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description | FIG. 1 shows diagrammatically an example of an X-ray examination apparatus 1 in which the present invention can be implemented. The X-ray source 2 emits an X-ray beam 15 for irradiating an object 16. Due to differences in X-ray absorption within the object 16, for example a patient to be radiologically examined, an X-ray image is formed on an X-ray sensitive surface 17 of the X-ray detector 3, which is arranged opposite the X-ray source. The X-ray detector 3 of the present embodiment is formed by an image intensifier pick-up chain which includes an X-ray image intensifier 18 for converting the X-ray image into an optical image on an exit window 19 and a video camera 23 for picking up the optical image. The entrance screen 20 acts as the X-ray sensitive surface of the X-ray image intensifier which converts X-rays into an electron beam which is imaged on the exit window by means of an electron optical system 21. The incident electrons generate the optical image on a phosphor layer 22 of the exit window 19. The video camera 23 is coupled to the X-ray image intensifier 18 by way of an optical coupling 24, for example a lens system or a fiber-optical coupling. The video camera 23 extracts an electronic image signal from the optical image, which signal is applied to a monitor 25 for the display of the image information in the X-ray image. The electronic image signal may also be applied to an image processing unit 26 for further processing. Between the X-ray source 2 and the object 16 there is arranged the X-ray filter 4 for local attenuation of the X-ray beam. The X-ray filter 4 comprises a large number of filter elements 5 in the form of capillary tubes whose X-ray absorptivity can be adjusted by application of an electric voltage, referred to hereinafter as adjusting voltage, to the inner side of the capillary tubes by means of the adjusting unit 7. FIG. 2 is a side elevation of an X-ray filter 4 of the X-ray examination apparatus of FIG. 1. The Figure shows seven capillary tubes by way of example, but a practical embodiment of an X-ray filter 4 of an X-ray examination apparatus in accordance with the invention may comprise a large number of capillary tubes, for example 16384 tubes in a 128-128 matrix arrangement. Each of the capillary tubes 5 communicates with the X-ray absorbing liquid 6 via an end 31. The inner side of the capillary tubes is covered by an electrically conductive layer 37, for example of gold or platinum, which layer 37 is coupled to a voltage line 35. The adhesion of the X-ray absorbing liquid to the inner side of the capillary tubes can be adjusted by means of an electric voltage applied to an electrically conductive layer 37 on the inner side of the capillary tubes 5. One end of the capillary tubes communicates with a reservoir 30 for an X-ray absorbing liquid. The capillary tubes are filled with a given quantity of X-ray absorbing liquid as a function of the electric voltage applied to the individual tubes. Because the capillary tubes extend approximately parallel to the X-ray beam, the X-ray absorptivity of the individual capillary tubes is dependent on the relative quantity of X-ray absorbing liquid in such a capillary tube. The electric adjusting voltage applied to the individual filter elements is adjusted by means of the adjusting unit 7, for example on the basis of brightness values in the X-ray image and/or the setting of the X-ray source 2. To this end, the adjusting unit is coupled to the output terminal 40 of the video camera and to the power supply 11 of the X-ray source 2. The construction of an X-ray filter 4 of this kind and the composition of the X-ray absorbing liquid are described in detail in the International Patent Application No. IB 95/00874 and in U.S. Pat. No. 5,666,396, which are both incorporated herein by reference. The height of the fluid level inside the capillary tubes is influenced by the electrocapillary pressure, also called electrowetting. The electrocapillary pressure p behaves as p=constxc2x7V2, with V the electrical potential applied between an in-capillary electrode (37 in FIG. 2) and the conducting liquid (6 in FIG. 2). The height of the fluid level inside the capillary tubes is further determined by the repelling force of the capillary tube walls and the externally applied hydrostatic pressure. In this respect it is noted that use is made of watery solutions and hydrophobic materials. The fluid level in the capillary tubes is a result of the balance between said three forces of which the electrocapillary pressure p is actively used to set the fluid level at a desired height. Dynamic measurements show that the switching takes place in 0.1-1 second (speed 1-10 cm/s, electrode length 1 cm). In an X-ray filter the liquid level in every capillary has to be individually controllable. If every capillary is connected to an individual wire, the number of required electronic control elements scales with N2. A well-know method to reduce the number of control elements to a number of the order N, is by matrix-addressing. Matrix addressing means that rows (indexed i, ixcex5{1 . . . N}, voltage Vi) are activated one-by-one while the programming signals are placed on column wires (indexed j, jxcex5{1 . . . N}, voltage Vj). In order to apply matrix addressing in an X-ray filter an electrical matrix structure is needed in every capillary tube, i.e. every capillary tube (i, j) needs to be connected to voltages Vi and Vj. Hereinafter three different examples of capillary tubes according to the invention are shown. FIG. 3 shows a cross sectional view of a first embodiment of capillary tube 45 of a device according to the invention. Capillary tube 45 comprises an electrode formed by a conducting layer, an insulator 46 and a hydrophobic coating 47. The electrode is divided into three segments 42, 43 and 44 in longitudinal direction of the tube. The segments are mutually electrically insulated and different voltages are applied thereto. A voltage of Vmem is applied to the lowest segment 42 by means of the row connection. A voltage of Vj is applied to the middle segment 43 by means of the column connection. A voltage of Vmem is applied to the highest segment 44. A voltage Vi is applied to the liquid which acts as an electrode. This embodiment is therefore also referred to as the liquid/in-capillary electrode embodiment. The segmentation of the data-electrode introduces a gap between the segments 42 and 43. In order for the liquid to rise over the above mentioned gap a threshold voltage should be applied to the data-electrode. Only for a large enough magnitude of Vixe2x88x92Vj the liquid will jump across the gap and rise above it. The gap size (i.e. the distance between the segments of the data-electrode) as well as the gap geometry determine the threshold-behavior. An example of a gap geometry that reduces the required threshold voltage is shown schematically in FIG. 6, where two electrode segments are indented in the direction of the liquid rise. In a similar fashion a local discontinuity of geometry (such as a local shape change, local opening-up and/or constriction of the capillary), of insulator properties (such as thickness or dielectric constant) or of hydrophobicity introduces a nonlinear behavior of liquid level versus applied voltage. The structuring of the metallic electrodes, insulator thickness or hydrophobic coating can be achieved in a filter that is composed of semi-planar plates or of foils. FIG. 4 shows a cross sectional view of a second embodiment of a capillary tube 55 of a device according to the invention. This embodiment is referred to as the in-capillary/in-capillary electrode embodiment. Capillary tube 55 comprises an electrode formed by a conducting layer, an insulator 56 and a hydrophobic coating 57. The electrode is divided into three segments 52, 53 and 54 in longitudinal direction of the tube. The segments are mutually electrically insulated and different voltages are applied thereto. A voltage of Vi is applied to the lowest segment 52 by means of the row connection. A voltage of Vj is applied to the middle segment 53 by means of the column connection. A voltage of Vmem is applied to the highest segment 54. A voltage Vliq with approximately zero value is applied to the liquid. At the mouth 51 of the capillary the electrodes 52 and 53 act as a valve between the supply channel and the bulk of the capillary thus introducing a threshold-like behavior. Only when a voltage with a predetermined value is applied to electrode 52 as well as to electrode 53 the liquid fills the capillary. The liquid does not rise if only one of the electrodes is activated. Due to the limited velocity of liquid movement (speed 1-10 cm/s), the meniscus senses a time-averaged electrocapillary pressure. To avoid that programmed rows loose their pattern in the time that other rows are being programmed, a memory function has to be added to every capillary tube. Such a memory function can be achieved with an extra electrode in the capillaries. This electrode can be shared by more than one capillary as is the case with Vmem in FIG. 3. The value of Vmem is chosen such that the capillary tube 55 remains filled once the liquid has risen, independent of the value of voltages Vi and Vj. This is referred to as the xe2x80x98memory effectxe2x80x99. The memory effect is advantageous because it allows for the sequential addressing of several rows. In order to empty the filled capillaries, a zero voltage should be applied to electrodes 52, 53 and 54 resulting in a reset of the capillaries. After resetting the capillaries can be reprogrammed. Preferably every row of capillaries has a separate Vmem connection allowing the resetting to occur in a row-wise fashion. FIG. 5 shows a cross sectional view of a third embodiment of a capillary tube of a device according to the invention. This embodiment is also referred to as the improved in-capillary/in-capillary electrode embodiment. FIG. 5 shows a preferred embodiment of an electrode architecture that allows filling and emptying of a single capillary tube. Every capillary tube is provided with an electrode sequence 62, 63, 64, 68, 69, whereby a voltage Vi is applied to electrode segments 62 and 69, a voltage Vj is applied to electrode segments 63 and 68 and a voltage Vmem is applied to electrode segment 64 so that the voltage sequence is Vi/Vj/Vmem/Vi/Vj. Vmem indicates the voltage applied to the memory electrode, electrode segment 64 in this case. The conducting fluid is supplied from below. In the examples given below, V=0 means that no potential is applied, so that the electrode is being de-wetted. V=1 means that a high potential is applied (e.g. V greater than 200 V), so that the electrode is being wetted. Suppose that all capillary tubes are empty and we want to fill only one capillary tube (i=n, j=m). We can do this by applying for example: Vi=1 for all i, Vj=0 for all j, and then Vmem=1, Vi=1 for all i, Vj=0 for all j, and then Vmem=1, Vi=0 for all i, Vj=0 for all j, and then Vmem=1, Vi=n=1, Vixe2x89xa0n=0, Vj=m=1, Vjxe2x89xa0m=0, (the capillary fills) and then Vmem=1, Vi=0 for all i, Vj=0 for all j. Suppose that all capillary tubes are full and we want to empty only one capillary tube (i=n, j=m). We can do this by applying for example: Vi=1 for all i, Vj=0 for all j, and then Vmem=0, Vi=1 for all i, Vj=0 for all j, and then Vmem=0, Vi=1 for all i, Vj=1 for all j, and then Vmem=0, Vi=n=0, Vixe2x89xa0n=1, Vj=1 for all j, and then Vmem=0, Vi=n=0, Vixe2x89xa0n=1, Vj=m=0, Vjxe2x89xa0m=1, (the capillary empties) and then Vmem=0, Vi=1 for all i, Vj=0 for all j, and then Vmem=1, Vi=1 for all i, Vj=0 for all j, and then Vmem=1, Vi=0 for all i, Vj=0 for all j. It is noted that grey-scale programming is possible when the architecture of FIG. 5 is repeated several times in a capillary tube. FIG. 6 schematically shows an embodiment of a capillary tube 71 according to the invention comprising two electrode segments 72 and 73, which are indented in the direction of the liquid rise. This gap geometry reduces the required threshold voltage. It will be understood that the indented parts can have a variety of shapes apart from the rectangular shape that is shown. It will be clear for a person skilled in the art that in the matrix structures described above the functions of rows and columns are interchangeable. Summarizing the invention provides the insight that in a device as described above the construction of the fluid elements can be designed such that it induces the desired threshold like behavior of the fluid rise without the necessity of extra components. The invention is of course not limited to the described or shown embodiment(s), but generally extends to any embodiment, which falls within the scope of the appended claims as seen in light of the foregoing description and drawings. |
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abstract | A magnetically shielded, efficient plasma generation configuration for a pulsed discharge extreme ultraviolet (EUV) light source comprises two opposed convex electrodes mounted with axes parallel to a static magnetic field. A limiter aperture disposed between the electrodes, in conjunction with the field lines, defines a hollow plasma cylinder connecting the electrodes. A high pulsed voltage and current compresses the plasma cylinder and its interior magnetic field onto the electrode surfaces to create a magnetic insulating layer at the same time as propelling the working gas from each side toward the space between the electrode tips. The plasma then collapses radially in a three-dimensional compression to form a dense plasma on the axis of the device with radiation of extreme ultraviolet light. |
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053735390 | abstract | A safety system grade dropped rod detection system for a pressurized water reactor (PWR) utilizes core exit thermocouples arranged in multiple trains and hot and cold leg RTDs to generate a safety system grade rod stop signal. The system generates from the temperature signals a relative power deviation (RD) and a curvature index (CI), which is the spatial second derivative of RD for each fuel assembly. The CI signatures not only provide rapid, reliable detection of dropped control rods, but also clearly identify failed and failing thermocouples. |
043022855 | summary | FIELD OF THE INVENTION The present invention relates to highly sensitive nuclearphysical means for quantitative determination of an impurity content in various materials, more specifically, for determination of content of lightweight elements and gas impurities such as oxygen, nitrogen, silicon and the like; in particular it concerns neutron activation analysis installations. The invention may be used at metallurgical and chemical plants, at general metallurgy and machine-building factories, in various branches of industry such as aviation, electronics and the like, as well as in agriculture. It may also be used to advantage for research in solid-state physics and material studies and in monitoring of semi-finished products. Use of aluminum, magnesium and their alloys as well as oxygen-free copper and titanium-magnesium alloys is preferable in the production of lightweight metals and alloys. Use of niobium, molibdenum, tantalum, tungsten, rhenium and like elements as well as special steels and alloys is preferable in the production of refractory and heat-resistant metals. PRIOR ART Known in the art are neutron activation analysis installations (cf. J. L. Duggan and I. L. Morgan "Industrial Applications of Small Accelerators", IEEE Transactions on Nuclear Science, 1975, NS-22, No. 3, pp 1216-1228) comprising a neutron generator whose target chamber communicates through a transport means with a test sample receiving and loading assembly which, in its turn, communicates with a test sample impurity concentration measuring unit. Such installations are used for quick determination of impurities, primarily, oxygen whose minimum concentration in the material is 5.multidot.10.sup.-3 % by mass. Materials having such an oxigen content may not be regarded as pure or highly pure. The known neutron activation analysis installations may not be used with pure and highly pure materials having an oxigen content of 1.multidot.10.sup.-3 % by weight, maximum, a disadvantage associated with the fact that the surface of test samples is contaminated before or during the analysis. The test sample surface contamination, say, whith oxigen may be due to its sorption from the atmosphere (or vacuum medium), moisture or oil vapour condensation and mechanical impurities from transport means. For example, the test sample surface may be heavily contaminated due to the injection of 16.sub.N recoil nuclei in oxygen determination via the 16.sub.O(n,p) 16.sub.N reaction from the atmosphere and the surface of object adjacent the sample during irradiation. The formed 16.sub.N radioactive recoil nucleus acquires kinetic energy sufficient to get onto the surface of the irradiated sample. A maximum energy of the 16.sub.N recoil nucleus is 1.8 MeV, the path in metals being 1.5 to 2.mu., while the path in the air is 4.4 mm. This activity source characterizes an imaginary quasi-oxygen content and not an actual oxygen content in the sample insofar as no difference can be made between the imaginary and actual oxygen in registration of the 16.sub.N activity. It is obvious that any treatment of the sample surface before irradiation does not exclude the effect of surface contamination on the analysis results. Also, in the event of sample surface removal after irradiation account should be taken of the total time spent on the treatment of the irradiated sample in contamination removal in view of the fact that a determination sensitivity may be degraded. Since the half life of the 16.sub.N isotope is 7.14 s, the sample surface treatment time should not exceed 1 to 1.5 half-life periods, i.e., it should be 10 s, maximum. Another known method involves the etching of irradiated samples in an aggressive medium for surface removal in doing oxygen content neutron activation analysis (cf. F. Dugain, M. Andre, A. Speecke "Radiochemical Radioanalytical Letters", 4, 121, 35, 1970). With the aforesaid method, the samples are etched manually by performing the following steps: placing the irradiated sample in a vessel containing an etching solution; holding the sample in the vessel as long as needed; removing the etched sample from the vessel; and transferring it into a vessel containing water for washing. The total treatment time amounts, in this case, to 20-30 s. Serious disadvantages of the aforesaid method are manual etching, a rather long sample treatment time, an increased radiation hazard, sample etching in still water causing sorption of radioactive nuclei from the etching solution, and also incomplete removal of the etching solution from the sample surface. Also known in the art is a neutron activation analysis installation for determining an oxygen content in highly pure substances (cf. USSR Inventor's Certificate No. 409,555 filed in 1973). As distinct from the aforementioned installation it includes an additional device by means of which the sample is etched after irradiation from a neutron generator. This additional device (irradiated sample surface layer removal unit) represents a rectangular teflon unit having four successively arranged vertical dead channels communicating with one another through guide cavities (slips) whose number suits the number of reagents required to treat the sample. The extreme channels are, respectively, provided whith sample inlet and outlet ports. Connections are incorporated in the channels to deliver the reagents. The vertical channels contain cylindrical pistons with receiving frames on ends thereof, into which the irradiated sample is successively rolled. The pistons with frames are lifted by two air cylinders which are connected in pairs to the respective pistons. The aforesaid installation has been generally unsatisfactory due to the fact that a rather long time is spent while the irradiated sample moves from the inlet port via all the channels to the outlet port, a limitation resulting in low response and intolerable sample activity loss, which, in its turn, drastically degrades the determination sensitivity. Moreover, the known installation does not permit analyzing conventional samples whithout etching insofar as no provision is made therein for direct communication between the test sample receiving and loading assembly and the impurity concentration measuring unit bypassing the irradiated sample surface layer removal unit. Also, the known installation has been open to the objection that its reliability is comparatively low because of the need to use several moveable cylinders with frames alternately receiving the sample and difficulties encountered in making the frames moving in a boiling acid mechanically strong. The sample is moved from one channel to another over slips filled with reagents by gravity, a limitation preventing the analysis of randomly shaped samples whose density is close to 1 g/cm.sup.3. BRIEF DESCRIPTION OF THE INVENTION It is an object of the present invention to expand a concentration measurement range by the use of a neutron activation analysis installation. Another object of the invention is to enhance an impurity determination sensitivity. A further object of the invention is to reduce a sample treatment time after irradiation. A still further object of the invention is to improve the construction of a neutron activation analysis installation with a view to increasing its reliability. The foregoing objects are accomplished by that in a neutron activation analysis installation comprising a neutron generator whose target chamber communicates through a transport means with a test sample receiving and loading assembly communicating, in its turn, with a test sample impurity concentration measuring unit, and also an irradiated sample surface layer removal unit, according to the invention, the receiving and loading assembly is in communication with the impurity concentration measuring unit over a channel having a through lateral port communicating on one side with the input of the irradiated sample surface layer removal unit, an irradiated sample distribution assembly being arranged on the other side of the port, said assembly representing an air cylinder with a hollow shaft having a bar located along the axis thereof and mounting on its end a sample receiver, said bar being disposed in a manner allowing its rotation about the longitudinal axis thereof and reciprocating motion through the port in the channel so that in one extreme position the bar does not reach the channel leaving it vacant, in the intermediate position the sample receiver is found in the channel blocking the latter, and in the other extreme position the sample receiver passes through the port in the channel getting into the surface layer removal unit. Preferably the mechanism turning the bar about its axis represents a piston contained within a hollow rod encompassing the bar, secured thereon in a manner allowing sliding motion along the latter and coupled to the rod by means of a carrier rigidly connected with the piston and installed in a manner allowing its motion through a screw slot in the rod. To enhance sensitivity and reliability of the installation, the irradiated sample surface layer removal unit preferably comprises at least three communicating chambers arranged successively in the direction of reciprocating motion of the bar, the position of the last chamber in the direction of progressive motion of the bar corresponding to the extreme position of the bar, while the air cylinder mounts air locks to suit the number of partitions between the communicating chambers. The neutron activation analysis installation forming the subject of the present invention permits high-accuracy quantitative determination of an impurity and macrocomponent content in various materials, an advantage associated with the fact that the effect of surface contamination on analysis results is excluded. An actual impurity content within the sample is, thus, determined and the probability of a systematic error is substantially reduced. The hereinproposed installation providing means for impurity determination within a wide concentration range (from tens to 1.multidot.10.sup.-5 % by weight) allows its use with conventional initial materials, whether contaminated or highly pure, without any design modifications. Furthermore, the possibility of analyzing various materials regardless of their properties in solid, powder and liquid phases close to a production site or research ground makes the hereinproposed installation sufficiently versatile to meet production, research and technological needs. Samples of virtually any shape having an indefinitely low density may be analyzed in the installation forming the subject of the present invention due to the fact that the chambers in the irradiated sample surface layer removal unit are arranged successively in the direction of reciprocating motion of the bar carrying the receiver with the irradiated sample. |
048428124 | abstract | Colloidal corrosion products which are referred to as crud are removed from nuclear reactor coolant streams by suspending zirconium oxide particles in the coolant stream. The crud will be attracted to the surfaces of the zirconia particles and caused to agglomerate thereon. Such zirconia/crud agglomerates may be readily filtered from the coolant. By providing scavenger particles which comprise active areas of zirconia on basically magnetite particles, after the crud is agglomerated to the active zirconia surfaces, the agglomerates may be removed from the coolant utilizing magnetic separation principles. |
053612809 | abstract | A nuclear fuel identification code reader has an optical sensor for detecting a nuclear fuel identification code marked on a fuel assembly and an ultrasonic wave sensor for detecting the nuclear fuel identification code. It further has first means for recognizing the nuclear fuel identification code based on information derived from the optical sensor and second means for recognizing the nuclear fuel identification code based on information derived from the ultrasonic wave sensor. When the nuclear fuel identification code cannot be recognized by the first means, the detection by the ultrasonic wave sensor and the recognition of the nuclear fuel identification code by the second means are effected. The nuclear fuel identification code can be recognized in a short time with a high accuracy. |
H00002097 | summary | TECHNICAL FIELD The technical field of this invention includes apparatus for discharging elongate pins from an area having a relatively low pressure to another area having relatively higher pressure, while minimizing leakage between the areas of differential pressure. BACKGROUND OF THE INVENTION In the production of nuclear fuel pins it is disirable to automatically assemble, clean and inspect the fuel pins within an automated fabrication system contained within an airtight enclosure. The airtight fabrication enclosure is preferably operated at a negative pressure of approximately 1 inch water column. Such a nuclear fuel pin fabrication system also uses an approximately pure helium atmosphere which must be maintained in a pure state even though finished fuel pins are intermittently being discharged from the system as finished product. It is an object of this invention to provide a pin discharge assembly which allows elongate pins to be discharged from a fabrication system operating at below ambient conditions with a minimum of gas inflow into the fabrication system. It is also an object of the invention to provide a pin discharge assembly which allows gases which may be emitted during discharge of an elongate pin to be contained and safely disposed of without emission into the area into which the elongate pin is being discharged. It is a further object of the invention to provide a pin discharge assembly which is easy to manufacture and to maintain. Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. |
047019425 | abstract | In radiology X-radiation from, an X-ray tube is directed toward a patient and received by an image means, which may be a film, to produce a visual image. The X-ray may be intended to detect a particular feature or area; however, the picture may be obscured by the unequal X-ray attenuation effect of the patient. That adverse effect is minimized by an attenuation mask which equalizes attenuation across the entire field. An individual mask is formed for each patient, on an almost real-time basis, by a first X-ray exposure which is analyzed to determine the extent and location of the patient's attenuation. The mask is produced, based upon that analysis, providing different attenuation at different areas, by depositing ink jet droplets, having suitable metal material, on an absorbent substrate. |
claims | 1. In a secondary-electron mapping-projection apparatus, an electrostatic projection-lens system comprising a front-power group and a rear-power group each having a middle electrode in common, the middle electrode and at least one electrode of the front-power group forming a front power, and the middle electrode and at least one electrode of the rear-power group forming a rear power, each of the front and rear powers being independently variable. 2. The projection-lens system of claim 1 , wherein: claim 1 each of the front and rear powers has a respective center position; and the respective center positions of at least one of the front and rear powers are variable by varying a respective voltage applied to the respective electrode, except the middle electrode. 3. The projection-lens system of claim 2 , wherein at least one electrode in the front-power group is configured as a multi-pole electrode including at least four poles. claim 2 4. The projection-lens system of claim 1 , wherein at least one electrode in the front-power group is configured as a multi-pole electrode including at least four poles. claim 1 5. A secondary-electron mapping-projection apparatus, comprising a projection-lens system as recited in claim 1 . claim 1 6. A secondary-electron mapping-projection apparatus, comprising a projection-lens system as recited in claim 2 . claim 2 7. A secondary-electron mapping-projection apparatus, comprising a projection-lens system as recited in claim 3 . claim 3 8. In a method for performing secondary-electron mapping-projection microscopy, a method for producing an image of a specimen surface at a pre-determined magnification, the method comprising: providing an electrostatic projection-lens system comprising a front-power group and a rear-power group each having a middle electrode in common, the middle electrode and at least one electrode of the front-power group forming a front power, and the middle electrode and at least one electrode of the rear-power group forming a rear power, each of the front and rear powers being independently variable; irradiating a region of the specimen surface with a charged particle beam so as to cause the specimen surface to emit secondary electrons; routing the secondary electrons into an end of the projection-lens system; and adjusting at least one of the front power and rear power to obtain an electron-image of the irradiated region of the specimen surface at a desired magnification. |
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description | This application claims priority to U.S. Provisional Application No. 60/816,706, entitled “Increased Tool Utilization/Reduction in MWBC for UV Curing Chamber,” filed Jun. 26, 2006, which is hereby incorporated herein by reference. Materials such as silicon oxide (SiOx), silicon carbide (SiC), and carbon doped silicon oxide (SiOCx) films find widespread use in the fabrication of semiconductor devices. One approach for forming such silicon-containing films on a semiconductor substrate is through the process of chemical vapor deposition (CVD) within a chamber. For example, a chemical reaction between a silicon supplying source and an oxygen supplying source may result in deposition of solid phase silicon oxide on top of a semiconductor substrate positioned within a CVD chamber. As another example, silicon carbide and carbon-doped silicon oxide films may be formed from a CVD reaction that includes an organosilane source including at least one Si—C bond. Water is often a by-product of such a CVD reaction of oganosilicon compounds. As such, water can be physically absorbed into the films as moisture or incorporated into the deposited film as Si—OH chemical bond. Either of these forms of water incorporation is generally undesirable. Accordingly, undesirable chemical bonds and compounds such as water are preferably removed from a deposited carbon-containing film. Also, in some particular CVD processes, thermally unstable organic fragments of sacrificial materials (resulting from porogens used during CVD to increase porosity) need to be removed. One common method used to address such issues is a conventional thermal anneal. The energy from such an anneal replaces unstable, undesirable chemical bonds with more stable bonds characteristic of an ordered film thereby increasing the density of the film. Conventional thermal anneal steps are generally of relatively long duration (e.g., often between 30 min to 2 hrs.) and thus consume significant processing time and slow down the overall fabrication process. Another technique to address these issues utilizes radiation such as infrared (IR), ultraviolet (UV), or visible radiation to aid in the post treatment of CVD-produced films such as silicon oxide, silicon carbide, and carbon-doped silicon oxide films. For example, U.S. Pat. Nos. 6,566,278 and 6,614,181, both to Applied Materials, Inc. and incorporated by reference herein in their entirety, describe the use of UV light for post treatment of CVD carbon-doped silicon oxide films. The use of UV radiation for curing and densifying CVD films can reduce the overall thermal budget of an individual wafer and speed up the fabrication process. A number of various UV curing systems have been developed which can be used to effectively cure films deposited on substrates. One example of such is described in U.S. application Ser. No. 11/124,908, filed May 9, 2005, entitled “High Efficiency UV Curing System,” which is assigned to Applied Materials and incorporated herein by reference for all purposes. During these curing techniques, as well as other such procedures, it is common for water molecules and various other species to be outgassed or otherwise released from the film or material being cured or processed. These species tend to collect on various exposed surfaces of the chamber, such as windows in the chamber, that can reduce the efficiency of the process. Further, the build-up of these species on the surfaces requires periodic cleaning of the chamber surfaces, such as after every 200 wafers processed, which results in significant tool downtime and a corresponding reduction in manufacturing throughput. The contamination levels after processing typically are used as a benchmark for cleaning intervals. It generally is desirable to have a high MWBC value (mean wafer between clean), or mean number of wafers processed between cleanings, in order to reduce costs and system downtime. In some swept source systems, for example, a MWBC of 800-1200 wafers is considered to be an undesirably low value of MWBC, caused by factors such as the condensation of outgassed materials on relatively cold surfaces of the processing chamber. For reasons including these and other deficiencies, and despite the development of various curing chambers and techniques, further improvements in this important technology area are continuously being sought. Systems and methods in accordance with embodiments of the present invention can prevent the collection of contaminants, outgassed species, and other materials on components of a processing chamber or other such housing. In one embodiment, a system for curing a workpiece includes a chamber housing, which can include curing chamber and a chamber for housing a radiation source, for example. A substrate support in the chamber housing is used to support a workpiece, such as a semiconductor wafer, being processed. A radiation source, such as an ultraviolet (UV) lamp, can direct radiation onto a workpiece supported on the substrate support in order to cure at least a layer or region of the workpiece. A pump liner is positioned in the chamber housing about the periphery of the workpiece, such as a ring-shaped liner positioned about the circular outer edge of a semiconductor wafer. The pump liner has gas inlet plenums and gas outlet plenums for receiving and exhausting a flow of purge gas. The pump liner also has a plurality of injection slits operable to direct a substantially laminar flow of purge gas across a surface of the workpiece being cured. A plurality of receiving slits are positioned opposite the plurality of injection slits and operable to receive the flow of gas directed across the wafer. The receiving slits are sized and shaped to receive the flow of gas and any species or contaminants outgassed or otherwise released from the workpiece during processing. In one embodiment, a pump liner for directing a flow of purge gas across a workpiece in a processing chamber includes a ring-shaped element formed of a material such as aluminum. The element has a central opening shaped to fit around a periphery of a workpiece, such as the outer edge of a semiconductor wafer. The ring-shaped element includes an inlet plenum operable to receive a flow of purge gas into a first channel in the ring-shaped element and an exhaust plenum operable to direct the flow of purge gas out of a second channel in the ring-shaped element. A plurality of injection ports positioned near the central opening of the ring-shaped element direct a laminar flow of the purge gas, received by the inlet plenum, from the first channel and across a surface of the workpiece. A plurality of receiving ports positioned near the central opening of the ring-shaped element, substantially opposite the plurality of injection ports, receive the flow of purge gas directed across the surface of the workpiece, as well as any species outgassed or otherwise released by the workpiece during processing. The injection and receiving ports can include slits or other openings that are sized and shaped to direct and receive the laminar flow of gas, and receive any species or contaminants outgassed or otherwise released from the workpiece during processing. The flow of purge gas is selected to have a sufficient mass and momentum so that the purge gas can carry the outgassed species. The pump liner directs the flow and outgassed species through the second channel and out of the ring-shaped element through the exhaust plenum. The pump liner can be heated through conduction and by irradiation from a curing source. The pump liner also can be anodized to increase the emissivity of the liner. The contact area between the pump liner and the chamber body can be minimized in order to minimize the amount of heat flow, and thus heat loss, from the pump liner to the chamber body. In one embodiment, a method for curing a workpiece includes positioning a workpiece to be cured on a workpiece support in a processing chamber. Radiation capable of curing at least a layer or region of the workpiece is directed toward a surface of the workpiece. A laminar flow of purge gas is provided across the irradiated surface of the workpiece. The laminar flow emanates from a pump liner having a plurality of injection slits and a plurality of receiving slits for directing and receiving the flow. The size, shape, position, and number of the slits are selected to generate the substantially laminar flow, as well as to transport any species outgassed from the irradiated surface of the workpiece. The flow of purge gas and the outgassed species are exhausted from the pump liner and the chamber after the flow passes across the irradiated surface and is received by the receiving slits of the pump liner. The contact area of the pump liner with the chamber body can be minimized in order to minimize heat flow and thus heat loss. These and other embodiments of the present invention, as well as its advantages and features, are described in more detail in conjunction with the text below and attached figures. Systems and methods in accordance with various embodiments of the present invention overcome the aforementioned and other deficiencies in existing anneal, cure, and other processing systems by providing a removal mechanism for outgassed species before those species can collect on the surfaces of the processing chamber. In some embodiments, a pump liner or other component for generating a flow of purge gas can be used in a chamber such as a vacuum chamber to direct a substantially laminar flow of gas across the surface of a wafer or other workpiece during a process such as a UV cure process. Such a flow can carry away any species outgassed by the workpiece. The liner can be passively heated by the convection in the chamber as well as the curing light source, such that the species do not collect on the liner and can be efficiently exhausted from the chamber. In one embodiment, the pump liner is anodized to increase the absorption efficiency of the liner. A window between the workpiece and the curing light source also can have a sufficient diameter to allow light from the source to fall directly onto the liner, in order to provide additional energy to heat the liner. The liner can be formed to have minimal contact with the bulk of the processing chamber body, which typically is kept at around 75° C. in one embodiment, in order to minimize heat flow (and thus loss) from the liner to the chamber body. The liner also can have slits of varying shape, width, and/or height in order to control the flow of gas across the workpiece surface, so that the flow direction is substantially laminar and so that the velocity of the gas across the wafer is substantially uniform from one side of the wafer to the other. FIGS. 1(a) and (b) shows an exemplary curing system 100 that can be used in accordance with one embodiment, although aspects of the present invention can be used advantageously in a number of other systems and applications as would be apparent to one of ordinary skill in the art in light of the description and suggestions contained herein. This system 100 includes a light source 102 for the curing process, such as a UV or IR lamp as known in the art. A reflector 104 is positioned between the lamp 102 and a substrate support 104, in order to focus light from the lamp toward the substrate support. The reflector can also be used to shape the footprint of the light on the substrate support. The substrate support 104 can be any appropriate device operable to support workpieces such as semiconductor wafers in place during a cure process. In one example, the workpiece support is a cylindrical chuck operable to support semiconductor wafers. The chuck can be translatable in order to position a wafer relative to the lamp, and can have a vacuum port or other apparatus for maintaining the wafer in position on the chuck during processing. The lamp 102 is positioned inside a processing chamber 122, which can include a window 108 to separate a lamp housing portion of the chamber from the substrate housing portion of the chamber. The window 108 can be any appropriate window, such as a dielectric window (e.g., quartz) that is transparent to the curing radiation from the lamp 102. The window may be of any appropriate dimension, so long as the window is strong enough to prevent fracture during operation and is thin enough so that substantially all of the radiation from the lamp passes through the window. The window 108, as well as any seal used between the window and the chamber walls, for example, separates the lamp 102 and reflector 104 from the substrate support 106, such that any materials outgassed from a workpiece during a cure procedure do not collect on or contaminate the lamp, reflector, or other optical components of the lamp housing portion of the processing chamber. The window also can have a shape that matches the area to be cured. For example, if the workpiece to be processed is a 300 mm semiconductor wafer, the window can be shaped to have a cylindrical cross-section (parallel to the surface of the wafer to be cured) of about 300 mm in cross section in order to expose the entire surface of the wafer to the radiation. The reflector also can ensure that the footprint of the light substantially matches this shape, so that substantially all of the light is focused for processing and does not contact the chamber walls or other components, which could undesirably heat these components. Even though the window 108 can substantially prevent any outgassed species or other contaminants or particles from entering the lamp housing portion and contaminating the lamp, the window itself is still subject to deposition, condensation, or collection of the species on the exposed surface of the window (near the workpiece). Further, other surfaces in the substrate housing portion still can be exposed to these species. In the embodiment of FIGS. 1(a) and 1(b), a pump liner 110 is provided in the substrate housing portion of the chamber for directing a laminar flow of gas across the exposed surface of a workpiece 112 on the substrate support 106. FIG. 1(b) shows components near the pump liner (shown in cross-section) in more detail that FIG. 1(a), and numbers are carried over between figures where appropriate. The liner be used to direct a flow of gas that is received from a gas source 114 and regulated by a gas flow controller 116, as known in the art. The liner 110 also can collect the flow of gas after passing across the workpiece 112 and direct the gas out of the chamber through an exhaust port 118, in order to remove any outgassed species and contaminants from the processing chamber. The flow creates a protective gas purge between the workpiece and the chamber window to protect against by-product buildup on the window. The laminar flow acts as a curtain to shield the window and also to sweep any outgassed residue away before the residue can collect on the window and surrounding chamber. The laminar flow of the protective purge gas can help to maximize uniformity of the flow and to avoid any recirculation zones. In one embodiment, the flow is from the back of the chamber to the front of the chamber in order to be parallel with the slit valve and reduce the effects of the valve on the flow pattern. The gas source 114 can be any appropriate source operable to provide a flow of an appropriate gas. A number of various gasses and gas combinations are known for use as purge gases, and can be used in such an implementation. In one embodiment, the purge gas used is primarily (or pure) argon due to the large molecular mass, which increases the momentum and energy of the gas “curtain.” In another embodiment, a combination of argon and helium was found to provide sufficient heat transfer while having sufficient mass and momentum to carry away the outgassed residue. Other suitable gases can include, for example, He, Ar, N2, O2, O3, H2, NH3, N2O, H2O (vapor), and NO. The pump liner can be any device, element, or component operable to direct a laminar flow of gas across a workpiece, such as a rectangular element directing a flow across the chamber, a pair of parallel liners, or a series of gas ports directing a series of input gas flows that combine to create a single gas flow across the wafer. Many of these designs can be problematic, however, as the gas flow patterns can be irregular, and can create turbulence or recirculation zones, such that the species are not evenly carried away, and can even be allowed to accumulate on the window or other components near these turbulent zones. For these reasons, as well as heating and other reasons discussed herein, various embodiments utilize a ring-shaped pump liner as will be discussed with respect to FIGS. 2-3. The pump liner regions shown in FIGS 1(a) and 1(b) correspond to portions of a single ring liner shown in cross-section. These liner portions also can be referred to as chamber pumping rings, providing a laminar flow of purge gas across the surface of a workpiece. The flow controller 116 and/or light source 102 can be monitored and/or controlled by a system controller 120 using control and other signals as known in the art. En one example, an intensity monitor (not shown) in the chamber can feed a monitor signal to the system controller 120, which can then display or relay this information to a user or operator via a user interface device. If the intensity is not sufficient, the system controller can generate a control signal instructing the lamp apparatus to increase the intensity used to expose the workpiece. If the system controller notices that the intensity cannot be maintained above a minimum intensity threshold, such as may be stored in a data storage device 126 for the system, then the system controller can generate an alert signal indicating that the lamp apparatus is not functioning properly, and may require maintenance such as the replacement of the bulb. The system controller can send this alert signal to an appropriate device, such as an alarm that alerts an operator of the system. In this example, the signal is sent to a user interface device 124, such as a personal computer or wireless-enabled PDA, which allows a user or operator of the system to be notified that the lamp assembly requires attention. The user interface also can allow the user or operator to observe the various monitored parameters and components of the system, and can allow the user or operator to adjust or control various settings and parameters for operation of the system as known in the art. As would be apparent to one of ordinary skill in the art, the system controller can monitor various aspects of the overall system, such as the flow rate, pressures, temperatures, gas component levels, etc., by receiving signals from the appropriate sensors, and can alert operators and/or control components to adjust parameters or perform maintenance as necessary. For example, the system controller can monitor the flow rate of gas through the pump liner, and can adjust the input flow in response thereto. Various other uses and applications of the system controller, user interface, and data storage would be apparent to one of ordinary skill in the art in light of the descriptions and suggestions contained herein. As shown in FIG. 1(b), the diameter of the dielectric window 108 can be such that radiation can reach the entire periphery of the workpiece, as well as at least an interior peripheral surface (with respect to the chamber) of a ring-shaped pump liner 110. In some embodiments, the reflector 104 alters the flood pattern of the light source 102 from a substantially rectangular area to a substantially circular shape that corresponds to the substantially circular semiconductor substrate being exposed and/or the substantially circular inner surface of the liner 110. Allowing the light to impinge on a surface of the pump liner allows the liner to be passively heated, as will be discussed in detail later herein. In some embodiments, the light source may comprise two or more individual light sources. In one such tool, first and second UV lamps generate a flood pattern for a single chamber. The UV lamps include a UV source (e.g., an elongated UV bulb) and a primary reflector, with a secondary reflector being positioned between the UV lamps and the chamber. The two UV lamps can be mounted at an angle to each other. In some embodiments the opposing angles are between 5-25 degrees relative to vertical. The inclusion of two lamps can result in a higher intensity of UV radiation being generated within the flood pattern, which in turn can result in faster curing times. A pump liner can be a single piece, or can include upper and lower liner portions that are mated together to form a single structure. For example, FIGS. 2(a) and 2(b) show top and bottom perspective views, respectively, of a lower liner portion 200, and FIGS. 3(a) and 3(b) show top and bottom perspective views, respectively, of an upper liner portion 300, in accordance with one embodiment. When mated together, the portions form a single ring-shaped structure having a pair of opposing channels 206/304, 208/306 therein. One of these channels has an inlet plenum 302, with the other having an outlet plenum 210, such that gas can be flowed into one of the channels, can exit the liner and flow across the wafer into the other channel, then be exhausted via the outlet. As shown in FIG. 2(a), an exemplary lower liner portion 200 includes a set of substantially parallel and opposing injection and receiving ports, or slits 202, which in this diagram are shown as grooves extending from one edge position of the lower liner portion to an opposing edge portion, which when the lower portion is mated with the upper portion form slits between the two portions. As shown, the upper liner 300 includes a gas input plenum 302 allowing gas to flow into the assembled liner and be directed into the first channel (formed by grooves 206 and 304) and out the slits 202 adjacent that first channel. The gas will flow across the surface of the wafer (along the direction of the arrows), just above the exposed surface of the wafer, and be received into slots 202 adjacent a second channel 208 (formed by grooves 208 and 306). The second channel includes an exhaust plenum 210 which allows the gas and any outgassed species and contaminants to be directed out of the pump liner, which can be connected through an exhaust port (such as port 118 in FIGS. 1(a) and (b)) and out of the chamber. Although this example includes an inlet plenum in one portion and the outlet plenum in the other portion, it should be understood that the plenums could be in the same portion or in the opposite liner portions, for example. As will be discussed later herein, it also can be seen that the upper and lower portions include contact members 212, 308, such as cylindrical feet or pads, that provide minimal contact between the pump liner and the surrounding chamber body. The chamber pumping liners also can have a minimum contact flange to reduce parasitic pumping away from the laminar flow path. The opposing slits 202 in the liner when assembled provide for a uniform, laminar gas purge between the wafer and the vacuum window. An example of such a flow is illustrated in the plot 400 of FIG. 4. As can be seen, the flow between the opposing slits is substantially linear and parallel. It is only areas at the edges and outside the opposing slits where a slight nonlinearity to the flow can be seen, but this non-linearity is not severe enough to negatively affect the flow. Maintaining proper slit spacing and flow rate can ensure that the flow is substantially laminar across the workpiece. Another way to minimize the occurrence of turbulence is to ensure substantially even flow rates across the wafer. Because the gas does not need to travel as far need the edges of the workpiece as near the middle, evenly sized slits can tend to cause uneven flow rates across the wafer. As such, a pump liner in accordance with various embodiments can include slits having a number, width, height, and/or spacing selected to provide a substantially even flow across the workpiece. In one example, the slit sizes at the first channel (having the inlet) are relatively small, on the order of about 0.020″, to increase the gas exit velocity and provide a uniform pressure distribution upstream of the inlet slits. The slit sizes near the second channel (having the outlet plenum) are larger (e.g., 3× to 5×) than the depth of the inlet slits in order to reduce pressure drop across the exhaust slits. The exhaust slits also can be deeper near the edge of the workpiece to increase gas flow at the sides of the workpiece (as opposed to the center). In another example, a total of six slits were used across the pump liner, varying in width from 1.0 to 2.0 inches and in height from 0.045 to 0.200 inches. The spacing between slits varied from 0.40 to 1.00 inches. The flow rate of Ar/He gas in this example was approximately 16 slm/16 slm. Further, although the slits are described to be rectangular in cross-section, it should be understood that other shapes can be used as well to help facilitate even flow across workpieces for various systems and applications. When designing the pump liner, it can be desirable to optimize various factors such as slit size and chamber pressure. For example, for a 16 slm Ar/16 slm He flow, slit sizes of 0.045 and 0.060 inches were found to have more recirculation of gas inside the wafer than slit sizes of 0.075 and 0.090 inches. Further, a chamber pressure of 3 Torr was found to have more recirculation than a chamber pressure of 6 Torr. Therefore, in this example it was found that larger slit sizes of 0.075 inches and 0.090 inches, along with a higher chamber pressure of 6 Torr, were desirable in order to minimize recirculation of gas and obtain a higher uniformity of flow. One particular contaminant of concern is porogen outgassed from a wafer during a UV curing process, which can deposit on the vacuum window. Porogen is described, for example, in U.S. Pat. Nos. 6,171,945 and 6,451,367, both of which are incorporated herein by reference. Any such buildup on the window can block the UV light from reaching the wafer, resulting in a continual degradation of the source efficiency. The gas purge created by the slits in the chamber pumping liner can effectively shield the window from the outgassed material, and can carry the material out of the chamber before the material can collect on the window. In order to optimize the removal of such outgassed materials, the gas flow can be maintained relatively close to the surface of the wafer. In one embodiment, the gas flow was kept at less than about 0.150″ above the surface of the wafer, although any separation in a range of from about 0.0 to about 1.00 inches would be acceptable in such an application. Other ranges may be utilized as appropriate for the system and/or application. Keeping the flow close to the wafer can help to minimize the gas volume needs to be swept away, and can help to raise the temperature. Also, the velocity increases at a constant pressure with a smaller volume, and the increased momentum of the purge gas helps to remove the outgassed species. Outgassed porogen also can collect in other areas of the chamber, resulting in particle generation and eventual contamination of the substrate. Since the gas flows between the inlet and outlet channels of the pump liner, the majority of such buildup can occur near the receiving slits of the liner. One way to reduce the amount of buildup on the liner is to raise and maintain the temperature of the liner so that the contaminants are less likely to adhere to, or condense on, the surface of the liner. Further, a heated liner can be more easily cleaned during a cleaning process. In one example, ozone is used as the cleaning agent for a post-cure clean so that it is not necessary to interrupt the vacuum integrity of the chamber. The ozone can be activated through the build-up or application of heat to dissociate and bond with the organic buildup. In one application, the ozone reacts with carbon based buildup and is subsequently pumped out of the chamber. It then can be desired to maintain the temperature of the liner is in the temperature range needed to activate the ozone reaction as evidenced by ozone etch rate data, such as a temperature range of 120 to 200° C. In one embodiment, the temperature range across a liner varied from about 120° C. to about 75° C. Thermal modeling of a design can be used to assist in selecting the position, shapes, and sizes of the slits, for example, in order to improve the MWBC of the system. In one embodiment, a liner temperature of at least 120° C. was found to be sufficient for a CIP aluminum liner, in a chamber where the liner otherwise remains between about 60° C. and 70° C. during processing (as measured near the exhaust and pumping port). The efficiency of the ozone clean is drastically increased at these temperatures, such that wet cleaning of the chamber is significantly delayed. In one example, the wet cleaning interval was increased from every 200 wafers to every 2000 wafers. In another example, the residue found on a liner after 100 wafers was substantially eliminated. In one embodiment the window was heated via application of heat from a heating element. Appropriate heating elements and methods for heating a window or other such element are known in the art and will not be discussed herein in detail. Heating the window can increase the cleaning interval up to after about every 10,000 wafers in one example. The additional cost and complexity to sufficiently heat the window while maintaining optimal processing conditions, however, may not be acceptable for all applications or manufacturers. In one embodiment, the temperature of the liner is raised via passive heating. The liner can receive heat energy from the cure light source, as well as the gas passing over the wafer being cured. While much of the heat energy will come from convection, the additional heat energy from the UV radiation can help increase the temperature of the liner during processing. In order to further improve the heating of the liner, the physical design of the liner and/or the chamber can be modified. In a first example, the amount of the liner coming into contact with the chamber body can be minimized. As shown in FIG. 2(b), for example, the lower liner portion 200 can include at least three contact members 216 configured to contact the chamber body and support the liner portions. By utilizing small contact members instead of allowing a large region of the liner to contact the chamber body, the conduction path to the surrounding chamber body is minimized such that the conductive heat loss to the surrounding environment can be significantly reduced. It should be understood that such contact portions could alternatively, or additionally, be placed on the chamber body or between the chamber and the liner. Other contact members can be used between the liner and chamber body as well, such as a metal ring or other such body as would be apparent to one of ordinary skill in the art in light of the teachings contained herein. In another example, at least a portion of the exterior surface of a chamber pumping liner can be anodized or otherwise coated or treated to drastically increase the emissivity of the external surface, thereby allowing for increased radiation heat transfer from already existing power sources, such as a ceramic heater and/or UV lamp. In one embodiment, an anodized pumping liner has an emissivity in the range of 0.9 versus that of 0.3 for polished aluminum. The increased emissivity of the aluminum allows the liner to capture radiant energy from existing energy sources, such as a ceramic heater or a UV lamp source. While an aluminum liner, for example, might reflect up to 70% of the light radiation from the light source, an anodized liner can absorb approximately 85-90% of the light energy, allowing for a significant increase in heating of the liner due to the light energy. The thickness of the anodized layer can be minimized, to be on the order of about 0.001 to 0.003 inches, for example, to increase the thermal conduction from the external anodized layer to the rest of the aluminum liner. The liner can be anodized using any appropriate anodizing process known or used in the art. In one example, the aluminum is cleaned by etching or use of a solvent, then placed in a solution such as a sulfuric or oxalic acid solution wherein the application of current causes a thick oxide layer (on the order of about 0.002 inches) to form on the liner, which has a consistency and thickness much greater than would be formed without the anodizing process. In still another example, the dielectric window between the lamp and the substrate support can be expanded in width/diameter so that light from the light source can impinge directly onto at least a portion of the liner. This provides additional heat energy to the liner, without the need for any components not already involved in the process. This wider window can be particularly effective when used with an anodized liner that is able to absorb a majority of the impinging light energy. In an exemplary system, the diameter of the dielectric window was increased from 13.25 to 14.75 inches, where the process chamber is designed to cure wafers having a diameter of 12.0 inches. This increased the heating of the liner by allowing more IR from UV curing source to reach the pumping liner. The inner diameter of the pumping liner can be selected such that the main gas flow volume is between the window on top, the wafer heater (and thus the wafer) on the bottom, and within the inner diameter of the pumping ring. Other areas of the chamber are effectively dead volumes where materials such as porogen cannot significantly condense before being pumped out. FIG. 5 shows a plot 500 of data for wafer performance (6×) with 502 and without 504 a laminar purge flow in accordance with one embodiment of the present invention. As can be seen, the process using a laminar flow of gas 502, such as may be introduced using a pump liner as described herein, showed acceptable shrinkage amounts through over 70 wafers. The process without the laminar flow showed a significant variation in shrinkage by about the tenth wafer, and substantial variation by about the 30th wafer. FIG. 6 illustrates steps of a method 600 for processing a workpiece in accordance with one embodiment of the present invention. This method will be described with respect to a UV curing process, although it should be understood that such a process is merely exemplary and steps similar to those recited in this method can be used with other such processes as would be apparent to one of ordinary skill in the art in light of the teachings and suggestions contained herein. In this method, a pump liner is positioned near a wafer support in a processing chamber 602. The pump liner can have a gas inlet plenum for receiving a source of purge gas, an exhaust plenum for exhausting the purge gas, and at least one pair of slits or other gas ports for directing a flow of purge gas across the surface of a workpiece. The pump liner also can be designed to have minimal contact with the chamber body in order to minimize the flow of heat from the liner. The pump liner also can be anodized or otherwise coated or processed in order to increase the temperature of the liner during processing of a workpiece. A workpiece to be processed is placed in the chamber 604. In this example, a semiconductor wafer is placed in a UV curing chamber. The pump liner, in this example a ring-shaped liner, is positioned about a periphery of a wafer. A source of purge gas then is directed to a pumping port of the liner in order to direct a flow of purge gas into a channel of the liner 606. The source of purge gas can be selected such that the flow of purge gas across the wafer has sufficient mass and/or momentum to carry away any species or contaminants outgassed from the wafer during curing. The radiation source, such as a UV lamp, can be activated in order to direct radiation onto the wafer for curing 608. The radiation source also can be positioned to direct radiation to at least a portion of the pump liner, in order to further heat the liner during the curing process. During curing of the wafer, a flow of purge gas can be directed across, and a small distance from, the surface of the wafer being cured 610. The pump liner can be designed such that the flow exits the liner from a series of slits or other injection ports that are positioned, shaped, and sized to provide a substantially even flow across the surface of the wafer with minimal turbulence in the flow. After the purge gas has flowed across the surface of the wafer, and collected any species outgassed from the wafer, the contaminated purge gas can be directed back into the pump liner through a plurality of receiving ports 612. These ports, or slits, can again be designed to allow for a substantially even flow across the wafer surface, and to provide for a minimal amount of turbulence near the receiving slits of the liner. The contaminated flow of purge gas can be exhausted from the liner via at least one exhaust plenum, and directed out of the system 614. The wafer then is removed from the system at the end of the curing process 616. If there are additional wafers to process 618, then another wafer is placed in the chamber. If not, then the process can end 620. In one embodiment, the contaminated gas is collected from the exhaust port of the liner and passed through at least one particulate filter than can remove substantially all of the outgassed species in the contaminate flow of purge gas. This filtered flow then can be directed back through the pump liner and across the wafer, reducing the amount of source gas used and reducing the exhaust requirements for the facility. The recirculation of gas can reduce operating costs, but can reduce MWBC in some embodiments as there can be some level of contaminants in the re-circulated purge gas that can collect on the pump liner. Although passive heating of the pumping liner can be an effective an relatively cost effective approach, there still is some time required near startup of the processing chamber before the liner reaches the desired temperature. As shown in FIG. 5, even processing of a few wafers can significantly impact performance. As such, certain embodiments incorporate a heater, either in the pumping liner or in thermal connection with the liner (e.g., on the liner), in order to pre-heat the liner to the desired temperature before the first wafer is processed, in order to further prevent the condensation of materials such as porogen on the liner. After reading the above description, other recipes that use center-fast deposition will occur to those of ordinary skill in the art. Other variations will also be apparent without departing from the spirit of the invention. These equivalents and alternatives are intended to be included within the scope of the present invention. Therefore, the scope of this invention should not be limited to the embodiments described, but should instead be defined by the following claims. |
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abstract | Disclosed are methods, apparatus, systems, processes and other inventions relating to: ion sources with controlled electro-pneumatic superposition, ion source synchronized to RF multipole, ion source with charge injection, optimized control in active feedback system, radiation supported charge-injection liquid spray, ion source with controlled liquid injection as well as various embodiments and combinations of each of the foregoing. |
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abstract | To provide an ion implantation device capable of correcting the temperature of the wafer. The ion implantation device of the present invention has: an irradiation means that radiates ions; a retention means that includes a disk 112 that retains at least one wafer W; a thermopile 122 that detects, in a noncontact manner, temperature information for a wafer W retained on disk 112; a cooling medium supply unit that enables heat exchange for a wafer W retained on disk 112; and a control unit that calculates the surface temperature of a wafer W retained on disk 112 based on the temperature information detected by thermopile 122 and that determines whether the calculated surface temperature for the wafer is within a permissible temperature range. |
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048448605 | claims | 1. In a fuel element support grid for supporting a plurality of nuclear fuel elements intermediate their ends in spaced relation for fluid flow therebetween, said grid including a polygonal perimeter and a plurality of fuel element compartments defined by pairs of first and second intersecting and slottedly interlocked wavy grid-forming strips attached to said perimeter and to each other, the improvement comprising: at least some of said compartments defined by pairs of first and second intersecting and slottedly interlocked strips, and some of said pairs of first and second strips including a pair of perimeter edge to perimeter edge matingly intersecting smoothly contoured integral fluid flow directing vane portions curving from the planes of their respective strip portions along at least one adjacent edge of each of the strips of the pair and said strips having bends at at least some intermediate points between strip intersections. 2. The fuel element support grid of claim 1 which includes means for attaching said pair of vane portions to each other, thereby attaching said first and second intersecting and slottedly interlocked strips of said pair of strips together. 3. The fuel element support grid of claim 1 in which the means for attaching said pair of vane portions to each other is a fusion bond. 4. The fuel element support grid of claim 3 in which the fusion bond is a weld. 5. The fuel element support grid of claim 1 in which all of the integral fluid flow directing vanes are on the downstream edges of the strips relative to the direction of fluid flow between the fuel elements. 6. The fuel element support grid of claim 2 in which the means for attaching said pair of vane portions to each other includes welds at the intersections of the edges of a plurality of pairs of the integral fluid flow directing vane portions remote from the areas of integral attachment of the vane portions to their respective strips. 7. The fuel element support grid of claim 2 in which the means for attaching said pair of vane portions to each other includes welds at the intersections of the edges of a plurality of pairs of the integral fluid flow directing vane portions adjacent to the areas of integral attachment of the vanes to their respective strips. 8. The fuel element support grid of claim 2 in which the means for attaching said pair of vane portions to each other includes welds at the intersections of the edges of a plurality of pairs of the integral fluid flow directing vane portions both remote from and adjacent to the areas of integral attachment of the vane portions to their respective strips. 9. The fuel element support grid of claim 2 in which the bends act as integral fuel arches within the profile of the wavy strip. 10. The fuel element support grid of claim 1 in which said bends include means for contacting a fuel element, said means lying within the profile of the strip presented to the flow of fluid through the grid. |
claims | 1. A system for patterning an object, comprising:a radiation source including a plurality of selectively addressable pn-junction elements, the radiation source generating patterned radiation through selective addressing of the plurality of selectively addressable pn-junction elements; anda projection system that projects the patterned radiation generated by the radiation source onto a target portion of the object. 2. The system of claim 1, wherein each of the pn-junction elements is doped with impurities to increase emission of radiation at a desired frequency. 3. The system of claim 1, wherein each of the pn-junction elements is covered by a layer of transparent oxide. 4. The system of claim 1, further comprising:a voltage source that provides a potential difference of at least about 4V to reverse bias selectively addressed ones of the pn-junction elements. 5. The system of claim 1, further comprising:a voltage source that provides a potential difference of about 5V to reverse bias selectively addresses ones of the pn-junction elements. 6. The system of claim 1, further comprising:a filter that selects a desired range of wavelengths from the radiation emitted by selectively addresses ones of the pn-junction elements. 7. A method used to pattern an object, comprising:selectively addressing an array of pn-junction elements to form a patterned beam of radiation; andprojecting the patterned beam of radiation onto a target portion of the object. 8. The method of claim 7, further comprising:doping the pn-junction elements with impurities to increase emission of radiation at a desired frequency. 9. The method of claim 7, further comprising:covering the pn-junction elements with layer of transparent oxide. 10. The method of claim 7, further comprising:providing a potential difference of at least about 4V to reverse bias the selectively addresses ones of the pn-junction elements. 11. The method of claim 7, further comprising:providing a potential difference of about 5V to reverse bias the selectively addresses ones of the pn-junction elements. 12. The method of claim 7, further comprising:filtering a desired range of wavelengths from the radiation emitted by the selectively addressed pn-junction elements. |
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044787847 | description | DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, a reactor 10 is illustrated schematically, it being housed within a larger containment building (not shown). The reactor 10 itself has an open top vessel or tank 12 which is enclosed on its sides and bottom within a guard vessel or tank 14 and shielding such as concrete walls 16. Preferably the cavity 17 located between the reactor vessel 12 and guard vessel 14 is sealed and filled with an inert gas, such as argon or helium, which could be monitored for leakage from reactor vessel 12. A deck 18 closes the vessel 12 at its open top and seals 19 maintain the vessel pressure-tight. Located within the vessel is a reactor core 20 surrounded by a radiation shield 21. The core can take any known form but generally would include a plurality of vertical passages (not shown) within which appropriate quantities of fuel and blanket materials are located. Upper internal structure 22 is located above the core and has sensors (not shown) to detect parameters of interest, such as the temperature of the primary coolant, and leads from the sensors are directed to monitor equipment (not shown) outside of the reactor vessel. The structure 22 also includes control linkages or mechanisms (not shown) for regulating the reactor power within the core. All of this internal structure 22 is suspended from the deck, and lines up vertically with the reactor core. One conventional means for supporting and aligning these components relative to the reactor core provides for three rotatable plugs of different sizes, the largest plug 24 being rotatable within the deck concentrically of the core, the intermediate plug 25 being rotatable within the largest plug 24 offset from its center, and the smallest plug 26 being rotatable in the intermediate plug 25 again offset from its center. Fuel loading and unloading mechanism (not shown) is carried by the smallest plug 26 as at circle 27 offset from its center so that rotation of the three plugs according to predetermined orientations can move it into precise vertical alignment over any of the reactor passages for loading and unloading and/or manipulation of the fuel relative to that passage. The reaction of the fuel generates heat, and the core 20 is cooled by a circulating primary coolant, typically molten sodium, which substantially fills the tank 12. Specifically, the primary coolant is circulated from a "cold pool" 28 within the vessel through pump 29 and line 30 upwardly through the core 20 to a "hot pool" 32 confined within irregularly shaped continuous wall structure 33 to inlet into one side of a primary heat exchanger 35. The primary coolant then flows through the heat exchanger back to the cold pool 28. Sliding seals 36 are located between the wall structure 33 and the heat exchanger 35 to separate the hot pool 32 from the cold pool 28 while yet allowing some thermal movement of the structural components. An intermediate coolant is circulated through the other side of the primary heat exchanger 35 (in heat conductive but fluid isolated relation relative to the primary coolant) via inlet and outlet lines 36 and 37 and a closed intermediate cooling loop (not shown) including a pump and an intermediate heat exchanger located outside the reactor vessel 12. The intermediate coolant would preferably be molten sodium also. A secondary coolant, generally water, would be circulated through the secondary heat exchanger (in heat conductive but fluid isolated relation relative to the intermediate coolant) in a closed secondary steamwater cooling loop with a power turbine (not shown) forming part of a conventional electrical power generating system. The secondary coolant is thereby essentially free of radioactive contaminants to minimize the risk of radioactive spill should any of the secondary coolant components in the steam-water loop fail and leakage occur. While reference has been made to the primary heat exchanger and other related cooling components only in the singular, most typically there would be several such primary heat exchangers and pumps, etc. located in the reactor vessel which would define parallel coolant loops to the steam utilizing turbine. Construction details need not be given since they form no part of the subject invention and are of conventional well known means. As noted above the deck 18 spans the open top of the vessel 12 and is structural in nature in that it suspends from it various reactor components including the primary coolant pumps 29 and heat exchangers 35, the rotary plugs 24, 25, 26 and the upper internal structure 22. The reactor vessel 12 can be in excess of 75 feet across its open top and the deck 18 is of corresponding size. It is yet desirable to form the deck 18 from conventional materials that are reasonably economical and easy to fabricate, while yet satisfying safety and structural requirements including thermal deflections and alignment requirements. The deck 18 (see FIGS. 2 and 3) typically has spaced upper and lower main horizontal plates 40a and 40b, flange plate 41, vertical plates 42a, 42b, etc., 43a, 43b, etc., and 45a, 45b, etc., and webs 46a, 46b, etc. In a preferred embodiment, the deck plates or webs are formed of structural plate material, such as steel, and are welded or otherwise secured relative to one another across continuous leak-proof seams so as to define a hollow but otherwise sealed unitary deck structure. With the main plates 40a and 40b and the vertical cylindrically shaped plates 45a and 45b welded together, the physical component like the heat exchangers 35 or pumps 29 can extend through and be supported by the deck. Reinforcing webs 46a and 46b can be welded in place at specific locations as needed. Thermal insulating barriers 47 of steel meshing and steel sheeting moreover are supported by walls 43a and 43b proximate the underside of the lower deck plate 40b, and radioactivity shielding 48b of ironized concrete is carried by the deck proximate the upper side of the lower deck plate. The deck 18 is exposed on its underside to the various "hot" and "cold" pools of primary coolant confined within the vessel 12. For example, the "cold" pool would typically be at temperatures in excess of 500.degree. F. and possibly up to 700.degree. F.; whereas the hot pool would typically be at temperatures in excess of 800.degree. F. and possibly up to 1000.degree. F. The upper deck plate 40a would typically be exposed to ambient air, possibly at 65.degree.-85.degree. F., in the confinement building. A preferred design for the deck structure provides that the lower deck plate 40b would be operated at temperatures less than 250.degree. F. and preferably even as low as 150.degree. F., while the upper deck plate 40a would be operated at temperatures less than 150.degree. F. and possibly even as low as 100.degree. F. This design temperature differential of 50.degree. to 150.degree. F. between the upper and lower deck plates, after once established, would thereafter have to be maintained. Otherwise, temperature differences exceeding this could cause thermal deflections which could be magnified between the components supported from the deck to create misalignment of these components, disruption of the seals between the components, or other problems. A conventional concept for cooling the deck structure has been by circulating a coolant, such as air, nitrogen, or water, within or through the deck structure. The deck would thus have many crosswise or radial passages 49 located immediately adjacent the lower deck plate and vertical passages 50 extended between and connecting these passages as coolant loops. For forced coolant circulation within the deck structure, a motor driver blower 51 is provided. The forced coolant circulation easily maintains the design temperature differential between the upper and lower deck plates. However, should the blower power source, viz., the conventional AC electrical power, standby power, or battery power be discontinued, the forced coolant circulation through the passages would cease and the design temperature differential between the upper and lower deck walls would be exceeded. Convective cooling is a possible "passive" system for use in emergency conditions, "passive" meaning that no input power is required to operate the system. The convective cooling system typically would use air as a cooling means and would have inlet and outlet passages (not shown) through the concrete barrier (with angled bends to eliminate radiation streaming from the reactor). However, convective cooling is not an attractive alternative by itself as it has low capacity and moreover requires that the deck structure be open to the atmosphere, and not sealed. This invention teaches an improved "passive" cooling means for maintaining the upper and lower deck plates within design temperature differences. The cooling means could act along or in parallel with conventional forced coolant circulating means; however, the disclosed cooling means can be designed to have adequate cooling capacity to meet most operating conditions. The subject invention thus provides thermal stability for the deck and positional stability of any reactor components carried by the deck. The invention utilizes a plurality of heat pipes 52a, 52b, 52c, etc., each of which has a vaporizing section 54 located to receive heat from the lower deck wall 40b, a primary condensing section 56 located to dissipate heat to the upper deck plate 40a, and a secondary condensing section 58 located beyond the upper deck plate and outside of the deck 18 itself to dissipate heat to the atmospheric air in the containment building. The secondary cooling section 58 could be made to be effective in only off-normal or emergency operating conditions, as will be disclosed. Each heat pipe 52 consists of a housing 60 of stainless steel, for example, having a coolant sealed therein. The coolant would be selected to vaporize at the input temperatures of the vaporizing section 54 and would condense at the output temperatures of the condensing sections 56 and 58. A coolant in the form of water or alcohol could be used for the range of operating temperature under consideration. A wick 62 would cover the inner walls of the housing 60, the wick being preferably formed of a meshed network of stainless steel having many very small pores or openings of the order of 100-150 mesh. Heat added to the heat pipe vaporizing section 54 would vaporize the liquid coolant therein which vapor would then flow axially along the center space toward the primary and secondary condensing sections 56 and 58 respectively. The primary condensing section 56, in heat dissipating relation to the upper deck wall 40, normally would condense the coolant vapors onto the wick 62. The coolant then would migrate by capillary action, and also gravity, depending on its orientation along the wick 62 from the condensing section 56 to the vaporizing section 54. The heat pipe 52 would be designed to operate within the input and output range of temperatures so that coolant condensate will always move via the wick 62 to the vaporizing section 54, and coolant vapor would move interiorally of the housing 60 to the condensing section 56 or 58; and under stabilized operating conditions, this coolant circulation would be continuous. Because vaporization and condensation are each involved in the action of the coolant in the pipe, the heat transferring capacity of the heat pipe 52 is very large, possibly 50-500 times greater than a solid copper pipe for example. However, the heat pipe 52 is yet entirely passive and requires no input electrical power. The secondary condensing section 58 is located outside of the deck 18 in the building atmosphere. However, it is housed within a small enclosure 64 having open sides, and damper doors 66 would normally close the open sides of the enclosure to isolate the condensing section from the air of the containment building. However, when the damper doors 66 are opened, air flow through the enclosure 64 is possible over the secondary condensation section 58. Fins 68 can be on the secondary condensing section 58 to provide good heat transfer with the ambient air. Each damper door 66 can be shifted between its closed and opened positions by means of a bimetal activator 70, which in a preferred embodiment would be exposed to the upper deck plate 40a to be responsive to the temperature of the deck plate. Under normal reactor operation, the temperature differential between the vaporizing section 54 and primary condensing section 56 of the heat pipe would be designed to be of the order of 50.degree.-150.degree. F. and the heat transferring capacities of the heat pipes could be sufficient to maintain the deck plates within this specified temperature differential. However, if the heat pipes are to be used only as a redundant or parallel system with the forced coolant circulation in the deck structure, the design capacity could be less. The anticipated heat withdrawn by the heat pipe system under normal reactor operation could typically only comprise 10-25% of the total deck cooling, and the forced coolant circulation would provide the balance. Upon a breakdown of the normal forced coolant circulation system, such as during a power failure, the design temperature differential between the upper and lower deck plates would be exceeded. This increase in the temperature of the deck would be sensed by the bimetal activator 70 to open the damper doors 66 to expose the secondary condensing section fins 68 to the air within the containment building. The building would be conditioned, so that the air temperature would be controlled and similar to normal atmospheric temperature of 65.degree.-85.degree. F. The secondary condensing section 58 greatly increases the cooling capacity of the heat pipe 52, although this extra capacity is used primarily for emergency only. Nonetheless, it might be possible to design the heat pipe system with sufficient overall capacity to act as the sole heat dissipating means for cooling the lower deck plate 40b and without any forced coolant circulating means in the deck. However, when acting as either the sole or as the redundant cooling means, the secondary condensing sections 58 of the heat pipes preferably would be isolated and inactive. Thus, the enclosures surround the heat pipes, and with the damper doors 66 closed during normal reactor operation, even though coolant vapor can pass into the secondary condensing section 58, little vapor condensation will take place with the doors closed as there is little or no air circulation to carry the heat away. However, the dissipating capacity of the heat pipes through the primary condensing sections and the upper deck plate 40a will be sufficient to maintain the operating temperatures balanced. It would be possible to modify each heat pipe somewhat by interposing thermally controlled valve means internally of the pipe housing at a location between the primary and secondary condensing sections. At normal operating temperatures, the valve means will be closed to isolate the secondary condensing section from the primary condensing section; whereas at elevated "emergency" temperatures, the valve means would be opened to allow coolant circulation to the secondary condensing section. Each heat pipe 52 further is designated to be removed periodically for inspection and/or maintenance, particularly as regards the integrity of the pressure confinement housing 60. Thus, separate heat conductive clamping sleeves 74 and 76 would fit over the respective vaporizing and primary condensing sections 54 and 56 of the heat pipe and would be secured also the the lower deck plate 40b and the upper deck plate 40a. This not only establishes good heat conductivity between the deck plates 40a and 40b and the heat pipe itself but also allows for the ready removal of the heat pipe. Generally, each sleeve 74, 76, preferably would extend one and possibly two feet axially along the heat pipe 52. A heat pipe 52 with a diameter of approximately an inch, for example, containing water at pressures of approximately 3 psia and working at a temperature of 140.degree. F. would have approximately one kilowatt of heat removing capacity. For a nuclear reactor having a diameter of 70 ft., for example, one hundred such heat pipes 52a, 52b, etc., distributed around the deck 18 would provide approximately 100 kilowatts of cooling capacity. The subject heat pipe cooling system can be used with minimal interferences with and/or without special designs of other components that would extend through or be part of the deck 18. This differs substantially from the typical forced coolant circulating system which requires many special interior and exterior ducts, exterior heat exchangers, as well as powered blowers. It thus might be possible to utilize the heat pipe cooling system on existing reactors as retrofit modification of the reactor cooling systems. Moreover, since each heat pipe wick 62 operates on a capillary principle, the heat pipe 52 need not be oriented vertically, but could run at an angle or even horizontally. The disclosed heat pipe cooling means can be used to cool reactor components other than the deck configuration as illustrated. For example, the heat pipe vaporizing section can be secured in heat transfer relation relative with the guard vessel 14 or to the cavity 17 between the reactor vessel 12 and the guard vessel. The condensing section can be exposed to a heat sink outside of and isolated from the vessel. A control including a temperature responsive mechanism, for example, could be used to regulate the cooling effectiveness of the heat pipe. Under normal operating reactor conditions and temperatures, little cooling would take place via the heat pipe; but above normal reactor temperatures would make the heat pipe more operative in the effort to remove such excess heat; thereby tending to avoid the adverse consequences of abnormal reactor temperatures and/or malfunctioning conditions. The heat pipe cooling means further could be designed with secondary condensing section, much like that illustrated in FIGS. 4 and 5, exposed to the same heat sink or a secondary heat sink only upon overheat situations. This would provide a redundant emergency reactor cooling system, operable passively and without the need for any secondary power. Accordingly, the invention is to be limited in scope only by the appended claims, and not by the actual specific disclosure illustrated. |
