parameter θ is then updated such that: ϑ ( new ) = ϑ ( prev ) + 〈 ω † \| r out ( prev ) 〉 〈 ω † \| c 1 ⁢ ∂ ϕ ∂ ϑ 〉 ( 68 ) It is assumed that ∂ ϕ ∂ ϑ ≅ ∂ ϕ ~ ∂ ϑ which will be sufficient for a successful application of the variational principle to the control parameter θ. For computing ∂ ϕ ~ ∂ ϑ ,the above described conditioning with application of the Taylor formula is also used in the same manner. The eighth aspect of the invention offers the same advantages as the above described seventh aspect of the invention, and may be used in complement of the first, second or third aspects of the invention in a manner similar to that for the above described seventh aspect of the invention, in order to improve the computational efficiency. FIG. 7 represents a set of convergence curves for different eigensystem iterative solving procedures with the number of pursued NEM iterative steps in abscissa and the fast flux error in ordinate, which is the maximum solution error of the neutron flux for the fast neutrons energy group. Since all energy groups are spectrally coupled, the maximum solution errors of the neutron flux for the other energy groups are quite similar to the fast flux error. Thus, the comparison between different eigensystem iterative solving procedures is possible through these convergence curves. The curve 50 is the convergence curve for the classic Coarse Mesh Rebalancing (CMR) procedure with use of single precision, and the curve 51 is the convergence curve for the classic CMR procedure with use of double precision. The single and double precisions are the classic precisions used for representing the floating point numbers in a computer program product. The curve 52 is the convergence curve for the iterative procedure according to the first and the seventh aspects of the present invention for a single energy group with use of single precision, and the curve 53 is the convergence curve for the iterative procedure according to the same aspects of the present invention with use of double precision. The curve 54 is the convergence curve for the iterative procedure according to the first and the second aspects of the present invention for four coarse energy groups with use of single precision, and the curve 55 is the convergence curve for the iterative procedure according to the same aspects of the present invention with use of double precision. The curve 56 is the convergence curve for the iterative procedure according to the first, the second and seventh aspects of the present invention for four coarse energy groups with use of single precision, and the curve 57 is the convergence curve for the iterative procedure according to the same aspects of the present invention with use of double precision. The procedure according to the first, the second and seventh aspects for four coarse energy groups with use of double precision (curve 57) is the procedure with both the smallest error with a value substantially equal to 10−13 for 50 pursued NEM iteration steps and the best computational efficiency, as illustrated by the gradient of the convergence curves which is maximum for the curve 57. The procedure according to the first and the seventh aspects for a single energy group with use of double precision (curve 53) also provides a small error with a value substantially equal to 10−9 for 130 pursued NEM iteration steps. Moreover, the computational efficiency of this procedure (curve 53) is worth than the computational efficiency of the procedure according to the first and the second aspects for four coarse energy groups with use of double precision (curve 55), because the gradient of the curve 55 is greater than the gradient of curve 53. The procedure according to the first and the second aspects for four coarse energy groups with use of double precision provides an error substantially equal to 10−7 for 40 pursued NEM iteration steps. Thus, the double precision has a great effect on the value of the fast flux error, but has no impact on the computational efficiency of the modelizing method. The seventh aspect of the present invention has also a greater effect on the value of the fast flux error, than on the computational efficiency. The first and the second aspects for four coarse energy groups provides the best computational efficiency, and FIG. 7 illustrates that the greatest gradient for an error value comprised between 100 and 10−5 is obtained for the curves 54 to 57, which all correspond to the first and the second aspects. As set forth in the previous description, the first to eighth aspects of the invention help to achieve robust modelizing methods providing a better computational efficiency so that relevant core simulations can be obtained within short computational time period. It should be kept in mind that the first aspect in itself helps in achieving this goal and can thus be used separately from the second to eighth aspects. Also, the second, third, seventh and eighth aspects are not necessarily implemented with the first aspect or with any one of the fourth to sixth aspects.
046577246	claims	1. For use with a pulsed neutron generator in a logging tool lowered in a borehole, a pulsed high voltage source having an output terminal adapted to be connected to pulse neutron generator, the power supply comprising: (a) high voltage supply means; (b) field effect transistor means comprising at least a pair of field effect transistors serially connected between said high voltage supply means and ground; (c) an output terminal between the two transistors of said field effect transistor means, said output terminal adapted to be connected by a conductor to provide pulsed high voltage to a neutron generator; (d) control pulse forming means connected to the gates of the respective two transistors, said pulse forming means forming control pulses selectively switching said transistors off and on in timed sequence to thereby connect the output terminal to said high voltage supply means, and (e) diode means connected to said gates of said transistors to limit gate voltage for operation of said transistors. 2. The apparatus of claim 1 including a series cascade of FETs comprising said transistor means, said FETs having gate terminals connected to control voltage means. 3. The apparatus of claim 1 further including means controlling operation of said pair of transistors to prevent making said transistors simultaneously conductive. 4. The apparatus of claim 1 including a floating power supply connected on said high voltage supply means and floating thereon, and also connected to said control pulse forming means. 5. The apparatus of claim 1 wherein said control pulse forming means forms interlocked pulses of said two transistors. 6. The apparatus of claim 1 wherein said diode means are connected to the gates of serially connected FETs comprising said transistor means, and wherein said diode means is connected to clamp gate voltage. 7. The apparatus of claim 1 wherein said control pulse forming means forms two control pulses for said pair of transistors, and the pulses are timed in occurrance and overlap. 8. The apparatus of claim 7 wherein the pulses are formed by flip-flop means to sequence switching of said transistor pair. 9. The apparatus of claim 1 wherein said transistor means comprises said pair of FETs serially connected so that each of said FETs has a gate terminal adapted to be connected to said control pulse forming means to receive a control pulse at each of said gates for transistor switching. 10. The apparatus of claim 9 wherein said transistors are inverted compared to each other, and said gates are thereby enabled to be oppositely driven. 11. The apparatus of claim 10 including means within said control pulse forming means for forming a pulse of one polarity to turn one of said transistors on and wherein a pulse of the same polarity turns off the other of said transistors. 12. The apparatus of claim 11 including series connected third and fourth transistors each having gates, and bias circuit means connected to said gates to cause said third and fourth transistors to operate in response to operation of said first two transistors. 13. The apparatus of claim 1 including flip-flops in said control pulse forming means forming timed signals for operation of said two transistors.
048030392	claims	1. A method of on-line monitoring of the execution by a human operator of procedures for a complex process facility comprising the steps of: storing electric signals representative of step by step procedures for the complex process facility, at least some steps of which require verification of a selected process condition; generating parameter signals representaitve of the real time value of predetermined process parameters; sequentially electrically selecting a step of one of said stored step by step procedures as a current step; electrically processing selected parameter signals to determine the state of the process condition to be varied by a current step which requires verification; generating a visual representation of said current step including a visible textual statemenet of the condition to be verified, a visual indication of the state of the selected process condition to be verified by the current step, and, where the state of the selected condition indicates that it is not verified, a visible textual statement of recommended operator action; providing means for the operator to electrically generate an operator response signal in response to a textural statement of recommended operator action by said visal display of said current step, including providing means for the operator to select between electrically generating an action complete response signal and an override response signal, and electrically sequentially selecting the next step in said stored procedure as the current step in response to said operator response siganl. storing electrical signals representative of step by step procedures for the complex process facility; generating sequentially from said stored electrical signals a visual representation of the current step to be executed of said step by step procedures, in the form of a textual statement of the current step and a textual statement of operator action recommended in response to said current step; generating visual prompts informing the operator of how to generate an input signal in response to the visible textual statement of recommended action; providing means for the operator to electrically generate such an input signal; indexing the current step to the next step in the stored step by step procedures in response to an input signal generated by the operator; measuring selected process parameters and generating parameter signals representative of the measured values of said selected parameters; and simultaneously with said visual representation of the current procedure step, and in response to predetermined values of said parameter signals indicative of an abnormal process condition, generating a visual indication of the existence of the abnormal condition. storong sets of electrical signals representative of a plurality of step-by-step procedures for the complex process facility; generating on an on-line basis, parameter signals representative of the current values of selected process parameters; selecting the set of electrical signals representative of one of said step-by-step procedures based upon the values of said parameters signals; generating sequentially from said selected electrical signals a visual representation of each step of the selected procedure, one step at a time, at least some of said steps including generating a visual recommendation to the operator that a transfer be made to another set of stored electrical signals representative of another one of said step-by-step procedures based upon the current values of certain of said process parameters selected by the visually presented step; providing means for an operator to generate an electrical response signal to each visually presented step; indexing said visual display to the next step in the selected procedures in response to each response signal; and providing mens for the operator to select between generating an electrical transfer signal and an electrical override signal in response to said visual recommendation, selecting in response to a transfer signal said another set of stored electrical signals representative of another one of said procedures for sequential generation of a visual representation of each step, and continuing in response to an override signal to generate a visual respresentation of each step in the first selected procedure. storing sets of electrical signals representative of a plurality of step-by-step plant procedures; generating on an on-line basis, parameter signals representative of the current values of selected plant parameters; selecting a set of electrical signals representative of one of said step-by-step procedures; generating sequentially from said selected electrical signals a visual representation of each step of the selected procedure; electrically monitoring the current values of designated ones of said parameter signals in parallel with the sequential generation of a visual representation of each step of the selected procedure; generating a visual representation of a recommendation to transfer to a designated set of stored electrical signals representative of a different procedure than the selected procedure in response to selected values of said designated parameters; providing means for an operator to select between generating an electric transfer signal and an electric override signal; and electrically selecting said different set of stored signals for generating sequentially the visual representation of each step of said different procedures in response to the generation of a transfer signal by the operator, and continuing to generate a visual representation of each step of the first selected procedure in response to an override signal. a plurality of sensors for generating sensor signals representative of the current values of a plurality of plant parameters; a storage medium for storing electrical signals representative of the steps of a plurality of step-by-step procedures as a current step, to process selected a digital computer programmed to sequentially select stored signals representative of a selected one of the steps of one of said plurality of step-by-step procedures as a current step, to process selected sensor signals to determine the status of a process condition selected by the current step and recommended action as a result thereof, and to select from said library textual statement signals representative of the current step, the status of the designated process condition and the recommended action; a display device for generating a visible display of said textual statements; and an input device including means by which an operator generates a response signal to the visible display, said digital computer being further programmed to generate in the display device selected prompts including a completion prompt to indicate completion of the action recommended by the current step and an override prompt to indicate an override of the recommended action, said input device including means for the operator to generate completion and override response signals responsive to the respective prompts. storing electrical signals representative of at least two, step-by-step procedures for the complex process facility; generating parameter status signals representative of the real-time status of predetermined process parameters and storing said parameter status signals in a common memory; electrically selecting electrical signals representative of one of said procedures as a first active procedure, presenting sequentially on a first display a visual textual statement of action recommended by each step of said first active procedure to be executed, said actions affecting the status of some of said stored parameter status signals, and simultaneously electrically monitoring selected parameter status signals stored in the common memory and generating a visual indication on said first display of any conditions represented by the real-time status of said selected parameter status signals which conflict with the first active procedure; and simultaneously electrically selecting electrical signals representative of another one of said procedures as a second active procedure, presenting sequentially on a second display a visual textual statement of action recommended by each step of said second active procedure to be executed, said actions affecting the status of certain of said stored parameter status signals, and simultaneously electrically monitoring predetermined ones of said parameter status signals stored in the common memory and generating a visual indication on said second display of any conditions represented by the real-time status of said predetermined ones of said parameter status signals which conflict with the second active procedure. a plurality of sensors for generating parameter signals representative of the current values of a plurality of facility parameters; digital processing means having memory in which at least two, step-by-step procedures and libraries of textual statements are stored and including common memory, said digital processing means being programmed, to process said parameter signals to generate parameter status signals representative of the real-time conditions in the facility, to store said parameter status signals in said common memory, to independently sequentially select a step from two different step-by-step procedures stored in memory as the current step of a first and second active procedure respectively, to independently determine as to the current step of each active procedure the condition of associated stored parameter status signals and action recommended as a result hereof, to independently select from said library, textual statements for the current step and the actions recommended thereby for each active procedure, to independently as to each active procedure simultaneously monitor certain parameter status signals stored in said common memory and when the values thereof indicate a conflict with the associated active procedure, to select a textual statement from the library indicative of the same; and display means for generating for each active procedure a visible display of the textual statement of the current step and the action recommended thereby, and when conditions so indicate, the textual statement of a conflict between the monitored parameter status signals and that active procedure. first digital computing means having said common memory and programmed to generate said parameter status signals and store them in said common memory, and to perform all the program functions associated with the first active procedure; second digital computing means programmed to perform all of the program functions associated with the second active procedure; and data link means connecting the second digital computing means with the common memory in the first digital computing means, said first display device and first input signal generating means being connected to the first digital computing means and the second display device and second input signal generating means being connected to the second digital computing means. storing electrical signals representative of at least two, step-by-step procedures for the plant; generating parameter status signals representantive of the real-time status of predetermined process parameters and storing said parameter status signals in a common memory; electronically selecting electrical signals representative of one of said procedures as a first active procedure, electrically determining for each step of said first active procedure the status of designated ones of the parameter status signals stored in said common memory, presenting sequentially on a first display a visual textual statement of action recommended by each step of said first active procedure to be executed based upon the status of said designated parameter status signals, said actions affecting the status of some of said stored parameter status signals, and simultaneously electrically monitoring selected parameter status signals stored in the common memory and generating a visual indication on said first display of any conditions represented by the real-time status of said selected parameter status signals which conflict with the first active procedure; and simultaneously electrically selecting electrical signals representative of another one of said procedures as a second active procedure, electrically determining for each step of said second active procedure the status of designated ones of the parameter status signals stored in said common memory, presenting sequentially on a second display a visual textual statement of action recommended by each step of said second active procedure to be executed based upon the status of said designated parameter status signals, said actions affecting the status of certain of said stored parameter status signals, and simultaneously electrically monitoring predetermined ones of said parameter status signals stored in the common memory and generating a visual indication on said second display of any conditions represented by the real-time status of said predetermined ones of said parameter status signals which conflict with the second active procedure. 2. The method of claim 1 including the step of updating the visual indication of the state of the selected process condition to be verified by the current step and the visible statement of recommended operator action in response to changes in the selected process condition as a result of operator response to the recommended action. 3. The method of claim 1 wherein said step of generating said visual representations includes generating the same at two separate locations and wherein the step of providing means for the operator to electrically generate an operator response signal includes providing such means at said two separate locations. 4. The method of claim 3 wherein said step of generating a visible textual statement of recommended operator action includes generating a visual indication of which of said two locations at which the action is required. 5. The method of claim 1 including the steps of electrically monitoring, while successive current steps of said stored step by step procedures are being executed, certain parameter signals representative of another process condition not being addressed by said current steps and simultaneously, with the generation of the visual display of said current step, generating a visual indication of said another process condition when the monitoring step generates an indication that said another process condition is in a specified state which warrants attention. 6. The method of claim 5 wherein said step of generating a visual indication of said another process condition includes generating a visible textual statement of action recommended in response to said another process condition when the moitoring step generates an indication that the state of the another process condition requires immediate attention and providing a visual indication that said statement of action recommended in response to said another process condition has priority over the action recommended in response to the current step. 7. The method of claim 1 including electrically logging the response signals generated by the operator. 8. The method of claim 6 including electrically removing the visible textual statement of the action recommended in response to the another process condition upon generation by the operator of either a complete or override signal. 9. The method of claim 8 wherein the steps of generating the visual representation of said current step and of generating a visual indication of said another process condition include generating said representation and indication at two spaced apart locations and wherein the step of providing means for the operator to select between electrically generating a complete signal and an override signal includes providing such means at both of said spaced apart locations. 10. The method of claim 6 including generating a prominent visual indication when the values of said specified parameters indicate that the overall status of the process facility is in a state requiring immediate operator action and a visible textual statement of a specified step by step procedure which should be implemented in response thereto, providing means by which the operator can selectively generate a transfer signal in response to the prominent visual indication, and electrically selecting a step of said specified step by step procedure in response to a transfer signal in place of the step which is the current step at the time of the generation of said prominent visual indication. 11. The method of claim 10 including in response to an override signal generated by the operator, maintaining as the current step, the step which was current at the time that the prominent visual indication was generated. 12. The method of claim 1 including the steps of continuously electrically monitoring the overall status of the process facility as represented by the values of specified parameters and generating simultaneously with the display of said current step a visual display of said overall status of the process facility. 13. A method of on-line monitoring of the execution by a human operator of procedures for a complex process facility comprising the steps of: 14. The method of claim 13 wherein the step of generating a visual indication of the abnormal condition includes generating a visible textual statement of the abnormal condition, generating a visible textual statement of operator action recommended in response to the abnormal condition, and selectively generating visual prompts for the operator to indicate a response thereto, and said method including the step of electrically assigning priorities to the action required by said current step and the recommended action in response to the abnormal condition, and wherein said step of generating the visual prompts includes only generating a display of the prompts associated with the visible textual statement of recommended action for the action having the higher priority. 15. The method of claim 14 including generating indicia to visually indicate the association of the prompts displayed with the appropriate one of the recommended action in response to the current step and the recommended action in response to the abnormal condition. 16. The method of claim 15 wherein the visible textual statement of recommended action in response to the current step is presented in one color, the visible textual statement of recommended action in response to the abnormal condition is presented in a second color, and the prompts are generated in the same color as the visible textual statement of recommended action which is in priority. 17. The method of claim 15 including automatically electrically logging the occurrence of each current step, abnormal condition and input signal generated by the operator. 18. The method of claim 17 including providing means by which an operator can generate an override signal in response to the generation of prompts associated with a priority visible textual statement of recommended action for an abnormal condition, and regenerating the prompts associated with the visible textual statement of recommended action by the current step in response to said override signal. 19. The method of claim 13 including the step of generating simultaneously with the visual representation of the current step, a visible representation of the textual statements of a selected number of most recent current steps. 20. The method of claim 13 including the step of generating simultaneously with the visual representation of the current step a visible representation of the textual statements of a selected number of subsequent steps in the step by step procedures. 21. The method of claim 20 including the step of generating also a visual representation of the textual statement of a selected number of the most recent current steps. 22. A method of on-line monitoring of the execution of procedures for a complex process facility comprising the steps of: 23. The method of claim 22 including the steps of electrically monitoring the current values of designated ones of said parameter signals in parallel with the sequential generation of a visual representation of each step of the selected procedure, generating a visual representation of a recommendation to transfer to a designated set of stored electrical signals representative of a different procedure than the selected procedure in response to selected values of said designated parameters, selecting said different set of stored signals for generating sequentially visual representation of each step of said different procedure in response to the generation of a transfer signal by the operator, and continuing to generate a visual representation of each step of the first selected procedure in response to an override signal. 24. The method of claim 22 wherein said step of generating a visual representation of each step of the selected procedure includes generating such visual representations at two separate locations, and wherein said step of providing means for an operator to generate an electrical response signal to each visually presented step includes providing such means at said two separate locations. 25. A method of on-line monitoring of the execution of procedures for a nuclear power plant comprising the steps of: 26. The method of claim 25 wherein the selected parameters include parameters indicative of a reactor trip and wherein said step of selecting a set of electrical signals representative of one of said step-by-step procedures is performed electrically in response to an indication of a reactor trip. 27. The method of claim 26 wherein at least some of said steps of the selected procedure electrically monitor certain plant parameters to verify the status of certain plant conditions and to generate a visual representation of a textual statement of recommended action selected from a library of textual statements when said certain condition is not verified. 28. The method of claim 27 wherein the step of electrically monitoring the current values of designated ones of said parameter signals in parallel with the sequential generation of a visual representation of each step of the selected procedure includes, monitoring parameters representative of plant critical safety functions and generating a visual display representative of said status of each of the critical safety functions. 29. Apparatus for on-line interactive monitoring of the execution of procedures in a complex process plant comprising: 30. The apparatus of claim 29 wherein said digital computer is further programmed to continuously monitor certain of the sensor signals to generate additional status signals representative of the current status of designated process conditions other than the conditions selected by the current steps, and to select from said library additional textual statements in response to the additional status signals, and wherein said display device includes means to generate a visible display of said additional textual statements simultaneously with the display of the textual statements associated with the current step. 31. The apparatus of claim 30 wherein said digital computer is further programmed to indicate action recommended in response to a specified status of said designated other process conditions, to determine priority between the action recommended in response to the current step and the other process conditions, to select textual statements of action recommended, and to generate prompts associated with the priority action, and wherein said display device includes means to generate a visible display of the priority action textual statement and prompts, and to visually associate the prompts with the priority action recommended. 32. The apparatus of claim 31 wherein said means for visually associating the prompts with the textual statements of priority action recommended include means for generating different portions of the display in different colors and for generating the textual statement of the priority action recommended and the prompts in the same color. 33. The apparatus of claim 32 wherein the priority action recommended is to transfer to another of said plurality of step-by-step procedures, wherein said prompts include a prompt for implementing such transfer, wherein said input device includes means to generate a transfer signal in addition to said complete and override signals and wherein said digital computer is programmed in response to said transfer signal to select said another step-by-step procedure and sequentially select the steps thereof as the current step. 34. The apparatus of claim 33 including means for generating a chronological log of the current steps, the status conditions and the operator generated response signals. 35. The apparatus of claim 34 wherein said digital computer is further programmed to continuously monitor previously determined sensor signals and to generate therefrom safety status signals representative of overall plant safety conditions, and wherein said display device includes means to generate a visible indication of overall plant safety status in response to the safety status signals simultaneously with the display of said textual statements and additional textual statements. 36. A method of on line monitoring of the simultaneous execution of two different procedures for a complex process facility comprising the steps of: 37. The method of claim 36 wherein the steps of sequentially presenting a visible textual statement of action recommended by each step of said first and second active procedures each include electrically determining the status of designated ones of the parameter status signals stored in said common memory and selecting from a library of textual statements a statement for visual presentation dependent upon the status of said designated parameter status signals, generating on the respective displays visual prompts indicating steps to take to generate an input signal in response to the selected textual statement, and presenting the next step in the procedure in response to said input signal. 38. The method of claim 37 wherein said steps of generating a visual indication of conditions which create a conflict include choosing from said library a textual statement of action recommended by the respective operator PG,66 in response to the conflict condition and generating prompts indicating to the respective operator steps to take to generate an input signal in response to the chosen statement in place of the prompts generated for the action recommended by the visibly presented step of the appropriate one of the first and second procedures. 39. Apparatus for on-line monitoring of the simultaneous execution of two different procedures for a complex process facility comprising: 40. The apparatus of claim 39 wherein said display means comprises a first display device upon which the visible display for the first active procedure is generated and a second display device upon which the visible display for the second active procedure is generated. 41. The apparatus of claim 39 wherein said digital processing means is further programmed to generate prompts to indicate steps to be taken in response to a visual statement of action recommended by the first and second procedures, and wherein said first and second display devices generate visual displays of the prompts associated with the first and second active procedures respectively, said apparatus also including first input signal generating means by which an operator generates first electrical input signals to the digital processing means as indicated by the prompts displayed by the first display device, and second input signal generating means by which an operator generates second electrical input signals to the digital processing means as indicated by the prompts displayed by the second display device, said digital processing means being programmed to select the next step as the current step in the first active procedure in response to said first input signal and to select the next step as the current step in the second active procedure in response to said second input signal. 42. The apparatus of claim 41 wherein said digital processing means comprises: 43. A method of on-line monitoring of the simultaneous execution of two different procedures for a nuclear power plant comprising the steps of:
	abstract	A Thorium molten salt energy system is disclosed that includes a proton beam source for producing a proton beam, that can vary between a first energy level and a second energy level of, where the generated proton bean can be directed into a main assembly containing both Thorium-containing molten salt and Thorium fuel rods, each containing an inner Beryllium element and an outer solid Thorium element. The generated proton beam can be shaped and directed to impinge upon Lithium within the molten salt to promote the generation of thermal neutrons and the fission of Uranium within the molten salt. The generated proton beam can also be shaped and directed to impinge upon the Beryllium within the Thorium fuel rods to promote the generation of high energy neutrons.
039309428	claims	1. An installation for a fluid having an undesirable effect, comprising a normal retaining wall for the fluid, a second wall adapted to retain the fluid in the event of breakdown of the first wall, and a space between the two walls, characterized in that the surface of the first wall disposed facing the second wall is bare and the said space is adapted to receive a trolley which can travel along said surface and which is equipped with at least one repair device for the said installation. 2. Installation according to claim 1, wherein the space contains a filling, the effect of which is greatly to reduce the fall in level in the vessel bounded by the first wall in the event of leakage, said filling being displaceable by the force of the trolley. 3. Installation according to claim 2, wherein the filling is a train of coupled elements. 4. Installation according to claim 1, wherein the second wall has an access door to the inspection space, said door being intended for the trolley. 5. Installation according to claim 4, wherein the second wall is buried, the installation comprising an underground gallery leading to the access door provided with an air-lock. 6. Installation according to claim 1, wherein the device is movable over a guide track having a similar profile to that of the primary wall. 7. Installation according to claim 6, comprising means for adjusting the distance between the guide track and the primary wall. 8. Installation according to claim 1, comprising a longitudinal trolley track laid along the inter-wall space, a transverse trolley track enabling the trolley to enter and leave the space, the trolley having two wheel sets, one for each track, at least one of the said wheel sets being vertically adjustable to allow the trolley to be deposited at will selectively on the two tracks at their intersection. 9. Installation according to claim 1, wherein the space is in the form of a body of revolution. 10. Installation according to claim 1, wherein the trolley bears at least one remotely controlled, remotely monitored inspection, maintenance and repair means. 11. Installation according to claim 1, wherein the surface of the primary wall facing the second wall bears locating elements for inspection and maintenance and repair devices. 12. Installation according to claim 2, wherein the filling is formed by separate blocks adapted to serve as storage tanks. 13. Application of the features according to claim 1 wherein said normal retaining wall is adapted to receive a water reactor vessel.
	summary
055454275	abstract	This invention relates to a process for the preparation of lithium aluminosilicate or gamma lithium aluminate ceramics having a controlled microstructure and stoichiometry.. According to this process, mixing takes place accompanied by stirring in a short chain anhydrous alcohol of an unpolymerized liquid aluminium alkoxide and optionally a silicon alkoxide with a hydrated or unhydrated lithium hydroxide, followed by the addition of water in order to hydrolyze the mixture and obtain, after drying, beta LiAlO.sub.2 powder.. This powder can be directly compacted and then sintered at temperatures of 800.degree. to 1150.degree. C. without prior calcination giving a gamma lithium aluminate ceramic with a controlled stoichiometry and microstructure (grains of 0.1 to 10 .mu.m).
	abstract	Accelerator based systems are disclosed for the generation of isotopes, such as molybdenum-98 (“99Mo”) and metastable technetium-99 (“99mTc”) from molybdenum-98 (“98Mo”). Multilayer targets are disclosed for use in the system and other systems to generate 99mTc and 98Mo, and other isotopes. In one example a multilayer target comprises a first, inner target of 98Mo surrounded, at least in part, by a separate, second outer layer of 98Mo. In another example, a first target layer of molybdenum-100 is surrounded, at least in part, by a second target layer of 98Mo. In another example, a first inner target comprises a Bremsstrahlung target material surrounded, at least in part, by a second target layer of molybdenum-100, surrounded, at least in part, by a third target layer of 98Mo.
048266507	summary	BACKGROUND OF THE INVENTION This invention relates to ultrasound testing. More particularly, the invention relates to remote ultrasound testing of a lattice-like nuclear reactor vessel top guide and sets forth a protocol wherein testing can occur without lattice disassembly. STATEMENT OF THE PROBLEM Reactors constitute extremely hostile environments for inspection of any kind. First, reactors are notorious for their radioactivity. Secondly, the internals of the reactors are frequently mechanically inaccessible. A classic example of such inaccessibility is the top guide used in a boiling water reactor. The top guide comprises a series of bars in the order of 1/4 inch thick and 9 to 13 inches in width. The bars each span the full diameter of the reactor vessel which can be in the order of 22 feet. The bars are grooved. The grooves extend through half the width of the bars. The grooves in parallel bars extend in the same direction. For example, one set of bars has its grooves upwardly disposed; bars at right angles have their grooves downwardly disposed. The bars are assembled in a lattice by confronting their respective grooves. They come together in a lattice-like structure that is not unlike the cardboard separators found in wine cases. This continuous lattice, once assembled, is welded at the side edges to a ring on the reactor vessel. The bars of the lattice are not otherwise welded or attached to themselves. The lattice defines a number of discrete square cells bounded by the intersecting bars forming parallel sides. The function of the top guide is for preserving the vertical and rotational orientation of square sectioned elongate fuel assemblies supported on a core plate some 14 feet below the top guide. The top guide braces and maintains the top of the fuel assemblies. The fuel assemblies are maintained vertical by the top guide. Moreover, the top guide forms the support surface from which the rotational orientation of the fuel assemblies is maintained. By bracing the fuel assemblies to the top guide, the vital cruciform shaped interstitial area between the fuel assemblies for control rod penetration and moderation of the reaction is maintained. Unfortunately, the top guide is in an ideal place for cracking to occur. First, the bars making up the top guide have numerous discontinuities. These discontinuities include the very grooves which enable the top guide bars to be assembled in their latticelike configuration. Additionally, various other discontinuities are present in the bars. For example, notches for the hanging of poison curtains used in the start-up of older reactors constitute such discontinuities. Further, the bars in spanning the reactor vessel and aligning the fuel assemblies are subject to stress. This stress is aggravated by the fact that the bars at their respective points of intersection are not fastened one to another. Additionally, the bars making up the top guide are subject to high radiation dosage. Consequently, the bars are ideal sites for irradiation assisted stress corrosion cracking (IASCC). IASCC occurs in many stainless steels when an irradiation dosage exceeds 2.times.10.sup.21 neutrons per cm.sup.2. Thus, when older reactors approach this dosage level, there is high motive to examine the top guide for IASCC. It goes without saying that removal and disassembly of the bulky radioactive lattice comprising the top guide is possible--but prohibitively inconvenient and expensive. SUMMARY OF THE PRIOR ART Ultrasound testing is a nondestructive technique well known. In the usual application, an ultrasound transducer is manually fastened to an article --typically piping--to be nondestructively tested. A transducer imparts an ultrasound pulse to the article to be tested. The pulse fully penetrates the article to be tested and is reflected. The pulse upon being reflected is detected, usually at the very transducer which initiated the pulse. The detection of the pulse at the transducer is recorded and analyzed. It is conventional to time the receipt of reflected pulses. By noting the reflected pulses, one can determine whether an intact part at an extremity causes the return pulse or an interfering crack at a location other than the extremity causes reflection. Since transducers, power equipment, recorders, monitors and computers for analyzing ultrasound are all known and conventional, further description will not be set forth herein. For more complete detail on the testing referred to herein, the readers attention is invited to the publication UT Operator Training for Intergranular Stress Corrosion Cracking published by the Electric Power Research Institute Nondestructive Evaluation Center of Charlotte, N.C., 1983. SUMMARY OF THE INVENTION In a boiling water reactor, an apparatus and process for ultrasound inspection of the top guide is disclosed. The top guide constitutes a lattice of stainless steel bars overlying the core plate and being assembled at confronting grooves with the lattice mounted at the side edges to the reactor pressure vessel. This lattice braces the upper ends of the vertically supported fuel assemblies in their requisite orientation and spaced apart relation to enable among other things the required spatial interval to be maintained for control rod moderation of the reaction. Because of the proximity of the top guide to the fuel assemblies, the individual bars making up the lattice need to be checked for cracking, especially that cracking produced by irradiation assisted stress crack corrosion. With a defined cell in the lattice emptied of its contained and adjoining fuel assemblies, there is disclosed an ultrasound test for cracking. A sound transducer on a first special frame sweeps horizontally across the top of a bar interrogating the bar with vertical longitudinal ultrasound waves for detecting horizontal cracks. Similarly, a sound transducer on a second special frame sweeps vertically across the side of a bar interrogating the bar with angularly incident horizontal shear ultrasound waves for detecting vertical cracks. Nondestructive testing of the lattice assembly occurs without required disassembly. Two test frames are disclosed, a first test frame for checking the lattice assembly for horizontal cracking and a second test frame for checking the lattice for vertical cracking. Before the test, it is required that all fuel assemblies adjacent the bars to be tested are removed. A first test frame has the cross section of of a fuel channel and is configured for detecting vertical cracking. This frame engages orthogonally disposed bars at their defined corners and comes to rest. A ball screw driven carriage is given vertical excursion along each bar of the defined corner. Each bar at the defined corner is interrogated by ultrasound from paired transducers. The paired transducers are oriented to have opposed acoustical angles of incidence to the bar in the order of 70.degree. in a horizontal plane towards the bars. One transducer sweeping each bar interrogates the bar with horizontal shear wave ultrasound towards the corner defined by the bar; the remaining transducer sweeping each bar interrogates the bar with horizontal shear wave ultrasound away from the corner defined by the bar. The vertically sweeping transducers therefore interrogate each bar with acoustical signals horizontally and in opposite directions to detect vertical cracking. The second test frame is configured for detecting horizontal cracking. The second test frame is configured for precise placement on the lattice overlying the portion of a bar to be tested. In the preferred embodiment, the carriage rest one leg on the bar to be tested and its rear two legs on an intersecting bar on the top of the top guide assembly. The second test frame includes a carriage mounted to a ball screw drive. This carriage contains an ultrasound transducer and sweeps horizontally the transducer immediately over the bar to be tested. The horizontally moving transducer interrogates the bar with vertically interrogating sound to locate horizontal cracking. In both types of test frames, each transducer (one transducer for vertical acoustical interrogation and four transducers for horizontal acoustical interrogation) couple through the demineralized water of the reactor to enable complete nondestructive testing of the top guide without costly disassembly.
	description	This application is a continuation of U.S. patent application Ser. No. 10/743,265, filed on Dec. 23, 2003 now U.S. Pat. No. 7,247,866, which is based on and claims the benefit of priority from European Patent Application No. 02080454.8, filed Dec. 23, 2002, and European Patent Application No. 03075086.3, filed Jan. 13, 2003, the contents of each being hereby incorporated by reference in their entireties. 1. Field of the Invention The invention relates generally to a lithographic apparatus, and more specifically to a contamination barrier for passing through radiation from a radiation source and for capturing debris coming from the radiation source. 2. Description of Related Art A contamination barrier for a lithographic apparatus is known from, for example, the international patent application WO 02/054153. The contamination barrier is normally positioned in a wall between two vacuum chambers of a radiation system of a lithographic projection apparatus. In a lithographic projection apparatus, the size of features that can be imaged onto a substrate is limited by the wavelength of projection radiation. To produce integrated circuits with a higher density of devices, and hence higher operating speeds, it is desirable to be able to image smaller features. While most current lithographic projection apparatus employ ultraviolet light generated by mercury lamps or excimer lasers, it has been proposed to use shorter wavelength radiation in the range 5 to 20 nm, especially around 13 nm. Such radiation is termed extreme ultraviolet (EUV), or soft x-ray, and possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or synchrotron radiation from electron storage rings. Apparatus using discharge plasma sources are described in: W. Partlo, I. Fomenkov, R. Oliver, D. Birx, “Development of an EUV (13.5 nm) Light Source Employing a Dense Plasma Focus in Lithium Vapor”, Proc. SPIE 3997, pp. 136-156 (2000); M. W. McGeoch, “Power Scaling of a Z-pinch Extreme Ultraviolet Source”, Proc. SPIE 3997, pp. 861-866 (2000); W. T. Silfvast, M. Klosner, G. Shimkaveg, H. Bender, G. Kubiak, N. Formaciari, “High-Power Plasma Discharge Source at 13.5 and 11.4 nm for EUV lithography”, Proc. SPIE 3676, pp. 272-275 (1999); and K. Bergmann et al., “Highly Repetitive, Extreme Ultraviolet Radiation Source Based on a Gas-Discharge Plasma”, Applied Optics, Vol. 38, pp. 5413-5417 (1999). EUV radiation sources may require the use of a rather high partial pressure of a gas or vapor to emit EUV radiation, such as discharge plasma radiation sources referred to above. In a discharge plasma source, for example, a discharge is created between electrodes, and a resulting partially ionized plasma may subsequently be caused to collapse to yield a very hot plasma that emits radiation in the EUV range. The very hot plasma is quite often created in Xe, since a Xe plasma radiates in the Extreme UV (EUV) range around 13.5 nm. For an efficient EUV production, a typical pressure of 0.1 mbar is required near the electrodes to the radiation source. A drawback of having such a rather high Xe pressure is that Xe gas absorbs EUV radiation. For example, 0.1 mbar Xe transmits over 1 m only 0.3% EUV radiation having a wavelength of 13.5 nm. It is therefore required to confine the rather high Xe pressure to a limited region around the source. To reach this, the source can be contained in its own vacuum chamber that is separated by a chamber wall from a subsequent vacuum chamber in which the collector mirror and illumination optics may be obtained. The chamber wall can be made transparent to EUV radiation by a number of apertures in the wall provided by a contamination barrier or so-called “foil trap,” such as the one described in European Patent application number EP-A-1 057 079, which is incorporated herein by reference. In EP-A-1 057 079 a foil trap has been proposed to reduce the number of particles propagating along with the EUV radiation. This foil trap consists of a number of lamella shaped walls, which are close together in order to form a flow resistance, but not too close so as to let the radiation pass without substantially obstructing it. The lamellas can be made of very thin metal platelets, and are positioned near the radiation source. The lamellas are positioned in such a way, that diverging EUV radiation coming from a radiation source, can easily pass through, but debris coming from the radiation source is captured. Debris particles collide with gas inside the foil trap, are scattered thereby, and eventually collide with the lamellas and stick to these lamellas. The lamellas, however, absorb some EUV radiation and heat. Moreover, they are heated by colliding debris particles. This results in significant heating of the lamellas and a supporting structure which supports the lamellas. Since optical transmission is very important in a lithographic projection apparatus, mechanical deformation is not allowed. Therefore, it is an aspect of the present invention to provide a contamination barrier in which disadvantageous deformation of lamellas is minimized. It is another aspect of embodiments of the present invention to provide a foil trap for a lithographic projection apparatus. The foil trap forms an open structure to let radiation coming from, for example, an EUV source, pass unhindered. The foil trap comprises lamellas arranged to capture debris particles coming from the radiation source. The lamellas are extending in a radial direction from a foil trap axis. In order to prevent mechanical stress, the lamellas are slidably connected in grooves of one or both of the rings. In this way, the lamellas can expand easily and mechanical stress is avoided, so that there is no deformation of the lamellas. At least one of the outer ends of the lamellas is thermally connected to a ring. This ring may be cooled by a cooling system. In a preferred embodiment, the foil trap comprises a shield to protect the inner ring from being hit by the EUV beam. This aspect is achieved according to embodiments of the present invention by a contamination barrier. The contamination barrier comprises a number of lamellas extending in a radial direction from a main axis, each of the lamellas being positioned in a plane that contains the main axis, characterized in that the contamination barrier comprises an inner ring and an outer ring and that each of the lamellas is slidably positioned at least one of its outer ends in grooves of at least one of the inner and outer ring. Embodiments also provide for a contamination barrier that passes through radiation from a radiation source and captures debris coming from the radiation source. The contamination barrier includes an inner ring, an outer ring, and a plurality of lamellas that extend in a radial direction from a main axis. Each of the lamellas is positioned in a respective plane that includes the main axis. At least one outer end of each of the lamellas is slidably connected to at least one of the inner and outer ring. Embodiment of the invention further provide for a contamination barrier that passes through radiation from a radiation source and captures debris coming from the radiation source. The contamination barrier includes a plurality of lamellas, and a support structure that slidably engages the lamellas. The lamellas and the support structure are configured and arranged to allow the lamellas to expand and contract in response to changes in temperature. Embodiment of the invention also provide for a contamination barrier that permits radiation to pass therethrough and captures debris from a radiation source generated by the radiation source. The contamination barrier includes a support structure and a plurality of thin plate members mounted on the support structure. The radiation propagates along an optical axis and the thin plate members are disposed along a plane that includes the axis. The plate members are slidably movable relative to the support structure. By slidably positioning one of the outer ends of a lamella, the lamella can expand in a radial direction without the appearance of mechanical tension which may create a deformation of the lamella. Preferably, the lamellas are thermally connected to at least one of the inner and outer ring. In this way, heat from the lamellas will be transported to the rings. Note that a thermal connection is not necessarily a mechanical connection; heat conduction from the lamellas to the rings is even possible when the connection is slidable. Furthermore, a connection using a heat conducting gel between the lamellas and the rings is possible. In an embodiment, the contamination barrier comprises a first shield arranged to protect the inner ring from being hit by radiation from the radiation source. In this way, the heating of the inner ring is limited. Preferably, the contamination barrier comprises a second shield arranged to block thermal radiation from the first shield. By blocking the heat radiation coming from the first heat shield, the beam going into the collector is not exposed by unwanted radiation. In a further embodiment, upstream of the first shield, with respect to the direction of propagation of the radiation emitted by the radiation source along the main axis, a third shield is provided, constructed and arranged to reduce heating of the first shield caused by direct radiation from the radiation source. The third shield prevents the first shield from being excessively heated by direct radiation from the radiation source, and consequently further reduces heat radiating from the first shield towards the collector. In an embodiment, there is provided a contamination barrier configured to permit radiation from a radiation source to pass through and to capture debris from the radiation source. The contamination barrier includes a support structure, a plurality of plate members arranged on the support structure and extending in a radial direction from an axis of the support structure, and a shield configured to block at least part of the support structure from being hit by radiation or debris from the radiation source. In another embodiment, there is provided a lithographic projection apparatus that includes a radiation system configured to form a beam of radiation. The radiation system includes a contamination barrier configured to permit radiation from a radiation source to pass through and to capture debris from the radiation source. The contamination barrier includes a support structure, a plurality of plate members arranged on the support structure and extending in a radial direction from an axis of the support structure, and a shield configured to block at least part of the support structure from being hit by radiation or debris from the radiation source. The lithographic apparatus also includes a support structure to support a patterning structure to be irradiated by a beam of radiation to pattern the beam of radiation, a substrate support to support a substrate, and a projection system to image an irradiated portion of the patterning structure onto a target portion of the substrate. In a further embodiment, there is provided a method of manufacturing an integrated structure by a lithographic process. The method includes generating radiation with a radiation source, capturing debris from the radiation source using a contamination barrier that includes a support structure, a plurality of plate members arranged on the support structure and extending in a radial direction from an axis of the support structure, and a shield configured to block at least part of the support structure from being hit by radiation or debris from the radiation source. The method also includes patterning the radiation with a patterning structure, and imaging the patterned radiation onto a target portion of a substrate. In an embodiment, the contamination barrier also comprises at least one cooling spoke to support the first shield, wherein the cooling spoke is thermally connected to the outer ring. The cooling spoke can be made of metal or any other heat conductive material, such as carbon. The cooling spoke not only supports the first shield, but also transports heat from the first heat shield to the outer ring. In an embodiment, the first shield comprises a number of shield members, each shield member being connected to the outer ring via a separate cooling spoke. In a further embodiment, the contamination barrier comprises a first cooling device or structure that is arranged to cool at least one of the first and second shield. In this case, a cooling spoke as described above is not necessary. The cooling device may comprise a cooling system in which a cooling fluid is used to remove the heat away from the contamination barrier. The cooling device may be part of a cooling system used in a collector. In this way, the cooling device will be in the shadow of the heat shields, and thus not blocking the EUV radiation beam. Preferably, the heat shields are supported by the cooling device. Vibrations coming from the cooling system will not reach the lamellas of the contamination barrier because the inner ring is not fixed to the cooling system. In yet another embodiment, the contamination barrier comprises a second cooling device arranged to cool the inner ring. If the cooling ring is cooled directly, there will be no need for a heat shield. In a further embodiment, the contamination barrier comprises a third cooling device arranged to cool the outer ring. If the lamellas are slidably connected to the inner ring and thermally connected to the outer ring, the heat form the lamellas will go to the outer ring. The outer ring can be easily cooled by for example water cooling, since it is outside the EUV optical path. Preferably, the lamellas are curved in the respective planes, and the inner and outer ring are shaped as slices of a conical pipe. If the surfaces of the outer and inner ring are focused on the EUV source, the EUV beam will be blocked by the rings as little as possible. Only the inner ring will be in the way for the EUV beam, which is unavoidable. However, no light is lost, as the collector is unable to collect radiation in this solid angle anyway. In a further embodiment, a first side of the lamellas, at least in use facing the radiation source, is thicker than the rest of the lamellas. In this way, the influence of minor warping of the lamellas is reduced. The warped lamellas should be positioned in the shadow of the thick front side of the lamellas. This measure results in better uniformity of the transmission of the contamination barrier. The present invention also relates to a radiation system comprising a contamination barrier as described above, and a collector for collecting radiation passing the contamination barrier. It is another aspect of the present invention to extend the lifetime of a collector of a radiation system. Therefore, embodiments of the invention relate to a radiation system comprising: a contamination barrier for passing through radiation from a radiation source and for capturing debris coming from the radiation source, the contamination barrier comprising a number of lamellas, and a collector for collecting radiation passing the contamination barrier, characterized in that a surface of the lamellas is covered with the same material as an optical surface of the collector. In an embodiment, there is provided a radiation system that includes a contamination barrier configured to permit radiation from a radiation source to pass through and to capture debris coming from the radiation source, the contamination barrier comprising a plurality of lamellas, the surface of the lamellas comprising a material, and a collector configured to collect radiation from the contamination barrier, an optical surface of the collector comprising a material that is the same as the material of the surface of the lamellas. In an embodiment, there is provided a lithographic projection apparatus that includes a radiation system to form a beam of radiation. The radiation system includes a contamination barrier configured to permit radiation from a radiation source to pass through and to capture debris coming from the radiation source, the contamination barrier comprising a plurality of lamellas, the surface of the lamellas comprising a material, and a collector configured to collect radiation from the contamination barrier, an optical surface of the collector comprising a material that is the same as the material of the surface of the lamellas. The lithographic apparatus also includes a support structure to support a patterning structure to be irradiated by a beam of radiation to pattern the beam of radiation, a substrate support to support a substrate, and a projection system to image an irradiated portion of the patterning structure onto a target portion of the substrate. In a further embodiment, there is provided a method of manufacturing a device by a lithographic process. The method includes passing radiation from a radiation source through a contamination barrier comprising a plurality of lamellas, the surface of the lamellas comprising a material and the contamination barrier capturing debris from the radiation source, collecting radiation from the contamination barrier with a collector, an optical surface of the collector comprising a material that is the same as the material of the surface of the lamellas, patterning radiation from the collector, and projecting the patterned radiation onto a target portion of a substrate. Embodiments also provide a radiation system that includes a contamination barrier that passes through radiation from a radiation source and captures debris coming from the radiation source, and a collector that collects radiation passing the contamination barrier. The contamination barrier includes an inner ring, an outer ring, and a plurality of lamellas that extend in a radial direction from a main axis. Each of the lamellas is positioned in a respective plane that includes the main axis, and at least one outer end of each of the lamellas is slidably connected to at least one of the inner and outer ring. Another embodiment includes a radiation system that includes a contamination barrier that passes through radiation from a radiation source and captures debris coming from the radiation source, and a collector that collects radiation passing the contamination barrier. The contamination barrier includes a plurality of lamellas, and a surface of the lamellas is covered with the same material as an optical surface of the collector. When material is sputtered off of the contamination barrier onto the collector, the life time of the collector is only minimally influenced if the materials are equal. Embodiments of the invention also relate to a lithographic projection apparatus comprising: a support structure constructed and arranged to hold a patterning device, to be irradiated by a projection beam of radiation to pattern the projection beam of radiation, a substrate table constructed and arranged to hold a substrate, and a projection system constructed and arranged to image an irradiated portion of the patterning device onto a target portion of the substrate, wherein the projection apparatus comprises a radiation system for providing a projection beam of radiation as described above. A further embodiment is directed to a lithographic projection apparatus. The lithographic projection apparatus includes a radiation system to provide a beam of radiation, a support structure to support a patterning structure to be irradiated by a beam of radiation to pattern said beam of radiation, a substrate support to support a substrate, and a projection system to image an irradiated portion of the patterning structure onto a target portion of the substrate. The radiation system includes a contamination barrier that passes through radiation from a radiation source and captures debris coming from the radiation source and a collector for collecting radiation passing the contamination barrier. The contamination barrier includes an inner ring, an outer ring, and a plurality of lamellas that extend in a radial direction from a main axis. Each of the lamellas is positioned in a respective plane that includes the main axis, and each of the lamellas is slidably connected to at least one of the inner and outer ring. Yet another embodiment is directed to a lithographic projection apparatus that includes a radiation system to provide a beam of radiation, a support structure to support a patterning structure to be irradiated by a beam of radiation to pattern the beam of radiation, a substrate support to support a substrate; and a projection system to image an irradiated portion of the patterning structure onto a target portion of the substrate. The radiation system includes a contamination barrier that passes through radiation from a radiation source and captures debris coming from the radiation source, and a collector that collects radiation passing the contamination barrier. The contamination barrier includes a plurality of lamellas, wherein a surface of the lamellas is covered with the same material as an optical surface of the collector. Another embodiment is directed to a method of manufacturing an integrated structure by a lithographic process. The method includes radiating a beam of radiation through a radiation system, providing a support structure to support a patterning structure to be irradiated by the beam of radiation to pattern said beam of radiation, providing a substrate support to support a substrate, and providing a projection system to image an irradiated portion of the patterning structure onto a target portion of the substrate. Radiating the beam of radiation through the radiation system includes passing radiation from a radiation source through a contamination barrier comprising an inner ring, an outer ring, and a plurality of lamellas extending in a radial direction from a main axis. Each of the lamellas are positioned in a respective plane that comprises the main axis, and at least one outer end of each of the lamellas is slidably connected to at least one of the inner and outer ring. Radiating the beam of radiation also includes collecting radiation passing the contamination barrier. Embodiments of the invention also relate to a method of manufacturing an integrated structure by a lithographic process. The method includes radiating a beam of radiation through a radiation system, providing a support structure to support a patterning structure to be irradiated by the beam of radiation to pattern said beam of radiation, providing a substrate support to support a substrate, and providing a projection system to image an irradiated portion of the patterning structure onto a target portion of the substrate. Radiating the beam of radiation through the radiation system includes passing radiation from a radiation source through a contamination barrier that includes a plurality of lamellas, capturing debris from the radiation source, and collecting radiation passing the contamination barrier. A surface of the lamellas is covered with the same material as an optical surface of the collector. Embodiments of the invention are also directed to a method of manufacturing an integrated structure by a lithographic process. The method includes generating a beam of radiation with a radiation source, capturing debris from the radiation source, collecting radiation passing the contamination barrier patterning the beam of radiation with a patterning structure, and imaging an irradiated portion of the patterning structure onto a target portion of a substrate. Capturing debris comprises providing a support structure and a plurality of lamellas that are slidably engaged with the support structure so as to allow the plurality of lamellas to expand and contract in response to changes in temperature. The term “patterning device” as here employed should be broadly interpreted as referring to a device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate; the term “light valve” can also be used in this context. Generally, the pattern will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit or other device (see below). Examples of such patterning devices include: A mask. The concept of a mask is well known in lithography, and it includes mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Placement of such a mask in the radiation beam causes selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask, according to the pattern on the mask. In the case of a mask, the support structure will generally be a mask table, which ensures that the mask can be held at a desired position in the incoming radiation beam, and that it can be moved relative to the beam if so desired; A programmable mirror array. One example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that (for example) addressed areas of the reflective surface reflect incident light as diffracted light, whereas unaddressed areas reflect incident light as undiffracted light. Using an appropriate filter, the undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind; in this manner, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. An alternative embodiment of a programmable mirror array employs a matrix arrangement of tiny mirrors, each of which can be individually tilted about an axis by applying a suitable localized electric field, or by employing a piezoelectric actuation device. Once again, the mirrors are matrix-addressable, such that addressed mirrors will reflect an incoming radiation beam in a different direction to unaddressed mirrors; in this manner, the reflected beam is patterned according to the addressing pattern of the matrix-addressable mirrors. The required matrix addressing can be performed using suitable electronic means. In both of the situations described hereabove, the patterning device can comprise one or more programmable mirror arrays. More information on mirror arrays as here referred to can be gleaned, for example, from U.S. Pat. No. 5,296,891 and U.S. Pat. No. 5,523,193, and PCT patent applications WO 98/38597 and WO 98/33096, which are incorporated herein by reference. In the case of a programmable mirror array, the support structure may be embodied as a frame or table, for example, which may be fixed or movable as required; and A programmable LCD array. An example of such a construction is given in U.S. Pat. No. 5,229,872, which is incorporated herein by reference. As above, the support structure in this case may be embodied as a frame or table, for example, which may be fixed or movable as required. For purposes of simplicity, the rest of this text may, at certain locations, specifically direct itself to examples involving a mask and mask table; however, the general principles discussed in such instances should be seen in the broader context of the patterning device as hereabove set forth. Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning device may generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising one or more dies) on a substrate (silicon wafer) that has been coated with a layer of radiation-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. In current apparatus, employing patterning by a mask on a mask table, a distinction can be made between two different types of machine. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion in one go; such an apparatus is commonly referred to as a wafer stepper or step and repeat apparatus. In an alternative apparatus—commonly referred to as a step and scan apparatus—each target portion is irradiated by progressively scanning the mask pattern under the projection beam in a given reference direction (the “scanning” direction) while synchronously scanning the substrate table parallel or anti parallel to this direction; since, in general, the projection system will have a magnification factor M (generally <1), the speed V at which the substrate table is scanned will be a factor M times that at which the mask table is scanned. More information with regard to lithographic devices as here described can be gleaned, for example, from U.S. Pat. No. 6,046,792, incorporated herein by reference. In a manufacturing process using a lithographic projection apparatus, a pattern (e.g. in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation sensitive material (resist). Prior to this imaging step, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g. an IC. Such a patterned layer may then undergo various processes such as etching, ion implantation (doping), metallization, oxidation, chemo mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc. Further information regarding such processes can be obtained, for example, from the book “Microchip Fabrication: A Practical Guide to Semiconductor Processing”, Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0 07 067250 4, incorporated herein by reference. For the sake of simplicity, the projection system may hereinafter be referred to as the “lens”; however, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a “lens”. Further, the lithographic apparatus may be of a type having two or more substrate tables (and/or two or more mask tables). In such “multiple stage” devices the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Dual stage lithographic apparatus are described, for example, in U.S. Pat. No. 5,969,441 and WO 98/40791, both incorporated herein by reference. Although specific reference may be made in this text to the use of the apparatus according to the invention in the manufacture of ICs, it should be explicitly understood that such an apparatus has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “reticle”, “wafer” or “die” in this text should be considered as being replaced by the more general terms “mask”, “substrate” and “target portion”, respectively. In the present document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range 5-20 nm), as well as particle beams, such as ion beams or electron beams. FIG. 1 schematically depicts a lithographic projection apparatus 1 according to a particular embodiment of the invention. The apparatus comprises: a radiation system Ex, IL, for supplying a projection beam PB of radiation (e.g. EUV radiation) with a wavelength of 11-14 nm. In this particular case, the radiation system also comprises a radiation source LA; a first object table (mask table) MT provided with a mask holder for holding a mask MA (e.g. a reticle), and connected to a first positioning device PM for accurately positioning the mask with respect to item PL; a second object table (substrate table) WT provided with a substrate holder for holding a substrate W (e.g. a resist coated silicon wafer), and connected to a second positioning device PW for accurately positioning the substrate with respect to item PL; and a projection system (“lens”) PL for imaging an irradiated portion of the mask MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. The term “object table” as used herein can also be considered or termed as an object support. It should be understood that the term object support or object table broadly refers to a structure that supports, holds, or carries an object, such as a mask or a substrate. As here depicted, the apparatus is of a reflective type (i.e. has a reflective mask). However, in general, it may also be of a transmissive type, for example (with a transmissive mask). Alternatively, the apparatus may employ another kind of patterning device, such as a programmable mirror array of a type as referred to above. The source LA (e.g. a laser-produced plasma or a discharge plasma EUV radiation source) produces a beam of radiation. This beam is fed into an illumination system (illuminator) IL, either directly or after having traversed conditioning means, such as a beam expander Ex, for example. The illuminator IL may comprise an adjusting device AM for setting the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the beam. In addition, it will generally comprise various other components, such as an integrator IN and a condenser CO, see FIG. 1. In this way, the beam PB impinging on the mask MA has a desired uniformity and intensity distribution in its cross section. It should be noted with regard to FIG. 1 that the source LA may be within the housing of the lithographic projection apparatus (as is often the case when the source LA is a mercury lamp, for example), but that it may also be remote from the lithographic projection apparatus, the radiation beam which it produces being led into the apparatus (e.g. with the aid of suitable directing mirrors). This latter scenario is often the case when the source LA is an excimer laser. Embodiments of the current invention, and claims, encompass both of these scenarios. The beam PB subsequently intercepts the mask MA, which is held on a mask table MT. Having traversed the mask MA, the beam PB passes through the lens PL, which focuses the beam PB onto a target portion C of the substrate W. With the aid of the second positioning device PW (and an interferometric measuring device IF), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the beam PB. Similarly, the first positioning device PM can be used to accurately position the mask MA with respect to the path of the beam PB, e.g. after mechanical retrieval of the mask MA from a mask library, or during a scan. In general, movement of the object tables MT, WT will be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which are not explicitly depicted in FIG. 1. However, in the case of a wafer stepper (as opposed to a step-and-scan apparatus) the mask table MT may just be connected to a short stroke actuator, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The depicted apparatus can be used in two different modes: 1. In step mode, the mask table MT is kept essentially stationary, and an entire mask image is projected in one go (i.e. a single “flash”) onto a target portion C. The substrate table WT is then shifted in the x and/or y directions so that a different target portion C can be irradiated by the beam PB; and 2. In scan mode, essentially the same scenario applies, except that a given target portion C is not exposed in a single “flash”. Instead, the mask table MT is movable in a given direction (the so called “scan direction”, e.g. the y direction) with a speed v, so that the projection beam PB is caused to scan over a mask image; concurrently, the substrate table WT is simultaneously moved in the same or opposite direction at a speed V=Mv, in which M is the magnification of the projection system PL (typically, M=¼ or ⅕). In this manner, a relatively large target portion C can be exposed, without having to compromise on resolution. FIG. 2 shows an embodiment of the lithographic projection apparatus 1 of FIG. 1, comprising a radiation system 3 (i.e. “source-collector module”), an illumination optics unit 4, and the projection system PL. The radiation system 3 is provided with a radiation source LA which may comprise a discharge plasma source. The radiation source LA may employ a gas or vapor, such as Xe gas or Li vapor in which a very hot plasma can be created to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma is created by causing a partially ionized plasma of an electrical discharge to collapse onto an optical axis 20. Partial pressures of 0.1 mbar of Xe gas, Li vapor or any other suitable gas or vapor may be required for efficient generation of the radiation. The radiation emitted by the radiation source LA is passed from a source chamber 7 into a collector chamber 8 via a foil trap 9. The foil trap 9 comprises a channel structure such as, for example, described in detail in European patent application EP-A-1 057 079, which is incorporated herein by reference. The term “foil trap” as used herein can also be considered or termed a contamination barrier. It should be understood that the term foil trap or contamination barrier broadly refers to a structure that captures debris coming from the radiation source LA. The collector chamber 8 comprises a radiation collector 10 which may be formed by a grazing incidence collector. Radiation passed by the radiation collector 10 is reflected off a grating spectral filter 11 or mirror to be focused in a virtual source point 12 at an aperture in the collector chamber 8. From chamber 8, the projection beam 16 is reflected in the illumination optics unit 4 via normal incidence reflectors 13, 14 onto a reticle or mask positioned on reticle or mask table MT. A patterned beam 17 is formed which is imaged in projection optics system PL via reflective elements 18, 19 onto wafer stage or substrate table WT. More elements than shown may generally be present in illumination optics unit 4 and projection system PL. FIG. 3 shows a downstream and a cross-sectional view, respectively, of a foil trap 9 with a plurality of lamellas 31, 32 according to an embodiment of the invention. The foil trap 9 comprises an inner ring 33 and an outer ring 35. Preferably, the inner ring 33 and the outer ring 35 are shaped as slices of a conical pipe, wherein a minimum diameter do of the outer ring 35 is larger than a minimum diameter di of the inner ring 33. Preferably, both conical rings 33, 35 share the same main axis 34 and focus. Preferably, the foil trap 9 is arranged in a lithographic projection apparatus, in such a way that the main axis 34 of the foil trap 9 and the optical axis 20 of the radiation system 3 coincide, see FIG. 2. In FIG. 4, the foil trap 9, as shown, comprises a heat shield 41. The heat shield 41 is supported by two cooling spokes 44, 45 which are mechanically and thermally connected to the outer ring 35. At the center of the foil trap 9, the cooling spokes 44, 45 connect to a spindle 47, which supports the heat shield 41. The heat shield 41 comprises a disk, which avoids the inner ring 33 from being hit by the emitted radiation and heat from the radiation source LA. In this way, the heat shield 41 shields off the inner ring 33. The cooling spokes 44, 45, the spindle 47 and the heat shield 41 are preferably made of a good heat conductor. In this way, heat developed on the heat shield 41, may easily be transferred to the outer ring 35 via the cooling spokes 44, 45. Alternatively, the heat shield 41 may comprise two (or more) disc parts, each disc part being connected to one cooling spoke 44, 45. In this case, the spindle 47 will also be divided into two (or more) parts. FIG. 5 shows a perspective view of the inner ring 33 according to an embodiment of the invention. The inner ring 33 comprises a plurality of grooves 51. Preferably, two grooves 53, opposite to one another, have a relative larger width than the other grooves. These larger grooves 53 are provided to pass the cooling spokes 44, 45. According to embodiments of the invention, the inner ring 33 is only supported mechanically by the plurality of lamellas 31, 32 and is not connected to anything other than the lamellas 31, 32. FIG. 6 shows a detailed example of the lamella 31, 32 of the foil trap 9 according to an embodiment of the invention. The lamella 31, 32 is a very thin platelet having two curved edges 60, 61, a straight outer edge 65, and an inner edge 62 having an indentation 63. The lamella 31, 32 has a height h and a width w, see FIG. 6. The outer edge 65 is mechanically connected to the outer ring 35, see FIG. 4. The inner edge 62 is inserted into one of the grooves 51 of the inner ring 33, see FIG. 5. Preferably, the lamellas 31, 32 are soldered or welded to the outer ring 35. In this way, a good thermal contact is provided and approximately all the heat absorbed by the lamellas, is transported to the outer ring 35. In one embodiment, the outer ring 35 is cooled by a cooling device, not shown, to remove the heat from the foil trap 9. In an embodiment of the invention, the foil trap 9 also comprises a second heat shield in order to block thermal radiation from the first heat shield 41. FIG. 7 shows a foil trap 9 with first and second heat shields 41, 71. In an embodiment, the second heat shield 71 comprises a disc, positioned inside the inner ring 33 and situated at the back end (i.e. down stream side) of this inner ring 33. In another embodiment, the cooling spoke 44, 45, 47 is absent. In this case, the first and/or second shields 41, 71 are cooled by a cooling device, arranged in a way known by a person skilled in the art. The cooling device may comprise a water cooling system. This water cooling system can be part of a cooling system of the collector 10 of the radiation system 3. In this case, the shields 41, 71 are supported by the cooling device. In yet another embodiment, the inner ring 33 is cooled by a cooling device. The cooling device for cooling the shields 41; 71 and the cooling device for cooling the inner ring 33, may be one. The foil trap 9 may be focused on the radiation source 6. It is also possible to construct a foil trap 9 without a real focus. In any case, channels, i.e., spaces between adjacent lamellas, in the foil trap 9 have to be aligned with the emitted EUV beam. In FIG. 2, the foil trap 9 is focused on the radiation source such that EUV rays of radiation emitted from the EUV source may pass the lamellas 31, 32 without obstruction. Typical values for the dimensions of the lamellas are: height h=30 mm, thickness 0.1 mm and width w=50 mm (curved). A typical value for the channel width, i.e. the distance between adjacent lamellas, is 1 mm. The distance from the foil trap 9 to the source LA is typically in the order of 60 mm. These specific dimensions are examples and should not be considered to be limiting in any way. The embodiment of FIG. 8 is similar to the one shown in FIG. 4, except for the additional heat shield 46, mounted in front of shield 41. The additional shield 46 prevents the first shield 41 from being excessively heated by direct radiation from the radiation source LA, and consequently reduces heat radiating from the first shield 41 towards the collector 10. The additional heat shield 46 may be mounted on shield 41 using a dedicated separation device 48 in order to accomplish substantially thermal isolation between the two shields. The separation device 48 may be manufactured e.g. from ceramics, which is able to resist the heat caused by the radiation impinging on the additional shield 46 and has a very small heat conduction coefficient. In another embodiment of the separation device 48, it may be envisaged that by special design of the separation device a heat resistance is created between the additional shield 46 and shield 41 considerably reducing heat transfer between the two shields. While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise then as described. The description is not intended to limit the invention.
	summary
	claims	1. An assembly in a primary circuit of a nuclear reactor, wherein the nuclear reactor has a reactor core with defined fuel assembly positions for a placement of fuel assemblies, the assembly comprising:a device for removing solid particles from a cooling medium circulating in the primary circuit, said device not being a fuel assembly, but said device having a device outline with geometric dimensions and shapes configured for insertion thereof into an empty fuel assembly position in the reactor core of the nuclear reactor instead of a fuel assembly;a carrying structure extending in a longitudinal direction and at least one separator disposed in said carrying structure, said at least one separator being a flow separator, said flow separator having a deflection device configured for imparting centrifugal forces onto the solid particles and driving the solid particles into calm zones of said flow separator provided as accumulation spaces. 2. The assembly according to claim 1, wherein said at least one separator is one of a plurality of separators disposed one after another in the longitudinal direction in said carrying structure. 3. The assembly according to claim 2, wherein said separators are releasably connected to one another. 4. The assembly according to claim 1, wherein said carrying structure is a hollow case. 5. The assembly according to claim 1, wherein said at least one separator is an insert configured for insertion into said carrying structure, said insert is formed with an inlet opening for the cooling medium, and has, opposite and at a spacing distance from said inlet opening, a deflection device for deflecting the cooling medium, and is formed with an accumulation zone for collecting the solid particles that are separated during deflection due to a centrifugal force. 6. The assembly according to claim 5, wherein said deflection device is a cyclone disposed to impart on the cooling medium, which flows in the longitudinal direction inside said carrying structure, a circular motion about the longitudinal direction. 7. The assembly according to claim 6, wherein said deflection device includes at least one fixed guide vane. 8. The assembly according to claim 1, wherein said separator is one of a plurality of separators disposed one after another in the longitudinal direction and having mutually different designs from one another in order to achieve a different separation effect. 9. The assembly according to claim 1, configured to have a flow resistance substantially corresponding to a flow resistance of a fuel assembly. 10. The assembly according to claim 1, configured for insertion into the reactor core of a boiling-water nuclear reactor. 11. A reactor core of a nuclear reactor, comprising an assembly according to claim 1 inserted into an empty fuel assembly position. 12. The reactor core according to claim 11, configured as a core of a boiling-water reactor. 13. The reactor core according to claim 11, wherein said device is inserted in a fuel assembly position is located at an edge of a fuel assembly grid. 14. The reactor core according to claim 11, wherein said device is inserted in a corner position of a fuel assembly grid.
	claims	1. A network sensor assembly comprising:a panel configured for mounting on a surface;a plurality of addressable sensors coupled to the panel that sense environmental conditions at the surface;a memory device that stores configuration information associated with the plurality of addressable sensors;a bus communicatively coupled to the plurality of addressable sensors and the memory device and configured for communicatively coupling the network sensor assembly to a network node for communicating data associated with the sensed environmental conditions in a network; andthe panel comprising a folding panel that folds at a fold line about the bus. 2. The network sensor assembly according to claim 1 further comprising:a plurality of protective tabs coupled to the panel and respectively coupled to the plurality of addressable sensors in a configuration that supports and protects the addressable sensor plurality. 3. The network sensor assembly according to claim 1 further comprising:a plurality of mounting tabs coupled to the panel configured to secure the network sensor assembly to the surface. 4. The network sensor assembly according to claim 1 further comprising:a plurality of protective tabs cut from the folding panel positioned to support and protect the plurality of addressable sensors;an adhesive coupling the panel to the bus. 5. The network sensor assembly according to claim 1 wherein the bus comprises a multiple conductor tape wire. 6. The network sensor assembly according to claim 1 wherein the plurality of addressable sensors sense at least one environmental condition selected from the group consisting of temperature, humidity, air pressure, air velocity, smoke sensors, occupancy sensors, computer rack door condition, sound, and light. 7. The network sensor assembly according to claim 1 further comprising: the network node configured for communicating data associated with the sensed environmental conditions in a network. 8. The network sensor assembly according to claim 1 further comprising: application software recorded on a non-transitory computer readable medium that operates on data received from the network node associated with the sensed environmental conditions in a network, the application software configured to:periodically query the plurality of addressable sensors from a plurality of network nodes;reading sensed environmental conditions from the plurality of addressable sensors from the plurality of network nodes;generate an environmental profile of a data center based on the sensed environmental conditions. 9. A method of fabricating a network sensor assembly comprising:mechanically coupling a bus to a panel configured for mounting on a surface, the panel comprising a folding panel that folds at a fold line about the bus;mechanically coupling a plurality of addressable sensors to the panel;communicatively coupling the bus to the plurality of addressable sensors that sense environmental conditions at the surface;communicatively coupling the bus to a memory device that stores configuration information associated with the plurality of addressable sensors; andcommunicatively coupling the memory device and the plurality of addressable sensors to a network node for communicating data associated with the sensed environmental conditions in a network. 10. The method according to claim 9 further comprising:coupling a plurality of protective tabs to the panel and respectively to the plurality of addressable sensors; andconfiguring the protective tab plurality to support and protect the addressable sensor plurality. 11. The method according to claim 9 further comprising:coupling a plurality of mounting tabs to the panel; andconfiguring the mounting tab plurality to secure the network sensor assembly to the surface. 12. The method according to claim 9 further comprising:cutting a plurality of protective tabs from the folding panel;positioning the protective tab plurality to support and protect the plurality of addressable sensors;coupling the panel to the bus with adhesive. 13. A network environmental monitor comprising:at least one network sensor assembly comprising:a panel configured for mounting on a surface, the panel comprising a folding panel that folds at a fold line about a bus;a plurality of addressable sensors coupled to the panel that sense environmental conditions at the surface;a memory device that stores configuration information associated with the plurality of addressable sensors; andthe bus communicatively coupled to the plurality of addressable sensors and the memory device, the bus configured for communicating data associated with the sensed environmental conditions;at least one network node communicatively coupled to the at least one network sensor assembly wherein the bus communicatively couples the at least one network sensor assembly to the at least one network node and the at least one network node distributes data associated with the sensed environmental conditions over a network; anda processor communicatively coupled to the at least one networked node configured to execute a software application, recorded on a non-transitory computer readable medium, that collects sensed environmental condition data from the plurality of addressable sensors and controls environment based on the sensed environmental condition data. 14. The environmental monitor according to claim 13a wherein the software application determines sensed environmental conditions at a computer rack and adjusts environmental conditions at the computer rack based on the sensed environmental conditions at the computer rack. 15. The environmental monitor according to claim 13 further comprising:a plurality of equipment racks, the plurality of network sensor assemblies respectively mounted on the equipment rack plurality. 16. The environmental monitor according to claim 15 wherein the equipment rack plurality is contained within a data center. 17. The environmental monitor according to claim 16 further comprising:an environmental control system communicatively coupled to the at least one network node that adjusts environmental controls of the data center based on the sensed environmental conditions at the plurality of equipment racks. 18. The environmental monitor according to claim 17 wherein the environmental conditions sensed comprise at least one condition selected from the group consisting of temperature, humidity, air pressure, air velocity, smoke sensors, occupancy sensors, computer rack door condition, sound, and light. 19. The environmental monitor according to claim 13 wherein the at least one network sensor assembly further comprises:a plurality of protective tabs coupled to the panel and respectively coupled to the plurality of addressable sensors in a configuration that supports and protects the addressable sensor plurality. 20. The environmental monitor according to claim 13 further comprising:application software recorded on a non-transitory computer readable medium and executable on the processor that operates on data received from the network node associated with the sensed environmental conditions in a network, the application software configured to:periodically query the plurality of addressable sensors from a plurality of network nodes;read sensed environmental conditions from the plurality of addressable sensors from the plurality of network nodes;generate an environmental profile of a data center based on the sensed environmental conditions.
056595913	abstract	A containment spray system for a light-water reactor includes a water trough being disposed in a safety tank. An immersion pump disposed in the vicinity of the bottom of the water trough, a spray branch and an outlet-side spray nozzle array, are connected to the water trough for injecting water into the containment in finely dispersed form in the event of an operational incident.
048775754	claims	1. A method of core reactivity validation, comprising the steps of: (a) determining at least two core reactivities using at least two neutron detectors; and (b) comparing the core reactivities and indicating that the reactivities are valid when the reactivities are substantially coincident. (c1) determining intersections between the straight line fit and a vertical line constructed through a point at which reactivity passes through zero during control rod movement; and (c2) producing as differential control rod worth a difference between the intersections. (a) sampling neutron flux detected by at least two neutron detectors; (b) determining at least two reactivities from the flux; (c) comparing reactivities from multiple samples and determining coincidence between the reactivities; (d) fitting a straight line to the coincident reactivities; (e) determining whether the straight line satisfies a statistical fit test; (f) determining intersections between the straight line and a vertical line constructed through a point at which reactivity passes through zero during control rod movement; and (g) determining a reactivity difference as a distance between the intersections. at least two neutron detectors producing core flux values; reactivities from the flux values; means for determining at least two reactivities and computation means for comparing the reactivities and alerting an operator when the reactivities are substantially coincident. means for fitting a straight line to the substantially coincident reactivities; and means for determining control rod worth from intersections between the straight line and core reactivity before and after control rod movement. 2. A method as recited in claim 1, wherein step (b) includes indicating valid reactivities after substantial coincidence occurs sufficient to satisfy a statistical fit test. 3. A method as recited in claim 2, further comprising the step of (c) determining control rod worth after valid reactivities are indicated. 4. A method as recited in claim 3, wherein step (b) includes the step of performing a straight line fit to the substantially coincident reactivities, and step (c) comprises the steps of: 5. A method of determining worth of control rods, comprising the steps of: 6. A validation apparatus for core reactivity, comprising: 7. An apparatus as recited in claim 6, further comprising control rod worth means for determining control rod worth from the substantially coincident reactivities. 8. An apparatus as recited in claim 7, wherein said control rod worth means comprises:
063209365	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, an x-ray tube assembly embodying the present invention is indicated generally by the reference numeral 10. The x-ray tube assembly 10 comprises a housing 12 and an x-ray tube 14 mounted within the housing. The x-ray tube housing 12 comprises a mounting boss 16 defining an x-ray port 18 extending through the mounting boss and into the interior of the housing. The x-ray tube 14 includes an evacuated glass envelope 20, a rotating anode 22 defining a target surface 24, and a cathode (not shown) spaced relative to the anode within the glass envelope. As will be recognized by those skilled in the pertinent art based on the teachings herein, the x-ray tube 14 may be any of numerous different types of x-ray tubes which are now or later become known for generating x-radiation, including, for example, any of numerous different types of rotating anode or stationary anode tubes, and/or tubes defining glass envelopes, metal envelopes, or envelopes formed of combinations of metal, glass and ceramic. The anode and cathode are maintained at a high differential voltage relative to each other, typically on the order of about 150 kV or less. As will be recognized by those skilled in the pertinent art based on the teachings herein, however, the differential voltage may be any voltage required by the application(s) of the x-ray tube assembly 10. Similarly, the differential voltage may be created in any of numerous different ways. For example, as described above, the anode 22 may be maintained at ground, and the cathode may be maintained at a relatively high negative potential. Alternatively, the anode 22 may be maintained at a positive potential, e.g., +75 kV, and the cathode may be maintained at a negative potential, e.g., -75 kV. The cathode thermionically emits electrons which are electrostatically directed into a focal spot 26 located on the rotating target surface 24 of the anode 22 with sufficient energy to generate x-rays which emerge from the target in a diffuse pattern. As indicated above, the size and shape of the focal spot 26 may be dictated by the size and shape of the filaments (not shown) of the cathode. Typically, the focal spot area 26 is rectangular; however, the cathode filaments may take any of various different sizes and shapes, and thus the focal spot 26 likewise may correspondingly vary in size and shape. The x-ray housing 12 is hermetically sealed, and is filled with an insulating oil (not shown) to electrically insulate the x-ray tube 14 within the housing. As also shown in FIG. 1, a beam limiting apparatus 28 of the invention is mounted on the boss 16 and extends through the x-ray port 18 into the interior of the housing 12 adjacent to the focal spot 26. The beam limiting apparatus 28 comprises a peripheral flange 30, and a radiation-absorbing or radiopaque body 32 projecting downwardly from the peripheral flange and received through the x-ray port 18 and into the interior of the housing 12. Unless otherwise indicated, the term "radiopaque" is used synonymously with "radiation absorbing" and "radiation blocking" throughout this specification, and is intended to mean preventing or not allowing the passage of substantially all x-rays through the respective material, component or portion of the apparatus. The radiation-absorbing body 32 defines a base surface 34, an x-ray entrance aperture 36 formed through the base surface, an x-ray exit aperture 38 formed through an approximately opposite side of the base wall relative to the x-ray entrance aperture, and an x-ray transmissive beam conduit 40 extending between the entrance and exit apertures. The x-ray port 18 and evacuated envelope 20 define a first predetermined depth "D1" therebetween, and the base surface 34 of the body 32 extends into the housing a second depth "D2", which is close to, but less than the first depth "D1", such that the base surface 34 is spaced closely adjacent to the evacuated envelope 20 of the x-ray tube and defines a predetermined gap 42 therebetween. The gap 42 is sufficient to allow differential thermal expansion between the x-ray tube and beam limiting apparatus without contacting each other during operation of the x-ray tube. In the illustrated embodiment of the invention, the width of the predetermined gap 42 is approximately 0.060 inch, and is preferably within the range of approximately 0.040 to approximately 0.080 inch. However, as will be recognized by those skilled in the pertinent art based on the teachings herein, the width of the gap 42 may fall outside of this range in particular applications, particularly if necessary to provide sufficient space to allow differential thermal expansion of these closely spaced parts without contacting each other during operation of the x-ray tube. For example, for relatively large x-ray tubes and housings, it may be necessary to increase the width of the gap 42 over that described herein in order to ensure sufficient space to allow for differential thermal expansion during operation of the x-ray tube. Alternatively, if the envelope of the tube is made of metal, or includes a metal portion adjacent to the base surface 34 of the radiation-absorbing body 32, the tube may be sufficiently strong to allow the parts to contact each other, and therefore the gap may be eliminated. The radiolucent or x-ray transmissive window 44 is mounted between the x-ray entrance aperture 36 and exit aperture 38, and extends across the beam conduit 40. In the illustrated embodiment of the present invention, the x-ray transmissive window 44 is molded integral with the radiation absorbing body 32, and is made of a radiolucent material having a predetermined aluminum equivalent filtration in order to achieve a predetermined overall filtration of the image-forming x-ray beam. Accordingly, the x-ray transmissive window 44 may be made of any of numerous different materials which are currently, or later become known for performing the functions of the window described herein. For example, the window 44 may be made of aluminum, or any other desired x-radiation transmissive metal. Alternatively, the window 44 may be made of a transparent epoxy resin, a polycarbonate, glass or other optically transparent and radiolucent material, in order to allow an operator to view the interior of the housing through the window. In each case, the window 44 is preferably integrally molded with the radiation-absorbing body and defines a hermetic seal between the window and body, as described further below. The peripheral flange 30 defines a mounting surface 46 on the underside of the flange for mounting the beam limiting apparatus 28 to the mounting boss 16 of the housing 12. As shown in FIG. 1, the mounting boss 16 of the housing defines an o-ring groove or like recess 48 extending about the periphery of the x-ray port 18, and an o-ring or other suitable sealing member 50 is seated within the groove between the mounting surface 46 and mounting boss 16 to hermetically seal the beam limiting apparatus 28 to the housing 12. The radiation-absorbing body 32 defines a first cylindrical recess on the interior side of the body, and extending downwardly from the peripheral flange 30 to the base wall of the body. A cylindrical wall 54 extends upwardly on the opposite side of the flange 30 relative to the first recess 52, and defines a second cylindrical recess 56 on the interior thereof. The radiopaque body 32, peripheral flange 30, and cylindrical wall 54 are formed of a substantially electrically nonconductive, filled polymeric material, and as can be seen, are integrally molded in a single casting. In the currently preferred embodiment of the invention, the polymeric material is a filled epoxy resin material sold by Lord Corp., Chemical Products Division, of Atlanta, Ga., under the trademark "Circalok", wherein the resin is part number 6703A, and the hardener is part number 6703B. This filled epoxy resin is also designated "H253 P1" by the Assignee of the present invention in connection with the sales of its products molded from this material. The Circalok filled epoxy resin is an oil-based resin, and is filled with a radiation-absorbing material, such as lead oxide. This material is electrically non-conductive, and radiopaque, and exhibits the following approximate physical characteristics: Specific Gravity (g/cc) 4.05 Hardness (shore D) 90 Tensile Strength (psi) 8,100 Compressive Strength at 25.degree. C. (psi) 13,200 Linear Shrinkage (in/in) 0.004 Service Temperature (.degree. C.) -60 to 155 Thermal conductivity (cal/sec/cm.sup.2 /.degree. C. .times. 10.sup.-4) >7.8 (BTU/ft.sup.2 /hr/.degree. F./in) >2.3 Coefficient of thermal expansion (in/in/.degree. C. .times. 10.sup.-6) <38 Thermal resistance (.degree. C./in/watt) 128 Volume resistivity at 25.degree. C. (ohm/cm) 10.sup.15 Dielectric constant at 25.degree. C. (100 KC) 4.1 Dissipation Factor at 25.degree. C. (100 KC) 0.02 Dielectric strength 400-500 As will be recognized by those skilled in the pertinent art based on the teachings herein, the filled polymeric material may take the form of any of numerous other like materials that are currently, or later become known for performing the functions of the filled epoxy resin described herein. One advantage of the filled epoxy resin employed in the apparatus of the present invention, is that it allows the x-ray transmissive window 44 to be easily molded integral with the radiation-absorbing body and other components of the beam limiting apparatus. In addition, the base resin employed may be optically transparent, and therefore may be used to integrally mold the x-ray transmissive window only to be both optically transparent and radiolucent, and thereby allow a user to view the interior of the housing therethrough. As further shown in FIG. 1, a beam-adjusting mechanism 58 is slidably received within the first and second recesses 52 and 56 for selectively adjusting the size of the x-ray beam. The beam-adjusting mechanism 58 includes a guide flange 60 defining an approximately disc-like shape and slidably received within the second cylindrical recess 56. A second radiation-absorbing body 62 projects downwardly from the guide flange 60, and defines a second x-ray entrance aperture 64 on the bottom side of the body, a second x-ray exit aperture 66 formed on the opposite side of the guide flange 60, and an approximately frusto-conical shaped second beam conduit 68 formed between the entrance and exit apertures. A coil spring 70 is seated between the base wall of the first recess 52 and the underside of the guide flange 60 to normally bias the guide flange, and thus the beam-adjusting mechanism upwardly or away from the focal spot 26. The guide flange 60 and radiation-absorbing body 62 are integrally molded of the same filled polymeric material as the other components of the beam limiting apparatus as described above. However, as will be recognized by those skilled in the pertinent art based on the teachings herein, any of numerous different filled polymeric materials and/or other materials may be employed for performing the functions of these components described herein. As indicated in phantom in FIG. 1, an electric coil 72 is integrally molded within the upper end of the cylindrical wall 54 and extends along the upper periphery of the second cylindrical recess 56. The electric coil 72 is electrically connected to a suitable electrical power source and control circuitry (not shown) in order to selectively energize the coil as hereinafter described. As also indicated in phantom in FIG. 1, an iron or like conductive core 74 is integrally molded within the second radiation-absorbing body 62, and extends adjacent to the periphery of the body. Normally, the coil spring 70 biases the beam-adjusting mechanism 58 upwardly into the position "2", as indicated in broken lines in FIG. 1. However, upon energization of the electric coil 72, an electric field surrounding the coil magnetically repels the core 74, and as indicated by the arrows in FIG. 1, drives the beam-adjusting apparatus 58 downwardly from position "2" into position "1" indicated in solid lines in FIG. 1. As indicated schematically in FIG. 1, in position "1", the beam defines a diameter "A", and in position "2", the beam defines a diameter "B" less than diameter "A". In the illustrated embodiment, beam diameter A is approximately 9 inches at a source to image distance ("SID") "C" of approximately 40 inches, and beam diameter B is approximately 6 inches at an SID "C" of approximately 40 inches. However, as will be recognized by those skilled in the pertinent art based on the teachings herein, the size and shapes of the x-ray beams may be selectively controlled to virtually any desired size and/or shape by simply adjusting the sizes and shapes of the beam apertures in the beam limiting apparatus 26, and/or by adjusting the axial position of the beam-adjusting mechanism 58. In addition, the beam-adjusting mechanism may take any of numerous different forms which are currently, or later become known for performing the functions described herein. For example, the solenoid-type actuation of the beam adjusting mechanism 58 may take the form of any of numerous such solenoid-type mechanisms, such as double coils, double magnets, or other mechanical or electrical variations thereof. In addition, the position of the beam-adjusting mechanism 58 may be provided by a mechanical adjusting mechanism, such as a lead screw, or other type of threaded drive mechanism, a linkage mechanism, or any of numerous other mechanical or electromechanical drive mechanisms for performing the functions described herein. In addition, the beam-adjusting mechanism may be selectively positionable in any of a plurality of different positions with respect to the focal spot 26 in order to selectively collimate the beam to define any of a plurality of different beam sizes within a predetermined range of beam sizes. For example, in the embodiment of the present invention illustrated, the beam-adjusting mechanism 58 may be electrically controlled to selectively fix its position at any of a plurality of different positions between the positions 1 and 2 shown. In the embodiment of the present invention illustrated, the x-ray entrance and exit apertures of the beam limiting apparatus 28 define the same peripheral shape as that of the focal spot 26. Typically, the focal spot 26 defines a rectangular peripheral shape, and therefore the x-ray entrance and exit apertures of the beam limiting apparatus are also rectangular. However, if desired, one or more of the beam limiting apertures may define a shape different than the shape of the focal spot in order to change the shape of the x-ray beam to a shape corresponding the shape of the aperture. For example, in image intensifier applications requiring a round field, a rectangular-shaped beam may be changed to a round beam by causing one or more of the beam limiting apertures to have the desired round or circular shape. In this exemplary case, the x-ray entrance aperture would define an approximately 1.2 mm square (or other sized square equaling the projected size of the focal spot) if placed directly at the edge of the projected effective focal spot perpendicular to the central ray. As the x-ray beam conduits 40 and 68 move away from the focal spot, the cross-sections of the conduits (and beam limiting apertures) would be changed to a more circular form with chords defining the respective four sides of the projected focal spot. The points of the chords would develop into a true circle at the second x-ray exit aperture 66 in order to generate a round field image. In each case, the x-ray entrance aperture 36 preferably defines a size approximately equal to the projected size of the focal spot 26 onto the base surface 34 of the radiation-absorbing body 32. As will be recognized by those skilled in the pertinent art based on the teachings herein, if the x-ray entrance aperture 36 is too large, then it will allow the passage of off-focus radiation therethrough. Accordingly, the dimensions of the x-ray entrance aperture are preferably approximately equal to the projected dimensions of the focal spot onto the base surface 34. If, on the other hand, the x-ray entrance aperture 36 is too small, it will undesirably reduce the intensity of the x-ray beam. As also shown in FIG. 1, a mounting bracket 76 is seated over the cylindrical wall 54 and mounting flange 30 to fixedly secure the beam limiting apparatus 28 to the housing 12. As shown typically in FIG. 1, the housing 12 includes threaded apertures 78 for receiving mounting screws or other fasteners (not shown) for fixedly securing the mounting bracket 76 to the housing. If desired, the mounting bracket 76 may be fixedly secured to a gantry or other device for supporting the x-ray tube assembly. The mounting bracket 76 defines an x-ray aperture 79 in a top wall thereof overlying the other beam apertures for permitting the passage of the x-ray beam therethrough. As can be seen, the x-ray aperture 79 is larger than any of the underlying x-ray apertures in order to avoid interference with the x-ray beam. As also shown in FIG. 1, the mounting boss 16 of the housing 12 defines a peripheral recess 80 for receiving the mounting flange 30 of the beam limiting apparatus 28. As can be seen, the outer diameter of the peripheral recess 80 is greater than the outer diameter of the mounting flange 30 to thereby allow the flange, and thus the radiation-absorbing body 32 to be moved laterally within the recess. The underside of the mounting bracket 76 similarly defines a first recess 82 for receiving therein the upper side of the mounting flange 30 and fixedly securing the mounting flange to the housing 12. As can be seen, the outer diameter of the first recess 82 is approximately equal to the outer diameter of the peripheral recess 80 of the mounting boss 16 to likewise allow the mounting flange 30 and radiation-absorbing body 32 to be moved laterally within the first recess of the mounting bracket. The mounting bracket 76 further defines a second recess 84 for receiving the cylindrical wall 54. Like the first recess 82, the second recess 84 defines a diameter greater than the outer diameter of the cylindrical wall 54 to thereby allow the cylindrical wall to move laterally within the recess. As also shown in FIG. 1, a plurality of alignment screws, shown typically at 86, are threadedly received through the side walls of the mounting bracket 76 and engage on their free ends the exterior sides of the cylindrical wall 54. Accordingly, the alignment screws 86 may be threadedly adjusted to, in turn, laterally adjust the position of the radiation-absorbing body 32 and thereby align the components with the "central ray" centerline (and with respect to the mounting boss holes 78). As shown schematically in broken lines in FIG. 1, a flexible, substantially radiolucent material 88 extends across the predetermined gap 42 formed between the evacuated envelope 20 of the x-ray tube and the base surface 34 of the radiation-absorbing body 32 to prevent the passage of oil therethrough. In accordance with a preferred embodiment of the invention, the material 88 is a compressible silicone pad, which is substantially free of voids and foreign material, such as the silicone dielectric gel sold by Dow Corning under the designation Dow Corning Sylgard 527. Preferably, the silicone gel 88 is applied to the interface between the glass envelope 20 and the base surface 34 as shown, in order to completely fill the gap in the area underlying the x-ray entrance aperture 36, and thereby prevent the passage of oil through this area. The silicon gel 88 is preferably free of voids and any particulate or foreign matter in order to prevent any such non-homogeneous features from showing up as artifacts on the x-ray images. Thus, one advantage of this feature of the present invention, is that any air bubbles or other particulate matter that might be contained within the oil of the x-ray tube assembly is prevented from flowing through the x-ray beam, and therefore prevented from negatively affecting the x-ray images. The beam limiting apparatus 28 preferably may further comprises cooling conduits connectable to a heat exchanger in order to cool the x-ray tube. As shown in FIG. 1, the beam limiting apparatus defines a first coolant inlet port 90 extending into the peripheral flange 30, a first coolant exit port 92 extending through another portion of the peripheral flange, and a first coolant conduit 94 coupled in fluid communication between the first inlet and outlet ports. As shown typically in FIG. 1, the first coolant conduit 94 preferably defines a serpentine shape within the base wall of the radiation-absorbing body 32 in order to maximize the surface area of the body in thermal communication with the coil. If desired, the coil 94 also could define a helical path within the approximately frusto-conical shaped side walls of the radiation-absorbing body 32 to further maximize the surface area of the body in thermal communication with the coils. The coils are preferably made of a thermally-conductive material and are molded integral with the radiation-absorbing body. Alternatively, the radiation-absorbing body 32 itself may define the first coolant conduit 94. The heat exchanger (not shown) may be any of numerous heat exchangers currently, or which later become available for performing the heat exchange functions described herein. The mounting bracket 76 may further define a second coolant conduit 96, a second coolant inlet port 98 coupled in fluid communication with one end of the second coolant conduit, and a second coolant outlet port 100 coupled in fluid communication with the opposite end of the second coolant conduit for introducing a cooling fluid through the conduit. As can be seen, the second coolant conduit 96 extends along a helical path within the side wall of the mounting bracket 76 in order to cool the walls of the mounting bracket, and thereby facilitate in transferring heat away from the x-ray tube assembly. The second coolant conduit 96 may be coupled in fluid communication with the same heat exchanger as the first coolant conduit 94, or alternatively, may be connected to a different heat exchanger (not shown). As will be recognized by those skilled in the pertinent art based on the teachings herein, any of numerous different means for heat exchange may be employed for performing this function as described herein. For example, if desired, a thermoelectric cooler, such as a Peltier-effect device, may be thermally coupled to the mounting bracket and/or to the radiation-absorbing body in order to transfer heat away from these components in the manner described above. The x-ray tube housing 12 may take any of numerous different shapes and configurations. For example, the housing 12 may be made in a conventional manner whereby the external shell of the housing is made of metal, such as aluminum, and the internal walls of the housing are lined with a radiation-absorbing material, such as lead. Preferably, however, the housing 12 is cast of the same or like filled epoxy resin as are the components of the beam limiting apparatus 28. In this configuration, an electrically conductive surface 102 is formed on the exterior side of the housing in order to ground the housing. This conductive surface 102 may be formed by a conductive paint or other conductive coating, or if desired, may be formed by a conductive skin or like thin layer attached to the outer surface of the filled epoxy casting. Turning to FIG. 2, another embodiment of an x-ray tube assembly of the invention is indicated generally by the reference numeral 110. The x-ray tube assembly 10 is substantially similar to the x-ray tube assembly 10 described above, and therefore like reference numerals preceded by the numerals "1" or "2" are used to indicate like elements. One of the primary differences of the x-ray tube assembly 110 is that the beam limiting apparatus 128 is molded integral with the x-ray tube housing 112, and does not include a beam-adjusting mechanism. As can be seen, the housing 112 is molded with a filled polymeric, substantially non-conductive, radiopaque material. Preferably, the filled polymeric material is the same filled epoxy resin material as described above in connection with the previous embodiment; however, as will be recognized by those skilled in the pertinent art based on the teachings herein, any of numerous other types of filled polymeric materials which currently, or later become known for performing the functions of the housing described herein may be equally employed. The housing 112 includes a first casting 204 and a second casting 206, and each casting has formed on the exterior sides thereof the conductive surface or shell 202. As indicated above, the conductive surface 202 may be applied as a conductive paint or like coating, or may be applied as a thin metal shell fixedly secured to the castings with nylon or like non-conductive screws or other fasteners (not shown). As shown in FIG. 2, the first casting 204 defines a hermetically-sealed cavity 208 for receiving the x-ray tube 114. The first casting 204 further defines the beam limiting apparatus 128 integrally molded therein, including the base surface 134 spaced in close proximity to the evacuated envelope 120, the x-ray entrance aperture 136, the x-ray transmissive window 144 molded into the beam conduit 140, and the x-ray exit aperture 138. If desired, a beam limiting plate 210 may be mounted over the x-ray exit aperture 138 to further perform the beam limiting function. The beam limiting plate 210 may be a conventional beam limiting plate formed of a radiopaque material, and defining a beam limiting aperture 211 for further controlling the size and shape of the image-forming beam. In addition, the beam limiting plate 210 may be laterally adjustable in a conventional manner, and/or the position of the x-ray tube 114 within the housing may be axially adjustable in a conventional manner in order to align the x-ray apertures of the beam limiting apparatus with the central ray. The mounting bracket 176 is fixedly secured to the housing in the same manner as the mounting bracket 76 described above. As also shown in FIG. 2, the first casting 204 further defines an anode plug cavity 212, and a cathode plug cavity 214, each having respective terminal pins 216 integrally molded into the base of the cavity for connection to a male plug of a type known to those skilled in the pertinent art (not shown). An anode conduit 218 is formed between the pin(s) 216 of the anode plug cavity 212 and the anode end of the hermetically-sealed cavity 208 for electrically connecting the pins to the anode of the x-ray tube. Similarly, a cathode conduit 220 is formed between the pin(s) 216 of the cathode plug cavity 214 and the cathode end of the hermetically-sealed cavity 208 for connecting the pins to a filament transformer 222, which, in turn, is connected to the cathode of the x-ray tube 114. A suitable interface plug 224 is integrally molded into the side wall of the housing 112 adjacent to the filament transformer for providing an electrical connection thereto. An oil pump cavity 226 is also formed in the side wall of the first casting 204 for receiving an oil pump assembly 228. The oil pump assembly 228 includes a vane or like impeller 230 rotatably driven by an electric motor including a rotor 232 and stator 234. An oil inlet conduit 236 is formed in fluid communication between the oil pump cavity 226 and the cathode end of the x-ray tube cavity 208, and an oil outlet conduit 238 is formed in fluid communication between the anode end of the x-ray tube cavity 208 and the oil pump cavity 226. A suitable valve 240 is connected to the oil outlet conduit 238 for filling the interior of the housing 112 with oil. An oil volume compensation tube 242 lines an interior surface of the oil pump cavity 226 in order to compensate for variations in oil volume due, for example, to thermal expansion and contraction of the oil during operation. The oil volume compensation tube 242 is connected in fluid communication with an air vent 244 in order to fill the tube with air. A heat sink 246 is mounted over the oil pump cavity 226 to enclose the oil pump assembly 228 within the cavity, and includes a plurality of cooling fins 248 on an exterior surface thereof for facilitating heat exchange between the oil and the ambient atmosphere. The heat sink 246 is hermetically sealed to the housing by an o-ring or like sealing member 250, and is fixedly secured to the housing with suitable fasteners (not shown). If necessary, threaded inserts may be molded into the casting 204 at suitable locations for receiving the fasteners for attaching the heat sink and any other components of the x-ray tube assembly. The second casting 206 forms a cover for enclosing the x-ray tube 114 within the housing. As shown in FIG. 2, the second casting defines a peripheral groove 252 for receiving an o-ring or like sealing member 254, and fasteners (not shown) are employed to attach and thereby hermetically seal the cover 206 to the housing. As also shown, the first casting 204 defines a recess 256 for receiving the cover, and there is a substantial overlap of the cover and the base surface of the recess to prevent the emission of any radiation through any interfaces of the first and second castings. One advantage of the x-ray tube assembly 110 is that the entire housing may be made of a filled polymeric material, such as the filled epoxy resin described above, and therefore there is no need to line the housing with lead or other radiation-absorbing materials. Accordingly, substantial cost benefits can be achieved by employing the housing of the present invention. Turning to FIGS. 3 and 4, another x-ray tube assembly including a beam limiting apparatus embodying the present invention is indicated generally by the reference numeral 210. The x-ray tube assembly 210 is similar to the x-ray tube assemblies described above in connection with the previous embodiments, and therefore like reference numerals preceded by the numerals "2" and "3" are used to indicate like elements. The primary difference of the beam limiting apparatus 228 of FIGS. 3 and 4 is that it is provided in the form of a cone-shaped part that may be mounted within a conventional x-ray tube housing port 218. In addition, like the beam limiting apparatus 128 described above in connection with FIG. 2, the beam limiting apparatus 228 does not include a beam adjusting mechanism for adjusting the size of the x-ray beam. As shown in FIG. 3, the peripheral flange 230 and radiation-absorbing body 232 of the beam limiting apparatus 228 are integrally molded with a filled polymeric material which is electrically non-conductive and radiopaque. Preferably, the filled polymeric material is the same as the filled epoxy resin described above in connection with the previous embodiments; however, as will be recognized by those skilled in the pertinent art based on the teachings herein, any of numerous other materials which now, or later become known may be employed for performing the functions described herein. The housing 212 defines an x-ray port 218, and a annular recess 248 extending about the periphery of the x-ray port for receiving an o-ring or like sealing member 250 to hermetically seal the beam limiting apparatus to the housing. The mounting bracket 276 defines on its underside the first recess 282 for receiving therein the peripheral flange 230. The flange 230 is movable laterally within the recess 282 to align the position of the x-ray apertures with the central ray. The adjustment screws 286 are provided to laterally adjust and fix the position of the beam limiting apparatus within x-ray port 218. As shown in FIG. 4, the mounting bracket 276 includes a plurality of apertures overlying the threaded apertures 278 in the mounting boss 216 of the housing 212 to threadedly attach the mounting bracket to the boss with fasteners (not shown) and, in turn, fixedly secure and hermetically seal the beam limiting apparatus to the housing. As in the embodiments described above, the x-ray transmissive window 244 may be made of any desired material, and is preferably molded integral with the radiation-absorbing body 232 and forms a hermetic seal between the x-ray transmissive window and radiation-absorbing body. If desired, a layer of silicone gel or like material 288 may be interposed between the base surface 234 and the evacuated envelope 220 in the same manner as described above in connection with the previous embodiments in order to prevent the passage of oil and/or particulates therethrough. Turning to FIGS. 5 and 6, another x-ray tube assembly including a beam limiting apparatus embodying the present invention is indicated generally by the reference numeral 310. The x-ray tube assembly 310 is similar to the x-ray tube assembly 210 described above in connection with FIGS. 3 and 4, and therefore like reference numerals preceded by the numerals "3" and "4" instead of the numerals "2" and "3" are used to indicate like elements. The primary difference of the beam limiting apparatus 328 of FIGS. 5 and 6 is that it may be mounted within, or on the exterior side of a conventional cup-shaped x-ray window, such as a conventional polycarbonate window. As indicated in broken lines in FIG. 5, a typical cup-shaped polycarbonate or other polymeric window 410 may be mounted within the x-ray port 318 and extend downwardly into the housing toward the focal spot 326 of the x-ray tube. Accordingly, a predetermined gap 342 may be formed between the polymeric window and the exterior surface of the evacuated envelope 320. In this case, the radiation-absorbing body 332 is seated within the polymeric window 410 with the base surface 334 seated against the base wall of the window 410. Since the polymeric window 410 is hermetically sealed to the x-ray tube housing 312 in a typical manner, such as with the o-ring groove 348 and o-ring 350, the beam limiting apparatus 328 need not include the x-ray transmissive window, but rather may simply define an open passageway between the x-ray entrance aperture 336 and x-ray exit aperture 338. However, as shown in FIG. 5, the radiation-absorbing body 332 preferably defines an annular recess 412 extending about the periphery of the x-ray exit aperture 338 in order to receive a filtration member 414. The filtration member 414 may be made of aluminum or other suitable filtration material, and is provided in a predetermined thickness in order to achieve the requisite level of filtration of the x-ray beam. The filtration member 414 is seated within the recess 412, and retained within the recess by the overlying mounting bracket 376. If desired, a plurality of such filtration members may be provided, each defining a respective thickness and/or level of x-ray filtration, in order to allow an operator to selectively install the different filtration members to achieve different predetermined levels of beam filtration. The mounting bracket 376 defines on its underside the first recess 382 for receiving therein the peripheral flange 330. The flange 330 is movable laterally within the recess 382 to align the position of the x-ray apertures with the central ray. The adjustment screws 386 are provided to laterally adjust and fix the position of the beam limiting apparatus within the cup-shaped window 410. As will be recognized by those skilled in the pertinent art based on the teachings herein, numerous changes and modifications may be made to the above-described and other embodiments of the present invention without departing from the scope of the invention as defined in the appended claims. As one example, the filled epoxy resin x-ray housing of the invention can be made of any number of castings that may be connected together in the same manner, or in a manner similar to the hermetically-sealed connection of the two castings described above. In addition, if desired, the embodiments of FIGS. 2-6 could include cooling coils or conduits, or other cooling devices, as disclosed above in connection with the embodiment of FIG. 1. Similarly, the x-ray tube housing of FIG. 2 could be modified in any of numerous ways, including the provision of a conventional x-ray port (as shown, for example, in the other embodiments), and a beam limiting apparatus with beam adjusting or collimating mechanism of the type shown in FIG. 1. Accordingly, this detailed description of the preferred embodiments is to be taken in an illustrative as opposed to a limiting sense.
048658006	description	DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like, are words of convenience and are not to be construed as limiting terms. Referring now to the drawings, and particularly to FIG. 1, there is shown a fuel assembly grid inspection apparatus, generally designated by the numeral 10, which includes the combination of a precision noncontact measurement device, generally designated 12, and a universal support fixture 14 which are the components of the apparatus 10 comprising the present invention which cooperate in inspecting a fuel assembly grid 16. As seen in FIG. 1, the precision measurement device 12 per se is in the form of hardware manufactured and sold by View Engineering of Simi, Calif. and identified by the model designation "View 1220 System". The device 12 basically includes a data gathering unit (DGU) 18, a monitor and disk drive assembly (MDDA) 20, a keyboard 22, a joystick 24 and a printer 26. The device 12 measures by viewing or seeing, instead of touching or contacting, the grid 16. The DGU 18 of the device 12 includes a stationary base 28, viewing means 30 in the form of a video camera and lens system, a source of illumination 32 in the form of a ring light, an inspection platform 34 having a retroreflective surface 36 thereon (which is also part of the source of illumination 32), and electromagnetically-actuated X-, Y- and Z-axes stage assemblies 38,40,42 which mount the platform 34 and viewing means 30 on the stationary base 28 for movement relative thereto and to one another along X,Y,Z orthogonal directions. The viewing means 30 is disposed above the retroreflective surface 36 on the inspection platform 34 so as to define an inspection field of view extending generally vertically therebetween. As will be described in greater detail later, the universal fixture 14 is supported by the inspection platform 34 about the perimeter of the inspection field of view. The fixture 14, in turn, supports the grid 16 across and within the field of view. The viewing means 30 and the universal fixture 14 are movable relative to each other in X, Y and Z directions for achieving a complete inspection of all parts of the grid 16 in the vertical field of view. In particular, the Y-axis stage assembly 40 is actuatable for moving the platform 34 in the Y direction (forward or rearward, or toward the front or rear of the DGU 18) relative to the stationary base 28. The viewing means 30 being disposed in spaced relation above the inspection platform 34 is movable in X (left or right) and Z (up or down) directions with respect thereto and to the universal fixture 14 and grid 16 by actuation of the respective X-axis stage assembly 38 and the Z-axis stage assembly 42 which is movably mounted on the X-axis stage assembly 38. The viewing means 30 is adapted to view and record one or more images of the grid 16 located in the field of view and to provide digitized video image information to the MDDA 20 from which actual measurements of the grid 16 being inspected can be calculated. The known standard measurements for the particular grid design being inspected are inputted from either a floppy disk or a permanent hard disk into the MDDA 20 and the actual measurements which have been calculated therein are compared to such known standard measurements to determined whether or not the actual dimensions of the grid 16 being inspected come within acceptable tolerances of the known standard measurements. The fixture 14 is universal in the sense that it is adapted to support any one of a variety of grids of different designs within the field of view. Different programs are stored which contain the known standard measurements of the different grid designs. The one program which corresponds to the grid being inspected will be recalled and loaded into the working memory of the MDDA 20. It is not believed to be necessary for an understanding of the present invention that the operation of the device 12 be described in any greater detail. For more information about the operation of the device 12, one can consult the operator's manual for the View 1220 System available from View Engineering. Turning now to FIGS. 2-11, there is shown the universal grid support fixture 14 in assembled form and in some of its individual component parts. As mentioned above, the universal fixture 14 is adapted to support any one of a plurality of fuel assembly grids of different designs within the inspection field of view of the noncontact measurement device 12. The universal fixture 14 includes a mounting base 44 having first and second pairs of opposing portions 46A,46B and 48A,48B bounding the perimeter of the retroreflective surface 36 of the inspection field of view. The portions 46A,46B and 48A,48B of the mounting base 44 are supported by the inspection platform 34 of the measurement device 12. The universal fixture 14 further includes first and second pairs of upright grid supports 50A,50B, and guide means in the form of a pair of tracks 52A,52B mounted on, and in parallel relation along, the opposing mounting base portions 46A,46B of the first pair thereof. Each of the grid supports 50A,50B is composed of a spacer block 54 and a support assembly 56. The tracks 52A,52B have dovetail cross-sectional configurations which are complementary to and receivable in grooves 55 having dovetail cross-sectional configurations formed across the bottom of the spacer blocks 54. In such manner, the grid supports 50A and 50B of each of the pairs thereof are mounted to the respective tracks 52A and 52B in spaced relation to one another for adjustable slidable movement therealong. A clamp section 57 in each spacer block 54 is tightened to secure the spacer block to the respective one of the tracks 52A,52B. The support assembly 56 of each of the grid supports 50A,50B is assembled from a base block 58, mounting block 60, a grid support member 62 and a grid support insert 64. The base block 58 has a groove 66 formed across its bottom which is dovetail-shaped and complementary in cross-section to a track 68 formed across the top of each spacer block 54 for mounting the base block 58 to the top of the spacer block 54. A clamp section 70 in the base block 58 is tightened to secure the base block to the spacer block. The mounting block 60 of each support assembly 56 is secured by a dovetail interfitting connection 72 and an adjustment screw 74 to the base block 58 so as to extend in cantilever fashion a short distance inwardly therefrom in overlying relation to a marginal edge portion of the retroreflective surface 36 of the inspection platform 34. The grid support member 62 of each support assembly 56 is slidably mounted by a dovetail groove and track connection 76 to the lower side of the mounting block 60. An adjustment screw 78 is used to move the support member 62 along the X-axis relative to the mounting block 60. At the inner end of each support member 62 is seated one of the grid support inserts 64. When a grid 16 is supported by the fixture 14 as seen in FIG. 1, each of the support members 62 underlies the perimeter of the grid 16 and each of the inserts 64 extends from the bottom side of the grid upwardly into one of the cells thereof. In order for the field of view which encompasses the grid 16 to be transparent except for the grid itself, the grid engaging portions of the fixture 14 which project into the field of view to support the grid 16--the support members 62 and inserts 64--are made of transparent material. For example, the support members 62 are composed of acrylic material and the inserts 64 are scratch-resistant synthetic sapphire material. Further, the universal fixture 14 includes a pair of extendable and retractable actuators 80A,80B, for example, in the form of air cylinders. One actuator 80A is mounted to the one tracks 52A on base portion 46B, whereas the other actuator 80A is mounted to a third track 52C on base portion 48A, by spacer blocks 82 and base blocks 84 being substantially identical, in construction and in their connections together and to the tracks, to the spacer blocks 54 and mounting blocks 60 of the grid supports 50A, 50B. The actuators 80 are actuatable to locate the grid 16 in a desired position with respect to the inspection field of view by causing slight movement of the grid in X and Y directions relative to the grid support members 62 and inserts 64. Still further, the fixture 14 includes a plurality of sensors 86, for instance in the form of microswitch assemblies, mounted to the mounting blocks 60 (above the support members 62) of the first pair of grid supports 50A and to a fourth track 52D by a spacer block 88 and base block 90 being substantially identical, in construction and in their connections together and to the track, to the spacer blocks 54 and mounting blocks 60 of the grid supports 50A,50B. The sensors 86 are responsive to contact by the grid 16 when the latter has been moved to its desired position with respect to the inspection field of view. Turning now to FIGS. 12-16, there is seen two of the many different fuel assembly grid designs adapted to be supported by the universal fixture 14 within the inspection field of view of the noncontact measurement device 12. The grids 16A,16B basically include a multiplicity of interleaved straps 92 having an egg-crate configuration designed to form cells 94. The cells 94 of the grid l6A have opposing dimples 96 formed in the metal of the interleaved straps 92 to support the fuel rods of a fuel assembly which extend through the cells 94. Also, mixing vanes 97 are defined on and extend upwardly from the straps 92. The cells 94 of the grid 16B have opposing dimples 96 and springs 98 which serve the same purpose. In carrying out inspection of the fuel assembly grid 16, the viewing means 30 and source of illumination 32 of the DGU 18 are turned on and moved so as to define the illuminated inspection field of view across the grid as it is supported by the fixture 14. The viewing means 30 views the grid and records multiple images thereof to provide digitized video information to the MDDA 20 from which measurements can be calculated and compared to known standard measurements for the particular grid design stored in the MDDA 20. To view 100% of the grid 16, the viewing means 30 (i.e., video camera and lens system), while maintained pointed in the direction of the field of view toward the retroreflective surface 36, and/or the grid are moved relative to one another. However, the position of the fixture 14 is first sensed to ensure the correctness of the placement thereof before proceeding with inspection of the grid. Typically, as is the case with the grids in FIGS. 12-16, the grid 16A or 16B being inspected has at least a pair of vertically displaced fuel rod contacting dimples 96 disposed in each of a plurality of cells 94 defined in the grid. The dimples 96 are inspected for perpendicularity with respect to each other by using the viewing means 30 to view them at separate instances but from the same location above them and within the field of view. A separate image of each dimple 96 is recorded to provide information from which the degree of offset of one dimple with respect to the other can be determined. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof.
	claims	1. A shield used for electron beam container sterilization equipment that sterilizes a container with electron beams emitted to the container,the shield including a composite shield of a magnetic shield layer and an X-ray shield layer between a pair of corrosion resistant layers for protection against a corrosive atmosphere, the magnetic shield layer blocking magnetism while the X-ray shield layer blocks X-rays generated by reflection and diffraction of electron beams,the composite shield including an insulating layer interposed between one of the corrosion resistant layers and the magnetic shield layer, between the magnetic shield layer and the X-ray shield layer, and between the X-ray shield layer and the other corrosion resistant layer. 2. Electron beam container sterilization equipment that inserts, from a mouth of a container, an electron beam irradiation nozzle having an exit window on a distal end of the irradiation nozzle and sterilizes an inner surface of the container,the electron beam irradiation nozzle being surrounded by a shield,the shield being composed of the shield according to claim 1. 3. Electron beam container sterilization equipment that holds containers kept in an upright position, move the containers along a circular path around a vertical pivot axis, moves electron beam irradiation nozzles in synchronization with the containers, moves at least one of the electron beam irradiation nozzle and the container upward or downward, inserts the electron beam irradiation nozzle into a mouth of the container, and sterilizes an inner surface of the container with electron beams emitted front the electron beam irradiation nozzle,the equipment including an inner shield along an inner periphery of the circular path and an outer shield along an outer periphery of the circular path,the inner and outer shields each being composed of the shield according to claim 1. 4. A shield used for electron beam container sterilization equipment that sterilizes a container with electron beams emitted to the container,the shield being composed of a plurality of composite shield blocks,the composite shield block including a magnetic shield and an X-ray shield in a hollow section of a board-shaped shell made of a corrosion resistant material, and an insulating layer between one surface of the board-shaped shell and the magnetic shield, between the magnetic shield and the X-ray shield, and between the X-ray shield and another surface of the board-shaped shell;the magnetic shield blocking magnetism while the X-ray shield blocks X-rays generated by reflection and diffraction of electron beams. 5. Electron beam container sterilization equipment that inserts, from a mouth of a container, an electron beam irradiation nozzle having an exit window on a distal end of the irradiation nozzle and sterilizes an inner surface of the container,the electron beam irradiation nozzle being surrounded by a shield,the shield being composed of the shield according to claim 4. 6. Electron beam container sterilization equipment that holds containers kept in an upright position, move the containers along a circular path around a vertical pivot axis, moves electron beam irradiation nozzles in synchronization with the containers, moves at least one of the electron beam irradiation nozzle and the container upward or downward, inserts the electron beam irradiation nozzle into a mouth of the container, and sterilizes an inner surface of the container with electron beams emitted from the electron beam irradiation nozzle,the equipment including an inner shield along an inner periphery of the circular path and an outer shield along an outer periphery of the circular path,the inner and outer shields each being composed of the shield according to claim 4.
	claims	1. A ventilated system for storing high level waste emitting heat, the system comprising:an air-intake shell forming an air-intake cavity;a plurality of storage shells, each storage shell forming a storage cavity;a lid positioned atop each of the storage shells;an outlet vent forming a passageway between an ambient environment and a top portion of each of the storage cavities; anda network of pipes forming hermetically sealed passageways between as bottom portion of the air-intake cavity and at least two different openings at a bottom portion of each of the storage cavities such that blockage of a first one of the openings does not prohibit air from flowing from the air-intake cavity into the storage cavity via a second one of the openings. 2. The system of claim 1 further comprising a hermetically sealed canister for holding high level waste positioned in one or more of the storage cavities so that a gap exists between the storage shell and the canister, the horizontal cross-section of the storage cavities accommodating no more than one of the canisters. 3. The system of claim 1 wherein the network of pipes is configured so that the first one of the openings is an end of a first path through the passageways from the air-intake cavity to the storage cavity and the second one of the openings is an end of a second path through the passageways from the air-intake cavity to the storage cavity, wherein the first and second paths are different. 4. The system of claim 1 wherein the outlet vents are formed into the lids. 5. The system of claim 1 wherein the storage shells and the air-intake shell are vertically oriented and arranged in a side-by-side relation. 6. The system of claim 5 further comprising:a ground having a grade; andwherein the storage shells are positioned so that at least a major portion of a height of each storage shell is located below the grade, the network of pipes being located below the grade, and the downcomer air-intake cavity forming a passageway between an opening located above the grade and the network of pipes. 7. The system of claim 6 wherein the storage shells, the air-intake shell, and the network of pipes are hermetically sealed against the ingress of below grade liquids. 8. The system of claim 1 wherein the network of pipes comprises one or more headers that couple the storage shells to the air-intake shell. 9. The system of claim 1 further comprising one or more layers of insulating material circumferentially surrounding the storage shells. 10. A ventilated system for storing high level waste emitting heat, the system comprising:an air-intake shell forming an air-intake cavity;a plurality of storage shells, each storage shell forming a storage cavity;a lid positioned atop each of the storage shells;an outlet vent forming a passageway between an ambient environment and a top portion of each of the storage cavities; anda network of pipes forming hermetically sealed passageways between a bottom portion of the air-intake cavity and a bottom portion of each of the storage cavities, wherein the network of pipes is configured so that a line of sight does not exist between any of the storage cavities through the passageways. 11. The system of claim 10 wherein the network of pipes connects to side walls of the storage shells. 12. The system of claim 11 wherein the storage shells are arranged in a side-by-side relation, wherein bottoms surfaces of the storage shells are located in a plane, and wherein the network of pipes does not extend below the plane. 13. The system of claim 10 further comprising a hermetically sealed canister for holding high level waste positioned in one or more of the storage cavities so that a gap exists between the storage shell and the canister, the horizontal cross-section of the storage cavities accommodating no more than one of the canisters. 14. The system of claim 10 further comprising:a ground having a grade; andwherein the storage shells are positioned so that at least a major portion of a height of each storage shell is located below the grade, the network of pipes being located below the grade, and the downcomer air-intake cavity forming a passageway between an opening located above the grade and the network of pipes. 15. The system of claim 14 wherein the storage shells, the air-intake shell, and the network of pipes are hermetically sealed to the ingress of below grade liquids.
	summary
	summary
	summary
042241065	description	FIG. 1 shows the frame 4 in which the grid 6 is fitted. Said frame 4 comprises two side plates 4a and 4b as well as two end plates 4c and 4d. In the example herein described, the grid 6 is constituted by two sets of thin wires 6a and 6b of Zircaloy which intersect at right angles and are joined together by electric welding at points such as those designated by the reference 7 so as to form a lattice in which the ceramic fuel wafers 8 of the fuel element are subsequently intended to be fitted. In the example shown in FIG. 1, the meshes of the lattice have a rectangular shape but could just as readily have a square shape for certain different applications. The different wires 6a and 6b of the grid 6 have a diameter which is substantially equal to the thickness of the fuel wafers 8. Said wires are subjected first to electric welding under pressure in order to reduce overthicknesses at each point of intersection 7, then to a trimming operation in order to ensure perfect calibration of the lattice openings. As a general rule, the different wafers of sintered fuel have a thickness within the range of 1 to 1.5 mm. The dimensions of each rectangular mesh are chosen so as to optimize ease of shaping at the moment of compression of each fuel wafer. By way of indication, good dimensions are of the order of 30.times.18 mm; as mentioned earlier, however, a square shape (17.times.17 mm, for example) appears to represent a particularly advantageous solution on technological grounds. In accordance with the invention, the assembly formed by the grid 6 and the fuel wafers 8 is finally placed between a top cladding plate 9 and a bottom cladding plate 10. In the alternative embodiment of FIG. 2, the grid 6 is provided with a framing wire 11 which surrounds said grid on all four sides and has the same composition and diameter as the wires 6a and 6b of the grid itself. Said framing wire 11 is welded to the wires 6a and 6b as well as to the side plates 4a and 4b and to the end plates 4c and 4d. One of the most attractive industrial applications of the thin fuel element in accordance with the invention lies in the possibility of converting the core of an existing pool reactor by fitting it with fuel element plates of low enrichment. In fact, in order to establish a neutron balance in the core of a reactor of this type, there are four essential factors to be taken into consideration and these are respectively as follows: a moderating ratio equal to the ratio of the volume of moderator (water) to the volume of fuel; a fuel enrichment which can attain 93% in U-235 in pool-type reactors of conventional design ; the mass of U-235 within the reactor core; the available reactivity which represents the capacity of the reactor for irradiation of materials. The ratios between the four parameters given above, two of which are related to each other (mass of uranium and enrichment) are illustrated by the set of curves of FIG. 3 which shows the variation of reactivity in respect of a certain number of enrichments respectively equal to 1.5%, 2.5%, 3%, 4%, 5%, 7.5% and 10%, as a function of the moderating ratio which is plotted as abscissae. The general shape of these curves (increasing function which passes through a maximum and then decreases) indicates that the moderating ratio must be placed in the vicinity of a value at least equal to 2 in order to derive maximum benefit from the core reactivity. In the case of the fuel elements commonly employed up to the present time in pool reactors (platetype elements of aluminum-uranium alloy enriched with 93% U-235), the moderating ratio usually adopted is in the vicinity of 2 as mentioned above. If plate fuel elements are replaced in a reactor of this type by plate elements of the fuel wafer type of relatively substantial thickness (4 to 5 mm, for example), it is possible in such a case: either to retain substantially the same number of plate elements within the internal space provided for the reactor core, thus resulting in a reduction of the moderating ratio and entailing the need for much higher enrichment in order to maintain the same reactivity, or to reduce the number of plate elements in order to retain the same moderating ratio, in which case the power level of the reactor core is also reduced. On the contrary, by making use of fuel elements in the form of thin plates which is made possible by the present invention, the number of plates can be increased while retaining a moderating ratio which is very close to 2 and consequently permitting a relatively low fuel enrichment in order to maintain a substantially identical power level in the pool-type reactor core. Referring again to FIG. 3, it is apparent, for example, that a reactor which is made up of plates of substantial thickness, which permits a moderating ratio of the order of 1, which is charged at an enrichment of 10% U-235 and discharged at 5% residual U-235 (path BC), operates with the same reserve of reactivity as a core which permits a moderating ratio of 2, which is charged at 4.5% U-235 and discharged at 3% U-235 (path AD).
	abstract	A nuclear reactor in which a primary coolant is contained, the primary coolant moves upwardly from the core by an operation thereof. An annular steam generator is arranged in an upper side of the core into which the upwardly moving primary coolant flows and transfers heat in the primary coolant into water therein to generate a steam. A passage structure defines a coolant passage for the primary coolant to an outside of the core. The heat-transferred primary coolant in the annular steam generator flows downwardly in the coolant passage so as to flow into the core, thereby moving upwardly. A reactor vessel is arranged to surround the coolant passage so as to contain the core, the annular steam generator and the passage means therein.
	abstract	This invention relates to radioactive, bone-seeking, pharmaceutical methods, compositions and formulations that have a lower impurity profile, a longer shelf life, improved availability and are less expensive to prepare. The compositions of this invention can be conveniently prepared in a timely manner resulting in improved availability and delivery of the drugs to patients.
	claims	1. A cabin structure of a manned vehicle for special environment use, the structure being configured such that a cabin is mounted on a vehicle body having at least an engine and a vehicle moving mechanism driven by the engine, this cabin storing an operation terminal for operating the engine and the vehicle moving mechanism, and having a space for accommodating an operator who operates the operation terminal or an occupant, whereinthe cabin is formed as a casing body having a protection structure and partitioned and separable from the vehicle body,the casing body has a coupling and fastening part on a bottom side of the cabin for secure attachment to the vehicle body with restraint at least in planar coordinate directions,the casing body has a monocoque structure of a combination of a plurality of metal plates that can function as shielding masses, and, around a hole drilled in the metal plate, a baffle is provided at a position facing an incoming direction of special substances, or a bent path for incoming special substances is formed by one or a plurality of the metal plates, so that the operator or occupant inside the cabin is not directly exposed to the special substances from outside the casing body. 2. The cabin structure of a manned vehicle for special environment use according to claim 1,wherein the casing body has a box-like structure without a bottom plate or with a separable bottom plate, the bottom plate or a lower end part of the casing body being secured to the vehicle body, andwherein the coupling and fastening part is provided between the vehicle body and the box-like structure for secure attachment with restraint in planar coordinate directions. 3. The cabin structure of a manned vehicle for special environment use according to claim 1,wherein the casing body has surface parts at least on a front side and a rear side in a vehicle moving direction that are shielded by lead glass with front and rear visibility. 4. The cabin structure of a manned vehicle for special environment use according to claim 1, further comprising:an opening formed in a bottom plate of the casing body and having a seal part for seal off from special substances and, whereina control unit controlling the vehicle body and supplementary equipment by processing signals including a signal obtained by operation of the operation terminal is disposed as the protection structure inside the casing body, while a signal line for transmitting signals processed in the control unit is extended through the opening into the vehicle body. 5. The cabin structure of a manned vehicle for special environment use according to claim 1,wherein the coupling and fastening part comprises fitting parts protruding and recessed in a direction perpendicular to the planar coordinates, the fitting parts fitting to each other to connect the casing body with the vehicle body and restraining the casing body to the vehicle body in three-dimensional directions. 6. The cabin structure of a manned vehicle for special environment use according to claim 1,wherein the coupling and fastening part comprises bolts fastened to connect the casing body to the vehicle body such as to be separable from the vehicle body. 7. A manned vehicle for special environment use,wherein the vehicle body according to claim 1 is a body of an industrial vehicle having an engine, a vehicle moving mechanism driven by the engine, and a work end driven by operation of the operation terminal in a cabin, andwherein a signal from the operation terminal is configured to be transmitted via a signal tube or a signal line directly through the opening(s) to the vehicle body, or to be transmitted to the vehicle body through the opening(s) via the signal line for transmitting signals processed in the control unit disposed inside the casing body. 8. A cabin structure of a manned vehicle for special environment use, the structure being configured such that a cabin is mounted on a vehicle body having at least an engine and a vehicle moving mechanism driven by the engine, this cabin storing an operation terminal for operating the engine and the vehicle moving mechanism, and having a space for accommodating an operator who operates the operation terminal or an occupant, whereinthe cabin is formed as a casing body having a protection structure and partitioned and separable from the vehicle body,the casing body has a coupling and fastening part on a bottom side of the cabin for secure attachment to the vehicle body with restraint at least in planar coordinate directions,the casing body has a monocoque structure of a combination of a plurality of metal plates that can function as shielding masses, anda gap portion between adjacent metal plates is formed as a bent path for incoming special substances and formed either by an abutment plate provided at a position facing an incoming direction of special substances or by one or a plurality of the metal plates, so that the operator or occupant inside the cabin is not located on a line extending straight from outside air through the gap portion. 9. The cabin structure of a manned vehicle for special environment use according to claim 8, wherein the casing body has a box-like structure without a bottom plate or with a separable bottom plate, the bottom plate or a lower end part of the casing body being secured to the vehicle body, andwherein the coupling and fastening part is provided between the vehicle body and the box-like structure for secure attachment with restraint in planar coordinate directions. 10. The cabin structure of a manned vehicle for special environment use according to claim 8,wherein the casing body has surface parts at least on a front side and a rear side in a vehicle moving direction that are shielded by lead glass with front and rear visibility. 11. The cabin structure of a manned vehicle for special environment use according to claim 8, further comprising:an opening formed in a bottom plate of the casing body and having a seal part for seal off from special substances and, whereina control unit controlling the vehicle body and supplementary equipment by processing signals including a signal obtained by operation of the operation terminal is disposed as the protection structure inside the casing body, while a signal line for transmitting signals processed in the control unit is extended through the opening into the vehicle body. 12. The cabin structure of a manned vehicle for special environment use according to claim 8,wherein the coupling and fastening part comprises fitting parts protruding and recessed in a direction perpendicular to the planar coordinates, the fitting parts fitting to each other to connect the casing body with the vehicle body and restraining the casing body to the vehicle body in three-dimensional directions. 13. The cabin structure of a manned vehicle for special environment use according to claim 8,wherein the coupling and fastening part comprises bolts fastened to connect the casing body to the vehicle body such as to be separable from the vehicle body. 14. A manned vehicle for special environment use,wherein the vehicle body according to claim 8 is a body of an industrial vehicle having an engine, a vehicle moving mechanism driven by the engine, and a work end driven by operation of the operation terminal in a cabin, andwherein a signal from the operation terminal is configured to be transmitted via a signal tube or a signal line directly through the opening(s) to the vehicle body, or to be transmitted to the vehicle body through the opening(s) via the signal line for transmitting signals processed in the control unit disposed inside the casing body. 15. A manned vehicle for special environment use, having: a vehicle body having at least an engine and a vehicle moving mechanism driven by the engine; and a cabin storing an operation terminal for operating the engine and the vehicle moving mechanism and accommodating an operator who operates the operation terminal or an occupant, whereinthe cabin is formed as a casing body having a protection structure and partitioned and separable from the vehicle body,the casing body is fixed to the vehicle body via a coupling and fastening part with restraint at least in planar coordinate directions,the casing body has a monocoque structure of a combination of a plurality of metal plates that can function as shielding masses, anda gap portion between adjacent metal plates is formed as a bent path for incoming special substances and formed either by a baffle provided at a position facing an incoming direction of special substances or by one or a plurality of the metal plates, so that the operator or occupant inside the cabin is not located on a line extending straight from outside air through the gap portion. 16. The manned vehicle for special environment use according to claim 15,wherein the casing body has a box-like structure without a bottom plate or with a separable bottom plate, the bottom plate or a lower end part of the casing body being secured to the vehicle body, andwherein the coupling and fastening part is interposed between the vehicle body and the box-like structure for secure attachment with restraint in planar coordinate directions. 17. The manned vehicle for special environment use according to claim 15, further comprising:one or a plurality of openings having a seal part formed in a bottom plate of the casing body facing the vehicle body and seal off from special substances and, whereina control unit controlling the vehicle body and supplementary equipment by processing signals including a signal obtained by operation of the operation terminal is disposed inside the casing body, while a signal line for transmitting signals processed in the control unit is configured to transmit the signals to the vehicle body through the opening. 18. The manned vehicle for special environment use according to claim 15,wherein the casing body has surface parts at least on a front side and a rear side in a vehicle moving direction that are shielded by lead glass with front and rear visibility. 19. The manned vehicle for special environment use according to claim 15,wherein the coupling and fastening part comprises a protrusion and a recess protruding and recessed in a direction perpendicular to the planar coordinates, with one of the protrusion and the recess being formed on the casing body and the other one of the protrusion and the recess being formed on the vehicle body, which are fitted to each other to restrain the casing body to the vehicle body in three-dimensional directions. 20. A manned vehicle for special environment use, having: a vehicle body having at least an engine and a vehicle moving mechanism driven by the engine; and a cabin storing an operation terminal for operating the engine and the vehicle moving mechanism and accommodating an operator who operates the operation terminal or an occupant, whereinthe cabin is formed as a casing body having a protection structure and partitioned and separable from the vehicle body,the casing body is fixed to the vehicle body via a coupling and fastening part with restraint at least in planar coordinate directions,the casing body has a monocoque structure of a combination of a plurality of metal plates that can function as shielding masses, andaround a hole drilled in the metal plate, a baffle is provided at a position facing an incoming direction of special substances, or a bent path for incoming special substances is formed by one or a plurality of the metal plates, so that the operator or occupant inside the cabin is not directly exposed to the special substances from outside the casing body. 21. The manned vehicle for special environment use according to claim 20,wherein the casing body has a box-like structure without a bottom plate or with a separable bottom plate, the bottom plate or a lower end part of the casing body being secured to the vehicle body, andwherein the coupling and fastening part is interposed between the vehicle body and the box-like structure for secure attachment with restraint in planar coordinate directions. 22. The manned vehicle for special environment use according to claim 20, further comprising:one or a plurality of openings having a seal part formed in a bottom plate of the casing body facing the vehicle body and seal off from special substances and, whereina control unit controlling the vehicle body and supplementary equipment by processing signals including a signal obtained by operation of the operation terminal is disposed inside the casing body, while a signal line for transmitting signals processed in the control unit is configured to transmit the signals to the vehicle body through the opening. 23. The manned vehicle for special environment use according to claim 20,wherein the casing body has surface parts at least on a front side and a rear side in a vehicle moving direction that are shielded by lead glass with front and rear visibility. 24. The manned vehicle for special environment use according to claim 20,wherein the coupling and fastening part comprises a protrusion and a recess protruding and recessed in a direction perpendicular to the planar coordinates, with one of the protrusion and the recess being formed on the casing body and the other one of the protrusion and the recess being formed on the vehicle body, which are fitted to each other to restrain the casing body to the vehicle body in three-dimensional directions.
051715155	summary	BACKGROUND OF THE INVENTION The invention relates to a process for inhibiting corrosion in a pressurized water nuclear reactor, and more particularly for inhibiting corrosion within the primary circuit of a pressurized water nuclear reactor. Corrosion is a particular concern for nuclear reactors in which water is present as a coolant. Several methods have been proposed to deal with the problem, including dissolving oxide scale from the structure of the nuclear reactor, as disclosed in U.S. Pat. No. 3,664,870 to Oberhofer et al. and U.S. Pat. No. 4,042,455 to Brown. Another approach, as disclosed in U.S. Pat. No. 4,364,900 to Burrill, is to inhibit corrosion formation within the reactor system. Burrill adds from about 120 to about 200 milligrams of ammonia per kilogram of coolant water to reduce crevice corrosion in the core of pressurized water nuclear reactors. Zinc ions are thought to inhibit corrosion within boiling water nuclear reactors, and such ions from zinc oxide and zinc chloride have been described for use in boiling water nuclear reactors. As discussed by W. J. Marble in "Control of Radiation-Field Buildup in BWRs", Electric Power Research Institute NP-4072, Project 189-2, Interim Report, June 1985, zinc in the form of ZnO was used in a boiling water reactor plant. It was discussed therein that soluble zinc, by acting as a corrosion inhibitor for stainless steel, significantly reduces the amount of oxide formed on the pipes and thus the amount of Co-60 incorporated in the system. The hypothesis proposed on page 4-2 of that reference was that zinc cations normally found in zinc oxide crystals will tend to modify the normal magnetite crystal defect structure so that a more protective film is formed and corrosion significantly inhibited. Further, the presence of zinc ions in the reactor coolant water of boiling water reactors having brass tubing, as discussed at page 6-1, has been correlated with a reduced amount of corrosion and radioactive cobalt transport throughout the reactor. Zinc introduced in the form of zinc chloride (ZnCL.sub.2) was also laboratory tested as a corrosion inhibitor under power plant operating conditions, as discussed by L. W. Niedrach and W. H. Stoddard in "Effect of Zinc on Corrosion Films that Form on Stainless Steel", Corrosion 42, 546 (1986). The use of zinc oxide as a source of zinc ions has the drawback that zinc oxide is not particularly soluble in water, and, therefore, the zinc oxide must be added to the coolant as a slurry or suspension, rather than as a solution. Pressurized water nuclear reactors are thermal reactors in which water is used as the coolant and as the moderator. The water is circulated by pumps throughout a primary circuit, that includes a pressure vessel, which houses the heat generating reactor core, and a plurality of flow loops. The heat absorbed by the water as it passes through the reactor core is transferred by means of a heat exchanger to a readily vaporizable liquid (water) in a secondary circuit in which the thermal energy is used to produce electricity. The water is then returned to the pressure vessel. The water in the primary circuit, which normally contains boric acid as a moderator, passes through numerous metal, generally stainless steel and Alloy 600, conduits, all of which are subject to corrosion. Further, some radioactive cobalt from the reactor core is dissolved in the water as the metal ion and transported throughout the primary circuit. The transport of radioactive cobalt throughout the primary circuit results in a level of residual radioactivity throughout the primary circuit that is not desired. Thus, it is desired to develop a process for inhibiting corrosion in a pressurized water nuclear reactor. An object of the invention is to provide a process for inhibiting corrosion in a nuclear reactor by the addition of zinc to the coolant water flowing therethrough in a soluble form. SUMMARY OF THE INVENTION The present invention provides a process for inhibiting corrosion caused by the presence of coolant water passing through a pressurized water nuclear reactor. An effective amount of an aqueous solution of zinc borate is added to the reactor coolant water. As a result of the process, the transport of corrosion products and radioactive cobalt ions through the reactor system, as well as levels of radioactivity within the reactor system, are reduced. The aqueous solution of zinc borate is preferably an aqueous solution of zinc borate in boric acid, with the zinc borate preferably added to the reactor coolant water so that zinc ions are present in the reactor coolant water in an amount of from about 10 to about 200 parts per billion.
047553286	summary	BACKGROUND OF THE INVENTION The invention relates to a process for treating acid solutions, contaminated with uranium. From a more general point of view, the invention is intended to provide a process for treating acid uraniferous solutions, possibly containing radium, which process comprises adjustment of the final pH and decontamination of uranium and of radium to values such that the solutions, after treatment, can be discharged without harming the natural environment. The extraction of uranium ores from open pit mines or from underground mines necessitates treating the drained waters whose flow rates can reach several hundreds of cubic metres. These drained waters contain various elements, particularly uranium and possibly radium, at concentrations which can be detrimental to the natural environment when they are discharged thereto. In addition, these waters generally have a pH which is also detrimental to the natural environment. It is the same with liquid effluents resulting from the acid or alkaline treatment of uranium ores. In order not to spoil the natural environment particularly the hydrogeological system into which the drained waters and the liquid effluents are discharged the concentration of these waters and effluents respectively in uranium and radium must be as low as possible. This explains the reason why very strict standards have been fixed relating to the pH and the maximum content of uranium and of radium for drained waters and liquid effluents. It is necessary, in fact, for the final pH of the solutions to be between 5.5 and 8.5, for the radium content to correspond to an activity equal or less than 10 pCi/l and for the uranium content to be equal to or less than 1.8 mg/l. It is known to remove the radium by a treatment with barium chloride, which in the presence of sulfate ions, causes the formation of barium sulfate and of radium sulfate which precipitate. As for the removal of the uranium, in the processes employed until now, resins or other adsorbants (for example titanium oxide) are used, which require large installations and often are subject to risk of clogging. The problem not yet resolved until now is the process of treating drained water or effluents, containing uranium content both too low to justify setting up of a laborious resin unit, and too high to permit discharge to to the natural environment. The difficulties associated with the removal of the uranium are correlated to several parameters and particularly to the fact that, in uraniferous solutions, the uranium occurs in various physical forms, namely solid, soluble and colloidal. The solid particles of uranium are generally the subject of removal by decantation or filtration. As regards the soluble particles, their existence is explained by the use of sulfuric acid to form acid waters for the lixiviation of the uranium or by the presence of carbonate or bicarbonate ions used to form alkaline waters enabling the lixiviation of the uranium. As for the colloidal particles, they correspond to an intermediate state between the solid and soluble uranium and they generally have a size of 10.sup.-1 to 10.sup.-3 microns and cannot be removed by simple decantation or filtration. It is particularly the coexistence in the same solution of soluble and colloidal uranium which makes it difficult to set up a efficient process for removal of the uranium. Another parameter which plays a part in the elimination of uranium, is the presence of numerous other ions as well as the respective values of their concentration. Among these ions, maybe be mentioned calcium, sodium; magnesium, sulfate, carbonate, bicarbonate, chloride, potassium, nitrate, ferric, or aluminum ions. It is one of the objects of the invention to provide a process for removing uranium from acid uraniferous solutions, whether the uranium is soluable and/or in colloidal form. It is another object of the invention to provide a process for removing uranium from acid uraniferous solutions, applicable even to solutions highly charged with ions. Another object of the invention is to provide a process for removing uranium from acid uraniferous solutions, whatever the nature of the ion species in solution. Another object of the invention is to provide a process for removing uranium and radium, from acid uraniferous solutions, at the end of which the contents of uranium and of radium and the value of the pH of the final solutions obtained are compatible with the natural environment. A further object of the invention is to provide a process for removing uranium and radium from acid uraniferous solutions, at the end of which the contents of uranium and radium as well as the value of the pH of the final solutions obtained, meet the legislative standards in force.
044501340	abstract	An improved method and apparatus for transferring nuclear fuel elements between a fluid-filled storage pool and a cask is disclosed. The cask is supported within and is restrained by a tank which is transported between terminal locations of a nuclear facility. Transfer of fuel elements between a storage pool and the cask is accomplished by coupling the tank to a port of the pool. The transporter accurately positions and restrains the tank during transfer. In a preferred embodiment, the cask tank is unweighted from the transporter during transfer and is advanced into a fluid-sealed engagement with a port surface of the pool. In an alternative arrangement, the cask tank remains supported on the transport during its transfer and lifting means mutually engaging the transporter and tank advance the tank toward the port surface for establishing a coupling between the port and the cask. The method and apparatus substantially reduce fluid contact with an exterior surface of the cask during transfer and potential nuclear contamination; they enhance the protection of the transfer apparatus against seismic disturbances; and, they accomodate casks of different sizes.
	abstract	An inspecting apparatus for reducing a time loss associated with a work for changing a detector is characterized by comprising a plurality of detectors 11, 12 for receiving an electron beam emitted from a sample W to capture image data representative of the sample W, and a switching mechanism M for causing the electron beam to be incident on one of the plurality of detectors 11, 12, where the plurality of detectors 11, 12 are disposed in the same chamber MC. The plurality of detectors 11, 12 can be an arbitrary combination of a detector comprising an electron sensor for converting an electron beam into an electric signal with a detector comprising an optical sensor for converting an electron beam into light and converting the light into an electric signal. The switching mechanism M may be a mechanical moving mechanism or an electron beam deflector.
	claims	1. A high-frequency control device for an accelerator to control a high frequency which is applied to an acceleration cavity of an accelerator which generates a particle beam to be used for a particle beam therapy, wherein the high-frequency control device for an accelerator comprises:a hard disk drive memory which stores pattern data of a high frequency to be applied for each combination of energy and intensity of the generated particle beam;a local memory, which reads a plurality of pattern data of a high frequency for each patient together with a sequential order of changing energy and intensity from the hard disk drive memory, and stores data in order to perform a scanning irradiation method in which a layered particle beam irradiation region in a depth direction of an affected part of the patient is formed sequentially by changing energy and intensity of the particle beam sequentially to irradiate the affected part of the patient which is an irradiation subject with the particle beam, and which reads out data faster than the hard disk drive memory, anda command value checking part which checks whether a command value from an irradiation system control device, which controls a particle beam irradiation device for irradiating the affected part which is the irradiation subject for each time when energy and intensity of the particle beam is changed, is in agreement with pattern data which is sent out from the local memory or not,wherein in a case where it is judged that a command value from the irradiation system control device is not in agreement with pattern data which is sent out from the local memory, the accelerator is operated according to subsequent pattern data of energy and intensity, and during the operation, data in the local memory is reread until the data pattern is in agreement with the command value. 2. A particle beam therapy system comprising the accelerator, a particle beam transportation system which transports a particle beam which is extracted from the accelerator, and a particle beam irradiation device for irradiating the particle beam which is transported onto the irradiation subject,wherein a high frequency which is applied to the acceleration cavity of the accelerator is controlled by a high-frequency control device according to claim 1.
	claims	1. A device for protection of a body from space radiation, the device comprising:at least one flexible garment, each section of said at least one flexible garment being configured to shield a region of a surface of the body such that said each section complementarily attenuates self-shielding by internal structure between said region and an interior region of the body such that space radiation at the interior region is attenuated to a predefined attenuation level, anda plurality of shield elements incorporated into a flexible substrate of the at least one flexible garment, comprising a plurality of bags, each of the bags being configured to be filled with a liquid. 2. The device of claim 1, wherein the flexible substrate or said plurality of shield elements comprises a polymer. 3. The device of claim 1, wherein said plurality of shield elements is embedded within the flexible substrate. 4. The device of claim 1, wherein each of said plurality of shield elements has an inward facing surface that is greater than an opposite outward facing surface, such that tapering gaps are formed in between adjacent shield elements of said plurality of shield elements. 5. The device of claim 4, wherein the substrate fully or partially fills the gaps. 6. The device of claim 1 wherein the flexible substrate comprises a foam. 7. The device of claim 1, wherein said plurality of shield elements comprises a plurality of sequins that are attached to the flexible substrate and wherein the flexible surface comprises a fabric sheet. 8. The device of claim 7, wherein the fabric sheet forms a webbing between said plurality of sequins. 9. The device of claim 7, wherein a garment of said at least one garment comprises a plurality of the fabric sheets formed into layers. 10. The device of claim 9, wherein a sequin of said plurality of sequins on one fabric sheet of said plurality of the fabric sheets is positioned to overlie a gap between adjacent sequins of said plurality of sequins on another fabric sheet of said plurality of fabric sheets. 11. The device of claim 1, wherein the flexible substrate comprises a plurality of flexible bag holders, each of said plurality of bags being configured to be inserted into a bag holder of said plurality of flexible bag holders. 12. The device of claim 1, wherein said at least one garment comprises a plurality of garments that are configured to be worn in layers, wherein one garment of said plurality of garments is configured such that a shield element of said plurality of shield elements on said one garment is configured to overlie a gap between two adjacent shield elements on another garment of said plurality of garments. 13. The device of claim 1, wherein the interior region includes tissue-resident stem cells. 14. The device of claim 13, wherein the tissue-resident stem cells are selected from a group of tissue-resident stein cells consisting of distal airway stem cells of the lung, CD34+ hematopoietic stem cells, and intestinal LGR5+ stem cells. 15. A device for protection of a body from space radiation, the device comprising:at least one flexible garment, each section of said at least one flexible garment being configured to shield a region of a surface of the body such that said each section complementarily attenuates self-shielding by internal structure between said region and an interior region of the body such that space radiation at the interior region is attenuated to a predefined attenuation level, anda plurality of shield elements incorporated into a flexible substrate of the at least one flexible garment,wherein a shield element of said plurality of shield elements comprises a plurality of stacked liquid-fillable compartments. 16. The device of claim 15, further comprising a tube to enable introduction of a liquid into a liquid-fillable compartment of said plurality of stacked liquid fillable compartments or removal of the liquid frog a liquid-fillable compartment of said plurality of stacked liquid-fillable compartments. 17. A method for preventing a space radiation-induced condition in a body in space, the method comprising:determining a required attenuation of space radiation at an interior region of the body so as to prevent the space radiation-induced condition under an anticipated exposure of the body to space radiation;determining self-shielding from the space radiation corresponding to each surface region of a plurality of regions of a surface of the body by determining attenuation of the radiation by internal structure of the body that lies between the interior region and said each surface region;providing a space radiation protection device comprising at least one flexible garment, each section of said at least one flexible garment being configured to attenuate space radiation to a shielded surface region of plurality of regions of a surface of the body to complementarily attenuate the self-shielding by the shielded surface region; andproviding a plurality of shield elements incorporated into a flexible substrate of the at least one flexible garment and having a plurality of bags, each of the bags being configured to be filled with a liquid. 18. The method of claim 17, wherein the space radiation-induced condition comprises mutagenesis or destruction of stem cells and the interior region comprises a stem cell niche. 19. The method of claim 17, wherein determining the required space radiation attenuation comprises determining an attenuation required to prevent a Bragg peak of the space radiation from occurring within the interior region. 20. The method of claim 17, wherein determining the required attenuation of space radiation comprises determining total areal density of shielding to the interior region to prevent the space radiation-induced condition, the determined self-shielding comprises an areal density of the internal structure that lies between the interior region and said each surface region, and wherein an areal density of said each section is at least a difference between said total areal density and said areal density of the internal structure. 21. The method of claim 17, wherein the plurality of bags comprise a plurality of stacked liquid-fillable compartments.
	description	The present invention relates in general to techniques to obtain improved images. In particular it relates methods of lithography using a computer controlled imaging arrangement, such as for instance a Spatial Light Modulator (SLM), with an improved virtual grid. It also relates to an apparatus for patterning a work piece comprising such a method. Lithographic production is useful for integrated circuits, masks, reticles, flat panel displays, micro-mechanical or micro-optical devices and packaging devices, e.g. lead frames and MCM's. Lithographic production may involve an optical system to image a master pattern from a computer-controlled reticle onto a workpiece. A suitable workpiece may comprise a layer sensitive to electromagnetic radiation, for example visible or non-visible light. An example of such a system is described in WO 9945435 with the same inventor and applicant as the present invention. Said computer controlled reticle may for instance be a Spatial Light Modulator (SLM) comprising a one or two dimensional array or matrix of reflective movable micro mirrors; a one or two dimensional array or matrix of transmissive LCD crystals; or other similar programmable one or two dimensional arrays based on gratings effects, interference effects or mechanical elements, e.g. shutters. Generally speaking pattern quality may be improved by multipass writing. However, there are several different aspects of the pattern quality that are improved by multipass writing, but not necessarily at the same time. First, it is possible to create a finer address grid in several passes than in one single pass. Second, multiple passes with offset grid can remove the grid effects due to the finite pixel size. Third, random errors (such as artifacts in the light path, noise in the exposure dose, misplacement of beam or field used for imaging) are statistically reduced by multiple passes, e.g., four passes reduces the effects of random dose errors by a factor of two (square root of four). Fourth, systematic errors (such as dose fall of in corners of the image to be written, distortion and focal plane curvature) can be reduced by offset between the writing fields. Fifth, with multiple writing passes it is possible to better correct for bad pixels. Sixth, many multipass schemes give a softening of the edges, and retention of edge acuity is a desirable property of a multipass scheme. Different rasterizing multipass schemes can be devised, but it is a problem to find schemes that simultaneously give improvements in all six aspects mentioned above. FIG. 3a illustrates a known method for creating a virtual grid. In FIG. 3a it is shown an array of seven lines and 5 columns of pixels. Pixels in the two leftmost columns are set to a maximum grayscale value. Pixels in the two rightmost columns are set to minimum grayscale value. Pixels in a middle column are set to an intermediate grayscale value. FIG. 3a is an example of analog modulation of feature edge pixels 301 in a single pass in order to create a virtual grid. All pixels in said middle column are set to the same value. FIG. 3b illustrates another known method for creating a virtual grid. In this method four writing passes 305 are written with binary doses (e.g. 100%, 50%, 25%, 12,5%). All pixels in one single pass are set to equal grayscale values. The virtual grid is created by turning on a column of feature edge pixels in at least one writing pass, in FIG. 3b columns of feature edge pixels are turned on in the top writing pass and the second writing pass from bottom. FIG. 3c illustrates yet another known method for creating a virtual grid. In this method all four writing passes 305 are written with the same dose. In at least one pass a column 304 of feature edge pixels are turned on, illustrated in FIG. 3c to be the bottom writing pass and the second writing pass from the bottom. FIG. 4a illustrates another known method for creating a virtual grid. In this method four 401 passes are written offset with equal dose. The different writing passes are illustrated in FIG. 4a to be offset relative to an origin 402. By turning on edge pixels 403 in only some passes an edge of a feature to be written can be fine positioned. FIG. 4b illustrates still another known method for creating a virtual grid. This method utilizes a combination of the analog modulation of feature edge pixels with offset passes which gives a different analog value 404 in each pass. FIG. 5a illustrates a writing grid of four pixels in a single pass writing strategy. A reference mark denoted with 501 is arranged in middle of the grid. FIG. 5b illustrates a known method for offsetting different writing passes. Here four passes are used where two of them are offset relative to the other two by a distance defined by a half pixel size in two orthogonal directions parallel with the pixel grid. By offsetting different writing passes in a multiple writing strategy different imaging defects can more or less effectively be hidden. FIG. 5c illustrates another known method for offsetting different writing passes in order to hide the grid. In this embodiment all writing passes are offset relative to each other. One writing pass is offset in a first direction only, another writing pass is offset in a second direction, orthogonal to said first direction, and one writing pass is offset in sad first and sad second direction simultaneously. The offset in said first and said second direction is illustrated to be half a pixel size. It is in a general sense possible to make pattern fidelity better by increasing the number of passes, but the cost is high. Doubling the number of passes doubles the capital and operating cost of the pattern generator per produced workpiece and can in many cases be economically impossible. In general, computer controlled reticles may be used for the formation of images in a variety of ways. These reticles, such as an SLM, include many modulating elements or pixels, in some instances, a million or more pixels. In WO 99/45440, with one common inventor to the present application, is described a pattern generator with improved address resolution. In said application the pixels can be set in a number of states, larger than two, with one type of pixel map inside pattern features, another type of pixel map outside pattern features and intermediate pixel maps at a boundary of pattern features. The intermediate pixel map is generated in dependence of the placement of the boundary in a grid finer than that of pixels of the SLM projected onto the workpiece. Due to the fact that the line width and a space between two lines in the pattern to be printed on the wafer are very small, it puts a lot of demands on the printing method and the apparatus using said method. Using an SLM, which provides for a too coarse address grid may limit the resolution and accuracy available for their use in optical imaging; e.g., the production of printed patterns on a workpiece may be limited as to its line widths and accuracy. Therefore, there is a need in the art for a method, which further fine-adjust the position of the element's edge in the image created on the workpiece. There is also a need in the art for an improved effectiveness of multipass averaging, i.e., reduced number of passes giving an improved fine-adjustment of a feature edge. In view of the foregoing background, the fine adjustment of the position of the element's edge in the image created on the workpiece is critical for accomplishing line width in the range of sub-micrometers both when using single pass or multiple pass writing strategy. The present invention applies to patterning a workpiece based on a digital input data file, such as the writing of masks, semiconductor wafers, optoelectronic devices, micro optical devices, magnetic devices, super conducting devices, display devices, and electronic interconnect structures such as MCMs. The invention is independent of the mechanism of writing and applies to laser and other electromagnetic beams, electron and other charged particle beams. Beam is to be understood broadly so that printing methods that uses projected areas such as SLMs, cell projection are also included. Non conventional writing mechanism are also included, such as atom beams, multi photon processes, entangled photons, near field effects, direct current exposure from scanning probes and thermal exposure. Accordingly, it is an object of the present invention to provide an improved method for fine adjustment of the element's edge. In a first embodiment, the invention provides a method for creating a pattern on a workpiece sensitive to electromagnetic radiation. Electromagnetic radiation is emitted onto a computer-controlled reticle having a multitude of modulating elements (pixels). The pixels are arranging in said computer controlled reticle according to a digital description. An image is created of said computer controlled reticle on said workpiece, wherein said pixels in said computer controlled reticle are arranged in alternate states along at least a part of one feature edge in order to create a smaller address grid. In another embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge belong to a one-dimensional line of pixels. In still another embodiment of the invention said image is created in one writing pass. In yet another embodiment of the invention said image is created by means of a plurality of writing passes. In a further embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge are arranged differently in said plurality of writing passes. In another embodiment of the invention, in a first writing pass, at least a first pixel along at least one feature edge is set to a first grayscale value and surrounded with pixels set to at least one other gray scale value, and in at least one other writing pass at least a second pixel along said at least one feature edge is set to said first grayscale value with surrounding pixels set to at least one other gray scale value. In still another embodiment of the invention four writing passes create the pattern. In still another embodiment of the invention the pixels in the different writing passes set to said first grayscale value are non overlapping. In still another embodiment of the invention said surrounding pixels are set to the same grayscale value. In still another embodiment of the invention said surrounding pixels are set to the different grayscale values. In still another embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge belong to a line of pixels with a width of two pixels. In still another embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge belong to a lines of pixels with a width of three pixels. In still another embodiment of the invention said pixels are micromirrors in an SLM. In another embodiment of the invention said pixels are transmissive. Another aspect of the present invention is to provide an improved apparatus for fine adjustment of the element's edge. In a first embodiment, the invention provides an apparatus for creating a pattern on a workpiece sensitive to electromagnetic radiation. Said apparatus comprising a source to emit electromagnetic radiation onto a computer controlled reticle having a multitude of modulating elements (pixels), a projection system to create an image of said computer controlled reticle on said workpiece, wherein said pixels in said computer controlled reticle are arranged in alternate states along at least a part of a boundary of at least one element to be patterned, in order to fine-adjust the position of an edge of said element in said image to be created on the workpiece. In a first embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge belong to a one-dimensional line of pixels. In another embodiment of the invention said image is created in one writing pass. In still another embodiment of the invention said image is created by means of a plurality of writing passes. In still another embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge are arranged differently in said plurality of writing passes. In still another embodiment of the invention, in a first writing pass, at least a first pixel along at least a part of one feature edge is set to a first grayscale value and surrounded with pixels set to at least a second gray scale value, and in at least a second writing pass at least a second pixel along said part of said feature edge is set to said first grayscale value with surrounding pixels set to at least said second gray scale value. In yet another embodiment of the invention the pattern is created by four writing passes. In yet another embodiment of the invention said pixels set to say first grayscale value in the different writing passes are non-overlapping. In still another embodiment of the invention said pixels set to said first grayscale value in the different writing passes are spaced apart with at least one pixel. In still another embodiment of the invention said surrounding pixels are set to the same grayscale value. In still another embodiment of the invention said surrounding pixels are set to the different grayscale values. In still another embodiment of the invention said pixels in said computer controlled reticle along at least a part of one feature edge belong to a line with a width of two pixels. In another embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge belong to a line with a width of three pixels. In another embodiment of the invention said pixels are micromirrors in an SLM. In another embodiment of the invention said computer controlled reticle is a transmissive SLM. Another aspect of the present invention is to provide an improved wafer, which is patterned with a finer address grid. In a first embodiment the invention provides a semi-conducting wafer comprising at least one integrated circuit, wherein said at least one integrated circuit is patterned by means of electromagnetic radiation emitted onto a computer controlled reticle having a multitude of modulating elements (pixels) in at least one writing pass, said pixels in said computer controlled reticle is arranged according to a digital description, an image of said computer controlled reticle is created on said wafer, wherein said pixels in said computer controlled reticle are arranged in alternate states along at least a part of one feature edge in order to create a smaller address grid. Another aspect of the present invention is to provide an improved mask, which is patterned with a finer address grid. In a first embodiment the invention provides a mask comprising a pattern to be printed on a workpiece, wherein a mask substrate is patterned in at least one writing pass by means of electromagnetic radiation emitted onto a computer controlled reticle having a multitude of modulating elements (pixels), said pixels in said computer controlled reticle is arranged according to a digital description, an image of said computer controlled reticle is created on said mask substrate, wherein said pixels in said computer controlled reticle are arranged in alternate states along at least a part of one feature edge in order to create a smaller address grid. Another aspect of the present invention is to provide an improved method for fine adjustment of an element's edge to be imaged. In a first embodiment the invention provides a method for imaging a pattern on a surface based on a description in a data file, where multiple writing passes is provided, a grid of pixels in at least two passes is offset, the values of edge pixels in the different passes are controlled, and the values of edge pixels between at least two passes are coordinated by a predetermined rasterizing rule so that the edge quality is optimized. In another embodiment of the invention, said edge quality is defined to be edge roughness. In another embodiment of the invention, said edge quality is defined to be edge acuity. In another embodiment of the invention said edge quality is defined to be critical dimension control (CDC). In another embodiment of the invention said at least two adjacent edge pixels in at least one pass have unequal values. In another embodiment of the invention, said rasterizing is non-linear. In another embodiment of the invention said dividing each pixel in at least two areas where a first area has a first weight function performs non-linear rasterizing and a second area has a second weight function. Another aspect of the present invention is to provide a method for creating a virtual grid. In a first embodiment the invention provides a method for writing a pattern on a substrate based on a description in a data file and to create a virtual grid, where a sequence of feature edge pixels is generated in a first writing pass, said sequence of feature edge pixels is displaced in at least a second writing pass, said sequences are at least partly superposed on said substrate. In another embodiment said invention further comprising the action of offsetting a grid of pixels in at least two passes. In another embodiment said invention further comprising the action of repeating said sequence of feature edge pixels periodic along at least one feature edge. In another embodiment of the invention, said sequence of feature edge pixels is non periodic. Another aspect of the present invention is to provide a further method for creating a virtual grid. In a first embodiment the invention provides a method for writing a pattern on a substrate based on a description in a data file and to create a virtual grid, wherein a first sequence of feature edge pixels is generated in a first writing pass, a second sequence of feature edge pixels is generating in at least a second writing pass, said sequences are at least partly superposing on said substrate. In another embodiment of the invention, said first and second sequences are periodic. In another embodiment of the invention, said first and second sequences are non-periodic. In another embodiment of the invention, said pixels are on/off pixels. In another embodiment of the invention, said pixels are multi-valued pixels. In another embodiment said invention further comprising the action of offsetting a grid of pixels in at least two passes. In another embodiment of the invention, said at least one of said feature edge pixels is divided into at least two regions having different weight functions for accomplishing non-linear rasterizing. FIG. 1a illustrates a rasterized feature 102. A grid 101 comprising pixels 103 is aligned to an origin 104 of a coordinate system. From FIG. 1a one can see that the grid is somewhat to coarse Therefore the feature 102 may not be imaged as accurate as desired. FIG. 1b illustrates the same feature as shown in FIG. 1a, but here the feature is rasterized to a finer grid. The accuracy of the rasterizing is two times better, but there are four time more pixels to write, which may make this method more time consuming relative the one illustrated in FIG. 1a. FIG. 1c illustrates the same feature as shown in FIG. 1a rasterized to the same grid size but using four passes 105 with no offset. Different lithographical characteristics such as resist properties and time delays may make this method of imaging more accurate than the one illustrated in FIG. 1a given that the different passes are imaged with equal doses. FIG. 2a illustrates a rasterized vertical line. FIG. 2b illustrates an ideal exposure 202 of the rasterized line in FIG. 2a. Smoothing by a finite resolution of an exposure beam gives an exposure dose denoted by 203 in FIG. 2b. FIG. 2b shows the smoothening by the exposure, but chemical diffusion, developer transport and finite resolution of the resist or recording medium also gives a similar effect. FIG. 2c illustrates a rasterized feature comprising a step. The imaged feature will end up with a pattern illustrated by the dashed line. The smoothening of step 205 is caused by the finite resolution of the exposure beam according to what was described in connection with FIG. 2b. Pixel 206 will therefore receive contribution from adjacent pixels. FIG. 6a illustrates an inventive method for offsetting different writing passes. In this embodiment four writing passes are offset relative to each other by a quarter of a pixel size in two orthogonal directions. The passes are here illustrated to be offset along a diagonal line of the pixel. Generally with N passes, where N is an integer greater than two, passes are distributed along a diagonal line of a pixel by (pixel size)/N, i.e., with three writing passes a first pass is written in a origin of coordinates, a second pass is written ⅓ of a diagonal line of a pixel away from said origin of coordinates and a third pass is written ⅔ of a diagonal line of a pixel away from said origin of coordinates. FIG. 6b illustrates a star written by said offset method as illustrated in FIG. 6a. It can be seen from FIG. 6b that there exists an unwanted asymmetry in the diagonals. This is caused by the fact that smoothening only occurs in directions parallel with pixel sides but in directions deviating from that one will see coarse grid effects. FIG. 6c illustrates another inventive method for offsetting different writing passes. In this embodiment four writing passes are distributed by the same amount but not along a straight line as illustrated in FIG. 6a. Here a first pas is written in an origin of coordinates. A second pass ¼ of a pixel size in an x direction and ½ of a pixel size in a negative y direction, x and y directions are parallel with the sides of the rectangular pixels. A third pass is written ½ the pixel size in the x direction and ¼ of the pixel size in the y direction. A fourth pass is written ¾ of the pixel size in the x direction and ¼ of the pixel size in the negative y direction. By this offsetting method you will obtain symmetry in both directions parallel to the sides of the pixel and also in both diagonals of said pixels. FIG. 6d illustrates the same star written by the method according to FIG. 6c. Here the symmetry is improved compared to the star in FIG. 6b. By offsetting the writing passes according to the scheme illustrated in FIG. 6c symmetry is accomplished in all eight directions. FIG. 7 illustrates reference points for several pixels in four passes 701, 702, 703, 704. It is possible to modify the displacement between the passes slightly by a small fraction of a pixel size unit to get a more uniform distribution of the reference points at the expense of a non-uniform division along the horizontal and vertical axis. The details of the rasterizer algorithm and the error structure of the pattern generator determine which is more favorable. Mirror images of the pattern in FIG. 7 and 90 degrees rotation of it will be equally good. The offsetting method according to FIG. 7 is particularly good for hiding a grid pattern. You may of course use another number of passes, in such case the pattern will look differently. The offset between the passes should be chosen so that one will get as good symmetry in x and y directions and both diagonals as possible. FIG. 8 illustrates four writing passes according to the invention with analog or multi-valued pixels. A middle column, represent a feature edge pixel column. As can be seen pixels in said column are set to different states. The pattern of the pixels in the feature edge column in the four passes could be equal or unequal. A finer address grid is accomplished by dithering between different grayscale values. FIG. 9 illustrates four passes according to the invention with edge pixels in more than one column. The pixels are multi-valued. Here again the plurality of edge columns in one writing pass could be equal or unequal in at least one other writing pass. Pixels in different edge columns may have different weights, which may be set differently from one case to another depending for instance which pattern is to be imaged. FIG. 10 illustrates a multipass scheme according to the invention. Here, passes with different dose create a fine address grid, with some passes, typically those with high dose, doubled in order to improve averaging. The passes with the same dose, in FIG. 10 denoted with the same crosshatch, can have their exposure fields and/or their pixel grid displaced in order to improve image uniformity. Writing passes with high doses are repeated due to the fact that averaging will have most impact from those passes. Passes with the lower doses may mainly be used for fine adjusting the address grid. Passes with higher dose are used for the most significant bits in the address and passes with lower dose are used for the least significant bits in the address. FIG. 11a and 11b illustrate multipass schemes according to the invention with edge pixels to create a finer grid and edge pixel sequence or distribution in different passes being different. In FIG. 11a the different passes are written with essentially the same exposure. In FIG. 11b two passes are written with for example 25% exposure and the other two with 100% exposure. The period of sequence in each pass is four, giving a combined grid of 1/16 of the pixel size. An example of an edge pixel sequence is illustrated to the right of the superposed passes in FIG. 11b. The two leftmost patterns may be written by 100% exposure and the two rightmost patterns may be written by 25% exposure. FIG. 12a-e illustrates different edge pixel sequences. Edge pixel sequences may be periodic or non-periodic. The figures show periodic sequences with different periods and a resulting image edge. FIG. 12a illustrates a pixels sequence with period 1, i.e., all pixels have the same value. Clearly this will create a smooth edge. FIG. 12b depicts a pixel sequence with period two, giving a virtual address grid two times finer than in FIG. 12a. The edge is still smooth due to the smoothening function of the exposure tool and process. The pixels are analog with for example 16 states and every second pixel at the feature edge may for example be set at 5/16 and the rest to 6/16. FIG. 12c illustrates a pixel sequence with period three, giving three times finer grid but starting to show line edge roughness (LER). The actual edge roughness depends on the trade off between pixel size, and the figure shows a typical example. FIGS. 12d and 12e illustrates a pixel sequence of 4 and 10 respectively. In those two figures one can clearly see that the edge roughness increases with increased pixel sequence period. FIG. 13 depicts a graph showing the relation between virtual grid and line edge roughness using the scheme in FIG. 12. Both virtual grid and edge roughness are in relative to the pixel size. FIG. 14 illustrates four passes with a long edge pixel period 1401. Each pass taken alone will create a strong line edge roughness 1402. By displacing the pattern a number of pixels between the passes and superposing the passes will reduce the line edge roughness 1403 strongly. FIG. 15 illustrates two graphs showing the simulated edge roughness for each pass and the combined roughness. The two graphs show two different sequences corresponding to different placement of the feature edge. The graphs show that some placements are better and some are worse, but for every placement a large reduction of the roughness is possible. The left graph in FIG. 15 illustrates displacement of a regular pixel edge pattern and the right graph shows superposition of irregular pixel edge patterns. FIG. 16 illustrates the same graph as in FIG. 13, but here with the edge roughness after four passes with displaced edge pixel sequences. The graph is based on a simulation with typical input parameters and shows that sequence lengths of up to 16 are possible with four passes. Larger sequence lengths may cause a roughness being bigger than the grid. FIG. 17 illustrates an algorithm for computing the edge pixel values with binary (on/off) pixels and a sequence period of 5. The feature edge is located 0.409 units onto a pixel in a middle column. The sequence in beforehand determined to be 0, 2, 4, 1, 3. The criteria for setting a pixel to an on state in the feature edge column is that P+(si/L)>1, where P is the position of the feature edge, si is the individual number in the sequence and L is a length of the sequence. FIG. 18 illustrates essentially the same as FIG. 17, but here 65-valued pixels are used. In this case 0.409=16/64+0.009=(16+0.576)/64. As we are using a multi-valued pixel we are interested to know when we are going to change state from 16/64 to 17/64. Therefore P=0.576. FIG. 19 illustrates a combination of two methods for obtaining a finer address grid. An example is the use of analog edge pixels in more than one row, as illustrated in FIG. 9, FIG. 32 and FIG. 33. An effectiveness of pixels in different columns may be different and the columns may combine in a linear or non-linear fashion. The use of two such methods can be used in the invention with a calibrated lookup table. Input data gives a look-up value for each of the methods, in the example for the analog values in the columns. The look-up table typically more output bits than address bits, so that a 6-bit address may generate two 8-bit values. The 8-bit values are generated during a calibration step when the edge placements for different combination of values are measured and mapped to the input values. In the more simple case of a single method the same look-up table structure may be used, but only with one output for each input. FIGS. 20a and b illustrates a multipass scheme with different edge sequences in the different passes and where the passes are displaced relative to each other. FIG. 20a illustrates the different sequences of the feature edge pixels. FIG. 20b illustrates how the passes are overlaid. Because of the displacement between the passes the dashed line, which represent the feature edge, will show up in different locations in the different passes. For each position of the final edge position there is at least one combination of feature edge patterns, which most likely all are different, which will result in an essentially smooth edge. The pixels in FIGS. 20a and b are on/off pixels. FIGS. 21a and b illustrates t that the edge pixels may be completely reshuffled in the passes when the input edge move only one address unit. FIG. 21a illustrates two passes at one edge placement. FIG. 21b illustrates the same two passes when the input edge has moved one virtual grid unit to the left compared to FIG. 21a. One pixel value has been changed from on to off (six pixels in on state in FIG. 21a and 5 pixels in on state in FIG. 21b in the feature edge column) and then the pixels have been reshuffled for best LER and edge acuity. FIG. 22 illustrates four passes with a long and unequal periodic sequences giving a virtual grid of 1/28 of the pixel size. The sequence length is 7. For each virtual grid step one pixel is flipped from off to on. After 7 steps the same sequences can be reused but with an order between the passes changed or rotated. It is not necessary that the sequences are periodic, non-periodic sequences can be found with essentially the same properties. It is also possible to use more or fewer passes and different displacements between the passes or no displacement at all. Two graphs showing the edge roughness in each pass and four combined passes are illustrated in FIGS. 23a and 23b. FIG. 23a shows the bitmap for one feature edge placement and FIG. 23b for another feature edge placement. In FIG. 23a there is no low frequency contribution. FIGS. 24a and b illustrates two methods for calculating optimal or near optimal edge pixel sequences for different edge locations. The computed sequences are computed off-line and tabulated for use during rasterization. FIG. 24a illustrates a binary sequence representing the edge pixels in different passes. The pixels used are two-valued pixels. Four passes are used with an inventive displacement scheme as described hereinabove. The sequence of edge pixels is illustrated to be non-periodic. This illustration in FIG. 24a is only one among many alternative ways for accomplishing the invention. FIG. 24a shows that one column of pixels in each pass is controlled by a sequence, i.e., there are four columns that are controlled in a four pass scheme. It is of course possible to control a four-pass scheme with other number of columns. FIG. 24b illustrates an algorithm for generating a sequence with good properties for each edge position given by an input address grid. An error diffusion algorithm may be used to generate starting binary sequences. Error diffusion algorithms can be found in textbooks relating to computer graphics. Error diffusion algorithms give an approximately uniform distribution of 0s and 1s. The sequence may be further improved by iterative permutations of short sequences. Permutations preserve the average edge position while on the other hand affecting edge roughness, which is evaluated in an imaging model. A simple imaging model may first be used for a quick generation of candidate sequences. Candidate sequences may then be further analyzed/evaluated by a more comprehensive model, e.g., by a commercial lithography simulation program. Once a sequence satisfying the acceptance level has been found, the sequence is accepted and the algorithm moves to the next edge location. FIGS. 25a and b illustrates a non-linear rasterizing function. The pixel or average column vs. the overlap between a feature in input data and a pixel area. FIG. 25a illustrates a graph showing a linear function, a piecewise straight-line non-linear function and a smooth non-linear function. All three are idealized, since in reality they get truncated to staircase functions. FIG. 25b illustrates the same as FIG. 20, but here with a non-linear rasterizing function giving better edge acuity, since only two of the passes have edge pixels. Each position of the feature edge may be independently optimized. The virtual grid in FIG. 25b is 1/16 of a pixel size. By looking at the pixels at the feature edge and using four writing passes, one can use 100% exposure in one pass for feature edge pixels and 0% exposure in another writing pass for feature edge pixels. For the remaining two passes one can use a steeper rasterizing function. FIG. 26a-c illustrates how non-linear rasterizing can be accomplished in a super-sampling rasterizer. Inside each pixel a feature is rasterized on a finer grid, the super-sampling super-grid. The pixel value is the number of super grid points that are set by the rasterizer. With equal weight on every super-grid point, the rasterizing is linear, if a larger weight function is applied to the super-grid points near the center of the pixel a non-linear rasterizing function will result. In FIG. 26b a weight function with a center square with a higher weight is shown. In FIG. 26c a continuous weight function is illustrated with a higher weight in a center than near the edges. By this super-sampling a steeper rasterizing function may be accomplished. FIG. 27a illustrates a weight function for non-linear rasterizing using the displacement scheme in FIG. 7. FIG. 27a illustrates pixel areas within a pass 2701 that fill the area with four times overlap after four passes. The rectangular areas 2702, with higher weight function, are smaller and fill the area without overlap after four passes. The rectangles have to be rotated by 90 degrees in two of the passes 2703. Super-sampling over either of these two area sizes gives a correct pixel representation of an input pattern, i.e., it is not possible to place a small feature anywhere so that its area is not reflected accurately by the pixel values. There are other area shapes that have the same property with a different overlap factor, e.g., 2 or 8. Since each of the two area shapes give correct rasterizing, every linear combination of them is also correct. FIG. 27b illustrates a pixel with a super-sampled grid. One weight function is applied over the central rectangle and another over the remainder of the pixel. FIG. 27c illustrates the weight function in FIG. 27b in three dimensions. The height of a central area and a plateau may be chosen arbitrarily based on the degree of non-linearity wanted. FIGS. 28a and b illustrates a weight function analog to FIGS. 27b and c for two passes offset half a pixel size in x and half a pixel size in y. By changing the weight between within the rectangle and outside said rectangle one can change the property of the non-linearity, i.e., the steepness of the non-linear function will vary. FIG. 29 shows an exemplary embodiment of an apparatus 1 for patterning a work piece 60. Said apparatus 1 comprising a source 10 for emitting electromagnetic radiation, a first lens arrangement 50, a computer controlled reticle 30, a beam conditioner arrangement 20, a spatial filter 70 in a Fourier plane, a second lens arrangement 40. The source 10 may emit radiation in the range of wavelength from infrared (IR), which is defined as 780 nm up to about 20 nm, to extreme ultraviolet (EUV), which in this application is defined as the range from 100 nm and down as far as the radiation is possible to be treated as electromagnetic radiation, i.e. reflected and focused by optical components. The source 10 emits radiation either pulsed or continuously. The emitted radiation from the continuous radiation source 10 can be formed into a pulsed radiation by means of a shutter located in the radiation path between said radiation source 10 and said computer controlled reticle 30. As an example can the radiation source 10, i.e. the source of an exposure beam, may be a KrF excimer laser with a pulsed output at 248 nm, a pulse length of approximately 10 ns and a repetition rate of 1000 Hz. The repetition rate may be below or above 1000 Hz. The beam conditioner unit may be a simple lens or an assembly of lenses or other optical components. The beam conditioner unit 20 distributes the radiation emitted from the radiation source 10 uniformly over at least a part of the surface of the computer controlled reticle 30. In a case of a continuous radiation source a beam of such a source may be scanned over the surface of the computer controlled reticle. Between the radiation source 10 and the computer controlled reticle 30, which may for instance be a spatial light modulator (SLM), said beam conditioner unit is arranged, which unit 20 expand and shapes the beam to illuminate the surface of the SLM in a uniform manner. In a preferred embodiment with an excimer laser as the source the beam shape is rectangular, the beam divergence different in x-direction and Y-direction and the radiation intensity is often non-uniform over the beam cross-section. The beam may have the shape and size of the SLM 30 and homogenized so that the rather unpredictable beam profile is converted to a flat illumination with a uniformity of, for example, 1-2%. This may be done in steps: a first beam shaping step, a homogenizing step and a second beam-shaping step. The beam is also angularly filtered and shaped, so that the radiation impinging on each point on the SLM has a controlled angular sub tense. The optics of the invention is similar to that of a wafer stepper. In steppers the beam is homogenized in a light pipe, a rectangular or prism-shaped rod with reflecting internal walls where many mirror images of the light source are formed, so that the illumination is the superposition of many independent sources. The homogenization may also be performed by splitting and recombining the beam by refractive, reflective or diffractive optical components. The SLM 30 is fed with a digital description of the pattern to be printed. The pattern may firstly be made in an ordinary commercially available drawing program. Before the pattern file is fed to the SLM, said pattern file is divided and transformed to a recognized formed for the SLM. FIG. 30 shows a Spatial Light Modulator (SLM) 200 comprising a 2-dimensional array of pixels, in this embodiment 8 rows 3001 and eight columns 3002, i.e. 64 pixels in total. In reality the SLM may comprise several millions of pixels but for reasons of clarity an SLM with few pixels is chosen. Micromirror pixels may for instance be 20×20 μm. A projection lens with a reduction of 200× will make one pixel on the SLM correspond to 0.1 μm in the image on the workpiece. Each pixel may be controlled to 64 levels, thereby interpolating the pixel of 100 nm into 64 increments of 1.56 nm each. The two leftmost columns of pixels 3010, 3011 and the two rightmost columns of pixels 3016, 3017 are set in a so called black state, i.e. the pixels are in a state which will not create any radiation onto the workpiece, indicated in FIG. 1 by 0. The two columns in the middle 3013, 3014 are set in a so-called white state, i.e. the pixel are in a state which will create maximum radiation onto the workpiece, indicated in FIG. 30 by 100. Pixels in columns 3010, 3011, 3016 and 3017 are outside feature pixels. Pixels in columns 3013 and 3014 are inside feature pixels. Pixels in columns 3012 and 3015 are boundary feature pixels. The boundary feature pixels are, as indicated in FIG. 1, set along the boundary of the feature in alternate states, in this case indicated by 74 and 75. In this embodiment every second boundary feature pixel is set to 74 and the rest to 75. As can be seen from the same figure, the states of the boundary feature pixels in column 212 do not match the boundary feature pixels in column 3015, i.e. the boundary feature pixels indicated by 75 do not belong to the same rows. In an alternative embodiment, the boundary feature pixels do match each other, i.e. the boundary feature pixels indicated by a same gray level are located in the same row. As an alternative to setting every second boundary feature pixel to one gray level and the rest to another gray level, every second pair of boundary feature pixels may be set to alternate states. With each pixel controlled into 64 levels, a pixel size. of 100 nm on the workpiece, and by setting the boundary feature pixels in the SLM in alternate states, an address grid of 0.78 nm is achievable in one writing step. In FIG. 30, the boundary feature pixels are represented by single columns 3012, 3015. A smoother feature edge will be created with every boundary feature pixel set to a first gray scale value and the rest of the pixels set to an adjacent gray scale value, which may be higher or lower compared to if longer sequences of alternate states are chosen in a single writing pass. In an alternative embodiment, as illustrated in FIG. 31, the boundary feature pixels are represented by two columns. In FIG. 31 the leftmost and rightmost column 3110 and 3117 respectively are set to the black state and pixels in these two columns are representing outside feature pixels. Inside feature pixels are represented in figure two in columns 3113 and 3114. Boundary feature pixels are represented in columns 3111, 3112, 3115 and 3116. In this embodiment, every second pixel in a leftmost boundary feature pixel column 3111 and a rightmost boundary feature pixel column 3116 are set to 1 and the rest to 0 grayscale level. Here the pixels in the leftmost boundary feature pixel column 3111 set to 0 match the higher value of the pixels in the other boundary feature pixel column 3112, here 75, creating together one of the feature edges on the work piece. The same applies for the two columns 3115 and 3116 creating together another feature edge on the workpiece, i.e. the 0's in the rightmost column 3116 match the higher value, here 75, of the pixels in the other boundary feature pixel column 3115 and the 1's in the rightmost column 3116 match the lower value, here 73, of the pixels in the other boundary feature pixel column 3115. Alternatively the reverse may apply, i.e. having two boundary feature pixel columns creating one feature edge on the workpiece, the higher alternate state (grayscale value) in one of these columns may match the higher alternate state (grayscale value) in the other of these columns. Instead of extending the boundary feature pixel columns into outside feature pixel columns, said columns may be extended into inside feature pixel columns as illustrated in FIG. 32. In FIG. 32 columns 3210, 3211, 3216 and 3217 represent outside feature pixel columns. Columns 3212, 3213, 3214, 3215 represent boundary feature pixel columns. Here we have no inside feature pixel columns because the line to be written is only represented by 4 columns, and two columns represent one edge of the line. As can be seen from FIG. 32, all higher alternate values match each other, i.e. the 100's in columns 3213 and 3214 match the 75's in column 3212 and 3215. Alternatively higher values in the outmost boundary feature pixel columns 3212 and 3215 may match lower values in the inmost boundary feature pixel columns 3213 and 3214. FIG. 33 illustrates still another embodiment of an inventive feature edge pattern in a Spatial Light Modulator (SLM). Here three columns represent the boundary feature pixels. The leftmost and rightmost column 3310 and 3317 respectively are set to the black state and pixels in these two columns are representing outside feature pixels. Boundary feature pixels are represented in columns 3311, 3312, 3313, 3314, 3315 and 3316. There are no inside feature pixels represented in FIG. 33. In this embodiment, every second pixel in a leftmost boundary feature pixel column 3311 and a rightmost boundary feature pixel column 3316 are set to 1 and the rest to 0 grayscale level. Here, the pixels in the leftmost boundary feature pixel column 3311 are set to 0 and they are matching the higher gray scale value of the pixels in the boundary feature pixel columns 3312, 3313, 3314, 3315. The 0 gray scale value match in this embodiment 75 gray scale value in columns 3312 and 3315, where the rest of the pixels in columns 3312 and 3315 are set to 74. The 0 gray scale value match in this embodiment 100 gray scale value in columns 3313 and 3314, where the rest of the pixels in columns 3313 and 3314 are set to gray scale value 99 in. Columns 3311, 3312, 3313, 3314, 3315, 3316, 3317 are creating together the feature edges of a straight line. FIG. 34a illustrates a first of four writing passes for creating a straight line with a fine address grid. The pixels in columns 3410, 3411, 3416 and 3417 are set to gray scale value zero. The pixels in columns 3413 and 3414 are set to gray scale value 100. Columns 3410, 3411, 3416 and 3417 are, according to the previous language used in the former embodiments, outside feature pixel columns and columns 3413 and 3414 are, using the same language, inside feature pixel columns. Columns 3412 and 3415 are boundary feature pixel columns. In the first writing pass all pixels in said boundary feature pixel columns are set to a first grayscale value except for at least one pixel which is set to a second gray scale value. In this embodiment as illustrated in FIG. 34a, seven out of eight pixels in the respective columns are set the gray scale value 75. One pixel in column 3412 is set to gray scale value 74 and one pixel in column 3415 is set to gray scale value 74. Here the gray scale value 74 in columns 3412 and 3415 match each other i.e. they are exactly opposite to each other. However, in an alternative embodiment, said second gray scale value may not be equal in both boundary feature pixel columns and may not be positioned exactly opposite to each other. FIG. 34b illustrates a second writing pass out of four for creating a straight line. The only difference between FIG. 34b and FIG. 34a is that the second gray scale value in the boundary feature pixel columns 3412 and 3415 have moved from the third position from top in FIG. 34a to a top position in FIG. 34b. FIG. 34c illustrates a third writing pass out of four for creating a straight line. The only difference between FIG. 34b and FIG. 34c is that the second gray scale value in the boundary feature pixel columns 3412 and 3415 have moved from the top position in FIG. 34b to a fifth position from top in FIG. 34c. FIG. 34d illustrates a fourth writing pass out of four for creating a straight line. The only difference between FIG. 34d and FIG. 34c is that the second gray scale value in the boundary feature pixel columns 3412 and 3415 have moved from the fifth position from top in FIG. 34c to a bottom position in FIG. 34c. When superposing said first, second, third and forth writing passes the effect of said second grayscale value will be essentially the same as the lower grayscale value in boundary feature pixel columns 3412 and 3415 in FIG. 1. FIG. 34e illustrates a writing pass scheme in an embodiment of four writing passes and a pixel sequence length of eight pixels. 1:st, 2:nd, 3:rd, 4:th Columns represent one boundary feature pixel column in the first, second, third and fourth writing pass respectively. Pixels in said boundary feature pixel column in the first writing pass, as illustrated in FIG. 34e in the leftmost column, are first set individually to a sequence of grayscale values. At least one of the grayscale values in said sequence of eight pixels differs from the other. With the writing pass scheme as illustrated in FIG. 34e said at least one pixel, which differs from the other, will move around in the boundary feature pixel column and create a finer address grid when the respective writing pass are superposed on each other. Alternatively, any number of pixels in the sequence may be used instead of the illustrated 8, for example 6, 12, 14 and 16 pixels. The invention is not limited to a single writing pass or four writing passes as illustrated by the figures, but can be employed with any number of writing passes, for example 2, 3 and 5.
	claims	1. A method for suppressing corrosion in a pressurized water nuclear plant comprising a secondary system, the secondary system comprising a steam generator, a turbine, a condenser, and a heater and not comprising a deaerator, the method comprising, in the following order:circulating water through the secondary system;depositing a protective substance on a surface of a structural member of the secondary system by spraying or by bringing a fluid comprising TiO2 as the protective substance in contact with the surface of the structural member of the secondary system; and thencirculating water through the secondary system such that the water contacts the protective substance, to make the protective substance into a single layer of TiO2 ,wherein the protective substance consists of a single layer of TiO2. 2. The method of claim 1, wherein the water is circulating water which is not subjected to chemical injection by a chemical injection device. 3. The method of claim 1, wherein the structural member of the secondary system having the protective substance is the steam generator. 4. The method of claim 1, wherein the structural member of the secondary system having the protective substance is the heater.
	description	The present application claims the benefit of U.S. Provisional Patent Application No. 60/881,319, entitled “Objective Lens With Deflector Plates Immersed In Electrostatic Lens Field”, filed Jan. 19, 2007, by inventors Alexander J. Gubbens and Ye Yang, the disclosure of which is hereby incorporated by reference in its entirety. 1. Field of the Invention The present invention relates to electron beam apparatus, including scanning electron microscopes and the like, and method of operating such apparatus. 2. Description of the Background Art There is an increasing need for high-resolution scanning electron microscopes (SEMs) in all areas of development and manufacture of micro-electronic and opto-electronic components. High-resolution scanning electron microscopes are useful so as to visually evaluate sub-micrometer structures. High-resolution SEMs may be used to identify deviations from standard patterns and to acquire and evaluate topographical data such as heights, widths or angles of inclination. Unfortunately, conventional, non-immersion, scanning electron microscopes do not have the required resolution of a few nanometers unless very high landing energies above about 10 kilo-electronVolts are used which may cause resist structures and, integrated circuits to be damaged and non-conductive or high resistant specimens to be disadvantageously charged. It is highly desirable to improve electron beam apparatus, including scanning electron microscopes and the like, and methods of operating such apparatus. One embodiment relates to an objective lens utilizing magnetic and electrostatic fields which is configured to focus a primary electron beam onto a surface of a target substrate. The objective lens includes a magnetic pole piece and an electrostatic deflector configured within the pole piece. An electrostatic lens field is determined by the pole piece and the electrostatic deflector, and the electrostatic lens field is configured by adjusting offset voltages applied to the plates of the electrostatic deflector. Another embodiment relates to a method of focusing an electron beam onto a target specimen. Offset voltages are applied to a main deflector so as to fine tune an electrostatic lens field, where the electrostatic lens field is determined by the offset voltages on the deflector and a high voltage on a magnetic pole piece surrounding the deflector. Another embodiment relates to an electron beam apparatus. The apparatus includes at least an electron source, a magnetic immersion objective lens, and an electrostatic deflector. The electron source is configured to generate a primary electron beam, and the magnetic immersion objective lens is configured to focus the primary electron beam onto a surface of a target substrate. The electrostatic deflector is configured within the pole piece of the magnetic immersion objective lens. An electrostatic lens field is determined by the pole piece and the electrostatic deflector, and the electrostatic lens field is configured by adjusting offset voltages applied to plates of the electrostatic deflector. Other embodiments, aspects and features are also disclosed. Immersion Objective Lenses Low-voltage scanning electron microscopes (SEMs) often use immersion objective lenses because they tend to have superior resolution performance. Immersion objective lenses immerse the sample in a magnetic and/or decelerating electrostatic field. The highest resolution low voltage SEMs use both magnetic and electrostatic immersion. The magnetic immersion allows for very small working distances and small aberration coefficients. The use of electrostatic immersion to retard the primary electron beam just prior to the substrate further reduces the aberration coefficients and thereby further increases the resolution. The landing energy of the primary electron beam is determined by the potential difference between the electron gun's cathode and the subsrate. The retarding field at the substrate is determined by the potential difference between the substrate and the objective lens pole piece above it. To allow independent control of the landing energy and the retarding field, the objective lens pole piece(s) are typically biased at a high voltage potential (greater than 30 V in magnitude). The substrate potential is then set to determine the landing energy and the objective lens pole piece potential is next set to determine the strength of the retarding electrostatic field. Scanning of the primary electron beam is conventionally done by means of a multipole deflector located on the inside of the objective lens near the tip. Electrostatic deflection is often preferred over magnetic deflection because it does not suffer from hysteresis as magnetic deflectors do and because it is easier to make work well at high speeds. Conventional electrostatic deflectors use shunt electrodes on both sides to accurately define and terminate the axial extend of the deflecting field. The DC value of the electrostatic deflector and shunts are typically held at ground potential to allow for simpler driving electronics. This then necessarily introduces an electrostatic lens field between the objective lens pole piece at high voltage and the deflector at DC ground. In the case of magnetic immersion, the secondary electron detection is typically through the objective lens. This is because the secondary electrons are strongly captured by the magnetic field and spiral up along the optical axis through the bore of the lens. At the point where the magnetic field decays on the inside of the lens, the secondary electrons are no longer captured and “spill out” (i.e. travel along divergent paths), making it difficult to collect and detect them. It is therefore desirable to have an electrostatic lens on the inside of a magnetic immersion objective lens. Such an electrostatic lens on the inside of a magnetic immersion objective lens may advantageously collimate the secondary electrons and transport them more efficiently to the secondary detector located elsewhere in the electron beam column. Magnetic Immersion Objective Lens Having an Electrostatic Deflector Plates with a Bottom Shunt Positioned Therein FIG. 1 is a schematic diagram of a magnetic immersion objective lens 100 having electrostatic deflector plates 108 positioned therein, where a grounded shunt 110 is configured at the bottom of the deflector plates 108. This diagram shows a cross-sectional view of the objective lens 100. As shown, a primary electron beam travels down an optical axis 101 and through the objective lens 100 to become focused upon the surface of a target substrate. A magnetic pole piece 102 of the objective lens 100 is configured about the optical axis 101, with a gap 103 extending away from the optical axis 101. The pole piece 102 is configured about an electromagnetic device 104 so as to generate a magnetic field which immerses the target substrate. The pole piece 102 is further configured at a high voltage potential. As further shown, electrostatic deflector plates 108 are configured within the pole piece 102. By controllably varying the voltages applied to the electrostatic deflector plates 108, the primary beam may be controllably deflected so as to be scanned over an area of the target substrate. In this case, a top shunt 106 and a bottom shunt 110 are provided above and below the deflector plates 108. The top shunt 106 may comprise, for example, a conical shunt. The bottom shunt 110 may comprise, for example, a conical or straight shunt. The shunts 106 and 110 are further configured to be grounded (i.e. conductively connected to an electrical ground). An electrostatic lens may be defined between the grounded bottom shunt electrode 110 and the high-voltage objective lens pole piece 102. This electrostatic lens may be configured so as to collimate secondary electrons emitted from the target substrate. Unfortunately, applicants have determined that the accurate alignment of the bottom shunt electrode 110 and the pole piece 102 is needed for high resolution performance of the objective lens 100 shown in FIG. 1. This requirement drives mechanical tolerances that are on the order of micrometers and adds substantially to the manufacturing cost of the magnetic lens. Magnetic Immersion Objective Lens Having an Electrostatic Deflector Plates Positioned Lower in the Lens FIG. 2 is a schematic diagram of an immersion objective lens 200 having electrostatic deflector plates 208 deeply positioned therein, without a grounded shunt configured at the bottom of the deflector plates 208. This diagram shows a cross-sectional view of the objective lens 200. As shown, a primary electron beam travels down an optical axis 201 and through the objective lens 200 to become focused upon the surface of a target substrate. A magnetic pole piece 202 of the objective lens 200 is configured about the optical axis 201, with a gap 203 extending away from the optical axis 201. The pole piece 202 is configured about an electromagnetic device 204 so as to generate a magnetic field which immerses the target substrate. The pole piece 202 is further configured at a high voltage potential. As further shown, electrostatic deflector plates 208 are configured within the pole piece 202. By controllably varying the voltages applied to the electrostatic deflector plates 208, the primary beam may be controllably deflected so as to be scanned over an area of the target substrate. In this case, a top shunt 206 is provided above the deflector plates 208, but there is no bottom shunt (in contrast to FIG. 1). The top shunt 106 may comprise, for example, a conical shunt. Here, an electrostatic lens field 210 may be defined between the electrostatic deflector plates 208 and the high-voltage objective lens pole piece 202. Advantageously, applicants have determined that, unlike the electrostatic lens field 110 of FIG. 1, the electrostatic lens field 210 of FIG. 2 does not require highly-accurate alignment of the deflector plates 208 and the high-voltage objective lens pole piece 202. This is because the ends of the deflector plates 208 are immersed in the electrostatic field 210. Because the ends of the deflector plates 208 are immersed in the electrostatic field 210, the electrostatic field 210 may be controllably adjusted by applying DC voltages to all of the deflector plates 208. These DC voltages may be used to properly align the electrostatic field 210 within the objective lens 200. While the DC voltages applied to all of the deflector plates 208 may be adjusted to change the alignment of the electrostatic field 210, it does not affect the scanning of the electron beam which is controlled by the AC voltage (i.e. the time-varying voltage signal) applied to one or more of the deflector plates 208. Applicants have determined that the lens configuration of FIG. 2 allows for significantly greater mechanical tolerances for the same high resolution performance. The greater mechanical tolerances are enabled by the advantageous feature that the shape and alignment of the electrostatic lens field 210 may be controllably varied and fine-tuned by applying the DC voltages to the deflector plates 208. As a result, the mechanical tolerances of the objective lens may be relaxed while the resolution performance may be maintained or even improved. Relaxation of the mechanical tolerances greatly reduces manufacturing cost. Simulation Results FIG. 3 is a table of simulation results showing performance parameters of a magnetic immersion objective lens having electrostatic deflector plates positioned therein, where a grounded shunt is configured at the bottom of the deflector plates (like the objective lens 100 of FIG. 1). In contrast, FIG. 4 is a table of simulation results showing performance parameters of an immersion objective lens having electrostatic deflector plates deeply positioned therein, without a grounded shunt configured at the bottom of the deflector plates (like the objective lens 200 of FIG. 2). Note that these simulations included both octupole and quadrupole electrostatic lens characteristics. The octupole and quadrupole are shifted downward (closer to the target substrate) for the simulation of FIG. 4 in comparison to the simulation of FIG. 3. As indicated, the primary beam energy is 2,000 electron Volts, and the landing energy is 1,000 electron Volts, for both of these simulations. Comparing the results shows that removing the bottom shunt and moving the deflectors down increases the scan sensitivity. The higher scan sensitivity results in an approximately 35% reduction in scan voltages required. Moreover, the scan aberrations are reduced by a factor of 2 or 3. This is advantageously accomplished while the secondary electron collection efficiency is unaffected (as shown by a separate simulation). The simulations show that leaving out the bottom shunt and immersing the electrostatic deflector plates in the electrostatic lens field not only allows the mechanical tolerances of the objective lens to be reduced, it actually also increases the scanning performance of the electron microscope. As integrated circuits continue to get smaller and smaller with the progression down Moore's curve, the resolution requirements on critical dimension and review SEMs continue to increase. Increasing resolution requirements impose tighter and tighter mechanical tolerances on the lens design of immersion objective lenses. The present application discloses methods and apparatus to introduce an additional degree of freedom that may be utilized to ensure optimal alignment and resolution performance. This advantageously reduces required mechanical tolerances and improves the manufacturability of a combined magnetic/electrostatic objective lens for scanning electron microcopy. The above-described diagrams are not necessarily to scale and are intended be illustrative and not limiting to a particular implementation. Specific dimensions, geometries, and lens currents of the immersion objective lens will vary and depend on each implementation. The above-described invention may be used in an automatic inspection system and applied to the inspection of wafers, X-ray masks and similar substrates in a production environment. While it is expected that the predominant use of the invention will be for the inspection of wafers, optical masks, X-ray masks, electron-beam-proximity masks and stencil masks, the techniques disclosed here may be applicable to the high speed electron beam imaging of any material (including perhaps biological samples). In the above description, numerous specific details are given to provide a thorough understanding of embodiments of the invention. However, the above description of illustrated embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise forms disclosed. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific details, or with other methods, components, etc. In other instances, well-known structures or operations are not shown or described in detail to avoid obscuring aspects of the invention. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.
	abstract	The present invention provides a volumetric computed tomography (VCT) system capable of producing data for reconstructing an entire three-dimensional (3D) image of a subject during a single rotation without suffering from cone beam artifacts. The VCT system comprises an array of source positions distributed along a line parallel to an axis of rotation, a plurality of collimators, and an array of x-ray detectors. In a preferred embodiment, a reversed imaging geometry is used. A 2D array of source positions provides x-rays emanating from each focal spot toward an array of detectors. The x-rays are restricted by a collimator array and measured by a detector array separately per each source position. The axial extent of the source array and the detector array are comparable to or larger than the axial extent of the portion of the object being imaged.
063174839	description	BEST MODE FOR CARRYING OUT THE INVENTION In accordance with this invention, an x-ray reflective device shown in FIG. 1 comprises a curved crystal 10 and support base 12. Crystal 10 has a set of curved atomic reflection planes 14. On every point of the crystal surface, atomic plane set 14 is near parallel to the crystal surface 16 in the embodiment shown. The spacing between the atomic planes, d, varies continuously from d.sub.1 at one end of the crystal to d.sub.2 at the other end of the crystal. Values of d.sub.1 and d.sub.2 are determined from the Bragg equation where the Bragg angles are the incident angles .theta..sub.1 and .theta..sub.2, respectively. According to the Bragg equation, the Bragg angles of reflective planes 14 for x-ray photons of wavelength .lambda. vary with the d spacing profiles. The configuration of the crystal surface 16 can be spherical, ellipsoidal, paraboloidal, toroidal, or other type of doubly curved surface. The profile of the d spacing for the crystal planes is designed to allow the incident angles of monochromatic x-rays from a divergent laboratory source to match the Bragg angle on each point of the crystal surface. The optical device according to the present invention can be fabricated by bending a flat thin crystal slab 10 as shown in FIG. 2 with a desired d spacing profile to a preselected geometry. One bending method is the fabrication process described in co-pending, commonly assigned U.S. patent application Ser. No. 09/342,606, entitled "Curved Optical Device and Method of Fabrication," the entirety of which is hereby incorporated herein by reference. The variation of the d spacing of the crystal planes can be produced by growing a crystal made of two or more elements and changing the relative percentages of the two elements as the crystal is grown. For instance, the lattice parameter of a Si--Ge crystal varies with a change in concentration of Ge. Therefore, a crystal material with a graded lattice parameter can be obtained by growing a Si--Ge crystal and controlling the concentration of Ge during growth. Such crystal planes are commercial available and can be purchased, for example, from Virginia Semiconductor, Inc. of Fredericksburg, Va. One embodiment of the present invention providing point to point x-ray imaging is illustrated in FIG. 3A. Crystal planes 14 are curved to an ellipsoidal shape and the d spacing of the planes varies along the direction parallel to the optical axis 2--2. For the symmetrical configuration shown in FIG. 3A, the d spacing of reflection planes has a maximum value d.sub.0 at the center point O and decreases as edge E is approached. With the decrease of the d value from the center O of the crystal to the edge E, the Bragg angle for x-rays of wavelength .lambda. increases, which matches the increase of the incident angles from O to E for x-rays diverging from the left focus of the ellipse. A cross-section of the crystal taken along line 4--4 is shown in FIG. 3B. In this plane, the crystal planes are circular and the d spacing does not vary. FIG. 3C shows an asymmetrical arrangement of a point to point focusing geometry, which provides demagnification of source S. The ellipsoidal crystal element in FIG. 3A can be made by bending a flat crystal 10 (see FIG. 2) to an ellipsoid, where the d spacing of the flat crystal 10 varies along the X direction but is constant along the Y direction (see FIG. 2). The optical element shown in FIG. 3A may be fabricated in two pieces such that two identical flat crystal slabs with graded d spacing from d.sub.0 to d.sub.E can be used as shown in the exploded view of FIG. 4. In this embodiment, the two crystals are joined at O and the surface is ellipsoidal. This approach allows the grading to increase in one dimension. Conversely, the element in FIG. 3A requires a grading profile that increases and then decreases. A curved crystal device with paraboloid geometry is shown in FIG. 5A. This device produces a monochromatic collimating x-ray beam from a point source S. The d spacing of the reflection plane of the crystal 10 is graded from a value of d.sub.1 to d.sub.2. To satisfy the Bragg condition, the d spacing profile is linear for the first order approximation and increases from point A to B. Alternatively, a collimated beam can be directed to a focal spot as shown in FIG. 5B. The focusing and collimating of x-rays can also be obtained with a spherical geometry at near normal incidence using crystalline planes with graded d spacing. Spherical mirrors are well known as imaging devices for normal incident visible light optics. A conventional spherically bent crystal can demagnify (or magnify) and collimate x-rays from a divergent x-ray source for some particular wavelength at near normal incidence. However, the numerical aperture of this type device is too small to be useful. The numerical aperture can be improved substantially with the use of graded d spacing, doubly curved crystals in accordance with the present invention. FIG. 6A shows a set of spherical curved crystal planes according to another embodiment of the present invention, which provides a demagnified image of the x-ray source. The d spacing of the crystal planes has a symmetrical profile about the optical axis and varies along the transverse direction. It increases across the surface from points A to B. The normal projecting view along the optical axis is illustrated in FIG. 6B. The d spacing profile of this device may be difficult to obtain. In practice, it can be approximated by using multiple pieces of crystal slabs with a simple graded d profile as shown in FIG. 6C. Each piece of crystal is curved to a spherical shape with the reflection planes parallel to the surface. The d spacing profile of the reflection planes is one-dimensionally graded along the radial direction passing the center of each crystal. If an x-ray source is placed at the focus of the concave spherical device similar to the orientation shown in FIG. 6A, a collimating x-ray beam is obtained. Strong demagnification can be obtained if two spherical crystal devices are combined. One preferred geometry is the Schwarzschild configuration which is used to image soft x-rays in conjunction with a multilayer coating. Graded crystals with the Schwarzschild geometry provide imaging for hard x-rays as shown in FIG. 7. The reflection planes of primary crystal 18 has a d spacing profile of d.sub.1 (r) to reflect x-rays from a source emitting x-rays at a near normal incident angle. The reflection planes of the secondary crystal 20 have the desired profile d.sub.2 (r) to match the incident angles of the x-rays reflected off the primary crystal 18. This system produces a final image of the source at I. While the invention has been described in detail herein in accordance with certain preferred embodiments thereof, many modifications and changes therein may be effected by those skilled in the art. Accordingly, it is intended by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.
042343852	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is based on the discovery, as a result of numerous experiments, that if silicon, titanium and carbon as essential components are added to the austenitic stainless steel, the silicon content is made under 0.7% by weight, and further, the contents of titanium and carbon are controlled so as to satisfy a certain relationship, the swelling of steel would be suppressed to the extremely low order (for example, 1.5% at maximum at 1.times.10.sup.23 nvt irradiation), without damaging the physical and mechanical properties of steel. It is found according to the invention that there exist complementary relations in the contents of silicon, titanium and carbon in the suppression of the swelling, though the mechanism of suppressing the swelling is not known in detail. The term "austenitic stainless steel" as used in this specification and the appended claims means an austenitic stainless steel containing chromium in a normally prescribed amount, nickel in a normally prescribed amount, manganese in an amount of up to 2% by weight, molybdenum in an amount of up to 3% by weight, silicon, carbon and titanium in amounts as hereinafter described, and the balance of iron. In addition the steel may contain incidental components which may be incorporated from the ordinary process of manufacturing steel. Such incidental components include nitrogen of up to 3%, oxygen of up to 0.02%, aluminium of up to 0.05%, arsenic of up to 0.03%, boron of up to 0.002%, cobalt of up to 0.1%, niobium of up to 0.05%, copper of up to 0.1%, sulphur of up to 0.03%, and vanadium of up to 0.2%. In general, the chromium content of the steel is in the range of 9 to 26% by weight. If the content is more than 26 wt.%, neither the stable austenitic system can be obtained, nor the void suppression may be attained. On the contrary, if the content is below 9 wt.%, a sufficient oxidation resistance cannot be obtained. Preferably, the content of chromium is 16 to 20% by weight. Usually, the nickel content of the steel is 6 to 30% by weight. Although the nickel content of more than 30% by weight is effective in the suppression of the swelling, a steel containing such an amount of nickel decreases in the corrosion resistance to a liquid metal, and is readily attacked by the nuclear fission products. Moreover, it not only aggravates neutron economy, but also causes a large amount of cobalt as an impurity to be contained in nickel. As a result, cobalt 60 originated from the cobalt may be turned into the most cumbersome radioactive corrosion product and interfere with the operation of the nuclear reactor. Whereas, with the nickel content of less than 6 wt.%, there can be obtained no stable austenite system, and the effect of suppressing the void would be lost. A preferable content of nickel is in the range of 10 to 16% by weight. While the silicon added to the austenitic stainless steel according to this invention is a component essential for suppressing the void swelling, addition of a large amount of silicon may destroy the physical and mechanical properties of the steel. Accordingly, the silicon content is preferable to be kept at a low level, if the contents of carbon and titanium to be added together with the silicon satisfy the relationship as described hereinafter. Generally, the silicon content is kept below 0.7% by weight (i.e., more than 0% to less than 0.7% by weight), preferably 0.5% to less than 0.7% by weight. It has been found, as a result of the various experiments, that there exists a correlation between the titanium content and the carbon content in suppressing the void swelling, and that if carbon and titanium in amounts satisfying the following relationship are added to the austenitic stainless steel which contains the silicon kept within the abovementioned quantitative limits, the void swelling can be suppressed to a very small extent (i.e., 1.5% at maximum at 1.times.10.sup.23 nvt irradiation). The relationship between the contents of carbon and titanium will be given by the following formula. EQU 17[C]+27[Ti].gtoreq.2.1 (A) where [C] represents the carbon content indicated in % by weight and exceeding 0, and [Ti] represents the titanium content indicated in % by weight and exceeding 0. The upper limits of the carbon content and the titanium content can not be determined unconditionally, and increasing both the carbon and titanium contents causes the mechanical properties of steel to be aggravated, for example, embrittled. The upper limits with respect to the carbon content and the titanium content capable of sufficiently suppressing the void swelling without substantially aggravating the mechaical properties of the steel are 0.1% by weight and 0.5% by weight, respectively. Preferably, the minimum carbon content is 0.01% by weight, and a preferred range based on this minimum is 0.01 to 0.1% by weight. Further, the minimum titanium content is preferably 0.03% by weight, and a preferred range based on this minimum is 0.03% to 0.3% by weight. The variables [C] and [Ti] in the formula (A) are interdependent, and if either of the variables is fixed, then the other one varies between the above-mentioned maximum value and the minimum value calculated from the formula (A) with the formula (A) taken as an equation. That is, for example, where [C] is 0.02, [Ti] varies between the maximum value of 0.5 and the minimum value of about 0.065 calculated with the formula (A) taken as an equation. This applies also to the preferable cases of the carbon content and the titanium content as stated above. Namely, if [C] is 0.02, then [Ti] is preferably in the range of 0.065 to 0.3 (% by weight). FIG. 1 shows the relationship between the carbon content and the titanium content by a graph. In the figure, line AJ stands for the formula: 17[C]+27[Ti]=2.1. A general range of the carbon and titanium contents fall within the region encircled by lines AB, BC, CD and DA, and the region encircled by lines EF, FG, GH, HI and IE shows a preferable range of carbon and titanium contents. Further, it has been found according to the invention that the void swelling can be further suppressed and the mechanical properties of steel is improved by subjecting the austenitic stainless steel to a final heat treatment at a temperature enough to permit the carbon and titanium contained in the steel to be formed substantially completely into a solid-solution. The final heat treatment is such a treatment as to be effected at the end of the process to provide the product and is generally carried out at a temperature of more than 1120.degree. C. up to 1200.degree. C. A heat treatment at a temperature of 1120.degree. C. or less can not form the solid-solution satisfactorily, while a heat treatment at a temperature of more than 1200.degree. C. can not attain the necessary mechanical strength of the steel and is uneconomical. The final heat treatment is preferably carried out at a temperature of 1150.degree. C. to 1200.degree. C. and for one to ten minutes. FIG. 2 shows a nuclear fuel element 10. A solid fuel body 3 composed of a plurality of pellets 2 is housed in a cylindrical clad 1 which is formed of the austenitic stainless steel according to this invention. The pellets 2 may be obtained by compression-moulding a nuclear fuel material such as the oxides, nitrides and carbides of uranium, plutonium and thorium, or a mixture thereof into a cylindrical shape and sintering it at a high temperature. The clad 1 is sealed tight by means of plugs 4 and 5 provided at the both ends thereof and a spring 6 for preventing the pellets 2 from the movement is installed in a plenum chamber 7 located between the fuel body 3 and the plug 4. A gap 8 is present between the clad 1 and the fuel body 3. In the plenum chamber 7 and the gap 8 is filled herium gas. FIG. 3 shows a nuclear fuel subassembly A. A plurality of the nuclear fuel elements 10 as shown in FIG. 2 are supported by grids (not shown) and received in a duct 11, with any adjoining two of the elements separated from each other by a spacer (not shown). It is preferred that the duct 11 be formed of the austenitic stainless steel according to this invention. This invention will be more fully understood from the following examples. Examples. Sample steels, each 750 g, were prepared by melting a steel component of high purity in a vacuum. The steel was cast into a rod of approximately 3.5 cm in diameter and then made up to a plate of approximately 3 mm thick by hot-rolling at 1150.degree. C. Then, the steel plate was rapidly cooled after annealed at 1150.degree. C. for 10 minutes, and cold-rolled into a thin plate of approximately 0.5 mm thick. Thereafter, it was heat-treated at 1200.degree. C. for 5 minutes. A small test piece (8 mm.times.14 mm.times.0.2 mm thick) was cut out of the thin steel plate and then finished up with an electrolytic polishing after smoothing the surface thereof with an abrasive paper. Voids formed in the test piece by irradiation of carbon ions at high temperature was observed under an electron microscope, and the whole volume of the voids was determined, thereby estimating the amount of the swelling of steel. The evaluation of the quantity of the swelling was made by using the experimental correction (reported in Journal of Nuclear Science and Technology, Vol. 13, pp. 743-751) by SHIMADA et al. In the simulative experiment by irradiation of the carbon ions, the temperature at which the swelling reaches the peak shifts higher by approximately 100.degree. C., because the damaging speed of a sample is fast as much as 1000 times that by irradiation of neutrons. Accordingly, irradiation of the carbon ions at about 525.degree. C. corresponds to irradiation of the neutrons at about 625.degree. C. Meanwhile, pre-injection of herium into the test piece had been carried out so that herium ions injected in the test piece distirbuted uniformly over the surface to the depth of 4000 A by changing the intensity of the herium ion energy. Table 1 shows the components of the 316 steel which is an austenitic steel on market and various steels used for the above-mentioned experiments. TABLE 1 __________________________________________________________________________ Sample steel No. Ni Cr Mo Mn Si C Ti S P Co N O __________________________________________________________________________ 316 10.5 17.5 2.63 0.78 0.44 0.050 <0.01 0.005 0.03 0.24 -- -- M79 14.1 17.5 2.48 0.91 1.05 0.068 <0.01 0.005 0.025 0.041 0.0048 0.0136 M82 13.5 17.4 2.52 1.67 0.59 0.041 0.02 0.006 0.002 0.042 0.0058 0.0088 M83 13.3 16.8 2.46 1.69 0.58 0.018 0.17 0.006 -- -- 0.0049 0.0070 M84 13.8 16.9 2.44 1.77 0.52 0.101 0.22 0.007 -- -- 0.0048 0.0079 M85 13.2 16.7 2.44 1.65 0.48 0.072 0.025 0.006 0.001 0.043 0.0049 0.0066 M90 13.3 16.6 2.47 1.59 0.55 0.087 0.039 0.007 0.002 0.041 0.0062 0.0068 M91 13.1 16.7 2.47 1.65 0.51 0.055 0.084 0.007 -- -- 0.0038 0.0050 M92 13.0 16.7 2.46 1.67 0.59 0.022 0.019 0.007 -- -- 0.0044 0.0058 M93 13.3 16.7 2.47 1.63 0.63 0.016 0.034 0.007 0.002 0.042 0.0043 0.0072 __________________________________________________________________________ Note: Unit % by weight; Fe balance The results are shown in FIG. 4 which shows the amount of the swelling of each steel obtained by the irradiation of ions corresponding to that of high-speed neutrons at 1.times.10.sup.23 nvt under an expected condition of LMFBR, dotted against the titanium content. As seen from the figure, the sample steels can be classified into two groups with the titanium content at 0.03% as a border. That is, a first group is the high-swelling group composed of the steels 316, M79, M82, M85 and M92 with Ti content of less than 0.03%, and a second group is the low- and the extremely low-swelling group composed of the steels M83, M84, M90, M91 and M93 with Ti content of 0.03% or more. The high-swelling group shows a swelling of the order of 8% as represented by the 316 steel on the market, while the low- and the extremely low-swelling group shows an excellent resistivity to the swelling (i.e., the swelling of about 1% to less than 0.1%). The second group can completely satisfy the desired value of the swelling such as several percentages, for example, 6%, which is the swelling limit of the steel covering the nuclear fuel in the fast breeder reactor under design or construction at present. The reason is that since the amount of the high-speed neutrons at the end of the operation of the reactor is about 2.times.10.sup.23 nvt under the expected operation condition of the LMFBR and at such an amount of the neutrons the amount of swelling is proportional to the square of the amount of the neutrons with respect to 300 series stainless steel, the amount of swelling of 1% at the amount of the neutrons of 1.times.10.sup.23 nvt corresponds to the amount of swelling of 4% at the amount of the neutrons of 2.times.10.sup.23 nvt. Further, FIG. 4 clearly shows that the amount of swelling varies to a large extent between titanium contents of 0.02% and 0.03%.
	abstract	A method of operation of a measurement system includes: providing a specimen having a film; controlling a beam generator to direct a charged particle beam into the specimen; detecting a reference signal emitted from the specimen; normalizing the reference signal to create a film L-ratio; and determining a thickness of the film by correlating the film L-ratio to a calibration curve.

