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claims | 1. A reactor vibration monitoring device, comprising:ultrasonic wave transmission means disposed on an outside surface of a reactor pressure vessel, for transmitting ultrasonic pulses to an interior of the reactor pressure vessel;ultrasonic wave receiving means disposed on the outside surface of the reactor pressure vessel, for receiving reflected pulses including ultrasonic waves of the ultrasonic pulses reflected by an inspection object disposed in the reactor pressure vessel;preprocessing means for performing processing to exclude reflected ultrasonic pulses reflected in a wall of the reactor pressure vessel from a reflected pulse signal received by the ultrasonic wave receiving means; andcalculation means for determining vibrations of the inspection object from the reflected pulse signal processed by the preprocessing means, based on an observation time of the inspection object, wherein:the ultrasonic wave transmission means is a pulse train generating means for transmitting an ultrasonic pulse train to the reactor pressure vessel; andthe preprocessing means calculates a correlation value between a waveform of the ultrasonic pulse train and the reflected pulse signal at the observation time. 2. A reactor vibration monitoring device, comprising:ultrasonic wave transmission means disposed on an outside surface of a reactor pressure vessel, for transmitting ultrasonic pulses to an interior of the reactor pressure vessel;ultrasonic wave receiving means disposed on the outside surface of the reactor pressure vessel, for receiving reflected pulses including ultrasonic waves of the ultrasonic pulses reflected by an inspection object disposed in the reactor pressure vessel;preprocessing means for performing processing to exclude reflected ultrasonic pulses reflected in a wall of the reactor pressure vessel from a reflected pulse signal received by the ultrasonic wave receiving means; andcalculation means for determining vibrations of the inspection object from the reflected pulse signal processed by the preprocessing means, based on an observation time of the inspection object, wherein:the preprocessing means performs low frequency component extraction processing of squaring an amplitude of the reflected pulsed signal and extracts a component having a frequency lower than a predetermined frequency. 3. A reactor vibration monitoring device, comprising:ultrasonic wave transmission means disposed on an outside surface of a reactor pressure vessel, for transmitting ultrasonic pulses to an interior of the reactor pressure vessel;ultrasonic wave receiving means disposed on the outside surface of the reactor pressure vessel, for receiving reflected pulses including ultrasonic waves of the ultrasonic pulses reflected by an inspection object disposed in the reactor pressure vessel;preprocessing means for performing processing to exclude reflected ultrasonic pulses reflected in a wall of the reactor pressure vessel from a reflected pulse signal received by the ultrasonic wave receiving means; andcalculation means for determining vibrations of the inspection object from the reflected pulse signal processed by the preprocessing means, based on an observation time of the inspection object, wherein:the preprocessing means stores a differential processing-specific waveform in advance, and performs differential processing of the reflected pulse signal and the differential processing-specific waveform. 4. The reactor vibration monitoring device according to claim 3, comprising interrupting means for interrupting the ultrasonic pulses transmitted from the ultrasonic wave transmission means for an arbitrary time, between an inner surface of the reactor pressure vessel and the inspection object, and whereinthe preprocessing means stores, as the differential processing-specific waveform, a signal that is received by the ultrasonic wave receiving means with the ultrasonic pulses interrupted by the interrupting means. 5. The reactor vibration monitoring device according to claim 3, comprising:a partial replica of the reactor pressure vessel; andreplica ultrasonic wave transmission means and replica ultrasonic wave receiving means arranged on the partial replica in a same positional relationship as that of the ultrasonic wave transmission means and the ultrasonic wave receiving means, and whereinthe preprocessing means stores, as the differential processing-specific waveform, a signal received by the replica ultrasonic wave receiving means when the replica ultrasonic wave transmission means transmits ultrasonic waves to the partial replica. 6. The reactor vibration monitoring device according to claim 3, wherein the preprocessing means identifies the reflected ultrasonic pulses reflected in the wall of the reactor pressure vessel based on a wall thickness of the reactor pressure vessel and the attached positions of the ultrasonic wave transmission means and the ultrasonic wave receiving means. 7. The reactor vibration monitoring device according to claim 3, wherein the preprocessing means stores, as the differential processing-specific waveform, the reflected ultrasonic pulses reflected in the wall of the reactor pressure vessel based on a wall thickness of the reactor pressure vessel and the attached positions of the ultrasonic wave transmission means and the ultrasonic wave receiving means. 8. The reactor vibration monitoring device according to claim 3, comprising position adjusting means for adjusting a relative position between the ultrasonic wave transmission means and the ultrasonic wave receiving means. 9. The reactor vibration monitoring device according to claim 3, wherein the preprocessing means performs extraction processing of identifying or extracting from the reflected pulse signal a time domain where ultrasonic pulses reflected by the inspection object are included, based on positions of the ultrasonic wave transmission means, the inspection object, and the ultrasonic wave receiving means. 