054811171 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a side view of a nuclear fuel assembly 2. The exemplary VVER 1000 nuclear fuel assembly 2 is manufactured by Westinghouse Electric Corporation which is the assignee of the present invention. The fuel assembly 2 includes a top nozzle 4, a hexagonal array of a plurality of fuel rods 6 and a bottom nozzle 8. The top nozzle 4, the fuel rods 6 and the bottom nozzle 8 are positioned about a central longitudinal axis 9 of the fuel assembly 2. The top nozzle 4 includes a cylindrical outer barrel 10 having a top end 11 and two lifting lugs 13 (only one is shown), a cylindrical inner barrel 12 which telescopes into the outer barrel 10, and a shoulder 14 between the outer barrel 10 and the inner barrel 12. The fuel rods 6 are held in the hexagonal array by a plurality of hexagonal grids 16 spaced longitudinally along the fuel rods 6. The exemplary fuel assembly 2 includes nine hexagonal grids 16 (i.e., GRID 1-GRID 9). Each of the grids 16 has six sides A-D and E-F (shown in FIG. 5 A ). The bottom nozzle 8 includes a longitudinally extending recess 18 (shown in shadow) formed by a hexagonal barrel 20, a spherical taper 22, and a cylindrical barrel 24 which has a diameter smaller than the hexagonal barrel 20. Disposed on the cylindrical barrel 24 are two alignment pins 25 (only one is shown). The spherical taper 22 interconnects the hexagonal barrel 20 and the cylindrical barrel 24 which forms a bottom end 26 of the fuel assembly 2. The longitudinally extending recess 18 tapers toward the bottom end 26 and, also, forms an internal shoulder between the hexagonal barrel 20 and the bottom end 26. Referring to FIGS. 2A-2B, a plan view of a shipping container 28 is illustrated. The exemplary. MCC-5 shipping container 28, which houses two of the fuel assemblies 2 (not shown) of FIG. 1, is described in certificate of compliance No.9239, Docket 71-9239, U.S. Nuclear Regulatory Commission, Division of Fuel Cycle and Material Safety, Office of Nuclear Material Safety and Safeguards, Washington, D.C. 20555, which is incorporated herein by reference. As illustrated by FIG. 11, the container 28 includes an outer housing 30 having a cover 31 (shown in shadow) and an inner support frame 32 which is attached within the housing 30. The support frame 32 is interconnected with the housing 30 by a shock mounting frame 34 and a plurality of shock mountings 36. The support frame 32 has a vertically extending surface 38 and two horizontal surfaces 40, which are perpendicular to the vertical surface 38, for separating and supporting, respectively, two of the fuel assemblies 2 (not shown) of FIG. 1. As will be explained in greater detail below, the support frame 32 supports the top nozzle 4, the hexagonal grids 16, and the bottom nozzle 8 of the fuel assembly 2 of FIG. 1. Also, each side of the vertical surface 38 of the support frame 32 abuts one of the sides (i.e., side A or side D) of the grids 16 of the two fuel assemblies 2. Referring to FIGS. 1 and 2A-2B, the following describes a first support apparatus 42 for one fuel assembly 2, it being understood that a second support apparatus 44, which supports another fuel assembly 2, is generally identical to the first support apparatus 42. The exemplary first support apparatus 42 includes a top nozzle holder 46 having an end holder 48 and an intermediate support or shoulder holder 50. The end holder 48 abuts a top support 51 which is fixedly mounted on the horizontal surface 40. The end holder 48 is secured to the horizontal surface 40 by a clamping frame assembly 52. Similarly, the shoulder holder 50 is secured to the horizontal surface 40 by a clamping frame assembly 54. The end holder 48 holds and encloses the top end 11 of the top nozzle 4. The shoulder holder 50 holds the shoulder 14 of the top nozzle 4. The first support apparatus 42 further includes nine grid supports 56 for supporting the hexagonal array of the nine hexagonal grids 16 (i.e., GRID 1-GRID 9). The grid supports 56 are mounted to the horizontal surface 40. The first support apparatus 42 also includes nine clamping frame assemblies 58 for clamping the hexagonal array at the nine hexagonal grids 16. Each of the nine clamping frame assemblies 58 clamps a corresponding one of the nine grids 16 to a corresponding one of the nine grid supports 56. Located between adjacent ones of the nine grid supports 56 and the corresponding nine clamping frame assemblies 58 are eight guide plates 60 for guiding the insertion of the fuel assembly 2 into the container 28 and between adjacent ones of the grid supports 56. Two additional guide plates 62,64 are located between the shoulder holder 50 and one grid support 56 (see FIG. 2A) at one end of the container 28, and between another grid support 56 and a bottom nozzle holder 66 (see FIG. 2B), respectively, at the other end of the container 28. The bottom nozzle holder 66, which holds the bottom nozzle 8 of the fuel assembly 2, is secured to an end support 68 which is fixedly mounted to the horizontal surface 40. The bottom nozzle holder 66 includes a recess holder 70 for holding the bottom nozzle 8 within the longitudinally extending recess 18. The bottom nozzle holder 66 further includes a spacer 72. The spacer 72 has a hole 74 (shown in shadow) for inserting the cylindrical barrel 24 therein and a tapered surface 76 for abutting the spherical taper 22 in order to space the bottom end 26 of the fuel assembly 2 from the end support 68. FIG. 3 is an isometric view of the end holder or top nozzle support 48 for holding and supporting the top end 11 of the top nozzle 4 of FIG. 1. The top nozzle support 48 includes a pentagonal spacer member 80, a resilient spacer 82 (partially shown in shadow) and a support member 84 having a support ring 85 welded thereto. As shown in FIG. 2A, the top nozzle support 48 is secured to the horizontal surface 40 of the support frame 32 of FIG. 11 by the clamping frame assembly 52 which clamps two sides 86,88 of the spacer member 80. Also, two other sides 90,92 of the spacer member 80 abut the surfaces 38,40, respectively, of the support frame 32. A fifth side 93 of the spacer member 80 is unsupported. Continuing to refer to FIG. 3, two internal dowels 94 (shown in shadow) appropriately align the spacer member 80 and the support member 84. These members 80,84 are attached by a plurality of bolts 96 and washers 98. The exemplary resilient spacer 82 (e.g., a MIL-C-6183A, type II, class 2, grade B cork cushion or equivalent) is adhesively attached to the top of the support member 84 within the support ring 85. The support ring 85 has two relief slots 99 for the lifting lugs 13 of the top nozzle 4 of FIG. 1. The support ring 85 forms a surface 100, which is supported by the support member 84 and the spacer member 80, for holding the top end 11 of the top nozzle 4 therein. The resilient spacer 82 separates the support member 84 from the top end 11. The spacer member 80 provides dimensional compatibility with the top support 51 of FIG. 2A and, furthermore, axially supports the relatively heavy, 70-pound, exemplary top nozzle 4 of FIG. 1. In this manner, any transportation induced damage to the guide thimble tubes 101 (one is shown in FIG. 4B) of the top nozzle 4 is precluded. Referring to FIG. 4A, an exploded isometric view of a resilient split ring 102 as used with a resilient split support 104 is illustrated. As shown in FIG. 4B, the shoulder holder 50, which includes the split ring 102 and the split support 104, holds and supports the cylindrical inner barrel 12 of the top nozzle 4 on the horizontal surface 40. The exemplary split ring 102 and the exemplary split support 104 are formed from cast polyurethane. The small radial clearance 106 between the inner barrel 12 and the outer barrel 10 facilitates pre-load of the top nozzle hold-down springs 108 during assembly and operation of the fuel assembly 2. During normal transportation in the container 28 of FIGS. 2A-2B, the inner barrel 12 may vibrate. This vibration may be detrimental to the guide thimble tubes 101 of the top nozzle 4. Continuing to refer to FIG. 4A, the split ring 102 has a gap 110 which facilitates positioning of the split ring 102 around the inner barrel 12. The split support 104 has a bore 112 running therethrough, a gap 114, and a counter-bore 116 for encasing the split ring 102 therein adjacent a shoulder 118 of the top nozzle 4. The exemplary gaps 110,114 each have an opening of about 0.180 inch. The split ring 102 and the split support 104 are installed around the top nozzle 4 when the container 28 of FIGS. 2A-2B is in an upright position. The split ring 102 is first installed over the outer barrel 10 and, then, is positioned around the inner barrel 12. Next, the split support 104 is slid down over the outer barrel 10 in order to encase the split ring 102 in the counter-bore 116 adjacent the shoulder 118. The gap 114 of the split support 104 of the first support apparatus 42 is positioned toward the upper side of the container 28 of FIG. 2A. The corresponding gap of the split support (not shown) for the second support apparatus 44, which is located between the surfaces 90A,93A, is positioned toward the lower side of the container 28 of FIG. 2A. As will be discussed in greater detail with FIG. 6A below, the clamping frame assembly 54 tends to close the gap 114 of the split support 104. In turn, the gap 110 of the split ring 102 also closes. As this gap 110 is closed, the split support 104 becomes tight around both the outer barrel 10 and the split ring 102 and, hence, the inner barrel 12 is secured from vibration during normal transportation. In this manner, the shoulder holder 50 precludes damage to the guide thimble tubes 101. FIG. 5A is a vertical sectional view of the shipping container 28 of FIGS. 2A-2B including one of the grid supports 56. Each of the grid supports 56 includes supports 120 and 122 for supporting the second side B and the third side C, respectively, of the hexagonal grid 16 (shown in shadow). The grid support 56 also has a base plate 124 for fixedly supporting the supports 120,122 thereto, a bearing pad 126 for slidably supporting the base plate 124, and a plurality of shoulder screws 128. As will be discussed in greater detail below with FIG. 5D, the shoulder screws 128 facilitate and limit a sliding motion of the base plate 124 on the bearing pad 126. The beating pad 126 is attached to the horizontal surface 40 by a plurality of flat screws 130 as shown in FIG. 5C. Attached below the horizontal surface 40 is a neutron absorber plate 132. Attached to the side of the vertical surface 38 is a cork cushion 134. This cushion 134 abuts the side A of the hexagonal grid 16. Each of the exemplary supports 120,122 has a wedge shape with about a 120.degree. angle 136 therebetween. In this manner, the angle 136 is generally the same as the 120.degree. angle between the sides B,C of the hexagonal grid 16 of FIG. 1. A cork cushion 138, similar to the resilient spacer 82 of FIG. 3, is adhesively attached to each of the supports 120,122 for supporting the corresponding sides B,C of the hexagonal grid 16. FIGS. 5B and 5C illustrate plan views of the base plate 124 and the bearing pad 126, respectively. The base plate 124 includes two sets of dowel pins 140,142 for aligning the supports 120,122 of FIG. 5A thereon. The base plate 124 also includes six recessed holes 144 (shown in shadow) for use with six flat screws 146 in order to attach the supports 120,122. The base plate 124 further includes six oblong mounting holes 148 which are described in greater detail below with FIG. 5D. The exemplary bearing pad 126 is made of teflon PTFE material and has six recessed holes 150. The bearing pad 126 also has six holes 152, which have a diameter about the length of the oblong mounting holes 148, for the shoulder screws 128 of FIG. 5A. The six flat screws 130, which are recessed within the six recessed holes 150, fixedly mount the bearing pad 126 to the horizontal surface 40 of FIG. 5A. Referring to FIG. 5D, a cross sectional view of the shoulder screw 128 of FIG. 5A is illustrated. Each shoulder screw 128 limits movement of the grid support 56 on the horizontal surface 40. Each shoulder screw 128 has a non-threaded portion 154 which passes through one of the oblong mounting holes 148 of the base plate 124 and, also, passes through one of the other holes 152 of the beating pad 126. Each shoulder screw 128 also has a threaded portion 156 which is threadably attached to the horizontal surface 40. Each of the oblong mounting holes 148 has a counterbore 158 which separates a head 160 of the corresponding shoulder screw 128 from the base plate 124. A stainless steel shim or washer 162 separates the non-threaded portion 154 from the horizontal surface 40. Because of normal manufacturing tolerances in the hexagonal grids 16 of FIG. 1, the cork cushions 138 of the two supports 120,122 cannot be rigid and, hence, must adapt to preclude grid deformation. The counter-bore 158 and the oblong nature of the mounting holes 148 of the base plate 124 provide a clearance between each of the shoulder screws 128 and the base plate 124. This clearance and the teflon bearing pad 126 allow the grid support 56 to slide freely with respect to the horizontal surface 40. The shoulder screws 128, hence, facilitate and limit this sliding motion in the direction which is perpendicular to the longitudinal axis 9 of FIG. 1 and the vertical surface 38 (i.e., a left/right motion with respect to FIG. 5A). The degree of freedom of this motion is, thus, about the longitudinal length of the oblong holes 148 less the diameter of the non-threaded portion 154 of the shoulder screw 128. The width of the oblong holes 148 and the non-threaded portion 154 prevent the sliding motion in the direction which is parallel to the longitudinal axis 9 and the vertical surface 38 (i.e., a left/right motion with respect to FIG. 5D). In this manner, each of the grid supports 56 accommodates for the gamut of dimensions of the hexagonal grid 16 of the fuel assembly 2 of FIG. 1. Once the fuel assembly 2 is centered on the grid support 56, and pressure is applied to the three sides D-F of the grid 16 by the clamping frame assembly 58 of FIGS. 2A-2B and 6B, both the fuel assembly 2 and the grid support 56 move until the side A of the grid 16 contacts the cork surface 134 adjacent the vertical surface 38. FIG. 6A is a side view of the clamping frame assemblies 52 and 54 for the top nozzle support 48 of FIG. 3 and the shoulder holder 50 of FIG. 4B, respectively. FIG. 6B is a side view of the clamping frame assembly 58 for the grid support 56 of FIG. 5A. With the exception of an additional pressure pad 164 in FIG. 6B, these clamping frame assemblies 52,54,58 are identical. FIGS. 6A and 6B also illustrate clamping frame assemblies 52',54' and 58', respectively, for a second fuel assembly 2'. Such assemblies 52',54',58', which are used with the second support apparatus 44 of FIGS. 2A-2B, are mirror images of the corresponding clamping frame assemblies 52,54,58 for use with the first support apparatus 42 of FIGS. 2A-2B. Referring to FIG. 6B, the clamping frame assembly 58 includes three pressure pads 164,166,168 for use with the sides F,E,D, respectively, of the hexagonal grid 16 (shown in shadow). The pressure pads 164,166,168 are adjustably mounted to a frame 170. The frame 170 is pivotally mounted to a pivot mount 172 which is attached to the horizontal surface 40. The frame 170 may be locked in a closed position 173 by a bail lock pin 174 (shown on the clamping frame assembly 58') to a top pivot mount 176 which is fixedly attached to the vertical surface 38. Whenever the bail lock pin 174 is removed, the frame 170 may be unlocked to an open position 177 (shown in shadow). Each of the pressure pads 166,168 includes two U-shaped snubbers 178, 179 having two arms 180 (only one of which is shown). Each pair of the arms 180 is adjustably attached to a slot 182 (shown in shadow) in the frame 170 by a hex head bolt 184, a flat washer 186 and an elastic stop nut (not shown). Each of the snubbers 178,179 is pinned to the corresponding one of the pressure pads 166,168 by a pin 190 and two retaining tings 192 (only one of which is shown). An adjustment mechanism 194 for the pressure pads 166,168 includes a swing bolt 196, two hex nuts 198,199, two washers 200, two spacers 202 (only one is shown in shadow), a pin 204, and two retaining tings 206 (only one is shown). The pin 204 and two retaining tings 206 mount the two spacers 202 to two arms 208 (only one is shown) of each of the pressure pads 166,168. The spacers 202 are attached to each side of one end of the swing bolt 196. The swing bolt 196 is adjustably attached to the frame 170 by the pair of nuts 198,199 and washers 200 on each side thereof. An adjustment mechanism 194A and snubbers 178,179A for the pressure pad 164 includes a longer length swing bolt 196A and the longer length snubber 179A to accommodate the side F of the hexagonal grid 16 (shown in shadow). The hex nuts 198 function as locking nuts. By tightening each of the pressure pad hex nuts 199, the pressure pads 164,166,168 of the clamping frame assembly 58 apply pressure to the corresponding sides F-D of the hexagonal grid 16. The three pressure pads 164,166,168 secure the fuel assembly 2 to the grid support 56 of FIG. 5A and, in turn, to the horizontal surface 40. Accordingly, movement of the fuel assembly 2 during a hypothetical accident condition scenario is precluded. As discussed above, the pressure pad 164 is not used with the clamping frame assemblies 52,54 of FIG. 6A. For the shoulder holder 50 of FIG. 4B, by tightening the pressure pad hex nuts 199 of the clamping frame assembly 54, the pressure pads 166,168 apply pressure to close the exemplary 0.180 inch gap 114 of the split support 104 of FIG. 4A. This gap 114 is positioned between the pads 166,168 which correspond to the two sides 86A,88A, respectively, of FIG. 4A. The clamping frame assembly 52 applies a similar pressure to the two corresponding sides 86,88 of the top nozzle support 48 of FIG. 3. FIG. 7A is an isometric view of an alternative guide plate 62', it being understood that the other guide plates 60,64 have a similar form, except for the width (on the longitudinal axis 9 of the fuel assembly 2 of FIG. 1) as shown in FIGS. 2A-2B, and except as discussed below with the guide plate 62 of FIG. 7B. The guide plate 62' has an upper guide side 212 and a lower side 213. The exemplary guide plate 62' is fabricated from thin steel plate and has two surfaces 214,216 for guiding the sides B,C, respectively, of the hexagonal grid 16 of FIG. 1. Each of these two surfaces 214,216 has about a 120.degree. angle 218 therebetween, which corresponds to the angle 136 of FIG. 5A. The guide plate 62' also includes two legs 220 each of which has a foot 222 and two mounting holes 224 (shown in shadow). The guide plate 62' is attached to the horizontal surface 40 of FIGS. 2A-2B by four fasteners 226. Also referring to FIGS. 1 and 2A-2B, whenever the fuel assembly 2 is loaded in the upright position of the container 28, the fuel assembly 2 is lowered down until the bottom nozzle 8 engages fully in the spacer 72 of the bottom nozzle holder 66. In order to preclude potential damage to the hexagonal grids 16 and the grid supports 56 during loading of the fuel assembly 2, the guide plates 60,62,64 are formed to match the 120.degree. angle of the fuel assembly 2 and, hence, preclude the fuel assembly 2 from hanging-up on the grid supports 56 during such loading. Also referring to FIG. 7B, the guide plate 62 is similar to the guide plate 62' of FIG. 7A, the principal difference being the lower side 213 which has a coating 228 including at least 0.027 gram/cm.sup.2 of gadolinium oxide. In this manner, high enrichment (e.g., 4.80 to 5.00 weight percent U.sup.235) fuel assemblies may be transported by the container 28 of FIGS. 2A-2B. The container 28, in the same manner as the shipping container described in U.S. Pat. No. 4,780,268, also contains horizontal segmented neutron absorber plates 132 (shown in FIGS. 5A and 5D) in addition to vertical absorber plates (not shown). By using the absorber guide plates 60,62,64, the container 28 contains a sufficient amount of neutron absorbers and is able to transport such high enrichment fuel assemblies. FIG. 8 is a vertical sectional view of the bottom nozzle holder 66 including the recess holder 70 for holding the bottom nozzle 8 (shown in shadow) within the longitudinally extending recess 18 thereof. The exemplary bottom nozzle holder 66 also includes the spacer 72 (shown in shadow) having the hole 74 (shown in shadow) for inserting the cylindrical barrel 24 therein and the tapered surface 76 for abutting the spherical taper 22. The spacer 72 abuts the end support 68 and spaces the bottom end 26 of the fuel assembly 2 therefrom. The end support 68 is fixedly mounted to the horizontal surface 40 by a plurality of bolts 230 (only one of which is shown). The bottom nozzle holder 66 is a hold-down device which functions as a cam and a wedge to lock the bottom nozzle 8 to the end support 68. The recess holder 70 includes a wedge mechanism 232 for wedging against the bottom nozzle 8 within the longitudinally extending recess 18 and a moving mechanism 234 for moving the wedge mechanism 232 against the bottom nozzle 8 within the recess 18. The wedge mechanism 232 grips a shoulder or tapered bore 236 within the bottom nozzle 8. The moving mechanism 234 moves and engages the wedge mechanism 232 against the tapered bore 236. The wedge mechanism 232 includes three grippers 238 (shown in FIG. 9) each of which have a pivot end 240 and a gripping end 242 for gripping the shoulder 236 within the bottom nozzle 8. The moving mechanism 234 includes a base 244 on which the pivot end 240 of each of the grippers 238 is pivotally mounted by a pivot pin 246 and two retaining tings 248 (only one of which is shown). The moving mechanism 234 also includes a cam/wedge plate 250 for moving the gripping end 242 of each of the grippers 238 and an operating mechanism 252. The exemplary plate 250 and grippers 238 are made from 17-4 PH precipitate hardened stainless steel. The operating mechanism 252 moves the plate 250 which engages and moves each of the gripping ends 242 radially and angularly outward toward the shoulder 236. The operating mechanism 252 also includes three extension springs 254 (shown in FIG. 9). Each of the three springs 254 is attached between two adjacent grippers 238 by a double-loop wire 256. The double-loop wire 256 is attached near the center 258 of each of the exemplary grippers 238. The three springs 254 provide a net inward force of sufficient magnitude to keep the grippers 238 in contact with the plate 250. In this manner, during loading of the fuel assembly 2, the recess holder 70 is in a "closed" position (see FIG. 9) and, hence, the grippers 238 do not interfere with the bottom nozzle 8. Also referring to FIG. 9, the plate 250 includes three cam surfaces 260,262,264 for camming a corresponding one of the gripping ends 242 of the three grippers 238. When engaged (as shown in shadow), the cam surfaces 260,262,264 move each of the gripping ends 242 radially and angularly outward toward the shoulder 236. When disengaged, as shown, the three springs 254 force the gripping ends 242 radially and angularly inward away from the shoulder 236 and toward the cam surfaces 260,262,264. Continuing to refer to FIG. 8, the operating mechanism 252 further includes a hold-down screw 266, a locking collar 268, and a compression spring 270. The screw 266, which rotates the plate 250, has a head 272 and a shaft 274. The head 272 abuts a surface 276 of the end support 68. The shaft 274 has a non-threaded portion 278 and a threaded portion 280. The non-threaded portion 278, which is adjacent the head 272, passes through a hole 282 of the end support 68 and a hole 284 of the base 244. The threaded portion 280 is adjacent the non-threaded portion 278, opposite from the head 272, and is threaded through a threaded hole 286 of the plate 250. The holes 282,284,286 are positioned on the central longitudinal axis 9 of the fuel assembly 2. The locking collar 268, which is fixedly attached to the threaded portion 280, is separated from the plate 250 by the compression spring 270. As shown in FIG. 8, the collar 268 is normally separated from the base 244. Whenever the collar 268 is installed sufficiently fight on the screw 266, the recess holder 70 self-centers within the bottom nozzle 8. The compression spring 270, which is biased between the plate 250 and the collar 268, provides a pre-load force for the screw 266. The exemplary screw 266, which is fabricated from cold worked stainless steel, provides a sufficient pre-load to the bottom nozzle holder 66 such that the fuel assembly 2 in general, and the bottom nozzle 8 in particular, are securely held to the end support 68 and, hence, are secured to the horizontal surface 40. The remaining parts of the exemplary bottom nozzle holder 66 are fabricated from 300 series stainless steel. The exemplary screw 266 and, thus, the bottom nozzle holder 66, provide a design load of four times the weight (i.e., 4G) of the exemplary fuel assembly 2. The screw 266 also provides a quick disconnect mechanism to disengage the bottom nozzle holder 66 for removal of the fuel assembly 2. The base 244 is inserted adjacent the end support 68 and within the bottom end 26 of the fuel assembly 2. As discussed above, the main function of the compression spring 270 is to induce a pre-load between the screw 266 and the plate 250. When the screw 266 is turned to place the recess holder 70 in a full "open" position (shown in shadow in FIG. 9), the pre-load provides a friction couple between the screw 266 and the plate 250. This friction couple is of sufficient magnitude to overcome a friction couple between the grippers 238 and the plate 250. Subsequently, turning the screw 266 rotates the plate 250 which engages the grippers 238. The locking collar 268 provides a contiguous flat biasing surface for the compression spring 270. The spring 270 rotates with the screw 266 and facilitates actuation of the plate 250 to the open position. The compression spring 270 functions in a similar manner during disengagement of the bottom nozzle holder 66. The screw 266 is turned to release the 4G pre-load. Whenever the pre-load and the interference between the plate 250 and the grippers 238 are relieved, the plate 250 rotates with the screw 266. In turn, the gripping ends 242 of the three grippers 238 follow the contour of the cam surfaces 260,262,264 until the grippers 238 reach the closed position. Referring to FIGS. 8 and 9, the plate 250 further includes three blocking surfaces 288,290,292 between adjacent ones of the three cam surfaces 264-260,260-262,262-264, respectively, for blocking rotation of the plate 250. Each of the blocking surfaces 288,290,292 abuts the corresponding one of the gripping ends 242 of the grippers 238 whenever the plate 250 is fully disengaged in the closed position. The plate 250 provides both cam and wedge functions. When the three contoured cam surfaces 260,262,264 are moved relative to the corresponding grippers 238, a displacement profile engages (or disengages) the grippers 238. Additional torquing of the screw 266 causes the plate 250 to rotate to the fully open position. When the recess holder 70 is in the fully open position, the plate 250 functions as a wedge. Torquing of the screw 266 pulls or forces the plate 250 toward the base 244. Then, the grippers 238 are forced radially outward relative to the plate 250 in order to engage the inside shoulder 236 of the bottom nozzle 8. This provides a mechanical interference between the plate 250 and the grippers 238 and locks the grippers 238 in place. Accordingly, this engagement of the bottom nozzle holder 66 provides the necessary fuel assembly pre-load and secures the fuel assembly 2 to the end support 68. The plate 250 further includes three dowel pins or blocking tabs 294,296,298 for blocking rotation of the fully engaged plate 250. Each of the blocking tabs 294,296,298 is attached to one of the cam surfaces 260,262,264, respectively, in order that each one of the blocking tabs 294,296,298 abuts the corresponding one of the gripping ends 242 of the three grippers 238 in the fully open position. On the other hand, to unlock the bottom nozzle holder 66, the screw 266 is turned to remove the pre-load. Continued turning of the screw 266 causes the plate 250 to rotate to the fully closed position. The rotation of the plate 250 stops at the closed position when the grippers 238 contact the blocking surfaces 288,290,292. Additional loosening of the screw 266 moves the plate 250 away from the base 244. In turn, the grippers 238 move radially inward and, thus, provide maximum clearance for removing the fuel assembly 2 (e.g., the bottom nozzle 8) from the container 28 of FIGS. 2A-2B (e.g., the bottom nozzle holder 66). FIG. 10 is an isometric view of the bottom nozzle spacer 72. Also referring to FIGS. 1 and 2A-2B, the spacer 72 spaces the bottom end 26 of the fuel assembly 2 from the end support 68. The exemplary spacer 72 is made of ASTM 240, type 304 stainless steel in order to preclude contamination of the bottom nozzle 8 by the exemplary end support 68 which is made of carbon steel. The spacer 72 has a machined cavity or hole 74 for inserting the cylindrical barrel 24 therein and a tapered surface 76 for abutting the spherical taper 22. Whenever the container 28 is in the upright position, the fuel assembly 2 is lowered therein. When the fuel assembly 2 is within 3-4 inches of the fully lowered position, the bottom nozzle 8 is manually guided into the hole 74 of the spacer 72. The spacer 72, thus, provides a seating or bearing surface 300 which supports the weight of the fuel assembly 2 during loading in the upright position of the container 28 and, also, holds and supports the bottom nozzle 8 by the spherical taper 22 in both longitudinal and axial directions during transportation of the fuel assembly 2. The spacer 72 also has plural relief slots 301 for accepting the two alignment pins 25 of the bottom nozzle 8. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given the full breadth of the claims appended and any and all equivalents thereof. |
description | 1. Field of the Invention This invention relates to a method of testing an electronics module for an underwater well installation, for example a so-called Subsea Electronics Module (SEM), testing equipment and a testing system for testing such a module. 2. Description of Related Art The control of subsea fluid extraction wells is generally managed by a Subsea Electronics Module (SEM), which is typically housed in a Subsea Control Module (SCM), which is in turn mounted on a subsea Xmas tree located on the sea bed, above the fluid extraction well. Existing SEMs contain a number of printed wiring boards which perform dedicated functions, such as the operation of hydraulic Directional Control Valves (DCVs), with communication to and from the SEM via a modem. In existing systems, the testing of the SEM, typically by Automatic Test Equipment (ATE) has had to be effected via the only communication port, i.e. the modem. FIG. 1 schematically shows such a conventional testing arrangement. An ATE 1 incorporates a processor 2 which generates required test signals. These are fed via a modem 3 to a modem 4 located in a SEM 5. The output of the modem 4 feeds the required test signals to a plurality of Data acquisition and Control (D & C) cards 6, also located in the SEM 5. Furthermore, testing has to use a production communication protocol, which is sequential and slow. One of the requirements is to perform active testing of the operation of the SEM during vibration tests and, currently, the vibration testing time limit (as to the standards) does not permit thorough testing of all required aspects of the SEM. It is an aim of the present invention to overcome these problems and permit stressing of an electronics module by fully exercising it under test control, including during time limited vibration testing, which is far better at revealing faults than the previous relatively slow sequential method. This aim is achieved by utilizing high speed Local Area Network (LAN) communication, such as Ethernet, between ATE and the module to enable much faster exercising of the latter's electronics. The invention allows much more comprehensive testing of SEMs, prior to subsea installation, at a much lower cost than existing modem linked systems, due to the substantial reduction of testing time. Existing ATE typically employs a single processor to provide the test signals, since the speed of the process is limited by the slow communication to the SEM. However this invention, which makes use of much faster LAN communication makes the employment of multiple processors, working in parallel, an attractive enhancement of the ATE, which can then effect even faster SEM testing. In accordance with a first aspect of the present invention, there is provided a method of testing an electronics module for an underwater well installation, comprising the steps of: providing a test equipment comprising a processor and a Local Area Network (LAN) switch, such that the processor may communicate with the switch; providing an electronics module comprising a data acquisition means and a second LAN switch, such that the data acquisition means may communicate with the second switch; passing test data from the processor to the data acquisition means via the first and second LAN switches; and monitoring the response of the electronics module in response to the test data. In accordance with a second aspect of the present invention there is provided testing equipment for testing an electronics module for use at a well installation, comprising: a processor for outputting test data; and a LAN switch, connected such that the processor may communicate with the switch. In accordance with a third aspect of the present invention, there is provided a testing system for an electronics module for use at a well installation, comprising the test equipment according to the second aspect, and an electronics module comprising a data acquisition means and a second Local Area Network (LAN) switch, such that the data acquisition means may communicate with the second switch. Other possible features of the invention are set out in the accompanying claims. FIG. 2 shows an arrangement in accordance with the present invention utilizing a multiple processor ATE connected to a modem SEM via a LAN, in this case Ethernet, network. Automatic Test Equipment 7 incorporates a multiplicity of processors 8 (three being shown in the figure) which operate in parallel, each outputting packages of test signal data to an Ethernet switch 9. A Subsea Electronics Module (SEM) 11 comprises a second Ethernet switch 10. Together, the Ethernet switches 9 and 10 form part of a Local Area Network (LAN) system, such that communication is enabled between the ATE 7 and SEM 11. SEM 11 further includes data acquisition means, such as a plurality of Data acquisition and Control (D&C) electronics cards 12, in FIG. 2 four such cards 12 are shown. These may communicate both externally and internally via the LAN. In use, test data signals from the processors 8 are sent to the D&C cards 12 via switches 9 and 10 across the LAN. The SEM's response, sent back to the ATE 7 via the LAN, is monitored to evaluate the operation of the SEM. The test may involve vibration testing. Typically, this testing is carried out prior to deployment of the SEM 11. Such testing is generally automatically performed. Modern well communication systems often employ high speed optical modems and LAN/Ethernet networks, between the well control platform of an installed production well complex and the SEMs. This enables the SEM 11 to be tested during operation, i.e. following deployment at the well installation. In this case, the same LAN as used for the platform-installation communication would also be used for the testing. In this way, the inventive system enables high speed and comprehensive testing of the SEM, due to the high speed of test data from the parallel-operating processors 8, feeding test data via the relatively high speed LAN. 1) Automatic testing of a SEM is made faster, malting it cost effective to fully test all aspects of the SEM electronics. Full testing of SEMs was not previously cost effective as the testing time took too long, and during vibration testing was not possible. (It should be noted that vibration testing of a SEM is limited by the testing standards in order to avoid excessive mechanical stressing of the device under test.) 2) Multiple processors in the ATE may be used, operating in parallel to minimize testing time and thus costs. 3) The detailed testing of SEMs during well operation, for example for fault location, is made possible. The above described embodiments are exemplary only, and various alternatives are possible within the scope of the claims. For example, the LAN may use a standard other than Ethernet, for example Wi-Fi. |
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claims | 1. A system for acquiring a radiation image of an object, said system comprising:a radiation source configured to emit radiation;a scintillator plate configured to receive the radiation through the object;a first imaging apparatus configured to acquire scintillation light emitted from the scintillator plate; anda second imaging apparatus configured to acquire scintillation light emitted from the scintillator plate,whereinthe scintillator plate comprisesa partition member configured to transmit radiation,a first wavelength conversion member configured to be arranged on one surface of the partition member and convert the radiation into scintillation light, anda second wavelength conversion member configured to be arranged on the other surface of the partition member and convert the radiation into scintillation light,the first imaging apparatus acquires the scintillation light emitted from the first wavelength conversion member, andthe second imaging apparatus acquires the scintillation light emitted from the second wavelength conversion member. 2. The system according to claim 1,wherein the partition member has a property of blocking the scintillation light. 3. The system according to claim 1,wherein a reflective surface configured to reflect the scintillation light is formed on the partition member. 4. The system according to claim 1,wherein the first imaging apparatus has an optically-coupled first imaging lens, andthe second imaging apparatus has an optically-coupled second imaging lens. 5. The system according to claim 4,wherein the first imaging lens is focused on a surface of the first wavelength conversion member, andthe second imaging lens is focused on a surface of the second wavelength conversion member. 6. The system according to claim 1,wherein the first imaging apparatus and the second imaging apparatus are controlled to simultaneously acquire the scintillation light with emitting radiation by the radiation source. 7. A system for acquiring a radiation image of an object, said system comprising:a radiation source configured to emit radiation;a scintillator plate configured to receive the radiation through the object;a first imaging apparatus configured to acquire scintillation light emitted from the scintillator plate; anda second imaging apparatus configured to acquire scintillation light emitted from the scintillator plate,whereinthe scintillator plate comprisesa partition member configured to transmit radiation,a first wavelength conversion member configured to be arranged on one surface of the partition member and convert the radiation into scintillation light, anda second wavelength conversion member configured to be arranged on the other surface of the partition member and convert the radiation into scintillation light,the first imaging apparatus acquires the scintillation light emitted from the first wavelength conversion member,the second imaging apparatus acquires the scintillation light emitted from the second wavelength conversion member, andthe partition member is manufactured by joining plate members on which the respective first and second wavelength conversion member are arranged, to each other on the side opposite to the respective first and second wavelength conversion member. 8. The system according to claim 7,wherein the partition member has a property of blocking the scintillation light. 9. The system according to claim 7,wherein a reflective surface configured to reflect the scintillation light is formed on the partition member. 10. The system according to claim 7,wherein the first imaging apparatus has an optically-coupled first imaging lens, andthe second imaging apparatus has an optically-coupled second imaging lens. 11. The system according to claim 10,wherein the first imaging lens is focused on a surface of the first wavelength conversion member, andthe second imaging lens is focused on a surface of the second wavelength conversion member. 12. The system according to claim 7,wherein the first imaging apparatus and the second imaging apparatus are controlled to simultaneously acquire the scintillation light with emitting radiation by the radiation source. 13. A method of acquiring a radiation image of an object, said method comprising:emitting radiation;by a first scintillator, converting the radiation received through the object into first scintillation light;by a partition member, blocking out the first scintillation light;by a second scintillator, converting the radiation received through the first scintillator and the partition member into second scintillation light;by a first imaging apparatus having an optically-coupled first imaging lens, acquiring the first scintillation light; andby a second imaging apparatus having an optically-coupled second imaging lens, acquiring the second scintillation light,wherein the partition member is arranged between the first scintillator and the second scintillator. 14. The method according to claim 13,wherein the first imaging lens is focused on a surface of the first scintillator, andthe second imaging lens is focused on a surface of the second scintillator. 15. The method according to claim 13,wherein the first imaging apparatus and the second imaging apparatus are controlled to simultaneously acquire the scintillation light with emitting radiation. 16. A system for acquiring a radiation image of an object, said system comprising:a radiation source configured to emit radiation;a first scintillator configured to convert the radiation received through the object into first scintillation light;a partition member configured to block out the first scintillation light;a second scintillator configured to convert the radiation received through the first scintillator and the partition member into second scintillation light;a first imaging apparatus, having an optically-coupled first imaging lens, configured to acquire the first scintillation light; anda second imaging apparatus, having an optically-coupled second imaging lens, configured to acquire the second scintillation light,wherein the partition member is arranged between the first scintillator and the second scintillator. 17. The system according to claim 16,wherein the first imaging lens is focused on a surface of the first scintillator, andthe second imaging lens is focused on a surface of the second scintillator. 18. The system according to claim 16,wherein the first imaging apparatus and the second imaging apparatus are controlled to simultaneously acquire the scintillation light with emitting radiation by the radiation source. |
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summary | ||
061047724 | summary | BACKGROUND OF THE INVENTION Field of the Invention The invention relates to a method and an apparatus for introducing a self-propelled in-pipe manipulator into a pipeline. Pipelines in system parts relevant to safety, such as the primary loop of a nuclear power plant, must be inspected and maintained at regular intervals. In particular, regulation inspection of weld seams on the insides of such pipelines is necessary. The equipment used for the inspection or the work is put into an inspection or machining position by self-propelled vehicles, as a rule. Such self-propelled in-pipe manipulators are known, for instance, from German Patent DE 34 12 519 C2. That patent discloses an in-pipe manipulator in which a radially adjustable inspection system carrier is disposed between two support surfaces. It can be rotated about the longitudinal axis of the in-pipe manipulator and in that way enables inspection of the inner surface of the pipe over its entire circumference. European Patent 0 204 694 B1 discloses an in-pipe manipulator in which a machining device on a chassis that can be driven on wheels is supported in a revolving shackle that is disposed on an L-shaped bearing rotatably supported on an end surface of the vehicle. When pipelines are inspected or machined, a problem which arises among others is that the weld seams to be inspected or machined may be located immediately behind an opening through which the in-pipe manipulator has to be introduced into the pipe. In principle, such weld seams located directly at the pipe opening cannot be detected by the in-pipe manipulator that is known, for instance, from German Patent DE 34 12 519 C2, because that in-pipe manipulator is not ready for use until both of its two support flanges have been positioned all the way into the pipe. In the device known from European Patent 0 204 694 B1, it is indeed possible to inspect or machine in the peripheral region of a pipe, but under some circumstances that requires turning the in-pipe manipulator around and introducing it into the pipe facing in the opposite direction, if inspection or work positions at the beginning and ending regions of a pipe are to be detected. SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a method and an apparatus for introducing a self-propelled in-pipe manipulator into a pipeline, which overcome the hereinafore-mentioned disadvantages of the heretofore-known apparatuses and methods of this general type and which also make it possible to inspect or machine at positions located directly in an opening, mouth or inlet region of the pipe. With the foregoing and other objects in view there is provided, in accordance with the invention, in a method for introducing a self-propelled in-pipe manipulator into a pipeline having an opening and branching off from a nuclear steam generator, the improvement which comprises positioning a hollow body receiving the in-pipe manipulator and having at least one open end surface in the steam generator at the opening of the pipeline; and driving the in-pipe manipulator on its own from the hollow body into the pipeline. In this way, the inspection manipulator can drive to inspection or work positions directly at the opening of the pipe, since the hollow body acts as a kind of extension of the tube and permits fixation of the in-pipe manipulator even when it has not yet been driven into the pipeline or has driven only partway into the pipeline. In this way, the in-pipe manipulator can also detect inspection and work positions located at the beginning or ending region of a pipe. The function of the hollow body which is used thus goes beyond the function of an aid in introducing non-self-propelled in-pipe manipulators that are advanced from the outside, of the kind that are known, for instance, from UK Patent Application GB 2 247 505 A. That patent discloses merely a chute, with the aid of which a camera that can be advanced through a flexible plastic rod can be threaded into a pipeline extending crosswise to a connection stub. In accordance with another mode of the invention, the hollow body is a hollow cylinder, which in particular is positioned centrally relative to the opening of the pipeline. In accordance with a further mode of the invention, which is suitable, in particular, for introducing a self-propelled in-pipe manipulator into a pipeline branching off from a nuclear steam generator, the hollow body is pivotably fixed on a boom or crosspiece. With the aid of this boom, the hollow body is introduced into the steam generator through a manhole in the steam generator and there is positioned, by displacement of the boom and by swiveling, above an opening of the pipeline in such a way the center axis of the hollow body and the center axis of the pipeline are virtually aligned with one another in the region of this opening. With the objects of the invention in view, there is also provided, in an apparatus for introducing a self-propelled in-pipe manipulator into an interior of a pipeline having an opening and branching off from a steam generator, the improvement comprising a hollow body for receiving the in-pipe manipulator and for entering into the steam generator, the hollow body having at least one open end surface; and a positioning device to be introduced at least partway into the steam generator, the hollow body disposed on the positioning device for positioning the hollow body at the opening of the pipeline and permitting the in-pipe manipulator to drive on its own into the pipeline. In accordance with another feature of the invention, the hollow body is a hollow cylinder. In accordance with a concomitant feature of the invention, the positioning device includes a displaceable boom, on which the hollow body is pivotably disposed. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a method and an apparatus for introducing a self-propelled in-pipe manipulator into a pipeline, it is nevertheless not intended to be limited to the details shown since various modifications and structural changes may be made without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. |
claims | 1. An inspecting apparatus comprising:an electron source for generating an electron beam;an electromagnetic wave source for generating an electromagnetic wave;a detection unit located in a vacuum chamber; andan electro-optical system for guiding, to the detection unit, a secondary electron beam emitted from a sample when the sample is irradiated by an electron beam generated from the electron source and for guiding, to the detection unit, photoelectrons emitted from the sample when the sample is irradiated by an electromagnetic wave generated from the electromagnetic wave source, wherein a two-dimensional image of the sample is acquired by the detection unit. 2. An inspecting apparatus according to claim 1, wherein the detection unit comprises;a plurality of detectors each for receiving an electron beam and photoelectrons emitted from the sample to acquire image data representative of the sample; anda switching mechanism for causing the electron beam and the photoelectrons to be incident on one of the plurality of detectors. 3. An inspecting apparatus according to claim 2, wherein the plurality of detectors comprise any one of:a combination of a first detector having an electron sensor for converting an electron beam into light and converting the light into an electric signal and a second detector having an electron sensor for converting an electron beam into an electric signal,a combination of a third detector having an electron sensor for converting an electron beam into an electric signal and a fourth detector having an electron sensor for converting an electron beam into an electric signal, anda combination of a fifth detector having an electron sensor for converting an electron beam into light and converting the light into an electric signal and a sixth detector having an electron sensor for converting an electron beam into light and converting the light into an electric signal. 4. An inspecting apparatus according to claim 3, wherein the electron sensor of the first, fifth and sixth detectors is any one of a TDI sensor and a CCD sensor having a plurality of pixels and wherein the electron sensor of the second, third and fourth detectors is any one of an EB-CCD sensor and an EB-TDI sensor having a plurality of pixels. 5. An inspecting apparatus according to claim 3, wherein the switching mechanism comprises any one of:a moving mechanism for mechanically moving one of the detectors included in the any one of the combinations to a position at which the one of the detectors does not prevent the other of the detectors from receiving the secondary electron beam and the photoelectrons, anda deflector for selectively switching a traveling direction of the secondary electron beam and the photoelectrons between one of the detectors included in the any one of the combinations and the other of the detectors. 6. An inspecting apparatus according to claim 1 , wherein said electromagnetic wave source is capable of generating one of UV light, DUV light, laser light, and X-ray. 7. An inspecting apparatus according to claim 1, wherein said electro-optical system comprises a projection optical system. 8. An inspecting apparatus according to claim 7, wherein the electro-optical system is operable to control trajectories of the secondary electron beam and the photoelectrons. 9. An inspecting apparatus according to claim 7, the electro-optical system comprises an electron amplifier for amplifying the secondary electron beam and the photoelectrons and a noise-cut aperture. 10. An inspecting apparatus comprising:an electron source for generating an electron beam;a detection unit located in a vacuum chamber; andan electro-optical system including a primary optical system for guiding, to a sample, an electron beam generated from the electron source and a secondary optical system for guiding, to the detection unit, electrons which have transmitted the sample, wherein a two-dimensional image of the sample is acquired by the detection unit. 11. An inspecting apparatus according to claim 10, wherein the detection unit comprises:a plurality of detectors each for receiving an electron beam which has transmitted the sample to acquire image data representative of the sample; anda switching mechanism for causing the transmitted electron beam to be incident on one of the plurality of detectors. 12. An inspecting apparatus according to claim 10, wherein the plurality of detectors comprise any one of:a combination of a first detector having an electron sensor for converting an electron beam into light and converting the light into an electric signal and a second detector having an electron sensor for converting an electron beam into an electric signal,a combination of a third detector having an electron sensor for converting an electron beam into an electric signal and a fourth detector having an electron sensor for converting an electron beam into an electric signal, anda combination of a fifth detector having an electron sensor for converting an electron beam into light and converting the light into an electric signal and a sixth detector having an electron sensor for converting an electron beam into light and converting the light into an electric signal. 13. An inspecting apparatus according to claim 12, wherein the electron sensor of the first, fifth and sixth detectors is any one of a TDI sensor and a CCD sensor having a plurality of pixels and wherein the electron sensor of the second, third and fourth detectors is any one of an EB-CCD sensor and an EB-TDI sensor having a plurality of pixels. 14. An inspecting apparatus according to claim 11, wherein the switching mechanism comprises any one of:a moving mechanism for mechanically moving one of the detectors included in the any one of the combinations to a position at which the one of the detectors does not prevent the other of the detectors from receiving the secondary electron beam and the photoelectrons, anda deflector for selectively switching a traveling direction of the secondary electron beam and the photoelectrons between one of the detectors included in the any one of the combinations and the other of the detectors. 15. An inspecting apparatus according to claim 10, wherein the electro-optical system comprises:an aperture for adjusting an amount of electron beam; anda zoom lens for adjusting an angle at which an electron beam is incident on the aperture. 16. An inspecting apparatus according to claim 10, wherein the secondary optical system comprises:an electrode for adjusting a strength of an electric field between the sample and the electrode; anda lens for magnifying the transmitted electron beam. 17. An inspecting apparatus according to claim 10, wherein the sample is any one of a semiconductor wafer, a semiconductor device, an exposure mask, a stencil mask, a micro-machine and MEMS parts. 18. The inspecting apparatus according to claim 1, further comprising a hollow fiber adapted to induce the electromagnetic wave emitted from the electromagnetic wave source to a viewing field region. |
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040240185 | claims | 1. A liquid metal cooled fast breeder nuclear reactor comprising: a primary vessel containing a pool of coolant, a reactor core submerged in the pool of coolant, a transfer rotor submerged in the pool of coolant alongside the reactor core, the transfer rotor being rotatable about a vertical axis and having an annular series of apertures disposed about said axis, a plurality of elongate thimble shape containers for receiving fuel assemblies disposed one in each of said apertures, a plurality of helical coil compression springs mounted on and carried by said rotor each spring operatively engaging and elastically supporting one of said containers in upright position in its aperture, and at least one hydraulic dash pot located directly below the path of the containers arranged so that, by rotation of the rotor, the containers are successively brought into register with the dash pot, the construction and arrangement being such that the momentum of a falling fuel element is transferred to the container and then to the dashpot, and after arrest of the container and fuel element they are returned to normal operating position of the container by the associated compression spring. 2. A liquid metal cooled fast breeder nuclear reactor according to claim 1 having a second helical coil compression spring in each aperture of the rotor, the second helical coil compression spring being reactively opposed to the first helical coil compression spring and the container being elastically suspended between the springs. 3. A liquid metal cooled fast breeder reactor according to claim 2 wherein the dash pot comprises a piston within a static cylinder, the piston having a horizontal plane surface arranged for impact with a descending container. 4. A liquid metal cooled fast breeder nuclear reactor according to claim 2, wherein the hydraulic dash pot comprises a static cylinder arranged for receiving the lower end of a descending container, the lower end of each container being adapted to form a piston for the dash pot. |
042016908 | claims | 1. A process for the dissolution of irradiated nuclear fuel in nitric acid comprising the steps of (a) contacting the irradiated nuclear fuel material with nitric acid in a dissolver vessel, (b) providing an atmosphere of carbon dioxide over the dissolver vessel, (c) directing a portion of the atmosphere to the first of a pair of heat exchangers, (d) passing a refrigerant through the first of the heat exchangers to cause condensation of said portion of the atmosphere in the first of the heat exchangers, (e) simultaneously with step (d) passing a liquid at a temperature above the evaporation temperature of carbon dioxide through the second of the pair of heat exchangers to cause evaporation of a portion of the atmosphere which has been condensed in the second of the pair of heat exchangers, (f) after steps (c) (d) and (e) directing a further portion of the atmosphere to the second of the pair of heat exchangers, (g) passing a liquid at a temperature above the evaporation temperature of carbon dioxide through the first of the pair of heat exchangers to cause evaporation of the portion of the atmosphere which had condensed therein, (h) simultaneously with step (g) passing a refrigerant through the second of the pair of heat exchangers to cause condensation of said further portion of the atmosphere therein, (i) repeating steps (c) to (h) to provide a driving force for circulating the atmosphere round the plant by the alternate condensation and evaporation of portions of the atmosphere. 2. A process as claimed in claim 1 including the additional steps of drying the atmosphere circulating in the plant to remove water vapour and cooling the atmosphere to cause removal of iodine before the portions of the atmosphere are directed to the heat exchangers. 3. A process as claimed in claim 1 including the additional step of purging the heat exchangers during the condensation steps to remove gases which do not condense. |
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abstract | The invention provides a cooling system which includes at least one and preferably a plurality of coolant chambers arranged around a heat source, typically a nuclear reactor. A coolant inlet pipe enters the or each coolant chamber at a high level and extends downwardly through the coolant chamber to a discharge end positioned at a low level within the coolant chamber. At least one anti-siphon bleed opening is provided in that portion of the coolant pipe which is positioned at the highest level within the coolant chamber. |
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052162559 | abstract | A system for applying radiation treatment under computer control is disclosed. The system has a radiation source, which generates a variable intensity radiation beam, and a collimator. The collimator has a plurality of movable plates disposed in the path of the radiation beam and is oriented in a direction perpendicular to the beam axis. The apparatus is capable of actuating the plates independently during the radiation treatment, in response to a first control signal. The beam changes in width when the plates are so actuated. The collimator is rotated in response to a second control signal. The intensity of the radiation beam may be varied as a function of the plate position. A total radiation dosage is applied during two intervals. The first interval precedes the collimator rotation, and the second interval follows the rotation. |
abstract | A multi charged particle beam writing method includes dividing a maximum irradiation time per a shot into a digit number of first irradiation time periods, each of which is calculated by multiplying a corresponding second gray scale value by the quantization unit, where second gray scale values are gray scale values defined in decimal numbers converted from each digit value of data of binary numbers; dividing second irradiation time periods, which are a part of the first irradiation time periods into third irradiation time periods; dividing irradiation of each beam into the first irradiation steps of the third irradiation time periods and second irradiation steps of the remaining undivided first irradiation time periods; and irradiating a target object, in order, with the multi beams such that the groups are respectively composed of combination of at least two irradiation steps of first irradiation steps and second irradiation steps and the groups continue in order. |
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062401580 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An X-ray projection exposure apparatus of the present invention includes an X-ray source, and an X-ray illumination optical system which directs X-rays generated by the X-ray source towards a mask having a prescribed mask pattern. An X-ray projection focusing optical system receives the X-rays from the mask and projects and focuses an image of the mask pattern onto a substrate. A mask stage holds the mask, a substrate stage holds the substrate, and a position detection optical system optically detects alignment marks formed on the mask and the substrate. The projection focusing optical system includes a plurality of reflective mirrors that reflect X-rays, and at least a portion of the position detection optical system is disposed among the plurality of reflective mirrors. At least the portion of the position detection optical system may be disposed between the reflective mirror closest to the substrate and the reflective mirror second closest to the substrate among the plurality of reflective mirrors which constitutes the projection focusing optical system. The position detection optical system may include an illumination optical system that illuminates a mark formed on the mask. The light reflected from the mark on the mask may be guided towards a mark on the substrate via at least some of the reflective mirrors of the X-ray projection focusing optical system. A detection optical system may detect the marks on the substrate. The position detection system may include a motion mechanism. The numerical aperture of the position detection optical system may be about 1/2 or less. At least a portion of the position detection optical system disposed among the plurality of reflective mirrors may include a half-mirror. The position detection optically system may include a temperature adjustment mechanism. In another aspect, an X-ray projection exposure apparatus of the present invention includes an X-ray source and an illumination optical system which directs X-rays generated by the X-ray source towards a mask having a prescribed mask pattern. A projection focusing optical system receives the X-rays from the mask and projects and focuses an image of the mask pattern onto a substrate. A substrate stage holds the substrate, and a position detection device optically detects the position of the substrate in the direction of the optical axis of the projection focusing optical system. The projection focusing optical system includes a plurality of reflective mirrors that reflect X-rays, and at least a portion of the position detection device is disposed among the plurality of reflective mirrors. At least a portion of the position detection device may be disposed between the reflective mirror closest to the substrate and the reflective mirror second closest to the substrate among the plurality of reflective mirrors constituting the projection focusing optical system. A through-hole may be formed in the reflective mirror closest to the substrate, and detection light used for position detection will pass through the through-hole. A motion mechanism may be installed in the position detection device, and a temperature adjustment mechanism may be installed in the position detection device. In still another aspect of the present invention, an X-ray projection exposure apparatus includes an X-ray source, an illumination optical system which directs X-rays generated by the X-ray source towards a mask having a prescribed mask pattern, a projection focusing optical system which receives the X-rays from the mask and projects and focuses an image of the mask pattern onto a substrate, a substrate stage which holds the substrate, and a position detection mechanism which optically detects the position of the substrate in the direction of the optical axis of the projection focusing optical system. The projection focusing optical system may be constructed of a plurality of reflective mirrors that reflect X-rays, and the reflective mirror that is closest to the substrate has a space which provides the passage of detection light for the position detection mechanism in its back surface facing the substrate. The space which provides the passage of the detection light for the position detection mechanism may be a tapered part formed in the reflective mirror that is closest to the substrate, or a groove or through-hole formed in the reflective mirror that is closest to the substrate. The present invention also provides an X-ray projection exposure apparatus including an X-ray source, an illumination optical system which directs X-rays generated by the X-ray source onto a mask having a prescribed mask pattern, a projection focusing optical system which receives the X-rays from the mask and projects and focuses an image of the mask pattern onto a substrate, a substrate stage which holds the substrate, and a position detection mechanism which optically detects the position of the substrate in the direction of the optical axis of the projection focusing optical system. The projection focusing optical system includes a plurality of reflective mirrors that reflect X-rays, and the reflective mirror that is closest to the substrate among the plurality of reflective mirrors may be held by a holder which has a space providing the passage of detection light for the position detection mechanism in a surface of the holder facing the substrate. The space which provides the passage of the detection light for the position detection mechanism may be a tapered part formed in the holder, or a groove or through-hole formed in the holder. Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. First Preferred Embodiment FIG. 1 schematically shows an X-ray projection exposure apparatus according to a first preferred embodiment of the present invention. This embodiment includes an X-ray source 101, an X-ray illumination optical system 102, an X-ray projection focusing optical system 103, a stage 105 which holds a mask 104, a stage 107 which holds a wafer 106, and alignment detection devices 181 and 182. A mask pattern, which is to be transferred onto a wafer 106 without magnification or with a certain magnification, is formed on the mask 104. The X-ray projection focusing optical system 103 includes a plurality of reflective mirrors arranged so as to focus the image of the mask pattern on the mask 104 onto the wafer 106. The X-ray projection focusing optical system 103 has an annular band shape field of views so that a portion of the mask pattern on the mask 104 is transferred onto the wafer 106 at a time. During exposure, a desired exposure region on the wafer 106 is exposed by synchronously scanning the mask 104 and wafer 106 with the X-rays from the X-ray illumination optical system 102 at respective constant speeds. In the present preferred embodiment, a laser plasma X-ray source is used as the X-ray source 101; the exposure wavelength is set at 13 nm, and a reflective type mask is used as the mask 104, with the transfer magnification (reduction factor) being 1/4, for example. Since the transfer magnification is 1/4, the scanning speed of the wafer stage is set at one quarter of the scanning speed of the mask stage. In FIG. 1, the optical paths of the X-ray beam used as X-ray exposing light is not illustrated to avoid complication of the figure. The exposing optical paths are similar to those depicted in FIG. 15. The X-ray projection focusing optical system 103 includes a plurality of reflective mirrors 131 through 134 which reflect X-rays. In order to improve the X-ray reflectivity of the reflective mirrors, the surfaces of the mirrors are preferably coated with a multi-layer film. The alignment detection devices 181 and 182 (alignment detection system) are configured to optically detect the positions of alignment marks on the mask 104 and wafer 106. This system includes an illumination optical system as alignment detection device 181 for illuminating with detection light an alignment mark on the mask 104 and an alignment mark on the wafer 106 and a detection optical system as alignment detection device 182 for detecting the detection light that has interacted with these alignment marks. In the present preferred embodiment, a device that performs alignment using a field-image-alignment system (FIA system) is employed as the alignment devices. However, other types of devices may also be used. In this configuration, because the detection light used for alignment detection is reflected by the reflective mirrors of the X-ray projection focusing optical system, the alignment detection that includes the effects of the projection focusing optical system can be performed, thereby providing for superior alignment detection mechanism. When the X-ray projection focusing optical system is constructed of the reflective mirrors as in the present invention, the light used for alignment detection (white light, for example) also is free from aberration so that good alignment detection can be performed. In the present preferred embodiment, as shown in FIG. 1, the alignment mark on the mask 104 is illuminated with detection light 185 by the illumination optical system as alignment detection device 181, and the detection light 186 reflected from the mask 104 is successively reflected by the reflective mirrors 131 through 134 of the X-ray projection focusing optical system 103 so as to be guided towards the alignment mark on wafer 106 as detection light 187. Then, the light 188 reflected from the surface of the wafer 106 is detected by the detection optical system as alignment detection device 182. This way, the image of the alignment mark on the mask 104 are projected onto the wafer 106 through the X-ray projection focusing optical system 103. This projected image and the alignment mark on the wafer are together detected by the detection optical system as alignment detection device 182. As a result, the positional relationship between the mask 104 and the wafer 106 can be obtained from the positional relationship between the alignment mark on the wafer and the projected image of the alignment mark on the mask. As shown in FIG. 1, a portion of the detection optical system as alignment detection device 182 detecting the image of the alignment mark on the wafer 106 is disposed among the plurality of the reflective mirrors constituting the X-ray projection focusing optical system 103 (i.e., inserted into the X-ray projection focusing optical system 103). Accordingly, detection light from the alignment mark on the wafer 106 can be directed to the detection optical system as alignment detection device 182 without necessitating an extra gap between the reflective mirror 134 and wafer 106, and superior alignment detection can be performed. In the present preferred embodiment, a reflective mirror of the detection optical system 182 for detecting the detection light from the alignment mark on the wafer 106 is disposed between the reflective mirrors 131 and 134. However, there is no particular restriction on which part of the alignment device is disposed inside the X-ray projection focusing optical system 103. Also, it is sufficient if at least some portion of the detection optical system is disposed between two reflective mirrors in the X-ray projection focusing optical system 103 so that the detection light from the alignment mark on the wafer 106 can be detected. Furthermore, such a portion of the detection optical system may be disposed at any location as along as the detection optical system can extract the detection light that has interacted with the alignment mark on the wafer 106. However, if such a portion is disposed between the reflective mirrors 131 and 134, the detection optical system as alignment detection device 182 of the alignment device can be installed in the vicinity of the wafer 106. Thus, the configuration of the present preferred embodiment is relatively preferable because a deterioration in the S/N ratio, which may occur by the intensity drop in the detection light through reflections at additional reflective mirrors, can be prevented. The illumination optical system as alignment detection device 181 and the detection optical system as alignment detection device 182 may also be installed in the reversed configuration. FIG. 2 schematically illustates such a configuration. In the apparatus shown in FIG. 1, an alignment mark formed on wafer 106 is illuminated with detection light 185 by the illumination optical system as alignment detection device 181, and the detection light 186 reflected from the wafer 106 is further reflected by the reflective mirrors 131 through 134 of the X-ray projection focusing optical system 103 so as to be guided to the mask 104. The detection light 188 reflected from the mask 104 is detected by the detection optical system as alignment detection device 182. As a slight modification, it is also possible to detect the alignment mark on the wafer 106 directly without interaction with the mask 104. To this end, it is sufficient if the detection light from the alignment mark on the wafer 106, which has passed through the X-ray projection focusing optical system 103, is guided directly to the detection optical system as alignment detection device 182 without interacting with the mask 104. In FIG. 2, the portion of the illumination optical system as alignment detection device 181 is disposed among the plurality of mirrors of the X-ray projection focusing optical system 103. In this example, this penetrating portion includes a reflective mirror for reflecting the detection light emitted from the illumination optical system as alignment detection device 181. As in the case of FIG. 1 described above, the detection light can be directed to a desired position on the wafer by disposing the portion of the alignment device among the plurality of reflective mirrors in a similar manner to that in FIG. 1. Accordingly, the alignment device can be constructed without necessitating an extra gap between the reflective mirror 134 and wafer 106. In the case of FIG. 2, a portion of the illumination optical system as alignment detection device 181 is inserted between the reflective mirrors 131 and 134, and therefore, the illumination optical system as alignment detection device 181 can be installed in the vicinity of the wafer 106. Thus, the configuration of this example is preferable because a deterioration in the S/N ratio, which may occur by the intensity drop in the detection light through reflections at additional reflective mirrors, can be prevented. In these cases where the alignment light (detection light) is reflected by the reflective mirrors of the X-ray focusing optical system, it is desirable to arrange the system so that there is no interference between the light incident on the wafer and the reflected light. As a means of accomplishing this, it is desirable that the numerical aperture of the optical system of the alignment device be set at about half of the numerical aperture of the X-ray projection focusing optical system or less. Light beams 185 through 188 of the alignment device are shown in FIG. 1. Here, since the numerical aperture of the alignment optical system is set at half of the numerical aperture of the X-ray projection focusing optical system, the light 187 incident on the wafer and the reflected light 188 do not interfere with each other. Similarly, in FIG. 2, the light 185 and light 186 do not interfere. Furthermore, half-mirrors may also be used in a portion of the alignment optical system. FIG. 3 shows a portion of an apparatus in which a half-mirror 189 is used in a portion of the detection optical system. As a result of the use of such an arrangement, it is possible for the light incident on the wafer and the reflected light to share a portion of their light paths, so that the marks can be detected. If a pellicle mirror is used as a half-mirror, the effect of refraction by the half-mirror is reduced; accordingly, such use is desirable. Of course, it is also possible to construct the alignment device as shown in FIG. 1, and to use half-mirrors as the inserting portion of the detection optical system. It is desirable that the alignment marks be disposed at the periphery of the exposure field of view of the X-ray focusing optical system. Especially in the case of an annular band-form field of view, the marks on the mask can be accurately projected onto the wafer if marks are disposed at the periphery at both ends in the circular-arc direction of the annular band. In cases where a portion of the alignment detection device blocks the X-rays constituting the exposing light, it is desirable that a motion mechanism 183 be installed in the alignment detection device 181, 182 (FIGS. 1 and 2), so that the alignment device can be retracted during exposure. For example, mechanical means can be used for this motion mechanism. In such a case, all or part of the alignment detection device can be retracted during exposure. In FIGS. 1 and 2, motion mechanism 183 are installed in each of the illumination optical system as alignment detection device 181 and the detection optical system as alignment detection device 182. However, it is also possible to install such a motion mechanism in only one of these systems, if desired. Furthermore, it is also possible to detect marks at a plurality of points on the mask and the wafer using the motion mechanism 183 by changing the position of the alignment devices 181, 182. In such a case, it is desirable that the alignment detection device 181, 182 be caused to undergo parallel movement within a plane perpendicular to the optical axis of the projection focusing optical system 103. Furthermore, when a plurality of marks are detected, the wafer stage and the mask stage may be synchronized. When a plurality of marks on the wafer are detected with respect to a single mark on the mask, it is possible to perform measurements with only the mask stage being moved. Furthermore, it is also possible to install a plurality of alignment detection devices to detect a plurality of points on the wafer. A temperature of adjustment mechanism 184 may also be installed in the alignment detection device 181, 182. Water cooling, a cooling medium or a Peltier element, etc., may be used as such a temperature adjustment mechanism. In this way, the heat generated from the alignment device can be suppressed; accordingly, the effect of heat on the projection focusing optical system can be suppressed, so that thermal deformation of projection focusing optical system can be prevented. As a result, the desired small aberration of the projection focusing optical system can easily be maintained. When exposure was performed using the above-mentioned apparatus, it is possible to project and transfer the mask pattern onto the wafer at a desired position. As a result, it becomes possible to obtain a resist pattern with a minimum size of 0.1 .mu.m in a desired position over the entire surface of a region corresponding to one or more semiconductor chips on the wafer, so that high-precision devices can be manufactured. On the other hand, in the conventional designs of X-ray projection exposure apparatus described in the background section above, since the X-ray projection focusing optical system sacrifices its focusing power in order to allow the installation of an alignment device, the focusing performance is poor, and a resist pattern of the desired shape cannot be obtained in the exposed region. By using the X-ray projection exposure apparatus of the present invention, as described above, it is possible to install an alignment device while maintaining the desired small aberration of the projection focusing optical system. Furthermore, by installing a motion mechanism, a plurality of points on the wafer can be detected. As a result, the pattern on the mask can be projected and transferred onto the wafer in a desired position, so that high-precision devices can be manufactured. Second Preferred Embodiment A schematic diagram of an X-ray projection exposure apparatus according to a second preferred embodiment of the present invention is shown in FIG. 4. This apparatus is constructed mainly from an X-ray source 201, an illumination optical system 202, a projection focusing optical system 203, a stage 205 which holds a mask 204, a wafer stage 207 which holds a wafer 206, and a focal point detection device 208. A pattern, which is equal in size to the pattern that is to be drawn on the wafer, or which is to be enlarged, is formed on the mask 204. The projection focusing optical system 203 is constructed from a plurality of reflective mirrors, and is arranged so that the pattern on the mask 204 is focused on the wafer 206. The projection focusing optical system 203 has an annular band-form field of view, so that a portion of the mask pattern region of the mask 204 is transferred onto the wafer 206. A desired region is exposed by synchronously scanning the mask and the wafer at respective constant speeds during exposure. In the present preferred embodiment, for example, a laser plasma X-ray source is used as the X-ray source; the exposure wavelength is set at 13 nm, and a reflective type mask is used as the mask 204, with the transfer magnification set at 1/4. Since the transfer magnification is 1/4, the speed of the wafer stage is set at one-quarter of the speed of the mask-stage. The projection focusing optical system 203 is constructed from a plurality of reflective mirrors 231 through 234 that reflect X-rays. It is desirable that the surfaces of the reflective mirrors be coated with a multi-layer film in order to improve the X-ray reflectivity. The focal point detection device 208 used in the exposure apparatus shown in FIG. 4 is a device which optically detects the surface position of the wafer. Here, a device of the type using a triangulation system in which the surface of the wafer 206 is obliquely illuminated by illuminating light 281, and the reflected light 282 is detected by a photo-detector, is used. However, it is also possible to use some other type of focal point detection device. At least a portion of the focal point detection device 208 is disposed between two of the above-mentioned plurality of mirrors 231 through 234 (i.e., in the X-ray projection focusing optical system 203). As a result, the focal point detection device 208 can be installed without creating an extra gap between the wafer 206 and the reflective mirror 231 that is closest to the water among the reflective mirrors constituting the projection focusing optical system. Consequently, focal point detection can be accomplished without sacrificing the optical performance of the focusing optical system. In this case, it is desirable that the focal point detection device 208 be installed so that the light path of the exposing X-rays 209 is not blocked. The entire focal point detection device 208 may be installed inside the projection focusing optical system 203. However, in order to prevent blocking of the exposing X-rays 209, it is desirable that a portion of the focal point detection device 208 be installed outside the projection focusing optical system 203. In the present preferred embodiment, the focal point detection device 208 is installed between the reflective mirror 231 that is closest to the wafer 206 and the reflective mirror 233 that is second closest to the wafer 206 (among the plurality of reflective mirrors 231 through 234 constituting the projection focusing optical system 203). In this case, the focal point detection device 208 can easily be installed without blocking the exposing X-rays 209. Accordingly, such an arrangement is desirable. FIG. 5 is a schematic diagram which illustrated an X-ray projection exposure apparatus constructed according to a modified second preferred embodiment of the present invention. The apparatus shown in FIG. 5 differs from the apparatus shown in FIG. 4 in that some of the reflective mirrors 231 and 234 have through-holes 235 and 236. Since the remaining constructions are the same as in the apparatus shown in FIG. 4, a detailed description will be omitted. These through-holes 235 and 236 are formed so that the reflective mirrors 231 and 234 do not block the exposing X-rays. In such a case, the focal point detection device 208 is disposed so that the light paths 281 and 282 pass through the through-hole 235 in the reflective mirror 231 closest to the wafer. In this case, it is desirable that the through-hole 235 have a size and shape such that the incident light 281 and reflected light 282 are not blocked. Furthermore, it is also possible to form a through-hole which is used for the passage of the light path of the focal point detection device 208 in the reflective mirror 231 separately from the through-hole 235 through which X-rays pass. Moreover, although this depends on the focal point detection system used, in the case of a system in which light is obliquely incident on the wafer as in the present preferred embodiment, it is also desirable to form a through-hole in a holder 290 which holds the reflective mirror 231 (depending on the angle of incidence .theta. in FIG. 5), so that light used for focal point detection can pass through. If a motion mechanism 283 is installed in the focal point detection device 208, a plurality of points on the wafer can be detected, accordingly, such installation is desirable. This motion mechanism can be performed mechanically. In this case, it is desirable that the focal point detection device 208 be caused to undergo parallel movement in a plane perpendicular to the optical axis of the projection focusing optical system 203. In this way, tilting of the wafer surface can also be detected. Furthermore, it is also possible to install a plurality of focal point detection devices to detect a plurality of points on the wafer. Also, it is desirable that a temperature adjustment mechanism 284 be installed in the focal point detection device 208. Water cooling, a cooling medium or a Peltier element, etc., may be used as such a temperature adjustment mechanism. In this way, the heat generated from the focal point detection device can be suppressed; accordingly, the effect of heat on the projection focusing optical system can be suppressed, and thermal deformation of the projection focusing optical system can be suppressed. As a result, the desired small aberration of the projection focusing optical system can easily be maintained. For example, it is desirable that the temperature of the focal point detection device be controlled to within .+-.0.1.degree. C. Furthermore, these devices (a temperature adjustment mechanism 284 and/or motion mechanism 283) may also be installed in the apparatus shown in FIG. 4. The apparatus shown in FIG. 4 is advantageous in that a large installation space may be obtained for the focal point detection device. However, if the reflective mirrors become axially asymmetrical, measurement may become difficult. Furthermore, there may be cases in which assembly and adjustment (especially adjustment for eccentricity) become difficult. Accordingly, in cases where the above-mentioned problems arise, the use of the apparatus shown in FIG. 5 is preferable in constructing a high-performance projection focusing optical system. When exposure is performed using the above-mentioned apparatuses, detection of the focal position of the wafer can be accomplished with a high degree of precision. As a result, resist patterns with a minimum line-width of 0.1 .mu.m can be obtained with a desired shape throughout a region corresponding to one or more semiconductor chips on the wafer. On the other hand, in the conventional designs of X-ray projection exposure apparatus described in the background section above, resist patterns with a desired shape cannot be obtained in some portion of the exposed region. By using the X-ray projection exposure apparatus of the present invention, as described above, it is possible to install a focal point detection device while maintaining the desired small aberration of the projection focusing optical system. Furthermore, it is possible to detect a plurality of points on the wafer by installing the motion mechanism. As a result, the surface position of the wafer can be adjusted to within the range of the depth of focus of the projection focusing optical system, and resist patterns with a desired shape can be formed in desired regions. Third Preferred Embodiment A schematic diagram of an X-ray projection exposure apparatus constructed according to a third preferred embodiment of the present invention is shown in FIG. 6. This apparatus is constructed mainly from an X-ray source 301, an illumination optical system 302, a projection focusing optical system 303, a stage 305 which holds a mask 304, a wafer stage 307 which holds a wafer 306, and a focal point detection device 308. A pattern, which is equal in size to the pattern that is to be drawn on the wafer, or which is to be enlarged, is formed on the mask 304. The projection focusing optical system 303 is constructed of a plurality of reflective mirrors, and is arranged so that the pattern on the mask 304 is focused on the wafer 306. The projection focusing optical system 303 has an annular band-form field of view, so that a portion of the mask pattern region of the mask 304 is transferred onto the wafer 306. A desired region is exposed by synchronously scanning the mask and wafer at respective constant speeds during exposure. In the present preferred embodiment, for example, a laser plasma X-ray source is used as the X-ray source; the exposure wavelength is set at 13 nm; and a reflective type mask is used as the mask 304, with the transfer magnification set at 1/4. Since the transfer magnification if 1/4, the speed of the wafer stage is set at one-quarter of the speed of the mask stage. The projection focusing optical system 303 is constructed of a plurality of non-spherical reflective mirrors 331 through 334. It is desirable that the surfaces of the reflective mirrors be coated with a multi-layer film in order to improve the reflectivity. The focal point detection device 308 used in the present preferred embodiment is a device which optically detects the surface position of the wafer. Here, a device of the type using a triangulation system in which the surface of the wafer 306 is obliquely illuminated by illuminating light 381, and the reflected light 382 is detected by a photo-detector, is used. However, it is also possible to use some other type of focal point detection device. A tapered portion (taper) 383 is formed on the back surface of the reflective mirror 331, which is located closest to the wafer among the reflective mirrors 331 through 334. Accordingly, the focal point detection device 308 can be installed without any interference between the detection light beams 381 and 382 and the reflective mirror 331. An enlarged schematic diagram in the vicinity of the reflective mirror 331 and water 306 is shown in FIG. 7B, and a plan view of the reflective mirror 331 from the wafer side is shown in FIG. 7A. The taper 383 is formed so that the light beams 381 and 382 are not blocked by the reflective mirror 331. Furthermore, a smaller taper angle and width result in a larger rigidity of the reflective mirror 331, and are therefore desirable. For example, it is advisable to set the angle of the taper 383 so that this angle is substantially equal to the angle of incidence of the light 381 on the wafer 306. In the present preferred embodiment, the angle of incidence of the light 381 on the wafer 306 is set at 5 degrees, and the taper angle is set at 7 degrees. The taper 383 may be formed around the entire periphery of the reflective mirror as shown in FIG. 7A, or may be formed only in the portion through which the light passes. In cases where a taper is formed only in the portion through which the light passes, it is desirable to select the direction of incidence of the light in an appropriate manner and to locate the taper so that the portion of the back surface of the reflective mirror 331 that directly reflects X-rays is not affected. In FIGS. 7A and 7B, taper 383 is formed on the back surface of the reflective mirror 331. However, it is also possible to form a groove. In this way, it is possible to install the focal point detection device 308 so that there is no interference between the light beams 381 and 382 and the reflective mirror 331. An enlarged schematic diagram in the vicinity of the reflective mirror 331 and wafer 306 is shown in FIG. 8B, and a plan view of the reflective mirror 331 from the wafer side is shown in FIG. 8A. A groove 384 is formed so that the light beams 381 and 382 are not blocked by the reflective mirror 331. In FIG. 8B, the groove 384 is formed so that there is no interference with the light beam 382. However, it is also possible to form a groove on the side of the light beam 381. Furthermore, a smaller depth and length of the groove 384 result in a larger rigidity of the reflective mirror 331, and are therefore desirable. Furthermore, in cases where the depth of the groove is large as a result of the reflective mirror 331 and wafer 306 being installed extremely close to each other, or as a result of the angle of incidence of the light used for focal point detection being large, etc., a through-hole may be formed instead of a grove. When a through-hole is formed, the amount of grinding of the reflective mirror can be reduced; accordingly, the focal point detection device 308 can be installed without lowering the rigidity of the reflective mirror. If the cross-sectional shape of the through-hole is made substantially the same as the cross-sectional shape of the light beam, the cross-sectional area and the volume of the hole can be reduced; accordingly, such an arrangement is desirable. For example, in a case where the cross-sectional shape of the light beam is elliptical, it is desirable that the cross-sectional shape of the hole be formed as an ellipse or as a rectangle, which substantially inscribed the elliptical cross section of the light beam. Furthermore, in cases where the light beam is a focused light beam, it is desirable that a taper be formed in a hole or groove as well (such a taper is formed in the forward direction of the light beam). Moreover, in regard to the location where such a groove or through-hole is to be formed, a drop in the performance of the mirror can be prevented if the direction of incidence of the light beam is appropriately selected, and if the location where the groove or through-hole is formed is set so that the portion of the front surface of the reflective mirror 331 that directly reflects X-rays is not affected. In the present preferred embodiment, the light beams used for focal point detection are illustrated as they lie within the plane of the figures for convenience of illustration However, it is also possible to direct the detection light in a direction perpendicular to the plane of the page, for example. In such a case, the groove or hole is located at an appropriate area. A schematic diagram of an X-ray projection exposure apparatus constructed according to a modified third preferred embodiment of the present invention is shown in FIG. 9. The apparatus used in the present preferred embodiment is similar to the apparatus shown in FIG. 6. Accordingly, like elements are labeled with the same symbols, and detailed descriptions of such like components are omitted. The apparatus shown in FIG. 9 differs from the apparatus shown in FIG. 6 in that the reflective mirror 331 is held by a holder 337. (The other reflective mirrors may also be held by holders; however, this is not illustrated in the figures.) In cases where the projection focusing optical system is constructed using a plurality of reflective mirrors, it is desirable that the reflective mirrors be held by holders. It is desirable that the holders have a sufficient rigidity to allow the holders to hold the reflective mirrors. For example, the projection focusing optical system can be constructed using a metal frame, with the reflective mirrors fastened to the holders by an adhesive agent, etc., and the holders being mechanically fastened to the metal frame. In the X-ray projection exposure apparatus of the present preferred embodiment, a space which allows the passage of the light from the position detection mechanism 308 is formed in the holder 337 of the reflective mirror 331 so that there is no interference with the light from the focal point detection device. In FIG. 9, a tapered portion (taper) 385 is formed. As a result, the focal point detection device 308 can be installed without any interference between the light beams 381 and 382 and the holder 337. An enlarged schematic diagram in the vicinity of the reflective mirror 331, holder 337, and wafer 306 is shown in FIG. 10B, and a plan view of the reflective mirror 331 and holder 337 from the wafer side is shown in FIG. 10A. A taper 385 is formed so that the light beams 381 and 382 are not blocked by the holder 337. Furthermore, a smaller taper angle and width result in a larger rigidity of the holder 337, and are therefore desirable. For example, it is advisable that the angle of the taper 385 be set roughly equal to the angle of incidence of the light 381 on the wafer. As in the above-mentioned preferred embodiment, the taper 385 may be formed around the entire periphery of the holder as shown in FIG. 10A, or may be formed only in the portion through which the light passes. As in the above-mentioned preferred embodiment, the tapered part of the holder 337 may also be a groove. In this way, the focal point detection device 308 can be installed without any interference between the light beams 381 and 382 and the holder 337. An enlarged schematic diagram of the area in the vicinity of the reflective mirror 331, holder 337, and wafer 306 is shown in FIG. 11B, and a plan view of the reflective mirror 331 and holder 337 from the wafer side is shown in FIG. 11A. A groove 386 is formed so that the light beams 381 and 382 are not blocked by the holder 337. Furthermore, a smaller depth and length of the groove 386 result in a larger rigidity of the holder 337, and are therefore desirable. In cases where the depth of the groove is large, it is also possible to form a through-hole instead of a groove. This way, it is possible to install the focal point detection device 308 without lowering the rigidity of the holder. In the apparatuses shown in FIGS. 9 to 11B, cases in which a space such as a taper, etc., was formed only in the holder were illustrated. However, if a different arrangement, which requires that the reflective mirror closest to the wafer and the light from the focal point detection device interfere with each other, is desired, it is preferable to form a space such as a taper, etc., in the reflective mirror as well as in the holder. Furthermore, it is also possible to install a plurality of focal point detection devices to detect a plurality of points on the wafer. In such a case, it is desirable to form spaces in the reflective mirror and holder so that there is no interference with any of the light beam from the focal point detection devices. Furthermore, it is desirable to install a temperature adjustment mechanism having cooling water, a cooling medium or a Peltier element, etc., in the focal point detection device. By installing such a temperature adjustment mechanism, it is possible to suppress the generation of heat from the focal point detection device, thus preventing adverse effects on the projection focusing optical system 303. When exposure is performed using the above-mentioned apparatuses, detection of the focal point of the wafer can be accomplished with a high degree of precision. As a result, resist patterns with a minimum size of 0.1 .mu.m can be obtained with a desired shape throughout a region corresponding to one or more semiconductor chips on the wafer. On the other hand, in the case of the conventional designs of X-ray projection exposure apparatus described in the background section above, resist patterns with a desired fine pattern shape cannot be obtained in the exposed region. By using the X-ray projection exposure apparatus of the present invention, as described above, it is possible to install a focal point detection device while maintaining the desired small aberration of the projection focusing optical system. As a result, the surface position of the wafer can be adjusted to within the range of the depth of focus of the projection focusing optical system, and resist patterns with a desired shape can be formed in desired regions. It will be apparent to those skilled in the art that various modifications and variations can be made in the X-ray projection exposure apparatus of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. |