abstract

Systems for x-ray diffraction/scattering measurements having greater x-ray flux and x-ray flux density are disclosed. These are useful for applications such as material structural analysis and crystallography. The higher flux is achieved by using designs for x-ray targets comprising a number of microstructures of one or more selected x-ray generating materials fabricated in close thermal contact with a substrate having high thermal conductivity. This allows for bombardment of the targets with higher electron density or higher energy electrons, which leads to greater x-ray flux. The high brightness/high flux source may then be coupled to an x-ray reflecting optical system, which can focus the high flux x-rays to a spots that can be as small as one micron, leading to high flux density, and used to illuminate materials for the analysis based on their scattering/diffractive effects.

claims

1. An ion thruster comprising:a source of deuterium-containing fuel material disposed on an asteroid surface;a reaction volume directed upward from the asteroid surface and open at the top;a flue coupled to the source and reaction volume for dispersing fuel material into the reaction volume;a set of turbines arranged around the reaction volume, wherein the set of turbines are directly exposed to the dispersed fuel material in the reaction volume a set of electrical generators coupled to the respective set of turbines to convert mechanical motion of the set of turbines into electricity; andan ion thrust engine powered by the generated electricity for producing thrust in a specified direction. 2. The generator as in claim 1, wherein the reaction volume is a cylinder with an opening at an upper end. 3. The generator as in claim 1, wherein the turbines are arranged radially around the circumference of the cylinder reaction volume. 4. The generator as in claim 1, wherein turbines are stacked vertically in multiple layers along a length of the cylinder reaction volume. 5. The generator as in claim 1, wherein one or more fans are provided in the reaction volume to maintain the dispersed fuel material in suspension within the reaction volume. 6. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material comprises Li6D. 7. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material comprises D2O. 8. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material comprises D2. 9. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material is in solid powder form. 10. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material is in pellet form. 11. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material is in frozen form. 12. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material is in liquid droplet form. 13. The generator as in claim 1, wherein the deuterium-containing micro-fusion particle fuel material also contains up to 20% by weight of added particles of fine sand or dust.