10. A reactor vibration monitoring method, comprising:an ultrasonic wave transmission step in which ultrasonic wave transmission means is installed on an outside surface of a reactor pressure vessel and transmits ultrasonic pulses to an interior of the reactor pressure vessel;an ultrasonic wave receiving step in which ultrasonic wave receiving means is installed on the outside surface of the reactor pressure vessel and receives reflected pulses including ultrasonic waves of the ultrasonic pulses reflected by an inspection object in the reactor pressure vessel;a preprocessing step of performing processing to exclude reflected ultrasonic pulses occurring in a wall of the reactor pressure vessel from a reflected pulse signal received by the ultrasonic wave receiving means; anda calculation step of determining vibrations of the inspection object from the reflected pulse signal processed in the preprocessing step based on observation time of the inspection object, wherein:the preprocessing step includes: storing a differential processing-specific waveform in advance, and performing differential processing of the reflected pulse signal and the differential processing-specific waveform. |
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039717321 | claims | 1. In an apparatus for fixing radioactive or toxic waste including an extruder having a mixing chamber; means for feeding the waste and a carrier material to the mixing chamber; means for mixing the waste and the carrier material in the mixing chamber and advancing the mixture therein; means defining a heating zone in said mixing chamber for heating the material therein; a vapor outlet device communicating with the heating zone; an observation window closing off an upper portion of the vapor outlet device remote from the mixing means; a condenser connected after the vapor outlet device; a distillate accumulator connected after the condenser; means defining an extruder outlet through which the mixture is discharged from the extruder; a loading device connected to the extruder outlet for successively charging containers with the mixture emerging from the extruder outlet; the improvement comprising a. first means disposed in said vapor outlet device for cleaning said observation window; b. second means disposed in said vapor outlet device for removing deposits from a portion of said vapor outlet device that is adjacent said mixing means; c. two alternatingly operating, vertically oriented filters connected between said condenser and said distillate accumulator for removing carrier particles from the condensate withdrawn from said condenser; each filter having means defining a filter inlet at an upper part of the filter and connected to said condenser; and means defining a filter outlet at a lower part of the filter and connected to said distillate accumulator and; d. an interrupter bowl forming part of said loading device and being movably supported adjacent said extruder outlet for receiving the material from said extruder outlet during an exchange of an empty container for a filled container below said extruder outlet. a. a steam conduit extending into said vapor outlet device; b. an annular distributor conduit connected to said steam conduit and extending generally along the inside of said tubular wall; c. a plurality of steam lances connected to and extending from said distributor conduit in the direction of said mixing means; and d. an outlet nozzle attached to each steam lance; each outlet nozzle being oriented towards said wall. a. a steam conduit extending into said vapor outlet device; and b. an outlet nozzle attached to the steam conduit of said first means and oriented towards said observation window. a. a steam conduit extending into said vapor outlet device; b. a tube member having a plurality of free ends and connected to said steam conduit of said first means; and c. a nozzle attached to each end of said tube member, each nozzle of said first means being oriented towards said observation window. 2. An apparatus as defined in claim 1, wherein said vapor outlet device has a generally tubular, vertically oriented wall; said second means comprising 3. An apparatus as defined in claim 2, said first means comprising 4. An apparatus as defined in claim 3, further comprising an intermediate ring inserted into said wall and being contiguous therewith; said ring supporting said steam conduits; said observation window being secured to said wall above said intermediate ring. 5. An apparatus as defined in claim 2, said first means comprising 6. An apparatus as defined in claim 5, wherein said tube member has a U-shape. 7. An apparatus as defined in claim 5, wherein said tube member is comb-shaped. 8. An apparatus as defined in claim 1, wherein each said filter comprises a tubular, transparent member filled with an oil-absorbing material. 9. An apparatus as defined in claim 8, further comprising two vertically spaced sieves disposed in each filter for defining a first volume portion thereof, said oil-absorbing material filling out said first volume portion; the upper sieve bounding a second volume portion extending above said first volume portion. 10. An apparatus as defined in claim 1, each said container having a charge opening; said interrupter bowl having a diameter that is smaller than the diameter of each charge opening, the volume of said interrupter bowl is sufficiently large to accommodate material from said extruder outlet during at least four container exchanges. |