summary | ||
051611775 | claims | 1. A substrate holding apparatus for holding a substrate to be exposed by radiation, which is transported by a substrate transporting apparatus, said apparatus comprising: a substrate stage having a substrate holding surface for attracting a substrate, said substrate holding surface being divided into an inner peripheral portion and an outer peripheral portion by at least a groove formed in said substrate stage; a magnetic member fitted into said groove of said substrate stage; at least a magnetic unit embedded in said magnetic member, said magnetic unit including a permanent magnet and an electromagnet for eliminating a magnetic force of said permanent magnet when energized; and moving means for moving said magnetic member together with said magnetic unit in a direction of the depth of said groove between a first position in which the magnetic force of said permanent magnet is effective for the substrate on said substrate holding surface and a second position in which the magnetic force of said permanent magnet is ineffective for the substrate on said substrate holding surface. a substrate stage having a substrate holding surface for attracting a substrate; at least a magnetic unit movably disposed in said substrate stage, said magnetic unit including a permanent magnet and an electromagnet for eliminating a magnetic force of said permanent magnet when energized; and moving means for moving said magnetic unit between a first position in which the magnetic force of said permanent magnet is effective for the substrate on said substrate holding surface and a second position in which the magnetic force of said permanent magnet is ineffective for the substrate on said substrate holding surface. bringing the magnetic unit to the second position; putting the substrate on the substrate holding surface by a substrate transporting apparatus; bringing the magnetic unit to the first position; disabling the electromagnet; releasing the substrate from the substrate transporting apparatus; re-grasping the substrate by the substrate transporting apparatus; energizing the electromagnet; bringing the magnetic unit to the second position; disabling the electromagnet; positioning the substrate by the substrate transporting apparatus; energizing the electromagnet; bringing the magnetic unit to the first position; disabling the electromagnet; and releasing the substrate from the substrate transporting apparatus. 2. A substrate holding apparatus according to claim 1, wherein said groove has a stepped portion formed between a narrow-width portion at the side of said substrate holding surface and a wide-width portion at its bottom side, said magnetic member includes an upper portion whose width is substantially equal to that of said narrow-width portion of said groove and a bottom portion whose width is substantially equal to that of said wide-width portion of said groove and which forms a space between said bottom portion and said wide-width portion and said moving means comprises means for selectively supplying gas to and discharging gas from said space. 3. A substrate holding apparatus according to claim 2, further comprising sealing means for sealing said space. 4. A substrate holding apparatus according to claim 1, wherein said groove of said substrate stage is continuously formed along a periphery of said mask stage, a first screw is cut on a surface for defining an outer peripheral surface of said groove, a second screw engaging said first screw is cut on an outer peripheral surface of said magnetic member, longitudinal grooves are formed on the outer peripheral surface of said said magnetic member and said moving means includes a gear disposed in said substrate stage for engaging said longitudinal grooves and a motor for rotating said gear. 5. A substrate holding apparatus according to claim 1, wherein said substrate stage has an annular shape. 6. A substrate holding apparatus according to claim 1, wherein a plurality of said magnetic units are disposed equidistantly. 7. A substrate holding apparatus for holding a substrate to be exposed by radiation, which is transported by a substrate transporting apparatus, said apparatus comprising: 8. A method for positioning a substrate on a substrate holding surface of a substrate holding apparatus comprising a substrate stage having a substrate holding surface for attracting a substrate, at least one magnetic unit movably disposed in the substrate stage, the magnetic unit including a permanent magnet and an electromagnet for eliminating a magnetic force of the permanent magnet when energized and moving means for moving the magnetic unit between a first position in which the magnetic force of the permanent magnet is effective for the substrate on the substrate holding surface and a second position in which the magnetic force of the permanent magnet is ineffective for the substrate on the substrate holding surface, said method comprising the steps of: |
052590097 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS A portion of a boiling water reactor (BWR) fuel rod assembly employing the spacer system of the invention for retaining fuel rods 13 is generally shown at 10 in FIG. 1. Although the present invention will be described in relation to such a fuel assembly, it will be readily understood by those skilled in the art that the present invention can be used with any type of nuclear fuel assembly, not just BWR fuel assemblies or the BWR fuel assembly shown in FIG. 1. The fuel assembly shown in FIG. 1 has a central water channel which extends along the length of the fuel assembly. A common problem in typical boiling water reactors is that the central region of the fuel assemblies may be undermoderated and over-enriched. In order to increase the flow of moderator, an elongated central water channel is provided which includes a centrally disposed path for the flow of moderator/coolant along the length of the fuel rods in order to improve neutron moderation and economy. The central water channel can be of any cross-sectional area and/or geometry, positioned centrally and symmetrically within the outer channel, or asymmetrically displaced from the central axis within the outer channel, and can be oriented around its central axis so that its walls which extend the length of the assembly are either parallel or non-parallel to the walls of the outer channel. In FIG. 1, central water channel 15 is centrally located within outer channel 11. Outer rectangular channel 11 has retained therein a plurality of rod spacers 12 arranged at different elevations along the length of fuel assembly 10. The bottom-most spacer 12 at the end of the assembly, is shown in FIG. 1. Rod spacers are located at selected spaced intervals, and in a preferred embodiment are typically positioned at 15 to 22-inch intervals along the length of the fuel rod bundle. Another rod spacer 12 positioned along the length of fuel assembly 10 is shown in phantom above the bottom spacer 12. Other spacers, although not shown, are similarly positioned along the length of fuel assembly 10. FIG. 2 is a perspective view looking from the side and down the fuel assembly 10 depicted in FIG. 1 and shows a lower portion of the assembly, including bottom spacer 12, with the outer channel 11 removed. Although most of the fuel rods 13 are not shown in FIG. 2 for clarity of illustration, each of the spacer strips 20 are all shown in their "loaded" position, as explained hereinafter. Each of rod spacers 12 is formed of a lower lattice or grid 12a and a closely adjacent upper lattice or grid 12b. Fuel rods 13 are securely retained by each of the upper and lower lattices of each spacer. Spacers 12 each have four outer sidewalls 9a, b, c, d, which extend along the width and depth of outer channel 11 as shown in FIGS. 1 and 2. Dividing or stiffening plates 18, 19 divide each spacer 12 into nine separate subregions. Eight of such regions (14a through 14h) shown in FIG. 1 contain fuel rods 13 and one region houses central channel member 15. Although any number of plates can be used and form subregions having equal or unequal cross-sectional areas, it will also be readily understood by those skilled in the art that the present invention can be practiced with or without dividing plates which form subregions. FIGS. 3 and 4 are plan views looking up from the bottom of the fuel assembly. The structure of spacers 12 is shown in the perspective view of FIG. 2 and the plan view of FIGS. 3 and 4 showing a cross-sectional view of one subregion, and more particularly region 14a of lower lattice 12a illustrated in FIG. 1. Each of the upper and lower lattices 12b, 12a of spacers 12 is formed of spacer strips. Spacer strips 20a through 20f are provided for each of the upper and lower lattices 12b, 12a of each spacer 12 within each subregion 14a through 14h. Spacer strips 20a and 20f of subregion 14a of lower lattice 12a shown in FIG. 3 are positioned along sidewall 9a and stiffening plate 18, respectively. Ends 22, 23 of each of spacer strips 20a through 20f are respectively received and secured in slots 24 and 25 in stiffening plate 19 and side wall 9b. In lieu of slots for supporting the ends of the spacer strips, welds may be provided. As can be seen in FIG. 1, the orientation of spacer strips 20a through 20f alternate by 90.degree. from subregion to subregion in a lateral direction. Also, as can be seen in FIGS. 1 and 2, for each spacer, spacer strips 20a through 20f in each of the subregions of lower lattice 12a are oriented at 90.degree. relative to spacer strips 20a through 20f in adjacent upper lattice 12b. As shown in FIG. 4, each of spacer strips 20a-f has corrugations 30. Each corrugation 30 is three-sided and extends vertically to form a three-sided groove or channel. Each corrugation has a face 31. With the fuel rods 13 loaded into spacer lattice 12a as shown in FIG. 3, faces 31 of corrugations 30 of spacer strip 20b abut with the oppositely positioned and reversed faces 31 of corrugations 30 of spacer strip 20c. Where adjacent and reversed faces 31 of corrugations 30 of spacer strips 20b and 20c abut one another, faces 31 are welded to one another in every other column, as indicated by the asterisk * at 33. Thus, in each row, the abutting corrugations alternate welded and unwelded. Similarly, the alternate abutting faces 31 of spacer strips 20d and 20e are welded together at 33. In addition, alternate faces 31 of spacer 20a are welded to side wall 9a, and alternate faces 31 of spacer strip 20f are similarly welded at 33 to stiffening plate 18 as shown in FIGS. 3 and 4. Thus, weld points alternate in each row and column within the spacer. The significance of the alternating weld points, is apparent from the FIG. 4 which is of the same spacer shown in FIG. 3, but before loading fuel rods 13 in the spacer. As is shown in FIG. 4, faces 31 of corrugations 30 of adjacent spacer strips which are not welded together are spaced apart due to the resilience and shape of the individual spacer strips. The spaced apart relationship of unloaded spacers are shown as gaps 37b-37d in FIG. 4. The space or gap between face 31 of spacer strip 20a and wall 9a is shown as 37a and the spaces between faces 31 of strip 20f and stiffening plate 18 are shown as 37e and 37f in the unloaded spacer shown in FIG. 4. Thus, in the unloaded condition, corrugations 30 are not in line along a row, but rather are displaced and staggered or tilted by the integral spring force provided by the spacer strip material. The positioned fuel rods 13, once they are loaded in the unloaded spacer strips, are shown in phantom in FIG. 4. Accordingly, with the fuel rods loaded, corrugations 30 are in line such as shown in FIG. 3 and exert a retaining pressure on the fuel rods 13 which are positioned between the opposite facing concave corrugations which form rod supporting cells 38. Thus, supporting cells are created between oppositely facing concave portions of the corrugations. With the exception of the fuel rod in each outer corner of the fuel assembly, each fuel rod 13 in each cell 38 is supported by two spring edges 34 of corrugation 30 forcing rod 13 against two stationary supports 35 of corrugation 30 as shown in FIGS. 3 and 4. As can best be seen in FIGS. 1 and 2, the spacer strips in each subregion of the upper lattice grid 12b are oriented 90.degree. relative to those in lower lattice grid 12a. Thus, the direction of the forces applied by spring edges 34 against the fuel rods and the fuel rods against supports 35 in upper lattice grid 12b are similarly oriented 90.degree. relative to the forces in lower lattice grid 12a. Furthermore, as is evident from FIG. 1, the alternating direction of the spacer strips from subregion to subregion provides improved uniformity for both flow resistance and lateral strength. The arrangement provides a very strong overall support arrangement which opposes a failure due to lateral loading. In the region between four loaded adjacent fuel rods 13, an open space 39 is formed by two adjacent spacer strips (FIG. 3). Open spaces 39 which are formed by spacer strips between any four adjacent fuel rods within a subregion allow steam bubbles to flow unobstructed up the center between the four adjacent fuel rods, while allowing primarily liquid moderator to flow around the fuel rods, thus enhancing heat transfer. Four such open areas 39 are provided in each subassembly in the embodiment shown in FIG. 3. In addition, several other partial open areas 40 are also provided. Spring relaxation as a result of irradiation of spacer strips 20, and more particularly spring edges 34 and stationary support 35 of corrugations 30, is reduced by constructing the stiffening plates 18, 19 of annealed zircaloy and spacer strips 20a, 20b, 20c, 20d, 20e, and 20f of cold worked stress relieved zircaloy. The greater irradiation induced growth rate of the cold worked material restrained by the lower growth rate of the annealed material tends to cause the resilient spacer strips to move toward the fuel rods and provide a spring force against the fuel rods, reducing irradiation induced spring relaxation. As shown in FIGS. 2 and 5, each of the spacers 12 preferably has inwardly bent guiding tabs 16 extending from the top edge of side walls 9a, b, c and d at the upper spacer lattice 12b. Inwardly bent guiding tabs 16 allow ease of placement of the outer channel 11 over the spacers. Inwardly bent guiding tabs 16 and outwardly bent tabs 17 also serve the purpose of directing liquid water which has condensed on the outer and inner channels 11, 15 towards the fuel rods, enhancing local heat transfer. According to another feature of the invention, kick-outs 41 positioned on side walls 9a, 9b, 9c and 9b (FIG. 5) and tabs 42a, 42b (FIG. 2) positioned at the top of stiffening plates 18, 19 may be provided. Kick-outs 41 and tabs 42a, 42b are arranged to impart a circular motion to the two-phase coolant flow. This circular motion tends to coalesce small water droplets into larger water droplets aiding in their transfer to the fuel rod surfaces. Tests have shown that the net effect is an increase in water film thickness on the fuel rod, resulting in an improvement in local heat transfer. While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the true spirit and scope of the present invention. |
description | The invention relates to a cleaning method, an apparatus and a cleaning system. A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. Optical element surfaces (e.g. in Extreme Ultraviolet (EUV) lithography apparatus) may suffer from contamination growth (e.g. carbonization) during apparatus operation. Such contamination may be introduced by the environment of the optical surfaces (e.g. vacuum environment, resist, radiation source, etc.). In an EUV lithography apparatus, multilayer mirrors typically provide these optical surfaces. To get rid of such contamination, cleaning of components is required. An example cleaning method is based on cleaning mirrors, in the optical path, with atomic hydrogen produced by, for example, a hot filament. According to an embodiment, there is provided a method to clean one or more optical elements of an apparatus, the apparatus being configured to project a beam of radiation onto a target portion of a substrate and comprising a plurality of optical elements arranged in a sequence in a path of the radiation beam, wherein the method comprises cleaning a second optical element of the sequence, which receives a second radiation dose during operation of the apparatus, utilizing a cumulatively shorter cleaning period than a first optical element of the sequence, which receives a first radiation dose during operation of the apparatus, the second radiation dose being lower than the first radiation dose. According to an embodiment, there is provided a device manufacturing method, comprising: projecting a beam of radiation onto a target portion of a substrate utilizing a sequence of optical elements, wherein the optical elements receive different radiation doses and the contamination rates of the optical elements are correlated with the radiation doses; executing a number of cleaning cycles to clean at least one of the optical elements, each cleaning cycle involving cleaning an optical element of the sequence based on the radiation dose received by the optical element, so that an optical element that has received a low radiation dose is cleaned during a shorter time period or less often than an optical element that has received a radiation dose that is higher than the low radiation dose. According to an embodiment, there is provided an apparatus, comprising: an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and a cleaning system configured to clean one or more optical elements of the apparatus, the cleaning system being configured to clean an optical element of the projection system during a cumulatively shorter cleaning period than an optical elements of the illumination system. According to an embodiment, there is provided a cleaning system adapted to clean one or more optical elements of an apparatus, the optical elements being arranged in a path of a radiation beam used during a process carried out by the apparatus, wherein the cleaning system is configured to clean only one or some of the optical elements that are arranged in the path of the radiation beam, depending on the amount of radiation received by each of such elements during the process. FIG. 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. FIG. 2 depicts a further embodiment thereof. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam PB (e.g. UV radiation, particularly substantially comprising EUV radiation); a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam PB by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. Various optical elements PS1, PS2, PS3, . . . , PSN (the projection system comprising N optical elements) are schematically indicated in FIG. 1. For example, the projection system optical elements may comprise a plurality of mirrors PS1, PS2, PS3, . . . , PSN in an EUV type projection beam lithographic apparatus. The illumination system may include various types of optical elements, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical elements, or any combination thereof, for directing, shaping, or controlling radiation. FIG. 2 shows part of an illuminator having a plurality of optical elements IL1, IL2, IL3, IL4. For example, the illumination system may comprise a plurality of mirrors IL1, IL2, IL3, IL4 in an EUV type projection beam lithographic apparatus. Thus, the apparatus comprises a sequence of optical elements, which elements are arranged in the path of the radiation R, the sequence of optical elements comprising, for example, elements IL1, IL2, IL3, IL4 of the illumination system IL (located upstream viewed from the patterning device MA, with respect to a direction of radiation beam propagation) and elements PS1, PS2, PS3, . . . , PSN of the projection system (located downstream viewed from the patterning device MA, with respect to a direction of radiation beam propagation). The support structure holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.” The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit. The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix. The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”. As here depicted, the apparatus is of a reflective type (e.g. employing a reflective mask). Alternatively, the apparatus may be of a transmissive type (e.g. employing a transmissive mask). The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more support structures). In such “multiple stage” machines 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 exposure. The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure. Referring to FIG. 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system if required, may be referred to as a radiation system. In an embodiment, the radiation source is a plasma EUV source, for example a tin (Sn) plasma EUV source. For example, in such a radiation source, Sn atoms may be heated (e.g., electrically) using a low power laser. The EUV radiation source may also be a different radiation source, for example a Li or Xe ‘fueled’ plasma radiation source. Also, during use, small amounts of plasma may escape from the source SO, towards a collector K and the illuminator IL. The collector K may collect radiation R from the radiation source SO. The collector K may be arranged to transmit the collected radiation R to the illumination system IL. Particularly, the collector K may be arranged to focus incoming radiation, received from the radiation source, onto a small focusing area or point. Further, there may be provided one or more debris mitigation systems, for example so called foil traps (not shown as such), located between the source SO and collector K to capture/mitigate debris emanating from the source SO. The illuminator IL may comprise an adjuster for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may comprise various other components, such as an integrator and a condenser. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section. The radiation beam PB is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Being reflected by the patterning device MA, the radiation beam PB passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam PB. Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device MA with respect to the path of the radiation beam PB, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the support structure MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies. The depicted apparatus could be used in at least one of the following modes: 1. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at once (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. 2. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. 3. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above. Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed. Generally, all optical elements of a lithographic apparatus may be contaminated over time. Resulting optical losses are undesired and may lead to lower throughput and malfunction of devices manufactured by the apparatus. Thus, the apparatus may be provided with a cleaning system 10, 20, 50 configured to clean one or more optical elements of the apparatus. The cleaning system can be configured in any of various ways. Various suitable cleaning devices as such are known from the prior art, and may be implemented in one or more embodiments of the invention. As an example, the cleaning system may comprise one or more cleaning units 10, 20, located or positionable in the apparatus to clean one or more optical elements of the apparatus. In FIGS. 1 and 2, for example, a plurality of first cleaning units 10 are provided to clean optical elements IL1-IL4 of the illuminator system IL. Also, one or more cleaning units 20 might be available in the projection system PS to clean optical elements PS1, PS2, PS3, . . . PSN of the projection system PS. In an embodiment, the optical elements that are to be cleaned by the cleaning system 10, 20, 50 are selected from the sequence of optical elements arranged in the path of the radiation beam R. For example, a cleaning unit 10, 20 may be configured to provide or generate a certain cleaning medium or means (schematically shown by arrows 11 in FIG. 2), for example a cleaning substance, gas, ions, radicals, radiation, particles and/or a different cleaning means, and to effect contact between the cleaning medium/means and an element to be cleaned. For example, in an embodiment, a cleaning unit 10, 20 may be configured to generate hydrogen radicals (using, for example, a hot filament or an RF field). According to an embodiment, a cleaning unit can be configured to carry out a method, which comprises providing a H2 containing gas in at least part of the apparatus, producing hydrogen radicals 11 from H2 from the H2 containing gas, and having the surface of an optical element IL1-IL4, PS1, . . . PSN (to be cleaned) come into contact with at least part of the hydrogen radicals 11 and removing at least part of a contamination deposition from that surface. As an example, the mentioned deposition may comprise one or more elements selected from B, C, Si, Ge and Sn. Also, at least part of the hydrogen radicals 11 may be generated from H2 from the H2 containing gas by a filament, a plasma, radiation, or a catalyst configured to convert H2 into hydrogen radicals. Moreover, the H2 containing gas may further comprises a halogen gas. However, it will be appreciated by the skilled person that a cleaning unit may be configured to operate in a different manner. In an embodiment, there may be provided a controller 50 configured to control the cleaning system, for example to activate and deactivate one or more cleaning units 10, 20. The controller 50 (which is schematically depicted in FIG. 2) may be configured in any of various ways, for example comprising suitable hardware, software, a computer, processor, microelectronics, wired and/or wireless communication means to communicate with the cleaning units 10, 20, and/or a memory device 51 to store cleaning process related data, as will be appreciated by the skilled person. For example, the memory 51 may contain cleaning rates of cleaning processes to be applied to the one or more optical elements. In an embodiment, these cleaning rates may differ, depending on the cleaning processes, the contamination to be removed and the optical element to be cleaned by the respective cleaning processes, as will be appreciated by the skilled person. The cleaning rates may have been determined empirically or in a different manner. In the apparatus of FIGS. 1 and 2, a first optical element IL1 of the illuminator receives an initial relatively high EUV radiation dose of radiation R from the source/collector assembly (generally, the radiation dose is the radiation power received per surface area of the respective optical element over a certain time period and may be expressed in mJ/mm2). This high initial EUV radiation dose is indicated by ‘100%’ in FIG. 2. In an embodiment, the optical surfaces of the subsequent optical elements IL2-IL4, PS1-PSN may be substantially fully irradiated by the radiation beam. Also, for example, in the case that the optical elements IL1-IL4, PS1-PSN are mirrors, mirror reflection losses may mainly cause optical losses along the sequence of optical elements, the optical losses as such leading to reduction of EUV radiation dose downstream along the sequence of elements. Further, in an example, the configuration may be such that there is a spectrum change in the radiation of the radiation beam during operation. For example, a first optical element PS1 of the sequence may receive radiation having a higher EUV spectrum ratio of the overall spectrum than subsequent optical elements of the sequence. In an embodiment, a majority of the optical elements of the sequence of optical elements receive at most 75% of the EUV radiation dose that has been received by the previous optical element of the sequence of elements (the previous optical element being arranged upstream with respect to the respective element in the sequence). For example, in case of the optical elements IL1-IL4 of the illuminator IL, in an embodiment, each subsequent optical element of the illuminator system IL receives at most 50% of the EUV radiation dose that has been received by the previous optical element of the illuminator system IL. In an embodiment, in the case of the optical elements IL1-IL4 of the illuminator IL, the second optical element IL2 of the illuminator IL receives at most 50% of the initial EUV radiation dose received by the first optical element IL1 of the illuminator IL, the third optical element IL3 of the illuminator IL receives at most 33% of the EUV radiation dose received by the second optical element IL2. Also, for example, the fourth optical element IL4 of the illuminator IL receives less than 10% of the initial EUV radiation dose, particularly less than 1% and more particularly less than 0.5% of the initial radiation dose, received by the first optical element IL1. Thus, as is indicated in FIG. 2, the second optical element IL2 of the illumination system IL (that is located downstream of the first optical element IL1 of that system IL) may receive a smaller EUV radiation dose than the initial dose of 100% received by the first optical element IL1 of that system. As an example, indicated in FIG. 2, the second optical element IL2 receives 50% of the initial dose, the third optical element IL3 receives 10% of the initial dose and the fourth optical element IL4 receives 0.75% of the initial dose. In a further embodiment, each optical element PS1-PSN of the projection system PS receives less than 10% of the above-mentioned initial EUV radiation dose, particularly less than 1% of the initial radiation dose and more particularly less than 0.5% of the initial radiation dose, received by the first optical element IL1. According to an embodiment, there is provided a method to clean one or more optical elements of the lithography apparatus, wherein the cleaning method comprises cleaning one or more first optical elements Il1, IL2, IL3 of a sequence of optical elements, which receive a relatively high (first) radiation dose during operation of the apparatus, utilizing a cumulatively longer cleaning period than one or more second optical elements IL4, PS1-PSN of the sequence that receive a lower (second) radiation dose during operation of the apparatus. Herein, the cleaning period may be longer as measured cumulatively over an operational lifetime of the apparatus, for example over at least 1 year or over a plurality of years. In other words, the cleaning method comprises cleaning one or more second optical elements IL4, PS1-PSN of the sequence, which receive a relatively low (second) radiation dose during operation of the apparatus, utilizing a cumulatively shorter cleaning period than a cumulative cleaning period applied to one or more first optical elements Il1, IL2, IL3 of the sequence that receive a higher (first) radiation dose during operation of the apparatus. For example, the optical elements IL4, PS1-PSN that receive a second, lower radiation dose may be cleaned less often than the first optical elements IL1, IL2, IL3 that receive a first, high radiation dose, such that there is provided a cumulatively shorter cleaning period. Thus, a first optical element may be cleaned utilizing a relatively long cleaning period as such (and thus, a second optical element may be cleaned utilizing a relatively short cleaning period as such, the short cleaning period being much shorter than the long cleaning period applied to the first optical element). An advantage is that the cleaning may be carried out more swiftly in this manner. Additionally or alternatively, since the second optical elements IL4, PS1-PSN are cleaned less often and/or during a relatively short time period, or not at all (i.e., the respective cumulative cleaning period for each of the second optical elements IL4, PS1-PSN=0 seconds), chances of any cleaning related degradation of those second optical elements IL4, PS1-PSN may be reduced or minimized (or, may be tolerated since less optical elements are involved), thus lengthening the operational lifetime of those elements IL4, PS1-PSN of the apparatus. The present embodiment may provide relatively long time intervals between overall apparatus cleaning sequences. For example, in an embodiment, each second optical element is located downstream with respect of a first optical element, viewed along the optical path of the radiation beam. As in FIG. 1, the apparatus may comprise a support structure constructed to hold a patterning device MA in a certain patterning device position in the path of the radiation beam, wherein all first optical elements IL1, IL2, IL3 are located upstream with respect to the patterning device position, viewed with respect to a direction of propagation of the radiation beam, wherein at least a number of the second optical elements PS1-PSN are located downstream with respect to the patterning device position. An embodiment of the invention is based on the notion that different optical elements receive different amounts of radiation (for example, EUV radiation) and that the contamination rate of an optical element may depend on the radiation dose received by the optical element. Particularly, the contamination rate may scale substantially linearly with the radiation dose, probably since the radiation promotes or induces contaminants (present in the interior space of the apparatus) to decompose and/or to bond to and/or react with the optical elements. Also, in an embodiment, contamination behavior may be dependent on the spectrum of the radiation. For example, as follows from the above, the contamination growth may scale with or be dependent on the ratio of EUV radiation in the radiation beam (for example the ratio of EUV radiation with respect to a higher wavelength Deep Ultra Violet (DUV) radiation). Thus, for example, in an embodiment, the method may comprise cleaning one or more second optical elements of the sequence, which receives a second radiation dose of a predetermined part of the spectrum during operation of the apparatus, utilizing a cumulatively shorter cleaning period than one or more first optical elements of the sequence, which receives a first radiation dose of the predetermined part of the spectrum during operation of the apparatus, the second radiation dose being lower than the first radiation dose. As an example, the above-mentioned predetermined part of the spectrum may comprise the EUV part of the spectrum. It is believed that no one has perceived that a cleaning strategy of the optical elements of the apparatus may be adapted in a simple manner to make use of these notions. Thus, in the past, all optical elements of the apparatus were cleaned using substantially the same cleaning periods for each of the elements. Particularly, in the past, it was assumed that contamination growth on, for example, EUV mirrors is independent of the mirror location in the optical path and independent of radiation intensity, so that a similar contamination growth on each mirror was expected. Consequently this would lead to cleaning of each mirror with equivalent cleaning times. Furthermore, the lifetime budget, i.e. irreversible reflection loss, had to be distributed homogenously among each mirror of the optical column. Thus, cleaning methods in the past had been relatively complex and time-consuming compared to the one or more embodiments of cleaning methods described herein. Further, since all optical elements of the sequence were cleaned in past methods, the lifetimes of the optical elements were shortened considerably, thus leading to high maintenance and replacement cost. This may be avoided by one or more embodiments of the invention. In an embodiment, the cleaning system, 10, 20, 50 may be specifically adapted to carry out one or more of the above-described cleaning methods. For example, the controller 50 may be programmed to control the cleaning units 10, 20 such that the desired cleaning strategy is carried out, for example such that only one or some of the optical elements that are arranged in the path of a radiation beam are cleaned depending on the amount of radiation received by each of those elements during the lithography process. In an embodiment, the cleaning system may comprise or be coupled to a radiation loss detector that is configured to detect a radiation loss of radiation passing the illumination system IL and projection system PS of the apparatus. Then, the cleaning system 10, 20, 50 may be adapted to automatically start a cleaning cycle to clean, for example, at least one element of the illumination system IL when a detected radiation loss reaches a certain amount of radiation loss. For example, only the illuminator optical elements IL1, IL2, IL3 may be cleaned. In an embodiment, the cleaning system 10, 20, 50 may comprise or be coupled to a contamination detector 53 that is configured to detect contamination of at least one optical element IL2 of the illumination system IL (and/or at least one optical element of the projection system PS), wherein the cleaning system 10, 20, 50 is adapted to automatically start a cleaning cycle to clean a number of the optical elements, arranged in the radiation beam path, when the detector 53 detects that contamination of an optical element has reached a certain amount of contamination. The contamination detector 53 may be configured in any of various ways and may be arranged to detect contamination of the optical element IL2 optically, electrically, using a detector signal or beam, by detecting secondary electron emission or reflectivity loss and/or in any different manner, depending on, among other factors, the type of optical element, as will be appreciated by the skilled person. For example, a lithographic device manufacturing method may comprise projecting a beam of radiation onto a target portion of a substrate utilizing a sequence of optical elements, wherein the optical elements receive different radiation doses and contamination rates of the optical elements are correlated (for example substantially linearly) with the radiation doses. The method further includes a number of cleaning cycles to clean an optical element of the sequence, each cleaning cycle involving cleaning the optical element in dependence on the radiation dose received thereby, so that an optical element IL4, PS1-PSN that has received a second relatively low radiation dose is cleaned during a shorter time period or less often than another optical element IL1, IL3, IL3 that has received a first radiation dose higher than the second radiation dose. In an embodiment, for example, the above-mentioned first radiation dose may be in the range of 10-100% of the initial radiation dose received by the first optical element IL1 of the illuminator system IL, or in the range of 1-100% of the initial radiation dose, or in the range of 0.5-100% of the initial radiation dose. For example, the above-mentioned second radiation dose may be less than 10% of the initial radiation dose received by the first optical element IL1, or less than 1% of the initial radiation dose, or less than 0.5% of the initial radiation dose. Further, in an embodiment, the above-mentioned radiation doses may relate to a specific part of the spectrum (or spectral band), for example the EUV band. In an embodiment, the method may comprise the applying of any of various cleaning cycles between lithography operating periods of the apparatus, wherein during one or more of the cleaning cycles only the one or more first optical elements IL1, IL2, IL3 of the sequence are being cleaned, and not the one or more second optical elements of the sequence. Thus, an advantageous cleaning strategy may involve not cleaning the second optical elements at all during a long time period, for example during one or several months, but still cleaning the first optical elements IL1, IL2, IL3 a number of times during such a long time period. For example, a first optical element IL1 of the sequence of optical elements, which is part of an illuminator, may be cleaned at least 10 times more often than a second optical element PS1-PSN of the sequence optical elements, the second element being part of a downstream projection system PS of the apparatus. In an embodiment, the cleaning system 10, 20, 50 is configured to clean one or more optical elements of the projection system of the apparatus for a cumulatively 100 times shorter cleaning period, or at 100 times less often or never, than one or more optical elements of the illumination system of the apparatus (particularly measured over a relatively long period of one or more years). In an embodiment, the cleaning method may comprise: providing (for example detecting or calculating) radiation dose information, the information including or relating to the amount of radiation each of one or more optical elements IL1-IL4, PS1-PSN receives during operation of the apparatus; and providing a cleaning period for cleaning one or more of the optical elements IL1-IL4, PS1-PSN, such that a length of the cleaning period concerning an optical element is correlated to the respective radiation dose information of that optical element. For example, the correlation may be a substantially linear correlation, wherein the cleaning period to be applied to a certain optical element of the sequence scales substantially positively linearly with a radiation dose received by that element during a lithography process. Alternatively, or in addition, the correlation may be a binary correlation, wherein the cleaning period to be applied to a certain optical element of the sequence has a length t=T seconds when that element receives the above-mentioned high radiation dose during a lithography process, but has a length t=0 seconds if that element receives the above-mentioned low radiation dose during the lithography process. Also, any of a number of other types of correlation may be applied, as will be appreciated by the skilled person. As an example, the memory 51 of the cleaning system 50 may hold one more of: radiation information including or relating to the amount of radiation one or more of the optical elements of the apparatus receives during operation of the apparatus; and a cleaning period for cleaning each of one or more the optical elements, the length of the cleaning period concerning an optical element being correlated to the respective radiation dose information of that optical element, and a cleaning rate of a cleaning process for cleaning each of one or more optical elements, wherein the cleaning system is configured to use the radiation information, or the cleaning period, or cleaning rates, or any combination of the foregoing, to clean one or more optical elements during a respective cleaning cycle. For example, in an embodiment, a cleaning method may include detecting contamination of one or more optical elements IL1-IL4, PS1-PSN, or measuring a radiation intensity loss of a radiation beam subsequently passing one or more optical elements, or both, wherein the first optical element IL1-IL3 may be cleaned in the case when: one or more optical elements IL1-IL4, PS1-PSN has reached a certain contamination threshold; and/or a radiation intensity loss of a radiation beam subsequently passing one or more optical elements has reached a certain threshold. FIG. 3 shows a flow chart of an embodiment, wherein a lithographic process 100 is carried out, for example by an apparatus shown in FIG. 1. Part of the process 100 may involve measuring radiation loss through the sequence of optical elements IL1-IL4, PS1-PSN of the lithography system (step 101), for example a loss through only one of these optical elements or a loss concerning all of these optical elements. Then, it is determined whether or not the radiation loss has reached a certain threshold value ‘threshold1’ (step 102). In the case that this contamination threshold value has indeed been reached, the lithography process may be interrupted and one or more cleaning cycles 103 may be started. Herein, only the optical elements of the sequence are cleaned that have received a large radiation dose during the lithography process, for example one or more optical elements IL1, IL2, IL3 of the illumination system IL. After a first cleaning cycle 103, desirably, the radiation loss is measured again (step 104) and compared with a second threshold value ‘threshold2’ (step 105). The cleaning cycle 103 may be repeated in the case that a desired low radiation loss has not yet been achieved by a previous cleaning cycle. In the case that a desired low radiation loss has been reached (i.e., loss<threshold2), the lithography process may be started (via step 106). FIG. 3 also shows an alternative cleaning cycle 103′, in which first optical elements IL1-IL3 are cleaned much longer than second optical elements IL4, PS1-PSN (i.e. the second optical elements IL4, PS1-PSN are cleaned within a much shorter time period than the first optical elements IL1-IL3). As an example, some of the illuminator optical elements IL1-IL3 are cleaned during at least an hour, and the remaining elements IL4, PS1-PSN are only cleaned during a much shorter time period of one or several minutes. For example, the first illuminator optical element IL1 is cleaned much longer (at least 2 times longer, e.g., 10 hours) than the second illuminator optical element IL2 (e.g., 5 hours), and the second illuminator optical element IL2 is cleaned longer (at least 2 times longer) than the third illuminator optical element IL3 (e.g., 1 hour). Naturally, the length of a cleaning period regarding each element depends on the type of contamination and cleaning rate of a respective cleaning method applied to the element. For example, this alternative step 103′ may make use of above-mentioned information that includes or relates to the amount of radiation one or more optical elements IL1-IL4, PS1-PSN of the apparatus receives during operation of the apparatus, such that the length of the cleaning period concerning an optical element is correlated to the respective radiation dose information of that optical element (see above). FIG. 4 shows another flow chart, which differs from FIG. 3 in a step 201 is provided to detect contamination of or near one or more of the optical elements of the sequence. In the case that a detected contamination has exceeded a certain threshold value ‘threshold3’, a cleaning cycle is commenced. For example, the cleaning cycle may be similar to that described above concerning FIG. 3. In FIG. 4, an alternative cleaning cycle 203 is depicted, wherein only the optical elements of the sequence are cleaned that are expected to have experienced a contamination related optical loss (particularly a contamination related reflection loss, in the case that the optical elements are mirrors) of more than 1%. For example, an optional step 210 may be provided comprising utilizing a stored data set to determine the expected optical (reflection) loss of the optical elements. Particularly, such a data set (that may be stored in the controller memory 51) may have been pre-calculated or determined by experiment, and may include a certain amount of contamination of one or more of the optical elements IL1-IL4, PS1-PSN and/or a loss of radiation passing the sequence of optical elements IL1-IL4, PS1-PSN. The data set may also comprise respective predetermined (calculated or by experiment) optical losses of the optical elements. Alternatively, in step 210, optical losses of the optical elements may be calculated or estimated using the information of the data set, and a predetermined (substantially linear) correlation between optical loss by the optical element, contamination of that element and radiation dose received by that element. After a cleaning cycle 203, an optional verification step 204 may be carried out to determined whether the contamination has been removed to a sufficient degree. Alternatively or in addition, steps 104-105 may be carried out to detect radiation loss regarding one or more optical elements of the sequence. An embodiment of the method may provide short machine downtime, i.e. the time in which no illumination may be performed, since the time required for each cleaning step as well as the number of needed cleaning cycles may be reduced considerably over the lifetime of the optical system of the apparatus. Also, a time interval in between cleanings may be relatively long. A further benefit may be that high intensity illuminated mirrors may be cooled during operation; this makes cleaning easier since this cooling may be applied during cleaning which makes the recovery time after cleaning smaller. Further, since cleaning might also introduce negative effects to the reflectivity of the optics (e.g. a little metal deposition each time the mirror is cleaned, depending on the cleaning process), the reduction in required number of cleaning cycles may result in a higher lifetime of the optical system. In an embodiment, as follows from the above, a cleaning strategy may be provided for an EUV optical system based on an intensity dependence of contamination growth on EUV mirrors under illumination with EUV photons under a specified (dominated by water and hydrocarbon partial pressure) vacuum environment. For example, a primary contaminant to be removed may be carbon contamination. For example, within the optical column of an EUV lithography system, the radiation intensity (for example of EUV radiation) may drop from 100% on the first mirror IL1 of the illumination system to approx. 0.01% on the last mirror PSN of the projection system. The contamination process during illumination with pulsed photons under specified vacuum conditions (dominated by water and hydrocarbon partial pressure) may be highly dominated by EUV induced carbon growth which in addition may be highly intensity dependent (e.g., a linear dependence of carbon growth with intensity). Therefore, following this notion, it may be expected that the contamination growth within an EUV lithography system may also differ from mirror to mirror leading to thicker carbon layers on the first, high intensity mirrors IL1-IL3 compared to the last, low intensity mirrors of the projection system PS. Thus, in an embodiment, only the first three mirrors IL1-IL3 accumulate so much carbon that cleaning processes are necessary to be performed. The carbon contamination on all the other mirrors may be neglected more or less. Additionally, the number of required cleaning cycles on these first three mirrors IL1-IL3 may be reduced because the total available lifetime budget, i.e. irreversible reflection loss budget, only needs to be distributed over three mirrors instead of all mirrors IL1-IL3, PS1-PSN. One or more embodiments of the invention may provide one or more various merits. For example, the number of cleaning cycles may be reduced considerably and/or cleaning times may be reduced. Optics lifetime may be enhanced and/or downtime of the system may be reduced. Since a more efficient cleaning scenario is implemented, one or more embodiment may provide cost significant reduction. The above-mentioned first optical element may be located in any of various positions in the sequence of optical elements, for example in an upstream location, downstream location or there-between. The same holds for the above-mentioned second optical element. Further, one or more embodiments have been described in relation to optical elements. One or more embodiments may additionally or alternatively be applied to one or more other non-optical elements of the lithography apparatus, such as one or more structures exposed to contamination and optionally radiation. Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured. The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams. The term “lens”, where the context allows, may refer to any one or combination of various types of optical elements, including refractive, reflective, magnetic, electromagnetic and electrostatic optical elements. While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below. |
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description | 1. Field of the Invention The present invention relates to a radiation therapy treatment planning (hereafter referred to as RTP) machine to plan for cancer treatment with radiation therapy. The present invention more specifically relates to an RTP machine preferably used for treatment planning in cases where radiation is applied while changing the radiation field by a multileaf collimator. 2. Description of the Related Art Radiation therapy is one method of cancer treatment utilizing radiation. In radiation therapy it is preferable that high radiation dosage is irradiated on the target, and radiation dosage as low as possible is irradiated on organs other than the target. Therefore, a treatment plan is necessary for applying radiation therapy. A machine to deliver this treatment plan is referred to as an RTP machine. FIG. 6 is a perspective view showing the constitution of a radiation therapy treatment machine called a linear accelerator (hereafter referred to as linac). The linac includes a gantry 61, a collimator 62, a rotation shaft 64 for the gantry 61, a couch 65, and a rotation shaft 66 for the couch 65. Gantry 61 incorporates a beam source in its head, and rotates about rotation shaft 64 in the directions indicated by arrow A in the drawing. Collimator 62 is connected with the head of gantry 61, and rotates in the directions indicated by arrow B in the drawing. Collimator 62 incorporates a multileaf collimator, and the radiation ray from the radiation source inside gantry 61 is masked to any field shape, and then, irradiates toward couch 65. Couch 65 is utilized to support the patient, and rotates about couch rotation shaft 66 in the directions of C in the drawing. Couch rotation shaft 66 coincides with a vertical line in a state where collimator 62 is facing downward. In general, the gantry angle 0 degrees is defined in the linac when collimator 62 is facing directly downward, and the angle increases clockwise. FIG. 6 shows where the gantry angle is 0 degrees. In general, a linac can rotate from 180 degrees to 180 degrees passing through 0 degrees. When the radiation ray irradiates the target, it is necessary to irradiate from a direction that avoids critical organs such as the eyeball and the spinal cord by changing the gantry angle, the collimator angle, and the couch angle. FIG. 7 is a perspective view showing the construction of a multileaf collimator (hereafter referred to as MLC). In this drawing, the MLC includes upper jaws 71, lower jaws 72, and leaves 73. Upper jaws 71 move to open and close in directions indicated by arrows L1 and L2. Lower jaws 72 include a number of leaves 73, and move to open and close in directions W1 and W2. The individual leaves 73 move independently to alter the radiation field shape. The intersection between gantry rotation shaft 64 and a perpendicular line extending down from the beam source is referred to as an isocenter. A plane which has this isocenter as a center is in line with the gantry rotation shaft 64, and crosses at right angles with a perpendicular line extending down from the gantry head is referred to as an isocenter plane. An isocenter is often used as a reference point for dosage calculation, and a beam usually irradiates such that the center of the target would be at the isocenter. The field shape of radiation usually refers to this shape on the isocenter plane. FIG. 8 shows a sectional view representing the radiation field on the isocenter plane formed by the MLC. The drawing indicates the upper jaws 71, the lower jaws 72, the location of the pointed radiation beam source 85 of the linac, the isocenter plane 86, the center axis of the radiation beam 84, and the radiation field 87. The beam emitted from beam source 85 forms radiation field 87 on isocenter plane 86, blocking the ray by using upper jaws 71 and leaves 73 of lower jaws 72. The radiation therapy technique, where the isocenter is positioned inside the patient's body and irradiates with a fixed gantry, is referred to as the SAD technique. The radiation therapy technique, where the isocenter is positioned on the patient skin, is referred to as the SAD technique. The radiation therapy technique, which irradiates the target while the gantry is rotating, is referred to as rotational therapy. The isocenter is usually positioned inside the patient's body with the rotational therapy. The radiation therapy technique, where the radiation field matches the target shape with the fixed gantry, is referred to as irregular field radiation therapy. In addition, the radiation therapy technique, which irradiates with fixed beams while the gantry angle switches, is referred to as irregular field multi-beam radiation therapy. The radiation therapy technique, where the radiation field formed by the MLC matches the target shape by adjusting the leaf positions while the gantry is rotating to concentrate radiation on the target, is referred to as conformal therapy. FIG. 9 shows how the radiation field shape of conformal therapy changes during the gantry rotation. Reference number 91 indicates the radiation field shape when the gantry angle is 216 degrees, reference number 92 indicates the radiation field shape when the gantry angle is 288 degrees, reference number 93 indicates the radiation field shape when the gantry angle is 0 degrees, reference number 94 indicates the radiation field shape when the gantry angle is 72 degrees, and reference number 95 indicates the radiation field shape when the gantry angle is 144 degrees. Conformal therapy is a method to rotate the linac beam source around the target, and simultaneously, to adjust the positions of the MLC installed at the beam source of the radiation ray so as to form the radiation field to correspond with the shape of the affected part. Actual examples to generate MLC positions from a target shape are disclosed in the Japanese Patent Application Publication H01-214343, Japanese Patent Application Publication H08-131566, and others. The following section briefly describes how to generate the MLC positions. Computer Tomography, CT, images are examined to diagnose the location and the shape of the cancer. The CT images are used to confirm the location of the affected part in three dimensions by examining images usually at intervals of 1 cm around the affected part of the patient. Then, the contours of the affected part namely the cancer are extracted from this group of the CT images. For conformal therapy, the MLC leaf positions are usually calculated from contours which are extracted from the CT images projected in two dimensions seen from the gantry angle with a certain width of margin processing. In other words, while the gantry is rotating and irradiating, the shape of the cancer at the gantry angle is changing so that the leaves are being moved to fit the changes so as to alter the radiation field to dose radiation to the cancer effectively and to avoid irradiating to normal tissue as much as possible. This calculation for the MLC leaf positions is conducted by a Multileaf-Collimator-Position-Calculation-Unit. IMRT is one type of irregular field multi-beam radiation therapy which has been utilized recently. IMRT is an abbreviation of Intensity Modulated Radiation Therapy, and is one radiation therapy technique used to modulate the beam intensity to irradiate unevenly in order to distribute optimal dosage. Actual examples of this beam intensity modulated radiation therapy are the step-and-shoot method and the sliding-window method. FIG. 10 is a drawing showing the radiation field shapes by the MLC of the step-and-shoot method. In this drawing, reference numbers 101a, 101b, 101c, and 101d are segments of the radiation field shapes when the gantry angle is 216 degrees, reference number 102 indicates the radiation field shape when the gantry angle is 288 degrees, reference number 103 indicates the radiation field shape when the gantry angle is 0 degrees, reference number 104 indicates the radiation field shape when the gantry angle is 72 degrees, and reference number 105 indicates the radiation field shape when the gantry angle is 144 degrees. The step-and-shoot method is conducted as one irregular field multi-beam radiation therapy. The radiation field shapes at each angle consist of multiple radiation fields where the MLC forms discretionary shapes referred to as segments. In this example, four segments are used for each radiation angle, and each segment accumulates radiation dosage by turning the beam on and off. In the example in FIG. 10, where the gantry angle is 216 degrees, irradiation is provided with four patterns as segment 101a, 101b, 101c, and 101d. At other gantry angles, irradiation is similarly provided with different shapes of radiation fields at multiple times, and each dosage is accumulated in order to distribute optimal dosage. FIG. 11 is a drawing showing the MLC radiation field shape of the sliding window method. In this drawing, reference number 111 indicates the radiation field shape when the gantry angle is 216 degrees, reference number 112 indicates the radiation field shape when the gantry angle is 288 degrees, reference number 113 indicates the radiation field shape when the gantry angle is 0 degrees, reference number 114 indicates the radiation field shape when the gantry angle is 72 degrees, and reference number 115 indicates the radiation field shape when the gantry angle is 144 degrees. The sliding window method is conducted as one type of irregular field multi-beam radiation therapy, and irradiates with beams, the intensity of which are modulated by the MLC which continuously moves while irradiating. Reference numbers 111, 112, 113, 114, and 115 show how the MLC leaf positions change. In contrast to the step-and-shoot method, the beam is not turned on or off during one irradiation. This irradiation is conducted from each irradiation direction (gantry angle). This method is to distribute the optimal dosage by accumulating each series of irradiation at each angle with moving and controlling the MLC. An RTP machine is constituted of hardware equipment such as a computer main unit, a keyboard, a monitor, a scanner, a printer, and software to control them. It plans how to operate the linac based on methods such as the aforementioned different types of radiation therapy, and creates data to control the gantry angle, the collimator angle, the MLC positions, the couch angle, the radiation dosage, and others. The created data is input into a linac, which operates according to the data, and a radiation therapy is provided as planned by the RTP machine. In conformal therapy and IMRT sliding window method, the leaf positions change during the irradiation. An MLC is constituted of a number of metal leaves, and the individual leaves are driven by motors to control their positions. Therefore, when the leaves move, the leaf motion speed is limited by the motor revolution speed limit, and the leaf motion acceleration is also limited by the leaf momentum and the motor torque. When MLC leaf motion speed or acceleration exceeds the tolerance and then a leaf positioning error has occurred due to going over the acceptable range, the linac usually detects an error and deactivates itself. Though there are some types of linacs which are capable of resuming after the MLC positioning has been completed, in general the operator has to reset the treatment parameters according to the deactivated status. In either case, since radiation output of a linac cannot rise quickly, there would be an error with the treatment plan. In case of a pneumatic drive or a hydraulic drive to control the MLC, there would still be a speed and torque limit as with the motor drive. The objective of the present invention is to devise an RTP machine which is capable of generating data reflected by the MLC leaf limits of the motion speed and acceleration. The present invention provides a radiation therapy treatment planning machine for use with a multileaf collimator. In one aspect of the present invention, the machine comprises: a Multileaf-Collimator-Position-Calculation-Unit operable to generate multileaf collimator leaf positions as a time series; a Motion-Speed-Calculating-Unit operable to calculate leaf motion speed based on the generated time series leaf positions; a Motion-Speed-Limit-Establishing-Unit operable to establish a motion speed limit of the leaves; and a Motion-Display-Unit operable to indicate leaf motion information and to indicate the motion information of an area where the calculated motion speed exceeds the established motion speed limit. In one embodiment of the above aspect, the Motion-Speed-Limit-Establishing-Unit comprises a Motion-Speed-Limit-Inputting-Unit operable to input a motion speed limit of the leaves as the established motion speed limit. Further the machine can comprise: a Motion-Acceleration-Calculating-Unit operable to calculate leaf motion acceleration based on the time series leaf positions generated by the Multileaf-Collimator-Position-Calculation-Unit; and a Motion-Acceleration-Limit-Inputting-Unit operable to input a motion acceleration limit of the leaves, wherein the Motion-Display-Unit is further operable to indicate the motion information of an area where the calculated motion acceleration exceeds the inputted acceleration limit. In another embodiment of the above aspect, the Motion-Speed-Limit-Establishing-Unit comprises a Motion-Speed-Limit-Setting-Unit operable to set a predetermined motion speed limit of the leaves as the established motion speed limit. Further the machine can comprise: a Motion-Acceleration-Calculating-Unit operable to calculate leaf motion acceleration based on the time series leaf positions generated by the Multileaf-Collimator-Position-Calculation-Unit; and a Motion-Acceleration-Limit-Setting-Unit operable to set a predetermined motion acceleration limit of the leaves, wherein the Motion-Display-Unit is further operable to indicate the motion information of an area where the calculated motion acceleration exceeds the predetermined set acceleration limit. In another embodiment of the above aspect, the machine can further comprise: a Motion-Acceleration-Calculating-Unit operable to calculate leaf motion acceleration based on the time series leaf positions generated by the Multileaf-Collimator-Position-Calculation-Unit, wherein the Motion-Display-Unit is further operable to indicate the motion information of an area where the calculated motion acceleration exceeds a motion acceleration limit. In another aspect of the present invention, the machine comprises: a Multileaf-Collimator-Position-Calculation-Unit operable to generate multileaf collimator leaf positions as a time series; a Motion-Speed-Calculating-Unit operable to calculate leaf motion speed based on the generated time series leaf positions; a Motion-Speed-Limit-Establishing-Unit operable to establish a motion speed limit of the leaves; and a Leaf-Position-Correction-Unit operable to correct the leaf positions of an area, where the calculated motion speed exceeds the inputted motion speed limit, in order for the leaf motion speed to be equal to or less than the established motion speed limit. In one embodiment of the above aspect, the Motion-Speed-Limit-Establishing-Unit can comprises a Motion-Speed-Limit-Inputting-Unit operable to input a motion speed limit of the leaves as the established motion speed limit. Further the machine can comprise a Motion-Acceleration-Calculating-Unit operable to calculate leaf motion acceleration based on the leaf positions corrected by the Leaf-Position-Correction-Unit; and a Motion-Acceleration-Limit-Inputting-Unit operable to input a motion acceleration limit of the leaves, wherein the Leaf-Position-Correction-Unit is further operable to correct the leaf positions of an area, where the calculated motion acceleration exceeds the inputted acceleration limit, in order for the leaf motion acceleration to be equal to or less than the inputted acceleration limit. In any event, leaf positions can be corrected toward a direction to widen the radiation field shape when the Leaf-Position-Correction-Unit corrects the leaf positions of an area where the calculated motion speed exceeds the inputted motion speed limit in order for the leaf motion speed to be equal to or less than the inputted motion speed limit. Alternatively, leaf positions can be corrected toward a direction to narrow the radiation field shape when the Leaf-Position-Correction-Unit corrects the leaf positions of an area where the calculated motion speed exceeds the inputted motion speed limit in order for the leaf motion speed to be equal to or less than the inputted motion speed limit. In another embodiment of the above aspect, the Motion-Speed-Limit-Establishing-Unit can comprise a Motion-Speed-Limit-Setting-Unit operable to set a predetermined motion speed limit of the leaves as the established motion speed limit. Further the machine can comprise: a Motion-Acceleration-Calculating-Unit operable to calculate leaf motion acceleration based on the leaf positions corrected by the Leaf-Position-Correction-Unit; and a Motion-Acceleration-Limit-Setting-Unit operable to set a predetermined motion acceleration limit of the leaves, wherein the Leaf-Position-Correction-Unit is further operable to correct the leaf positions of an area, where the calculated motion acceleration exceeds the predetermined set acceleration limit, in order for the leaf motion acceleration to be equal to or less than the predetermined set acceleration limit. In any event, leaf positions can be corrected toward a direction to widen the radiation field shape when the Leaf-Position-Correction-Unit corrects the leaf positions of an area where the calculated motion speed exceeds the predetermined set motion speed limit in order for the leaf motion speed to be equal to or less than the predetermined set motion speed limit. Alternatively, leaf positions can be corrected toward a direction to narrow the radiation field shape when the Leaf-Position-Correction-Unit corrects the leaf positions of an area where the calculated motion speed exceeds the predetermined set motion speed limit in order for the leaf motion speed to be equal to or less than the predetermined set motion speed limit. In another aspect of the present invention, the machine comprises: a Multileaf-Collimator-Position-Calculation-Unit operable to generate multileaf collimator leaf positions as a time series; a Motion-Acceleration-Calculating-Unit operable to calculate leaf motion acceleration based on the generated time series leaf positions; Motion-Acceleration-Limit-Establishing-Unit operable to establish a motion acceleration limit of the leaves; and a Motion-Display-Unit operable to indicate leaf motion information of an area where the calculated motion acceleration exceeds the established acceleration limit. Still further, the Motion-Acceleration-Limit-Establishing-Unit can comprise a Motion-Acceleration-Limit-Inputting-Unit operable to input a motion acceleration limit of the leaves as the established motion acceleration limit. Alternatively, the Motion-Acceleration-Limit-Establishing-Unit can comprise a Motion-Acceleration-Limit-Setting-Unit operable to set a predetermined motion acceleration limit of the leaves as the established motion acceleration limit. In another aspect of the present invention, the machine comprises: a Multileaf-Collimator-Position-Calculation-Unit operable to generate multileaf collimator leaf positions as a time series; a Motion-Acceleration-Calculating-Unit operable to calculate leaf motion acceleration based on the generated time series leaf positions; Motion-Acceleration-Limit-Establishing-Unit to establish a motion acceleration limit of the leaves; and a Leaf-Position-Correction-Unit operable to correct the leaf positions of an area, where the calculated motion acceleration exceeds the established motion acceleration limit, in order for the leaf motion acceleration to be equal to or less than the established motion acceleration limit. Still further, the Motion-Acceleration-Limit-Establishing-Unit can comprise a Motion-Acceleration-Limit-Inputting-Unit operable to input a motion acceleration limit of the leaves as the established motion acceleration limit. Alternatively, the Motion-Acceleration-Limit-Establishing-Unit can comprise a Motion-Acceleration-Limit-Setting-Unit operable to set a predetermined motion acceleration limit of the leaves as the established motion acceleration limit. The RTP machine, according to the present invention, is capable of having different functions to display and correct the leaf positions when either the speed or the acceleration exceeds the limit. In the present invention, when the leaf positions are corrected in order for the leaf motion to be equal to or less than the limit, there are two ways to correct the leaf positions: firstly toward a direction to widen the radiation field shape (to open the leaves) and secondly toward a direction to narrow the radiation field shape (to close the leaves). Which method is adopted depends on the case. The Multileaf-Collimator-Position-Calculation-Unit, the Motion-Speed-Calculating-Unit, the Motion-Speed-Limit-Inputting-Unit, the Motion-Speed-Limit-Setting-Unit, the Motion-Display-Unit, the Leaf-Position-Correction-Unit, the Motion-Acceleration-Calculating-Unit, the Motion-Acceleration-Limit-Inputting-Unit and the Motion-Acceleration-Limit-Setting-Unit are all functions which have been programmed into the software in the present invention. The Multileaf-Collimator-Position-Calculation-Unit is a function of the software to generate MLC leaf positions conventional publicly-known RTP machines. The Motion-Speed(Acceleration)-Calculating-Unit is a function of the software which calculates leaf motion speed (or acceleration) based on the time series leaf positions generated by the Multileaf-Collimator-Position-Calculation-Unit. The Motion-Speed(Acceleration)-Limit-Inputting-Unit is a function of the software which shows an input screen, lets an operator input the leaf speed (or acceleration) limit and sets the input value. The Motion-Speed(Acceleration)-Limit-Setting-Unit is a function of the software which reads the speed (or acceleration) limit from the software itself—or from a parameter list—and sets the value. The Motion-Display-Unit is a function of the software to display at least the area where the leaf motion speed (or acceleration) calculated by the Motion-Speed(Acceleration)-Calculating-Unit exceeds the limit, e.g., it displays the area on the monitor screen or on the print-out. The Leaf-Position-Correction-Unit is a function of the software to correct the leaf positions of the area where the calculated motion speed (or acceleration) exceeds the limit, in order for the leaf motion speed (or acceleration) to be equal to or less than the limit. According to the present invention, the RTP machine restricts the MLC leaf motion speed and acceleration within the limit or displays the area where the motion exceeds the limit and warns the operator. Accordingly, when the linac actually treats a patient, it is possible to prevent a dosage distribution different to that the treatment plan because of the MLC leaf positioning error and it is possible to prevent the linac from stopping as a result of detecting the error and de-activating itself. The following embodiment is described as an example of conformal therapy. Conformal therapy is a method to continuously irradiate while a gantry rotates and an MLC changes. For conformal therapy, MLC leaf positions are usually calculated from projected contours which are extracted from the CT images in two dimensions seen from the gantry angle of the rotation with a certain width of margin processing. While the gantry is rotating and irradiating, the shape of the cancer (target) at the gantry angle changes continuously, the leaves are moved to fit the changes. For a conformal therapy plan, the leaf positions are usually generated with each two degrees of the gantry angle and the leaf position's resolution is generally 1 mm. For conformal therapy, rotation of the gantry means elapse of time, namely, changing angle means passing time. The time series leaf positions are generated by the Multileaf-Collimator-Position-Calculation-Unit, and this Multileaf-Collimator-Position-Calculation-Unit is conventionally and publicly known in. The RTP machine of the present embodiment includes a Motion-Speed-Calculating-Unit, a Motion-Speed-Limit-Inputting-Unit, a Motion-Display-Unit, a Leaf-Position-Correction-Unit, a Motion-Acceleration-Calculating-Unit and a Motion-Acceleration-Limit-Inputting-Unit in addition to a Multileaf-Collimator-Position-Calculation-Unit. The leaf speed limit of the linac is input at the Motion-Speed-Limit-Inputting-Unit. The leaf acceleration limit of the linac is input at the Motion-Acceleration-Limit-Inputting-Unit. FIG. 1 shows a trace of a pair of the leaves from the gantry rotation start angle to the end angle in conformal therapy. In the drawing, reference number 11 indicates a curve of a leaf's trace in conformal therapy, and reference number 12 indicates a curve of an opposite of the leaf's trace in conformal therapy. An MLC consists of a number of leaf pairs; a leaf pair consists of two leaves. Curve 11 and curve 12 represent the traces of each leaf of the leaf pair. The leaf speed is the difference of the leaf positions (gradient of curve 11 and curve 12) between a certain time interval (in each two degrees), and the leaf acceleration is the difference of the speeds between a certain interval (in each two degrees). The Motion-Speed-Calculating-Unit calculates motion speed of the individual leaves based on the time series leaf positions (corresponding to curve 11 and curve 12) generated by the Multileaf-Collimator-Position-Calculation-Unit. The Motion-Acceleration-Calculating-Unit calculates the motion acceleration of the leaves based on the time series leaf positions (corresponding to the curve 11 and curve 12) generated by the Multileaf-Collimator-Position-Calculation-Unit. The following section describes the Leaf-Position-Correction-Unit. The Leaf-Position-Correction-Unit compares the leaf motion speed (or acceleration) which is calculated by the Motion-Speed(Acceleration)-Calculating-Unit with the preset limit, and when the leaf motion speed (or acceleration) exceeds the limit, the Leaf-Position-Correction-Unit controls the leaf positions in order to be equal to or less than the limit. In FIG. 1, reference (a) is a dotted line of a case which opens the leaf, reference (b) is a dotted line of a case which closes the leaf, reference number 14 is an area where the leaf speed exceeds the limit, reference number 15 is a start point of the area where the leaf speed exceeds the limit, reference number 16 is an end point of the area where the leaf speed exceeds the limit, and reference number 17 is an intersection of the dotted line (a) and curve 11. It is assumed that curve 11 and curve 12 have 2 degrees and 1 mm resolution. The drawing shows the clockwise gantry rotation from 180 degrees as the lowest point to 180 degrees passing through 0 degrees as the highest point. On curve 11, there is area 14 where the leaf speed exceeds the limit around 0 degrees. The dotted line (a) shows an example where the leaf position correction starts from start point 15 of area 14 toward the direction to open the leaf compared with the position before the correction, and the dotted line (b) shows an example where the correction starts from end point 16 of area 14 toward the direction to close the leaf In general, when there are no critical organs near the organ having cancer to be irradiated, the correction to close the leaf may cause insufficient dosage of irradiation, therefore the correction to open the leaf is preferable. When there is a critical organ near the cancer, the condition determines which correction would be more preferable, to open or to close. FIG. 2 is an enlarged view at start point 15 of area 14 in FIG. 1. In this drawing, reference number 21a indicates a point next to start point 15, reference number 21b indicates a point next to start point 15 after the correction, 22a is a point next to 21a, and 22b is a point next to 21b after the correction. The leaf motion speed limit is generally 2 to 9 mm per 2 degrees and the value depends on the linac. The present embodiment is an example where the leaf motion control uses 2 mm per 2 degrees as the leaf motion speed limit. Symbols □ in the drawing are leaf positions corresponding to the curve 11 in FIG. 1, and symbols Δ are leaf positions when the motion control is applied, and corresponds to the dotted line (a) in FIG. 1. The leaf motion distance from start point 15 to point 21a is 3 mm. This value exceeds the motion limit of 2 mm, and motion control is applied at point 21a. Wherein the motion distance from start point 15 is limited to 2 mm. Point 22a is compared with point 21b, and since the accumulated difference is 5 mm, this point is controlled in order for the difference to be equal to or less than 2 mm and moved to point 22b. This operation is sequentially applied to each point, thereby the dotted line (a) in FIG. 1 is eventually obtained. FIG. 4 is an example where the acceleration limit control is applied of intersection 17 in FIG. 1. In the drawing, reference number 41 indicates the speed from the preceding point at intersection 17, reference number 42 indicates the speed to the following point at intersection 17, reference number 43 indicates the speed at which the acceleration limit control is applied to the speed indicated at reference number 41, reference number 44 indicates the speed at which the acceleration limit control is applied to the speed indicated at reference number 42, and reference number 45 indicates the leaf position at which the acceleration limit control is applied to intersection 17. In the present embodiment, it is assumed that the acceleration limit is 2. Since the speed indicated at reference number 41 is −2, and the speed indicated at reference number 42 is 1, the acceleration at intersection 17 is the difference between them, 3. Since a leaf is usually made of metal and has considerable weight, the direction of motion cannot be changed quickly due to the inertia. The output of the driving motors have a torque limit in addition to a revolution speed limit, and the motion of the leaf at intersection 17 could be a cause of a positioning error. The following section describes an acceleration limit control processing. The Motion-Acceleration-Calculating-Unit calculates leaf motion acceleration based on the time series leaf positions which are generated by the Multileaf-Collimator-Position-Calculation-Unit (corresponding to curve 11 and curve 12) and corrected by the Leaf-Position-Correction-Unit (corresponding to the dotted line (a) or (b)). The Leaf-Position-Correction-Unit corrects the leaf positions when the leaf motion acceleration exceeds the limit. In this case, since the acceleration at intersection 17 exceeds the limit, the speed indicated at reference number 41 and the speed indicated at reference number 42 at intersection 17 are both corrected with the same value to decrease the difference between them. In the present embodiment, the speed indicated at reference number 41 is corrected to the speed indicated at reference number 43, and the speed indicated at reference number 42 is corrected to the speed indicated at reference number 44 by a factor of 1 for each. Based on the equation that speed×distance=position and to maintain the continuity of the positions, the summation of the corrected areas should be 0 (zero). In this case, the area from reference number 41 to reference number 43 and the area from reference number 42 to reference number 44 are equal with opposite direction, therefore they cancel each other out, and the summation of the areas becomes 0 (zero). As a result of the leaf position correction, the operation moves point 17 to point 45 and makes the acceleration at point 45 to a factor of 1 which is equal to or less than the acceleration limit. The described section is an operation to apply to a pair of leaves, the described operations are applied to other MLC leaves to calculate speed and acceleration and to correct leaf positions. While in the present embodiment, the motion speed (acceleration) limit is an input parameter by the operator, it is also possible to comprise a Motion-Speed(Acceleration)-Limit-Setting-Unit which provides the parameter as the linac own value (written in the parameter list) or to comprise a fixed parameter in the program. The method to correct the leaf positions in the case of excessive speed or excessive acceleration in the present embodiment is simply an example, and it should be noted that different methods could be adopted. The following section describes an example of IMRT sliding window method. FIG. 5 shows motion of a pair of leaves during irradiation with IMRT sliding window method. In the drawing, reference number 51 indicates a curve of a leaf's trace with the sliding window method, reference number 52 indicates a curve of the opposite leaf's trace with the sliding window method, reference (a) is a dotted line of a case which opens the leaf, and reference (b) is a dotted line of a case which closes the leaf. With the sliding window method, the leaves move and the radiation field shape changes during irradiation. Since there is an area where the motion distance exceeds the limit around the center of the drawing, the leaf positions are corrected to the dotted lines (a) and (b) by the Leaf-Position-Correction-Unit. The condition determines which correction would be more preferable, to open or to close. In place of the Leaf-Position-Correction-Unit of the present embodiment, or along with the Leaf-Position-Correction-Unit, it is possible to comprise a Motion-Display-Unit. The Motion-Display-Unit shows the information of the area where the motion speed (acceleration) calculated by the Motion-Speed(Acceleration)-Calculating-Unit exceeds the speed (acceleration) limit. As an example, the speed (acceleration) which exceeds the limit can be indicated on the display with the gantry angles. Similarly, a chart like FIG. 1 can be displayed (e.g. area 14 where the speed exceeds the limit is a red line, and the other areas are black lines). By using this information to warn the operator, it is possible to adjust the irradiation parameter to avoid a warning arising. As described in the present embodiment, by using the irradiation data for linacs generated by the RTP machine according to the present invention, it is possible to prevent the suspension of treatment due to an MLC positioning error, which exceeds its tolerance, thereby making it possible to improve the efficiency of the radiation therapy and to decrease the patient's discomfort. |