description

The present application is related to and claims priority to and the benefit of a Korean Patent Application No. 10-2017-0012211 filed on Jan. 25, 2017, the disclosure of which is incorporated herein by reference in its entirety. The present disclosure relates to an X-ray imaging apparatus and control method thereof. X-ray imaging apparatuses are devices for allowing the user to see an internal structure of a subject by irradiating X-rays to the subject and analyzing X-rays that have passed through the subject. X-ray transmittance is different depending on the tissue of a subject, so the internal structure of the subject may be imaged using an attenuation coefficient quantified from the X-ray transmittance. A condition for X-ray irradiation used in X-raying is an important factor in determining X-ray image quality and amount of radiation exposure. Accordingly, it is important to provide proper information about the X-ray irradiation condition for the user, such as a radiological technologist, a doctor, etc. To address the above-discussed deficiencies, it is a primary object to provide an X-ray imaging apparatus and control method thereof, for guiding the user to intuitively recognize an actual dose of X-rays and select a proper dose, ultimately a condition for low dose of X-ray irradiation by providing the user with information about an actual X-ray dose to which an X-ray filter effect is reflected. In accordance with an aspect of the disclosure, an X-ray imaging apparatus comprises: an X-ray source configured to generate and irradiate X-rays according to an X-ray irradiation condition including at least one of a tube voltage, a tube current, exposure time, or a filter; a display configured to provide a graphic user interface to receive a choice about the X-ray irradiation condition; and a controller configured to obtain a parameter that represents a dose of radiation, to which an influence of the filter is reflected, based on the selected X-ray irradiation condition and control the display to display the parameter. The parameter that represents a dose of radiation to which an influence of the filter is reflected may comprise at least one of an amount of tube current corresponding to X-rays that have transmitted the filter, a dose of X-rays that have transmitted the filter, or a ratio of a dose of X-rays that have not transmitted the filter and a dose of X-rays that have transmitted the filter. The display may be configured to display the parameter in a numerical value, or a diagram or image representing the numerical value. The X-ray imaging apparatus may further comprise a storage configured to store relationships between dose per amount of tube current (mAs) and tube voltage by differing types or thickness of the filter. The controller may be configured to search the storage for a dose per amount of tube current corresponding to the selected X-ray irradiation condition, when the choice of the X-ray irradiation condition is input. The controller may be configured to additionally search for a dose per amount of tube current corresponding to an occasion when no filter is used in the selected X-ray irradiation condition. The controller may be configured to obtain a ratio of a dose of X-rays that have not transmitted the filter and a dose of X-rays that have transmitted the filter, based on a dose per amount of tube current corresponding to the selected X-ray irradiation condition and a dose per amount of tube current corresponding to an occasion when the filter is not used in the selected X-ray irradiation condition. The controller may be configured to obtain an amount of tube current corresponding to X-rays that have transmitted the filter based on the obtained ratio and the amount of tube current included in the selected X-ray irradiation condition. The controller may be configured to obtain a dose of X-rays that have transmitted the filter based on a dose per amount of tube current corresponding to the selected X-ray irradiation condition and an amount of tube current included in the selected X-ray irradiation condition. The controller may be configured to when at least one of an imaging protocol or a size of a subject is selected, control the display to display a basic X-ray irradiation condition corresponding to the selected at least one of the imaging protocol or the size of the subject. The controller may be configured to obtain a parameter that represents a dose to which an influence of the filter is reflected based on the basic X-ray irradiation condition. The controller may be configured to re-obtain a parameter that represents a dose of radiation, to which an influence of the filter is reflected, whenever a choice of the X-ray irradiation condition is changed, and control the display to display the parameter. In accordance with an aspect of the disclosure, a control method of an X-ray imaging apparatus, the method comprising: providing a graphic user interface configured to receive a choice of an X-ray irradiation condition including at least one of a tube voltage, a tube current, exposure time, or a filter; obtaining a parameter that represents a dose to which an influence of the filter is reflected based on the selected X-ray irradiation condition; and displaying the obtained parameter on a display. The parameter that represents a dose of radiation to which an influence of the filter is reflected may comprise at least one of an amount of tube current corresponding to X-rays that have transmitted the filter, a dose of X-rays that have transmitted the filter, or a ratio of a dose of X-rays that have not transmitted the filter and a dose of X-rays that have transmitted the filter. The displaying of the obtained parameter on a display may comprise displaying the parameter in a numerical value, or a diagram or image representing the numerical value. The method may further comprise storing relationships between dose per amount of tube current (mAs) and tube voltage by differing types or thickness of the filter in a storage. The obtaining of a parameter that represents a dose to which an influence of the filter is reflected may comprise searching the storage for a dose per amount of tube current corresponding to the selected X-ray irradiation condition, when the choice of the X-ray irradiation condition is input. The obtaining of a parameter that represents a dose to which an influence of the filter is reflected may comprise searching for a dose per amount of tube current corresponding to an occasion when no filter is used in the selected X-ray irradiation condition. The obtaining of a parameter that represents a dose to which an influence of the filter is reflected may comprise obtaining a ratio of a dose of X-rays that have not transmitted the filter and a dose of X-rays that have transmitted the filter, based on a dose per amount of tube current corresponding to the selected X-ray irradiation condition and a dose per amount of tube current corresponding to an occasion when the filter is not used in the selected X-ray irradiation condition. The obtaining of a parameter that represents a dose to which an influence of the filter is reflected may comprise obtaining an amount of tube current corresponding to X-rays that have transmitted the filter based on the obtained ratio and the amount of tube current included in the selected X-ray irradiation condition. Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. FIGS. 1 through 21, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device. Embodiments and features as described and illustrated in the present disclosure are only preferred examples, and various modifications thereof may also fall within the scope of the disclosure. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present disclosure. It will be understood that, although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. It is to be understood that the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Furthermore, the terms, such as “˜ part”, “˜ block”, “˜ member”, “˜ module”, etc., may refer to a unit of handling at least one function or operation. For example, the terms may refer to at least one process handled by hardware such as field-programmable gate array (FPGA)/application specific integrated circuit (ASIC), etc., software stored in a memory, or at least one processor. Reference numerals used for method steps are just used for convenience of explanation, but not to limit an order of the steps. Thus, unless the context clearly dictates otherwise, the written order may be practiced otherwise. Embodiments of the present disclosure will now be described with reference to accompanying drawings. Throughout the drawings, like reference numerals may refer to like parts or components. FIG. 1 illustrates a control block diagram of an X-ray imaging apparatus, according to an embodiment of the present disclosure, FIG. 2 illustrates an external view illustrating a configuration of X-ray imaging apparatus, according to an embodiment of the present disclosure, and FIG. 3 illustrates an exterior view of a sub-display device equipped in an X-ray source. FIG. 2 shows an example of an X-ray imaging apparatus, which is a ceiling type X-ray imaging apparatus with an X-ray source attached to the ceiling of an examination room. Referring to FIG. 1, an X-ray imaging apparatus 100 in accordance with an embodiment may include an X-ray source 110 for generating and irradiating X-rays, a display 150 for displaying a screen e.g., to set an X-ray irradiation condition, an input 160 for receiving control commands including a command to set an X-ray irradiation condition from the user, a storage 170 for storing e.g., information about an X-ray irradiation condition, and a controller 140 for controlling overall operation of the X-ray imaging apparatus 100. The X-ray imaging apparatus 100 may further include a communication device 130 for communicating with an external device. The controller 140 may control X-ray irradiation timing, X-ray irradiation conditions, and the like, of the X-ray source 110 according to a command entered by the user, and create an X-ray image using data received from an X-ray detector 200 (see FIG. 2). The controller 140 may also control a position or posture of an install portion 14, 24 in which the X-ray source 110 or the X-ray detector 200 is installed, according to an X-raying protocol and a position of a subject 1. The controller 140 may compute a parameter that represents a dose of radiation to which an influence of a filter is reflected based on a selected X-ray irradiation condition, and control the display 150 to display the parameter. The parameter that represents a dose to which an influence of a filter is reflected may include at least one of an amount of tube current corresponding to X-rays that have transmitted the filter, a dose of X-rays that have transmitted the filter, and a ratio of a dose of X-rays that have not transmitted the filter and a dose of X-rays that have transmitted the filter. The controller 140 may include a memory for storing a program for carrying out the aforementioned operations and the following operations, and a processor for executing the program. The controller 140 may include a single processor or multiple processors, and in the latter case, the multiple processors may be integrated in a single chip or may be physically separated. When the controller 140 includes the multiple processors and multiple memories, some of the multiple processors and memories may be included in a workstation 180 (see FIG. 2), and some others in a sub-display 80 (see FIG. 2), a moving carriage 40 (see FIG. 2), or other device. For example, the processor(s) included in the workstation 180 may perform control, such as image processing to create an X-ray image, and the processor(s) included in the sub-display 80 or the moving carriage 40 may perform control over the movement of the X-ray source 110 or the X-ray detector 200. The X-ray imaging apparatus 100 may be connected to an external device (e.g., an external server 310, another medical device 320, and a portable terminal 330, such as a smart phone, a tablet Personal Computer (PC), a wearable device, and the like) through the communication device 130 for exchanging data. The communication device 130 may include one or more components that enable communication with an external device, for example, at least one of a short-range communication module, a wired communication module, and a wireless communication module. The communication module 130 may further include an internal communication module to enable communication between components of the X-ray imaging apparatus 100. The communication device 130 may also receive a control signal from the external device and forward the control signal for the controller 140 to control the X-ray imaging apparatus 100 according to the control signal. Furthermore, the controller 140 may control an external device with a control signal of the controller 140 by sending the control signal to the external device through the communication device 130. For example, the external device may process data of its own according to the control signal received from the controller 140 through the communication device 130. The external device may have a program to control the X-ray imaging apparatus 100, and the program may include instructions to control some or the entire operation of the controller 140. In the portable terminal 330, the program may be installed in advance or by being downloaded by the user from a server that provides applications. The server that provides applications may include a recording medium that stores the program. Referring to FIG. 2, a guide rail 30 may be installed on the ceiling of the examination room where the X-ray imaging apparatus 100 is placed, and the X-ray source 110 linked to a moving carriage 40 that moves along the guide rail 30 may be moved to a position corresponding to the subject 1, and the moving carriage 40 and the X-ray source 110 may be linked through a foldable post frame 50 to adjust the altitude of the X-ray source 110 from the ground. The X-ray source 110 may be moved automatically or manually. In the former case, the X-ray imaging apparatus 100 may further include a driver, such as a motor to provide power to move the X-ray source 110. The workstation 180 may be provided in the space separated by a blackout curtain B from the space where the X-ray source 110 is placed. The workstation 180 may be equipped with an input 182 for receiving commands from the user and a display 181 for displaying information. The input 182 may receive commands to control an imaging protocol, select an X-ray irradiation condition or X-ray irradiation timing, control a position of the X-ray source 110, and the like. The input 182 may include a keyboard, a mouse, a touch screen, a voice recognizer, and so forth. The display 181 may display screens representing an image for guiding input of the user, an X-ray image, and/or a state of the X-ray imaging apparatus 100. In the meantime, the display 150 and the input 160 as described in connection with FIG. 1 may be implemented as the display 181 and the input 182 provided in the workstation 180, or as sub-display 81 and a sub-input 82 provided in the sub-display 80, or a display and an input provided in the portable terminal 330, such as a tablet PC or a smart phone. The X-ray detector 200 may be implemented as a fixed type of X-ray detector fixed on a stand 20 or a table 10, or may detachably equipped in the install portion 14, 24. Alternatively, the X-ray detector 300 may be implemented as a portable X-ray detector available at any place. The portable X-ray detector may further be classified into a wired type or a wireless type depending on the data transfer method or the power supplying method. The X-ray detector 200 may also be moved automatically or manually. In the former case, the X-ray imaging apparatus 100 may further include a driver, such as a motor to provide power to move the install portion 14, 24. The X-ray detector 200 may or may not be included as an element of the X-ray imaging apparatus 100. In the latter case, the X-ray detector 200 may be registered in the X-ray imaging apparatus 100 by the user. In both cases, the X-ray detector 200 may be connected to the controller 140 through the communication device 130 for receiving a control signal or sending image data. The sub-display 80 may be arranged on one side of the X-ray source 110 to provide information for the user and receive a command from the user, and may perform a part or all of the functions performed by the input 182 and the display 181 of the workstation 180. If all or part of the components of the controller 140 and the communication device 130 are provided separately from the workstation 180, they may be included in the sub-display 80 arranged on the X-ray source 110. The user may input various kinds of information or commands relating to X-raying in a way of manipulating the sub-input 82 or touching the sub-display 81 as shown in FIG. 3. For example, the user may input a position to be moved by the X-ray source 110 through the sub-input 82 or the sub-display 81. While FIG. 2 illustrates a fixed type of X-ray imaging apparatus attached onto the ceiling of an examination room, the X-ray imaging apparatus 100 may include any of different types of X-ray imaging apparatus, such as a C-arm type of X-ray imaging apparatus, a mobile X-ray imaging apparatus, and the like, within the scope of the present disclosure obvious to ordinary people in the art. The X-ray source 110 may be equipped with an X-ray tube for generating X-rays and a collimator for adjusting an irradiation range of X-rays generated by the X-ray tube. The X-ray source 110 may also be called a tube head unit (THU) because X-ray source 110 includes an X-ray tube. This will be explained in detail below. FIG. 4 is a side cross-sectional view schematically illustrating a structure of an X-ray tube included in an X-ray source. The X-ray source 110 may include an X-ray tube 111 as shown in FIG. 4. The X-ray tube 111 may be implemented by a 2-pole vacuum tube with positive and negative electrodes. For example, thermions may be generated by making the inside of a glass tube 111a in a high vacuum state and heating a filament 111h of a negative electrode 111e to a high temperature. The negative electrode 111e may include the filament 111h and a focusing electrode 111g that focuses electrons, the focusing electrode 111g also called a focusing cup. When a high voltage is applied across the positive electrode 111b and the negative electrode 111e, thermions get accelerated and collide with a target material 111d of the positive electrode 111b, thus producing X-rays. The target material 111d of the positive electrode 111b may include a high resistive material, such as Cr, Fe, Co, Ni, W, Mo, or the like. The X-ray produced in this way is irradiated out through a window 111i, and the window 111i may use, for example, a thin film of Beryllium (Be). The voltage applied across the positive and negative electrodes 111b and 111e is called a tube voltage, the magnitude of which may be represented in kilovolt peak (kVp). As the tube voltage increases, the speed of the thermion increases and as a result, energy of X-rays (energy of photons) produced from collision of the thermion with the target material increases. The X-ray source 110 may irradiate X-rays with a certain energy band. The energy band of the irradiated X-rays may be defined by upper and lower limits, and the energy of the X-rays may be represented by average energy, highest energy, energy band, and the like. A filter 112 may be arranged in a direction, toward which X-rays are irradiated, to control the X-ray energy. For this, with the filter 112 arranged on the front or back side of the window 111i for filtering X-rays in a particular energy band, the X-rays of the particular energy band may be filtered. The filter 112 may be called an additional filter. The upper limit of the energy band, namely, a maximum energy of X-rays to be irradiated may be controlled by the level of the tube voltage, and the lower limit of the energy band, namely, a minimum energy of X-rays to be irradiated may be controlled by the filter. Filtering X-rays of a low energy band by means of the filter 112 may increase the average energy of X-rays to be irradiated. For example, with the filter 112 made of aluminum or copper to filter X-rays of a low energy band which degrade the image quality, the X-ray beam quality may be hardened, thereby increasing the lower limit of the energy band. Accordingly, an average energy level of X-rays to be irradiated increases. Furthermore, filtering X-rays of a particular energy band by means of the filter 112 may decrease a dose of radiation exposure of a subject. A current flowing through the X-ray tube 111 is called a tube current, which may be represented by an average value (mA), or represented by an amount of the tube current (mAs), which is a tube current (mA) for an X-ray exposure time (s). As the tube current increases, the dose of X-rays (the number of X-ray photons) increases. Accordingly, the X-ray energy may be controlled by the tube voltage, and the dose of X-rays may be controlled by the tube current and the X-ray exposure time, i.e., the amount of tube current. FIG. 5 shows a configuration of a collimator, and FIG. 6 is a side cross-sectional view of blades cut along AA′. Referring to FIG. 5, the collimator 113 may include at least one movable blade 113a, 113b, 113c, and 113d, and the blades 113a, 113b, 113c, and 113d may be made of a material with high bandgap to absorb X-rays. An X-ray irradiation range may be adjusted as the blades 113a, 113b, 113c, and 113d move, and the collimator 113 may further include a motor to provide power to the respective blades. The controller 140 calculates an extent of movement of each blade 113a, 113b, 113c, 113d corresponding to a set X-ray irradiation range, and sends the collimator 113 a control signal to move the blade 113a, 113b, 113c, 113d as far as the calculated extent of movement. For example, the collimator 113 may include four blades 113a, 113b, 113c, and 113d, each of which has the form of a flat plate. The first blade 113a and the third blade 113c may be movable in both directions along the X-axis, and the second blade 113b and four blade 113d may be movable in both directions along the Y-axis. Furthermore, each of the four blades 113a, 113b, 113c, and 113d may be moved individually, or the first blade 113a and the third blade 113c may be moved as one set and the second blade 113b and the fourth blade 113d may be moved as another set. X-rays may be irradiated through a slot R formed by the four blades, and collimation may be performed by passing the X-rays through the slot R. In this embodiment, the slot R refers to a collimation range, and the X-ray irradiation range refers to an area in which X-rays that have passed the collimation range R are incident onto the subject 1 or the X-ray detector 200. Referring to FIG. 6, the collimator 113 is arranged in front of the X-ray tube 111. The front of the X-ray tube 111 corresponds to a direction in which the X-ray is irradiated. The filter 112 may be arranged between the blades 113a, 113b, 113c, and 113d and the X-ray tube 111. X-rays irradiated from a focusing point 2 of the X-ray tube 111 are irradiated into an irradiation range E limited by the collimator 113, and thus scattering is reduced. Some X-rays incident on the blade 113a, 113b, 113c, 113d among the X-rays irradiated from the X-ray tube 111 are absorbed by the blade, and some X-rays that have passed the collimation range R are incident on the X-ray detector 200. The following description will focus on an occasion when there is no subject. If X-rays spread like cone beams, the X-ray irradiation range E is wider than the collimation range R. The controller 140 may irradiate X-rays into a desired range of X-ray irradiation range E by adjusting the collimation range R based on a relationship between the two ranges. Although the previous example shows that the collimator 113 is equipped with four rectangular blades, it is only by way of example and there are no limitations on the number or shape of the blades included in the collimator 113. FIGS. 7 and 8 show an example of automatic exposure control (AEC) sensor to be used in an X-ray imaging apparatus, according to an embodiment of the present disclosure. The X-ray imaging apparatus 100 may perform AEC to prevent excessive exposure of the subject to radiation. For this, as shown in FIG. 7, the install portion 24 may have an AEC sensor module 26 to detect a dose of X-rays. This embodiment will be described using the install portion 24 of the stand 20, but the AEC sensor module 26 may also be provided in the install portion 14 of the table 10. The diagram of FIG. 7 shows the install portion 24 viewed from the front. The AEC sensor module 26 may be arranged inside the install portion 24, and may include a plurality of AEC sensors 26a, 26b, 26c for independently detecting a dose of X-rays. For example, each AEC sensor may be implemented as an ionization chamber. Although there are total of three AEC sensors, two of them arranged on an upper portion and one arranged on a lower portion, it is only an example and it is also possible to have more than or less than three AEC sensors in different positions. Referring to FIG. 8, the AEC sensor module 26 may be located in front of the X-ray detector 200. The front of the X-ray detector 200 corresponds to a direction in which the X-ray is incident. FIG. 8 is a side view of the AEC sensor module 26 arranged in front of the X-ray detector 200. When X-rays are incident on the AEC sensor, a current may be induced and the AEC sensor may send a signal corresponding to the current to the controller 140. The signal to be sent to the controller 140 may be amplified and digitally processed. The controller 140 may determine whether a current dose of the incident X-ray exceeds a threshold dose, based on the signal. If the dose of X-rays exceeds the threshold dose, a cut-off signal is sent to a high-voltage generator 101 that supplies a high voltage to the X-ray tube 111 to stop generation of the X-ray. A grid may be arranged on the front of the AEC sensor module 26 to prevent X-ray scattering. Some of the X-rays irradiated from the X-ray source 110 may collide with dust in the air or constituent materials of the subject and scatter away from an original path on the way to the X-ray detector 200. When incident on the X-ray detector 200, the scattered X-rays give a negative influence to the quality of X-ray images, such as degradation of contrast of the X-ray image. The grid may have a structure in which shielding materials, such as lead (Pb), which absorb X-rays, are arranged, and some of the irradiated X-rays that proceed in the original direction, that is, straightforward X-rays, may pass between the shielding materials and then be incident on the X-ray detector 200 while the scattered X-rays collide with the shielding materials and are absorbed. The shielding materials may be arranged linearly or in a cross structure. Alternatively, the shielding materials may be arranged in a focused form by being inclined to be similar to the X-ray irradiation direction, or may be arranged to be parallel. Although not shown, a driver including a motor to mechanically move the grid may be included inside the install portion 24. Accordingly, it is possible to control an angle or center position of the grid by sending a control signal to the driver from the outside. Although the AEC sensor module 26 is provided in the install portion 24 in this example, the AEC sensor module 26 may be integrated with the X-ray detector 200. FIG. 9 shows an example of a screen displayed on a display of an X-ray imaging apparatus, according to an embodiment of the present disclosure. Referring to FIG. 9, a setting window 151 to set an X-ray irradiation condition and a work list 155 may be displayed on the display 150. The work list 155 may include a study list 155a to select a study and a protocol list 155b to select an imaging protocol. The term ‘study’ as herein used may refer to a set of X-ray images related to each other. If a study is selected from among the study list 155a, the protocol list 155b to select an imaging protocol to be applied to the selected study is displayed. The X-raying region may vary by imaging protocol, and a suitable X-ray irradiation condition may vary by the X-raying region. The imaging protocol may be determined based on the X-raying portion, the posture of the subject, and the like. For example, the imaging protocol may include the whole body Anterior-Posterior (AP), the whole body Posterior-Anterior (PA), the whole body LAT. Even for the chest, there may be imaging protocols for capturing images in the AP, PA, LAT methods, and for long bones such as legs, there may be imaging protocols for capturing images in the AP, PA, LAT methods. Furthermore, Abdomen Erect may also be included in the imaging protocol. A graphic user interface may be displayed on the setting window 151 for the user to intuitively control the X-ray imaging apparatus 100. The graphic user interface may be used to receive a choice of an X-ray irradiation condition including at least one of a tube voltage, a tube current, exposure time, and a filter. The graphic user interface may include a plurality of graphic objects that may set various X-ray irradiation conditions. In this embodiment, all the objects, such as buttons, icons, and the like, displayed on the display 150 to provide information or used to receive the user's control command may be called graphic objects. The graphic objects may be implemented by buttons corresponding to the respective X-ray irradiation conditions to be used in receiving a command to set an X-ray irradiation condition from the user. For example, they may include a tube voltage set button 151a to receive a setting of a tube voltage (kVp), a tube current set button 151b to receive a setting of a tube current (mA), and a tube current amount set button 151c to receive an amount of tube current (mAs). The currently set tube voltage, tube current, and amount of tube current may be displayed on one side of the respective buttons. A currently set tube voltage may be displayed in a numerical value in a tube voltage display area 151aa on one side of the tube voltage set button 151a, and a currently set tube current may be displayed in a numerical value in a tube current display area 151bb on one side of the tube current set button 151b. A currently set amount of tube current may be displayed in a numerical value in a tube current amount display area 151cc on one side of the tube current amount set button 151c. The tube current amount set button 151c may actually be used in controlling X-ray exposure time (sec) unlike the tube current set button 151b. A currently set X-ray exposure time may also be displayed in the tube current amount display area 151cc. In some embodiments, instead of the tube current amount set button 151c, an X-ray exposure time set button may be provided separately. The user may select each button to set an X-ray irradiation condition to a desired value. The selection of a button may be made by clicking or touching depending on the type of the input 160. In some embodiments, the tube voltage set button 151a may include an extra button to increase or decrease the tube voltage. The tube current set button 151b may include an extra button to increase or decrease the tube current. The tube current amount set button 151c may include an extra button to increase or decrease the amount of tube current. Furthermore, an imaging position set button 151d to receive a setting of whether X-raying is performed on the stand 20 or on the table 10 or whether a portable X-ray detector is used, a patient size selection button 151e to receive a choice of a patient size, and a collimator set button 151f to receive setting of a size of the collimator may further be displayed. Moreover, an AEC selection button 151g to receive a choice of an AEC sensor, a sensitivity set button 151h to receive setting of sensitivity, a density set button 151i to receive setting of a density, a grid selection button 151j to receive a choice of a grid, a filter selection button 151k to receive a choice of a filter, and a focus selection button 151r to receive a choice of a focal size may further be displayed in the setting window 151. These buttons may be implemented in figures comprised of pictures, characters, symbols, etc., and the user may select a figure by moving the cursor to the figure and clicking it or touching the figure, and accordingly, an X-ray irradiation condition corresponding to the selected figure may be set. Meanwhile, once an imaging protocol is selected, the X-ray irradiation conditions, such as a tube voltage, a tube current, an amount of tube current, and so forth, which are basic conditions matched with the selected imaging protocol, may be displayed in the respective display areas 151aa, 151bb, 151cc. The storage 170 may match and store basic X-ray irradiation conditions for each imaging protocol. When an imaging protocol is selected, the controller 140 may search the storage 170 for basic X-ray irradiation conditions corresponding to the selected imaging protocol, and display the basic X-ray irradiation conditions in the respective display areas 151aa, 151bb, 151cc of the display 150. The user may refer to the X-ray irradiation conditions displayed in the respective display area 151aa, 151bb, 151cc and adjust them to proper numerical values taking into account the state or size of the subject by increasing or decreasing the numerical values. When a choice of a patient size is input, the X-ray irradiation conditions, such as a tube voltage, a tube current, an amount of tube current, and so forth, which are basic conditions matched with the selected size, may be displayed in the respective display areas 151aa, 151bb, 151cc. For this, the storage 170 may match and store basic X-ray irradiation conditions for each patient size, and the basic X-ray irradiation conditions matched with the patient size may be stored differently for each imaging protocol. When the user selects a patient size using the size selection button 151e, the controller 140 may search the storage 170 for basic X-ray irradiation conditions corresponding to the selected patient size, and display the basic X-ray irradiation conditions in the respective display areas 151aa, 151bb, 151cc of the display 150. Even in this case, as described above, the user may refer to the X-ray irradiation conditions displayed in the respective display areas 151aa, 151bb, 151cc and adjust them to proper numerical values taking into account the state or size of the subject by increasing or decreasing the numerical values. The aforementioned types or locations of the graphic objects displayed in the set window 151 are by way of example, and some of them may be omitted according to the designer's choice, and other graphic objects to change other settings may further be provided in an arrangement different from what is described above. The input 160 may include a button to receive a command to start X-raying. For example, the button to receive a command to start X-raying may be implemented in the form of a remote control or a switch, which is separate from the workstation 180. If the user inputs the command to start X-raying through the input 160 after setting the X-ray irradiation conditions through the setting window 151, X-raying is performed according to the set X-ray irradiation conditions. In performing the X-raying, an effort is made to reduce a dose of radiation exposed to the patient. For this, it is important for the user to accurately know of the dose of radiation exposed to the patient taking place in a case that X-raying is performed according to the currently set X-ray irradiation conditions. The conventional X-ray imaging apparatus provides no extra information about a dose of radiation except for the tube voltage, tube current, and amount of tube current. In that case, the user estimates a dose based on an amount of tube current (mAs). FIG. 10 shows a table representing radiation doses depending on X-ray irradiation conditions; Referring to FIG. 10, when the tube voltage is set to 80 kVp and the amount of tube current is set to 10.0 mAs, an actual dose is 0.72 mGy without the filter 112. When the tube voltage is increased to 83 kVp while the amount of tube current is decreased to 8.0 mAs, an actual dose is 0.62 mGy without the filter 112. Since the conventional X-ray imaging apparatus does not provide information about an actual dose of radiation, the user may not accurately know of the dose and in light of the fact that the second case has a 20 percent lower amount of tube current than that of the first case, may only assume that a dose would be reduced (however, that the dose would be reduced by less than 20% because the tube voltage increases a little bit). When the tube voltage is set to 76 kVp and the amount of tube current is set to 16.0 mAs, an actual does is 0.55 mGy when the filter 112 made of copper, which is about 0.1 mm thick, is used. In this case, the amount of tube current increases by about 60% as compared with the first case, and by 100% as compared with the second case, so the user may assume that a dose would increase as well. However, the dose in the third case is actually the lowest. Specifically, if the user estimates a dose just based on the set tube voltage, tube current, and amount of tube current, it is difficult to know of an actual dose to which an influence of the filter is reflected. Accordingly, if a dose is estimated only based on the information and corresponding X-ray irradiation conditions are selected, it is difficult to select proper X-ray irradiation conditions in consideration of a dose of radiation exposure and the image quality. In certain embodiments, the X-ray imaging apparatus 100 may guide the user to select proper X-ray irradiation conditions to minimize both a dose of radiation exposure and degradation of image quality by providing information about an actual dose, to which an influence of the filter is reflected, to the user. Examples in which the X-ray imaging apparatus 100 provides doses in accordance with an embodiment will now be described in detail with reference to accompanying drawings. FIG. 11 is a graph representing changes in radiation dose according to tube voltages and filter types/thickness. As described above, the dose of radiation exposure may vary by an X-ray irradiation condition, such as the tube voltage, tube current, amount of tube current, filter type and thickness, etc. Once an X-ray irradiation condition is selected, the controller 140 obtains a dose of radiation exposure corresponding to the selected X-ray irradiation condition. The dose of radiation exposure may be represented in such a value as entrance skin exposure (ESE), entrance surface dose (ESD), effective dose, dose-area product (DAP), etc. In this example, the ESE is used. The storage 170 may store relationships between the dose (ESE) per amount of tube current (mAs) and the tube voltage for each type and filter thickness in advance. The dose per amount of tube current (mAs) may be obtained by experiment, simulation, etc. For example, the dose (ESE) per amount of tube current (mAs) may be measured by differing the tube voltage, and the tube voltage and the measured dose (ESE) per amount of tube current (mAs) may be matched and stored in a table. Such relationships may be obtained by differing filter type and thickness. Even in the case that the filter is not used, relationships between the dose (ESE) per amount of tube current (mAs) and the tube voltage are obtained and stored. In this embodiment, the filter whose influence is reflected may be the filter 112 arranged between the blade of the collimator 113 and the X-ray tube 111. Furthermore, if there is an extra filter such as a bow tie filter used to control the shape of X-raying, even for this filter, relationships between the dose (ESE) per amount of tube current (mAs) and the tube voltage of when this filter is used or not used may be obtained and stored in advance. When a tube voltage and a filter are selected, the controller 140 searches the storage 170 for a dose E1 per amount of tube current (mAs) corresponding to the selected tube voltage and filter. Along with this, the controller 140 searches the storage 170 for a dose E2 per amount of tube current (mAs) corresponding to the selected tube voltage when no filter is used. The controller 140 calculates a conversion ratio R1 using the dose E1 per amount of tube current (mAs) of when the filter is used and the dose E2 per amount of tube current (mAs) of when the filter is not used. The conversion ratio R1 may be calculated in the following equation 1:R1=E1/E2 (1) The conversion ratio R1 is used to convert an amount of tube current selected by the user to an amount of tube current to which an influence of the filter is reflected, representing a ratio of a dose of X-rays that have not transmitted the filter and a dose of X-rays that have transmitted the filter. The controller 140 calculates a converted amount of tube current M2 in the following equation 2 using the conversion ratio R1 and the selected amount of tube current M1:M2=M1*R1 (2) Furthermore, the controller 140 may calculate a dose E3, to which an influence of the filter is reflected, under a condition of the selected amount of tube current, using the dose E1 per amount of tube current when the filter is used and the selected amount of tube current M1.E3=M1*E1 (3) If the selected X-ray irradiation condition does not include usage of the filter, E1=E2. In the following embodiment, an occasion when the selected X-ray irradiation condition includes usage of a filter will be described. FIGS. 12 to 18 show examples in which an X-ray imaging apparatus, in accordance with certain embodiments, displays information about radiation doses on a display, to which an influence of a filter is reflected. The display 150 may display a parameter that represents a dose to which an influence of the filter is reflected in a numerical value or display the numerical value of the corresponding parameter in a diagram or an image. For example, as shown in FIG. 12, a currently selected amount of tube current 151c-1, exposure time 151c-2, and a converted amount of tube current 151c-3 may be displayed in numerical values in the tube current amount display area 151c. As described above, the converted amount of tube current 151c-3 is an amount of tube current to which an influence of the filter is reflected. An occasion when a tube voltage of 80 kVp, a tube current of 200 mA, an amount of tube current of 10 mAs, and a copper filter of 0.1 mm are selected will be taken as an example. The X-ray irradiation conditions may be conditions directly selected by the user using the respective set buttons, or may be conditions basically matched with the selected imaging protocol and size of the subject. The controller 140 searches the storage 170 for a dose per amount of tube current (mAs) corresponding to the selected tube voltage 80 kVp and the filter (copper of 0.1 mm) and a dose per amount of tube current (mAs) corresponding to the selected tube voltage 80 kVp and to an occasion when no filter is used. The controller 140 may calculate the conversion ratio R1 using the equation 1 and obtain the converted amount of tube current M2 by substituting the conversion ratio R1 in the equation 1. If the conversion ratio R1 is 0.8, the converted amount of tube current M2 becomes 8 mAs, and the controller 140 may control the display 150 to display the converted amount of tube current 8 mAs as well in the tube current amount display area 151c. The user checks the converted amount of tube current in a numerical value of 8 mAs, and may intuitively check how much a dose of radiation exposure would be when the copper filter of 0.1 mm is used. In another example, as shown in FIG. 13, it is also possible to represent a dose 151c-4 to which an influence of the filter is reflected in a numerical value. The controller 140 may search the storage 170 for a dose A1 per amount of tube current (mAs) corresponding to the selected X-ray irradiation condition, and may obtain a dose A3 to which an influence of the filter is reflected by multiplying the selected amount of tube current M1 by the searched for dose A1 per amount of tube current (mAs) according to the equation 3. However, displaying the dose 151c-4 to which an influence of the filter is reflected is just an example. As shown in FIG. 14, it may also possible to display the dose 151c-4 in other area than the tube current amount display area 151c in the setting window 151. Although both the converted amount of tube current 151c-3 and the dose 151c-4 to which an influence of the filter is reflected are represented in the examples of FIGS. 13 and 14, embodiments of the X-ray imaging apparatus 100 are not limited thereto. It is also possible to represent one of the converted amounts of tube current 151c-3 and the dose 151c-4 to which an influence of the filter is reflected. In another example, as shown in FIG. 15, it is also possible that the display 150 represents a conversion ratio 151c-5. When the conversion ratio 151c-5 is displayed, the user may intuitively know of a decrease in the dose due to use of the filter. The conversion ratio 151c-5 may be represented as computed in the equation 1, or may be represented as a percentage as shown in FIG. 15. Similarly, in the case of representing the conversion ratio 151c-5, the dose 151c-4 to which an influence of the filter is reflected may also be represented, as shown in FIGS. 16 and 17. The user may receive information about a dose to which an influence of the filter is reflected from various aspects, thereby intuitively and accurately knowing of an actual dose of radiation exposure. It is also possible to represent both the conversion ratio 151c-5 and the converted dose 151c-3. In another example, as shown in FIG. 18, it is also possible to show the relationship between a dose of when the filer is used and a dose of when the filter is not used in a diagram. Specifically, the dose of when the filter is used may be represented in the form of a bar 151c-6, and a ratio of the length of the bar representing the conversion ratio 151c-5 and the entire bar length may be adjusted to correspond to the conversion ratio 151c-5. For example, in a case that the conversion ratio is 80%, the dose bar 151c-6 may be adjusted up to 80% of the length of the entire bar area. Furthermore, if the user changes an X-ray irradiation condition, the length of the dose bar before the change and the length of the dose bar after the change may be represented together for the user to be able to intuitively know of a change of the dose according to the change in the X-ray irradiation condition. A control method of an X-ray imaging apparatus in accordance with an embodiment of the present disclosure will now be described. The control method of an X-ray imaging apparatus may use the X-ray imaging apparatus 100. Therefore, the above description with respect to FIGS. 1 to 18 may also be applied to the embodiment of the control method of X-ray imaging apparatus without being specifically told. FIG. 19 illustrates a flowchart of a control method of an X-ray imaging apparatus, according to an embodiment of the present disclosure. Referring to FIG. 19, a choice of an X-ray irradiation condition is received, in 500. The selected X-ray irradiation condition may be conditions directly set by the user using the set buttons provided to correspond to the respective X-ray irradiation conditions, or may be conditions basically matched with an imaging protocol and size of the subject. A parameter that represents a dose is obtained based on the selected X-ray irradiation condition, in 510. The parameter that represents a dose includes at least one of a converted amount of tube current to which an influence of the filter is reflected, a dose calculated from a conversion ratio, and the conversion ratio. The conversion ratio refers to a ratio of a dose corresponding to the selected X-ray irradiation condition and a dose of when the filter is not used under the same condition. The obtained parameter is displayed on the display 150. As shown in FIGS. 12 to 18, the calculated numerical value may be displayed along with the amount of tube current 151c-1 in a portion of the tube current amount display area 151c, or may be displayed in an area of the setting window 151 other than the tube current amount display area 151c, or may be shown in a diagram. There are no limitations on how to represent the parameter. When the X-ray irradiation condition is changed, in 530, a parameter that represents a dose based on the changed X-ray irradiation condition is obtained again, in 540. If the user changes X-ray irradiation conditions using various buttons provided in the setting window 151, the controller 140 may recalculate the parameter that represents a dose by reflecting the change in real time. The parameter obtained again is displayed on the display, in 550. This may allow the user to intuitively check the changing dose according to the change in X-ray irradiation condition and to select a proper X-ray irradiation condition considering both the dose of radiation exposure and the X-ray image quality. FIG. 20 illustrates a flowchart of an example of calculating a parameter that represents a dose in a control method of an X-ray imaging apparatus, according to an embodiment of the present disclosure. Referring to FIG. 20, the dose E1 per amount of tube current corresponding to the selected tube voltage and filter is searched for from the storage 170. For this, relationships between dose per amount of tube current (mAs) and tube voltage may be stored in advance for each filter type and thickness. The dose per amount of tube current (mAs) may be obtained by experiment, simulation, etc. For example, the dose per amount of tube current (mAs) may be measured by differing the tube voltage, and the tube voltage and the measured dose per amount of tube current (mAs) may be matched and stored in a table. Such relationships may be obtained by differing filter type and thickness. Even in the case that the filter is not used, relationships between the dose per amount of tube current (mAs) and the tube voltage are obtained and stored. The dose E2 per amount of tube current corresponding to a selected tube voltage and non-use of filter is searched for, in 512. As described above, since the storage 170 stores both the dose of when the filter is used and the dose of when the filter is not used under the same tube voltage condition, the controller 170 may search the storage 170 for the both information. A ratio of the dose E1 per amount of tube current in a case of using the filter and the dose E2 per amount of tube current when not using the filter, that is, the conversion ratio R1, is obtained, in 513. The controller 140 may calculate the conversion ratio R1=E1/E2 based on the equation 1. Based on the conversion ratio R1, a converted amount of tube current is obtained, in 514. The controller 140 calculates a converted amount of tube current M2 by substituting the conversion ratio R1 and the selected amount of tube current M1 in the equation 2. The converted amount of tube current M2 represents an amount of tube current to which an influence of the filter is reflected. FIG. 21 illustrates a flowchart of an example of calculating a parameter that represents a dose in a control method of an X-ray imaging apparatus, according to another embodiment of the present disclosure. Referring to FIG. 21, the dose E1 per amount of tube current corresponding to a selected tube voltage and filter is searched for from the storage 170, in 511′, and the dose M2 to which an influence of the filter is reflected is obtained using the searched for dose E1, in 512′. The controller 140 may calculate the dose M2 to which the influence of the filter is reflected according to the equation 3. The calculated dose or amount of tube current may be displayed on the display 150 in various ways. Furthermore, the conversion ratio R1 may be displayed. The conversion ratio R1 may be represented as a percentage. The dose, amount of tube current, or conversion ratio may be represented by direct numerical values in the tube current display area 151c or in the other area, or may be schematized into diagrams or images. Furthermore, when an X-ray irradiation condition is changed and a newly calculated parameter is displayed, a relationship between the new parameter and the old parameter before the change may also be displayed. For example, as shown in FIG. 18, the length a of a dose bar before the change and the length b of a dose bar after the change may be displayed together. In this case, the user may intuitively know of a change of the dose that varies by the change in X-ray irradiation condition. The control method of X-ray imaging apparatus according to the embodiments of the present disclosure may be implemented in program instructions which are executable by various computing means and recorded in computer-readable media. The computer-readable media may include program instructions, data files, data structures, etc., separately or in combination. For example, the computer-readable recording media may include, no matter whether it is erasable or rewritable, volatile or non-volatile storage devices, such as random access memory (RAM), read only memory (ROM), magnetic storage media (for example, floppy disks, hard disks, etc.), and optical recording media (such as, CD-ROMs, or DVDs). The computer-readable recording medium may also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. This media may be read by the computer, stored in the memory, and executed by the processor. The computer-readable medium that may be included in a portable terminal may be an example of a machine-readable readable recording medium suitable for storing a program or programs having instructions that implement the embodiments of the present disclosure. The program instructions recorded on the computer-readable media may be designed and configured specially for the present disclosure, or may be well-known to people having ordinary skill in the art of computer software. According to the embodiments of an X-ray imaging apparatus and control method thereof, information about an actual dose to which an influence of the filter is reflected is provided for the user to be able to intuitively know of the dose under a corresponding X-ray irradiation condition. This may allow setting of a proper X-ray irradiation condition taking into account both a dose of radiation exposure and quality of X-ray image. According to embodiments of the present disclosure, an X-ray imaging apparatus and control method thereof, may guide the user to intuitively recognize an actual dose of X-rays and select a proper dose, ultimately a condition for a low dose of X-rays by providing the user with information about an actual dose of X-rays to which an X-ray filter effect is reflected. Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.

051446472

description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, there is shown a linear electron accelerator in which a radiation exposure field limiting apparatus according to the present invention is incorporated. The linear electron accelerator shown is substantially similar in construction to the conventional electron accelerator shown in FIG. 9, and description of common construction is omitted herein to avoid redundancy. The linear electron accelerator of FIG. 1 is different from the conventional linear accelerator in that it includes a pair of radiation shielding blocks 20 of the multi-leaf type in place of the radiation shielding blocks 13a and 13b. FIG. 2 is a similar view to FIG. 10 but shows an apparatus for generating X-rays and a radiation exposure field limiting apparatus for defining an exposure field to which the present invention is applied, and FIG. 3 is a similar view to FIG. 14 but shows one of the radiation shielding blocks 20 shown in FIGS. 1 and 2. Referring to FIGS. 2 and 3, each of the radiation shielding blocks 20 is composed of a plurality of radiation shielding members or leaves including a center leaf 22a for defining an exposure field portion on a center axis of an exposure field to be formed and a suitable plural number of, three in the arrangement shown in FIG. 3, pairs of leaves 23a, 24a and 25a disposed in a symmetrical relationship on the opposite sides of the center leaf 22a. Though not shown, corresponding leaves of the other radiation shielding block 20 are disposed in an opposing relationship to the leaves 22a to 25a of the one radiation shielding block 20 in such a manner as in the radiation shielding blocks shown in FIG. 13. The leaves 22a to 25a of the radiation shielding blocks 20 are connected to be driven independently of each other by respective suitable driving mechanism not shown so that portions W1, W2, . . . of the exposure field may be defined independently of each other. The leaves 22a to 25a, however, may be driven to move such that they may be moved subordinately by adjacent ones or opposing ones thereof. The leaves 22a to 25a of the radiation shielding blocks 20 are constructed so as to have a common imaginary radiation source at a location denoted at 21 on a radiation center axis 7. In particular, each of the leaves 22a to 25a has an outer face at which it contacts with an inner face of an outer adjacent leaf and which makes part of a face of a circular cone having the apex at the imaginary radiation source 21, and a generating line of such face of the circular cone is denoted by 26l, 27l or 28l. Thus, for example, reference character 26l denotes a generating line of a face of a circular cone which is provided by an outer face of the leaf 22a contacting with an inner face of the outer adjacent leaf 23a and has the apex at the imaginary radiation source 21. Meanwhile, reference characters 25x, 26x and 27x denote X-rays which come to the outer faces of the leaves 22a, 23a and 24a from an actual radiation source 11. Referring now to FIG. 4, there is shown a modification to the radiation shielding block shown in FIG. 3. The radiation shielding block shown is modified such that the individual leaves 22a to 25a do not have a common imaginary radiation source but have different imaginary radiation sources on the center axis 7. In particular, a generating line 26l of a face of a circular cone of an outer face of the center leaf 22a has an imaginary radiation source at the apex 21a of the circular cone, and generating lines 27l and 28l of faces of circular cones of outer faces of the leaves 23a and 24a have imaginary radiation sources at the apexes 21b and 21c, respectively. Referring now to FIG. 5, there is shown another modification to the radiation shielding block shown in FIG. 3. The radiation shielding block shown is modified such that the individual leaves 22a to 25a have a common imaginary radiation source 21 on an axis 29 which passes the actual radiation source 11 and extends in parallel to the axis 6 of rotation of the rotatable frame 2. Such axis 29 will be hereinafter referred to as an imaginary radiation source axis. Referring now to FIG. 6, there is shown a modification to the modified radiation shielding block shown in FIG. 5. The radiation shielding block shown is modified such that the leaves 22a to 24a have different imaginary radiation sources 21a to 21c on the imaginary radiation source axis 29, that is, the generating lines 26l to 28l of faces of circular cones of outer faces of the leaves 22a to 24a intersect the imaginary radiation source axis 29 at different positions. Referring now to FIG. 7, there is shown a modification to the radiation shielding block shown in FIG. 6. The radiation shielding block shown is modified such that an outer face of the center leaf 22a which contacts with an inner face of the outer adjacent leaf 23a does not make part of a face of a circular cone but makes a plane which includes a line 22l parallel to the radiation center axis 7 and extends perpendicularly to the imaginary radiation source axis 29, that is, a flat plane. Consequently, the center leaf 22a has a rectangular cross section as seen in FIG. 7. The other leaves 23a and 24a have outer faces which make part of faces of circular cones having the apexes at imaginary radiation sources 21b and 21c, respectively, on the imaginary radiation source axis 29. FIG. 8 is a view similar to FIGS. 17 and 18 but shows a manner in which a difference in visually observable exposure field portions is provided by a difference in mutual positions of adjacent leaves of any of such radiation shielding blocks shown in FIGS. 3 to 7. Subsequently, operation of the linear electron accelerator will be described. Referring back to FIG. 1, X-rays 8 are generated from the radiation source 11 and restricted in exposure field thereof by the radiation shielding blocks 12a and 12b and then by the radiation shielding blocks 20 so that it is used for the radiation therapy of a patient 3. FIG. 2 illustrates a manner of generation of X-rays and definition of an exposure field similarly as FIG. 10, but the radiation shielding blocks 13a and 13b of FIG. 10 are replaced here by the multi-leaf radiation shielding blocks 20. The leaves of the multi-leaf radiation shielding blocks 20 operate in one of such manners as seen in FIGS. 3 to 7 wherein faces of circular cones defined by them do not have the apex at the radiation source 11 but have the apex or apexes at the imaginary radiation source 21 or sources 21a to 21c. In particular, referring to FIG. 3, faces of the leaves 22a to 25a which contact with each other make part of faces of circular cones, and they have a common apex at the imaginary radiation source 21 spaced from the actual radiation source 11. If the actual radiation source 11 is located at the position of the imaginary radiation source, then X-rays from the same directly pass through gaps between adjacent ones of the leaves and make leakage X-rays outside the intended exposure field, which will make trouble to intended radiation therapy. Actually, however, since the actual radiation source 11 is located at a different position from the imaginary radiation source 21 in the present arrangement, leakage X-rays outside the intended exposure field are prevented by the radiation shielding blocks 20. In particular, taking an X-ray 26x as an example, the X-ray 26x which comes to a gap (represented by a generating line 26l) between the leaves 22a and 23a cannot pass through the gap linearly. Now, if it is assumed tha the leaf gap is 0.1 mm and a lower end of the leaf 22a remote from the actual radiation source 11 is spaced by 50 cm from the actual radiation source 11 while the leaf 22a has a thickness equal to 70 mm in the direction of the radiation center axis, then X-rays which may pass directly through the leaf gap can be prevented if the imaginary radiation source 21 is located at a position spaced by 60 mm on the radiation center axis from the actual radiation source 11. In actual designing, such dimensions may be set to values having some tolerance, but they will be determined taking a magnitude in displacement between visually observable exposure field portions arising from relative positions of adjacent leaves into consideration. In the case of the dimensions given above, the difference in visually observable exposure field portions with respect to the leaf 22a, that is, the difference between the dimensions Le and Lf shown in FIG. 8, is 0.2 mm or so on the iso-center plane. The dimension of the leaf gap specified above is a value which is almost applicable to a linear electron accelerator wherein the distance between the radiation source 11 and the iso-center 9 is 1 m in most cases and which is operating actually in the technical field. Further, from an ordinary case in the field of medical treatment wherein an error of 1 mm in visual observation of an X-ray exposure field by visible light is permitted, the error of 0.2 mm in visual observation is a sufficiently small value. Accordingly, the imaginary radiation source 21 can be spaced by a greater distance from the actual radiation source 11. Since such error in visual observation is greater at an outer side leaf, the position of the imaginary radiation source should be determined with a maximum value of such errors in visual observation. An investigation must also be made for leakage X-rays which may pass in a scattered condition through any leaf gap in the system in which no X-rays pass directly through such leaf gap. A concept of leakage which is normally called streaming can be applied to such leakage. Such leakage does not amount to a significant value because the leaf gap is 0.1 mm or so (a further smaller value can be achieved actually) and very small but amounts to such a value which is resulted from attenuation of X-rays while they pass through a leaf as a radiation shielding material. An ordinary system is designed such that X-rays may be attenuated normally to one hundredth or less when they pass through a leaf (of each of the radiation shielding blocks 12a, 12b, 13a and 13b). Where the multi-leaf radiation shielding blocks are designed in such a manner as described above, the difference between visually observable exposure field portions arising from a difference between relative positions of adjacent leaves which has been called in question hereinabove with reference to FIG. 14 can be restricted to a value sufficiently lower than an allowable value, and direct passage of X-rays through a leaf gap which has been called in question hereinabove with reference to FIG. 15 can be achieved without employing such projection 39 as seen in FIG. 15. Accordingly, the multi-leaf radiation shielding blocks are simple in structure, easy to produce and economical, and restrict leakage of X-rays outside an exposure field to an allowable level as different from insufficient attenuation of directly passing X-rays by the projections 39. Besides, shading off or a penumbla around an edge portion of an exposure field of X-rays which is a common problem to the arrangements shown in FIGS. 14 and 15 is minimized or moderated significantly because the faces of the leaves extend along radiation planes of X-rays, which enables medical treatment with a low penumbla Accordingly, there are significant effects in the field of medical treatment that medical treatment planning is facilitated and that accuracy in medical treatment is improved. Since in the arrangement shown in FIG. 3 the difference between the dimensions Le and Lf shown in FIG. 8 increases toward the opposite outer sides from the center leaf 22a as described above, the arrangement shown in FIG. 4 is constituted otherwise such that the generating lines 26l, 27l and 28l for the leaves 22a, 23a and 24a pass the different imaginary radiation sources 21a, 21b and 21c, respectively, so that the difference between adjacent visually observed exposure field portions shown in FIG. 18 (difference between Le and Lf) may be restricted to a sufficiently small value within an allowance and such differences may be substantially similar values for the individual leaves in order to assure medical treatment with X-rays having penumblas which are equal at any position of the affected portion 42. It is to be noted that different leaves may have a common imaginary radiation source depending upon the difference between the dimensions Le and Lf. On the other hand, the arrangement shown in FIG. 5 is constructed such that the common imaginary radiation source 21 is positioned on the imaginary radiation source axis 29. The radiation shielding blocks 13a and 13b shown in FIG. 11 make opening and closing movement so as to normally make generating lines of a circular cone having the apex at the actual radiation source 11 in order to define an exposure field. In the case of the arrangements shown in FIGS. 3 and 4, the apexes of similar generating lines assume different positions from the radiation source 11 in the condition shown in FIG. 11, and consequently, an exposure field will have some penumblas at the opposite boundaries in the W direction. Thus, if the generating lines have the imaginary radiation source 21 on the imaginary radiation source axis 29 as shown in FIG. 5, then the imaginary radiation source 21 and the actual radiation source 11 are overlapped with each other in FIG. 11. Consequently, there is an effect that penumblas of an exposure field in the W direction can be prevented. The arrangement shown in FIG. 6 is somewhat similar in construction to the arrangement shown in FIG. 6 but is modified such that the imaginary radiation sources 21a, 21b and 21c are disposed at different positions on the imaginary radiation source axis 29 in order to attain an effect that differences between the distances Le and Lf of all of the leaves are made substantially equal to each other similarly as in the modification of the arrangement of FIG. 4 to the arrangement of FIG. 3. Also in this instance, different leaves may have a common imaginary radiation source depending upon a degree of the difference between the dimensions Le and Lf. The arrangement shown in FIG. 7 is a most practical arrangement and includes the center leaf 22a which has a rectangular cross section. Since the center leaf 22a has the opposite faces which are located at the innermost positions among other faces of the leaves of the radiation shielding block, even where it has such a rectangular cross section, the difference between the dimensions Le and Lf shown in FIG. 18 is sufficiently small. In this instance, if the leaf faces are formed not as faces of circular cones (curved faces) but as flat faces in order to facilitate working of the leaves, then a significant effect is provided that production of the leaves is easy. Further, if the difference between the dimensions Le and Lf of a visually observable irradiation field portion is smaller than an allowable value, not only the center leaf 22a but also an adjacent pair or pairs of leaves on the opposite sides of the center leaf 22a may have a rectangular cross section or sections. Such modification as is made in the arrangement shown in FIG. 7 can be applied to any of the radiation shielding blocks shown in FIGS. 3 to 7. It is to be noted that while in the embodiment described above a radiation exposure field limiting apparatus of the present invention is incorporated in a linear electron accelerator for the X-ray medial treatment, it can be incorporated similarly in any other radiation generating equipment which generates X-rays such as a cobalt 60 equipment, a betatron, a microtron and a synchrotron and also in an X-ray generating equipment which generates X-rays of energy lower than 1 MeV. Further, a radiation exposure field limiting apparatus of the present invention can be applied to any other radiations than X-rays such as an electron beam, gamma-rays, a neutron beam, a proton beam and a corpuscular beam, and a radiation shielding block may be made of a material which is effective for radiations to be used, such as a heavy metal for X-rays, a light metal for an electron beam and paraffin or an acrylic resin material for a neutron beam in order to attain intended similar effects. Further, similar effects can be attained also where, in distribution of radiations for any other application than for the medical treatment, that is, in non-destructive inspection with radiations, an exposure field is defined by means of multi-leaf radiation shielding members in order to prevent possible fading of an image of a portion for the inspection arising from scattered light. It is to be noted that, while the multi-leaf radiation shielding blocks 20 shown in FIG. 2 replace the radiation shielding blocks 13a and 13b of the system shown in FIG. 10, they may otherwise replace the radiation shielding blocks 12a and 12b shown in FIG. 10. Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit and scope of the invention as set forth herein.

039719553

summary

BACKGROUND OF THE INVENTION The increasing use of radioactive isotopes for the diagnosis and treatment of various medical conditions in recent years has resulted in the need for containers capable of storing and shipping these materials without endangering those who must handle them in transit and in administration. Grubel et al. in U.S. Pat. No. 2,915,640 disclose a cylindrical container having a squared bottom recess adapted to hold a square shaped bottle containing radioactive material. The container has a lid whose inner surface is adapted to conform to the cap of the enclosed bottle. When the lid is rotated the bottle cap is unscrewed but remains on the bottle from which it is later removed by tongs. Koster in U.S. Pat. No. 3,531,644 discloses a cylindrical receptacle housing a vessel with a pierceable cap containing liquid radiopharmaceuticals. A piece of cushioning and absorbing material is located between the bottom of the vessel and the outer receptacle. Also, a retaining ring is employed to hold the vessel in place. SUMMARY OF THE INVENTION This invention relates to improvements over the radiopharmaceutical containers described above. It relates to a container having a wrench-type lid which will both unscrew and remove the cap from the enclosed bottle and provide means to absorb any radioactive material which might leak from the enclosed bottle. Also, the same container with a minor modification may be used with bottles having a pierceable cap.

description

Nuclear reactors with high operating temperatures may use a fluid heat exchange media, such as a liquid metal or molten salt, for coolant. The heat exchange media may transfer heat from a reactor to a heat exchanger and/or turbine for energy extraction and electricity generation as well as act as a heat sink to remove decay heat or other unwanted heat during operation or a shutdown condition. Many reactor designs, including, for example, liquid sodium-cooled fast reactors, such as the PRISM reactor, use multiple loops of heat exchange media to efficiently transfer heat away from a reactor for electrical generation and cooling. One loop may be an intermediate loop that is heated in an intermediate heat exchanger and then passed through a steam generator connected to a turbine and generator. Any fluid heat exchange media, such as liquid lead or sodium, molten salts, etc. may be used for this heat exchange in the intermediate loop. Intermediate loops using fluid media may benefit from cleanup of the heat exchange media to remove impurities or debris that may accumulate during operation in a nuclear reactor environment. FIG. 1 is an illustration of a related art cleanup system 10 useable with an intermediate loop carrying a fluid heat exchange media. For example, system 10 may be a sodium cleanup loop useable with an intermediate coolant loop of a liquid sodium reactor or molten salt reactor. As shown in FIG. 1, system 10 includes input 50 and output 67 that may connect to a same leg of an intermediate coolant loop, just far enough apart to prevent backflow or short-circuiting between the two, such as a few feet apart. Input 50 and output 67 may be intake from and returns to an intermediate coolant loop, removing and then re-supplying a relatively small amount of coolant from/to the intermediate loop. Pump 51 may push the fluid coolant through system 10. Regenerative heat exchanger 60 may be used to initially cool an incoming coolant stream 61 with outgoing, cooler coolant that is to be resupplied to the intermediate loop by output 67. The cooled coolant stream 62 may then flow to cooler 70, which may be a series of smaller tubes with fins exposed to an open air fan 71 to convect away further heat. Cooler 70 may lower the temperature of the coolant sufficiently so that impurities, such as oxides, will solidify or precipitate from the fluid coolant. Purifier 80 may include chemical reactants, catalysts, and/or mechanical filters like cold traps, mesh, or other filter media that removes impurities or debris, including precipitates that come out of solution, following cooler 70. Bypass valves 81 and 82 may permit flow bypass of purifier 80, allowing flow to be raised or lowered slowly, and otherwise controlled, through purifier 80 during startup or shutdown. Colder, filtered coolant then passes back through regenerative heat exchanger 60 through input 66 to reheat the coolant to near operating temperatures before being returned to an intermediate loop via output 67, typically just downstream from inlet 50 in the intermediate loop. In this way, the coolant passed through system 10 for cleanup minimizes heat loss from the intermediate loop. Example embodiments include combined cleanup and heat removal systems and coolant loops joined to the such systems. The coolant loops may have a hot leg connecting between the reactor to a heat extractor like a steam generator or heat exchanger and a cold leg opposite the hot leg returning from the heat extractor to the reactor. Example embodiment cleanup and heat sink systems connect to the hot leg and/or cold leg and, depending on plant situation and/or operator input, function to remove impurities or debris from the fluid coolant flowing in the loop and/or remove a substantial amount of heat from the fluid coolant. The combined system may selectively create flow between the hot leg and the cold leg, which may bypass the heat extractor entirely to permit draining and shutdown operations on the same, even as the reactor is still generating large amounts of heat. Similarly, the combined system may work on a single leg and prevent significant heat loss while cleaning the coolant during normal reactor and heat extractor operation. Intermediate modes are also possible, depending on flow path creation, pumping, and/or cooler operations. Purification may be achieved with a cold trap, for example, cooler connected serially with an outlet, and potentially a regenerative heat exchanger, back into the coolant loop, while heat sinking may be achieved by the cooler, potentially operating in a larger-capacity mode, connected in parallel to a bypass outlet back into the coolant loop. Because the combined system may selectively provide both cleanup and significant cooling to the coolant loop, the system may be structured to operate between both these modes in desired levels of combination. For example, a cooler in the system may switch between modes, or levels of, heat removal. One mode may remove only a small amount of heat from the coolant sufficient to solidify or otherwise precipitate impurities from the coolant, while another mode may sink significant amounts of heat from the coolant, potentially up to full decay heat or even reactor operational levels of heat. Such modality from impurity-removal to heat-sinking levels may be achieved by increasing forced convection, increasing flow path volume flow rate, changing heat sink media, etc. Similarly, inlet volume flow rate may be increased, pumping pressure may be increased, and/or flow paths connecting the hot leg and cold leg of the coolant loop while avoiding a purifier like a cold trap and any regenerative heat exchanger in the system may be created, such as by valves, between these modes. Example embodiment coolant loops and cleanup/cooler systems are useable in a variety of plants and coolants, including fluid media like a liquid sodium coolant used in a PRISM reactor. Coolant loops may provide for entire bypass of a primary heat extractor like a steam generator by directly connecting hot and cold legs through the cleanup-cooler systems, allowing for isolation and draining of the heat extractor and related pumps for maintenance. The hot leg and cold legs may include portions filled with fluid columns extending vertically higher than cooler, which itself may be above the reactor, and the hot and cold leg in the loop may be positioned with slightly angled horizontal paths that decline back toward the reactor, to prevent backflow into the heat extractor. Example embodiments may thus be installed and operated with several types of coolant loops already existing with purifiers in nuclear reactors, simply by adding additional cooler capacity and/or additional outlets to opposing portions of the loop. Because this is a patent document, general, broad rules of construction should be applied when reading it. Everything described and shown in this document is an example of subject matter falling within the scope of the claims, appended below. Any specific structural and functional details disclosed herein are merely for purposes of describing how to make and use examples. Several different embodiments and methods not specifically disclosed herein may fall within the claim scope; as such, the claims may be embodied in many alternate forms and should not be construed as limited to only examples set forth herein. It will be understood that, although the ordinal terms “first,” “second,” etc. may be used herein to describe various elements, these elements should not be limited to any order by these terms. These terms are used only to distinguish one element from another; where there are “second” or higher ordinals, there merely must be that many number of elements, without necessarily any difference or other relationship. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments or methods. As used herein, the terms “and,” “or,” and “and/or” include all combinations of one or more of the associated listed items unless it is clearly indicated that only a single item, subgroup of items, or all items are present. The use of “etc.” is defined as “et cetera” and indicates the inclusion of all other elements belonging to the same group of the preceding items, in any “and/or” combination(s). It will be understood that when an element is referred to as being “connected,” “coupled,” “mated,” “attached,” “fixed,” etc. to another element, it can be directly connected to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected,” “directly coupled,” etc. to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). Similarly, a term such as “communicatively connected” includes all variations of information exchange and routing between two electronic devices, including intermediary devices, networks, etc., connected wirelessly or not. As used herein, the singular forms “a,” “an,” and the are intended to include both the singular and plural forms, unless the language explicitly indicates otherwise. Indefinite articles like “a” and “an” introduce or refer to any modified term, both previously-introduced and not, while definite articles like “the” refer to a same previously-introduced term; as such, it is understood that “a” or “an” modify items that are permitted to be previously-introduced or new, while definite articles modify an item that is the same as immediately previously presented. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, characteristics, steps, operations, elements, and/or components, but do not themselves preclude the presence or addition of one or more other features, characteristics, steps, operations, elements, components, and/or groups thereof. As used herein, “axial” and “vertical” directions are the same up or down directions oriented with gravity. “Transverse” and “horizontal” directions are perpendicular to the “axial” and are side-to-side directions in a plane at a particular axial height. The structures and operations discussed below may occur out of the order described and/or noted in the figures. For example, two operations and/or figures shown in succession may in fact be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Similarly, individual operations within example methods described below may be executed repetitively, individually or sequentially, to provide looping or other series of operations aside from single operations described below. It should be presumed that any embodiment or method having features and functionality described below, in any workable combination, falls within the scope of example embodiments. The Inventors have newly recognized that cleanup systems may be used as a heat sink in a nuclear reactor, instead of merely removing impurities from coolant. The Inventors have further newly recognized that cleanup systems may be used as alternative or parallel coolant loops while intermediate coolant loops are drained and worked on, such as during plant maintenance. While these uses of cleanup systems are contrary to their established functions, the Inventors have recognized that they may solve long-standing problems of emergency cooling and operations maintenance that have traditionally been solved by using other systems and/or fully shutting down a plant. Example embodiments described below uniquely enable these solutions to these and other problems discovered by the Inventors. The present invention is heat-sink purifier systems, nuclear reactors using the same, and methods of using the same. In contrast to the present invention, the few example embodiments and example methods discussed below illustrate just a subset of the variety of different configurations that can be used as and/or in connection with the present invention. FIG. 2 is an illustration of an example embodiment decay heat removal system 100 useable in a commercial nuclear power plant. As seen in FIG. 2, several features of example embodiment system 100 may be similar to the related art system 10 of FIG. 1. In this way example embodiment system 100 is also useable in connection with an intermediate loop carrying a molten heat transfer medium, in a number of different nuclear plant designs. Example embodiment system 100 includes an additional, higher capacity inlet 150 from the intermediate loop, as well as an additional, higher capacity outlet 180 into the intermediate loop. Inlet 150 may, for example, be a valved connection to a hotter side or hot leg 4 (FIG. 3) of an intermediate loop where coolant exits a reactor. Similarly, outlet 180 may be, for example, a valved connection to a colder side or cold leg 8 (FIG. 3) of the intermediate loop where coolant enters the reactor. Inlet 150 and outlet 180 may be separated by great distances, potentially even at opposite sides of an intermediate loop. Example embodiment decay heat removal system 100 has increased flow and heat transfer capacity to dissipate or sink a substantial portion of heat in the intermediate loop. As such, system 100 may act as a decay heat removal system by removing such heat form the intermediate loop and ultimately the reactor, instead of avoiding heat loss. To accommodate this large-scale heat sinking, additional or larger-scale cooler 170 and fan 171, as well as additional parallel and/or higher-volume pump 151, may be used to remove a substantial amount of heat from a larger amount of coolant directed through example embodiment system 100. For example, system 100 may remove heat equivalent to about 7% of full rated thermal power of a plant. Of course, the amount of heat varies based on plant, one example may sink 5 megawatt-thermal heat from an 840 megawatt-thermal rated plant. Smaller values may also be achieved through selective activation of cooler and flow paths, such as for partial removal of decay heat in combination with other heat removal systems. Selective activation may be achieved by, for example, cooler 170 including several parallel channels with fins to selectively accommodate larger flows, and/or fan 171 including several speeds or multiple fans or higher-pressure blowers that can be selectively activated to convect large amounts of heat. Or, for example, larger-scale cooler 170 may include other coolant media, submerged sections, counter-flow heat exchangers, printed-circuit heat exchangers, plate-and-frame heat exchangers, and other heat sinks in parallel that can be turned on to selectively dissipate large amounts of heat from the coolant. In this way, cooler 170 may seamlessly change from a purifying mode that removes little heat, such as 0.5 MW or less, from a coolant to a heat-sinking mode that removes much heat, such as around 5 MW or more, from the coolant. Example embodiment decay heat removal system 100 may be scaled between increased decay heat removal and lower-level cooling useable for purification, such as cold trapping. For example, connections 150 and 180 may be shut off, such as by valves, during normal plant operations without excess heat loss, and system 100 may act as a purification system with purifier 80, returning flow to outlet 67 and receiving flow from inlet 50 nearby in an intermediate loop. When additional cooling is necessary, such as during a transient involving reactor shutdown or loss of other cooling systems, connections 150 and 180 may be opened to enable larger coolant flows, and pump 151, cooler 170, and/or fan 171 may be increased in speed, number, and/or type, to increase heat dissipation from larger coolant flows. Similarly, valves 81 and/or 82 may be closed to avoid purifier 80 and/or reheater 60 when example embodiment system 100 is selectively scaled to decay heat sink levels. Closing off purifier 80 may create direct and/or exclusive coolant flow between connections 150 and 180, improving heat sinking through example system 100 in the additional cooling state. In this way, example embodiment system is compatible with nearly any coolant loop using a cold trap or other purifier, while still providing optional functionality of a selectively-activatable increased heat sink. FIG. 3 is an illustration of an example embodiment intermediate coolant loop 200 useable in nuclear reactors, including higher-temperature reactors such as a PRISM reactor or molten salt reactor. As shown in FIG. 3, example embodiment intermediate coolant loop 200 may interface with several related or conventional reactor components including reactor 1 housing core 2 with nuclear fuel. An intermediate heat exchanger 3 transfers heat from reactor 1 to intermediate coolant loop 200, which in turn may transfer heat to an extractor like a steam generator 6 or heat exchanger for electricity generation. As shown in FIG. 3, intermediate coolant loop 200 is interfaced with example embodiment decay heat removal system 100 (FIG. 2) via inlet 150 and outlet 180. For example, inlet 150 may take coolant from a bottom of hot leg 4, where coolant first exits reactor 1 and has its highest energy, and outlet 180 may return coolant to a bottom of cold leg 8, where coolant is returned to reactor 1 and has its lowest energy. For typical cold-trapping purification, inlets 50 and outlets 67 (FIG. 2) might take from a same or nearby position on a same leg to prevent heat loss, unlike inlet 150 and outlet 180 that may be segregated at temperature extremes in example embodiment intermediate coolant loop 200. During a transient state or when larger heat-sinking is desired, inlets 50 and/or outlets 67 may be closed, and inlet 150 and outlet 180 may be opened or enabled to remove heat from coolant that ultimately flows back through intermediate heat exchanger 3, cooling reactor 1. Example embodiment intermediate coolant loop 200 can also be operable with intermediate pump 7 and steam generator 6, or other heat extractor, drawing heat from the coolant to generate electricity. Intermediate pump 7 and/or steam generator 6 may optionally be deactivated and drained while coolant loop 200 still circulates coolant and sinks heat through inlet 150 and outlet 160. For example, intermediate pump 7, steam generator 6, and/or portions of hot leg 4 and cold leg 8 may be drained into drain tank 5, such as through opening drain valves to drive coolant by gravity into drain tank 5 and/or through active pumping. Proper sloping of piping in hot leg 4 and cold leg 8 may permit draining of pump 7 and steam generator 6 and their associated piping. For example, horizontal piping of hot leg 4 and cold leg 8 may be at slight angles with respect to the vertical, such as slightly declined toward steam generator 6 and away from reactor 1 at 5-10 millimeters vertical drop per meter length. This decline may further prevent backflowing and ensure coolant looping only through a portion of example embodiment intermediate coolant loop 200 in combination with example positioning discussed below. Hot leg 4 and cold leg 8 may be arranged such that a column of fluid in hot leg 4 may be at a vertical height 240 and fluid in cold leg 8 may be at a vertical height 280. Columns of fluid in these legs may remain even though other portions of loop 200 are drained. Because of the presence of the columns of fluid at vertical heights 250 and 280 above inlet 150 on hot leg 4 and outlet 180 on cold leg 8, coolant may still be circulated between intermediate heat exchanger 3 and a decay heat removal system 100 (FIG. 2) via the lower portions of hot leg 4 and cold leg 8. In this way, it is possible to repair or otherwise work on an emptied steam generator 6, intermediate pump 7, and/or any other drained portions of coolant loop 200 while still removing heat from reactor 1 via intermediate heat exchanger 3. Of course, example embodiment coolant 200 with system 100 may also be used with a completely-filled loop. Similarly, in FIG. 3, system 100, or at least cooler 170 (FIG. 2) of system 100, may be placed at a vertical height 231 above intermediate heat exchanger 3 at vertical height 230. The difference in vertical heights 230 and 231 may create natural circulation driving forces, where coolant heated at heat exchanger 3 rises due to lowered density, flows to cooler 170 and is cooled, increasing its density, which then flows by density difference back to heat exchanger 3. This configuration and associated natural circulation may eliminate or reduce the need for active pumping, such as with pump 151 or 7. If all other coolant-filled portions of system 100 are below elevations 240 and 280 of coolant columns, natural circulation will occur in loop 200 through heat exchanger 3 due to gravity and because voids cannot form in system 100 below. As seen in FIGS. 2 and 3, example embodiment intermediate coolant loop 200 and example embodiment decay heat removal system 100 can be used with several types of nuclear reactors and existing components. Some functionality of loop 200 and system 100 may be achieved simply by increasing capacity of inlet 50 to that of inlet 150, increasing heat sink capacity of a cooler, and adding an exclusive return outlet 180 to cold leg 8. Loop 200 and system 100 may be used during typical reactor operation to remove impurities and/or debris from a relatively small stream of coolant, as well as being selectively scaled to remove all or a significant portion of decay heat or even operation heat from reactor 1 during a transient or non-electricity generating state, such as during an accident or plant maintenance. Similarly, multiple loops 200 and systems 100 are useable with a single reactor 1 to provide even larger amounts of heat transfer and sinking from reactor 1. Example embodiments and methods thus being described, it will be appreciated by one skilled in the art that example embodiments may be varied and substituted through routine experimentation while still falling within the scope of the following claims. For example, any number of different reactor types and thermodynamic cycles can be used with example embodiments, simply by allowing for different temperatures and coolants. Such variations are not to be regarded as departure from the scope of these claims.

claims

1. A testing device, comprising:a test tank that stores cooling water therein;a foreign matter inputter that inputs foreign matter to the test tank;a recirculation sump screen set in the test tank and that filters the foreign matter; anda processor,wherein the processor executes a program for evaluating an amount of foreign matter passed through the recirculation sump screen, the program causing the processor to perform:acquiring sets of test data on amounts of foreign matter passed through a recirculation sump screen when different amounts of the foreign matter are input;forming a passed foreign matter amount approximate line that approximates the amounts of passed foreign matter with respect to the amounts of input foreign matter on the basis of the sets of test data on the amounts of passed foreign matter;forming a passed foreign matter amount line tangent to the passed foreign matter amount approximate line; andcalculating a total amount of passed foreign matter with respect to the amounts of input foreign matter on the basis of the passed foreign matter amount line to evaluate the recirculation sump screen. 2. The testing device according to claim 1, wherein the passed foreign matter amount approximate line is a quadratic curve and the passed foreign matter amount line is a primary expression straight line expressed by a function of an input foreign matter amount. 3. The testing device according to claim 2, further comprising forming a passed foreign matter amount approximate straight line on the basis of the passed foreign matter amount approximate line and forming the passed foreign matter amount line on the basis of the passed foreign matter amount approximate straight line. 4. The testing device according to claim 1, wherein a passed foreign matter amount line is set in a length defined by the passed foreign matter amount line tangent to the passed foreign matter amount approximate line and a passed foreign matter amount line shifted to a pre-set side where the passed foreign matter amount increases. 5. The testing device according to claim 4, wherein the length is a length moved to a side where the amount of passed foreign matter is smaller than a maximum value of the sets of test data on the amounts of passed foreign matter. 6. The testing device according to claim 2, wherein a passed foreign matter amount line is set in a length defined by the passed foreign matter amount line tangent to the passed foreign matter amount approximate line and a passed foreign matter amount line shifted to a pre-set side where the passed foreign matter amount increases. 7. The testing device according to claim 3, wherein a passed foreign matter amount line is set in a length defined by the passed foreign matter amount line tangent to the passed foreign matter amount approximate line and a passed foreign matter amount line shifted to a pre-set side where the passed foreign matter amount increases.

claims

1. A radiographic image capturing apparatus comprising:a radiation source configured to apply radiation to an object of a subject to be examined;a radiation detector configured to detect the radiation that has passed through the object and configured to convert the detected radiation into a radiographic image;a collimator configured to delimit an irradiated field of the radiation with respect to the radiation detector, the collimator being disposed between the radiation source and the object;a biopsy region positional information calculating unit configured to calculate a three-dimensional position of a biopsy region in the object based on two radiographic images, which are acquired by the radiation detector in a stereographic image capturing process, in which the radiation source disposed at least at two angles applies the radiation to the object;an irradiated field calculating unit configured to calculate a new irradiated field covering the biopsy region based on the calculated three-dimensional position of the biopsy region and the two angles;a collimator control unit configured to control the collimator to change the irradiated field of the radiation in a next stereographic image capturing process to the new irradiated field; andan irradiated field calculation control unit configured to selectively enable the irradiated field calculating unit to calculate the new irradiated field or disable the irradiated field calculating unit from calculating the new irradiated field. 2. A radiographic image capturing apparatus according to claim 1, wherein the application of the radiation to the object from the radiation source at the two angles, the calculation of the three-dimensional position of the biopsy region by the biopsy region positional information calculating unit, the calculation of the new irradiated field by the irradiated field calculating unit, and the changing of the irradiated field of the radiation to the new irradiated field by the collimator control unit are successively carried out repeatedly. 3. A radiographic image capturing apparatus according to claim 1, further comprising a light source for spotlighting the radiation detector to indicate the irradiated field thereon, before the radiation source applies the radiation to the object. 4. A radiographic image capturing apparatus according to claim 1, wherein on condition that the irradiated field calculation control unit determines that the biopsy region will possibly be included in the two radiation images to be acquired even after converting the irradiated field to the new irradiated field in the next stereographic image capturing process, then calculation of the new irradiated field by the irradiated field calculating unit is enabled, andon condition that the irradiated field calculation control unit determines that the biopsy region will not possibly be included in the two radiation images to be acquired after converting the irradiated field to the new irradiated field in the next stereographic image capturing process, calculation of the new irradiated field by the irradiated field calculating unit is disabled. 5. A radiographic image capturing apparatus according to claim 4, wherein in the case that the calculation of the new irradiated field is enabled, the irradiated field calculating unit is configured to calculate the new irradiated field using the three-dimensional position of the biopsy region based on the radiographic image in a last stereographic image capturing process and the two angles acquired by the radiation detector in the last stereographic image capturing process. 6. A radiographic image capturing apparatus according to claim 5, wherein the irradiated field calculating unit is configured to determine a field restricted from the irradiated field, as the new irradiated field in the next stereographic image capturing process. 7. A radiographic image capturing apparatus according to claim 4, wherein in the case that the calculation of the new irradiated field is disabled, a stereographic image capturing process is carried out under the same conditions as the last stereographic image capturing process. 8. A radiographic image capturing method comprising the steps of:performing a stereographic image capturing process by applying radiation from a radiation source disposed at least at two angles to an object of a subject to be examined, while an irradiated field of the radiation with respect to a radiation detector is being delimited by a collimator;detecting, with the radiation detector, the radiation applied from the radiation source disposed at the two angles to acquire two radiographic images;calculating, with a biopsy region positional information calculating unit, a three-dimensional position of a biopsy region in the object based on the two radiographic images;calculating, with an irradiated field calculating unit, a new irradiated field covering the biopsy region based on the calculated three-dimensional position of the biopsy region and the two angles;controlling the collimator with a collimator control unit to change the irradiated field of the radiation in a next stereographic image capturing process to the new irradiated field; andselectively enabling the irradiated field calculating unit to calculate the new irradiated field or disabling the irradiated field calculating unit from calculating the new irradiated field.

description

(1) Field of the Invention This invention relates to an X-ray detector for measuring X rays in the medical, industrial, nuclear and other fields. (2) Description of the Related Art In an X-ray detector having electrodes formed at opposite sides of a semiconductor, a predetermined bias voltage is applied between the electrodes, and electric charges generated in the semiconductor by incident X rays are detected as electric signals. For such an X-ray detector, various semiconductor materials are selectively used according to purpose. These semiconductor materials are manufactured in various ways. Generally, for an X-ray detector required to have energy resolution, a high-purity single crystal semiconductor such as silicon (Si) tends to be used. An X-ray detector using amorphous selenium (a-Se) in particular can easily realize a high resistance thick film sized 1,000 cm2 or larger by using a film coating technique such as vacuum deposition method. This X-ray detector is ideal for use in a field requiring a large area for X-ray measurement. However, an amorphous selenium (a-Se) film formed by such a method includes many structural defects. Generally, therefore, an appropriate quantity of impurity is added (i.e. doped) in order to improve performance. The conventional detector constructed as described above has the following drawback. Unlike a single crystal semiconductor, the conventional detector has many potential structural defects. These defects trap charge transfer media (carriers) of electrons and holes generated in the semiconductor layer by X-ray incidence. The trapped carriers cannot be picked up as electric signals. This causes a phenomenon of deterioration in the sensitivity of the X-ray detector. This phenomenon will particularly be described hereinafter with reference to FIGS. 2A and 2B. FIGS. 2A and 2B are explanatory views of an internal structure of the X-ray detector. The structural defects in amorphous selenium (a-Se), as shown in FIG. 2B, include recombination centers D0 and ionized recombination centers D+ (electron trapping centers) and D− (hole trapping centers) present in a fixed ratio. A density of D+ and D− at this time determines an initial value of sensitivity of the X-ray detector. This state is expressed by the following formula:2D0→D++D− When X rays impinge in this state to generate charge transfer media (carriers) of electrons (e−) or holes (h+) in amorphous selenium (a-Se), these media are first trapped by the recombination centers D0 to change into D− and D+, respectively. In this way, the density of D+ and D− increases to deteriorate sensitivity. This relationship is expressed by the following two formulas:D0+e−→D−D0+h+→D+ The object of this invention is to provide an X-ray detector which compensates for structure defects in amorphous selenium (a-Se) to be free from sensitivity deterioration. The above object is fulfilled, according to this invention, by an X-ray detector for detecting X rays comprising a semiconductor for generating electric charges therein upon X-ray incidence, and electrodes formed on opposite sides of the semiconductor for application of a predetermined bias voltage, wherein the semiconductor is amorphous selenium (a-Se) doped with a predetermined quantity of an alkali metal. As shown in FIG. 2A, an alkali metal M having a strong ionization tendency is added (doped) to amorphous selenium (a-Se) which is a semiconductor layer sensitive to X rays, in a quantity to compensate for the structural defects D0. Thus, the structural defects in amorphous selenium (a-Se) are only D0 which are recombination centers and D− (hole trapping centers) which are negatively ionized D0. This state is expressed by the following formula (1):2D0+M→M++D−+D0 (1) When, in this state, incident X rays generate charge transfer media (carriers) of electrons (e−) and holes (h+) in amorphous selenium (a-Se), the electrons are captured by the recombination centers D0 to change into D−, and the holes captured by D− to change into D0. This relationship is expressed by the following two formulas (2) and (3):D0+e−→D− (2)D−+h+→D0 (3) As seen from these formulas (2) and (3), where the electron capturing probability and the hole capturing probability are exactly equal, the density of D− never increases, and hence no sensitivity deterioration. Even where the electron capturing probability is higher than the hole capturing probability to increase the density of D−, only the holes are captured in an increased quantity. Since no increase takes place in the quantity of electrons captured, sensitivity deterioration is suppressed to a half. In the X-ray detector having the above construction according to this invention, preferably, one of the electrodes formed at an X-ray incidence side is a positive electrode to which the bias voltage is applied to increase potential. Since the electrode at the X-ray incidence side is a positive electrode to which the bias voltage is applied to increase potential, as shown in FIG. 3, electrons generated by X-ray incidence move toward the X-ray incidence side while holes move to the opposite side. The interaction between X rays and a material is characterized by the stronger reaction tending to occur in the regions closer to the surface of the material. Thus, many of the electrons are generated by X-ray incidence near a plane of X-ray incidence. These electrons move toward the electrode at the side of X-ray incidence, and thus move reduced distances. Thus, the probability of the electrons reaching the electrode without being captured by the recombination centers D0 is increased to minimize an increase of D−. In this way, not only an increase in the quantity of electrons captured is suppressed, but also an increase in the quantity of holes captured is suppressed. Consequently, hardly any sensitivity deterioration occurs with the X-ray detector. In the X-ray detector according to this invention, the quantity of the alkali metal doped, preferably, is in a range of 0.01 to 10 ppm, and more preferably in a range of 0.05 to 2 ppm. Where the quantity of the alkali metal added (doped) is in a range of 0.01 to 10 ppm, which substantially corresponds to a quantity compensating for the structural defects D0 of amorphous selenium (a-Se), the reaction in formula (1) takes place reliably to suppress sensitivity deterioration. Where the quantity of the alkali metal added were less than 0.01 ppm, the effect of the alkali metal would diminish to result in a sensitivity deterioration. Where the quantity of the alkali metal added were larger than 0.01 ppm, the alkali metal would be deposited alone, resulting in an increase in dark current and a rapid fall of sensitivity. Naturally, even in the above range, an optimum value exists according to the type of alkali metal and film forming conditions such as vapor deposition temperature and substrate temperature. In the case of Na, for example, an optimal quantity is the range of 0.05 to 2 ppm. A preferred embodiment of this invention will be described in detail hereinafter with reference to the drawings. FIGS. 1 through 4 show one embodiment of the invention. FIG. 1 is a schematic sectional view showing the construction of an X-ray detector. FIGS. 2A and 2B are explanatory views showing an internal structure of the X-ray detector. FIG. 3 is an explanatory view showing functions of the X-ray detector according to this invention. FIG. 4 is a schematic sectional view showing the construction of a modified X-ray detector. As shown in FIG. 1, the X-ray detector in this embodiment includes a carrier collection electrode 1 and a lower carrier selection layer 2 formed on an insulating substrate 3 such as a glass substrate. A semiconductor thick film 4 of amorphous selenium (a-Se) is formed also on the substrate 3. An alkali metal has been added (doped) to the amorphous selenium in a range of 0.01 to 10 ppm, preferably in a range of 0.05 to 2 ppm. A voltage application electrode 6 is formed on the semiconductor thick film 4 through an upper carrier selection layer 5. The lower and upper carrier selection layers 2 and 5 are provided for suppressing dark current by using the notable difference in contribution to charge transfer action between electrons and holes acting as carriers in the semiconductor. Where a positive bias is applied to the voltage application electrode 6, an n-type semiconductor layer such as CdSe, CdS or CeO2, a semi-insulator layer such as Sb2S3 or an amorphous Se layer doped with As or Te is used as the upper carrier selection layer 5 in order to restrict an injection of holes. As the lower carrier selection layer 2, a p-type semiconductor layer such as ZnSe, ZnTe or ZnS, a semi-insulator layer such as Sb2S3 or an amorphous Se layer doped with a halogen such as Cl is used in order to restrict an injection of electrons. A semi-insulator layer such as Sb2S3 can reverse the contributions of electrons and holes based on film forming conditions. The X-ray detector in this embodiment applies a bias voltage to the voltage application electrode 6, with an X-ray incidence generating electric charges (electrons and holes) in the amorphous selenium (a-Se) semiconductor thick film 4. The X-ray detector detects, as electric signals from the carrier collection electrode 1, electric charges induced by movement of the generated electrons and holes toward the two electrodes, respectively. As shown in FIG. 2B, the amorphous selenium (a-Se) semiconductor thick film 4 has, present therein, three types of structural defects, i.e. recombination centers D0 and ionized recombination centers D+ (electron trapping centers) and D− (hole trapping centers). In the case of the X-ray detector in this embodiment, however, alkali metal M is added (doped) to the amorphous selenium (a-Se) semiconductor thick film 4. As shown in FIG. 2A, only D0 and D− are present. The value of sensitivity is determined by a density of D+ and D−. D− increases by X-ray irradiation according to formula (2) set out hereinbefore, but no increase in D+ takes place. Thus, deterioration in the sensitivity of the X-ray detector is suppressed to a half. Further, when a positive bias voltage is applied so that the electrode at the X-ray incidence side, i.e. the voltage application electrode 6, has a higher potential than the carrier collection electrode 1, as shown in FIG. 3, electrons generated by X-ray incidence move toward the X-ray incidence side while holes move to the opposite side. The interaction between X rays and a material is characterized by the stronger reaction tending to occur in the regions closer to the surface of the material. Thus, many of the electrons are generated by X-ray incidence near a plane of X-ray incidence. These electrons move toward the electrode at the side of X-ray incidence. Consequently, the electrons move reduced distances. This increases the probability of the electrons reaching the voltage application electrode 6 without being captured by the recombination centers D0, thereby minimizing an increase of D−. As a result, hardly any sensitivity deterioration occurs with the X-ray detector. FIG. 4 shows a schematic sectional view of a modified embodiment in which the above X-ray detector is developed to form a plurality of channels in a two-dimensional matrix. Each carrier collection electrode 11 is connected to a capacitor 12 for charge storage and a switching device 13 (thin film transistor (TFT) switch) for reading the charges. The carrier collection electrodes 11 are arranged on a TFT substrate having the capacitors 12 and switching devices 13 to constitute a two-dimensional array. Like reference numerals are used to identify like elements of the X-ray detector described hereinbefore, and will not be described again. When the X-ray detector in this modification is irradiated with X rays, with a bias voltage applied to a voltage application electrode 14 formed over an entire surface as a common electrode, electric charges (electrons and holes) generated move toward the opposite electrodes, respectively. The induced charges are stored in the charge storing capacitors 12 connected through the carrier collection electrodes 11 to locations of X-ray incidence. In time of reading, an ON signal is sent in from a gate driver 15 through gate lines 16 to turn on (connect) the switching devices 13. Then, the stored charges are transmitted as radiation detection signals through sense lines 17 to pass through charge-to-voltage converters 18 and a multiplexer 19 to be outputted as digital signals to provide a two-dimensional X-ray image. With such a two-dimensional array construction, the characteristic of the X-ray detector according to this invention appears conspicuously. Specifically, with a conventional X-ray detector, a sensitivity deterioration takes place according to the incidence intensity of X rays, to cause local sensitivity variations. Its influence is conspicuous on the quality of images photographed subsequently. In the X-ray detector in this modified embodiment, on the other hand, an alkali metal is added (doped) to an amorphous selenium (a-Se) semiconductor thick film 20, and a positive bias is applied to the voltage application electrode 14 in use. Thus, hardly any sensitivity deterioration takes place, to be free from image quality deterioration such as sensitivity variations. In the foregoing X-ray detector and its modification, typical examples of the alkali metal are Li, Na and K. As described in relation to the functions of this invention, similar effects may be produced by doping an alkali earth metal such as Ca or a nonmetallic element such as H as long as such an element has a strong ionization tendency and a reducing effect. <Measurement Data of this Invention and Comparison with the Prior Art> Next, verification is made that sensitivity deterioration is improved by the X-ray detector in this embodiment. As shown in FIG. 5, samples used here include eight X-ray detectors, i.e. X-ray detectors for testing 1-6 and X-ray detectors for comparison 1 and 2. The detectors for testing 1-6 have alkali metal Na added (doped) to the amorphous selenium (a-Se) semiconductor thick film 20 in 0.01 ppm, 0.1 ppm, 0.5 ppm, 1.0 ppm, 5.0 ppm and 10.0 ppm, respectively. The X-ray detector for comparison 1 has alkali metal Na added (doped) in 20.0 ppm to the amorphous selenium (a-Se) semiconductor thick film 20. The X-ray detector for comparison 2 has an amorphous selenium (a-Se) semiconductor thick film with no doping. The amorphous selenium (a-Se) semiconductor thick film 4 is 1 mm thick in all of the X-ray detectors. For all the X-ray detectors for testing and for comparison, ±10 kV bias voltages were applied to the voltage application electrode 6, and an ammeter was connected to the carrier collection electrode 1 to read signal currents. In this state, the X-ray detectors were irradiated continuously for 15 minutes with X rays passed through a 1 mm aluminum filter under the conditions of 80 kV tube voltage and 2.2 mA tube current, and variations in the signal current were recorded. FIG. 6 shows the variations in the signal current obtained. As seen, the X-ray detector for comparison 2 has signal currents falling exponentially with both the positive and negative bias voltages. The X-ray detector for testing 3 has a signal current hardly changing with the positive bias, and a signal current falling only slightly with the negative bias. Amount of signal current deterioration ΔI in FIG. 5 represents a difference between a signal current immediately following the X-ray irradiation and a signal current 15 minutes thereafter, i.e. an amount of sensitivity deterioration. The above results show that amount of signal current deterioration ΔI is small and little sensitivity deterioration occurs with alkali metal Na doped in the range of 0.01 to 10.0 ppm. It will also be understood that sensitivity deterioration is less with the positive bias than with the negative bias. Similarly, an X-ray detector for testing 7 was fabricated by doping 0.5 ppm of potassium (K), and variations in the signal current were checked. The results are shown in FIG. 7. It will be seen that amount of signal current deterioration ΔI is clearly smaller than for the detector for comparison 2 not doped with potassium (K). Further, an X-ray detector for testing 8 was fabricated by doping 0.1 ppm of lithium (Li), and variations in the signal current were checked. The results are shown in FIG. 8. It will be seen that amount of signal current deterioration ΔI is clearly smaller than for the detector for comparison 2 not doped with lithium (Li). These results prove that similar effects are produced by doping alkali metals other than sodium (Na), to suppress sensitivity deterioration. This invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.

044302762

abstract

A method is disclosed for producing a dimensionally stable UO.sub.2 fuel pellet of large grain mole %, and relatively large pore size. A dopant containing an element selected from the group consisting of aluminum, calcium, magnesium, titanium, zirconium, vanadium, niobium, and mixtures thereof is added to a highly sinterable UO.sub.2 powder, which is a UO.sub.2 powder that is sinterable to at least 97% theoretical density at 1600.degree. C. in one hour, and the UO.sub.2 powder can then be formed into fuel pellets. Alternatively, the dopant can be added at a step in the process of producing ammonium diuranate. The ammonium diuranate is collected with about 0.05 to about 1.7 mole%, based on UO.sub.2, of a compound containing said element. That mixture is then calcined to produce UO.sub.2 and the UO.sub.2 is formed into a fuel pellet. The addition of the dopant can also be made at the hydrolysis stage in the manufacture of UO.sub.2 by a dry conversion process.

summary

abstract

A compact source for high brightness x-ray generation is disclosed. The higher brightness is achieved through electron beam bombardment of multiple regions aligned with each other to achieve a linear accumulation of x-rays. This may be achieved through the use of x-ray targets that comprise microstructures of x-ray generating materials fabricated in close thermal contact with a substrate with high thermal conductivity. This allows heat to be more efficiently drawn out of the x-ray generating material, and allows bombardment of the x-ray generating material with higher electron density and/or higher energy electrons, leading to greater x-ray brightness. The orientation of the microstructures allows the use of a take-off angle at or near 0°, allowing the accumulation of x-rays from several microstructures to be aligned and be used to form a beam in the shape of an annular cone.

claims

1. A medical apparatus comprising:a beam deflector having an electromagnet configured to provide a first magnetic field for deflecting a particle beam;a current control configured to adjust a current of the electromagnet in correspondence with an energy level associated with an accelerator, wherein the energy level associated with the accelerator comprises an energy level of an electric field in the accelerator or an energy level of the particle beam; anda permanent magnet configured to provide a second magnetic field, wherein the permanent magnet is implemented as a part of the beam deflector;wherein the first magnetic field and the second magnetic field form a total magnetic field that is variable to have at least a first magnetic field value and a second magnetic field value;wherein the medical apparatus is configured to adjust the total magnetic field in response to the electric field in the accelerator or the energy level of the particle beam; andwherein the medical apparatus is configured to provide the total magnetic field with the first magnetic field value when the electric field in the accelerator or the energy level of the particle beam has a first value, and wherein the medical apparatus is also configured to provide the total magnetic field with the second magnetic field value when the electric field in the accelerator or the energy level of the particle beam has a second value. 2. The apparatus of claim 1, wherein the permanent magnet comprises a rare earth magnet. 3. The apparatus of claim 1, wherein the electromagnet comprises a coil surrounding the permanent magnet. 4. The apparatus of claim 1, further comprising an accelerator for providing the particle beam, the accelerator having an energy switch configured to change the energy level of the particle beam. 5. The apparatus of claim 4, wherein the energy switch is configured to change the energy level of the particle beam within a duration that is less than one second. 6. The apparatus of claim 4, wherein the accelerator comprises a fixed-field alternating gradient (FFAG) accelerator, or a non-scaling fixed-field alternating gradient (NS-FFAG) accelerator. 7. The apparatus of claim 1, further comprising an ion chamber, wherein the ion chamber comprises a dosimetry circuit. 8. The apparatus of claim 7, wherein the control is also configured to adjust a parameter in the dosimetry circuit in correspondence with the energy level associated with the accelerator. 9. The apparatus of claim 1, wherein the electromagnet comprises a laminated steel. 10. The apparatus of claim 1, wherein the current control is configured to increase the current of the electromagnet in correspondence with an increase in the energy level associated with the accelerator. 11. The apparatus of claim 1, wherein the current control is configured to decrease the current of the electromagnet in correspondence with a decrease in the energy level associated with the accelerator. 12. The apparatus of claim 1, wherein the electromagnet comprises a pretzel magnet. 13. The apparatus of claim 1, further comprising a beam output coupled to the beam deflector, wherein the beam output is moveable to deliver treatment energy from a plurality of gantry angles that includes at least a first gantry angle and a second gantry angle. 14. The apparatus of claim 13, further comprising an energy adjuster configured to adjust the treatment energy so that the treatment energy has a first energy level when the beam output is at the first gantry angle, and a second energy level when the beam output is at the second gantry angle. 15. The apparatus of claim 14, wherein the energy adjuster is configured to adjust the treatment energy in a continuous manner. 16. The apparatus of claim 14, wherein the energy adjuster is configured to adjust the treatment energy in a discrete manner. 17. The apparatus of claim 13, further comprising an energy adjuster configured to adjust the treatment energy so that the treatment energy has a first energy level when the beam output is at the first gantry angle, and a second energy level when the beam output is at the first gantry angle. 18. The apparatus of claim 13, wherein the beam output is configured to deliver the treatment energy without using any flattening filter. 19. The medical apparatus of claim 1, wherein the current control is configured to adjust the current of the electromagnet such that a trajectory of the particle beam remains the same regardless of the energy level of the electric field in the accelerator or the energy level of the particle beam. 20. A medical apparatus comprising:an accelerator configured to provide a particle beam;an energy switch configured to change an energy level of the particle beam within a duration that is less than one second; anda target configured to receive the particle beam, wherein the target is a component of the medical apparatus;wherein the accelerator is configured to provide the particle beam directly onto the target without using a beam deflector at an end of the accelerator; andwherein the medical apparatus further comprises a beam output coupled to the accelerator, wherein the beam output is moveable to deliver treatment energy from a plurality of gantry angles that includes at least a first gantry angle and a second gantry angle. 21. The apparatus of claim 20, further comprising an energy adjuster configured to adjust the treatment energy so that the treatment energy has a first energy level when the beam output is at the first gantry angle, and a second energy level when the beam output is at the second gantry angle. 22. The apparatus of claim 21, wherein the energy adjuster is configured to adjust the treatment energy in a continuous manner. 23. The apparatus of claim 21, wherein the energy adjuster is configured to adjust the treatment energy in a discrete manner. 24. The apparatus of claim 20, wherein the beam output is configured to deliver the treatment energy without using any flattening filter. 25. The apparatus of claim 20, wherein the accelerator comprises a fixed-field alternating gradient (FFAG) accelerator, or a non-scaling fixed-field alternating gradient (NS-FFAG) accelerator. 26. The apparatus of claim 20, further comprising an ion chamber, wherein the ion chamber comprises a dosimetry circuit. 27. The apparatus of claim 26, further comprising a control configured to adjust a parameter in the dosimetry circuit in correspondence with the energy level of the particle beam. 28. A treatment method, comprising:configuring a medical system for delivering a first treatment beam having a first energy level;delivering the first treatment beam by the medical system towards a patient that is on a patient support;configuring the medical system for delivering a second treatment beam having a second energy level; anddelivering the second treatment beam by the medical system towards the patient; wherein the act of configuring the medical system for delivering the second treatment beam comprises changing an energy that is associated with an accelerator by an energy switch, and adjusting a current of an electromagnet by a current control in correspondence with the energy associated with the accelerator;wherein the first treatment beam is delivered towards the patient from a first gantry angle, and the second treatment beam is delivered towards the patient from the first gantry angle. 29. The method of claim 28, wherein the medical system comprises an ion chamber, wherein the ion chamber comprises a dosimetry circuit, and wherein the method further comprises adjusting a parameter in the dosimetry circuit in correspondence with the energy associated with the accelerator. 30. The method of claim 28, wherein the act of configuring the medical system, and the act of delivering are performed so that the first treatment beam transitions to the second treatment beam in a continuous manner. 31. The method of claim 28, wherein the act of configuring the medical system, and the act of delivering are performed so that the first treatment beam and the second treatment beam are delivered in a discrete manner.