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claims | 1. An equipment inspection support system that supports an inspection technician who is to perform equipment maintenance inspection by operating a terminal device for sequentially displaying details of work to be performed by the inspection technician and for receiving input of inspection result data from maintenance inspection work, and a status information acquisition device for acquiring status information concerning a maintenance and inspection work site, comprising:a contents storage unit for storing inspection item contents for each maintenance and inspection work to be transmitted to the terminal device, and interaction scenarios for determining an order of the inspection item contents to be transmitted to the terminal device according to equipment maintenance inspection procedures;a maintenance and inspection management unit for receiving the inspection result data from the terminal device, and for selecting and transmitting to the terminal device the inspection item contents stored in the contents storage unit based on the interaction scenario stored in the contents storage unit and the received inspection result data;a timing determination unit for determining timing for status information acquisition by the status information acquisition device based on the inspection item contents transmitted to the terminal device by the maintenance and inspection management unit and the inspection result data transmitted from the terminal device;a status information acquisition unit for collecting the status information acquired by the status information acquisition device according to the status information acquisition timing determined by the timing determination unit;a result data control unit for creating a result data correspondence table for associating the inspection result data received by the maintenance and inspection management unit with the status information collected by the status information acquisition unit; andan inspection result storage unit for storing inspection result data, status information, and result data correspondence table. 2. An equipment inspection support system according to claim 1, wherein the status information acquisition device is a video camera for acquiring image data of the maintenance and inspection work site. 3. An equipment inspection support system according to claim 2, wherein the status information acquisition device further comprises one or more sensors selected from the group consisting of a condenser microphone, odor sensor, temperature sensor, humidity sensor, tactile sensor, pressure sensor, and a sensor for acquiring status information concerning the maintenance and inspection work site other than image data. 4. An equipment inspection support system according to claim 3, wherein the timing determination unit comprises a result data judgment unit for judging whether the inspection result data is normal or abnormal; andwhen the status information acquisition device is a video camera, the status information collected by the status information acquisition unit is correlated with inspection result data and stored in the inspection result storage unit regardless of whether the judgment result by the result data judgment unit was normal or abnormal, and when the status information acquisition device is not a video camera, the status information collected by the status information acquisition unit is correlated with the inspection result data and stored in the inspection result storage unit only when the judgment by the result data judgment unit was abnormal. 5. An equipment inspection support system according to claim 3, wherein the timing determination unit comprises a result data judgment unit for judging whether the inspection result data is normal or abnormal; andthe status information collected by the status information acquisition unit is correlated with the inspection result data and stored in the inspection result storage unit only when the judgment by the result data judgment unit is abnormal. 6. An equipment inspection support system according to claim 2, further comprising an image recognition unit for analyzing image data transmitted from the status information acquisition device for comparison with the inspection result data transmitted from the terminal device, wherein when there are inconsistencies in the image recognition unit comparison results, inspection item contents giving instructions for re-inspection of the relevant inspection item are transmitted to the terminal device by the maintenance and inspection management unit. 7. An equipment inspection support system according to claim 2, further comprising an object of inspection detector for performing image recognition of image data from the status information acquisition device, determining the identification code attached to the equipment or device to be inspected, and determining conformity with the inspection item contents currently being processed by the maintenance and inspection management unit. 8. An equipment inspection support system according to claim 1, further comprising:an inspection result query unit for allowing a third party to query the inspection result data and status information stored in the inspection result storage unit; anda re-inspection instruction unit for causing, with respect to the maintenance and inspection work corresponding to the inspection result data and status information stored in the inspection result storage unit, inspection item contents that indicate additional inspection to be transmitted from the maintenance and inspection management unit to the terminal device, and/or causing the status information acquisition unit to reacquire the status information from the status information acquisition device. 9. An equipment inspection support system according to claim 1, wherein status information acquisition means inserts additional information such as maintenance and inspection work location, acquisition time, inspection technician data and the like into acquired status information using an invisible digital watermark. 10. An equipment inspection support method that supports an inspection technician who perform equipment maintenance inspection by operating a terminal device for sequentially displaying details of work to be performed by the inspection technician and for receiving input of inspection result data from the maintenance inspection work, and acquiring status information on a maintenance and inspection work site from a status information acquisition device, comprising:storing inspection item contents for each maintenance and inspection work to be transmitted to the terminal device, and interaction scenarios for determining an order of the inspection item contents to be transmitted to the terminal device according to equipment maintenance inspection procedures;receiving, in a maintenance and inspection management unit, the inspection result data from the terminal device, and selecting and transmitting to the terminal device the stored inspection item contents based on the stored interaction scenario and the received inspection result data;determining, in a timing determination unit, timing for the acquired status information based on the inspection item contents transmitted to the terminal device by the maintenance and inspection management unit and the inspection result data transmitted from the terminal device;collecting the acquired status information according to the status information acquisition timing determined by the timing determination unit;creating a result data correspondence table for associating the inspection result data received by the maintenance and inspection management unit with the acquired status information collected by the status information acquisition unit; andstoring the inspection result data, acquired status information, and result data correspondence table. 11. A computer-readable medium storing a program for causing a computer to execute an equipment inspection support method that supports an inspection technician who is to perform equipment maintenance inspection by operating a terminal device for sequentially displaying details of work to be performed by such inspection technician and for receiving input of inspection result data from the maintenance inspection work, and acquiring status information of a maintenance and inspection work site from a status information acquisition device, according to a process comprising:storing the inspection item contents for each maintenance and inspection work to be transmitted to the terminal device, and interaction scenarios for determining the order of the inspection item contents to be transmitted to the terminal device according to the equipment maintenance inspection procedures;receiving, in a maintenance and inspection management unit, the inspection result data from the terminal device, and selecting and transmitting to the terminal device the stored inspection item contents based on the stored interaction scenario and the received inspection result data;determining, in timing determination unit, timing for the acquired status information based on the inspection item contents transmitted to the terminal device by the maintenance and inspection management unit and the inspection result data transmitted from the terminal device;collecting the status information acquired by the status information acquisition device according to the status information acquisition timing determined by the timing determination unit;creating a result data correspondence table for associating the inspection result data received by the maintenance and inspection management unit with the status information collected by the status information acquisition unit; andstoring the inspection result data, status information, and result data correspondence table. |
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abstract | A system for passively cooling nuclear fuel in a pressurized water reactor during refueling that employs gravity and alignment of valves using battery reserves or fail in a safe position configurations to maintain the water above the reactor core during reactor disassembly and refueling. A large reserve of water is maintained above the elevation of and in fluid communication with the spent fuel pool and is used to remove decay heat from the reactor core after the reaction within the core has been successfully stopped. Decay heat is removed by boiling this large reserve of water, which will enable the plant to maintain a safe shutdown condition without outside support for many days. |
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062051954 | claims | 1. An apparatus for analyzing radiation emitted by an object in response to nuclear interrogation, the apparatus comprising: a radiation detector for detecting radiation emitted by the object in response to nuclear interrogation by a source of excitation energy and for producing detection signals responsive to the radiation; a coded aperture system having at least one coded aperture array of a predetermined configuration, positioned such that the emitted radiation is detected by the detector after passage through the coded aperture system; and a data processor for characterizing at least one characteristic of the object, the characteristic being indicated by the origin, amount and energy spectra of the radiation emitted from within the object, as determined by detection signals produced by the detector, and the predetermined configuration of the coded aperture array. 2. The apparatus of claim 1, wherein the data processor characterizes the object based upon the signals from the detector and based upon the predetermined configuration of the coded aperture array. 3. The apparatus of claim 1, wherein the excitation source is a gramma-ray source. 4. The apparatus of claim 1, wherein the excitation source is an X-ray source. 5. The apparatus of claim 1, wherein the detector has a substantially planar array of detector elements. 6. The apparatus of claim 1, wherein the detector comprises a scintillating material. 7. The apparatus of claim 1, wherein the detector further comprises a photomultiplier. 8. The apparatus of claim 1, wherein the coded aperture system is a one-dimensional pattern of coded apertures. 9. The apparatus of claim 1, wherein the coded aperture system is a substantially planar two-dimensional pattern of coded apertures. 10. The apparatus of claim 1, wherein the data processor comprises means for distinguishing an object containing contraband from an object not containing contraband. 11. The apparatus of claim 1, wherein the excitation source is a beam of fast neutrons. 12. The apparatus of claim 11, wherein the neutrons each have energies between about 1 MeV and about 15 MeV. 13. The apparatus of claim 1, wherein the radiation emitted in response to nuclear interrogation of the object is in the form of gamma rays. 14. The apparatus of claim 13, wherein the signals are representative of the location, number and energy spectra of the gamma rays. 15. The apparatus of claim 1, wherein the coded aperture system is a uniformly redundant array of coded apertures. 16. The apparatus of claim 15, wherein the uniformly redundant array of coded apertures are extended Hadamard cyclic difference set uniformly redundant arrays. 17. The apparatus of claim 1, wherein the data processor comprises an imaging means for yielding a three dimensional image of a predetermined characteristic of the object. 18. The apparatus of claim 17, wherein the predetermined characteristic of the object is the elemental composition of the object. 19. The apparatus of claim 17, wherein the predetermined characteristic of the object is the relative density of predetermined elements in the object. 20. The apparatus of claim 19, wherein the predetermined elements are selected from the group consisting of oxygen, carbon, nitrogen, hydrogen, and chlorine. |
abstract | An X-ray optical configuration (1), comprising a position for an X-ray source (2), a position for a sample (3), a first focusing element (4) for directing X-ray radiation from the position of the X-ray source (2) via an intermediate focus (5) onto the position of the sample (3), and an X-ray detector (6) that can be moved on a circular arc (7) of radius R around the position of the sample (3), is characterized in that the configuration also comprises a second focusing element (8) for directing part of the X-ray radiation emanating from the intermediate focus (5) onto the position of the sample (3), and an aperture system (9) for selecting between illumination of the position of the sample (3) exclusively and directly from the intermediate focus (5) (=first optical path (10′)), or exclusively via the second focusing element (8) (=second optical path (10″)). The configuration facilitates changing between reflection geometry and transmission geometry, in particular, wherein modification and adjustment devices are minimized or unnecessary. |
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043812805 | claims | 1. A trigger device for directing electron beam pulses toward a target comprising: an electron accelerator having a cathode for emitting electrons and an accelerating electrode having plural openings therein through which electrons exit said accelerator, said cathode being a multi-element cathode having a plurality of separate emitting portions for simultaneously generating separate electron beam pulses from a common source, said emitting portions being positioned adjacent respective openings, in said accelerating electrode for directing electrons from an emitting portion through a particular electrode opening, a plurality of curved dielectric linear pinch discharge tubes of equal length for directing the separate electron beam pulses to the target from different directions for symmetrically and simultaneously irradiating the target uniformly, each tube having a first end adjacent said accelerating electrode for receiving electrons therein from only one of said cathode emitting portions, a second end adjacent said target, and being filled with a plasma producing medium for providing electron transport through said tube. 2. A trigger device as set forth in claim 1 and further comprising a plurality of electrical conductors disposed along the length of each dielectric tube for developing a composite magnetic field within said tube and thereby controlling the position of electron beam transporting plasma within the tube. 3. A trigger device as set forth in claim 2 wherein said plurality of electrical conductors are disposed symmetrically around straight portions of said tubes and non-symmetrically around curved portion of said tubes for maintaining plasma flow away from the tube inner surfaces and toward the center of the tubes. 4. A trigger device as set forth in claim 3 wherein said plurality of electrical conductors are at least eight conductors and said non-symmetrically arranged portions of conductors are disposed to develop a stronger magnetic field on the outer radius of said curved tube portion than on the inner radius to effect bending of said electron beam and plasma within the tubes. 5. A trigger device as set forth in claim 4 wherein said plurality of tubes are four tubes, with respective first and second pair of said tubes each having the second end of said pair in coaxial alignment with each other and with said target therebetween for uniformily irradiating said target. 6. A trigger device as set forth in claim 4 wherein said plurality of dielectric tubes are 2 tubes, said tubes being disposed with the second ends thereof coaxially positioned for simultaneously irradiating said target from opposite directions, and means holding said target for developing a magnetic field parallel with the target axis for retarding heat loss in the radial direction and enhancing one-dimensional expansion in the direction of irradiation. |
abstract | A first and a second accumulated value calculating units are provided which, in a location where foil shadows by grid foil strips straddle pixels, identify this location based on geometry, and calculate straddle accumulated values of the foil shadows in the identified location. Even when the foil shadows by the grid foil strips straddle the pixels due to twisting and bending of the grid foil strips, such location is identified based on geometry and the straddle accumulated values of the foil shadows in the identified location are calculated. Therefore, even when changes are made in the pitches or pixel sizes of an X-ray grid and a flat panel X-ray detector (FPD), the foil shadows will be removed based on the straddle accumulated values. As a result, the foil shadows can be removed taking twisting and bending of the grid foil strips into consideration, and in a way to accommodate X-ray grids and FPDs of various sizes. |
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043702970 | abstract | A method and apparatus for dissociating steam in a fusion reaction central chamber. The charged particle energy from an ignited fusion fuel pellet is directed to and distributed in a suitable volume of steam, bringing the steam to temperature and pressure conditions leading to dissociation into hydrogen and oxygen. The resulting atomic and molecular velocities are sufficiently high to allow egress of the separated products through a suitable shaped nozzle prior to recombination, making it practical to separate and capture the dissociated products. |
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053735390 | summary | BACKGROUND OF THE INVENTION 1. Field Of The Invention This invention is directed to a pressurized water reactor having a safety system grade system for automatically blocking withdrawal of control rods in response to a dropped control rod. 2. Background Of The Invention The reactivity of a pressurized water reactor is controlled by regulating the concentration of a neutron absorber, such as boron, in reactor coolant circulated through the reactor core, and by control rods which can be inserted into the reactor core. Changes in boron concentration have a core wide effect while the insertion of control rods is more localized. Typically, the control rods are stepped into and out of the core, but can be dropped into the core rapidly to shut down the core should the need arise. It is possible that during normal operation one or more individual control rod drives could malfunction and drop control rods into the core. This results in a reduction in the reactivity of the core with consequent lowering of the average temperature of coolant exiting the core. When this lowering of the average temperature of the coolant exiting the core is detected by the control system, about ten seconds after the actual rod drop, the conventional control system responds to this reduction in temperature by withdrawing specified control rods in order to raise the core average temperature to a set point level. This can result in excessive heat rise in another part of the core as the control system attempts to compensate for the reduction in core reactivity. In a conventional pressurized water reactor, regulation of the boron concentration is used to control power level with the control rods being manipulated to control power distribution during transients. Even when load following with such a control strategy, only about one-third of the control rods are inserted into the reactor core at power. It has been analytically determined that with such a control scheme, even in the worst case, a dropped rod will not result in a dangerous over-temperature condition in another part of the core. Hence, while a dropped rod has an adverse effect on the operation of a conventional reactor, it is not a critical safety item. Assignee of the present invention has developed an advanced pressurized water reactor which is protected by passive safety systems. That is, no operator intervention is required to maintain safe operating conditions in the reactor despite various postulated malfunctions. The control strategy for this advanced pressurized water reactor calls for load following primarily with the control rods only and not through regulation of the boron concentration. This results in a wide variation in the combinations of banks of control rods inserted into the core to follow the load and maintain proper power distribution in the core. This makes it impractical to analytically determine whether, with all the possible combinations of rod insertions, there is no situation where a dropped rod would not cause fuel damage in another part of the core. Thus, there is a need with the advanced pressurized water reactor operated to load follow with the control rods rather than through regulation of boron concentration to have a reliable system for determining if there is a dropped rod. In order to meet the criteria of the advanced pressurized water reactor that all protection systems be passive, any system for detecting a dropped rod must be safety system grade. That is, it must have the degree of reliability that it can operate automatically without the intervention of the human operator. The safety system grade standards are set forth in IEEE Std. 603-1980 which is hereby incorporated by reference. The IEEE Std. 603-1980 standards are mandated by the U.S. Nuclear Regulatory Commission for applications over which the NRC has jurisdiction in Regulatory Guide 1.153 which is also incorporated by reference herein. It is known to have rod position indicators which track the stepping of the control rods in and out of the reactor core to provide an indication of rod position. It is also known to have rod bottom lights actuated by microswitches when a rod is fully inserted. However, neither of these systems is safety system grade. There are some safety system grade control rod position indicator systems, but they are expensive and cumbersome to maintain. U.S. Pat. No. 4,774,049 discloses a system which generates on-line, real time displays of reactor core power distributions, and in particular precisely calculates and displays two dimensional core power distributions relative to a reference position. With the use of the described system a skilled human observer can extract an indication of a dropped control rod. However, this system is not of safety system grade and, more importantly, it is not passive. Furthermore, it cannot readily allow the human observer to recognize a failing thermocouple. There is a need, therefore, for an improved, fully automatic system and method for identifying a dropped rod in a pressurized water reactor, and in particular for such a system which is safety system grade. There is also a need for such a system and method which can distinguish between a dropped rod and a failure in the system itself. SUMMARY OF THE INVENTION These and other needs are satisfied by the invention which is directed to a method and safety system grade apparatus for detecting a dropped rod in a pressurized water reactor. In particular, the invention is directed to a method and apparatus for detecting a dropped rod and automatically blocking the reactor rod control system from withdrawing control rods from the reactor core when a dropped rod is detected. A dropped rod is detected using core exit thermocouples and a processor which analyzes the signals generated by the thermocouples to identify a dropped rod. In particular, the thermocouple signals are used together with temperature sensors measuring average core inlet and outlet temperatures, preferable through hot and cold leg temperature sensors, to generate for each thermocouple position a relative power deviation between the temperature rise in the fuel assembly at the thermocouple location and the temperature rise across the reactor vessel, relative to reference conditions. The relative power deviations for the remaining fuel assemblies at which there are no thermocouples are extrapolated, preferably using known surface spline fit techniques. Curvature indices, which are indicative of the spatial second derivatives of the relative power distributions, are then calculated for all of the fuel assemblies. The curvature indices for the fuel assemblies having control rods, and for the adjacent fuel assemblies, preferably the laterally adjacent fuel assemblies, are then analyzed to detect a dropped rod and to differentiate a failed thermocouple from a dropped rod. |
046506357 | summary | FIELD OF THE INVENTION The invention relates to a process for the monitoring of leaks in the primary circuit of a pressurized water nuclear reactor. The primary circuit of nuclear reactors which are cooled with water under pressure corresponds to the part of this reactor which contains water under pressure for cooling the reactor core. This primary circuit therefore comprises the reactor vessel enclosing the core, the primary part of the steam generators, the inner volume of the pressurizer and of the pipes for circulating pressurized water, connecting each of the steam generators to the vessel independently, each of the parts of the circuit comprising a steam generator and a system of pipes which are connected to the vessel and form a loop of the primary circuit. The primary circuit is also connected to auxiliary circuits including the circuit for volumetric and chemical monitoring of the pressurized water. This auxiliary circuit which is arranged branching on the primary circuit makes it possible both to maintain the quantity of water in the primary circuit by replenishing, when required, with measured quantities of water and to monitor the chemical properties of the cooling water, particularly its content of boric acid which is involved in the operation of the reactor. During the periods when the chemical properties of the reactor water are adjusted, it may be necessary to carry out tappings or injections into the primary circuit, the quantities tapped or injected being known and controlled in a highly accurate manner. Outside these periods of injections or tappings, the valves connecting auxiliary circuits other than the circuit for volumetric and chemical control to the primary circuit are closed. The primary circuit is then theoretically isolated and completely sealed, with the result that the quantity of water in this primary circuit is theoretically constant. In practice, however, it is observed that this quantity of cooling water diminishes during the operation of the reactor, as a consequence of unavoidable leaks which can be monitored and perfectly evaluated or, on the contrary, unmonitored. The unmonitored leaks can themselves be localized or unlocalized and, in the latter case, the evaluation of the magnitude of these leaks is particularly difficult. It is nevertheless very important to have good knowledge of the leakage rate of the primary circuit, in order to undertake preventive actions before accidental leaks become more serious and call into question the safety of operation of the nuclear reactor. PRIOR ART Various processes have been proposed for detecting leaks in a closed circuit. It has been proposed, for example, to employ sound detectors to show the presence of a leak greater than a limit value at a location in the circuit. This process, however, does not make it possible to estimate the total of the leaks from the circuit and indications given are not really quantitative. There has also been proposed, in French Patent No. 2,214,992, a process making use of a level control in an expansion vessel arranged in the circuit and a measurement of the temperature of the fluid in the closed circuit. If the changes in level in the expansion vessel are incompatible with the change in the mean temperature of the fluid, it is concluded from this that the changes in level are due to leaks. A replenishment of liquid is then carried out in the expansion vessel until the level returns to a predetermined level which is a function of the mean temperature of the fluid. This process, which permits the presence of leaks to be detected, does not however allow them to be estimated quantitatively in a precise manner. U.S. Pat. No. 3,712,750 describes a process for detecting leaks in the cooling circuit of the primary circuit of a nuclear reactor. The leaks are collected in a drainage sump under the reactor vessel and the leak liquid collected evaporates in the reactor safety housing. During the treatment before recirculation of air in the reactor housing the traces of tritium which may be present in the water vapor present in this air are measured. The radioactivity in the reactor housing air can also be measured directly. This process, which permits the leaks to be determined in a more or less quantitative manner, is, however, highly complex in use. SUMMARY OF THE INVENTION The aim of the invention is therefore to offer a process for monitoring leaks in the primary circuit of a pressurized water nuclear reactor comprising a vessel enclosing the reactor core, at least two steam generators connected independently to the vessel by pipework for circulating water under pressure, a pressurizer, at least one auxiliary circuit for monitoring and replenishment of the water under pressure and stocktanks inserted in the primary circuit and in the auxiliary circuit, this monitoring process permitting a quantitative determination of the total leaks from the primary circuit with very high accuracy and employing only conventional, easily operated means of measurement. To this end, a sectioning of the internal volume of the primary circuit and of the circuit for volumetric and chemical monitoring, excluding the stocktanks, is determined, as a function of the characteristics of the primary circuit, into a set of volume elements in which the temperature and the pressure of the water are equal at any point in the volume element with a predetermined margin of error, during the operation of the reactor, at fixed time intervals, called "steps", during the operation of the reactor: the level of the pressurized water is measured inside each of the stocktanks, the pressure and the temperature of the pressurized water are measured in each of the volume elements, the mass of water in each of the stocktanks and in each of the volume elements is calculated as a function of the measured temperatures, pressures and levels, the total mass of water in the primary circuit is calculated by adding the masses of water in the volume elements and in the stocktanks, and for periods of time which correspond to a multiple of the step and which are offset by at least one step, the mean of the masses of water in the primary circuit and the difference of the mean values corresponding to two successive periods of time are calculated, the difference representing the leakage flow of the primary circuit. |
claims | 1. Lens system for a plurality of charged particle beams, comprising:a lens body with a first pole piece, a second pole piece and a plurality of lens openings for the respective charged particle beams;a common excitation coil arranged around the plurality of lens openings for providing a respective first magnetic flux to the lens openings; anda compensation coil arranged between the lens openings for providing a respective second magnetic flux to at least some of the lens openings so as to compensate for an asymmetry of the first magnetic flux, wherein the compensation coil is arranged such that axial extension of each of the lens openings is outside the compensation coil. 2. Lens system according to claim 1, wherein the compensation coil is arranged around a magnetic stub, the magnetic stub providing an essentially gapless connection between the first pole piece and the second pole piece. 3. Lens system according to claim 1, wherein the compensation coil is arranged such that all lens openings are outside of the compensation coil when viewed from an optical axis defined by the lens openings. 4. Lens system according to claim 1, wherein during operation the compensation coil carries a current in the opposite direction of a current carried by the excitation coil. 5. Lens system according to claim 1, wherein the lens openings are arranged in a two-dimensional arrangement. 6. Lens system according to claim 1, wherein the lens openings are arranged as an array having at least two rows and at least two columns. 7. Lens system according to claim 1, wherein the lens openings have, at least in one direction, a distance with respect to each other of less than 90 mm. 8. Lens system according to claim 1, wherein each one of the lens openings defines a respective optical axis and wherein during operation a lens field for each one of the openings has at least one plane of symmetry, the at least one plane of symmetry containing the respective optical axis. 9. Lens system according to claim 1, being symmetrical with respect to a plane of symmetry (S1, S2) containing a respective center of at least one of the lens openings. 10. Lens system according to claim 1, being symmetrical with respect to at least two planes of symmetry (S1, S2). 11. Lens system according to claim 1, wherein the plurality of lens openings is at least four lens openings. 12. Lens system according to any claim 1, further comprising, for each of the plurality of lens openings, an adjustment coil arranged around the respective lens opening. 13. Lens system according to claim 1, wherein at least one of the first pole piece and the second pole piece are provided as a single body of magnetic material. 14. Lens system according to claim 1, wherein in the region of the lens openings, a gap separates the first pole piece from the second pole piece. 15. Multiple charged particle beam device, comprising:a charged particle beam source for generating a plurality of charged particle beams; anda charged particle beam column comprising a lens system according to claim 1. 16. Method for operating a charged particle beam device, comprising:generating a plurality of charged particle beams;guiding each of the charged particle beams through a respective one of a plurality of lens openings of a lens body;generating a current, in a first direction, in a common excitation coil arranged around the plurality of lens openings, thereby providing a respective first magnetic flux to the lens openings; andgenerating a current, in a second direction opposite to the first direction, in a compensation coil arranged between the lens openings, thereby providing a respective second magnetic flux to at least some of the lens openings and compensating an asymmetry of the first magnetic flux, wherein the compensation coil is arranged such that axial extension of each of the lens openings is outside the compensation coil. 17. Method according to claim 16, wherein the lens openings are arranged as an array having at least two rows and at least two columns. 18. Method according to claim 16, wherein the lens openings have, at least in one direction, a distance with respect to each other of less than 90 mm. 19. Method according to claim 16, wherein the compensation coil is arranged such that all lens openings are outside of the compensation coil when viewed from an optical axis defined by the lens openings. |
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claims | 1. A specimen observation method whereby locations on a specimen displayed on an optical microscope image acquired by an optical microscope are observed by a charged-particle beam device, said specimen observation method, comprising the steps of:staining said optical microscope image for being acquired by said optical microscope,acquiring said optical microscope image by said optical microscope,acquiring an elemental mapping image based on detection of X-rays, said X-rays being emitted from said specimen when said specimen is scanned with said charged-particle beam,making a comparison between said optical microscope image stained and said elemental mapping image, andscanning locations on said specimen or a location on said specimen with said charged-particle beam, coincidence degrees between said optical microscope image stained and said elemental mapping image exceeding a predetermined value at said locations on said specimen, said coincidence degree being the highest at said location on said specimen, anddetecting said charged particles, and/or detecting position information on said locations or said location. 2. The specimen observation method according to claim 1, whereinsaid locations on said specimen are ranked in a descending order of said coincidence degrees. 3. The specimen observation method according to claim 1, whereina charged-particle beam image at said locations on said specimen and/or said location on said specimen, or said position information on said locations and/or said location are recorded as a single file, said coincidence degrees between said optical microscope image and said elemental mapping image exceeding said predetermined value at said locations on said specimen, said coincidence degree being the highest at said location on said specimen. |
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abstract | An x-ray chopper wheel assembly includes a disk chopper wheel and a source-side scatter plate that has a solid cross-sectional area that absorbs x-ray radiation and is substantially smaller than a solid cross-sectional area of the disk chopper wheel. The assembly also includes a support structure that secures the source-side scatter plate substantially parallel to the disk chopper wheel, with a source-side gap between the scatter plate and the disk chopper wheel being a distance that substantially prevents x-ray leakage. An additional, output-side scatter plate may also be provided to reduce x-ray leakage further. Embodiments enable safe operation while significantly reducing weight, which is advantageous for a variety of disk-chopper-wheel-based x-ray scanning systems, especially hand-held x-ray scanners. |
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059828382 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and portable apparatus which is used to detect substances, such as explosives and drugs, by neutron irradiation. More particularly, the present invention is directed towards an apparatus which utilizes gamma ray detection, said gamma rays emitted by the interrogated object after subjecting it to a neutron burst thereby providing the ability to calculate the concentration of an element in the object of interest. 2. Discussion of the Prior Art High explosives and illicit drugs are primarily composed of the chemical elements of hydrogen, carbon, nitrogen and oxygen. Systems for the detection of these elements are fairly well known. These systems utilize the irradiation of such material by neutrons and detection of gamma photons emitted by the materials after subjecting them to said neutron burst. One technique of such detection is neutron activation analysis. These prior art devices utilize the known effect of gamma ray emission from the nucleus of the objects being interrogated after irradiation. The concentration of these gamma rays can be detected by gamma ray detectors and the signals analyzed to determine the concentrations of chemical elements which make up the object being interrogated. These elements are found in explosives or illicit drugs in differing quantities, ratios and concentrations. By calculating and determining said ratios and concentrations, it is possible to identify and differentiate drugs and other contraband from sugar or other materials by measuring the amount of hydrogen,, carbon or other material contained in the interrogated object. It is further understood that the process of producing gamma photons by the interaction of the nucleus of the inspected material with neutrons from a neutron generator can be effected by either of three processes. These include fast neutron, thermal neutron and neutron activation reactions. Thermal neutron reactions occur by the capture of a neutron by a nucleus producing an isotope which is de-excited by the emission of gamma radiation. Fast neutron reactions result in the inelastic scattering of a neutron on a nucleus which is de-excited by the emission of prompt gamma radiation, this interaction occurring only with fast neutrons having a high enough energy which is at least equal to that of the prompt gamma radiation. Finally, neutron activation reactions occur by the activation of a nucleus by a thermal or fast neutron which creates a radioactive nucleus having a certain life and which disintegrates thereby emitting activation gamma radiation. Further, prior art devices which are disclosed in U.S. Pat. Nos. 5,293,414, 4,864,142 and 5,373,538 suffer from other problems including the non-portability of their devices and the effect of producing false positive results when interrogating the object. Such false positives can occur due to background radiation, failure to account for the orientation of the interrogated object and detectors and the statistical analysis which may cause a miscalculation of the occurrence of the appropriate materials. Most importantly, the need for an accurate and portable system for emission and detection of neutrons and gamma rays has been needed in order to properly allow the detection of explosives and other material in varying environmental situations and circumstances. SUMMARY OF THE INVENTION The present invention is for a portable method and apparatus for detection of particular elements by neutron irradiation. The apparatus utilizes a portable self-contained probe which contains gamma ray detectors and associated electronics, a neutron generator and power supply and shielding material which isolates the detectors from the neutron generator. The probe is small and is of such design that it may be placed in between or near interrogated objects. The probe additionally contains appropriate high voltage and low voltage power supplies in addition to associated data collection electronics. The probe is remotely connected to a low voltage power supply controller and a controller which properly maintains and controls the neutron generator. Further, the probe is remotely connected to a data acquisition computer which detects the appropriate signals generated by the gamma ray detectors and converts them to digital values. These values are then analyzed by elemental characterization software which determines in real time which constituent elements are present in the interrogated object. Finally, the present invention comprises a portable pulsed neutron detection system for detection of specific elements in an object, comprising: a portable probe, said probe having a pulsed neutron generator and at least one gamma ray detector; a controller operably connected to said pulsed neutron generator for varying the intensity and pulse characteristics of said pulsed neutron generator so as to emit a beam of neutrons from said generator; a data acquisition system operably connected to said at least one gamma ray detector for collecting data measured by said detector; and, means to analyze said data to determine the chemical composition of said object. |
claims | 1. A pig for transporting a container of biohazardous material, wherein the container comprises a bottle and a bottle closure, the pig comprising:a body comprising a compartment dimensioned to receive the container;a cap attachable to the body for closing the compartment thereby to shieldingly contain the biohazardous material in the container, the cap comprising:a collar sealingly engageable with the body and having an opening therethrough in communication with the compartment thereby to provide access to the bottle closure;a cap closure sealingly engageable within the opening of the collar to sealingly close the opening and cause the bottle closure to be gripped within the cap,wherein when the collar is disengaged from the body while the cap closure is engaged within the opening of the collar, the container remains gripped within the cap,wherein when the cap closure is released from the opening of the collar, the container is released from the cap. 2. The pig of claim 1, wherein the cap closure comprises an annulus projecting into the opening for causing the bottle closure to be gripped within the cap. 3. The pig of claim 2, further comprising a compression member dimensioned to be positioned intermediate the bottle closure and the annulus, the compression member being compressed against the bottle closure by the annulus while the cap closure is sealingly engaged within the opening of the collar. 4. The pig of claim 3, wherein the compression member comprises:a flange;spaced apart fingers supported by the flange and forming a circle complementary to an inner wall of the annulus, the spaced apart fingers resiliently compressible inwardly against the bottle closure by compressive engagement of the annulus. 5. The pig of claim 4, wherein the compression member comprises lugs extending from the flange and dimensioned to project into complementary bores in a lower edge of the collar. 6. The pig of claim 5, wherein the compression member is formed of a thermoplastic. 7. The pig of claim 1, further comprising a handle assembly encapsulating the body and comprising a handle that is extendable and rotatable through a plurality of orientations with respect to the body. 8. The pig of claim 7, wherein the handle assembly comprises:an upper collar associated with an upper end of the body;a lower collar associated with a lower end of the body;at least two struts extending between the upper collar and the lower collar thereby to maintain the upper collar and the lower collar in a fixed spaced relationship,the handle associated with and extending from the struts. 9. The pig of claim 8, wherein the handle comprises:two elongate arms depending from opposite ends of a cross member, each of the arms having an elongate channel therethrough,wherein each elongate channel is dimensioned to rotate and slide with respect to a respective knob being passed through each channel into a respective aperture in a corresponding strut while the knob is untightened to its respective aperture, wherein the handle is fixed in position with respect to the body while at least one of the knobs is tightened within its respective aperture. 10. The pig of claim 8, wherein at least the upper collar and the lower collar are formed from a thermoplastic material. 11. A system for transporting and providing access to a biohazardous material, the system comprising:a pig for transporting a container of biohazardous material, wherein the container comprises a bottle and a bottle closure, the pig comprising:a body comprising a compartment dimensioned to receive the container;a cap attachable to the body for closing the compartment thereby to shieldingly contain the biohazardous material in the container, the cap comprising:a collar sealingly engageable with the body and having an opening therethrough in communication with the compartment thereby to provide access to the bottle closure;a cap closure sealingly engageable within the opening of the collar to sealingly close the opening and cause the bottle closure to be gripped within the cap,wherein when the collar is disengaged from the body while the cap closure is engaged within the opening of the collar, the container remains gripped within the cap;wherein when the cap closure is released from the opening of the collar, the container is released from the cap; andan insert sealingly engageable within the opening of the collar while the cap closure is removed, the insert comprising an injection port extending fully therethrough in axial alignment with the compartment thereby to guide insertion of a syringe centrally through the container closure and into the container. 12. The system of claim 11, wherein the injection port is cylindrical and has a single diameter extending fully through the insert. 13. The system of claim 11, wherein the injection port has an upper portion extending partway through the insert and having a first diameter, and a lower portion extending from the upper portion through the rest of the insert and having a second diameter, the second diameter being smaller than the first diameter. 14. A compression member for insertion into a pig for transporting a container of biohazardous materials, the compression member comprising:a flange; andspaced apart fingers supported by the flange and together forming a circle, the fingers each having a substantially vertical component connected to and extending upwards from the flange and a substantially horizontal component connected to, and extending inwards towards the middle of the circle from, an end of the substantially vertical component that is distal from the flange, wherein spaced apart fingers are resiliently compressible inwardly towards the middle of the circle against the container by compressive engagement of a complementary annulus of the pig into which the compression member is dimensioned to be inserted. 15. The compression member of claim 14, wherein the compression member comprises lugs extending from the flange for frictional retention within the complementary annulus. 16. The compression member of claim 14 wherein the flange and fingers are formed of a thermoplastic material. 17. The compression member of claim 14, further comprising a web extending between each pair of adjacent fingers. 18. The compression member of claim 17, wherein the flange and fingers are formed from a first material and each web is formed from a second material that is less rigid than the first material. 19. The compression member of claim 18, wherein the first material is a thermoplastic and the second material is silicone. 20. The compression member of claim 14, wherein the flange comprises a sloped edge about its periphery for snap retention within the complementary annulus. |
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049833502 | summary | The present invention relates to controlling a nuclear power station and more specifically to detecting the fall of a control cluster into the core of the reactor of such a station. Such detection must be reliable even if a component or a set of components in a protective system happens to be faulty. It is important for the fall of a cluster to be detected with all the required safetY in spite of the possibility of such a faulty system. Clusters are constituted by neutron-absorbing rods and nuclear power, i.e. the power evolved by the reaction, is regulated and controlled by moving the clusters. They are distributed over the horizontal section of the core. They are vertically movable in both directions. For this purpose they are hooked onto an appropriate mechanism which is situated above the core and which is controlled to cause the absorbing rods of a cluster to penetrate into the core to a greater or lesser extent. A failure in this mechanism or in the hooking member may result in a cluster falling into the core. Such a fall gives rise to a local reduction in nuclear power, and thus to a reduction in the overall power of the core. Since there is a power-regulating servo loop, such a decrease is rapidly compensated by raising other control clusters. However, this gives rise to various drawbacks including neutron flux distortion, thereby slowing down combustion of the fuel elements close to the fallen cluster and accelerating combustion elsewhere. In addition, the range of action possible on the reaction is reduced. That is why it is desirable to detect such accidental falls as reliably and as quickly as possible in order to perform an emergency reactor stop and reestablish normal operation thereof. It is also necessary to avoid performing such an emergency stop if that is unnecessary, since such a stop is expensive, in particular because it reduces the availability of the nuclear power station for providing electricity. In a known method for detecting falls of control clusters, use is made of detection means which are also applicable to other types of accident. More precisely, these means detect the excessive temperatures caused by pockets of steam appearing at various points in the core along the rods constituting the fuel elements. When a cluster falls accidentally, the first rise in nuclear power to a certain level after the fall has taken place causes such an excess temperature or pocket of steam to appear along a fuel element whose combustion is accelerated by the flux distortion. Different automatic protection means then cause an emergencY reactor stop. Thereafter the cause of the stop is determined and the consequences of the accident are repaired prior to putting the reactor back into service. This known method suffers from the drawback that a fairly long period of time may elapse before the nuclear power is raised high enough to give rise to the above-described stop process, particularly if the anti-reactivity of the fallen cluster is relatively low. The combustion rate of some fuel elements can thus be increased, thereby initiating nucleated boiling. A particular object of the present invention is to provide reliable and rapid detection of the fall of a control cluster, even when the position and/or the low degree of anti-reactivity of the fallen cluster gives rise to only a small variation in nuclear power, while simultaneously avoiding as far as possible the danger of a false detection giving rise to an unnecessary emergency reactor stop. Another object of the invention, by virtue of such detection, is to provide better protection for the reactor of a power station against the damaging consequences which would arise from continuing the nuclear reaction in normal service after a cluster has fallen, while preserving the availability of the power station. The invention seeks to achieve these objects in a manner which is both simple and cheap. That is why the present invention provides a method of detecting the fall of a control cluster in a nuclear reactor, wherein "sensitive" parameters sensitive to displacements of the control clusters of the reactor are measured on a long-term basis, and a cluster fall signal is generated when one of said parameters varies at a speed greater than a predetermined alarm threshold corresponding to said parameter, the method being characterized by the fact that said sensitive parameters which are measured include parameters of at least a first type and a second type, said first type being constituted by position parameters representative of the positions of said control clusters themselves, and said second type being constituted by parameters which are sensitive to displacements of control clusters even when said clusters are situated at a distance from points where said parameters are measured, that the parameters of each of these two types are measured in at least two zones of the core of said reactor, and that said cluster fall signal is generated when at least two of said sensitive parameters varies at a rate greater than said corresponding alarm thresholds, with one of said two parameters being one of said position parameters. In a preferred disposition, said second type of sensitive parameter and optionally a third type of sensitive parameter are constituted by neutron flux parameters representative of the nuclear power evolved in each of said zones of the core or/and by heat flux parameters representative of the heat flux removed by cooling fluid flowing through each of said zones. The present invention also provides an apparatus for detecting the fall of a control cluster into the core of a nuclear reactor, said core comprising a plurality of zones each provided with: heat measurement means for providing a heat flux signal corresponding to said zone and representative of heat flux removed by the flow of a cooling fluid through said zone; PA1 neutron measuring means for providing a neutron flux signal corresponding to said zone and representative of nuclear power in said zone; and PA1 a plurality of control clusters, with each of said control clusters being provided with measurement means for providing a cluster position signal representative of the position of said cluster; PA1 said apparatus comprising differentiation and comparison means for receiving "sensitive" signals sensitive to the displacements of the control clusters and for providing corresponding alarm signals whenever said sensitive signals vary at a rate greater than corresponding predetermined alarm thresholds; and PA1 logical processor means for providing a cluster fall signal in the presence of a plurality of said alarm signals; PA1 said apparatus being characterized by the fact that said alarm signals include at least signals of a first type and of a second type, said first type being constituted by position alarm signals corresponding to said cluster position signals and a second type being constituted by heat alarm signals corresponding to said heat flux signals and/or by neutron alarm signals corresponding to said neutron flux signals, said logic processing means providing said cluster fall signal on receiving at least two of said alarm signals including at least one of said position alarm signals. PA1 said logic processing means comprise: PA1 said differentiation and comparison means are associated with said primary logic units in such a manner that, together with a corresponding portion of said means, each of said logic units constitutes an acquisition unit; PA1 said acquisition units constitute a succession corresponding to the succession of said zones in the core of the nuclear reactor; and PA1 each of said acquisition units receives a group of said cluster position signals corresponding to one of said core zones, said neutron flux signal corresponding to another core zone, and said heat flux signal corresponding to yet another core zone, such that said neutron flux signals, said heat flux signals, and said groups of cluster position signals are each received by one and one only of the acquisition units. The following preferred dispositions in accordance with the invention may also be adopted: primary logic units each of which receives said position alarm signals corresponding to at least one of said core zones and at least one of said second type alarm signals corresponding to another of said zones, and for providing a primary detection signal when at least one of said alarm signals is present; and PA2 a combination circuit receiving said primary detection signals and said position alarm signals and providing said cluster fall signal when at least two of said primary detection signals and at least one of said position alarm signals are present; An implementation of the invention is described by way of non-limiting example and with reference to the accompanying diagrammatic figures. In the description, those dispositions which are mentioned below as being preferred in accordance with the present invention should be considered as being used. It should also be understood that the elements described and shown may be replaced by other elements providing the same technical functions without going beyond the scope of the invention. |
abstract | An improved apparatus for determining the position of a drive rod within the interior of a drive rod housing includes a transmission antenna at one location on the housing and a receiving antenna at another location on the housing. An electromagnetic excitation signal sent to the transmission antenna is detected, at least in part, by the receiving antenna, and the received signal is processed with a vector network analyzer routine to model the drive rod housing as a wave guide having a filter response. A group delay is detected and is compared with a calibration data set which provides a current position of the drive rod that corresponds with the group delay. |
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046793771 | description | DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views. Also in the following desription, 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. In General Referring to the drawings, and particularly to FIG. 1, there is shown an elevational view of a fuel assembly, represented in vertically foreshortened form and being generally designated by the numeral 10. The fuel assembly 10 is the type used in a pressurized water reactor (PWR) and basically includes a lower end structure or bottom nozzle 12 for supporting the assembly on the lower core plate (not shown) in the core region of a reactor (not shown), and a number of longitudinally extending guide tubes or thimbles 14 which project upwardly from the bottom nozzle 12. The assembly 10 further includes a plurality of transverse grids 16 axially spaced along the guide thimbles 14 and an organized array of elongated fuel rods 18 transversely spaced and supported by the grids 16. Also, the assembly 10 has an instrumentation tube 20 located in the center thereof and an upper end structure or top nozzle 22 attached to the upper ends of the guide thimbles 14. With such an arrangement of parts, the fuel assembly 10 forms an integral unit capable of being conveniently handled without damaging the assembly parts. As mentioned above, the fuel rods 18 in the array thereof in the assembly 10 are held in spaced relationship with one another by the grids 16 spaced along the fuel assembly length. Each fuel rod 18 includes nuclear fuel pellets 24, and the opposite ends of the rod are closed by upper and lower end plugs 26,28 to hermetically seal the rod. Commonly, a plenum spring 30 is disposed between the upper end plug 26 and the pellets 24 to maintain the pellets in a tight, stacked relationship within the rod 18. The fuel pellets 24 composed of fissible material are responsible for creating the reactive power of the PWR. A liquid moderator/coolant such as water, or water containing boron, is pumped upwardly through the fuel assemblies of the core in order to extract heat generated therein for the production of useful work. To control the fission process, a number of control rods 32 are reciprocally movable in the guide thimbles 14 located at predetermined positions in the fuel assembly 10. Specifically, the top nozzle 22 includes a rod cluster control mechanism 34 having an internally threaded cylindrical member 36 with a plurality of radially extending flukes or arms 38. Each arm 38 is interconnected to a control rod 32 such that the control mechanism 34 is operable to move the control rods 32 vertically in the guide thimbles 14 to thereby control the fission process in the fuel assembly 10, all in a well-known manner. Hereinafter, the structure and operation of the prior art apparatus and the improved apparatus for applying the upper and lower end plugs 26,28 to the opposite ends of each fuel rod 18 will be described in relation to application of the upper end plug 26 to the upper end 40 of an elongated tube 42 of the fuel rod 18. It should be understood that such description applies equally to the application of the lower end plug 28 to a lower end 44 of the fuel rod tube 42. Prior Art End Plug Applying Apparatus As mentioned previously, the fuel rods 18 are hermetically sealed to isolate the fissile material contained therein from the surrounding environment. In order to ensure a reliable seal, it is important that the mechanical connections of the end plugs 26,28 with the opposite ends 40,44 of the elongated tube 42 of the fuel rod 18 be free of defects which could eventually produce leaks. With reference to FIG. 2, the mechanical connection of plug 26 to upper tube end 40 is formed by, first, a close frictional interfitting engagement between an external surface 46 of inner cylindrical portion 48 of the plug 26 and an internal surface 50 of the upper end 40 of the fuel rod tube 42, and, second, a girth weld (not shown) formed at the location of a butt joint of the end edge 52 of the tube upper end 40 and an annular shoulder 54 defined on the end plug 26 by the transition between the inner cylindrical portion 48 and an outer cylindrical portion 56 which has a diameter larger than that of the inner portion 48. The outside diameter of the inner insertable portion 48 of the plug 26 is slightly greater than the inside diameter of the fuel rod tube end 40 for producing a friction fit which expands the tube 42 slightly when the end plug inner portion 48 is inserted into the tube end 40. The outside diameter of the end plug outer portion 56 is such that it is generally equal to the outside diameter of the end 40 of the tube 42 once the latter has been expanded by the inserted inner portion 48 of the end plug. When one prior art end plug applying apparatus is used, such as shown in FIG. 2 and generally designated by the numeral 58, occasional damage would occur at edge portions of the end plug 26 and/or end 40 of the fuel rod tube 42. As seen in FIG. 2, the prior art apparatus 58 includes an elongated hollow cylindrical guide bushing 60 having inserted into its open end 62 the upper end 40 of the fuel rod tube 42 to which the end plug 26 is to be applied. A cylindrical ram 64, only fragmentarily shown in FIG. 2, is reciprocally moved within the bushing 60 by a conventional source of power (now shown), such as hydraulic or pneumatic pressure, between a retracted position and an extended position. In the retracted position of the ram 64, as seen in solid line form in FIG. 2, its leading face 66 is located to the left of an upper entrance opening 68 defined in the bushing 60. The opening 68 communicates the interior of the bushing 60 with a magazine (not shown) containing a vertical stack of end plugs 26 (the lower one of which is shown in fragmentary dashed outline form at 26a in FIG. 2). When the ram 64 is in its retracted position, the end plug fed from the magazine enters the opening 68 and is deposited at a loading position (as seen in dotted outline form at 26b in FIG. 2) in front of the leading face 66 of the ram. The ram 64 is then actuated to move forwardly past the opening 68 and toward the open end 62 of the bushing 60 to its extended position (not shown) in which the end plug is applied to the upper end 40 of the fuel rod tube 42 (as seen in dotted outline form at 26c in FIG. 2). The tube 42 is securely clamped by suitable means (not shown) at the open end 62 of the bushing 60 to withstand axial insertion forces which can exceed 500 pounds. During the forward stroke of the ram 64 (such as exemplified by the position of its leading face, as shown in dashed outline form at 66a in FIG. 2, intermediately of the retracted and extended positions of the ram) in which the end plug is carried ahead of it, occasionally the plug cocks, tips or tumbles (as seen in solid line form at 26 in FIG. 2) so that it does not meet the upper end 40 of the fuel rod tube 42 squarely. This can occur if the plug 26 is at the low end of its tolerance range and the guide bushing 60 is at the high end of its tolerance range. It can also occur if the motion of ram 64 is uneven. In the latter instance, the plug 26 will be propelled forward, losing contact with the leading face 66 of the ram 64. (Continuous contact with the ram face 66 tends to keep the plug 26 aligned with the tube end 40). Cocking or tipping of the upper end plug 26 (as compared to the lower end plug 28) is worsened by the presence of the plenum spring 30 at the upper end of the tube 42 which tends to resist application of the upper plug 26 to the upper tube end 40. As a consequence, the plug 26 does not seat properly, and oftentimes pieces of the plug 26 or upper tube end 40 are broken off as the inner cylindrical end portion 48 of the plug 26 is forced into the tube 42 (as seen at 26c in FIG. 2). The broken pieces not only damage the end plug 26, but also cause foreign objects to be deposited in the fuel rod 18. While normally the plenum spring 30 is only in the upper end 40 of the fuel rod tubhe 42, the same problems of cocking and tipping occur where there is no spring present at the lower end 44 of the tube 42. Improved End Plug Applying Apparatus The apparatus of the present invention, three alternative embodiments of which are disclosed herein, eliminates the problems associated with the abovedescribed prior art apparatus 58 which were caused primarily by the annular clearance between the external surface 70 of the outer portion 56 of the end plug 26 and the internal surface 72 of the guide bushing 60. In each of the alternative embodiments of the improved end plug applying apparatus of the present invention, which will now be described in detail, a guide means is provided having internal surface portions which define an internal guide channel which has a diameter less than the smallest allowable (or tolerable) plug diameter for the outer portion 56 of the end plug 26. Thus the external surface 70 of the plug 26 will always be in guiding contact with the guide channel of the guide means. The guide means is thereby conformable so that it provides intimate contact with the end plug 26 regardless of where the plug falls in its diametral range of tolerance. Turning now to FIGS. 3 and 4, there is shown the first alternative embodiment of the improved end plug applying apparatus of the present invention, being generally indicated by the numeral 74. The end plug applying apparatus 74 basically includes a housing 76, guide means in the form of a resiliently deformable bushing 78, and plug moving means such as a cylindrical ram 80. The housing 76 is in the form of a cylindrical cup 82 having an outwardly-turned annular flange 84 encompassing its mouth end 86 and an opening 88 formed in its opposite bottom end 90. The housing 76 also includes a cylinder 92 within which the ram 80 is reciprocally moved by any suitable source of power, such as hydraulic or pneumatic pressure as mentioned above. Specifically, the cylinder 92 has an end flange 94 against which the mouth end 86 of the housing cup 82 is placed and to which the cup is attached by a series of bolts 96 used to securely fasten the cup flange 84 to the periphery of the cylinder flange 94. The housing 76 has spaced inlet and outlet ends 98,100 adapted to receive the end plug 26 and tube end 40, respectively. The inlet end 98 of the housing 76 is defined by the open end of the cylinder 92 surrounded by the end flange 94. The cylinder 92 also has an upper opening 102 immediately behind the end flange 94 through which the end plug (as seen in dashed outline form at 26d in FIG. 3) is deposited by a feed magazine (not shown) into a loading position in front of the leading face 104 of the ram 80. The outlet end 100 of the housing 76 is defined by the opening 88 formed in the bottom end 90 of the housing cup 82. The resiliently-deformable bushing 78 forming the guide means of the first alternative embodiment of the improved apparatus 74 is disposed in the housing 76 and aligned in tandem with the inlet and outlet ends 98,100 of the housing along a common axis 106. The bushing 78 has a continuous internal side wall 108 defining a central bore 110 in coaxial alignment with the housing inlet and outlet ends 98,100. The internal side wall 108 defines the guide channel of the guide means and has a cross-sectional size, i.e. diameter, smaller than that of the outer external surface 70 of the outer portion 56 of the end plug 26. The bushing 78, due to being composed of resiliently deformable material, such as urethane, is adapted to expand and conform to the outer external surface 70 of the end plug 26 upon conrtact therewith. Thus, when the ram 80 is moved along the common axis 106, its leading face 104 engages and moves the end plug 26 from the inlet end 98 of the housing 76 through the guide channel defined by central bore 110 to the outlet end 100 of the housing. The movement of the end plug 26 through the central bore 110 causes yieldable expansion of the cross-sectional size of the bore such that the internal side wall 108 (which includes the surface portions defining the guide channel) conforms to the external surface 70 of the end plug 26 and thereby establishes and maintains guiding contact therewith as the end plug is moved through the bore 110 of the bushing 78. In one exemplary form of the first alternative embodiment of the improved apparatus 74, the housing cup 82 is bored out to form a portion of a mold for casting the guide bushing 78 in place. The housing 76 plus two core pieces (not shown) comprise the mold. The mold core pieces are sized about 0.001" below the minimum plug major diameter. The amount of interference thus varies from 0.001" to 0.003". The mold core pieces are ground and polished. This results in an exceptionally smooth bore 110 in the cast urethane bushing 78. The long wearing characteristic of the urethane material should result in a long service life for the bushing 78. Also, the bushing 78 is cast with a tapered entrance and exit sections 112, 114. A step can be added to act as a guide for tube end 40 if desired. Referring now to FIGS. 5 and 6, there is shown the second alternative embodiment of the improved end plug applying apparatus of the present invention, being generally indicated by the numeral 116. The end plug applying apparatus 116 basically includes a housing 118, guide means in the form of a plurality of runners 120 and resiliently expandable members 122, and end plug moving means such as a cylindrical ram 124. The housing 118 is in the form of a cylindrical fixture 126 having respectively defined therein a series of peripheral recesses 128, a series of elongated passageways 130, and a central hole 132. The housing 118 also includes a base 134 having a central opening 136 and to which is integrally connected the feed chute 138 of a magazine for supplying end plugs 26 to the central opening 136 in the housing base. The fixture 128 and base 134 of the housing 118 are attached together by a series of bolts 140 located within the recesses 128 which securely fasten the fixture 128 to spaced locations on the base 134 so as to align their respective central hole 132 and opening 136 along a common axis 142. The housing 118 has spaced inlet and outlet ends adapted to receive the end plug 26 and the tube end 40, respectively. The inlet end of the housing 118 is defined by the central opening 136 of the base 134, while the outlet end is defined by a central tapered hole 144 of circular plate 146 attached to the fixture 126 by a series of bolts 148 on a side opposite from the base 134. The radial passageways 130 within the fixture 126 are defined between the plate 146 and a circular wall portion 149 of the fixture which lies flush against the base 134. Furthermore, the passageways 130 are spaced from one another about the common axis 142 and the elongated axis of the runners 120 extend generally radially from the axis 142. Each of the plurality of runners 120 of the improved apparatus 116 is mounted in one of the passageways 130 in the housing 118 such that the runners 120 are maintained spaced apart from one another about the axis 142, extend generally parallel to and radially from the axis 142, and are move radially toward and away from the axis. The runners 120 have outer portions 150 extending outwardly from the passageways 130 and inner portions 152 extending inwardly from the passageways. The inner runner portions define longitudinally extending inner surfaces 154 exposed to and facing one another so as to define the guide channel for the end plug 26 therebetween. In an exemplary form, the runners 120 can be fabricated from hardened, chrome-plated and polished material with tapered lead-ins on opposite edges of their inner portions 152. Also, the edge 155 on each runner 120 adjacent the base 134 is caged by the circular wall portion 149 of the fixture 126 so as to limit radial movement of the runner 120 within the passageway 130 away from the axis 142. Circumscribing the housing 118, and stretched about the outer runner portions 150 in arcuate depressions 156 therein is the plurality of resilient expandable members 122, which can take any suitable form, such as garter springs or elastomer bands, for instance. The members 122 bias the runners 120 inwardly toward one another so as to maintain the cross-sectional size of the guide channel formed between the inner surfaces 154 on runner inner portions 152 less than the cross-sectional size of the outer portion 56 of the end plug 26. The material of the members 122 is stretchable and, thus, when the ram 124 is moved along the common axis 142 and its leading face 158 engages and moves the end plug from its initial position (as seen in dashed outline form at 26e in FIG. 6) into the guide channel, the members 122 yieldably allow movement of the runners 120 away from one another upon contact of the inner surfaces 154 thereof with the outer external surface 70 of the end plug 26. In such manner, the runner inner surfaces 154 defining the guide channel conform to the external surface 70 of the end plug 26 and thereby establish and maintain guiding contact therewith as the end plug is moved from the inlet to the outlet ends of the housing 118 to where the end plug is applied to the tube end 40. Turning finally to FIGS. 7 and 8, there is shown the third alternative embodiment of the improved end plug applying apparatus of the present invention, being generally indicated by the numeral 160. The end plug applying apparatus 160 basically includes a housing 162, guide means in the form of a plurality of rolls 164 and resiliently expandable elements 166, and plug moving means such as a cylindrical ram 168. The housing 162 is in the form of a cup-shaped cap 170, a base 172, and a hub assembly 174 disposed within the cap 170 and having an end flange 176 interposed between the cap 170 and base 172 with a series of bolts 178 securely fastening the cap 170, base 172 and hub flange 176 together. The base 172 has a central opening 180 which is aligned with a center bore 182 in a hub 183 of the hub assembly 174 along a common axis 184. A feed chute 186 of a magazine for supplying end plugs 26 to the central opening 180 in the base 172 is integrally connected thereto. The housing 162 has spaced inlet and outlet ends adapted to receive the end plug 26 and the tube end 40, respectively. The inlet end of the housing 162 is defined by the central opening 180 of the base 172, while the outlet end is defined by a central hole 188 in the outer end 190 of the cap 170. The hub 183 is aligned with and extends into the central hole 188 of the cap 170. A series of elongated recesses 192 are defined in the hub 183, spaced from one another about the common axis 184 and aligned generally parallel to one another and with the axis 184. Furthermore, the hub 183 is spaced radially inwardly from a continuous cylindrical wall 194 of the cap 170 which provides an annular space 196 therebetween. The hub assembly 174 includes a series of annular rings 198 disposed about and spaced along the hub 183 and fixed thereto by set screws 200 so as to define a series of circumferential slots 202 spaced from one another along the common axis 184 and intersecting the elongated recesses 192. Each of the plurality of elongated generally cylindrical rolls 164 of the improved apparatus 160 is mounted in one of the recesses 192 in the hub 183 such that the rolls are maintained spaced apart from one another about the common axis 184, disposed generally parallel thereto and to one another, and are movable radially toward and away from the axis. Each recess 192 has an inner end 204 defining an elongated opening 206 of a width less than that of the roll 164 such that the rolls have longitudinally-extending surface portions 208 exposed to and facing toward one another through the openings 206 so as to define the guide channel for the end plug 26 therebetween. In an exemplary form, the rolls 164 can be fabricated from hardened, chrome-plated and polished material with tapered lead-ins on opposite ends thereof. Also, the rolls 164 are caged by the portions of the annular rings 198 which overlie the recesses 192 so as to limit radial movement of the rolls within the recesses away from the axis 184. Circumscribing the housing 162 within the respective circumferential slots 202 formed by the annular rings 198, and stretch about the rolls 164, is the plurality of resilient expandable elements 166, which can take any suitable form, such as garter springs or elastomer bands, for example. The elements 166 bias the rolls 164 inwardly toward one another and toward the inner ends 204 of the recesses 192 so as to maintain the cross-sectional size of the guide channel formed between the inner surface portions 208 of the rolls less than the cross-sectional size of the outer portion 56 of the end plug 26. Due to the material of the elements 166 and, thus, when the ram 168 is moved along the common axis 184 and its leading face 210 engages and moves the end plug from its initial position (as seen in dashed outline form at 26f in FIG. 8) into the guide channel, the elements 166 yieldably allow deflection or movement of the rolls 164 away from one another upon contact of the inner surface portions 208 with the outer external surface 70 of the end plug 26. In such manner, the roll inner surface portions 208 defining th guide channel conform to the external surface 70 of the end plug 26 and thereby establish and maintain guiding contact therewith as the end plug is moved from the inlet to the outlet ends of the housing 162 to where the end plug is applied to the tube end 40. 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 forms hereinbefore described being merely a preferred or exemplary embodiments thereof. |
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047160136 | summary | BACKGROUND OF THE INVENTION Kimbrell discloses a nuclear reactor including a calandria which is mounted above the upper internals. The control-rod drives are passed through the hollow members of the calandria. The coolant is conducted generally axially (vertically) through the upper internals and it flows transversely past the outer surfaces of the hollow members of the calandria. These hollow members are constructed to minimize the stresses produced by the transverse flow of the coolant notwithstanding that the velocity of the coolant may be high (40 ft./sec.). Failure of the guides in the upper internals and of any control rods or control-rod drives of the reactor is thus precluded. The calandria is at a substantially higher level of the reactor than the outlet nozzles. While the Kimbrell nuclear reactor is on the whole satisfactory, its operation requires that after passing through the calandria, the coolant must flow through a relatively narrow channel between the calandria and the outlet nozzles. There is a substantial drop in the pressure of the coolant between the region where it leaves the calandria and the region where it flows out of the nozzles. In addition, there is substantial resistance to the inflow of cooling water through the outlet nozzles during an emergency. On the occurrence of a steam bubble, the steam would be collected in the reactor head and calandria and block the natural circulation of coolant through the core, calandria and outlet nozzles. It is an object of this invention to overcome the above-described disadvantages of the Kimbrell reactor. SUMMARY OF THE INVENTION In accordance with this invention a nuclear reactor is provided in which there is no substantial pressure drop in the coolant between the calandria and the outlet nozzles. Specifically, the outlet nozzles are substantially at the level of the upper calandria. The calandria includes a plurality of vertical hollow members supported between upper and lower horizontal supports. The drive rods pass through, and are protected by, these hollow members. The coolant flows in through holes in the lower support. The portion of the hollow members between the supports has a length such that the outlet area through the outlet nozzles spans only hollow members and is not blocked by parts of the supports. These hollow members also have a length such that excessive non-uniform pressure distribution of the coolant is precluded. Such non-uniform pressure distribution produces undesirable non-uniformity of the coolant pressure in the core. In nuclear reactors according to this invention, substantial losses in the outlet pressure of the coolant and outlet nozzle vortices are avoided. Nuclear reactors in which the inlet nozzles as well as the outlet nozzles are at the level of the calandria have additional advantages. The elevation of the coolant piping and specifically of the crossover leg; i.e, the leg between the steam generator and the primary coolant pumps, with respect to the core prevents core uncover for a high range of conditions of small breaks in the piping. The formation of a steam bubble does not preclude effective natural circulation when the primary coolant pump may be disabled. The steam bubble forms at the top and, in the Kimbrell reactor, would block the flow of coolant through the outlet nozzle. In the case of large breaks in the cold legs of the reactor, which cause reverse flow of coolant in the core, the large volume of coolant in the rod-guide region affords an additional measure of protection. The additional coolant permits prolonged core flow and effectively reduces the peak cladding temperature. During core reflood after blowdown a large static head exists on the coolant in the downcomer, i.e., the annulus through which the incoming accumulator flow passes, and this materially aids the core reflood rate. |
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claims | 1. A spherical radiation waste container for use in storage of fission products, separated from actinides in deep permanent ice, comprising: a spherical corrosion resistant container having a core filled with said fission products separated from actinides initially mixed with said fission products, and said fission products consisting essentially of Sr-90, Cs-137 as the dominant fission products, said fission products being in a metal matrix of spherical configuration to successfully encapsulate and store said fission products, said core and said metal matrix being dimensionally configured to define a waste container such that the radiation outside the waste container does not exceed human safety limits and such that the container surface reaches a temperature sufficiently high to melt ice, but not cause corrosion of the container surface, nor render the temperature at the center too high, and in manner wherein the time taken to reach the bottom of the said permanent ice, such as the Greenland icecap, is of the order of 7 years. 2. The container of claim 1 wherein the metal matrix is a lead (Pb) matrix. claim 1 3. The container of claim 1 wherein the corrosion resistant container is stainless steel. claim 1 |
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description | This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2003-24151 filed on Jan. 31, 2003, the entire contents of which are incorporated herein by reference. 1. Field of the Invention This invention relates to a working method and apparatus, which are capable of efficiently executing such an operation as inspection, examination operations or a preventive maintenance operation in a pressure vessel of a nuclear reactor in a boiling water nuclear reactor power plant. 2. Description of Related Art In a related art nuclear reactor, a conventional working method in a pressure vessel is described in Japanese Patent Publication (Kokai) No. 2001-281386. This conventional method is that a working apparatus is moved to accessed a reactor bottom portion after removing a fuel and control rod driving mechanism, and passing the apparatus through a reactor core portion. A conventional apparatus and method, which makes a working apparatus access the interior of a jet pump in a pressure vessel, are described in Japanese Patent Publication (Kokai) No. 2001-159696. This conventional apparatus includes a guide mechanism, which is inserted from an upper portion of the pressure vessel and is fixed to an inlet mixer of the jet pump. The guide mechanism is used since an upper opening of the jet pump is an opening from which the interior of the jet pump is hardly seen in a vertical direction. According to this conventional method, the working apparatus is inserted into and moved to access the interior of the jet pump smoothly by using the guide mechanism. Accordingly an advantage of an aspect of the present invention is to provide method and apparatus for executing an operation in a pressure vessel of a nuclear reactor, which are capable of making the operation apparatus access the interior of a jet pump and a bottom portion of a nuclear reactor without removing fuel and control rods and a control rod driving mechanism, and without using a guide mechanism to the jet pump. To achieve the above advantage, one aspect of the present invention is to provide a method for executing an operation in a pressure vessel of a nuclear reactor that comprises installing a body of an operation apparatus to the pressure vessel from the upper side of the nuclear reactor, the operation apparatus having a guide at an end of the body as it inclines with respect to an center axis of the body, inserting a guide into a side opening of a jet pump in the pressure vessel, and inserting the body to an interior of the jet pump as it follows the guide. To achieve the above advantage, another aspect of the present invention is to provide a apparatus for executing an operation in a pressure vessel of a nuclear reactor that comprises a body inserted from the upper side of the nuclear reactor to an interior of the jet pump which circulate water inside the pressure vessel, having a guide at the end, the guide being inclined with respect to the center axis of the body so as to be inserted into a side opening of the jet pump. To achieve the above advantage, another aspect of the present invention is to provide a apparatus for executing an operation in a pressure vessel of a nuclear reactor that comprises a body inserted from the upper side of the nuclear reactor to an interior of the jet pump which circulate water inside the pressure vessel, having a guide at the end, the guide having a surface being inclined with respect to an center axis of the body so as to be inserted into a side opening of the jet pump. In accordance with the aspects of the present invention, method and apparatus for executing an operation in a pressure vessel of a nuclear reactor capable of making an operation apparatus access the interior of a jet pump and a bottom portion of a nuclear reactor without removing fuel rods, control rods and a control rod driving mechanism and without using a guide mechanism to the jet pump. A first embodiment in accordance with the present invention will be explained with reference to FIG. 1 and FIG. 2. FIG. 1 is a perspective view showing the construction of the first embodiment of an operation apparatus. Operation apparatus 100 includes a body 1, a wire rope 2 fixed to an upper end portion of body 1, and a guide 3 fixed to a lower end portion of body 1 and having sizes which permit the guide 3 to be inserted into a side opening of a jet pump. The side opening of the jet pump is provided between an inlet mixer and a nozzle. The jet pump is a pump, which circulate water inside a pressure vessel of a nuclear reactor. Body 1 is made of an elongated tubular member 1a having a plurality of holes 1b in a circumferential wall. Body 1 is suspended by wire rope 2 using a hoist provided on an upper portion of a reactor (not shown). A hose 4 is connected to an end portion of an upper part of tubular member 1a. The water in a jet pump may be sucked through holes 1b formed in the circumferential wall of the tubular member 1a by a pump (not shown) connected to hose 4. Guide 3 includes a guide rod 5 fixed to body 1 so that guide rod 5 inclines at a predetermined angle with respect to a vertical axis, which is a center axis of body 1. In other words, guide rod 5 has a inclined surface with its cylindrical part (rod). The inclined surface inclines with respect to a vertical axis. The angle of guide rod 5 may be determined in advance of the operation. A weight 6 is provided to exert gravitational force on the guide rod 5 so that the angle of the guide rod 5 does not vary greatly during the insertion of the guide rod 5 into the jet pump. Guide rod 5 is fixed to a lower portion of the weight 6. Guide 3 is freely movably supported at a lower portion of body 1 by a joint 7, such as a universal joint. Guide 3 is supported so that it can be able to vary an angle with respect to vertical axis of body 1. A circumferential portion of joint 7 is covered with bellows 8 made of an elastic member, such as a rubber member. An operation of operation apparatus 100 as mentioned above will be described with reference to FIG. 2. Body 1 is suspended by wire rope 2, and is lowered from an upper portion of a reactor to a position in the vicinity of a side opening existing between an inlet mixer 11 and a nozzle 12 of a jet pump 10 provided in the interior of the reactor and extending in a vertical direction, as shown in FIG. 2. A lower end of guide rod 5 of guide 3, which is connected to a lower portion of the body 1 is first inserted gradually into the inlet mixer 11 along a tapering surface of the side opening. When body 1 is further suspended and lowered, body 1 is drawn due to the gravitational force of weight 6 of guide 3 which has already entered the interior of jet pump 10, as body 1 follows guide 3. Bellows 8, which covers joint 7, may have a function to restore guide 3 to a original position, since bellows 8 is made of an elastic member. Thus, guide 3 is biased to return to an appropriate position with respect to body 1. In this manner, body 1 is inserted into the interior of jet pump 10 substantially without varying the posture or the angle of operation apparatus 100 as a whole. The amount of weight 6 and restoring force of bellows 8 may be determined suitably by the sizes and the dimensions of the side opening existing between an inlet mixer 11 and a nozzle 12 of a jet pump 10 shown in FIG. 2, such that body 1 and guide 3 can be smoothly inserted into the interior of jet pump 10. Thus, bellows 8 may be provided without restoring force. In this case, guide 3 is freely movably supported at a lower portion of body 1 by a joint 7. This enables guide 3 to vary its angle (posture) with respect to vertical axis of body 1, so that body 1 and guide 3 can also be inserted smoothly with suitable determination of the amount of weight 6. In this embodiment, wire rope 2 is formed so that the amount of lowered movement of wire rope 2 lowered can be ascertained from an outer portion of the reactor. When a pump (not shown) is operated with body 1 inserted to a predetermined position in the jet pump, the water in jet pump 10 is sucked through holes 1b in the circumferential wall of tubular member 1a and via hose 4 connected to the upper opened end of tubular member 1a. The resultant water is guided from an outlet of the pump to an analytical filter provided in the exterior of the reactor. A suitable quantity of contaminants and the like is recovered from the water by the analytical filter, and the water thus purified is returned to the core water. When the operation finishes for recovering the contaminants and the like from water inside the interior of jet pump 10, body 1 is suspended and drawn up above the reactor by reversing the order of the steps of the operations mentioned above and executing the reversed operation, complete the whole operation. The above-described mode of embodiment shows a case where the contaminants and the like in the interior of jet pump 10 are recovered. In order to inspect the interior of jet pump 10, a television camera, an eddy current probe and an array type ultrasonic probe are fixed to holes 1b made in the circumferential wall of tubular member 1a, and these machines necessary for the inspection operation are connected to a controller, which is provided in the exterior of the reactor, via signal cables instead of the hose connected to the upper opened end of tubular member 1a. This enables the inspection of the interior of jet pump 10 to be carried out practically with ease. Body 1, in the embodiment, is made of tubular member 1a having a plurality of holes 1b in the circumferential wall of member 1a. Tubular member 1a may be provided with a position fixing mechanism with three pieces of arms, which are foldable and unfoldable around the axis of tubular member 1a and are arranged at regular intervals. Body 1 is inserted into jet pump 10 the position fixing mechanism set in a folded state, until body 1 reaches a predetermined position of jet pump 10. When body 1 reaches the predetermined position, the position fixing mechanism is unfolded so that the three pieces of arms touch the inner surface of jet pump 10. This enables body 1 to be positioned stably in jet pump 10. The embodiment shows a case where body 1 is used for executing the removal of contaminants from water existing in the interior of jet pump 10, or for executing the inspection of the interior of jet pump 10. In order to inspect a bottom portion of a nuclear reactor, body 1 being inserted into the interior of jet pump 10 is further lowered in a suspended state by wire rope 2 to the bottom portion of the nuclear reactor through the lower opening existing in the bottom portion of jet pump 10. This enables carrying out the same inspection operation as mentioned above practically using a television camera, an eddy current probe, an array type ultrasonic probe or the like. Thus, in the first embodiment of the present invention, operation apparatus 100, which includes body 1 and guide 3 with guide rod 5, is formed in such a size which permits operation apparatus 100 to be inserted into jet pump 10 from the side opening provided between inlet mixer 11 and nozzle 12. Guide rod 5 is fixed to the end portion of body 1 so that the end portion of guide rod 5 inclines at an appropriate angle with respect to vertical axis of body 1. Since guide rod 5 (and its surface) is inclined, body 1 can be inserted smoothly into jet pump 10 and be lowered to a predetermined position, without carrying out an operation for further moving guide 3 in the horizontal direction which is executed in a conventional working apparatus of this kind. Moreover, body 1 in the embodiment can also be inserted into a bottom portion of a nuclear reactor through the lower opening in the bottom portion of the jet pump 10. Guide rod 5 is fixed to a lower portion of body 1 via weight 6. Therefore, when guide rod 5 is inserted into jet pump 10, the gravitational force is constantly exerted on body 1 due to the weight 6. This causes body 1 to be drawn into jet pump 10 as body 1 follows guide 3. Accordingly, the posture or the angle of operation apparatus 100 substantially as a whole does not vary greatly, so that body 1 can be inserted smoothly into jet pump 10 as body 1 is guided by guide rod 5 into the side opening existing between inlet mixer 11 and nozzle 12 of the jet pump 10. Bellows 8 made of an elastic member is provided between a root portion of tubular member 1a and weight 6 so that the bellows cover the circumferential portion of the joint 7. Therefore, when body 1 of the working apparatus is inserted into the interior of the jet pump 10, the collision of the joint portion with the inlet mixer 11 and nozzle 12 may be prevented, which causes these parts to be damaged. Moreover, bellows 8 may have a function to restore guide 3 to a original state, in which guide rod 5 inclines at the appropriate angle with respect to the vertical axis of body 1 so that body 1 can be inserted more smoothly into jet pump 10. A second embodiment of an operation apparatus in accordance with the present invention will be explained with reference to FIGS. 3A and 3B. FIGS. 3A and 3B is a perspective view showing the construction of a second embodiment of operation apparatus 100. In this embodiment, explanations of some elements in FIGS. 3A and 3B are omitted, since the same symbol is used for the same element described in the first embodiment referring to FIGS. 1 and 2. This operation apparatus includes a body 1, a wire rope 2 fixed to an upper end portion of this body 1, and a guide 3 fixed to the end portion of body 1 and having sizes which permit the guide 3 to be inserted into a side opening of jet pump 10 which is provided between an inlet mixer and a nozzle, as described in the first embodiment. As shown in FIGS. 3A and 3B, guide 3 includes a inclined surface 5a, 5b, whose inclined angle is predetermined appropriately with respect to a center axis of body 1 in the embodiment. Surfaces 5a, 5b are the substitute of guide rod 5 shown in FIG. 1 of the first embodiment. Surface 5a, 5b may be formed at a lower end portion of weight 6, as a surface of a cone shown in FIG. 3A, or as an elliptical surface being formed, when a column is cut by a plane as shown in FIG. 3B. The operation of operation apparatus 100 as mentioned above is almost the same as what is described in the first embodiment. Body 1 is suspended by wire rope 2, and is lowered from an upper portion of a reactor to a position in the vicinity of a side opening existing between an inlet mixer 11 and a nozzle 12 of a jet pump 10, provided in the interior of the reactor and extending in a vertical direction as shown in FIG. 2 of the first embodiment. An end of surfaces 5a and 5b of guide 3 connected to a lower portion of the body 1 is first inserted gradually into the inlet mixer 11 along a tapering surface of the side opening. When body 1 is further suspended and lowered, body 1 is drawn due to the gravitational force of weight 6 of guide 3 which has already entered the interior of jet pump 10, as body 1 follows guide 3. Bellows 8, which covers joint7, may have a function to restore guide 3 to a original position, since bellows 8 is made of an elastic member. In this manner, body 1 is inserted into the interior of jet pump 10 substantially without varying the posture or the angle of operation apparatus 100 as a whole. In the second embodiment of the present invention, operation apparatus 100, which includes body 1 and guide 3 with inclined surfaces 5a or 5b, is formed in such sizes that permit operation apparatus 100 to be inserted into the jet pump from the side opening provided between the inlet mixer and nozzle. Weight 6 is fixed to the end portion of body 1 so that surfaces 5a and 5b, which is the lower end portion of weight 6, inclines at an appropriate angle with respect to the vertical axis of body 1. Therefore, in the same manner as the first embodiment, body 1 can be inserted smoothly into the jet pump to a predetermined position without carrying out an operation for fixing a guide to the jet pump which is executed in a conventional working apparatus of this kind. Moreover, body 1, in the embodiment, can also be inserted into a bottom portion of a nuclear reactor through the lower opening being formed in the bottom portion of the jet pump. Third embodiment of an operation apparatus in accordance with the present invention will be explained with reference to FIG. 4A and FIG. 4B. FIGS. 4A and 4B are plain views showing the operation apparatus. This operation apparatus includes a body 21, a wire rope 2 fixed to an upper end portion of this body 1, and a guide 26 fixed to the lower portion of body 21 and having sizes which permit the guide 26a to be inserted into a side opening of a jet pump which is provided between an inlet mixer and a nozzle. A body 21 includes a position fixing mechanism 22, which is connected to and suspended by a wire rope 2. Body 21 additionally includes a link mechanism 24, which is connected coaxially to position fixing mechanism 22, and has around-axis rotational joints 23a, 23b at a root portion and a lower end portion of link mechanism 24. The around-axis rotational joints 23a, 23b are rotatable around the axis of body 21. Body 21 further includes three bending joints 23c, 23d, 23e, which are secured between these around-axis rotational joints 23a, 23b, and link mechanism 24 by which the rotational joints are connected together. A working tool 25, which is used for the operation to be executed in the pressure vessel, is connected to the around-axis rotational joint 23b at the lower end portion of link mechanism 24 and is connected to a guide 26 fixed to the bending joint 23e at the lower end portion of link mechanism 24. Therefore, the position of working tool 25 and guide 26 may be controlled by link mechanism 24. Consequently, working tool 25 and guide 26 are pivoted around center axis of the body 21, and are also adjusted their angle with respect to the vertical axis so that working tool 25 is positioned appropriately to execute the operation. As the working tool 25, one of a television camera, an ultrasonic probe, a phased array UT head, an eddy current flaw detecting head, a laser irradiation head or a water injection nozzle is fixed exchangeably at the lower end portion of the link mechanism 24 of body 21. The position fixing mechanism 22 at the root portion of the link mechanism 24 is provided with two sets of fold-up supports, which are spaced between each other in a vertical direction. Each of the sets has at least three fold-up supports 27, which are unfoldable from the axis of the body 21. Body 21 is suspended by wire rope 2 using a hoist provided on an upper portion of a reactor, and is connected to a controller (not shown) which is provided outside the reactor via a cable, an optical fiber, a tube or the like. The operation of operation apparatus 100 mentioned above will be described with reference to FIGS. 5A and 5B. Working tool 25 is bent so that tool 25 is folded upward by bending joint 23e at the lower portion of link mechanism 24 with position fixing portion 22 in a folded state. Guide 26 is retained at the lower end portion of body 21 in an outwardly projecting (unfolded) state with a suitable angle with respect to a vertical axis of body 21. When body 21, in this condition, is suspended by the wire rope 2 and lowered into the reactor by using the hoist provided on an upper portion of the reactor, body 21 is further lowered in a suspended state to a position in the vicinity of a side opening existing between the inlet mixer and nozzle of the jet pump in the same manner as in the first embodiment. The lower end of guide 26 connected to bending joint 23e of link mechanism 24 is inserted first gradually into the interior of the inlet mixer along a tapering surface of the side opening. When it is ascertained that body 21, which is lowered in a suspended state reaches a predetermined position in the interior of jet pump 10, position fixing mechanism 22 provided at the root portion of body 21 is operated by the controller provided outside the reactor. When this position fixing mechanism 22 is operated, two sets of three fold-up supports 27 are fixed, as shown in FIGS. 5A and 5B, to body 21 so that fold-up supports 27 are unfolded (extended) from the axis of body 21 in the outward direction. End portion of each of fold-up supports 27 touches and stabilized against the surface of the interior of jet pump 10. Thus, Fold-up supports 27 are fixed to and stabilized against an inner circumferential surface of a tubular diffuser 13. In this embodiment, body 21 is firmly held on the inner circumferential surface of diffuser 13 by three fold-up supports 27 of each of the sets, so that body 21 is positioned at the center of tubular diffuser 13. In jet pump 10, a reference numeral 14 denotes a baffle plate, and 15 shows a shroud. When five rotational or bending joints 23a to 23e by which link mechanism 24 are connected together linearly are then driven, link mechanism 24 are turned in accordance with the angles of rotation of rotational joints 23a to 23e. Consequently, working tool 25 fixed to the lower end portion of link mechanism 24 is controlled and moved to a position of an object on which the operation executes in the interior of jet pump 10. Therefore, when one of working tools 25 including a camera, an ultrasonic probe, a phased array UT head, an eddy current flaw detecting head or a laser irradiation head is fixed to the working head, the inspection and repair of the interior of the jet pump 10 are executed. When these operations finish, body 21 is lifted in a suspended state to the upper portion of the reactor by reversing the order of the steps of the above-mentioned operation to complete the operations. The above embodiment shows a case where the inspection and repair of the interior of jet pump 10 are carried out by body 21. When the inspection of a bottom portion of a nuclear reactor is carried out, body 21 inserted into the interior of the jet pump is further lowered in a suspended state by the wire rope 2 to the bottom portion of the nuclear reactor through the lower opening existing in the bottom portion of the jet pump 10. A television camera, an eddy current probe, an array type ultrasonic probe or the like may execute the inspection of the bottom portion of the nuclear reactor. Thus, in the embodiment, body 21 is able to be inserted into the interior of jet pump 10 by merely fixing guide rod 26, which advances along a tapering surface of the side opening existing between the inlet mixer and nozzle of jet pump 10, to bending joint 23e at the lower end portion of link mechanism 24. Accordingly, without fixing a funnel-like guide apparatus to the inlet mixer portion of the jet pump as in the conventional art, the operation, such as inspection repair or modification of the interior of the jet pump can be carried out in a short period of time. In body 21, the position fixing mechanism 22 having sets of unfoldable fold-up supports 27, each of which has three fold-up supports, are provided at the root portion. Therefore, the position fixing holding power to the diffuser 13 can be increased. Under the position fixing mechanism 22, a link mechanism 24 formed by connecting links together linearly by rotational or bending joints 23a to 23e is provided, and a working tool 25 is detachably fixed to an end portion of the link mechanism 24. Therefore, it is possible that a working head, such as a camera or an ultrasonic probe access a required position in the interior of jet pump 10 easily. When an operation is carried out in a bottom portion of a nuclear reactor, body 21 inserted in the interior of jet pump 10 from the side opening as a same manner. After inserted body 21 inside jet pump 10, body 21 is further lowered in a suspended state to the bottom portion of the reactor through the lower opening existing in the bottom portion of jet pump 10. As a result, an inspection operation may be executed by using a television camera, an eddy current probe, an array type ultrasonic probe or the like. Therefore, a fuel assembly, fuel support metal members, control rods and a control rod driving mechanism may not be removed unlike a conventional working apparatus. This enables the working hours to be greatly shortened. A fourth embodiment of an operation apparatus in accordance with the present invention will be explained with reference to FIGS. 6A and 6B. FIGS. 6A and 6B are plain views showing the operation apparatus. In this embodiment explanations of some elements in FIGS. 6A and 6B are omitted, since the same symbol is used for the same element described in the third embodiment referring to FIGS. 4A and 4B. This operation apparatus includes a body 21, a wire rope 2 fixed to an upper end portion of this body 1, and a guide 26a fixed to the end portion of body 21 and having sizes. The sizes is to permit the guide 26a to be inserted into a side opening of a jet pump which is provided between an inlet mixer and a nozzle, as described in the third embodiment. Body 21 includes a position fixing mechanism 22 connected to and suspended by a wire rope 2. A link mechanism 24 is connected coaxially to this position fixing mechanism 22, and has around-axis rotational joints 23a, 23b at a root portion and a lower end portion of mechanism 24. Rotational joint 23a, 23b are rotatable around the axis of mechanism 24. Three bending joints 23c, 23d, 23e are provided between these around-axis rotational joints 23a, 23b, and links by which the rotational joints are connected together. In this embodiment, a working tool 25, which is used for executing an operation in the pressure vessel and is connected to the around-axis rotational joint 23b at the lower end portion of link mechanism 24, commonly serves as a guide 26a. The position of working tool 25, which corresponds to that of guide 26a, may be controlled by link mechanism 24. Thus, guide 26a is a working tool 25 which controls its angle with respect to the center axis of body 21. When operation apparatus 100 suspended by the wire rope 2 and lowered into the reactor by using the hoist provided on an upper portion of the reactor, body 21 is further lowered in a suspended state to a position in the vicinity of an opening existing between the inlet mixer and nozzle of the jet pump. The angle of working tool 25 is controlled and set to be able to be inserted into the side opening of the jet pump as guide 26a, as shown in FIG. 6B. When body 21 is further suspended and lowered, body 21 is drawn due to the gravitational force of weight of guide 26a which has already entered the interior of the jet pump, as body 21 follows guide 26a, in the same manner as in the third embodiment. In this condition, bending joints 23c, and 23d, and 23e may be controlled to bend body 21 and working tool 25 so that body 21 can smoothly be inserted into the jet pump. As described above, the fourth embodiment of the present invention, body 21 is rendered able to be inserted into the interior of the jet pump by working tool 25 as guide 26a, which advances along a tapering surface of the side opening existing between the inlet mixer and nozzle of the jet pump, to bending joint 23e at the lower end portion of link mechanism 24. Accordingly, in the same manner as the third embodiment, without fixing a funnel-like guide apparatus to the inlet mixer portion of the jet pump as in the conventional art, an operation, such as inspection of and repairs or modifications on the interior of the jet pump can be carried out in a short period of time. And it is possible that a working head, such as a camera or an ultrasonic probe accesses a required position in the interior of the jet pump easily in a same manner as described in the third embodiment. Other embodiments of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and example embodiments be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following. |
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050135210 | claims | 1. A fast neutron nuclear reactor which comprises a main vessel (1) enclosing liquid metal for cooling the reactor, an upper free level of said liquid metal being capable of moving inside an internal shell, during normal operation of the reactor, between two defined positions respectively referred to as high level (14a) and low level (14b), and, inside the main vessel (1), the internal shell (6) comprising at least one cylindrical sleeve (10) with a vertical axis, a top part of which is located above said high level (14a) of the liquid metal inside the main vessel, and an annular enclosure (20) on the internal periphery of the cylindrical sleeve (10) of the internal shell (6), open upwards at its top part and delimited by a secondary sleeve (21) arranged substantially coaxially and inside the cylindrical sleeve (10), and by an annular base (22) fixed to the bottom end of the cylindrical sleeve (21) and onto the internal surface of the cylindrical sleeve (10) of the internal shell, below the low level (14b) of the liquid metal, wherein the top end of the secondary sleeve (21) is located below the high level (14a) of the liquid metal. 2. Nuclear reactor according to claim 1, wherein the annular base (22), which is solid, forms a reinforcement for the cylindrical sleeve (10) of the internal shell (6) to limit the effects of seismic stresses. 3. Nuclear reactor according to claim 1, wherein the annular enclosure (20) has a width, in the radial direction of the cylindrical sleeve (10) of the internal shell (6), up to 20 cm, and a height, in the axial direction of the cylindrical sleeve (10), up to 1.5 m. 4. Nuclear reactor according to claim 3, wherein the top end of the secondary sleeve (21) of the annular enclosure (20) is arranged at a level situated substantially at 10 cm below the high level (14a) of the liquid metal. 5. Nuclear reactor according to claim 3, wherein the secondary sleeve (21) of the annular enclosure (20) is made from a sheet having a thickness of about 1.5 cm. |
claims | 1. An electron beam apparatus for collecting side-view and plane-view SEM images, the apparatus comprising:an electron source, the electron source providing an electron beam;an objective lens, the objective lens for providing a magnetic immersion function and a retarding function, the objective lens for focusing the electron beam onto a sample surface; andin-lens detectors, the in-lens detectors comprising two or more segments for receiving secondary electrons emanating from the sample surface, each detector segment collecting the secondary electrons emanating from the specimen with related azimuth and polar angle so that a side-view SEM image can be revealed after a signal processing, wherein one of the two or more segments includes an aperture to let the primary electron pass through. 2. The electron beam apparatus of claim 1 in which each of the in-lens detectors comprises at least two or more segments to collect the secondary electrons emanating from the sample with different azimuth angle, the diameter of the aperture being less than 3 millimeters. 3. The electron beam apparatus of claim 1 in which each of the in-lens detectors comprises at least two or more segments to collect the secondary electrons emanating from the sample with a different azimuth angle, one of the detector segments having a small hole on the optical axis to let primary electron pass through, the diameter of the hole being less than 3 millimeters. 4. The electron beam apparatus of claim 1, in which each of the in-lens detectors comprises at least two or more segments to collect the secondary electrons emanating from the sample with different azimuth angle, some of the detector segments forming a small hole on the optical axis to let primary electron pass through, the diameter of the hole being less than 3 millimeters. 5. The electron beam apparatus of claim 1, in which each of the in-lens detectors comprise at least two or more segments being set near by the optical axis of primary beam to collect the secondary electrons emanating from the sample with different azimuth and polar angle, the secondary electrons emanating from the sample with different azimuth and polar angle being guided to the detector by an ExB filter to form a side-view SEM image without affecting the primary beam. 6. A method for collecting side-view and plane-view SEM images, the apparatus comprising:providing an electron beam;providing a magnetic immersion function and a retarding function, the objective lens for focusing the electron beam onto a sample surface; andproviding in-lens detectors, the in-lens detectors comprising two or more segments for receiving secondary electrons emanating from the sample surface, each detector segment collecting the secondary electrons emanating from the specimen with related azimuth and polar angle so that a side-view SEM image can be revealed after a signal processing, wherein one of the two or more segments includes an aperture to let the primary electron pass through. 7. The method of claim 6 in which each of the in-lens detectors comprises at least two or more segments to collect the secondary electrons emanating from the sample with different azimuth angle, the diameter of the aperture being less than 3 millimeters. 8. The method of claim 6 in which each of the in-lens detectors comprises at least two or more segments to collect the secondary electrons emanating from the sample with a different azimuth angle, one of the detector segments having a small hole on the optical axis to let primary electron pass through, the diameter of the hole being less than 3 millimeters. 9. The method of claim 6, in which each of the in-lens detectors comprises at least two or more segments to collect the secondary electrons emanating from the sample with different azimuth angle, some of the detector segments forming a small hole on the optical axis to let primary electron pass through, the diameter of the hole being less than 3 millimeters. 10. The method of claim 6, in which each of the in-lens detectors comprise at least two or more segments being set near by the optical axis of primary beam to collect the secondary electrons emanating from the sample with different azimuth and polar angle, the secondary electrons emanating from the sample with different azimuth and polar angle being guided to the detector by an ExB filter to form a side-view SEM image without affecting the primary beam. 11. An electron beam apparatus for collecting side-view and plane-view SEM images, the apparatus comprising:an electron source, the electron source providing an electron beam;an objective lens, the objective lens for providing a magnetic immersion function and a retarding function, the objective lens for focusing the electron beam onto a sample surface; andin-lens detectors, the in-lens detectors comprising two or more segments for receiving secondary electrons emanating from the sample surface, the segments circling a center wherein the center has no detector, each detector segment collecting the secondary electrons emanating from the specimen with related azimuth and polar angle so that a side-view SEM image can be revealed after a signal processing. 12. The electron beam apparatus of claim 11 in which each of the in-lens detectors comprises at least two or more segments to collect the secondary electrons emanating from the sample with different azimuth angle, the plurality of detector segments forming a small hole on the optical axis to let the primary electron pass through, the diameter of the hole being less than 3 millimeters. 13. The electron beam apparatus of claim 11 in which each of the in-lens detectors comprises at least two or more segments to collect the secondary electrons emanating from the sample with a different azimuth angle, one of the detector segments having a small hole on the optical axis to let primary electron pass through, the diameter of the hole being less than 3 millimeters. 14. The electron beam apparatus of claim 11, in which each of the in-lens detectors comprises at least two or more segments to collect the secondary electrons emanating from the sample with different azimuth angle, some of the detector segments forming a small hole on the optical axis to let primary electron pass through, the diameter of the hole being less than 3 millimeters. 15. The electron beam apparatus of claim 11, in which each of the in-lens detectors comprise at least two or more segments being set near by the optical axis of primary beam to collect the secondary electrons emanating from the sample with different azimuth and polar angle, the secondary electrons emanating from the sample with different azimuth and polar angle being guided to the detector by an ExB filter to form a side-view SEM image without affecting the primary beam. |
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claims | 1. A monochromator for use with an X-ray radiator that emits X-rays having a spectral composition, said X-ray radiator having an operating voltage associated therewith, said monochromator comprising:a crystal having a property of spectrally restricting X-rays interacting therewith to a spectral range having a spectral composition, said spectral range encompassing multiple energies and exceeding a spectral range provided by Bragg's relation from single crystal lattice;a positioning device connected to said crystal to move said crystal relative to the X-rays emitted by said X-ray radiator to change said spectral composition of the X-rays; anda control device connected to said positioning device for automatically controlling said positioning device to control movement of said crystal dependent on said operating voltage. 2. A monochromator as claimed in claim 1 wherein said positioning device moves said crystal to alter an angle between at least a portion of said X-rays and said crystal. 3. A monochromator as claimed in claim 1 wherein said positioning device moves said crystal into and out of a path of said X-rays. 4. A monochromator as claimed in claim 1 wherein said spectral range comprises a restricted range energy spectrum with a maximum value, and wherein said control device sets said maximum value and controls said positioning device dependent on the maximum value that has been set. 5. A monochromator as claimed in claim 1 wherein said X-rays emitted by said X-ray radiator have an emitted energy spectrum with a first maximum value, and wherein said crystal spectrally restricts said X-rays emitted by said X-ray radiator to produce spectrally restricted energy spectrum with a second maximum value, and wherein said control device sets a factor between said first maximum value and said second maximum value and controls said positioning device dependent on said factor that has been set. 6. A monochromator as claimed in claim 5 wherein said control device sets said factor in a range between 0.3 and 0.8. 7. An X-ray device comprising: an X-ray radiator that emits X-rays having a spectral composition, said X-ray radiator having an operating voltage associated therewith; anda monochromator comprising a crystal having a property of spectrally restricting X-rays interacting therewith to a spectral range having a spectral composition, said spectral range encompassing multiple energies and exceeding a spectral range provided by Bragg's relation from single crystal lattice, a positioning device connected to said crystal to move said crystal relative to the X-rays emitted by said X-ray radiator to change said spectral composition of the X-rays, and a control device connected to said positioning device for automatically controlling said positioning device to control movement of said crystal dependent on said operating voltage. 8. An X-ray device as claimed in claim 7 wherein said positioning device moves said crystal to alter an angle between at least a portion of said X-rays and said crystal. 9. An X-ray device as claimed in claim 7 wherein said positioning device moves said crystal into and out of a path of said X-rays. 10. An X-ray device as claimed in claim 7 wherein said spectral range comprises a restricted range energy spectrum with a maximum value, and wherein said control device sets said maximum value and controls said positioning device dependent on the maximum value that has been set. 11. An X-ray device as claimed in claim 10 wherein said X-rays emitted by said X-ray radiator have an emitted energy spectrum with a first maximum value, and wherein said crystal spectrally restricts said X-rays emitted by said X-ray radiator to produce spectrally restricted X-rays having an energy spectrum with a second maximum value, and wherein said control device allows setting of a factor between said first maximum value and said second maximum value and controls said positioning device dependent on said factor that has been set. 12. An X-ray device as claimed in claim 11 wherein said control device sets said factor in a range between 0.3 and 0.8. |
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description | FIG. 1 shows an embodiment of a sterilising device comprising an irradiation arrangement according to the present invention. The irradiation arrangement comprises a particle accelerator. The particle accelerator comprises a particle source 1, a buncher 2 and linear accelerator 3. The particle source 1, in this embodiment an electron gun, which is built in a conventional manner, emits the particles to be used for the irradiation. In this embodiment, the electron gun 1 is of a Pierce type. The buncher 2 pushes the original continuous electron beam together in bunches and introduces the bunches as electron pulses into a linear accelerator 3. Thereby, fewer electrons end up outside any accelerable phase window in the linear accelerator 3, at the same time as the energy dispersion of the electron beam output from the accelerator reduces. In this embodiment, the buncher gives particle pulses of a frequency of 3 GHz. The linear accelerator accelerates the particles by means of electrical fields and sends in the particles towards a radiation chamber 4. In this embodiment, the particles are accelerated to an end energy of 1.5 to 2.5 MeV, and with a particle pulse current in the order of magnitude of 800 mA, which gives an average particle current of 2.4 mA. The pulse lengths are about 5 xcexcs and the pulse repetition frequency is 600 Hz. The particle beam is focussed by a quadropole magnet 6 at the exit of the linear accelerator, before it enters into a scanning magnet 7. The total arrangement comprising particle accelerator and radiation chamber is enclosed by radiation shields 5, consisting of lead, with an approximate thickness of 250 mm. In FIG. 2, an enlarged drawing of the radiation chamber is shown. When the particle beam leaves the accelerator, it is bent by the scanning magnet 7 in an angle xcex2 with respect to the original radiation axis. The angle xcex2 may in this embodiment vary between about 15 and 45 degrees, in both positive and negative directions. The scanning magnet is an electromagnet operated by a bipolar current supply, the output current of which may be programmed. The particle beam is incident in a direction of redeflection magnets 8, 9, positioned at each side. The redeflection magnet 8, 9 is in this embodiment a permanent magnet with a particular shape, which is described more in detail here below. When the particle beam enters between the pole pieces 9 of the redeflection magnets, it is bent into a path determined by the magnet flux in the pole gap which is adapted for a deflection angle of xcex2+90xc2x0, which implies that the particle beam leaves the field of the redeflection magnet in a path perpendicular to the original radiation axis. The particle beam passes a vacuum window 11, which normally consists of a thin metal foil of titanium or aluminum. In the central area of the radiation chamber 4, hereinafter referred to as the radiation sector 13, the products to be irradiated pass on a conveyor belt 14 (see FIG. 3). The radiation beam will therefore impinge on the products with a radiation angle of essentially 90 degrees with respect of the original radiation axis. Beam optics calculations have been performed to determine the size of the radiation spot. In this embodiment, the radiation spot at the position of the irradiated products is approximately 20 mm. The part of the radiation passing the radiation sector 13 and the two vacuum windows 11 without being absorbed, e.g. as a result of that there are no products in the radiation sector at the moment, continues a rectilinear path until it enters between the pole pieces 9 of the opposite redeflection magnet, is bent and absorbed by a cooled particle stopper 10, preferably made by copper or aluminum. FIG. 2 further shows a radiation chamber boundary 12. In FIG. 2, six of the innumerable possible particle paths a-f in the radiation chamber are shown. Each particle path is characterised by its exit angle xcex2 from the scanning magnet 7. By changing the output current from the current supply of the scanning magnet, the exit angle xcex2 may be changed. This exit angle uniquely determines the position where the particle beam enters into the magnet field of the redeflection magnets and is started to be bent. The bending of the particle beam is performed along a circular arch, the radius of which is determined by the mass and velocity of the particle and the strength of the magnetic field. This embodiment is based on a perpendicular irradiation of the products, which gives rise to a demand that the particle beam should leave the influence of the redeflection magnet under a right angle with respect of the original beam axis. If one starts from the position, where the particle beam enters into the magnet field of the redeflection magnet, and the bending radius is known, a position, where the beam has a perpendicular direction, is uniquely defined. This position has to coincide with the position where the particle beam leaves the magnet field, whereby the local appearance of the redeflection magnet uniquely is determined. Since the particle beams enter into the field of the redeflection magnet in different angles at different positions, the design of each small part of the redeflection magnet is determined by the demand of the perpendicular irradiation angle. A shape of the redeflection magnet 9 may thereby, mainly by pure geometrical considerations, easily be calculated. The same considerations are of course valid for the opposite redeflection magnet, when the angle xcex2 is negative. In the shown embodiment, the geometry of the redeflection magnet has been approximated to a circular arch. The centre of the circle is placed 0.77 cm from the entrance to the scanning magnet as measured along the entering beam and 97.2 cm from the axis of the entering beam. The circle has a radius of 139.8 cm. The angle of irradiation will in this case deviate from 90 degrees by less than 1 degree for all scanning positions. By changing the output current from the current supply of the scanning magnet, the particle beam may thus irradiate the products 13 perpendicularly at different positions, and by changing the polarity of the current, the products may also be irradiated from the other side. If the current through the scanning magnet has a high positive value, the particle beam is bent by a large angle and follows e.g. the particle path a and impinges on the irradiated product close to its inner, towards the accelerator facing, end. When the current then gradually is reduced, the exit angle from the scanning magnet will decrease, which in turn leads to that the particle beam hits the irradiated product increasingly further out, away from the accelerator. The particle beam c, with a rather small exit angle, impinges on the product at its farther end, and its exit angle is so small that it starts to become disturbed by the mechanical parts of the vacuum enclosure. A particle beam with an exit angle with lower absolute value, is thus not to any real use and forms only radiation losses, why the current supply of the scanning magnet rapidly changes its polarity to give rise to a particle beam d, with corresponding negative exit angle instead. This particle beam irradiates the outer part of the product, but now from the other side. By now gradually, in absolute figures, increase the current through the scanning magnet, a particle beam with a gradually larger negative exit angle is achieved, whereby the beam irradiates the product closer to the accelerator end. In order to return to the original state, it is advantageously to scan back in a similar manner, since one otherwise easily would get problems with rapid current changes in the scanning magnet. The particle beam during a complete scan, thus starts e.g. from the path a, scans over to the path c, then rapidly changes to the path d and scans over to the path f, after which it turns and scans back to the path d, rapidly changes over to path c and scans back to the original path a. In this embodiment, the largest exit angle is approximately 45xc2x0, while the angle of the smallest absolute value is approximately 15xc2x0. At the occasions, when the radiation sector is not fully covered by the products to be irradiated, e.g. for irregularly formed products or for interspaces between the products when they are transported past the radiation sector, a part of particle beam will pass the radiation sector 13 and the vacuum windows 11 without being absorbed. This radiation continues in a rectilinear path towards the opposite redeflection magnet 8, 9. When the beam enters between the pole pieces 9 of the redeflection magnet, it is bent into a curved path. Due to the direction of the magnetic field, this curvature will be directed away from the accelerator. Examples of such a path is indicated by g in FIG. 2. These paths will impinge on the particle stopper 10 positioned at either side, where the particles are absorbed and the heat generation thereby occurring is collected by the cooling medium of the particle stopper. In this way it is avoided that the radiation which is not absorbed by the products will destroy the irradiation arrangement from the inside or will cause incorrect dose distribution. In the present embodiment, the particle stopper is made of aluminium or copper and the cooling medium in the particle stopper is circulating water. Aluminium has the advantage to have a low cross section for X-ray emission, while copper has the advantage of conducting the heat very efficiently. Both materials may advantageously be used in vacuum applications. Each beam leaving the particle accelerator 1-3 has a certain emittance and energy dispersion. In the shown embodiment, the emittance has been assumed to be 5 mm mrad and the energy dispersion xc2x13%. This means that along the path of the beam, the cross section of the beam will vary slowly. Each element along the path of the beam has its characteristic manner to influence the properties of the particle beam. This means, that if one compares the size of the radiation spot at the radiation sector, with identical settings for the quadropole lens, between two different deflections in the scanning magnet, these will differ. Such a variation may give rise to an inhomogeneous irradiation of the product. To compensate for this effect, the quadropole lens 6 may in this embodiment of the invention be used to change the focusing properties of the particle beam at different deflection angles. It is important that the products at the conveyor belt are irradiated with an even dose over the entire irradiated area. Since the relation between the current of the scanning magnet and the radiation position on the product generally does not follow a linear relation, the scanning of the current has to be adapted in such a way that the irradiation of the product becomes even. An example of a typical current diagram for a scanning cycle is illustrated in FIG. 4. The scanning starts at the time t0, where the current I0 is sent through the scanning magnet, and the current then varies along a curve, whereby the scanning magnet scans the particle beam evenly over the surface of the product up to the time t1, where the current I1 is sent through the scanning magnet. The polarity of the current is rapidly turned and the product is irradiated from the other side. The negative current is increased from I2 to I3 according to a corresponding curve until the time t2, when the cycle turns and scans back in a corresponding manner. The cycle is completed at the time t4. The scanning of the current may be performed continuously or in the form of discrete steps in pace with the pulse frequency. Independently of used method, each new particle pulse will impinge on the product at a new position. In this embodiment, this step between successive particle beam pulses is about 15 mm at the product position, which means that two successive irradiation areas do overlap somewhat to ensure that all surfaces are irradiated. The total scanning width is about 400 mm, which sets the maximum width of the products to be irradiated. A total scanning cycle as described above is repeated with a frequency of 5.6 Hz. To achieve an absolutely homogeneous radiation dose over the entire surface of the product, a fine adjustment of the current profile may be performed after measurement of the radiation dose along the plane of irradiation. In the shown embodiment, the relation between the field strength of the scanning magnet and the scanning position in very close to linear. The deviation is calculated to be maximum 3%. This does not have such a big principal importance, but may simplify the practical use. The scanning magnet has in the shown embodiment a pole gap of 4 cm. The maximum magnetic field needed in the scanning magnet is 33 mT. By a bipolar current supply of 72 V and 6 A, 174 turns are required in the magnet coils. Change of irradiation side at the lowest used field as described above performed, is in this case from +10 mT toxe2x88x9210 mT. This should be done as fast as possible, without making the inductive voltage too large, and in the shown embodiment, this is performed during the duration of two pulses. The currents I0 and I3, respectively, thus correspond to the largest used deflection in the scanning magnet, in positive and negative direction, respectively, which in turn correspond to a radiation position in the radiation sector positioned at the end closest to the accelerator. In the same manner, the currents I1, and I2, respectively, correspond to a radiation position at the farther, away from the accelerator facing, end. If products with a size which do not occupy the entire width of the radiation sector are to be irradiated, the currents I0, I1, I2, and I3 may easily be adapted so as to not radiate the area outside the products. Such a control possibility of the radiation width, makes the use of the arrangement for different types of products very flexible. The products are brought through the radiation sector in the radiation chamber on a conveyor belt, which is more closely described below. The feeding velocity is adapted so as to give the products the necessary radiation dose. Requested feeding velocity is given by the radiation power, the scanning width and the required dose and for this embodiment it is 0.76 m/min at 6 kW radiation power, 30 cm scanning width and 25 kGy dose. The geometry of the irradiation arrangement is important. A system using directly impacting particles inevitable obtains different angle of incidence against the products since the beam is deflected from one and the same point. Either the distance between the scanning magnet and the product has to be large, or the angle of incidence will vary substantially for products of reasonable dimensions. For instance, an angle of incidence of 45 degrees against the product reduces the penetration depth by 30%. A system where all beams are redeflected before the irradiation may be constructed compact and give homogeneous angles of incidence. Furthermore, if the system is symmetric, the control of the scanning is facilitated even if this does not imply any fundamental difference. In the irradiation arrangement, the products are normally irradiated when they are placed in a horizontal position. At use of direct impact, it is required that the accelerator arrangement is directed substantially vertically, which gives the arrangement a large height and may be impossible to install in premises with normal roof height. By using redeflected beams, one may easily create a configuration where both the accelerator device and the products may be placed substantially horizontally. By using a relatively low particle energy, a particle accelerator of a relatively small size may be used, and the lower energy reduces the need for radiation shielding. The total size of the arrangement may, due to this and the geometrical arrangements described above, be reduced significantly and the described embodiment has a total volume of 8 m3 and covers an area of 4, 2 m2. The total mass is approximately 16,000 kg. This, together with the fact that the transport needs and the internal logistic problems at the irradiation arrangements are set aside by the double-sided irradiation, implies that the arrangement advantageously is used directly in a production line, which sets aside many problems in connection with transport and storage. In FIG. 3, a vertical section of an embodiment according to the present invention is shown, perpendicularly to the one shown in FIGS. 1 and 2, and which substantially shows the operation of the conveyor belt. The products, often in the form of tubes or other small details, packed in flabby bags, are to be transported past the particle beam with an even velocity to achieve a homogeneous radiation dose. By efficiency point of view, these products should be able to be positioned closely without risk for being moved or shadowing each other during the transport through the irradiation arrangement. This transport is performed by means of a conveyor belt, which comprises two webs 14, 15 of flexible net or the like, with a width larger than the one of the products, but which may pass through the radiation chamber 4. The products to be irradiated are transported jammed in between the two net webs. Wires or chains are arranged along the edges of the net webs, which are used to drive the net webs forward and to stay the net webs. The net webs are driven separately by one motor 17 each, but in a co-ordinated manner with each other, in a closed travelling path each. These travelling paths are connected to each other during the path at which the webs are passing through the particle radiation device, from the position 19 where the products are brought to the webs to the position 20 where the products are leaving the webs. Along this length, the wires or chains are jammed together at regular intervals by rolls 16, and in this manner the net webs jam the products to be irradiated between each other. In order for the conveyor belt to allow for irradiation from both sides and not obstruct the particles in any substantial amount, the net of the net webs 14, 15 are made of thin metal wire, with a diameter less than 1 mm, and with a distance between the wires of approximately 20 mm. The conveyor belt is in this manner very flexible and may easily be driven along a narrow and curved tunnel by the rolls 16 through a so-called labyrinth 18. The labyrinth is necessary for stopping the secondary X-ray radiation to penetrate out from the radiation chamber. Since the products are fixed by the net webs, this passage may be performed without risk for displacements of the products along the conveyor belt. It is thus guaranteed that the velocity of the products past the radiation corresponds to the velocity of the net webs, which may be measured and regulated from the outside. This velocity is regulated to give the products the right radiation dose. The entire irradiation device is supposed to be included in a production line and the products brought in at 19 are assumed to originate directly from a production device for the products. At the output side 20, a packaging machine may e.g. be disposed to take care of the radiation treated products. The previous detailed description of an embodiment has only been given to facilitate the understanding of the basic idea of the invention and no additional limitations beyond what is stated by the patent claims should be understood from this, since alterations are obvious for someone skilled in the art. All numerical examples given above are tied to the specific exemplified embodiment and are not generally true for the invention as such. Someone skilled in the art easily understands that e.g. the type of particle accelerator may be varied. The exact design of the particle extraction and acceleration is not of importance for the basic features of the invention. Given numerical examples are related to the exemplified embodiment and have generally no direct influence of the basic features of the invention, but will of course effect the design of other parts of the irradiation arrangement. The required particle energy is thus important for the design of the construction of the accelerator as well as the extent of the radiation shields. The pulse repetition frequency, the particle pulse current and the beam size effect e.g. the maximum scanning velocity. In the same manner, it is understood that many parts of the equipment may be changed for other types with a corresponding effect. One may as one example mention that, instead of the permanent magnets used in the embodiment above, one may use electromagnets as redeflection magnets. However, these are more sensitive to radiation damages and are generally more space consuming, why permanent magnets are to prefer. However, this choice does not influence the basic feature of the invention. The scanning magnet may in a similar way also be designed in alternative ways, where the exit angle of the beam from the magnet is easily controllable. Alternative solutions are also that the particle accelerator is designed with a controllable focusing action, or that this function is integrated with the scanning magnet. The vacuum window may in an analogue manner be designed in different ways and with different materials, but have the same basic properties, i.e. to isolate vacuum but to let the particle beam through with as small losses as possible. The particle stopper in the described embodiment consists of a separate means disposed at the redeflection magnets. Other imaginable solutions are e.g. that they are disposed with another geometry, but still acting in the manner stated in the claims. The absorption means do not even have to consist of a separate particle stopper, but its function may e.g. be integrated in other parts of the chamber, e.g. directly in the walls of the radiation chamber. The range of angles, within which the scanning magnet operates is of course dependent of the design of the magnet and its function, and by the geometrical configuration of the redeflection magnets and the radiation sector. Given numerical examples are related solely to the described embodiment. It is also understood that even if the above described embodiment operates with perpendicular irradiation of the products, other geometrical configurations may be thinkable. Such changes will thereby have repercussions on the exact geometrical design of the redeflection magnets and the control of the scanning magnet. The perpendicular irradiation is, however, considered as the most favourable, since it gives the largest penetration depth for a certain particle energy for substantially planar products. For arrangements dedicated for a product with a certain geometrical shape, the optimal geometrical configuration may be different, e.g. with other irradiation directions or positioning of the radiation sector. The details and in particular the given numerical indications of the control of the scanning magnet are also related only to the described embodiment. The same is of course valid for the design and the stated dimensions of the total size of the arrangement, which only serves to emphasize the advantage with the compact shape of the irradiation arrangement of the embodiment. The transport system described is also solely exemplifying. The detailed design of the net webs may and should be determined by which products are to be transported. The transport webs are here described as net webs, but fully covering webs of any thin radiation durable material with low electron absorption would also be imaginable, as well as webs which only covers parts of the products. |
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description | 1. Field of the Invention The present invention relates to a water filling technique capable of filling a reactor water level gauge with water even in an unexpected abnormal event where a reactor building is brought into a highly radioactive environment. 2. Description of the Related Art In a nuclear power plant, a reactor holds water, and hydraulic head pressure of water is measured to measure a reactor water level. An instrumentation pipe of a reactor water level gauge that measures a reactor water level is filled with water. As shown in FIG. 11, such instrumentation pipe 1a of a reactor water level gauge 1 is connected via a gauge test valve 2 to a pump 3. The gauge test valve 2 is opened, and the pump 3 is used to fill the instrumentation pipe 1a of the reactor water level gauge 1 with water from a makeup water system (MUW) or water in a tank 4 left overnight in terms of preventing inflow of air. In a reactor building 5, the makeup water system (MUW) is provided close to the instrumentation pipe 1a of the reactor water level gauge 1, and an MUW main valve 7a of the MUW pipe 7 and the gauge test valve 2 are connectable by a flexible pipe. The gauge test valve 2 is opened, and the MUW main valve 7a is opened to fill the instrumentation pipe 1a of the reactor water level gauge 1 with water, and a reactor water level can be measured by the reactor water level gauge 1. However, due to an earthquake, in the reactor water level gauge 1, water in the instrumentation pipe 1a in a reactor containment vessel 6 evaporates to cause a malfunction or an instruction error of measuring gauges. In addition, after the earthquake, the reactor containment vessel 6 is brought into an environment of 100° C. or more, the water in the instrumentation pipe 1a continuously evaporates without being condensed to cause an instruction error for measurement of the reactor water level. In FIG. 11, reference numeral 8 denotes a reactor pressure vessel, and reference numeral 9 denotes an existing transmitter. Further, the reactor building 5 housing gauges is brought into a highly radioactive environment after the earthquake, the gauge test valve 2 through which the instrumentation pipe 1a of the reactor water level gauge 1 is filled with water is not accessible, making it difficult to fill the instrumentation pipe 1a with water. For a conventional nuclear power plant, occurrence of an unexpected abnormal event such as an earthquake is not considered, and further, it is not assumed that the reactor building 5 is brought into a highly radioactive environment. Thus, inaccessibility to the gauge test valve 2 provided in the reactor building 5 is not considered. The present invention is achieved in view of the above described circumstances and has an object to provide a water filling system for a reactor water level gauge capable of filling the reactor water level gauge with water even in an unexpected abnormal event where a reactor building is brought into a highly radioactive environment. The above and other objects can be achieved according to the embodiment of the present invention by providing a water filling system for a reactor water level gauge including: a reactor water level gauge instrumentation pipe disposed in a reactor building; and a water filling instrumentation pipe connected to the reactor water level gauge instrumentation pipe and extended outside the reactor building to fill the reactor water level gauge instrumentation pipe in the reactor building with water. A separation valve to be opened or closed by a nitrogen gas from outside the reactor building may be provided for the water filling instrumentation pipe. Furthermore, to achieve the objects of the present invention, an embodiment provides a water filling system for a reactor water level gauge including: a reactor water level gauge instrumentation pipe disposed in a reactor building; and a water filling instrumentation pipe guided from the reactor water level gauge instrumentation pipe to an outside of the reactor building, the water filling instrumentation pipe being connected to a makeup water instrumentation pipe connected to a make-up water (MUW) pipe outside the reactor building. Furthermore, the objects of the present invention can be achieved by providing a water filling system for a reactor water level gauge including a water filling instrumentation pipe guided from a reactor water level gauge instrumentation pipe in a reactor building to an outside of the reactor building, the water filling instrumentation pipe being connected to an instrumentation pipe for instrumentation connected to a high pressure injection nitrogen gas supply pipe (HPIN) outside the reactor building for supplying nitrogen to open/close a separation valve provided in the water filling instrumentation pipe. According to the embodiment of the present invention of the characters mentioned above, The present invention can provide a water filling system for a reactor water level gauge capable of filling the reactor water level gauge instrumentation pipe in the reactor building with water, and filling the reactor water level gauge with water, even if an unexpected abnormal event occurs where the reactor building is brought into a highly radioactive environment and is inaccessible. Hereunder, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a configuration diagram of a water filling system for a reactor water level gauge according to a first embodiment. In a nuclear power plant, a reactor containment vessel 11 is provided in a reactor building 10, and houses a reactor pressure vessel 12. In the reactor containment vessel 11, a reactor water level gauge 13 that measures a water level in the reactor pressure vessel 12 is provided. The reactor water level gauge 13 includes a reactor water level gauge instrumentation pipes 15 in the reactor building, connected to two vertically upper and lower portions of the reactor pressure vessel 12. The two reactor water level gauge instrumentation pipes 15 in the reactor building are extended into the reactor building 10 through unshown penetration in the reactor containment vessel 11. Among two vertical connecting portions of the reactor pressure vessel 12, a condensation bath 14 can be provided on the upper connecting portion, and a plurality of, for example, four condensation baths 14 are provided outside the reactor pressure vessel 12. With a reactor, a water filling system 16 for a reactor water level gauge is configured, during normal operation, so that as shown in FIG. 10, the two upper and lower reactor water level gauge instrumentation pipes 15 in the reactor building are filled with water. One detecting instrumentation pipe 15a and the other detecting instrumentation pipe 15b branch off from each of the two reactor water level gauge instrumentation pipes 15 in the reactor building. One detecting instrumentation pipe 15a has the same configuration as an instrumentation pipe 1a of an existing reactor water level gauge 1 shown in FIG. 11, and the instrumentation pipes are provided, for example, on diametrically opposite outer sides of the reactor pressure vessel 12. In the detecting instrumentation pipes 15a, 15b of the reactor water level gauge 13, transmitters 18 (level transmitters (LT) 18a, 18b, respectively) are provided via gauge inlet valves 17, and transmitters 18 (18a, 18b) paired therewith are provided, for example, on a diametrically opposite side of the reactor pressure vessel 12 in the reactor building 10. One of the pair of transmitters 18 is the same as an existing transmitter 18a (corresponding to reference numeral 9 in FIG. 11), and the other is a dedicated transmitter 18b used in an emergency. A gauge test valve 19 is provided on an outlet side of the gauge inlet valve 17. The reactor water level gauge 13 includes the condensation bath 14, the reactor water level gauge instrumentation pipe 15 in the reactor building, the gauge inlet valve 17, the transmitter 18, and the gauge test valve 19. The reactor water level gauge 13 uses at least one of the transmitters 18a, 18b to measure a difference in water pressure between the two upper and lower reactor water level gauge instrumentation pipes 15 in the reactor building 10 to measure a water level of the reactor pressure vessel 12. The reactor water level gauge instrumentation pipe 15 in the reactor building further includes a water filling instrumentation pipe 20. The water filling instrumentation pipe 20 has one end connected to the reactor water level gauge instrumentation pipe 15 in the existing reactor building, and the other end guided so as to extend to an outside of the reactor building 10 such as outdoors, and includes a joint 38a. The joint 38a connects a water filling device 21. Further, a separation valve 23 is provided in a middle of the water filling instrumentation pipe 20. Each separation valve 23 separates the reactor water level gauge instrumentation pipe 15 in the reactor building and the reactor building 10 from outside. The separation valve 23 is connected by an operating instrumentation pipe 25. The operating instrumentation pipe 25 has one end connected to the separation valve 23, and the other end extended outside the reactor building 10 and including a joint 38b via a stop valve 22. A gas cylinder 24 can be connected to the joint 38b. There will be described an operation of the water filling system 16 for a reactor water level gauge of the structure described above, in an emergency, when an operator should evacuate to the outside of the reactor building 10. In an emergency, the water filling device 21 is connected to the joint 38a, and the gas cylinder 24 is connected to the joint 38b. A nitrogen gas (N2) or air is supplied by the gas cylinder 24 to open the stop valve 22 and open the separation valve 23. Then, the water filling device 21 is used to supply water to the detecting instrumentation pipe 15b to fill the reactor water level gauge instrumentation pipe 15 in the reactor building with water. FIG. 2 shows a first modification (modified embodiment) of the first embodiment. The first modification is such that a CRD pump (control rod drive mechanism) 40 is used to supply water to the reactor water level gauge instrumentation pipe 15 in the reactor building in the first embodiment of the water filling system 16 for a reactor water level gauge. As shown in FIG. 2, during operation of the plant, the CRD pump 40 supplies water to a CRD 39, and the CRD 39 supplies water to the reactor water level gauge instrumentation pipe 15. Since it cannot be expected that the CRD pump 40 operates at a time of an accident, if the reactor water level gauge instrumentation pipe 15 needs to be filled with water at the time of an accident, the water filling system 16 for the reactor water level gauge 13 uses the water filling instrumentation pipe 20 from the water filling device 21. Thus, the gas cylinder 24 is connected to open the separation valve 23, and the water filling device 21 is used to fill the reactor water level gauge instrumentation pipe 15 with water. The water filling procedure is the same as that represented in FIG. 1, and thus, detail there omitted herein. FIG. 3 shows a second modification (modified embodiment) of the first embodiment of the water filling system for a reactor water level gauge. The second modification has a structure in which the gauge test valve 19 is replaced by a separation valve 23. The separation valve 23 is provided below the transmitter 18a instead of the gauge test valve 19. The water filling instrumentation pipe 20 is extended from the separation valve 23 to an outside of the reactor building 10, and the water filling device 21 can be connected via a joint 38a outside the reactor building 10. Further, the separation valve 23 can be operated from outside the reactor building 10 by the water filling instrumentation pipe 20 and the gas cylinder 24. The water filling procedure is the same as in FIG. 1, and thus, detail will be omitted herein. This case has characteristic feature such that the number of gauge test valves 19 is smaller than in the first embodiment. FIG. 4 is a configuration diagram representing a water filling system for a reactor water level gauge according to a second embodiment. A water filling instrumentation pipe 20 in a water filling system 16A for a reactor water level gauge 13 is guided from a detecting instrumentation pipe 15b of a reactor water level gauge instrumentation pipe 15 in an existing reactor building to an outside of a reactor building 10 such as outdoors and connected to a water filling device 21. The water filling instrumentation pipe 20 includes a normally-closed stop valve 22 outside the reactor building 10 and a separation valve 23 in the reactor building 10. The separation valve 23 and the stop valve 22 are dual valves because high pressure is applied on the valves. The separation valve 23 provided in the water filling instrumentation pipe 20 is a normally-closed AO valve, and the separation valve 23 is connected to a gas cylinder 24 provided outside the reactor building 10 such as outdoors via an operating instrumentation pipe 25. The separation valve 23 is configured to be opened by a nitrogen gas (N2) or air supplied via the stop valve 22 by the gas cylinder 24 provided outside the reactor building 10. Meanwhile, in the reactor building 10, a makeup water pipe 27 is placed connecting to an MUW (makeup water system) that supplies water, a reactor building closed cooling water system (RCW), or an emergency countermeasure system tank. A makeup water instrumentation pipe 28 branches off from the makeup water pipe 27 and is guided outside the reactor building 10, and connected to the water filling device 21 outside the reactor building 10. Further, in FIG. 4, reference numeral 29 denotes an MUW valve. The makeup water instrumentation pipe 28 connected to the makeup water pipe 27 includes a separation valve 30 in the reactor building 10 and a normally-closed stop valve 31 outside the reactor building 10. The separation valve 30 of the makeup water instrumentation pipe 28 branching off from the makeup water pipe 27 is a normally-closed AO valve, connected by the operating instrumentation pipe 25 to the gas cylinder 24 provided outside the reactor building 10 such as outdoors, and opened by a nitrogen gas (N2) or air from the gas cylinder 24. The separation valve 30 can be opened to supply water from the MUW (makeup water system) into the water filling device 21. As shown in FIG. 5, the water filling device 21 provided outside the reactor building 10 such as outdoors includes a hand pump or an automatic pump 33 and a tank 34, and water from the MUW is supplied to the tank 34. The water from the MUW to the reactor water level gauge 13 or water left overnight in terms of preventing inflow of air is supplied to the tank 34. The water filling system 16A for a reactor water level gauge is configured so that the water filling device 21 provided outside the reactor building 10 such as outdoors can be used to supply water in the tank 34 through the water filling instrumentation pipe 20 to the reactor water level gauge instrumentation pipe 15 in the reactor building. Further, as shown in FIGS. 6 and 7, an air vent line 35 is provided upstream of the separation valve 23 in the water filling instrumentation pipe 20 as a water filling line. An air vent valve 36 as a normally-closed AO valve is provided in the air vent line 35 in FIG. 6 and connected to a funnel 37. The air vent valve 36 can be opened/closed by N2 (nitrogen gas) or air from the gas cylinder 24 provided outside the reactor building 10 such as outdoors. Before the reactor water level gauge instrumentation pipe 15 in the reactor building 10 is filled with water, the air vent valve 36 is opened with the water filling instrumentation pipe 20 being closed by the separation valve 23 so as to guide air contained in the water filling instrumentation pipe 20 to the funnel 37. In the water filling system 16A for a reactor water level gauge of this second embodiment, even if an unexpected abnormal event occurs where the reactor building 10 is brought into a highly radioactive environment and is inaccessible, the separation valves 23, 23 in the water filling instrumentation pipe 20, the separation valve 30 in the instrumentation pipe 28 connected to the makeup water pipe 27 shown in FIG. 4, and further the normally-closed AO valve such as the air vent valve 36 in the air vent line 35 shown in FIG. 6 can be opened by a nitrogen gas (N2) or air from the gas cylinder 24. Further, since the normally-closed AO valve can be opened by a nitrogen gas (N2) or air from the gas cylinder 24 even if power is shut down, the water filling device 21 provided outside the reactor building 10 such as outdoors can be used to fill the reactor water level gauge instrumentation pipe 15 in the reactor building 10 with water. Thus, the reactor water level gauge 13 can be filled with water. Even in an unexpected abnormal event where the reactor building 10 is brought into a highly radioactive environment and is inaccessible, and a reactor water level in the reactor pressure vessel 12 is reduced, the reactor water level or the like can be measured. As shown in FIG. 4, in the water filling system 16A for a reactor water level gauge of this embodiment, for example, an existing transmitter 18a and an added transmitter 18b for a severe accident are provided in pair in the reactor building 10 of the existing nuclear power plant, and the water filling instrumentation pipe 20 and the normally-closed separation valves 23, 23, 30 provided in the reactor building 10, and the air vent valve 36 shown in FIG. 6 are opened by a nitrogen gas (N2) or air pressure from the gas cylinder 24 even if power is shut down. Even if the reactor building 10 is brought into a highly radioactive environment and inaccessible, the reactor water level gauge instrumentation pipe 15 in the reactor building 10 can be independently filled with water. Thus, in an unexpected abnormal event, the transmitter 18b for a severe accident can be used with a minimum influence on the existing transmitter 18a, and the water filling instrumentation pipe 20 and the transmitter 18 can be independently operated when power is shut down. FIG. 8 shows a third embodiment of a water filling system for a reactor water level gauge. The water filling system 16B for a reactor water level gauge is basically different from the water filling system 16A for a reactor water level gauge in the second embodiment in a structure including no water filling device 21 outside the reactor building 10 such as outdoors. Other configurations are substantially the same as those in the second embodiment, and thus, the same components are denoted by the same reference numerals and overlapping descriptions will be omitted. The water filling system 16B for a reactor water level gauge of this third embodiment has a configuration in which internal pressure of an MUW or an RCW that supplies water can be used to fill a reactor water level gauge instrumentation pipe 15 in a reactor building with water. The water filling system 16B for a reactor water level gauge 13 is configured so that a makeup water instrumentation pipe 28 branching off from a makeup water pipe 27 is guided outside the reactor building 10, and the makeup water instrumentation pipe 28 is connected to a water filling instrumentation pipe 20 outside the reactor building 10. In the third embodiment, there is no need for a water filling device, and there is no need for an automatic pump or a manual pump 33 of the water filling device 21. The internal pressure of the MUW or the RCW can be used to fill the reactor water level gauge instrumentation pipe 15 in the reactor building with water, and thus, it is not necessary to locate a pump in the water filling system 16B for a reactor water level gauge, and there is also no need for a power supply required for an automatic pump in the water filling device 21 (FIG. 1), and there is no need to use a manual pump. According to the water filling system 16B for a reactor water level gauge in FIG. 8, the instrumentation pipe 28 connected to the makeup water pipe 27 and the water filling instrumentation pipe 20 are connected outside the reactor building 10 such as outdoors, and thus, the makeup water from the MUW, the RCW, or an emergency countermeasure system tank can be used from outside the reactor building 10 to fill the reactor water level gauge instrumentation pipe 15 in the reactor building with water through the water filling instrumentation pipe 20. The water filling system 16B for the reactor water level gauge 13 can include, in addition to an existing transmitter 18a, the makeup water instrumentation pipe 28 connected to the MUW pipe 27, the water filling instrumentation pipe 20, and a dedicated transmitter 18b for a severe accident used in an earthquake can be independently provided in the reactor building 10. Thus, even in an unexpected abnormal event where the reactor building 10 is brought into a highly radioactive environment and is inaccessible, a nitrogen gas (N2) or air from the gas cylinder 24 provided outside the reactor building 10 such as outdoors can be used to open a normally-closed separation valve 30 or an air vent valve 36 (see FIGS. 6 and 7) to fill the reactor water level gauge instrumentation pipe 15 in the reactor building with water. Thus, the reactor water level gauge 13 can be filled with water, the reactor water level can be measured, and even in an unexpected abnormal event, the water filling instrumentation pipe 20 and the transmitter 18 can be independently operated. FIG. 9 shows a fourth embodiment of a water filling system for a reactor water level gauge. The water filling system 16C for a reactor water level gauge is different from the water filling system 16A for a reactor water level gauge in the second embodiment in a structure in which nitrogen or air for opening/closing a separation valve can be supplied by a high pressure injection nitrogen gas supply system (HPIN) or a compression air system (IA). Other configurations are substantially the same as those in the second embodiment, and thus, the same components are denoted by the same reference numerals and overlapping descriptions will be omitted. The water filling system 16C for a reactor water level gauge of this fourth embodiment can be newly provided in a nuclear power plant, but it may be conceivable that an instrumentation pipe 20, an MUW pipe 27, and an existing transmitter 18a in an reactor building 10 provided in an existing nuclear power plant can be used to additionally constitute the water filling system 16C for a reactor water level gauge 13. The latter water filling system 16C for a reactor water level gauge is configured by adding, in the reactor building 10, a water filling instrumentation pipe 20, an instrumentation pipe 28 connected to the MUW pipe 27, and a dedicated transmitter 18b for a severe accident used in an earthquake, and providing, outside the reactor building 10, a tank for supplying a nitrogen gas (N2) or air or a water filling device 21, in an existing nuclear power plant. FIG. 10 shows a fifth embodiment of a water filling system for a reactor water level gauge. The water filling system 16D for a reactor water level gauge is different from the water filling system 16B for a reactor water level gauge in the third embodiment in a structure for monitoring pressure in a reactor water level gauge instrumentation pipe 15 in a reactor building 10. Other configurations are substantially the same as those in the third embodiment, and thus, the same components are denoted by the same reference numerals and overlapping descriptions will be omitted herein. The water filling system 16D for a reactor water level gauge of this fifth embodiment has a feature in which a transmitter (i.e., pressure transmitter (PT)) 42 detects pressure in a reactor water level gauge instrumentation pipe 15 in a reactor building 10. The transmitter 42 detects reactor pressure and hydraulic head pressure of the reactor water level gauge instrumentation pipe 15 in the reactor building 10 and can check a water draining state and effectiveness of water filling in the reactor water level gauge instrumentation pipe 15 in the reactor building. An instruction from the transmitter 42 can be monitored by an instruction unit 43 provided outside the reactor building 10 such as outdoors. The instruction from the transmitter 42 is monitored by the instruction unit 43 to thereby check or control the effectiveness of water filling from outside the reactor building 10 such as outdoors while water is being filled. The instruction from the transmitter 42 can be output to a control device 44 provided outside the reactor building 10 such as outdoors, a pressure or a change in pressure of the reactor water level gauge instrumentation pipe 15 in the reactor building is used to check that a condensation bath 14 of a reactor water level gauge 13 has been filled with water, and an operation of the pump 33 in the water filling device 21 can be stopped or the separation valve 23 can be opened/closed to control filling of the reactor water level gauge instrumentation pipe 15 with water. Thus, the reactor water level gauge 13 can be automatically filled with water. It is further to be noted that the first to fifth embodiments of the present invention described above may be appropriately combined. |
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abstract | An object of the invention is to realize a method and an apparatus for processing and observing a minute sample which can observe a section of a wafer in horizontal to vertical directions with high resolution, high accuracy and high throughput without splitting any wafer which is a sample. In an apparatus of the invention, there are included a focused ion beam optical system and an electron optical system in one vacuum container, and a minute sample containing a desired area of the sample is separated by forming processing with a charged particle beam, and there are included a manipulator for extracting the separated minute sample, and a manipulator controller for driving the manipulator independently of a wafer sample stage. |
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047050713 | claims | 1. In combination with a steam control valve for a power plant steam chest, said steam chest including a hollow elongated central member, said central member having a steam inlet means passing therethrough in predetermined position and a steam outlet means passing therethrough in predetermined position, said steam inlet means at a relatively higher pressure than said steam outlet means, throttle valve means positioned proximate said inlet means, said central member having control valve aperture means passing therethrough, said steam control valve including a cylindrical outer housing means having a lip member affixed to the upper end thereof, said lip member having an outside diameter greater than said control valve aperture, said outer housing means passing through said control valve aperture and maintained in predetermined position by said lip member, said outer housing means including a bottom muffler portion, said bottom muffler portion having window opening means of predetermined dimensions therethrough and spaced about the circumference thereof, the bottoms of said window opening means a predetermined distance above the bottom of said bottom muffler portion, said bottom muffler portion of said outer housing having an initial inside diameter greater than the final inside diameter of the remaining portion of said outer housing, a movable plug for controllably sealing said high pressure inlet means from said relatively low pressure outlet means, said movable plug coaxially aligned with said outer housing means and slidable within the interior of said housing means, shaft means for moving said plug at one end affixed to said plug in predetermined position, lifting means affixed to the other end of said shaft means for lifting said plug, said plug having groove means therein about the circumference thereof in predetermined position, circular seal ring means sized to be insertable into said groove means, the improvement which comprises: a bottom ring portion disposed between the bottom of said window opening means and the bottom of said bottom muffler portion, said window ring portion having a plurality of pockets therein about the inner circumference thereof, each of said pockets of predetermined dimensions and aligned with one of said window opening means, each of said pockets having a steam exit portion having an initial central diameter equal to the inside diameter of the bottom muffler portion of said outer housing and each of said pockets having a final central diameter at the steam entrance portion of said pocket a predetermined amount larger than the initial central diameter of said steam exit portion of said pocket, the steam entrance portion of each of said pockets are disposed within said bottom of said aligned window opening means, said steam exit portion of each of said pockets being a predetermined distance above the bottom of said outer housing, whereby when said plug is initially lifted by said lifting means, steam at said high pressure inlet means flows through said window opening means and through said pockets without damaging vibration of said outer housing means and plug. 2. The steam control valve of claim 1, wherein the wall portions of said ring portion proximate each of said pockets from said steam entrance portion to said steam exit portion is at an angle offset from the vertical. 3. The steam control valve of claim 1, wherein the side portions of the ring portion proximate said pockets have a predetermined curvature. |