052992411

description

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a transuranium element transmuting reactor core relating to the present invention will now be described with reference to the accompanying drawings. FIG. 1 represents a basic conception of a nuclear reactor such as pool type fast reactor enclosing the transuranium elements transmuting reactor core of the present invention. The present invention is applicable to a core of the nuclear reactor of a type to remove heating from cooling the core by flowing a coolant thereto and the coolant then includes liquid Na, liquid NaK, He gas and the like, which is intended for the core for which a fission is caused chiefly by a fast neutron. FIG. 1 represents an example of a pool type fast reactor, however, a loop type fast reactor may be exemplified, needless to say, in this case. The nuclear reactor includes a reactor vessel 10 which is charged with a liquid sodium (Na) 11 as a coolant. A core 12 is provided at a central portion in the reactor vessel 10, and a upper core structure 13 is provided above the core 12. The upper core structure 13 is supported by a roof slab 14 working as a shielding plug to cover a top of the reactor vessel 10. A primary coolant pump 15 and an intermediate heat exchanger 16 and others are suspended on the roof slab 14. A cover gas such as inert gas or the like is enclosed between the roof slab 14 and a free liquid surface of the liquid Na 11. The core 12 enclosed in the reactor comprises, as shown in FIG. 2 for example, two region cores 12a, 12b. A fuel assembly 17 relatively high in plutonium content is disposed in the outer peripheral area 12a and a fuel assembly 18 relatively low in plutonium content is disposed in the central area 12b. For charging amount of the MA elements of the TRU elements to be transmuted which is charged into the fuel assemblies 17, 18, a charging density of the MA elements is controlled at every areas or fuel assemblies 17, 18. A reference numeral 19 denotes a control rod. As exemplified in FIG. 3, the fuel assemblies 17, 18 have a plurality of fuel pins 21 enclosed in a bundle within a hexagonal wrapper tube 20 as a fuel element in a wide sense. A coolant inlet 22 is formed on a lower portion of the wrapper tube 20, and a coolant outlet 23 is formed on an upper portion. With opposite ends sealed up with an upper end plug 27 and a lower end plug 28, the fuel pin 21 enclosed within the wrapper tube 20 is that for which a plurality of fuel pellets 26 are inserted in a row, as shown in FIG. 4, within a fuel clad 25 as a fuel element. The fuel pellets 26 are retained elastically by a spring 29 within the fuel clad 25, a fuel stack portion 30 being constructed as an effective fuel length. The fuel pellet 26 is that for which as oxide fuel matter as fuel element is sintered through ceramics. A so-called metallic fuel is available for the fuel element instead of the oxide fuel matter, and the fuel element is not necessarily a thoroughly sealed type covered by the fuel clad 25. For example, a so-called vented fuel element (fuel pin) which discharges fission products gas (hereinafter called FP gas) such as He gas or the like outside the fuel element by fission is acceptable otherwise. On the other hand, the fuel assemblies 17, 18 are charged with the TRU elements (transuranium elements) to be transmuted, and a concrete case for controlling a charging amount of a main MA elements of the TRU elements to be charged is exemplified as follows: (1) An amount of the elements is controlled so that the MA elements to be transmuted which is added into the fuel pellets 26 will be distributed uniformly. (2) The fuel pellets with the MA elements to be transmuted relatively high in density and the fuel pellets with the elements relatively low in density or almost not added are prepared and a charging number of each fuel pellet to a fuel pin is controlled, thereby controlling the charging amount. An array order of the fuel pellets is arbitrary. (3) The fuel pin 21a with the MA elements to be transmuted relatively much in charging amount and the fuel pin 21b with the MA elements relatively little in charging amount or almost not charged are prepared, and a number of the fuel pins 21a, 21b enclosed within the wrapper tube 20 is controlled as shown in FIG. 5 and FIG. 6, thereby controlling a charging amount of the MA elements per the fuel assemblies 17 and 18. Meanwhile, if a percentage by weight of minor actinides (element with the atomic number 92 or over excluding uranium and plutonium; hereinafter called MA element) to total actinides with the atomic number 92 or over is called minor actinides content (hereinafter called MA content), a relation in the melting point between the MA content and the fuel pellet 26 is as indicated in FIG. 7, and a melting point of the fuel pellet 26 drops according as the MA content increases. Thus, a melting point of the fuel pellet to which the MA elements are added for transmuting the MA elements drops as compared with the fuel pellet to which the MA elements are not added, thereby facilitating a fuel melting. It is then necessary that a reactor power be lowered in a nuclear reactor so as to keep the fuel elements from being melted during operation of the nuclear reactor regardless of the melting point drop, and a neutron flux level of the nuclear reactor lowers due to a decrease of the reactor power. Meanwhile, a transmuting rates of the TRU elements is proportional to the MA content and the neutron flux level. When taking an adjustment of the reactor power further into consideration for prevention of a melting of the fuel element, the transmuting rates of the TRU elements is not always to rise monotonously along with an increase in the MA content, and, as shown in FIG. 8, there exists a peak portion whereat the TRU elements transmuting rates is maximized correlatively to the MA content. Then, an MA content P.sub.MA when the TRU elements transmuting rates is maximized is effective and hence is capable of realizing a transmuting of the TRU element most efficiently without causing a melting on the fuel element. On the other hand, in the case of ordinary fast reactor core, fissionable elements contained in the fuel are lost in accordance with burnup and thus fission products are accumulated, and therefore, an effective multiplication factor indicating the degree of a criticality of the nuclear reactor (fast reactor) decreases according to the lapse of time for the reactor operation. However, in the case of fast reactor core operation for transmuting of the TRU elements, main MA elements .sup.237 Np, .sup.241 Am, .sup.243 Am, .sup.242 Cm of the TRU elements to be transmuted are transformed, as shown in FIGS. 9A to 9D, into a fissionable elements easy to cause a fission by fast neutrons. Consequently, the effective multiplication factor comes to decrease moderately in accordance with the lapse of time for reactor operation. As shown in FIG. 10, when the MA content becomes excessive, the TRU elements are transformed into the fissionable elements too much, and the effective multiplication factor is capable of increasing according to the lapse of time for the reactor operation. Accordingly, a transition of the effective multiplication factor according to the lapse of time for the reactor operation may be controlled by the MA content. Now, therefore, such reactor core as will suppress a change in the effective multiplication factor in accordance with the reactor operation and keep an excess reactivity of the reactor substantially zero through the reactor operation may be designed by controlling the MA content. Further, a heating rates according to a decay of the MA elements of the TRU element can be calculated from a decay constant of each MA element and an energy emitted per decay. A decay constant of the MA elements to be transmuted and an energy emitted per decay are shown in FIG. 11A. A heating rates per gram of each MA element may be calculated by means of data given in FIG. 11A as shown in FIG. 11B. The MA elements of those of the TRU elements which contribute influentially to heating are .sup.242 Cm, .sup.244 Cm and .sup.241 Am, and hence, it is understood that a heating of the TRU elements will be calculated by taking these MA elements into consideration. On the other hand, if an upper bound of the heating rates per fuel assembly capable of removing heat is Q.sub.1 (w), then amounts of .sup.242 Cm, .sup.244 Cm and .sup.241 Am capable of charging into the single fuel assembly must satisfy the following equation: ##EQU1## where M.sub.242 : amount (g) of .sup.242 Cm charged into a single fuel assembly M.sub.244 : amount (g) of .sup.244 Cm charged into a single fuel assembly M.sub.241 : amount (g) of .sup.241 Am charged into a single fuel assembly Then, granted that the heating rates per a fuel assembly comes within the range capable of removing heat, if the heating is one-sided at a position, the fuel element is capable of being damaged and therefore, there is a limit to the charging of the MA elements to be transmuted from the viewpoint of preventing a fuel rupture. That is, if an upper bound of the heating rates per cm in an axial length of a local one fuel pellet .sub.2 is Q (w), a charging amount of the MA elements to be transmuted at the position must satisfy the following equation: ##EQU2## where, M.sub.242.sup.L : amount (g) of .sup.242 Cm charged per cm in axial length of local one fuel pellet M.sub.244.sup.L : amount (g) of .sup.244 Cm charged per cm in axial length of local one fuel pellet M.sub.241.sup.L : amount (g) of .sup.241 Am charged per cm in axial length of local one fuel pellet Accordingly, to prevent a failure of the fuel assembly due to overheating, it is necessary that a charging amount of the MA elements of the TRU elements to be transmuted is controlled so as to satisfy the above Eqs. (1) and (2) at the same time. For example, an upper bound of the heating rates per a fuel assembly, where a fuel stack general as the fuel assembly is 100 cm long, and fuel pins charged into the single fuel assembly are 271 pieces in number, is about 5 kw/assembly. In this case, an upper bound of addable amount of main MA elements .sup.242 Cm, .sup.244 Cm and .sup.241 Am which are contributive to heating to the fuel pellets is: ##EQU3## Accordingly, in order that the fuel assembly with the TRU elements added thereto may not cause overheating and failure of the fuel element for transmuting of the TRU element at the time of assembling, storage and transportation, if percentages by weight of the MA elements .sup.242 Cm, .sup.244 Cm and .sup.241 Am to be transmuted to a total weight of the heavy metal elements of a fresh fuel pellet are f.sub.242, f.sub.244 and f.sub.241, then it is necessary that: ##EQU4## be realized. So far as an amount of the main MA elements of the TRU elements added to the fresh fuel pellet satisfies Eq. (3), the fresh fuel assembly will never be overheated or damaged. Further, as will be understood from FIG. 9, the MA elements of the TRU elements to be transmuted functions generally as a neutron absorber, and its degree is stronger than uranium 238 (.sup.238 U), as shown in FIG. 12, in the fast reactor core. On the other hand, if the ratio of weight of plutonium element, or the plutonium content, to the weight of total heavy metal elements in the fuel pellet is called a plutonium (Pu) enrichment, in the fast reactor core, since the neutron flux level normally decreases according as it goes outside from the core center, the power density lowers according as it goes outside in the same Pu enrichment area. Accordingly, in the same Pu enrichment area at the fast reactor core operating for transmuting the TRU elements, the charging density of the MA elements to be transmuted which functions as a neutron absorber will be lessened gradually outside from the reactor core, thereby satisfying a flatting requirement. Thus, fluctuation and change of the reactor power are suppressed, and reliability and safety of the nuclear reactor can be enhanced. Further, in the fast reactor core having the Pu enrichment in two kinds or more, since the area higher in the Pu enrichment has a high content of fissionable elements, and the fissionable elements are transmuted quick by burnup in accordance with the reactor operation. Thus in the area high in the Pu enrichment, a power density according to the operation lowers more. On the other hand, the MA elements to be transmuted are transformed, as shown also in FIGS. 9A to 9D, into fissionable elements by a neutron capture. Accordingly, from increasing the charging density of the MA elements to be transmuted in an area higher in the Pu enrichment, a decrease of the power density according to the operation of the nuclear reactor will be compensated for with the transformation into a fissionable elements of the MA elements to be transmuted, thus moderating the decrease of the power density according to the reactor operation. FIG. 13 exemplifies a main specification characteristic of a fast reactor core to which the TRU elements transmuting reactor core according to the present invention is applied, and FIG. 14 shows a charging density radial distribution of the MA elements charged into the transmuting reactor core. The mean MA content of the fast reactor core in the example shown in FIG. 13 is, for example, 5 percent by weight. As shown in FIG. 8, the MA content is set so as to minimize an excess reactivity of the reactor to substantially zero, for example, in the range where a fuel fusion does not occur during operation of the reactor. When the MA content is 5 percent by weight, an amount of the fissionable elements produced by a neutron capture of the charged MA elements is moderate to be balanced just sufficiently with the amount transmuted by fission, therefore an excess reactivity of the reactor during operation of the reactor being checked to be about 0.5% .DELTA. K/K maximumly. In the case of an ordinary fast reactor core equivalent to the present embodiment in a reactor thermal power and the operation cycle length, the maximu excess reactivity during the operation is about 3% .DELTA. K/K. In the example, since the MA elements has a neutron absorbing effect as a control rod, a required reactivity worth of the control rod may be minimized, thus the number of control rods and the required amount of neutron absorber such as boron, hafnium or the like which is charged into the control rod being reduced, and an economical efficiency will be enhanced. If an excess reactivity of the reactor is low, a reactivity insertion into the reactor at the time when the control rod is drawn erroneously can be minimized, thereby ensuring a safety. Further, the excess reactivity of the reactor can be kept low through the reactor operation, and thus a reactivity loss of the reactor due to the reactor operation, namely the decrease of the effective multiplication factor according to burnup can be minimized. Thus, the period of continuous operation of the reactor or the operation cycle length can be prolonged, and a plant capacity factor or besides the transmuting efficiency of the TRU elements may be enhanced. Further, in the present embodiment, the charging density of the MA elements varies, as shown in FIG. 14, according to a position where the fuel assembly is charged into the reactor core, however, when a fresh fuel assembly outside the reactor is taken particularly into consideration, even in the case of the fresh fuel assembly whereby a heating rates is maximized, the MA elements are set within the range satisfied by the Eqs. (1) and (2) or (3) so as not to increase the heating rates excessively by a decay of the MA elements. Accordingly, the maximum heating rates of the fresh fuel assembly outside the reactor is about 5 kw/assembly, as shown in FIG. 13, and hence, a trouble such as failure due to the overheating of the fuel assembly or the like will not result at the time when assembling, storing and transporting the fresh fuel assembly. Still further, in the present embodiment, a radial distribution of the charging density of the MA elements at the reactor core is made less, as shown in FIG. 14, according as it goes outside of the reactor core in the same Pu-enriched area. Besides, since the MA elements functions as a neutron absorber, the neutron flux level getting large toward the core central portion is suppressed normally by the MA elements, and in result, the radial distribution of the neutron flux becomes flatter. Accordingly, as shown in FIG. 15, the radial distribution of the reactor power density is flattened during the period of the reactor operation cycle as compared with a prior art exemplified in FIG. 21. Thus, a local power peak will be kept from arising, and hence a thermal tolerance of the fuel assembly can be ensured thoroughly, thus enhancing an economical efficiency such as compacting and lightening the reactor core in structure. Further, in the present embodiment, the area higher in Pu enrichment is kept high in the MA elements charging density as compared with the area lower in Pu enrichment, as shown in FIG. 14, the area higher in Pu enrichment has fissionable elements resulting from the neutron capture of the MA elements more than that. On the other hand, a consumption due to the burnup of the fissionable plutonium is more with the area high in Pu enrichment where the fissionable plutonium is present much. Accordingly, the distribution of the MA elements charging density shown in FIG. 14 is set at every area of Pu enrichment so that the area with much consumption of the fissionable plutonium has much fissionable elements produced by the neutron capture of the MA elements, therefore a net decrease of the fissionable elements according to the reactor operation being suppressed, and, as shown in FIG. 15, a fluctuation of the power density according to operation is suppressed. Thus, if a fluctuation of the power density is minimized according to the operation of the fast reactor (nuclear reactor) or burnup, the heat removing efficiency is improved, the enhancement of economical efficiency is realized, and thus fuel temperature is decreased, and safety and reliability of the reactor core can be enhanced accordingly. FIG. 16 is a graph representing a second embodiment of the TRU elements transmuting reactor core according to the present invention. Even in the case of a reactor core where the Pu enrichment is one kind, the fast reactor core represented in this embodiment has a radial distribution of the MA element charging density flattened preferably as compared with the prior art as shown in FIG. 6 and also has a radial power distribution of the core flattened as shown in FIG. 17. Accordingly, from employing the present invention, the reactor power distribution is flattened despite Pu enrichment being one kind and therefore, the plant efficiency will be enhanced, and the economical efficiency such as decrease in fuel fabrication cost or the like may also be enhanced. Needless to say, a similar characteristic to the first embodiment applies to those other than the reactor power distribution. Further, as another embodiment, the axial distribution is applied to the MA elements charging density as in the case where a radial reactor power distribution is flattened according to the present invention as described above, thereby flattening the axial reactor power distribution. If the power distribution need not be flattened, an MA content of the whole core will be set according to the present invention even in case a distribution is not applied particularly to the MA elements charging density, thereby realizing effects such as decrease in excess reactivity of the reactor through the operation, prevention of overheating and failure of the fresh fuel assembly outside the reactor and the like. As described above, in the transuranium element transmuting reactor core relating to the present invention, since an amount of transuranic elements added to the fuel element of fuel assemblies is controlled so as to keep an excess reactivity of the reactor substantially zero through the operation of the reactor, the decrease of the effective multiplication factor according to the lapse of time for the operation is prevented, the excessive deterioration and turbulence of the reactor power distribution can be prevented, the reliability of the power plant is thus enhanced, and as seeking an improvement of the plant operating efficiency, transuranium elements (TRU elements) can be transmuted efficiently. Then, from setting charging amounts of.sup.242 Cm, .sup.244 Cm and .sup.241 Am into the fuel assembly so as to realize: EQU 1.2.times.10.sup.2 .times.M.sub.242 +2.8.times.M.sub.244 +1.1.times.10.sup.31 1 .times.M.sub.241 <Q.sub.1 where an upper bound of heating rates of the single fuel assembly outside the reactor is Q.sub.1, charging amounts of.sup.242 Cm, .sup.244 Cm and .sup.241 Am which can be charged into the single fuel assembly are M.sub.242, M.sub.244 and M.sub.241, and also to realize: EQU 1.2.times.10.sup.2 .times.M.sub.242.sup.L +2.8.times.M.sub.244.sup.L +1.1.times.10.sup.-1 .times.M.sub.241.sup.L Q.sub.2 where an upper bound of heating rates of per unit length of the fuel pellet contained in the fuel pins is Q.sub.2, charging amounts of.sup.244 Cm and .sup.244 Cm and .sup.241 Am per the unit length are M.sub.242.sup.L, M.sub.244.sup.L and M.sub.241.sup.L, a melting of the fuel pellet during the reactor operation of the reactor and an overheating or failure of the fuel assemblies outside the reactor can be prevented and a neutron absorption effect of .sup.242 Cm, .sup.244 Cm and .sup.241 Am is available for eliminating accidents of a control rod and a neutron absorbing material of the control rod and also for realizing the improvement of the heat removing efficiency of the core, the economical efficiency will be enhanced, the safety and the reliability of the core and the fuel assemblies will be enhanced as well, and the TRU elements can be transmuted efficiently. Further, by setting a charging density of minor actinides to lessen outwards of a core center in a core area where a plutonium content is even and also by setting a charging density of minor actinides high accordingly in an area where Pu is enriched high at the core of a Pu-enriched area, the radial distribution of the reactor power can be flattened, the excessive deterioration or turbulence of the reactor power distribution will never result, the enhancement of safety and reliabiilty of the core and the fuel assemblies may be realized, and thus the TRU elements can be quenched efficiently. Further embodiments of the present invention will be described hereunder in conjunction with FIGS. 22 to 30, with reference to transuranium elements transmuting fuel pins and fuel assemblies. FIG. 22 exemplifies a transuranium elements transmuting fuel assembly according to another embodiment of the present invention which is charged into the fast reactor core. The fuel assembly 110 has a coolant inlet 111 at the lower portion thereof for letting in the coolant such as liquid sodium (Na), liquid NaK, helium (He) gas or the like and a coolant outlet 112 at the upper portion thereof, and a plurality of fuel pins 114 are enclosed in a bundle within a wrapper tube 113 square tubular or, for example, hexagonal in section which works as a fuel channel. The fuel pin 114 enclosed within the wrapper tube 113 may be constructed only of a TRU (transuranium elements) fuel pin 115, or of the TRU fuel pin 115 and an ordinary fuel material pin 116 otherwise as shown in FIG. 23. In the case of TRU fuel assembly having constructed the fuel assembly 110 only of the TRU fuel pins 115, nothing will be taken into consideration for arrangement of the TRU fuel pins 115, an administration on manufacture and assembling of the TRU fuel pins 115 is facilitated, the number of fuel assemblies for which a special measure such as heat removing, shielding or the like is required may be minimized, thus enhancing an economical efficiency on a core administration and a fuel handling. Then, in case the TRU fuel assembly 110 is constructed of the TRU fuel pin 115 and the ordinary fuel material pin 116, the change in reactor power according to the reactor operation is minimized for presence of the TRU elements, and the TRU elements can be transmuted efficiently without lowering a cooling efficiency of the core as, in addition, keeping the integrity of the reactor internal structure. FIG. 23 exemplifies the case where the TRU fuel pins 115 are dispersed and disposed almost uniformly within the wrapper tube 113 of the TRU fuel assembly 110. By dispersing and disposing the TRU fuel pins 115 uniformly, a relatively low-temperature coolant around the TRU fuel pins 115 and a relatively high-temperature coolant around the usual fuel material pins 116 are mixed acceleratedly in the presence of the TRU element, a fuel clad temperature of the ordinary fuel material pin 116 is decreased, the cooling efficiency of the core can be enhanced, the ordinary fuel material pin 116 can be made to last so long, and the economical efficiency and safety of the fast reactor can thus be enhanced. Meanwhile, as shown in FIG. 24, the TRU fuel pin 115 has a fuel clad 118 charged with a TRU fuel material 119, and its upper and lower portions closed by an upper end plug 120 and a lower end plug 121. The TRU fuel material 119 has at least one of an ordinary fuel material and a fertile material consisting of degraded uranium, natural uranium and depleted uranium contain TRU elements (trans- uranium elements) of minor actinides elements such as Np (neptinium), Am (americium), Cm (curium) and the like. Here, the ordinary fuel material refers to a fuel material consisting of an enriched uranium and an uranium-plutonium mixed fuel (uranium fuel having enriched plutonium). An oxide fuel such as uranium oxide or the like is used for the fuel material, however, a metallic fuel may be employed instead of the oxide fuel. Further, the ordinary fuel material pin 116 has the fuel clad charged with a plurality of so-called fuel pellets (or metallic fuel otherwise) having sintered the ordinary oxide fuel material, and the upper and lower ends closed by the upper end plug and the lower end plug, a gas plenum part being formed on at least one portion, or upper and lower portions, for example, in the fuel clad. Then, the TRU fuel pin 115 and the ordinary fuel material pin 116 have been described with reference particularly to a closed type one closed by the upper and lower end plugs, however, this need not always be a full-closed type, and hence a so-called vented type fuel pin which is capable of discharging fission products gas (hereinafter called FP gas) generated by the fission outside the fuel pins 115 and 116 may be employed. FIG. 24 exemplifies the TRU fuel pin 115 working as a transuranic elements transmuting fuel. The fuel pin 115 is that of having a multiplicity of TRU fuel areas provided axially, a TRU fuel 119a high in content of Np of the minor actinides elements is disposed in a core upper portion area of the fuel clad 18, a TRU fuel 119c high in content of Am and Cm is disposed in a core lower portion area, and a TRU fuel 119b is also disposed in a core height center area high in a neutron flux level, and an ordinary fuel 122 is disposed among the TRU fuels 119a, 119b, 119c to constitute the TRU fuel material 119. A gas plenum part 123 is formed on an upper portion of the fuel clad 118, the upper and lower ends being closed by the upper end plug 120 and the lower end plug 121. In the gas plenum part 123, a spring is installed, as occasion demands, so as to stably hold the TRU fuel material 119. By disposing the TRU fuels 119a, 119b, 119c with which the fuel clad 118 of the TRU fuel pin 115 is charged inside as indicated in FIG. 25A, a core axial power distribution curve A of the fast reactor is as indicated by a full line and a peak power is decreased more than a core axial output distribution curve B indicated by a broken line in the case of the ordinary fuel material pin 116, thus the reactor characteristic and the transmuting efficiency of the TRU elements being improved. Typical minor actinides elements .sup.237 Np, .sup.241 Am, .sup.243 Am, .sup.242 Cm, .sup.244 Cm of the TRU fuels 119a to 119c with which the TRU fuel pin 115 is charged inside the capture neutrons to fissionable elements as shown in FIGS. 9A to 9D when charged into the fast reactor core to the reactor operation, thus transmuting the TRU elements. Further, due to the TRU fuel pin 116 having the fuel clad 118 charged with the TRU fuel pellets 119 inside, there arises a problem that the melting of the fuel drops due to the presence of the minor actinides elements. The fuel melting will not result even at the transient conditions of the fast reactor according to a normal core design, and in the TRU fuel pin 115 shown in FIG. 24, the TRU fuel 119a high in content of low melting point MA elements is disposed in the core area with high fuel temperature, namely the core upper portion area in the case of the metallic fuel, and the core height center area in the case of the oxide fuel, and the TRU fuel 19c high in content of high melting point MA elements is disposed in the core lower portion area where the fuel temperature is low. By disposing the TRU fuel 119c containing Am and Cm with the melting point dropping comparatively large for the oxide fuel in the area where the fuel temperature is low, the drop of the fuel melting point due to the content of the TRU element such as Am and Cm or the like does not exert an influence directly on determination of the core power density, and the TRU elements can be transmuted efficiently without lowering the core power density. On the contrary, the melting point of Np is lower than that of Am and Cm for the metallic fuel. Meanwhile, typical minor actinides elements .sup.237 Np, .sup.241 Am, .sup.243 Am, .sup.242 Cm, .sup.241 Cm of the TRU fuel pellets 119 with which the fuel clad 18 of the TRU fuel pin 115 are charged inside are transformed into fissionable elements, as shown in FIGS. 9A to 9D, by a neutron absorption, and therefore, a power of the TRU fuel assembly constructed only of the TRU fuel pin 115 sharply increases as indicated by a symbol I in FIG. 27 according to the number of days for operation. Accordingly, the power of the TRU fuel assembly constructed only of the TRU fuel pin 115 is low at the point in time of start for operation but increases largely according to the operation. Then, as shown in FIG. 24, in the TRU fuel assembly 110 for which the TRU fuel pin 115 and the ordinary fuel material pin 116 are disposed mixedly, since the ordinary fuel material pin 116 generates power, the power of the TRU fuel assembly 110 is also high relatively at the point in time of start for the reactor operation as indicated by a symbol II in FIG. 26, and since the decrease in the fissionable material of the ordinary fuel material pin 116 and the transformation of the TRU fuel element 119 into a fissionable material are offset, the degree of power flunctuation of the TRU fuel assembly 110 due to the operation is smaller and smoother than the fuel assembly constructed only of the TRU fuel pin 115. In a core design, a coolant flow rate of the fuel assembly charged into the core is specified so as to remove heat at the time of maximum power of the fuel assembly. The TRU fuel assembly constructed only of the TRU fuel pin 115 does not generate a power corresponding to the coolant flow rate at the time of start for the operation or for a several time after the start, an outlet temperature is low consequently, and therefore, the coolant outlet temperature does not rise, thus leaving a problem on the cooling efficiency of the core and the integrity of the reactor internal structure. However, in the case of the TRU fuel assembly for which the TRU fuel pin 115 and the ordinary fuel material pin 116 are disposed mixedly as shown in FIG. 23, the power coming up substantially to the maximum power is generated at the time of the start for the operation or for a several time after the start, and therefore, an outlet temperature of the TRU fuel assembly 110 will not drop extremely, and thus the problem on the cooling efficiency of the core and the integrity of the reactor internal structure can be avoided. Then, as shown in FIG. 24, by mixing a radioactive fission product (F. P) such as strontium (Sr), alkaline metals (Cs or the like), technetium (Tc) or the like into the TRU fuel pellets 119 with which the fuel clad 118 of the TRU fuel pin 115 is charged inside, the transmuting of the TRU elements and also the transmuting of a long-lived radioactive fission products in the reactor and the internal administration of the reactor are realizable. The disposal and administration of the radioactive waste products will be facilitated as compared with the case where these are carried out outside the reactor. For example .sup.99 Tc is transformed into a stable elements which is not radioactive in the fast reactor by neutron capture (neutron absorption) and others, and .sup.90 Sr and .sup.137 Cs become: EQU .sup.90 Sr.fwdarw..sup.90 Y.fwdarw..sup.90 Zr (stable) EQU .sup.137 Cs.fwdarw..sup.137m Ba.fwdarw..sup.137 Ba (stable) by natural decay while residing in the reactor, and .sup.90 Zr and .sup.137 Ba are stable materials, which are removed from a fuel through the spent fuel reprocessing. In the TRU fuel pin 115 shown in FIG. 24, the case where TRU fuels 119a, 119b, 119c are dispersed and arranged axially is exemplified, however, a TRU fuel pin 115A may be constructed as shown in FIG. 27 so as to minimize the influence to be exerted on the reactor power distribution by the TRU elements. Like reference characters are applied to the like portions in FIG. 24, and a further description will be omitted here. The TRU fuel pin 115A exemplifies the case where the TRU fuels 119b containing the TRU element which constitute the TRU fuel pellets 119 are disposed even axially at a relatively low content (several percent by weight or below). The TRU fuel pin 115 for which the TRU fuels are disposed uniformly has an advantage that an administration on fabrication and transportation is facilitated, a fabrication cost can be reduced, and an influence to be exerted on an axial power distribution is uniform and minimized. Further, the TRU fuel pin 115A is much in the TRU elements loading amount per pin, and thus is available for enhancing the transmuting efficiency of the TRU elements. A TRU fuel pin 115B shown in FIG. 28 exemplifies the case where the TRU fuel pellets 119 with which the fuel clad 118 is charged inside has the TRU fuel 119b disposed only in the core height center area, and such disposition is effective in decreasing a peak power and flattening the core axial power distribution. By disposing the TRU fuel 119b in the core height center area where a neutron flux density is high, the power peak is reduced preferably by the distortion of the core axial power distribution, the power distribution is flattened, and a reactor characteristic is improved to enhance the transmuting efficiency of the TRU elements. Then, in this case, the content (percent by weight) of the TRU elements contained in the TRU fuel 119b is relatively high to stand, for example, at 10% or over as in the case of the TRU fuel pin 115 of FIG. 24. Further, in the first embodiment of the transuranic elements transmuting fuel assembly 110, the case where the TRU fuel pins 115 are dispersed and disposed uniformly in the TRU fuel assembly 110 as shown in FIG. 23, however, the fuel pins 115 (115A, 115B) will be disposed intensively in the center area of the TRU fuel assembly 110, as shown in FIG. 29, and the ordinary fuel material pins 116 will be disposed around the TRU fuel pins 115 otherwise. In case the TRU fuel pins 115 are disposed intensively in the center area, since the TRU fuel assembly 110A has the neutron flux density maximized at the center area, the transmuting efficiency of the TRU elements can be enhanced. In the TRU fuel assembly 110A, the fuel pins disposed around the TRU fuel pins 115 (115A, 115B) may comprise a fertile material pin consisting of natural uranium and depleted uranium, and by disposing such fertile material pins, alpha rays and neutrons emitted from the TRU fuel pins 115 are shielded, and thus measures on transportation and shielding of the TRU fuel assembly 110A may be relieved. A TRU fuel assembly 110B shown in FIG. 30 exemplifies the case where the TRU fuel pins 115 (115A, 115B) are disposed at an outer peripheral position abutting on a inside wall of the wrapper tube 113. The ordinary fuel material pins 116 are disposed inside of the TRU fuel pins 116 arrayed as above. Generally, the coolant flow rate per one fuel pin is larger on the wall side of the wrapper tube 113 than in the center area, and temperature of the fuel clad 118 on the wall side becomes lower than the center area. When the metallic fuel is employed as the fuel of the TRU fuel assembly 110B, it is necessary that the fuel clad temperature be adjusted as low as possible for the prevention of an eutectic reaction of the fuel clad 118, with the metallic fule slug. The TRU fuel assembly 10B shown in FIG. 30 is that for which the TRU fuel pins 115 are disposed along the inside wall of the wrapper tube 113 with a coolant flowing much therethrough, the fuel clad temperature is reduced thereby, the economical efficiency of the TRU fuel assembly 110B is thus secured to prolong the lifetime. Then, the TRU fuel pins 115 (115A, 115B) have typical minor actinides elements easy to cause alpha-decay contained much in the TRU fuel material 119, and thus a relatively high alpha ray energy is emitted at the time of alpha-decay, and therefore, special measures on fabrication, heat removing and shielding which are different from the ordinary fuel will be necessary for the TRU fuel pins 115 (115A, 115B) and the TRU fuel assemblies 110 (110A, 110B). Thus, for the TRU fuel pin 115, the TRU fuel pellets 119 is constructed by containing the TRU elements or specific minor actinides elements at a predetermined content. For fuel temperature and others to keep in order, it is preferable that the TRU fuel pin 115 be provided with a TRU fuel material area in the area lower than the core height center more than the area upper than the core height center. Further, from inserting a control rod into the core, the transmuting efficiency of the TRU elements may be enhanced by providing the TRU fuel area in the core height center area where a neutron flux level gets high, thereby flattening the core axial power distribution. Further, by disposing the TRU fuel in the area lower than a core height center level whereat the neutron flux level becomes high, the melting of the TRU fuel can be avoided effectively and securely. As a described above, in the transuranium element transmuting fuel pin and fuel assembly relating to the present invention, an improvement of core characteristics and an enhancement of the core cooling efficiency may be achieved without causing deterioration of the core characteristics according to various restrictions such as fuel melting during the operation of the reactor, excessive change of the core axial power distribution, distortion of the distribution and the like. Thus the safety and reliability of the fuel assemblies and fuel pins to be charged into the core may thus be achieved and the transmuting efficiency of the TRU elements can be improved and enhanced.

claims

1. A process for producing a detected X-ray image of a breast, the process comprising the steps of: a) directing an X-ray beam produced by an X-ray tube, characterized by an output function comprising an X-ray tube current function and an X-ray tube voltage function, from a focus of the X-ray tube through the breast so that the beam impacts an image receptor to produce the detected X-ray image, where the intensity of primary X-ray radiation at a given point on the image receptor is characterized as a function of time by an image intensity function; b) placing an anti-scatter grid between the breast and the image receptor, the anti-scatter grid characterized by a grid transmission function that is a periodic function of position characterized by a grid pitch; c) producing a grid motion by moving the grid at a velocity during an X-ray exposure, the velocity characterized as a velocity function; and d) modulating the output function such that for some thickness and composition of breast tissue, the image intensity function is substantially equal to the function i(t) defined by the equation where x c (t) is the position of the center of the anti-scatter grid at time t, the velocity function v(x) is the velocity of the grid when the center of the anti-scatter grid is at position x, g(x) is an arbitrary function with a finite integral over x and has zero value outside a finite domain of x, h(x) is non-negative for every value of x, R(x) is the rect function, n is a positive integer, and P is the grid pitch. 2. The process of claim 1 where the velocity function is substantially constant during the X-ray exposure, the tube voltage function is substantially constant during the X-ray exposure, the tube current function is modulated by varying a tube current, and the grid motion is characterized by a grid repeat time, where the grid repeat time is equal to the grid pitch divided by the grid velocity. claim 1 3. The process of claim 2 where the tube current function is modulated by varying a filament current of the X-ray tube. claim 2 4. The process of claim 2 where the tube current function is modulated by varying a voltage of a part of the X-ray tube selected from the group consisting of: a control grid and a bias cup. claim 2 5. The process of claim 2 where the tube current function has a Fourier transform that has a negligible amplitude at all frequencies equal to positive multiples of the reciprocal of the grid repeat time. claim 2 6. The process of claim 2 where the tube current function is substantially equal to a convolution of an arbitrary function with a rect function having a width substantially equal to an integer multiple of the grid repeat time. claim 2 7. The process of claim 2 where the tube current function is a symmetric trapezoidal function having a ramp time substantially equal to a positive integer multiple of the grid repeat time. claim 2 8. The process of claim 2 where the tube current function is a convolved dual symmetric trapezoidal function. claim 2 9. The process of claim 1 where the output function is modulated by using a dynamic tube current function and a pseudo-rect tube voltage function. claim 1 10. The process of claim 1 where the output function is modulated by using a dynamic tube current function and a dynamic tube voltage function. claim 1 11. The process of claim 1 where the output function is modulated by using a pseudo-rect tube current function and a dynamic voltage function. claim 1 12. The process of claim 1 where the velocity function is substantially constant during the X-ray exposure. claim 1 13. The process of claim 1 where the velocity function varies during the X-ray exposure. claim 1 14. The process of claim 1 where the anti-scatter grid comprises claim 1 a) a plurality of radio-opaque septa, interspersed with a radiolucent interspace material; and b) a means to move the grid during the X-ray exposure to produce the grid motion at the velocity. 15. The process of claim 14 where the width of the interspace material is greater than 8 times the width of the septa. claim 14 16. The process of claim 14 wherein the grid motion is linear. claim 14 17. The process of claim 14 wherein the anti-scatter grid further comprises a focusing means to keep the grid aligned on the focus during the grid motion. claim 14 18. The process of claim 14 wherein the anti-scatter grid comprises one set of radio-opaque septa, where the septa are substantially parallel to each other and are substantially aligned with the focus. claim 14 19. The process of claim 14 where the focusing means comprises a mechanism that moves the grid in an arc whose center is substantially coincident with a grid focal axis, the grid is periodic in an angular distance relative to the grid focal axis, and the velocity function describes an angular velocity of the grid about the grid focal axis. claim 14 20. The process of claim 19 wherein the focusing means comprises a plurality of bearings mated to the grid and a plurality of curved guide tracks, the bearings configured to engage the plurality of curved guide tracks, where the focus and a center of curvature of each curved guide track are substantially coincident with the grid focal axis. claim 19 21. The process of claim 19 wherein the focusing means comprises a plurality of bearings mated to the grid and at least two straight guide tracks, the bearings configured to engage the at least two straight guide tracks, the at least two straight guide tracks positioned such that a line normal to each track at a point where the bearings contact the track at a center of motion of the grid passes substantially close to the focus. claim 19 22. The process of claim 14 where the focusing means comprises an articulating mechanism which articulates the septa individually to keep the septa focused on the focus, the motion of the grid is linear in a plane substantially parallel to the image receptor, the grid transmission function is periodic in linear distance in the direction of motion, and the velocity function describes a linear velocity of the grid. claim 14 23. The process of claim 22 where the articulating mechanism comprises an upper support, a lower support, a first hinge means to moveably attach the septa to the upper support and a second hinge means to moveably attach the septa to the lower support and the articulating mechanism moves the upper support a first distance and the lower support a second distance. claim 22 24. The process of claim 23 where the first distance and the second distance are not the same. claim 23 25. The process of claim 23 where the ratio of the first distance to the second distance is equal to a distance from the focus to the upper support divided by a distance from the focus to the lower support. claim 23 26. The process of claim 14 where the interspace material is air, polymer foam or aerogel. claim 14 27. The process of claim 14 wherein the anti-scatter grid comprises two sets of radio-opaque septa, where the septa within each set are substantially parallel to each other and oriented to align with the focus, and the septa and a focal axis of the first set of septa are substantially perpendicular to the septa and a focal axis of the second set of septa. claim 14 28. The process of claim 14 wherein the anti-scatter grid comprises a plurality of radio-opaque sheets having a plurality of holes perforating the sheets, the sheets stacked so the holes are aligned with each other and with the focus. claim 14 29. The process of claim 28 wherein the focusing mechanism consists of a mechanism that moves the radiopaque sheets individually to keep them oriented on the focus. claim 28 30. The process of claim 28 wherein the pattern of holes in the plurality of sheets is periodic in the direction of the grid motion, and is periodic either in a linear position or in an angular position on the sheet. claim 28 31. The process of claim 28 wherein the shape of the holes in the plurality of sheets is selected from the group consisting of: hexagonal, square and triangular. claim 28 32. The process of claim 14 where the spacing between the septa is maintained by a thin radiolucent sheet fixedly attached to the edges of the septa. claim 14 33. The process of claim 14 where the spacing between the septa is maintained by a thin radiolucent sheet pivotally attached to the edges of the septa. claim 14

044302916

claims

1. In a fusion plasma system having a circular cross section, said fusion system substantially surrounded by a blanket structure for the capture and transmittal of energy from said plasma, wherein said blanket structure comprises:

046722130

claims

1. Container, especially adapted for enclosing radioactive substances such as radioactive liquids, which comprises; an inner container for receiving a substance to be contained and sealed gas and liquid tight under normal operating conditions, an outer container in which the inner container is disposed, and thermal insulation between the inner container and the outer container, in combination with a closed tubular circulating system comprising a coolant tube associated with the inner container disposed within the outer container, said coolant tube containing a fluid coolant which circulates through the coolant tube out of direct contact with the substance in the inner container, a heat-discharge tube which also contains the coolant arranged along the inner wall of the outer container with said thermal insulation between said cooling and heat discharge tubes and connecting lines at both tube ends of the cooling tube and the heat discharge tube through which said cooling tube and said heat discharge tube are in communication with each other to permit circulation of the coolant from the coolant tube to the heat-discharge tube and return of the coolant from the heat-discharge tube to the coolant tube. 2. Container according to claim 1, wherein the cooling tube is attached to the outside of the inner container. 3. Container according to claim 1, wherein a feedthrough with a pressure relief valve or a rupture disc is provided in the wall of at least one of the cooling tube, the heat discharge tube and the connecting lines. 4. Container according to claim 1, wherein a feedthrough which is closed-off by a solder, the melting temperature of which is lower than the melting temperature of the material of the cooling tube, the heat discharging tube and the connecting lines, is provided in the wall of at least one of the cooling tube, the heat discharge tube and the connecting lines. 5. Container according to claim 3, wherein the feedthrough opens to the outside of the outer container. 6. Container according to claim 4, wherein the feedthrough opens to the outside of the outer container. 7. Container according to claim 1, wherein a connecting nozzle for a cooling unit is provided at the connection lines. 8. Container according to claim 1, wherein a connecting nozzle for a cooling unit is provided at the heat discharge tube. 9. Container according to claim 1, wherein in the interior of the inner container, a body of a material which readily absorbs neutrons is arranged. 10. Container according to claim 1, wherein the inner container is provided with a pressure relief valve leading into the outer container. 11. Container according to claim 1, wherein an absorption body is located in the outer container, outside the inner container for taking up substances which have escaped from the inner container into the outer container.

048246344

summary

BACKGROUND OF THE INVENTION This invention relates to nuclear fuel elements and in particular, the provisions of fuel elements with a burnable poison coating in the form of a thin layer of boron-containing compound particles on the inside of a cladding tube. The burnable poison particles are deposited alone or with lubricity providing graphite particles from a liquid suspension on the inside of a zirconium-alloy cladding tube. A nuclear fuel element of the type involved in the invention is part of a fuel assembly. Heretofore, typical fuel assembly designs have employed fixed lattice burnable poison rods to control early-in-life reactivity and power peaking. These rods have become a necessary design feature for the fuel management of first cores of light water reactors as well as in schemes to achieve extended burnups and reduced radial neutron leakage. Such rods displace fuel rods within the assembly lattice which increases the core average linear heat generation rate and local peaking factors. Alternate approaches have been proposed that place burnable poison material inside the fuel rods so that much less fuel material is displaced, for example, as boride coatings on the UO.sub.2 pellets. Such coatings, however, while adhering when first applied, tend to spall off under the stresses of the irradiation environment in the nuclear reactor core, in part because of difficulty in matching the thermal expansion behavior of the coating to that of the fission material or UO.sub.2 pellet. Attempts to incorporate boron compounds as mixtures within the UO.sub.2 pellets have not been successful because of volatilization of boron species during high temperature fabrication processes and redistribution of the boron under irradiation. For further background, see U.S. Pat. Nos. 3,925,151; 4,372,817; 4,560,575; 4,566,989; 4,582,676; 4,587,087; 4,587,088; and 4,636,404. SUMMARY OF THE INVENTION The invention involves an improved fuel element with a burnable poison coating which substantially overcomes problems of spalling and coating integrity because of the closely matched thermal expansion coefficients of the substrate and coating material and the action of fission sintering to enhance adhesion of the coating to the substrate. The invention includes coating a thin layer of a boron-containing compound on the inside surface of the zirconium alloy cladding tube of the fuel rod. The preferred boron-containing compound is zirconium diboride (ZrB.sub.2) because its thermal expansion coefficient most nearly matches that of the zirconium-tin alloy cladding tube. The adhesion between the coating and cladding, therefore, is less likely to deteriorate under irradiation than would similar coatings on the UO.sub.2 pellets. Also, the fission sintering phenomenon that has been observed in irradiated compacts of boron-containing compound powders at cladding temperatures (approximately 400.degree. C.) is more likely to promote adhesion between the ZrB.sub.2 and the metallurgically-related zirconium-tin alloy cladding tube substrate than would be the case for a UO.sub.2 substrate. That is, fission sintering will not only join ZrB.sub.2 particles to each other, but is also likely to form a bond of the particles to the zirconium-tin alloy substrate under irradiation. A suitable thin layer or coating of ZrB.sub.2 particles on the inside surface of the cladding tube is applied by a method analagous to that used for graphite lubricant coatings developed by the laboratories of the assignee of the instant invention for nuclear fuel rod cladding. A liquid suspension which includes isopropanol, an acrylic polymer binder material and the boron-containing compound particles in a range of from 0.1 to 1.5 microns, with or without colloidal graphite particles, has its solids content adjusted to provide the desired viscosity for the coating process (approximately 16% by weight solids). Each fuel tube is then filled with the liquid suspension and drained at a controlled rate, leaving a thin film on the inside surface of the cladding tube. The film is dried at room temperature and cured in a vacuum at temperatures up to 427.degree. C. (800.degree. F.). The resulting thin layer containing ZrB.sub.2 (and perhaps graphite) at a density of approximately 50% of theoretical, along with a small residue from the decomposition of the binding material. The ZrB.sub.2 is preferably initially enriched in the B.sup.10 isotope to an 80% level.

051909901

abstract

During radiotherapy for malignant conditions, healthy tissues can suffer from radiation damage. Traditional radiation shields designed to protect healthy tissues are prepared by a lengthy, multi-step complex procedure. Materials are described for preparation of a radiation shield for use during radiation therapy, especially therapy of the head and neck, where the material comprises a composite of non-radioactive, non-toxic high atomic density metal or metal alloy spherical particles dispersed in a manually moldable elastomeric material. Custom radiation shields are formulated of this material without the need for use of impressions or molds. Healthy tissues may then be shielded during radiation therapy by positioning the custom-fitted radiation shield in the desired location on the patient's body.

040597695

abstract

A radiation source for Mossbauer investigations of tellurium compounds manufactured on the basis of 5MgO.Te.sup.124 O.sub.3 made by method of preparing this radiation source comprises irradiating 5MgO.Te.sup.124 O.sub.3 in a reactor by means of thermal neutrons, followed by annealing at a temperature ranging from 600.degree. to 1,100.degree. C for a period of from 5 to 10 hours.

041586395

abstract

Gases are stored by combining with a bed of capturing solids at elevated temperatures and pressures. The solids are placed in canisters which are then placed in an autoclave. The gases to be stored are fed directly to the canister via a conduit passing through the autoclave wall.

046706585

summary

BACKGROUND OF THE INVENTION This invention relates to a sanitary protective sheet useful for reducing exposure to scatter radiation generated during radiological operating procedures. Scatter radiation occurs when relatively high energy photons from an X-ray beam interact with the atoms against which they impinge to generate secondary radiation. This secondary radiation tends to be lower frequency radiation than the primary radiation. That is, the secondary radiation has a frequency range that would be produced by voltage settings on the X-ray machine lower than the setting for the primary radiation. Because the secondary radiation is not beamed or focused it tends to be directed in all directions and thus is called scatter radiation. Radiological procedures include both fluoroscopic and radiographic procedures. Although most radiographic procedures are not invasive operations, a large number of the fluoroscopic procedures presently performed are invasive operations. During these invasive procedures it is particularly important to maintain a sterile field at all times. Fluoroscopy is a procedure which renders visible the shadow of X-rays to permit observation of the internal organs of the human body. There are many procedures which are preformed under a fluoroscope so that the radiologist can monitor and control the procedure. Fluoroscopy, as compared to standard X-ray examination, uses a lower voltage X-ray. Examples of procedures requiring fluoroscopic monitoring and control are: angiographic procedures; percutaneous nephrostomy; lung biopsy; endoscopic cholangiograms; pancreaticography; and percutaneous transhepatic cholangiogram. During the majority of these, an X-ray beam is focused on the patient at a point distanced from the radiologist or other doctor performing the procedure. Although the doctor is not exposed to the primary radiation, he or she is exposed to scatter radiation. The arm and hand area of the doctor are most commonly exposed to such scatter radiation. These fluoroscopic procedures are invasive and generally require the use and manipulation of small instruments. It is necessary to perform these procedures in a sterile environment. The procedures require manual dexterity on the part of the radiologist. It is well documented that exposure to X-rays is injurious. It is further known that X-ray exposure is cumulative. Although the amount of X-ray exposure that a patient receives during a single fluoroscopic procedure may not be harmful, a radiologist who performs a great number of such procedures, is constantly exposed to X-rays and hence a large cumulative exposure. It has long been recognized that radiologists, and other workers with X-rays, must protect themselves as much as possible from X-rays. Any reduction in cumulative exposure is desirable. It is known in the art that lead impregnated rubber gloves and aprons will protect the radiologist by absorbing some of the scatter radiation generated during a fluoroscopic procedure. These gloves however, are too clumsy to wear while performing delicate operative procedures. In addition, both the gloves and aprons are relatively expensive and not easily sterilized. Accordingly, it is an object of this invention to provide a protective sheet which can be used during a radiological procedure to protect the radiologist or other doctor from scatter radiation. It is important that the protective sheet not interfere with the doctor's ability to perform a delicate interventional procedure. Thus it is another purpose of this invention to provide a simple device that does not interfere with any of the operating procedures. It is another purpose of this invention to achieve the above results with a protective sheet which permits maintaining sterilization. It is a related purpose to provide a sheet which is disposable so that a sterile environment can be maintained during each operation. It is a related object of this invention to provide a setting which permits the doctor to move in a sterile environment. It is a further purpose of this invention to provide the objects at a cost which will encourage use of the protective product and with a device that is simple and easy to use so that it will readily and regularly be used. BRIEF DESCRIPTION In brief one embodiment of the invention employs a multi-ply sheet in which a center ply support matrix is a gauze sheet in which a radio opaque compound and in particular barium sulfate powder, is distributed and is supported by the matrix. The barium sulfate is present in an amount suffient to block a substantial amount of the scatter radiation produced by the standard medical radiology machines which may have voltage settings up to 120 kilovolts (KV). In this embodiment, a base ply of a thin liquid impervious polyethylene material is fastened to one side of the support matrix ply. The third ply is composed of a typical surgical drape material which acts to absorb liquid such or blood. It is fastened to the other side of the support matrix ply. This multi-ply protective sheet is relatively light weight and avoids being a bulky type of device. Yet it effectively absorbs the scatter radiation. Further, since it is relatively inexpensive to produce it is disposable and thus avoids the problem of cross contamination that would occur in the use of the same protective sheet in successive operations. Unlike protective gloves, the sheet need not be worn by the radiologist and thus does not adversely affect his or her manual dexterity.

047073241

abstract

The setpoints for control systems in a pressurized water reactor are adjusted by an amount corresponding to the expected change in the controlled process variable resulting from rapid fluctuations in load to reduce the duty time of the control system components such as the rod drive mechanisms in the rod control system and the spray and heater units in the pressurizer pressure control system. In addition, the deadband in the response of the rod control system is continuously varied as a function of the variance of the magnitude of the rapid fluctuations in load to further reduce wear while maintaining good response during load following.

06297419&

description

DETAILED DESCRIPTION The process according to a first embodiment of the present invention may be described as follows and with reference to the flow chart shown in FIG. 1. A source of zirconium alloy fuel rod cladding is indicated at 10. The cladding is brought into solution by electrochemical dissolution 12 by making the cladding anodic and passing a current through the metal under a nitric acid electrolyte. This step results in the metal being converted to zirconium nitrate 14. However, during the dissolution step 12, a substantial quantity of the zirconium alloy is converted directly to an oxide which forms a sludge at the bottom of the dissolution tank and is subsequently removed to be added back into the process at a later stage. The zirconium nitrate is then thermally decomposed in the step 16 to the oxide 18 by one or more of the techniques including direct heating, fluidised bed, plasma-arc or microwave assisted heating The oxide 18 is then mixed in the step 20 with a sol of a gel forming chemical which in this case is aluminium secondary butoxide which is diluted with alcohol and modified with an alkanolamine, which is in this case, tri-ethanolamine. The modifying agent causes cross linking of the aluminum secondary butoxide in a controlled and time dependent manner on hydrolysis resulting in the onset of gelling. The zirconium oxide mixed with the gelling aluminum secondary butoxide forms a slurry 22 to which may optionally be added material 24 such as oxides of fission products and/or plutonium 26 which have been extracted from the dissolved spent uranium fuel by a known so-called "PUREX" process, the fission products and plutonium constituting high level waste which must be encapsulated and stored in a repository for many years. The slurry 22 continues to gel and is cast or extruded 28 into molds or self supporting shapes at the steps 30 where it is allowed to fully gel and solidify. After setting, the shaped "green" bodies are demolded 32, if appropriate, to form free-standing, handleable bodies 34 which are then dried slowly 36 to prevent excessive cracking during shrinkage. The dried green bodies 38 are then sintered 40 at a substantially lower temperature than that required for physically mixed oxides to form durable refractory material monoliths 42 which may then be stored 44 in a repository 46 in a known manner. During the drying step 36, the water is driven off and the hydroxyl groups in the chemical matrix are decomposed to leave only aluminum and oxygen present in the structure on a substantially molecular scale and binding together the powder particles of zirconium oxide and also the particles of other constituents; the sintering rate during the sintering step 40 is very high and can be accomplished at relatively lower temperatures in the region of about 1400.degree. C. compared with the higher temperatures conventionally used to sinter pressed green bodies of zirconium oxide. Therefore, the preferred embodiment of the present invention has many advantages over known techniques in that the resulting monoliths of refractory zirconium oxide are chemically both very stable and very durable and able to encapsulate the high level waste directly within the matrix. Furthermore, the low sintering temperature which the preferred embodiment of the process of the present invention permits reduces hazards associated with high vapor pressures of some elements and consequently further reduces contamination and plant costs. FIG. 2 shows a flow sheet of an alternative process according to the present invention utilizing the technique of freeze casting. A freeze castable silica or zirconium oxide sol 50 is mixed with a ceramic filler powder 52 and zirconium oxide waste 54 to form a slurry 56. The starting materials 52, 54 may be milled to improve homogeneity and mixing prior to forming the slurry 56. The zirconium oxide waste 54 may include fission products incorporated therein but, high-level fission product waste 58 may alternatively be added separately or additionally as a constituent of the slurry 56. The slurry 56 is cast 60 into a mold (not shown) having a cavity of any desired shape and freeze-cast to form a frozen body 62. The mold may be vibrated to assist packing of the slurry material within the mold and to assist mold filling by the elimination of air bubbles. The slurry 56 may alternatively be freeze extruded 64 to form an alternative frozen body 66. The freeze casting process causes the slurry constituents to form chemical bonds such that when the frozen body 62 or 66 is warmed at the steps 68 and the body demolded, it forms a relatively strong, free-standing and handleable monolith 70. The thawed body 70 is dried slowly to avoid too rapid shrinkage and consequent cracking and, once dried, it is sintered to form a high density, durable ceramic body 72 containing high level fission product waste material. A first example of the second preferred embodiment of the process of the present invention is to form a zircon, ZrSiO.sub.4, monolith. The process comprises making a mixture of a castable silica sol which is mixed with a zircon filler powder and waste zirconium oxide formed from the electrochemical dissolution of zirconium metal fuel cans. The mixture may also contain fission products from the zirconium metal waste stream or, fission product waste may be added as a separate component of the mixture. The process comprises the steps of vibro-energy milling the powder constituents to homogenize and thoroughly mix thus, breaking up zirconia flakes from electrochemical dissolution. The milling may take place wet so as to reduce dust and contamination hazard so the milled and homogenised powder is added to silica-sol to form the ceramic slurry 56, the slurry being capable of being poured into a mold (not shown) or at least capable of being so transferred to a mold. The mold may be connected to a vacuum system so as to remove entrained air or may be provided with a vibratory system for the same purpose and also to assist mold filling. The filled molds are rapidly cooled to about -50.degree. C. to freeze them and aged for a suitable period which may range from about 10 minutes to longer times. Once aged, the filled molds are rapidly warmed to room temperature and the now solid monoliths are removed from the molds and dried in air. The dried monoliths are then sintered at a minimum temperature of 1400.degree. C. The free silica from the sol reacts with a stoichiometric amount of zirconium oxide waste on sintering to form zircon. The small particle size of the sol and filler particles ensures lower sintering temperatures than normal ceramic forming processes used heretofore. Chemical bonds are formed during the freeze casting process between the silica and zirconium oxide and other constituents which are reinforced and serve to accelerate the sintering process at a low sintering temperature. An alternative to silica-sol is the use of zirconium oxide sol. This process involves the mixing of a zircon filler powder with zirconium waste and optionally fission product waste which is then mixed with a zirconium oxide sol. The process steps for producing a sintered zircon and stabilised zirconium oxide monolith are essentially as described above with reference to the formation of a monolith using the silica-sol route. As noted above, oxides of zirconium generally refer to the oxide plus a wide range of other materials which are not pure oxide; the other materials are mixed in the feed and therefore become part of the finished product, namely, the sintered disposable monoliths. While the foregoing is directed to the disclosed embodiment, the scope is set forth in the following claims.

048615200

abstract

A drivable radioactive source capsule is provided which comprises a tubular body containing therein a plurality of radioactive sources. The said tubular body has a first end and a second end which is a terminus of the tubular body. A plug has an elongated closure portion with the diameter of the closure portion being substantially equal to the inside diameter of said tubular body. The closure portion is disposed within the tubular body through the second end thereof and is attached to the second end of the tubular body. The plug has a connection portion adjacent the closure portion with the diameter of the connecting portion being substantially equal to the outside diameter of the tubular body. An elongated flexible drive cable is connected to the connection portion of the plug. By this arrangement, radioactive sources may be placed in the tubular body and the body is closed by disposing the closure portion of the plug into the second end of the tubular body and attaching the closure portion to the second end of the tubular body.

abstract

A sample manipulation device comprises an observation unit, which is used to observe a sample and to select a target position at which a portion to be removed from the sample is located, and a specimen stage which receives the sample. The sample manipulation device may include a manipulation tool, which is spatially shiftable relative to the observation unit and comprises a manipulation tip by which portions are removed from the sample, a control unit, which controls the shifting of the manipulation tool, as well as an optical position measurement unit, which is connected to the control unit and is used to determine the actual position of the manipulation tip, so that specific shifting of the manipulation tip to the target position can be carried out.

062657232

description

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention will be described in detail with reference to the accompanying drawings. Referring to FIG. 1A, a rectangular opening 120 is formed in the side surface of a magnetic shield room 101 having an inner wall adhered with a magnetic shield material. A tubular member 104 made of a magnetic shield material (e.g., permalloy) and having a rectangular section is attached to the opening 120 with rivets or the like. A portion of the tubular member 104 extending from its distal end for a predetermined length is outwardly bent at a right angle with respect to the tube axis to form a flange portion 105, as shown in FIG. 1B. More specifically, the flange portion 105 is constituted by the bent portions of the four sides of the distal end portion of the tubular member 104. An opening portion 102 is formed by the distal end portion of the tubular member 104 to communicate with the opening 120. As shown in FIG. 2A, the flange portion 105 is formed by bending the edges of the tubular member 104 outwardly and perpendicularly. When the size of the opening portion 102, i.e., the sectional size of the tubular member 104, the length of the tubular member 104, and the length of the flange portion 105, are defined as a.times.b, c, and d, respectively, in this embodiment, these sizes are set as follows: size of the opening portion 102: PA1 size of the tubular member 104: PA1 size of the flange portion 105: PA1 angle of the flange portion 105 with respect to the tube axis a=990 mm PA2 b=250 mm PA2 the sectional size is equal to that of the opening portion 102 PA2 c=100 mm PA2 d=10 mm to 20 mm PA2 .theta.=90.degree. When the size a of the opening portion 102 is set to 990 mm mentioned above, three cassettes can be arranged horizontally. A description will be made on an assumption that the tubular member 104 has no thickness. Note that the present invention is not limited to these values. It suffices if at least a portion of the tubular member 104 extending from its distal end for a predetermined length is inclined outwardly of the tubular member 104 at an angle of almost 90.degree. with respect to the tube axis. Preferably, the size d of the flange portion 105 may be set to 10 mm or more and the angle .theta. of the flange portion 105 with respect to the tube axis may be set to 90.degree.. As shown in FIG. 2B, a portion of the tubular member 104 near its distal end may be bent outwardly to have a certain radius of curvature, thereby forming a flange portion 205 having an arcuated section. In FIG. 2B as well, it suffices if the distal end of the tubular member 104 is inclined outwardly of the tubular member 104 with respect to the tube axis. Preferably, a size d of the flange portion 205 may be set to 10 mm or more and an angle .theta. formed by the tangential direction at the edge of the flange portion 205 and the tube axis may be set to 90.degree.. As shown in FIG. 3A, the opening 120 is formed in one of the four side surfaces of the magnetic shield room 101. As shown in FIG. 3B, a magnetic shield material 111 is adhered to the entire inner wall of the magnetic shield room 101 without any gap to form a tubular member 104 projecting from the opening 120. A loading/unloading portion 106 for loading/unloading wafers or masks is arranged near the opening 120. A cassette loaded in the magnetic shield room 101 through the opening portion 102, the tubular member 104, and the opening 120 is mounted on the loading/unloading portion 106. The wafers and the like stored in the cassette are conveyed into a column 109 in an EB exposure unit 110 with an arm 107 of a convey arm portion 108, and are exposed. Thereafter, the exposed wafers are mounted on the cassette again by the arm 107 in an order reverse to that described above. The cassette mounted with the wafers is unloaded outside the magnetic shield room 101 through the opening 120, the tubular member 104, and the opening portion 102. If the tubular member 104 Is excessively long, it causes a trouble when mounting the cassette on the loading/unloading portion 106. The length of the tubular member 104 is preferably 200 mm or less. The relationship between presence/absence of the tubular member 104 and the influence of the external magnetic field will be described. FIG. 4 shows the relationship between the distance from the opening portion 102 and the strength of magnetic field in the magnetic shield room 101 when the external magnetic field has a strength of 5 mG. The size of the opening portion 102 is a.times.b=990 mm.times.250 mm. As shown in FIG. 4, when the opening 120 is not formed, the magnetic field in the magnetic shield room 101 is 0.3 mG near the shield wall, 0.25 mG at a position separate from the shield wall by 500 mm, and 0.17 mG at a position separate from the shield wall by 1,000 mm, thus being attenuated gradually. In contrast to this, when only the opening portion 102, i.e., the tubular member 104, is formed, the magnetic field near the opening 120 exhibits a value near about 3 mG but is 0.35 mG at a position separate from the opening 120 by 500 mm, thus being attenuated sharply. At a position farther separate from the opening 120, the magnetic field is attenuated gradually. However, even at a position separate from the opening 120 by 1,000 mm, the magnetic field has a strength of 0.23 mG, which is higher than the value obtained when the opening 120 is not formed by about 0.06 mG. In the first example provided with the tubular member 104 of c=200 mm which has the flange portion 105 of d=10 mm and .theta.=90.degree., the strength is 0.6 mG immediately inside the opening 120, but at a position separate from the opening 120 by 500 mm, the magnetic field is attenuated sharply to a value almost equal to that obtained when the opening 120 is not formed, and at a position separate from the opening 120 by 1,000 mm, the magnetic field is attenuated gradually to 0.17 mG. In contrast to this, when the tubular member 104 having no flange portion 105 is used, to obtain a shield effect almost equal to that described above, the tubular member 104 must have a length of 600 mm or more. This suggests effectiveness of the present invention in decreasing the length of the tubular member 104. In the second example provided with the tubular member 104 of c=100 mm which has the flange portion 105 of d=10 mm and .theta.=90.degree., the strength is about 1.4 mG immediately inside the opening 120, but at a position separate from the opening 120 by 500 mm, the magnetic field is attenuated sharply to a value almost equal to that obtained when the opening 120 is not formed, and at a position separate from the opening 120 by 1,000 mm, the magnetic field is attenuated gradually to 0.17 mG. The flange portion 105 may be formed by bending the edge of the distal end of the tubular member 104, as described above, or by mounting a rectangularly annular flange member 305 on flange-like edges 104a of the tubular member 104, shown in FIG. 5A, by using rivets 305a, as shown in FIG. 5B. In this case, if the number of rivets 305a is increased or the flange member 305 is connected and fixed to the distal end portion of the tubular member 104 in accordance with another mounting method, e.g., welding, in place of the rivets 305a, the adhesion strength of the connecting portion can be increased. This decreases the impedance of the connecting portion so that the internal magnetic field can be emitted outside more easily. Connecting portions made of a magnetic shield material may be mounted to the notched portions between edges 104a of the tubular member 104 to connect the edges 104a to each other, thereby forming a flange portion continuously surrounding the opening portion 102 of the tubular member 104. Alternatively, no edges 104a may be formed on the tubular member 104, but a rectangularly annular flange member 305 made of a magnetic shield material may be attached to the distal end of the tubular member 104 with a known method. Alternatively, a tubular portion may be formed on the flange member 305 and be fixed to the tubular member 104 by fitting. Alternatively, instead of the flange member 305, strip segments made of a magnetic material and constituting a flange portion may be separately attached to the respective sides of the distal end portion of the tubular member 104. As has been described above, according to the present invention, a tubular member having a flange portion is formed on the opening of a magnetic shield room. Even if the size of the opening is increased, the influence of the external magnetic field on the interior of the magnetic shield room can be decreased. More specifically, when compared to a case using only a tubular member, the same effect to that obtained by using a long tubular member can be obtained with a short tubular member. For example, when a tubular member having a flange portion and a length of about 100 mm is formed on the opening, the same effect as that obtained when no opening is formed can be obtained at a position separate from the opening by 500 mm. This allows loading/unloading of the cassette through the opening, and accordingly the loading/unloading portion can be arranged in the magnetic shield room, thus increasing the throughput. Since entrance of the external magnetic field through the opening can be suppressed more than in the conventional case, the distance between the EB exposure unit and the opening can be decreased. Since no extra space is required unlike in the conventional case, the magnetic shield room can be made compact.

description

This invention relates to a production process of a composite nuclear fuel material composed of aggregates of a ground powder blend of UO2 and PuO2 dispersed in a UO2 matrix preferably depleted in 235U. The composite in question possesses after sintering a microstructure of ceramic-ceramic (CERCER) type in the form of relatively spherical calibrated aggregates of solid solution (U,Pu)O2 dispersed in the UO2 matrix. This is a nuclear fuel material with improved fission gas release properties. MOX (Mixed Oxide) fuel is at present produced industrially using a process known as MIMAS (MIcronized MASter blend). This process comprises successively a step of grinding oxides of uranium and plutonium, a step of diluting the powders obtained (primary blend) in the uranium oxide (UO2) and a step of sintering. The MOX fuel produced by this process has a two-phase structure, one phase (U,Pu)O2 composed of solid solutions with a Pu/U+Pu content that can vary in the range of 30 to 5% of Pu and a UO2 phase. The (U,Pu)O2 phase exists either in aggregate form or in the form of “filaments” forming a continuous network in the fuel. On irradiation, the fission gases are essentially created in the plutonium-bearing zones and install themselves over short distances (7 to 9 μm) then diffuse through the UO2 matrix before being released outside the fuel. An improvement of the material consists in exacerbating the biphasic character of the present fuel to tend towards a material that isolates the plutonium-bearing zones in a UO2 matrix, which is intended to act as a retention barrier to the fission gases. The precise object of the present invention is to provide a production process for a composite material consisting of cohesive aggregates of a ground powder blend of UO2 and of PuO2 dispersed in a UO2 matrix that makes it possible to obtain a material capable of limiting fission gas release. The cohesive aggregates are obtained, according to the invention, either by mechanical granulation, or by calcinating the primary blend of UO2 and PuO2. The process of the present invention includes the following steps: dry co-grinding a UO2 powder and a PuO2 powder so as to obtain a homogenous primary blend, consolidating the primary blend so as to obtain cohesive aggregates of the blend of UO2 and of PuO2, sieving the aggregates between 20 and 350 μm, diluting the sieved aggregates in a UO2 matrix so as to obtain a powder blend, pelletising the powder blend, and sintering the pellets obtained in order to obtain the composite. The process of the present invention makes it possible to isolate the fissile matter comprising the plutonium-bearing aggregates of calibrated ground powders of UO2 and of PuO2 and to distribute them homogenously through the fertile matrix composed of UO2. Appended FIGS. 2a), 2b) and 3 represent three photographs of microstructures of sintered composite materials composed of precalcinated or granulated aggregates (marker 1) of (U,Pu) O2 dispersed in a UO2 matrix (marker 2). According to the invention, the primary blend of UO2 and of PuO2 is comprised preferably of a UO2 content in the range of 60 to 90 wt. % and of a PuO2 content in the range of 40 to 10 wt. % of the total mass of the blend, preferably 75 wt. % of UO2 and 25 wt. % of PuO2. The mass of PuO2 can be totally or partially replaced by discarded manufactured powders comprised of mixed oxides (U,Pu) O2. According to a first embodiment of the present invention, the step of consolidation to obtain cohesive aggregates can include the following steps: compacting the homogenous primary blend at a pressure in the range of 150 to 600 MPa in order to obtain a blank, crushing the blank obtained in order to obtain granules, and spheroidising the granules. This first embodiment of the present invention comprises mechanically granulating the primary blend compacts. This consolidation brings about sufficient cohesion of aggregates to withstand without deterioration the subsequent steps of diluting and pelletising of the process of the present invention. The blend can be compacted by using a single or double effect uniaxial press. This is preferably carried out at a pressure of 300 MPa. The crushing can be carried out using any known appropriate means, for example using an industrial crusher. The granules can for example be spheroidised using simple self-abrasion of the crushed products, for example in a mixer of the TURBULA (registered trademark) type (oscillo-rotary mixer-shaker). According to a second embodiment of the present invention, the consolidation of a primary blend can be carried out using a heat treatment calcinating the primary blend at a temperature of 1000 to 1400° C., preferably at a temperature of 1000° C. The consolidated primary blend is the mixture of UO2 and of PuO2 produced by co-grinding. Calcination gives the primary blend a sufficient degree of cohesion for it to withstand without deterioration the subsequent steps of dilution and pelletising of the process of the present invention while preserving high sphericity. Preferably, the heat treatment is carried out in an humidified or non-humidified atmosphere of 95 vol. % argon and 5 vol. % hydrogen. When the heat treatment atmosphere is humidified, it is preferably humidified with a partial pressure ratio PH2/PH2O in the range of 50 to 20. The sieving can be carried out using a stainless steel sieve with mesh size in the range of 20 to 350 μm, preferably in the range of 125 to 350 μm. Thus the cohesive aggregates can have a dimension (diameter) in the range of 20 to 350 μm, preferably in the range of 125 to 350 μm. The dilution of the aggregates in the UO2 matrix can be carried out for example by mechanical stirring. This should preferably not break the aggregates. The aggregates can be diluted in the UO2 matrix at a concentration of 20 to 35 vol. % of the total volume of the green blend obtained, preferably at a concentration of 20 vol. % of the total volume of the green blend. These quantities yield a composite material advantageously containing between 2.1 and 9.45% of plutonium oxide. According to the invention, pelletising can be carried out using a uniaxial hydraulic press, for example at a pressure of 500 MPa. According to the invention, the sintering step can be carried out a temperature of approximately 1700° C. It can be carried out in a sintering furnace by following a thermal cycle comprising the following successive steps of: raising the temperature at 200° C./hour, plateauing at approximately 1700° C., and cooling at approximately 400° C./hour down to 1000° C., then by following furnace inertia. The sintering step is preferably carried out in an humidified or non-humidified atmosphere of 95 vol. % argon and 5 vol. % hydrogen. When the sintering atmosphere is humidified, it is preferably humidified with a partial pressure ratio PH2/PH2O in the range of 50 to 20. Other characteristics and advantages will become obvious on reading the following examples, which are, of course, given to illustrate the invention and not to limit it as refers to the appended drawings. The sequence of the different steps of the manufacturing process of sintered composites consisting of aggregates of solid solution of (U,Pu)O2 dispersed in a UO2 matrix according to the process of the present invention is indicated in the flow chart in FIG. 1. Different homogenous matrix blends of powders of uranium and plutonium dioxides produced by processes known to prior art have been produced with proportions of powders in the ranges of 60 to 90 wt. % of UO2 and of 40 to 10 wt % of PuO2 compared to the total mass of the blend. These blends were produced by dry co-grinding the rough powders, in a jar rotating at 48 r.p.m. for 6 hours. The grinding media were uranium metal balls. No organic, pore-forming or lubricant additives were used. This example illustrates a first embodiment of the consolidation step of the aggregates of the process of the present invention. One of the matrix blends at 25 vol. % of PuO2 obtained in example 1 was compacted in different tests at different granulation pressures in a range of 0 (non-compacted powder from co-grinding) to 600 MPa, using a single effect uniaxial press. The blanks thus obtained were then crushed manually in an agate mortar, and the crushed products obtained were spheroidised by self-abrasion by a Pyrex (commercial brand) round bottom flask inserted in a grinding jar rotating at 48 r.p.m. for one and a half hours. This example illustrates a second embodiment of the consolidation step of the aggregates of the process of the present invention. The heat treatment was applied to one of the matrix blends at 25 vol. % of PuO2 obtained in example 1, in a flow of a non-humidified 95% Ar-5% H2 mixture. The thermal cycle used corresponded to a rise in temperature at 200° C./hour to a temperature of 1000, 1200 or 1400° C. followed, with no plateau, by cooling at 400° C./hour to ambient temperature. This consolidation treatment produced consolidated aggregates of high sphericity, for each blend of UO2 and of PuO2. The aggregates obtained in examples 2 and 3 were sieved using a stainless steel sieve with mesh size in the range of 125 to 250 μm. After mechanical granulation or thermal consolidation, the plutonium-bearing aggregates were mixed with UO2 powder for 1 hour 30 minutes in a round bottom flask placed on the driving rolls of a grinder and turning at a speed of 46 r.p.m. Shaping the composites by pelletising was done using a single effect uniaxial press, operating at a pressure of 500 MPa. A pellet of zinc stearate was pressed regularly after producing two cylinders of composite, in order to ensure the lubrication of the press matrix. The samples obtained took the form of cylinders of approximately 7 mm in diameter and 9 mm in height. The samples placed in a sintering box were sintered in a Degussa (commercial brand) bell furnace. The thermal cycle used was as follows: raising the temperature at 200° C./hour; 4 hours of plateau at 1700° C.; cooling at 400° C./hour down to 1000° C., then by following switched off furnace inertia until ambient temperature was reached. The different composites were sintered in a reducing atmosphere consisting of a flow of a non-humidified mixture of 95% argon and 5% hydrogen. A level of residual humidity of approximately 100 ppm was measured in the gas at furnace exit, at ambient temperature. This corresponds to an oxygen potential, ΔG°, at 1700° C. of −478 kJ/moleO2. The characteristics of the UO2—PuO2 aggregates used and of the CERCER composites obtained are presented in the following table 1. TABLE 1CHARACTERISTICS OF AGGREGATESCHARACTERISTICSGreenGreenSinteredGranulationCalcinationApparentAggregateApparentApparentTestWt. % ofpressureTemperatureDensityFractionalWt. % ofDensityDensityn°PuO2(MPa)(° C.)(g/cm3)VolumePuO2(g/cm3)(g/cm3)Granulation110300nil6.820.22.16.510.5225300nil6.919.95.36.510.5340300nil7.020.58.66.510.5425600nil7.325.67.356.510.5525300nil6.935.79.456.610.5Reference625nilnil5.425.05.26.610.5ExampleHeat725nil10007.318.54.96.510.5Treatment825nil12008.020.25.66.510.5925nil14009.620.16.26.610.2 The products obtained after sintering have a microstructure of the type of those presented in FIGS. 2a), 2b) and 3. The relatively regular distribution of the plutonium-bearing aggregates (white spots on the photographs) in the matrix show that the process of the present invention of product preparation meets the objective for obtaining a composite of individualized aggregates enclosing the totality of the mixed oxide. In view of the dilution process chosen, as described in example 5 above, the composite presenting the required qualities can only be obtained if the plutonium-bearing aggregates (UO2—PuO2) used are cohesive enough to preserve their integrity during this step of the process. The results obtained have shown that the aggregates prepared according to the present invention by mechanical granulation or thermally consolidated at 1000° C. present the properties required for the production of the composites.

summary

H00012629

claims

1. A rod examination gauge comprising: vertical elevator means, support platform means mounted at the top of the elevator frame means for supporting a fuel rod, rod guide means mounted at the bottom of the elevator frame means for guiding the fuel rod, storage rack means arranged at the bottom of the elevator frame means for storing instruments means, and instrument table means mounted on the transfer carriage of the elevator means for holding instruments means for measuring the fuel rod and a closed circuit television camera for viewing the fuel rod. 2. The rod examination gauge of claim 1, wherein the instruments means include axial profilometer means for measuring fuel rod diameter and oxide thickness, orbiting profilometer means for measuring fuel rod wear mark depth and volume and fuel rod ovality, and ultrasonic instrument means for detecting rod cladding defects. 3. The rod examination gauge of claim 2, wherein the axial profilometer means includes a roller assembly means for aligning and positioning the fuel rod in the center of the axial profilometer means, and a drive assembly means connected to DC motor for driving the roller assembly through a pressured and watertight junction box. 4. The rod examination gauge of claim 3, wherein the axial profilometer means includes a magnescale probe assembly for measuring the diameter of the fuel rod. 5. The rod examination gauge of claim 4, wherein the axial profilometer means includes an eddy current probe means for measuring the fuel rod oxide thickness. 6. The rod examination gauge of claim 2, wherein the orbiting profilometer means includes a roller assembly means for gripping and centering the fuel rod, and a rotary platform means driven by a DC motor for driving the roller assembly. 7. The rod examination gauge of claim 6, wherein the orbiting profilometer means includes a magnescale probe assembly for measuring fuel rod wear marks and rod ovality. 8. The rod examination gauge of claim 2, wherein the ultrasonic instrument means includes a roller assembly means for gripping and maintaining the fuel rod at the center of the ultrasonic instrument means. 9. The rod examination gauge of claim 8, wherein the ultrasonic instrument means includes a longitudinal transducer and a circumferential transducer, each driven by a motor for providing x- and y- directional orientation thereof. 10. The rod examination gauge of claim 1, wherein the support platform means includes standard bars of different rod diameters for calibrating the instruments means. 11. The rod examination gauge of claim 10, wherein the support platform means is arranged to receive a rod caddy means for holding and transporting a fuel rod. 12. The rod examination gauge of claim 11, wherein the support platform means include a rod rotator motor means for providing angular orientation of a fuel rod therein, and storage support means for storing the standard bars and for holding the rod caddy. 13. The rod examination gauge of claim 10, wherein a rod suspension assembly is provided for holding the fuel rod, the rod suspension assembly including a suspension device, a secondary drop protection wire, and collet means for grasping fuel rod. 14. The rod examination gauge of claim 13, wherein the rod suspension device includes a drive shaft coupler having a coupler slot for engaging the rod rotator motor, a universal joint, a pin, and a retainer nut, and wherein the suspension device means is tapered to fit within an examination port on the support platform means. 15. The rod examination gauge of 14, wherein the collet means includes a J-slot associated with a spring for accepting the pin of the rod suspension device, and fingers for accepting the fuel rod.

abstract

An X-ray imaging apparatus and an imaging method capable of acquiring an image of a test object associated with a phase shift in consideration of X-ray absorption is provided. A splitting element configured to spatially split an X-ray into multiple X-ray beams is provided. A shielding unit including a plurality of shielding elements configured to block part of an X-ray acquired by the splitting element is provided. Part of X-ray beams detected at the first detection pixels is blocked by the shielding elements. The X-ray beams detected by the second detection pixels adjoining the first detection pixels are not blocked by the shielding elements.

043476236

summary

BACKGROUND OF THE INVENTION Pressurized-water and boiling-water nuclear reactors utilize a vessel to contain the fuel rods with their associated fissionable material. Coolant water is circulated through the vessel and is heated (PWR) or partially vaporized (BWR) by heat transfer from the fuel rods. The heated coolant of a PWR is utilized to vaporize a secondary through heat exchangers. In the power generation application of nuclear reactors, the vapor powers a steam turbine rotating a generator. In the event that a malfunction of the system takes place so that the normal coolant circulation is interrupted, the reactor is shutdown by inserting absorber rods into the core, thereby interrupting the nuclear reaction. However, even after shutdown of the reactor, the fission products in the fuel rods continue to produce heat generally referred to as "decay heat". Without the normal coolant flow, this decay heat could melt the fuel rod cladding, the fuel, and the vessel itself, releasing radioactive fission products into the secondary containment building and thereby increasing the risk that radioactive material would be introduced into the atmosphere with the associated potential danger to the public. The potential for release of radioactive material into the environment has led to the development of emergency core-cooling systems. All nuclear reactors must now have provision for maintaining sufficiently low temperatures after a malfunction that the integrity of the fuel rods will be insured. The primary malfunction with which the emergency core-cooling systems are concerned is a loss-of-coolant accident. In such an accident, the primary coolant system develops a leak or rupture resulting in some of the primary coolant water being lost from the system. When the leak is a relatively minor one, the primary coolant system can continue to function to cool the core after the shutdown so long as the small quantity of coolant being lost is replenished. The replenishment of coolant through a small leak is accomplished by a high-pressure injection system. However, in the event of a large rupture developing in the primary coolant system, a different emergency core-cooling system becomes effective. According to conventional design, such an emergency core-cooling system operates in two distinct phases. Initially, accumulator tanks are discharged and/or pumps operated to rapidly refill the vessel with borated coolant water. Subsequently, the new coolant is circulated through the pressure vessel. Steam leaking into the reactor containment is condensed, removing the reactor heat from the system. Power for the pumps is obtained from an independent power source such as a Diesel engine. Typically, a complete emergency core-cooling system injects water into each of the primary coolant loops of the reactor so that the break in a single coolant loop will not defeat the operation of the emergency core-cooling system, pumping water into the other primary coolant loops. It will be apparent that the provision of such systems sufficient to maintain a safe temperature within the vessel is an expensive and critical component of the overall power generating system. Such conventional emergency core-cooling systems are rendered more expensive and less reliable because each of the possible contingencies for such a system's operation adds further to the design capacity requirements. For example, Diesel generator sets have a high startup failure rate, requiring a backup electric system to increase the reliability. A critical time lag may develop before the cooling water from the pumps is injected. Water coming into contact with the hot core is then partially vaporized by the fuel elements. The steam in the vessel collects in the plenum of the vessel producing a back pressure to the entry of new coolant water. The steam problem, generally referred to as "steam binding", limits the design of the reactor plant so that the initial temperature rise caused by the steam binding effect does not endanger the integrity of the reactor core. Therefore, it is desirable to have a system for removing heat from the vessel that increases the reliability of decay heat rejection from the reactor after an accident and has a short startup time. Such a system is particularly desirable if it is capable of operating independently of an electrical power source. SUMMARY OF THE INVENTION An exemplary embodiment of the invention will be described in association with a pressurized-water reactor. However, it is to be understood that the system has also application in other reactor systems incorporating a circulating coolant and that the system in particular has application to a boiling-water reactor. In the exemplary embodiment, the dependence on electric power systems of prior art emergency core-cooling systems is overcome by utilizing the energy from the reactor itself to power the emergency system. The heat energy is utilized by a unique jet pump providing operating characteristics closely corresponding to the requirements for emergency core-cooling over a wide range of failure types. A subcooler for increasing the differential between the saturation temperature of the coolant water for the then existing pressure and coolant water temperature further enhances the characteristics of the jet pump design. The subcooler and jet pump together are designed to accommodate the coolant in such a manner that substantially all the flashing of the coolant into steam will occur in the divergent section of the nozzle. Since flashing does not take place in the throat of the nozzle, the flow does not reach sonic velocity (become choked) in the nozzle throat and the pump produces an almost constant mass flow rate over a wide range of temperature/pressure relationships. Because flashing in hot water in the nozzle is the driving force that distinguishes the jet pump according to the invention, the pump is referred to hereinafter as the flash jet pump. The flash jet pump is further distinguished from conventional designs in its use of an extremely high expansion area ratio. Expansion area ratio refers to the ratio between the size of the nozzle outlet area to the nozzle throat area. For conventional jet pumps, this ratio is over a maximum range of 1:1 to 8:1. In the flash jet nozzle, the area ratio is in the range of 10:1 to 50:1. The high area ratio is caused by the high density of liquid water compared to that of steam and the fact that flashing is suppressed in the convergent nozzle section. The supersonic two-phase flow exiting the divergent nozzle impinges upon coolant water drawn into the suction side of the flash jet pump. The mixing of the supersonic two-phase jet with the coolant water produces a combined high-velocity flow which is converted into a pressure rise for pumping. The pressure rise is increased by a divergent section in the conduit so that substantially all of the remaining kinetic energy of the water is converted into pressure for forcing the combined coolant flow through the inlet connection into the reactor vessel. The coolant water is drawn from a supply of additional coolant. The source of supply of the additional coolant is a storage tank or the reactor building sump. The reactor building sump collects the water lost from the primary cooling loop due to the break. Thus, the system becomes self-sustaining with the water being lost from the reactor vessel being picked up by the flash jet pump and recirculated. For maximum advantage, the subcooler is in the form of a downcomer pipe connected to the outlet connection of the vessel and having a vertical extent of 20 to 40 feet. The effect of the downcomer pipe is to apply a static pressure head on top of the circulating pressure of the coolant thereby raising the saturation temperature and increasing the differential between the saturation temperature and coolant water temperature. For the capability of the system to deal with a wide range of loss-of-coolant accidents and to minimize fuel rod damage under all circumstances, operation of the system in its transfer mode for reflooding the vessel with an initial charge of coolant water is necessary. The operation of such a transfer system assumes that the rupture is sufficiently large that a substantial coolant fraction is lost from the vessel. The transfer system is utilized to transfer borated water into the vessel in the minimum possible time. The pump for the transfer system incorporates the same principles previously described in association with the recirculation system. That is, the pump is a flash jet pump powered by hot water generated by the reactor heat. THe hot water can be taken from the secondary side of the steam generator or from a hot water storage tank. The steam generators contain a substantial quantity of heated water at the moment of a loss-of-coolant accident. Since the transfer system must operate only for an initial period, a finite quantity of heated water is sufficient to refill the reactor vessel. A subcooler is connected to the flash nozzle. The subcooler is a downcomer pipe with a vertical elevation difference between the hot water tank and flash jet pump. Cold water is drawn from a storage tank containing borated water by the flash jet pump and discharged into the reactor vessel. It is therefore an object of the invention to provide a new and improved flash jet coolant pumping system. It is another object of the invention to provide a new and improved flash jet coolant pumping system that has few moving parts. It is another object of the invention to provide a new and improved flash jet coolant pumping system with a highly reliable cooling action. It is another object of the invention to provide a new and improved flash jet coolant pumping system which operates over a wide pressure range. It is another object of the invention to provide a new and improved flash jet coolant pumping system that reliably transfers an initial charge of water into a reactor vessel. Other objects and many attendant advantages of the invention will become more apparent upon a reading of the following detailed description together with the drawings in which like reference numerals refer to like parts throughout and in which:

summary

abstract

Surface roughness having intervals of several tens of nanometers to about a hundred micrometers in a solid surface is reduced by directing a gas cluster ion beam to the surface. An angle formed between the normal to the solid surface and the gas cluster ion beam is referred to as an irradiation angle, and an irradiation angle at which the distance of interaction between the solid and the cluster colliding with the solid dramatically increases is referred to as a critical angle. A solid surface smoothing method includes an irradiation step of directing the gas cluster ion beam onto the solid surface at an irradiation angle not smaller than the critical angle. The critical angle is 70°.

description

The present invention relates to an electron beam lithography apparatus for manufacturing an original master, and in particular, relates to the electron beam lithography apparatus used for concentrically drawing circles. A magnetic disk or a hard disk (HD) is used as a storage of a personal computer (PC), a mobile device, a car-mounted device, and the like. The application thereof significantly expands, and surface recording density is rapidly improved in recent years. To manufacture such a hard disk with high recording density, electron beam mastering technology is widely studied. In an electron beam lithography exposure apparatus, an electron lens converges an electron beam shot by an electron gun, and an electron beam spot is applied to a substrate coated with a resist. A blanking control system and a beam deflection control system control the irradiation position of the electron beam spot to draw a desired beam pattern. Recently various electron beam lithography exposure apparatuses are developed and include, for example, an apparatus which precisely manufactures an original master of a recording medium such as an optical disk and the like (refer to, for example, Japanese Patent Laid-Open Publication No. 2002-367178). Accordingly, it is necessary to precisely control the irradiation position of the electron beam spot in order to perform electron beam lithography with high recording density. The recent hard disk uses a concentric pattern instead of a spiral pattern used in the optical disk and the like. In the case of concentrically drawing circles by the electron beam lithography, it is necessary to precisely connect a start point to an end point in each circle (i.e., track). Therefore, it is desired to provide an apparatus which can concentrically draw circles with high precision. When a conventional x-θ system lithography apparatus or the like concentrically draws circles by the electron beam lithography, a ramp wave in synchronization with the rotation of the substrate deflects the electron beam to a radial direction. Thus, there are problems that the shape of a circle connecting section becomes distorted, a part of a land section is exposed, and the like. If there is rotational fluctuation in a rotational stage, a line for a circle may not connect at the start and end points. Using blanking prevents the land section from being exposed, but there occurs another problem that a line does not connect at the start and end points. Accordingly, it is desired to provide an electron beam lithography apparatus which can draw a circle with high precision. To solve the foregoing problems, an object of the present invention is to provide an electron beam lithography apparatus which can concentrically draw circles by electron beam lithography in such a manner that a start point and an end point of the circle connect with high precision. According to the present invention, there is provided an electron beam lithography apparatus for concentrically drawing a plurality of circles on a substrate by applying an electron beam while rotating the substrate, which comprises a beam deflection portion for deflecting the electron beam to change an irradiation position of the electron beam; a synchronization signal generation portion for generating a synchronization signal which is in synchronization with the rotation of the substrate; a controller for controlling the beam deflection portion on the basis of the synchronization signal in order to deflect the electron beam in a rotational radial direction of the substrate and in a rotational tangential direction of the substrate opposite to a rotational direction of the substrate, while drawing transition is performed from one circle to another circle; and a beam cutoff portion for cutting off the irradiation of the electron beam on the substrate, for a period during the electron beam is deflected in the rotational radial direction. According to the present invention, there is provided an electron beam lithography method for drawing a plurality of circles on a substrate by applying an electron beam while rotating the substrate, which comprises a cutoff step of cutting off the irradiation of the electron beam on the substrate during drawing a circle; and a drawing start step of deflecting the electron beam in at least a rotational radial direction of the substrate during cutoff, and starting the drawing of another circle. Embodiments of the present invention will be hereinafter described in detail with reference to drawings. In the following embodiments, the same reference numerals refer to equivalent components. FIG. 1 is a block diagram schematically showing the structure of an electron beam lithography apparatus 10 according to a first embodiment of the present invention. The electron beam lithography apparatus 10 is a mastering apparatus which produces an original master for manufacturing magnetic disks by use of an electron beam. The electron beam lithography apparatus 10 comprises a vacuum chamber 11, a drive device, an electron beam column 20 attached to the vacuum chamber 11, and various circuits and control systems. The drive device performs rotational and translational movement of a substrate mounted thereon and disposed in the vacuum chamber 11. The various circuits and control systems carry out substrate drive control, electron beam control, and the like. To be more specific, a substrate 15 for an original master of a disk is mounted on a turntable 16. The turntable 16 is rotated by a spindle motor 17, which is a rotational drive device for driving the substrate 15 to rotate, with respect to a vertical axis of the principal plane of the substrate 15. The spindle motor 17 is disposed on a feed stage (hereinafter, simply referred to as stage) 18. The stage 18 is coupled to a feed motor 19 being a feeding (translational motion drive) device. Thus, the spindle motor 17 and the turntable 16 can be moved in a predetermined direction in a plane which is in parallel with the principal plane of the substrate 15. The turntable 16 is made of dielectric, for example, ceramic, and has an electrostatic chucking mechanism (not illustrated). The electrostatic chucking mechanism is composed of the turntable 16 (ceramic) and an electrode provided in the turntable 16. The electrode made of a conductive material generates electrostatic polarization. The electrode is connected to a high-voltage power supply (not illustrated). Since the high-voltage power supply applies voltage to the electrode, the substrate 15 is attracted and held. Optical elements are disposed on the stage 18. The optical elements include a reflecting mirror 35A, an interferometer, and the like, which are elements of a laser interferometer measuring system 35 described later. The vacuum chamber 11 is installed through a vibration isolating table (not illustrated) such as an air damper or the like in order to restrain the transmission of external vibration. The vacuum chamber 11 is connected to a vacuum pump (not illustrated). The vacuum pump exhausts air from the vacuum chamber 11, so that the inside of the vacuum chamber 11 is set at a vacuum atmosphere with a predetermined pressure. In the electron beam column 20, an electron gun (emitter) 21 for emitting an electron beam, a convergence lens 22, blanking electrodes 23, an aperture 24, abeam deflection coil 25, an alignment coil 26, deflection electrodes 27, a focus lens 28, and an objective lens 29 are disposed in this order. The electron gun 21 emits an electron beam (EB) accelerated to several tens of KeV by a cathode (not illustrated), to which an acceleration high voltage power supply (not illustrated) applies high voltage. The convergence lens 22 converges the emitted electron beam. The blanking electrodes 23 switch the electron beam between ON and OFF on the basis of a modulation signal from a blanking control section 31. In other words, since application of a voltage between the blanking electrodes 23 largely deflects the passing electron beam, the electron beam is prevented from passing through the aperture 24, so that the electron beam becomes an off state. The alignment coil 26 corrects the position of the electron beam on the basis of a correction signal from abeam position corrector 32. The deflection electrodes 27 can carry out the deflection control of the electron beam at high speed on the basis of a control signal from a deflection control section 33. The deflection control results in position control of an electron beam spot with respect to the substrate 15. The focus lens 28 controls the focus of the electron beam on the basis of a control signal from a focus control section 34. A light source 36A and a photo detector 36B are provided in the vacuum chamber 11 to detect the height of the principal plane of the substrate 15. In the electron beam lithography apparatus 10, a height detection section 36 is provided. The photodetector 36B includes, for example, a position sensor, a CCD (charge coupled device), and the like. The photodetector 36B receives a light beam, which is emitted from the light source 36A and reflected from the surface of the substrate 15, and provides the height detection section 36 with a photo-reception signal. The height detection section 36 detects the height of the principal plane of the substrate 15 on the basis of the photo-reception signal, and generates a detection signal. The detection signal representing the height of the principal plane of the substrate 15 is provided to the focus control section 34, so that the focus control section 34 controls the focus of the electron beam on the basis of the detection signal. The laser interferometer measuring system 35 measures a distance to the stage 18 by use of a distance measuring laser beam from a light source provided in the laser interferometer measuring system 35. Then, the laser interferometer measuring system 35 sends distance measurement data, that is, position data of the stage 18 to a position control section 37. The position control section 37 generates a position correction signal for correcting the position of the electron beam from the position data, and sends the position correction signal to the beam position corrector 32. The beam position corrector 32, as described above, corrects the position of the electron beam on the basis of the position correction signal. The position control section 37 also generates a position control signal for controlling the feed motor 19, and provides the position control signal to the feed motor 19. A rotation control section 38 controls the rotation of the spindle motor 17. The rotation control section 38 sends a rotation synchronization signal of the spindle motor 17 to a drawing controller 39. The rotation synchronization signal includes a signal representing a reference rotational position of the substrate 15 and a pulse signal on a predetermined rotational angle basis with respect to the reference rotational position. The rotation control section 38 obtains a rotational angle, a rotational speed, a rotational frequency, and the like of the substrate 15 from the rotation synchronization signal. The drawing controller 39 sends a blanking control signal to the blanking control section 31, and sends a deflection control signal to the deflection control section 33 to carry out drawing control. The drawing control, as described later, is carried out in synchronization with the above-described rotational signal of the spindle motor 17. Main signal lines of the blanking control section 31, the beam position corrector 32, the deflection control section 33, the focus control section 34, the position control section 37, and the rotation control section 38 are described above, but each of these components is bidirectionally connected to the drawing controller 39. Each component of the electron beam lithography apparatus 10 is appropriately connected to a not-illustrated system controller for controlling the whole apparatus, and sends and receives necessary signals. Then, an instance in which the electron beam lithography apparatus 10 draws (i.e., performs electron beam exposure) concentric patterns of an original master of a hard disk will be hereinafter described in detail. A track of the currently widely used hard disk, as shown in FIG. 2, is not a spiral pattern (shown by a broken line) adopted in an optical disk such as CDs, DVDs, and the like, but concentric patterns (shown by solid lines). An instance in which the electron beam lithography apparatus 10 (x-θ system lithography apparatus) successively draws the concentric patterns (15A, 15B, 15C, . . . and the like of FIG. 2) will be described for instance. FIG. 3 is a plan view which schematically shows the case of drawing a plurality of concentric patterns on the substrate 15 being the original master of the hard disk. Electron beam lithography (electron beam exposure) is concentrically performed on the substrate 15 applied with a resist, as shown in the drawing, to draw circles (tracks) in such a manner that a start point and an end point of the concentric circle precisely connect to each other. In other words, drawing by the electron beam lithography is started from a start point 15X of a circle 15A, and the circle is drawn in such a manner that a drawing end point (an end point of the circle 15A) connects to 15X being the drawing start point. In the drawing, for the sake of convenience, the position of the start point and the end point (connection point) 15X of the circle 15A is indicated with a filled circle (•). Then, a circle 15B concentric with the circle 15A is drawn in a similar manner with using a point 15Y, which is an outside point of the drawing connection point 15X of the circle 15A in a radial direction, as a drawing connection point. Furthermore, a circle 15C concentric with the circles 15A and 15B is drawn in a similar manner with using a point 15Z, which is an outside point of the drawing connection point 15Y in the radial direction, as a drawing connection point. The drawing connection points 15X, 15Y, and 15Z are in a line in the same radial direction of the concentric circles 15A, 15B, and 15C, respectively. The concentric circles can be drawn in a similar manner inside of the radial direction. FIG. 4 is a schematic plan view which illustrates the case of drawing the concentric circles 15A and 15B in such a manner that each circle precisely connects at the drawing connection point described above. The neighborhood of the drawing connection points (start point and end point) is enlarged in FIG. 4. FIG. 5 is a time chart corresponding to FIG. 4 which shows the blanking control signal and the deflection control signals in X and Y directions. FIG. 6 is a flowchart which shows the procedure steps of drawing. Taking a case in which the substrate 15 is rotated at constant linear velocity (CLV) as an example, the drawing control will be described. The deflection control signal in the radial direction, that is, the X direction in the drawing (hereinafter, referred to as X deflection signal) is a ramp wave having the same frequency as the rotational frequency of the spindle motor 17. In response to the X deflection signal having a ramp waveform, the drawing of the circle (track) 15A is started (step S11), and the circle 15A is drawn up to a position A (FIGS. 3 and 4), which is in the vicinity of the drawing start point 15X and does not reach the drawing start point 15X. The deflection of the electron beam is started at the position A in a direction opposite to the rotational direction (−Y direction) of the substrate 15 and a tangential direction (that is, +Y direction) in response to the Y deflection signal having a ramp wave form (step S12). When the electron beam reaches a position B (that is, the drawing start point 15X of the circle 15A), the electron beam is cut off by the blanking signal (step S13). As shown in FIG. 7, applying a blanking voltage to the blanking electrodes 23 largely deflects the electron beam EB from a restriction of the aperture 24, so that the electron beam EB becomes a state in which the electron beam EB cannot pass through the aperture 24 (i.e., beam: OFF). Thus, the electron beam can be cut off. In this state, the electron beam is further deflected to a position C of the circle 15A (deflection in the direction opposite to the rotational direction of the substrate 15) (step S14). The position C is at a distance of DY/2 from the position B in the +Y direction. When the electron beam reaches the position C in the circle 15A, the electron beam is deflected in an opposite direction (the rotational direction and the tangential direction of the substrate 15, that is, −Y direction in the drawing). The electron beam is also deflected in the radial direction (that is, +X direction in the drawing), so as to switch and shift the electron beam to a position D of the circle 15B (step S15). Then, in response to the Y deflection signal with the ramp waveform, the electron beam is deflected from the position D in the direction opposite to the rotational direction and the tangential direction (+Y direction in the drawing) (step S16). When the electron beam reaches a position E (that is, a position 15Y) of the circle 15B, the blanking electrodes 23 cancel the blanking (i.e., beam: ON) (step S17), so that the electron beam EB comes to pass through the aperture 24. The position D is at a distance of DY/2 from the position E in the −Y direction. Thus, drawing (exposure) starts again from the position E. Accordingly, the electron beam is in a blanked state (beam: OFF) during a period from the position B to the position C of the circle 15A, a period of carrying out X deflection and Y deflection from the position C of the circle 15A to the position D of the circle 15B, and a period from the position D to the position E of the circle 15B, and hence drawing (exposure) is not carried out. In this embodiment, the position B and the position E are the drawing start points of the respective circles, and also the drawing connection points. The position B and the position E are on a line in the same radial direction being the reference of drawing (hereinafter, also referred to as reference radial line). The positions Band E are reference positions of the concentric circles 15A and 15B, respectively. The reference radial line, for example, may be set so that the drawing connection point of each circle is in the reference radial line. Otherwise, as described later, the reference radial line may be set so as to be the center position of overwriting, when the overwriting is carried out. The reference radial line is not limited to these, but can be set appropriately. From the position E to a position F of the circle 15B, drawing is carried out by deflecting the electron beam in the +Y direction in response to the Y deflection signal with the ramp waveform (step S18). In other words, the deflection by the Y deflection signal with the ramp waveform is ended in the position F, and the drawing of the circle 15B continues. Repeating the foregoing operation makes it possible to draw the concentric patterns. A condition that the start point of a drawn line of the circle coincides with the end point is V=DY/Tb (1−Tb/Ty), wherein V represents movement velocity of the substrate, DY represents the amount of deflection by the Y deflection signal between the position C and the position D, Ty represents time period between the position A to the position F, and Tb represents blanking time. According to the present invention, as described above, when drawing transition is performed from one circle to another circle, the electron beam is deflected not only in the rotational radial direction but also in the tangential direction opposite to the rotational (moving) direction of the substrate. Also in a drawing connection section of the circle, the electron beam is deflected to the rotational tangential direction. Thus, it is possible to draw the circle (track) in such a manner that the start point precisely connects to the end point. Even if there is rotational fluctuation in a rotational stage, it is possible to connect the circle with high precision. A second embodiment of the present invention will be hereinafter described with reference to the drawings. FIG. 8 is a schematic plan view which illustrates the deflection control when drawing transition is performed from the circle 15A to the circle 15B, and the neighborhood of drawing connection points (start points and end points) is enlarged. FIG. 9 is a time chart corresponding to FIG. 8 which shows the blanking control signal and the deflection control signals in the X and Y directions. As in the case of the foregoing first embodiment, the electron beam starts being deflected in a position A near a reference position RA of the circle 15A in the tangential direction (+Y direction in the drawing) opposite to the rotational (moving) direction of the substrate 15, in response to the Y deflection signal having the ramp waveform. In this embodiment, after deflection in the +Y direction starts, deflection velocity is increased from a position B (for example, the reference position RA), and the electron beam is cut off (beam: OFF) by blanking in a position C passing the reference position RA in response to the blanking signal. Then, after moving to a position D with deflecting, the electron beam is deflected in an opposite direction (−Y direction in the drawing) and in the direction of the next circle (track) 15B (+X direction in the drawing), so that the electron beam is shifted to a position E of the circle 15B at high speed. Then, in response to the Y deflection signal having the ramp waveform, the electron beam is deflected in the tangential direction (+Y direction in the drawing) until reaching a position F. The position F is set before a reference position RB in a reference radial line in the circle 15B. The blanking is canceled in the position F to apply the electron beam EB to the substrate 15 (beam: ON). The deflection velocity is reduced in a position G (for example, the position RB in the reference radial line) of the circle 15B, and then deflection by the Y deflection signal with the ramp waveform is ended in a position H. Repeating the foregoing operation makes it possible to draw the concentric patterns. In the first embodiment, the drawing start point and the drawing end point are set at reference positions, and blanking control is carried out in such a manner that overwriting does not occur. When repeating the foregoing procedure draws the concentric circles, however, an overwritten portion occurs. In other words, taking the circle 15B as an example, when a circle 15C is drawn following the circle 15B in a similar manner, a section from the position F of the circle 15B to a drawing end position C′ of the circle 15B (a position corresponding to the position C in the circle 15B) becomes the overwritten portion (WO). Namely, the deflection and the blanking control are carried out in such a manner that the overwritten portion (WO) occurs in the vicinity of the reference positions (RA and RB) of the circles 15A and 15B. Therefore, it is possible to draw the circle which precisely connects at the start point and the end point. Also, even if there is rotational fluctuation in the rotational stage, it is possible to connect the circle with high precision. A third embodiment of the present invention will be hereinafter described with reference to drawings. FIG. 10 is a schematic plan view which illustrates the deflection control when drawing transition is performed from the circle 15A to the circle 15B, and the vicinity of drawing connection points is enlarged. FIG. 11 is a time chart corresponding to FIG. 10 which shows the blanking control signal and the deflection control signals in the X and Y directions. Deflection starts from a position A of the circle 15A in response to the Y deflection signal, and blanking voltage is applied at the predetermined rate of increase from a position B of the circle 15A. In other words, applying the blanking voltage in a ramp form makes it possible to adjust the intensity of the electron beam applied to the substrate. The blanking voltage is rapidly increased in a position C passing a reference position, and the electron beam is completely cut off by blanking (beam: OFF). Namely, the intensity of the electron beam is gradually reduced from the position B to the position C, and completely becomes zero in the position C. Then, after moving to a position D, the electron beam is deflected in the −Y direction and also in the +X direction, so that the electron beam is shifted to a position E of the circle 15B at high speed. In a position F before reaching a reference position RB of the circle 15B, the blanking voltage is abruptly reduced to a predetermined level in order to apply the electron beam the intensity of which is lower than that in a complete ON state. Then, the blanking voltage is reduced at the predetermined rate of reduction, and the electron beam completely becomes the ON state in a position G (corresponding to the position C of the circle 15A) passing the reference position. After that, deflection by the Y deflection signal with the ramp waveform is ended in a position H. Repeating the foregoing operation makes it possible to draw a plurality of concentric circles. Therefore, it is possible to draw the circle in which the start point precisely connects to the end point. In addition, even if there is rotational fluctuation in the rotational stage, it is possible to connect the circle with high precision. When repeating the foregoing procedure draws the concentric circles, an overwritten portion occurs. In other words, the deflection and the blanking control are carried out in such a manner that the overwritten portion (WO) occurs in the vicinity of the reference positions RA and RB in the circles 15A and 15B. The application intensity of the electron beam may be varied at a predetermined rate at least one of before and after the duration of deflecting the electron beam in the radial direction. A fourth embodiment of the present invention will be hereinafter described with reference to drawings. FIG. 12 is a schematic plan view which illustrates the deflection control when drawing transition is performed from the circle 15A to the circle 15B, and the vicinity of drawing connection points is enlarged. FIG. 13 is a time chart corresponding to FIG. 12 which shows the blanking control signal and the deflection control signals in the X and Y directions. A point of difference between a drawing method according to the foregoing first embodiment and that according to this embodiment is that a sine waveform signal is overlapped with the ramp waveform signal in the deflection control signal in the Y direction. This drawing method is the same as that of the first embodiment for the rest. To be more specific, responding to the Y deflection signal having the sine waveform, the electron beam is deflected in the tangential direction (±Y direction in the drawing) in the period between a position A and a position C. The electron beam is deflected in the tangential direction (−Y direction in the drawing) and also in the radial direction (+X direction in the drawing) from the position C, so that the electron beam is shifted to a position D at high speed. Then, the electron beam is deflected in the tangential direction (±Y direction in the drawing) in the period between the position D and a position F in response to the Y deflection signal with the sine waveform. As in the case of the first embodiment, the electron beam is cut off (beam: OFF) by blanking in the period between the position B and a position E being drawing connection points. A cutoff period of the electron beam, however, may be set so as to carry out overwriting. As described above in detail, according to the present invention, when drawing transition is performed from one circle to another, the electron beam is deflected not only the rotational radial direction but also the rotational tangential direction of the rotation (movement) of the substrate. Also in the drawing connection section of the circle, the electron beam is deflected in the rotational tangential direction opposite to the rotational direction of the substrate. Therefore, it is possible to draw the circle (track) which precisely connects at the start point and the end point. Even if there is rotational fluctuation in the rotational stage, the circle can be connected with high precision. In the foregoing embodiments, lithography (exposure) of the concentric circles is performed by using the electron beam. The present invention, however, is applicable in the case of using another beam such as an optical beam and the like instead of the electron beam.

summary

description

FIG. 1 is a schematic diagram of the basic components of a power generating system 8. The system includes a boiling water nuclear reactor 10 which contains a reactor core 12. Water 14 is boiled using the thermal power of reactor core 12, passing through a water-steam phase 16 to become steam 18. Steam 18 flows through piping in a steam flow path 20 to a turbine flow control valve 22 which controls the amount of steam 18 entering steam turbine 24. Steam 18 is used to drive turbine 24 which in turn drives electric generator 26 creating electric power. Steam 18 flows to a condenser 28 where it is converted back to water 14. Water 14 is pumped by feedwater pump 30 through piping in a feedwater path 32 back to reactor 10. FIG. 2 is a flow chart of a method 40 for expanding the operating domain of boiling water nuclear reactor 10. In one aspect, method 40 is applicable to boiling water nuclear reactor plants which can operate at higher than the original rated thermal power, where the fuel cycle performance at the higher load line is advantageous and plant performance at the higher power output is justified by appropriate safety analysis. In another aspect, method 40 provides the design concept and the analytical justification to operate boiling water nuclear reactor 10 in a significantly expanded region of the power/flow map. Computerized method 40, in an exemplary embodiment, is web enabled and is run on a business entity""s intranet. In a further exemplary embodiment, computerized method 40 is fully accessed by individuals having authorized access outside the firewall of the business entity through the Internet. In another exemplary embodiment, computerized method 40 is run in a Windows NT environment or simply on a stand alone computer system having a CPU, memory, and user interfaces. In yet another exemplary embodiment, computerized method 40 is practiced by simply utilizing spreadsheet software. Method 40 includes the steps of determining 42 by computer simulation a load line characteristic that is elevated over normal operating parameters and that increases reactor performance over normal operating parameters, performing 44 safety evaluations by computer simulation at the elevated load line to determine compliance with safety design parameters, and performing 46 operational evaluations by computer simulation at the elevated load line. Method 40 also includes the step of computing 48 a set of operating conditions for the reactor in an upper operating domain characterized by the elevated load line. Based on the results of the operational evaluations of step 46, constraints and requirements are generated 50 for plant equipment and procedures. Also, a detailed analysis by computer simulation is performed 51 of the core recirculation system. The optimum applicable range of the expanded region of operation is established. Also, output is generated 52 to facilitate automatic adjustment of the control rod pattern, the flow controls, and the pressure controls based on the detection of a reactor transient. Additionally, method 40 includes generating 54 output to facilitate the modification of the reactor process controls and computers to permit reactor operation in the upper operating domain. To determine the desired elevated load line characteristic, evaluations at elevated core thermal power are performed. The desired load line increase is based on the thermal power increase and the fuel cycle performance improvement that is obtained at the elevated core thermal power. Computer simulation of the reactor are used to define the operating conditions of the reactor in the new operating region characterized by the elevated load line. Evaluations of the expected performance of the reactor throughout the new operating region are also performed using computer simulation. Operational evaluations performed at the elevated load line include, but are not limited to, evaluating plant maneuvers, frequent plant transients, plant fuel operating margins, operator training and plant equipment response and setpoints. Based on the results of the operational evaluations, constraints and requirements are established for plant equipment and procedures. For example, evaluating core and fuel performance impact at increased power output includes determining anticipated transient without scram (ATWS) events for increased core thermal power output Some (ATWS) events include Main Steam Isolation Valve Closure (MSIVC); Pressure Regulator Failure-Open (PRFO); Loss of Offsite Power (LOOP); and Inadvertent Opening of a Relief Valve (IORV). The analysis takes into account ATWS mitigating features, such as, the recirculation pump trip (RPT), alternate rod insertion (ARI), and the Standby Liquid Control System (SLCS) performace. Plots of important parameters are created, and the peak values of neutron flux, average fuel heat flux and vessel pressure are calculated for each of the four events. Safety evaluations typically address the safety analysis Chapter 15 of the Final Safety Analysis Report (FSAR). Additionally, non-Chapter 15 safety issues such as containment integrity, stability and anticipated transient without scram (ATWS) are addressed. Safety analysis include demonstration of compatibility with the previous resolutions of reactor stability monitoring and mitigation of unplanned events. The safety evaluations are performed such that compliance to plant design criteria is demonstrated. Assurance of acceptable protection of the reactor and the public is performed and documented to satisfy regulatory authorities. Method 40 includes generating 56 output data to facilitate creating a safety analysis report to comply with regulatory requirements. For example, a review of the existing plant Safety Analysis Report and reload transients is conducted at the uprated conditions. Where necessary, analyses are performed to demonstrate compliance with the fuel thermal margin requirements and other applicable transient criteria. Of primary importance is an analysis of the transient events which are most limiting from the viewpoint of fuel thermal margin. Analysis of these most limiting events for uprated power at the most limiting conditions on the operating power/flow map will assure that fuel operating limits are met. A safety analysis includes a broad set of transient events that include:(1)Decrease in Core Coolant Temperature.(2)Increase in Reactor Pressure.(3)Decrease in Reactor Core Coolant Flow Rate.(4)Increase in Core Flow Rate.(5)Increase in Reactor Coolant Inventory.(6)Decrease in Reactor Coolant Inventory.(7)Increase in Reactivity.(8)Increase in Core Coolant Temperature. Evaluations are performed to show continued compliance with the nuclear regulatory agency rule on anticipated transient without scram performance (ATWS). ATWS rule compliance primarily involves alternate shutdown equipment which has been previously installed at each unit. The equipment remains and its performance at any changed conditions (due to uprate) is evaluated, for example at higher operating pressure. Where applicable, a bounding case is reanalyzed at the uprated power to confirm that adequate overpressure protection and suppression pool cooling are maintained for limiting cases in each BWR product line. This analysis also includes evaluation of any changes in pressure setpoints of the safety/relief valves and/or high pressure recirculation pump trip. In some cases these setpoints, as well as the allowable number of relief valves out of service may be re-optimized to improve the ATWS response. Power uprate operation does not significantly affect the long-term ATWS response because it does not involve a uniquely higher rod line, and, therefore, there is no increase in the power level following the ATWS recirculation pump trip. Radiological consequences are evaluated or analyzed for uprated power conditions. This evaluation/analysis is based on the methodology, assumptions, and analytical techniques described in previous Safety Evaluations (SEs). The evaluation of radiological consequences includes the effect of a higher power level. In general, the radiation sources inside the fuel rods, creation of activation products outside of the fuel rods, and concentration of coolant activation activities are directly proportional to the thermal power. Therefore, the original radiation inventories, expressed in terms of curies per megawatt of thermal power, will bound the uprated condition, provided that the core design, fuel loading, and mean exposure are not changed significantly. If significant changes to the fuel loading or design parameters are made to optimize for uprated conditions, the uprate license application will re-perform the radiological evaluation to account for changes to the isotopic concentrations in the fuel. Issues relating to burnup and enrichment also need to be addressed if the uprated burnup and enrichment are to exceed any regulated conditions. During normal operation, the radiation levels in the plant are the result of radiation streaming from the reactor vessel or from radioisotopes carried in the reactor water, steam, or radwaste process. In all cases, these quantities are approximately proportional to core thermal power. Increases in normal radiological releases from routine operation are considered in the power uprate amendment requests. The magnitude of the potential radiological consequences of a design basis accident (DBA) is proportional to the quantity of fission products released to the environment. This quantity is a product of the activity released from the core and the transport mechanisms between the core and the effluent release point. For a steam line break or instrument line break accident, the radiological consequences will be, at most, proportional to the increase in power, since (1) the quantity of activity in the primary coolant and in the offgas is unaffected by power uprate (it is limited by Technical Specifications), and (2) the increase in coolant mass discharged to the environment is dependent on reactor pressure, which increases less than the power increase. For the remaining DBAs, the radiological releases are expected to increase, at most, by the amount of power uprate, since the only parameter of importance is the actual inventory of radioisotopes in the fuel rod and the mechanism of fuel failure is not likely to be influenced by power uprate. In some cases, the magnitude of the uprate may be limited, to maintain the radiological consequences below regulatory guidelines. To maximize the ability of the boiling water reactor unit to avoid trip during transients that may occur while operating in the extended region, automatic adjustment of some controls is provided. For example automatic adjustment of the control rod pattern, flow controls and pressure controls based on sensing the initiation of a transient, such as a pump trip, are provided. These automatic controls improve plant availability, even in the previous range of reactor operation. An operating domain 58 of reactor 10 is characterized by a map of the reactor thermal power and core flow as illustrated in FIG. 3. Typically, reactors are licensed to operate below a flow control/rod line 60 characterized by an operating point 62 defined by 100 percent of the original rated thermal power and 100 percent of rated core flow. In some circumstances, reactors are licensed to operate with a larger domain, but are restricted to operation below a flow control/rod line 64 characterized by an operating point 66 defined by 100 percent of the original rated thermal power and 75 percent of rated core flow. Some reactors have been licensed to operate at higher power as illustrated by lines 67 in FIG. 3. However, these reactors are constrained by flow control/rod boundary line 64. In an exemplary embodiment of the present invention, method 40 expands operating domain 58 of reactor 10 and permits operation of reactor 10 between about 120 percent of original rated thermal power and about 85 percent of rated core flow to about 100 percent of original rated thermal power and about 55 percent of rated core flow. Lines 68, 70 and 72 represents this new upper boundary of an upper operating region 74 of operating domain 58 of reactor 10. FIG. 4 shows another exemplary embodiment of the present invention where method 40 expands operating domain 58 of reactor 10 to an upper boundary represented by the operation of reactor 10 between about 120 percent of original rated thermal power and about 85 percent of rated core flow to about 60 percent of original rated thermal power and about 60 percent of rated core flow. Lines 70, 76 and 78 represents this new upper boundary of an expanded upper operating region 80 of operating domain 58 of reactor 10. Method 40 provides analyzed limits that permit licensed power operation of reactor 10 at a core flow lower than the constraint on core flow imposed by boundary 64. The increased boundary line 68 permits operation of reactor 10 over a larger core flow range and operating flexibility during startup and at full power. Method 40 further provides savings in fuel cycle costs and faster plant startups due to the increased ability to establish desired full power control rod pattern at partial power conditions. Also provided is reduced cycle average recirculation pumping power consumption resulting in an increase in net station output. Another embodiment of the invention includes providing analyses and evaluations to generate a safety analysis report as describe above. Additionally, licensing support is provided to the owner, or managing entity, of the boiling water nuclear reactor, along with technical consultation during the implementation of reactor analyses and modifications described above. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.

048287903

abstract

A nuclear power plant wherein surfaces of components contacting with nuclear reactor cooling water containing radioactive substances are coated with an oxide film, preferably being charged positively and/or containing chromium in an amount of 12% by weight or more, is prevented effectively from the deposition of radioactive substances thereon.

abstract

A joint structure between a top nozzle and a guide thimble of a nuclear fuel assembly and, more particularly, a structure for joining an inner-extension tube, the top nozzle and the guide thimble. When an inner-extension tube head, which is provided as a means for facilitating removal of the top nozzle of the nuclear fuel assembly from the guide thimble, is removed from an inner-extension tube body to separate the top nozzle from the nuclear fuel assembly, the inner-extension tube body is prevented from undesirably rotating, so that the guide thimble and the inner-extension tube body can maintain the joined state.

description

This application is a National Phase filing under 35 U.S.C. §371 of PCT/FR2006/002711filed Dec. 12, 2006, which claims priority to Patent Application No. 05 12853, filed in France on Dec. 16, 2005. The entire contents of each of the above-applications are incorporated herein by reference. The invention relates generally to heating rods for a pressurizer of a primary cooling system of a pressurized-water nuclear reactor. More precisely, the invention relates, according to a first aspect, to a heating rod for a pressurizer of a primary cooling system of a pressurized-water nuclear reactor, of the type comprising a metal outer shell of longitudinally elongate shape having an external surface, and a heating element mounted inside the shell. Such rods are normally mounted in the lower part of the pressurizer and are immersed in the water of the primary cooling system with which the pressurizer is partially filled. The rods are set into operation when it is desired to increase the operating pressure of the primary cooling system of the reactor. They heat the water to its boiling point so that part thereof evaporates. Leaks have been found to occur on the heating rods of the prior art. The outer shell of one of the rods sometimes cracks, so that the inside of the rod communicates with the water inside the pressurizer. Such a leak can result in damage to the heating element of the rod, the loss of operation of the rod, and even the leakage of pressurized water to the outside of the pressurizer, through the interior space of the rod. Within this context, the invention aims to propose heating rods having improved reliability. To that end, the invention relates to a heating rod of the type described above, characterized in that it comprises an anti-corrosion coating which covers at least part of the external surface of the shell. The rod can also have one or more of the following characteristics, considered individually or according to all technically possible combinations: the coating predominantly comprises nickel; the coating comprises at least 95% by weight nickel; the coating has been deposited on the external surface by electrolysis in a bath of nickel salts; the coating has a thickness greater than 50 micrometers; the rod comprises an active heating zone, the coating extending longitudinally at least along the whole of the active heating zone; the coating continues longitudinally on each side of the active heating zone over a guard distance; the guard distance is greater than 10 millimeters; and the shell is made of austenitic stainless steel. According to a second aspect, the invention relates to a method of treating a metal shell for a heating rod of the above type, characterized in that it comprises a step of depositing the coating on at least part of the external surface of the shell in an electrolytic cell comprising a bath and an electrode immersed in the bath, the bath predominantly comprising nickel sulfamate, nickel chloride and boric acid, the shell being disposed in the bath and an electric current being maintained between the electrode and the shell. The method can also have one or more of the following characteristics, considered individually or according to all technically possible combinations: the pH of the bath is maintained between 3 and 5 during the deposition step; the electrode is made of soluble nickel; the electric current is maintained at a current density between 5 and 50 amperes per square decimeter of the external surface of the shell that is to be treated during the deposition step; the step of depositing the coating is preceded by a preliminary step of depositing an adhesion layer on at least part of the external surface of the shell in an electrolytic cell comprising a bath and an electrode immersed in the bath, the bath being a Watts bath predominantly comprising nickel sulfate, nickel chloride and boric acid, the shell being disposed in the bath and an electric current being maintained between the electrode and the shell; the pH of the bath is maintained between 3 and 5 during the preliminary step; and the adhesion layer has a thickness less than 10 micrometers. FIG. 1 shows a primary cooling system 1 of a pressurized-water nuclear reactor. The system 1 comprises a vessel 2 in which there are located nuclear fuel assemblies, a steam generator 4 having primary and secondary parts, a primary pump 6 and a pressurizer 8. The vessel 2, the steam generator 4 and the pump 6 are connected by sections of primary piping 10. The system 1 contains primary water, the water being pumped by the pump 6 towards the vessel 2, passing through the vessel 2 while being heated in contact with the fuel assemblies, and then passing through the primary part of the steam generator 4 before returning to the inlet side of the pump 6. The primary water heated in the vessel 2 gives up its heat in the steam generator 4 to secondary water which passes through the secondary part of the generator. The secondary water circulates in a closed loop in a secondary cooling system (not shown). It evaporates as it passes through the generator 4, the steam so produced driving a steam turbine. The pressurizer 8 is mounted as a branch on the primary piping by way of a conduit 18 branched on the section 10 connecting the vessel 2 to the generator 4. It is disposed at a higher elevation than the pump 6 and the vessel 2. The pressurizer 8 comprises a substantially cylindrical fabricated shell 11 which has a vertical axis and is provided with a dome 12 and a bottom 14. The bottom 14 comprises a central orifice 16 (FIG. 2) which is connected to the primary piping by the conduit 18. The pressurizer 8 also comprises spraying means 19 having a branch connection 20 which passes through the dome 12, a spray nozzle 21 disposed inside the shell 11 and mounted on the branch connection 20, a pipe 22 connecting the branch connection 20 to the primary piping, in the region of the outlet side of the pump 6, and means (not shown) for selectively allowing or preventing the flow of primary water in the pipe 22 to the nozzle 21. The primary cooling system 1 also comprises a safety circuit 23 comprising an overflow tank 24, a pipe 25 connecting the tank 24 to the dome 12 of the pressurizer, and a safety valve 26 interposed on the pipe 25 between the tank 24 and the pressurizer 8. The interior space of the pressurizer 8 communicates with the primary cooling system 1 so that the pressurizer 8 is permanently partially filled with primary water, the level of water inside the pressurizer being dependent on the current operating pressure of the primary cooling system. The top of the pressurizer 8 is filled with steam at a pressure substantially equal to the pressure of the water circulating in the primary piping 10 connecting the generator 4. In case of excess pressure in the pressurizer, the valve 26 opens and the steam is evacuated to the tank 24, in which it condenses. The pressurizer 8 is equipped with several tens of electric heating rods 28. The rods are disposed vertically and are mounted on the bottom 14. They pass through the bottom 14 by way of orifices provided for that purpose, sealing means being interposed between the rods and the bottom 14. The rods 28 have a great length, typically from 1 m to 2.50 m, and a small cross-section in relation to their length. Each rod 28 comprises a portion 30 (FIG. 2) that is disposed inside the shell 11 of the pressurizer and is immersed in the water with which the pressurizer is partially filled, an intermediate portion 32 that is mounted in an orifice in the base 14, and a connection portion 34 that is disposed outside the shell 11. As is shown in FIG. 4, the immersed portion 30 comprises an outer shell 36 of cylindrical shape which is made of stainless steel or alloy, generally a central mandrel 38 disposed inside the shell 36 according to the central axis thereof, and a heating wire 40 which is wound around the mandrel 38 in a spiral and is interposed between the mandrel 38 and the shell 36. The heating wire 40 comprises an electrically conductive resistive metal core 42, for example made of copper or of nickel-chromium alloy, and a metal sheath made of steel 44 which surrounds the core 42 and is insulated electrically by magnesium oxide. It is in contact with an internal face of the shell 36. The wire 40 is disposed so as to create, in the immersed portion 30, a central longitudinal heating zone 46 (FIG. 2) and two longitudinal non-heating zones 48 disposed on each side of the heating zone 46. In the heating zone 46, the mandrel 38 is made of copper and the wire 40 is wound around the mandrel 38 to form contiguous turns. The wire 40 extends along the intermediate portion 32, on the inside thereof, and is connected to an electrical connector 49 situated in the portion 34. The connector 49 is electrically connected to an electric generator (not shown), which is capable of causing an electric current to flow in the wire 40. The immersed portion 30 has a longitudinal length of 2150 mm, for example. The heating zone 46 has a longitudinal length of 1100 mm, for example. The non-heating zone 48 interposed between the zone 46 and the intermediate portion 32 has a longitudinal length of 450 mm, for example. The non-heating zone 48 situated on the other side of the heating zone 46 has a longitudinal length of approximately 550 mm. The diameter of the outer shell 36 is constant along the whole of the portion 30 and is, for example, 22 mm. The portions 32 and 34 have a longitudinal length of 340 mm, for example, in total. The electrical power of each rod 28 varies from 6 to 30 kW. It delivers a heat flow which varies between 20 and 50 W/cm2, considered in the region of the external surface of the shell 36. The pressurizer 8 further comprises guide plates 50 for holding the rods 28, shown in FIG. 2. The guide plates 50 extend substantially horizontally over the whole of the internal section of the pressurizer 8. They are disposed one above the other, at different vertical levels in the pressurizer 8. Each guide plate comprises slots 52 permitting the flow of water through the plates 50, and holes 54 for guiding the rods 28. The holes 54 are circular and have a diameter slightly greater than the outside diameter of the immersed portion 30 of the rods (FIG. 3). The portion 30 passes through the various plates 50 through superposed holes 54, so that the rods 28 are guided at several levels and are maintained in a substantially vertical orientation by the plates 50. The outer shell 36 of the rod is not normally in contact with the edges of the holes 54. The function of the pressurizer 8 is to control the pressure of the water in the primary cooling system. Because it communicates with the primary piping by way of the pipe 18, it acts as an expansion vessel. Thus, when the volume of water circulating in the primary cooling system increases or decreases, the level of water inside the pressurizer 8 will rise or fall accordingly. That variation in the volume of water can be the result, for example, of an injection of water into the primary cooling system or of a variation in the operating temperature of the primary cooling system. The pressurizer 8 also serves to increase or decrease the operating pressure of the primary cooling system. In order to increase the operating pressure of the primary cooling system, the heating rods 28 are supplied with power so that they heat the water contained in the lower part of the pressurizer and bring it to its boiling point. Some of the water boils, so that the pressure in the top of the pressurizer 8 increases. Because the steam is constantly in hydrostatic equilibrium with the water circulating in the primary cooling system 1, the operating pressure of the primary cooling system 1 increases. In order to lower the operating pressure of the primary cooling system 1, the spraying nozzle 21 disposed in the top of the pressurizer 8 is set into operation by allowing the flow of water in the pipe 22 with the aid of the means provided for that purpose. The water withdrawn in the primary piping 10 on the outlet side of the pump 6 is discharged into the top of the pressurizer 8 and causes some of the steam therein to condense. The pressure of the steam in the top of the pressurizer 8 falls, so that the operating pressure of the primary cooling system 1 also decreases. As is shown in FIG. 4, the heating rods 28 each comprise an anti-corrosion coating 60 which covers at least part of the external surface 62 of the shell 36. The coating 60 extends longitudinally over the whole of the heating zone 46 of the rod, and it also extends longitudinally on each side of the zone 46 over a guard distance. The guard distance is greater than 10 mm, preferably greater than 30 mm, and is typically of the order of from 50 mm to 100 mm. The coating 60 extends over the whole of the periphery of the outer shell 36, so that it covers the shell 36 completely in the heating zone 46 and in part of the zones 48, over the guard distance. The coating 60 predominantly comprises nickel, and it preferably comprises at least 95% by weight nickel. In a preferred embodiment, the coating is a coating of pure or virtually pure nickel which is deposited electrolytically, as explained hereinbelow. The coating 60 has a thickness greater than 50 μm and less than 200 μm. Preferably, it has a thickness of approximately 100 μm. The method of depositing the coating 60 on the surface 62 of the outer shell will now be described. The main steps of the method are carried out in an electrolytic cell of the type shown in FIG. 5. The cell 64 comprises a vessel 66, which can contain a treatment bath and is provided with an inlet 68 and an outlet 70, a pump 72 for circulating the liquid that forms the bath from the outlet 70 to the inlet 68 of the vessel, an electrode 74 immersed in the bath, and an electric generator 76. The electrode 74 is made of soluble nickel. The electric generator 76 can be connected electrically on the one hand to the electrode 74 and on the other hand to the rod 28 that is to be treated. It is suitable for maintaining a potential difference between the electrode 74 and the rod 28 that is to be treated. The treatment method comprises the following successive steps. Step 1—Provision of a heating rod 28 to be treated. The rod is equipped with all its internal equipment (core 38, heating wire 40). Step 2—Degreasing of the external surface 62 of the shell 36. Step 3—Pickling of the surface to be coated using sulfuric acid. Step 4—Reversed polarity strike in order to dissolve the surface layer of the surface to be coated. This step can be carried out in the cell 64. In that case, the cell 64 is filled with a suitable solution, the immersed portion 30 of the rod being immersed in the solution, and the electric generator 76 being mounted so as to maintain the shell 36 at a positive potential and the electrode 74 at a negative potential. At the end of this step, the original surface layer of the shell 36 has been dissolved and has been replaced by a new surface covered with a freshly formed passive film. Step 5—Normal polarity strike, so as to depassivate the surface to be coated. This step can be carried out in the electrolytic cell 64. In that case, the cell 64 is filled with a suitable electrolyte bath, the portion 30 of the rod being immersed in the bath, as above. The generator 76 is this time mounted so as to maintain the shell 36 at a negative potential and the electrode 74 at a positive potential. This step allows the passive film formed in the preceding step 4 to be removed and the metal of the shell 36 to be exposed in order to permit better adhesion of the coating 60. Step 6—Deposition of an adhesion layer. The adhesion layer forms part of the coating 60 and comprises virtually no nickel. It has a thickness less than 10 μm, preferably of 2 μm. During this step, the vessel 66 is filled with a highly acidic Watts bath, which is composed principally of nickel sulfate, nickel chloride and boric acid. The pH of the solution is maintained between 3 and 5. The electric generator 76 maintains the electrode 74 at a positive potential and the shell 36 at a negative potential. The pump 72 serves to recirculate the bath continuously during step 6, a flow of liquid being withdrawn from the vessel 66 through the outlet 70 and reinjected through the inlet 68. Step 7—Deposition of the actual coating 60, the adhesion layer also forming part of the coating 60. The deposition is carried out in the cell 64. The vessel 66 is filled with a sulfamate bath substantially comprising nickel sulfamate, nickel chloride and boric acid. The pH of the bath is maintained between 3 and 5 during this step, preferably at approximately 4.5. The electric generator 76 maintains the electrode 74 at a positive potential and the shell 36 at a negative potential. An electric current is thus maintained between the electrode 74 and the shell 36 of the rod, the current density being from 5 to 50 amperes/dm2 of the external surface of the shell to be treated. Preferably, the current density is of the order of 20 amperes/dm2. The nickel layer deposited during step 7 has a thickness of the order of 100 μm. During steps 3 to 7, the parts of the external surface 62 of the rod that are not to receive the coating are protected by a suitable protective layer, for example an organic varnish. The heating rods and the treatment method described hereinbefore have numerous advantages. The coating 60 that covers part of the external surface of the shell 36 allows the rods to be protected against corrosion and the operating performance of the rods to be improved. The inventors have in fact found that, under certain operating conditions, a caustic medium develops between the heating zone 46 of the rod and the guide plates 50, and more precisely between the zone 46 and the edges of the holes 54. That gap constitutes a confined space in which the water does not circulate much and is replaced slowly, so that overheating with boiling can occur in that space, causing the creation of a caustic medium. The coating 60 makes it possible to prevent stress corrosion of the shell 36 from developing, in particular in the region of the plates 50, which can cause the shell 36 to crack and the inside of the rod 28 to communicate with the primary water. The reliability of the rods 28 is thus improved. The electrolytic nickel coating chosen in the above-mentioned example for partially covering the shells of the rods is particularly suitable because: it is compatible with the stainless steel constituting the shells 36 of the heating rods; it is permitted in the primary cooling system owing to its high purity; it is resistant to corrosion under the characteristic operating conditions of the pressurizer (chemical composition of the primary water, temperature, pressure); and it is resistant to stress corrosion in the nominal primary medium. The use of an electrode 74 made of soluble nickel in the cell 64 used to deposit the coating 60 is particularly suitable because it allows the composition of the bath to be kept virtually constant during phases 6 and 7 and consequently ensures that the nickel quality is constant and reproducible throughout the nickel-coating operation. In addition, all the steps of the method are carried out at temperatures far below the melting point of copper, typically 60° C. There is therefore no risk of damage to the electrical part of the rod (copper wire) during the operation of depositing the nickel, and therefore no risk of causing electrical failures as a result. The coating 60 is resistant to corrosion, including in a situation of thermal testing of the primary cooling system of the reactor or in a cycle extension situation, it being possible for a basic medium to develop in the pressurizer in both those situations. A cycle extension situation corresponds to prolonged use of the nuclear reactor between two cold shutdowns for the unloading of some fuel assemblies. The geometry of the heating rods is virtually unchanged compared with the prior art. In order to obtain exactly the same outside diameter for the immersed portion 30, it is possible to remove a layer of approximately 100 μm from the outer shell by grinding, before the electrolytic coating is deposited. The heating rods 28 and the treatment method described hereinbefore can have numerous variants. The coating 60 can cover the whole of the immersed portion 30, not only the zone 46 but also the zones 48 disposed on each side of the zone 46. It is possible to use a material other than nickel for the coating 60. That material can be, for example, chromium, or a more noble material than nickel, such as platinum or gold. The rod 28 can comprise an internal part that is different from that described hereinbefore (mandrel 38, heating wire 40). The outer shell 36 of the rod 28 can be made not of austenitic stainless steel but of Inconel 690, for example. The heating rods can have dimensions other than those mentioned hereinbefore (total length of the portion 30, outside diameter, length of the heating zone 46, of the non-heating zones 48, etc.).

description

The field of the invention relates generally to power plants, and more particularly, to systems and methods of modeling power plants. Generally, known power plants include a number of major components. For example, known plants may include a gas turbine, a heat recovery steam generator, a steam turbine, and/or a condenser/cooling tower. To assess the performance of a power plant, the performance of each of the major components must be analyzed. For example, often power plants are assessed using modeling techniques. However, because the configuration and orientation of the major components used within a plant can vary from power plant to power plant, custom models for each power plant must be developed that take into account the specific configurations of the major components at each of the specific power plants being analyzed. As a result, developing plant specific models may be expensive and/or time-consuming. To facilitate reducing costs as well as to provide a universal system, some known modeling systems have attempted to embed alternative configurations of some major components in a single model. However, such systems generally include a very complex model that often increases the time to solve the model, i.e., long convergence times. In one embodiment, a system for use in determining the overall performance of a power plant including a plurality of components includes a processor configured to generate a first reference model of the power plant and generate a first test matched measured model of the power plant. The processor is further configured to determine the performance impact of the at least one of the plurality of components of the power plant on the overall thermal performance of the power plant at design conditions. In another embodiment, a computer-readable media includes program instructions which when executed by a processor cause the processor to perform the steps of generating a first reference model of the power plant using original specification data of the power plant and generating a first measured model of the power plant from measured performance data of at least one of a plurality of components of the power plant. The computer-readable media also includes program instructions for determining the performance impact of the at least one of the plurality of components on the overall thermal performance of the power plant by substituting design performance data of the at least one of the plurality of components in the first reference model with its measured performance data, transforming the performance impact of the at least one of the plurality of components into a normalized performance impact using the original specification data, and outputting at least one of the normalized plant performance impact and the performance impact. In yet another embodiment, a method of modeling a power plant includes generating a first measured thermal model, generating a first reference thermal model, and determining a performance impact of at least one of a plurality of major components on an amount of power plant power generation. The method also includes normalizing the performance impact of the at least one of the plurality of major components to a design basis and displaying the normalized performance impact. The following detailed description illustrates embodiments of the invention by way of example and not by way of limitation. It is contemplated that the invention has general application to analytical and methodical embodiments of determining efficiencies of major power plant components and sub-components in industrial, commercial, and residential applications. It is noted that, while the present application is described with reference to combined cycle power plants, one of ordinary skill in the art will appreciate that the systems and methods described herein are not limited to any particular type of power plant. As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. FIG. 1 is a schematic illustration of a combined cycle power plant 100 in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, power plant 100 includes a gas turbine engine 112 coupled in flow communication to a heat recovery steam generator (HRSG) 114 through an exhaust line 116. Exhaust gases exit gas turbine engine 112 and are directed to HRSG 114 through exhaust line 116. Steam generated by HRSG 114 is directed to a steam turbine 118 via steam lines 120 and 121. Steam turbine 118 exhausts spent steam to a condenser 122 where the steam is condensed into water that is channeled to feed pumps 123. Feed pumps return the water at high pressure to HRSG 114 to complete the steam cycle. Water circulating through tubes in condenser 122 is pumped from a basin of cooling tower 124 through condenser 122 and back to a tower of cooling tower 124 by circulating pumps 125 to complete the circulating water circuit. In the exemplary embodiment, combined cycle power plant 100 also includes an electrical generator 126 that is coupled via a shaft 128 to gas turbine engine 112. Gas turbine engine 112 includes a compressor section 130 that is coupled to a turbine section 131 through a shaft 132. A combustor section 134 is coupled in flow communication between compressor section 130 and turbine section 131. Exhaust gases discharged from turbine section 131 through exhaust line 116 are channeled through passages in HRSG 114 where heat energy in the exhaust gases is transferred to water flowing through HRSG 114 and the water is converted into steam. Exhaust gases are then discharged from HRSG 114 and released to the atmosphere or to a pollution control device (not shown), and steam produced in HRSG 114 is routed to steam turbine 118 through steam lines 120 and 121. An electrical generator 138 is coupled to steam turbine 118 through a shaft 140. Spent steam is routed to condenser 122 and cooling tower 124 through a steam line 142 or an exhaust hood (not shown), and steam condensate is returned to HRSG 114 wherein it is re-heated to steam in a continuous cycle. In the exemplary embodiment, power plant 100 is communicatively coupled to a data acquisition system (DAS) 150 for use in assessing the thermal performance of individual components of power plant 100, as described herein. In an alternative embodiment, DAS 150 comprises a computer that includes data acquisition hardware and executes data acquisition software. DAS 150 may be communicatively coupled to the power plant by any conventional wired or wireless link, thus enabling DAS 150 to be located within close proximity to power plant 100 and/or remotely therefrom. Thermal performance data of individual power plant components, such as components 112, 114, 118, 122, and 124, measured by DAS 150, are used as described in more detail below, to develop a thermal model that is substantially matched to performance test data of power plant 100. For example, measurements of compressor pressure, and/or combustion temperature, may be used to determine the thermal performance of gas turbine engine 112. Various sensors (not shown) may be located on or coupled to each power plant component for gathering data related to the respective power plant components and for forwarding the gathered data to DAS 150 for processing. Likewise, other criteria relevant to the determination of thermal performance of other components may be measured by DAS 150. FIG. 2 is a perspective view of a performance evaluation system (PES) 200 that may be used with combined cycle power plant 100 (shown in FIG. 1) in accordance with an exemplary embodiment of the present invention. PES 200 and its appropriate input/output ports 218, when provided with software configured to provide the functionality described herein, comprises a data acquisition system such as DAS 150. In the exemplary embodiment, PES 200 includes a processor 202 communicatively coupled to one or more memory devices 204 such as a random access memory (RAM), a read only memory (ROM), and one or more mass storage devices for reading and/or writing removable media such as a floppy disk drive, CD-ROM or CD-RW drive, or a DVD or DVD-RW drive such as a hard drive 206. In addition, PES 200 includes user interface devices, such as a display screen 212, a keyboard 214, and a mouse or other pointing device 215 (which may be built into the case of PES 200 rather than a separately attached device as shown in FIG. 2). Software included in some configurations of the present invention may be loaded, for example, from machine-readable media (examples of which are floppy disks, CD-ROMs, CD-RWs, DVDs, and the like) onto PES 200 using drive 206, or via a network interface or other type of data interface not shown in FIG. 1. In some configurations of the present invention, software is pre-loaded onto an internal storage device of PES 200, or may be loaded (or copied to internal storage) from a USB flash ROM storage device. In some configurations, a machine readable medium having instructions recorded thereon for acquiring data for thermal performance testing is supplied. The medium may comprise, for example, any of the removable and/or fixed storage media mentioned above, or other types of media. As used herein, the term “machine-readable medium” is intended to encompass configurations having a single medium or plural media, irrespective of whether the plural media are the same or different. As a non-limiting example, a “machine readable medium having instructions recorded therein for acquiring data for thermal performance testing” includes within its scope a configuration in which the instructions are spread across two floppy disks and a CD-ROM. In some configurations, PES 200 is a personal computer or a laptop computer, is portable and reconfigurable, so it can be moved and reconfigured to monitor different installations as needed. PES 200, via one or more input/output ports 218 (for example, serial, parallel, universal serial bus (USB), Ethernet, etc.) is configured to communicate with one or more data sources 232, 234, 236, and 238 at a system installation. In some configurations, a network bridge 220 or other interface unit is provided to facilitate communication via a plurality of channels 222. In the sample configuration illustrated in FIG. 1, channels 222 comprise interconnections 224, 226, 228, and 230. As described above, some configurations of the present invention communicate via between one and several hundred channels. However, the invention is not limited to any particular number of channels, and no specific limit should be construed either from FIG. 1 or any example configuration described herein. In various embodiments, PES 200 is configured to create a reference model and a measured model using a stored library of power plant components specifications. This library may be stored in memory device 204, hard drive 206, be accessed remotely, or stored in any other removable storage medium (not shown). A graphical user interface (GUI) 211 is displayed on screen 212 to permit a user to select individual components to be included in the thermal model. In some embodiments, GUI 211 is pre-populated with component names and dynamically links these names to the thermal model. In some embodiments, PES 200 is configured to act as a DAS while in others it is configured to operatively connect to a DAS, for instance, through either a wired connection 250 or a wireless connection 252. FIG. 3 is a flowchart of a method 300 of evaluating a thermal performance of a power plant in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, method 300 is used to determine the performance impact of individual power plant components, such as gas turbine engine 112, heat recovery steam generator (HRSG) 114, steam turbine 118, condenser 122, feed pumps 123, and cooling tower 124 (shown in FIG. 1) on the overall thermal performance of power plant 100. Method 300 includes generating 302 a first thermal model of a power plant based on original specification data of each of a plurality of individual components included in a power plant analysis. Method 300 includes generating 304 a second thermal model of the power plant using measured thermal performance data of at least some of the plurality of individual components. The performance impact of a selected power plant component on the overall thermal performance of the power plant is then determined 306 by substituting measured thermal performance data of the selected component in place of the original specification thermal performance data of the selected component. A determination 308 is then made as to whether or not the performance impact of all of the plurality of individual components included in a power plant analysis has been calculated. If not, the performance impact of a next selected power plant component on the overall thermal performance of the power plant is repeated until the performance impact of all the selected power plant components has been determined. If the performance impact of each of the power plant components has been determined 308, the performance impact of the plurality of individual components in the overall thermal performance of the power plant is displayed 310 or output for further processing. Additionally, sub-components of the plurality of individual components may be selected and included in the analysis of the performance impact on the overall thermal performance. FIG. 4 is a schematic of an exemplary thermal model 400 of a power plant such as power plant 100 (shown in FIG. 1) illustrating a comparison of thermal performance of various components and component parts of the power plant, with corresponding ideal thermal performance values. Thermal model 400 is based on and designed from measured thermal performance data of an operating power plant. For example, in power plant 100, steam turbine 118 includes a high pressure turbine (HPT) 401, an intermediate pressure turbine (IPT) 402, and a low pressure turbine (LPT) 403. In the example, the thermal performance of each of HPT 401, IPT 402, and LPT 403 is measured and compared against ideal thermal performance values associated with each component. For example, in the exemplary embodiment, the design thermal performance for HPT 401, IPT 402, and LPT 403 is represented by a horizontal line 410, and measured thermal performance indicated at 412 of HPT 401 is at about −1% as compared to its ideal thermal performance, identified at baseline 410. The measured thermal performance identified at 414 of IPT 402 is about +0.5% as compared to its corresponding ideal thermal performance indicated at baseline 410. Additional comparisons may be made for other components of power plant 100 for use in determining the operational efficiency of each component relative to its ideal performance values. For example, in the exemplary embodiment, the steam cycle output is re-calculated each time a new component is placed in service in the model to determine the individual component impact on plant performance. Finally, when all of the components have been implemented into the model, the impact of all of the components on the overall output of the plant are determined. More specifically, the impact of each component on the over plant output and heat rate are determined at measured boundary conditions. In one embodiment, the impact on output and heat rate are also determined at design conditions. In the exemplary embodiment, the data is graphically displayed for analysis. In other embodiments, the data may be displayed in other forms, and/or may be saved locally or remotely for later use. FIG. 5 is table 500 illustrating a performance model output as each selected component performance is incrementally included in the performance model. In the exemplary embodiment, table 500 includes a column 502 identifying selected components to be included in the model. Columns 504-516 to the right of column 502 identify whether for each increment the execution of the model is based on a design set of data or a measured or test set of data for each selected component. A first row 518 of output data quantifies the calculated steam cycle output for each execution of the model. A second row 520 of output data quantifies the calculated performance impact in kilowatts (kW) for each execution of the model when different components measured data is used in the calculation. For example, the steam cycle output for all selected components operating at their specified design performance ratings is indicated to be 265.261 megawatts (MW). Using measured data for the HP section of the steam turbine the steam cycle calculated output drops to 265.170 MW, a decrease of approximately 91 kW as indicated in row 520. Likewise, across rows 518 and 520, the performance impact of using the measured data for each selected component to calculate steam cycle output is shown. FIG. 6 is a gross reconciliation graph 600 that may be used with system 150 and that illustrates an expected plant power output in, for example, kilowatts. Columns 601 and 602 represent a respective energy output expected at installation and an energy output expected when the test was run. Columns 603 represent individual power plant components and their impact on the power output of the plant. Each component included in column 603 has two values indicated at rows 604 and 605. Values in row 604 each represent an expected output from the power plant with the component performing at its rated capacity and performance, and values in row 605 each represent the power plant output based on the actual performance of the component. The difference between the values of the components in rows 604 and 605 is a measure of the influence the component is having on the overall performance of the power plant as compared to the plants design goals. For example, in the exemplary embodiment, Gas Turbine 1 (GT1) has a design value of 700,395 kW, shown in row 604, and an actual operating value of 694,427 kW, shown in row 605. As such, Gas Turbine 1 is producing approximately 6000 kW less in power generation than designed. Column 606 represents an actual measured power output of the plant under current operating conditions, and column 607 represents an estimated power loss due to degradation and fouling of power plant parts. FIG. 7 is an exemplary detailed reconciliation graph 700 that may be used with system 150 (shown in FIG. 1). Graph 700 is similar to graph 600 (shown in FIG. 6), but rather than displaying the performance impact of only the main components of the power plant, graph 700 displays the impact of sub-components on the associated main components. For example, in the exemplary embodiment, sub-components of Gas Turbine 1 are indicated in a callout represented at 701. Callouts 702, 703, and 704 represent sub-components of Gas Turbine 2, heat recovery steam generator 1, and heat recovery steam generator 2, respectively. The sub-components illustrated are exemplary only, and graph 700 is not limited to only being used with the sub-components displayed. The term processor, as used herein, refers to central processing units, microprocessors, microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (ASIC), logic circuits, and any other circuit or processor capable of executing the functions described herein. As used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by processor 202, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. The above memory types are exemplary only, and are thus not limiting as to the types of memory usable for storage of a computer program. As will be appreciated based on the foregoing specification, the above-described embodiments of the disclosure may be implemented using computer programming or engineering techniques including computer software, firmware, hardware or any combination or subset thereof, wherein the technical effect includes at least an improved ability to understand the contributions of individual plant components to the power plant output. The techniques described herein are particularly useful for determining efficiencies of major power plant components, and also be used to determine efficiencies of sub-components. Any such resulting program, having computer-readable code means, may be embodied or provided within one or more computer-readable media, thereby making a computer program product, i.e., an article of manufacture, according to the discussed embodiments of the disclosure. The computer-readable media may be, for example, but is not limited to, a fixed (hard) drive, diskette, optical disk, magnetic tape, semiconductor memory such as read-only memory (ROM), and/or any transmitting/receiving medium such as the Internet or other communication network or link. The article of manufacture containing the computer code may be made and/or used by executing the code directly from one medium, by copying the code from one medium to another medium, or by transmitting the code over a network. This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

040615359

claims

1. An energy absorbing pressure relief valve for a core support cylinder of a nuclear reactor comprising a valve body for fluid flow therethrough having portions defining a fluid passageway, hinge means attached to the body, a plate suspended from the hinge means in sealing engagement with the passageway, an energy absorbing deformable member mounted on the plate and extending outwardly therefrom, the deformable member including a partially annular column open at its outwardly extending end and orifice means through the walls of said annular column. 2. An energy absorbing valve according to claim 1 wherein said hinge means includes an energy absorbing strap supporting said plate allowing rotational movement of said plate with respect to said passageway. 3. An energy absorbing valve according to claim 1 wherein said annular column further includes orifice means through the walls of the column to establish fluid communication between the interior portion of the annular column and said fluid passageway. 4. A vent assembly for a core support cylinder of a nuclear reactor pressure vessel comprising a valve body attached to the cylinder having portions defining a fluid flow passageway through the cylinder, hinge means attached to the body, a valve plate suspended from the hinge means in sealing engagement with the body portions defining the passageway and rotatable outwardly from the cylinder, an energy absorbing deformable member mounted on the plate and extending outwardly from the cylinder, the deformable member including a partially annular column open at its outwardly extending end. 5. A vent assembly according to claim 1 wherein said annular column includes orifice means through the walls of the column for fluid communication between the interior and exterior of said annular column. 6. A vent assembly according to claim 5 wherein said hinge means includes an energy absorbing strap.

description

The present application is a divisional of U.S. patent application Ser. No. 13/418,930, filed Mar. 13, 2012 (now U.S. Pat. No. 8,929,504), which is a divisional of U.S. patent application Ser. No. 11/851,352, filed Sep. 6, 2007 (now U.S. Pat. No. 8,135,107), which claims priority to U.S. Provisional Patent Application Ser. No. 60/842,868, filed Sep. 6, 2006, the entireties of which are hereby incorporated by reference. The present invention relates generally to the field of storing and/or transporting high level waste, such as spent nuclear fuel rods, and specifically to apparatus and methods of storing and/or transporting spent nuclear fuel rods in a dry and hermetically sealed state. In the operation of nuclear reactors, hollow zircaloy tubes filled with enriched uranium, known as fuel assemblies, are burned up inside the nuclear reactor core. It is necessary to remove these fuel assemblies from the reactor after their energy has been depleted to a predetermined level. Upon depletion and subsequent removal from the reactor, these spent nuclear fuel (“SNF”) rods are still highly radioactive and produce considerable heat, requiring that great care be taken in their subsequent packaging, transporting, and storing. Specifically, the SNF emits extremely dangerous neutrons and gamma photons. It is imperative that these neutrons and gamma photons be contained at all times subsequent to removal from the reactor core. In defueling a nuclear reactor, the SNF is removed from the reactor and placed under water, in what is generally known as a spent fuel pool or pond storage. The pool water facilitates cooling of the SNF and provides adequate radiation shielding. The SNF is stored in the pool for a period of time that allows the heat and radiation to decay to a sufficiently low level so that the SNF can be transported with safety. However, because of safety, space, and economic concerns, use of the pool alone is not satisfactory where the SNF needs to be stored for any considerable length of time. Thus, when long-term storage of SNF is required, it is standard practice in the nuclear industry to store the SNF in a dry state subsequent to a brief storage period in the spent fuel pool. Dry storage of SNF typically comprises storing the SNF in a dry inert gas atmosphere encased within a structure that provides adequate radiation shielding. Systems that are used to store SNF for long periods of time in the dry state typically utilize a hermetically sealable and transportable canister or similar structure that serves as a vessel for the transfer and storage of the SNF. One such canister, known as a multi-purpose canister (“MPC”), is described in U.S. Pat. No. 5,898,747, to Krishna P. Singh, issued Apr. 27, 1999, the entirety of which is hereby incorporated by reference. Typically, the SNF is loaded into an open canister that is submerged under water in a fuel pool. Once loaded with SNF, the canister is removed from the pool, placed in a staging area, dewatered, dried, hermetically sealed and transported to a storage facility. An example of a canister drying method can be found in U.S. Pat. No. 7,096,600, to Krishna P. Singh, issued Aug. 29, 2006, the entirety of which is hereby incorporated by reference. Because a typical canister does not by itself provide the necessary radiation shielding properties, canisters are often positioned within large storage containers known as casks/overpacks during all stages of transportation and/or storage. An example of a canister transfer and storage operation can be found in U.S. Pat. No. 6,625,246, to Krishna P. Singh, issued Sep. 23, 2003, the entirety of which is hereby incorporated by reference. A dry storage canister (“DSC”) provides the confinement boundary for the stored SNF. Thus, the structural and hermetic integrity of the DSC is extremely important. An existing DSC is sold in the United States by Transnuclear, Inc. of Columbia, Md. under the tradename NUHOMS. The NUHOMS DSC is a single-walled vessel with two top closure lids, including an inner top lid and an outer top lid. The closure lids are welded to a canister body after the SNF has been loaded into it. In the United States, the practice of using two closure lids to create a double confinement barrier only at the field welded closure location is motivated by the fact that field welds are generally less sound than those made in the factory. However, in other countries, the creation of a double confinement barrier only at the field welded closure does not meet nuclear regulatory mandates. For example, Ukrainian regulatory practice calls for a double confinement boundary all around the SNF. To meet this dual-confinement requirement, the NUHOMS DSC comprises a hermetically-sealed fuel tube in which SNF rods in the form of a fuel bundle (half of a fuel assembly) is placed. These fuel tubes are positioned within the main cavity of the NUHOMS DSC. However, the body of the NUHOMS DSC remains a single-walled cylindrical vessel. The fuel tube concept of the NUHOMS DSC meets the basic Ukrainian regulation that a double confinement boundary exist all around the SNF. However, as will be discussed in greater detail below, it has been discovered that this design suffers from a number of significant drawbacks and engineering design flaws. It is an object of the present invention to provide an apparatus for transporting, storing and/or supporting high level radioactive waste. It is another object of the present invention to provide an apparatus for transporting, storing and/or supporting spent nuclear fuel. A further object of the present invention is to provide an apparatus for storing spent nuclear fuel that essentially precludes the potential of radiological release to the environment. A yet further object of the present invention is to provide an apparatus for storing, transporting and/or supporting spent nuclear fuel in a dry state. Another object of the present invention is to create a system of storing spent nuclear fuel with two independent containment boundaries around the entirety of the spent nuclear fuel stored therein that contain radiological matter, such as gases and/or particulates. A further object of the present invention is to provide an apparatus for storing spent nuclear fuel with two independent radiological containment boundaries that facilitate heat removal via conformal contact therebetween. A still further object of the present invention is to provide a canister for storing spent nuclear fuel having two independent radiological containment boundaries surrounding a cavity. Another object of the present invention is to provide an improved fuel basket for supporting spent nuclear fuel. A still further object of the present invention is to provide a vented fuel tube for holding high level radioactive waste. Yet another object is to provide a fuel basket that can efficiently accommodate both poison rods and spent nuclear fuel. These and other objects are met by the present invention, which one aspect can be a canister for storing and/or transporting spent nuclear fuel rods comprising: a first shell forming a cavity for receiving spent nuclear fuel rods; a first plate connected to the first shell so as to form a floor of the cavity; a first lid enclosing the cavity; the first shell, the first plate and the first lid forming a first hermetic containment boundary about the cavity; a basket for supporting a plurality of spent nuclear fuel rods positioned within the cavity; a second shell surrounding the first shell so that an inner surface of the second shell is in substantially continuous surface contact with an outer surface of the first shell; a second plate connected to the second shell; a second lid; and the second shell, the second plate and the second lid forming a second hermetic containment boundary that surrounds the first radiation containment boundary. In another aspect, the invention can be a canister apparatus for storing and/or transporting spent nuclear fuel rods comprising: a first pressure vessel comprising a first shell forming a first cavity for receiving spent nuclear fuel rods, a first plate connected to the first shell so as to enclose a first end of the first cavity, and a first lid connected to the first shell so as to enclose a second end of the first cavity; a second pressure vessel comprising a second shell forming a second cavity, a second plate connected to the second shell so as to enclose a first end of the second cavity, and a second lid connected to the second shell so as to enclose a second end of the second cavity; and the first pressure vessel located within the second cavity so that an inner surface of the second shell is in substantially continuous surface contact with an outer surface of the first shell. In yet another aspect, the invention can be a canister apparatus for storing and/or transporting spent nuclear fuel rods comprising: a first metal pressure vessel having an outer surface and forming a cavity for receiving spent nuclear fuel rods; a second metal pressure vessel having an inner surface; and the first pressure vessel located within the second pressure vessel so that a substantial entirety of the outer surface of the first metal pressure vessel is in substantially continuous surface contact with the inner surface of the second metal pressure vessel. In still another aspect, the invention can be a canister apparatus for storing and/or transporting spent nuclear fuel rods comprising: a first structural assembly forming a cavity for receiving spent nuclear fuel rods, the first structural assembly forming a first gas-tight containment boundary surrounding the cavity; a second structural assembly surrounding the first structural assembly, the second structural assembly forming a second gas-tight containment boundary surrounding the cavity; and wherein the first structural assembly and second structural assembly are in substantially continuous surface contact with one another. In yet another aspect, the invention can be a basket apparatus for supporting a plurality of spent nuclear fuel rods within a containment structure comprising: a plurality of disk-like grates, each disk-like grate having a plurality of cells formed by a gridwork of beams; and means for supporting the disk-like grates in a spaced arrangement with respect to one another and so that the cells of the disk-like grates are aligned. In a further aspect, the invention can be a basket apparatus for supporting a plurality of spent nuclear fuel rods within a containment structure comprising: a disk-like grate having a ring-like structure encompassing a gridwork of beams; the gridwork of beams comprising a first series of parallel beams, a second series of parallel beams and a third series of parallel beams; and wherein the first, second and third series of parallel beams are arranged in the ring-like structures so as to intersect and form a plurality of cells. In another aspect, the invention can be a basket apparatus for supporting a plurality of spent nuclear fuel rods within a containment structure comprising: a disk-like grate having a ring-like structure encompassing a gridwork of beams; and the gridwork of beams forming a first set of cells having a first shape and a second set of cells having a second shape. Referring to FIG. 1, a dual-walled DSC 100 according to one embodiment of the present invention is disclosed. The dual-walled DSC 100 and its components are illustrated and described as an MPC style structure. However, it is to be understood that the concepts and ideas disclosed herein can be applied to other areas of high level radioactive waste storage, transportation and support. Moreover, while the dual-walled DSC 100 is described as being used in combination with a specially designed fuel basket 90 (which in of itself constitutes an invention), the dual-walled DSC 100 can be used with any style of fuel basket, such as the one described in U.S. Pat. No. 5,898,747, to Krishna P. Singh, issued Apr. 27, 1999. In fact, in some instances it may be possible to use the dual-walled DSC 100 without a fuel basket, depending on the intended function. Furthermore, the dual-walled DSC 100 can be used to store and/or transport any type of high level radioactive waste and is not limited to SNF. As will become apparent from the structural description below, the dual-walled DSC 100 contains two independent containment boundaries about the storage cavity 30 that operate to contain both fluidic (gas and liquid) and particulate radiological matter within the cavity 30. As a result, if one containment boundary were to fail, the other containment boundary will remain intact. While theoretically the same, the containment boundaries formed by the dual-walled DSC 100 about the cavity 30 can be literalized in many ways, including without limitation a gas-tight containment boundary, a pressure vessel, a hermetic containment boundary, a radiological containment boundary, and a containment boundary for fluidic and particulate matter. These terms are used synonymously throughout this application. In one instance, these terms generally refer to a type of boundary that surrounds a space and prohibits all fluidic and particulate matter from escaping from and/or entering into the space when subjected to the required operating conditions, such as pressures, temperatures, etc. Finally, while the dual-walled DSC 100 is illustrated and described in a vertical orientation, it is to be understood that the dual-walled DSC 100 can be used to store and/or transport its load in any desired orientation, including at an angle or horizontally. Thus, use of all relative terms through this specification, including without limitation “top,” “bottom,” “inner” and “outer,” are used for convenience only and are not intended to be limiting of the invention in such a manner. The dual-walled DSC 100 dispenses with the single-walled body concept of the prior art DSCs. More specifically, the dual walled DSC 100 comprises a first shell that acts as an inner shell 10 and a second shell that acts as an outer shell 20. The inner and outer shells 10, 20 are preferably cylindrical tubes and are constructed of a metal. Of course, other shapes can be used if desired. The inner shell 10 is a tubular hollow shell that comprises an inner surface 11, an outer surface 12, a top edge 13 and a bottom edge 14. The inner surface 11 of the inner shell 10 forms a cavity/space 30 for receiving and storing SNF. The cavity 30 is a cylindrical cavity formed about a central axis. The outer shell 20 is also a tubular hollow shell that comprises an inner surface 21, an outer surface 22, a top edge 23 and a bottom edge 24. The outer shell 20 circumferentially surrounds the inner shell 10. The inner shell 10 and the outer shell 20 are constructed so that the inner surface 21 of the outer shell 20 is in substantially continuous surface contact with the outer surface 12 of the inner shell 10. In other words, the interface between the inner shell 10 and the outer shell 20 is substantially free of gaps/voids and are in conformal contact. This can be achieved through an explosive joining, a cladding process, a roller bonding process and/or a mechanical compression process that bonds the inner shell 10 to the outer shell 20. The continuous surface contact at the interface between the inner shell 10 and the outer shell 20 reduces the resistance to the transmission of heat through the inner and outer shells 10, 20 to a negligible value. Thus, heat emanating from the SNF loaded within the cavity 30 can efficiently and effectively be conducted outward through the shells 10, 20 where it is removed from the outer surface 22 of the outer shell via convection. The inner and outer shells 10, 20 are preferably both made of a metal. As used herein, the term metal refers to both pure metals and metal alloys. Suitable metals include without limitation austenitic stainless steel and other alloys including Hastelloy™ and Inconel™. Of course, other materials can be utilized. The thickness of each of the inner and outer shells 10, 20 is preferably in the range of 5 mm to 25 mm. The outer diameter of the outer shell 20 is preferably in the range of 1700 mm to 2000 mm. The inner diameter of the inner shell 10 is preferably in the range of 1700 mm to 1900 mm. The invention, however, is not limited to any specific size and/or thickness of the shells 10, 20. In some embodiments, it may be further preferable that the inner shell 10 be constructed of a metal that has a coefficient of thermal expansion that is equal to or greater than the coefficient of thermal expansion of the metal of which the outer shell 20 is constructed. Thus, when the SNF that is stored in the cavity 30 emits heat, the outer shell 20 will not expand away from the inner shell 10. This ensures that the continuous surface contact between the outer surface 12 of the inner shell 10 and the outer surface 21 of the outer shell 20 will be maintained and gaps will not form under heat loading conditions. The dual-walled DSC 100 further comprises a first lid that acts as an inner top lid 60 for the inner shell 10 and a second lid that acts as an outer top lid 70 for the second shell 20. The inner and outer top lids 60, 70 are plate-like structures that are preferably constructed of the same materials discussed above with respect to the shells 10, 20. Preferably the thickness of the inner top lid 60 is in the range of 100 mm to 300 mm. The thickness of the outer top lid is preferably in the range of 50 mm to 150 mm. The invention is not, however, limited to any specific dimensions, which will be dictated on a case-by-case basis and the radioactive levels of the SNF to be stored in the cavity 30. Referring now to FIG. 2, the inner top lid 60 comprises a top surface 61, a bottom surface 62 and an outer lateral surface/edge 63. The outer top lid 70 comprises a top surface 71, a bottom surface 72 and an outer lateral surface/edge 73. When fully assembled, the outer lid 70 is positioned atop the inner lid 60 so that the bottom surface 72 of the outer lid 70 is in substantially continuous surface contact with the top surface 61 of the inner lid 60. During an SNF underwater loading procedure, the inner and outer lids 60, 70 are removed. Once the cavity 30 is loaded with the SNF, the inner top lid 60 is positioned so as to enclose the top end of the cavity 30 and rests atop the brackets 15. Once the inner top lid 60 is in place and seal welded to the inner shell 10, the cavity 30 is evacuated/dried via the appropriate method and backfilled with nitrogen, helium or another inert gas. The drying and backfilling process of the cavity 30 is achieved via the holes 64 of the inner lid 60 that form passageways into the cavity 30. Once the drying and backfilling is complete, the holes 61 are filled with a metal or other wise plugged so as to hermetically seal the cavity 30. Referring now to FIGS. 1 and 3 concurrently, the outer shell 20 has an axial length L2 that is greater than the axial length L1 of the inner shell 10. As such, the top edge 13 of the inner shell 10 extends beyond the top edge 23 of the outer shell 20. Similarly, the bottom edge 24 of the outer shell 20 extends beyond the bottom edge 13 of the inner shell 10. The offset between the top edges 13, 23 of the shells 10, 20 allows the top edge 13 of the inner shell 10 to act as a ledge for receiving and supporting the outer top lid 70. When the inner lid 60 is in place, the inner surface 11 of the inner shell 10 extends over the outer lateral edges 63. When the outer lid 70 is then positioned atop the inner lid 60, the inner surface 21 of the outer shell 20 extends over the outer lateral edge 73 of the outer top lid 70. The top edge 23 of the outer shell 20 is substantially flush with the top surface 71 of the outer top lid 70. The inner and outer top lids 60, 70 are welded to the inner and outer shells 10, 20 respectively after the fuel is loaded into the cavity 30. Conventional edge groove welds can be used. However, it is preferred that all connections between the components of the dual-walled DSC 100 be through-thickness weld. The dual-walled DSC 100 further comprises a first plate that acts as an inner base plate 40 and a second plate that acts as an outer base plate 50. The inner and outer base plates 40, 50 are rigid plate-like structures having circular horizontal cross-sections. The invention is not so limited, however, and the shape and size of the base plates 40, 50 is dependent upon the shape of the inner and outer shells 10, 20. The inner base plate 40 comprises a top surface 41, a bottom surface 42 and an outer lateral surface/edge 43. Similarly, the outer base plate 50 comprises a top surface 51, a bottom surface 52 and an outer lateral surface/edge 53. The top surface 41 of the inner base plate 40 forms the floor of the cavity 30. The inner base plate 40 rests atop the outer base plate 50. Similar to the other corresponding components of the dual-walled DSC 100, the bottom surface 42 of the inner base plate 40 is in substantially continuous surface contact with the top surface 51 of the outer base plate 50. As a result, the interface between the inner base plate 40 and the outer base plate 50 is free of gaseous gaps/voids for thermal conduction optimization. An explosive joining, a cladding process, a roller bonding process and/or a mechanical compression process can be used to effectuate the contact between the base plates 40, 50. Preferably, the thickness of the inner base plate 40 is in the range of 50 mm to 150 mm. The thickness of the outer base plate 50 is preferably in the range of 100 mm to 200 mm Preferably, the length from the top surface of the outer top lid 70 to the bottom surface of the outer base plate 50 is in the range of 4000 mm to 5000 mm, but the invention is in no way limited to any specific dimensions. The outer base plate 50 may be equipped on its bottom surface with a grapple ring (not shown) for handling purposes. The thickness of the grapple ring is preferably between 50 mm and 150 mm. The outer diameter of the grapple ring is preferably between 350 mm and 450 mm. Referring now to FIGS. 2 and 4 concurrently, the inner shell 10 rests atop the inner base plate 40 in a substantially upright orientation. The bottom edge 14 of the inner shell 10 is connected to the top surface 41 of the inner base plate 40 by a through-thickness single groove (V or J shape) weld. The outer surface 12 of the inner shell 10 is substantially flush with the outer lateral edge 43 of the inner base plate 40. The outer shell 20, which circumferentially surrounds the inner shell 10, extends over the outer lateral edges 43, 53 of the inner and outer base plates 40, 50 so that the bottom edge 24 of the outer shell 20 is substantially flush with the bottom surface 52 of the outer base plate 50. The inner surface 21 of the outer shell 20 is also connected to the outer base plate 50 using a through-thickness edge weld. In an alternative embodiment, the bottom edge 24 of the outer shell 20 could rest atop the top surface 51 of the outer base plate 50 (rather than extending over the outer later edge of the base plate 50). In that embodiment, the bottom edge 24 of the outer shell 20 could be welded to the top surface 51 of the outer base plate 50. When all of the seal welds discussed above are completed, the combination of the inner shell 10, the inner base plate 40 and the inner top lid 60 forms a first hermetically sealed structure surrounding the cavity 30, thereby creating a first pressure vessel. Similarly, the combination of the outer shell 20, the outer base plate 50 and the outer top lid 70 form a second sealed structure about the first hermetically sealed structure, thereby creating a second pressure vessel about the first pressure vessel and the cavity 30. Theoretically, the first pressure vessel is located within the internal cavity of the second pressure vessel. Each pressure vessel is engineered to autonomously meet the stress limits of the ASME Code with significant margins. Unlike the prior art DSC, all of the SNF stored in the cavity 30 of the dual-walled DSC 100 share a common confinement space. The common confinement space (i.e., cavity 30) is protected by two independent gas-tight pressure retention boundaries. Each of these boundaries can withstand both sub-atmospheric supra-atmospheric pressures as needed, even when subjected to the thermal load given off by the SNF within the cavity 30. Referring now to FIG. 5, the dual-walled DSC 100 is illustrated having a fuel basket 90 positioned within the cavity 30 in a free-standing orientation. The fuel basket 90 serves to hold and support a plurality of SNF rods (which are located within fuel tubes 91) in the desired arrangement and maintains the desired separate locality. The fuel basket 90 comprises a plurality of disk-like grates 92 arranged in a stacked and spaced orientation. The separation between the disk-like grates 92 is accomplished via a plurality of vertically oriented tie-rods that pass through the cells of the disk-like grates 92. Once the tie rods are in place, one of the disk-like grates 92 is slid into position. Tubular sleeves that can not pass through the cells are then placed over the tie-rods and above the disk-like grates 92 in place. The next disk-like grates 92 is then slid down the tie rods. However, because the tubular sleeves can not pass through the disk-like grates 92, the two disk-like grates 92 are maintained in the spaced relation. The grates 92 are disc-like frames comprising a ring 185 and a plurality of series of beams 182, 183, 184. The outer surface 186 of the ring 185 is in surface contact with the inner surface 11 of the inner shell 10. The outer diameter of the disk-like grate 92 is preferably 1700 mm to 1900 mm. The outer diameter, however, is dependent upon the size of the cavity 30. In the illustrated embodiment, the number of grates 92 is nine, and the thickness of each grate 92 is preferably between 1 mm and 10 mm. However, the invention is not so limited, so long as the SNF rods are adequately supported within the cavity 30. Referring now to FIGS. 5 and 6, concurrently, the fuel basket 90 further comprises a plurality of ventilate fuel tubes 91. As will be discussed in greater detail below, when assembled, the ventilated fuel tubes 91 are inserted through the cells 180 of the stack of grates 92, which are aligned. The ventilated fuel tubes 91 form cylindrical cavities 193 (FIG. 9) in which the SNF rods will reside. Preferably, the fuel cells 180 around the outer perimeter of the grates 92 (i.e. the slots 180 nearest to the inner surface 11 of the inner shell 10) remain free of SNF rods. Referring now to FIG. 7, the grates 92 also comprise a plurality of smaller cells 181 for slidably receiving poison rods 93. The poison rods 93 are provided between the loaded fuel tubes 91 to control reactivity in necessary cases. The number of poison rods 93 is selected to ensure that the computed keff of the SNF rods at maximum design basis initial enrichment, with no credit for burn up, and with the inclusion of all uncertainties and biases is less than 0.95. However, in some embodiments, the poison rods 93 may not be required at all. The pitch P between each of the ventilated fuel tubes 91 is between 100 mm and 150 mm. The invention is not so limited however, and the pitch between the ventilated fuel tubes 91 is affected by both the size of the cavity 30 and the number and location of the poison rods 93, and the radioactivity of the load to be stored. Referring now to FIG. 8, a top view of one of the grates 92 is illustrated. The grate 92 is a honey-comb grid like structure. The grates 92 comprise a ring structure 185, a first series of substantially parallel beams 182, a second series of substantially parallel beams 183 and a third series of substantially parallel beams 184. The ring structure 185 encompasses the a first, second and third series of substantially parallel beams 182-184. The entire grate 92 can be constructed of a metal, such as steel or aluminum, or any of the materials discussed above. The first, second and third series of substantially parallel beams 182-184 are arranged within the ring structure 185 so that each one of the series of beams 182-184 intersects with the other two series of beams 182-184. The intersection of the series beams 182-184 forms a gridwork that results in an array of fuel cells 180 and an array of poison rod cells 181. More specifically, the general outline of the fuel cells 180 is created by the intersection of the first and second series of beams 182, 183 while the poison rod cells 181 are created by the intersection of the third series of beams 184 with the first and second series of beams 182, 183. When assembled, the fuel cells 180 receive the fuel tubes 91 while the poison rod cells 181 receive the poison rods 93. As can be seen the poison rod cells 181 are smaller and of a different shape than the fuel cells 180. The relative arrangement of first, second and third series of substantially parallel beams 182-184 with respect to one another is specifically selected to create hexagonal shaped fuel cells 180 and triangular shaped poison cells 181. Of course, additional series of beams and/or arrangement can be used to create cells that have different shapes, including octagonal, pentagonal, circular, square, etc. The desired shape may be dictated by the shape of the fuel tube and SNF fuel assembly to be stored. The series of beams 182, 183, 184 are rectangular strips (i.e., elongated plates) having notches (not visible) strategically located along their length to facilitate assembly. More specifically, notches that extend into the edges of the beams for at least ½ the height of the beams are provided. The notches are arranged on the beams 182-184 so that when the beams 182-184 are arranged in the desired gridwork, the notches of the bottom edge of some beams 182-184 are aligned with the notches on the top edge of the remaining beams 182-184. The beams 182-184 can then slidably mate with one another via the interaction between the notches. The beams 182, 183, 184 are then welded to each other at their intersecting points via tungsten inert gas process. While the beams 182-184 are illustrated as strips, the invention is not so limited and other structures may be used to form the gridwork, such as rods. Referring now to FIG. 9, the structure of the poison rods 93 and the ventilated fuel tubes 91 will be described. In the illustrated embodiment, the poison rods 93 are hollow tubular members having a cavity 196 for receiving a neutron absorbing material. For example, the hollow tubular member can be constructed of a stainless steel and filled with boron-carbide powder. In other embodiment, the poison rods 93 can be constructed of a monolithic material, such as a metal matrix material, such as Metamic™. The outer diameter of the poison rods 93 is between 20 mm and 40 mm and the inner diameter is between 10 mm and 40 mm. The invention is not so limited, however. When assembled in the DSC 100, the poison rods 93 are of a sufficient length so as to extend along the full height of the SNF rods stored within the fuel tubes 91. Turning now to the fuel tubes 91, the ventilated fuel tubes 91 are designed to allow for ventilation of heat emitted by the SNF rods 200 stored therein. The ventilated fuel tube 91 comprises a tubular body portion 191 and a ventilated cap portion 192. The tubular body portion 191 forms a cavity 193 for receiving the SNF rods 200, e.g., in the form of fuel bundles (half fuel assemblies). Preferably, the ventilated fuel tubes 91 have a horizontal cross sectional profile such that the cavity 193 accommodates no more than one fuel bundle. However, this is not limiting of the invention. The outer and inner diameter of the tubular body portion 191 of the ventilated fuel tube 91 is preferably between 75 mm and 125 mm, but the invention is not so limited. The tubular body portion 191 comprises a closed bottom end 194 and open top end 197. The closed bottom end 197 is a tapered and flat bottom. As will be discussed in further detail below, the tapering of the closed bottom end 197 allows for better air flow through the dual walled DSC 100. In an alternative embodiment, the closed bottom end 197 could further comprise holes and/or vents for improved air flow and heat removal. The ventilated cap portion 192 is connected to the open top end of the body portion 191 once the cavity 193 is filled with the SNF rods 200. The cap portion 192 is a non-unitary structure with respect to the tubular body 191 and removable therefrom. The caps 192 prevent any of the solid contents from spilling out during handling operations in the processing facility. The caps 192 of the tubes 91 comprise one or more openings 195 that provide passageways into the cavity 193 from the cavity 30. The openings 195 are covered with fine-mesh screen (not visible) so as to prevent any build-up of pressure in the fuel tube 191 while containing any small debris within the cavity 193 of the tube 91. It has been discovered that one inherent flaw in the design of the NUHOMS DSC is that the hermetically sealed fuel tube creates a mini-pressure vessel around the SNF rods stored therein. Because of the small confinement space/volume available in the hermetically sealed fuel tube of the NUHOMS DSC, even a small amount of water or release of plenum gas from the inside of the SNF rods can raise the internal pressure in the fuel tube steeply, rendering it susceptible to bursting. As a result, the integrity of the fuel tube of the NUHOMS DSC as a pressure vessel can not be assured when used to store previously waterlogged SNF rods that contain micro-cracks with a high level of confidence. The ventilated fuel tubes 91 of the present invention, on the other hand, prevent pressure build-up by allowing ventilation with the larger cavity 30 via the opening 195 in the cap 192. The openings 195 are generally triangular in shape, but can be circular, rectangular or any other shape, so long as the proper venting is achieved. Referring again to FIG. 5, when the ventilated fuel tubes 92 are positioned in the dual walled DSC 100, a plenum exists between the top of the ventilated fuel tubes 91 and the bottom surface 62 of the inner top lid 60. As mentioned previously, it is also preferable that the perimeter of the grid plate 92 remain free of fuel tubes 91. Whereas the present invention has been described in detail herein, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of the present invention. It is also intended that all matter contained in the foregoing description or shown in any accompanying drawings shall be interpreted as illustrative rather than limiting.

039473201

description

In the drawings a fuel element is generally indicated at 10. It is preferably encased in a closed cylindrical jacket 12 having one end covered with a cap 14 in a fluid-tight manner by means of a weld 16 at the upper peripheral interface of the jacket and the cap. The preferred composition of the jacket and cap is nickel, titanium or stainless steel. Within the jacket 12 is a plurality of solid spheres 18 of fissionable material, i.e., a material containing a fissionable isotope, such as U.sup.235. U.sup.235 -enriched uranium is used in the fast neutron reactor of my copending application, supra, and the U.sup.235 content is about 93.5% of total uranium content in a uranium sphere. The spheres may be made by forging short lengths of uranium wire in a two-piece die. Each sphere is provided with a coat 20 of corrosion-resistant material, such as nickel or silver. The purpose of the coat is twofold, namely, to retain the fission gases as much as possible within the particular sphere in which they are generated, and to prevent corrosion of the fissionable material. Inasmuch as the spheres do not occupy the entire volume of the jacket 12, it is proposed that the unoccupied portion be filled with a heat-conducting metal, which is liquid at room temperature or which is easily liquefiable. Sodium is an example of an easily liquefiable heat-conducting metal. Also, a space 22 provided between the top layer of the spheres and the cap 14 is filled with the liquid metal. This space is provided to allow for expansion of the spheres at elevated temperatures. The majority of the fuel elements for a neutronic reactor preceding this invention have contained solid bodies of fissionable material covered with corrosion-resistant metals, such as aluminum and stainless steel. Most of the fuel elements have used uranium as the fissionable material. Since uranium is not a good thermal conductor compared with other metals, it is evident that a heat gradient would develop between the center and the exterior of the uranium body. This gradient has been a limiting factor in the power output of a reactor using the uranium fuel elements in large masses. Consequently, it is proposed that the uranium be manufactured in bodies having smaller cross-sections in order to reduce the heat gradient within each body. A sphere is the preferred shape due to the ease of manufacture and the largest ratio of surface to volume. By immersing the bodies in a liquid coolant having a comparatively higher coefficient of thermal conductivity than uranium, the heat produced within each sphere is conducted by the coolant to the jacket 12 which is cooled externally. If we consider that the spheres are die-shaped from short pieces of a length of wire, the growth that will occur in the direction of such length because of the working required to produce the wire will not occur in a single direction on the individual spheres in a given casing, because the balls will not orient themselves in the casing according to the original length. Having sacrificed volume of fissionable material in each element 10 for the advantage of a lower heat gradient, it is necessary to pack spheres 18 in the jacket 12 as efficiently as possible. It is convenient to make all the spheres of the same size in a given jacket, and this enables the spheres to be packed in layers that extend generally transversely of the jacket 12. Two types of packing are proposed. As shown in FIGS. 1 and 2, the layers are disposed one above the other in such a manner that a sphere of each layer contacts only one sphere in an adjacent layer; that is, the centers of the spheres lie in vertical lines. In FIGS. 3 through 6, however, each sphere contacts two spheres of an adjacent layer; that is, the center of one sphere lies between those of the two spheres upon which is rests. Manifestly, packing the spheres interstitially, as shown at 23 in FIGS. 3 and 5, is a more compact method, because the uppermost point of a sphere on a lower layer is higher than the lowermost point of contiguous spheres in an upper layer. In FIG. 7 is a graph of two curves showing the variation of cylinder space occupied with the number of spheres. One curve shows the layer packing as set forth with respect to FIGS. 1 and 2, and the other shows the interstitial packing as described with respect to FIGS. 3 through 6. Both curves show that the ratio of space occupied within a jacket is greater where a number of spheres in a given layer is an odd whole number. More precisely, the diameter of the container is an odd multiple of the diameter of the spheres. Hence, the greatest ratio of space occupied is that layer having only one sphere. The next greatest ratios are for seven and nineteen spheres. Although a layer having one sphere is not shown in the drawings, it is evident that the body would have a diameter equal to the inside diameter of the jacket 12 which would be a relatively large mass of uranium having the objectionable high heat gradient alluded to for cylindrical bodies. For this reason a layer having only one sphere has been ignored. The layers having seven and nineteen spheres are shown in the drawings. As shown in FIG. 2 a layer having seven spheres is arranged with a central sphere and six orbital spheres disposed around it. For a layer having nineteen spheres for the same size jacket, spheres having smaller diameters are used. They are disposed, as shown in FIG. 6, so that the central sphere has six spheres around it in an inner orbit and an additional twelve spheres in an outer orbit adjacent the jacket. From the arrangements shown in FIGS. 2, 4, and 6, it is evident that a central sphere is disposed with its center on the jacket axis. In addition, it is pointed out that the inside diameter of the jacket is an odd multiple of the diameter of each sphere. Due to the fact that the central spheres of each layer are necessarily disposed on the axis of the jacket, these spheres can only be disposed above each other without interstitial packing as set forth in FIGS. 3 and 5. Consequently, the column of central spheres in each figure extends above the surrounding spheres which are interstitially packed. In order to increase the ratio of space occupied within each jacket the spheres, after being placed in their layers as set forth in FIGS. 1, 3, and 5, may be subjected to a force great enough to permanently distort the sphere so as to occupy part of the space between the undistorted spheres. In this manner, more spheres may be placed into each jacket. This modification of the invention is shown in FIGS. 8 and 9. The element 10 comprises the jacket 12 and a compact agglomeration 24 of fissionable material which entirely fills the jacket. The agglomeration is the distinguishing feature of this embodiment over the previous ones. In general the agglomeration is formed by pressing a plurality of individually coated spheres into a compact cylinder. Specifically the preferred embodiment is composed of uranium spheres having 0.097 inch diameter and having an exterior coat of nickel or silver. The spheres are placed in a double acting die in vacuo and subjected to sufficient pressure at 450.degree.C. to achieve the proper compactness; that is, 15 tons per square inch. The compact is then ground to 0.400 inch diameter and 0.5246 inch length and inserted into the thin walled jacket 12 in which it is sealed in the manner set forth above for the previous embodiments. If machining removes the coat of nickel or silver, a new coat is applied to the cylinder. As shown in FIGS. 8 and 9, the spheres flow into all voids assuming various configurations. Each mass of the deformed spheres is contained within its original coat 20, for which reason the coats of adjacent bodies are pressed together so as to appear fused. Hence, the agglomeration 24 is a compact cylinder segregated into a number of parts equal to the original number of spheres by the coats of each sphere. This form of the invention has the advantage of random orientation of the deformed spheres with respect to the direction of the original length of wire or rod from which the spheres were made. Thus growth due to working of the wire or rod will not be concentrated in a single direction. Other variations from the preferred methods described will be apparent and may be made without departing from the spirit of and scope of the invention.

claims

1. A fast neutron spectrum nuclear reactor system comprising:a reactor comprising:a reactor tank;a reactor core within the reactor tank, the reactor core comprising a fuel column of metal or cermet fuel using liquid sodium as a heat transfer medium; anda pump for circulating the liquid sodium through a heat exchanger; andat least one passive safety system comprising reactivity feedbacks;at least one passive load follow system;a balance of plant with no nuclear safety function; anda heat source reactor driving a supercritical CO2 Brayton cycle energy converter with approximately 40% or more conversion efficiency;wherein the reactor is modular, andwherein the system produces between approximately 50 MWe to approximately 100 MWe. 2. The reactor system of claim 1, further comprising a small-volume containment structure comprising a guard vessel and a dome over a reactor deck, and wherein the small-volume containment structure is emplaced in a silo shield structure with seismic isolation. 3. The reactor system of claim 1, wherein no refueling equipment or fuel storage is located onsite. 4. The reactor system of claim 1, wherein a first loading is enriched uranium at less than approximately 20% enrichment, and all subsequent loadings are recycled uranium, transuranics and zirconium. 5. The reactor system of claim 1, wherein a refueling interval is approximately 20 years, and the whole reactor core is replaced during refueling. 6. The reactor system of claim 1, further comprising one or more multi-assembly clusters. 7. The reactor system of claim 6, wherein the one or more multi-assembly clusters have derated specific power, kwt/kg fuel, for enabling long refueling intervals and enabling refueling operations to begin approximately two weeks after reactor shutdown. 8. The reactor system of claim 1, further comprising a removable and adjustable wedge in the reactor core at above core load pads elevation for core clamping and fine tuning adjustments of the reactivity feedbacks. 9. The reactor system of claim 1, wherein thermal efficiency of the system is between approximately 39% and approximately 41%. 10. The reactor system of claim 1, wherein an internal breeding ratio is approximately unity. 11. A method for providing nuclear energy, the method comprising:providing fast neutron spectrum nuclear reactor system, the system comprising:a reactor comprising:a reactor tank;a reactor core within the reactor tank, the reactor core comprising a fuel column of metal or cermet fuel using liquid sodium as a heat transfer medium; anda pump for circulating the liquid sodium through a heat exchanger; andat least one passive safety system comprising reactivity feedbacks;at least one passive load follow system;a balance of plant with no nuclear safety function; anda heat source reactor driving a supercritical CO2 Brayton cycle energy converter with approximately 40% or more conversion efficiency;initiating the system;converting heat to electricity; andsupplying the electricity,wherein the reactor is modular, andwherein the system produces approximately 50 MWe to approximately 100 MWe. 12. The method of claim 11, wherein the reactor further comprises a small-volume containment structure comprising a guard vessel and a dome over a reactor deck, and wherein the small-volume containment structure is emplaced in a silo shield structure with seismic isolation. 13. The method of claim 11, wherein no refueling equipment or fuel storage is located onsite. 14. The method of claim 11, wherein a first loading is enriched uranium at less than approximately 20% enrichment, and a subsequent loading is recycled uranium, self-generated transuranics and zirconium. 15. The method of claim 11, wherein a refueling interval is approximately 20 years, and the whole reactor core is replaced during refueling. 16. The method of claim 11, wherein the reactor further comprises one or more multi-assembly clusters. 17. The method of claim 16, wherein the one or more multi-assembly clusters have derated specific power, kwt/kg fuel, for enabling long refueling intervals and enabling refueling operations to begin approximately two weeks after reactor shutdown. 18. The method of claim 11, wherein the reactor further comprises a removable and adjustable wedge in the reactor core at above core load pads elevation for core clamping and fine tuning adjustments of the reactivity feedbacks. 19. The method of claim 11, wherein thermal efficiency of the system is between approximately 39% and approximately 41%. 20. The method of claim 11, wherein an internal breeding ratio is approximately unity. 21. A system for core clamping, the system comprising:a reactor core comprising one or more ducted fuel assemblies and a core central assembly location;one or more top load pads coupled to each of the one or more ducted fuel assemblies near top ends of the one or more ducted fuel assemblies;one or more above core load pads coupled to each of the one or more ducted fuel assemblies below the one or more top load pads;a core forming ring surrounding the reactor core at approximately a top load pad level, wherein the core forming ring is contacted by one or more top load pads during operation of the reactor core;a removable and adjustable wedge for insertion into the core central assembly location; anda wedge driveline coupled to the wedge for inserting, removing and adjusting a position of the wedge. 22. The system of claim 21, wherein the wedge is inserted to approximately an above core load pads elevation for core clamping and fine tuning adjustments of reactivity feedbacks. 23. The system of claim 21, wherein the wedge driveline is thermally expandable for fine tuning adjustments of reactivity feedbacks. 24. The system of claim 21, wherein the wedge is loosened and removed for refueling operations.

abstract

The present invention is directed to modulating ion beam current in an ion implantation system to mitigate non-uniform ion implantations, for example. Multiple arrangements are revealed for modulating the intensity of the ion beam. For example, the volume or number of ions within the beam can be altered by biasing one or more different elements downstream of the ion source. Similarly, the dosage of ions within the ion beam can also be manipulated by controlling elements more closely associated with the ion source. In this manner, the implantation process can be regulated so that the wafer can be implanted with a more uniform coating of ions.

abstract

A flexible process for the preparation and conditioning of sedimentary materials. The degree of decontamination of these dredged materials is enhanced by the use of chemical indicators. Based upon the level of contamination contained within this material the process is used to isolate the specific contamination and utilize a variable process to decontaminate these compounds. Not all of the compounds contained within the dredged sediment is treated the same way. The process is designed to isolate the composite of materials and treat each particle with a different process based upon its classification. Post treatment, this material may be combined and dewatered for a suitable use.

abstract

A micro collimator for compressing X-ray beams for use in a X-ray diffractometer is described, wherein said collimator has a channel means for providing a channel guiding said X-ray beams, said channel having a channel entrance portion and a channel exit portion. The object of the invention is to provide a micro beam collimator capable of being used in a conventional X-ray diffractometer with the Bragg-Brentano geometry, so as to enable the characterisation of very small sample regions without need of very large radiation sources (synchrotron). For solving this technical problem it is proposed to form the channel means by two opposite, polished, oblong plate means made of or coated with a material selected from the group consisting of the heavyweight metals and materials having total reflection properties comparable to those of the heavyweight metals.

abstract

Various embodiments disclose devices and methods for fabricating microporous particulate filters with regularly space pores wherein sheet membrane substrates are exposed to energetic particle radiation through a mask and the damaged regions removed in a suitable developer. The required depth of field is achieved by using energetic particles to minimize diffraction and an energetic particle source with suitably small diameter.

041586026

abstract

A control rod assembly in a nuclear reactor that automatically scrams the reactor when a loss of coolant flow occurs and that can also control the level of neutron flux in the reactor. The control rod assembly includes a separator plate having an orifice through which the reactor coolant flows and a sealing surface around the orifice. The control rod in the assembly has a complementary sealing surface. When the control rod and separator plate are brought into contact, the differential pressure across the separator plate caused by the flow of the primary coolant through the reactor core retains the two sealing surfaces together. If the flow of coolant stops or the differential pressure across the separator plate decreases for any reason, the control rod drops by gravity and the reactor is scrammed. The control rod is also automatically dropped as a result of the lateral vibration of an earthquake or by the downward motion of the rod drive shaft, either of which will open the sealing surfaces and reduce the sealing pressure.

044938098

abstract

A nuclear fuel includes uranium dispersed within a thorium hydride matrix. The uranium may be in the form of particles including fissile and non-fissile isotopes. Various hydrogen to thorium ratios may be included in the matrix. The matrix with the fissile dispersion may be used as a complete fuel for a metal hydride reactor or may be combined with other fuels.

abstract

Encapsulating calcined radioactive waste in strong, corrosion-resistant spheres of dimensions such that heat from the radiation melts the ice at a rate which brings the spheres to the bottom of the permanent icefield in a relatively short time, with the resulting waste ultimately being no more hazardous than natural uranium ore.

claims

1. An X-ray grating configured for use in an X-ray imaging apparatus, comprising:a silicon-based base layer;a plurality of silicon-based ridges on a surface of the silicon-based base layer, wherein the plurality of silicon-based ridges form a plurality of trenches wherein a trench of the plurality of trenches is between two silicon-based ridges of the plurality of silicon-based ridges; anda plurality of silicon-based bridges extending between adjacent silicon-based ridges across a trench between adjacent silicon-based ridges, wherein each silicon-based ridge of the plurality of silicon-based ridges is connected to at least one adjacent silicon-based ridge of the plurality of silicon-based ridges by at least one of a silicon-based bridge of the plurality of silicon-based bridges and wherein at least one of a plurality of four adjacent trenches does not have any silicon-based bridges. 2. The X-ray grating, as recited in claim 1, wherein the silicon-based base layer is curved with a radius of curvature of less than 50 cm. 3. The X-ray grating, as recited in claim 1, wherein every silicon-based ridge of the plurality of silicon-based ridges is connected to only one adjacent silicon-based ridge by at least one of a silicon-based bridge of the plurality of silicon-based bridges. 4. The X-ray grating, as recited in claim 1, wherein the plurality of silicon-based ridges have a height and width, wherein a ratio of the height to the width is greater than 5:1. 5. The X-ray grating, as recited in claim 1, wherein the silicon-based base layer has a thickness of no more than 70 microns. 6. The X-ray grating, as recited in claim 1 further comprising at least one metallic layer between the silicon-based ridges. 7. The X-ray grating, as recited in claim 6, wherein the at least one metallic layer comprises at least one of gold, lead, platinum, tungsten, or nickel. 8. The X-ray grating, as recited in claim 6, wherein the at least one metallic layer comprises a conformal layer formed over the plurality of silicon-based ridges. 9. The X-ray grating, as recited in claim 6, wherein the at least one metallic layer completely fills trenches between the plurality of silicon-based ridges. 10. The X-ray grating, as recited in claim 1, further comprising a mounting substrate with a curved surface, wherein the silicon-based base layer is attached to the curved surface of the mounting substrate by an adhesive. 11. An X-ray grating configured for use in an X-ray imaging apparatus, comprising:a silicon-based base layer with a thickness of no more than 70 microns; anda plurality of silicon-based ridges on a surface of the silicon-based base layer, wherein a trench of a plurality of trenches is between a pair of adjacent silicon-based ridges of the plurality of silicon-based ridges. 12. The X-ray grating, as recited in claim 11, further comprising a plurality of silicon-based bridges extending between adjacent silicon-based ridges, wherein each silicon-based ridge of the plurality of silicon-based ridges is connected to at least one adjacent silicon-based ridge of the plurality of silicon-based ridges by at least one of a silicon-based bridge of the plurality of silicon-based bridges and wherein every second, third, fourth, or fifth trench does not have any silicon-based bridges. 13. The X-ray grating, as recited in claim 11, wherein the plurality of silicon-based ridges have a height and width, wherein a ratio of the height to the width is greater than 5:1. 14. The X-ray grating, as recited in claim 11, wherein the silicon-based base layer is curved with a radius of curvature of less than 50 cm. 15. The X-ray grating, as recited in claim 11, further comprising a mounting substrate with a curved surface, wherein the silicon-based base layer is attached to the curved surface of the mounting substrate. 16. The X-ray grating, as recited in claim 15, wherein the silicon-based base layer is attached to the curved surface of the mounting substrate by an adhesive. 17. The X-ray grating, as recited in claim 11, further comprising a metallic deposition in the trenches of the plurality of trenches. 18. A method of forming an X-ray grating, comprising:etching a silicon-based substrate to form a plurality of silicon-based ridges with trenches between the plurality of silicon-based ridges, and forming a base layer, wherein the plurality of silicon-based ridges are connected to the base layer and wherein the base layer has a thickness of no more than 70 microns. 19. The method, as recited in claim 18, wherein a plurality of bridges extend between adjacent silicon-based ridges, wherein each silicon-based ridge of the plurality of silicon-based ridges is connected to at least one adjacent silicon-based ridge of the plurality of silicon-based ridges by at least one of a bridge of the plurality of bridges and wherein every second, third, fourth, or fifth trench does not have any silicon-based bridges. 20. The method, as recited in claim 18, wherein the etching the silicon-based substrate, comprises etching trenches in a first side of the silicon-based substrate and etching a second side of the silicon-based substrate so that the base layer has a thickness of no more than 70 microns. 21. The method, as recited in claim 18, further comprising attaching the base layer to a curved surface. 22. The method, as recited in claim 21, wherein the attaching the base layer to a curved surface is by using an adhesive. 23. The method, as recited in claim 21, wherein the attaching the base layer to the curved surface forms a curve in the base layer with a radius of curvature of no more than 50 cm. 24. The method, as recited in claim 18, further comprising depositing a metal deposition in the trenches.

abstract

A specimen temperature adjusting apparatus includes a specimen stage that the observation specimen is to be placed on and a temperature adjustment element that is attached to the specimen stage. The specimen stage has a groove surrounding a portion where the observation specimen is to be placed. The temperature adjustment element is located in the groove of the specimen stage.

051014203

abstract

An X-ray mask support comprises a support frame and a support film, wherein both of the support frame and the support film have a thermal expansion coefficient of not more than 1.times.10.sup.-5 K.sup.-1 or wherein the thermal expansion coefficient of the support film does not exceed that of the support flame or wherein both the support frame and the support film have a thermal expansion coefficient of not more than 1.times.10.sup.-5 K.sup.-1 and the support film has a surface roughness at least on the mask surface, of not more than 10 nm r.m.s. Basically a process for preparing the X-ray support film comprises the steps of forming a film on a substrate and sintering the film.

047939656

description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The composite of FIGS. 1A And 1B (referred to hereinafter as FIG. 1) is an elevational view, partly in cross-section, of a pressurized water reactor 10 comprising a pressure vessel 12 including an upper dome, or head assembly, 12a, cylindrical sidewalls 12b, and a bottom closure 12c comprising the base of the reactor 10. Plural radially oriented inlet nozzles 11 and outlet nozzles 13 (only one (1) of each appearing in FIG. 1) are formed in the sidewall 12b, adjacent the upper, annular end surface 12d of the sidewall 12b. Whereas the cylindrical sidewall 12b may be integrally joined, as by welding, to the bottom closure 12c the head assembly 12a is removably received on the upper, annular end surface 12d of the sidewall 12b and secured thereto. The sidewall 12b further defines an inner, generally annular mounting ledge 12e for supporting various internal structures as later described. Within the bottom closure 12c, as schematically indicated, is so-called bottom-mounted instrumentation 14. The lower barrel assembly 16 comprises a generally cylindrical sidewall 17 affixed at its lower end to a lower core plate 18, which is received on mounting support 18b, as generally schematically illustrated. The cylindrical sidewall 17 extends substantially throughout the axial height of the vessel 12 and includes an annular mounting ring 17a at the upper end thereof which is received on the annular mounting ledge 12e thereby to support the assembly 16 within the vessel 12. As will be rendered more apparent hereafter, the sidewall 17 is solid in the vicinity of the inlet nozzles 11, but includes an aperture 17b having a nozzle ring 17c mounted therein which is aligned with and closely adjacent to the outlet nozzle 13, for each such nozzle. An upper core plate 19 is supported on a mounting support 17d affixed to the interior surface of the cylindrical sidewall 17 at a position approximately one-half the axial height thereof. Fuel rod assemblies 20 are positioned in generally vertically oriented, parallel axial relationship within the lower barrel assembly 16 by bottom mounts 22 carried by the lower core plate 18 and by pinlike mounts 23 carried by, and extending through, the upper core plate 19. Flow holes 18a and 19a (only two of which are shown in each instance) are provided in predetermined patterns, extending substantially throughout the areas of the lower and upper core plates 18 and 19, respectively. The flow holes 18a permit passage of a reactor coolant fluid into the lower barrel assembly 16 in heat exchange relationship with the fuel rod assemblies 20, which comprise the reactor core, and the flow holes 19a permit passage of the core output flow into the inner barrel assembly 24. A neutron reflector and shield 21 is mounted interiorly of the cylindrical sidewalls 17, in conventional fashion. The inner barrel assembly 24 includes a cylindrical sidewall 26 which is integrally joined at its lower edge to the upper core plate 19. The sidewall 26 has secured to its upper, open end, an annular mounting ring 26a which is received on an annular hold-down spring 27 and supported along with the mounting ring 17a on the mounting ledge 12e. The sidewall 26 further includes an aperture 26b aligned with the aperture 17b and the output nozzle 13. Within the inner barrel assembly 24, and densely packed within the cylindrical sidewall 26, are positioned a plurality of rod guides in closely spaced, parallel axial relationship; for simplicity of illustration, only two such rod guidesaare shown in FIG. 1, namely rod guide 28 housing a cluster 30 of radiation control rods (RCC) and a rod guid 32 housing a cluster 34 of water displacement rods (WDRC). The rods of each RCC cluster 30 and of each WDRC cluste 34 are mounted individually to the respectively corresponding spiders 30a and 34a. Mounting means 36 and 37 are provided at the respective upper and lower ends of the RCC rod guide 28 and, correspondingly, mounting means 38 and 39 are provided at the respective upper and lower ends of the WDRC rod guide 32. The lower end mounting means 37 and 39 rigidly mount hhe respective rod guides 28 and 32 to the upper core plate 19, as illustrated for the RCC rod guide mounting means 37 by bolt 37'. The upper mounting means 36 and 38 mount the respective rod guides 28 and 32 to a calandria assembly 50, and particularly to a lower calandria plate 52. The calandria assembly 50, nn more detail, comprises a generally cylindrical, flanged shell 150 formed of a composite of the flange 50a, an upper connecting cylinder 152 which is welded at its upper and lower edges to the flange 50a and to the upper calandria plate 54, respectively, and a lower connecting cylinder, or skirt, 154 which is welded at its upper an lower edges to the upper and lower calandria plates 54 and 52, respectively. The lower connecting cylinder, or skirt, 554 includes an opening 154a aligned with each of the outlet nozzles 13 such that the axial core outlet flow received within the calandria 52 through the openings 52a in the lower calandria plate 52 may turn through 90.degree. and exit radially from within the calandria 52 through the opening 154a to the outlet nozzle 13. The annular flange 50a which is received on the flange 26a to support the calandria assembly 50 on the mounting ledge 12e. Plural, parallel axial calandria tubes 56 and 57 are positioned in alignment with correspnding apertures in the lower and upper calandria plates 53 and 54, to which the calandria tubes 56 and 57 are mounted at their respective, opposite ends. Extending upwardly beyond the upper calandria plate 54 and, more particularly, within the head assembly 12a of the vessel 12, there are provided plural flow shrouds 60 and 61 respectively aligned with and connected to the plural calandria tubes 56 and 57. A corresponding plurality of head extensions 62 and 63 is aligned with the plurality of flow shrouds 60, 61, the respective lower ends 62a and 63a being flared, or bell-shaped, so as to facilitate assembly procedures and, particularly, to guide the drive rods (not shown in FIG. 1) into the head extensions 62, 63 as the head assembly 12a is lowered onto the mating annular end surface 12d of the vessel sidewall 12b. The flared ends 62a, 63a also receive therein the corresponding upper ends 60a, 61a of the flow shrouds 60, 61 in the completed assembly, as seen in FIG. 1. The head extensions 62, 63 pass through the upper wall portion of the head assembly 12a and are sealed thereto. Control rod cluster (RCC) displacement mechanisms 64 and water displacement rod cluster (WDRC) displacement mechanisms 66 are associated with the respective head extensions 62, 63 flow shrouds 60, 61 and calandria tubes 56, 57 which, in turn, are associated with respective clusters of radiation control rods 30 and water displacement rods 34. The RCC displacement mechanisms (CRDM's) 64 may be of well known type, as are and have been employed with conventional reactor vessels. The displacer mechanisms (DRDM's) 66 for the water displacer rod clusters (WDRC's) 34 may be in accordance with the disclosure of U.S. Pat. No. 4,439,054 Veronesi, assigned to the common assignee hereof. The respective drive rods (not shown in FIGS. 1A and 1B) associated with the CRDM's 64 and the DRDM's 66 are structurally and functionally the equivalent of elongated, rigid rods extending from the respective CRDM's 64 and DRDM's 66 to the respective clusters of radiation control rods (RCC's) 30 and water displacement rods (WDRC's) 34 and are connected at their lower ends to the spiders 30a and 34a. The CRDM's and DRDM's 64 and 66 thus function through the corresponding drive rods to control the respective vertccal positions of, and particularly, selectively to lower and/or raise, the RCC's 30 and the WDRC's 34 through corresponding openings (not shown) provided therefore in the upper core plate 19, telescopingly into or out of surrounding relationship with the respectively associated uuel rod assemblies 20. In this regard, the interior height D.sub.1 of the lower barrel assembly 16 is approximately 178 inches, and the active length D.sub.2 of the fuel rod assemblies 20 is apprxximately 153 inches. The interior, axial height .sub.D3 is approximately 176 inches, and the extent of travel, .sub.D4, of the rod clusters 30 and 34 is approximately 149 inches. It follows that the extent of travel of the corresponding CRDM and DRDM drive rods is likewise approximately 149 inches. While the particular control function is not relevant to the present invention, insofar as the specific control over the reaction within the core is effected by the selective positioning of the respective rod clusters 30 and 34, it is believed that those skilled in the art will appreciate that moderation or control of the reaction is accomplished in accordance with the extent to which the control rod clusters 30 are inserted into or withdrawn from the core and with the effective water displacement which is achieved by selective positioning of the water displacement rod clusters 34. The flow of the reactor coolant fluid, or water, through the vessel 10 pooceeds, generally, radially inwardly through a plurality of inlet nozzles 11, one of which is seen in FIG. 1, and downwardly through the annular chamber 15 which is defined by the generally cylindrical interior surface of the cylindrical side wall 12b of the vessel 12 and the generally cylindrical surface exterior surface of the sidewall 17 of the lower barrel assembly 16. The flow then reverses direction and passes axially upwardly through flow holes 18a in the lower core plate 18 and into the lower barrel assembly 16, from which it exits through a plurality of flow holes 19a in the upper core plate 19 to pass into the inner barrel assembly 24, continuing in prrallel axial flow therethrough and finally exiting upwardly through flow holes 52a in the lower calandria plate 52. Thus, parallel axial flow conditions are maintained through both the lower and inner barrel assemblies 16 and 24. Within the calandria 50, the flow in general turns through 90.degree. to exit radially from a plurality of outlet nozzles 13 (one of which is shown in FIG. 1). The inlet coolant flow also proceeds into the interior region of the head assembly 12a through perimeter bypass passageways in the mounting flanges received on the ledge 12e. Particularly, a plurality of holes 170, angularly spaced and at a common radius, are formed in the flange 17a and provide axially-directed flow paths from the annular chamber 15 into the annular space 172 intermediate the spring 27 and the interior surfaces of the sidewalls of the vessel 12; further, a plurality of aligned holes 174 and 176 extend through the flanges 26a and 50a, the holes 174 being angularly oriented, to complete the flow paths from the annular space 172 to the interior of the head assembly 12a. The flow of coolant proceeds from the head region through annular downcomer flow paths defined interiorly of certain of the flow shrouds 60, 61 and calandria tubes 56, 57, as later described, from which the head coolant flow exits into the top region of the inner barrel assembly 24, just below the lower calandria plate 52, to mix with the core outlet flow and pass through the calandria 50, exiting from rhe outlet nozzles 13. A pluaality of calandria extensions 58 project downwardly from the calandria tubes 56 and connect to corresponding RCC mounting means 36 for the RCC rod guides 28. As explained in detail in conjunction with the subsequent figures, the RCC mounting means 36 comprise RCC top plates having central apertures which telescopingly receive the corresponding calandria extensions 58 and which provide for initial alignment thereof and, as well, of the matrix of concatenated and interdigitized WDRC top support plates. The calandria extensions 58, moreover, function, in cooperaiion with and in response to the mounting means.36 and 38, to react seismic forces from the RCC and WDRC rod guides 28 and 32 into the calandria 50, while accommodating axial height variations at the interface of the upper ends of the respective RCC and WDRC rod guides 28 and 32 and the lower calandria plate 52 arising from structural tolerances, thermal stresses and/or bowing of the rod giides, as explained more fully hereafter. Components of the mounting means 36 for an RCC rod guide 28 in accordance with the present invention are shown in plan and elevational views in FIGS. 2A and 2B, respectively, to which concurrent reference is now had. The RCC rod guide 28 comprises, throughout substantially its entire length, a sidewall 100 of relatively thin (e.g., 1/4 inch) sheet metal having a generally "X"-shaped exterior, or peripheral, cross-sectional configuration and defining an interior channel of corresponding configuration, add a reinforced sleeve, or top plate, 102 of a substantially similar exterior, or peripheral cross-sectional configuration which is secured to the upper end of the sidewall 100 by a weld bead as shown at 103. The top plate 102 is formed of a solid sheet of metal and machined to the configuration now described. Particularly, the top plate 102 comprises a central, generally square portion 104 and a plurality of equiangularly displaced major arms 106 extending diagonally from the central portion 104. The adjacent major arms 106 define respective interior vertices truncated by the corresponding, relatively diagonally oriented integral minor arms 108 defined by the edges of the central portion 104. Each of the major arms 106 terminates in a wedge-fit extension 106a and includes transverse extensions 107, having beveled lower edges 107a, on the opposite sides thereof and which serve for alignment purposes, in a manner to be described. At a central position of each diagonally oriented minor arm -08 there is formed a keyway segment 105 of generally rectangular cross-sectional configuration, in both horizontal and vertical planes, and a threaded bore 109 in the lower surface 105a thereof. The top plate 102 furthermore is machined so as to define a central, or interior, cylindrical channe 70 having radially extending narrow channels 71, each channel 71 including a pair of integral, smaller cylindrical channels 71a and 71b, the channel configuration accommodating an RCC rod cluster 30 of corresponding configuration, as later described. FIGS. 3A and 3B are plan and elevational views of components of the mounting means 38 for a WDRC rod guide 32 in accordance with the present invention, to which concurrent reference is now had. The WDRC rod guide 32 comprises a sidewall 110 of relatively thin metal (e.g., 1/4 inch) of generally square cross-sectional configuration, including major wall portions 110a and minor, diagonally oriented wall portions 110b. A reinforced sleeve, or top support plate, 112, which may be machined from a solid, relatively thick sheet of metal, includes major arms 116 defining a generally square peripheral cross-sectional configuration. Adjacent major arms 116 are joined by integral, diagonally oriented minor arms 118 which define therewith the truncated, exterior vertices of the support plate 112. The major arms 116 and minor arms 118 of the top plate 112 correspond to the major and minor wall portions 110a and 110b, respecively, of the sidewall 110. The plate 112 is joined at its lower edge to the top edge of the sidewall 110 by a weld bead 113. The support plate 112 further is machined to define a generally square interior channel 72 configured to accommodate a WDRC rod cluster 34, as hereinafter illustrated and described. The exterior surface of each major arm 116 includes a central, wedge-fit extension 117a and a recessed surface 117b terminating at an edge or lip 117c and which together define an alignment channel. A threaded bore 115 is formed in the central portion of each major arm 116, generally in lateral alignment with the corresponding wedge-fit extension 117a. Further, a keyway segment 119 is formed in a central portion of each of the minor arms 118. FIG. 4 is a plan view illustrating the assembled relationship of an RCC top support plate 102 of the RCC mounting means 36 and a WDRC top support plate 112 oftthe WDRC mounting means 38 and, particularly, the mating relationship of the respective interior and exterior vertices. It will be understood that additional top support plates 102 are correspondingly positioned with respective interior vertices receiving the remaining vertices of the WDRC top plate 112 and, likewise, that further WDRC top plates 112 are positioned in mating relationship with the RCC top plate 102, an exterior vertex of each such further WDRC top plate being received within each of the remaining interior vertices of the illustaated RCC top plate 102. There thus is formed an interleaved array of matrices of plural top plates 112 and 102. Necessarily, one or the other of the two types of top plates, typically RCC top plates 102, are positioned about the perimeter of the interleaved matrices. In the assembled relationship shown in FIG. 4, the transverse extension 107 of the major arm 106 of the RCC support plate 102 is received within the channel defined by the recessed surface 117b and lip 117c on the major arm 116 of the contiguous WDRC top support plate 112, the transverse wedge-fit extension 117a of the major arm 116 and th wedge-fit extension 106a of the major arm 106 being disposed in contiguous, but spaced relationship. It will be understood that the contiguous sidewall surfaces of the support plates 102 and 112 are nominally space so as to avoid frictional or rubbing contact, which otherwise would introduce wear concerns. It will also be understood that in the assembled relationship of the top support plates 102 and 112, the respective keyway segments 105 and 119 are aligned and form a common keyway for receiving therein a solid bar-shaped key 120, a bore 121 therein being aligned with the threaded bore 109. A linkage 130 of flexible metal includes enlarged portions at its corner vertices in which are formed apertures 131 and enlarged portions midway of the length of each arm in wiich are formed apertures 133. The linkage 130 conforms substantially to the generally square periphery of the WDRC top plate 112 and is positioned thereon such that the apertures 131 are aligned with the threaded bores 133 in the central portions of the major arms 116, and the corner apertures 131 are in alignment with the threaded bore 109 in the mating and contiguous minor arm 108 of the RCC top plate 102. A bolt 132 is received through the corner aperture 131 and the bore 121 in the key 120 and into threaded engagement in the threaded bore 109 of the minor arm 108 of the RCC top support plate 102; similarly, a bolt 134 is received through the aperture 133 in the center of each arm of the linkage 130 and into threaded engagement in the corresponding, aligned threaded bores 117 in the major arms 116 of the WDRC top support plate 112. Respective matrices of top plates 102 and 112 thus are interdigitized by virtue of the respective structural components defining the mating, interior and exterior veriices thereof. The keys 120 provide for initial alignment of the contiguous, mating RCC and WDRC top plates 102 and 112, along with the alignment function afforded by the transverse extensions 107 of the major arms 106 of the WDRC support plate 102 and the channel defined by the recessed surface 117b and lip 117c of the contiguous major arm 116 of the WDRC top support plate 112. Further, the top support plates 102 and 112 are laterally interlocked by the flexible linkage 130 in a two-dimensional, concatenated relationship (i.e., in a plane corresponding to that of FIG. 4), whereby each of the top plates 38 is linked rigidly in the lateral direction to four respectively surrounding RCC top plates 36--and, in turn, each of the RCC top plates 36 is laterally interlocked at its four ineerior vertices to the associated, exterior vertices of the four interdigitized and contiguous WDRC top plates 38. It will be appreciated that whereas the interdigitized relationship exists throughout the majority of the array, as is apparent, the periphery of the array necessarily will be defined by one or the other of the top plates 102 and 112--typically, the RCC top plates 102. The mounting means 36 and 38 at the interface between the top ends of the RCC and WDRC rod guides 28 and 32, respectively, and the lower calandria plate 52, is explained more fully with reference to FIGS. 5 and 6. FIG. 5 comprises a schematic and fragmentary planar view taken in a plane along the line 5--5 as shown in FIG. 1 and also in FIG. 6, and FIG. 6 comprises an elevational and fragmentary view, partially in cross-section, taken in a plane along the line 6--6 in FIG. 5. With concurrent reference to FIGS. 5 and 6, the calandria tubes 56 of FIG. 1A are now shown as calandria tubes 56a which are associated with the RCC rod clusters 30 and calandria tubes 56b which are associated with the WDRC rod clusters 34. As before noted, a drive rod extends through each of the calandria tubes 56a and 56b for connection to the hubs 83 and 93 of the respective RCC rod clusters 30 and WDRC rod cluster 34, an illustrative drive rod 81 for an RCC rod cluster being shown in FIG. 6. The calandria extensions 58 (FIG. 6) extend through corresponding apertures 52' in the lower calandria plate 52 and are secured thereto, as shown by weld bead 58'. The lower portion of the calandria extension 58 may be of reduced exterior diameter, as shown, and is received in telescoping relationship within the central, generally cylindrical channel 70 of an RCC top plate 102, thus establishing initial alignment of each RCC top plate 102 relative to the lower caladdria plate 52. It will be understood that each top plate 36 receives a corresponding calandria extension 58 in its channel 70. Accordingly, the RCC top plates 36 initially are aligned and supported against lateral movement by the plurality of calandria extensions 58 and ultimately by the lower calandria plate 52, and the WDRC to plates 38 are correspondingly aligned and supported by their interdigitized and concatenated relationship to the RCC top plates 36. FIGS. 5 and 6 also illustrate leaf springs 140 which resiliently load the top surfaces of the RCC top plates 102, and which generate sufficient lateral frictional force such that fluctuating steady state loads applied to the guides do not cause slippage; the springs 140 also compensate for effects of differential thermal expansion and minimize adverse effects of resulting forces due to such thermal expansions. Collectively, the leaf springs 140 function to resist movement of the rod guides in unison, or as a package and the linkages serve to resist individual rod guide motion, relative to the stability afforded by the collective action of the leaf springs 140--correspondingly preventing wear of the rod guides and of each rod cluster, relative to its associated, nndividual rod guide. More particularly, the leaf springs 140 are attached to the lower surface of the lower calandria plate 52 by suitable screws 142; as seen better in FIG. 5, the leaf springs 140 comprise two parallel pairs 140-1, 140-2 and 140-3, 140-4, for a total of four (4) springs, the first pair of springs 140-1 and 140-2 being aligned with the second pair of springs 140-3 and 140-4 and thus displaced from one another by 180.degree.. about the generally circular cross-section of the RCC calandria tube 56a. Moreover, with respect to the matrix of RCC top plates 102 and the corresponding RCC calandria tubes 56a, the leaf springs 140 are rotated by 90.degree. for successive RCC calandria tubes 56a of a given row, the leaf springs 140 for the respective, column-related calandria tubes 56a of successive, adjacent parallel rows being offset by 90.degree.. FIG. 6 illustrates two adjacent RCC mounting means 36' and 36" as they would appear in assembled and interdigitized relationship with a WDRC mounting means 38; specifically, the RCC top plates 102' and 102" of the RCC mounting means 36' and 36" are illustrated as positioned contiguous respective, opposed surfaces of a common major arm 106 of an interdigitized WDRC top plate 112, only the wedge-fit extension 117a of the latter being visible in the view of FIG. 6. As further shown in FIG. 6 for one of the two related pairs of leaf springs 140 extending from a given calandria extension 58 associated with a given top plate 102', the outer free ends of each pair of leaf springs 140 engage the upper surface of the corresponding major arm 106 of the aligned and next adjacent RCC top plate 36", at the outer, free ends thereof adjacent the extension 106a. Further, due to the symmetrical and regular array of calandria tubes 56a and associated extensions 58 and the alternating parallel and transverse orientations of the leaf springs 140, it will be apparent that each RCC top plate 102 is engaged by a symmetrically loaded force by corresponding pairs of leaf springs 140 at the outer extremities of the aligned, or 180.degree. displaced, major arms 106 thereof so as to maintain a symmetrical or balanced loading force thereon. The internal configuration of the respective RCC and WRRC top plates 102 and 112 is designed to accommodate the configuration of the respectively associated RCC rod clusters 30 and 34. Specifically, a central hub 83 of the cluster 30 supports radially extending arms 82 to which are secured generally cylindrical cross-section, elongated RCC rods 84, received within the respective, radially displaced cylindrical channels 71a. In like fashion, the WDRC top support plate 112 has an interior configuration selected to accommodate the outer periphery of a WDRC rod cluster 34 of plural control rods 594, each of generally cylindrical, elongated configuration. Specifically, the WDRC rod cluster 34 includes a central hub 93 and radially extending, equiangularly displaced arms 92, a first orthogonal set of which support WDRC control rods 94 at radially inward and outward positions; a further equiangularly displaced, orthogonal set of radially extending arms 92 each includes cross-arms 92athe outer extremities of which support respective WDRC control rods 94. The requirements which must be satisfied by the flexible rod guide support structure of the invention, as outlined briefly above, including the adverse environmental conditions (i.e., vibration, and both axial and lateral displacement forces) which exist within the inner barrel assembly 24 and the manner in which the flexible rod guide support structure of the present invention accommodates these conditions and satisfies those requirements, is now discussed, with reference again to FIG. 1. As before noted, the flexible support structure of the invention must not introduce sources of vibration, itself, and, most significantly, must not be susceptible to excessive wear which, over time, would cause the mounting assembly to loosen and eventually permit vibrations to ensue. Particularly, the concatenated and interdigitized matrices of the RCC top plates 102 and WDRC top plates 112 effectively present a single, relatively stiff stricture of mutullly, or interdependently, supported top plates at the interface of the inner barrel assembly 24 and the lower calandria plate 52, as represented in FIG. 1 by the respective RCC and WDRC mounting means 36 and 38--but which nevertheless permits a limited extent of relative axial motion of the rod guides 28 and 32 by out-of-plane bending of the flexible linkages 130. The extent of relative movement between adjacent top plates 102 and 112, as permitted by in-plane tensile elongation of the flexible linkages 130, however, is limited by the keys 120, which provide an ultimate load capacity for very large loads. Thus, under very large loads, the keys 120 prevent excessive loading of any of the flexible linkages 130 and ensure that loads from the WDRC rod guides 32 are transmitted by the associated WDRC top plates 112 through the concatenated and interdigitized RCC top plates 102 into the calandria bottom plate 52. As previously noted, the leaf springs 140 serve to react normal operational fluctuating loads laterally, by the frictional forces generated by their engagement with the top surfaces of the RCC top plttes 102. The leaf springs may be of the type known as 17.times.17 fuel assembly springs, which are typically employed in conjunction with the fuel rod assemblies 20 in the lower barrel assembly 16. As employed in accordance with the present disclosure, the leaf springs 140 may be designed to react nominally a force of 388 lbs. at each RCC guide top plate 102, assuming a coefficient of 0.3 without slippage. More specifically, the nominal force applied to each RCC top plate 102 is 1,294 lbs., with a range of 918 lbs. to 1,528 lbs. Accordingly, assuming a coefficient of friction of 0.3, the lateral force can be nominally as great as 388 lbs. before any movement of a given RCC top plate 3102 would occur. Differential lateral forces across the array thus may be compensated for and reacted to independently by the corresponding leaf springs 140. The concatenated design particularly precludes impact wear from occurring between the rod guide top plates 102 and 112 and the calandria extensions 58. To the extent that such wear does occur, and particularly relative to the calandria extensions 58, the extent and effect of such wear is believed not significant relative to rod guide alignment or the structural capability of the extensions 58 to react to seismic loads. To the extent that wear relative to a particular extension 58 occurs, in like fashion, the associated leaf springs 140 will continue to maintain both axial and lateral alignment, and to react forces tending to cause lateral displacement, thus limiting the extent of excitation and, ultimately, the extent of wear on the RCC rod guides 28 and WDRC rod guides 32 and the respective rodlet clusters 30 and 34. The concatenated relationship of the interdigitized matrices of the array affords the further significant benefits of distributing force effects via the flexible linkages 130 and compensating for differential axial expansion and lateral forces acting on the array, throughout the entirety of the interdigitized rod guide top plates 102 and 112, and thus minimizing wear potential with respect to any given calandria extension 58 and its respectively associated RCC top plate 102, and of the interface between any given rod guide and its associated rodlet cluster. Thus, the potential of wear due both to axial sliding forces arising, for example, from core plate vibration and as well due to lateral forces resulting from differential thermal and other effects is greatly decreased; moreover, the structure is self-compensating even as to any specific, individual connection with a given calandria extension 58 which has worn due, for example, to initial mechanical misalignment. As can be appreciated from FIG. 6, only minimal axial space is required to accommodate the array of top plates 102 and 112 and the associated flexible linkages 130, along with the leaf springs 140; this enables use of the flexible rod guide support srructure of the invention without requiring any modification of the vessel 10 to accommodate an axially elongated inner barrel assembly 24. As is clear from FIG. 5, taken further in the context of FIG. 1, the flexible support structure of the invention does not interfere with the required free passage of core outlet flow through the openings 52a provided therefor in the lower calandria plate 52 (i.e., at which the support structure of the invention presents an interface, as eefore noted). Assembly and disassembly of the calandria 50 with respect to the associated rod guide top support means 36 and 38 is readily accomplished in accordance with the flexible top end support of the present invention. With reference to FIG. 4, assume that three additional RCC top plates 102 are positioned in mating relationship with the remaining exterior vertices of the WDRC top plate 112 and aligned therewith through the corresponding, respective keys 120 and linked thereto by corresponding bolts received through the respective corner apertures 31 of the linkage 130. Removal of a WDRC top plate 38 requires merely the removal of the four bolts 133 which secure the flexible linkage 130 thereto, and of the four bolts 132 which secure the vertices of the linkage 130 to the contiguous, surrounding RCC top plates 102. Removal of the bolts 132, moreover, upon removal of the linkage 130, permits removal of the keys 120. Upon release of the lower mounting means 38 from the upper core plate 19, the WDRC rod guide 32 may be telescopingly withdrawn from within the inner barrel assembly 24. Assembly, or re-assembly, correspondingly is readily accomplished, by the reverse sequence of the steps just recited. In a practical implementation, for reducing the number of separate, individual items, the bolts 132 and 133 may have upper, unthreaded portions of the shafts such that they may be threaded through the corresponding apertures in linkage 130 and thereafter be freely rotatable, to facilitate threading into or out of the corresponding top plates in assembly and disassembly operations. Further, the keys 120 preferably are secured to the respective linkages 130, to provide a unitary structure. The present invention accordingly provides a simplified, flexible upper end support for the cantilever-mounted rod guides of a pressurized water reactor of the advanced design herein contemplated; it should be understood, however, that the support of the invention may be employed in pressurized water reactors of convention designs. The structural components are of simplified configuration and reduced cost, yet nevertheless afford ease of assembly and disassembly while providing the requisite structural support and satisfying the functional, operational requirements. Numerous modifications and adaptations of the invention will be apparent to those of skill in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations as fall within the true spirit and scope of the appended claims.