055368964 | summary | TECHNICAL FIELD The present invention relates to the field of processing organic waste, "processing" in the present case referring to the breaking down of said waste via the thermal route with the primary aim of affording opportunities for reducing its volume to thereby lessen handling and storage problems. More particularly, it concerns a new method and new apparatus for processing solid organic sulphur-containing waste in which the thermal breakdown embraces pyrolysis of the waste. The new method of the invention not only achieves the aim of volume reduction, but also provides, for example, such benefits as the elimination of the sulphur content from the exhaust gases, and similarly any radioactive content, in an effective and straight forward manner. The invention is therefore especially useful for the processing of ionic exchange media from nuclear facilities, which media display a certain degree of radioactivity and therefore would otherwise require conventional measures in relation to ultimate waste disposal and deposition. BACKGROUND OF THE INVENTION The nuclear industry annually produces a significant amount of waste which is classified as radioactively contaminated ion exchange media. In Sweden, such waste is managed in various fashions in the individual nuclear facilities prior to ultimate disposal in bedrock chambers. This management is technically complex and as a rule leads to increased volumes which influences storage costs. A process resulting in diminished volume at reasonable cost should therefore be commercially interesting. Ion exchange medium is an organic material. The base is usually a styrene polymer with grafted sulphonic acid and amine groups. The material is therefore burnable, but air is supplied during combustion and sulphur and nitrogen oxides are formed which in turn must be separated in some manner. Additionally, during combustion the temperature becomes sufficiently high for radioactive caesium to be partially vapourised. The residual radioactivity will also accompany the resulting fly ash to some extent. This necessitates a very high performance filter system. Accordingly, both technical and economic problems are associated with the combustion technique. An alternative to combustion is pyrolysis. However, previously known pyrolysis methods in this technical field are deficient in several aspects and in particular no one has earlier succeeded in devising a pyrolysis process which provides a comprehensive solution to the problem of sulphur and nitrogen-containing radioactive waste, and to do so under acceptable economic stipulations. The following can be mentioned as examples of the known technology in this respect: SE-B 8405113-5 which describes single stage pyrolysis in a fluidised bed followed by conversion of tars in the resulting gas to non-condensable gas using limestone as catalyst. U.S. Pat. No. 4,628,837, U.S. Pat. No. 4,636,335 and U.S. Pat. No. 4,654,172 which all describe pyrolysis of ion exchange resins where the pyrolysis is certainly carried out in two stages but where both of these stages are directed towards pyrolysis of the ion exchange media itself i.e. the solid product. Speaking generally, both stages moreover are carried out at relatively low temperatures. Furthermore, none of these specifications recites any comprehensive solution to the problem of solid organic sulphur-containing waste such as is the case with the method of the present invention. DESCRIPTION OF THE INVENTION The principal objective of the present invention is to provide a method for processing solid wastes of the abovementioned type, which method results in a "dead" (to use a biological term), compactable pyrolysis residue and thereby an effective reduction in the volume of the waste. Another objective of the invention is to provide a method which, in addition to the abovementioned volume reduction, affords effective processing of the resulting exhaust gases. A further objective of the invention is to provide a method which also affords an extremely high retention of the radioactivity present in the pyrolysis residue. A still further objective of the invention is to provide a method which is straight forward in technical respects and which is therefore also cost effective taking everything into account as regards volume reduction of the solid waste and management of the resulting exhaust gases. The abovementioned objectives are attained via a method which in general terms can be thought of as a two step pyrolysis, in which it is essential that the first pyrolysis step is carried out on the solid waste and at a relatively low temperature while the second pyrolysis step is carried out on the resulting gases and at a higher temperature, these two pyrolysis steps being followed by a step in which the gas is exposed to a sulphide-forming metal, optionally after an intermediate step in which the gas is first subjected to reducing conditions. More particularly, the method of the invention is distinctive in that a) the waste is subjected to pyrolysis at a temperature of at the most 700.degree. C., preferably 600.degree. C. at the most, to form a gas which contains organic sulphur compounds, and a solid pyrolysis residue which contains radioactive material from the waste, PA1 b) the gas is separated from the pyrolysis residue and subjected to a pyrolysis, which can alternatively be designated as cracking, for breaking down the organic sulphur compounds in the gas to carbonaceous compounds with a lower or low number of carbons and inorganic sulphur compounds, PA1 c) optionally exposing the gas from step b) to a bed of a solid reductant under reducing conditions so that any sulphur oxides present are reduced to hydrogen sulphide, and PA1 d) exposing the gas from step b), or alternatively step c) if this was carried out, to a bed of a sulphide-forming metal under conditions in which the sulphur compounds from the preceding step form metal sulphides with said metal. PA1 A) a pyrolysis reactor for carrying out pyrolysis on the solid waste, preferably at a temperature in the range 400.degree.-700.degree. C., especially 400.degree.-600.degree. C., PA1 B) a pyrolysis or cracking reactor for carrying out pyrolysis on the gases emanating from reactor A), preferably at a temperature in the range above 700.degree. C. and up to 1300.degree. C. when a catalyst is not used and 600.degree.-1300.degree. C. when a catalyst is present, PA1 C) optionally, a bed of a solid reductant for the reduction of any sulphur dioxide present in the gas, and PA1 D) a bed of a sulphide-forming metal for the formation of metal sulphide with the gas from step B) or alternatively with the gas from step C). In other words, the initial step involves subjecting the solid waste to pyrolysis at a temperature of 700.degree. C. at the most, preferably 600.degree. C. at the most, the term "pyrolysis" being used in its conventional sense, i.e. chemical decomposition or breakdown of a substance by the action of heat and without any real supply of oxygen or at least so little oxygen supply that no real combustion is effected. The pyrolysis thereby leads to breaking down of the carbonaceous waste to a relatively fluffy pyrolysis residue which can be drawn off from the bottom of the pyrolysis reactor employed and can thereafter be imparted a significantly smaller volume by compression. Additionally, by keeping the temperatures no higher than those recited above, practically speaking all of the radioactive materials, in particular .sup.137 Cs, are retained in the pyrolysis residue and therefore measures and consequent costs to remove additional radioactivity can be minimized. Any fly ash formed can, however, be removed from the resulting gas in a per se known manner, preferably in a ceramic filter in the pyrolysis reactor. In this way, the radioactive material in the fly ash caught in the filter can be returned to the pyrolysis residue. In the practice of the invention, it has proven possible in this fashion to attain very high retention of the radioactivity in the pyrolysis residue. In this regard, trials carried out on ion exchange media from a nuclear power station show a retention of almost 10.sup.6 :1, i.e. the decontamination factor DF is of the order 10.sup.6. Aside from said radioactive material, the pyrolysis residue contains carbon and possibly iron compounds such as iron oxides and iron sulphides. Trials in this connection, show the retention of sulphur in the pyrolysis residue to be >90%. No immediately critical lower limit is apparent for the pyrolysis in step a) but rather this limit is dictated, if anything, by effectiveness and/or cost. However, for practical purposes, a lower limit can generally be set at 400.degree. C. and therefore a preferred embodiment of the method of the invention involves stage a) being carried out at a temperature in the range 400.degree.-700.degree. C., preferably 400.degree.-600.degree. C., especially 450.degree.-600.degree. C., e.g 450.degree.-550.degree. C. Additionally, as the method of the invention as a whole has proven to be extremely effective both as regards the solids content and the evolved gases, step a) is preferably carried out without any catalyst for the breakdown of the carbon compounds in the waste which, of course, means that the method of the invention is very cost effective as the catalyst costs in comparable contexts often represent a large part of the total costs. Pyrolysis step a) can be carried out in per se known fashion as regards the type of pyrolysis reactor, e.g. in a fluidized bed, but in the overall set-up of the method in the context of the invention, "flash pyrolysis" has proven to give exceptionally good results. The expression flash pyrolysis is used herein in its conventional sense, i.e. with a relatively rapid flow-through of material. In other words, it is a matter of a short residence time, normally less than 30 seconds and even more usually a significantly shorter time, e.g. less than 15 seconds. An especially preferred flash pyrolysis is carried out in a gravity or flash reactor for which a suitable residence time can be 3-15 seconds, even better 4-10 seconds, e.g. 5-8 seconds such as around 6 seconds. Suitable residence times are, however, easily determined by the man skilled in the art in each individual case. In the present case, it will be understood that "solid waste" does not concern a solution of the material in question. It need not however necessarily concern a dry material but also material with a certain degree of moisture content, e.g. up to 50%, usually 10-30% such as is often the case when using ion exchange media. However, for flash pyrolysis, for example, it can be convenient to condition the material prior to pyrolysis a), which means a certain degree of drying and optionally, comminution. In this regard, a material in powder form has proven to give very good results in the initial pyrolysis a). The gas which is formed during pyrolysis in step a) contains decomposition products from the organic waste referred to as "tars". These tars principally contain pure hydrocarbons and water vapour, and organic sulphur compounds and amines when the waste is of the sulphur and nitrogen-containing ion exchange media type. The gas is separated from the pyrolysis residue and subjected to pyrolysis in a second step b) for which the temperature is selected in such a manner that, while paying attention to the other conditions, the organic sulphur-containing compounds therein with a moderately high number of carbons are cracked to compounds with a low or lower number of carbons and inorganic sulphur compounds. If the waste is nitrogen-containing, inorganic nitrogen compounds are formed as well. The temperature for step b) is selected, in other words, generally in accordance with the composition of the gas resulting from step a). Usually this means that the temperature of step b) is higher than that of step a), at least if a cracking catalyst is not used. If the temperature of step a) is high, this can, for example, mean that the temperature of step b) is higher than 700.degree. C. However, especially when a cracking catalyst is used as is further described below, the temperature of step b) can lie somewhat below the temperature of step a), or at least lower than the upper limit for step a). This can mean a temperature in excess of 600.degree. C. or more preferably in excess of 650.degree. C. The upper temperature limit is not especially critical as regards the desired breakdown but rather it is processing technology (materials science) or economic factors which set this upper limit. For example, it can thus be difficult from a cost effectiveness viewpoint to utilize materials which withstand a higher temperature than around 1500.degree. C. A preferred temperature is therefore up to 1500.degree. C. However, a more optimal upper temperature limit is 1300.degree. C. and therefore a convenient temperature range, especially without a catalyst, is above 700.degree. C. and up to 1300.degree. C. A particularly preferred temperature range for step b) is, however, above 700.degree. C. and up to 1000.degree. C. and best of all above 700.degree. C. and up to 850.degree. C. Corresponding preferred temperatures when using a catalyst are 600.degree.-1300.degree. C., especially 650.degree.-1300.degree. C. or better still 650.degree.-1000.degree. C., e.g 650.degree.-850.degree. C. The pyrolysis conditions for step b) are, however, not nearly as critical as for step a), in that it is primarily a matter of a complete breakdown of the sulphur content and any nitrogen containing carbon compounds with a moderate number of carbons to carbon compounds with a lower number of carbons, without any immediately interfering side-reactions or biproducts. Therefore, the pyrolysis in step b) can alternatively also be denoted as cracking in accordance with generally accepted terminology. Cracking leads to a high production of soot. The higher the temperature, the more soot is formed. The soot production will probably require high temperature filtration of the cracking gases, for which conventional techniques are available. A simpler and more timesaving methodology, however, is the previously described tar condensation prior to cracking. The condensation alternative additionally leads to good separation of the organic sulphur compounds. By analogy with the above, step b) can therefore also be conveniently carried out, in certain cases as touched on above, in the presence of a cracking catalyst known in the past in similar contexts. Lime, e.g. dolomite lime, can be mentioned as such a catalyst in connection with step b). When the gases from step a) contain tar products and water, a preferred embodiment of the method of the invention thus involves the gas, prior to step b), being subjected to condensation conditions such that tar products therein condense out and are separated before the gas is conducted to said step b). In this context, "tar products" will be understood to include carbonaceous compounds which are, of course, in gaseous form after pyrolysis in step a) but which drop out in the form of a more or less viscous tar mixed with water. The condensate can be separated by fractionated condensation into a low viscosity tar of high calorific value, water and a viscous sulphur-rich tar. Greater refinement of the pyrolytic or cracking process in step b) is brought about through said tar separation and thereby more cost effective execution. If sulphur oxides, especially SO.sub.2, are present in the gases emanating from the pyrolysis step, they must be attended to in an appropriate manner bearing in mind the strict requirements which now apply to the release of sulphur oxides and other sulphur compounds. This is attained in a simple and effective fashion in the method of the invention directly in the integrated process by virtue of the gas from stage b) being exposed in a stage c) to a bed of a solid reductant under reducing conditions so that the sulphur oxides are reduced, principally to hydrogen sulphide and carbon disulphide. Carbon, in particular, has proven to work extremely well as a reductant in relation to the method of the invention. Additionally, carbon results in the sort of end products, especially carbon dioxide, which are harmless and in principle can be released direct to the atmosphere. The temperature for the step c) reduction is selected by the man skilled in the art in this field in such a fashion that the sought after reactions are attained. This preferably means that the reduction is carried out at a temperature in the range 700.degree.-900.degree. C., the approximately 800.degree. C. temperature level probably lying near the optimum. Step c) additionally leads to a reduction in nitrogen oxides in the event that these are present in the gas after the pyrolysis steps. In the event that a high temperature filter of the carbonaceous filter type or similar is utilized for filtering out the soot in the post step b) gas, this filter can be regarded as a reduction means for use in the optional step c) of the invention. Finally, the gas in a step d) is exposed to a bed of a sulphide-forming metal under conditions in which the remaining sulphur compounds form metal sulphides with said metal. In this context, it is the gas from reduction step c), if present, or the gas from the second pyrolysis step b). In each case it is primarily a matter of transforming hydrogen sulphide to metal sulphide. Preferably, iron is used as sulphide-forming metal as iron is a cheap material and results in a harmless product, principally in the form of the iron disulphide, pyrite. Other metals, however, are also conceivable of which nickel can be mentioned as an example. The temperature for this step d) is also selected by the man skilled in the art in this field so that the sought after reactions are attained. An especially preferred temperature range, however, is 400.degree.-600.degree. C., the approximately 500.degree. C. level being especially suitable in many cases. Very volatile organic gases which do not condense out in the condensation step and which form during cracking also penetrate the reductants used in step c) and the sulphide forming reactor used in step d). Effluent requirements for these materials in Sweden are such that conversion or separation is required. When the gases are oxidizable, they can be destroyed by oxidation (combustion), e.g. catalytic oxidation. Oxidation is suitable for the pyrolysis of ion exchange media because the exhaust gases are chlorine-free and therefore no dioxins are formed. As has been touched upon earlier, both the solid end-product and the gaseous end-products of the method of the invention are amenable to handling. The resulting ash, for example, is thus particularly suitable for post-treatment in the form of simple compression, where the practice of the invention has proven that the volume can be reduced by as much as up to 75%. Furthermore, the resulting gases are rich in light organic compounds which implies a gas with a high heat content which can be burnt. Additionally, the sort of gases being referred to are non-injurious to the surroundings, e.g. carbon dioxide, gaseous nitrogen, gaseous hydrogen and water vapour, and therefore the method of the invention, as a whole, represents unparalleled advantages in relation to the known technique. In order that the method should proceed in an effective fashion and especially in order that the release of radioactive or unpleasant or dangerous gases through system leakage should be avoided, with consequent risks to working personnel, a further preferred embodiment involves carrying out the method under a certain degree of vacuum or negative pressure, conveniently by arranging a suction pump or gas evacuation pump downstream of step d). The invention additionally relates to apparatus for carrying out the method of the invention, which apparatus comprises: Additionally, as regards the apparatus of the invention, all of the features and preferred embodiments of the method described above are also suitable in connection therewith. These details therefore need not be repeated. However, the following especially preferred embodiments of the apparatus can be mentioned. Specifically, the pyrolysis reactor A) is a gravity reactor. Preferably, a condenser for the condensation of tar products in the gas is located prior to reactor B). A filter for the separation of any fly ash from the gas is preferably located in reactor A). The apparatus preferably includes a filter for the separation of soot from the gas from reactor B). Preferably a compactor is included for compression of the pyrolysis residue resulting from reactor A). Conveniently, an afterburner is present after bed D) for combustion of said gas. |
abstract | A vacuum system, in particular an EUV lithography system, includes: a vacuum housing, in which a vacuum environment is formed, and also at least one component (14), e.g., an optical element, having a surface (14a) which is subjected to contaminating particles in the vacuum environment. A surface structure (18) is formed at the surface in order to reduce adhesion of the contaminating particles, said surface structure having pore-shaped depressions (24) separated from one another by webs (25). The optical element has a substrate (19), and a multilayer coating (20) applied to the substrate and configured to reflect EUV radiation (6). The surface structure formed at the surface (14a) of the multilayer coating (20) reduces adhesion of contaminating particles (17) via pore-shaped depressions (24) separated from one another by webs (25). |
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060144181 | claims | 1. A weld of a zirconium alloy rod, comprising: a bead and a heat affected zone adjacent to said bead, wherein grain boundaries in said heat affected zone comprises 4.0 to 30% by weight Nb and 0.9 to 20% by weight Fe. 0.6 to 2.0% by weight of Nb, 0.5 to 1.5% by weight of Sn, 0.05 to 0.3% by weight of Fe, and Zr and incidental impurities. 0.8 to 1.2% by weight of Nb, 0.8 to 1.1% by weight of Sn, 0.08 to 0.12% by weight of Fe, and Zr and incidental impurities. a cladding tube, end caps, and the weld of claim 1, connecting said cladding tube and said end caps. 0.6 to 2.0% by weight of Nb, 0.5 to 1.5% by weight of Sn, 0.05 to 0.3% by weight of Fe, and Zr and incidental impurities. 0.8 to 1.2% by weight of Nb, 0.8 to 1.1% by weight of Sn, 0.08 to 0.12% by weight of Fe, and Zr and incidental impurities. cooling a heat-affect zone of said weld at a rate of 5-70.degree. C./sec.; wherein said heat affected zone has been prepared by welding a cladding tube and an end plug together, wherein said cladding tube comprises 0.6 to 2.0% by weight of Nb, 0.5 to 1.5% by weight of Sn, 0.05 to 0.3% by weight of Fe, and Zr and incidental impurities. sealing by welding a cladding tube and end plugs, thereby forming beads and heat affected zones adjacent to said beads; and cooling said heat-affect zones at a rate of 5-70.degree. C./sec.; wherein said cladding tube comprises 0.6 to 2.0% by weight of Nb, 0.5 to 1.5% by weight of Sn, 0.05 to 0.3% by weight of Fe, and Zr and incidental impurities. generating heat by fission of a nuclear fuel inside the fuel rod of claim 7 . 2. The weld of claim 1, wherein said weld comprises: 3. The weld of claim 1, wherein said weld comprises: 4. The weld of claim 2, wherein said weld consists essentially of Nb, Sn, Fe, Zr and incidental impurities. 5. The weld of claim 3, wherein said weld consists essentially of Nb, Sn, Fe, Zr and incidental impurities. 6. The weld of claim 5, further consisting essentially of Cr. 7. A fuel rod, comprising: 8. The fuel rod of claim 7, wherein said cladding tube comprises: 9. The fuel rod of claim 7, wherein said cladding tube comprises: 10. The fuel rod of claim 8, wherein said cladding tube consists essentially of Nb, Sn, Fe, Zr and incidental impurities. 11. The fuel rod of claim 9, wherein said cladding tube consists essentially of Nb, Sn, Fe, Zr and incidental impurities. 12. The fuel rod of claim 11, wherein said cladding further consists essentially of Cr. 13. A method of enhancing the corrosion resistance of a weld, comprising: 14. The method of claim 13, wherein said cladding tube comprises 0.8 to 1.2% by weight of Nb, 0.8 to 1.1% by weight of Sn, 0.08 to 0.12% by weight of Fe, and Zr and incidental impurities. 15. The method of claim 13, wherein said cladding tube consists essentially of Nb, Sn, Fe, Zr and incidental impurities. 16. The method of claim 14, wherein said cladding tube consists essentially of Nb, Sn, Fe, Zr and incidental impurities. 17. The method of claim 15, wherein said cladding tube further consists essentially of Cr. 18. A method of making a fuel rod, comprising: 19. The method of claim 18, wherein said cladding tube comprises 0.8 to 1.2% by weight of Nb, 0.8 to 1.1% by weight of Sn, 0.08 to 0.12% by weight of Fe, and Zr and incidental impurities. 20. The product produced by the method of claim 13. 21. The product produced by the method of claim 18. 22. A method of generating electrical power, comprising: |
abstract | An object of the invention is to provide a reactor instrumentation system that can be easily repaired or replaced. The invention includes: an instrumentation tube provided in a reactor core; a gas flow pipe provided in the instrumentation tube; a suction mechanism for supplying gas containing oxygen to the gas flow pipe; and a nuclide analysis device for measuring a nuclide in the gas in the gas flow pipe. According to the invention, it is possible to provide a reactor instrumentation system that can be easily repaired or replaced. |
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046438467 | abstract | A process for the treatment of radioactive sodium is provided which comprises the steps of forming radioactive sodium amalgam by mixing radioactive sodium with mercury; reacting the radioactive sodium amalgam with water to form mercury and radioactive sodium hydroxide; recycling the mercury into the step of forming radioactive sodium amalgam to be mixed with the radioactive sodium; and solidifying the radioactive sodium hydroxide in the presence of a solidifying material to be confined in a stable solidified body. |
048896829 | claims | 1. The passive cooling natural circulation system for the containment structure of a nuclear reactor plant which provides overpressure protection within the containment housing, comprising a nuclear reactor assembly having a pressure vessel with a heat producing core of fissionable fuel enclosed therein and at least one conduit in fluid communication with the interior of the pressure vessel extending out therefrom, a drywell chamber adjacent to said pressure vessel, a suppression pool chamber for retaining a cooling liquid and having a conduit providing fluid communication between said drywell chamber and suppression pool chamber, a compartment providing a liquid refill pool for liquid water isolated from radioactive fission products located overhead of the suppression pool chamber, a multiplicity of conduits arranged in a staggered array extending downward into the suppression pool chamber adjoining a wall thereof, said conduits being joined at their lower extremities with an adjacent conduit through a junction to provide a closed circuit therethrough for the passage of fluid down into the suppression pool chamber from above and return up to above said chamber, said multiplicity of adjacent conduits having such terminal end extending upward from their lower junction in fluid communication with the refill pool compartment overhead of the suppression pool chamber have one terminal end in fluid communication with the refill pool compartment on one side of a baffle provided therein and the other terminal end in fluid communication with the refill pool compartment on the other side of the baffle whereby liquid contained within the overhead refill pool compartment can circulate down via the conduits through the contents of the suppression pool chamber and return back up to the refill pool compartment thereby removing heat from the containment structures. 2. The passive cooling natural circulation system of claim 1, wherein the conduits joined at their lower extremities through a junction with an adjacent conduit have one terminal end in fluid communication with the refill pool compartment through a first header and the other terminal end in fluid communication with the refill pool compartment through a second header. 3. The passive cooling natural circulation system of claim 1, wherein the multiplicity of conduits arranged in a staggered array extending downward into the suppression pool chamber adjoining a wall thereof and joined at their lower extremities with an adjacent conduit through a junction have one conduit section extending upward from a junction with a surface exposed to the interior of the suppression pool chamber and its contents and another conduit section extending upward from the junction positioned intermediate the chamber wall and the conduit section with the exposed surface. 4. A passive cooling natural circulation system for the containment structure of a nuclear reactor plant which provides overpressure protection within the containment housing, comprising a nuclear reactor assembly having a pressure vessel with a heat producing core of fissionable fuel enclosed therein and at least one conduit in fluid communication with the interior of the pressure vessel extending out therefrom, a drywell chamber adjacent to said pressure vessel, a suppression pool chamber for retaining a cooling liquid and having a conduit providing fluid communication between said drywell chamber and suppression pool chamber, a compartment providing a liquid refill pool for water isolated from radioactive fission products located overhead of the suppression pool chamber, a multiplicity of conduits arranged in a staggered array extending downward into the suppression pool chamber adjoining a wall thereof, said conduits being joined at their lower extremities with an adjacent conduit through a junction to provide a closed circuit therethrough and having one terminal end in fluid communication with the refill pool compartment on one side of a baffle provided therein and the other terminal end in fluid communication with the refill pool compartment on the other side of the baffle to provide a closed circuit for the passage of fluid down from the refill pool compartment into the suppression pool chamber and return back up to the refill pool compartment. 5. The passive cooling natural circulation system of claim 6, wherein the conduits joined at their lower extremities though a junction with an adjacent conduit have one terminal end in fluid communication with the refill pool compartment through a first header and the other terminal end in fluid communication with the refill pool compartment through a second header. 6. The passive cooling natural circulation system of claim 6, wherein the multiplicity of conduits arranged in a staggered array extending downward into the suppression pool chamber adjoining a wall thereof and joined at their lower extremities with an adjacent conduit through a junction having one conduit section extending upward from a junction with a surface exposed to the interior of the suppression pool chamber and its contents and another conduit section extending upward from the junction positioned intermediate the chamber wall and the conduit section with the exposed surface. 7. A passive cooling natural circulation system for the containment structure of a nuclear reactor plant which provides overpressure protection within the containment housing, comprising a nuclear reactor assembly having a pressure vessel with a heat producing core of fissionable fuel enclosed therein and at least one conduit in fluid communication with the interior of the pressure vessel extending out therefrom, a drywell chamber adjacent to said pressure vessel, a suppression pool chamber for retaining a cooling liquid and having a conduit providing fluid communication between said drywell chamber and suppression pool chamber, a compartment providing a liquid refill pool for liquid water isolated from radioactive fission products located overhead of the suppression pool chamber, a multiplicity of paired concentric conduits in telescoping arrangement extending downward into the suppression pool chamber intermediate the walls thereof, said conduits being joined at their lower extremities with an adjacent conduit through a junction to provide a closed circuit therethrough for the passage of fluid down into the suppression pool chamber from above and return up to above said chamber, said multiplicity of paired concentric conduits having such terminal and extending upward from their lower junction in fluid communication with the refill pool compartment overhead of the suppression pool chamber whereby liquid contained within the overhead refill pool compartment can circulate down via the conduits through the contents of the suppression pool chamber and return back up to the refill pool compartment thereby removing heat from the containment structures. 8. The passive cooling natural circulating system of claim 7, wherein the multiplicity of conduits comprise units of two conduits paired together in concentric telescoping arrangement and being joined at their lower extremities through a junction to provide a closed circuit through the two paired conduits for the passage of fluid down into the suppressive pool chamber from above and return up to above said chamber. 9. The passive cooling natural circulating system of claim 7, wherein the multiplicity of conduits comprising units of two conduits paired together in telescoping arrangement include a smaller diameter inner pipe for cold flow concentrically surrounded by a larger diameter outer pipe for hot flow. 10. The passive cooling natural circulating system of claim 9, wherein the multiplicity of conduits comprising units of two conduits paired together in telescoping arrangement with a smaller diameter inner pipe for cold flow concentrically surrounded by a larger diameter outer pipe for hot flow include a plurality of small outlying branch pipes extending in fluid communication from the larger diameter outer pipe and deployed in an adjacent parallel pattern thereto for partial hot flow parallel with said large diameter outer pipe concentrically surrounding the smaller inner pipe for cold flow. |
053176065 | claims | 1. An automation system for nuclear power plants, comprising: operation plan making means for, after a nuclear power plant has been operated according to an operation plan under abnormal condition, making an operation plan to return to the normal operating condition, which had existed before the plant condition deviated from the normal operation range, from a condition that the operation according to the operation plan under abnormal condition has been finished; means for storing said operation plan under abnormal condition to decrease the reactor power to a level of power within said normal operation range when the operating condition of said nuclear power plant deviates from said normal operation range; means for deciding from detected plant data whether or not to perform an operation according to said operation plan under abnormal condition; control and arithmetic means for outputting control commands according to the operation plan; means for transmitting said operation plan under abnormal condition to said control and arithmetic means when said decision means makes a decision to perform an operation according to said operation plan under abnormal condition; supervisory control means having the control and arithmetic means for outputting control commands according to said new operation plan when said operation plan under abnormal condition has been executed; and control means for controlling controlled operation conditions of the plant according to said control commands. 2. An automation system for nuclear power plants according to claim 1, wherein said supervisory control means includes means for storing a normal operation plan, and wherein said means for transmitting said operation plan under abnormal condition is changeover means for transmitting one of said normal operation plan and said operation plan under abnormal condition to said control and arithmetic means. 3. An automation system for nuclear power plants according to claim 2, wherein said means for storing a normal operation plan stores a normal operation plan and said new operation plan which is applied after an operation plan under abnormal condition has been executed. 4. An automation system for nuclear power plants according to claim 1, wherein said operating plan making means includes a simulator for evaluating the adequacy of said new operation plan. 5. An automation system for nuclear power plants according to claim 1, wherein said operation plan making means comprises a knowledge base for storing knowledge necessary for making said new operation plan, and inference means for making said new operation plan by inference using said knowledge. 6. An automation system for nuclear power plants according to claim 5, wherein said operation plan making means includes a core one-point-approximated simulator, and wherein said inference means is means for executing inference by using calculated values obtained by said core one-point-approximated simulator. 7. An automation system for nuclear power plants according to claim 4, wherein said operation plan making means comprises a knowledge base for storing knowledge necessary for making said new operation plan, and inference means for making said new operation plan by inference using said knowledge. 8. An automation system for nuclear power plants according to claim 7, wherein said operation plan making means includes a core one-point-approximated simulator in addition to said simulator, and wherein said inference means is means for executing inference by using calculated values obtained by said core one-point-approximated simulator. |
claims | 1. A method for preparing a specimen for application of microanalysis thereto, the method comprising:forming an initial conductive layer over only a localized area of interest, said initial conductive layer formed through a low-energy beam deposition process;removing a volume of material surrounding said area of interest by forming a pair of trenches in a bulk material having said area of interest formed thereon, thereby forming a membrane including said area of interest and said initial conductive layer over said area of interest; andremoving said membrane from said bulk material. 2. The method of claim 1, wherein said low-energy beam deposition process comprises electron beam deposition. 3. The method of claim 2, wherein said initial conductive layer further comprises at least one of: platinum, tungsten, gold, aluminum, titanium, and combinations thereof. 4. The method of claim 1, wherein said initial conductive layer is formed at a thickness of about 10 nanometers (nm) to about 100 nm. 5. The method of claim 4, wherein said initial conductive layer is formed over an area of about 1 micron by about 10 microns. 6. The method of claim 4, further comprising implementing a high-energy beam deposition process for increasing the thickness of said initial conductive layer. 7. The method of claim 6, wherein said high-energy beam deposition process comprises ion beam deposition. 8. The method of claim 1, wherein said removing a volume of material surrounding said area of interest is implemented by focused ion beam milling. 9. A method for preparing a specimen for application of microanalysis thereto, the method comprising:forming an initial conductive layer over a defined, localized area of interest on a substrate, without blanket coverage of said initial conductive layer on the entire substrate, said initial conductive layer formed through an electron beam deposition process;removing a volume of substrate material surrounding said area of interest, thereby forming the specimen, including said area of interest and said initial conductive layer over said area of interest; andremoving the specimen from said substrate material. 10. The method of claim 9, wherein the microanalysis comprises tunneling electron microscopy (TEM). 11. The method of claim 10, wherein said initial conductive layer further comprises at least one of: platinum, tungsten, gold, aluminum, titanium, and combinations thereof. 12. The method of claim 9, wherein said initial conductive layer is formed at a thickness of about 10 nanometers (nm) to about 100 nm. 13. The method of claim 12, wherein said initial conductive layer is formed over an area of about 1 micron by about 10 microns. 14. The method of claim 12, further comprising implementing a high-energy beam deposition process for increasing the thickness of said initial conductive layer. 15. The method of claim 14, wherein said high-energy beam deposition process comprises ion beam deposition. 16. The method of claim 9, wherein said removing a volume of substrate material surrounding said area of interest is implemented by focused ion beam milling. |
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description | This application is a National Phase of PCT/EP2009/067901, filed Dec. 23, 2009, entitled, “ALUMINO-BOROSILICATE GLASS FOR CONFINING RADIOACTIVE LIQUID EFFLUENTS, AND METHOD FOR PROCESSING RADIOACTIVE EFFLUENTS”, and which claims priority of, French Patent Application No. 08 59131, filed Dec. 30, 2008, the contents of which are incorporated herein by reference in their entirety. The invention relates to an alumino-borosilicate glass for the confinement, containment, isolation of radioactive liquid effluents with medium activity especially effluents generated by operations for definitive shutdown (designated as MAD in French) of fuel cycle plants. The invention also relates to a vitrification adjuvant, especially in the form of a glass frit or of a mixture of chemical products, especially of oxides, in the form of a powder. The invention further relates to a method for treating radioactive liquid effluents of medium activity by calcination of these effluents, with view to obtaining a calcinate (calcine), by adding a vitrification adjuvant especially in the form of a glass frit or of a mixture of chemical products in the form of a powder to said calcinate, and melting of the calcinate and of the vitrification adjuvant in a cold crucible in order to obtain the alumino-borosilicate glass. The technical field of the invention may generally be defined as that of the treatment of radioactive elements, and more particularly radioactive elements of medium activity, by confinement, containment, isolation, coating or immobilization. These radioactive elements of medium activity are especially decontamination effluents generated by rinsing during operations for definitive shutdown (“MAD”) of plants for reprocessing nuclear fuel. The chemical composition of these decontamination effluents mainly depends on the different reagents used. These reagents may be based on nitric acid or soda, or else in certain case these may be more specific effluents based on sodium carbonate or cerium nitrate. Presently, radioactive effluents of medium activity such as the decontamination effluents mentioned above are essentially treated by bituminization or cementation. The coating method by bituminization consists of hot mixing the waste as sludges (salts) with bitumen. The obtained mixture is dehydrated and cast into a container where it is cooled. The bitumen coating thus ensures homogeneous dispersion of the salts and immobilization (blocking) of the radionuclides within the matrix. The bituminization method was developed in France as early as the 1960's for conditioning precipitation sludges resulting from the treatment of liquid effluents, and it was applied industrially. It is a well proven method which benefits from a wide feedback of experience. The bitumen was selected as a material for coating radioactive waste of low to medium radioactivity for its high agglomerating power, its high chemical inertia, its impermeability, its low solubility in water, its low application temperature, and its moderate cost. On the other hand, bituminization has several major drawbacks: the bitumen has reduced stability to irradiation, which causes swelling of the coated materials over time, especially because of the production of hydrogen by radiolysis; in order to avoid any risk of fire, in the production phase of the coated materials, the operating range of the bituminization installations is quite limited. Indeed, during the manufacturing of the bituminous coated material, exothermic reactions may occur, and therefore they have to be controlled at the very best; the mechanical strength of bitumens is very low because of their strong creep; the volume of waste generated by this matrix is significant, taking into account the activity of the “MAD” effluents. Cement, or more generally hydraulic binders are widely used in the nuclear industry. They are used for immobilizing solid waste of low and medium activity within containers or else they are used as a conditioning matrix for coating waste of medium activity. Cementation is also used for coating waste in solution or in powdery form such as evaporation concentrates, sludges from chemical processing, ion exchange resins . . . . Cements indeed combine many favorable properties for processing this type of waste, i.e. moderate costs, simplicity of application, good mechanical strength and, generally, stability over time. In the case of cementation of liquid waste, the methods are most often continuous. Thus, for example, the cement and the waste are dosed separately and introduced into a kneader, and then the obtained mixture is then poured into a container. Cementation however has two significant drawbacks: after coating, the volume of the waste has doubled; cement is an evolving material, and certain constituents of the waste and of the cement may interact. This may perturb hydration of the matrix and therefore affect the life expectancy of the obtained materials; the waste has to be preprocessed for limiting its subsequent interactions with the cement. Although various chemical compositions of hydraulic binders are presently under investigation in order to find a remedy to the aforementioned drawbacks, none of them is still totally satisfactory. Moreover, vitrification methods are known (see especially “Les Techniques de l'Ingénieur”, BN 3660-1 to BN 3660-31) which consist of incorporating into a glass with a suitable composition, all the elements contained in high activity effluents as well as the dissolution fines. The main advantage of glasses comes from the fact that they are amorphous, which gives them outstanding remarkable properties but which also have drawbacks, i.e.; the acceptable proportion of foreign elements by a glass is limited, and the load in the glass of calcinate from the calcination of the effluents, and of fines, generally remains quite small; glasses are metastable materials. But the main defect of the glass matrices is their sensitivity to chemical attacks, and the problems related to alteration by lixiviation of the glass matrices which are significant. The sensitivity of glasses towards lixiviation is directly related to the presence of alkaline elements such as sodium, the departure of which by diffusion causes weakening of the glassy lattice. In order to partially compensate for the detrimental role of sodium, boron is added to the silica glass in order to thereby provide glasses, so-called “borosilicate glasses”. Thus, a glass which is highly used in the vitrification of fission products (with high activity) from UOX1 fuels is the so-called R7T7 glass which is a borosilicate glass, the composition of which is the following: SiO 45%, B2O 14%, Na2O 10%, Al2O3 5%, oxides of fission products, Zr, U, metal particles 13%, including platinoids (RuO2, Rh, Pd), and the remainder of other Fe, Ni, Cr, Ca, Zn, P oxides. As described in the “Techniques de l'Ingénieur”, the industrial continuous vitrification process consists of feeding a melting pot or crucible heated by a medium frequency induction oven with the calcinate of the solutions of the fission products FP and of the glass frit. The digestion takes place from 1,000 to 1,200° C. for a few hours and cylindrical 0.2 cubic meter containers are filled in two casts, released by a thermal valve. The calcinate is prepared by evaporating, by drying and calcining for example at 500° C. the solutions of fission products, the composition of which is suitably adjusted in a continuously fed rotary oven and heated by a resistor. Packages of high activity waste (“HA”) are thereby produced. Glasses for confining, containing, isolating, radioactive liquid effluents of medium activity especially generated by “MAD” operations have never been described in the prior art. Therefore as regards the foregoing, there therefore exists a need for a material allowing confinement of radioactive liquid effluents of medium activity, and especially effluents generated by operations for definitively shutting down nuclear fuel reprocessing plants, which does not have the drawbacks of bitumens and hydraulic binders as described above. The goal of the present invention is i.e. to provide a material which meets this need, and which especially has great stability to irradiation, excellent mechanical strength, great resistance to chemical attacks, which is easy to apply, and which only undergoes a reduced volume increase after confinement, containment, isolation of the effluents. The goal of the present invention is further to provide such a material for the confinement of radioactive liquid effluents which does not have the drawbacks, limitations, defects and disadvantages of the materials for confinement of radioactive liquid effluents of the prior art, and which overcomes the problems presented by these materials. This goal and further other ones are, according to the invention, achieved by an alumino-borosilicate glass for the confinement, containment, isolation of a radioactive liquid effluent of medium activity, characterized in that it has the following composition expressed in percentages by mass based on the total mass of the glass: a) SiO2: 45 to 52 b) B2O3: 12 to 16.5 c) Na2O: 11 to 15 d) Al2O3: 4 to 13 e) One or more ETR element(s) (Transition Elements) selected from oxides of transition elements such as Fe2O3, Cr2O3, MnO2, TcO2, and platinoids such as RuO2, Rh, Pd: 0 to 5.25; f) One or more TRA element(s) (Rare Earth) selected from rare earth oxides such as La2O3, Nd2O3, Gd2O3, Pr2O3, CeO2, and from actinides oxides such as UO2, ThO2, Am2O3, PuO2 CmO2, NpO2: 0 to 3.5; g) ZrO2: 0 to 4 h) Other elements AUT constitutive of the effluent: 0 to 4; and in that the composition of the glass further meets the following inequations:SiO2+Al2O3<61% (1)71%<SiO2+B2O3+Na2O<80.5% (2)B2O3/Na2O>0.9 (3)0.7 Al2O3−ETR<5% (4)Al2O3/ETR>2.5 (5)0.127(B2O3+Na2O)>AUT. (6) The SiO2, Al2O3, B2O3, Na2O, ETR, AUT, contents expressed as percentages by mass based on the total mass of the glass are entered into these inequations. Advantageously, at least one of ETR, TRA and AUT is greater than 0. Preferably ETR is greater than 0. Advantageously, ETR, TRA and AUT are all greater than 0. Still preferably, the glass contains at the same time Fe2O3, Cr2O3, MnO2, TcO2, RuO2, Rh, Pd, La2O3, Nd2O3, Gd2O3, Pr2O3, CeO2, UO2, ThO2, Am2O3, PuO2CmO2, NpO2, SO3, P2O5, MoO3, optionally BaO and optionally ZrO2; i.e. the content of all these compounds is greater than 0. Advantageously, when ETR is greater than 0, the glass contains Fe2O3 for example in an amount from 1 to 5% by mass, preferably from 2 to 4% by mass. A glass suitable for the confinement, containment, isolation of radioactive liquid effluents of medium activity especially generated by “MAD” operations has never been described nor suggested in the prior art. The glasses according to the invention lead to the manufacturing of standard containers for waste of type B which are totally distinguished from glass packages CSD-V prepared with the “R7T7 glass” as described above, not only by their chemical composition but also by their activity level (which is generally lower by a factor of 50 to 100 when compared to the R7T7 glass) and their intrinsic thermal power which is generally of about 2.5 kW for a CSD-V packet prepared from R7T7 glass. The R7T7 glass matrices have allowed confinement, containment, isolation of high activity effluents but these matrices are precisely specifically adapted to the confinement of high activity effluents and it is found that they are not adapted to the confinement of radioactive liquid effluents of medium activity such as those generated by operations for definitively shutting down (“MAD”) nuclear fuel reprocessing plants. Indeed, specific problems are posed for the confinement of radioactive effluents of medium activity, and it was absolutely not obvious that the vitrification of radioactive waste, successfully applied with high activity radioactive waste, may be used with radioactive liquid effluents waste of medium activity, considering the specificity of the latter. The teachings relating to vitrification of high activity effluents can by no means be directly transposed to the vitrification of effluents of medium activity. Indeed, it was found that with the glass according to the invention, because of its very specific composition and of particular conditions which govern this composition, it was for the first time possible to confine radioactive liquid effluents of medium activity especially effluents generated by “MAD” operations. By thereby allowing confinement of waste of medium activity in a glass, the invention gets rid of the drawbacks related to bituminization or to cementation and provides the confinement of waste, radioactive liquid effluents of medium activity, with all the advantages inherent to vitrification. Further, the glass according to the invention may surprisingly be easily elaborated by a process of the calcination, cold crucible vitrification type, as already described above. The glasses according to the invention actually have a specific composition range which imparts to the glass all the properties required for elaboration in a cold crucible and which ensures durable confinement, containment, isolation by very good resistance to lixiviation in the whole of this composition range. In other words, the glass according to the invention not only meets the constraints of the contemplated vitrification process, and this in the whole of its composition range, but also the constraints related to lixiviation. More specifically, the glass according to the invention may be elaborated in a range of temperatures from 1,200° C. to 1,300° C., which is perfectly compatible with vitrification by a cold crucible, and it further has a viscosity comprised between 20 dPa·s and 100 dPa·s (20 to 100 Poises), at the elaboration temperature, for example 1,250° C., and an electric resistance comprised between 2 and 10 Ω·cm at the elaboration temperature, for example 1,250° C., which meets the constraints of the vitrification process. From the point of view of the resistance of the glass to lixiviation, the glass according to the invention, in the whole composition range defined above, meets the requirements with which a satisfactory long-term behavior may be ensured. Thus, its initial alteration (weathering) rate V0 is less than 10 g·m−2·d−1 at 100° C., preferably less than 5 g·m−2·d−1 at 100° C., and its equilibrium pH in a static test is less than 10, preferably less than 9.5 at 90° C. Generally, the other elements constitutive of the effluent (“AUT”) are selected from molybdate, phosphate and sulphate anions, and barium oxide BaO. In other words, the other elements are generally selected from the following oxides: SO3, P2O5, MoO3, BaO. The glasses according to the invention are elaborated from a specific vitrification adjuvant containing the following oxides: SiO2, B2O3, Na2O, Al2O3, ZrO2, CaO, Li2O, Fe2O3, NiO and CoO in specific proportions, this vitrification adjuvant being added to the calcinate (calcine) produced by calcination of the liquid effluents of medium activity to be treated so as to have a glass composition located with, in the composition range, a calcination adjuvant also called a “dilution adjuvant” may further be added to the effluent beforehand in the solution or during calcination. Thus, the invention further relates to a vitrification adjuvant characterized in that it has the following composition, expressed in percentages by mass: SiO2: 58 to 65% B2O3: 15 to 19% Na2O: 5 to 10% Al2O3: 0 to 3% Li2O: 1 to 4% CaO: 1.5 to 4% ZrO2: 0 to 3% Fe2O3: 2 to 4% NiO: 0 to 2% CoO: 0 to 2% An exemplary composition of this adjuvant is given below, also expressed in percentages by mass: SiO2: 62.85% B2O3: 17.12% Na2O: 7.50% Al2O3: 1.00% Li2O: 2.71% CaO: 3.87% ZrO2: 1.25% Fe2O3: 3.00% NiO: 0.35% CoO: 0.35% The vitrification adjuvant may be in the form of a glass frit comprising the aforementioned specific oxides or else of a mixture of chemical products, especially of oxides, in the form of powders. Preferably, the vitrification adjuvant is in the form of a glass frit. This specific glass frit has a composition with which it is possible to obtain a glass in the composition range according to the invention, especially from any radioactive liquid effluent, the average, minimum, and maximum composition of which is found in the ranges defined further on. However, the chemical composition of the vitrification adjuvant may be modified depending on the variation of the contents of chemical elements of the liquid effluent to be treated. The invention also relates to a method for treating a radioactive liquid effluent of medium activity, wherein calcination of said effluent, to which is optionally added a calcination adjuvant is carried out, in order to obtain a calcinate, and a vitrification adjuvant is then added to said calcinate, it is proceeded with melting of said calcinate and of said vitrification adjuvant in a cold crucible in order to obtain a glass melt, and said glass melt is then cooled down, whereby the alumino-borosilicate glass as defined above is obtained. The method according to the invention is particularly suitable for the treatment of a radioactive liquid effluent of medium activity which contains the following elements in the following contents: Na: from 30 g/L to 80 g/L B: from 0 g/L to 5 g/L Mn: from 0 g/L to 1 g/L Ce: from 0 g/L to 14 g/L Fe: from 0 g/L to 3 g/L Ni: from 0 g/L to 1 g/L Cr: from 0 g/L to 1 g/L Zr: from 0 g/L to 16 g/L Mo: from 0 g/L to 10 g/L P: from 0 g/L to 4 g/L S: from 0 g/L to 1.7 g/L Ba: from 0 g/L to 7 g/L Gd: from 0 g/L to 1 g/L Tc: 1 g/L or less Actinides: from 0 g/L to 8 g/L Platinoids: 1 g/L or less; the total content of said elements being from 30 g/L to 154.7 g/L. Let us specify that the specified contents above are actually elemental contents. The liquid effluent above is defined by a composition range expressed by minimum and maximum contents of each of the elements as well as by total minimum and maximum contents. Within these ranges, it is possible to define so-called reference contents thereby defining a reference composition also corresponding to a reference effluent which is the effluent of the medium activity type which may be treated by the method according to the invention in order to provide a glass having the whole of the advantageous properties listed above. This so-called “reference” radioactive liquid effluent contains the following elements in the following so-called “average” or “reference” contents: Na: 55 g/L B: 2.5 g/L Mn: 0.5 g/L Ce: 7 g/L Fe: 1.5 g/L Ni: 0.5 g/L Cr: 0.5 g/L Zr: 8 g/L Mo: 5 g/L P: 2 g/L S: 0.85 g/L Ba: 3.5 g/L Gd: 0.5 g/L Tc: 1 g/L Actinides: 4 g/L Platinoids: 1 g/L; the total content of said elements being 93.35 g/L. The composition range of the borosilicate glassy conditioning matrix according to the invention is particularly suitable for the radioactive effluents mentioned above. Within the range of the composition of the glass matrices according to the invention, the physico-chemical properties of these matrices are such that at high temperature, it is possible to elaborate them with a method of the calcination vitrification type. Advantageously, the vitrification adjuvant is as defined above. Generally the melting of the calcinate stemming from the calcination of the effluent and of the optional calcination, dilution adjuvants, and of the vitrification adjuvant is carried out at a temperature from 1,200° C. to 1,300° C., preferably 1,250° C. The invention will now be described in detail in the following description, given as an illustration and not as a limitation, more particularly in connection with the method for treating radioactive effluents of medium activity. The radioactive liquid effluent of medium activity which may be treated by the method according to the invention may especially be a nitric aqueous effluent containing nitrates of metals or metalloids. The effluent treated by the method according to the invention will generally have the composition as already specified above. The method according to the invention includes two main steps. The first step is a step for calcination of the effluent during which evaporation, drying and then calcination, denitration of a portion of the nitrates if the effluent contains any of them, occur. It may be noted that the salts of the effluent generally consist in a very large majority of nitrates or hydroxides which are decomposed in the calciner. The second step is a vitrification step by dissolution in a confinement glass of the calcinate produced during the calcination step. The calcination step is generally carried out in a rotating tube heated for example to a temperature of about 400° C. by an electric oven. The solid calcinate is milled by a loose bar placed inside the rotating tube heated to the intended temperature. During the calcination of certain solutions, in particular solutions rich in sodium nitrate, in other words solutions with high sodium content in a nitric medium, adhesion of the calcinate on the walls of the rotating tube may be observed, which may lead to total blocking of the tube of the calciner. The answer consists of adding to the effluent at least one compound supposed to be non-tacky called a dilution adjuvant or calcination adjuvant, such as aluminium nitrate, iron nitrate, zirconium nitrate, rare earth nitrates, or mixtures thereof in order to allow their calcination while avoiding clogging of the calciner. Preferably according to the invention, an adjuvant consisting of a mixture of aluminium nitrate and of iron nitrate, preferably in a proportion of 0.66<Al2O3/(Al2O3+Fe2O3)<1 wherein the contents are oxide mass contents, is used as a calcination adjuvant. Further, the ratio of Na2O to the sum of the oxides in the calcinate is generally less than or equal to 0.3. The treatment method according to the invention comprises after the calcination step a step for vitrifying the calcinate. This vitrification step consists of dissolving the calcinate in a confinement glass. For this purpose, a vitrification adjuvant comprising the following oxides: SiO2, B2O3, Na2O, Al2O3, ZrO2, CaO, Li2O, Fe2O3, NiO and CoO, is added to the calcinate stemming from the calcination of the effluent to which a dilution adjuvant was optionally added. This vitrification adjuvant generally comprises the aforementioned oxides in specific proportions for obtaining a glass in the composition range of the invention, depending on the composition of the effluent. This vitrification adjuvant is generally as defined above. The vitrification adjuvant may be in the form of a mixture of powders, or else in the form of a glass frit including the oxides. It is generally advantageous to use a glass frit which requires less melting energy than the mixture of powders. The vitrification adjuvant is added to a defined amount of the calcinate so as to observe the composition range defined above and it is proceeded with the melting of the whole. According to the invention, the glass melt obtained has physico-chemical properties, i.e. viscosity as well as resistivity properties which make it totally suitable for vitrification by a cold crucible. The glass is elaborated at a temperature generally from 1,200° C. to 1,300° C., for example 1,250° C. in a cold crucible heated by induction. The glass is homogenized in the crucible by mechanical mixing and/or bubbling, when the upper level of the oven is attained, a cast of glass is carried out in a container, the amount of cast glass is for example of the order of 200 kg. It is then proceeded with cooling of the glass melt in order to obtain the glass according to the invention which is an alumino-borosilicate glass with high chemical durability, having the advantageous properties mentioned above and meeting the criteria defined above. The invention will now be described with reference to the following examples, given as an illustration and not as a limitation: Three compositions of radioactive liquid effluents of medium activity stemming from “MAD” operations will be treated below: the aforementioned reference solution is vitrified with the reference glass frit, by seeking a rated, nominal, waste incorporation level of 12% (Example 1); a sodium-rich solution is treated with a vitrification adjuvant in the form of a frit (Example 2); a low-sodium solution is treated with a vitrification adjuvant in the form of powders (Example 3). The selection of the frits or adjuvants is dictated by optimization of the incorporation level of waste. All the glasses have to be contained within the composition range mentioned above. Composition of the wasteComposition of the wastein elementsin oxide percentNa: 55 g/LNa2O = 56.42%B: 2.5 g/LB2O3 = 6.13%Mn: 0.5 g/LMnO2 = 0.60%Ce: 7 g/LCe2O3 = 6.24%Fe: 1.5 g/LFe2O3 = 1.63%Ni: 0.5 g/LNiO = 0.48%Cr: 0.5 g/LCr2O3 = 0.56%Zr: 8 g/LZrO2 = 8.23%Mo: 5 g/LMoO3 = 5.71%P: 2 g/LP2O5 = 3.49%S: 0.85 g/LSO3 = 1.61%Ba: 3.5 g/LBaO = 2.97%Gd: 0.5 g/LGd2O3 = 0.46%Tc: 1 g/LTcO2 = 1.01%Actinides: 4 g/LActinide oxides = 3.45%Platinoids: 1 g/LPlatinoids = 1.00% The solution is too rich in sodium oxide for being calcined in this condition, and it is necessary to add a vitrification adjuvant in order to meet the calcination criterion: Na2O/(sum of the oxides in the calcinate) ratio equal to 0.3. It is necessary to add aluminium and iron nitrate in order to reduce the amount of sodium in the calcinate. In this case, for 100 g of calcinate, it is necessary to add the equivalent of 88.07 g of alumina and iron oxide in order to obtain a calcinable solution. On the other hand, the constraints of the vitrifiable range imposes for a waste level of 12% a Al2O3/(Al2O3+Fe2O3) ratio provided by the calcination adjuvant of greater than or equal to 0.91. The calcinate is brought to a temperature of about 400° C. The composition of the calcinate in percent by mass is given below. Na2O=30.00% B2O3=3.26% Al2O3=42.61% MnO2=0.32% Ce2O3=3.32% Fe2O3=5.08% NiO=0.26% Cr2O3=0.30% ZrO2=4.37% MoO3=3.04% P2O5=1.85% SO3=0.86% BaO=1.58% Gd2O3=0.25% TcO2=0.54% Actinide oxides=1.84% Platinoids=0.53% A 12% incorporation level imposes, with the reference frit, the addition of 77.43% of frit and 32.57% of calcinate in order to obtain the final glass. The elaboration temperature is 1,220° C. SiO2=48.66% Na2O=12.58% B2O3=13.99% Al2O3=10.39% CaO=3.00% Li2O=2.10% MnO2=0.07% Ce2O3=0.75% Fe2O3=3.47% NiO=0.33% CoO=0.27% Cr2O3=0.07% ZrO2=1.96% MoO3=0.69% P2O5=0.42% SO3=0.19% BaO=0.36% Gd2O3=0.06% TcO2=0.12% Actinide oxides=0.41% Platinoids=0.12% In this example, a sodium-rich solution is treated by calcination-vitrification with use of a frit. Composition of the wasteComposition of the wastein elementsin oxide percentNa: 80 g/LNa2O = 65.31%B: 2.5 g/LB2O3 = 4.88%Mn: 0.5 g/LMnO2 = 0.48%Ce: 7 g/LCe2O3 = 4.97%Fe: 1.5 g/LFe2O3 = 1.30%Ni: 0.5 g/LNiO = 0.39%Cr: 0.5 g/LCr2O3 = 0.44%Zr: 8 g/LZrO2 = 6.55%Mo: 5 g/LMoO3 = 4.54%P: 2 g/LP2O5 = 2.77%S: 0.85 g/LSO3 = 1.28%Ba: 3.5 g/LBaO = 2.37%Gd: 0.5 g/LGd2O3 = 0.37%Tc: 1 g/LTcO2 = 0.80%Actinides: 4 g/LActinide oxides = 2.75%Platinoids: 1 g/LPlatinoids = 0.80% The solution is too rich in sodium oxide for being calcined as it stands, it is necessary to add a vitrification adjuvant in order to meet the calcination criterion: Na2O/(sum of the oxides in the calcinate) ratio equal to 0.3. It is necessary to add aluminium and iron nitrate in order to reduce the amount of sodium in the calcinate. In this case, for 100 g of calcinate, it is necessary to add the equivalent of 117.71 g of alumina and iron oxide in order to obtain a calcinable solution. On the other hand, the constraints of the vitrifiable range impose for a waste level of 12%, an Al2O3/(Al2O3+Fe2O3) ratio provided by the calcination adjuvant of greater than or equal to 0.85. The calcinate is brought to a temperature of about 400° C. The composition of the calcinate in percent by mass is given below: Na2O=30.00% B2O3=2.24% Al2O3=44.88% MnO2=0.22% Ce2O3=2.28% Fe2O3=9.79% NiO=0.18% Cr2O3=0.20% ZrO2=3.01% MoO3=2.09% P2O5=1.27% SO3=0.59% BaO=1.09% Gd2O3=0.17% TcO2=0.37% Actinide oxides=1.26% Platinoids: =0.37% In this case, the waste load level is limited by the acceptable alumina content in the glass i.e. 13%. The maximum load level is 12.56%, obtained with the reference frit by adding 72.65% of frit and 27.35% of calcinate in order to obtain the final glass. The elaboration temperature is 1,250° C. The composition of the glass is the following: SiO2=45.65% Na2O=13.65% B2O3=13.05% Al2O3=13.00% CaO=2.81% Li2O=1.97% MnO2=0.06% Ce2O3=0.62% Fe2O3=4.86% NiO=0.33% CoO=0.25% Cr2O3=0.06% ZrO2=1.74% MoO3=0.57% P2O5=0.35% SO3=0.16% BaO=0.30% Gd2O3=0.05% TcO2=0.10% Actinide oxides=0.35% Platinoids=0.10% In this example, a low-sodium solution is treated by calcination-vitrification with use of a frit. Composition of the wasteComposition of the wastein elementsin oxide percentNa: 40 g/LNa2O = 48.49%B: 2.5 g/LB2O3 = 7.25%Mn: 0.5 g/LMnO2 = 0.71%Ce: 7 g/LCe2O3 = 7.37%Fe: 1.5 g/LFe2O3 = 1.93%Ni: 0.5 g/LNiO = 0.57%Cr: 0.5 g/LCr2O3 = 0.66%Zr: 8 g/LZrO2 = 9.72%Mo: 5 g/LMoO3 = 6.75%P: 2 g/LP2O5 = 4.12%S: 0.85 g/LSO3 = 1.91%Ba: 3.5 g/LBaO = 3.51%Gd: 0.5 g/LGd2O3 = 0.55%Tc: 1 g/LTcO2 = 1.19%Actinides: 4 g/LActinide oxides = 4.08%Platinoids: 1 g/Llatinoids = 1.18% The solution is too rich in sodium oxide for being calcined as it stands, it is necessary to add a vitrification adjuvant in order to meet the calcination criterion: Na2O/(sum of the oxides in the calcinate) ratio equal to 0.3. It is necessary to add aluminium and iron nitrate in order to reduce the amount of sodium in the calcinate. In this case for 100 g of calcinate, it is necessary to add the equivalent of 61.64 g of alumina and iron oxide in order to obtain a calcinable solution. On the other hand, the constraints of the vitrifiable range impose an Al2O3/(Al2O3+Fe2O3) ratio provided by the calcination adjuvant of greater than or equal to 0.85. The calcinate is brought to a temperature of about 400° C. The load level in Example 3 is limited by the amount of silica stemming from the glass frit. The composition of the powder mixture may be optimized in order to obtain the maximum waste incorporation level. An adjuvant composition meeting the criteria of the composition range is the following: 67.5% of SiO2 in the form of fine sand; 19.8% of B2O3 in the form of granulated boric acid (H3BO3); 3% Na2O in the form of sodium carbonate or in the solution of the form of sodium nitrate; 4% CaO in the form of wollastonite (CaSiO3); 2% Fe2O3 in the form of FeO; 0.25% NiO in the form of NiO; 0.45% CoO in the form of CoO. The maximum incorporation level is attained when the silica limit is attained i.e. 66.67% of powders for 33.33% of calcinate, which corresponds to a waste load level of 20.62%. The elaboration temperature is 1,200° C. The chemical forms of the different adjuvants are given as examples and may be replaced with other products. The glass composition is the following: SiO2=45.00% Na2O=12.00% B2O3=14.69% Al2O3=10.80% CaO=2.67% Li2O=2.00% MnO2=0.15% Ce2O3=1.52% Fe2O3=3.64% NiO=0.28% CoO=0.30% Cr2O3=0.14% ZrO2=2.00% MoO3=1.39% P2O5=0.85% SO3=0.39% BaO=0.72% Gd2O3=0.11% TcO2=0.25% Actinide oxides=0.84% Platinoids=0.24%. |
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description | This application claims the benefit of priority to U.S. Provisional Patent Application No. 62/795,185, filed on Jan. 22, 2019. This invention was made with government support under Grant Number EB016572 awarded by the National Institutes of Health. The government has certain rights in the invention. Efficient shielding of ionizing X-ray and gamma radiation is required in medical, nuclear and space industries. High Z elements, such as lead, tungsten, bismuth, and uranium, are often used to attenuate X-ray radiation. The shielding ability is dependent on the density and mass of the material, leading to heavy shielding materials. There are limited choices in reducing the mass of a given material for X-ray radiation except using graded-Z shielding composed of a laminate of several materials of different atomic numbers. Further, most shielding materials are rigid solids and lack flexibility for conformal protection. To form conformal protection, a promising way is to shrink the size of effective metals and add them into a polymer matrix. Even though polymer matrices are inferior to metals for radiation shielding, they offer advantages such as flexibility, workability, chemical stability, and low cost. Lead powders are added into fabrics to form shielding aprons and coverings, but the formation of pin holes in polymer-metal composites allow incident photons to penetrate polymer regions, leading to issue of low shielding ability. In order to compensate for pin holes, extra amount of materials has to be used to achieve sufficient protection which makes units heavier than needed. The challenge of forming conformal lightweight polymer composites is twofold. It is hard to find a process that can incorporate metal powders in polymer sheets with sufficient metal content for effective radiation attenuation and robust enough to avoid structural deterioration, such as tearing and cracking of polymer. Particles densely packed along incoming radiation direction in composites can stop penetrating photons and enhance shielding ability of polymer-metal composites. The key to formation of densely packed structures is narrow size distribution of particles and uniform dispersion of particles in polymer sheets, which can be stacked to form multilayers with desired shielding. Nanoparticles of high-Z elements have been added in polymer to block X-ray radiation, but the nanoparticles tend to form aggregates in polymer, or leach out of polymer and cause toxic effect to human. Most importantly, the classical mass dependent radiation attenuation is prevalent, and there is no experimental proof over the mass benefit of using nanoparticles in polymer composites. From materials aspect, lead is widely used in powder-loaded shielding sheets, but is very toxic, and may leak due to aging, damage, embrittlement, and cracking of polymer. It is therefore imperative to use other non-toxic metals to minimize negative impact. One aspect of the invention relates to a new lightweight nanoparticle-composite for enhanced radiation shielding, where ultra-small bismuth nanoparticles added in a polymer can block X-ray radiation several times more efficiently than microparticles at the same nanoparticle-to-polymer mass ratio. The enhancement in radiation shielding is primarily attributed to close packing of nanoparticles normal to incoming X-ray direction, which is enabled by strong affinity of nanoparticles to interstitial space of cellulose nanofibers and even distribution of nanoparticles inside polymer. Given its low cost, light weight, and structure conformability, bismuth nanoparticle-polymer composite will find its use in a wide range of fields related to personal radiation protection. In some embodiments, the invention relates to a composite material, comprising a polymer, a plurality of metal nanoparticles, and a surface-modifying agent. In some embodiments, the surface-modifying agent is nanocellulose. In some embodiments, the invention relates to a film comprising a film comprising one or more composite materials. In some embodiments, the invention relates to a method for shielding a subject from electromagnetic radiation, comprising placing the composite material between the subject and a source of electromagnetic radiation, thereby reducing a dose of electromagnetic radiation received by the subject. Efficient shielding of ionizing X-ray and y radiation is required in medical, nuclear, and space industries. High Z elements, such as lead, tungsten, bismuth, and uranium, are often used to attenuate X-ray radiation, where the shielding ability is dependent on the density and mass of the material, leading to heavy shielding materials. There are limited choices in reducing the mass of a given material for X-ray radiation except using graded-Z shielding composed of a laminate of several materials of different atomic numbers. Most shielding materials are rigid solids and lack flexibility for conformal protection. To form conformal protection, a promising way is to shrink the size of effective metals and add them into a polymer matrix. Even though polymer matrices are inferior to metals for radiation shielding, they offer advantages, such as flexibility, workability, chemical stability, and low cost. Lead powders are added into fabrics to form shielding aprons and coverings, but the formation of pinholes in polymer-metal composites allows incident photons to penetrate polymer regions, leading to issue of low shielding ability. To compensate for pinholes, extra amount of materials has to be used to achieve sufficient protection, which makes units heavier than needed. The void issue can be solved by using ultra-small nanoparticles packed efficiently, so that voids are minimum, and a small amount of nanoparticles can be used to achieve the same shielding capacity. The polymer-nanoparticle composite can be used to make personal radiation shielding equipment such as facemasks, outfits, gloves, and vests. The potential impact is that this polymer composite can achieve better protection against radiation, and can be made lighter than current lead containing protections. The polymers can include cellulose, polyamide, polyacrylonitrile, polyethylene or polypropylene. In some embodiments, the invention relates to a nanoparticle-polymer composite for enhanced shielding of X-ray radiation, in which bismuth nanoparticles made with cellulose nanofibers form composite with polydimethylsiloxane (PDMS) (FIG. 1). The X-ray radiation shielding abilities of the nanoparticle-polymer composite was assessed in transmission mode and compared to those of microparticle composites. It was found that the nanoparticles can effectively shield X-ray radiation at much lower nanoparticle-to-polymer mass ratio without sacrificing mechanical strength of polymer. A four-fold reduction in the total mass of bismuth material is identified at 2% mass ratio when 5 nm nanoparticles are used in composite to shield a given flux and energy of radiation, compared to when bismuth microparticles are used. The enhanced radiation shielding is attributed to close packing of nanoparticles normal to incoming X-ray direction, which is enabled by strong affinity of nanoparticles to the interstitial space of cellulous nanofibers and even distribution of nanoparticles in polymer matrix. Given its low cost, light weight and structure conformability, bismuth nanoparticle-polymer composite will find its use in a wide range of fields related to personal radiation protection. FIG. 2 contains an AFM image of cellulose nanofibers (A), whose average length and diameter are 150-200 nm, and 5 nm, respectively. The nanofibers are composed of bundles of fibers, and there are interstitial spaces among fibers, as shown in the TEM image in (B). Bismuth ions can bind to oxygen moieties at interstitial spaces of cellulose nanofibers, and can be reduced to bismuth metal atoms, which aggregate to nanoparticles with size in 2-10 nm range evenly distributed over cellulose nanofibers. XRD results shown in FIG. 2 confirms the crystalline nature of bismuth nanoparticles (D), where the diffraction rings and pattern were indexed with metallic bismuth. No diffraction peak or ring has been found for the lattice structure of bismuth oxide (Bi2O3), meaning that the oxidation of bismuth nanoparticles has been prevented by cellulose nanofibers. DSC results of the cellulous nanofiber-protected nanoparticles (C), demonstrate a melting temperature at around 150° C., which is much lower than that of bulk bismuth at 271° C. The melting temperature reduction was induced by size dependent melting temperature of nanoparticles, and was used to confirm that the diameter of bismuth nanoparticles is around 2 nm using following equation: T T m = 1 - 4 σ H ρ d ( 1 ) where T and Tm are melting points of nanoparticles (423 K), and bulk materials (544 K), respectively, H is the latent heat of fusion of bismuth (54 J/g), ρ is the density of bismuth (9.78 g/cm3), d is the size of nanoparticles, and σ is the interfacial energy of bismuth (0.0544 J/m2). Adding bismuth nanoparticles-decorated nanofibers into a polymer matrix provided a composite that maintained the flexibility of the polymer. FIG. 3 shows an optical image of a bended composite film which contains 1% by mass of bismuth nanoparticles (A). The film strongly absorbs visible light over a large wavelength range and appears completely dark. FIG. 3 also shows an SEM image (B) collected on the surface of a composite with 8% nanoparticles, where nanoparticles dispersed homogeneously on the surface are visible at high magnification. EDX result, as shown in FIG. 3, demonstrates signals of bismuth element against background silicon (B, inset). The Young's modulus of the composite decreases with increase in the nanoparticle loading (C), meaning that introduction of bismuth nanoparticles leads to more defects in the polymer and weakens its strength, but the composite is sufficiently elastic at 4% by mass of nanoparticles. In contrast, the composite formed by polymer and bismuth microparticles is much weaker (Young's modulus of 5×104 kPa) compared to that formed by nanoparticles of the mass same ratio. In light of recent discovery that cellulose can provide highest mechanical strength compared to its weight, it is possible that polymer fibers with incorporated bismuth nanoparticles could be woven into fabrics. Gas permeability of nanoparticle-polymer composite was examined with water retention experiment where the composite was immersed into water and the mass of the composite was measured over time. FIG. 3 also shows the mass of a composite increases to 1.3 times of its initial mass in 5 days (D). The porosity of the composite is then estimated to be about 35.4% given the density of the composite of 1,180 kg/m3. The X-ray attenuation ability of bismuth nanoparticle-polymer composite was assessed by exposing composite films (thickness of 5 mm) to a cone shaped X-ray beam, and allowing transmitted X-ray expose an underlying GafChromic™ film. FIG. 4 shows the optical images of composite films and X-ray exposed GafChromic™ films (A), where more transparent composite film contains less nanoparticles, and causes more exposure in GafChromic™ film (darker). The optical density of exposed GafChromic™ films recorded with densitometer was used to determine the intensity of transmitted X-ray beam (B), where the transmitted dose of 60 kV X-ray beam decreases from 0.941 to 0.032 Gy as the mass ratio of bismuth nanoparticles in composite film increases from 0 to 4%. The attenuation ratio of bismuth nanoparticles reaches 96.6 at 8.0% by mass compared to polymer film of the same thickness. At higher X-ray energy, all composite samples become less effective at attenuating higher energy photons, and more X-ray photons pass through the composite film to expose GafChromic™ film. The stabilities of nanoparticle-polymer composites against 60 kV X-ray exposure were measured and no degradation has been observed over 2.5 h period. The stabilities of bismuth nanoparticle-polymer composite in HCl (0.1 M) and NaOH (2 N) solutions were examined after immersing composites in respective solutions for two weeks. No significant change in attenuation ability was found before and after immersion, meaning that the nanoparticles are protected by the surrounding polymer matrix and thus immune to acid and base conditions. Both X-ray and optical transmissions of the nanoparticle-polymer composites have been determined. FIG. 5 shows the optical graphs of five composite films containing 0, 1.0, 2.0, 4.0 and 8.0% of bismuth nanoparticles (A), where the film color changes from transparent to dark when the mass ratio of nanoparticles increases. FIG. 5 also shows the light transmissions of 5 mm thick polymer composites containing different amount of bismuth nanoparticle, bismuth microparticles and lead microparticles (B). FIG. 5 additionally shows the relative intensities of 60 kV X-ray transmitted through the polymer films that contain bismuth nanoparticles, bismuth microparticles and lead microparticles (C). Both plots show the same trend of change in transmission as the amount of particles increases. Both plots show a significant reduction in transmission (large slope) when the mass ratio of nanoparticles is below 2%; after that, the slope is small and there is only small reduction in transmission. FIG. 5 also shows micrographs of polymer composites of bismuth microparticles (E) and lead microparticles (F) with diameter of 5 μm have been made and examined, where the X-ray (and optical) transmissions and the mass ratios of microparticles show similar trend, and the slopes are smaller than those of nanoparticle composites. The nearly identical trends observed in optical and radiation transmissions of particle-polymer composites suggest a common basis for nanoparticle-enhanced radiation shielding and visible light blocking. Cellulous nanofibers facilitate even distribution of bismuth nanoparticles in polymer, which allows a minimal amount of bismuth material to cover the whole area exposed to light or X-ray beam. Given the low attenuation ability of polymer, the shielding abilities of the composites can be derived by considering particle size and their packing in the direction normal to incoming X-ray. The intensity (I) of X-ray (or light) after passing through a length of d cm in a diluted solution with n particles per unit volume can be determined as follows: I I 0 = exp ( - n C d ) ( 2 ) where his the intensity of incoming X-ray or light, and C is the extinction coefficient (cross section) at certain energy (wavelength) of single particle that depends on the material property and particle geometry. The mass balance of particles in the particle-polymer composite can be established asNρ4/3πr3=xρmVcomp (3)where N is the total number of particles in the composite with volume Vcomp, r is the radius of particle, x is the mass ratio of the particles in the composite, ρ, ρm are the densities of particle and polymer, respectively. Given the low mass ratio of particles, the density of the composite can be taken as that of the polymer. Therefore, the number of particles per unit volume can be derived as: n = N V = 3 x ρ m 4 ρ π r 3 ( 4 ) The intensity of transmitted X-ray (or light) can be determined by combining equations (2) and (4) using I I 0 = exp ( - k x ) , where k = 3 ρ m c d 4 ρπ r 3 ( 5 ) The X-ray (or light) attenuation ability of the composites can be assessed with k values, which can be derived by fitting optical (B) and X-ray (C) transmission data, as shown in FIG. 5, to equation (4). It is found that bismuth nanoparticles have a k value of 91.68 (black), which is approximately four times higher than those of bismuth powder (26.27) and lead powder (19.67). The good agreement between the simulation and transmission results suggests the equation can be used to predict the shielding ability of any materials. The X-ray shielding ability of the nanoparticle-polymer composite was compared to those of microparticle-polymer composite and bismuth sheet at the mass attenuation coefficient (μ/ρ) of 5.74 cm2/g for 60 keV monoenergetic X-ray using Lambert-Beer law I I 0 = exp ( - μ ρ d ) ( 6 ) As shown in FIG. 5, it was found the shielding ability of a 0.5 cm thick polymer containing 2% (mass) of 5 nm nanoparticles is equivalent to that of 0.32 cm thick bismuth sheet, and also equivalent to 1.75 cm thick polymer containing 2% (mass) of 5 μm bismuth power, (C, inset). If the 0.5 cm 2% nanoparticle-polymer composite is used in abdomen computed tomography scanning, it can reduce dose received by human body from 8 to less than 0.017 mSv, which is equivalent to the reduction of background radiation from 2.7 years to less than 1 month. The enhanced radiation shielding with the nanoparticle composites can be attributed to the size effect. Given the same mass ratio of nanoparticles in composites, the number of individual particles is larger in the case of nanoparticles compared to microparticles, the voids between nanoparticles are smaller, and the nanoparticle multi-layers are stacked together to block X-ray beams. In addition, multiple scattering of X-ray photon increases as the number of particles increases, which increases the optical pathway of X-ray photons and leads to high absorption. In the case of larger particles, voids between particles are larger and less multiple scattering of X-ray occurs due to smaller number of particles. In order to achieve the same shielding effect, more particles will have to be used to cover inter-particle spaces and cause more scattering, which could cause mass increase of the composite. In principle, making even smaller nanoparticles or metal atoms will enhance the shielding effect further, however, metal atoms in polymer may leak due to high diffusion ability. The nanoparticles of the present disclosure are sufficiently large that the diffusion into the aqueous solution is minimized. In some embodiments, the invention relates to ultra-small bismuth nanoparticles made with cellulose nanofibers added into a polymer. The cellulose nanofibers form an interpenetrating network with polymer chains and ensure homogeneous dispersion of bismuth nanoparticles. The radiation attenuation ability of the composite was assessed in transmission mode, and compared to that of microparticle composites. It was found that the nanoparticles can effectively shield X-ray radiation at lower mass ratio in polymer matrix. The enhanced radiation shielding is attributed to close packing of nanoparticles normal to incoming X-ray direction, which is enabled by strong affinity of the nanoparticles to the interstitial space of nanofibers and uniform distribution of the nanoparticles in polymer. Exemplary Features of the Technology Effective radiation shielding achieved with light-weight polymer-nanoparticle composite Simple preparation of nanoparticles with nanocellulose matrix Even distribution of nanoparticles within polymer Dense packing of nanoparticles with minimum void space Flexibility, workability, chemical stability, and low cost of polymer-nanoparticle compositeExemplary Advantages and Improvements Over Existing Methods, Devices, or Materials Existing polymer composites with microparticles (powders) contain larger voids, and thus require more powders to achieve sufficient shielding, which makes protection equipment heavier and more expensive. Ultra-small bismuth nanoparticles can be packed densely in polymer to minimize void space. Existing polymer composites with microparticles (powders) are mechanically weaker, and the metal powders may leak. Polymer composites with nanoparticles are tougher, and can last longer than existing microparticle-based ones. Light-weight and low-cost radiation and electromagnetic shielding equipment (apron, vest, outfit).Exemplary Commercial Applications Light and low-cost radiation and electromagnetic wave attenuated apron for pregnant women X-ray protection shield used healthcare employees for diagnostic X-ray examinations Radiation protection for workers in heavy metal manufacturing companies X-ray shield outfits or masks for communities working in ground nuclear weapons testing Cosmic ray protection for pilots or astronauts in aerospace research As used herein, “nanocellulose” refers to one or more of cellulose nanofibers, bacterial nanocellulose, or cellulose nanocrystals, which may generally, on average, have a width of from about 3 to about 50 nm (cellulose nanofibers), about 20 to about 100 nm (bacterial nanocellulose) or about 3 to about 20 nm (cellulose nanocrystals) and a length of about 0.1 to about 5 micrometers (μm) (cellulose nanofibers), about 1 to about 5 μm (bacterial nanocellulose) or about 50 to about 100 nm (cellulose nanocrystals). Examples of production and use of cellulose nanofibers, bacterial nanocellulose, and/or cellulose nanocrystals are described in U.S. Pat. Nos. 8,9746,34, 8,900,706, and 8,710,213, and U.S. Patent Application Publication Nos. 2017/0283764 and 2015/0225486, each of which is incorporated herein by reference in its entirety. As used herein, “electromagnetic radiation” refers to radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays. For example, electromagnetic radiation can refer to ionizing radiation, such as high frequency ultraviolet radiation, X-rays and gamma rays. The term “X-rays” refers to photons with energies in the range from about 100 eV to about 200 keV. As used herein, “surface-modifying agent” refers to an organic or inorganic molecule or a polymer that can covalently or non-covalently attach to the surface of the metal nanoparticle and modify the surface of the nanoparticle in a way that increases the interaction between the surface of the nanoparticle and the polymer matrix. The improved interaction of the nanoparticles with the polymer matrix increases dispersion of the nanoparticles in the polymer and decreases aggregation of the nanoparticles. Examples of surface-modifying agents are described, for example, in U.S. Pat. Nos. 7,629,027, and 9,650,536, and U.S. Patent Application Publication No. 2006/0083694, each of which is incorporated herein by reference in its entirety. In some embodiments, the present disclosure relates to a composite material, comprising a polymer, a plurality of metal nanoparticles, and a surface-modifyng agent. In certain embodiments, the surface-modifying agent is nanocellulose. In certain embodiments, the polymer is selected from the group consisting of polydimethylsiloxane (PDMS), cellulose, polyamide, polyacrylonitrile, polypropylene, polyvinyl chloride, epoxy resin, polyimide, polyurethane, polyurethane polyvinylidene fluoride, and polyvinyledene difluoride. In some embodiments, the polymer is PDMS. In some embodiment, the plurality of metal nanoparticles comprises nanoparticles, wherein each of the nanoparticles comprises: one or more elements with atomic numbers 20-118, oxides of one or more elements with atomic numbers 20-118, or sulfates of one or more elements with atomic numbers 20-118. In certain embodiments, the plurality of metal nanoparticle comprises metal nanoparticles selected from the group consisting of lead nanoparticles, tungsten nanoparticles, bismuth nanoparticles, and uranium nanoparticles. For example, the plurality of metal nanoparticle comprises bismuth nanoparticles. In some embodiments, the average size of the metal nanoparticles is from about 1 nm to about 40,000 nm, or from about 1 nm to about 40 nm, or from about 1 nm to about 20 nm. For example, the average size of metal nanoparticles may be about 5 nm. In some embodiments, the amount of the metal nanoparticles in the composite material is from 0.5 wt. % to about 40 wt. %. For example, the amount of the metal nanoparticles in the composite is about 2 wt. %. In some embodiments, nanocellulose comprises cellulose nanofibers. In some embodiments, nanocellulose comprises cellulose nanocrystals. In certain embodiments, the amount of nanocellulose in the composite material is from 0.5 wt. % to about 40 wt. %. In some embodiments, the present disclosure relates to a film comprising one or more composite materials. In certain embodiments, the thickness of the film is from about 100 nm to about 10 cm. For example, the thickness of the film is about 0.5 cm. In some embodiments, the present disclosure relates to a method for shielding a subject from electromagnetic radiation, comprising placing one or more composite materials between the subject and a source of electromagnetic radiation, thereby reducing a dose of electromagnetic radiation received by the subject. In certain embodiments, the dose of electromagnetic radiation received by the subject is reduced by amount from 90% to 100%, such as by 90%, by 91%, by 92%, by 93%, by 94%, by 95%, by 96%, by 97%, by 99%, or by 100%. For example, the dose of electromagnetic radiation received by the subject is reduced by amount from 95% to 99%. In some embodiments the dose of electromagnetic radiation received by the subject is reduced by 96%. In some embodiments, electromagnetic radiation is X-ray radiation. Materials and Methods The following chemicals were obtained from Aldrich and used without purification: tetramethyl-1-piperidinyloxy (TEMPO), bismuth nitrate ((Bi(NO3)3.5H2O), sodium borohydride (NaBH4), sodium hypochlorite (NaClO), sodium bromide (NaBr), dimethyl sulfoxide (DMSO). and hydrogen chloride (HCl). Polydimethylsiloxane (Slygard 184 PDMS) was obtained from Dow Chemical, and Celgar kraft bleached softwood pulp was obtained from VWR. Cellulose nanofibers were prepared from softwood pulp with TEMPO oxidation method: 5 g of cellulose fibers, 78 mg of TEMPO, and 514 mg of NaBr were mixed in 100 mL water and added to a NaClO solution (5%) where pH was adjusted to 10 by addition of diluted HCl. After 10 hours the cellulose nanofibers were centrifuged, purified by dialysis until eluate was neutralized, and dispersed in water under ultrasonication. Bismuth nanoparticles were made as follows: 0.0485 g of Bi(NO3)3.5H2O was dissolved in 10 mL deionized (DI) water under nitrogen atmosphere, followed by addition of 1 mL suspension of 2.0% (by mass) cellulose nanofibers with stirring for 10 minutes. Addition of 700 μL of 1 M NaBH4 aqueous solution to the above mixture caused nanoparticle formation. The nanoparticle suspension was centrifuged with de-ionized (DI) water. After removing the supernatant, the nanoparticles were frozen at −20° C., and placed under vacuum (0.133 mBar at −50° C.) for 24 hours to complete lyophilization. Polymer composite film was made by adding lyophilized nanoparticles into a mixture of PDMS prepolymer (10 parts) and curing agent (1 part), agitating the mixture and removing bubbles, casting the mixture in a petri dish to form a film, and heating the obtained film at 60° C. for 5 hours to complete polymerization. The polymer composite films with bismuth and lead microparticles were also prepared for comparison. Microparticles were dispersed in a mixture of PDMS prepolymer and curing agent, the mixture was agitated, casted to form a film, and heated at 60° C. for 5 hours to complete polymerization and obtain the film. Nanoparticles were imaged with a high-resolution transmission electron microscope (JEOL 1010, TEM) operated at an accelerating voltage of 100 kV. An aqueous suspension of nanoparticles was dropped on carbon coated copper grids and dried at room temperature. The microparticles and the cross sections of polymer composites were imaged with a Zeiss scanning electronic microscope (Ultra 55 SEM) operated at an accelerating voltage of 5 kV in secondary electron mode. A Faxitron X-ray machine with copper target was operated in the voltage range of 60 to 100 kV and 10 mA to generate monenergistic X-ray. The X-ray dose rate was determined with reflective-type XR-RV3 GafChromic™ films (a radiation sensitive dosimetry film, International Specialty Products, Wayne) that are sensitive in the 0.05 to 15 Gy range within energy range of 30 keV to 30 MeV. The optical density of exposed GafChromic™ films was recorded with a transmission densitometer (Tobias TBX1000/1500). The X-ray shielding abilities of PDMS films with different particles (bismuth and lead) and different composition (0, 1, 2, 3, and 4 wt %) were evaluated by GafChromic™ films under different voltage. The distance between outlet of X-ray tube and sample was adjusted to control the flux (dose) of X-ray. The tensile strength of composite film was measured on a test instrument (Electro Force 3200 TA Instruments) at 0.08 mm/s tensile velocity. A PerkinElmer differential scanning calorimetry (DSC7) was used to determine the melting temperature of bismuth nanoparticles and microparticles. An atomic force microscope (Dimension Edge, Bruker) was used to image cellulose nanofibers in tapping mode at scan rate of 1 Hz. An Ultima IV X-ray diffractometer (Rigaku, Japan) with Cu Kα radiation was used to obtain X-ray diffraction (XRD) patterns of nanoparticles. All publications and patents mentioned herein are hereby incorporated by reference in their entirety as if each individual publication or patent was specifically and individually indicated to be incorporated by reference. In case of conflict, the present application, including any definitions herein, will control. Equivalents While specific embodiments of the subject invention have been discussed, the above specification is illustrative and not restrictive. Many variations of the invention will become apparent to those skilled in the art upon review of this specification and the claims below. 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048470082 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention and Contract Statement The invention relates to primary containment media for the disposal of high-level radioactive nuclear waste. The United States Government has rights in this invention pursuant to Contract No. DE-W-7405-eng-26 between the U.S. Department of Energy and Union Carbide Corporation. 2. Discussion of Background and Prior Art In the past, nuclear waste has been temporarily stored, frequently as a liquid or as a sludge in conjunction with a liquid. The art has recognized that means must be provided for permanent disposal of the waste, preferably as highly stable solids. Such solids must have certain characteristics which make such solids safe and economical for the long-term (10.sup.3 to 10.sup.5 years) retention of radioactive waste isotopes. Because of the long half-lives of some radionuclides (e.g., certain actinide isotopes), it is necessary that the selected storage medium exhibit certain properties in order to achieve the desired long-term stability. Some of the factors which must be considered in the selection of a storage medium include: high chemical stability, i.e., low corrosion rates; structural stability; simple to manufacture; acceptable preparation temperature; ability to store a high proportion of waste to insure minimum storage volume; and availability to components making up the storage medium. Various glass compositions have been suggested and tested for suitability as a storage medium. The borosilicate glasses have been considered among the more promising compositions. However, the borosilicate glasses have demonstrated significant instability under hydrothermal conditions, i.e., exposure to water at temperatures greater than 100.degree. C. Such hydrothermal conditions can be encountered in deep geological repositories. Two highly desirable properties of any potential nuclear waste glass are a low preparation temperature and a low melt viscosity at the glass processing temperature. Pure lead phosphate glasses exhibit both of these properties [see: Argyle, J. F., and F. A. Hummel, J. Amer. Ceram. Soc. 43 (1960) 452; Osterheld, R. K. and R. P. Langguth, J. Amer. Chem. Soc. 59 (1955) 76; Ray, N. H., Glass Tech. 16 (1975) 107; Klonkowski, A., Phys. and Chem. Glasses 22 (1981) 163; and Furdanowicz, H. and L. C. Klein, Glass Tech. 24 (1983) 198]. Unfortunately, it is well known that these substances are susceptable to aqueous corrosion and that they tend to devitrify at temperatures as low as 300.degree. C. [see: Furdanowicz, H., et al., ibid.; Ray, N. H., C.J. Lewis, J.N.C. Laycock and W.D. Robinson, Glass Tech. 14 (1973) 50; and Longman, G.W., and G. D. Wignall, J. Mat. Sci. 8 (1973) 212]. Scientific Basis for Nuclear Waste Management, Vol. 1, Edited by G. J. McCarthy, Plenum Press (1979), pp. 43-50, 69 to 81 and 195 to 200. The phosphate glasses described in the reference include sodium aluminum phosphate glasses, or very complicated combinations of metal oxides and P.sub.2 O.sub.5. Of those phosphate glasses in the reference, only p. 74, Table 2, shows a composition containing lead oxide along with phosphorus pentoxide and nuclear waste oxides. The ratio of the phosphorus to lead content is very high and the phosphate glasses discussed therein are a multicomponent mixture of up to eight oxides. In addition, the composition ranges given for each oxide in the reference on page 74 covers such a broad spectrum of possible phosphate glasses that the table has no significance due to the lack of specificity resulting from an effectively infinite array of permutations and combinations of glass constituents and concentrations. See also: Scientific Basis for Nuclear Waste Management, Vol. 2, Edited by C. J. M. Northrup, Jr., Plenum Press (1980), p. 109 to 116; Report BNL-50130, Development of the Phosphate Glass Process for Ultimate Disposal of High-Level Radioactive Waste, R. F. Drager, et al., January 1968; and Symposium on Management of Radioactive Wastes from Fuel Reprocessing, Nov. 27 to Dec. 1, 1972, pp. 593-612. No non-patent reference was found that indicated that lead-iron phosphate glasses have ever been seriously considered as a viable potential storage medium for the immobilization of nuclear wastes. The glass and ceramic fields include the following domestic patents. U.S. Pat. No. 3,365,578 (Grover et al.) discloses placing radioactive waste in a Na-Pb-Fe-phosphate/silicate glass, within a steel vessel. (Other Na-Pb-phosphate systems are disclosed in the examples of Grover et al.) To recap, Grover et al. teaches the use of a glass containing both Pb and phosphate for nuclear waste containment. U.S. Pat. No. 4,314,909 (Beall et al.) teaches glass-ceramic which is used for waste storage and which consists of monazite, pollucite and ZrO.sub.2 and/or mullite. The glass-ceramic can contain up to 20 percent of P.sub.2 O.sub.5. Beall et al. does not mention the presence of Pb. U.S. Pat. No. 4,351,749 (Ropp I) teaches nuclear waste storage blocks which include a polymeric phosphate glass from a trivalent metal selected from Al, In or Ga. U.S. Pat. No. 4,382,974 (Yannopoulos) discloses a glass containing nuclear waste which is stabilized by the application of synthetic monazite by means of chemical vapor deposition or detonation gun. The monazite contains 27 to 35 weight percent of P.sub.2 O.sub.5. No Pb is mentioned in Yannopoulos. U.S. Pat. No. 3,161,600 (Barton I) and U.S. Pat. No. 3,161,601 (Barton II), respectively, show Sr and Cs sequestrated in phosphate glasses. U.S. Pat. No. 3,120,493 (Clark et al.) teaches a process wherein ruthenium volatilization is suppressed during the evaporation and calcination of nuclear waste solutions by the addition of phosphite or hypophosphite. A glass-like solid is obtained. U.S. Pat. No. 4,049,779 (Ropp II) teaches stable phosphate glasses of formula M(H.sub.2 PO.sub.4)n, wherein M may be Pb and n is 2 or 3 (for divalent or trivalent M), which are prepared via H.sub.3 PO.sub.4 and a metal compound by adding a precipitant, crystallizing from solution and then melting the material. While Ropp II discloses lead phosphate glasses, it is not directed to nuclear waste disposal, although it does not mention stability to leaching. U.S. Pat. No. 3,994,823 (Ainger et al.) discloses lead zirconate ceramic, which may also contain Bi. U may be added to reduce electrical resistivity. The ceramic of Ainger et al. is not aimed at nuclear waste storage. SUMMARY OF THE INVENTION An object of the invention is to provide an improved glass composition and a method of making same for the primary containment of high-level radioactive nuclear waste. Another object of the invention is to provide a wasteform less subject to corrosion or ionic release than the prior art waste forms. A further object of the invention is to provide a stable wasteform which can be processed (i.e., that will dissolve the waste constituents) at a temperature lower than borosilicate glasses. A still further object of the invention is to provide a stable wasteform that exhibits a lower viscosity than borosilicate glass in the temperature range between 825.degree. and 1050.degree. C. A yet further object of the invention is to provide a stable wasteform for high-level radioactive nuclear wastes which is adaptable for use with existing glass fabrication technology. Other objects and advantages of the invention are set out herein or are obvious herefrom to one ordinarily skilled in the art. The objects and advantages of the invention are achieved by the composition and process of the invention. To achieve the foregoing and other objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention involves a glass composition for the immobilization and disposal of high-level radioactive nuclear waste. Lead-iron phosphate glasses with several different compositions can be used as hosts for high level radioactive wastes. The lead-iron phosphate glass frit that is combined with the nuclear waste and melted to form radioactive waste monoliths can be prepared using either of two simple processes. In one process, the appropriate amounts of PbO and Fe.sub.2 O.sub.3 are combined with (NH.sub.4)H.sub.2 PO.sub.4 and the glass is formed by heating the mixture to about 850.degree. C. A second procedure for forming the lead-iron phosphate glass frit involves simply mixing PbO and Fe.sub.2 O.sub.3 with the appropriate amount of P.sub.2 O.sub.5. The formation of the lead-iron phosphate glass frit can be accomplished in standard chemical processing facilities, since radioactive material is not involved at this stage of the production of a nuclear glass waste form. The most economical process would be used, but for the purposes of discussing the formation of the frit and its characteristics, the discussion is temporarily limited to the second process involving only the simple oxides. In this case, the practical concentration limits for the three oxide constituents of the host glass (i.e., PbO, Fe.sub.2 O.sub.3, and P.sub.2 O.sub.5) are listed in Table I. Pure lead phosphate glass (i.e., a glass that does not contain either iron or nuclear waste) can be prepared by fusing PbO (lead oxide) with P.sub.2 O.sub.5 (phosphorous pentoxide) between 800.degree. and 900.degree. C. The composition of the resulting glass frit can be continuously varied by adjusting the ratio of lead oxide to phosphorus oxide. If the weight percentage of lead oxide exceeds about 66 percent, however, a crystalline form of lead phosphate and not a glass is formed. Hence, the composition (66 wt. percent of PbO) represents a critical limit in the sense that compositions which contain larger amounts of lead oxide which can be melted together with P.sub.2 O.sub.5 to form a suitable host glass for nuclear waste is not as well as defined. The composition consisting of about 45 wt. percent of PbO and 55 wt. percent of P.sub.2 O.sub.5 was taken to represent the practical lower limit for the amount of lead oxide, since the viscosity of the molten glass increased rapidly as the PbO content was reduced below 45 wt. percent. The higher the melt viscosity, the harder the glass is to pour and the higher the processing temperature becomes. High processing temperatures for nuclear waste and undesirable since volatile radioactive species may be lost through vaporization, and the operation and maintenance of high temperature equipment in a remote processing facility are not economical. The amount of iron oxide which must be added to form the lead-iron phosphate waste glass depends on the iron concentration already present in the nuclear waste. High-level defense waste typically contains about 50 wt. percent of Fe.sub.2 O.sub.3 (see Table II, first simulated nuclear waste composition), and, for this type of nuclear waste, no additional iron is added to the pure lead phosphate frit for the formation of a very stable nuclear waste glass. For most high-level commercial waste of the type generated by light water nuclear power reactors (see Table II, second simulated nuclear waste composition), however, additional iron oxide must be added to the pure lead phosphate glass in order to form a sufficiently stable, corrosion resistant nuclear waste glass. The effects of iron oxide on the properties of pure lead phosphate glasses are critical. The addition of iron oxide to these glasses improves the corrosion resistance by a factor of more than 10,000 (see FIG. 3) and results in the formation of glasses that do not exhibit any evidence of devitrification after being heated in air at 575.degree. C. for 100 h. Perhaps most significantly, extremely stable lead-iron phosphate glasses can be prepared and poured easily at temperatures between 800.degree. and 900.degree. C. The results illustrated in FIG. 3 can be used in tailoring the composition of the lead-iron phosphate glass frit depending upon the iron concentration of a given type of nuclear waste. The highly stable waste form is realized when the iron concentration is adjusted to correspond to a content of about 9.0 wt. weight of Fe.sub.2 O.sub.3 relative to the total weight of the glass composition. Preferably the final nuclear waste glass composition contains about 9 weight percent of Fe.sub.2 O.sub.3. Also preferably the Fe.sub.2 O.sub.3 can be added to the glass composition in the form of one of the metal oxides present in the radioactive nuclear waste material. The Fe.sub.2 O.sub.3 can also be added to the glass composition as a separate component. Preferably the radioactive nuclear waste material is present in an amount of about 15 weight percent, based on the total weight of the glass composition, in the glass composition. The invention can also generally be described as a stable primary containment medium for disposal of high-level radioactive nuclear wastes comprising lead-iron phosphate glass having a composition in the ranges indicated in Table I plus preferably about 15 weight percent of a mixture of metal oxide nuclear waste material. Such nuclear waste material can be, for example, of the type in interim storage at nuclear facilities or a combination of such interim storage type and the type of high level waste generated by commercial power reactors. The advantages of lead-iron phosphate nuclear waste glasses as compared to borosilicate nuclear waste glass are: 1. Corrosion resistance at elevated temperature between 90.degree. and 135.degree. C. is at least 100 to 1000 times better; 2. Lower processing temperature for the wasteform (260.degree. to 110.degree. C. lower); 3. Lower melt viscosity in the 800.degree. to 1050.degree. C. temperature range; 4. Waste loading per unit volume which is at least as good as the practical waste loadings per unit volume achievable by using borosilicate glasses; 5. The ability to use a relatively inexpensive aluminum, aluminum alloy or stainless steel cannister for the glass casting step in processing; and 6. The lead-iron phosphate nuclear waste glass can be prepared using basically the same technology that has been developed to produce large monoliths of borosilicate nuclear waste glass. The lead-iron phosphate glass wasteform of the invention provides an excellent containment medium for wastes such as those in interim storage at government nuclear facilities and high-level wastes generated by commercial nuclear power reactors. The invention also includes a process for preparing the glass composition of the invention. The process includes admixing about 34 to about 55 weight percent, based on the total weight of the glass composition, of phosphorus oxide, about 45 to about 66 weight percent, based on the total weight of the glass composition, of lead oxide, and about 0 to about 9 weight percent of Fe.sub.2 O.sub.3, based on the total of the glass composition and the amount of iron content in the nuclear waste to be processed. The admixture, to which about 15 weight percent of nuclear waste oxides have been added, is then melted to provide a liquid melt of a lead-iron phosphate glass. Usually the melt is heated to and kept at 800.degree. to 1050.degree. C. About 10 to about 20 weight percent, based on the total weight of the glass composition, of radioactive nuclear waste material containing at least one metal oxide is added to the liquid melt of lead phosphate glass. Preferably the radioactive nuclear waste material contains sufficient Fe.sub.2 O.sub.3 to provide preferably about 9 weight percent, baesd on the total weight of the glass composition, of Fe.sub.2 O.sub. 3 in the glass composition. The liquid melt is then solidified to provide the glass composition for the immobilization and disposal of the radioactive nuclear waste material. Preferably the phosphorus oxide is used in the form of ammonium orthophosphate monohydrogen, i.e., (NH.sub.4).sub.2 HPO.sub.4. The addition steps for the nuclear waste and the Fe.sub.2 O.sub.3 can be be conducted simultaneously or in any desired sequence. In an alternative to the preferred embodiment of the invention, all or part of the Fe.sub.2 O.sub.3 used in the glass composition can be added as a separate component. In such case the Fe.sub.2 O.sub.3 can be added directly to a liquid melt of lead phosphate glass and/or added to the radioactive nuclear waste material before such is added to the liquid melt of the lead phosphate glass. The lead-iron phosphate nuclear waste glass of the invention is a very stable, easily prepared storage medium for some important classes of nuclear waste. Relative to borosilicate nuclear waste glass, the lead-iron phosphate nuclear waste glass has several distinct advantages. These advantages of the invention glass compositions include: (1) a corrosion resistance at 90.degree. C. that is about 1000 times higher than a comparable borosilicate glass in the pH range between 5 and 9, which is mostly due to the presence of iron in the phosphate glass composition, (2) a processing temperature that is 100.degree. to 250.degree. C. lower than that currently required to process borosilicate glass, and (3) a lower melt viscosity in the 800.degree. to 1050.degree. C. range. The presence of iron is primarily responsible for the very high corrosion resistance of the lead-iron phosphate nuclear waste glass of the invention relative to that of the pure lead phosphate glass. The lead-iron phosphate glass of the invention is an excellent storage medium for high-level radioactive nuclear waste. Reference will now be made in detail to the present preferred embodiment of the invention, some of the advantages of which are illustrated in the accompanying drawings. |
description | The present application is a continuation of U.S. patent application Ser. No. 11/297,329, filed on Dec. 9, 2005, now U.S. Pat. No. 7,164,129, which is a continuation of U.S. patent application Ser. No. 10/938,637, filed on Sep. 13, 2004, now U.S. Pat. No. 7,012,254, which is a continuation of U.S. patent application Ser. No. 09/871,739, filed on Jun. 4, 2001, now U.S. Pat. No. 6,878,934, the disclosures of which are herewith incorporated by reference in their entirety. The present invention relates generally to electron microscopes, and particularly, to a method and device for observing a specimen in a field of view of an electron microscope. When a specimen (sample) transmission image in a field of view is measured, analyzed or searched by a conventional electron microscope, the operator directly operates the specimen stage and corrects focus thereby locating a desired field of view in a magnified specimen transmission image projected on a scintillator. This operation is very complex, time-consuming and tedious for the operator. As a result, this operation invites human error such as overlooking a necessary field of view and reducing observation efficiency and accuracy. For instance, as shown in FIG. 2, when a specimen image is to be observed or a field of view is to be searched, a thin-film specimen to be observed is mounted on a specimen holding mesh or a micro-grid and the specimen holding mesh or the micro-grid is fixed to a specimen holder. When a region to be searched is divided into nine sections, as shown in FIG. 2, magnified transmission images of the specimen are classified into three types as shown in FIGS. 2(A), 2(B), and 2(C). When observing a field of view, such as field “5” (FIG. 2(B)), a magnified transmission image of a form 61 on the specimen can be obtained. But, when the observing field of view is “1,” “4,” or “7” in FIG. 2, a magnified transmission image of only a shadow or an edge portion of the specimen holding mesh is obtained and therefore the entire field of view is completely dark (FIG. 2(A)). Also, when the observing field of view is, for instance, field “9,” nothing is present in the field of view and therefore it is completely white (FIG. 2(C)). These fields of view, namely, “1,” “4,” “7” and “9,” are not appropriate for observation. Thus, with conventional methods and devices for observing a specimen in a field of view of an electron microscope, it is not possible to efficiently exclude fields of view inappropriate for observation, search, or analysis as shown in FIGS. 2(A) and 2(C). In other words, when the conventional electron microscope automatically moves a field of view to search for a target form, the conventional electron microscope searches both a field of view appropriate for search in which the specimen is present and an unnecessary field of view inappropriate for search in which the specimen is not present. It is accordingly an object of the present invention to provide a method and device for observing a specimen in a field of view of an electron microscope that can automatically and efficiently determine whether or not a picked-up field of view is appropriate for making a search for a target form of a specimen and thereby efficiently extract only necessary fields of view. In an object of the present invention, a method of observing a specimen in a field of view of an electron microscope is provided, comprising the acts of setting the magnification of the electron microscope, setting conditions for moving the field of view, setting a starting position for the field of view and moving the field of view based upon the condition. Further, the invention provides illuminating the specimen with an electron beam having a first angle and forming a first transmission image of the specimen in the field of view, adjusting the electron beam to a second angle and forming a second transmission image of the specimen in the field of view and calculating a degree of coincidence between the first and second transmission images. In another object of the present invention, a method of observing a specimen in a field of view of an electron microscope is provided, comprising the acts of setting the magnification of the electron microscope, setting conditions for moving the field of view, setting a starting position for the field of view and moving the field of view based upon the condition. The invention further provides illuminating the specimen with an electron beam in one direction and forming a line profile transmission image of the specimen in the field of view and then observing the field of view if a change in the line profile is found. In yet another object of the present invention, a method of observing a specimen in a field of view of an electron microscope is provided comprising the acts of setting the magnification of the electron microscope, setting conditions for moving the field of view, setting a starting position for the field of view and moving the field of view based upon the condition. The invention further provides illuminating the specimen with an electron beam and forming a transmission image of the specimen in the field of view, selecting a pattern from the transmission image and matching the selected pattern with a preset pattern and observing the field of view if a match is found between the selected pattern and the preset pattern. In an object of the present invention, an electron microscope is provided comprising a support for supporting a specimen, a deflector for deflecting an electron beam to the specimen to create a transmission image, an image pickup device for obtaining the transmission image and a processor coupled to the image pickup device being programmed for observing a specimen in a field of view of an electron microscope. The programming comprises the acts of setting the magnification of the electron microscope, setting conditions for moving the field of view, setting a starting position for the field of view and moving the field of view based upon the condition, The invention further provides illuminating the specimen with an electron beam having a first angle and forming a first transmission image of the specimen in the field of view, adjusting the electron beam to a second angle and forming a second transmission image of the specimen in the field of view and calculating a degree of coincidence between the first and second transmission images. In another object of the present invention an electron microscope is provided comprising a support for supporting a specimen, a deflector for deflecting an electron beam to the specimen to create a transmission image, an image pickup device for obtaining the transmission image and a processor coupled to the image pickup device being programmed for observing a specimen in a field of view of an electron microscope. The programming comprises the acts of setting the magnification of the electron microscope, setting conditions for moving the field of view, setting a starting position for the field of view and moving the field of view based upon the condition. The invention further provides illuminating the specimen with an electron beam in one direction and forming a line profile transmission image of the specimen in the field of view and observing the field of view if a change in the line profile is found. In yet another object of the present invention an electron microscope is provided comprising a support for supporting a specimen, a deflector for deflecting an electron beam to the specimen to create a transmission image, an image pickup device for obtaining the transmission image and a processor coupled to the image pickup device being programmed for observing a specimen in a field of view of an electron microscope. The programming comprises the acts of setting the magnification of the electron microscope, setting conditions for moving the field of view, setting a starting position for the field of view and moving the field of view based upon the condition. The invention further provides illuminating the specimen with an electron beam and forming a transmission image of the specimen in the field of view selecting a pattern from the transmission image and matching the selected pattern with a preset pattern and observing the field of view if a match is found between the selected pattern and the preset pattern. Exemplary embodiment of the present invention will be described below in connection with the drawings. Other embodiments may be utilized and structural or logical changes may be made without departing from the spirit or scope of the present invention. Like items are referred to by like reference numerals throughout the drawings. Referring now to the drawings, FIG. 1 illustrates a schematic functional block diagram showing an example of a transmission electron microscope according to the present invention. Although any number of electron beam deflecting coils may be employed, two deflecting coils over a specimen and two deflecting coils under the specimen or a total of four electron beam deflecting coils are used as an example in this case. It is to be noted that all of the embodiments below will be described on an assumption that they employ the transmission electron microscope shown in FIG. 1. An electron beam 73 emitted from an electron gun 1 and then accelerated is applied through magnetic fields of a first irradiation lens coil 2, a second irradiation lens coil 3, and an objective lens coil 4 to a specimen 14 held on a specimen stage 13. The electron beam 73 transmitted by the specimen 14 is magnified by a first intermediate lens coil 5 and a second intermediate lens coil 6, and then further magnified by a first projection lens coil 7 and a second projection lens coil 8, whereby a magnified transmission image 59 of the specimen is formed on a scintillator 16. In this example, coils using electromagnetic field force are used as lenses for deflecting the electron beam and magnifying the specimen transmission image; however, electrostatic deflection and electrostatic lenses using electrostatic force may also be employed to deflect the electron beam and magnify the specimen transmission image. The magnified transmission image 59 of the specimen converted into an optical image by the scintillator 16 is picked up by a pickup device, for example a TV camera 17. An image signal from the TV camera is captured for processing by a microprocessor 46 via a TV camera controller 33 and an image capturing interface 34, and thereafter displayed as an image on a CRT 50 controlled by a CRT controller 49. In this example, when the magnified transmission image is captured by the microprocessor 46, the scintillator 16 and the TV camera are used; however, a detector such as a MCP (Micro Channel Plate) capable of directly converting an electron beam into an electric signal may also be used. The microprocessor 46 controls exciting power supplies 18, 19, 20, 21, 22, 23, and 24 that feed the first irradiation lens coil 2, the second irradiation lens coil 3, the objective lens coil 4, the first intermediate lens coil 5, the second intermediate lens coil 6, the first projection lens coil 7, and the second projection lens coil 8 of the transmission electron microscope via DACs (digital-to-analog converters) 35, 36, 37, 38, 39, 40, and 41, respectively. Similarly, the microprocessor 46 controls exciting power supplies 25, 26, 27, and 28 feeding a first deflecting coil 9 and a second deflecting coil 10 over the specimen and a first deflecting coil 11 and a second deflecting coil 12 under the specimen via DACs 42, 43, 44, and 45, respectively. The microprocessor 46 is connected, via a bus, with an external storage unit 47 such as a hard disk, an arithmetic unit 48, a magnification changing rotary encoder 53, a keyboard 55, a RAM 57, a ROM 58 and the like. The magnification changing rotary encoder 53 is connected to the bus via an I/F (interface) 51. A specimen stage 13 is driven by a fine adjustment motor 29 for driving the stage connected to the microprocessor 46 via a motor driver 30. Next, as an example of image computation according to the present invention, principles of determining a degree of coincidence between two images by a phase only correlation method and principles of automatic focus correction will be described. A magnified specimen transmission image 1 of M×N pixels to serve as a reference as shown in FIG. 3(A) is recorded as ƒ1(m, n) in a storage unit. Next, a magnified specimen transmission image picked up by passing a current through two upper electron beam deflecting coils and providing an appropriate inclining deflection angle α to an electron beam applied to the specimen is recorded as a transmission image 2 or ƒ2(m, n) of M×N pixels in the storage unit, where m=0, 1, 2, . . . , M−1; n=0, 1, 2, . . . , N−1. Discrete Fourier images F1(u, v) and F2(u, v) of the transmission images ƒ1(m, n) and ƒ2(m, n) are defined by the following [Equation 1] and [Equation 2], respectively: F 1 ( u , v ) = ∑ m = 0 M - 1 ∑ n = 0 N - 1 f 1 ( m , n ) ⅇ - j2π ( mu / M + nv / N ) = A ( u , v ) ⅇ jα ( u , v ) [ Equation 1 ] F 2 ( u , v ) = ∑ m = 0 M - 1 ∑ n = 0 N - 1 f 2 ( m , n ) ⅇ - j2π ( mu / M + nv / N ) = B ( u , v ) ⅇ jβ ( u , v ) [ Equation 2 ] where u=0, 1, 2, . . . , M−1; v=0, 1, 2, . . . , N−1; A (u, v) and B(u, v) are amplitude spectra; and α (u, v) and β (u, v) are phase spectra. According to the phase only correlation method, when an image translation between two images occurs, the position of a correlation peak is displaced by the amount of the translation. A method of deriving an amount of translation will be described in the following. First, it is assumed that when the transmission image ƒ2(m, n) is translated in a direction of m by r′, f3(m, n)=ƒ2(m+r′, n). A discrete Fourier image F3(u, v) of f3(m, n) is obtained from [Equation 2] and thereby expressed as [Equation 3]. F 3 ( u , v ) = ∑ m = 0 M - 1 ∑ n = 0 N - 1 f 2 ( m + r ′ , n ) ⅇ - j2π ( mu / M + nv / N ) = B ( u , v ) ⅇ j ( β + 2 π r ′ u / M ) [ Equation 3 ] If the amplitude spectrum B(u, v) is set to be a constant, a phase image not dependent on image contrast and lightness is obtained. A phase image F3′(u, v) of f3 is expressed as the following [Equation 4]. Similarly, a phase image F1′(u, v) of ƒ1 is expressed as the following [Equation 5].F3′(u, v)=ej(β+2πr′u/M) [Equation 4]F1′(u, v)=ejα(u,v) [Equation 5] By multiplying the phase image F1′(u, v) by a complex conjugate of F3′(u, v), a synthetic phase image H13(u, v) represented by the following [Equation 6] is obtained. A correlation strength image or a correlation index (degree of coincidence between two images) g13(r, s) is expressed as the following [Equation 7] as a result of inverse Fourier transformation of the synthetic image H13(u, v). H 13 ( u , v ) = F 1 ′ ( u , v ) ( F 3 ′ ( u , v ) ) * = ⅇ j ( α - β - 2 π r ′ u / M ) [ Equation 6 ] g 13 ( r , s ) = ∑ u = 0 M - 1 ∑ v = 0 N - 1 ( H 13 ( u , v ) ) ⅇ j2π ( ur / M + vs / N ) = ∑ u = 0 M - 1 ∑ v = 0 N - 1 ( ⅇ j ( α - β - 2 π r ′ u / M ) ) ⅇ j2π ( ur / M + vs / N ) = g 1 2 ( r - r ′ ) [ Equation 7 ] When the correlation strength image obtained by [Equation 7] is normalized and a value obtained from [Equation 7] is zero, two images are recognized to be completely different from each other. On the other hand, a value obtained is 100, the two images are recognized to be identical with each other. In other words, a value of “0” is equal to 0% and a value of “100” is equal to 100%. According to [Equation 7], when there is a positional displacement r′ in a direction of m between two images, the correlation peak position of the correlation strength image is displaced by −r′. Thus, the phase only correlation method makes it possible to determine a degree of coincidence and a displacement between a transmission image 1 and a transmission image 2 without depending on the contrast or lightness of the images. When a peak of a correlation strength image occurs at a position displaced by ΔG [pixel] as a result of computational processing of two specimen transmission images from [Equation 1] to [Equation 7], ΔG [pixel] corresponds to a displacement on a light receiving plane of a detector such as a TV camera, and therefore ΔG is converted into a displacement Δx on the plane of the specimen. The displacement Δx between two images on the plane of the specimen is calculated by the following [Equation 8], where diameter of the detecting light receiving plane is L [m], magnification of the electron microscope on the light receiving plane is M, and the number of pixels of the detector is Ld [pixel]. It is to be noted that [Equation 8] includes an image displacement δ resulting from spherical aberration of an electron lens; therefore a true displacement Δxt of a field of view is obtained by subtracting δ from Δx. The displacement δ on the plane of the specimen is expressed as [Equation 9] by using a spherical aberration Cs and an electron beam deflection angle α. Accordingly, the image displacement Δxt occurring between the two magnified specimen transmission images is represented by [Equation 10]. Δ x = ( Δ G L d ) × ( L M ) [ Equation 8 ] δ = Cs · a 3 [ Equation 9 ] Δ x t = Δ x - δ = ( Δ G L d ) × ( L M ) - Cs · α 3 [ Equation 10 ] A relation between the image displacement Δxt and a focal shift Δf is represented by the following [Equation 11]. This relation allows the focal shift Δf to be calculated from the image displacement Δxt. Δ f = Δ x t α [ Equation 11 ] An objective current correction value is calculated from the focal shift Δf obtained by [Equation 11]. There is a relation of [Equation 12] between focal length f of the electron lens and an objective lens current I, where N is a number of turns of the electron lens coil, E* is an accelerating voltage obtained by relativistic correction, and I is an objective lens current value. Thus, focusing is attained by adding the objective current correction value obtained from the relation of [Equation 12] to the objective current value. f ∝ ( IN E * ) 2 [ Equation 12 ] Embodiments of the present invention will next be specifically described. FIG. 4 is a flowchart of a first embodiment showing a method comprising the steps of automatically moving or selecting a field of view, determining whether the field of view has a brightness (gradation) inappropriate for observation or search, and then efficiently observing or searching for only an appropriate field of view by using the transmission electron microscope shown in FIG. 1. At a step 11 in FIG. 4, magnification of the transmission electron microscope is set so as to obtain an arbitrary specimen transmission image. The magnification for the specimen transmission image is inputted by the magnification changing rotary encoder 53. A pulse wave generated by the rotary encoder 53 is converted into a digital signal by the I/F 51. On the basis of the digital signal inputted from the I/F 51, the microprocessor 46 refers to magnification display data preset in the ROM 58 to display a corresponding magnification on the CRT 50. At the same time, the microprocessor 46 outputs data of the first irradiation lens coil 2, the second irradiation lens coil 3, the objective lens coil 4, the first intermediate lens coil 5, the second intermediate lens coil 6, the first projection lens coil 7, and the second projection lens coil 8, which data is prestored in the ROM 58, to the DACs 35, 36, 37, 38, 39, 40, and 41, respectively, so that data of the lens system is converted into analog signals. The DACs output analog signals to the exciting power supplies 18, 19, 20, 21, 22, 23, and 24 to pass current through the lens coils of the lens system. Next, conditions for automatically moving a field of view are set at a step 12. A moving speed of the field of view and a range of search are inputted by the keyboard 55 or a mouse 56, then processed by the microprocessor, and stored in the storage unit. At a step 13, an origin of field movement is set. As shown for example in FIG. 2, the origin 64 of field movement is set at a corner of a field of view displayed on the display apparatus (CRT) 50 by using an input device such as a mouse. A coordinate position set as the origin by the processing of the microprocessor 46 is stored in the storage unit 47. At a step 14, the field of view is moved in a sequence of “1”→“2”→“3”→ . . . →“9” in FIG. 2, for example, under the conditions for moving the field of view set at the steps 12 and 13. It is to be noted that the movement of the observing field of view 62 is not limited to the sequence from the field “1” to the field “9,” as shown in FIG. 2, rather, the observing field of view 62 may be moved to a randomly selected field. The observing field of view may be moved by an electromagnetic method using electron beam deflecting coils disposed over and under the specimen, a mechanical method using a specimen stage driver, or a stage driving mechanism using a piezoelectric device or the like. FIG. 5(a) is a schematic diagram of assistance in explaining a method of electromagnetically moving the field of view. At a command from the microprocessor 46, and under the conditions for moving the field of view set at the step 12, the two electron beam deflecting coils disposed over the specimen (the first deflecting coil 9 and the second deflecting coil 10 over the specimen) translate the electron beam 73 from a position of an electron beam optical axis 72 passing through a field 70 at the center of the specimen to that of a deflected electron beam 67. The electron beam 73 is thus applied to the specimen 14. The deflected electron beam 67 is applied to a field 71 at a distance d from the center of the specimen. The electron beam after passing through the specimen is returned to the electron-beam optical axis 72 by the electron beam deflecting coils disposed under the specimen, that is, the first deflecting coil 11 and the second deflecting coil 12 under the specimen. As a result, a magnified specimen transmission image after the movement of the field of view is obtained. FIG. 5(b) is a schematic diagram of assistance in explaining a method of mechanically moving the field of view. In this case, the microprocessor 46 controls the motor driver 30 under the conditions for moving the field of view set at the step 12 and thereby drives the fine adjustment mechanism 13 for the specimen stage by means of the stage driving motor 29 to slightly-move the specimen. In the case of the field moving method using a piezoelectric device, the stage driving motor is replaced with a piezoelectric device to perform slight movement of the specimen. At a step 15 in FIG. 4, the movement of the field of view is stopped. Conditions for stopping the movement of the field of view are determined by the conditions for moving the field of view set at the step 12 and a size of each field of view defined by the magnification inputted at the step 11. The field of view is moved and stopped such that an image of the field of view will not be superimposed on an image of the next observing field of view. At a step 16, a specimen transmission image is picked up in a state in which the field of view is stopped. The electron beam transmitted by the specimen 14 goes through the objective lens 4, the first intermediate lens 5, the second intermediate lens 6, the first projection lens 7, and the second projection lens 8, and then forms a magnified specimen transmission image 59 on the scintillator 16. The TV camera 17 picks up the image projected on the scintillator 16, and the image capturing interface 34 registers the magnified image in the storage unit as a transmission image 1. At a step 17, whether the transmission image 1 picked up at the step 16 is appropriate for observation or not is determined. Whether the field of view of the transmission image 1 has a brightness (gradation) appropriate for observation or not may be determined by a method of making a line profile of the picked-up field of view and thereby measuring the brightness (gradation), a method of determining a phase-amplitude correlation between two transmission images in the same field of view that are taken under different electro-optical conditions and thereby making a determination by a degree of coincidence between the two images (correlation function), and a method of determining a phase only correlation between two transmission images taken under different conditions and thereby making a determination by a degree of coincidence between the two images. When it is determined that the field of view is not appropriate for observation as a result of determining whether the field of view is appropriate for observation or not by the above determination methods, the processing returns to the step 14. On the other hand, when it is determined that the field of view is appropriate for observation, the processing proceeds to a step 18. FIGS. 6(A), 6(B), 6(C), and 6(D) are diagrams of assistance in explaining a method of determining a state of a picked-up field of view by using a line profile of the field of view. As shown in FIG. 6(A), x and y coordinates are set and a measuring line 74 as shown in the figure is drawn in an x-direction and/or a y-direction, so that change in brightness on the measuring line is measured as a line profile. FIGS. 6(B), 6(C), and 6(D) each show an example of a result of measurement in the x-direction. In the case of a 256-level gray-scale image, when all the pixels of a line profile have a level 256 or a level zero as shown in FIGS. 6(B) and 6(D) as a result of the measurement, it means that a magnified image of a mesh or a region with no specimen, respectively, is picked up in the field of view, and therefore that field of view is not appropriate for observation. FIG. 6(C) shows an example of a line profile of a field of view appropriate for observation. When a form 61 is present in a field of view 62, as shown in FIG. 6(A), the form appears as change in contrast as the electron beam passes through the specimen, whereby a line profile as shown in FIG. 6(C) is obtained. It is to be noted that only one measuring line 74 is drawn in the x-direction in FIG. 6(A); however, an arbitrary number of measuring lines may be drawn or the entire field of view may be scanned. It is also preferable that a plurality of measuring lines are drawn not only in the x-direction but also in the y-direction to obtain line profiles on these measuring lines. FIG. 7 is a flowchart of assistance in explaining a method of determining a state of a field of view by the phase only correlation. A series of operations from a step 11 to a step 15 is the same as in FIG. 4. At a step 16′, a magnified transmission image projected on the scintillator 16 is picked up by the TV camera 17. The magnified transmission image is stored in the storage unit as a transmission image 1. Next, at a step 17′, the electron beam to be applied to the specimen is inclined by a deflection angle α, and at the next step 18′, a magnified transmission image projected on the scintillator 16 is stored in the storage unit as a transmission image 2. At a step 19′, the transmission image 1 and the transmission image 2 are called up from the storage unit, and then the arithmetic unit 48 creates discrete Fourier transformation data of each of the images and thereby calculates a degree of coincidence between the transmission image 1 and the transmission image 2 by the phase only correlation method described by using the foregoing Equations 1 to 7. At a step 20′, whether the current field of view is on the mesh and therefore is not appropriate for field observation or search or whether the field of view is appropriate for field observation or search is determined by using the degree of image coincidence between the transmission image 1 and the transmission image 2 obtained at the step 19′. When the degree of coincidence between the transmission image 1 and the transmission image 2 is zero, it is determined that the field of view is not to be measured, and the processing returns to the step 14 to search for the next field of view. When the degree of coincidence between the transmission image 1 and the transmission image 2 is not zero nor 100, it is determined that the field of view is an appropriate region to be measured, and the processing proceeds to a step 21′ (corresponding to the step 18 in FIG. 4). When the degree of coincidence between the transmission image 1 and the transmission image 2 is 100, it is determined that either the current field of view picks up an image on the mesh (FIG. 2(A)) or no form is present in the field of view because of breakage of the specimen or the like (FIG. 2(C)), and the processing returns to the step 14. In theory, the degree of coincidence of 100 indicates that two images completely coincide with each other, however, results of experiments have shown that the two images at the degree of coincidence of 100 are either deep black as shown in FIG. 2(A) or purely white as shown in FIG. 2(C). Thus, an image of a deep black field of view indicates that the image is taken on a specimen holding mesh 6, while an image of a purely white field of view indicates that no form is present in the field of view because of breakage of the specimen. Incidentally, a current apparatus takes about 0.9 to 1 seconds to perform calculation and make a determination for a single field of view by the phase only correlation method. Description will next be made about how the degree of coincidence between two images each having a uniform tone throughout all of its pixels M×N becomes zero or 100. A function of an image 1 and a function of an image 2 are defined as ƒ1(m, n) and ƒ2(m, n), respectively, where m=0, 1, 2, . . . , M=1; n=0, 1, 2, . . . , N−1. The image 1 and the image 2 are uniform in brightness (gradation) throughout all of the pixels. Because of the above conditions, ƒ2(m, n) is expressed as [Equation 13]. Hence, [Equation 14] and [Equation 15] are derived from [Equation 1] and [Equation 2]. f 1 ( m , n ) = f 2 ( m , n ) [ Equation 13 ] F 1 ( u , v ) = ∑ m = 0 M - 1 ∑ n = 0 N - 1 f 1 ( m , n ) ⅇ - j2π ( mu / M + nv / N ) = A ( u , v ) ⅇ jα ( u , v ) [ Equation 14 ] F 2 ( u , v ) = ∑ m = 0 M - 1 ∑ n = 0 N - 1 f 1 ( m , n ) ⅇ - j2π ( mu / M + nv / N ) = A ( u , v ) ⅇ jα ( u , v ) [ Equation 15 ] When for the phase only correlation method, an amplitude component A(u, v) of [Equation 14] and [Equation 15] is set to be a constant of one, and [Equation 14] and [Equation 15] are set to be F1′(u, v) and F2′(u, v), respectively, [Equation 16] and [Equation 17] are obtained.F1′(u, v)=ejα(u,v) [Equation 16]F2′(u, v)=ejα(u,v) [Equation 17] A synthetic phase image H(u, v) obtained by multiplying [Equation 16] by a complex conjugate of [Equation 17] is represented by [Equation 18]. H ( u , v ) = F 1 ′ ( u , v ) { F 2 ′ ( u , v ) } * = ⅇ j ( α - α ) = 1 [ Equation 18 ] Then, a correlation index (correlation strength image) g(r, s) is expressed as [Equation 19] as a result of inverse Fourier transformation of [Equation 18]. g ( r , s ) = ∑ m = 0 M - 1 ∑ n = 0 N - 1 { H ( u , v ) } ⅇ j2π ( ur / M + vs / N ) = { MN ( r = 0 , s = 0 ) 0 ( r ≠ 0 , s ≠ 0 ) [ Equation 19 ] When an obtained value MN is normalized, a correlation index of 100 or zero is obtained. Phase-amplitude correlation may also be used as a method of determining a state of a field of view. The flow of operation of the phase-amplitude correlation method is the same as that of the steps 16′ to 20′ in FIG. 7 using the phase only correlation method, but its principles of calculation are different from those of the phase only correlation method. A method of calculating a degree of image coincidence by using the phase-amplitude correlation method will be described in the following. A magnified specimen transmission image is recorded in the storage unit as a transmission image 1 or ƒ1(m, n) of M ×N pixels, where m=0, 1, 2, . . . , M−1; n=0, 1, 2, . . . , N−1. Then, current is applied to the two upper electron beam deflecting coils 9 and 10, and a magnified specimen transmission image that is in the same field of view as the transmission image 1 and picked up by providing a certain inclining deflection angle α to the electron beam 73 applied to the specimen 14 is recorded in the storage unit as a transmission image 2 or ƒ2(m, n) of M×N pixels. Discrete Fourier images F1(u, v) and F2(u, v) of the transmission images ƒ1(m, n) and ƒ2(m, n) are defined by the foregoing [Equation 1] and [Equation 2], respectively. A synthetic image H12(u, v) represented by the following [Equation 20] is obtained by multiplying the discrete Fourier transformation image F1(u, v) of the transmission image 1 by a complex conjugate of the discrete Fourier transformation image F2(u, v) of the transmission image 2. A correlation strength image or a correlation index (degree of coincidence between the two images) g12(r, s) is expressed as the following [Equation 21] as a result of inverse Fourier transformation of the synthetic image H12(u, v). H 12 ( u , v ) = F 1 ( u , v ) · ( F 2 ( u , v ) * ) = A ( u , v ) B ( u , v ) ⅇ j ( α - β ) [ Equation 20 ] g 12 ( r , s ) = ∑ u = 0 M - 1 ∑ v = 0 N - 1 ( H12 ( u , v ) ) ⅇ j2π ( ur / M + vs / N ) [ Equation 21 ] The correlation strength image obtained by [Equation 21] is normalized. When an obtained value is zero, the two images are recognized to be completely different from each other, while when the obtained value is 100, the two images are recognized to be identical with each other. According to the phase-amplitude correlation method, as in the phase only correlation method, when a degree of coincidence of zero or 100 is obtained, it is determined that the current field of view is not appropriate for observation or search, and the processing returns to the step 14. Returning to FIG. 4, at a step 18 (step 21′ in FIG. 7), after it is determined that the current field of view is appropriate for observation or search, the magnified specimen transmission image 59 projected on the scintillator 16 is picked up by the TV camera 17, stored in the storage unit 47 as image data, and then displayed on the CRT 50 via a CRT driver 49 or used for composition analysis or the like. Also, coordinates of the selected field of view are stored in the storage unit 47. Finally, at a step 19 in FIG. 4 (step 22′ in FIG. 7), whether the processing flow is ended or not is determined on the basis of the conditions for moving the field of view set at the step 12, and when the processing flow is not to be ended, the processing returns to the step 14 to search for the next field of view. By performing the operation described above, it is possible to automatically move or select the field of view, determine whether the selected field of view is appropriate for observation or not, and thereby efficiently observe only appropriate fields of view. As an example of actual measurement, suppose that the specimen has a diameter of 2 mm, and the specimen is magnified to 100 mm in diameter at a transmission image magnification of 10000 to make a search. In this case, size of each field of view corresponds to about 10 μm on the plane of the specimen. Observation of the entire region of the specimen requires 40000 images to be picked up. However, in practice, since the specimen is held by the specimen holding mesh, images of the mesh are taken and therefore nothing can be seen in some fields of view, or the specimen is not present in some fields of view, as shown in FIG. 2. It can be estimated that the region of the mesh is about ½ of the entire search region of 2 mm in diameter, and the fields of view where the specimen is present constitute 1/10 of the entire region. Therefore, the fields of view appropriate for observation in the entire search region constitute about 1/20 of the 40000 fields of view for image pickup. According to the first embodiment, it is possible to automatically select only fields of view appropriate for observation, reduce the number of images to be picked up to 1/20, and accordingly reduce time required for search to about 1/20. FIG. 8 is a flowchart of a second embodiment showing a method comprising the steps of automatically moving or selecting a field of view, determining whether the field of view is appropriate for observation or search, thereby efficiently observing or searching for only an appropriate field of view, and when it is determined that the field of view is not appropriate for observation, automatically adjusting electro-optical conditions. In FIG. 8, input of magnification at a step 21, setting of conditions for moving a field of view at a step 22, setting of origin of movement at a step 23, moving the field of view at a step 24, and stopping the movement of the field of view at a step 25 are the same as in the steps 11 to 15 of FIG. 4, and therefore their repeated description will be omitted. At a step 26, a magnified specimen transmission image 59 projected on the scintillator 16 is picked up by the TV camera 17, and then whether or not the current field of view is appropriate for observation or measurement is determined by using the line profile method, the phase only correlation method, or the phase-amplitude correlation method described above. When it is determined at the step 26 that the current field of view is appropriate for observation, the processing proceeds to a step 28 to measure, observe, or analyze the magnified specimen transmission image. When it is determined at the step 26 that the current field of view is not appropriate for observation, the processing proceeds to a step 27. At the step 27, items that may be considered the factors in rendering the field of view inappropriate for observation are automatically examined to adjust electro-optical conditions. In this case, the following four items are examined and adjusted: (1) the electron beam, (2) lens conditions of the irradiation lenses, (3) electron beam current, and (4) an aperture or a position of a movable objective diaphragm. The item (1) is provided to examine a possibility that the electron beam is not emitted when the entire field of view is black. The item (2) is provided to examine a possibility that irradiation lens conditions of very low density of the specimen irradiation electron beam render the magnified transmission image undetectable with the sensitivity of the TV camera. The item (3) is provided to check for shortage of emission current or filament current. The item (4) is provided to examine a possibility that the aperture of the movable objective diaphragm is selected to be smaller than necessary, and thereby renders the field of view dark and undetectable by the TV camera, and a possibility that the aperture position of the movable diaphragm is not aligned with the optical axis of the electron beam. Results of the four items are compared with preset values. When it is determined that the results do not satisfy the preset values, adjustment is made for each of the items to satisfy the preset value. When it is determined as a result of another image pickup that the current field of view is not appropriate for observation even though the results satisfy conditions of the above items, the processing returns to the step 24 to search for the next field of view. On the other hand, when the current field of view satisfies the preset values and it is determined that the field of view is appropriate for image pickup as a result of adjustment, the processing proceeds to the step 28 to observe, store, measure, or analyze the transmission image in that current field of view. Also, coordinates of the selected field of view are stored in the storage unit 47. Finally, the processing proceeds to the step 29, and whether the processing flow is ended or not is determined on the basis of the conditions for moving the field of view set at the steps 22 and 23. When measurement is to be made again in accordance with the same processing flow, the processing returns to the step 24. The operation described above enables automatic observation without omission by automatically moving or selecting a field of view, determining whether the selected field of view is appropriate for observation or not, and adjusting electro-optical conditions in an inappropriate field of view for a second determination process. According to the second embodiment, it is possible to minimize omission in search due to insufficient adjustment of electro-optical conditions and prevent human error, for example an error of not emitting the electron beam. FIG. 9 is a flowchart of a third embodiment showing a method comprising the steps of automatically moving or selecting a field of view, presetting an arbitrary search target pattern similar to a search target form, determining whether the field of view has a brightness (gradation) inappropriate for observation or search, efficiently searching for only an appropriate field of view, automatically adjusting electro-optical conditions of the transmission electron microscope apparatus when it is determined that the field of view is inappropriate for observation or search, searching the field of view for a form having the same pattern as the search target pattern, and measuring, displaying and storing the number of forms obtained by the search. Suppose that in the third embodiment, a triangular form shown in FIG. 10(A), for example, is set as a search target pattern and a field of view is automatically moved, whereby a field of view taken as shown in FIG. 10(B) is obtained. A form having the same pattern as the triangle chosen as a search target pattern is automatically recognized and marked, and also the number of search target forms in the field of view is outputted for display. At a step 31 in FIG. 9, a magnification is set to obtain a specimen transmission image. A magnification for a specimen transmission image is set, and lens currents that correspond to the magnification are outputted to the respective lens coils. At a step 32, a pattern (search target pattern) having the same shape as a search target form is set by using the keyboard 55 or the mouse 56. The search target pattern can be set by using conditions such as a range of angles between sides of the pattern, ellipticity, ratio in length between major and minor axes. The search target pattern may also be set by calling up a shape prestored in the storage unit. Setting of conditions for moving a field of view at a step 33, setting of origin of field movement at a step 34, moving the field of view at a step 35, stopping the movement of the field of view at a step 36, and picking up a magnified specimen transmission image at a step 37 are the same as in the steps 12 to 16 of FIG. 4, and therefore their repeated description will be omitted. At a step 38, whether or not the current field of view is appropriate for observation or search is determined. Whether or not the current field of view is appropriate for observation or search may be determined by using the line profile method, the phase only correlation method, or the phase-amplitude correlation method described above. When it is determined that the field of view is appropriate for observation, the processing proceeds to a step 40. When it is determined that the field of view is not appropriate for observation, the processing proceeds to a step 39. At the step 39, as in the step 27 in FIG. 8, factors that render the field of view inappropriate for observation are automatically examined, and then electro-optical conditions are adjusted. As described above, when it is determined as a result of a second image pickup that the current field of view is not appropriate for observation even though conditions of the check items are satisfied, the processing returns to the step 35 to search for the next field of view. On the other hand, when the current field of view satisfies the preset values and it is determined that the field of view is appropriate for image pickup as a result of adjustment, the processing proceeds to the step 40. At the step 40, a form 61 judged to be the same as the search target pattern set at the step 32 is extracted from the field of view judged to be appropriate for measurement or observation. At the next step 41, the microprocessor 46 determines the number of search target forms extracted from the field of view taken at the step 37, and stores a result of the determination or an image of the field of view in the storage unit 47, or analyzes or takes a photograph of the search target forms. Also, coordinates of the selected field of view are stored in the storage unit 47. A field of view where search target forms are detected is differentiated from a field of view where no search target forms are detected, for display on the display apparatus 50. For example, a field of view where search target forms are present is displayed in red, while a field of view where search target forms are not present is displayed in gray. FIG. 16 is a schematic diagram showing an example of display on the display apparatus 50. In this example, an operating state display section 81 and a field display section 82 displaying a magnified image of a current observing field of view are placed side by side on a display screen 80 of the display apparatus 50. The operating state display section 81 displays a schematic diagram 83 of the specimen holding mesh 6, and at the same time schematically displays positional relation of each observing field of view to the specimen holding mesh. Also, when the operating state display section 81 displays fields of view, fields of view where search target forms are present are differentiated from fields of view where no search target forms are present by using different colors, as described above. Returning to FIG. 9, finally whether the automatic search operation is repeated under the conditions for moving the field of view set at the steps 33 and 34 or whether the automatic search operation is ended is determined (step 42). When the automatic search operation is to be repeated, the processing returns to the step 35 to repeat the series of operations thus far described. The operations described above allow the electron microscope that automatically moves or selects a field of view to search for only a field of view appropriate for observation, automatically adjust electro-optical conditions for an inappropriate field of view having an insufficient brightness so that the field of view can be used for observation, and automatically search for search target forms. In addition, the electron microscope does not carry out a search on the mesh or in a section in which the specimen is broken, where it is obvious that the specimen cannot be seen in the field of view. According to the third embodiment, as in the previous embodiments, a search for target forms, which has been conventionally carried out by the operator after taking photographs, can be made instantly and simultaneously with image pickup. In addition, since only fields of view appropriate for observation are automatically extracted, it results in an improved efficiency as compared with a method that picks up images of the entire region of the specimen to search for target forms. Suppose that a specimen 2 mm in diameter is magnified to 100 mm in diameter at a transmission image magnification of 10000, photographs are taken of all fields of view on the specimen holding mesh, and the photographs taken are searched for target forms by manpower. Then, since it is necessary to pick up a total of 40000 images, the search requires about 670 hours, assuming that it takes one minute to search a single photograph for target forms. According to the third embodiment, it is possible to search for target structural forms by automatically extracting only the fields of view that can be used for observation of the specimen and therefore are not in sections where the specimen is broken or on the mesh. Since fields of view appropriate for observation constitute 1/20 of the entire region of the specimen and a current apparatus takes about one second to search a single field of view for target forms, the time required to search for forms is dramatically reduced. By adjusting electro-optical conditions, it is possible to minimize omission in search due to insufficient adjustment of electro-optical conditions and prevent human error, for example an error of not emitting the electron beam. Also, it is possible to control change in electro-optical conditions with time that might result from automatic observing operation over a long period of time, and to thereby keep observing conditions stable. In addition, since fields of view including target forms are clearly distinguished by using a different color and coordinates of the fields of view are stored in the storage unit, it is easy to observe or analyze the fields of view again after completion of the search operation. When observation is to be made again, a displayed field of view is selected, and on the basis of coordinates stored in association with the field of view, the specimen stage 13 is driven or the target field of view is moved by the electron beam deflector. Then, it is possible to obtain a magnified transmission image of a desired field of view instantly. FIG. 11 is a flowchart of a fourth embodiment showing a method comprising the steps of automatically moving or selecting a field of view, determining whether the current field of view is appropriate for observation or search, automatically correcting focus, and automatically searching for a form pattern having an arbitrary preset search target shape. In FIG. 11, setting of a magnification at a step 51, setting of a search target pattern at a step 52, setting of conditions for automatically moving a field of view at a step 53, setting of origin of field movement at a step 54, moving the field of view at a step 55, and stopping the movement of the field of view at a step 56 are the same as in the steps 31 to 36 of FIG. 9, and therefore their repeated description will be omitted. In steps 57 to 60, a correlation between two images is calculated by discrete Fourier transformation using only the phase components of the two images. First, at the step 57, a magnified specimen transmission image 59 obtained by the electron beam 73, which perpendicularly falls on the specimen along the electron beam optical axis 72, is projected on the scintillator 16 and then picked up by the TV camera 17. This transmission image is set to be a transmission image 1. At the next step 58, the two electron beam deflecting coils over the specimen provide the electron beam falling on the specimen with an arbitrary inclining deflection angle with respect to the electron beam optical axis. Then, a magnified specimen transmission image that is obtained by the inclined electron beam and in the same field of view as the transmission image 1 on the scintillator is picked up by the TV camera as a transmission image 2. At the step 60, an index of correlation (degree of coincidence) between the transmission image 1 and the transmission image 2 is obtained by discrete Fourier transformation using only the phase components of the two images. The principles of the calculation have been illustrated earlier by using Equations 1 to 7. On the basis of the correlation index calculated at the step 60, whether or not the current field of view has a brightness appropriate for search is determined at a step 61. After the result of the determination is obtained, the processing is branched off into four ways to be taken according to the value of the correlation index. (1) When the correlation index is zero, it is determined that the current field of view cannot be used for search or measurement, and the processing returns to the step 55 to search for another field of view. (2) When the correlation index is 100, it is determined that the current field of view is on the specimen holding mesh, or the specimen is not present in the field of view because of breakage of the specimen or the like and therefore a magnified specimen transmission image cannot be obtained properly. The processing returns to the step 55 to search for another field of view. (3) When the correlation index is more than a preset reference value and is not 100, it is determined that the current field of view is appropriate for measurement or search, and the processing proceeds to the next step 62. The reference value of the correlation index is preset as a threshold value necessary to satisfactorily perform automatic focus correction for a magnified specimen transmission image. The correlation index varies depending on the amount of displacement between the two transmission images, contrast between forms and background of the transmission images, S/N of the images and the like. The threshold value in the flowchart of FIG. 11 is set at five, which is a value obtained by experiment. At the step 62, automatic focus correction is made according to the method illustrated by Equations 8 to 12. After completion of the automatic focus correction, the processing proceeds to a step 63. (4) When the correlation index is less than the reference value and is not zero, it is determined that the current field of view is appropriate for measurement or search but exact automatic focus correction cannot be ensured. The processing proceeds to the step 63. At the step 63, the search target pattern having an arbitrary shape set at the step 52 is called up from the storage unit, and then the microprocessor makes a search to determine whether the desired form pattern is present in the current field of view. At the step 64, the number of forms judged to have the same form pattern as the search target pattern as a result of search is counted and the image is registered, displayed, or analyzed. Also, coordinates of the selected field of view are stored in the storage unit 47. A field of view where search target forms are detected is differentiated from a field of view where no search target forms are detected, for display on the display apparatus. For example, a field of view where search target forms are present is displayed in red, while a field of view where search target forms are not present is displayed in gray. Also, coordinates of each of the fields of view including search target forms are displayed on the display apparatus, and are at the same time stored in the storage unit. Finally, at a step 65, whether automatic field search is to be continued or not is determined. When search is to be made again, the processing returns to the step 55 to repeat the series of operations. When search is not to be made again, the processing is ended. As in the case of the third embodiment, the fourth embodiment allows the electron microscope automatically moving a field of view and searching for target structure to search for only a field of view appropriate for observation. According to a conventional automatic search method, it is not possible to separate fields of view appropriate for observation from fields of view inappropriate for observation. On the other hand, when a search for target structure is made in only the fields of view appropriate for observation, as in the fourth embodiment, the time required for the search is greatly reduced. In addition, lens focal length might be changed in each of the fields of view because of breakage or warping of the specimen, but since automatic focus correction is made when the field of view is moved, it is possible to prevent a decrease in pattern matching accuracy due to blurred images resulting from defocus. Moreover, when a search has been made once and a field of view including a target structure is to be observed again, it is possible to obtain a magnified transmission image in the target field of view instantly by selecting coordinates stored in the storage unit and thereby driving the specimen stage 13 or using the electron beam deflector. FIG. 12 is a flowchart of a fifth embodiment showing a method of increasing accuracy in automatic search and thereby improving reliability in the electron microscope that automatically moves or selects a field of view and automatically searches for a form matching a search target pattern of an arbitrary shape. In FIG. 12, setting of a magnification at a step 71, setting of a search target pattern at a step 72, setting of conditions for automatically moving a field of view at a step 73, setting of origin of field movement at a step 74, moving the field of view at a step 75, and stopping the movement of the field of view at a step 76 are the same as in the steps 31 to 36 of FIG. 9 or in the steps 51 to 56 of FIG. 11, and therefore their repeated description will be omitted. At a step 77, a magnified specimen transmission image 59 in a selected field of view projected on the scintillator 16 is taken by the TV camera 17. The taken transmission image is stored in the storage unit. In contrast measurement at a step 78, the taken image is called up from the storage unit, and then the microprocessor creates line profiles of signal intensity (brightness). Line profiles corresponding to a specimen transmission image are shown in FIGS. 13(1), 13(2), and 13(3). Ratio in signal intensity (brightness) between a background 65 and a form 61 in the specimen in the specimen transmission image (left side) of FIG. 13 is expressed as a contrast C. When a measuring line 74 is drawn so as to cross forms in the field of view and a signal intensity distribution on the measuring line is graphed, a line profile as shown on the right side of FIG. 13 is obtained (the axis of abscissas denotes picture elements [pixel] and the axis of ordinates denotes signal intensity (brightness) [arb.u]). When signal intensity of the background is set to be I0 and signal intensity of the form is set to be I1, the contrast C is defined by the following [Equation 22].C=I1/I0 [Equation 22] FIGS. 13(1), 13(2), and 13(3) show specimen transmission images obtained by changing the contrast experimentally, each of which includes a total of 34 search target forms. Numerals provided in the transmission images denote forms 75 that are judged to be the same as the search target pattern as a result of search. At a contrast C=1.1 in FIG. 13(1), no forms can be detected. At a contrast C=1.2 in FIG. 13(2), 25 of the 34 forms can be detected. At a contrast C=1.6 in FIG. 13(3), all of the 34 forms can be detected. Thus, the number of searchable forms varies depending on the contrast of the specimen transmission image. The numbers of forms detected are shown in Table 1. TABLE 1Contrast CNumber of particles detectedDetection accuracy (%)2.0341001.6341001.5341001.332941.225751.100 When percentage of the number of particles detected to the total number of forms of 34 is defined as detection accuracy, then detection accuracies for different contrasts are graphed as shown in FIG. 14. As is understood from FIG. 14, the detection accuracy increases as the contrast is enhanced. A difference between signal intensity of the form and noise in the background signal or statistical variation is small in a low-contrast image, and therefore the signal intensity of the form and noise in the background signal or statistical variation cannot be separated from each other, thus decreasing search accuracy. In order to increase the detection accuracy and thereby improve reliability in measurement, steps 78 to 80 are carried out. A relation between contrast and detection accuracy obtained on the basis of experimental results as shown in FIG. 14 is prestored in the ROM. At a step 79, whether a measured contrast allows detection accuracy to become 100 or not is determined. According to the flowchart of FIG. 12, C>1.4 is used as a reference in such determination. At the step 79, when C>1.4, it is determined that a detection accuracy of 100% can be ensured, and the processing proceeds to a step 81. When C≦1.4, it is determined that the detection accuracy is insufficient, and the processing proceeds to the step 80 to make contrast adjustment. At the step 80, electro-optical conditions are adjusted to enhance the contrast. The transmission electron microscope has the following four methods (1) to (4) for enhancing contrast: (1) to reduce the aperture of the movable objective diaphragm, (2) to provide an appropriate amount of defocusing, (3) to subject the taken image to image processing by the microprocessor, and (4) to decrease the accelerating voltage. The methods (1) and (2) will be described and detailed description of the methods (3) and (4) will be omitted here. The method (1) utilizes the principle that when the aperture of the movable objective diaphragm is reduced to prevent undesired scattering of the electron beam, an image of pure information on the specimen is formed, and thereby the contrast of the image is enhanced. The microprocessor 46 operates a movable diaphragm driving mechanism 31 connected to the movable objective diaphragm 15 via a driving mechanism driver 32 so as to make the aperture of the movable objective diaphragm 15 smaller for enhanced contrast. The method (2) utilizes the principle of Fresnel diffraction. The Fresnel diffraction produces a fringe (Fresnel fringe) in an electron microscope image when defocusing occurs. The Fresnel fringe enhances the contrast between the forms and the background. A method of moderately defocusing an image is commonly used as an electron microscope photographic technique. At the step 80, processing for improving the contrast is performed by to any one of the methods (1) to (4). For example, an appropriate amount of defocusing corresponding to the magnification is provided to enhance the contrast. After the contrast is adjusted at the step 80, the processing returns to the step 77 to determine whether a proper contrast is obtained or not again. When it is determined at the step 79 that a proper contrast is obtained, the transmission image in the field of view is searched for a form pattern that matches the search target pattern preset at the step 72. At the next step 82, the number of forms judged to have the same form pattern as the search target pattern is counted and the image is registered, displayed, or analyzed. Also, coordinates of the selected field of view are stored in the storage unit 47. Finally, at a step 83, whether automatic field search is to be continued or not is determined. When search operation is to be performed again, the processing returns to the step 75 to repeat the series of operations. When search is not to be made again, the processing is ended. Accuracy in pattern matching search, in which the electron microscope automatically moving or selecting a field of view searches for fields of view including a target structural pattern, depends on the contrast of a magnified specimen transmission image, as described with reference to FIGS. 13(1), 13(2), and 13(3). By measuring and automatically adjusting the contrast of a transmission image, as in the fifth embodiment, it is possible to increase accuracy in search for a target structure. Because of nonuniformity in staining during specimen preparation, the contrast of all fields of view of even the same specimen is not necessarily constant. Thus, by measuring and automatically adjusting the contrast of each field of view, it is possible to increase search accuracy. FIG. 15 is a flowchart of a sixth embodiment showing a method for the electron microscope that automatically moves or selects a field of view and automatically searches for a form matching a search target pattern of an arbitrary shape, the method including the steps of making automatic focus correction and automatic contrast adjustment of a specimen transmission image, and thereby searching for desired forms with high accuracy and high detection efficiency. An image computation of the sixth embodiment employs an arithmetic method for obtaining a phase-component-only phase-amplitude correlation from discrete Fourier transformation of transmission images. In FIG. 15, operations from a step 91 to a step 96 are the same as those in the steps 31 to 36 shown in FIG. 9, and therefore their detailed description will be omitted. At steps 97 to 101, the same operations as in the steps 57 to 61 of FIG. 11 are performed. At the step 97, a magnified specimen transmission image obtained by the electron beam, which perpendicularly falls on the specimen along the electron beam optical axis, is picked up and recorded as a transmission image 1. At the step 98, the two electron beam deflecting coils over the specimen provide the electron beam falling on the specimen with a certain inclining deflection angle with respect to the electron beam optical axis. Then, a magnified specimen transmission image that is obtained by the deflected electron beam and in the same field of view as the transmission image 1 is picked up and recorded as a transmission image 2. At the step 100, an index of correlation (degree of coincidence) between the transmission image 1 and the transmission image 2 is obtained by discrete Fourier transformation using only the phase components of the two images. The principles of the calculation have been illustrated earlier by using Equations 1 to 7. By using the arithmetic result obtained at the step 100, whether or not the current field of view is appropriate for search is determined at a step 101. After the result of the determination is obtained, the processing is branched off into three ways to be taken according to the value of the correlation index. (1) When the correlation index is zero or does not satisfy an equation of a predetermined threshold value, the processing proceeds to a step 102. In the sixth embodiment, the threshold value is set at five, which is a value obtained by experiment. (2) When the correlation index is 100, it is determined that either the current field of view is on the specimen holding mesh or the specimen is not present in the field of view because of breakage of the specimen or the like. The processing returns to the step 95 to search for another field of view. (3) When the correlation index is more than the arbitrarily set threshold voltage and is not 100, the processing proceeds to a step 104. At the step 102, factors that cause the field of view to be judged inappropriate for observation are automatically examined to adjust electro-optical conditions. As in the step 27 in the flowchart of FIG. 8 described in the second embodiment, the following items are examined and adjusted: (1) emission of the electron beam, (2) lens conditions of the irradiation lenses, (3) electron beam current, and (4) the aperture or the aperture position of the movable objective diaphragm. Then, at a step 103, transmission images are picked up, and a degree of coincidence between the images is calculated from the phase components of the discrete Fourier images, as in the steps 97 to 100. At the step 103, when the degree of coincidence is zero, it is determined that the field of view is not appropriate for observation, and the processing returns to the step 95. When the degree of coincidence is not zero, it is determined that the field of view can be used for observation, and the processing proceeds to the step 104. At the step 104, current of the objective lens or height of the specimen stage is adjusted by using a result of a positional displacement calculation performed in the image computation to thereby effect automatic focus correction. At a step 105, a magnified specimen transmission image 59 projected on the scintillator 16 is picked up as a transmission image 3 by the TV camera 17, and stored in the storage unit 47. The focus of the transmission image 3 is corrected and therefore the specimen transmission image is in focus. As described with reference to FIGS. 13(1), 13(2), and 13(3) and FIG. 14, accuracy in automatic search for forms is decreased unless a sufficient contrast of a magnified specimen transmission image is ensured. Therefore, in steps 106 to 108, the transmission image 3 taken at the step 105 is measured to determine whether the transmission image 3 has a contrast sufficient to obtain a satisfactory search accuracy, and accordingly the contrast is automatically adjusted. At the step 106, the transmission image 3 is called up from the storage unit, and then the microprocessor 46 creates a line profile of signal intensity (brightness). The contrast of the transmission image is calculated from the line profile. Then, whether or not the contrast allows detection accuracy to become 100 is determined by using the relation between contrast and detection accuracy in FIG. 14 obtained on the basis of experimental results and prestored in the ROM 58. Since the detection accuracy reaches 100 at a contrast of 1.4 or higher, a threshold value of determination is set at 1.4 in the sixth embodiment. At the step 107, when the contrast is 1.4 or higher, the processing proceeds to a step 109. On the other hand, when the contrast is below 1.4, the processing proceeds to the step 108. At the step 108, as in the step 80 of FIG. 12, the contrast is adjusted. The four methods for enhancing the contrast are as follows: (1) to reduce the aperture of the movable objective diaphragm, (2) to provide an appropriate amount of defocusing, (3) to subject the taken image to image processing by the microprocessor, and (4) to decrease the accelerating voltage. In this case, an appropriate amount of defocusing corresponding to the observing magnification is provided to the in-focus image obtained by automatic focus correction at the step 104 to thereby enhance the contrast of the image. At the step 108, defocusing data preset so as to correspond to observing magnifications and stored in the ROM 58 is called up, lens data to be supplied to the objective lens coil 4 is outputted to the DAC 37, and then an analog signal is supplied to the lens exciting power supply 20 to thereby output lens current. After an appropriate amount of defocusing is provided at the step 108, the processing returns to the step 105, where a magnified specimen transmission image having an enhanced contrast is picked up and stored in the storage unit. When it is determined that the contrast in signal intensity between the background and the form of the transmission image 3 is 1.4 or higher, the processing proceeds to the step 109 to automatically search the field of view for a form having a pattern that matches the search target pattern set at the step 92. The search target pattern is called up from the storage unit, and then the microprocessor searches the field of view for a form having the same pattern as the search target pattern. Forms judged to have the same pattern as the search target pattern are marked, the number of such forms is counted, and the transmission image is registered in the storage unit and displayed on the display apparatus. The search target forms are subjected to composition analysis as required (step 110). Also, coordinates of the selected field of view are stored in the storage unit 47. Finally, at a step 111, whether automatic field search is to be continued or not is determined. When search operation is to be performed again to search for the next field of view, the processing returns to the step 95 to repeat the series of flow processes from the step 95 down. When the search is not to be made again, the processing is ended. The electron microscope automatically moving or selecting a field of view takes several hours or more to search a single specimen for a target structure, depending on the observing magnification of the electron microscope. If the search operation is performed for the several hours unattended, there is a possibility that the magnified transmission image may lose a sufficient brightness because of ending life of the filament of the electron gun or an abnormal current, for example. Also, the unattended and high-speed search operation makes it impossible to make adjustments by intervention of the operator during the automatic search operation. The sixth embodiment incorporates and combines all the features of the first to fifth embodiments. A conventional electron microscope automatically moving or selecting a field of view takes photographs of fields of view on the mesh or in a section in which the specimen is broken, where obviously no structure is present, to search for a target structure pattern. On the other hand, the electron microscope of the sixth embodiment skips search for a structure pattern in fields of view where no structure should be present or observation is not possible, thereby making it possible to complete the search operation in about 1/20 of the search time of the conventional electron microscope. In addition, it is possible to automatically adjust electro-optical conditions that are changed with time by repeated search operations over a long time. With the electron microscope of the sixth embodiment automatically searching a field of view, it is possible to automatically correct objective lens focal length changed by breakage or warping of part of the specimen, and to automatically correct contrast changed by nonuniformity in specimen staining. Thus, it is possible to search for target structures with high accuracy and high efficiency. Furthermore, coordinates and an image where a target structure is present are recorded and stored in the storage unit, and therefore when the magnified specimen transmission image is to be observed, taken, or analyzed again after specimen search operation, it is possible to obtain instant access to the target specimen position. Hence, specimen search operation using an electron microscope, which has conventionally been complex and required considerable labor and time of the operator, can be performed automatically with high accuracy and in a short time. Accordingly, the present invention provides a method of observing a specimen in a field of view of an electron microscope comprising the acts of illuminating the specimen with an electron beam having a first angle and forming a first transmission image of the specimen in the field of view and adjusting the electron beam to a second angle and forming a second transmission image of the specimen in the field of view and calculating a degree of coincidence between the first and second transmission images. Although the invention has been described above in connection with exemplary embodiments, it is apparent that many modifications and substitutions can be made without departing from the spirit or scope of the invention. Accordingly, the invention is not to be considered as limited by the foregoing description, but is only limited by the scope of the appended claims. |