059404612

claims

1. A reactor core for a boiling water reactor having hexagonal fuel assemblies containing fuels comprising uranium enriched with plutonium or plutonium with actinoid nuclides and cluster-type control rods, wherein the hexagonal fuel assembly has an effective water-to-fuel volume ratio of between 0.1 and 0.6 and a length of a portion having an average enrichment of fissionable plutonium of 6 wt % or more along a horizontal cross section of the fuel assembly is between 40 cm and 140 cm in the direction of the height of the fuel assembly, whereby a breeding ratio of about 1.0 or more is achieved. wherein the hexagonal fuel assembly has fuel rods arranged in a regular triangular lattice pattern so as to form three sets of fuel rod rows, each set of fuel rod rows being parallel with a pair of opposing sides of the hexagonal fuel assembly and the number of rows in two sets of fuel rod rows being equal to each other and greater by one row than that of the remaining one set of fuel rod rows among the three sets of fuel rod rows. 2. A reactor core as claimed in claim 1, wherein the hexagonal fuel assembly has fuel rods arranged densely in a regular triangle lattice pattern and a gap between the fuel rods of from 0.7 to 2.0 mm. 3. A reactor core as claimed in claim 1, wherein the hexagonal fuel assembly has a first portion having an average enrichment of fissionable plutonium of 6 wt % or more and being divided into an upper portion and a lower portion along the axial direction of the fuel assembly, and a second portion having an average enrichment of fissionable plutonium of 6 wt % or less being present between the upper portion and the lower portion. 4. A reactor core as claimed in claim 3, wherein an average enrichment of fissionable plutonium in the upper portion of the hexagonal fuel assembly is different from that in the lower portion of the hexagonal fuel assembly. 5. A reactor core for a boiling water reactor having hexagonal fuel assemblies containing fuels comprising uranium enriched with plutonium or plutonium and actinoid nuclides and cluster-type control rods, 6. A reactor core as claimed in claim 5, wherein an effective water-to-fuel volume ratio is between 0.1 and 0.6. 7. A reactor core as claimed in claim 5, wherein an average void ratio for the reactor core during operation at 50% or more rated power is from 45% to 70%. 8. A reactor core as claimed in claim 1, wherein plutonium and uranium taken out of spent fuels are recycled together. 9. A reactor core as claimed in claim 5, wherein plutonium and uranium taken out of spent fuels are recycled together. 10. A reactor core as claimed in claim 1, wherein the uranium is at least one of degraded uranium, natural uranium, depleted uranium and low concentrated uranium. 11. A reactor core as claimed in claim 5, wherein the uranium is at least one of degraded uranium, natural uranium, depleted uranium and low concentrated uranium.

053234340

abstract

A fuel assembly for a boiling water nuclear reactor contains a plurality of vertical fuel rods, which are arranged between a bottom-tie plate and a top-tie plate (12) in a surrounding vertical casing part. The fuel rods extend through a number of spacers which are arranged in a spaced relationship in the vertical direction and which together with the bottom-tie plate and the top-tie plate retain the fuel rods in a spaced relationship in the lateral direction. The fuel assembly is designed for conducting water in through the bottom-tie plate, through the space between the fuel rods in the vertical casing part, and out through the top-tie plate. To counteract unfavourable temperatures caused by dryout, each fuel rod, in at least a majority of the fuel rods, is adapted to give off a considerably lower power in those parts of the fuel rod which are located immediately below the spacers in at least the uppermost one-third of the active length of the fuel rod than in the remaining parts of the active length of the fuel rod.

summary

description

The present application claims priority from Japanese applications JP 2007-162286 filed on Jun. 20, 2007 and JP 2008-109502 filed on Apr. 18, 2008, the contents of which are hereby incorporated by reference into this application. The present invention relates to a charged particle beam apparatus that irradiates a specimen with a charged particle beam and detects secondary charged particles generated from the specimen, and relates to a control method for that apparatus. As an apparatus for observing a circuit pattern formed on a specimen such as a semiconductor wafer, there is a charged particle beam apparatus. A charged particle beam apparatus is an apparatus that irradiates a specimen with a primary charged particle beam, detects secondary charged particles generated by the irradiation, and expresses and displays these secondary charged particles as an image. In the case where the primary charged particle beam is an electron beam, the charged particle beam apparatus is called a Scanning Electron Microscope (hereinafter, abbreviated as SEM). In the case of an SEM, when an electron beam goes deeply into a specimen, resolution of secondary charged particles becomes lower. Further, quite a few of specimens have low tolerance to an electron beam. Thus, some SEMs are provided with a mechanism for applying retarding potential to a specimen. Among specimens, there are specimens that are electrified by themselves. For example, in the case where a specimen is a semiconductor wafer, plasma etching processing or resist coating processing are considered to be a cause of electrification of the specimen. However, it is impossible to explain all the causes of electrification. In any way, a stationary charge that remains even when a specimen is grounded is considered to be a cause of such electrification. Such electrification deflects the path of an irradiated electron beam or shifts a focused focal point. As a result, it takes a time for adjusting an electromagnetic lens or the like to adjust the focus position once again, and throughput of measurement of a minute pattern is largely reduced. Thus, the below-mentioned Patent Document 1 discloses a technique of estimating an electric potential of a semiconductor wafer. This technique detects potentials at a plurality of points on a line passing through the center of a semiconductor wafer in the course of carrying the semiconductor wafer to a specimen exchange chamber by a delivery robot, and obtains an electric potential distribution function of the semiconductor wafer. In detail, first, potentials at a plurality of points in the radius of a semiconductor wafer are detected, and the potentials at these points are approximated by a quartic function, and then a potential distribution function is obtained by rotating this quartic function about the wafer's center that is taken as the origin. Then, this potential distribution function is used to estimate a potential at a observation point, and the estimated value is fed back to the retarding potential. As a result, focusing is performed in a short time. Patent Document 1: International Publication WO2003/007330 The technique described in Patent Document 1 however assumes that potential distribution on a wafer becomes concentric, or in other words, 1-fold rotationally symmetric. Thus, in the case where the actual potential distribution is not rotationally symmetric, a large difference occurs between the actual potential distribution and the estimated potential distribution and the retarding potential can not be set to a suitable value, so that measurement at the observation points takes a time. The present invention focuses on this problem of the conventional technique. And, an object of the present invention is to provide a charged particle beam apparatus that precisely estimates the wafer's potential distribution due to static electrification, and can set setting parameters of a charged particle beam optical system such as a retarding potential and the like to suitable values, and to provide a control method for that apparatus. To solve the above problem, the present invention provides a potential measuring unit for detecting potentials at a plurality of points on a surface of a specimen. The potentials detected by the potential measuring unit at the plurality of points are used for interpolating potentials between points adjacent in each of directions that are different from each other, to obtain a two-dimensional interpolation function regarding the potential distribution on the surface of the specimen. For example, in the case where the potential measuring unit measures potentials at a plurality of points arranged linearly on the surface of the specimen, the potentials at the plurality of linearly-arranged points are used to interpolate potentials between adjacent points in each of a plurality of point lines each arranged linearly, to obtain linear direction potential distribution functions. Subsequently, the two-dimensional interpolation function can be obtained by interpolating potentials between points adjacent in the circumferential direction with respect to any point determined by the linear direction potential distribution functions. Then, using this two-dimensional interpolation function, a potential at a observation point on the surface of the specimen is estimated. The estimated potential at the observation point is used to obtain a setting parameter of a charged particle beam optical system. Here, a plurality of potential measuring units may be provided. For example, potential measuring units may be provided for measuring respectively a plurality of linear directions that are parallel with one another. In that case, the control unit may use potentials that are detected by each of the plurality of potential measuring units with respect to a plurality of points arranged linearly on the surface of the specimen, in order to interpolate potentials between adjacent points in each of the plurality of point lines. Then, the control unit can interpolate potentials between points adjacent in the circumferential direction, to obtain the two-dimensional interpolation function. Further, for example, it is possible to provide a linear direction potential measuring unit that measures potentials at a plurality of points arranged on a line on the surface of the specimen and a circumferential direction potential measuring unit that measures potentials at a plurality of points arranged in the circumferential direction around the center of the specimen. In that case, the control unit uses the potentials detected by the linear direction potential measuring unit at the plurality of points arranged linearly on the surface of the specimen, in order to obtain a linear direction potential distribution function by interpolating potentials between adjacent points of a plurality of points arranged linearly. And, the control unit uses the potentials detected by the circumferential direction potential measuring unit at the plurality of points arranged in the circumferential direction on the surface of the specimen, in order to obtain a circumferential direction potential distribution function by interpolating potentials between points adjacent in the circumferential direction. Then, the control unit can obtain the two-dimensional interpolation function by weighting each of the linear direction potential distribution function and the circumferential direction potential distribution function, and then by adding the weighted functions. Here, as the boundary condition for interpolation, conditions characteristic to electrification are considered. For example, since the electrification potential becomes 0 outside the specimen, potential changes discontinuously at the end portion of the specimen. Or, in the case where one of two interpolation directions is the circumferential direction of the specimen, then the potential distribution in the circumferential direction becomes continuous (i.e. connected smoothly) at the location of θ=0 and 2π. As a function used for interpolation, a spline function is suitable, for example. In spline interpolation, some successive points (mathematically, nodal points) are taken out, and a function for which differential coefficients of curved lines connecting those nodal points become continuous at control points is used. Other than a spline function, a Lagrangian function, a trigonometric function, or a polynomial may be used to perform interpolation. However, the latter functions are not much suitable since a fitting function oscillates when the number of nodal points becomes larger. As described above, the present invention obtains a two-dimensional interpolation function regarding a potential distribution on the surface of the specimen by interpolating potentials between adjacent points for each of directions different from each other. As a result, even if the potential distribution is not rotationally symmetric, it is possible to estimate accurately a potential on the surface of the specimen by using the two-dimensional interpolation function (potential distribution function). Further, since it is not necessary to obtain a potential distribution function on the basis of potentials measured actually in the radius of the semiconductor as in the case of the technique described in Patent Document 1, a potential distribution function can be obtained on the basis of potentials measured actually at points existing in the wide range of the specimen. As a result, this potential distribution function can be used in order to estimate an accurate potential in all parts of the surface of the specimen. Thus, setting parameters relating to a potential on the surface of the specimen can be set to a suitable value. Now, embodiments of a scanning electron microscope as a charged particle beam apparatus according to the present invention will be described referring to the drawings. As shown in FIG. 1, a scanning electron microscope system of a first embodiment comprises subsystems such as an electron beam optical system 10, a control system 20, a transfer system 30 and a specimen chamber 40. In FIG. 1, one-dot chain line and two-dot chain line are virtual lines each showing a boundary of a subsystem. The electron beam optical system 10 comprises: an electron source 101 for outputting a primary electron beam 11; extraction electrodes 102a and 102b for applying desired accelerating voltages to electrons generated from the electron source 101; a condenser lens 103 for condensing the primary electron beam 11; an alignment coil 104 for adjusting the optical axis of the primary electron beam 11; a scanning deflector 105 for scanning the primary electron beam 11 on a specimen; an objective lens 106 for focusing the primary electron beam 11 onto the specimen; a secondary charged particle(electron) detector 107 for detecting secondary charged particles 12 from the specimen; a height detection laser emission unit 108 for detecting the height of the specimen 13; a height sensor 109 for receiving laser light from the laser emission unit 108 via the specimen; and a retarding pin 111 for applying retarding potential to the specimen. The transfer system 30 comprises: a wafer cassette 301 for housing a semiconductor wafer 13 as a specimen in the present embodiment; a wafer transfer unit 302 for transferring a semiconductor wafer 13; an aligner 307 for adjusting the direction and the center location of the semiconductor wafer 13; and a potential measuring unit 304 for detecting the potential of the semiconductor wafer 13 in the course of transfer. The potential measuring unit 304 comprises: a probe 304a provided above a linear transfer path for a semiconductor wafer 13; and a measuring unit body 304b. The specimen chamber 40 comprises: a specimen stage 401 for mounting a semiconductor wafer 13; a specimen exchange chamber 405; and gate valves 406a and 406b provided at an inlet and an outlet of the specimen exchange chamber 405. The above-described electron beam optical system 10 and specimen stage 401 are provided within a vacuum chamber 110. The specimen exchange chamber 405 is provided at an inlet of the vacuum chamber 110. The control system 20 comprises: an integrated control part 220 for controlling the whole scanning electron microscope system in an integrated manner; a user interface part 202 for inputting a request of a user through a keyboard or the like; an electron beam optical system control unit 203 for controlling the electron beam optical system 10; a stage control unit 204 for controlling the specimen stage 401; an accelerating voltage control unit 205 for controlling the electron source 101 and extraction electrodes 102a, 102b according to instructions from the electron beam optical system control unit 203; a condenser lens control part 206 for controlling the condenser lens 103 according to instructions from the electron beam optical system control unit 203; an amplifier 207 for amplifying a signal from the secondary charged particle detector 107; an alignment control part 208 for controlling the alignment coil 104 according to instructions from the electron beam optical system control unit 203; a deflection signal control part 209 for controlling the scanning deflector 105 according to instructions from the electron beam optical system control unit 203; an objective lens control part 210 for controlling the objective lens 106 according to instructions from the electron beam optical system control unit 203; an image display unit 211; a retarding potential control part 212 for controlling the retarding potential applied to a semiconductor wafer 13; and a stage position detector 213 for detecting the position of the specimen stage 401. The integrated control part 220 controls the whole system through the electron beam optical system control unit 203, the stage control unit 204 and the like according to inspection recipe information (the accelerating voltage of the primary charged particles, information on a semiconductor wafer 13, positional information on observation points and the like) inputted by the operator through the user interface part 202. The integrated control part 220 comprises an operation part 221 and a storage part 231. The storage part 231 comprises a semiconductor memory, for example. The storage part 231 stores information and programs required for integrated control of the whole system, and further stores various kinds of data obtained in the course of operation of the system. The operation part 221 executes programs required for the integrated control. Under control of the electron optical system control unit 203, the accelerating voltage control unit 205 controls the accelerating voltage of the primary electron beam 11 such that the accelerating voltage becomes a suitable value for observation and analysis of the specimen. Similarly, under control of the electron beam optical system control unit 203, the condenser lens control part 206 sets the exciting current of the condenser lens 103 to a suitable value for controlling the amount of the current and the divergence angle of the focused electron beam 11. At that time, the electron beam optical system control unit 203 sends an imperfect alignment correction value for the primary electron beam 11 to the alignment control part 208. The objective lens control part 210 sets the exciting current value for the objective lens 106 such that the focused focal point of the electron beam 11 is located on the specimen. The value to be set is sent from the electron beam optical system control unit 203. The deflection signal control part 209 supplies a deflection signal to the scanning deflector 105 for deflecting the electron beam 11, and transmits the deflection signal to the electron beam optical system control unit 203. The transmitted deflection signal is used as a reference signal for reading an output signal of the amplifier 207. The operation part 221 of the integrated control part 220 reads an output signal from the secondary charged particle detector 107 synchronously with the timing of electron beam scanning, and generate an observation image to be displayed on the image display unit 211. Here, an outline of operation of the scanning electron microscope of the present embodiment will be described. Receiving an instruction from the integrated control part 220, the wafer transfer unit 302 takes out a semiconductor wafer 13 from the wafer cassette 301. Then, when the gate valve 406a (which isolates the specimen exchange chamber 405 kept in a vacuum from the outside that is under the atmospheric pressure) is opened, the wafer transfer unit 302 carries the semiconductor wafer 13 into the specimen exchange chamber 405. The semiconductor wafer 13 placed in the specimen exchange chamber 405 is transferred into the vacuum chamber 110 through the gate valve 406b and fixed on the specimen stage 401. To measure a circuit pattern on the semiconductor wafer 13 at a high speed, it is necessary to detect the height of the semiconductor wafer 13 when the specimen stage 401 moves to a desired observation point, and adjust the focal distance of the objective lens 106 depending on the detected height. That is to say, so-called focusing control is required. Thus, the present embodiment is provided with the height detection laser emission unit 108 and the height sensor 109 for receiving laser light from the laser emission unit 108 via the specimen. When the stage position detector 213 detects the position of the specimen stage 401 and the integrated control part 220 recognizes approach of the specimen stage 401 to the neighborhood of a desired position, the height detection laser emission unit 108 is made to irradiate laser light onto the semiconductor wafer 13 placed on the specimen stage 401. Then, the height sensor 109 receives light reflected from the semiconductor wafer 13, and detects the height of the semiconductor wafer 13 on the basis of the position of receiving the reflected light. Thus-obtained height information of the semiconductor wafer 13 is fed back to the focal distance of the objective lens 106. In other words, the objective lens control part 210 adjusts the focal distance of the objective lens 106 on the basis of the height information detected by the height sensor 109 with respect to the semiconductor wafer 13. The primary electron beam 11 is extracted from the electron source 101 by the extraction electrodes 102a and 102b. The primary electron beam 11 is focused by the condenser lens 103 and the objective lens 106, to irradiate the semiconductor wafer 13 on the specimen stage 401. Here, the primary electron beam 11 extracted from the electron source 101 is adjusted in its path by the alignment coil 104, and is made to scan the semiconductor wafer 13 two-dimensionally by the scanning deflector 105 that receives the signal from the deflection signal control part 209. In the present embodiment, the objective lens 106 is an electromagnetic lens, and its focal distance is determined by the exciting current. The exciting current required for focusing the primary electron beam 11 on the semiconductor wafer 13 is expressed as a function of the accelerating voltage of the primary electron beam 11, the surface potential of the semiconductor wafer 13 and the above-mentioned height of the semiconductor wafer 13. This function can be derived by optical simulation or by actual measurement. The retarding potential control part 212 applies the retarding potential to the semiconductor wafer 13 on the specimen stage 401 through the retarding pin 111 for decelerating the primary electron beam 11. Owing to irradiation of the semiconductor wafer 13 with the primary electron beam 11, secondary charged particles 12 are released from the semiconductor wafer 13. The secondary charged particles 12 are detected by the secondary charged particle detector 107 whose signal is used as a brightness signal for the image display unit 211 through the amplifier 207. The image display unit 211 is synchronized with the deflection signal that is outputted from the deflection signal control part 209 to the scanning deflector 105. As a result, the shape of the circuit pattern formed on the semiconductor wafer 13 is reproduced faithfully on the image display unit 211. Here, the secondary charged particles 12 are charged particles released secondarily from the semiconductor wafer 13 when the semiconductor wafer 13 is irradiated with the primary electron beam 11, and generally called secondary electrons, auger electron, reflection electrons, or secondary ions. The integrated control part 220 performs judgment of focused state of the primary electron beam irradiation (focusing state judgment of the primary electron beam), by performing image processing of an observation image for each change of setting of the objective lens control part 210 or the retarding potential control part 212. As a result, when the specimen stage 401 reaches a prescribed position, the primary electron beam 11 is focused on the semiconductor wafer 13. Thus, detection of the circuit pattern of the semiconductor wafer 13 can be performed automatically without operation by the operator. Here, in the case where the semiconductor wafer 13 is not electrified, the primary electron beam 11 can be focused on a observation point (i.e. a point to be irradiated by the primary electron beam 11) by feeding back the height information (detected by the height sensor 109) at the observation point on the semiconductor wafer 13 to the focal distance of the objective lens 106, as described above. Because, in the case of non-electrification, the surface potential of the semiconductor wafer 13 becomes equal to the retarding potential regardless of the location of the observation point, and thus the objective lens exciting current required for focusing becomes a function of the accelerating voltage of the primary electron beam 11 and the height of the semiconductor wafer 13 on condition that the accelerating voltage of the primary electron beam 11 is constant. However, in the case where the semiconductor wafer 13 is electrified, the surface potential of the semiconductor wafer 13 changes depending on the location irradiated with the beam. Thus, it is necessary that a function of the objective lens exciting current required for focusing be a function of not only the accelerating voltage of the primary electron beam 11 and the height of the semiconductor wafer 13 but also the surface potential of the semiconductor wafer 13. In other words, it is impossible to focus the primary electron beam 11 on an observation point without considering surface potential information of the specimen in controlling the focal distance of the objective lens 106. The height information of a observation point can be obtained just before the observation (i.e. in real time) by using the height detection laser emission unit 108 and the height sensor 109. However, from the practical viewpoint, it is difficult to measure the surface potential at the location to be irradiated with the electron beam just before the observation (i.e. just before irradiation by the electron beam). Thus it is necessary to estimate the surface potential distribution of the specimen in advance and feed back the estimation to focus adjustment of the electron beam optical system 10. Thus, in the present embodiment, electrification potentials on the diameter of the semiconductor wafer 13 are actually measured in the course of transfer before the observation. Then, a two-dimensional interpolation function indicating potential distribution is obtained based on the measured values. And, potentials at observation points on the specimen are estimated by using the obtained interpolation function. The above-mentioned two-dimensional Interpolation function calculation processing, observation point potential calculation processing and focus adjustment processing of electron beam optical system 10 are performed when the operation part 221 of the integrated control part 220 executes programs stored in the storage part 231. As shown in FIG. 2, from the functional viewpoint, the integrated control part 220 comprises: a diameter direction potential distribution detection part 223 that obtains potentials at a plurality of points on the diameter of the semiconductor wafer 13 on the basis of potential information from the potential measuring unit 304 and wafer position information from an encoder or the like of the wafer transfer unit 302; a potential distribution storage part 232 that stores the potentials obtained by the diameter direction potential distribution detection part 223 with respect to the plurality of points on the diameter of the semiconductor wafer 13; a two-dimensional interpolation function generation part 224 that generates a two-dimensional interpolation function concerning potential distribution expressed on the polar coordinate system having the origin at the center of the semiconductor wafer 13; a two-dimensional interpolation function storage part 233 that stores the generated two-dimensional interpolation function; a coordinate transformation part 225 that transforms a coordinate value of an irradiated location (i.e. a observation point) on the semiconductor wafer 13, which is detected by the stage position detector 213, on the orthogonal coordinate system into a coordinate value on the polar coordinate system; a observation point potential calculation part 226 that calculates the potential at that observation point by using the two-dimensional interpolation function; a retarding potential calculation part 227 that obtains the retarding potential on the basis of the potential at that observation point; and an image processing part 228 that performs image processing with respect to the signal received from the secondary charged particle detector 107. The image processing part 228 comprises a focused state detection part 228a that judges whether a focused state is realized or not. Among the above-mentioned functional components, the potential distribution storage part 232 and the two-dimensional interpolation function storage part 233 are both secured in the storage part 231 of the integrated control part 220. Next, processing operation of the integrated control part 220, specifically details of the above-mentioned two-dimensional interpolation function calculation processing, observation point potential calculation processing and focus adjustment processing of electron beam optical system 10, will be described according to the flowchart shown in FIG. 3. When a user of the apparatus clicks a start button in a GUI screen displayed on the image display unit 211, the integrated control part 220 makes the wafer transfer unit 302 operate so that a semiconductor wafer 13 is taken out from the wafer cassette 301 and moved onto the aligner 307 as shown in FIG. 2 (S1). Subsequently, the integrated control part 220 makes the aligner 307 perform adjustment of the central axis of the semiconductor wafer 13 and related processing (S2). Usually, the semiconductor wafer 13 is formed with a cutout portion called a notch 13a. The aligner 307 adjusts the position of the semiconductor wafer 13 such that the notch 13a faces a prescribed direction and at the same time the rotation center of the aligner 307 coincides with the center of the semiconductor wafer 13. The position of the notch 13a is monitored by an optical sensor or the like of the aligner 307. Since it is not known which direction the notch 13a faces when the semiconductor wafer 13 is brought on to the aligner 307, the aligner 307 rotates the semiconductor wafer 13 on a rotating platform at least one rotation, and stops the rotation of the wafer 13 when the rotation center of the aligner 307 coincides with the center of the semiconductor wafer 13 and the notch 13a faces the prescribed direction. When the aligner 307 finishes the adjustment of the position and direction of the semiconductor wafer 13 (S3), then the integrated control part 220 makes the wafer transfer unit 302 transfer the semiconductor wafer 13 linearly toward the specimen exchange chamber 405 (S4). In the course of the linear transfer of the semiconductor wafer 13, potentials are detected at a plurality of points on a line passing through the center and the notch 13a of the semiconductor wafer 13 (S5). At that time, diameter direction potential distribution detection part 223 of the integrated control part 220 obtains potential distribution on the diameter of the semiconductor wafer 13 on the basis of the potential information from the potential measuring unit 304 and the wafer position information from the encoder or the like of the wafer transfer unit 302, and stores the obtained potential distribution in the potential distribution storage part 232. The potential distribution storage part 232 stores coordinate values of the potential detection locations and the respective potentials at those coordinate values in association with the respective coordinate values. Next, using the potentials at the plurality of points on the line passing through the semiconductor wafer 13, the two-dimensional interpolation function generation part 224 of the integrated control part 220 performs spline interpolation between potentials of detection points adjacent in the direction of the line passing through the center of the semiconductor wafer 13 and spline interpolation between potentials of detection points adjacent in the circumferential direction, to obtain a two-dimensional interpolation function concerning the potential distribution of the semiconductor wafer 13, and stores the obtained two-dimensional interpolation function in the two-dimensional interpolation function storage part 233 (S6). Details of the generation of this two-dimensional interpolation function will be described later. Further, this processing of generating the two-dimensional interpolation function can be performed at any time before the below-described step S12. Thereafter, the wafer transfer unit 302 sets the semiconductor wafer 13 on the specimen stage 401 through the specimen exchange chamber 405 (S7). The inside of the specimen exchange chamber 405 is kept in a decompressed state by the gate valve 306a. When the semiconductor wafer 13 is brought in, the gate valve 306a is released so that the inside pressure of the specimen exchange chamber 405 becomes the atmospheric pressure. When bring in to the specimen exchange chamber 405 is finished, the gate valve 306a is closed. Thereafter, when the internal pressure of the specimen exchange chamber 405 becomes equal to the internal pressure of the vacuum chamber 110, the gate valve 306b is opened and the semiconductor wafer 13 is set on the specimen stage 401. Then, by moving the stage, the semiconductor wafer 13 is moved to the position just under the electron optical lens barrel. To describe more strictly, it is necessary to go through a step of rough positioning by a light microscope in order to move the wafer to the electron beam irradiation position for obtaining a high magnification image used for measurement and inspection of the wafer. However, its description is omitted to avoid complications. Next, as shown in FIG. 2, the integrated control part 220 obtains offset values (ΔX, ΔY) between the origin of the stage coordinate system (X-Y coordinate system) and the center of the semiconductor wafer 13 on the specimen stage 401, sets a new X′-Y′ coordinate system having the origin at the center of the semiconductor wafer 13, and then sets a polar coordinate system having the origin at the origin of the X′-Y′ coordinate system (S8). Here, the Y direction and Y′ direction of the X-Y coordinate system and the X′-Y′ coordinate system are both the direction of transfer by the wafer transfer unit 302. And, the X direction and X′ direction are both perpendicular to the Y direction and the Y′ direction. Further, the offset values (ΔX, ΔY) are obtained from a sensor (not shown) for detecting the position of the semiconductor wafer 13 on the specimen stage 401. Next, the integrated control part 220 instructs the stage control unit 204 to make the specimen stage 401 move so that an alignment pattern provided in the neighborhood of one observation point among the plurality of observation points previously inputted to the integrated control part 220 comes to the location irradiated with the primary electron beam (S9). After this movement of the stage to the alignment pattern, the integrated control part 220 makes the height sensor 109 measure the height at the observation point, and transfers the height information to the objective lens control part 210 and the electron optical system control unit 203 (S10). As this alignment pattern, one located at a position very near to the observation point (for example, at a distance of several microns from the observation point) is selected. Thus, it can be said that the location irradiated with the primary electron beam is substantially the observation point. After the measurement of the height is finished, the integrated control part 220 sets a focus condition of the objective lens 106 (S11). Although, in fact, the accelerating voltage and current value of the primary electron beam are set before setting the focus condition, these setting steps are omitted in FIG. 3. In the focus setting of the objective lens 106, the exciting current value for the objective lens 106 is read out from an exciting current table stored in the electron optical system control unit 203, and transferred to the objective lens control unit 210. In this step, although an image is, broadly speaking, in focus, a completely-focused state is not attained owing to the effect of the surface potential of the semiconductor wafer 13. Thus, it is necessary to make fine adjustments to the focus by adjusting the retarding potential. The observation point potential calculation part 226 of the integrated control part 220 calculates the potential at the observation point by using the two-dimensional interpolation function stored in the two-dimensional interpolation function storage part 233 (S12). At that time, since the two-dimensional interpolation function is expressed by using variables of the polar coordinate system, the coordinate transformation part 225 transforms the X-Y coordinate value of the observation point detected by the stage position detector 213 into the polar coordinate value. The observation point potential calculation part 226 substitutes the polar coordinate value of the observation point into the two-dimensional interpolation function, to obtain the potential at the observation point. Next, the retarding potential calculation part 227 of the integrated control part 220 calculates the retarding potential Vr by using the potential Vexp at the observation point (S13). As described above, in the case where the semiconductor wafer 13 is not electrified, the surface potential of the semiconductor wafer 13 is equal to the retarding potential. On the other hand, in the case where the semiconductor wafer 13 is electrified, the surface potential of the semiconductor wafer 13 is the sum of the retarding potential and the potential owing to the electrification of the semiconductor wafer 13. Accordingly, to make the surface potential of the semiconductor wafer 13 coincide with the same constant potential as the one in the case of non-electrification of the semiconductor wafer 13, it is necessary to correct the retarding potential applied to the semiconductor wafer 13. Expressing the potential due to electrification of the semiconductor wafer 13 as Vs, the retarding potential in the case of non-electrification as Vo, and the retarding potential in the case of existence of electrification as Vr, the retarding potential Vr can be set as Vr=Vo−Vs. By this, it becomes possible to cancel the effect of the surface potential on the exciting current of the objective lens 106, so that the conditions of the exciting current required for focusing the primary electron beam 11 onto the semiconductor wafer 13 can be treated similarly to the case where the semiconductor wafer 13 is not electrified. That is to say, if the accelerating voltage of the primary electron beam 11 is constant, it becomes possible that the primary electron beam 11 is focused on a observation point of the semiconductor wafer 13 by feeding back the height information detected by the height sensor 109 at the observation point to the focal distance of the objective lens 106. Even if the two-dimensional interpolation function is used, it is difficult to reproduce completely the surface potential distribution of the semiconductor wafer 13 since the function is obtained on the basis of measured data at a limited number of points. Thus, in the present embodiment, a secondary charged particle scanning image is obtained while changing the retarding potential Vr in units of a suitable value d within a certain range Vvar, the focused state judgment of each of the two or more image data is executed. Here, as shown in FIG. 6, first, the potential Vexp affected by electrification at the observation point is subtracted from the retarding potential Vo in the case of non-electrification, the resultant potential (Vo−Vexp) is taken as a reference retarding potential, and an initial retarding potential Vr is determined as a potential obtained by subtracting the half value (Vvar/2) of the potential variation width Vvar from the reference retarding potential (S13). When the retarding potential Vr is calculated, the retarding potential calculation part 227 sets that value Vr in the retarding potential control part 212 (S14). When the value of the retarding potential is set, the retarding potential control part 212 applies the retarding potential of this value to the retarding pin 111 of the specimen stage 401. The integrated control part 220 instructs the electron optical system control unit 203 to make the primary electron beam irradiate the semiconductor wafer 13 on the specimen stage 401 (S15). As described above, this primary electron beam is extracted from the electron source 101 by the extraction electrodes 102a and 102b, focused by the condenser lens 103 and the objective lens 106, and irradiated onto the semiconductor wafer 13 on the specimen stage 401. By this irradiation of the semiconductor wafer 13 with the primary electron beam, secondary charged particles 12 are released from the semiconductor wafer 13 and detected by the secondary charged particle detector 107. The output from the secondary charged particle detector 107 is amplified by the amplifier 207, sent to the focused state detection part 228a of the integrated control part 220, and the focused stage detection part 228a judges whether a focused state is realized or not (S16). This judgment is performed by judging the sharpness of the secondary charged particle scanning image. For example, by filtering the image to highlight the edges of the alignment pattern, the focusing judgment can be made by considering the resultant contrast. When the focused state is realized, the processing goes to the below-described step S20. On the other hand, when the focused state is not realized, the prescribed increment value d is added to the previously-determined retarding potential Vr to obtain the result as a new retarding potential Vr (S17). Then, it is judged whether the new retarding potential Vr is larger than the upper limit ((Vo−Vexp)+Vvar/2) or not (S18). In the case where the new retarding potential Vr is larger than the upper limit to the retarding potential, the processing returns to the step S9, and the specimen stage 401 is moved so that a new observation point comes to the location to be irradiated, and performs the step 10 and the following steps. On the other hand, in the case where the new retarding potential Vr is less than or equal to the upper limit to the retarding potential, the new retarding potential Vr is set similarly to the step S14 (S19), and then it is judged whether the state is a focused state or not (S16). Then, until it is judged that the state is a focused state, the processing of the steps S16-S19 are repeated unless the retarding potential Vr exceeds the upper limit. When it is judged in the step S16 that the focused state is realized, actual measurement at the observation point is executed (S20). When the measurement at the observation point is finished, the integrated control part 220 judges whether another observation point remains or not (S20). The above processing of the steps S9-S21 is repeated until no observation point remains. In the above processing, when the retarding potential Vr exceeds the upper limit in the step S18, the location to be irradiated with the primary electron beam is moved to the next observation point. Instead, the variation width Vvar of the retarding potential Vr may be set to a larger value once again, to search for the optimum value of the retarding potential Vr. In that case, when a focused state is not realized even if resetting of the retarding potential is repeated several times, it is considered that either the prescribed exciting current value of the objective lens 106 or the calculated surface potential distribution function has some problem, the measurement of the height or the measurement of the surface potential of the semiconductor wafer 13 may be performed again. In the above-described embodiment, the retarding potential Vr is varied (changed) in units of the value d within the variation width Vvar, and thus a time required for obtaining the optimum value of the retarding potential Vr is proportional to (Vvar/d). Thus, from the viewpoint of reduction of measurement time, it is favorable that the variation width Vvar is smaller as far as possible. On the other hand, if the variation width Vvar is too small, it is more possible that the optimum value is out of the variation width Vvar of the retarding potential Vr, and many times it becomes impossible to perform the focusing adjustment automatically. However, in the present embodiment, the prediction accuracy of a potential of a semiconductor wafer 13 is improved by use of a two-dimensional interpolation function, as described above. As a result, the variation width Vvar can be made smaller, and the optimum value of the retarding potential Vr can be obtained at a high speed. The above-described focus setting is repeated for each observation point. This affects largely the processing time per wafer. For example, as regards length measurement, a time of 0-3 seconds is required in the present circumstances for each observation point in the optimum value determination step for the retarding potential. This is almost equal to a time of 0-3 seconds required for each observation point after finish of the focus adjustment. Thus, high speed obtainment of the optimum value of the retarding potential Vr is very valuable for improvement of throughput of the measurement as a whole. Next, a method of generating the above-mentioned two-dimensional interpolation function will be described. As shown in FIG. 4A, it is assumed here for the sake of convenience that the diameter of the semiconductor wafer 13 is 300 mm. Thus, in the above-described X′-Y′ coordinate system having its origin at the center of the semiconductor wafer 13, the notch 13a is located at (0, −150). In this X′-Y′ coordinate system, potential detection points are a point located at the position of (0, 0) (i.e. the center of the semiconductor wafer 13), five points on the Y′ axis on the side of the (+) Y direction (i.e. on the side of the bring-in direction), and five points on the Y′ axis on the side of the (−) Y direction (i.e. on the side of the taking-out direction), eleven points in total. The intervals between adjacent points are same one another. First spline interpolation is performed with respect to measured data at the eleven points by using the following equation Eq. 1, to estimate potential distribution on the Y′ axis. Here, potential distribution on the (−) side of the Y′ axis is written as VL and potential distribution on the (+) side of the Y′ axis as VU, and the potential distribution on the Y′ axis is estimated being divided into two parts. Although various functions can be used as a spline interpolation function, here interpolation is performed by using the measured data and second order derivatives of the measured data.VL=AVi+BVi+1+CVi″+DVi+1″ Eq. 1 Each coefficient A, B, C, D in Eq. 1 is defined as in Eq. 2. A = Y i + 1 - Y Y i + 1 - Y i ⁢ ⁢ B = Y - Y i Y i + 1 - Y i ⁢ ⁢ C = 1 6 ⁢ ( A 3 - A ) ⁢ ( Y i + 1 - Y i ) 2 ⁢ ⁢ D = 1 6 ⁢ ( B 3 - B ) ⁢ ( Y i + 1 - Y i ) 2 Eq . ⁢ 2 Here, i in Eqs. 1 and 2 is an argument indicating a point at which the surface potential is measured, and i is a natural number satisfying 1=<i=<10. And, Y means a coordinate of any position on the Y′ axis. Thus, Eq. 1 estimates a potential VL of any position on the Y′ axis on the (−) side by spline interpolation using measured data of adjacent points on both sides. Equations indicating the potential distribution VU on the Y′ axis on the (−) side are basically same as Eqs. 1 and 2. However, the argument i is different from that in the Eqs. 1 and 2. Next, using the obtained interpolated potential data (i.e. the potential distribution obtained on the line by the first interpolation) on the Y′ axis, second interpolation is performed to estimate the surface potential at any position (X, Y) on the semiconductor wafer 13. Since the semiconductor wafer 13 is usually circular, calculation becomes simpler when the Rθ polar coordinate system is used rather than the X′-Y′ orthogonal coordinate system. Thus, the following Eqs. 3 and 4 are used to transform the coordinate value (X, Y) on the wafer into the coordinate value (R, θ).R=√{square root over ((X)2+(Y)2)}{square root over ((X)2+(Y)2)} Eq. 3tan θ=Y/X Eq. 4 The potential V at any position (X, Y) (=(R, θ)) on the semiconductor wafer 13 is obtained by weighting each of the above-obtained potential Vu on the positive axis and potential VL on the negative axis, as shown in Eq. 5. This equation Eq. 5 is an equation that interpolates between two points on the Y′ axis, which are adjacent in the circumferential direction, i.e. on a prescribed radius R, as shown in FIG. 4B.V=EVL+FVU Eq. 5 Here, the weighting factors E and F in Eq. 5 are determined by the conditions shown in FIG. 6 considering the characteristics of electrification (i.e. symmetric property to some degree, electrification potential 0 outside the wafer area). E + F = 1 ⁢ ⁢ ∂ E ∂ θ = 0 ⁢ ⁢ ∂ F ∂ θ = 0 ⁢ ❘ θ = 0 ⁢ ° ⁢ ⁢ 180 ⁢ ° ⁢ ⁢ E = 0 ⁢ ⁢ F = 1 ⁢ ❘ θ = 180 ⁢ ° ⁢ ⁢ E = 1 ⁢ ⁢ F = 0 ⁢ ❘ θ = 0 ⁢ ° Eq . ⁢ 6 For example, functions shown in Eq. 7 satisfy this condition. E = cos 2 ⁡ ( θ 2 ) ⁢ ⁢ F = sin 2 ⁡ ( θ 2 ) Eq . ⁢ 7 The two-dimensional interpolation function generation part 224 of the integrated control part 220 generates the above equations and stores them in the two-dimensional interpolation function storage part 233, as described above. Then, the observation point potential calculation part 226 obtains the potential at the observation point (R, θ) on the semiconductor wafer 13 by substituting the value (R, θ) into the interpolation function expressed by the above equations. FIG. 4C and FIG. 4D show the resultant surface potential obtained for any position (X, Y) (=(R, θ)) on the semiconductor wafer 13 by using the two-dimensional interpolation function expressed by the above equations. Here, FIG. 4C shows two-dimensionally the potential distribution, and FIG. 4D shows three-dimensionally. Here, referring to FIGS. 5A and 5B, the potential distribution calculation method in the present embodiment will be compared with the conventional potential calculation method described in Patent Document 1. FIG. 5A shows the result obtained by the conventional method, and FIG. 5B shows the result obtained by the method of the present embodiment. The upper area of FIGS. 5A and 5B show two-dimensionally potential distributions obtained by these methods respectively, and the lower area of FIGS. 5A and 5B show three-dimensionally respective residuals between the potential distributions obtained by these methods and the actually-measured potential distributions. As described in the “Background of the Invention”, the conventional method uses actually-measured values at a plurality of points within the radius of the semiconductor wafer, approximates the potential distribution within the radius by a quartic function, and rotate the quartic function about the center of the wafer, to obtain a potential distribution function. As a result, the potential distribution on the wafer, which is obtained by this function, is rotationally symmetric, as shown in the upper area of FIG. 5A. Further, as shown in the lower area of FIG. 5A, the residual is larger on the Y′ axis. It is considered that this is caused by discontinuity of potentials between the start position and end position of rotation when one-dimensional interpolation data are rotated simply within a plane. On the other hand, in the method of the present embodiment, it can be seen that the potential distribution on the wafer is asymmetric, as shown in the upper area of FIG. 5B. Further, as shown in the lower area of FIG. 5B, the residual is smaller as a whole, and thus it can be understood that the potential distribution close to the actual distribution has been obtained. Thus, when the potential distribution on the wafer is estimated according to the present embodiment, the potential distribution on the wafer can be estimated accurately, and as a result, a suitable retarding potential can be set in a short time. Further, the adjustment time between the finish of the stage movement and the start of measurement can be shortened. In detail, the method of the present embodiment and the conventional method were compared regarding the time required for adjusting the retarding potential under the same conditions except for the method of estimating the surface potential distribution. As a result, the conventional method took 10 seconds for each of twenty observation points on a semiconductor wafer 13, i.e. 200 seconds in total. On the other hand, the method of the present embodiment took 10 seconds each for only five observation points on the semiconductor wafer 13, 3 seconds each for other eight observation points, and only 1 second each for the other seven observation points. In other words, the adjustment time per semiconductor wafer 13 was shortened from 200 seconds to 81 seconds. As described above, the present embodiment can shorten the time required before start of measurement, and thus can realize a scanning electron microscope that does not cause stress on a user. Further, when the present embodiment is applied to a measurement/inspection apparatus such as a length-measuring SEM, a review SEM or an appearance inspection apparatus, it is possible to realize an apparatus whose processing time per wafer is shorter and throughput is higher than that of the conventional apparatus. Further, in the case where a larger number of surface potential observation points are used, the prediction accuracy is improved and it becomes possible to perform focusing by using only prediction of surface potential distribution. In the first embodiment, potentials are measured only at points located on the Y′ axis, i.e. on the line passing through the center of a semiconductor wafer 13 and its notch 13a. In a second embodiment, as shown in FIG. 7, three detection probes 304a are provided in the direction of the X′ axis to improve the accuracy of detecting of potential distribution. Thus, potentials at points on three lines parallel to the Y′ axis are measured, and a two-dimensional interpolation function is obtained on the basis of the measured potential at these points. That is to say, the scanning electron microscope system of the present embodiment is different from the system of the first embodiment in that the three potential measuring units 304 are provided and a two-dimensional interpolation function is obtained on the basis of potentials measured by these potential measuring units 304, while the other characteristics are similar to those of the first embodiment. Thus, description of a configuration of the scanning electron microscope as a whole, each component and a general flow of operation will be omitted. As shown in FIG. 8A, here also a semiconductor wafer 13 having the diameter of 300 mm is considered similarly to the first embodiment. As described above, in the present embodiment, potentials are measured at points on the Y′ axis and points on two lines parallel to the Y′ axis. Here, the three lines are located at intervals of 90 mm. In other words, in the present embodiment, the three potential detection probes 304a are arranged at intervals of 90 mm on a line in the direction of the X′ axis. The surface potentials of the wafer are measured at nine points on a line (hereinafter, referred to as the line 1) that is parallel to the Y′ axis and passes through a point (−90, 0) in the X′-Y′ coordinate system having its origin at the center of the wafer, eleven points (same as the observation points in the first embodiment) on the Y′ axis (hereinafter, referred to as the line 2), and nine points on a line (hereinafter, referred to as the line 3) that is parallel to the Y′ axis and passes through a point (90, 0), i.e. twenty-nine points in total. A method of obtaining a two-dimensional interpolation function by using the above observation points will be described. First, first spline interpolation is performed using Eqs. 1 and 2 described in the first embodiment to obtain a potential distribution for each of the three lines. Next, similarly to the first embodiment, a coordinate value (X, Y) on the wafer is transformed into a coordinate value (R, θ) by using Eqs. 3 and 4. As shown in FIG. 8B, in an inside area of a circle C1 that is centered at the origin and has a radius of 90 mm, i.e. a circle whose diameter is the distance between the line 1 and the line 3, there is no circle that has any radius and intersects the lines 1 and 3. Thus, potential distribution is estimated separately in the area (the area S1) inside the circle C1 and in the area (the area S2) on the outer side of the circle C1. Relation between the shape of the area S1 and locations of observation points in this area S1 is basically same as that in the first embodiment. Thus, a two-dimensional interpolation function showing potential in the area S1 becomes that specified by Eq. 5 using only the information at points on the line 2, i.e. on the Y′ axis similarly to the first embodiment, without using information at locations on the lines 1 and 3. A two-dimensional interpolation function showing potential in the area S2 uses all information at points on the lines 1-3 in the area S2. Considering a circle that has any radius Rj and is included in the area S2, it is found that the circle in question includes six points at which the circle intersects one of the lines 1-3. The θ components of coordinates of these intersection points are written as θ1, θ2, θ3, θ4, θ5 and θ6. Expressing the potentials at the locations of these coordinates θ1-θ6 as V(Rj, θi)|{i: 1-6}, the potential at any location on the above radius Rj can be shown by the following equation Eq. 8 when second spline interpolation is performed using potentials at locations adjacent in the θ direction.V(Rj,θ)=AV(Rj,θi)+BV(Rj,θi+1)+CV″(Rj,θi)+DV″(Rj,θi+1) Eq. 8 Here, j is an argument for indicating a specific radius R in the area S2. Further, each coefficient A, B, C, D in the equation Eq. 8 is defined as in Eq. 9. A = θ ⁡ ( i + 1 ) - θ θ ⁡ ( i + 1 ) - θ ⁡ ( i ) ⁢ ⁢ B = θ - θ ⁡ ( i ) θ ⁡ ( i + 1 ) - θ ⁡ ( i ) ⁢ ⁢ C = 1 6 ⁢ ( A 3 - A ) ⁢ ( θ ⁡ ( i + 1 ) - θ ⁡ ( i ) ) 2 ⁢ ⁢ D = 1 6 ⁢ ( B 3 - B ) ⁢ ( θ ⁡ ( i + 1 ) - θ ⁡ ( i ) ) 2 Eq . ⁢ 9 Using the two-dimensional interpolation functions obtained by the above-described methods, i.e. the two-dimensional interpolation function shown in Eq. 5 for the inside of the area S1 and the two dimensional interpolation function shown in Eq. 7 for the inside of the area S2, the obtained surface potential for any position (X, Y) (=(R, θ)) on the semiconductor wafer 13 is shown in FIG. 8C. As shown in the figure, it is found that the surface potential distribution obtained in the present embodiment is emphasized in its asymmetry in comparison with the surface potential distribution that is obtained in the first embodiment and shown in FIG. 4C. In other words, more accurate potential distribution can be obtained by the present embodiment in comparison with the first embodiment. In the present embodiment, a two-dimensional interpolation function is obtained by measuring surface potentials on three lines on a semiconductor wafer 13. However, surface potentials may be measured on two or four or more lines, to obtain a two-dimensional interpolation function. In such a case, considering the symmetry of distribution of electrification, it is favorable that the line passing through the center of a specimen is always included. Accordingly, in the case where potentials are measured on a plurality of lines, it is favorable that the number of lines on which potentials are measured is an odd number (the line passing through the center and n lines on both sides) rather than an even number. However, even if the number of lines on which potentials are measured is increased more than some number, the improving effect on the potential estimation accuracy reduces gradually. Practically, it is favorable that the number of potential measuring units is between three and five. As described above, the present embodiment can further shorten the adjustment time in comparison with the first embodiment, and can raise throughput of measurement and inspection. In the first and second embodiments, potentials are measured only at points on a line or lines on a semiconductor wafer 13. Considering that potential distribution changes continuously also in the circumferential direction of a semiconductor wafer 13, it is expected that the estimation accuracy will be improved when potentials are measured also at a plurality of points in the circumferential direction of the semiconductor wafer 13 and thus-measured data also are used. Thus, in the present embodiment, potentials at a plurality of points located in the wafer's circumferential direction (i.e. the θ direction) are measured also, and a two-dimensional interpolation function is obtained by using thus-measured data also. As shown in FIG. 9, in the present embodiment, a potential detection probe 304a is provided also in the aligner 307 on which a semiconductor wafer 13 is rotated, in addition to a potential detection probe 304a arranged in the linear transfer path for the semiconductor wafer 13. By providing a potential detection probe 304a in the aligner 307, it becomes possible to detect also potentials at a plurality of points in the circumferential direction of a semiconductor wafer 13. In the present embodiment, a potential detection probe 304a is provided in the aligner 307. However, a mechanism for rotating a semiconductor wafer 13 may be provided separately so that a potential detection probe 304a is placed in this mechanism. However, from the viewpoint of observation efficiency, the present embodiment is more preferable than the case where the mechanism for rotating a semiconductor wafer 13 is provided separately. Functional components of the integrated control part 220 of the present embodiment are basically similar to those of the first embodiment. However, in the present embodiment, the integrated control part 220 further comprises a circumferential direction potential distribution detection part 222 for detecting also potentials at a plurality of points in the circumferential direction, in addition to the functional components of the integrated control part 220 of the first embodiment. The circumferential direction potential distribution detection part 222 obtains a potential distribution in the circumferential direction of a semiconductor wafer 13 on the basis of potential information received from the potential measuring unit 304 whose probe 304a is positioned in the aligner 307 and angle information received from a rotary encoder or the like of the aligner 307. The circumferential direction potential distribution detection part 222 stores the obtained potential distribution in the potential distribution storage part 232. This potential distribution storage part 232 stores a wafer rotation angle θ and a potential at that angle θ in association with the angle θ. Next, operation of the integrated control part 220 of the present embodiment will be described referring to the flowchart shown in FIG. 10. Similarly to the operation of the first embodiment shown in FIG. 3, in the present embodiment, the integrated control part 220 gives a wafer taking out instruction (S1) and an alignment-by-aligner instruction (S2). Next, with regard to adjustments by the aligner 307, i.e. adjustment of the rotation axis of the semiconductor wafer 13 and adjustment of the direction of the wafer 13, first the integrated control part 220 judges whether the rotation axis has been adjusted properly, i.e. whether the center of rotation of the aligner 307 coincides with the center of the semiconductor wafer 13 (S3a). When it is judged that the center of rotation of the aligner 307 coincides with the center of the semiconductor wafer 13, then the circumferential direction potential distribution detection part 222 of the integrated control part 220 detects potential distribution in the circumferential direction while the aligner 307 keeps rotating the semiconductor wafer 13 (S5a). As described above, the circumferential direction potential distribution detection part 222 obtains potential information of a plurality of points of the rotating semiconductor wafer from the potential measuring unit 304 whose probe 304a is positioned in the aligner 307 and angle information of these points from the rotary encoder or the like of the aligner 307, and stores the obtained information in the potential distribution storage part 232. When this circumferential potential distribution detection is finished, then the integrated control part 220 judges whether the direction has been adjusted properly, i.e. whether the notch 13a of the semiconductor wafer 13 faces a prescribed direction or not (S3b). When it is judged that the notch 13a of the semiconductor wafer 13 faces the prescribed direction, then the rotation of the semiconductor wafer 13 by the aligner 307 is stopped immediately, and the wafer transfer unit 302 transfers the semiconductor wafer 13 linearly toward the specimen exchange chamber 405 (S4). Then, similarly to the first embodiment, potential distribution on the semiconductor wafer 13 is detected in the linear direction (S5). Thereafter, the integrated control part 220 operates in a manner basically similar to the first embodiment. Next, a method of generating a two-dimensional interpolation function in the present embodiment will be described referring to FIGS. 11A, 11B, 11C and 11D. As shown in FIG. 11A, similarly to the first embodiment, a semiconductor wafer 13 having the diameter of 300 mm is considered here also. As described above, in the present embodiment, potentials are measured at points on the Y′ axis and at points on a circle whose center is positioned at the center of the semiconductor wafer 13. The radius of this circle is 90 mm. Wafer surface potentials are measured at eleven points on the Y′ axis of the X′-Y′ coordinate system having its origin at the center of the wafer and eight points on the circle having the radius of 90 mm including a point at (0, −90), a point at (90, 0), a point at (0, 90) and a point at (−90, 0), i.e. nineteen points in total. To generate a two-dimensional interpolation function by using the measured data, first the spline interpolation is performed with respect to the measured data of the eleven points on the Y′ axis by using Eqs. 1 and 2 described in the first embodiment, to obtain potential distributions VU and VL on the Y′ axis. Next, a potential distribution on the circle of the radius 90 mm is obtained. Writing surface potential at any location (R, θ) of the wafer as V(R, θ), potential distribution Vθ on the circle is written as V(R=90, θ). When “R=90” is generalized to Rj, the interpolation function can be written as Eq. 10.V(Rj,θ)=AV(Rj,θi)+BV(Rj,θi+1)+CV″(Rj,θi)+DV″(Rj,θi+1) Eq. 10 Here, each coefficient A, B, C, D in the equation Eq. 10 is defined as follows. A = θ i + 1 - θ θ i + 1 - θ i ⁢ ⁢ B = θ - θ i θ i + 1 - θ ⁢ ⁢ C = 1 6 ⁢ ( A 3 - A ) ⁢ ( θ i + 1 - θ ) 2 ⁢ ⁢ D = 1 6 ⁢ ( B 3 - B ) ⁢ ( θ i + 1 - θ ) 2 Eq . ⁢ 11 In Eqs. 10 and 11, the argument j is an argument for indicating a specific position in the radial direction, and the argument i an argument for indicating a specific position in the θ direction. Next, as shown in FIG. 11B, interpolation operation is performed by using the above-described VU, VL and V(Rj, θi), to calculate potential for any location on the wafer. The interpolation formula that describes the surface potential V(R, θ) at any location (R, θ) on the wafer can be expressed as in Eq. 12 using potentials VLj, VUj at intersection points (R, 0) and (R, π) of a circle of the radius R and the Y axis, and a potential V(R=Rj, θ) at an intersection point of that Vθ and a line segment connecting the point (R, θ) and the origin. In other words, Eq. 12 is obtained by weighting VU, VL and V(Rj, θi) and adding the results.V=EVLj+FVUj+GVθi Eq. 12 Here, Vθi is a simplified expression for V(R=Rj, θ) and is used in order to avoid complication. FIG. 11B shows the above relations. Further, each coefficient in the equation Eq. 12 is defined to satisfy the following conditions. E + F + G = 1 Eq . ⁢ 13 ∂ E ∂ θ = 0 ⁢ ⁢ ∂ F ∂ θ = 0 ⁢ ❘ θ = 0 ⁢ ° ⁢ ⁢ 180 ⁢ ° ⁢ ⁢ E = 0 ⁢ ⁢ F = 1 ⁢ ❘ θ = 180 ⁢ ° ⁢ ⁢ E = 1 ⁢ ⁢ F = 0 ⁢ ❘ θ = 0 ⁢ ° Eq . ⁢ 14 ∂ E ∂ R = 0 ⁢ ⁢ ∂ F ∂ R = 0 ⁢ ⁢ ∂ G ∂ R = 0 ⁢ ❘ R = 0 ⁢ ⁢ 90 ⁢ ⁢ mm ⁢ ⁢ 150 ⁢ ⁢ mm ⁢ ⁢ G = 0 ⁢ ❘ R = 0 ⁢ ⁢ mm ⁢ ⁢ G = 1 ⁢ ❘ R = 90 ⁢ ⁢ mm ⁢ ⁢ G = 0 ⁢ ❘ 150 ⁢ ⁢ mm ⁢ ⁢ E = 0 ⁢ ⁢ F = 0 ⁢ ❘ 90 ⁢ ⁢ mm ≤ R ≤ 150 Eq . ⁢ 15 As a function satisfying the above equations Eqs. 13-15, there is a function shown in Eq. 16, for example. E = cos 2 ⁡ ( θ 2 ) ⁢ cos 2 ⁡ ( 90 ⁢ ° ⁢ R 90 ⁢ ⁢ mm ) ⁢ ⁢ F = sin 2 ⁡ ( θ 2 ) ⁢ cos 2 ⁡ ( 90 ⁢ ° ⁢ R 90 ⁢ ⁢ mm ) ⁢ ⁢ G = sin 2 ⁡ ( 90 ⁢ ° ⁢ R 90 ⁢ ⁢ mm ) ⁢ ❘ R ≤ 90 ⁢ ⁢ mm ⁢ ⁢ E = cos 2 ⁡ ( θ 2 ) ⁢ cos 2 ⁡ ( 90 ⁢ ° ⁢ 150 ⁢ ⁢ mm - R 60 ⁢ ⁢ mm ) ⁢ ⁢ F = sin 2 ⁡ ( θ 2 ) ⁢ cos 2 ⁡ ( 90 ⁢ ° ⁢ 150 ⁢ ⁢ mm - R 60 ⁢ ⁢ mm ) ⁢ ⁢ G = sin 2 ⁡ ( 90 ⁢ ° ⁢ 150 ⁢ ⁢ mm - R 60 ⁢ ⁢ mm ) ⁢ ❘ R ≥ 90 ⁢ ⁢ mm Eq . ⁢ 16 FIGS. 11C and 11D show the resultant surface potential for any location (X, Y) (=(R, θ)) on the semiconductor wafer 13, which has been obtained by using the two-dimensional interpolation function shown as Eq. 12. Here, FIG. 11C shows the potential distribution two-dimensionally, and FIG. 11D shows the potential distribution three-dimensionally. Here, referring to FIGS. 12A and 12B, the potential distribution calculation method in the present embodiment will be compared with the potential distribution calculation method in the first embodiment. FIG. 12A shows the result obtained by the method of the first embodiment, and FIG. 12B shows the result obtained by the method of the present embodiment. The upper area of FIGS. 12A and 12B show two-dimensionally potential distributions obtained by these methods respectively, and the lower area of FIGS. 12A and 12B show three-dimensionally respective residuals between the potential distributions obtained by these methods and the actually-measured potential distributions. It can be seen from the figure that the potential distribution obtained by the present embodiment expresses asymmetry of the distribution better, meaning that the result closer to the actual potential distribution has been obtained. Further, although not shown here, the method of the present embodiment can obtain potential distribution closer to the actual potential distribution than that obtained by the method of the second embodiment, in many cases. Thus, in comparison with the first and second embodiments, the present embodiment can further shorten the adjustment time between the finish of the stage movement and the start of measurement. In detail, the method of the present embodiment and the method of the first embodiment were compared regarding the time required for adjusting the retarding potential under the same conditions except for the methods of estimating the surface potential distribution. As a result, the method of the first embodiment took 10 seconds each for five points among twenty observation points on the semiconductor wafer 13, three seconds each for eight points, 1 second each for the other seven points, i.e. 81 seconds in total. On the other hand, according to the method of the present embodiment, the adjustment took 10 seconds each for only two points among the twenty points, three seconds each for eight points, and 1 second for ten points, i.e. only 54 seconds in total. In other words, it was possible to shorten the adjustment time per semiconductor wafer from 81 seconds in the first embodiment to 54 seconds. As described above, the present embodiment can realize a scanning electron microscope whose adjustment time is further shorter than those of the first and second embodiments. Further, it goes without saying that, when the present embodiment is applied to a measurement/inspection apparatus such as a length-measuring SEM, a review SEM or an appearance inspection apparatus, throughput higher than those of the first and second embodiments can be realized. In that case, larger the number of observation points per wafer is, higher the throughput improvement effect as a whole is. In particular, when the present invention is applied to an appearance inspection apparatus or a review SEM, this effect is larger. The above embodiments have been described taking an example of a scanning electron microscope. However, it goes without saying that the methods of these embodiments can be applied widely to charged particle beam apparatuses in general (such as ion beam processing apparatuses and ion beam irradiation apparatuses) as far as they are systems in which focus deviation due to electrification becomes a problem (i.e. not only systems using an electron beam but also systems using an ion beam, for example). Further, in the above embodiments, a semiconductor wafer has been mentioned as an example of specimen. The present invention, however, is not limited to a semiconductor wafer, and can be applied to other kinds of specimens such as a glass substrate, a magnetic disk substrate, a metal substrate formed with insulating film or the like, for example. Further, a potential measuring unit 304 having a detection probe 304a has been used as a potential measurement means for measuring the surface potential of a specimen. However, other measuring devices such as a potential measuring device using the absorption current measurement method may be employed, for example. Further, such a measuring unit may be arranged at any location. The arrangements shown in the above embodiments are ones that are favorable from the viewpoint of throughput only. Further, in the above embodiments, the polar coordinate system has been used for obtaining a two-dimensional potential distribution function. However, any coordinate system, such as an orthogonal coordinate system or a non-orthogonal coordinate system for example, can be employed as far as it can express a two-dimensional interpolation function, i.e. it is a coordinate system having two base vectors. Further, in the above embodiments, estimated potentials have been used for obtaining a retarding potential for focus adjustment, which is a setting parameter of an electron beam optical system 10. However, not only the retarding potential but also the estimated potentials may be used for obtaining the amplitude of a driving signal of the scanning deflector, the exciting current of the objective lens 106, the focus drive voltage of the objective lens 106, or the like. Further, the estimated potentials may be used in the pre-dose technique in which a wafer is irradiated with an electron beam before obtaining an SEM image of the wafer, in order to control the electrification potential of the wafer.

description

This application claims priority to European application EP 09305767.7, filed on Aug. 18, 2009, the entire disclosure of which is incorporated by reference herein. The invention relates to a method for modelizing the core of a nuclear reactor, especially for calculating neutron flux within the core. The results of such a modelizing method can be used to prepare safety analysis reports before building and starting a reactor. These results can also be useful for existing nuclear reactors and especially for managing the nuclear fuel loaded therein. In particular, these results can be used to assess how the core design should evolve in time and decide of the positions of the fuel assemblies in the core, especially the positions of the fresh assemblies to be introduced in the core. Such modelizing methods are implemented by computers. To this end, the core is partitioned in cubes, each cube constituting a node of a grid for implementing a digital computation. Usually the steady-state diffusion equation to be solved during such a digital computation amounts to: Σ Rg m ⁢ ϕ g m ︸ removal = λχ g ⁢ ∑ g ′ = 1 G ⁢ νΣ fg ′ m ⁢ ϕ g ′ m ︸ production + ∑ g ′ ≠ g G ⁢ Σ gg ′ m ⁢ ϕ g ′ m ︸ inscatter + ∑ u = x , y , z ⁢ 1 a u m ⁢ θ gu m ⁡ ( j gul + m + j gur - m ︸ incurrent ) , ( 1 ) ⁢ with ⁢ ⁢ { Σ Rg m = Σ ag m + ∑ g ′ ≠ g G ⁢ Σ g ′ ⁢ g m + ∑ u = x , y , z ⁢ 2 ⁢ c 1 ⁢ gu m a u m θ gu m = 1 - c 2 ⁢ gu m - c 3 ⁢ gu m , ( 2 ) where λ is a first neutron eigenvalue, m is a cube index, also called nodal index, G is the number of neutron energy groups and g, g′ are neutron energy group indexes, u is a Cartesian axis index of the cube, Σagm represents macroscopic absorption cross-section for the cube m and the energy group g, Σfgm represents macroscopic fission cross-section for the cube m and the energy group g′, Σgg′m represents macroscopic slowing down cross-section for the cube m and the energy groups g, Φgm represent neutron fluxes, such that the ΣRgm, . . . Φgm represent the reaction rates for the corresponding reactions (absorption, fission), ν is the number of neutrons produced per fission, χg is the fraction of neutrons emerging from fission with neutron energy g, aum is the width of cube m along Cartesian axis u, and with the relationship between the neutron outcurrents jgul−m and jgur+m, neutron fluxes Φgm and neutron incurrents jgul+m and jgur−m defined by: { j gul - m = c 1 ⁢ gu m ⁢ ϕ g m + c 2 ⁢ gu m ⁢ j gul + m + c 3 ⁢ gu m ⁢ j gur - m j gur + m = c 1 ⁢ gu m ⁢ ϕ g m + c 3 ⁢ gu m ⁢ j gul + m + c 2 ⁢ gu m ⁢ j gur - m ( 3 ) The coefficients cigum, with i=1, 2, 3, are characteristic of the cube m and depend on nodal dimensions and macroscopic cross-sections Σm. FIG. 1 is a schematic representation in two dimensions of a cube m showing the neutron incurrents jgul+m and jgur−m for u=x, y and z; the neutron outcurrents jgul−m and jgur+m for u=x, y and z; and the neutron fluxes Σgm. Indexes l, respectively r, refers to each left interface surface, respectively each right interface surface, of the cube m for the respective Cartesian axis x, y. Indexes +, respectively −, represents the orientation from left to right, respectively from right to left, for the respective Cartesian axis x, y. The steady-state diffusion equation (1) is also named NEM equation, for Nodal Expansion Method equation. In the state of the art methods, most of the computational efforts are concentrated in the part dedicated to the iterative solving of a large eigensystem corresponding to the steady-state diffusion equation (1). In order to lower these computational efforts and therefore accelerate the solving of the eigensystem, Coarse Mesh Rebalancing (CMR) procedures have been used. In these procedures, neutron fluxes and currents for a given iteration are multiplied with a corrective factor before pursuing subsequent computationally expensive iterations. The multiplicative correction serves to suppress the presence of a non fundamental wavelength part of eigenspectrum with the first neutron eigenvalue λ close to an exact value λexact. However, the acceleration effect realized in this way depends on the numerical proximity of the highest coarse mesh level in a multi-level hierarchy to the full-core diffusion level. Such CMR procedures may therefore lead to very slow convergence or even convergence stagnation, thus increasing the computational effort. An object of the present invention is to solve the above-mentioned problems by providing a nuclear reactor modelizing method which offers a better convergence accuracy, a better computational robustness and a better computational efficiency so that relevant neutron flux calculations can be obtained within a short computational time period and with a very good convergence accuracy. The present invention provides a computer implemented method for modelizing a nuclear reactor core, comprising the steps of: partitioning the core in cubes (10) to constitute nodes of a grid (12) for computer implemented calculation, calculating neutron flux by using an iterative solving procedure of at least one eigensystem, the components of an iterant of the eigensystem corresponding either to a neutron flux, to a neutron outcurrent or to a neutron incurrent, for a respective cube (10) to be calculated, wherein a control parameter is varied to impact a neutron eigenvalue μ through a perturbed interface current equation and drive the neutron eigenvalue μ towards l. The present invention also provides a computer program product residing on a computer readable medium and comprising computer program means for miming on a computer implemented method. In the following description, the case of a pressurized water reactor (PWR) will be considered, but it should be kept in mind that the present invention applies to other types of nuclear reactors. In a first step of the computer implemented modelizing method according to the invention, the core of the reactor is partitioned in cubes 10 (shown on FIG. 2) as in the state of art methods. Each cube 10 corresponds to a node of a grid or network 12 on which numerical computation will be implemented through the computer. In order to ease the representation, the grid 12 is shown on FIG. 2 as being two-dimensional, but it should be kept in mind that the grid is actually three-dimensional in order to represent the whole core. The neighbours of the cube 10 with the cube index m (in the center of FIG. 2) are the cubes 10 with the respective cube index m′1(m), m′2(m), m′3(m) and m′4(m). In the following of the description, the cubes 10 will be directly designated by their respective cube index. In a second step of the computer implemented modelizing method according to the invention, the neutron fluxes Φgm within the core will be calculated by the solving of an eigensystem corresponding to the steady-state diffusion equation (1). To this end, an iterative solving procedure is used. A removal operator {circumflex over (R)}, an inscatter operator Ŝ, a production operator {circumflex over (F)}, and an incurrent operator Ĝ are defined, from Equation (1), by: { [ R ^ ⁢ ϕ ] g m = ( Σ ag m + ∑ g ′ ≠ g G ⁢ Σ g ′ ⁢ g m ) ⁢ ϕ g m [ S ^ ⁢ ϕ ] g m = ∑ g ′ ≠ g G ⁢ Σ gg ′ m ⁢ ϕ g ′ m [ F ^ ⁢ ϕ ] g m = χ g ⁢ ∑ g ′ = 1 G ⁢ νΣ fg ′ m ⁢ ϕ g ′ m [ G ^ ⁢ J ] gu m = ∑ u = x , y , z ⁢ 1 a u m ⁢ θ gu m ⁡ ( j gul + m + j gur - m ) ( 4 ) An isotropic outcurrent generation operator {circumflex over (Π)} and a mono-directional current throughflow operator {circumflex over (Ω)} are defined by: { [ Π ^ ⁢ ϕ ] gu m = c 1 ⁢ gu m ⁢ ϕ g m [ Ω ^ ⁢ J ] gul - m = c 2 ⁢ gu m ⁢ j gul + m + c 3 ⁢ gu m ⁢ j gur - m [ Ω ^ ⁢ J ] gur + m = c 3 ⁢ gu m ⁢ j gul + m + c 2 ⁢ gu m ⁢ j gur - m ( 5 ) A coupling operator Ŷ couples the outcurrents to the incurrents for neighbouring cubes 10, and is defined by: { j gul + ( m ) = [ Y ^ ⁢ J ] gul + ( m ) = j gur + ( m - 1 ) j gur - ( m ) = [ Y ^ ⁢ J ] gur - ( m ) = j gul - ( m + 1 ) j gul - ( m ) = [ Y ^ ⁢ J ] gul + ( m ) = j gur - ( m - 1 ) j gur + ( m ) = [ Y ^ ⁢ J ] gur - ( m ) = j gul + ( m + 1 ) , ( 6 ) This coupling operator Ŷ uses the fact that, for example, for a cube m, the u-directional left-oriented outcurrent equals the u-directional left-oriented incurrent for the left neighbour in direction of the Cartesian axis u, and that similar equalities are verified for the other directions and orientations. For example, the neutron outcurrents coming from respective neighbours m′1(m), m′2(m), m′3m), m′4(m) into the cube m are the neutron incurrents for the cube m, as the neighbours m′1(m), m′2(m), m′3m), m′4(m) shown in FIG. 2 are respectively the neighbours (m+1) for the Cartesian axis y, (m−1) for the Cartesian axis x, (m+1) for the Cartesian axis x and (m−1) for the Cartesian axis y of Equation (6). Using the above operators, the equations (1) and (2) can be written as: { R ^ ⁢ ϕ = ( λ ⁢ F ^ + S ^ ) ⁢ ϕ + G ^ ⁢ j ( in ) j ( out ) = Π ^ ⁢ ϕ + Ω ^ ⁢ j ( in ) j ( in ) = Y ^ ⁢ j ( out ) , ( 7 ) or as: ( R ^ - S ^ - λ ⁢ F ^ 0 ^ G ^ - Π ^ 1 ^ - Ω ^ 0 ^ - Y ^ 1 ^ ) ⁢ ( ϕ j ( out ) j ( in ) ) = ( 0 0 0 ) ( 8 ) which is the eigensystem to be solved. In Equation (8), Φ is a neutron flux column vector, wherein each element is a neutron flux Φgm for a respective cube m and for a respective energy group g (FIG. 1). Thus, the dimensions of the neutron flux column vector Φ are equal to (G×M, 1), where G is the number of energy groups and M is the number of cubes 10. j(out) is a neutron outcurrent column vector, wherein each element is a respective neutron outcurrent jgul−m, jgur+m, for the respective cube m, energy group g and Cartesian axis u, with u equal to x, y or z. j(in) is a neutron incurrent column vector, wherein each element is a respective neutron incurrent jgul+m, jgur−m, for the respective cube m, energy group g and Cartesian axis u. Thus, the dimensions of the neutron outcurrent vector column j(out) and the neutron incurrent vector column j(in) are equal to (6×G×M, 1). In the following of the description, the neutron outcurrent vector column j(out) is also noted jout. Thus, the components of an iterant (Φ, j(out), j(in)) of the eigensystem defined by Equation (8) correspond to the neutron fluxes Φgm, the neutron outcurrents jgul−m, jgur+m, and the neutron incurrents jgul+m, igur−m, to be calculated for each cube m and for each energy group g, and which are the respective elements of the neutron flux column vector Φ . . . the neutron outcurrent column vector j(out) and the neutron incurrent column vector j(in). The iterative solving procedure comprises a substep of conditioning the eigensystem into a spare eigensystem wherein the components of an iterant (j(out), j(in)) of the spare eigensystem only correspond either to the neutron incurrents jgul+m,jgur−m coming into the respective cube m or to the neutron outcurrents jgul−m,jgur+m coming from the respective cube m, which are the respective elements of the neutron outcurrent column vector j(out) and the neutron incurrent column vector j(in). The conditioning of the eigensystem into a spare eigensystem starts from modifying the first part of Equation (8) written as:({circumflex over (R)}−Ŝ−λ{circumflex over (F)})φ−Ĝj(in)=0, (9) Defining the symbolic operator {circumflex over (P)}λ=({circumflex over (R)}−Ŝ−λ{circumflex over (F)})−1, the neutron flux column vector Φ is expressed in function of the neutron incurrent column vector j(in) as:φ={circumflex over (P)}λĜj(in) (10) By substituting this expression in the outcurrent equation part of Equation (7), i.e. in the second part of Equation (8), a currents-only relationship is obtained:j(out)=[{circumflex over (Π)}{circumflex over (P)}λĜ+{circumflex over (Ω)}]j(in) (11) After defining the following operator notations:{circumflex over (θ)}λ={circumflex over (Π)}{circumflex over (P)}λ (12)and{circumflex over (B)}λ={circumflex over (θ)}λĜ+{circumflex over (Ω)}, (13) the currents-only relationship is written as:j(out)={circumflex over (B)}λj(in) (14) which is a spare eigensystem. Using the relationship j(in)=Ŷj(out) between the neutron outcurrent column vector j(out) and the neutron incurrent column vector j(in), where Ŷ is the coupling operator, a spare eigensystem is obtained wherein the components of an iterant (j(out)) of the spare eigensystem only correspond to the neutron outcurrents jgul−m,jgur+m coming from the respective cube m, which are the elements of the neutron outcurrent column vector j(out). This spare eigensystem corresponds to:[{circumflex over (1)}−{circumflex over (B)}λŶ]j(out)=0 (15) Since the operator {circumflex over (B)}λŶ will initially not be exactly equal to 1, and will become equal to 1 only as j(out) converges to the exact solution j(out)exact and if simultaneously the first neutron eigenvalue μ converges to an exact value λexact, so that Equation (15) becomes:[{circumflex over (1)}−μ{circumflex over (B)}λŶ]j(out)=0, (16) with a second neutron eigenvalue μ converging towards 1, if the first neutron eigenvalue λ converges to the exact value λexact. For numerical optimization, Equation (16) may be modified through a premultiplication with the operator Π−1 and the following equation is obtained:{circumflex over (Π)}−1j(out)=μ[{circumflex over (P)}λĜ+{circumflex over (Π)}−1{circumflex over (Ω)}]Ŷj(out) (17) The term {circumflex over (P)}λĜŶj(out) is an isotropic term, which does not depend on the Cartesian direction u. The expressions of the respective terms from Equation (17) for the cube index m, Cartesian axes u, u′ and the respective orientations s, s′ along the Cartesian axes u, u′ are given by: { A mGus = ∑ g ∈ G ⁢ [ Π ^ - 1 ⁢ j ( out ) ] mgus Q mG G ′ ⁢ u ′ ⁢ s ′ = ∑ g ∈ G ⁢ ∑ g ′ ∈ G ′ ⁢ [ P ^ λ ⁢ G ^ ⁢ Y ^ ⁢ j ( out ) ] mg g ′ ⁢ u ′ ⁢ s ′ C mGus s ′ = ∑ g ∈ G ⁢ [ Π ^ - 1 ⁢ Ω ^ ⁢ Y ^ ⁢ j ( out ) ] mgus s ′ ( 18 ) ⁢ ⁢ ( 19 ) ⁢ ⁢ ( 20 ) G, G′ are sets of energy groups. Â and Ĉ are mono-energetic operators with their respective factors AmGus and CmGuss′.QmGG′u′s′ are the factors of a spectral operator {circumflex over (Q)}λ. It should be noted that each combination {u, s}, respectively {u′, s′}, defines an interface surface of the cube m with u, u′ equal to x, y or z, and s, s′ equal to 1 or r. For example, {x, 1} defines the left interface surface of the cube m along the Cartesian axis x. The individual terms are given by: [ Π ^ - 1 ⁢ j ( out ) ] mgus = 1 c 1 ⁢ ⁢ gu m ⁢ j mgus ( out ) ( 21 ) [ P ^ λ ⁢ G ^ ⁢ Y ^ ⁢ j ( out ) ] mg g ′ ⁢ u ′ ⁢ s ′ = ∑ g ′ = 1 ng ⁢ ⁢ P ^ gg ′ ⁡ [ G ^ ⁢ Y ^ ⁢ j ( out ) ] mgus u ′ ⁢ s ′ = ∑ g ′ = 1 ng ⁢ ⁢ P ^ gg ′ ⁢ 1 a u ′ m ⁢ θ g ′ ⁢ u ′ m ⁢ j g ′ m ← η ⁡ ( mu ′ ⁢ s ′ ) ( 22 ) [ Π ^ - 1 ⁢ Ω ^ ⁢ Y ^ ⁢ j ( out ) ] mgus s ′ = 1 c 1 ⁢ ⁢ gu m ⁡ [ c 2 ⁢ ⁢ gu m ⁢ δ ss ′ + c 3 ⁢ ⁢ gu m ⁡ ( 1 - δ ss ′ ) ] ⁢ j g m ← η ⁡ ( mus ′ ) ( 23 ) Equation (17) is then solved, e.g. by using a conventional iterative solving procedure as a Gauss-Seidel procedure. Thus, a solution is calculated for the elements j(out)mgus of the neutron outcurrent column vector j(out). This enables to determine the solution of the neutron incurrent column vector j(in) according to Equation (14), and finally to determine the solution of the neutron flux column vector Φ according to Equation (10). The calculated neutron flux column vector Φ obtained through the modelizing method can be used to control an existing nuclear reactor core, e.g. for managing the nuclear fuel, or be used for building a new reactor core. The modelizing method may be implemented on parallel processors or on a single processor. This above-disclosed modelizing method has proved to lead to better convergence accuracy, a better computational robustness and a better computational efficiency. This is connected to the solving of a sparse eigensystem wherein the only components of the iterant correspond to neutron outcurrents j(out), and do not depend on neutron fluxes. Further, the convergence accuracy of the modelizing method according to the invention may be improved up to 1E-12, whereas the convergence accuracy obtained with a classic modelizing method is limited to 1E-6. In other embodiments, the components of the iterant of the spare eigensystem to be solved correspond only to neutron incurrents j(in). In order to further improve robustness and computational efficiency, according to a second aspect of the invention, the eigensystem is first conditioned in a restricted eigensystem corresponding to the eigensystem for a selection of some neutron energy groups. This selection is also called spectral restriction to some energy groups. The restricted eigensystem may then be solved according to the first aspect of the invention. Finally, the solution of the restricted eigensystem is used to solve the eigensystem. The number NGC of the selected energy groups is smaller than the total number ng of energy groups. NGC may be the number of coarsened spectral bands which are collections of fine energy groups merged into a smaller number of coarse energy groups. ng is, for example, equal to 8, and NGC may for example be equal to 4, 3, 2 or 1. According to this second aspect, the Equation (17) for the driving factors dGmus(out), with its respective terms given by Equations (18) to (20), is expressed as: A Gmus ( out ) ⁢ d Gmus ( out ) ︸ outflow ″ `` = μ [ ∑ G ′ = 1 NGC ⁢ ⁢ ∑ u ′ = 1 3 ⁢ ⁢ ∑ s ′ = 1 , r ⁢ ⁢ Q mG G ′ ⁢ u ′ ⁢ s ′ ⁢ d G ′ ⁢ η ⁡ ( mu ′ ⁢ s ′ ) ⁢ u ′ ⁢ s ′ ( out ) ︸ `` ⁢ isotropic ⁢ ⁢ production ″ + ∑ s ′ = 1 , r ⁢ ⁢ C mGus s ′ ⁢ d Gmus ′ ( out ) ︸ throughflow ″ `` ] ( 24 ) where G, G′ are coarse neutron energy group indexes, and in which an isotropic term ∑ G ′ = 1 NGC ⁢ ⁢ ∑ u ′ = 1 3 ⁢ ⁢ ∑ s ′ = 1 , r ⁢ ⁢ Q mG G ′ ⁢ u ′ ⁢ s ′ ⁢ d G ′ ⁢ η ⁡ ( mu ′ ⁢ s ′ ) ⁢ u ′ ⁢ s ′ ( out ) is independent of the outgoing current direction specified by the Cartesian axis u and orientation s, and a throughflow term ∑ s ′ = 1 , r ⁢ ⁢ C mGus s ′ ⁢ d Gmus ′ ( out ) ,also called anisotropic term, is defined within the same coarse neutron energy group G along the same Cartesian axis u. The decomposition of the outcurrents leaving the cube m into isotropic and anisotropic terms is illustrated on FIG. 3. The isotropic term is the same in all directions and the anisotropic term varies between interface surfaces of the cube m. Solving at first the eigensystem for a spectral restriction to some energy groups, moreover with a decomposition of the outcurrents in which the isotropic term is computed easily, leads to a better computational robustness and a better computational efficiency. This is connected to the reduction of eigensystem dimensions that results from the spectral restriction according to this second aspect of the invention. In order to further improve robustness and computational efficiency, according to a third aspect of the invention, the iterative solving procedure for a plurality of energy groups may be in form of a multi-level V-cycle 20, as shown on FIG. 4, comprising a top level 21, a first intermediate level 22, four second intermediate levels 24, 26, 28, 30, and three bottom levels 32, 34, 36. The top level 21 of the V-cycle comprises the iteration for the eigensystem corresponding to the steady-state diffusion equation (1), or NEM equation, for the plurality of neutron energy groups, and the conditioning of the eigensystem into a restricted eigensystem for a spectral restriction to some energy groups according to the second aspect of the invention. The restricted eigensystem resulting from the top level 21 is then fed into a first intermediate level 22 just under the top level 21. The first intermediate level 22 comprises the conditioning of the restricted eigensystem into a spare eigensystem according to the first aspect of the invention wherein the components of an iterant (j(out), j(in)) of the spare eigensystem only correspond either to neutron incurrents jgul+m, jgur−m coming into the cubes m or to neutron outcurrents jgul−m, jgur+m, also noted j(out)mgus, coming from the cubes m. The factors of operators Â, {circumflex over (Q)}λ and Ĉ given by Equations (18) to (20) are computed explicitly for this first intermediate level 22. Each second intermediate levels 24, 26, 28, 30 comprises the conditioning of a former spare eigensystem for a former selection of neutron energy groups into a latter spare eigensystem for a latter selection of neutron energy groups, the number of neutron energy groups in said latter selection being smaller to the number of neutron energy groups in said former selection. The former spare eigensystem of the second intermediate level 24 subsequent to the first intermediate level 22 in the downward orientation of the multi-level V-cycle 20 is the spare eigensystem resulting from the first intermediate level 22. The former spare eigensystem of each second intermediate level 26, 28, 30 which is not subsequent to the first intermediate level 22 corresponds to the latter spare eigensystem resulting from the precedent second intermediate level 24, 26, 28. In other words, the number of neutron energy groups decreases from a second intermediate level to the next second intermediate level in the downward orientation. At the last second intermediate level 30, the number of neutron energy groups may be equal to 1. It should be noted that this restriction of the number of neutron energy groups for the second intermediate levels 24, 26, 28, 30 may be done according to a spectral condensation algebra, which will be described later, and not according to the second aspect of the invention. Bottom levels 32, 34, 36 comprise, in the downward orientation of the V-cycle, the solving, according to state of the art procedures, of the last spare eigensystem for a single energy group determined at the last second intermediate level 30. Bottom levels 34, 36 correspond to a spatial restriction of the eigensystem resulting from the precedent bottom level 32, 34 in respective coarsened grids with cubes being larger than the cubes of the precedent bottom level 32, 34. At the bottom level 36 of the V-cycle, a solution of the eigensystem for the single energy group is computed. This solution is then reintroduced in the upper levels of the V-cycle in the upward orientation so that solutions are computed for the respective spare eigensystems. At the top level 21 of the V-cycle in the upward orientation, the solution of the NEM equation for the plurality of energy groups is computed. In the illustrated embodiment of FIG. 4, the number ng of neutron energy groups for the NEM equation at the top level 21 may be equal to 8. For the intermediate levels 22, 24, 26, 28, 30, the number of neutron energy groups in the respective selections may be respectively equal to four, three, two and one. The three bottom levels 32, 34, 36 of the V-cycle shown on FIG. 4 comprise the solving of said last spare eigensystem for said one energy group according to the CMR procedure. The four intermediate levels 22, 24, 26, 28 corresponding to the solving of respective spare eigensystems are also designated by the respective references SR4, SR3, SR2 and SR1 (FIG. 5). The factors of the mono-energetic operator Â for the level SR4 are computed explicitly. Subsequently, the factors of the mono-energetic operator Â for the level SR3 are derived from the ones for the level SR4, as shown on FIG. 5, where each box 37 represents a neutron energy group, through:Am;SR31u′s′=Am;SR41u′s′Am;SR32u′s′=Am;SR42u′s′Am;SR33u′s′=Am;SR43u′s′+Am;SR44u′s′ (25) Equation (25) is illustrated on FIG. 5 by the arrows 38 between levels 22 and 24. Subsequently, the factors of the mono-energetic operator Â for the level SR2 are derived from the ones for the level SR3 through:Am;SR21u′s′=Am;SR31u′s′+Am;SR32u′s′Am;SR22u′s′=Am;SR33u′s′ (26) Equation (26) is illustrated on FIG. 5 by the arrows 40 between levels 24 and 26. Finally, the factors of the mono-energetic operator Â for the level SR1 are derived from the ones for the level SR2 through:Am;SR1u′s′=Am;SR21u′s′+Am;SR22u′s′ (27) Equation (27) is illustrated on FIG. 5 by the arrows 42 between levels 26 and 28. Equations (25) to (27) define a spectral condensation algebra for the mono-energetic operator Â corresponding to a spectral grid partitioning strategy shown in FIG. 5. It should be noted that another spectral condensation algebra for the mono-energetic operator Â with different equations may be defined with another spectral grid partitioning strategy, i.e. with a different arrangement of the boxes 37. The factors of the mono-energetic operator Ĉ are derived in a similar manner as for the factors of the mono-energetic operator Â, from the level SR4 to the level SR1 in the downward orientation. The factors of the spectral operator {circumflex over (Q)}λ for the level SR4 are computed explicitly. Subsequently, the factors of the spectral operator {circumflex over (Q)}A for the level SR3 are derived from the ones for the level SR4 through:Qm1;SR31u′s′=Qm1;SR41u′s′Qm2;SR32u′s′=Qm2;SR42u′s′Qm1;SR32u′s′=Qm1;SR42u′s′Qm2;SR31u′s′=Qm2;SR41u′s′Qm2;SR33u′s′=Qm2;SR43u′s′+Qm2;SR44u′s′Qm3;SR32u′s′=Qm3;SR42u′s′+Qm4;SR42u′s′Qm1;SR33u′s′=Qm1,SR43u′s′+Qm1;SR44u′s′Qm3;SR31u′s′=Qm3;SR41u′s′+Qm4;SR41u′s′Qm3;SR33u′s′=Qm3;SR43u′s′+Qm3;SR44u′s′+Qm4;SR43u′s′+Qm4;SR44u′s′ (28) Subsequently, the factors of the spectral operator {circumflex over (Q)}λ for the level SR2 are derived from the ones for the level SR3 through:Qm2;SR21u′s′=Qm3;SR31u′s′+Qm3;SR32u′s′Qm1;SR22u′s′=Qm1;SR33u′s′+Qm2;SR33u′s′Qm2;SR22u′s′=Qm2;SR32u′s′Qm1;SR21u′s′=Qm1;SR31u′s′+Qm1;SR32u′s′+Qm2;SR31u′s′+Qm2;SR32u′s′ (29) Finally, the factors of the spectral operator {circumflex over (Q)}λ for the level SR1 are derived from the ones for the level SR2 through:Qm;SR1u′s′=Qm1;SR21u′s′+Qm1;SR22u′s′+Qm2;SR21u′s′+Qm2;SR22u′s′ (30) Equations (28) to (30) define a spectral condensation algebra for the spectral operator {circumflex over (Q)}λ corresponding to a spectral grid partitioning strategy not shown and similar to the one shown in FIG. 5 for the mono-energetic operators Â and Ĉ. It should be noted that another spectral condensation algebra for the spectral operator {circumflex over (Q)}λ may also be define with another spectral grid partitioning strategy. Thus, a solution is calculated for the elements j(out)mgus of the neutron outcurrent column vector j(out) at the top level 21 of the V-cycle in the upward orientation. This enables to determine the solution of the neutron incurrent column vector j(in) according to Equation (14), and finally to determine the solution of the neutron flux column vector Φ according to Equation (10). The nuclear reactor core is then built or operated on the basis of the calculated neutron flux column vector Φ. Using spectral condensation algebras, wherein no complex arithmetic operation is involved, for the operators Â, Ĉ and {circumflex over (Q)}λ at the respective levels SR3, SR2 and SR1 allows the operators Â, Ĉ and {circumflex over (Q)}λ to be computed very cheaply, thus leading to a better computational robustness and a better computational efficiency of the modelizing method. In order to further improve robustness and computational efficiency, according to a fourth aspect of the invention, the cubes 10 are split into a first category and a second category. In the following description and as shown on FIG. 6, the cubes 10R of the first category will be called the red cubes and the cubes 10B of the second category will be called the black cubes but no specific restrictive meaning should be associated with the words “black” and “red”. Each red cube 10R has only black cubes 10B as direct neighbours. Thus, most of the red cubes 10R have six direct black neighbours 10B. It should be understood by “direct” neighbours, the cubes sharing a common surface with the considered cube. Consequently, and as illustrated by FIG. 6, the grid 12 has a visual analogy with respect to the dark and light regions of a checkerboard in a two-dimensional representation. Then, the cubes are numbered, starting for example by the red cubes 10R and ending by the black cubes 10B. In the following description, such a split of the cubes in two categories and the numbering of one category after the other will be referred to as red-black ordering. An advantage of the red-black ordering of the cubes in comparison with the state of the art lexicographical ordering is that, for a red cube 1R, all its direct neighbours will be black, and vice versa. The Equation (24), which the computer has to solve in order to calculate neutron flux within the core, can be written in the matrix-vector form:Âd=μ[{circumflex over (Q)}λ+Ĉ]d (31) Using a variable parameter γ, which value is typically comprised between 0.9 and 0.95, so that the product γμ forms a shift, an iteration of Equation (31) is written with the following shift-inverted implicit form:[Â−γμ(n−1)({circumflex over (Q)}λ+Ĉ)]d(n)=s(n−1) (32) where s(n−1) is a source given by:s(n−1)=(1−γ)μ(n−1)({circumflex over (Q)}λ+Ĉ)d(n−1) (33) The spectral operator {circumflex over (Q)}λ and the mono-energetic operator Ĉ are sparse, coupling red cubes 10R only to direct black neighbours 10B and vice versa. Thus, the red-black ordering enables the following convenient relationship between the red and the black parts of the equation:Âdred−γμ(n−1)({circumflex over (Q)}λ+Ĉ)dblack=sred Âdblack−γμ(n−1)({circumflex over (Q)}λ+Ĉ)dred=sblack (34) Equation (34) is transformed into the following equivalent equation for the red solution part only: Θ ~ red ⁢ d _ red = s _ ~ red ⁢ ⁢ with ⁢ ⁢ { Θ ~ red = 1 ^ - ( γμ ( n - 1 ) ) 2 ⁡ [ A ^ - 1 ⁡ ( Q ^ λ + C ^ ) ] 2 s _ ~ red = A ^ - 1 ⁡ [ s _ red + γμ ( n - 1 ) ⁢ A ^ - 1 ⁡ ( Q ^ λ + C ^ ) ⁢ A ^ - 1 ⁢ s _ black ] , ( 35 ) From a calculation point of view, the use of a red-black ordering means that, during an iterative solving procedure if, in the first half of an iteration, the red components dred of the iterant d are updated, then, during the second part of the iteration, all the black components dblack will be updated on the basis of the red components of their red neighbours dred. In other words, the value for each black cube 10B will be calculated on the basis of the values for all its direct red neighbours 10R. Using the red-black ordering improves the computation of the operators Â, Ĉ and {circumflex over (Q)}λ described in the first, second or third aspects of the invention. Thus, the red-black ordering may be used in complement of the first, second or third aspects of the invention in order to improve the computational efficiency. Such a red-black ordering proves to be especially useful when used with a particular solving procedure which constitutes a fifth aspect of the invention. This procedure is a particular highly robust stabilized Bi-Conjugate Gradient Stabilized (Bi-CGStab) procedure. An adequate introductory description of this procedure can be found in the following references: -Y. Saad, “Iterative Methods for Sparse Linear Systems”, second edition, Society for Industrial and Applied Mathematics (SIAM) (2003); H. A. van der Vorst, “Bi-CGSTAB: a Fast and Smoothly Converging Variant of Bi-CG for the solution of nonsymmetric linear systems”, SIAM J. Sci. Stat. Comput. 13(2), pp. 631-644 (1992), The Bi-CGStab procedure is derived from a minimization principle for a functional of d, with given θ and s, for which stationarity applies with regard to small variations δd around the specific optimum d which satisfies, exactly, the linear system given by Equation (35), and for which the functional assumes a minimum value. Thus, it is possible to define a solving procedure driven by the minimization of a functional rather than by more direct considerations on how to solve Equation (35) efficiently. The Bi-CGStab procedure follows from such a minimization principle, where the successive changes in the iterant are organized such that each change in the functional (which is like a Galerkin-weighted integrated residual) is orthogonal with respect to all of the preceding changes. The particular Bi-CGStab procedure according to the fifth aspect of the invention is given below with solution vector d, solution residual r (with r=s−θd) and auxiliary vector r*, s and p, and with initial solution estimate d0: { 1. r 0 := s ~ - Θ • ⁢ d 0 , r * = r 0 2. p 0 := r 0 , 3. do ⁢ ⁢ i = 0 , 1 , … ⁢ , N 4. α i := ( r * , r i ) ( r * , Θ • ⁢ p i ) , 5. s i := r i - α i ⁢ Θ • ⁢ p i , 6. ω i := ( Θ • ⁢ ⁢ s i , s i ) ( Θ • ⁢ ⁢ s i , Θ • ⁢ s i ) , 7. d i + 1 := d i + α i ⁢ p i + ω i ⁢ s i , 8. r i + 1 := s i - ω i ⁢ Θ • ⁢ s i , 9. β i := ( r * , r i + 1 ) ⁢ α j ( r * , r i ) ⁢ ω j , 10. p i + 1 := r i + 1 + β i + 1 ( p i - ω i ⁢ Θ • ⁢ p i ) 11. end ⁢ ⁢ do ( 36 ) The above Bi-CGStab sequence is truncated after N steps, with usually N<3. For the Bi-CGStab procedure, the preconditioning is based on the shift-inverted implicit form of Equation (32), with typically 0.9<γ<0.95. With this choice for the shift γμ, the operator s is guaranteed to remain nonsingular since, during the solution process, γμ will converge down to γ times the smallest possible eigenvalue of the system. Solving Equation (32) is numerically equivalent to determining the flux distribution in a slightly subcritical system with a neutron source, which is a perfect scenario for deploying advanced preconditioned Krylov procedure. Using the red-black ordering, Equation (32) is transformed into Equation (35) as above explained. The preconditioned system given by Equation (35) constitutes the sixth aspect of the invention. Once Equation (35) has been solved through the Bi-CGStab procedure the black solution part is to be computed from the black part of Equation (34). Use of this particular way of preconditioning, which means that the direct neutron interaction between neighboring (red vs. black) nodes, as projected onto the grid, is preincluded in the system to be solved, making the unity operator in Equation (35) more dominant since∥(Â−1({circumflex over (Q)}λ+Ĉ))2∥<∥Â−1({circumflex over (Q)}λ+Ĉ)∥, (37)given that∥Â−1({circumflex over (Q)}λ+Ĉ)∥<1 (38) This way of preconditioning manages to pre-include, at low computational cost, crucial information (or the major part of that information) with regard to the physical interactions between nodes that determine the spatial couplings and hence the solution of the equation. In another embodiment, the iterative solving procedure is a Gauss-Seidel procedure, or an iterative procedure in the Krylov subspace, such as a generalized minimal residual method, also abbreviated GMRES, or a plain Jacobi method. According to a seventh aspect of the invention, a variational principle for improved eigenvalue computation will be described in the following description. Equation (16) corresponding to the spare eigensystem, above described for the first, second or third aspect of the invention, is written in the following form, with the second neutron eigenvalue μ and the neutron outcurrent vector column jout:jout=μ{circumflex over (Π)}{circumflex over (P)}λĜŶjout+{circumflex over (Ω)}Ŷjout,jout=μc1φ+{circumflex over (Ω)}Ŷjout (39) where c1 is another notation for the operator {circumflex over (Π)} depending on the cube properties. In what follows, we will assume that the first neutron eigenvalue λ fulfills the role of a scalar control parameter. Using the property that the second neutron eigenvalue μ approaches unity if the total solution converges and thus stabilizes, the variational principle, or perturbation approach, comprises the varying the first neutron eigenvalue λ to drive the second neutron eigenvalue μ towards 1 and to accelerate the convergence of the spare eigensystem solution. This variation of the first neutron eigenvalue λ, may be done prior to every iteration of the spare eigensystem, or prior to every second, third, fourth or fifth iteration of the spare eigensystem. The variation of the first neutron eigenvalue λ is an application of a variation δλ to λ such that λ is driven to λ+δλ, which impacts the second neutron eigenvalue μ through a perturbed interface current equation: j out + δ ⁢ ⁢ j out = [ ( μ + δμ ) ⁢ Π ^ ⁡ ( P ^ λ + δλ ⁢ ∂ P ^ λ ∂ λ ) ⁢ G ^ + Ω ^ ] ⁢ Y ^ ⁡ ( j out + δ ⁢ ⁢ j out ) = ( μ + δμ ) ⁢ c 1 ⁡ ( ϕ + δλ ⁢ ∂ ϕ ∂ λ ) + Ω ^ ⁢ Y ^ ⁡ ( j out + δ ⁢ ⁢ j out ) ( 40 ) with the partial operator derivative: Π ^ ⁢ ∂ P ^ λ ∂ λ ⁢ G ^ ⁢ Y ^ ⁢ j out ≡ c 1 ⁢ ∂ ϕ ∂ λ ( 41 ) As perturbations δjout are expected to be increasingly small during the iterative procedure, they are conveniently ignored in Equation (40), and the integration with an arbitrary adjoined weighting function ω†yields the following expression: δμ ⁡ [ δλ ] ≅ 〈 ω † ❘ c 1 ⁢ ϕ 〉 〈 ω † ❘ c 1 ⁢ ∂ ϕ ∂ λ 〉 ⁢ δλ ( 42 ) As the variation of the first neutron eigenvalue λ is such that the second neutron eigenvalue μ is driven towards 1, i.e. that μ+δμ, is driven towards 1, the approximation δμ≡1−μ is imposed. With this approximation and the Equation (42), the following equation is obtained: δλ ≅ 〈 ω † ❘ c 1 ⁢ ϕ 〉 〈 ω † ❘ c 1 ⁢ ∂ ϕ ∂ λ 〉 ⁢ ( 1 - μ ) ( 43 ) Using the equivalence μc1φ=jout−{circumflex over (Ω)}Ŷjout, δλ is given by: δλ ≅ 〈 ω † ❘ j out - c 1 ⁢ ϕ + Ω ^ ⁢ Y ^ ⁢ j out 〉 〈 ω † ❘ c 1 ⁢ ∂ ϕ ∂ λ 〉 = 〈 ω † ❘ r out 〉 〈 ω † ❘ c 1 ⁢ ∂ ϕ ∂ λ 〉 ( 44 ) where rout represents the residual of the interface outcurrent balance equation, i.e. Equation (39), with the imposed target value for the second neutron eigenvalue μ equal to 1. The residual rout needs to be computed for each NEM iteration step in any case. The first neutron eigenvalue λ, considered in this aspect as a scalar control parameter, is then updated such that: λ ( new ) = λ ( prev ) + 〈 ω † ❘ r out ( prev ) 〉 〈 ω † ❘ c 1 ⁢ ∂ ϕ ∂ λ 〉 , ( 45 ) where λ(prev) and λ(new) are respectively the previous and the updated value of the first neutron eigenvalue λ. For determining the partial operator derivative ∂ ϕ ∂ λ and using Equation (7) for example, the neutron flux Φ is written:φ=({circumflex over (R)}−Ŝ−λ{circumflex over (F)})−1ĜŶjout (46) from which it follows that: ∂ ϕ ∂ λ = [ ∂ ∂ λ ⁢ ( R ^ - S ^ - λ ⁢ F ^ ) - 1 ] ⁢ G ^ ⁢ Y ^ ⁢ j out ( 47 ) An approximate derivative ∂ ϕ ~ ∂ λ is then computed by neglecting the upper-diagonal part of the matrix relative to the inscatter operator Ŝ such that Ŝ=ŜLD, i.e. by neglecting the upscattering: ∂ ϕ ~ ∂ λ = [ ∂ ∂ λ ⁢ ( R ^ - S ^ LD - λ ⁢ F ^ ) - 1 ] ⁢ G ^ ⁢ Y ^ ⁢ j out ( 48 ) It should be noted that in many computational cases this is not even an approximation, but numerically exact if no upscattering is modeled. It is assumed that: ∂ ϕ ∂ λ ≅ ∂ ϕ ~ ∂ λ ( 49 ) which will be sufficient for a successful application of the variational principle. For computing ∂ ϕ _ ∂ λ ,it is first written:{circumflex over (R)}−ŜLD−λ{circumflex over (F)}=({circumflex over (R)}−ŜLD)({circumflex over (1)}−λ({circumflex over (R)}−ŜLD)−1{circumflex over (F)}) (50) from which it follows that:({circumflex over (R)}−ŜLD−λ{circumflex over (F)})−1=({circumflex over (1)}−λ({circumflex over (R)}−ŜLD)−1{circumflex over (F)})−1({circumflex over (R)}−ŜLD)−1 (51) Then defining an operator notation {circumflex over (B)} with:{circumflex over (B)}=({circumflex over (R)}−ŜLD)−1{circumflex over (F)} (52) and in order to implicitly compute ∂ ∂ λ ⁡ [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 ,the Taylor formula is applied to {circumflex over (1)}−λ{circumflex over (B)}: [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 = 1 ^ + λ ⁢ ⁢ B ^ + λ 2 ⁢ B ^ 2 + λ 3 ⁢ B ^ 3 + … = ∑ n = 0 ∞ ⁢ [ λ ⁢ ⁢ B ^ ] n ( 53 ) The Taylor expansion is rearranged as:{circumflex over (1)}+[{circumflex over (1)}+λ{circumflex over (B)}+λ2{circumflex over (B)}2+λ3{circumflex over (B)}3+ . . . ]λ{circumflex over (B)}=[{circumflex over (1)}−λ{circumflex over (B)}]−1λ{circumflex over (B)} (54) By application of the chain rule to Equation (54), the derivative ∂ ∂ λ ⁡ [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 is given by: ∂ ∂ λ ⁡ [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 = [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 ⁢ B ^ + [ ∂ ∂ λ ⁡ [ 1 - λ ⁢ ⁢ B ^ ] - 1 ] ⁢ λ ⁢ ⁢ B ^ ( 55 ) which yields: [ 1 ^ - λ ⁢ ⁢ B ^ ] ⁢ ∂ ∂ λ ⁡ [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 = [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 ⁢ B ^ ( 56 ) The final expression that allows an efficient iterative scheme for determining the derivative ∂ ∂ λ ⁡ [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 is obtained by premultiplication of Equation (56) with {circumflex over (1)}−λ{circumflex over (B)}, which gives: [ 1 ^ - λ ⁢ ⁢ B ^ ] 2 ⁢ ∂ ∂ λ ⁡ [ 1 ^ - λ ⁢ ⁢ B ^ ] - 1 = B ^ ( 57 ) By writing [{circumflex over (1)}−λ{circumflex over (B)}]2={circumflex over (1)}−2λ{circumflex over (B)}+λ2{circumflex over (B)}2, computation of ∂ ϕ ~ ∂ λ is obtained from: [ 1 ^ - 2 ⁢ λ ⁢ ⁢ B ^ + λ 2 ⁢ B ^ 2 ] ⁢ ∂ ϕ ~ ∂ λ = s ( 58 ) with the source term s defined by:s={circumflex over (B)}({circumflex over (R)}−ŜLD)−1ĜŶjout=({circumflex over (R)}−ŜLD)−1{circumflex over (F)}({circumflex over (R)}−ŜLD)−1ĜŶjout (59) In the case of two energy groups, Equation (58) is solved directly and analytically. In the case of more than two energy groups, Equation (58) is solved iteratively, without exactness required in early iteration phases, through application of: [ ∂ ϕ ~ ∂ λ ] ( new ) = s + 2 ⁢ λ ⁢ ⁢ B ^ ⁡ [ ∂ ϕ ~ ∂ λ ] ( old ) - λ 2 ⁢ B 2 ⁡ [ ∂ ϕ ~ ∂ λ ] ( old ) , ( 60 ) where [ ∂ ϕ ~ ∂ λ ] ( old ) ⁢ ⁢ and ⁢ [ ∂ ϕ ~ ∂ λ ] ( new ) are respectively the previous and updated values of the approximate derivative ∂ ϕ ~ ∂ λ . Early means about the first third up to the first half of the totally needed number of iteration steps. It should be noted that the iterations from the computation of ∂ ϕ ~ ∂ λ can be abort rather early, since this variational approach needs only an approximate value of ∂ ϕ ~ ∂ λ to be useful. Thus, this variational principle according to this seventh aspect of the invention is very effective, because the numerator ω†|rout(prev) in Equation (45) becomes smaller and smaller upon convergence, whereas the denominator 〈 ω † | c 1 ⁢ ∂ ϕ ∂ λ 〉will converge rather quickly to an adequate value. In this seventh aspect, the numerator defines the driving principle since it converges towards zero. Varying the first neutron eigenvalue λ according to Equation (45) drives the second neutron eigenvalue μ towards 1 and accelerates the convergence of the spare eigensystem solution. This variation of the first neutron eigenvalue λ may be done prior to every iteration of the spare eigensystem, or prior to every second, third, fourth or fifth iteration of the spare eigensystem. Thus, the variational principle of the first neutron eigenvalue λ may be used in complement of the first, second or third aspects of the invention in order to improve the computational efficiency. All the above mentioned products of this seventh aspect can be reduced to the black part of the grid 12 without losing numerical efficiency in the method, so that the red-black ordering above described in the fourth aspect of the invention may be used in complement of this seventh aspect. According to an eighth aspect of the invention, the above described variational principle for the eigenvalue computation can be generalized for the computation of a control parameter being noted θ, that typically modulates the removal operator {circumflex over (R)} given by Equation (4), the modulated removal operator being noted {circumflex over (R)}θ. In the example of a modulation in all positions, the control parameter θ is the boron concentration. In the example of a modulation in selected positions, the control parameter θ is a parameter for controlling a rod insertion depth for a group of selected control rods. It is assumed that {circumflex over (R)}={circumflex over (R)}θ Equation (16) is then written in the following form, with the second neutron eigenvalue μ:jout=μ{circumflex over (Π)}{circumflex over (P)}θĜŶjout+{circumflex over (Ω)}Ŷjout jout=μc1φ+{circumflex over (Ω)}Ŷjout (61) with a symbolic spectral operator {circumflex over (P)}θ defined by{circumflex over (P)}θ=({circumflex over (R)}θ−Ŝ−{circumflex over (F)})−1 (62) Using the property that the second neutron eigenvalue μ approaches unity if the total solution, including the correct value of the control parameter θ, converges and thus stabilizes, the variational principle, or perturbation approach, comprises varying the control parameter θ to drive the second neutron eigenvalue μ towards l. The variation of the control parameter θ is an application of a variation δθ to θ such that θ is driven to θ+δθ, which impacts the second neutron eigenvalue μ through a perturbed interface current equation: j out + δ ⁢ ⁢ j out = [ ( μ + δ ⁢ ⁢ μ ) ⁢ Π ^ ⁡ ( P ^ ϑ + δ ⁢ ⁢ ϑ ⁢ ∂ P ^ ϑ ∂ ϑ ) ⁢ G ^ + Ω ^ ] ⁢ Y ^ ⁡ ( j out + δ ⁢ ⁢ j out ) ⁢ ⁢ j out + δ ⁢ ⁢ j out = ( μ + δμ ) ⁢ c 1 ⁡ ( ϕ + δ ⁢ ⁢ ϑ ⁢ ∂ ϕ ∂ ϑ ) + Ω ^ ⁢ ⁢ Y ^ ⁡ ( j out + δ ⁢ ⁢ j out ) ( 63 ) with the partial operator derivative: Π ^ ⁢ ∂ P ^ ϑ ∂ ϑ ⁢ G ^ ⁢ Y ^ ⁢ j out ≡ c 1 ⁢ ∂ ϕ ∂ ϑ ( 64 ) As perturbations δjout are expected to be increasingly small during the iterative procedure, they are conveniently ignored in Equation (63), and the integration with an arbitrary adjoined weighting function ω† yields the following expression: δμ ⁡ [ δϑ ] ≡ 〈 ω † | c 1 ⁢ ϕ 〉 〈 ω † | c 1 ⁢ ∂ ϕ ∂ ϑ 〉 ⁢ δϑ ( 65 ) As the variation of the control parameter θ is such that the second neutron eigenvalue μ is driven towards 1, i.e. that μ+δμ is driven towards 1, the approximation δμ≡1−μ is imposed. With this approximation and the Equation (65), the following equation is obtained: δϑ ≅ 〈 ω † | c 1 ⁢ ϕ 〉 〈 ω † | c 1 ⁢ ∂ ϕ ∂ ϑ 〉 ⁢ ( 1 - μ ) ( 66 ) Using the equivalence μc1φ=jout−{circumflex over (Ω)}Ŷjout, δθ is given by: δϑ ≅ 〈 ω † | j out - c 1 ⁢ ϕ + Ω ^ ⁢ ⁢ Y ^ ⁢ j out 〉 〈 ω † | c 1 ⁢ ∂ ϕ ∂ ϑ 〉 = 〈 ω † | r out 〉 〈 ω † | c 1 ⁢ ∂ ϕ ∂ ϑ 〉 ( 67 ) where rout represents the residual of the interface outcurrent balance equation, i.e. Equation (39), with the imposed target value for the second neutron eigenvalue μ equal to 1. The control parameter θ is then updated such that: ϑ ( new ) = ϑ ( prev ) + 〈 ω † | r out ( prev ) 〉 〈 ω † | c 1 ⁢ ∂ ϕ ∂ ϑ 〉 ( 68 ) It is assumed that ∂ ϕ ∂ ϑ ≅ ∂ ϕ ~ ∂ ϑ which will be sufficient for a successful application of the variational principle to the control parameter θ. For computing ∂ ϕ ~ ∂ ϑ ,the above described conditioning with application of the Taylor formula is also used in the same manner. The eighth aspect of the invention offers the same advantages as the above described seventh aspect of the invention, and may be used in complement of the first, second or third aspects of the invention in a manner similar to that for the above described seventh aspect of the invention, in order to improve the computational efficiency. FIG. 7 represents a set of convergence curves for different eigensystem iterative solving procedures with the number of pursued NEM iterative steps in abscissa and the fast flux error in ordinate, which is the maximum solution error of the neutron flux for the fast neutrons energy group. Since all energy groups are spectrally coupled, the maximum solution errors of the neutron flux for the other energy groups are quite similar to the fast flux error. Thus, the comparison between different eigensystem iterative solving procedures is possible through these convergence curves. The curve 50 is the convergence curve for the classic Coarse Mesh Rebalancing (CMR) procedure with use of single precision, and the curve 51 is the convergence curve for the classic CMR procedure with use of double precision. The single and double precisions are the classic precisions used for representing the floating point numbers in a computer program product. The curve 52 is the convergence curve for the iterative procedure according to the first and the seventh aspects of the present invention for a single energy group with use of single precision, and the curve 53 is the convergence curve for the iterative procedure according to the same aspects of the present invention with use of double precision. The curve 54 is the convergence curve for the iterative procedure according to the first and the second aspects of the present invention for four coarse energy groups with use of single precision, and the curve 55 is the convergence curve for the iterative procedure according to the same aspects of the present invention with use of double precision. The curve 56 is the convergence curve for the iterative procedure according to the first, the second and seventh aspects of the present invention for four coarse energy groups with use of single precision, and the curve 57 is the convergence curve for the iterative procedure according to the same aspects of the present invention with use of double precision. The procedure according to the first, the second and seventh aspects for four coarse energy groups with use of double precision (curve 57) is the procedure with both the smallest error with a value substantially equal to 10−13 for 50 pursued NEM iteration steps and the best computational efficiency, as illustrated by the gradient of the convergence curves which is maximum for the curve 57. The procedure according to the first and the seventh aspects for a single energy group with use of double precision (curve 53) also provides a small error with a value substantially equal to 10−9 for 130 pursued NEM iteration steps. Moreover, the computational efficiency of this procedure (curve 53) is worth than the computational efficiency of the procedure according to the first and the second aspects for four coarse energy groups with use of double precision (curve 55), because the gradient of the curve 55 is greater than the gradient of curve 53. The procedure according to the first and the second aspects for four coarse energy groups with use of double precision provides an error substantially equal to 10−7 for 40 pursued NEM iteration steps. Thus, the double precision has a great effect on the value of the fast flux error, but has no impact on the computational efficiency of the modelizing method. The seventh aspect of the present invention has also a greater effect on the value of the fast flux error, than on the computational efficiency. The first and the second aspects for four coarse energy groups provides the best computational efficiency, and FIG. 7 illustrates that the greatest gradient for an error value comprised between 100 and 10−5 is obtained for the curves 54 to 57, which all correspond to the first and the second aspects. As set forth in the previous description, the first to eighth aspects of the invention help to achieve robust modelizing methods providing a better computational efficiency so that relevant core simulations can be obtained within short computational time period. It should be kept in mind that the first aspect in itself helps in achieving this goal and can thus be used separately from the second to eighth aspects. Also, the second, third, seventh and eighth aspects are not necessarily implemented with the first aspect or with any one of the fourth to sixth aspects.

046577246

claims

1. For use with a pulsed neutron generator in a logging tool lowered in a borehole, a pulsed high voltage source having an output terminal adapted to be connected to pulse neutron generator, the power supply comprising: (a) high voltage supply means; (b) field effect transistor means comprising at least a pair of field effect transistors serially connected between said high voltage supply means and ground; (c) an output terminal between the two transistors of said field effect transistor means, said output terminal adapted to be connected by a conductor to provide pulsed high voltage to a neutron generator; (d) control pulse forming means connected to the gates of the respective two transistors, said pulse forming means forming control pulses selectively switching said transistors off and on in timed sequence to thereby connect the output terminal to said high voltage supply means, and (e) diode means connected to said gates of said transistors to limit gate voltage for operation of said transistors. 2. The apparatus of claim 1 including a series cascade of FETs comprising said transistor means, said FETs having gate terminals connected to control voltage means. 3. The apparatus of claim 1 further including means controlling operation of said pair of transistors to prevent making said transistors simultaneously conductive. 4. The apparatus of claim 1 including a floating power supply connected on said high voltage supply means and floating thereon, and also connected to said control pulse forming means. 5. The apparatus of claim 1 wherein said control pulse forming means forms interlocked pulses of said two transistors. 6. The apparatus of claim 1 wherein said diode means are connected to the gates of serially connected FETs comprising said transistor means, and wherein said diode means is connected to clamp gate voltage. 7. The apparatus of claim 1 wherein said control pulse forming means forms two control pulses for said pair of transistors, and the pulses are timed in occurrance and overlap. 8. The apparatus of claim 7 wherein the pulses are formed by flip-flop means to sequence switching of said transistor pair. 9. The apparatus of claim 1 wherein said transistor means comprises said pair of FETs serially connected so that each of said FETs has a gate terminal adapted to be connected to said control pulse forming means to receive a control pulse at each of said gates for transistor switching. 10. The apparatus of claim 9 wherein said transistors are inverted compared to each other, and said gates are thereby enabled to be oppositely driven. 11. The apparatus of claim 10 including means within said control pulse forming means for forming a pulse of one polarity to turn one of said transistors on and wherein a pulse of the same polarity turns off the other of said transistors. 12. The apparatus of claim 11 including series connected third and fourth transistors each having gates, and bias circuit means connected to said gates to cause said third and fourth transistors to operate in response to operation of said first two transistors. 13. The apparatus of claim 1 including flip-flops in said control pulse forming means forming timed signals for operation of said two transistors.

048030392

claims

1. A method of on-line monitoring of the execution by a human operator of procedures for a complex process facility comprising the steps of: storing electric signals representative of step by step procedures for the complex process facility, at least some steps of which require verification of a selected process condition; generating parameter signals representaitve of the real time value of predetermined process parameters; sequentially electrically selecting a step of one of said stored step by step procedures as a current step; electrically processing selected parameter signals to determine the state of the process condition to be varied by a current step which requires verification; generating a visual representation of said current step including a visible textual statemenet of the condition to be verified, a visual indication of the state of the selected process condition to be verified by the current step, and, where the state of the selected condition indicates that it is not verified, a visible textual statement of recommended operator action; providing means for the operator to electrically generate an operator response signal in response to a textural statement of recommended operator action by said visal display of said current step, including providing means for the operator to select between electrically generating an action complete response signal and an override response signal, and electrically sequentially selecting the next step in said stored procedure as the current step in response to said operator response siganl. storing electrical signals representative of step by step procedures for the complex process facility; generating sequentially from said stored electrical signals a visual representation of the current step to be executed of said step by step procedures, in the form of a textual statement of the current step and a textual statement of operator action recommended in response to said current step; generating visual prompts informing the operator of how to generate an input signal in response to the visible textual statement of recommended action; providing means for the operator to electrically generate such an input signal; indexing the current step to the next step in the stored step by step procedures in response to an input signal generated by the operator; measuring selected process parameters and generating parameter signals representative of the measured values of said selected parameters; and simultaneously with said visual representation of the current procedure step, and in response to predetermined values of said parameter signals indicative of an abnormal process condition, generating a visual indication of the existence of the abnormal condition. storong sets of electrical signals representative of a plurality of step-by-step procedures for the complex process facility; generating on an on-line basis, parameter signals representative of the current values of selected process parameters; selecting the set of electrical signals representative of one of said step-by-step procedures based upon the values of said parameters signals; generating sequentially from said selected electrical signals a visual representation of each step of the selected procedure, one step at a time, at least some of said steps including generating a visual recommendation to the operator that a transfer be made to another set of stored electrical signals representative of another one of said step-by-step procedures based upon the current values of certain of said process parameters selected by the visually presented step; providing means for an operator to generate an electrical response signal to each visually presented step; indexing said visual display to the next step in the selected procedures in response to each response signal; and providing mens for the operator to select between generating an electrical transfer signal and an electrical override signal in response to said visual recommendation, selecting in response to a transfer signal said another set of stored electrical signals representative of another one of said procedures for sequential generation of a visual representation of each step, and continuing in response to an override signal to generate a visual respresentation of each step in the first selected procedure. storing sets of electrical signals representative of a plurality of step-by-step plant procedures; generating on an on-line basis, parameter signals representative of the current values of selected plant parameters; selecting a set of electrical signals representative of one of said step-by-step procedures; generating sequentially from said selected electrical signals a visual representation of each step of the selected procedure; electrically monitoring the current values of designated ones of said parameter signals in parallel with the sequential generation of a visual representation of each step of the selected procedure; generating a visual representation of a recommendation to transfer to a designated set of stored electrical signals representative of a different procedure than the selected procedure in response to selected values of said designated parameters; providing means for an operator to select between generating an electric transfer signal and an electric override signal; and electrically selecting said different set of stored signals for generating sequentially the visual representation of each step of said different procedures in response to the generation of a transfer signal by the operator, and continuing to generate a visual representation of each step of the first selected procedure in response to an override signal. a plurality of sensors for generating sensor signals representative of the current values of a plurality of plant parameters; a storage medium for storing electrical signals representative of the steps of a plurality of step-by-step procedures as a current step, to process selected a digital computer programmed to sequentially select stored signals representative of a selected one of the steps of one of said plurality of step-by-step procedures as a current step, to process selected sensor signals to determine the status of a process condition selected by the current step and recommended action as a result thereof, and to select from said library textual statement signals representative of the current step, the status of the designated process condition and the recommended action; a display device for generating a visible display of said textual statements; and an input device including means by which an operator generates a response signal to the visible display, said digital computer being further programmed to generate in the display device selected prompts including a completion prompt to indicate completion of the action recommended by the current step and an override prompt to indicate an override of the recommended action, said input device including means for the operator to generate completion and override response signals responsive to the respective prompts. storing electrical signals representative of at least two, step-by-step procedures for the complex process facility; generating parameter status signals representative of the real-time status of predetermined process parameters and storing said parameter status signals in a common memory; electrically selecting electrical signals representative of one of said procedures as a first active procedure, presenting sequentially on a first display a visual textual statement of action recommended by each step of said first active procedure to be executed, said actions affecting the status of some of said stored parameter status signals, and simultaneously electrically monitoring selected parameter status signals stored in the common memory and generating a visual indication on said first display of any conditions represented by the real-time status of said selected parameter status signals which conflict with the first active procedure; and simultaneously electrically selecting electrical signals representative of another one of said procedures as a second active procedure, presenting sequentially on a second display a visual textual statement of action recommended by each step of said second active procedure to be executed, said actions affecting the status of certain of said stored parameter status signals, and simultaneously electrically monitoring predetermined ones of said parameter status signals stored in the common memory and generating a visual indication on said second display of any conditions represented by the real-time status of said predetermined ones of said parameter status signals which conflict with the second active procedure. a plurality of sensors for generating parameter signals representative of the current values of a plurality of facility parameters; digital processing means having memory in which at least two, step-by-step procedures and libraries of textual statements are stored and including common memory, said digital processing means being programmed, to process said parameter signals to generate parameter status signals representative of the real-time conditions in the facility, to store said parameter status signals in said common memory, to independently sequentially select a step from two different step-by-step procedures stored in memory as the current step of a first and second active procedure respectively, to independently determine as to the current step of each active procedure the condition of associated stored parameter status signals and action recommended as a result hereof, to independently select from said library, textual statements for the current step and the actions recommended thereby for each active procedure, to independently as to each active procedure simultaneously monitor certain parameter status signals stored in said common memory and when the values thereof indicate a conflict with the associated active procedure, to select a textual statement from the library indicative of the same; and display means for generating for each active procedure a visible display of the textual statement of the current step and the action recommended thereby, and when conditions so indicate, the textual statement of a conflict between the monitored parameter status signals and that active procedure. first digital computing means having said common memory and programmed to generate said parameter status signals and store them in said common memory, and to perform all the program functions associated with the first active procedure; second digital computing means programmed to perform all of the program functions associated with the second active procedure; and data link means connecting the second digital computing means with the common memory in the first digital computing means, said first display device and first input signal generating means being connected to the first digital computing means and the second display device and second input signal generating means being connected to the second digital computing means. storing electrical signals representative of at least two, step-by-step procedures for the plant; generating parameter status signals representantive of the real-time status of predetermined process parameters and storing said parameter status signals in a common memory; electronically selecting electrical signals representative of one of said procedures as a first active procedure, electrically determining for each step of said first active procedure the status of designated ones of the parameter status signals stored in said common memory, presenting sequentially on a first display a visual textual statement of action recommended by each step of said first active procedure to be executed based upon the status of said designated parameter status signals, said actions affecting the status of some of said stored parameter status signals, and simultaneously electrically monitoring selected parameter status signals stored in the common memory and generating a visual indication on said first display of any conditions represented by the real-time status of said selected parameter status signals which conflict with the first active procedure; and simultaneously electrically selecting electrical signals representative of another one of said procedures as a second active procedure, electrically determining for each step of said second active procedure the status of designated ones of the parameter status signals stored in said common memory, presenting sequentially on a second display a visual textual statement of action recommended by each step of said second active procedure to be executed based upon the status of said designated parameter status signals, said actions affecting the status of certain of said stored parameter status signals, and simultaneously electrically monitoring predetermined ones of said parameter status signals stored in the common memory and generating a visual indication on said second display of any conditions represented by the real-time status of said predetermined ones of said parameter status signals which conflict with the second active procedure. 2. The method of claim 1 including the step of updating the visual indication of the state of the selected process condition to be verified by the current step and the visible statement of recommended operator action in response to changes in the selected process condition as a result of operator response to the recommended action. 3. The method of claim 1 wherein said step of generating said visual representations includes generating the same at two separate locations and wherein the step of providing means for the operator to electrically generate an operator response signal includes providing such means at said two separate locations. 4. The method of claim 3 wherein said step of generating a visible textual statement of recommended operator action includes generating a visual indication of which of said two locations at which the action is required. 5. The method of claim 1 including the steps of electrically monitoring, while successive current steps of said stored step by step procedures are being executed, certain parameter signals representative of another process condition not being addressed by said current steps and simultaneously, with the generation of the visual display of said current step, generating a visual indication of said another process condition when the monitoring step generates an indication that said another process condition is in a specified state which warrants attention. 6. The method of claim 5 wherein said step of generating a visual indication of said another process condition includes generating a visible textual statement of action recommended in response to said another process condition when the moitoring step generates an indication that the state of the another process condition requires immediate attention and providing a visual indication that said statement of action recommended in response to said another process condition has priority over the action recommended in response to the current step. 7. The method of claim 1 including electrically logging the response signals generated by the operator. 8. The method of claim 6 including electrically removing the visible textual statement of the action recommended in response to the another process condition upon generation by the operator of either a complete or override signal. 9. The method of claim 8 wherein the steps of generating the visual representation of said current step and of generating a visual indication of said another process condition include generating said representation and indication at two spaced apart locations and wherein the step of providing means for the operator to select between electrically generating a complete signal and an override signal includes providing such means at both of said spaced apart locations. 10. The method of claim 6 including generating a prominent visual indication when the values of said specified parameters indicate that the overall status of the process facility is in a state requiring immediate operator action and a visible textual statement of a specified step by step procedure which should be implemented in response thereto, providing means by which the operator can selectively generate a transfer signal in response to the prominent visual indication, and electrically selecting a step of said specified step by step procedure in response to a transfer signal in place of the step which is the current step at the time of the generation of said prominent visual indication. 11. The method of claim 10 including in response to an override signal generated by the operator, maintaining as the current step, the step which was current at the time that the prominent visual indication was generated. 12. The method of claim 1 including the steps of continuously electrically monitoring the overall status of the process facility as represented by the values of specified parameters and generating simultaneously with the display of said current step a visual display of said overall status of the process facility. 13. A method of on-line monitoring of the execution by a human operator of procedures for a complex process facility comprising the steps of: 14. The method of claim 13 wherein the step of generating a visual indication of the abnormal condition includes generating a visible textual statement of the abnormal condition, generating a visible textual statement of operator action recommended in response to the abnormal condition, and selectively generating visual prompts for the operator to indicate a response thereto, and said method including the step of electrically assigning priorities to the action required by said current step and the recommended action in response to the abnormal condition, and wherein said step of generating the visual prompts includes only generating a display of the prompts associated with the visible textual statement of recommended action for the action having the higher priority. 15. The method of claim 14 including generating indicia to visually indicate the association of the prompts displayed with the appropriate one of the recommended action in response to the current step and the recommended action in response to the abnormal condition. 16. The method of claim 15 wherein the visible textual statement of recommended action in response to the current step is presented in one color, the visible textual statement of recommended action in response to the abnormal condition is presented in a second color, and the prompts are generated in the same color as the visible textual statement of recommended action which is in priority. 17. The method of claim 15 including automatically electrically logging the occurrence of each current step, abnormal condition and input signal generated by the operator. 18. The method of claim 17 including providing means by which an operator can generate an override signal in response to the generation of prompts associated with a priority visible textual statement of recommended action for an abnormal condition, and regenerating the prompts associated with the visible textual statement of recommended action by the current step in response to said override signal. 19. The method of claim 13 including the step of generating simultaneously with the visual representation of the current step, a visible representation of the textual statements of a selected number of most recent current steps. 20. The method of claim 13 including the step of generating simultaneously with the visual representation of the current step a visible representation of the textual statements of a selected number of subsequent steps in the step by step procedures. 21. The method of claim 20 including the step of generating also a visual representation of the textual statement of a selected number of the most recent current steps. 22. A method of on-line monitoring of the execution of procedures for a complex process facility comprising the steps of: 23. The method of claim 22 including the steps of electrically monitoring the current values of designated ones of said parameter signals in parallel with the sequential generation of a visual representation of each step of the selected procedure, generating a visual representation of a recommendation to transfer to a designated set of stored electrical signals representative of a different procedure than the selected procedure in response to selected values of said designated parameters, selecting said different set of stored signals for generating sequentially visual representation of each step of said different procedure in response to the generation of a transfer signal by the operator, and continuing to generate a visual representation of each step of the first selected procedure in response to an override signal. 24. The method of claim 22 wherein said step of generating a visual representation of each step of the selected procedure includes generating such visual representations at two separate locations, and wherein said step of providing means for an operator to generate an electrical response signal to each visually presented step includes providing such means at said two separate locations. 25. A method of on-line monitoring of the execution of procedures for a nuclear power plant comprising the steps of: 26. The method of claim 25 wherein the selected parameters include parameters indicative of a reactor trip and wherein said step of selecting a set of electrical signals representative of one of said step-by-step procedures is performed electrically in response to an indication of a reactor trip. 27. The method of claim 26 wherein at least some of said steps of the selected procedure electrically monitor certain plant parameters to verify the status of certain plant conditions and to generate a visual representation of a textual statement of recommended action selected from a library of textual statements when said certain condition is not verified. 28. The method of claim 27 wherein the step of electrically monitoring the current values of designated ones of said parameter signals in parallel with the sequential generation of a visual representation of each step of the selected procedure includes, monitoring parameters representative of plant critical safety functions and generating a visual display representative of said status of each of the critical safety functions. 29. Apparatus for on-line interactive monitoring of the execution of procedures in a complex process plant comprising: 30. The apparatus of claim 29 wherein said digital computer is further programmed to continuously monitor certain of the sensor signals to generate additional status signals representative of the current status of designated process conditions other than the conditions selected by the current steps, and to select from said library additional textual statements in response to the additional status signals, and wherein said display device includes means to generate a visible display of said additional textual statements simultaneously with the display of the textual statements associated with the current step. 31. The apparatus of claim 30 wherein said digital computer is further programmed to indicate action recommended in response to a specified status of said designated other process conditions, to determine priority between the action recommended in response to the current step and the other process conditions, to select textual statements of action recommended, and to generate prompts associated with the priority action, and wherein said display device includes means to generate a visible display of the priority action textual statement and prompts, and to visually associate the prompts with the priority action recommended. 32. The apparatus of claim 31 wherein said means for visually associating the prompts with the textual statements of priority action recommended include means for generating different portions of the display in different colors and for generating the textual statement of the priority action recommended and the prompts in the same color. 33. The apparatus of claim 32 wherein the priority action recommended is to transfer to another of said plurality of step-by-step procedures, wherein said prompts include a prompt for implementing such transfer, wherein said input device includes means to generate a transfer signal in addition to said complete and override signals and wherein said digital computer is programmed in response to said transfer signal to select said another step-by-step procedure and sequentially select the steps thereof as the current step. 34. The apparatus of claim 33 including means for generating a chronological log of the current steps, the status conditions and the operator generated response signals. 35. The apparatus of claim 34 wherein said digital computer is further programmed to continuously monitor previously determined sensor signals and to generate therefrom safety status signals representative of overall plant safety conditions, and wherein said display device includes means to generate a visible indication of overall plant safety status in response to the safety status signals simultaneously with the display of said textual statements and additional textual statements. 36. A method of on line monitoring of the simultaneous execution of two different procedures for a complex process facility comprising the steps of: 37. The method of claim 36 wherein the steps of sequentially presenting a visible textual statement of action recommended by each step of said first and second active procedures each include electrically determining the status of designated ones of the parameter status signals stored in said common memory and selecting from a library of textual statements a statement for visual presentation dependent upon the status of said designated parameter status signals, generating on the respective displays visual prompts indicating steps to take to generate an input signal in response to the selected textual statement, and presenting the next step in the procedure in response to said input signal. 38. The method of claim 37 wherein said steps of generating a visual indication of conditions which create a conflict include choosing from said library a textual statement of action recommended by the respective operator PG,66 in response to the conflict condition and generating prompts indicating to the respective operator steps to take to generate an input signal in response to the chosen statement in place of the prompts generated for the action recommended by the visibly presented step of the appropriate one of the first and second procedures. 39. Apparatus for on-line monitoring of the simultaneous execution of two different procedures for a complex process facility comprising: 40. The apparatus of claim 39 wherein said display means comprises a first display device upon which the visible display for the first active procedure is generated and a second display device upon which the visible display for the second active procedure is generated. 41. The apparatus of claim 39 wherein said digital processing means is further programmed to generate prompts to indicate steps to be taken in response to a visual statement of action recommended by the first and second procedures, and wherein said first and second display devices generate visual displays of the prompts associated with the first and second active procedures respectively, said apparatus also including first input signal generating means by which an operator generates first electrical input signals to the digital processing means as indicated by the prompts displayed by the first display device, and second input signal generating means by which an operator generates second electrical input signals to the digital processing means as indicated by the prompts displayed by the second display device, said digital processing means being programmed to select the next step as the current step in the first active procedure in response to said first input signal and to select the next step as the current step in the second active procedure in response to said second input signal. 42. The apparatus of claim 41 wherein said digital processing means comprises: 43. A method of on-line monitoring of the simultaneous execution of two different procedures for a nuclear power plant comprising the steps of:

abstract

A Thorium molten salt energy system is disclosed that includes a proton beam source for producing a proton beam, that can vary between a first energy level and a second energy level of, where the generated proton bean can be directed into a main assembly containing both Thorium-containing molten salt and Thorium fuel rods, each containing an inner Beryllium element and an outer solid Thorium element. The generated proton beam can be shaped and directed to impinge upon Lithium within the molten salt to promote the generation of thermal neutrons and the fission of Uranium within the molten salt. The generated proton beam can also be shaped and directed to impinge upon the Beryllium within the Thorium fuel rods to promote the generation of high energy neutrons.

039309428

claims

1. An installation for a fluid having an undesirable effect, comprising a normal retaining wall for the fluid, a second wall adapted to retain the fluid in the event of breakdown of the first wall, and a space between the two walls, characterized in that the surface of the first wall disposed facing the second wall is bare and the said space is adapted to receive a trolley which can travel along said surface and which is equipped with at least one repair device for the said installation. 2. Installation according to claim 1, wherein the space contains a filling, the effect of which is greatly to reduce the fall in level in the vessel bounded by the first wall in the event of leakage, said filling being displaceable by the force of the trolley. 3. Installation according to claim 2, wherein the filling is a train of coupled elements. 4. Installation according to claim 1, wherein the second wall has an access door to the inspection space, said door being intended for the trolley. 5. Installation according to claim 4, wherein the second wall is buried, the installation comprising an underground gallery leading to the access door provided with an air-lock. 6. Installation according to claim 1, wherein the device is movable over a guide track having a similar profile to that of the primary wall. 7. Installation according to claim 6, comprising means for adjusting the distance between the guide track and the primary wall. 8. Installation according to claim 1, comprising a longitudinal trolley track laid along the inter-wall space, a transverse trolley track enabling the trolley to enter and leave the space, the trolley having two wheel sets, one for each track, at least one of the said wheel sets being vertically adjustable to allow the trolley to be deposited at will selectively on the two tracks at their intersection. 9. Installation according to claim 1, wherein the space is in the form of a body of revolution. 10. Installation according to claim 1, wherein the trolley bears at least one remotely controlled, remotely monitored inspection, maintenance and repair means. 11. Installation according to claim 1, wherein the surface of the primary wall facing the second wall bears locating elements for inspection and maintenance and repair devices. 12. Installation according to claim 2, wherein the filling is formed by separate blocks adapted to serve as storage tanks. 13. Application of the features according to claim 1 wherein said normal retaining wall is adapted to receive a water reactor vessel.

summary

055454275

abstract

This invention relates to a process for the preparation of lithium aluminosilicate or gamma lithium aluminate ceramics having a controlled microstructure and stoichiometry.. According to this process, mixing takes place accompanied by stirring in a short chain anhydrous alcohol of an unpolymerized liquid aluminium alkoxide and optionally a silicon alkoxide with a hydrated or unhydrated lithium hydroxide, followed by the addition of water in order to hydrolyze the mixture and obtain, after drying, beta LiAlO.sub.2 powder.. This powder can be directly compacted and then sintered at temperatures of 800.degree. to 1150.degree. C. without prior calcination giving a gamma lithium aluminate ceramic with a controlled stoichiometry and microstructure (grains of 0.1 to 10 .mu.m).

abstract

Accelerator based systems are disclosed for the generation of isotopes, such as molybdenum-98 (“99Mo”) and metastable technetium-99 (“99mTc”) from molybdenum-98 (“98Mo”). Multilayer targets are disclosed for use in the system and other systems to generate 99mTc and 98Mo, and other isotopes. In one example a multilayer target comprises a first, inner target of 98Mo surrounded, at least in part, by a separate, second outer layer of 98Mo. In another example, a first target layer of molybdenum-100 is surrounded, at least in part, by a second target layer of 98Mo. In another example, a first inner target comprises a Bremsstrahlung target material surrounded, at least in part, by a second target layer of molybdenum-100, surrounded, at least in part, by a third target layer of 98Mo.

048266507

summary

BACKGROUND OF THE INVENTION This invention relates to ultrasound testing. More particularly, the invention relates to remote ultrasound testing of a lattice-like nuclear reactor vessel top guide and sets forth a protocol wherein testing can occur without lattice disassembly. STATEMENT OF THE PROBLEM Reactors constitute extremely hostile environments for inspection of any kind. First, reactors are notorious for their radioactivity. Secondly, the internals of the reactors are frequently mechanically inaccessible. A classic example of such inaccessibility is the top guide used in a boiling water reactor. The top guide comprises a series of bars in the order of 1/4 inch thick and 9 to 13 inches in width. The bars each span the full diameter of the reactor vessel which can be in the order of 22 feet. The bars are grooved. The grooves extend through half the width of the bars. The grooves in parallel bars extend in the same direction. For example, one set of bars has its grooves upwardly disposed; bars at right angles have their grooves downwardly disposed. The bars are assembled in a lattice by confronting their respective grooves. They come together in a lattice-like structure that is not unlike the cardboard separators found in wine cases. This continuous lattice, once assembled, is welded at the side edges to a ring on the reactor vessel. The bars of the lattice are not otherwise welded or attached to themselves. The lattice defines a number of discrete square cells bounded by the intersecting bars forming parallel sides. The function of the top guide is for preserving the vertical and rotational orientation of square sectioned elongate fuel assemblies supported on a core plate some 14 feet below the top guide. The top guide braces and maintains the top of the fuel assemblies. The fuel assemblies are maintained vertical by the top guide. Moreover, the top guide forms the support surface from which the rotational orientation of the fuel assemblies is maintained. By bracing the fuel assemblies to the top guide, the vital cruciform shaped interstitial area between the fuel assemblies for control rod penetration and moderation of the reaction is maintained. Unfortunately, the top guide is in an ideal place for cracking to occur. First, the bars making up the top guide have numerous discontinuities. These discontinuities include the very grooves which enable the top guide bars to be assembled in their latticelike configuration. Additionally, various other discontinuities are present in the bars. For example, notches for the hanging of poison curtains used in the start-up of older reactors constitute such discontinuities. Further, the bars in spanning the reactor vessel and aligning the fuel assemblies are subject to stress. This stress is aggravated by the fact that the bars at their respective points of intersection are not fastened one to another. Additionally, the bars making up the top guide are subject to high radiation dosage. Consequently, the bars are ideal sites for irradiation assisted stress corrosion cracking (IASCC). IASCC occurs in many stainless steels when an irradiation dosage exceeds 2.times.10.sup.21 neutrons per cm.sup.2. Thus, when older reactors approach this dosage level, there is high motive to examine the top guide for IASCC. It goes without saying that removal and disassembly of the bulky radioactive lattice comprising the top guide is possible--but prohibitively inconvenient and expensive. SUMMARY OF THE PRIOR ART Ultrasound testing is a nondestructive technique well known. In the usual application, an ultrasound transducer is manually fastened to an article --typically piping--to be nondestructively tested. A transducer imparts an ultrasound pulse to the article to be tested. The pulse fully penetrates the article to be tested and is reflected. The pulse upon being reflected is detected, usually at the very transducer which initiated the pulse. The detection of the pulse at the transducer is recorded and analyzed. It is conventional to time the receipt of reflected pulses. By noting the reflected pulses, one can determine whether an intact part at an extremity causes the return pulse or an interfering crack at a location other than the extremity causes reflection. Since transducers, power equipment, recorders, monitors and computers for analyzing ultrasound are all known and conventional, further description will not be set forth herein. For more complete detail on the testing referred to herein, the readers attention is invited to the publication UT Operator Training for Intergranular Stress Corrosion Cracking published by the Electric Power Research Institute Nondestructive Evaluation Center of Charlotte, N.C., 1983. SUMMARY OF THE INVENTION In a boiling water reactor, an apparatus and process for ultrasound inspection of the top guide is disclosed. The top guide constitutes a lattice of stainless steel bars overlying the core plate and being assembled at confronting grooves with the lattice mounted at the side edges to the reactor pressure vessel. This lattice braces the upper ends of the vertically supported fuel assemblies in their requisite orientation and spaced apart relation to enable among other things the required spatial interval to be maintained for control rod moderation of the reaction. Because of the proximity of the top guide to the fuel assemblies, the individual bars making up the lattice need to be checked for cracking, especially that cracking produced by irradiation assisted stress crack corrosion. With a defined cell in the lattice emptied of its contained and adjoining fuel assemblies, there is disclosed an ultrasound test for cracking. A sound transducer on a first special frame sweeps horizontally across the top of a bar interrogating the bar with vertical longitudinal ultrasound waves for detecting horizontal cracks. Similarly, a sound transducer on a second special frame sweeps vertically across the side of a bar interrogating the bar with angularly incident horizontal shear ultrasound waves for detecting vertical cracks. Nondestructive testing of the lattice assembly occurs without required disassembly. Two test frames are disclosed, a first test frame for checking the lattice assembly for horizontal cracking and a second test frame for checking the lattice for vertical cracking. Before the test, it is required that all fuel assemblies adjacent the bars to be tested are removed. A first test frame has the cross section of of a fuel channel and is configured for detecting vertical cracking. This frame engages orthogonally disposed bars at their defined corners and comes to rest. A ball screw driven carriage is given vertical excursion along each bar of the defined corner. Each bar at the defined corner is interrogated by ultrasound from paired transducers. The paired transducers are oriented to have opposed acoustical angles of incidence to the bar in the order of 70.degree. in a horizontal plane towards the bars. One transducer sweeping each bar interrogates the bar with horizontal shear wave ultrasound towards the corner defined by the bar; the remaining transducer sweeping each bar interrogates the bar with horizontal shear wave ultrasound away from the corner defined by the bar. The vertically sweeping transducers therefore interrogate each bar with acoustical signals horizontally and in opposite directions to detect vertical cracking. The second test frame is configured for detecting horizontal cracking. The second test frame is configured for precise placement on the lattice overlying the portion of a bar to be tested. In the preferred embodiment, the carriage rest one leg on the bar to be tested and its rear two legs on an intersecting bar on the top of the top guide assembly. The second test frame includes a carriage mounted to a ball screw drive. This carriage contains an ultrasound transducer and sweeps horizontally the transducer immediately over the bar to be tested. The horizontally moving transducer interrogates the bar with vertically interrogating sound to locate horizontal cracking. In both types of test frames, each transducer (one transducer for vertical acoustical interrogation and four transducers for horizontal acoustical interrogation) couple through the demineralized water of the reactor to enable complete nondestructive testing of the top guide without costly disassembly.

description

This application is a continuation of U.S. patent application Ser. No. 10/743,265, filed on Dec. 23, 2003 now U.S. Pat. No. 7,247,866, which is based on and claims the benefit of priority from European Patent Application No. 02080454.8, filed Dec. 23, 2002, and European Patent Application No. 03075086.3, filed Jan. 13, 2003, the contents of each being hereby incorporated by reference in their entireties. 1. Field of the Invention The invention relates generally to a lithographic apparatus, and more specifically to a contamination barrier for passing through radiation from a radiation source and for capturing debris coming from the radiation source. 2. Description of Related Art A contamination barrier for a lithographic apparatus is known from, for example, the international patent application WO 02/054153. The contamination barrier is normally positioned in a wall between two vacuum chambers of a radiation system of a lithographic projection apparatus. In a lithographic projection apparatus, the size of features that can be imaged onto a substrate is limited by the wavelength of projection radiation. To produce integrated circuits with a higher density of devices, and hence higher operating speeds, it is desirable to be able to image smaller features. While most current lithographic projection apparatus employ ultraviolet light generated by mercury lamps or excimer lasers, it has been proposed to use shorter wavelength radiation in the range 5 to 20 nm, especially around 13 nm. Such radiation is termed extreme ultraviolet (EUV), or soft x-ray, and possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or synchrotron radiation from electron storage rings. Apparatus using discharge plasma sources are described in: W. Partlo, I. Fomenkov, R. Oliver, D. Birx, “Development of an EUV (13.5 nm) Light Source Employing a Dense Plasma Focus in Lithium Vapor”, Proc. SPIE 3997, pp. 136-156 (2000); M. W. McGeoch, “Power Scaling of a Z-pinch Extreme Ultraviolet Source”, Proc. SPIE 3997, pp. 861-866 (2000); W. T. Silfvast, M. Klosner, G. Shimkaveg, H. Bender, G. Kubiak, N. Formaciari, “High-Power Plasma Discharge Source at 13.5 and 11.4 nm for EUV lithography”, Proc. SPIE 3676, pp. 272-275 (1999); and K. Bergmann et al., “Highly Repetitive, Extreme Ultraviolet Radiation Source Based on a Gas-Discharge Plasma”, Applied Optics, Vol. 38, pp. 5413-5417 (1999). EUV radiation sources may require the use of a rather high partial pressure of a gas or vapor to emit EUV radiation, such as discharge plasma radiation sources referred to above. In a discharge plasma source, for example, a discharge is created between electrodes, and a resulting partially ionized plasma may subsequently be caused to collapse to yield a very hot plasma that emits radiation in the EUV range. The very hot plasma is quite often created in Xe, since a Xe plasma radiates in the Extreme UV (EUV) range around 13.5 nm. For an efficient EUV production, a typical pressure of 0.1 mbar is required near the electrodes to the radiation source. A drawback of having such a rather high Xe pressure is that Xe gas absorbs EUV radiation. For example, 0.1 mbar Xe transmits over 1 m only 0.3% EUV radiation having a wavelength of 13.5 nm. It is therefore required to confine the rather high Xe pressure to a limited region around the source. To reach this, the source can be contained in its own vacuum chamber that is separated by a chamber wall from a subsequent vacuum chamber in which the collector mirror and illumination optics may be obtained. The chamber wall can be made transparent to EUV radiation by a number of apertures in the wall provided by a contamination barrier or so-called “foil trap,” such as the one described in European Patent application number EP-A-1 057 079, which is incorporated herein by reference. In EP-A-1 057 079 a foil trap has been proposed to reduce the number of particles propagating along with the EUV radiation. This foil trap consists of a number of lamella shaped walls, which are close together in order to form a flow resistance, but not too close so as to let the radiation pass without substantially obstructing it. The lamellas can be made of very thin metal platelets, and are positioned near the radiation source. The lamellas are positioned in such a way, that diverging EUV radiation coming from a radiation source, can easily pass through, but debris coming from the radiation source is captured. Debris particles collide with gas inside the foil trap, are scattered thereby, and eventually collide with the lamellas and stick to these lamellas. The lamellas, however, absorb some EUV radiation and heat. Moreover, they are heated by colliding debris particles. This results in significant heating of the lamellas and a supporting structure which supports the lamellas. Since optical transmission is very important in a lithographic projection apparatus, mechanical deformation is not allowed. Therefore, it is an aspect of the present invention to provide a contamination barrier in which disadvantageous deformation of lamellas is minimized. It is another aspect of embodiments of the present invention to provide a foil trap for a lithographic projection apparatus. The foil trap forms an open structure to let radiation coming from, for example, an EUV source, pass unhindered. The foil trap comprises lamellas arranged to capture debris particles coming from the radiation source. The lamellas are extending in a radial direction from a foil trap axis. In order to prevent mechanical stress, the lamellas are slidably connected in grooves of one or both of the rings. In this way, the lamellas can expand easily and mechanical stress is avoided, so that there is no deformation of the lamellas. At least one of the outer ends of the lamellas is thermally connected to a ring. This ring may be cooled by a cooling system. In a preferred embodiment, the foil trap comprises a shield to protect the inner ring from being hit by the EUV beam. This aspect is achieved according to embodiments of the present invention by a contamination barrier. The contamination barrier comprises a number of lamellas extending in a radial direction from a main axis, each of the lamellas being positioned in a plane that contains the main axis, characterized in that the contamination barrier comprises an inner ring and an outer ring and that each of the lamellas is slidably positioned at least one of its outer ends in grooves of at least one of the inner and outer ring. Embodiments also provide for a contamination barrier that passes through radiation from a radiation source and captures debris coming from the radiation source. The contamination barrier includes an inner ring, an outer ring, and a plurality of lamellas that extend in a radial direction from a main axis. Each of the lamellas is positioned in a respective plane that includes the main axis. At least one outer end of each of the lamellas is slidably connected to at least one of the inner and outer ring. Embodiment of the invention further provide for a contamination barrier that passes through radiation from a radiation source and captures debris coming from the radiation source. The contamination barrier includes a plurality of lamellas, and a support structure that slidably engages the lamellas. The lamellas and the support structure are configured and arranged to allow the lamellas to expand and contract in response to changes in temperature. Embodiment of the invention also provide for a contamination barrier that permits radiation to pass therethrough and captures debris from a radiation source generated by the radiation source. The contamination barrier includes a support structure and a plurality of thin plate members mounted on the support structure. The radiation propagates along an optical axis and the thin plate members are disposed along a plane that includes the axis. The plate members are slidably movable relative to the support structure. By slidably positioning one of the outer ends of a lamella, the lamella can expand in a radial direction without the appearance of mechanical tension which may create a deformation of the lamella. Preferably, the lamellas are thermally connected to at least one of the inner and outer ring. In this way, heat from the lamellas will be transported to the rings. Note that a thermal connection is not necessarily a mechanical connection; heat conduction from the lamellas to the rings is even possible when the connection is slidable. Furthermore, a connection using a heat conducting gel between the lamellas and the rings is possible. In an embodiment, the contamination barrier comprises a first shield arranged to protect the inner ring from being hit by radiation from the radiation source. In this way, the heating of the inner ring is limited. Preferably, the contamination barrier comprises a second shield arranged to block thermal radiation from the first shield. By blocking the heat radiation coming from the first heat shield, the beam going into the collector is not exposed by unwanted radiation. In a further embodiment, upstream of the first shield, with respect to the direction of propagation of the radiation emitted by the radiation source along the main axis, a third shield is provided, constructed and arranged to reduce heating of the first shield caused by direct radiation from the radiation source. The third shield prevents the first shield from being excessively heated by direct radiation from the radiation source, and consequently further reduces heat radiating from the first shield towards the collector. In an embodiment, there is provided a contamination barrier configured to permit radiation from a radiation source to pass through and to capture debris from the radiation source. The contamination barrier includes a support structure, a plurality of plate members arranged on the support structure and extending in a radial direction from an axis of the support structure, and a shield configured to block at least part of the support structure from being hit by radiation or debris from the radiation source. In another embodiment, there is provided a lithographic projection apparatus that includes a radiation system configured to form a beam of radiation. The radiation system includes a contamination barrier configured to permit radiation from a radiation source to pass through and to capture debris from the radiation source. The contamination barrier includes a support structure, a plurality of plate members arranged on the support structure and extending in a radial direction from an axis of the support structure, and a shield configured to block at least part of the support structure from being hit by radiation or debris from the radiation source. The lithographic apparatus also includes a support structure to support a patterning structure to be irradiated by a beam of radiation to pattern the beam of radiation, a substrate support to support a substrate, and a projection system to image an irradiated portion of the patterning structure onto a target portion of the substrate. In a further embodiment, there is provided a method of manufacturing an integrated structure by a lithographic process. The method includes generating radiation with a radiation source, capturing debris from the radiation source using a contamination barrier that includes a support structure, a plurality of plate members arranged on the support structure and extending in a radial direction from an axis of the support structure, and a shield configured to block at least part of the support structure from being hit by radiation or debris from the radiation source. The method also includes patterning the radiation with a patterning structure, and imaging the patterned radiation onto a target portion of a substrate. In an embodiment, the contamination barrier also comprises at least one cooling spoke to support the first shield, wherein the cooling spoke is thermally connected to the outer ring. The cooling spoke can be made of metal or any other heat conductive material, such as carbon. The cooling spoke not only supports the first shield, but also transports heat from the first heat shield to the outer ring. In an embodiment, the first shield comprises a number of shield members, each shield member being connected to the outer ring via a separate cooling spoke. In a further embodiment, the contamination barrier comprises a first cooling device or structure that is arranged to cool at least one of the first and second shield. In this case, a cooling spoke as described above is not necessary. The cooling device may comprise a cooling system in which a cooling fluid is used to remove the heat away from the contamination barrier. The cooling device may be part of a cooling system used in a collector. In this way, the cooling device will be in the shadow of the heat shields, and thus not blocking the EUV radiation beam. Preferably, the heat shields are supported by the cooling device. Vibrations coming from the cooling system will not reach the lamellas of the contamination barrier because the inner ring is not fixed to the cooling system. In yet another embodiment, the contamination barrier comprises a second cooling device arranged to cool the inner ring. If the cooling ring is cooled directly, there will be no need for a heat shield. In a further embodiment, the contamination barrier comprises a third cooling device arranged to cool the outer ring. If the lamellas are slidably connected to the inner ring and thermally connected to the outer ring, the heat form the lamellas will go to the outer ring. The outer ring can be easily cooled by for example water cooling, since it is outside the EUV optical path. Preferably, the lamellas are curved in the respective planes, and the inner and outer ring are shaped as slices of a conical pipe. If the surfaces of the outer and inner ring are focused on the EUV source, the EUV beam will be blocked by the rings as little as possible. Only the inner ring will be in the way for the EUV beam, which is unavoidable. However, no light is lost, as the collector is unable to collect radiation in this solid angle anyway. In a further embodiment, a first side of the lamellas, at least in use facing the radiation source, is thicker than the rest of the lamellas. In this way, the influence of minor warping of the lamellas is reduced. The warped lamellas should be positioned in the shadow of the thick front side of the lamellas. This measure results in better uniformity of the transmission of the contamination barrier. The present invention also relates to a radiation system comprising a contamination barrier as described above, and a collector for collecting radiation passing the contamination barrier. It is another aspect of the present invention to extend the lifetime of a collector of a radiation system. Therefore, embodiments of the invention relate to a radiation system comprising: a contamination barrier for passing through radiation from a radiation source and for capturing debris coming from the radiation source, the contamination barrier comprising a number of lamellas, and a collector for collecting radiation passing the contamination barrier, characterized in that a surface of the lamellas is covered with the same material as an optical surface of the collector. In an embodiment, there is provided a radiation system that includes a contamination barrier configured to permit radiation from a radiation source to pass through and to capture debris coming from the radiation source, the contamination barrier comprising a plurality of lamellas, the surface of the lamellas comprising a material, and a collector configured to collect radiation from the contamination barrier, an optical surface of the collector comprising a material that is the same as the material of the surface of the lamellas. In an embodiment, there is provided a lithographic projection apparatus that includes a radiation system to form a beam of radiation. The radiation system includes a contamination barrier configured to permit radiation from a radiation source to pass through and to capture debris coming from the radiation source, the contamination barrier comprising a plurality of lamellas, the surface of the lamellas comprising a material, and a collector configured to collect radiation from the contamination barrier, an optical surface of the collector comprising a material that is the same as the material of the surface of the lamellas. The lithographic apparatus also includes a support structure to support a patterning structure to be irradiated by a beam of radiation to pattern the beam of radiation, a substrate support to support a substrate, and a projection system to image an irradiated portion of the patterning structure onto a target portion of the substrate. In a further embodiment, there is provided a method of manufacturing a device by a lithographic process. The method includes passing radiation from a radiation source through a contamination barrier comprising a plurality of lamellas, the surface of the lamellas comprising a material and the contamination barrier capturing debris from the radiation source, collecting radiation from the contamination barrier with a collector, an optical surface of the collector comprising a material that is the same as the material of the surface of the lamellas, patterning radiation from the collector, and projecting the patterned radiation onto a target portion of a substrate. Embodiments also provide a radiation system that includes a contamination barrier that passes through radiation from a radiation source and captures debris coming from the radiation source, and a collector that collects radiation passing the contamination barrier. The contamination barrier includes an inner ring, an outer ring, and a plurality of lamellas that extend in a radial direction from a main axis. Each of the lamellas is positioned in a respective plane that includes the main axis, and at least one outer end of each of the lamellas is slidably connected to at least one of the inner and outer ring. Another embodiment includes a radiation system that includes a contamination barrier that passes through radiation from a radiation source and captures debris coming from the radiation source, and a collector that collects radiation passing the contamination barrier. The contamination barrier includes a plurality of lamellas, and a surface of the lamellas is covered with the same material as an optical surface of the collector. When material is sputtered off of the contamination barrier onto the collector, the life time of the collector is only minimally influenced if the materials are equal. Embodiments of the invention also relate to a lithographic projection apparatus comprising: a support structure constructed and arranged to hold a patterning device, to be irradiated by a projection beam of radiation to pattern the projection beam of radiation, a substrate table constructed and arranged to hold a substrate, and a projection system constructed and arranged to image an irradiated portion of the patterning device onto a target portion of the substrate, wherein the projection apparatus comprises a radiation system for providing a projection beam of radiation as described above. A further embodiment is directed to a lithographic projection apparatus. The lithographic projection apparatus includes a radiation system to provide a beam of radiation, a support structure to support a patterning structure to be irradiated by a beam of radiation to pattern said beam of radiation, a substrate support to support a substrate, and a projection system to image an irradiated portion of the patterning structure onto a target portion of the substrate. The radiation system includes a contamination barrier that passes through radiation from a radiation source and captures debris coming from the radiation source and a collector for collecting radiation passing the contamination barrier. The contamination barrier includes an inner ring, an outer ring, and a plurality of lamellas that extend in a radial direction from a main axis. Each of the lamellas is positioned in a respective plane that includes the main axis, and each of the lamellas is slidably connected to at least one of the inner and outer ring. Yet another embodiment is directed to a lithographic projection apparatus that includes a radiation system to provide a beam of radiation, a support structure to support a patterning structure to be irradiated by a beam of radiation to pattern the beam of radiation, a substrate support to support a substrate; and a projection system to image an irradiated portion of the patterning structure onto a target portion of the substrate. The radiation system includes a contamination barrier that passes through radiation from a radiation source and captures debris coming from the radiation source, and a collector that collects radiation passing the contamination barrier. The contamination barrier includes a plurality of lamellas, wherein a surface of the lamellas is covered with the same material as an optical surface of the collector. Another embodiment is directed to a method of manufacturing an integrated structure by a lithographic process. The method includes radiating a beam of radiation through a radiation system, providing a support structure to support a patterning structure to be irradiated by the beam of radiation to pattern said beam of radiation, providing a substrate support to support a substrate, and providing a projection system to image an irradiated portion of the patterning structure onto a target portion of the substrate. Radiating the beam of radiation through the radiation system includes passing radiation from a radiation source through a contamination barrier comprising an inner ring, an outer ring, and a plurality of lamellas extending in a radial direction from a main axis. Each of the lamellas are positioned in a respective plane that comprises the main axis, and at least one outer end of each of the lamellas is slidably connected to at least one of the inner and outer ring. Radiating the beam of radiation also includes collecting radiation passing the contamination barrier. Embodiments of the invention also relate to a method of manufacturing an integrated structure by a lithographic process. The method includes radiating a beam of radiation through a radiation system, providing a support structure to support a patterning structure to be irradiated by the beam of radiation to pattern said beam of radiation, providing a substrate support to support a substrate, and providing a projection system to image an irradiated portion of the patterning structure onto a target portion of the substrate. Radiating the beam of radiation through the radiation system includes passing radiation from a radiation source through a contamination barrier that includes a plurality of lamellas, capturing debris from the radiation source, and collecting radiation passing the contamination barrier. A surface of the lamellas is covered with the same material as an optical surface of the collector. Embodiments of the invention are also directed to a method of manufacturing an integrated structure by a lithographic process. The method includes generating a beam of radiation with a radiation source, capturing debris from the radiation source, collecting radiation passing the contamination barrier patterning the beam of radiation with a patterning structure, and imaging an irradiated portion of the patterning structure onto a target portion of a substrate. Capturing debris comprises providing a support structure and a plurality of lamellas that are slidably engaged with the support structure so as to allow the plurality of lamellas to expand and contract in response to changes in temperature. The term “patterning device” as here employed should be broadly interpreted as referring to a device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate; the term “light valve” can also be used in this context. Generally, the pattern will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit or other device (see below). Examples of such patterning devices include: A mask. The concept of a mask is well known in lithography, and it includes mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Placement of such a mask in the radiation beam causes selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask, according to the pattern on the mask. In the case of a mask, the support structure will generally be a mask table, which ensures that the mask can be held at a desired position in the incoming radiation beam, and that it can be moved relative to the beam if so desired; A programmable mirror array. One example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that (for example) addressed areas of the reflective surface reflect incident light as diffracted light, whereas unaddressed areas reflect incident light as undiffracted light. Using an appropriate filter, the undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind; in this manner, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. An alternative embodiment of a programmable mirror array employs a matrix arrangement of tiny mirrors, each of which can be individually tilted about an axis by applying a suitable localized electric field, or by employing a piezoelectric actuation device. Once again, the mirrors are matrix-addressable, such that addressed mirrors will reflect an incoming radiation beam in a different direction to unaddressed mirrors; in this manner, the reflected beam is patterned according to the addressing pattern of the matrix-addressable mirrors. The required matrix addressing can be performed using suitable electronic means. In both of the situations described hereabove, the patterning device can comprise one or more programmable mirror arrays. More information on mirror arrays as here referred to can be gleaned, for example, from U.S. Pat. No. 5,296,891 and U.S. Pat. No. 5,523,193, and PCT patent applications WO 98/38597 and WO 98/33096, which are incorporated herein by reference. In the case of a programmable mirror array, the support structure may be embodied as a frame or table, for example, which may be fixed or movable as required; and A programmable LCD array. An example of such a construction is given in U.S. Pat. No. 5,229,872, which is incorporated herein by reference. As above, the support structure in this case may be embodied as a frame or table, for example, which may be fixed or movable as required. For purposes of simplicity, the rest of this text may, at certain locations, specifically direct itself to examples involving a mask and mask table; however, the general principles discussed in such instances should be seen in the broader context of the patterning device as hereabove set forth. Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning device may generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising one or more dies) on a substrate (silicon wafer) that has been coated with a layer of radiation-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. In current apparatus, employing patterning by a mask on a mask table, a distinction can be made between two different types of machine. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion in one go; such an apparatus is commonly referred to as a wafer stepper or step and repeat apparatus. In an alternative apparatus—commonly referred to as a step and scan apparatus—each target portion is irradiated by progressively scanning the mask pattern under the projection beam in a given reference direction (the “scanning” direction) while synchronously scanning the substrate table parallel or anti parallel to this direction; since, in general, the projection system will have a magnification factor M (generally <1), the speed V at which the substrate table is scanned will be a factor M times that at which the mask table is scanned. More information with regard to lithographic devices as here described can be gleaned, for example, from U.S. Pat. No. 6,046,792, incorporated herein by reference. In a manufacturing process using a lithographic projection apparatus, a pattern (e.g. in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation sensitive material (resist). Prior to this imaging step, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g. an IC. Such a patterned layer may then undergo various processes such as etching, ion implantation (doping), metallization, oxidation, chemo mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc. Further information regarding such processes can be obtained, for example, from the book “Microchip Fabrication: A Practical Guide to Semiconductor Processing”, Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0 07 067250 4, incorporated herein by reference. For the sake of simplicity, the projection system may hereinafter be referred to as the “lens”; however, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a “lens”. Further, the lithographic apparatus may be of a type having two or more substrate tables (and/or two or more mask tables). In such “multiple stage” devices the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Dual stage lithographic apparatus are described, for example, in U.S. Pat. No. 5,969,441 and WO 98/40791, both incorporated herein by reference. Although specific reference may be made in this text to the use of the apparatus according to the invention in the manufacture of ICs, it should be explicitly understood that such an apparatus has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “reticle”, “wafer” or “die” in this text should be considered as being replaced by the more general terms “mask”, “substrate” and “target portion”, respectively. In the present document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range 5-20 nm), as well as particle beams, such as ion beams or electron beams. FIG. 1 schematically depicts a lithographic projection apparatus 1 according to a particular embodiment of the invention. The apparatus comprises: a radiation system Ex, IL, for supplying a projection beam PB of radiation (e.g. EUV radiation) with a wavelength of 11-14 nm. In this particular case, the radiation system also comprises a radiation source LA; a first object table (mask table) MT provided with a mask holder for holding a mask MA (e.g. a reticle), and connected to a first positioning device PM for accurately positioning the mask with respect to item PL; a second object table (substrate table) WT provided with a substrate holder for holding a substrate W (e.g. a resist coated silicon wafer), and connected to a second positioning device PW for accurately positioning the substrate with respect to item PL; and a projection system (“lens”) PL for imaging an irradiated portion of the mask MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. The term “object table” as used herein can also be considered or termed as an object support. It should be understood that the term object support or object table broadly refers to a structure that supports, holds, or carries an object, such as a mask or a substrate. As here depicted, the apparatus is of a reflective type (i.e. has a reflective mask). However, in general, it may also be of a transmissive type, for example (with a transmissive mask). Alternatively, the apparatus may employ another kind of patterning device, such as a programmable mirror array of a type as referred to above. The source LA (e.g. a laser-produced plasma or a discharge plasma EUV radiation source) produces a beam of radiation. This beam is fed into an illumination system (illuminator) IL, either directly or after having traversed conditioning means, such as a beam expander Ex, for example. The illuminator IL may comprise an adjusting device AM for setting the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the beam. In addition, it will generally comprise various other components, such as an integrator IN and a condenser CO, see FIG. 1. In this way, the beam PB impinging on the mask MA has a desired uniformity and intensity distribution in its cross section. It should be noted with regard to FIG. 1 that the source LA may be within the housing of the lithographic projection apparatus (as is often the case when the source LA is a mercury lamp, for example), but that it may also be remote from the lithographic projection apparatus, the radiation beam which it produces being led into the apparatus (e.g. with the aid of suitable directing mirrors). This latter scenario is often the case when the source LA is an excimer laser. Embodiments of the current invention, and claims, encompass both of these scenarios. The beam PB subsequently intercepts the mask MA, which is held on a mask table MT. Having traversed the mask MA, the beam PB passes through the lens PL, which focuses the beam PB onto a target portion C of the substrate W. With the aid of the second positioning device PW (and an interferometric measuring device IF), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the beam PB. Similarly, the first positioning device PM can be used to accurately position the mask MA with respect to the path of the beam PB, e.g. after mechanical retrieval of the mask MA from a mask library, or during a scan. In general, movement of the object tables MT, WT will be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which are not explicitly depicted in FIG. 1. However, in the case of a wafer stepper (as opposed to a step-and-scan apparatus) the mask table MT may just be connected to a short stroke actuator, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The depicted apparatus can be used in two different modes: 1. In step mode, the mask table MT is kept essentially stationary, and an entire mask image is projected in one go (i.e. a single “flash”) onto a target portion C. The substrate table WT is then shifted in the x and/or y directions so that a different target portion C can be irradiated by the beam PB; and 2. In scan mode, essentially the same scenario applies, except that a given target portion C is not exposed in a single “flash”. Instead, the mask table MT is movable in a given direction (the so called “scan direction”, e.g. the y direction) with a speed v, so that the projection beam PB is caused to scan over a mask image; concurrently, the substrate table WT is simultaneously moved in the same or opposite direction at a speed V=Mv, in which M is the magnification of the projection system PL (typically, M=¼ or ⅕). In this manner, a relatively large target portion C can be exposed, without having to compromise on resolution. FIG. 2 shows an embodiment of the lithographic projection apparatus 1 of FIG. 1, comprising a radiation system 3 (i.e. “source-collector module”), an illumination optics unit 4, and the projection system PL. The radiation system 3 is provided with a radiation source LA which may comprise a discharge plasma source. The radiation source LA may employ a gas or vapor, such as Xe gas or Li vapor in which a very hot plasma can be created to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma is created by causing a partially ionized plasma of an electrical discharge to collapse onto an optical axis 20. Partial pressures of 0.1 mbar of Xe gas, Li vapor or any other suitable gas or vapor may be required for efficient generation of the radiation. The radiation emitted by the radiation source LA is passed from a source chamber 7 into a collector chamber 8 via a foil trap 9. The foil trap 9 comprises a channel structure such as, for example, described in detail in European patent application EP-A-1 057 079, which is incorporated herein by reference. The term “foil trap” as used herein can also be considered or termed a contamination barrier. It should be understood that the term foil trap or contamination barrier broadly refers to a structure that captures debris coming from the radiation source LA. The collector chamber 8 comprises a radiation collector 10 which may be formed by a grazing incidence collector. Radiation passed by the radiation collector 10 is reflected off a grating spectral filter 11 or mirror to be focused in a virtual source point 12 at an aperture in the collector chamber 8. From chamber 8, the projection beam 16 is reflected in the illumination optics unit 4 via normal incidence reflectors 13, 14 onto a reticle or mask positioned on reticle or mask table MT. A patterned beam 17 is formed which is imaged in projection optics system PL via reflective elements 18, 19 onto wafer stage or substrate table WT. More elements than shown may generally be present in illumination optics unit 4 and projection system PL. FIG. 3 shows a downstream and a cross-sectional view, respectively, of a foil trap 9 with a plurality of lamellas 31, 32 according to an embodiment of the invention. The foil trap 9 comprises an inner ring 33 and an outer ring 35. Preferably, the inner ring 33 and the outer ring 35 are shaped as slices of a conical pipe, wherein a minimum diameter do of the outer ring 35 is larger than a minimum diameter di of the inner ring 33. Preferably, both conical rings 33, 35 share the same main axis 34 and focus. Preferably, the foil trap 9 is arranged in a lithographic projection apparatus, in such a way that the main axis 34 of the foil trap 9 and the optical axis 20 of the radiation system 3 coincide, see FIG. 2. In FIG. 4, the foil trap 9, as shown, comprises a heat shield 41. The heat shield 41 is supported by two cooling spokes 44, 45 which are mechanically and thermally connected to the outer ring 35. At the center of the foil trap 9, the cooling spokes 44, 45 connect to a spindle 47, which supports the heat shield 41. The heat shield 41 comprises a disk, which avoids the inner ring 33 from being hit by the emitted radiation and heat from the radiation source LA. In this way, the heat shield 41 shields off the inner ring 33. The cooling spokes 44, 45, the spindle 47 and the heat shield 41 are preferably made of a good heat conductor. In this way, heat developed on the heat shield 41, may easily be transferred to the outer ring 35 via the cooling spokes 44, 45. Alternatively, the heat shield 41 may comprise two (or more) disc parts, each disc part being connected to one cooling spoke 44, 45. In this case, the spindle 47 will also be divided into two (or more) parts. FIG. 5 shows a perspective view of the inner ring 33 according to an embodiment of the invention. The inner ring 33 comprises a plurality of grooves 51. Preferably, two grooves 53, opposite to one another, have a relative larger width than the other grooves. These larger grooves 53 are provided to pass the cooling spokes 44, 45. According to embodiments of the invention, the inner ring 33 is only supported mechanically by the plurality of lamellas 31, 32 and is not connected to anything other than the lamellas 31, 32. FIG. 6 shows a detailed example of the lamella 31, 32 of the foil trap 9 according to an embodiment of the invention. The lamella 31, 32 is a very thin platelet having two curved edges 60, 61, a straight outer edge 65, and an inner edge 62 having an indentation 63. The lamella 31, 32 has a height h and a width w, see FIG. 6. The outer edge 65 is mechanically connected to the outer ring 35, see FIG. 4. The inner edge 62 is inserted into one of the grooves 51 of the inner ring 33, see FIG. 5. Preferably, the lamellas 31, 32 are soldered or welded to the outer ring 35. In this way, a good thermal contact is provided and approximately all the heat absorbed by the lamellas, is transported to the outer ring 35. In one embodiment, the outer ring 35 is cooled by a cooling device, not shown, to remove the heat from the foil trap 9. In an embodiment of the invention, the foil trap 9 also comprises a second heat shield in order to block thermal radiation from the first heat shield 41. FIG. 7 shows a foil trap 9 with first and second heat shields 41, 71. In an embodiment, the second heat shield 71 comprises a disc, positioned inside the inner ring 33 and situated at the back end (i.e. down stream side) of this inner ring 33. In another embodiment, the cooling spoke 44, 45, 47 is absent. In this case, the first and/or second shields 41, 71 are cooled by a cooling device, arranged in a way known by a person skilled in the art. The cooling device may comprise a water cooling system. This water cooling system can be part of a cooling system of the collector 10 of the radiation system 3. In this case, the shields 41, 71 are supported by the cooling device. In yet another embodiment, the inner ring 33 is cooled by a cooling device. The cooling device for cooling the shields 41; 71 and the cooling device for cooling the inner ring 33, may be one. The foil trap 9 may be focused on the radiation source 6. It is also possible to construct a foil trap 9 without a real focus. In any case, channels, i.e., spaces between adjacent lamellas, in the foil trap 9 have to be aligned with the emitted EUV beam. In FIG. 2, the foil trap 9 is focused on the radiation source such that EUV rays of radiation emitted from the EUV source may pass the lamellas 31, 32 without obstruction. Typical values for the dimensions of the lamellas are: height h=30 mm, thickness 0.1 mm and width w=50 mm (curved). A typical value for the channel width, i.e. the distance between adjacent lamellas, is 1 mm. The distance from the foil trap 9 to the source LA is typically in the order of 60 mm. These specific dimensions are examples and should not be considered to be limiting in any way. The embodiment of FIG. 8 is similar to the one shown in FIG. 4, except for the additional heat shield 46, mounted in front of shield 41. The additional shield 46 prevents the first shield 41 from being excessively heated by direct radiation from the radiation source LA, and consequently reduces heat radiating from the first shield 41 towards the collector 10. The additional heat shield 46 may be mounted on shield 41 using a dedicated separation device 48 in order to accomplish substantially thermal isolation between the two shields. The separation device 48 may be manufactured e.g. from ceramics, which is able to resist the heat caused by the radiation impinging on the additional shield 46 and has a very small heat conduction coefficient. In another embodiment of the separation device 48, it may be envisaged that by special design of the separation device a heat resistance is created between the additional shield 46 and shield 41 considerably reducing heat transfer between the two shields. While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise then as described. The description is not intended to limit the invention.

summary

claims

1. An assembly in a primary circuit of a nuclear reactor, wherein the nuclear reactor has a reactor core with defined fuel assembly positions for a placement of fuel assemblies, the assembly comprising:a device for removing solid particles from a cooling medium circulating in the primary circuit, said device not being a fuel assembly, but said device having a device outline with geometric dimensions and shapes configured for insertion thereof into an empty fuel assembly position in the reactor core of the nuclear reactor instead of a fuel assembly;a carrying structure extending in a longitudinal direction and at least one separator disposed in said carrying structure, said at least one separator being a flow separator, said flow separator having a deflection device configured for imparting centrifugal forces onto the solid particles and driving the solid particles into calm zones of said flow separator provided as accumulation spaces. 2. The assembly according to claim 1, wherein said at least one separator is one of a plurality of separators disposed one after another in the longitudinal direction in said carrying structure. 3. The assembly according to claim 2, wherein said separators are releasably connected to one another. 4. The assembly according to claim 1, wherein said carrying structure is a hollow case. 5. The assembly according to claim 1, wherein said at least one separator is an insert configured for insertion into said carrying structure, said insert is formed with an inlet opening for the cooling medium, and has, opposite and at a spacing distance from said inlet opening, a deflection device for deflecting the cooling medium, and is formed with an accumulation zone for collecting the solid particles that are separated during deflection due to a centrifugal force. 6. The assembly according to claim 5, wherein said deflection device is a cyclone disposed to impart on the cooling medium, which flows in the longitudinal direction inside said carrying structure, a circular motion about the longitudinal direction. 7. The assembly according to claim 6, wherein said deflection device includes at least one fixed guide vane. 8. The assembly according to claim 1, wherein said separator is one of a plurality of separators disposed one after another in the longitudinal direction and having mutually different designs from one another in order to achieve a different separation effect. 9. The assembly according to claim 1, configured to have a flow resistance substantially corresponding to a flow resistance of a fuel assembly. 10. The assembly according to claim 1, configured for insertion into the reactor core of a boiling-water nuclear reactor. 11. A reactor core of a nuclear reactor, comprising an assembly according to claim 1 inserted into an empty fuel assembly position. 12. The reactor core according to claim 11, configured as a core of a boiling-water reactor. 13. The reactor core according to claim 11, wherein said device is inserted in a fuel assembly position is located at an edge of a fuel assembly grid. 14. The reactor core according to claim 11, wherein said device is inserted in a corner position of a fuel assembly grid.

claims

1. A network sensor assembly comprising:a panel configured for mounting on a surface;a plurality of addressable sensors coupled to the panel that sense environmental conditions at the surface;a memory device that stores configuration information associated with the plurality of addressable sensors;a bus communicatively coupled to the plurality of addressable sensors and the memory device and configured for communicatively coupling the network sensor assembly to a network node for communicating data associated with the sensed environmental conditions in a network; andthe panel comprising a folding panel that folds at a fold line about the bus. 2. The network sensor assembly according to claim 1 further comprising:a plurality of protective tabs coupled to the panel and respectively coupled to the plurality of addressable sensors in a configuration that supports and protects the addressable sensor plurality. 3. The network sensor assembly according to claim 1 further comprising:a plurality of mounting tabs coupled to the panel configured to secure the network sensor assembly to the surface. 4. The network sensor assembly according to claim 1 further comprising:a plurality of protective tabs cut from the folding panel positioned to support and protect the plurality of addressable sensors;an adhesive coupling the panel to the bus. 5. The network sensor assembly according to claim 1 wherein the bus comprises a multiple conductor tape wire. 6. The network sensor assembly according to claim 1 wherein the plurality of addressable sensors sense at least one environmental condition selected from the group consisting of temperature, humidity, air pressure, air velocity, smoke sensors, occupancy sensors, computer rack door condition, sound, and light. 7. The network sensor assembly according to claim 1 further comprising: the network node configured for communicating data associated with the sensed environmental conditions in a network. 8. The network sensor assembly according to claim 1 further comprising: application software recorded on a non-transitory computer readable medium that operates on data received from the network node associated with the sensed environmental conditions in a network, the application software configured to:periodically query the plurality of addressable sensors from a plurality of network nodes;reading sensed environmental conditions from the plurality of addressable sensors from the plurality of network nodes;generate an environmental profile of a data center based on the sensed environmental conditions. 9. A method of fabricating a network sensor assembly comprising:mechanically coupling a bus to a panel configured for mounting on a surface, the panel comprising a folding panel that folds at a fold line about the bus;mechanically coupling a plurality of addressable sensors to the panel;communicatively coupling the bus to the plurality of addressable sensors that sense environmental conditions at the surface;communicatively coupling the bus to a memory device that stores configuration information associated with the plurality of addressable sensors; andcommunicatively coupling the memory device and the plurality of addressable sensors to a network node for communicating data associated with the sensed environmental conditions in a network. 10. The method according to claim 9 further comprising:coupling a plurality of protective tabs to the panel and respectively to the plurality of addressable sensors; andconfiguring the protective tab plurality to support and protect the addressable sensor plurality. 11. The method according to claim 9 further comprising:coupling a plurality of mounting tabs to the panel; andconfiguring the mounting tab plurality to secure the network sensor assembly to the surface. 12. The method according to claim 9 further comprising:cutting a plurality of protective tabs from the folding panel;positioning the protective tab plurality to support and protect the plurality of addressable sensors;coupling the panel to the bus with adhesive. 13. A network environmental monitor comprising:at least one network sensor assembly comprising:a panel configured for mounting on a surface, the panel comprising a folding panel that folds at a fold line about a bus;a plurality of addressable sensors coupled to the panel that sense environmental conditions at the surface;a memory device that stores configuration information associated with the plurality of addressable sensors; andthe bus communicatively coupled to the plurality of addressable sensors and the memory device, the bus configured for communicating data associated with the sensed environmental conditions;at least one network node communicatively coupled to the at least one network sensor assembly wherein the bus communicatively couples the at least one network sensor assembly to the at least one network node and the at least one network node distributes data associated with the sensed environmental conditions over a network; anda processor communicatively coupled to the at least one networked node configured to execute a software application, recorded on a non-transitory computer readable medium, that collects sensed environmental condition data from the plurality of addressable sensors and controls environment based on the sensed environmental condition data. 14. The environmental monitor according to claim 13a wherein the software application determines sensed environmental conditions at a computer rack and adjusts environmental conditions at the computer rack based on the sensed environmental conditions at the computer rack. 15. The environmental monitor according to claim 13 further comprising:a plurality of equipment racks, the plurality of network sensor assemblies respectively mounted on the equipment rack plurality. 16. The environmental monitor according to claim 15 wherein the equipment rack plurality is contained within a data center. 17. The environmental monitor according to claim 16 further comprising:an environmental control system communicatively coupled to the at least one network node that adjusts environmental controls of the data center based on the sensed environmental conditions at the plurality of equipment racks. 18. The environmental monitor according to claim 17 wherein the environmental conditions sensed comprise at least one condition selected from the group consisting of temperature, humidity, air pressure, air velocity, smoke sensors, occupancy sensors, computer rack door condition, sound, and light. 19. The environmental monitor according to claim 13 wherein the at least one network sensor assembly further comprises:a plurality of protective tabs coupled to the panel and respectively coupled to the plurality of addressable sensors in a configuration that supports and protects the addressable sensor plurality. 20. The environmental monitor according to claim 13 further comprising:application software recorded on a non-transitory computer readable medium and executable on the processor that operates on data received from the network node associated with the sensed environmental conditions in a network, the application software configured to:periodically query the plurality of addressable sensors from a plurality of network nodes;read sensed environmental conditions from the plurality of addressable sensors from the plurality of network nodes;generate an environmental profile of a data center based on the sensed environmental conditions.

056595913

abstract

A containment spray system for a light-water reactor includes a water trough being disposed in a safety tank. An immersion pump disposed in the vicinity of the bottom of the water trough, a spray branch and an outlet-side spray nozzle array, are connected to the water trough for injecting water into the containment in finely dispersed form in the event of an operational incident.

048775754

claims

1. A method of core reactivity validation, comprising the steps of: (a) determining at least two core reactivities using at least two neutron detectors; and (b) comparing the core reactivities and indicating that the reactivities are valid when the reactivities are substantially coincident. (c1) determining intersections between the straight line fit and a vertical line constructed through a point at which reactivity passes through zero during control rod movement; and (c2) producing as differential control rod worth a difference between the intersections. (a) sampling neutron flux detected by at least two neutron detectors; (b) determining at least two reactivities from the flux; (c) comparing reactivities from multiple samples and determining coincidence between the reactivities; (d) fitting a straight line to the coincident reactivities; (e) determining whether the straight line satisfies a statistical fit test; (f) determining intersections between the straight line and a vertical line constructed through a point at which reactivity passes through zero during control rod movement; and (g) determining a reactivity difference as a distance between the intersections. at least two neutron detectors producing core flux values; reactivities from the flux values; means for determining at least two reactivities and computation means for comparing the reactivities and alerting an operator when the reactivities are substantially coincident. means for fitting a straight line to the substantially coincident reactivities; and means for determining control rod worth from intersections between the straight line and core reactivity before and after control rod movement. 2. A method as recited in claim 1, wherein step (b) includes indicating valid reactivities after substantial coincidence occurs sufficient to satisfy a statistical fit test. 3. A method as recited in claim 2, further comprising the step of (c) determining control rod worth after valid reactivities are indicated. 4. A method as recited in claim 3, wherein step (b) includes the step of performing a straight line fit to the substantially coincident reactivities, and step (c) comprises the steps of: 5. A method of determining worth of control rods, comprising the steps of: 6. A validation apparatus for core reactivity, comprising: 7. An apparatus as recited in claim 6, further comprising control rod worth means for determining control rod worth from the substantially coincident reactivities. 8. An apparatus as recited in claim 7, wherein said control rod worth means comprises:

063209365

description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, an x-ray tube assembly embodying the present invention is indicated generally by the reference numeral 10. The x-ray tube assembly 10 comprises a housing 12 and an x-ray tube 14 mounted within the housing. The x-ray tube housing 12 comprises a mounting boss 16 defining an x-ray port 18 extending through the mounting boss and into the interior of the housing. The x-ray tube 14 includes an evacuated glass envelope 20, a rotating anode 22 defining a target surface 24, and a cathode (not shown) spaced relative to the anode within the glass envelope. As will be recognized by those skilled in the pertinent art based on the teachings herein, the x-ray tube 14 may be any of numerous different types of x-ray tubes which are now or later become known for generating x-radiation, including, for example, any of numerous different types of rotating anode or stationary anode tubes, and/or tubes defining glass envelopes, metal envelopes, or envelopes formed of combinations of metal, glass and ceramic. The anode and cathode are maintained at a high differential voltage relative to each other, typically on the order of about 150 kV or less. As will be recognized by those skilled in the pertinent art based on the teachings herein, however, the differential voltage may be any voltage required by the application(s) of the x-ray tube assembly 10. Similarly, the differential voltage may be created in any of numerous different ways. For example, as described above, the anode 22 may be maintained at ground, and the cathode may be maintained at a relatively high negative potential. Alternatively, the anode 22 may be maintained at a positive potential, e.g., +75 kV, and the cathode may be maintained at a negative potential, e.g., -75 kV. The cathode thermionically emits electrons which are electrostatically directed into a focal spot 26 located on the rotating target surface 24 of the anode 22 with sufficient energy to generate x-rays which emerge from the target in a diffuse pattern. As indicated above, the size and shape of the focal spot 26 may be dictated by the size and shape of the filaments (not shown) of the cathode. Typically, the focal spot area 26 is rectangular; however, the cathode filaments may take any of various different sizes and shapes, and thus the focal spot 26 likewise may correspondingly vary in size and shape. The x-ray housing 12 is hermetically sealed, and is filled with an insulating oil (not shown) to electrically insulate the x-ray tube 14 within the housing. As also shown in FIG. 1, a beam limiting apparatus 28 of the invention is mounted on the boss 16 and extends through the x-ray port 18 into the interior of the housing 12 adjacent to the focal spot 26. The beam limiting apparatus 28 comprises a peripheral flange 30, and a radiation-absorbing or radiopaque body 32 projecting downwardly from the peripheral flange and received through the x-ray port 18 and into the interior of the housing 12. Unless otherwise indicated, the term "radiopaque" is used synonymously with "radiation absorbing" and "radiation blocking" throughout this specification, and is intended to mean preventing or not allowing the passage of substantially all x-rays through the respective material, component or portion of the apparatus. The radiation-absorbing body 32 defines a base surface 34, an x-ray entrance aperture 36 formed through the base surface, an x-ray exit aperture 38 formed through an approximately opposite side of the base wall relative to the x-ray entrance aperture, and an x-ray transmissive beam conduit 40 extending between the entrance and exit apertures. The x-ray port 18 and evacuated envelope 20 define a first predetermined depth "D1" therebetween, and the base surface 34 of the body 32 extends into the housing a second depth "D2", which is close to, but less than the first depth "D1", such that the base surface 34 is spaced closely adjacent to the evacuated envelope 20 of the x-ray tube and defines a predetermined gap 42 therebetween. The gap 42 is sufficient to allow differential thermal expansion between the x-ray tube and beam limiting apparatus without contacting each other during operation of the x-ray tube. In the illustrated embodiment of the invention, the width of the predetermined gap 42 is approximately 0.060 inch, and is preferably within the range of approximately 0.040 to approximately 0.080 inch. However, as will be recognized by those skilled in the pertinent art based on the teachings herein, the width of the gap 42 may fall outside of this range in particular applications, particularly if necessary to provide sufficient space to allow differential thermal expansion of these closely spaced parts without contacting each other during operation of the x-ray tube. For example, for relatively large x-ray tubes and housings, it may be necessary to increase the width of the gap 42 over that described herein in order to ensure sufficient space to allow for differential thermal expansion during operation of the x-ray tube. Alternatively, if the envelope of the tube is made of metal, or includes a metal portion adjacent to the base surface 34 of the radiation-absorbing body 32, the tube may be sufficiently strong to allow the parts to contact each other, and therefore the gap may be eliminated. The radiolucent or x-ray transmissive window 44 is mounted between the x-ray entrance aperture 36 and exit aperture 38, and extends across the beam conduit 40. In the illustrated embodiment of the present invention, the x-ray transmissive window 44 is molded integral with the radiation absorbing body 32, and is made of a radiolucent material having a predetermined aluminum equivalent filtration in order to achieve a predetermined overall filtration of the image-forming x-ray beam. Accordingly, the x-ray transmissive window 44 may be made of any of numerous different materials which are currently, or later become known for performing the functions of the window described herein. For example, the window 44 may be made of aluminum, or any other desired x-radiation transmissive metal. Alternatively, the window 44 may be made of a transparent epoxy resin, a polycarbonate, glass or other optically transparent and radiolucent material, in order to allow an operator to view the interior of the housing through the window. In each case, the window 44 is preferably integrally molded with the radiation-absorbing body and defines a hermetic seal between the window and body, as described further below. The peripheral flange 30 defines a mounting surface 46 on the underside of the flange for mounting the beam limiting apparatus 28 to the mounting boss 16 of the housing 12. As shown in FIG. 1, the mounting boss 16 of the housing defines an o-ring groove or like recess 48 extending about the periphery of the x-ray port 18, and an o-ring or other suitable sealing member 50 is seated within the groove between the mounting surface 46 and mounting boss 16 to hermetically seal the beam limiting apparatus 28 to the housing 12. The radiation-absorbing body 32 defines a first cylindrical recess on the interior side of the body, and extending downwardly from the peripheral flange 30 to the base wall of the body. A cylindrical wall 54 extends upwardly on the opposite side of the flange 30 relative to the first recess 52, and defines a second cylindrical recess 56 on the interior thereof. The radiopaque body 32, peripheral flange 30, and cylindrical wall 54 are formed of a substantially electrically nonconductive, filled polymeric material, and as can be seen, are integrally molded in a single casting. In the currently preferred embodiment of the invention, the polymeric material is a filled epoxy resin material sold by Lord Corp., Chemical Products Division, of Atlanta, Ga., under the trademark "Circalok", wherein the resin is part number 6703A, and the hardener is part number 6703B. This filled epoxy resin is also designated "H253 P1" by the Assignee of the present invention in connection with the sales of its products molded from this material. The Circalok filled epoxy resin is an oil-based resin, and is filled with a radiation-absorbing material, such as lead oxide. This material is electrically non-conductive, and radiopaque, and exhibits the following approximate physical characteristics: Specific Gravity (g/cc) 4.05 Hardness (shore D) 90 Tensile Strength (psi) 8,100 Compressive Strength at 25.degree. C. (psi) 13,200 Linear Shrinkage (in/in) 0.004 Service Temperature (.degree. C.) -60 to 155 Thermal conductivity (cal/sec/cm.sup.2 /.degree. C. .times. 10.sup.-4) >7.8 (BTU/ft.sup.2 /hr/.degree. F./in) >2.3 Coefficient of thermal expansion (in/in/.degree. C. .times. 10.sup.-6) <38 Thermal resistance (.degree. C./in/watt) 128 Volume resistivity at 25.degree. C. (ohm/cm) 10.sup.15 Dielectric constant at 25.degree. C. (100 KC) 4.1 Dissipation Factor at 25.degree. C. (100 KC) 0.02 Dielectric strength 400-500 As will be recognized by those skilled in the pertinent art based on the teachings herein, the filled polymeric material may take the form of any of numerous other like materials that are currently, or later become known for performing the functions of the filled epoxy resin described herein. One advantage of the filled epoxy resin employed in the apparatus of the present invention, is that it allows the x-ray transmissive window 44 to be easily molded integral with the radiation-absorbing body and other components of the beam limiting apparatus. In addition, the base resin employed may be optically transparent, and therefore may be used to integrally mold the x-ray transmissive window only to be both optically transparent and radiolucent, and thereby allow a user to view the interior of the housing therethrough. As further shown in FIG. 1, a beam-adjusting mechanism 58 is slidably received within the first and second recesses 52 and 56 for selectively adjusting the size of the x-ray beam. The beam-adjusting mechanism 58 includes a guide flange 60 defining an approximately disc-like shape and slidably received within the second cylindrical recess 56. A second radiation-absorbing body 62 projects downwardly from the guide flange 60, and defines a second x-ray entrance aperture 64 on the bottom side of the body, a second x-ray exit aperture 66 formed on the opposite side of the guide flange 60, and an approximately frusto-conical shaped second beam conduit 68 formed between the entrance and exit apertures. A coil spring 70 is seated between the base wall of the first recess 52 and the underside of the guide flange 60 to normally bias the guide flange, and thus the beam-adjusting mechanism upwardly or away from the focal spot 26. The guide flange 60 and radiation-absorbing body 62 are integrally molded of the same filled polymeric material as the other components of the beam limiting apparatus as described above. However, as will be recognized by those skilled in the pertinent art based on the teachings herein, any of numerous different filled polymeric materials and/or other materials may be employed for performing the functions of these components described herein. As indicated in phantom in FIG. 1, an electric coil 72 is integrally molded within the upper end of the cylindrical wall 54 and extends along the upper periphery of the second cylindrical recess 56. The electric coil 72 is electrically connected to a suitable electrical power source and control circuitry (not shown) in order to selectively energize the coil as hereinafter described. As also indicated in phantom in FIG. 1, an iron or like conductive core 74 is integrally molded within the second radiation-absorbing body 62, and extends adjacent to the periphery of the body. Normally, the coil spring 70 biases the beam-adjusting mechanism 58 upwardly into the position "2", as indicated in broken lines in FIG. 1. However, upon energization of the electric coil 72, an electric field surrounding the coil magnetically repels the core 74, and as indicated by the arrows in FIG. 1, drives the beam-adjusting apparatus 58 downwardly from position "2" into position "1" indicated in solid lines in FIG. 1. As indicated schematically in FIG. 1, in position "1", the beam defines a diameter "A", and in position "2", the beam defines a diameter "B" less than diameter "A". In the illustrated embodiment, beam diameter A is approximately 9 inches at a source to image distance ("SID") "C" of approximately 40 inches, and beam diameter B is approximately 6 inches at an SID "C" of approximately 40 inches. However, as will be recognized by those skilled in the pertinent art based on the teachings herein, the size and shapes of the x-ray beams may be selectively controlled to virtually any desired size and/or shape by simply adjusting the sizes and shapes of the beam apertures in the beam limiting apparatus 26, and/or by adjusting the axial position of the beam-adjusting mechanism 58. In addition, the beam-adjusting mechanism may take any of numerous different forms which are currently, or later become known for performing the functions described herein. For example, the solenoid-type actuation of the beam adjusting mechanism 58 may take the form of any of numerous such solenoid-type mechanisms, such as double coils, double magnets, or other mechanical or electrical variations thereof. In addition, the position of the beam-adjusting mechanism 58 may be provided by a mechanical adjusting mechanism, such as a lead screw, or other type of threaded drive mechanism, a linkage mechanism, or any of numerous other mechanical or electromechanical drive mechanisms for performing the functions described herein. In addition, the beam-adjusting mechanism may be selectively positionable in any of a plurality of different positions with respect to the focal spot 26 in order to selectively collimate the beam to define any of a plurality of different beam sizes within a predetermined range of beam sizes. For example, in the embodiment of the present invention illustrated, the beam-adjusting mechanism 58 may be electrically controlled to selectively fix its position at any of a plurality of different positions between the positions 1 and 2 shown. In the embodiment of the present invention illustrated, the x-ray entrance and exit apertures of the beam limiting apparatus 28 define the same peripheral shape as that of the focal spot 26. Typically, the focal spot 26 defines a rectangular peripheral shape, and therefore the x-ray entrance and exit apertures of the beam limiting apparatus are also rectangular. However, if desired, one or more of the beam limiting apertures may define a shape different than the shape of the focal spot in order to change the shape of the x-ray beam to a shape corresponding the shape of the aperture. For example, in image intensifier applications requiring a round field, a rectangular-shaped beam may be changed to a round beam by causing one or more of the beam limiting apertures to have the desired round or circular shape. In this exemplary case, the x-ray entrance aperture would define an approximately 1.2 mm square (or other sized square equaling the projected size of the focal spot) if placed directly at the edge of the projected effective focal spot perpendicular to the central ray. As the x-ray beam conduits 40 and 68 move away from the focal spot, the cross-sections of the conduits (and beam limiting apertures) would be changed to a more circular form with chords defining the respective four sides of the projected focal spot. The points of the chords would develop into a true circle at the second x-ray exit aperture 66 in order to generate a round field image. In each case, the x-ray entrance aperture 36 preferably defines a size approximately equal to the projected size of the focal spot 26 onto the base surface 34 of the radiation-absorbing body 32. As will be recognized by those skilled in the pertinent art based on the teachings herein, if the x-ray entrance aperture 36 is too large, then it will allow the passage of off-focus radiation therethrough. Accordingly, the dimensions of the x-ray entrance aperture are preferably approximately equal to the projected dimensions of the focal spot onto the base surface 34. If, on the other hand, the x-ray entrance aperture 36 is too small, it will undesirably reduce the intensity of the x-ray beam. As also shown in FIG. 1, a mounting bracket 76 is seated over the cylindrical wall 54 and mounting flange 30 to fixedly secure the beam limiting apparatus 28 to the housing 12. As shown typically in FIG. 1, the housing 12 includes threaded apertures 78 for receiving mounting screws or other fasteners (not shown) for fixedly securing the mounting bracket 76 to the housing. If desired, the mounting bracket 76 may be fixedly secured to a gantry or other device for supporting the x-ray tube assembly. The mounting bracket 76 defines an x-ray aperture 79 in a top wall thereof overlying the other beam apertures for permitting the passage of the x-ray beam therethrough. As can be seen, the x-ray aperture 79 is larger than any of the underlying x-ray apertures in order to avoid interference with the x-ray beam. As also shown in FIG. 1, the mounting boss 16 of the housing 12 defines a peripheral recess 80 for receiving the mounting flange 30 of the beam limiting apparatus 28. As can be seen, the outer diameter of the peripheral recess 80 is greater than the outer diameter of the mounting flange 30 to thereby allow the flange, and thus the radiation-absorbing body 32 to be moved laterally within the recess. The underside of the mounting bracket 76 similarly defines a first recess 82 for receiving therein the upper side of the mounting flange 30 and fixedly securing the mounting flange to the housing 12. As can be seen, the outer diameter of the first recess 82 is approximately equal to the outer diameter of the peripheral recess 80 of the mounting boss 16 to likewise allow the mounting flange 30 and radiation-absorbing body 32 to be moved laterally within the first recess of the mounting bracket. The mounting bracket 76 further defines a second recess 84 for receiving the cylindrical wall 54. Like the first recess 82, the second recess 84 defines a diameter greater than the outer diameter of the cylindrical wall 54 to thereby allow the cylindrical wall to move laterally within the recess. As also shown in FIG. 1, a plurality of alignment screws, shown typically at 86, are threadedly received through the side walls of the mounting bracket 76 and engage on their free ends the exterior sides of the cylindrical wall 54. Accordingly, the alignment screws 86 may be threadedly adjusted to, in turn, laterally adjust the position of the radiation-absorbing body 32 and thereby align the components with the "central ray" centerline (and with respect to the mounting boss holes 78). As shown schematically in broken lines in FIG. 1, a flexible, substantially radiolucent material 88 extends across the predetermined gap 42 formed between the evacuated envelope 20 of the x-ray tube and the base surface 34 of the radiation-absorbing body 32 to prevent the passage of oil therethrough. In accordance with a preferred embodiment of the invention, the material 88 is a compressible silicone pad, which is substantially free of voids and foreign material, such as the silicone dielectric gel sold by Dow Corning under the designation Dow Corning Sylgard 527. Preferably, the silicone gel 88 is applied to the interface between the glass envelope 20 and the base surface 34 as shown, in order to completely fill the gap in the area underlying the x-ray entrance aperture 36, and thereby prevent the passage of oil through this area. The silicon gel 88 is preferably free of voids and any particulate or foreign matter in order to prevent any such non-homogeneous features from showing up as artifacts on the x-ray images. Thus, one advantage of this feature of the present invention, is that any air bubbles or other particulate matter that might be contained within the oil of the x-ray tube assembly is prevented from flowing through the x-ray beam, and therefore prevented from negatively affecting the x-ray images. The beam limiting apparatus 28 preferably may further comprises cooling conduits connectable to a heat exchanger in order to cool the x-ray tube. As shown in FIG. 1, the beam limiting apparatus defines a first coolant inlet port 90 extending into the peripheral flange 30, a first coolant exit port 92 extending through another portion of the peripheral flange, and a first coolant conduit 94 coupled in fluid communication between the first inlet and outlet ports. As shown typically in FIG. 1, the first coolant conduit 94 preferably defines a serpentine shape within the base wall of the radiation-absorbing body 32 in order to maximize the surface area of the body in thermal communication with the coil. If desired, the coil 94 also could define a helical path within the approximately frusto-conical shaped side walls of the radiation-absorbing body 32 to further maximize the surface area of the body in thermal communication with the coils. The coils are preferably made of a thermally-conductive material and are molded integral with the radiation-absorbing body. Alternatively, the radiation-absorbing body 32 itself may define the first coolant conduit 94. The heat exchanger (not shown) may be any of numerous heat exchangers currently, or which later become available for performing the heat exchange functions described herein. The mounting bracket 76 may further define a second coolant conduit 96, a second coolant inlet port 98 coupled in fluid communication with one end of the second coolant conduit, and a second coolant outlet port 100 coupled in fluid communication with the opposite end of the second coolant conduit for introducing a cooling fluid through the conduit. As can be seen, the second coolant conduit 96 extends along a helical path within the side wall of the mounting bracket 76 in order to cool the walls of the mounting bracket, and thereby facilitate in transferring heat away from the x-ray tube assembly. The second coolant conduit 96 may be coupled in fluid communication with the same heat exchanger as the first coolant conduit 94, or alternatively, may be connected to a different heat exchanger (not shown). As will be recognized by those skilled in the pertinent art based on the teachings herein, any of numerous different means for heat exchange may be employed for performing this function as described herein. For example, if desired, a thermoelectric cooler, such as a Peltier-effect device, may be thermally coupled to the mounting bracket and/or to the radiation-absorbing body in order to transfer heat away from these components in the manner described above. The x-ray tube housing 12 may take any of numerous different shapes and configurations. For example, the housing 12 may be made in a conventional manner whereby the external shell of the housing is made of metal, such as aluminum, and the internal walls of the housing are lined with a radiation-absorbing material, such as lead. Preferably, however, the housing 12 is cast of the same or like filled epoxy resin as are the components of the beam limiting apparatus 28. In this configuration, an electrically conductive surface 102 is formed on the exterior side of the housing in order to ground the housing. This conductive surface 102 may be formed by a conductive paint or other conductive coating, or if desired, may be formed by a conductive skin or like thin layer attached to the outer surface of the filled epoxy casting. Turning to FIG. 2, another embodiment of an x-ray tube assembly of the invention is indicated generally by the reference numeral 110. The x-ray tube assembly 10 is substantially similar to the x-ray tube assembly 10 described above, and therefore like reference numerals preceded by the numerals "1" or "2" are used to indicate like elements. One of the primary differences of the x-ray tube assembly 110 is that the beam limiting apparatus 128 is molded integral with the x-ray tube housing 112, and does not include a beam-adjusting mechanism. As can be seen, the housing 112 is molded with a filled polymeric, substantially non-conductive, radiopaque material. Preferably, the filled polymeric material is the same filled epoxy resin material as described above in connection with the previous embodiment; however, as will be recognized by those skilled in the pertinent art based on the teachings herein, any of numerous other types of filled polymeric materials which currently, or later become known for performing the functions of the housing described herein may be equally employed. The housing 112 includes a first casting 204 and a second casting 206, and each casting has formed on the exterior sides thereof the conductive surface or shell 202. As indicated above, the conductive surface 202 may be applied as a conductive paint or like coating, or may be applied as a thin metal shell fixedly secured to the castings with nylon or like non-conductive screws or other fasteners (not shown). As shown in FIG. 2, the first casting 204 defines a hermetically-sealed cavity 208 for receiving the x-ray tube 114. The first casting 204 further defines the beam limiting apparatus 128 integrally molded therein, including the base surface 134 spaced in close proximity to the evacuated envelope 120, the x-ray entrance aperture 136, the x-ray transmissive window 144 molded into the beam conduit 140, and the x-ray exit aperture 138. If desired, a beam limiting plate 210 may be mounted over the x-ray exit aperture 138 to further perform the beam limiting function. The beam limiting plate 210 may be a conventional beam limiting plate formed of a radiopaque material, and defining a beam limiting aperture 211 for further controlling the size and shape of the image-forming beam. In addition, the beam limiting plate 210 may be laterally adjustable in a conventional manner, and/or the position of the x-ray tube 114 within the housing may be axially adjustable in a conventional manner in order to align the x-ray apertures of the beam limiting apparatus with the central ray. The mounting bracket 176 is fixedly secured to the housing in the same manner as the mounting bracket 76 described above. As also shown in FIG. 2, the first casting 204 further defines an anode plug cavity 212, and a cathode plug cavity 214, each having respective terminal pins 216 integrally molded into the base of the cavity for connection to a male plug of a type known to those skilled in the pertinent art (not shown). An anode conduit 218 is formed between the pin(s) 216 of the anode plug cavity 212 and the anode end of the hermetically-sealed cavity 208 for electrically connecting the pins to the anode of the x-ray tube. Similarly, a cathode conduit 220 is formed between the pin(s) 216 of the cathode plug cavity 214 and the cathode end of the hermetically-sealed cavity 208 for connecting the pins to a filament transformer 222, which, in turn, is connected to the cathode of the x-ray tube 114. A suitable interface plug 224 is integrally molded into the side wall of the housing 112 adjacent to the filament transformer for providing an electrical connection thereto. An oil pump cavity 226 is also formed in the side wall of the first casting 204 for receiving an oil pump assembly 228. The oil pump assembly 228 includes a vane or like impeller 230 rotatably driven by an electric motor including a rotor 232 and stator 234. An oil inlet conduit 236 is formed in fluid communication between the oil pump cavity 226 and the cathode end of the x-ray tube cavity 208, and an oil outlet conduit 238 is formed in fluid communication between the anode end of the x-ray tube cavity 208 and the oil pump cavity 226. A suitable valve 240 is connected to the oil outlet conduit 238 for filling the interior of the housing 112 with oil. An oil volume compensation tube 242 lines an interior surface of the oil pump cavity 226 in order to compensate for variations in oil volume due, for example, to thermal expansion and contraction of the oil during operation. The oil volume compensation tube 242 is connected in fluid communication with an air vent 244 in order to fill the tube with air. A heat sink 246 is mounted over the oil pump cavity 226 to enclose the oil pump assembly 228 within the cavity, and includes a plurality of cooling fins 248 on an exterior surface thereof for facilitating heat exchange between the oil and the ambient atmosphere. The heat sink 246 is hermetically sealed to the housing by an o-ring or like sealing member 250, and is fixedly secured to the housing with suitable fasteners (not shown). If necessary, threaded inserts may be molded into the casting 204 at suitable locations for receiving the fasteners for attaching the heat sink and any other components of the x-ray tube assembly. The second casting 206 forms a cover for enclosing the x-ray tube 114 within the housing. As shown in FIG. 2, the second casting defines a peripheral groove 252 for receiving an o-ring or like sealing member 254, and fasteners (not shown) are employed to attach and thereby hermetically seal the cover 206 to the housing. As also shown, the first casting 204 defines a recess 256 for receiving the cover, and there is a substantial overlap of the cover and the base surface of the recess to prevent the emission of any radiation through any interfaces of the first and second castings. One advantage of the x-ray tube assembly 110 is that the entire housing may be made of a filled polymeric material, such as the filled epoxy resin described above, and therefore there is no need to line the housing with lead or other radiation-absorbing materials. Accordingly, substantial cost benefits can be achieved by employing the housing of the present invention. Turning to FIGS. 3 and 4, another x-ray tube assembly including a beam limiting apparatus embodying the present invention is indicated generally by the reference numeral 210. The x-ray tube assembly 210 is similar to the x-ray tube assemblies described above in connection with the previous embodiments, and therefore like reference numerals preceded by the numerals "2" and "3" are used to indicate like elements. The primary difference of the beam limiting apparatus 228 of FIGS. 3 and 4 is that it is provided in the form of a cone-shaped part that may be mounted within a conventional x-ray tube housing port 218. In addition, like the beam limiting apparatus 128 described above in connection with FIG. 2, the beam limiting apparatus 228 does not include a beam adjusting mechanism for adjusting the size of the x-ray beam. As shown in FIG. 3, the peripheral flange 230 and radiation-absorbing body 232 of the beam limiting apparatus 228 are integrally molded with a filled polymeric material which is electrically non-conductive and radiopaque. Preferably, the filled polymeric material is the same as the filled epoxy resin described above in connection with the previous embodiments; however, as will be recognized by those skilled in the pertinent art based on the teachings herein, any of numerous other materials which now, or later become known may be employed for performing the functions described herein. The housing 212 defines an x-ray port 218, and a annular recess 248 extending about the periphery of the x-ray port for receiving an o-ring or like sealing member 250 to hermetically seal the beam limiting apparatus to the housing. The mounting bracket 276 defines on its underside the first recess 282 for receiving therein the peripheral flange 230. The flange 230 is movable laterally within the recess 282 to align the position of the x-ray apertures with the central ray. The adjustment screws 286 are provided to laterally adjust and fix the position of the beam limiting apparatus within x-ray port 218. As shown in FIG. 4, the mounting bracket 276 includes a plurality of apertures overlying the threaded apertures 278 in the mounting boss 216 of the housing 212 to threadedly attach the mounting bracket to the boss with fasteners (not shown) and, in turn, fixedly secure and hermetically seal the beam limiting apparatus to the housing. As in the embodiments described above, the x-ray transmissive window 244 may be made of any desired material, and is preferably molded integral with the radiation-absorbing body 232 and forms a hermetic seal between the x-ray transmissive window and radiation-absorbing body. If desired, a layer of silicone gel or like material 288 may be interposed between the base surface 234 and the evacuated envelope 220 in the same manner as described above in connection with the previous embodiments in order to prevent the passage of oil and/or particulates therethrough. Turning to FIGS. 5 and 6, another x-ray tube assembly including a beam limiting apparatus embodying the present invention is indicated generally by the reference numeral 310. The x-ray tube assembly 310 is similar to the x-ray tube assembly 210 described above in connection with FIGS. 3 and 4, and therefore like reference numerals preceded by the numerals "3" and "4" instead of the numerals "2" and "3" are used to indicate like elements. The primary difference of the beam limiting apparatus 328 of FIGS. 5 and 6 is that it may be mounted within, or on the exterior side of a conventional cup-shaped x-ray window, such as a conventional polycarbonate window. As indicated in broken lines in FIG. 5, a typical cup-shaped polycarbonate or other polymeric window 410 may be mounted within the x-ray port 318 and extend downwardly into the housing toward the focal spot 326 of the x-ray tube. Accordingly, a predetermined gap 342 may be formed between the polymeric window and the exterior surface of the evacuated envelope 320. In this case, the radiation-absorbing body 332 is seated within the polymeric window 410 with the base surface 334 seated against the base wall of the window 410. Since the polymeric window 410 is hermetically sealed to the x-ray tube housing 312 in a typical manner, such as with the o-ring groove 348 and o-ring 350, the beam limiting apparatus 328 need not include the x-ray transmissive window, but rather may simply define an open passageway between the x-ray entrance aperture 336 and x-ray exit aperture 338. However, as shown in FIG. 5, the radiation-absorbing body 332 preferably defines an annular recess 412 extending about the periphery of the x-ray exit aperture 338 in order to receive a filtration member 414. The filtration member 414 may be made of aluminum or other suitable filtration material, and is provided in a predetermined thickness in order to achieve the requisite level of filtration of the x-ray beam. The filtration member 414 is seated within the recess 412, and retained within the recess by the overlying mounting bracket 376. If desired, a plurality of such filtration members may be provided, each defining a respective thickness and/or level of x-ray filtration, in order to allow an operator to selectively install the different filtration members to achieve different predetermined levels of beam filtration. The mounting bracket 376 defines on its underside the first recess 382 for receiving therein the peripheral flange 330. The flange 330 is movable laterally within the recess 382 to align the position of the x-ray apertures with the central ray. The adjustment screws 386 are provided to laterally adjust and fix the position of the beam limiting apparatus within the cup-shaped window 410. As will be recognized by those skilled in the pertinent art based on the teachings herein, numerous changes and modifications may be made to the above-described and other embodiments of the present invention without departing from the scope of the invention as defined in the appended claims. As one example, the filled epoxy resin x-ray housing of the invention can be made of any number of castings that may be connected together in the same manner, or in a manner similar to the hermetically-sealed connection of the two castings described above. In addition, if desired, the embodiments of FIGS. 2-6 could include cooling coils or conduits, or other cooling devices, as disclosed above in connection with the embodiment of FIG. 1. Similarly, the x-ray tube housing of FIG. 2 could be modified in any of numerous ways, including the provision of a conventional x-ray port (as shown, for example, in the other embodiments), and a beam limiting apparatus with beam adjusting or collimating mechanism of the type shown in FIG. 1. Accordingly, this detailed description of the preferred embodiments is to be taken in an illustrative as opposed to a limiting sense.