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045267138 | summary | The present invention relates to a process and system for treatment of radioactive waste, and more particularly to a process and system for treatment of radioactive waste which employ a thin film evaporator for drying the waste liquid into powder. Various radioactive wastes are generated from radioactive material handling facilities such as nuclear power plant. For example in a boiling water type nuclear reactor plant, radioactive waste liquid is produced as a result of regeneration of ion exchange resin, which is mainly composed of sodium sulfate. In order to reduce the volume of the resultant radioactive waste liquid, the waste liquid is concentrated about 20 weight percent, and thereafter is made into powder by a thin film evaporator. In the thin film evaporator, the waste liquid evaporates on a heat transfer surface and powders are obtained by wiping thin films formed on the heat transfer surface. The film evaporator is advantageous for obtaining higher heat transfer coefficient because no scale of thin film remains on the heat transfer surface, which is formed on the heat transfer surface and acts as heat transfer resistance. However, as wiper blades which wipe thin film are rotating while acting forces on the heat transfer surface, the tip portions of the wiper blades wear so quickly as to cause reduction of heat transfer coefficient due to insufficient wiping effect. As a result, worn out wiper blades are frequently exchanged for new ones, however, frequent exchanges of the blades cause reduction of operating rate of the film evaporator. An object of the present invention is to provide an improved process and system for treatment of radioactive waste, which employs a thin film evaporator with an improved operating condition. According to one feature of the present invention, radioactive substances dissolved in a waste liquid is separated as powder by a thin film evaporator having wiping blades. Optimum operating condition of the evaporator is obtained by controlling rotational speed of the wiping blades and quantity of the radioactive substances treated in the evaporator. By operating the evaporator at the optimum operating conditions, worn out of the wiper blades and over load of waste liquid on the evaporator are advantageously eliminated. According to a preferred embodiment of the present invention, the rotational speed of the wiping blades is controlled in accordance with evaporation characteristics between the rotational speed and radioactive substances to be powderized. According to another embodiment of the present invention, the rotational speed of the wiping blades is fixed at a predetermined value and flow rate of the waste liquid and the concentration of the radioactive substances are controlled to obtain an optimum operation condition. |
abstract | Microstructured nuclear fuel adapted for nuclear power system use includes fissile material structures of micrometer-scale dimension dispersed in a matrix material. In one method of production, fissile material particles are processed in a chemical vapor deposition (CVD) fluidized-bed reactor including a gas inlet for providing controlled gas flow into a particle coating chamber, a lower bed hot zone region to contain powder, and an upper bed region to enable powder expansion. At least one pneumatic or electric vibrator is operationally coupled to the particle coating chamber for causing vibration of the particle coater to promote uniform powder coating within the particle coater during fuel processing. An exhaust associated with the particle coating chamber and can provide a port for placement and removal of particles and powder. During use of the fuel in a nuclear power reactor, fission products escape from the fissile material structures and come to rest in the matrix material. After a period of use in a nuclear power reactor and subsequent cooling, separation of the fissile material from the matrix containing the embedded fission products will provide an efficient partitioning of the bulk of the fissile material from the fission products. The fissile material can be reused by incorporating it into new microstructured fuel. The fission products and matrix material can be incorporated into a waste form for disposal or processed to separate valuable components from the fission products mixture. |
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044709528 | description | BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 illustrates a reactor pressure vessel 10. The head of the vessel is removed revealing its interior wall surface 11 and an open upper edge surrounded by a flange 12. Threaded studs 14 for securing the head extend upwardly from the flange 12. Many of the studs 14 are omitted for ease of illustration. Mounted at diametrically opposed locations within the vessel 10 and closely adjacent to its inner wall are a pair of vertical guide rods 16a, b mouted on the inner wall by guide rod brackets 17a, b. Normally these rods are employed for positioning components as they are lowered into the reactor vessel 10. As shown in FIGS. 1 and 2, a buoyant annular frame comprised of a curved channel iron 18 having top and bottom flanges A and B has a plurality of floats 24 connected to it by float brackets 23. A crane (not shown) lowers the frame 18 into the reactor pressure vessel 10 by means of a support cable 20 connected to a lifting lug 13 secured to a plurality of lifting legs 21 by lifting leg yoke 22. The lifting legs 21 are coupled to the curved channel iron 18 by brackets 19. A pair of trolleys 26a and 26b are movably mounted on the curved channel iron 18 and carry nozzle manifolds 27 bearing a plurality of nozzles 28 for directing water under high pressure at the interior wall surface 11. Water under pressure is conducted from a remote source to the nozzle manifolds 27 by water supply line manifold 15 and water supply lines 36. As best shown in FIG. 4, a reversible air motor 30 is mounted atop an air motor bracket 31 which is affixed to one of the floats 24 which float upon the water W in the vessel. Compressed air is conveyed to the air motor 30 by an air supply line 38 and via an air valve 34, a pair of air valve connection lines 42a, b and intake ports 62a, b. Spent air is exhausted from the motor 30 through exhaust line 40. A flexible coupling 33 extends from the air motor 30 to a grooved drum 32 which is situated between the top surface A and the lower surface B of the curved channel iron 18. Guide plates 44a, b (FIGS. 1 and 4) connected to curved channel iron 18 extend radially outward from the curved channel iron and engage vertical guide rods 16a, b mounted on the interior wall of the vessel by brackets 17. FIG. 3 further illustrates the support cable 20 which passes through the eye of lifting lug 13. The lifting lug 13 is coupled to yoke 22 which bears the water supply line manifold 15. The manifold 15 is connected to the water supply lines 36 by quick disconnect couplings 54 for ease of assembly and disassembly. FIG. 3 also shows first drive cable 39 which passes around a portion of the circumference of the curved channel iron 18 and runs on cable guide rollers 25. Each end of first drive cable 39 terminates with a cable coupler 43 (FIG. 7) which is fixed to a different one of the trolleys 26a, b. As is best viewed in FIG. 7, at least one of the ends of first drive cable 39 is connected to its trolley by a cable tensioning spring 29. A central portion of first drive cable 39 is wound around the grooved drum 32. A second drive cable 60 runs on the same guide rollers 25 and extends half way around the curved channel iron 18 but connects those ends of the trolleys 26a, b not linked to first drive cable 39. The views provided by FIGS. 4 and 9 reveal the details of air valve 34. It is a three-way valve controlled by a vertically movable plunger 56 extending through it having an upper plunger roller 35 and a lower plunger roller 37 at its ends. FIG. 6 shows an enlarged view of the means of connection between curved channel iron 18, lifting leg bracket 19, and lifting leg 21. Also shown is one of the cable guide rollers 25 which is situated on the exterior cylindrical wall E of the curved channel iron 18. The guide rollers 25 span the vertical dimension of the curved channel iron 18, extending between its top flange A and its bottom flange B. FIGS. 7 and 8 illustrate the decontamination means including trolley 26a having arms 45 and rollers 47 connected to trolley 26a by guide roller bracket 52. Spray nozzle manifold 27 is mounted upon the trolley 26a by manifold spacer 41. Water supply line 36 is coupled to spray nozzle manifold 27 by manifold coupling 48. Returning now to FIG. 9, valve actuator 46a is shown mounted on trolley 26a and positioned to engage the rollers 35 and 37 of air valve plunger 56. FIG. 9 depicts the action of valve actuators 46a and b on the air valve plunger 56. Each valve actuator 46a, b has at its end a roller pusher 58a, b capable of depressing the plunger 56 toward the air valve 34 when one of the moving trolleys 26a, b brings its valve actuator 46a, b into contact with plunger roller 35 or 37 on the plunger 56. The pair of trolleys 26a, b distinguished in FIG. 9 as trolleys 26a and 26b, are shown as having their valve actuators 46a, b mounted in different parallel planes. Roller pusher 58a is positioned to engage upper plunger roller 35, while roller pusher 58b is connected to its trolley 26b such that it will engage lower plunger roller 37. When it is desired to decontaminate the nuclear reactor pressure vessel, the apparatus of this invention is lowered into position by the main crane using support cable 20. The apparatus is positioned such that guide plates 44a and 44b engage vertical guide rods 16a and 16b to prevent rotation of the curved channel iron 18 about its vertical axis. Water supply line 36 is connected to a source of high pressure water which may have, for example, a capacity of 10 to 25 gallons per minute at a pressure of 5,000 to 10,000 psi. A source of compressed air is also connected to air supply line 38. When compressed air is caused to pass through line 38, air motor 30 rotates grooved drum 32 and first drive cable 39, which is kept taut by a cable tensioning spring 29, is moved around the curved channel iron 18 pulling both trolleys 26a, b about the frame on their rollers 47 in the same direction. As the trolleys 26a, b run on the curved channel iron 18, water is ejected from the nozzles 28 which washes down the interior surface 11 of the vessel. The travel of the trolleys 26a, b is controlled by air valve 34 and valve actuators 46a, b. When either trolley 26a, b reaches air valve 34, its valve actuator 46a, b engages a plunger roller 35 or 37 on plunger 56. The depression (or raising) of the plunger 56, caused by sliding action of either of the roller pushers 58a or b over rollers 35 or 37, alters the flow of compressed air through the valve 34 and, in turn, reverses the direction of rotation of the air motor 30 by alternating the supply of compressed air between lines 42a and 42b. Air motor 30 is reversible, such that the introduction of compressed air into one port, 62a, results in clockwise rotation and introduction of compressed air into the other, 62b, produces a torque in the opposite direction. The trolleys 26a, b therefore run on the curved channel iron 18 in a reciprocating fashion, each travelling approximately one half the pressure vessel circumference until its valve actuator 46a, b engages a plunger roller 35 or 37 on plunger 56 of the air valve 34 and reverses the travel of the trolleys 26a, b attached to it. The trolleys then continue back half-way around the curved channel iron 18 until the other trolley's actuator 46a, b engages the air valve plunger roller 35 or 37 on plunger 56 and the cycle repeats. As the trolleys continue to oscillate, the reactor vessel is drained. As the level of water W drops, it carries the decontamination apparatus with it. A limit switch (not shown) may be employed to stop the air motor 30 when the curved channel iron 18 approaches the core shroud. Since high pressure water is expelled from identical sets of nozzles 28 situated at opposite sides of the curved channel iron, adverse reaction effects are canceled, thereby permitting the apparatus to be of relatively lightweight construction. By means of this apparatus, a reactor pressure vessel may be decontaminated in approximately 1-2 hours as compared with a time of up to 8 hours using conventional washdown procedures. Furthermore, the decontamination is effected uniformly over the internal surface of the vessel from the flange to the top of the core shroud without subjecting a workman to physical stress and a hazardous radioactive environment. It is believed that the many advantages of this invention will now be apparent to those skilled in the art. It will also be apparent that a number of variations and modifications may be made in this invention without departing from its spirit and scope. In this application, the term "annular frame" is used to connote any ring-like configuration which substantially forms a closed loop with an opening in the center. The present invention, although depicted in FIG. 1 as having a circular frame, is therefore not limited to this preferred embodiment. A frame comprised of four straight members forming a rectangle, for example, would therefore fall within this broad concept of an annular frame. Accordingly, the foregoing description is to be construed as illustrative only, rather than limiting. This invention is limited only by the scope of the following |
description | This application claims priority to U.S. Application No. 61/718,215 filed Oct. 25, 2012, the contents of which are incorporated by reference herein. This invention relates to a composition and process for processing radioactive waste materials to render them suitable for shipment and/or storage. Radioactive waste materials, especially those resulting from the processing of uranium and plutonium, are particularly dangerous to transport to sites for final disposition, such as long-term storage or further processing. Such waste encompasses a wide range of material, and may include piping, building materials, machinery and equipment, furniture, weapons casings and the like. Radioactive waste, especially from the processing of uranium and plutonium, is usually buried for its final disposition. The current state of technology includes the steps of filling all of the interstitial spaces in the radioactive material with cement, and then micro-encapsulating the material with more cement. There are several shortcomings to this method. First, the resultant encapsulating material is very heavy. Cement has a typical density about 120 lbs/ft3, so it would not be unusual to have a large piece of contaminated equipment weigh in excess of 100,000 lbs. This necessitates the use of expensive, heavy equipment to move these structures. Second, the pouring of cement in situ over the encapsulated material (i.e. in the landfill) is an extraordinarily inefficient use of space. A large amount of cement is spilled over the sides of the material due to the inexact nature of pouring cement. This causes much more landfill space to be used than would be the case with a more focused process. Third, cement is well known to crack when exposed to tensile stress, temperature extremes, or when non-optimal water/cement ratios are used. When cracking in these monolithic structures occurs, there is a greater risk that radioactive waste will migrate from the structure into an uncontrolled environment. The use of polyurethanes for the purpose of encapsulation of radioactive materials is known in the prior art. The known prior art describes the use of one of several types of cement/mortar, sand, filler, or other additives to the polyurethane to either create a high density monolithic block, or as an aid for radiation attenuation. The novelty of the present invention resides in the lack of solid fillers or cement/mortar, as well as the optional inclusion of an elastomeric coating to encapsulate and protect the radioactive material from possible damage in transport. UK Patent No. GB2047946 to Pordes et al. discloses the encapsulation of radioactive waste material, particularly wet ion exchange resin, by dispersing the waste in an aqueous emulsion of an organic polyol, a polyisocyanate and an hydraulic cement, and allowing the emulsion to react and form a monolithic block. U.S. Pat. No. 7,250,119 to Sayala discloses the use of naturally occurring minerals in synergistic combination with formulated modified cement grout matrix, polymer modified asphaltene and maltene grout matrix, and polymer modified polyurethane foam grout matrix to provide a neutron and gamma radiation shielding product. U.S. Pat. No. 4,100,860 to Gablin et al. discloses a shipping container overpack for transportation of radioactive materials, and includes a leakproof receptacle for containing and protecting the material against accidental release. The receptacle has spaced inner and outer shells into which polyurethane foam is poured to create a stress skin structure. U.S. Pat. No. 4,486,512 to Tozawa et al. discloses a waste sealing container constructed by depositing a foundation of zinc over a steel base, then coating an organic synthetic resin paint containing a metal phosphate over the foundation coating, and thereafter coating an acryl resin, epoxy resin, and/or polyurethane paint. The above-described processes and resulting structures retain many of the disadvantages of the prior art, and thus a more cost-effective, efficient and safe means of processing radioactive waste for shipping and storage is needed. Therefore, it is an object of the invention to provide encapsulation materials and methods for application in the field of radioactive materials that do not require a cementitious material or grout as a constituent part of the material. It is another object of the invention to provide a mechanism for safe transport of radioactive materials with far less weight (approximately 1/20th the weight of cement) and occupying far less space in its burial site. It is another object of the invention to provide encapsulation materials and methods for application in the field of radioactive material that provides superior tensile strength and elongation that will resist cracking for long periods of time, unlike cementitious materials, which are subject to deterioration over time. The present invention includes the use of a foaming plastic, optionally covered with an elastomeric coating, for the purpose of encapsulating radioactive material that may or may not have been coated with a primer to render it attenuated and properly encased for safe transport while mitigating the risk of radioactive materials escaping. These and other objects of the invention are achieved by providing process for encapsulating a radioactive object to render the object suitable for shipment and/or storage, and including the steps of preparing a plastic material, causing the plastic material to react with a foaming agent, generating a foaming plastic, encapsulating the radioactive object in the foaming plastic, and allowing the foaming plastic to solidify around the radioactive object to form an impervious coating. According to one aspect of the invention, the step of encapsulating the radioactive object includes the steps of filling a void in the object with the foaming plastic and encasing the object in an outer layer of foaming plastic. According to another aspect of the invention, the step of encapsulating the radioactive object includes the step of placing the object in a bag before encasing the object in an outer layer of foaming plastic. According to another aspect of the invention, the step of encapsulating the radioactive object includes the step of applying an outer layer of an elastomeric coating to the object. According to another aspect of the invention, a process for encapsulating a radioactive object to render the object suitable for shipment and/or storage is provided, and includes the steps of preparing a plastic material, causing the plastic material to react with a foaming agent, generating a foaming plastic, placing a radioactive object in a container, encapsulating the container in the foaming plastic, and allowing the foaming plastic to solidify around the container to form an impervious coating. According to another aspect of the invention, the method includes the steps of evacuating displaced air from the container as the container is encapsulated and transferring the air to another treatment location. According to another aspect of the invention, a method of encapsulating a radioactive object to render the object suitable for shipment and/or storage includes the steps of preparing a plastic material, causing the plastic material to react with a foaming agent, generating a foaming plastic, and encapsulating the object in the foaming plastic. The step of encapsulating the object in the foaming plastic includes the steps selected from the group consisting of placing a radioactive object in a container, encapsulating the container in the foaming plastic, and allowing the foaming plastic to solidify around the container to form an impervious coating; and encapsulating the radioactive object in the foaming plastic, allowing the foaming plastic to solidify around the radioactive object to form an impervious coating. According to another aspect of the invention, the step of encapsulating the radioactive object includes the steps of filling a void in the object with the foaming plastic and encasing the object in an outer layer of foaming plastic. According to another aspect of the invention, various formulations are disclosed having various physical characteristics suitable for encapsulating objects in a foaming plastic in preparation for shipment and storage. Referring now specifically to the drawings, FIG. 1 is a flow diagram showing by way of example an iteration of the method steps that may be used to carry out the method according to one preferred embodiment of the invention. First, candidate objects are examined to determine the appropriateness for treating with foaming plastic in downstream steps. Some objects may be incinerated or processed by different methods. Those objects, such as described above, selected for processing are prepared based on the type and physical characteristics of the object. For example, objects such as piping may first be cleaned and loose material, particularly in the interior of the pipe, either removed or primed onto the surface. The selection and preparation steps will determine the particular process to be used in the next steps. As shown in FIG. 1, large objects, such as machinery, barrels, and the like may be placed in a container, and then encapsulated by filling the container with foaming plastic. Other materials, such a piping, may be first injected with foam, then the exterior encapsulated with foaming plastic. The foaming plastic expands into interstitial cracks, fractures and surface irregularities. This effectively fixes the radioactive material in place in or on the object and protects it from later contact or removal. Whether or not the object is encased with an outer layer of foam plastic, the object may then optionally be placed in a bag to further protect against eventual leakage. Once completely encapsulated according to the selected method steps, the object is ready to be shipped to a burial site for burial. Referring now to FIG. 2, a typical object that may be radioactively contaminated, a length of pipe 10, is processed by priming or otherwise stabilizing the interior surface, then forming holes 12 in the pipe 10. The method is advantageous when dealing with long lengths of pipe, hose or other elongate object where, due to the length of the object, it may be impractical to inject foaming plastic into the object through or adjacent one end. Plastic is foamed in a foam generator 14 and conveyed through a hose 16 to the holes 12, and foam “F” is injected into the holes 12 successively from one end of the pipe 10 to the other. A temporary or permanent cap 20 may be placed over the ends of the pipe 10 as shown to prevent foam from exiting the pipe 10 through its ends. After injection of the foam in complete, the holes 12 are plugged or capped. FIGS. 3 and 4 illustrate that once the pipe 10 has been filled with foam “F” as shown in FIG. 2, the exterior of the pipe 10 may optionally be coated with a layer 22 of foam “F”. Referring to FIG. 5, an object, for example, a length of I-beam 30 is first sealed in a heavy plastic bag 32. Then, foam “F” is used to completely encapsulate the bagged I-beam 30. Optionally, an elastomeric coating 34 may be placed over the foam “F”. The elastomeric coating 34 will provide greater resistance to tensile and tear stress, damage during transport, and cracking. Referring now to FIGS. 6 and 7, a method for encapsulating large, bulky objects is explained. By way of example, barrels 40, which may themselves be contaminated and/or containing radioactively-contaminated waste, liquid or solid, are placed on pallets 42 and fastened in a suitable manner, as by straps 44. One or more pallets 42 and barrels 40 are then placed in a container 46, for example, as shown in FIG. 7, and then the entire container 46 is filled with foam “F” by injecting it from the foam generator 14 through hose 16. In some instances it will be necessary to provide an outlet 48 to permit contaminated air displaced by the introduction of the foam “F” to be removed to another location 50 for treatment. After the container 46 is filled, it is shipped to a suitable location for burial. More generally, a foaming plastic such as the foam “F” can be used to encapsulate primed or unprimed radioactive waste, thus containing and immobilizing the waste, making it safe to transport to a landfill. The foaming plastic can be poured, sprayed, or otherwise dispensed in and around the contaminant, allowing the foam to rise and fill the interstitial spaces. The foam can also be dispensed over already encapsulated objects that may or may not be primed to render it completely macro-encapsulated and attenuated for further transport. The foam can be injected into pipes, ductwork, or other contaminated spaces where it will fill the voids and immobilize any radioactive materials. The methods of forming a foam generally include providing a blowing agent composition of the present disclosure, adding (directly or indirectly) the blowing agent composition to a foamable composition, and reacting the foamable composition under the conditions effective to form a foam or cellular structure. Any of the methods well known in the art, such as those described in “Polyurethanes Chemistry and Technology,” Volumes I and II, Saunders and Frisch, 1962, John Wiley and Sons, New York, N.Y., which is incorporated herein by reference, may be used or adapted for use in accordance with the foam embodiments. Polyisocyanate-based foams are prepared, e.g., by reacting at least one organic polyisocyanate with at least one active hydrogen-containing compound in the presence of the blowing agent composition described in this application. An isocyanate reactive composition can be prepared by blending at least one active hydrogen-containing compound with the blowing agent composition. According to preferred embodiments of the invention, the blend contains at least 1 and up to 50, preferably up to 25 weight percent of the blowing agent composition, based on the total weight of active hydrogen-containing compound and blowing agent composition. Active hydrogen-containing compounds include those materials having two or more groups which contain an active hydrogen atom which reacts with an isocyanate. Preferred among such compounds are materials having at least two hydroxyl, primary or secondary amine, carboxylic acid, or thiol groups per molecule. Polyols, i.e., compounds having at least two hydroxyl groups per molecule, are especially preferred due to their desirable reactivity with polyisocyanates. Additional examples of suitable active hydrogen containing compounds can be found in U.S. Pat. No. 6,590,005. For example, suitable polyester polyols include those prepared by reacting a carboxylic acid and/or a derivative thereof or a polycarboxylic anhydride with a polyhydric alcohol. The polycarboxylic acids may be any of the known aliphatic, cycloaliphatic, aromatic, and/or heterocyclic polycarboxylic acids and may be substituted, (e.g., with halogen atoms) and/or unsaturated. Examples of suitable polycarboxylic acids and anhydrides include oxalic acid, malonic acid, glutaric acid, pimelic acid, succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, trimellitic acid anhydride, pyromellitic dianhydride, phthalic acid anhydride, tetrahydrophthalic acid anhydride, hexahydrophthalic acid anhydride, endomethylene tetrahydrophthalic acid anhydride, glutaric acid anhydride acid, maleic acid, maleic acid anhydride, fumaric acid, and dimeric and trimeric fatty acids, such as those of oleic acid which may be in admixture with monomeric fatty acids. Simple esters of polycarboxylic acids may also be used such as terephthalic acid dimethylester, terephthalic acid bisglycol and extracts thereof. The polyhydric alcohols suitable for the preparation of polyester polyols may be aliphatic, cycloaliphatic, aromatic, and/or heterocyclic. The polyhydric alcohols optionally may include substituents which are inert in the reaction, for example, chlorine and bromine substituents, and/or may be unsaturated. Suitable amino alcohols, such as monoethanolamine, diethanolamine or the like may also be used. Examples of suitable polyhydric alcohols include ethylene glycol, propylene glycol, polyoxyalkylene glycols (such as diethylene glycol, polyethylene glycol, dipropylene glycol and polypropylene glycol), glycerol and trimethylolpropane. Suitable additional isocyanate-reactive materials include polyether polyols, polyester polyols, polyhydroxy-terminated acetal resins, hydroxyl-terminated amines and polyamines, and the like. These additional isocyanate-reactive materials include hydrogen terminated polythioethers, polyamides, polyester amides, polycarbonates, polyacetals, polyolefins, polysiloxanes, and polymer polyols. Other polyols include alkylene oxide derivatives of Mannich condensates, and aminoalkylpiperazine-initiated polyethers as described in U.S. Pat. Nos. 4,704,410 and 4,704,411. The low hydroxyl number, high equivalent weight alkylene oxide adducts of carbohydrate initiators such as sucrose and sorbitol may also be used. In the process of making a polyisocyanate-based foam, the polyol(s), polyisocyanate and other components are contacted, thoroughly mixed and permitted to expand and cure into a cellular polymer. The particular mixing apparatus is not critical, and various types of mixing head and spray apparatus may be used. It is often suitable, but not necessary, to preblend certain of the raw materials prior to reacting the polyisocyanate and active hydrogen-containing components. For example, it is often useful to blend the polyol(s), blowing agent, surfactant(s), catalyst(s) and other components except for polyisocyanates, and then contact this mixture with the polyisocyanate. Alternatively, all the components may be introduced individually to the mixing zone where the polyisocyanate and polyol(s) are contacted. It is also possible to pre-react all or a portion of the polyol(s) with the polyisocyanate to form a prepolymer. The invention is further described according to the several examples set out below: A rigid polyurethane foam with the following composition and physical properties was produced by dispensing through high pressure impingement mix equipment. INGREDIENT%Polyol blend34.78Crosslinkers1.45Water0.48Fire retardant3.60Viscosity suppressant1.09Surfactants0.72Catalysts0.14Blowing agent6.04Polymeric Isocyanate51.70TOTAL100.00 Free Rise Core Density: 2.4 lbs/ft3 Molded Core Density: 2.8 lbs/ft3 Compressive Strength: 37 lbs/in2 UL Bulletin 94: Passes HBF Mil-PRF-26514GMeets Type 1, Class 1Mil-PRF-83671BMeets Class 1, Category 1 The foam was dispensed into pipes ranging in diameter from 2 inches to 8 inches. The foam completely filled the pipe, rendering the radioactive material encapsulated. The piping could then be safely cut into sections without the risk of releasing radioactive materials, and safely transported to a designated site for burial. A rigid polyurethane foam with the following composition and physical properties was produced by dispensing through high pressure impingement mix equipment: INGREDIENT%Polyol blend34.45Crosslinkers3.83Water0.05Fire retardant3.83Viscosity suppressant1.41Surfactants0.72Catalysts0.12Blowing agent3.44Polymeric Isocyanate52.15TOTAL100.00 Free Rise Core Density: 6.3 lbs/ft3 Compressive Strength: 135 lbs/in2 UL Bulletin 94: Passes HBF The foam was pumped into large cylindrical spaces up to 40 inches diameter and 40 inches high for encapsulation of uranium converters. It allowed the converters, which comprise hundreds of tubes for uranium enrichment, to then be safely moved in their entirety to a designated site for burial. There was no need to cut the converters and potentially risk leaking radioactive material. A rigid polyurethane foam with the following composition and physical properties was produced by dispensing through high pressure impingement mix equipment: INGREDIENT%Polyol blend39.38Crosslinkers1.65Water0.12Viscosity suppressant3.07Surfactants0.47Catalysts0.12Blowing agent2.36Polymeric Isocyanate52.83TOTAL100.00 Free Rise Core Density: 6.0 lbs/ft3 Compressive Strength: 160 lbs/in2 The foam is used to encapsulate and immobilize large volume spaces. This can be a dumpster-like container, piping, ductwork, or any large volume space with or without interstitial spaces to fill. A rigid polyurethane foam with the following composition and physical properties was produced by dispensing through high pressure impingement mix equipment: INGREDIENT%Polyol blend33.50Crosslinkers4.78Water0.10Fire retardant4.31Viscosity suppressant0.57Surfactants0.38Catalysts1.82Blowing agent2.39Polymeric Isocyanate52.15TOTAL100.00 Free Rise Core Density: 6.5 lbs/ft3 Compressive Strength: 150 lbs/in2 The foam is sprayed onto equipment or encapsulating bags to smooth out the surface, and attenuate the radioactive material. A polyurea elastomeric coating with the following composition and physical properties was produced by dispensing through high pressure impingement mix equipment to form an outer coating: INGREDIENT%Polyetheramine blend42.31Amine Crosslinker4.81Moisture Scavenger0.96Isocyanate Prepolymer51.92TOTAL100.00 Tensile Strength: 3000 lbs/in2 Tear Strength: 436 lbs/in Elongation: 364% Shore Hardness: 70 Shore D The elastomeric material is sprayed over equipment or encapsulating bags or foaming plastic encapsulants to create a durable outer coating that is resistant to puncture, tensile stress, and damage during transport to its final disposition. A composition and process for encapsulating radioactive wastes to render them suitable for shipment according to the invention have been described with reference to specific embodiments and examples. Various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description of the preferred embodiments of the invention and best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation, the invention being defined by the claims. |
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046410333 | description | DESCRIPTION OF BEST MODE AND OTHER EMBODIMENTS FOR CARRYING THE INVENTION FIG. 1 illustrates an exemplary illuminator 10 using an optical system in accordance with the present invention. Referring to this figure, an electrodeless lamp 11 comprises a microwave chamber 12 containing a lamp bulb 13 excitable by microwave energy 14. Microwave chamber 12 has a circular aperture 15 covered by a planar circular mesh 16 which is secured to the spherical wall of chamber 12. Both the spherical and mesh portions of chamber 12 are made of a conductive material such as copper or aluminum. Additionally, a portion of the inner surface of the chamber wall opposite to aperture 15 may be coated with a deep UV reflecting material. The spherical wall of chamber 12 also has a rectangular slot 18 in the position shown for coupling microwave energy to the lamp bulb. The envelope of lamp bulb 13 is preferably spherical in shape and is disposed at the center of spherical chamber 12. The envelope is made of high purity, high OH (wet) quartz, which is a highly transmissive material for deep UV radiation. Bulb 13 has a quartz stem 20 for mounting the envelope in the chamber. In order to provide cooling of bulb 13 during its operating, the bulb is rotated by an electric motor 22 while streams of compressed air are directed at the bulb by nozzles 21 and 23 which are connected by appropriate conduits to a source of compressed air 24. Bulb stem 20 is in effect an extension of motor shaft 26. Microwave energy 14 is generated by a magnetron 30 which is energized by a power supply 32. Microwave energy 14 is fed from magnetron 30 to chamber 12 through slit 18 by a rectangular waveguide 34. Lamp bulb 13 is filled with a plasma forming medium, such as mercury dispersed in a noble gas, and the microwave energy passing through slot 18 excites the plasma substantially throughout the volume of the bulb envelope. This causes the bulb envelope to emit ultraviolet radiation which is directed through the ultraviolet transmissive window formed by circular mesh 16. It has been found that the radiation that is emitted by such electrodeless lamps is much richer in the deep UV part of the radiation spectrum than the radiation omitted by conventional UV arc lamps. The spherical envelope of lamp 13 therefore effectively emits a uniform stream of ultraviolet radiation 36 in the direction of a lens array in the form of an optical assembly 37. Assembly 37 forms part of an optical train for coupling the ultraviolet radiation exiting from mesh 16 to wafer 38 as efficiently as possible. A mask 40 for providing an irradiation pattern to a photoresistive coating on wafer 38 is disposed in contact with the wafer coating. The system illustrated in FIG. 1 is therefore known as a contact or proximity photolithographic system. However, as indicated above, the invention is applicable to a wide variety of other types of optical systems and apparatuses, including those for merely transmitting, e.g., fiber optics, and also projecting types having a projector instead of an illuminator. Optical assembly 37 may be comprised of a series of lens elements, such as lenses 42, 44, 46 and 51 shown diagrammatically in FIG. 1. Lenses 42, 44 and 46 interact to form a condensor array. Downstream of lens 46 is a collimating lens 51. The optical train further includes a filter mirror 52 which reflects the longer ultraviolet wavelengths and the visible and infrared components of the radiation while transmitting deep ultraviolet wavelengths in the range of 190 to 260 nm. The UV light transmitted by optical assembly 37 to filter mirror 52 is fed through a shutter 54 which controls the duration (amount) of the ultraviolet radiation to which semi-conductor wafer 38 is to be exposed. Shutter 54 is electronically controlled in conjunction with power supply 32 for magnetron 30 by a controller 56 which controls the shutter speed and lamp bulb intensity in response to an ultraviolet senser 58 so as to provide the desired dose of radiation to the coating on semi-conductor wafer 38. The final element of the optical train is a collimating lens 60 which transmits a uniform UV radiation field to mask 40. The collimated field is large enough to fill the required diameter of the wafer surface with ultraviolet light of the required irradiance as formed by the optics of optical assembly 37. Because of its high transmittance of deep UV radiation, high purity, high OH content quartz is a preferred material for the multiple lenses of optical assembly 37 and collimator lens 60, as well as for the envelope of bulb 13. One or more of these lenses also may be coated with an optical coating composition to provide a thin film of anti-reflective material. In accordance with the present invention, the lenses of optical assembly 37 are each heated to and maintained at a temperature of at least about 280.degree. C., preferably a temperature in the range of about 300.degree.-400.degree. C., more preferably a temperature in the range of about 300.degree. C.-350.degree. C., during operation of the illuminator. Heating is preferably accomplished by ceramic heating bands 62 containing a resistance wire 63 connected to a source of electricity (not shown). The bands may be wound in spiral coils around a cylindrical lens housing 64, which is preferably of aluminum, steel or some other heat conductive material. The heating bands may be enclosed in a casing 65 clamped around housing 64. Housing 64 preferably contains a gas, such as air, which also is heated and transfers heat from the walls of the housing to each of the lenses by gas connection. In the absence of such heating of optical assembly 37, the time required to deliver the desired dose of radiation to the surface of semi-conductor wafer 38 can double in about 1,000 hours of operation due to ultraviolet degradation of the lenses of the optical train. This degradation is in the form of significant increases in the absorption band which develops at and on either side of about 215 nm as previously described. This degradation has been found to be particularly pronounced in lenses occupying the position of lens 46 in FIG. 1. The heating of collimator lens 60 may be optional because this lens is subjected to much lower levels of ultraviolet radiation than the lenses of optical assembly 37. However, in many applications, it also may be desirable to maintain the temperature of collimator lens 60 at the elevated temperatures specified above during operation of the illuminator. Lens 60 may be heated by wrapping coils of a heating band or tape around a conductive lens mounting 70 in a manner similar to the application of heating bands 62 around housing 64 of optical assembly 37. As an alternative, the collimator lens 60 may be provided with an annular heating tape 72 in conductive contact with the lens material. Heating tape 72 is preferably located outside of the optical path near the periphery of lens 60 so as not to interfere with the useful optical area of the lens or otherwise impair its transmission capabilities. The annular shape of tape 72 is interrupted at one location by a narrow radial gap 74 so that resistance wire 76 within the tape can be connected to a source of electrical energy (not shown). As previously indicated, a thin layer of metal or other electrically resistive material may be coated directly onto the body of the lens to provide an annular ring-like structure similar to that of tape 72. Such coatings also are capable of conductively heating an optical lens. The provision of an electrically resistive coating on a lens is described in U.S. Pat. No. 3,495,259 which already has been referred to above. Direct conductive heating of lenses by heating tape or other coatings also may be used for each of the lenses in optical assembly 37 as an alternative or supplement to the heating of housing 64 by heating bands 62. According to the invention, therefore, radiation degradation of optical elements, such as lenses and fiber optics waveguides, is prevented by maintaining these optical elements at a temperature above that at which the lens material could be annealed to remove defect centers or other causes of selective absorption of certain wavelengths which develop upon prolonged irradiation of these elements. Such heating may be achieved by a number of different techniques, including irradiation, hot air convection and/or direct contact with a heating member such as a heating tape or a thin layer of metal or other coating placed on one or more surfaces of the optical elements. Where a heating member is in direct contact with an optical element, it is positioned so as not to interfere with the optically useful area of the element or the equipment in which it is located. The width, thickness and length of a heating member in direct contact with the material of an optical element are selected to achieve the level of sustained heating desired, and depend on the size of the optical element to be heated and the available power supply. The amount of electrical resistance necessary for a required heat output can be determined by conventional means. If the central portions or other optically useful area of a lens cannot be heated sufficiently on account of the temperature gradient between the heated periphery and the optically useful area, an increase in the heating temperature of the resistance member may be necessary. Alternatively, supplemental heating may be provided by direct radiative heating and/or convection heating with hot gases such as air, particularly where the optical elements are enclosed within a housing of heat conductive material. In such optical embodiments, heating of the housing causes direct radiative heating of the lens and also will heat air within the housing for convection heating of the lenses. Heat also may be transmitted to the optical elements by conduction through lens mountings of conducting material. Degradation in the presence of deep ultraviolet radiation may first become noticeable after about 200 hours of exposure at an irradiation level of about 150 milliwatts per square centimeter. Accordingly, the total amount (dose) of ultraviolet energy accumulated after 200 hours at this irradiation level is about 100 kilojoules per square centimeter. The amount of absorption in the wavelength band around 215 nm increases with further irradiation and becomes particularly pronounced after about 800 hours, which exposure time at 150 milliwatts per square centimeter is equivalent to a total accumulated dose of about 400 kilojoules per square centimeter. This phenomenon of increased ultraviolet absorption with increased time of exposure is illustrated in FIG. 3 for different lenses which have been exposed to about 150 milliwatts per square centimeter of deep ultraviolet radiation for different lengths of time. Thus, line 77 represents the level of absorption by a new lens, line 78 the absorption of a lens exposed for 300 hours, and line 79 the absorption of a lens exposed for 800 hours. The lenses measured in developing the data for FIG. 3 were those occupying the position of lens 46 of FIG. 1 taken from three different optical assemblies, one being new and the other two being exposed for the times indicated. The transmittance of each of these lenses was measured separately with a laboratory set-up using a deuterium lamp producing a deep ultraviolet continuum in the range of 200-250 nm. The output from the deuterium lamp was directed through a small, round hole in a diaphragm to create a narrow beam of deep ultraviolet radiation through the middle of the lens. This narrow beam was then passed through a diffuser and into the slit of a monochromator apparatus for measuring the intensity of radiation as a function of its wavelength. The output of the monochromator was then fed to a computer for storage and subsequent print-out of the graphs making up FIG. 3. The same laboratory set-up used for FIG. 3 also was used in developing the data of FIGS. 4-6 discussed below. Referring to FIG. 4, this figure illustrates the change in transmittance of a lens element at 215 nm with the time of exposure without the application of heat (line 80). This figure further illustrates that where another lens element is maintained continuously at 300.degree. C., the radiation degradation represented by line 80 does not occur even after 1,000 hours of exposure (line 82). In FIG. 5, there is shown the graph of two lenses that are each irradiated without heating for the first 1,000 hours of operation and accordingly undergo degradation as indicated by the single line 83 starting at about 95% transmittance and decreasing to about 70% transmittance. Both lenses were then annealed at about 400.degree. C. for about 3 hours. Irradiation was then resumed for about another 100 hours of operation with a continuation of heating to at least about 300.degree. C. of the lens represented by line 84 and a discontinuance of heating of the lens represented by line 86. The dotted line 85 between lines 84 and 86 is a representation of what had been predicted from prior literature on the possible effects of annealing radiation degraded slicia. As indicated by the rapid divergence of lines 85 and 86, the unheated lens after being annealed returned to its degraded state at a rate far exceeding its rate of degradation as a new lens. The extremely rapid degradation of an annealed lens as shown by line 86 was an entirely unexpected result of testing related to the present invention. In marked contrast, the annealed lens of which heating was continued did not exhibit any such degradation but maintained its annealed transmittance at a level which is only about 3-5 percent less than that of a new lens. The broken portions of lines 84 and 86 beyond 1,100 hours are not based on actual measurements but represent an extrapolation of the performance of these lenses based on the test results described. FIG. 6 is similar to FIG. 5 except that the graphs represent a summation of the transmittance of all lenses in optical assemblies corresponding to optical assembly 37 of FIG. 1, instead of the transmittance of a single lens such as lens 46. Thus, line 88 represents an optical assembly 37 that is not heated for 1,000 hours but is then wrapped with a heating tape and thereafter heated to about 300.degree. C. for the remainder of its exposure to deep ultraviolet radiation. For comparison, line 90 is representative of an optical assembly 37 which is annealed only for about 3 hours at about 400.degree. C. and thereafter heating is discontinued upon further exposure of the assembly to deep ultraviolet radiation. Again, the unexpectedly rapid degradation of the annealed assembly was observed and is illustrated by the rapid divergence of line 90 from a dotted line 89 representing what had been predicted from prior literature on the possible effects of annealing radiation degraded silica. FIGS. 7 and 8 represent a comparison of the total output of an illuminator of the type shown in FIG. 1 without use of the heating band 62 and after annealing for about 2 hours with use of the heating band 62, respectively. In this illuminator, each of the lenses were coated with an antireflective coating to decrease reflection and thereby increase transmittance of the deep ultraviolet radiation. The test set-up for these measurements was basically that shown in FIG. 1 except that the wafer 38 and mask 40 were eliminated and the UV sensor 58 moved into the plane vacated by wafer 38. In this case, the ultraviolet sensor was the detector element of an irradiation measuring apparatus known as a "Mimir" which is capable of measuring the level of irradiation over relatively short intervals or bands of deep ultraviolet radiation. Thus, the irradiation in milliwatts per square centimeter was measured for each band width of 5 nm from 200 nm to 280 nm. These band width intervals and the measured irradiation by these wavelengths are shown in the first two columns of the table portions of FIGS. 7 and 8. The last column of these tables is a summation of the second column to give the integrated amount of radiation incident upon the UV sensor over the entire range from 200 nm to 280 nm. The graph portion of FIGS. 7 and 8 is a plot of the first two columns of the table, with the total area under the curve from 200 nm to 280 nm in increments of 5 nm being given by the third column of the table. The illuminator tested had been operated for 2,400 hours, which was the time of exposure of the optical system to deep UV irradiation and is indicative of the total dose delivered to the optical elements. Prior to making each set of measurements, the ultraviolet lamp 13 was operated for about 20 minutes in order to achieve stability within the optical system. The nomenclature of the table portion of FIGS. 7 and 8 is further described as follows. The tests were run on Mar. 22, 1984. There is then given the serial number of the lamp bulb, the illuminator unit number, and the optical assembly number. The optical assembly providing the data for FIG. 7 had no heating band throughout 2,400 hours of illuminator operation. A heating band was then applied to the optical assembly of FIG. 7 and was activated to heat this optical assembly to about 300.degree.-350.degree. C. for about 2 hours in order to provide the data for FIG. 8. The headings of the table have already been explained above. The nomenclature of the graph portion of FIGS. 7 and 8 is further described as follows. To show particularly that the invention eliminates degradation at wavelengths on either side and at about 215 nm, a band of from 210 nm to 240 nm was selected and the irradiation measured by the Mimir instrument was integrated over this range. The integrated irradiation without heating over this band width was 9.1 milliwatts per square centimeter as compared to an irradiation of 15.1 milliwatts per square centimeter where the optical system had been heated to more than 300.degree. C. for an annealing period of about 2 hours. Annealing invention thereby resulted in an increase of over 60% in the level of UV irradiation delivered by the illuminator to the semi-conductor wafer in the wavelength range of 210 nm to 240 nm. The remaining nomenclature associated with the graph portions of FIGS. 7 and 8 indicate that the lamp was calibrated in February at a power supply level of 650 milliamperes and 3.4 kilovolts, and that the ultraviolet sensor generated a maximum signal of 0.16 volts for the unheated optical system as compared to a maximum signal of 0.22 volts for the heated optical system. Although it could not be confirmed by experimental data, some of the measured degradation indicated by FIG. 7 may have been due to radiation degradation of the composition with which the lenses were coated. In this regard, the invention is also applicable to optical coatings which upon exposure to radiation become degraded by an increase in absorption by the coating of one or more wavelengths of the radiation to which the coating is exposed. This degradation must then be reversible upon annealing the coating. In other words, coatings may also contain silica and other materials that can be degraded by exposure to radiation and then annealed to temporarily remove such degradation. Maintaining these coatings at a temperature above the annealing temperature throughout exposure of the coating to radiation will avoid such radiation degradation in the same manner that degradation of a silica lens is avoided by application of the invention. There thus has been disclosed a method and apparatus for preventing radiation degradation of optical elements and systems employed in a wide variety of applications, such as fiber optics and deep ultraviolet photolithography. The numerous advantages realized by practicing the invention have heretofore been discussed in detail. The heating methods and apparatuses disclosed for practicing the invention may find use in numerous processes other than fiber optics and photolithography. Accordingly, while specific preferred embodiments have been illustrated and described, many variations of these embodiments will fall within the scope of the invention which is defined only by the claims below. |
claims | 1. A nuclear fuel assembly tie plate comprising: intersecting strips delimiting therebetween tubular guide cells each for allowing a fuel rod to extend through the tie plate, the strips delimiting therebetween tubular flow cells separate from the guide cells, each flow cell for allowing coolant flow through the tie plate, the guide cells and flow cells being arranged at nodes of a lattice defined by a repeating pattern comprising four comer nodes in a square lattice arrangement and a central node at the center of the four comer nodes, with one of the guide cells at each comer node, the guide cells at the comer nodes separated by a first pair of parallel spaced strips of the intersecting strips intersecting a second pair of parallel spaced strips of the intersecting strips, the first and second pairs of parallel strips delimiting a four-walled central flow cell at the center node, the repeating pattern being a 3×3 array of nodes in a square or rectangular lattice arrangement with the four guide cells at the corner nodes, the central flow cell at the center node and four intermediate flow cells at four intermediate side nodes between the comer nodes; and wherein the guide cells and flow cells positioned at the nodes of the repeating pattern are delimited between a group of four parallel strips of the intersecting strips intersecting a group of four parallel strips of the intersecting strips, wherein in each group the spacing between the pairs of strips delimiting the central flow cell between them greater than the spacing between the pair of strips delimiting the guide cells between them. 2. The fuel assembly tie plate according to claim 1, wherein the central flow cell has a cross-sectional area greater than that of each guide cell. 3. The fuel assembly tie plate according to claim 1, wherein each guide cell has a square-shaped cross-section. 4. The fuel assembly tie plate according to claim 1, wherein each central flow cell has a square-shaped cross-section. 5. The fuel assembly tie plate according to claim 1, wherein each intermediate flow cell has a cross-sectional area greater than that of the guide cells. 6. The fuel assembly tie plate according to claim 1, wherein each intermediate flow cell has a rectangular-shaped cross-section. 7. The fuel assembly tie plate according to claim 1, wherein the intersecting strips have planar guide cell portions delimiting guide cell side walls. 8. The fuel assembly tie plate according to claim 1, wherein the intersecting strips have guide cell portions delimiting guide cell side walls curved inwardly with respect to the guide cell. 9. The fuel assembly tie plate according to claim 1, wherein the intersecting strips have guide cell portions delimiting guide cell side walls curved outwardly with respect to the guide cell. 10. The fuel assembly tie plate according to claim 1, wherein the intersecting strips have guide cell portions delimiting guide cell side walls provided with dimples protruding from the guide cell portion inwardly in the corresponding guide cell. 11. A nuclear fuel assembly comprising the tie plate according to claim 1. 12. A nuclear fuel upper nozzle comprising the tie plate according to claim 1. 13. A nuclear fuel assembly comprising:the upper nozzle according to claim 12; anda bundle of fuel rods, at least one of the guide cells receiving a fuel rod with a transverse clearance between the fuel rod and guide cell side walls of the at least one guide cell. |
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041938437 | summary | BACKGROUND OF THE INVENTION 1. Field of Invention The invention relates to a method and an apparatus for locating defective fuel rods within fuel assemblies of water cooled nuclear reactors, and the like. 2. Description of the Prior Art The core of a light water-cooled reactor, for instance, typically consists of about 40 to 50 thousand fuel rods which are usually arranged in groups of about 200 rods to form a fuel assembly. A fuel assembly for a reactor of this nature consists of two end fittings, control rod guide tubes and spacer grids for positioning the rods. The fuel rods consist of Zircaloy-4 cladding tubes which contain the fuel in oxide form and are closed at both ends with welded caps. During prolonged operation, several rods may develop leaks so that cooling water can seep in or radioactive material can escape. The coolant purification system of the nuclear reactor is capable of handling a certain amount of radioactive fission products. However, it is desirable to keep the radiation level as low as possible in order to protect the operating personnel. Accordingly, the fuel assemblies are usually subjected to a so-called "seepage test" during shutdowns of the reactor, e.g. during refueling. The fuel assembly is placed in a water filled storage tank for this test. The fuel rods and the water heat up by residual decay. If a fuel assembly contains a defective rod, the fission products escape during the heating into the water. Through sampling of the water it can be determined whether the fuel assembly contains defective rods. This method is a totalizing method which determines only whether the fuel assembly contains defective rods. It cannot, however, identify the position or the location of the defect. U.S. Pat. No. 3,983,741 suggests removing the upper end fitting from the fuel assembly, and slipping an immersion cask over the exposed fuel rod end caps while keeping the upper ends of the fuel rods above the water. Water seeping into defective rods evaporates due to the decay heat. Instrumentation can detect temperature differences of rods containing steam. It is known from U.S. Pat. No. 3,945,245 to remove the end fittings from the fuel assembly, to slip a heating element on the endcaps of the fuel rods and to detect the generation of steam or condensate in the rods containing water by ultrasonic means. Therefore, in accordance with these patents, it is possible to locate defective fuel rods. A disadvantage of these methods is that the end fitting of the fuel assembly must be removed and special provisions must be made to evaporate the ingressed water before the defective rods can be found by the instrumentation. A further disadvantage is that in many fuel assembly designs only the lower end fitting is removable. The lower fuel assembly end fitting is installed in the reactor at the bottom end of the fuel rods. Therefore, before this end fitting can be removed the fuel assembly must be turned 180 degrees under the water in the fuel storage pool, an additional time consuming operation. The seepage test, the disassembly of the end fitting and the evaporation of the leaked-in water, require a time consumption which is a loss in availability of the power plant. In addition, every operator of a nuclear power plant strives to keep the testing times of the fuel elements at a minimum to reduce the exposure time of the maintenance crew. When the allowable exposure limit is exceeded, a new crew must be employed. Thus, a need has arisen to find a simpler inspection method for locating defective fuel rods which could reduce the required time and minimize the radiation exposure of the maintenance crew. SUMMARY OF THE INVENTION This task has been solved, by insertion of ultrasonic transducer heads into the spaces between the individual fuel rods disposed to touch the fuel rods and to emit ultrasonic waves perpendicularly to their axes. The resulting difference in the resonance is an indication of leaked-in water. During the periodic fuel replacement outages about one-third of the fuel assemblies (batch I) are removed from the reactor core as fully spent fuel. The other two-thirds, which consist of two further batches having different U-235 enrichments are relocated according to a certain carefully planned scheme and placed in different positions in the core for optimum utilization. An advantageous provision of this invention is the ability to inspect (test) the fuel assemblies during the relocation in the water filled canal arranged above the reactor. It has become advantageous to test the fuel assemblies of "batch I" during the transport from the water filled canal to the fuel storage pool. The fuel assemblies of batch I which contain defective fuel rods are stored in separate storage tanks in order to prevent the escape of fuel or radioactive materials into the storage pool. The detector transducer heads are preferably applied in the region of the lower gas space of the fuel rods where, according to experience, the leaked-in water accumulates when the reactors are not under pressure. Normally, the testing of fuel rods is accomplished at that condition. The device used to perform the inspection method of this invention contains a carriage provided with comblike fingers. The carriage is arranged to slide along guides of a support plate. The fingers are fitted with ultrasonic heads which are pressed against the fuel rods by springs. The comb-like fingers are arranged on only one side of the carriage and the ultrasonic heads are attached at the free end of the fingers. An advantageous embodiment is obtained when the support plate is attached to the fuel-handling machine. The testing in this manner can be performed during the transportation of a fuel assembly. It has proven also beneficial to make the entire fingers from a material which conducts ultrasonic waves so that the ultrasonic heads do not have to be placed at the free ends of the fingers. The method of this invention has the advantage that testing can be accomplished immediately after removal of the fuel assembly from the reactor core at a significant time saving. The disassembly of the end fitting and the waiting for the evaporation in the defective fuel rods is not required. Thus, the expensive seepage test becomes superfluous, because the present simple and fast method does not require a pre-testing for fuel assemblies containing defective fuel rods. A considerable time saving is achieved in comparison with the previous methods. Refueling time can therefore be considerably shortened thereby improving the economics of the power plant's operation. |
042119286 | summary | THE PRIOR ART As is shown in FIG. 1 of the accompanying drawings, systems for the handling of radioactive material 1 involve the provision of a storage unit 2 having a mass 3 of radiation-shielding material with a passage 4 through it, in which the radioactive material can be safely stored when not in use, as is shown in FIG. 1 at A, and from which the radioactive material can be moved to a use location, as for making a radiograph, as is shown in FIG. 1 at C. Typically, the radioactive material 1 is connected to drive means comprising a flexible cable 5 in a guide tube 6. The guide tube is generally provided in three essentially equal-lengths 6A, 6B and 6C, each of which can be disconnectibly coupled to the storage unit 2. Under control of a reel and crank arrangement 7 the drive cable 5 pushes the radioactive material out of the passage 4 and through the third guide tube 6C to a snout 8 located where the radiograph is to be made, as shown in FIG. 1 at B and C. The portion of drive cable 5 in the second guide tube 6B supplies the cable necessary to fill the first and third guide tubes 6A and 6C when a radiograph is being made. A disconnectible coupler 9 is fitted in the drive cable 5 so that when the radioactive material 1 is in the stored position the drive cable can be parted outside the storage unit for uncoupling the cable 5 and the guide tubes 6A and 6B from the storage unit. The part of drive cable 5 between the coupler 9 and the radioactive material 1 is known as the leader 11, and the coupling apparatus 10 between the guide tubes 6A and 6B and the storage unit 2 generally contains means to lock the leader against movement through the passage 4 when the drive means are uncoupled and removed. U.S. Pat. Nos. 3,147,383 and 3,593,594 describe prior systems in which these features are found. When the passage 4 through the storage unit is curved as shown in FIG. 1 the mere location of the radioactive material 1 in the middle part of the passage provides storage which shields the region surrounding the storage unit from radiation emitted by the radioactive material. The provision of a curved passage through the mass 3 of radiation-shielding material is, however, more costly than the provision of a straight-through passage, and the conduit which defines the curved passage is subject to wear after the parts holding and guiding the radio-active material have been pushed through it repeatedly. An early system for exposing a body of radioactive material by moving a rod through a straight passage is described in Gilks U.S. Pat. No. 2,551,491. In the patent a substantial part of the shielding material is moved away from the storage unit, to make the exposure. A form of straight-through exposure system which provides for locating the body of radio-active material remote from the storage unit, under control of a crank-type manipulator as shown in FIG. 1, is illustrated in British Pat. No. 712,009, of Stein; that system, however, uses two separate shielding masses, one rotatable inside the other, in a complex structure, to move the radioactive material from a shielded storage position to a posture in which it can be moved to an exposure position. It also shows a primitive claw-type coupling/decoupling mechanism for the drive cable which does not provide access for manipulating a cable coupling/decoupling mechanism of the more reliable modern form, as is illustrated, for example, in U.S. Pat. No. 3,237,977. A need exists for a modern system for handling radioactive material which incorporates a storage unit having a straight-through passage in its radiation-shielding mass and is compatible with current requirements of safety, utility, convenience, and lost cost. GENERAL NATURE OF THE INVENTION The present invention provides a storage unit for a system of the general type illustrated in FIG. 1 wherein the passage through the radiation shielding material is straight, the storage unit being fittable at a first end with a coupler of modern design for the drive cable and manipulating means, and at the second end with conduit means to guide the radioactive material to a location where a radiograph is to be made. A shutter or cover is provided for the second end, with interlock means to block the second end of the straight passage when the radioactive material is stored in the storage unit. The shutter is mounted on the storage unit for sliding movement transverse to the second end of the passage between first and second limits, the shutter in said first limit blocking the second end, the shutter having a hole through it which registers with the passage when the shutter is in the second limit. Shutter-retaining means are provided within the passage adjacent the second end, and resilient means cooperate with the retaining means and said storage unit for urging the retaining means to project an end-part toward the shutter. Means are provided in the shutter for receiving this end-part when the shutter is in the second limit, and thereby retaining the hole in register with the passage. Means coupled to the capsule are provided for pulling the retaining means away from the shutter against the action of the resilient means under control of the manipulating means, for withdrawing the end-part from the receiving means, and thereby permitting the shutter to move toward the first limit, again blocking the second end. |
047568666 | claims | 1. Nitrogen concentration detection apparatus useful for the detection of nitrogen concentration in an article containing suspect nitrogen comprising: a source of x-ray energy exceeding 30.64 MeV, said x-rays causing the following reaction EQU .sup.14 N(gamma, 2n).sup.12 N in nitrogen in said article but having insufficient energy to cause a significant reaction .sup.16 O(gamma, n.sup.3 H).sup.12 N, said significant reaction being that which would interfere with .sup.12 N production desired from interaction with .sup.14 N; at least two gamma ray detectors aligned near the path of said generated x-ray for detecting the 511 keV annihilation gamma radiation produced by the reaction of .sup.14 N(gamma, 2n).sup.12 N; and means for conveying said article proximate said x-ray source and said gamma ray detectors. providing an x-ray source having x-rays exceeding 30.64 MeV in the range sufficient to cause a significant reaction EQU .sup.14 N(gamma, 2n).sup.12 N but insufficient to cause a significant reaction .sup.16 O(gamma, n.sup.3 H).sup.12 N, said significant reaction being that which would interfere with .sup.12 N production desired from interaction with .sup.14 N; irradiating a suspect article to determine the presence of nitrogen with radiation sufficient to cause the reaction .sup.14 N(gamma, 2n).sup.12 N where gamma is x-radiation, and n is a neutron; detecting delayed annihilation radiation from said .sup.14 N(gamma, 2n).sup.12 N in the range of 511 keV on opposite sides of said articles for simultaneous scintillation events; and moving said article and beam relative to one another to quantitatively map said article in three dimensions, relative to its nitrogen content. a high energy electron source having an output electron beam in the order of 35 MeV; a target for said high energy electron source to produce x-radiation in the range exceeding 30.64 MeV; deflection magnets adjacent said target for deflecting the electron beam of said microtron to cause said electron beam to scan; a conveyer suitable to transport an article containing suspect nitrogen through the path of said electron beam scan; and a stack of scintillation detectors for detecting the 511 keV annihilation gamma radiation produced by the reaction .sup.14 N(gamma, 2n).sup.12 N where: gamma is x-radiation; n is a neutron; and .sup.14 N and .sup.12 N are isotopes of nitrogen. a source of x-ray energy exceeding 30.64 MeV, said x-rays causing the following reaction EQU .sup.14 N(gamma, 2n).sup.12 N in nitrogen in said article but having insufficient energy to cause a significant reaction .sup.16 O(gamma,n.sup.3 H).sup.12 N; said significant reaction being that which would interfere with .sup.12 N production derived from interaction with .sup.14 N means for conveying along a conveyor path said article by said scanning x-ray beam; and, means for scanning said source of x-rays across said article and said conveyor path; first and second linear arrays of annihilation radiation detectors aligned parallel to the path of said generated x-rays for detecting the 511 keV annihilation gamma radiation produced by the reaction of N(gamma, 2n).sup.12 N, one array disposed on one side of a said conveyor path and the other array disposed on the opposite side of said conveyor path whereby a tomographic plot of the nitrogen in said articles can be made. 2. The apparatus of claim 1 and wherein the x-ray energy source has an energy level of less than 40 MeV. 3. The apparatus of claim 1 and including means for scanning said x-rays from said x-ray energy source. 4. The apparatus of claim 1 and including two linear arrays of gamma ray detectors aligned parallel to the path of said generated x-rays, one array disposed on one side of said article and the other detector disposed on the opposite side of said article to give a three-dimensional tomographic image of the nitrogen content of the article. 5. A method of scanning a series of conveyed articles for randomly placed nitrogen concentrations in the order of 20% to 30% by weight comprising the steps of: 6. The method of claim 5 and wherein said moving step includes conveying said article. 7. Method of claim 5 and wherein said mapping includes pulsating said x-radiation incident upon said article and examining said article for 11 milliseconds after each pulsation for said reaction. 8. Nitrogen concentration detection apparatus comprising in combination: 9. The apparatus of claim 8 and wherein said high energy electron source has an energy level less than 40 MeV. 10. The apparatus of claim 1 and wherein said source of x-rays is an electrom beam from a microtron or linear accelerator impacting a heavy element target. 11. The apparatus of claim 8 and including first and second stacks of solid state detectors on opposite sides of said conveyor. 12. Nitrogen concentration detection apparatus useful for the tomographic mapping of nitrogen concentrations in an article containing suspect nitrogen comprising: |
039393550 | claims | 1. In a lock assembly for securing an isotope source in a radioisotope camera shield, a pigtail extending from said source and adapted to extend and withdraw the isotope source relative to the camera shield, a hollow lock casing adapted to be secured to the radioisotope camera shield and having a longitudinal lock chamber opening to the camera shield, and a lock barrel chamber extending at right angles with respect to said lock casing, a stop on the source pigtail, a lock barrel in said barrel chamber, and biased in an extended position relative to said lock barrel chamber, a key cylinder in said lock barrel, means operable by turning movement of said key cylinder to hold said lock barrel in a retracted position relative to said chamber or release said lock barrel to be extended from said chamber, and three cooperating movable elements for locking and releasing said stop, two being operated by turning of the key cylinder and retracted or extended movement of the lock barrel and the third being operated by withdrawal tension on the pigtail and requiring an overt act on the pigtail in addition to turning of the key cylinder and release of the lock barrel to release the pigtail for extension outside of the camera shield for use. 2. The lock assembly of claim 1, wherein the first of said three cooperating movable elements includes a stop lever pivoted within said lock chamber and biased to engage said stop and retain the source pigtail within the camera, the second includes hook means pivoted to said lock barrel to depend therefrom into said longitudinal lock chamber and biased to engage and lift said stop lever out of the path of said stop on the source pigtail upon extended movement of the lock barrel with respect to the lock chamber, and the third includes a lock spool slidable along said lock chamber and biased toward the camera in locking position in the lock chamber and moved to release said stop lever by tension on the source pigtail and stop. 3. The lock assembly of claim 2, wherein the stop lever has a trip member thereon disposed intermediate the ends thereof and adapted to be engaged by said lock hook upon extensible movement of said lock barrel from said lock chamber and lift said stop lever out of the path of said stop on the source pigtail upon reverse movement of said lock spool away from the camera shield. 4. The lock assembly of claim 3, wherein spring means bias said lock hook to engage said trip member, second spring means bias said stop lever to engage said stop on said source pigtail, and wherein said trip member has an upper surface camming said lock hook to engage and lift said trip member and stop lever upon extension of said lock barrel relative to said lock barrel chamber. 5. The lock assembly of claim 4, wherein spring means stronger than the spring means biasing said lock lever to engage said truncated ball on the source pigtail, lift said lock barrel relative to said lock barrel chamber upon release of the lock barrel by the key and move said hook to engage said lock lever and move said lock lever upward to its upper limit of travel. 6. The lock assembly of claim 5, wherein said first and second springs are oppositely acting torsion springs and said third spring is at least one compression spring. 7. The lock assembly of claim 5, wherein the trip member is held from upward movement by said lock spool and released by reverse movement of said lock spool out of the path of said trip member. 8. The lock assembly of claim 7, wherein said trip member has a downwardly facing abutment surface adapted to be engaged by said lock hook and has an oppositely facing abutment surface adapted to be engaged by said lock spool to hold said stop lever in a locking position until reverse pull on said source pigtail removing said spool out of registry with said stop surface. 9. The lock assembly of claim 4, wherein said trip member has a downwardly facing abutment surface adapted to be engaged by said lock hook to lift said stop member upon extensible movement of said lock barrel, and has an oppositely facing abutment surface adapted to be engaged by said lock spool, and engaged by said lock spool by the bias of said lock spool toward said camera, to hold said stop lever in a locking position until reverse pull on the pigtail moving said lock spool out of registry with said oppositely facing surface of said trip member to release said trip member and lock lever and condition said lock lever to release said stop on said source pigtail upon a predetermined reverse pull on the source pigtail. 10. The lock assembly of claim 9, wherein the first and second spring means are oppositely acting torsion springs and at least one compression spring stronger than said torsion springs serves to extend said lock barrel upon release by the key cylinder. 11. The lock assembly of claim 10, wherein the barrel chamber has a shell therein forming a liner for said chamber and bearing for said lock barrel, wherein a guide connection is provided between said shell and lock barrel to guide said lock barrel for rectilinear movement relative to said shell, and wherein a pin and aperture lock is provided between said lock barrel and shell and retractable by turning movement of the key cylinder to a release position. 12. The lock assembly of claim 11, wherein stop means are provided engageable by said stop spool to prevent complete withdrawal of the source pigtail from the camera shield. 13. The lock assembly of claim 11, wherein the truncated ball is automatically trapped at the full retracted position of the pigtail and ball. 14. The lock assembly of claim 11, wherein means are provided to prevent depression of the barrel while the source pigtail is in exposed position. |
052767205 | description | DETAILED DESCRIPTION OF THE INVENTION Referring initially to FIG. 1, a nuclear BWR system is shown generally at 1. Reactor 10 containing a core, 3, and working fluid, 5, can be seen to be housed within reactor containment 12 which also defines drywell 14. Working fluid 5 generally consists of liquid water which is vaporized upon circulation in a heat transfer relationship with core 3 and passed via a main steam line to a turbine (not shown). Additionally, reactor 10 may contain gaseous noncondensibles, such as inert gases and the like. Also housed within containment 12 is wetwell 16 which is also defined by wall 18. Annular pressure suppression pool 20 is contained within wetwell 16 and connects drywell 14 and wetwell 16 via vent 22. Disposed outside of containment 12 is upper pool 24 which contains a containment condenser, shown generally at 26. Alternatively, containment condenser 26 may be disposed within containment 12. With respect to implementation of the emergency cooling system that is the subject of the instant invention, reactor 10 may be seen to be communicable in a postulated emergency situation with drywell 14 via vent 28. In a postulated LOCA or other emergency situation wherein the main steam line from the reactor is closed or steam flow therethrough is reduced, a gaseous-phase steam and noncondensible mixture will flow from reactor 10 into drywell 14 upon the actuation of vent 28. The direction of the emergency situation flow from reactor 10 into drywell 14 is as represented by arrows 30 and 32. As the gaseous steam and noncondensibles released from reactor vessel 10 may result in a sudden increase in pressure in drywell 14, pressure suppression pool 16 is provided to dampen such transitory phenomena and thereby ensure the structural integrity of containment 12 such that no radioactive materials are released to the environment. When the pressure in drywell 14 exceeds that in containment condenser 26, the gaseous steam and noncondensible mixture will flow from drywell 14 into containment condenser 26 via line 34 as represented by arrow 36. At least a portion of the latent and specific heats of the steam and noncondensible mixture are removed from drywell 14 via transfer to upper pool 26 and exhaustion through vent 38 as represented by arrow 40. The heat transfer from the steam and noncondensible mixture to upper pool 24 via containment condenser 26 results in the condensation of at least a portion of the steam component of the steam and noncondensible mixture passed through containment condenser 26. Condensate is passed from containment condenser 26 to reactor 10 via line 44 as represented by arrow 46. The noncondensed balance of the steam and noncondensible mixture is returned to drywell 14 via outlet 48. Upon return to drywell 14, the noncondensed balance is mixed with the steam and noncondensible mixture passed from reactor 10 to drywell 14. The steam added to drywell 14 via vent 28 from reactor 10 coupled with temperature differentials and condensation in containment condenser 26 will result in the development of a recirculation flow to containment condenser 26 via line 34. With continued reference to FIG. 1, the advantages of the instant invention are revealed upon a closer examination of containment condenser 26. Containment condenser 26 may be seen to comprise a shroud, 50, defining a plenum, 52, in fluid communication with outlet 48 and a plurality of vertical tubes, 54, for passage therethrough of the steam and noncondensible mixture. Tubes 54, which may be linear or helical coils, may be seen to extend in fluid communication with a steam dome, 56, connected to drywell 14 via line 34. At least a portion of the steam component of the steam and noncondensible mixture may condense in tubes 54 and flow therethrough along their inner surfaces. As the condensate is passed from tubes 54 into plenum 52, the shear effect on the noncondensible component of the steam and noncondensible mixture is increased. This increased shear and the higher density of the noncondensibles compared to steam, in effect, drag the noncondensibles out of containment condenser 26. Inasmuch as the heat transfer in containment condenser 26 is governed by the diffusion of steam vapor molecules through a noncondensible layer to a laminar condensate film flowing on the inner surfaces of tubes 54, the presence of noncondensibles in containment condenser 26 may be seen as an impediment to the removal of heat form containment 12. By providing for the removal of noncondensibles from containment condenser 26, the heat transfer between upper pool 24 and containment condenser 26 is enhanced. Moreover, as there is no accumulation of noncondensibles in containment condenser 26, the need for a vent line from containment condenser 26 to suppression pool 20 is eliminated. Instead, the noncondensibles and any noncondensed steam may be vented directly into drywell 14. Consequently, the vacuum breaker check valve between drywell 14 and wetwell 16, and the active cooling systems for wetwell 16, normally associated with emergency cooling systems also become superfluous. Alternatively, as shown at 58, tubes 54 may be oriented at an angle from between about 20.degree. and 40.degree. with respect to vertical. Orientation at such inclination allows condensate to collect on one side of the inner surfaces of tubes 54, making the condensate thinner along the rest of the tube and thereby increasing the heat transfer rate from containment condenser 26 to upper pool 24. Preferably, the length of plenum 52 is about twice the length of tubes 54. Advantageously, flowtrips may be incorporated into tubes 54. Flowtrips may be used to dropletize (i.e., the formation of liquid dropelets) the condensate (shown generally at 60) flowing along the inner surfaces of tubes 54. Dropletizing increases the shear between the condensate and the noncondensibles and thereby enhances the dragging of the noncondensibles out of tubes 54 and containment condenser 26. For vertical tubes 54, flowtrips may be incorporated into the tubes at a preferred spacing of between about 20-50 hydraulic diameters. For slanted tubes 58, flowtrips may be incorporated into the tubes adjacent plenum 52. Referring to FIGS. 2-5, possible embodiments of flowtrips according to the instant invention are shown. Referring to FIG. 2 initially, a flow trip is shown as comprising a cylindrical channel, 62, circumscribed into the inner surface 64 of tube 54 and terminating into generally V-shaped flutes, 62a-c. Condensate 66 flowing down channel 62 of tube 54 is tripped by flutes 62a-c, dropletized, and directed towards annular center 68 of tube 54. Looking to FIG. 3, it may been seen that flutes 62a-c terminating channel 62 may be equilaterally spaced about inner surface 64 of tube 54. Turning to FIG. 4, another embodiment of a flowtrip according to the instant invention is shown as comprising three, equilateral-spaced fins, 70a-c. As may be seen in connection with FIG. 5, fins 70a-c may extend from inner surface 64 of tube 54 towards annular center 68. Fins 70a-c may be acutely angled with respect to inner surface 64 of tube 54. Condensate 66 flowing down inner surface 64 of tube 54 is tripped by fins 70a-c, dropletized, and directed towards annular center 68 of tube 54. As to materials of construction, preferably all components are manufactured from materials appropriate for their use within a nuclear BWR. Further, it will be appreciated that various of the components shown and described herein may be altered or varied in accordance with the conventional wisdom in the field and certainly are included within the present invention, provided that such variations do not materially vary within the spirit and precepts of the present invention as described herein. |
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