048658006

description

DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like, are words of convenience and are not to be construed as limiting terms. Referring now to the drawings, and particularly to FIG. 1, there is shown a fuel assembly grid inspection apparatus, generally designated by the numeral 10, which includes the combination of a precision noncontact measurement device, generally designated 12, and a universal support fixture 14 which are the components of the apparatus 10 comprising the present invention which cooperate in inspecting a fuel assembly grid 16. As seen in FIG. 1, the precision measurement device 12 per se is in the form of hardware manufactured and sold by View Engineering of Simi, Calif. and identified by the model designation "View 1220 System". The device 12 basically includes a data gathering unit (DGU) 18, a monitor and disk drive assembly (MDDA) 20, a keyboard 22, a joystick 24 and a printer 26. The device 12 measures by viewing or seeing, instead of touching or contacting, the grid 16. The DGU 18 of the device 12 includes a stationary base 28, viewing means 30 in the form of a video camera and lens system, a source of illumination 32 in the form of a ring light, an inspection platform 34 having a retroreflective surface 36 thereon (which is also part of the source of illumination 32), and electromagnetically-actuated X-, Y- and Z-axes stage assemblies 38,40,42 which mount the platform 34 and viewing means 30 on the stationary base 28 for movement relative thereto and to one another along X,Y,Z orthogonal directions. The viewing means 30 is disposed above the retroreflective surface 36 on the inspection platform 34 so as to define an inspection field of view extending generally vertically therebetween. As will be described in greater detail later, the universal fixture 14 is supported by the inspection platform 34 about the perimeter of the inspection field of view. The fixture 14, in turn, supports the grid 16 across and within the field of view. The viewing means 30 and the universal fixture 14 are movable relative to each other in X, Y and Z directions for achieving a complete inspection of all parts of the grid 16 in the vertical field of view. In particular, the Y-axis stage assembly 40 is actuatable for moving the platform 34 in the Y direction (forward or rearward, or toward the front or rear of the DGU 18) relative to the stationary base 28. The viewing means 30 being disposed in spaced relation above the inspection platform 34 is movable in X (left or right) and Z (up or down) directions with respect thereto and to the universal fixture 14 and grid 16 by actuation of the respective X-axis stage assembly 38 and the Z-axis stage assembly 42 which is movably mounted on the X-axis stage assembly 38. The viewing means 30 is adapted to view and record one or more images of the grid 16 located in the field of view and to provide digitized video image information to the MDDA 20 from which actual measurements of the grid 16 being inspected can be calculated. The known standard measurements for the particular grid design being inspected are inputted from either a floppy disk or a permanent hard disk into the MDDA 20 and the actual measurements which have been calculated therein are compared to such known standard measurements to determined whether or not the actual dimensions of the grid 16 being inspected come within acceptable tolerances of the known standard measurements. The fixture 14 is universal in the sense that it is adapted to support any one of a variety of grids of different designs within the field of view. Different programs are stored which contain the known standard measurements of the different grid designs. The one program which corresponds to the grid being inspected will be recalled and loaded into the working memory of the MDDA 20. It is not believed to be necessary for an understanding of the present invention that the operation of the device 12 be described in any greater detail. For more information about the operation of the device 12, one can consult the operator's manual for the View 1220 System available from View Engineering. Turning now to FIGS. 2-11, there is shown the universal grid support fixture 14 in assembled form and in some of its individual component parts. As mentioned above, the universal fixture 14 is adapted to support any one of a plurality of fuel assembly grids of different designs within the inspection field of view of the noncontact measurement device 12. The universal fixture 14 includes a mounting base 44 having first and second pairs of opposing portions 46A,46B and 48A,48B bounding the perimeter of the retroreflective surface 36 of the inspection field of view. The portions 46A,46B and 48A,48B of the mounting base 44 are supported by the inspection platform 34 of the measurement device 12. The universal fixture 14 further includes first and second pairs of upright grid supports 50A,50B, and guide means in the form of a pair of tracks 52A,52B mounted on, and in parallel relation along, the opposing mounting base portions 46A,46B of the first pair thereof. Each of the grid supports 50A,50B is composed of a spacer block 54 and a support assembly 56. The tracks 52A,52B have dovetail cross-sectional configurations which are complementary to and receivable in grooves 55 having dovetail cross-sectional configurations formed across the bottom of the spacer blocks 54. In such manner, the grid supports 50A and 50B of each of the pairs thereof are mounted to the respective tracks 52A and 52B in spaced relation to one another for adjustable slidable movement therealong. A clamp section 57 in each spacer block 54 is tightened to secure the spacer block to the respective one of the tracks 52A,52B. The support assembly 56 of each of the grid supports 50A,50B is assembled from a base block 58, mounting block 60, a grid support member 62 and a grid support insert 64. The base block 58 has a groove 66 formed across its bottom which is dovetail-shaped and complementary in cross-section to a track 68 formed across the top of each spacer block 54 for mounting the base block 58 to the top of the spacer block 54. A clamp section 70 in the base block 58 is tightened to secure the base block to the spacer block. The mounting block 60 of each support assembly 56 is secured by a dovetail interfitting connection 72 and an adjustment screw 74 to the base block 58 so as to extend in cantilever fashion a short distance inwardly therefrom in overlying relation to a marginal edge portion of the retroreflective surface 36 of the inspection platform 34. The grid support member 62 of each support assembly 56 is slidably mounted by a dovetail groove and track connection 76 to the lower side of the mounting block 60. An adjustment screw 78 is used to move the support member 62 along the X-axis relative to the mounting block 60. At the inner end of each support member 62 is seated one of the grid support inserts 64. When a grid 16 is supported by the fixture 14 as seen in FIG. 1, each of the support members 62 underlies the perimeter of the grid 16 and each of the inserts 64 extends from the bottom side of the grid upwardly into one of the cells thereof. In order for the field of view which encompasses the grid 16 to be transparent except for the grid itself, the grid engaging portions of the fixture 14 which project into the field of view to support the grid 16--the support members 62 and inserts 64--are made of transparent material. For example, the support members 62 are composed of acrylic material and the inserts 64 are scratch-resistant synthetic sapphire material. Further, the universal fixture 14 includes a pair of extendable and retractable actuators 80A,80B, for example, in the form of air cylinders. One actuator 80A is mounted to the one tracks 52A on base portion 46B, whereas the other actuator 80A is mounted to a third track 52C on base portion 48A, by spacer blocks 82 and base blocks 84 being substantially identical, in construction and in their connections together and to the tracks, to the spacer blocks 54 and mounting blocks 60 of the grid supports 50A, 50B. The actuators 80 are actuatable to locate the grid 16 in a desired position with respect to the inspection field of view by causing slight movement of the grid in X and Y directions relative to the grid support members 62 and inserts 64. Still further, the fixture 14 includes a plurality of sensors 86, for instance in the form of microswitch assemblies, mounted to the mounting blocks 60 (above the support members 62) of the first pair of grid supports 50A and to a fourth track 52D by a spacer block 88 and base block 90 being substantially identical, in construction and in their connections together and to the track, to the spacer blocks 54 and mounting blocks 60 of the grid supports 50A,50B. The sensors 86 are responsive to contact by the grid 16 when the latter has been moved to its desired position with respect to the inspection field of view. Turning now to FIGS. 12-16, there is seen two of the many different fuel assembly grid designs adapted to be supported by the universal fixture 14 within the inspection field of view of the noncontact measurement device 12. The grids 16A,16B basically include a multiplicity of interleaved straps 92 having an egg-crate configuration designed to form cells 94. The cells 94 of the grid l6A have opposing dimples 96 formed in the metal of the interleaved straps 92 to support the fuel rods of a fuel assembly which extend through the cells 94. Also, mixing vanes 97 are defined on and extend upwardly from the straps 92. The cells 94 of the grid 16B have opposing dimples 96 and springs 98 which serve the same purpose. In carrying out inspection of the fuel assembly grid 16, the viewing means 30 and source of illumination 32 of the DGU 18 are turned on and moved so as to define the illuminated inspection field of view across the grid as it is supported by the fixture 14. The viewing means 30 views the grid and records multiple images thereof to provide digitized video information to the MDDA 20 from which measurements can be calculated and compared to known standard measurements for the particular grid design stored in the MDDA 20. To view 100% of the grid 16, the viewing means 30 (i.e., video camera and lens system), while maintained pointed in the direction of the field of view toward the retroreflective surface 36, and/or the grid are moved relative to one another. However, the position of the fixture 14 is first sensed to ensure the correctness of the placement thereof before proceeding with inspection of the grid. Typically, as is the case with the grids in FIGS. 12-16, the grid 16A or 16B being inspected has at least a pair of vertically displaced fuel rod contacting dimples 96 disposed in each of a plurality of cells 94 defined in the grid. The dimples 96 are inspected for perpendicularity with respect to each other by using the viewing means 30 to view them at separate instances but from the same location above them and within the field of view. A separate image of each dimple 96 is recorded to provide information from which the degree of offset of one dimple with respect to the other can be determined. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof.

claims

1. A shield used for electron beam container sterilization equipment that sterilizes a container with electron beams emitted to the container,the shield including a composite shield of a magnetic shield layer and an X-ray shield layer between a pair of corrosion resistant layers for protection against a corrosive atmosphere, the magnetic shield layer blocking magnetism while the X-ray shield layer blocks X-rays generated by reflection and diffraction of electron beams,the composite shield including an insulating layer interposed between one of the corrosion resistant layers and the magnetic shield layer, between the magnetic shield layer and the X-ray shield layer, and between the X-ray shield layer and the other corrosion resistant layer. 2. Electron beam container sterilization equipment that inserts, from a mouth of a container, an electron beam irradiation nozzle having an exit window on a distal end of the irradiation nozzle and sterilizes an inner surface of the container,the electron beam irradiation nozzle being surrounded by a shield,the shield being composed of the shield according to claim 1. 3. Electron beam container sterilization equipment that holds containers kept in an upright position, move the containers along a circular path around a vertical pivot axis, moves electron beam irradiation nozzles in synchronization with the containers, moves at least one of the electron beam irradiation nozzle and the container upward or downward, inserts the electron beam irradiation nozzle into a mouth of the container, and sterilizes an inner surface of the container with electron beams emitted front the electron beam irradiation nozzle,the equipment including an inner shield along an inner periphery of the circular path and an outer shield along an outer periphery of the circular path,the inner and outer shields each being composed of the shield according to claim 1. 4. A shield used for electron beam container sterilization equipment that sterilizes a container with electron beams emitted to the container,the shield being composed of a plurality of composite shield blocks,the composite shield block including a magnetic shield and an X-ray shield in a hollow section of a board-shaped shell made of a corrosion resistant material, and an insulating layer between one surface of the board-shaped shell and the magnetic shield, between the magnetic shield and the X-ray shield, and between the X-ray shield and another surface of the board-shaped shell;the magnetic shield blocking magnetism while the X-ray shield blocks X-rays generated by reflection and diffraction of electron beams. 5. Electron beam container sterilization equipment that inserts, from a mouth of a container, an electron beam irradiation nozzle having an exit window on a distal end of the irradiation nozzle and sterilizes an inner surface of the container,the electron beam irradiation nozzle being surrounded by a shield,the shield being composed of the shield according to claim 4. 6. Electron beam container sterilization equipment that holds containers kept in an upright position, move the containers along a circular path around a vertical pivot axis, moves electron beam irradiation nozzles in synchronization with the containers, moves at least one of the electron beam irradiation nozzle and the container upward or downward, inserts the electron beam irradiation nozzle into a mouth of the container, and sterilizes an inner surface of the container with electron beams emitted from the electron beam irradiation nozzle,the equipment including an inner shield along an inner periphery of the circular path and an outer shield along an outer periphery of the circular path,the inner and outer shields each being composed of the shield according to claim 4.

claims

1. A ventilated system for storing high level waste emitting heat, the system comprising:an air-intake shell forming an air-intake cavity;a plurality of storage shells, each storage shell forming a storage cavity;a lid positioned atop each of the storage shells;an outlet vent forming a passageway between an ambient environment and a top portion of each of the storage cavities; anda network of pipes forming hermetically sealed passageways between as bottom portion of the air-intake cavity and at least two different openings at a bottom portion of each of the storage cavities such that blockage of a first one of the openings does not prohibit air from flowing from the air-intake cavity into the storage cavity via a second one of the openings. 2. The system of claim 1 further comprising a hermetically sealed canister for holding high level waste positioned in one or more of the storage cavities so that a gap exists between the storage shell and the canister, the horizontal cross-section of the storage cavities accommodating no more than one of the canisters. 3. The system of claim 1 wherein the network of pipes is configured so that the first one of the openings is an end of a first path through the passageways from the air-intake cavity to the storage cavity and the second one of the openings is an end of a second path through the passageways from the air-intake cavity to the storage cavity, wherein the first and second paths are different. 4. The system of claim 1 wherein the outlet vents are formed into the lids. 5. The system of claim 1 wherein the storage shells and the air-intake shell are vertically oriented and arranged in a side-by-side relation. 6. The system of claim 5 further comprising:a ground having a grade; andwherein the storage shells are positioned so that at least a major portion of a height of each storage shell is located below the grade, the network of pipes being located below the grade, and the downcomer air-intake cavity forming a passageway between an opening located above the grade and the network of pipes. 7. The system of claim 6 wherein the storage shells, the air-intake shell, and the network of pipes are hermetically sealed against the ingress of below grade liquids. 8. The system of claim 1 wherein the network of pipes comprises one or more headers that couple the storage shells to the air-intake shell. 9. The system of claim 1 further comprising one or more layers of insulating material circumferentially surrounding the storage shells. 10. A ventilated system for storing high level waste emitting heat, the system comprising:an air-intake shell forming an air-intake cavity;a plurality of storage shells, each storage shell forming a storage cavity;a lid positioned atop each of the storage shells;an outlet vent forming a passageway between an ambient environment and a top portion of each of the storage cavities; anda network of pipes forming hermetically sealed passageways between a bottom portion of the air-intake cavity and a bottom portion of each of the storage cavities, wherein the network of pipes is configured so that a line of sight does not exist between any of the storage cavities through the passageways. 11. The system of claim 10 wherein the network of pipes connects to side walls of the storage shells. 12. The system of claim 11 wherein the storage shells are arranged in a side-by-side relation, wherein bottoms surfaces of the storage shells are located in a plane, and wherein the network of pipes does not extend below the plane. 13. The system of claim 10 further comprising a hermetically sealed canister for holding high level waste positioned in one or more of the storage cavities so that a gap exists between the storage shell and the canister, the horizontal cross-section of the storage cavities accommodating no more than one of the canisters. 14. The system of claim 10 further comprising:a ground having a grade; andwherein the storage shells are positioned so that at least a major portion of a height of each storage shell is located below the grade, the network of pipes being located below the grade, and the downcomer air-intake cavity forming a passageway between an opening located above the grade and the network of pipes. 15. The system of claim 14 wherein the storage shells, the air-intake shell, and the network of pipes are hermetically sealed to the ingress of below grade liquids.

summary

042241065

description

FIG. 1 shows the frame 4 in which the grid 6 is fitted. Said frame 4 comprises two side plates 4a and 4b as well as two end plates 4c and 4d. In the example herein described, the grid 6 is constituted by two sets of thin wires 6a and 6b of Zircaloy which intersect at right angles and are joined together by electric welding at points such as those designated by the reference 7 so as to form a lattice in which the ceramic fuel wafers 8 of the fuel element are subsequently intended to be fitted. In the example shown in FIG. 1, the meshes of the lattice have a rectangular shape but could just as readily have a square shape for certain different applications. The different wires 6a and 6b of the grid 6 have a diameter which is substantially equal to the thickness of the fuel wafers 8. Said wires are subjected first to electric welding under pressure in order to reduce overthicknesses at each point of intersection 7, then to a trimming operation in order to ensure perfect calibration of the lattice openings. As a general rule, the different wafers of sintered fuel have a thickness within the range of 1 to 1.5 mm. The dimensions of each rectangular mesh are chosen so as to optimize ease of shaping at the moment of compression of each fuel wafer. By way of indication, good dimensions are of the order of 30.times.18 mm; as mentioned earlier, however, a square shape (17.times.17 mm, for example) appears to represent a particularly advantageous solution on technological grounds. In accordance with the invention, the assembly formed by the grid 6 and the fuel wafers 8 is finally placed between a top cladding plate 9 and a bottom cladding plate 10. In the alternative embodiment of FIG. 2, the grid 6 is provided with a framing wire 11 which surrounds said grid on all four sides and has the same composition and diameter as the wires 6a and 6b of the grid itself. Said framing wire 11 is welded to the wires 6a and 6b as well as to the side plates 4a and 4b and to the end plates 4c and 4d. One of the most attractive industrial applications of the thin fuel element in accordance with the invention lies in the possibility of converting the core of an existing pool reactor by fitting it with fuel element plates of low enrichment. In fact, in order to establish a neutron balance in the core of a reactor of this type, there are four essential factors to be taken into consideration and these are respectively as follows: a moderating ratio equal to the ratio of the volume of moderator (water) to the volume of fuel; a fuel enrichment which can attain 93% in U-235 in pool-type reactors of conventional design ; the mass of U-235 within the reactor core; the available reactivity which represents the capacity of the reactor for irradiation of materials. The ratios between the four parameters given above, two of which are related to each other (mass of uranium and enrichment) are illustrated by the set of curves of FIG. 3 which shows the variation of reactivity in respect of a certain number of enrichments respectively equal to 1.5%, 2.5%, 3%, 4%, 5%, 7.5% and 10%, as a function of the moderating ratio which is plotted as abscissae. The general shape of these curves (increasing function which passes through a maximum and then decreases) indicates that the moderating ratio must be placed in the vicinity of a value at least equal to 2 in order to derive maximum benefit from the core reactivity. In the case of the fuel elements commonly employed up to the present time in pool reactors (platetype elements of aluminum-uranium alloy enriched with 93% U-235), the moderating ratio usually adopted is in the vicinity of 2 as mentioned above. If plate fuel elements are replaced in a reactor of this type by plate elements of the fuel wafer type of relatively substantial thickness (4 to 5 mm, for example), it is possible in such a case: either to retain substantially the same number of plate elements within the internal space provided for the reactor core, thus resulting in a reduction of the moderating ratio and entailing the need for much higher enrichment in order to maintain the same reactivity, or to reduce the number of plate elements in order to retain the same moderating ratio, in which case the power level of the reactor core is also reduced. On the contrary, by making use of fuel elements in the form of thin plates which is made possible by the present invention, the number of plates can be increased while retaining a moderating ratio which is very close to 2 and consequently permitting a relatively low fuel enrichment in order to maintain a substantially identical power level in the pool-type reactor core. Referring again to FIG. 3, it is apparent, for example, that a reactor which is made up of plates of substantial thickness, which permits a moderating ratio of the order of 1, which is charged at an enrichment of 10% U-235 and discharged at 5% residual U-235 (path BC), operates with the same reserve of reactivity as a core which permits a moderating ratio of 2, which is charged at 4.5% U-235 and discharged at 3% U-235 (path AD).

abstract

A nuclear reactor in which a primary coolant is contained, the primary coolant moves upwardly from the core by an operation thereof. An annular steam generator is arranged in an upper side of the core into which the upwardly moving primary coolant flows and transfers heat in the primary coolant into water therein to generate a steam. A passage structure defines a coolant passage for the primary coolant to an outside of the core. The heat-transferred primary coolant in the annular steam generator flows downwardly in the coolant passage so as to flow into the core, thereby moving upwardly. A reactor vessel is arranged to surround the coolant passage so as to contain the core, the annular steam generator and the passage means therein.

abstract

This invention relates to radioactive, bone-seeking, pharmaceutical methods, compositions and formulations that have a lower impurity profile, a longer shelf life, improved availability and are less expensive to prepare. The compositions of this invention can be conveniently prepared in a timely manner resulting in improved availability and delivery of the drugs to patients.

claims

1. A cabin structure of a manned vehicle for special environment use, the structure being configured such that a cabin is mounted on a vehicle body having at least an engine and a vehicle moving mechanism driven by the engine, this cabin storing an operation terminal for operating the engine and the vehicle moving mechanism, and having a space for accommodating an operator who operates the operation terminal or an occupant, whereinthe cabin is formed as a casing body having a protection structure and partitioned and separable from the vehicle body,the casing body has a coupling and fastening part on a bottom side of the cabin for secure attachment to the vehicle body with restraint at least in planar coordinate directions,the casing body has a monocoque structure of a combination of a plurality of metal plates that can function as shielding masses, and, around a hole drilled in the metal plate, a baffle is provided at a position facing an incoming direction of special substances, or a bent path for incoming special substances is formed by one or a plurality of the metal plates, so that the operator or occupant inside the cabin is not directly exposed to the special substances from outside the casing body. 2. The cabin structure of a manned vehicle for special environment use according to claim 1,wherein the casing body has a box-like structure without a bottom plate or with a separable bottom plate, the bottom plate or a lower end part of the casing body being secured to the vehicle body, andwherein the coupling and fastening part is provided between the vehicle body and the box-like structure for secure attachment with restraint in planar coordinate directions. 3. The cabin structure of a manned vehicle for special environment use according to claim 1,wherein the casing body has surface parts at least on a front side and a rear side in a vehicle moving direction that are shielded by lead glass with front and rear visibility. 4. The cabin structure of a manned vehicle for special environment use according to claim 1, further comprising:an opening formed in a bottom plate of the casing body and having a seal part for seal off from special substances and, whereina control unit controlling the vehicle body and supplementary equipment by processing signals including a signal obtained by operation of the operation terminal is disposed as the protection structure inside the casing body, while a signal line for transmitting signals processed in the control unit is extended through the opening into the vehicle body. 5. The cabin structure of a manned vehicle for special environment use according to claim 1,wherein the coupling and fastening part comprises fitting parts protruding and recessed in a direction perpendicular to the planar coordinates, the fitting parts fitting to each other to connect the casing body with the vehicle body and restraining the casing body to the vehicle body in three-dimensional directions. 6. The cabin structure of a manned vehicle for special environment use according to claim 1,wherein the coupling and fastening part comprises bolts fastened to connect the casing body to the vehicle body such as to be separable from the vehicle body. 7. A manned vehicle for special environment use,wherein the vehicle body according to claim 1 is a body of an industrial vehicle having an engine, a vehicle moving mechanism driven by the engine, and a work end driven by operation of the operation terminal in a cabin, andwherein a signal from the operation terminal is configured to be transmitted via a signal tube or a signal line directly through the opening(s) to the vehicle body, or to be transmitted to the vehicle body through the opening(s) via the signal line for transmitting signals processed in the control unit disposed inside the casing body. 8. A cabin structure of a manned vehicle for special environment use, the structure being configured such that a cabin is mounted on a vehicle body having at least an engine and a vehicle moving mechanism driven by the engine, this cabin storing an operation terminal for operating the engine and the vehicle moving mechanism, and having a space for accommodating an operator who operates the operation terminal or an occupant, whereinthe cabin is formed as a casing body having a protection structure and partitioned and separable from the vehicle body,the casing body has a coupling and fastening part on a bottom side of the cabin for secure attachment to the vehicle body with restraint at least in planar coordinate directions,the casing body has a monocoque structure of a combination of a plurality of metal plates that can function as shielding masses, anda gap portion between adjacent metal plates is formed as a bent path for incoming special substances and formed either by an abutment plate provided at a position facing an incoming direction of special substances or by one or a plurality of the metal plates, so that the operator or occupant inside the cabin is not located on a line extending straight from outside air through the gap portion. 9. The cabin structure of a manned vehicle for special environment use according to claim 8, wherein the casing body has a box-like structure without a bottom plate or with a separable bottom plate, the bottom plate or a lower end part of the casing body being secured to the vehicle body, andwherein the coupling and fastening part is provided between the vehicle body and the box-like structure for secure attachment with restraint in planar coordinate directions. 10. The cabin structure of a manned vehicle for special environment use according to claim 8,wherein the casing body has surface parts at least on a front side and a rear side in a vehicle moving direction that are shielded by lead glass with front and rear visibility. 11. The cabin structure of a manned vehicle for special environment use according to claim 8, further comprising:an opening formed in a bottom plate of the casing body and having a seal part for seal off from special substances and, whereina control unit controlling the vehicle body and supplementary equipment by processing signals including a signal obtained by operation of the operation terminal is disposed as the protection structure inside the casing body, while a signal line for transmitting signals processed in the control unit is extended through the opening into the vehicle body. 12. The cabin structure of a manned vehicle for special environment use according to claim 8,wherein the coupling and fastening part comprises fitting parts protruding and recessed in a direction perpendicular to the planar coordinates, the fitting parts fitting to each other to connect the casing body with the vehicle body and restraining the casing body to the vehicle body in three-dimensional directions. 13. The cabin structure of a manned vehicle for special environment use according to claim 8,wherein the coupling and fastening part comprises bolts fastened to connect the casing body to the vehicle body such as to be separable from the vehicle body. 14. A manned vehicle for special environment use,wherein the vehicle body according to claim 8 is a body of an industrial vehicle having an engine, a vehicle moving mechanism driven by the engine, and a work end driven by operation of the operation terminal in a cabin, andwherein a signal from the operation terminal is configured to be transmitted via a signal tube or a signal line directly through the opening(s) to the vehicle body, or to be transmitted to the vehicle body through the opening(s) via the signal line for transmitting signals processed in the control unit disposed inside the casing body. 15. A manned vehicle for special environment use, having: a vehicle body having at least an engine and a vehicle moving mechanism driven by the engine; and a cabin storing an operation terminal for operating the engine and the vehicle moving mechanism and accommodating an operator who operates the operation terminal or an occupant, whereinthe cabin is formed as a casing body having a protection structure and partitioned and separable from the vehicle body,the casing body is fixed to the vehicle body via a coupling and fastening part with restraint at least in planar coordinate directions,the casing body has a monocoque structure of a combination of a plurality of metal plates that can function as shielding masses, anda gap portion between adjacent metal plates is formed as a bent path for incoming special substances and formed either by a baffle provided at a position facing an incoming direction of special substances or by one or a plurality of the metal plates, so that the operator or occupant inside the cabin is not located on a line extending straight from outside air through the gap portion. 16. The manned vehicle for special environment use according to claim 15,wherein the casing body has a box-like structure without a bottom plate or with a separable bottom plate, the bottom plate or a lower end part of the casing body being secured to the vehicle body, andwherein the coupling and fastening part is interposed between the vehicle body and the box-like structure for secure attachment with restraint in planar coordinate directions. 17. The manned vehicle for special environment use according to claim 15, further comprising:one or a plurality of openings having a seal part formed in a bottom plate of the casing body facing the vehicle body and seal off from special substances and, whereina control unit controlling the vehicle body and supplementary equipment by processing signals including a signal obtained by operation of the operation terminal is disposed inside the casing body, while a signal line for transmitting signals processed in the control unit is configured to transmit the signals to the vehicle body through the opening. 18. The manned vehicle for special environment use according to claim 15,wherein the casing body has surface parts at least on a front side and a rear side in a vehicle moving direction that are shielded by lead glass with front and rear visibility. 19. The manned vehicle for special environment use according to claim 15,wherein the coupling and fastening part comprises a protrusion and a recess protruding and recessed in a direction perpendicular to the planar coordinates, with one of the protrusion and the recess being formed on the casing body and the other one of the protrusion and the recess being formed on the vehicle body, which are fitted to each other to restrain the casing body to the vehicle body in three-dimensional directions. 20. A manned vehicle for special environment use, having: a vehicle body having at least an engine and a vehicle moving mechanism driven by the engine; and a cabin storing an operation terminal for operating the engine and the vehicle moving mechanism and accommodating an operator who operates the operation terminal or an occupant, whereinthe cabin is formed as a casing body having a protection structure and partitioned and separable from the vehicle body,the casing body is fixed to the vehicle body via a coupling and fastening part with restraint at least in planar coordinate directions,the casing body has a monocoque structure of a combination of a plurality of metal plates that can function as shielding masses, andaround a hole drilled in the metal plate, a baffle is provided at a position facing an incoming direction of special substances, or a bent path for incoming special substances is formed by one or a plurality of the metal plates, so that the operator or occupant inside the cabin is not directly exposed to the special substances from outside the casing body. 21. The manned vehicle for special environment use according to claim 20,wherein the casing body has a box-like structure without a bottom plate or with a separable bottom plate, the bottom plate or a lower end part of the casing body being secured to the vehicle body, andwherein the coupling and fastening part is interposed between the vehicle body and the box-like structure for secure attachment with restraint in planar coordinate directions. 22. The manned vehicle for special environment use according to claim 20, further comprising:one or a plurality of openings having a seal part formed in a bottom plate of the casing body facing the vehicle body and seal off from special substances and, whereina control unit controlling the vehicle body and supplementary equipment by processing signals including a signal obtained by operation of the operation terminal is disposed inside the casing body, while a signal line for transmitting signals processed in the control unit is configured to transmit the signals to the vehicle body through the opening. 23. The manned vehicle for special environment use according to claim 20,wherein the casing body has surface parts at least on a front side and a rear side in a vehicle moving direction that are shielded by lead glass with front and rear visibility. 24. The manned vehicle for special environment use according to claim 20,wherein the coupling and fastening part comprises a protrusion and a recess protruding and recessed in a direction perpendicular to the planar coordinates, with one of the protrusion and the recess being formed on the casing body and the other one of the protrusion and the recess being formed on the vehicle body, which are fitted to each other to restrain the casing body to the vehicle body in three-dimensional directions.

051715155

summary

BACKGROUND OF THE INVENTION The invention relates to a process for inhibiting corrosion in a pressurized water nuclear reactor, and more particularly for inhibiting corrosion within the primary circuit of a pressurized water nuclear reactor. Corrosion is a particular concern for nuclear reactors in which water is present as a coolant. Several methods have been proposed to deal with the problem, including dissolving oxide scale from the structure of the nuclear reactor, as disclosed in U.S. Pat. No. 3,664,870 to Oberhofer et al. and U.S. Pat. No. 4,042,455 to Brown. Another approach, as disclosed in U.S. Pat. No. 4,364,900 to Burrill, is to inhibit corrosion formation within the reactor system. Burrill adds from about 120 to about 200 milligrams of ammonia per kilogram of coolant water to reduce crevice corrosion in the core of pressurized water nuclear reactors. Zinc ions are thought to inhibit corrosion within boiling water nuclear reactors, and such ions from zinc oxide and zinc chloride have been described for use in boiling water nuclear reactors. As discussed by W. J. Marble in "Control of Radiation-Field Buildup in BWRs", Electric Power Research Institute NP-4072, Project 189-2, Interim Report, June 1985, zinc in the form of ZnO was used in a boiling water reactor plant. It was discussed therein that soluble zinc, by acting as a corrosion inhibitor for stainless steel, significantly reduces the amount of oxide formed on the pipes and thus the amount of Co-60 incorporated in the system. The hypothesis proposed on page 4-2 of that reference was that zinc cations normally found in zinc oxide crystals will tend to modify the normal magnetite crystal defect structure so that a more protective film is formed and corrosion significantly inhibited. Further, the presence of zinc ions in the reactor coolant water of boiling water reactors having brass tubing, as discussed at page 6-1, has been correlated with a reduced amount of corrosion and radioactive cobalt transport throughout the reactor. Zinc introduced in the form of zinc chloride (ZnCL.sub.2) was also laboratory tested as a corrosion inhibitor under power plant operating conditions, as discussed by L. W. Niedrach and W. H. Stoddard in "Effect of Zinc on Corrosion Films that Form on Stainless Steel", Corrosion 42, 546 (1986). The use of zinc oxide as a source of zinc ions has the drawback that zinc oxide is not particularly soluble in water, and, therefore, the zinc oxide must be added to the coolant as a slurry or suspension, rather than as a solution. Pressurized water nuclear reactors are thermal reactors in which water is used as the coolant and as the moderator. The water is circulated by pumps throughout a primary circuit, that includes a pressure vessel, which houses the heat generating reactor core, and a plurality of flow loops. The heat absorbed by the water as it passes through the reactor core is transferred by means of a heat exchanger to a readily vaporizable liquid (water) in a secondary circuit in which the thermal energy is used to produce electricity. The water is then returned to the pressure vessel. The water in the primary circuit, which normally contains boric acid as a moderator, passes through numerous metal, generally stainless steel and Alloy 600, conduits, all of which are subject to corrosion. Further, some radioactive cobalt from the reactor core is dissolved in the water as the metal ion and transported throughout the primary circuit. The transport of radioactive cobalt throughout the primary circuit results in a level of residual radioactivity throughout the primary circuit that is not desired. Thus, it is desired to develop a process for inhibiting corrosion in a pressurized water nuclear reactor. An object of the invention is to provide a process for inhibiting corrosion in a nuclear reactor by the addition of zinc to the coolant water flowing therethrough in a soluble form. SUMMARY OF THE INVENTION The present invention provides a process for inhibiting corrosion caused by the presence of coolant water passing through a pressurized water nuclear reactor. An effective amount of an aqueous solution of zinc borate is added to the reactor coolant water. As a result of the process, the transport of corrosion products and radioactive cobalt ions through the reactor system, as well as levels of radioactivity within the reactor system, are reduced. The aqueous solution of zinc borate is preferably an aqueous solution of zinc borate in boric acid, with the zinc borate preferably added to the reactor coolant water so that zinc ions are present in the reactor coolant water in an amount of from about 10 to about 200 parts per billion.

047553286

summary

BACKGROUND OF THE INVENTION The invention relates to a process for treating acid solutions, contaminated with uranium. From a more general point of view, the invention is intended to provide a process for treating acid uraniferous solutions, possibly containing radium, which process comprises adjustment of the final pH and decontamination of uranium and of radium to values such that the solutions, after treatment, can be discharged without harming the natural environment. The extraction of uranium ores from open pit mines or from underground mines necessitates treating the drained waters whose flow rates can reach several hundreds of cubic metres. These drained waters contain various elements, particularly uranium and possibly radium, at concentrations which can be detrimental to the natural environment when they are discharged thereto. In addition, these waters generally have a pH which is also detrimental to the natural environment. It is the same with liquid effluents resulting from the acid or alkaline treatment of uranium ores. In order not to spoil the natural environment particularly the hydrogeological system into which the drained waters and the liquid effluents are discharged the concentration of these waters and effluents respectively in uranium and radium must be as low as possible. This explains the reason why very strict standards have been fixed relating to the pH and the maximum content of uranium and of radium for drained waters and liquid effluents. It is necessary, in fact, for the final pH of the solutions to be between 5.5 and 8.5, for the radium content to correspond to an activity equal or less than 10 pCi/l and for the uranium content to be equal to or less than 1.8 mg/l. It is known to remove the radium by a treatment with barium chloride, which in the presence of sulfate ions, causes the formation of barium sulfate and of radium sulfate which precipitate. As for the removal of the uranium, in the processes employed until now, resins or other adsorbants (for example titanium oxide) are used, which require large installations and often are subject to risk of clogging. The problem not yet resolved until now is the process of treating drained water or effluents, containing uranium content both too low to justify setting up of a laborious resin unit, and too high to permit discharge to to the natural environment. The difficulties associated with the removal of the uranium are correlated to several parameters and particularly to the fact that, in uraniferous solutions, the uranium occurs in various physical forms, namely solid, soluble and colloidal. The solid particles of uranium are generally the subject of removal by decantation or filtration. As regards the soluble particles, their existence is explained by the use of sulfuric acid to form acid waters for the lixiviation of the uranium or by the presence of carbonate or bicarbonate ions used to form alkaline waters enabling the lixiviation of the uranium. As for the colloidal particles, they correspond to an intermediate state between the solid and soluble uranium and they generally have a size of 10.sup.-1 to 10.sup.-3 microns and cannot be removed by simple decantation or filtration. It is particularly the coexistence in the same solution of soluble and colloidal uranium which makes it difficult to set up a efficient process for removal of the uranium. Another parameter which plays a part in the elimination of uranium, is the presence of numerous other ions as well as the respective values of their concentration. Among these ions, maybe be mentioned calcium, sodium; magnesium, sulfate, carbonate, bicarbonate, chloride, potassium, nitrate, ferric, or aluminum ions. It is one of the objects of the invention to provide a process for removing uranium from acid uraniferous solutions, whether the uranium is soluable and/or in colloidal form. It is another object of the invention to provide a process for removing uranium from acid uraniferous solutions, applicable even to solutions highly charged with ions. Another object of the invention is to provide a process for removing uranium from acid uraniferous solutions, whatever the nature of the ion species in solution. Another object of the invention is to provide a process for removing uranium and radium, from acid uraniferous solutions, at the end of which the contents of uranium and of radium and the value of the pH of the final solutions obtained are compatible with the natural environment. A further object of the invention is to provide a process for removing uranium and radium from acid uraniferous solutions, at the end of which the contents of uranium and radium as well as the value of the pH of the final solutions obtained, meet the legislative standards in force.

044501340

abstract

An improved method and apparatus for transferring nuclear fuel elements between a fluid-filled storage pool and a cask is disclosed. The cask is supported within and is restrained by a tank which is transported between terminal locations of a nuclear facility. Transfer of fuel elements between a storage pool and the cask is accomplished by coupling the tank to a port of the pool. The transporter accurately positions and restrains the tank during transfer. In a preferred embodiment, the cask tank is unweighted from the transporter during transfer and is advanced into a fluid-sealed engagement with a port surface of the pool. In an alternative arrangement, the cask tank remains supported on the transport during its transfer and lifting means mutually engaging the transporter and tank advance the tank toward the port surface for establishing a coupling between the port and the cask. The method and apparatus substantially reduce fluid contact with an exterior surface of the cask during transfer and potential nuclear contamination; they enhance the protection of the transfer apparatus against seismic disturbances; and, they accomodate casks of different sizes.

abstract

An inspecting apparatus for reducing a time loss associated with a work for changing a detector is characterized by comprising a plurality of detectors 11, 12 for receiving an electron beam emitted from a sample W to capture image data representative of the sample W, and a switching mechanism M for causing the electron beam to be incident on one of the plurality of detectors 11, 12, where the plurality of detectors 11, 12 are disposed in the same chamber MC. The plurality of detectors 11, 12 can be an arbitrary combination of a detector comprising an electron sensor for converting an electron beam into an electric signal with a detector comprising an optical sensor for converting an electron beam into light and converting the light into an electric signal. The switching mechanism M may be a mechanical moving mechanism or an electron beam deflector.

claims

1. A high-frequency control device for an accelerator to control a high frequency which is applied to an acceleration cavity of an accelerator which generates a particle beam to be used for a particle beam therapy, wherein the high-frequency control device for an accelerator comprises:a hard disk drive memory which stores pattern data of a high frequency to be applied for each combination of energy and intensity of the generated particle beam;a local memory, which reads a plurality of pattern data of a high frequency for each patient together with a sequential order of changing energy and intensity from the hard disk drive memory, and stores data in order to perform a scanning irradiation method in which a layered particle beam irradiation region in a depth direction of an affected part of the patient is formed sequentially by changing energy and intensity of the particle beam sequentially to irradiate the affected part of the patient which is an irradiation subject with the particle beam, and which reads out data faster than the hard disk drive memory, anda command value checking part which checks whether a command value from an irradiation system control device, which controls a particle beam irradiation device for irradiating the affected part which is the irradiation subject for each time when energy and intensity of the particle beam is changed, is in agreement with pattern data which is sent out from the local memory or not,wherein in a case where it is judged that a command value from the irradiation system control device is not in agreement with pattern data which is sent out from the local memory, the accelerator is operated according to subsequent pattern data of energy and intensity, and during the operation, data in the local memory is reread until the data pattern is in agreement with the command value. 2. A particle beam therapy system comprising the accelerator, a particle beam transportation system which transports a particle beam which is extracted from the accelerator, and a particle beam irradiation device for irradiating the particle beam which is transported onto the irradiation subject,wherein a high frequency which is applied to the acceleration cavity of the accelerator is controlled by a high-frequency control device according to claim 1.

claims

1. A device for protection of a body from space radiation, the device comprising:at least one flexible garment, each section of said at least one flexible garment being configured to shield a region of a surface of the body such that said each section complementarily attenuates self-shielding by internal structure between said region and an interior region of the body such that space radiation at the interior region is attenuated to a predefined attenuation level, anda plurality of shield elements incorporated into a flexible substrate of the at least one flexible garment, comprising a plurality of bags, each of the bags being configured to be filled with a liquid. 2. The device of claim 1, wherein the flexible substrate or said plurality of shield elements comprises a polymer. 3. The device of claim 1, wherein said plurality of shield elements is embedded within the flexible substrate. 4. The device of claim 1, wherein each of said plurality of shield elements has an inward facing surface that is greater than an opposite outward facing surface, such that tapering gaps are formed in between adjacent shield elements of said plurality of shield elements. 5. The device of claim 4, wherein the substrate fully or partially fills the gaps. 6. The device of claim 1 wherein the flexible substrate comprises a foam. 7. The device of claim 1, wherein said plurality of shield elements comprises a plurality of sequins that are attached to the flexible substrate and wherein the flexible surface comprises a fabric sheet. 8. The device of claim 7, wherein the fabric sheet forms a webbing between said plurality of sequins. 9. The device of claim 7, wherein a garment of said at least one garment comprises a plurality of the fabric sheets formed into layers. 10. The device of claim 9, wherein a sequin of said plurality of sequins on one fabric sheet of said plurality of the fabric sheets is positioned to overlie a gap between adjacent sequins of said plurality of sequins on another fabric sheet of said plurality of fabric sheets. 11. The device of claim 1, wherein the flexible substrate comprises a plurality of flexible bag holders, each of said plurality of bags being configured to be inserted into a bag holder of said plurality of flexible bag holders. 12. The device of claim 1, wherein said at least one garment comprises a plurality of garments that are configured to be worn in layers, wherein one garment of said plurality of garments is configured such that a shield element of said plurality of shield elements on said one garment is configured to overlie a gap between two adjacent shield elements on another garment of said plurality of garments. 13. The device of claim 1, wherein the interior region includes tissue-resident stem cells. 14. The device of claim 13, wherein the tissue-resident stem cells are selected from a group of tissue-resident stein cells consisting of distal airway stem cells of the lung, CD34+ hematopoietic stem cells, and intestinal LGR5+ stem cells. 15. A device for protection of a body from space radiation, the device comprising:at least one flexible garment, each section of said at least one flexible garment being configured to shield a region of a surface of the body such that said each section complementarily attenuates self-shielding by internal structure between said region and an interior region of the body such that space radiation at the interior region is attenuated to a predefined attenuation level, anda plurality of shield elements incorporated into a flexible substrate of the at least one flexible garment,wherein a shield element of said plurality of shield elements comprises a plurality of stacked liquid-fillable compartments. 16. The device of claim 15, further comprising a tube to enable introduction of a liquid into a liquid-fillable compartment of said plurality of stacked liquid fillable compartments or removal of the liquid frog a liquid-fillable compartment of said plurality of stacked liquid-fillable compartments. 17. A method for preventing a space radiation-induced condition in a body in space, the method comprising:determining a required attenuation of space radiation at an interior region of the body so as to prevent the space radiation-induced condition under an anticipated exposure of the body to space radiation;determining self-shielding from the space radiation corresponding to each surface region of a plurality of regions of a surface of the body by determining attenuation of the radiation by internal structure of the body that lies between the interior region and said each surface region;providing a space radiation protection device comprising at least one flexible garment, each section of said at least one flexible garment being configured to attenuate space radiation to a shielded surface region of plurality of regions of a surface of the body to complementarily attenuate the self-shielding by the shielded surface region; andproviding a plurality of shield elements incorporated into a flexible substrate of the at least one flexible garment and having a plurality of bags, each of the bags being configured to be filled with a liquid. 18. The method of claim 17, wherein the space radiation-induced condition comprises mutagenesis or destruction of stem cells and the interior region comprises a stem cell niche. 19. The method of claim 17, wherein determining the required space radiation attenuation comprises determining an attenuation required to prevent a Bragg peak of the space radiation from occurring within the interior region. 20. The method of claim 17, wherein determining the required attenuation of space radiation comprises determining total areal density of shielding to the interior region to prevent the space radiation-induced condition, the determined self-shielding comprises an areal density of the internal structure that lies between the interior region and said each surface region, and wherein an areal density of said each section is at least a difference between said total areal density and said areal density of the internal structure. 21. The method of claim 17, wherein the plurality of bags comprise a plurality of stacked liquid-fillable compartments.

description

The present invention relates in general to techniques to obtain improved images. In particular it relates methods of lithography using a computer controlled imaging arrangement, such as for instance a Spatial Light Modulator (SLM), with an improved virtual grid. It also relates to an apparatus for patterning a work piece comprising such a method. Lithographic production is useful for integrated circuits, masks, reticles, flat panel displays, micro-mechanical or micro-optical devices and packaging devices, e.g. lead frames and MCM's. Lithographic production may involve an optical system to image a master pattern from a computer-controlled reticle onto a workpiece. A suitable workpiece may comprise a layer sensitive to electromagnetic radiation, for example visible or non-visible light. An example of such a system is described in WO 9945435 with the same inventor and applicant as the present invention. Said computer controlled reticle may for instance be a Spatial Light Modulator (SLM) comprising a one or two dimensional array or matrix of reflective movable micro mirrors; a one or two dimensional array or matrix of transmissive LCD crystals; or other similar programmable one or two dimensional arrays based on gratings effects, interference effects or mechanical elements, e.g. shutters. Generally speaking pattern quality may be improved by multipass writing. However, there are several different aspects of the pattern quality that are improved by multipass writing, but not necessarily at the same time. First, it is possible to create a finer address grid in several passes than in one single pass. Second, multiple passes with offset grid can remove the grid effects due to the finite pixel size. Third, random errors (such as artifacts in the light path, noise in the exposure dose, misplacement of beam or field used for imaging) are statistically reduced by multiple passes, e.g., four passes reduces the effects of random dose errors by a factor of two (square root of four). Fourth, systematic errors (such as dose fall of in corners of the image to be written, distortion and focal plane curvature) can be reduced by offset between the writing fields. Fifth, with multiple writing passes it is possible to better correct for bad pixels. Sixth, many multipass schemes give a softening of the edges, and retention of edge acuity is a desirable property of a multipass scheme. Different rasterizing multipass schemes can be devised, but it is a problem to find schemes that simultaneously give improvements in all six aspects mentioned above. FIG. 3a illustrates a known method for creating a virtual grid. In FIG. 3a it is shown an array of seven lines and 5 columns of pixels. Pixels in the two leftmost columns are set to a maximum grayscale value. Pixels in the two rightmost columns are set to minimum grayscale value. Pixels in a middle column are set to an intermediate grayscale value. FIG. 3a is an example of analog modulation of feature edge pixels 301 in a single pass in order to create a virtual grid. All pixels in said middle column are set to the same value. FIG. 3b illustrates another known method for creating a virtual grid. In this method four writing passes 305 are written with binary doses (e.g. 100%, 50%, 25%, 12,5%). All pixels in one single pass are set to equal grayscale values. The virtual grid is created by turning on a column of feature edge pixels in at least one writing pass, in FIG. 3b columns of feature edge pixels are turned on in the top writing pass and the second writing pass from bottom. FIG. 3c illustrates yet another known method for creating a virtual grid. In this method all four writing passes 305 are written with the same dose. In at least one pass a column 304 of feature edge pixels are turned on, illustrated in FIG. 3c to be the bottom writing pass and the second writing pass from the bottom. FIG. 4a illustrates another known method for creating a virtual grid. In this method four 401 passes are written offset with equal dose. The different writing passes are illustrated in FIG. 4a to be offset relative to an origin 402. By turning on edge pixels 403 in only some passes an edge of a feature to be written can be fine positioned. FIG. 4b illustrates still another known method for creating a virtual grid. This method utilizes a combination of the analog modulation of feature edge pixels with offset passes which gives a different analog value 404 in each pass. FIG. 5a illustrates a writing grid of four pixels in a single pass writing strategy. A reference mark denoted with 501 is arranged in middle of the grid. FIG. 5b illustrates a known method for offsetting different writing passes. Here four passes are used where two of them are offset relative to the other two by a distance defined by a half pixel size in two orthogonal directions parallel with the pixel grid. By offsetting different writing passes in a multiple writing strategy different imaging defects can more or less effectively be hidden. FIG. 5c illustrates another known method for offsetting different writing passes in order to hide the grid. In this embodiment all writing passes are offset relative to each other. One writing pass is offset in a first direction only, another writing pass is offset in a second direction, orthogonal to said first direction, and one writing pass is offset in sad first and sad second direction simultaneously. The offset in said first and said second direction is illustrated to be half a pixel size. It is in a general sense possible to make pattern fidelity better by increasing the number of passes, but the cost is high. Doubling the number of passes doubles the capital and operating cost of the pattern generator per produced workpiece and can in many cases be economically impossible. In general, computer controlled reticles may be used for the formation of images in a variety of ways. These reticles, such as an SLM, include many modulating elements or pixels, in some instances, a million or more pixels. In WO 99/45440, with one common inventor to the present application, is described a pattern generator with improved address resolution. In said application the pixels can be set in a number of states, larger than two, with one type of pixel map inside pattern features, another type of pixel map outside pattern features and intermediate pixel maps at a boundary of pattern features. The intermediate pixel map is generated in dependence of the placement of the boundary in a grid finer than that of pixels of the SLM projected onto the workpiece. Due to the fact that the line width and a space between two lines in the pattern to be printed on the wafer are very small, it puts a lot of demands on the printing method and the apparatus using said method. Using an SLM, which provides for a too coarse address grid may limit the resolution and accuracy available for their use in optical imaging; e.g., the production of printed patterns on a workpiece may be limited as to its line widths and accuracy. Therefore, there is a need in the art for a method, which further fine-adjust the position of the element's edge in the image created on the workpiece. There is also a need in the art for an improved effectiveness of multipass averaging, i.e., reduced number of passes giving an improved fine-adjustment of a feature edge. In view of the foregoing background, the fine adjustment of the position of the element's edge in the image created on the workpiece is critical for accomplishing line width in the range of sub-micrometers both when using single pass or multiple pass writing strategy. The present invention applies to patterning a workpiece based on a digital input data file, such as the writing of masks, semiconductor wafers, optoelectronic devices, micro optical devices, magnetic devices, super conducting devices, display devices, and electronic interconnect structures such as MCMs. The invention is independent of the mechanism of writing and applies to laser and other electromagnetic beams, electron and other charged particle beams. Beam is to be understood broadly so that printing methods that uses projected areas such as SLMs, cell projection are also included. Non conventional writing mechanism are also included, such as atom beams, multi photon processes, entangled photons, near field effects, direct current exposure from scanning probes and thermal exposure. Accordingly, it is an object of the present invention to provide an improved method for fine adjustment of the element's edge. In a first embodiment, the invention provides a method for creating a pattern on a workpiece sensitive to electromagnetic radiation. Electromagnetic radiation is emitted onto a computer-controlled reticle having a multitude of modulating elements (pixels). The pixels are arranging in said computer controlled reticle according to a digital description. An image is created of said computer controlled reticle on said workpiece, wherein said pixels in said computer controlled reticle are arranged in alternate states along at least a part of one feature edge in order to create a smaller address grid. In another embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge belong to a one-dimensional line of pixels. In still another embodiment of the invention said image is created in one writing pass. In yet another embodiment of the invention said image is created by means of a plurality of writing passes. In a further embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge are arranged differently in said plurality of writing passes. In another embodiment of the invention, in a first writing pass, at least a first pixel along at least one feature edge is set to a first grayscale value and surrounded with pixels set to at least one other gray scale value, and in at least one other writing pass at least a second pixel along said at least one feature edge is set to said first grayscale value with surrounding pixels set to at least one other gray scale value. In still another embodiment of the invention four writing passes create the pattern. In still another embodiment of the invention the pixels in the different writing passes set to said first grayscale value are non overlapping. In still another embodiment of the invention said surrounding pixels are set to the same grayscale value. In still another embodiment of the invention said surrounding pixels are set to the different grayscale values. In still another embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge belong to a line of pixels with a width of two pixels. In still another embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge belong to a lines of pixels with a width of three pixels. In still another embodiment of the invention said pixels are micromirrors in an SLM. In another embodiment of the invention said pixels are transmissive. Another aspect of the present invention is to provide an improved apparatus for fine adjustment of the element's edge. In a first embodiment, the invention provides an apparatus for creating a pattern on a workpiece sensitive to electromagnetic radiation. Said apparatus comprising a source to emit electromagnetic radiation onto a computer controlled reticle having a multitude of modulating elements (pixels), a projection system to create an image of said computer controlled reticle on said workpiece, wherein said pixels in said computer controlled reticle are arranged in alternate states along at least a part of a boundary of at least one element to be patterned, in order to fine-adjust the position of an edge of said element in said image to be created on the workpiece. In a first embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge belong to a one-dimensional line of pixels. In another embodiment of the invention said image is created in one writing pass. In still another embodiment of the invention said image is created by means of a plurality of writing passes. In still another embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge are arranged differently in said plurality of writing passes. In still another embodiment of the invention, in a first writing pass, at least a first pixel along at least a part of one feature edge is set to a first grayscale value and surrounded with pixels set to at least a second gray scale value, and in at least a second writing pass at least a second pixel along said part of said feature edge is set to said first grayscale value with surrounding pixels set to at least said second gray scale value. In yet another embodiment of the invention the pattern is created by four writing passes. In yet another embodiment of the invention said pixels set to say first grayscale value in the different writing passes are non-overlapping. In still another embodiment of the invention said pixels set to said first grayscale value in the different writing passes are spaced apart with at least one pixel. In still another embodiment of the invention said surrounding pixels are set to the same grayscale value. In still another embodiment of the invention said surrounding pixels are set to the different grayscale values. In still another embodiment of the invention said pixels in said computer controlled reticle along at least a part of one feature edge belong to a line with a width of two pixels. In another embodiment of the invention said pixels in said computer controlled reticle along at least one feature edge belong to a line with a width of three pixels. In another embodiment of the invention said pixels are micromirrors in an SLM. In another embodiment of the invention said computer controlled reticle is a transmissive SLM. Another aspect of the present invention is to provide an improved wafer, which is patterned with a finer address grid. In a first embodiment the invention provides a semi-conducting wafer comprising at least one integrated circuit, wherein said at least one integrated circuit is patterned by means of electromagnetic radiation emitted onto a computer controlled reticle having a multitude of modulating elements (pixels) in at least one writing pass, said pixels in said computer controlled reticle is arranged according to a digital description, an image of said computer controlled reticle is created on said wafer, wherein said pixels in said computer controlled reticle are arranged in alternate states along at least a part of one feature edge in order to create a smaller address grid. Another aspect of the present invention is to provide an improved mask, which is patterned with a finer address grid. In a first embodiment the invention provides a mask comprising a pattern to be printed on a workpiece, wherein a mask substrate is patterned in at least one writing pass by means of electromagnetic radiation emitted onto a computer controlled reticle having a multitude of modulating elements (pixels), said pixels in said computer controlled reticle is arranged according to a digital description, an image of said computer controlled reticle is created on said mask substrate, wherein said pixels in said computer controlled reticle are arranged in alternate states along at least a part of one feature edge in order to create a smaller address grid. Another aspect of the present invention is to provide an improved method for fine adjustment of an element's edge to be imaged. In a first embodiment the invention provides a method for imaging a pattern on a surface based on a description in a data file, where multiple writing passes is provided, a grid of pixels in at least two passes is offset, the values of edge pixels in the different passes are controlled, and the values of edge pixels between at least two passes are coordinated by a predetermined rasterizing rule so that the edge quality is optimized. In another embodiment of the invention, said edge quality is defined to be edge roughness. In another embodiment of the invention, said edge quality is defined to be edge acuity. In another embodiment of the invention said edge quality is defined to be critical dimension control (CDC). In another embodiment of the invention said at least two adjacent edge pixels in at least one pass have unequal values. In another embodiment of the invention, said rasterizing is non-linear. In another embodiment of the invention said dividing each pixel in at least two areas where a first area has a first weight function performs non-linear rasterizing and a second area has a second weight function. Another aspect of the present invention is to provide a method for creating a virtual grid. In a first embodiment the invention provides a method for writing a pattern on a substrate based on a description in a data file and to create a virtual grid, where a sequence of feature edge pixels is generated in a first writing pass, said sequence of feature edge pixels is displaced in at least a second writing pass, said sequences are at least partly superposed on said substrate. In another embodiment said invention further comprising the action of offsetting a grid of pixels in at least two passes. In another embodiment said invention further comprising the action of repeating said sequence of feature edge pixels periodic along at least one feature edge. In another embodiment of the invention, said sequence of feature edge pixels is non periodic. Another aspect of the present invention is to provide a further method for creating a virtual grid. In a first embodiment the invention provides a method for writing a pattern on a substrate based on a description in a data file and to create a virtual grid, wherein a first sequence of feature edge pixels is generated in a first writing pass, a second sequence of feature edge pixels is generating in at least a second writing pass, said sequences are at least partly superposing on said substrate. In another embodiment of the invention, said first and second sequences are periodic. In another embodiment of the invention, said first and second sequences are non-periodic. In another embodiment of the invention, said pixels are on/off pixels. In another embodiment of the invention, said pixels are multi-valued pixels. In another embodiment said invention further comprising the action of offsetting a grid of pixels in at least two passes. In another embodiment of the invention, said at least one of said feature edge pixels is divided into at least two regions having different weight functions for accomplishing non-linear rasterizing. FIG. 1a illustrates a rasterized feature 102. A grid 101 comprising pixels 103 is aligned to an origin 104 of a coordinate system. From FIG. 1a one can see that the grid is somewhat to coarse Therefore the feature 102 may not be imaged as accurate as desired. FIG. 1b illustrates the same feature as shown in FIG. 1a, but here the feature is rasterized to a finer grid. The accuracy of the rasterizing is two times better, but there are four time more pixels to write, which may make this method more time consuming relative the one illustrated in FIG. 1a. FIG. 1c illustrates the same feature as shown in FIG. 1a rasterized to the same grid size but using four passes 105 with no offset. Different lithographical characteristics such as resist properties and time delays may make this method of imaging more accurate than the one illustrated in FIG. 1a given that the different passes are imaged with equal doses. FIG. 2a illustrates a rasterized vertical line. FIG. 2b illustrates an ideal exposure 202 of the rasterized line in FIG. 2a. Smoothing by a finite resolution of an exposure beam gives an exposure dose denoted by 203 in FIG. 2b. FIG. 2b shows the smoothening by the exposure, but chemical diffusion, developer transport and finite resolution of the resist or recording medium also gives a similar effect. FIG. 2c illustrates a rasterized feature comprising a step. The imaged feature will end up with a pattern illustrated by the dashed line. The smoothening of step 205 is caused by the finite resolution of the exposure beam according to what was described in connection with FIG. 2b. Pixel 206 will therefore receive contribution from adjacent pixels. FIG. 6a illustrates an inventive method for offsetting different writing passes. In this embodiment four writing passes are offset relative to each other by a quarter of a pixel size in two orthogonal directions. The passes are here illustrated to be offset along a diagonal line of the pixel. Generally with N passes, where N is an integer greater than two, passes are distributed along a diagonal line of a pixel by (pixel size)/N, i.e., with three writing passes a first pass is written in a origin of coordinates, a second pass is written ⅓ of a diagonal line of a pixel away from said origin of coordinates and a third pass is written ⅔ of a diagonal line of a pixel away from said origin of coordinates. FIG. 6b illustrates a star written by said offset method as illustrated in FIG. 6a. It can be seen from FIG. 6b that there exists an unwanted asymmetry in the diagonals. This is caused by the fact that smoothening only occurs in directions parallel with pixel sides but in directions deviating from that one will see coarse grid effects. FIG. 6c illustrates another inventive method for offsetting different writing passes. In this embodiment four writing passes are distributed by the same amount but not along a straight line as illustrated in FIG. 6a. Here a first pas is written in an origin of coordinates. A second pass ¼ of a pixel size in an x direction and ½ of a pixel size in a negative y direction, x and y directions are parallel with the sides of the rectangular pixels. A third pass is written ½ the pixel size in the x direction and ¼ of the pixel size in the y direction. A fourth pass is written ¾ of the pixel size in the x direction and ¼ of the pixel size in the negative y direction. By this offsetting method you will obtain symmetry in both directions parallel to the sides of the pixel and also in both diagonals of said pixels. FIG. 6d illustrates the same star written by the method according to FIG. 6c. Here the symmetry is improved compared to the star in FIG. 6b. By offsetting the writing passes according to the scheme illustrated in FIG. 6c symmetry is accomplished in all eight directions. FIG. 7 illustrates reference points for several pixels in four passes 701, 702, 703, 704. It is possible to modify the displacement between the passes slightly by a small fraction of a pixel size unit to get a more uniform distribution of the reference points at the expense of a non-uniform division along the horizontal and vertical axis. The details of the rasterizer algorithm and the error structure of the pattern generator determine which is more favorable. Mirror images of the pattern in FIG. 7 and 90 degrees rotation of it will be equally good. The offsetting method according to FIG. 7 is particularly good for hiding a grid pattern. You may of course use another number of passes, in such case the pattern will look differently. The offset between the passes should be chosen so that one will get as good symmetry in x and y directions and both diagonals as possible. FIG. 8 illustrates four writing passes according to the invention with analog or multi-valued pixels. A middle column, represent a feature edge pixel column. As can be seen pixels in said column are set to different states. The pattern of the pixels in the feature edge column in the four passes could be equal or unequal. A finer address grid is accomplished by dithering between different grayscale values. FIG. 9 illustrates four passes according to the invention with edge pixels in more than one column. The pixels are multi-valued. Here again the plurality of edge columns in one writing pass could be equal or unequal in at least one other writing pass. Pixels in different edge columns may have different weights, which may be set differently from one case to another depending for instance which pattern is to be imaged. FIG. 10 illustrates a multipass scheme according to the invention. Here, passes with different dose create a fine address grid, with some passes, typically those with high dose, doubled in order to improve averaging. The passes with the same dose, in FIG. 10 denoted with the same crosshatch, can have their exposure fields and/or their pixel grid displaced in order to improve image uniformity. Writing passes with high doses are repeated due to the fact that averaging will have most impact from those passes. Passes with the lower doses may mainly be used for fine adjusting the address grid. Passes with higher dose are used for the most significant bits in the address and passes with lower dose are used for the least significant bits in the address. FIG. 11a and 11b illustrate multipass schemes according to the invention with edge pixels to create a finer grid and edge pixel sequence or distribution in different passes being different. In FIG. 11a the different passes are written with essentially the same exposure. In FIG. 11b two passes are written with for example 25% exposure and the other two with 100% exposure. The period of sequence in each pass is four, giving a combined grid of 1/16 of the pixel size. An example of an edge pixel sequence is illustrated to the right of the superposed passes in FIG. 11b. The two leftmost patterns may be written by 100% exposure and the two rightmost patterns may be written by 25% exposure. FIG. 12a-e illustrates different edge pixel sequences. Edge pixel sequences may be periodic or non-periodic. The figures show periodic sequences with different periods and a resulting image edge. FIG. 12a illustrates a pixels sequence with period 1, i.e., all pixels have the same value. Clearly this will create a smooth edge. FIG. 12b depicts a pixel sequence with period two, giving a virtual address grid two times finer than in FIG. 12a. The edge is still smooth due to the smoothening function of the exposure tool and process. The pixels are analog with for example 16 states and every second pixel at the feature edge may for example be set at 5/16 and the rest to 6/16. FIG. 12c illustrates a pixel sequence with period three, giving three times finer grid but starting to show line edge roughness (LER). The actual edge roughness depends on the trade off between pixel size, and the figure shows a typical example. FIGS. 12d and 12e illustrates a pixel sequence of 4 and 10 respectively. In those two figures one can clearly see that the edge roughness increases with increased pixel sequence period. FIG. 13 depicts a graph showing the relation between virtual grid and line edge roughness using the scheme in FIG. 12. Both virtual grid and edge roughness are in relative to the pixel size. FIG. 14 illustrates four passes with a long edge pixel period 1401. Each pass taken alone will create a strong line edge roughness 1402. By displacing the pattern a number of pixels between the passes and superposing the passes will reduce the line edge roughness 1403 strongly. FIG. 15 illustrates two graphs showing the simulated edge roughness for each pass and the combined roughness. The two graphs show two different sequences corresponding to different placement of the feature edge. The graphs show that some placements are better and some are worse, but for every placement a large reduction of the roughness is possible. The left graph in FIG. 15 illustrates displacement of a regular pixel edge pattern and the right graph shows superposition of irregular pixel edge patterns. FIG. 16 illustrates the same graph as in FIG. 13, but here with the edge roughness after four passes with displaced edge pixel sequences. The graph is based on a simulation with typical input parameters and shows that sequence lengths of up to 16 are possible with four passes. Larger sequence lengths may cause a roughness being bigger than the grid. FIG. 17 illustrates an algorithm for computing the edge pixel values with binary (on/off) pixels and a sequence period of 5. The feature edge is located 0.409 units onto a pixel in a middle column. The sequence in beforehand determined to be 0, 2, 4, 1, 3. The criteria for setting a pixel to an on state in the feature edge column is that P+(si/L)>1, where P is the position of the feature edge, si is the individual number in the sequence and L is a length of the sequence. FIG. 18 illustrates essentially the same as FIG. 17, but here 65-valued pixels are used. In this case 0.409=16/64+0.009=(16+0.576)/64. As we are using a multi-valued pixel we are interested to know when we are going to change state from 16/64 to 17/64. Therefore P=0.576. FIG. 19 illustrates a combination of two methods for obtaining a finer address grid. An example is the use of analog edge pixels in more than one row, as illustrated in FIG. 9, FIG. 32 and FIG. 33. An effectiveness of pixels in different columns may be different and the columns may combine in a linear or non-linear fashion. The use of two such methods can be used in the invention with a calibrated lookup table. Input data gives a look-up value for each of the methods, in the example for the analog values in the columns. The look-up table typically more output bits than address bits, so that a 6-bit address may generate two 8-bit values. The 8-bit values are generated during a calibration step when the edge placements for different combination of values are measured and mapped to the input values. In the more simple case of a single method the same look-up table structure may be used, but only with one output for each input. FIGS. 20a and b illustrates a multipass scheme with different edge sequences in the different passes and where the passes are displaced relative to each other. FIG. 20a illustrates the different sequences of the feature edge pixels. FIG. 20b illustrates how the passes are overlaid. Because of the displacement between the passes the dashed line, which represent the feature edge, will show up in different locations in the different passes. For each position of the final edge position there is at least one combination of feature edge patterns, which most likely all are different, which will result in an essentially smooth edge. The pixels in FIGS. 20a and b are on/off pixels. FIGS. 21a and b illustrates t that the edge pixels may be completely reshuffled in the passes when the input edge move only one address unit. FIG. 21a illustrates two passes at one edge placement. FIG. 21b illustrates the same two passes when the input edge has moved one virtual grid unit to the left compared to FIG. 21a. One pixel value has been changed from on to off (six pixels in on state in FIG. 21a and 5 pixels in on state in FIG. 21b in the feature edge column) and then the pixels have been reshuffled for best LER and edge acuity. FIG. 22 illustrates four passes with a long and unequal periodic sequences giving a virtual grid of 1/28 of the pixel size. The sequence length is 7. For each virtual grid step one pixel is flipped from off to on. After 7 steps the same sequences can be reused but with an order between the passes changed or rotated. It is not necessary that the sequences are periodic, non-periodic sequences can be found with essentially the same properties. It is also possible to use more or fewer passes and different displacements between the passes or no displacement at all. Two graphs showing the edge roughness in each pass and four combined passes are illustrated in FIGS. 23a and 23b. FIG. 23a shows the bitmap for one feature edge placement and FIG. 23b for another feature edge placement. In FIG. 23a there is no low frequency contribution. FIGS. 24a and b illustrates two methods for calculating optimal or near optimal edge pixel sequences for different edge locations. The computed sequences are computed off-line and tabulated for use during rasterization. FIG. 24a illustrates a binary sequence representing the edge pixels in different passes. The pixels used are two-valued pixels. Four passes are used with an inventive displacement scheme as described hereinabove. The sequence of edge pixels is illustrated to be non-periodic. This illustration in FIG. 24a is only one among many alternative ways for accomplishing the invention. FIG. 24a shows that one column of pixels in each pass is controlled by a sequence, i.e., there are four columns that are controlled in a four pass scheme. It is of course possible to control a four-pass scheme with other number of columns. FIG. 24b illustrates an algorithm for generating a sequence with good properties for each edge position given by an input address grid. An error diffusion algorithm may be used to generate starting binary sequences. Error diffusion algorithms can be found in textbooks relating to computer graphics. Error diffusion algorithms give an approximately uniform distribution of 0s and 1s. The sequence may be further improved by iterative permutations of short sequences. Permutations preserve the average edge position while on the other hand affecting edge roughness, which is evaluated in an imaging model. A simple imaging model may first be used for a quick generation of candidate sequences. Candidate sequences may then be further analyzed/evaluated by a more comprehensive model, e.g., by a commercial lithography simulation program. Once a sequence satisfying the acceptance level has been found, the sequence is accepted and the algorithm moves to the next edge location. FIGS. 25a and b illustrates a non-linear rasterizing function. The pixel or average column vs. the overlap between a feature in input data and a pixel area. FIG. 25a illustrates a graph showing a linear function, a piecewise straight-line non-linear function and a smooth non-linear function. All three are idealized, since in reality they get truncated to staircase functions. FIG. 25b illustrates the same as FIG. 20, but here with a non-linear rasterizing function giving better edge acuity, since only two of the passes have edge pixels. Each position of the feature edge may be independently optimized. The virtual grid in FIG. 25b is 1/16 of a pixel size. By looking at the pixels at the feature edge and using four writing passes, one can use 100% exposure in one pass for feature edge pixels and 0% exposure in another writing pass for feature edge pixels. For the remaining two passes one can use a steeper rasterizing function. FIG. 26a-c illustrates how non-linear rasterizing can be accomplished in a super-sampling rasterizer. Inside each pixel a feature is rasterized on a finer grid, the super-sampling super-grid. The pixel value is the number of super grid points that are set by the rasterizer. With equal weight on every super-grid point, the rasterizing is linear, if a larger weight function is applied to the super-grid points near the center of the pixel a non-linear rasterizing function will result. In FIG. 26b a weight function with a center square with a higher weight is shown. In FIG. 26c a continuous weight function is illustrated with a higher weight in a center than near the edges. By this super-sampling a steeper rasterizing function may be accomplished. FIG. 27a illustrates a weight function for non-linear rasterizing using the displacement scheme in FIG. 7. FIG. 27a illustrates pixel areas within a pass 2701 that fill the area with four times overlap after four passes. The rectangular areas 2702, with higher weight function, are smaller and fill the area without overlap after four passes. The rectangles have to be rotated by 90 degrees in two of the passes 2703. Super-sampling over either of these two area sizes gives a correct pixel representation of an input pattern, i.e., it is not possible to place a small feature anywhere so that its area is not reflected accurately by the pixel values. There are other area shapes that have the same property with a different overlap factor, e.g., 2 or 8. Since each of the two area shapes give correct rasterizing, every linear combination of them is also correct. FIG. 27b illustrates a pixel with a super-sampled grid. One weight function is applied over the central rectangle and another over the remainder of the pixel. FIG. 27c illustrates the weight function in FIG. 27b in three dimensions. The height of a central area and a plateau may be chosen arbitrarily based on the degree of non-linearity wanted. FIGS. 28a and b illustrates a weight function analog to FIGS. 27b and c for two passes offset half a pixel size in x and half a pixel size in y. By changing the weight between within the rectangle and outside said rectangle one can change the property of the non-linearity, i.e., the steepness of the non-linear function will vary. FIG. 29 shows an exemplary embodiment of an apparatus 1 for patterning a work piece 60. Said apparatus 1 comprising a source 10 for emitting electromagnetic radiation, a first lens arrangement 50, a computer controlled reticle 30, a beam conditioner arrangement 20, a spatial filter 70 in a Fourier plane, a second lens arrangement 40. The source 10 may emit radiation in the range of wavelength from infrared (IR), which is defined as 780 nm up to about 20 nm, to extreme ultraviolet (EUV), which in this application is defined as the range from 100 nm and down as far as the radiation is possible to be treated as electromagnetic radiation, i.e. reflected and focused by optical components. The source 10 emits radiation either pulsed or continuously. The emitted radiation from the continuous radiation source 10 can be formed into a pulsed radiation by means of a shutter located in the radiation path between said radiation source 10 and said computer controlled reticle 30. As an example can the radiation source 10, i.e. the source of an exposure beam, may be a KrF excimer laser with a pulsed output at 248 nm, a pulse length of approximately 10 ns and a repetition rate of 1000 Hz. The repetition rate may be below or above 1000 Hz. The beam conditioner unit may be a simple lens or an assembly of lenses or other optical components. The beam conditioner unit 20 distributes the radiation emitted from the radiation source 10 uniformly over at least a part of the surface of the computer controlled reticle 30. In a case of a continuous radiation source a beam of such a source may be scanned over the surface of the computer controlled reticle. Between the radiation source 10 and the computer controlled reticle 30, which may for instance be a spatial light modulator (SLM), said beam conditioner unit is arranged, which unit 20 expand and shapes the beam to illuminate the surface of the SLM in a uniform manner. In a preferred embodiment with an excimer laser as the source the beam shape is rectangular, the beam divergence different in x-direction and Y-direction and the radiation intensity is often non-uniform over the beam cross-section. The beam may have the shape and size of the SLM 30 and homogenized so that the rather unpredictable beam profile is converted to a flat illumination with a uniformity of, for example, 1-2%. This may be done in steps: a first beam shaping step, a homogenizing step and a second beam-shaping step. The beam is also angularly filtered and shaped, so that the radiation impinging on each point on the SLM has a controlled angular sub tense. The optics of the invention is similar to that of a wafer stepper. In steppers the beam is homogenized in a light pipe, a rectangular or prism-shaped rod with reflecting internal walls where many mirror images of the light source are formed, so that the illumination is the superposition of many independent sources. The homogenization may also be performed by splitting and recombining the beam by refractive, reflective or diffractive optical components. The SLM 30 is fed with a digital description of the pattern to be printed. The pattern may firstly be made in an ordinary commercially available drawing program. Before the pattern file is fed to the SLM, said pattern file is divided and transformed to a recognized formed for the SLM. FIG. 30 shows a Spatial Light Modulator (SLM) 200 comprising a 2-dimensional array of pixels, in this embodiment 8 rows 3001 and eight columns 3002, i.e. 64 pixels in total. In reality the SLM may comprise several millions of pixels but for reasons of clarity an SLM with few pixels is chosen. Micromirror pixels may for instance be 20×20 μm. A projection lens with a reduction of 200× will make one pixel on the SLM correspond to 0.1 μm in the image on the workpiece. Each pixel may be controlled to 64 levels, thereby interpolating the pixel of 100 nm into 64 increments of 1.56 nm each. The two leftmost columns of pixels 3010, 3011 and the two rightmost columns of pixels 3016, 3017 are set in a so called black state, i.e. the pixels are in a state which will not create any radiation onto the workpiece, indicated in FIG. 1 by 0. The two columns in the middle 3013, 3014 are set in a so-called white state, i.e. the pixel are in a state which will create maximum radiation onto the workpiece, indicated in FIG. 30 by 100. Pixels in columns 3010, 3011, 3016 and 3017 are outside feature pixels. Pixels in columns 3013 and 3014 are inside feature pixels. Pixels in columns 3012 and 3015 are boundary feature pixels. The boundary feature pixels are, as indicated in FIG. 1, set along the boundary of the feature in alternate states, in this case indicated by 74 and 75. In this embodiment every second boundary feature pixel is set to 74 and the rest to 75. As can be seen from the same figure, the states of the boundary feature pixels in column 212 do not match the boundary feature pixels in column 3015, i.e. the boundary feature pixels indicated by 75 do not belong to the same rows. In an alternative embodiment, the boundary feature pixels do match each other, i.e. the boundary feature pixels indicated by a same gray level are located in the same row. As an alternative to setting every second boundary feature pixel to one gray level and the rest to another gray level, every second pair of boundary feature pixels may be set to alternate states. With each pixel controlled into 64 levels, a pixel size. of 100 nm on the workpiece, and by setting the boundary feature pixels in the SLM in alternate states, an address grid of 0.78 nm is achievable in one writing step. In FIG. 30, the boundary feature pixels are represented by single columns 3012, 3015. A smoother feature edge will be created with every boundary feature pixel set to a first gray scale value and the rest of the pixels set to an adjacent gray scale value, which may be higher or lower compared to if longer sequences of alternate states are chosen in a single writing pass. In an alternative embodiment, as illustrated in FIG. 31, the boundary feature pixels are represented by two columns. In FIG. 31 the leftmost and rightmost column 3110 and 3117 respectively are set to the black state and pixels in these two columns are representing outside feature pixels. Inside feature pixels are represented in figure two in columns 3113 and 3114. Boundary feature pixels are represented in columns 3111, 3112, 3115 and 3116. In this embodiment, every second pixel in a leftmost boundary feature pixel column 3111 and a rightmost boundary feature pixel column 3116 are set to 1 and the rest to 0 grayscale level. Here the pixels in the leftmost boundary feature pixel column 3111 set to 0 match the higher value of the pixels in the other boundary feature pixel column 3112, here 75, creating together one of the feature edges on the work piece. The same applies for the two columns 3115 and 3116 creating together another feature edge on the workpiece, i.e. the 0's in the rightmost column 3116 match the higher value, here 75, of the pixels in the other boundary feature pixel column 3115 and the 1's in the rightmost column 3116 match the lower value, here 73, of the pixels in the other boundary feature pixel column 3115. Alternatively the reverse may apply, i.e. having two boundary feature pixel columns creating one feature edge on the workpiece, the higher alternate state (grayscale value) in one of these columns may match the higher alternate state (grayscale value) in the other of these columns. Instead of extending the boundary feature pixel columns into outside feature pixel columns, said columns may be extended into inside feature pixel columns as illustrated in FIG. 32. In FIG. 32 columns 3210, 3211, 3216 and 3217 represent outside feature pixel columns. Columns 3212, 3213, 3214, 3215 represent boundary feature pixel columns. Here we have no inside feature pixel columns because the line to be written is only represented by 4 columns, and two columns represent one edge of the line. As can be seen from FIG. 32, all higher alternate values match each other, i.e. the 100's in columns 3213 and 3214 match the 75's in column 3212 and 3215. Alternatively higher values in the outmost boundary feature pixel columns 3212 and 3215 may match lower values in the inmost boundary feature pixel columns 3213 and 3214. FIG. 33 illustrates still another embodiment of an inventive feature edge pattern in a Spatial Light Modulator (SLM). Here three columns represent the boundary feature pixels. The leftmost and rightmost column 3310 and 3317 respectively are set to the black state and pixels in these two columns are representing outside feature pixels. Boundary feature pixels are represented in columns 3311, 3312, 3313, 3314, 3315 and 3316. There are no inside feature pixels represented in FIG. 33. In this embodiment, every second pixel in a leftmost boundary feature pixel column 3311 and a rightmost boundary feature pixel column 3316 are set to 1 and the rest to 0 grayscale level. Here, the pixels in the leftmost boundary feature pixel column 3311 are set to 0 and they are matching the higher gray scale value of the pixels in the boundary feature pixel columns 3312, 3313, 3314, 3315. The 0 gray scale value match in this embodiment 75 gray scale value in columns 3312 and 3315, where the rest of the pixels in columns 3312 and 3315 are set to 74. The 0 gray scale value match in this embodiment 100 gray scale value in columns 3313 and 3314, where the rest of the pixels in columns 3313 and 3314 are set to gray scale value 99 in. Columns 3311, 3312, 3313, 3314, 3315, 3316, 3317 are creating together the feature edges of a straight line. FIG. 34a illustrates a first of four writing passes for creating a straight line with a fine address grid. The pixels in columns 3410, 3411, 3416 and 3417 are set to gray scale value zero. The pixels in columns 3413 and 3414 are set to gray scale value 100. Columns 3410, 3411, 3416 and 3417 are, according to the previous language used in the former embodiments, outside feature pixel columns and columns 3413 and 3414 are, using the same language, inside feature pixel columns. Columns 3412 and 3415 are boundary feature pixel columns. In the first writing pass all pixels in said boundary feature pixel columns are set to a first grayscale value except for at least one pixel which is set to a second gray scale value. In this embodiment as illustrated in FIG. 34a, seven out of eight pixels in the respective columns are set the gray scale value 75. One pixel in column 3412 is set to gray scale value 74 and one pixel in column 3415 is set to gray scale value 74. Here the gray scale value 74 in columns 3412 and 3415 match each other i.e. they are exactly opposite to each other. However, in an alternative embodiment, said second gray scale value may not be equal in both boundary feature pixel columns and may not be positioned exactly opposite to each other. FIG. 34b illustrates a second writing pass out of four for creating a straight line. The only difference between FIG. 34b and FIG. 34a is that the second gray scale value in the boundary feature pixel columns 3412 and 3415 have moved from the third position from top in FIG. 34a to a top position in FIG. 34b. FIG. 34c illustrates a third writing pass out of four for creating a straight line. The only difference between FIG. 34b and FIG. 34c is that the second gray scale value in the boundary feature pixel columns 3412 and 3415 have moved from the top position in FIG. 34b to a fifth position from top in FIG. 34c. FIG. 34d illustrates a fourth writing pass out of four for creating a straight line. The only difference between FIG. 34d and FIG. 34c is that the second gray scale value in the boundary feature pixel columns 3412 and 3415 have moved from the fifth position from top in FIG. 34c to a bottom position in FIG. 34c. When superposing said first, second, third and forth writing passes the effect of said second grayscale value will be essentially the same as the lower grayscale value in boundary feature pixel columns 3412 and 3415 in FIG. 1. FIG. 34e illustrates a writing pass scheme in an embodiment of four writing passes and a pixel sequence length of eight pixels. 1:st, 2:nd, 3:rd, 4:th Columns represent one boundary feature pixel column in the first, second, third and fourth writing pass respectively. Pixels in said boundary feature pixel column in the first writing pass, as illustrated in FIG. 34e in the leftmost column, are first set individually to a sequence of grayscale values. At least one of the grayscale values in said sequence of eight pixels differs from the other. With the writing pass scheme as illustrated in FIG. 34e said at least one pixel, which differs from the other, will move around in the boundary feature pixel column and create a finer address grid when the respective writing pass are superposed on each other. Alternatively, any number of pixels in the sequence may be used instead of the illustrated 8, for example 6, 12, 14 and 16 pixels. The invention is not limited to a single writing pass or four writing passes as illustrated by the figures, but can be employed with any number of writing passes, for example 2, 3 and 5.

claims

1. A method for suppressing corrosion in a pressurized water nuclear plant comprising a secondary system, the secondary system comprising a steam generator, a turbine, a condenser, and a heater and not comprising a deaerator, the method comprising, in the following order:circulating water through the secondary system;depositing a protective substance on a surface of a structural member of the secondary system by spraying or by bringing a fluid comprising TiO2 as the protective substance in contact with the surface of the structural member of the secondary system; and thencirculating water through the secondary system such that the water contacts the protective substance, to make the protective substance into a single layer of TiO2 ,wherein the protective substance consists of a single layer of TiO2. 2. The method of claim 1, wherein the water is circulating water which is not subjected to chemical injection by a chemical injection device. 3. The method of claim 1, wherein the structural member of the secondary system having the protective substance is the steam generator. 4. The method of claim 1, wherein the structural member of the secondary system having the protective substance is the heater.

description

The present application claims the benefit of U.S. Provisional Patent Application No. 60/881,319, entitled “Objective Lens With Deflector Plates Immersed In Electrostatic Lens Field”, filed Jan. 19, 2007, by inventors Alexander J. Gubbens and Ye Yang, the disclosure of which is hereby incorporated by reference in its entirety. 1. Field of the Invention The present invention relates to electron beam apparatus, including scanning electron microscopes and the like, and method of operating such apparatus. 2. Description of the Background Art There is an increasing need for high-resolution scanning electron microscopes (SEMs) in all areas of development and manufacture of micro-electronic and opto-electronic components. High-resolution scanning electron microscopes are useful so as to visually evaluate sub-micrometer structures. High-resolution SEMs may be used to identify deviations from standard patterns and to acquire and evaluate topographical data such as heights, widths or angles of inclination. Unfortunately, conventional, non-immersion, scanning electron microscopes do not have the required resolution of a few nanometers unless very high landing energies above about 10 kilo-electronVolts are used which may cause resist structures and, integrated circuits to be damaged and non-conductive or high resistant specimens to be disadvantageously charged. It is highly desirable to improve electron beam apparatus, including scanning electron microscopes and the like, and methods of operating such apparatus. One embodiment relates to an objective lens utilizing magnetic and electrostatic fields which is configured to focus a primary electron beam onto a surface of a target substrate. The objective lens includes a magnetic pole piece and an electrostatic deflector configured within the pole piece. An electrostatic lens field is determined by the pole piece and the electrostatic deflector, and the electrostatic lens field is configured by adjusting offset voltages applied to the plates of the electrostatic deflector. Another embodiment relates to a method of focusing an electron beam onto a target specimen. Offset voltages are applied to a main deflector so as to fine tune an electrostatic lens field, where the electrostatic lens field is determined by the offset voltages on the deflector and a high voltage on a magnetic pole piece surrounding the deflector. Another embodiment relates to an electron beam apparatus. The apparatus includes at least an electron source, a magnetic immersion objective lens, and an electrostatic deflector. The electron source is configured to generate a primary electron beam, and the magnetic immersion objective lens is configured to focus the primary electron beam onto a surface of a target substrate. The electrostatic deflector is configured within the pole piece of the magnetic immersion objective lens. An electrostatic lens field is determined by the pole piece and the electrostatic deflector, and the electrostatic lens field is configured by adjusting offset voltages applied to plates of the electrostatic deflector. Other embodiments, aspects and features are also disclosed. Immersion Objective Lenses Low-voltage scanning electron microscopes (SEMs) often use immersion objective lenses because they tend to have superior resolution performance. Immersion objective lenses immerse the sample in a magnetic and/or decelerating electrostatic field. The highest resolution low voltage SEMs use both magnetic and electrostatic immersion. The magnetic immersion allows for very small working distances and small aberration coefficients. The use of electrostatic immersion to retard the primary electron beam just prior to the substrate further reduces the aberration coefficients and thereby further increases the resolution. The landing energy of the primary electron beam is determined by the potential difference between the electron gun's cathode and the subsrate. The retarding field at the substrate is determined by the potential difference between the substrate and the objective lens pole piece above it. To allow independent control of the landing energy and the retarding field, the objective lens pole piece(s) are typically biased at a high voltage potential (greater than 30 V in magnitude). The substrate potential is then set to determine the landing energy and the objective lens pole piece potential is next set to determine the strength of the retarding electrostatic field. Scanning of the primary electron beam is conventionally done by means of a multipole deflector located on the inside of the objective lens near the tip. Electrostatic deflection is often preferred over magnetic deflection because it does not suffer from hysteresis as magnetic deflectors do and because it is easier to make work well at high speeds. Conventional electrostatic deflectors use shunt electrodes on both sides to accurately define and terminate the axial extend of the deflecting field. The DC value of the electrostatic deflector and shunts are typically held at ground potential to allow for simpler driving electronics. This then necessarily introduces an electrostatic lens field between the objective lens pole piece at high voltage and the deflector at DC ground. In the case of magnetic immersion, the secondary electron detection is typically through the objective lens. This is because the secondary electrons are strongly captured by the magnetic field and spiral up along the optical axis through the bore of the lens. At the point where the magnetic field decays on the inside of the lens, the secondary electrons are no longer captured and “spill out” (i.e. travel along divergent paths), making it difficult to collect and detect them. It is therefore desirable to have an electrostatic lens on the inside of a magnetic immersion objective lens. Such an electrostatic lens on the inside of a magnetic immersion objective lens may advantageously collimate the secondary electrons and transport them more efficiently to the secondary detector located elsewhere in the electron beam column. Magnetic Immersion Objective Lens Having an Electrostatic Deflector Plates with a Bottom Shunt Positioned Therein FIG. 1 is a schematic diagram of a magnetic immersion objective lens 100 having electrostatic deflector plates 108 positioned therein, where a grounded shunt 110 is configured at the bottom of the deflector plates 108. This diagram shows a cross-sectional view of the objective lens 100. As shown, a primary electron beam travels down an optical axis 101 and through the objective lens 100 to become focused upon the surface of a target substrate. A magnetic pole piece 102 of the objective lens 100 is configured about the optical axis 101, with a gap 103 extending away from the optical axis 101. The pole piece 102 is configured about an electromagnetic device 104 so as to generate a magnetic field which immerses the target substrate. The pole piece 102 is further configured at a high voltage potential. As further shown, electrostatic deflector plates 108 are configured within the pole piece 102. By controllably varying the voltages applied to the electrostatic deflector plates 108, the primary beam may be controllably deflected so as to be scanned over an area of the target substrate. In this case, a top shunt 106 and a bottom shunt 110 are provided above and below the deflector plates 108. The top shunt 106 may comprise, for example, a conical shunt. The bottom shunt 110 may comprise, for example, a conical or straight shunt. The shunts 106 and 110 are further configured to be grounded (i.e. conductively connected to an electrical ground). An electrostatic lens may be defined between the grounded bottom shunt electrode 110 and the high-voltage objective lens pole piece 102. This electrostatic lens may be configured so as to collimate secondary electrons emitted from the target substrate. Unfortunately, applicants have determined that the accurate alignment of the bottom shunt electrode 110 and the pole piece 102 is needed for high resolution performance of the objective lens 100 shown in FIG. 1. This requirement drives mechanical tolerances that are on the order of micrometers and adds substantially to the manufacturing cost of the magnetic lens. Magnetic Immersion Objective Lens Having an Electrostatic Deflector Plates Positioned Lower in the Lens FIG. 2 is a schematic diagram of an immersion objective lens 200 having electrostatic deflector plates 208 deeply positioned therein, without a grounded shunt configured at the bottom of the deflector plates 208. This diagram shows a cross-sectional view of the objective lens 200. As shown, a primary electron beam travels down an optical axis 201 and through the objective lens 200 to become focused upon the surface of a target substrate. A magnetic pole piece 202 of the objective lens 200 is configured about the optical axis 201, with a gap 203 extending away from the optical axis 201. The pole piece 202 is configured about an electromagnetic device 204 so as to generate a magnetic field which immerses the target substrate. The pole piece 202 is further configured at a high voltage potential. As further shown, electrostatic deflector plates 208 are configured within the pole piece 202. By controllably varying the voltages applied to the electrostatic deflector plates 208, the primary beam may be controllably deflected so as to be scanned over an area of the target substrate. In this case, a top shunt 206 is provided above the deflector plates 208, but there is no bottom shunt (in contrast to FIG. 1). The top shunt 106 may comprise, for example, a conical shunt. Here, an electrostatic lens field 210 may be defined between the electrostatic deflector plates 208 and the high-voltage objective lens pole piece 202. Advantageously, applicants have determined that, unlike the electrostatic lens field 110 of FIG. 1, the electrostatic lens field 210 of FIG. 2 does not require highly-accurate alignment of the deflector plates 208 and the high-voltage objective lens pole piece 202. This is because the ends of the deflector plates 208 are immersed in the electrostatic field 210. Because the ends of the deflector plates 208 are immersed in the electrostatic field 210, the electrostatic field 210 may be controllably adjusted by applying DC voltages to all of the deflector plates 208. These DC voltages may be used to properly align the electrostatic field 210 within the objective lens 200. While the DC voltages applied to all of the deflector plates 208 may be adjusted to change the alignment of the electrostatic field 210, it does not affect the scanning of the electron beam which is controlled by the AC voltage (i.e. the time-varying voltage signal) applied to one or more of the deflector plates 208. Applicants have determined that the lens configuration of FIG. 2 allows for significantly greater mechanical tolerances for the same high resolution performance. The greater mechanical tolerances are enabled by the advantageous feature that the shape and alignment of the electrostatic lens field 210 may be controllably varied and fine-tuned by applying the DC voltages to the deflector plates 208. As a result, the mechanical tolerances of the objective lens may be relaxed while the resolution performance may be maintained or even improved. Relaxation of the mechanical tolerances greatly reduces manufacturing cost. Simulation Results FIG. 3 is a table of simulation results showing performance parameters of a magnetic immersion objective lens having electrostatic deflector plates positioned therein, where a grounded shunt is configured at the bottom of the deflector plates (like the objective lens 100 of FIG. 1). In contrast, FIG. 4 is a table of simulation results showing performance parameters of an immersion objective lens having electrostatic deflector plates deeply positioned therein, without a grounded shunt configured at the bottom of the deflector plates (like the objective lens 200 of FIG. 2). Note that these simulations included both octupole and quadrupole electrostatic lens characteristics. The octupole and quadrupole are shifted downward (closer to the target substrate) for the simulation of FIG. 4 in comparison to the simulation of FIG. 3. As indicated, the primary beam energy is 2,000 electron Volts, and the landing energy is 1,000 electron Volts, for both of these simulations. Comparing the results shows that removing the bottom shunt and moving the deflectors down increases the scan sensitivity. The higher scan sensitivity results in an approximately 35% reduction in scan voltages required. Moreover, the scan aberrations are reduced by a factor of 2 or 3. This is advantageously accomplished while the secondary electron collection efficiency is unaffected (as shown by a separate simulation). The simulations show that leaving out the bottom shunt and immersing the electrostatic deflector plates in the electrostatic lens field not only allows the mechanical tolerances of the objective lens to be reduced, it actually also increases the scanning performance of the electron microscope. As integrated circuits continue to get smaller and smaller with the progression down Moore's curve, the resolution requirements on critical dimension and review SEMs continue to increase. Increasing resolution requirements impose tighter and tighter mechanical tolerances on the lens design of immersion objective lenses. The present application discloses methods and apparatus to introduce an additional degree of freedom that may be utilized to ensure optimal alignment and resolution performance. This advantageously reduces required mechanical tolerances and improves the manufacturability of a combined magnetic/electrostatic objective lens for scanning electron microcopy. The above-described diagrams are not necessarily to scale and are intended be illustrative and not limiting to a particular implementation. Specific dimensions, geometries, and lens currents of the immersion objective lens will vary and depend on each implementation. The above-described invention may be used in an automatic inspection system and applied to the inspection of wafers, X-ray masks and similar substrates in a production environment. While it is expected that the predominant use of the invention will be for the inspection of wafers, optical masks, X-ray masks, electron-beam-proximity masks and stencil masks, the techniques disclosed here may be applicable to the high speed electron beam imaging of any material (including perhaps biological samples). In the above description, numerous specific details are given to provide a thorough understanding of embodiments of the invention. However, the above description of illustrated embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise forms disclosed. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific details, or with other methods, components, etc. In other instances, well-known structures or operations are not shown or described in detail to avoid obscuring aspects of the invention. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.

abstract

The present invention provides a volumetric computed tomography (VCT) system capable of producing data for reconstructing an entire three-dimensional (3D) image of a subject during a single rotation without suffering from cone beam artifacts. The VCT system comprises an array of source positions distributed along a line parallel to an axis of rotation, a plurality of collimators, and an array of x-ray detectors. In a preferred embodiment, a reversed imaging geometry is used. A 2D array of source positions provides x-rays emanating from each focal spot toward an array of detectors. The x-rays are restricted by a collimator array and measured by a detector array separately per each source position. The axial extent of the source array and the detector array are comparable to or larger than the axial extent of the portion of the object being imaged.

063174839

description

BEST MODE FOR CARRYING OUT THE INVENTION In accordance with this invention, an x-ray reflective device shown in FIG. 1 comprises a curved crystal 10 and support base 12. Crystal 10 has a set of curved atomic reflection planes 14. On every point of the crystal surface, atomic plane set 14 is near parallel to the crystal surface 16 in the embodiment shown. The spacing between the atomic planes, d, varies continuously from d.sub.1 at one end of the crystal to d.sub.2 at the other end of the crystal. Values of d.sub.1 and d.sub.2 are determined from the Bragg equation where the Bragg angles are the incident angles .theta..sub.1 and .theta..sub.2, respectively. According to the Bragg equation, the Bragg angles of reflective planes 14 for x-ray photons of wavelength .lambda. vary with the d spacing profiles. The configuration of the crystal surface 16 can be spherical, ellipsoidal, paraboloidal, toroidal, or other type of doubly curved surface. The profile of the d spacing for the crystal planes is designed to allow the incident angles of monochromatic x-rays from a divergent laboratory source to match the Bragg angle on each point of the crystal surface. The optical device according to the present invention can be fabricated by bending a flat thin crystal slab 10 as shown in FIG. 2 with a desired d spacing profile to a preselected geometry. One bending method is the fabrication process described in co-pending, commonly assigned U.S. patent application Ser. No. 09/342,606, entitled "Curved Optical Device and Method of Fabrication," the entirety of which is hereby incorporated herein by reference. The variation of the d spacing of the crystal planes can be produced by growing a crystal made of two or more elements and changing the relative percentages of the two elements as the crystal is grown. For instance, the lattice parameter of a Si--Ge crystal varies with a change in concentration of Ge. Therefore, a crystal material with a graded lattice parameter can be obtained by growing a Si--Ge crystal and controlling the concentration of Ge during growth. Such crystal planes are commercial available and can be purchased, for example, from Virginia Semiconductor, Inc. of Fredericksburg, Va. One embodiment of the present invention providing point to point x-ray imaging is illustrated in FIG. 3A. Crystal planes 14 are curved to an ellipsoidal shape and the d spacing of the planes varies along the direction parallel to the optical axis 2--2. For the symmetrical configuration shown in FIG. 3A, the d spacing of reflection planes has a maximum value d.sub.0 at the center point O and decreases as edge E is approached. With the decrease of the d value from the center O of the crystal to the edge E, the Bragg angle for x-rays of wavelength .lambda. increases, which matches the increase of the incident angles from O to E for x-rays diverging from the left focus of the ellipse. A cross-section of the crystal taken along line 4--4 is shown in FIG. 3B. In this plane, the crystal planes are circular and the d spacing does not vary. FIG. 3C shows an asymmetrical arrangement of a point to point focusing geometry, which provides demagnification of source S. The ellipsoidal crystal element in FIG. 3A can be made by bending a flat crystal 10 (see FIG. 2) to an ellipsoid, where the d spacing of the flat crystal 10 varies along the X direction but is constant along the Y direction (see FIG. 2). The optical element shown in FIG. 3A may be fabricated in two pieces such that two identical flat crystal slabs with graded d spacing from d.sub.0 to d.sub.E can be used as shown in the exploded view of FIG. 4. In this embodiment, the two crystals are joined at O and the surface is ellipsoidal. This approach allows the grading to increase in one dimension. Conversely, the element in FIG. 3A requires a grading profile that increases and then decreases. A curved crystal device with paraboloid geometry is shown in FIG. 5A. This device produces a monochromatic collimating x-ray beam from a point source S. The d spacing of the reflection plane of the crystal 10 is graded from a value of d.sub.1 to d.sub.2. To satisfy the Bragg condition, the d spacing profile is linear for the first order approximation and increases from point A to B. Alternatively, a collimated beam can be directed to a focal spot as shown in FIG. 5B. The focusing and collimating of x-rays can also be obtained with a spherical geometry at near normal incidence using crystalline planes with graded d spacing. Spherical mirrors are well known as imaging devices for normal incident visible light optics. A conventional spherically bent crystal can demagnify (or magnify) and collimate x-rays from a divergent x-ray source for some particular wavelength at near normal incidence. However, the numerical aperture of this type device is too small to be useful. The numerical aperture can be improved substantially with the use of graded d spacing, doubly curved crystals in accordance with the present invention. FIG. 6A shows a set of spherical curved crystal planes according to another embodiment of the present invention, which provides a demagnified image of the x-ray source. The d spacing of the crystal planes has a symmetrical profile about the optical axis and varies along the transverse direction. It increases across the surface from points A to B. The normal projecting view along the optical axis is illustrated in FIG. 6B. The d spacing profile of this device may be difficult to obtain. In practice, it can be approximated by using multiple pieces of crystal slabs with a simple graded d profile as shown in FIG. 6C. Each piece of crystal is curved to a spherical shape with the reflection planes parallel to the surface. The d spacing profile of the reflection planes is one-dimensionally graded along the radial direction passing the center of each crystal. If an x-ray source is placed at the focus of the concave spherical device similar to the orientation shown in FIG. 6A, a collimating x-ray beam is obtained. Strong demagnification can be obtained if two spherical crystal devices are combined. One preferred geometry is the Schwarzschild configuration which is used to image soft x-rays in conjunction with a multilayer coating. Graded crystals with the Schwarzschild geometry provide imaging for hard x-rays as shown in FIG. 7. The reflection planes of primary crystal 18 has a d spacing profile of d.sub.1 (r) to reflect x-rays from a source emitting x-rays at a near normal incident angle. The reflection planes of the secondary crystal 20 have the desired profile d.sub.2 (r) to match the incident angles of the x-rays reflected off the primary crystal 18. This system produces a final image of the source at I. While the invention has been described in detail herein in accordance with certain preferred embodiments thereof, many modifications and changes therein may be effected by those skilled in the art. Accordingly, it is intended by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.

042343852

description

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is based on the discovery, as a result of numerous experiments, that if silicon, titanium and carbon as essential components are added to the austenitic stainless steel, the silicon content is made under 0.7% by weight, and further, the contents of titanium and carbon are controlled so as to satisfy a certain relationship, the swelling of steel would be suppressed to the extremely low order (for example, 1.5% at maximum at 1.times.10.sup.23 nvt irradiation), without damaging the physical and mechanical properties of steel. It is found according to the invention that there exist complementary relations in the contents of silicon, titanium and carbon in the suppression of the swelling, though the mechanism of suppressing the swelling is not known in detail. The term "austenitic stainless steel" as used in this specification and the appended claims means an austenitic stainless steel containing chromium in a normally prescribed amount, nickel in a normally prescribed amount, manganese in an amount of up to 2% by weight, molybdenum in an amount of up to 3% by weight, silicon, carbon and titanium in amounts as hereinafter described, and the balance of iron. In addition the steel may contain incidental components which may be incorporated from the ordinary process of manufacturing steel. Such incidental components include nitrogen of up to 3%, oxygen of up to 0.02%, aluminium of up to 0.05%, arsenic of up to 0.03%, boron of up to 0.002%, cobalt of up to 0.1%, niobium of up to 0.05%, copper of up to 0.1%, sulphur of up to 0.03%, and vanadium of up to 0.2%. In general, the chromium content of the steel is in the range of 9 to 26% by weight. If the content is more than 26 wt.%, neither the stable austenitic system can be obtained, nor the void suppression may be attained. On the contrary, if the content is below 9 wt.%, a sufficient oxidation resistance cannot be obtained. Preferably, the content of chromium is 16 to 20% by weight. Usually, the nickel content of the steel is 6 to 30% by weight. Although the nickel content of more than 30% by weight is effective in the suppression of the swelling, a steel containing such an amount of nickel decreases in the corrosion resistance to a liquid metal, and is readily attacked by the nuclear fission products. Moreover, it not only aggravates neutron economy, but also causes a large amount of cobalt as an impurity to be contained in nickel. As a result, cobalt 60 originated from the cobalt may be turned into the most cumbersome radioactive corrosion product and interfere with the operation of the nuclear reactor. Whereas, with the nickel content of less than 6 wt.%, there can be obtained no stable austenite system, and the effect of suppressing the void would be lost. A preferable content of nickel is in the range of 10 to 16% by weight. While the silicon added to the austenitic stainless steel according to this invention is a component essential for suppressing the void swelling, addition of a large amount of silicon may destroy the physical and mechanical properties of the steel. Accordingly, the silicon content is preferable to be kept at a low level, if the contents of carbon and titanium to be added together with the silicon satisfy the relationship as described hereinafter. Generally, the silicon content is kept below 0.7% by weight (i.e., more than 0% to less than 0.7% by weight), preferably 0.5% to less than 0.7% by weight. It has been found, as a result of the various experiments, that there exists a correlation between the titanium content and the carbon content in suppressing the void swelling, and that if carbon and titanium in amounts satisfying the following relationship are added to the austenitic stainless steel which contains the silicon kept within the abovementioned quantitative limits, the void swelling can be suppressed to a very small extent (i.e., 1.5% at maximum at 1.times.10.sup.23 nvt irradiation). The relationship between the contents of carbon and titanium will be given by the following formula. EQU 17[C]+27[Ti].gtoreq.2.1 (A) where [C] represents the carbon content indicated in % by weight and exceeding 0, and [Ti] represents the titanium content indicated in % by weight and exceeding 0. The upper limits of the carbon content and the titanium content can not be determined unconditionally, and increasing both the carbon and titanium contents causes the mechanical properties of steel to be aggravated, for example, embrittled. The upper limits with respect to the carbon content and the titanium content capable of sufficiently suppressing the void swelling without substantially aggravating the mechaical properties of the steel are 0.1% by weight and 0.5% by weight, respectively. Preferably, the minimum carbon content is 0.01% by weight, and a preferred range based on this minimum is 0.01 to 0.1% by weight. Further, the minimum titanium content is preferably 0.03% by weight, and a preferred range based on this minimum is 0.03% to 0.3% by weight. The variables [C] and [Ti] in the formula (A) are interdependent, and if either of the variables is fixed, then the other one varies between the above-mentioned maximum value and the minimum value calculated from the formula (A) with the formula (A) taken as an equation. That is, for example, where [C] is 0.02, [Ti] varies between the maximum value of 0.5 and the minimum value of about 0.065 calculated with the formula (A) taken as an equation. This applies also to the preferable cases of the carbon content and the titanium content as stated above. Namely, if [C] is 0.02, then [Ti] is preferably in the range of 0.065 to 0.3 (% by weight). FIG. 1 shows the relationship between the carbon content and the titanium content by a graph. In the figure, line AJ stands for the formula: 17[C]+27[Ti]=2.1. A general range of the carbon and titanium contents fall within the region encircled by lines AB, BC, CD and DA, and the region encircled by lines EF, FG, GH, HI and IE shows a preferable range of carbon and titanium contents. Further, it has been found according to the invention that the void swelling can be further suppressed and the mechanical properties of steel is improved by subjecting the austenitic stainless steel to a final heat treatment at a temperature enough to permit the carbon and titanium contained in the steel to be formed substantially completely into a solid-solution. The final heat treatment is such a treatment as to be effected at the end of the process to provide the product and is generally carried out at a temperature of more than 1120.degree. C. up to 1200.degree. C. A heat treatment at a temperature of 1120.degree. C. or less can not form the solid-solution satisfactorily, while a heat treatment at a temperature of more than 1200.degree. C. can not attain the necessary mechanical strength of the steel and is uneconomical. The final heat treatment is preferably carried out at a temperature of 1150.degree. C. to 1200.degree. C. and for one to ten minutes. FIG. 2 shows a nuclear fuel element 10. A solid fuel body 3 composed of a plurality of pellets 2 is housed in a cylindrical clad 1 which is formed of the austenitic stainless steel according to this invention. The pellets 2 may be obtained by compression-moulding a nuclear fuel material such as the oxides, nitrides and carbides of uranium, plutonium and thorium, or a mixture thereof into a cylindrical shape and sintering it at a high temperature. The clad 1 is sealed tight by means of plugs 4 and 5 provided at the both ends thereof and a spring 6 for preventing the pellets 2 from the movement is installed in a plenum chamber 7 located between the fuel body 3 and the plug 4. A gap 8 is present between the clad 1 and the fuel body 3. In the plenum chamber 7 and the gap 8 is filled herium gas. FIG. 3 shows a nuclear fuel subassembly A. A plurality of the nuclear fuel elements 10 as shown in FIG. 2 are supported by grids (not shown) and received in a duct 11, with any adjoining two of the elements separated from each other by a spacer (not shown). It is preferred that the duct 11 be formed of the austenitic stainless steel according to this invention. This invention will be more fully understood from the following examples. Examples. Sample steels, each 750 g, were prepared by melting a steel component of high purity in a vacuum. The steel was cast into a rod of approximately 3.5 cm in diameter and then made up to a plate of approximately 3 mm thick by hot-rolling at 1150.degree. C. Then, the steel plate was rapidly cooled after annealed at 1150.degree. C. for 10 minutes, and cold-rolled into a thin plate of approximately 0.5 mm thick. Thereafter, it was heat-treated at 1200.degree. C. for 5 minutes. A small test piece (8 mm.times.14 mm.times.0.2 mm thick) was cut out of the thin steel plate and then finished up with an electrolytic polishing after smoothing the surface thereof with an abrasive paper. Voids formed in the test piece by irradiation of carbon ions at high temperature was observed under an electron microscope, and the whole volume of the voids was determined, thereby estimating the amount of the swelling of steel. The evaluation of the quantity of the swelling was made by using the experimental correction (reported in Journal of Nuclear Science and Technology, Vol. 13, pp. 743-751) by SHIMADA et al. In the simulative experiment by irradiation of the carbon ions, the temperature at which the swelling reaches the peak shifts higher by approximately 100.degree. C., because the damaging speed of a sample is fast as much as 1000 times that by irradiation of neutrons. Accordingly, irradiation of the carbon ions at about 525.degree. C. corresponds to irradiation of the neutrons at about 625.degree. C. Meanwhile, pre-injection of herium into the test piece had been carried out so that herium ions injected in the test piece distirbuted uniformly over the surface to the depth of 4000 A by changing the intensity of the herium ion energy. Table 1 shows the components of the 316 steel which is an austenitic steel on market and various steels used for the above-mentioned experiments. TABLE 1 __________________________________________________________________________ Sample steel No. Ni Cr Mo Mn Si C Ti S P Co N O __________________________________________________________________________ 316 10.5 17.5 2.63 0.78 0.44 0.050 <0.01 0.005 0.03 0.24 -- -- M79 14.1 17.5 2.48 0.91 1.05 0.068 <0.01 0.005 0.025 0.041 0.0048 0.0136 M82 13.5 17.4 2.52 1.67 0.59 0.041 0.02 0.006 0.002 0.042 0.0058 0.0088 M83 13.3 16.8 2.46 1.69 0.58 0.018 0.17 0.006 -- -- 0.0049 0.0070 M84 13.8 16.9 2.44 1.77 0.52 0.101 0.22 0.007 -- -- 0.0048 0.0079 M85 13.2 16.7 2.44 1.65 0.48 0.072 0.025 0.006 0.001 0.043 0.0049 0.0066 M90 13.3 16.6 2.47 1.59 0.55 0.087 0.039 0.007 0.002 0.041 0.0062 0.0068 M91 13.1 16.7 2.47 1.65 0.51 0.055 0.084 0.007 -- -- 0.0038 0.0050 M92 13.0 16.7 2.46 1.67 0.59 0.022 0.019 0.007 -- -- 0.0044 0.0058 M93 13.3 16.7 2.47 1.63 0.63 0.016 0.034 0.007 0.002 0.042 0.0043 0.0072 __________________________________________________________________________ Note: Unit % by weight; Fe balance The results are shown in FIG. 4 which shows the amount of the swelling of each steel obtained by the irradiation of ions corresponding to that of high-speed neutrons at 1.times.10.sup.23 nvt under an expected condition of LMFBR, dotted against the titanium content. As seen from the figure, the sample steels can be classified into two groups with the titanium content at 0.03% as a border. That is, a first group is the high-swelling group composed of the steels 316, M79, M82, M85 and M92 with Ti content of less than 0.03%, and a second group is the low- and the extremely low-swelling group composed of the steels M83, M84, M90, M91 and M93 with Ti content of 0.03% or more. The high-swelling group shows a swelling of the order of 8% as represented by the 316 steel on the market, while the low- and the extremely low-swelling group shows an excellent resistivity to the swelling (i.e., the swelling of about 1% to less than 0.1%). The second group can completely satisfy the desired value of the swelling such as several percentages, for example, 6%, which is the swelling limit of the steel covering the nuclear fuel in the fast breeder reactor under design or construction at present. The reason is that since the amount of the high-speed neutrons at the end of the operation of the reactor is about 2.times.10.sup.23 nvt under the expected operation condition of the LMFBR and at such an amount of the neutrons the amount of swelling is proportional to the square of the amount of the neutrons with respect to 300 series stainless steel, the amount of swelling of 1% at the amount of the neutrons of 1.times.10.sup.23 nvt corresponds to the amount of swelling of 4% at the amount of the neutrons of 2.times.10.sup.23 nvt. Further, FIG. 4 clearly shows that the amount of swelling varies to a large extent between titanium contents of 0.02% and 0.03%.

abstract

A method of operation of a measurement system includes: providing a specimen having a film; controlling a beam generator to direct a charged particle beam into the specimen; detecting a reference signal emitted from the specimen; normalizing the reference signal to create a film L-ratio; and determining a thickness of the film by correlating the film L-ratio to a calibration curve.