056174659 | description | DESCRIPTION OF THE INVENTION As illustrated in FIG. 1 in conjunction with FIG. 2, X-ray source 7 provides an X-ray output, or beam, 8 that is directed to a positioning unit 10 positioning an object, or a body portion, 11 at a scan area 12. X-rays passing through the object, or body portion, 11 are received at fixed, or stationary, X-ray converter screen 14, preferably a standard high efficiency phosphor converter screen having the size of the field of view (FOV) to be scanned, with the converter screen being mounted in holder 15 so that the converter screen is a curved membrane, as indicated in FIG. 2. Light signals are generated at converter screen 14 in response, and proportional to, received X-rays, as is well known, and the light signals are provided to sensor/coupling unit 16. Sensor/coupling unit 16 includes a coupler 18, preferably a fiber optic (FO) coupler such as a fiber optic window (FO-window) or a fiber optic reducer (FO-reducer) with an input face, or portion, 19 engaging the side of converter plate 14 opposite to the side of the converter plate facing the X-ray source. Sensor/coupling unit 16 also includes a sensor 20, preferably a single stage (or multiple stage) charge coupled device (CCD) or, preferably, a time delay integrated (TDI) CCD. X-ray source 7 is mounted at the pivot end 22 of mounting, or swing, arm 23, and sensor/coupling unit 16 is mounted at the free end 24 of the swing arm. When so mounted, X-ray source 7 is essentially pivoted to effect field of view (FOV) motion, while sensor/coupling unit 16 is moved in an arc below converter screen 14 to effect full FOV coverage (the curvature of the converter screen is the same as the arcuate path of travel of the sensor/coupling unit). In such swing arm systems, the sensor is maintained in register with the X-ray beam and the coupler remains closely adjacent to the converter screen (with the input face of the coupler engaging the converter screen) since the curvature of the converter screen is the same as the arcuate path followed by the sensor/coupling unit. As indicated in FIG. 1, movement of mounting arm 23 is controlled by actuator unit 26, implemented, for example, by a conventional mechanical and/or motor arrangement. Actuator unit 26 is controlled by control unit 28, which unit also controls sensor 20. Sensor 20 provides an electrical output signal indicative of the object, or body portion of a patient, then being subjected to X-rays, and the analog output signal is normally converted to a digital signal at digital conversion unit 30, and the digital signal is then typically coupled to an electronic unit, preferably an electronic readout and/or storage unit 32, which unit normally includes a computer 34 having data storage 36 and monitor 38 connected therewith. An air gap between X-ray converter screen 14 and input face 19 of coupler 18 cannot be tolerated since the presence of such an air gap would result in an unacceptable loss of resolution. It is therefore necessary that positive contact, or engagement, between converter screen 14 and input face 19 be maintained throughout the scan. To assure and/or establish positive contact between converter screen 14 and input face 19, a force is provided: to urge the converter screen in a direction toward the input face of the coupler (such as by introducing a cushion, preferably an air cushion, 40 between positioning unit 10 and converter screen 14, as indicated in FIG. 3); to pull the converter screen and the input face toward one another (such as by introducing a vacuum between the converter screen and the input face of the coupler using a vacuum source 42 and tube 43, as indicated in FIG. 4); and/or to bias the sensor/coupling unit toward the converter screen (such as by introducing springs 45 between a reference, plate 46 and the sensor of the sensor/coupling unit, as indicated in FIG. 5). In some types of systems, such as, for example, in gantry type systems, the X-ray source and sensor/coupler follow a straight line path. In this type of system, the converter screen is also flat, rather than having a curvature as shown in FIG. 2, with the system operating in the same manner with respect to maintaining positive engagement between the fixed converter screen and the input face of the movable coupler. This invention is not meant to be limited to use in the medical field, but has been found to be useful in medical applications and/or procedures to X-ray predetermined body portions (such as, for example, to X-ray breasts when used in a mammogram system). In addition, this invention is also not meant to be limited to a single, or multiple, CCD or TDI-CCD arrangement, and can be used, for example, with multiple ones of such sensors to obtain stereo or volumetric imaging information. For stereo imaging, two such sensors are utilized, and, for volumetric imaging, three such sensors are utilized. As can be appreciated from the foregoing, this invention provides a system and method for X-ray imaging wherein signals from a fixed converter screen are coupled to a movable sensor through a movable coupler having an input face maintained in engagement with the converter screen. |
abstract | A molten salt reactor includes a containment vessel, a reactor core, a neutron reflector spaced from the containment vessel, and liquid fuel enclosed within the core. The liquid fuel is comprised of a nuclear fission material dissolved in a molten salt. A heat exchanger is positioned external to the containment vessel. A plurality of heat transfer pipes are provided for transferring heat from the core to the heat exchanger. Each pipe has a first and a second end. The first end of each pipe is positioned within the reactor core for absorbing heat from the fuel. The heat exchanger receives the second end of each heat transfer pipe. At least two or more reactor shut down systems are provided. At least one shut down system may be a passive system and at least one or both shut down systems may be an active or a manually operated system. |
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042809215 | summary | FIELD OF THE INVENTION The present invention is concerned with a method for the volume reduction, immobilization, and treatment of hazardous waste materials for disposal, storage prior to disposal, or storage prior to retrieval. The present invention is especially advantageous in the treatment of hazardous chemically toxic and hazardous radioactive wastes. The present invention is particularly directed to a process for immobilizing and solidifying with volume reduction of a wide variety of hazardous chemically toxic and/or hazardous radioactive anhydrous salts and/or ashes in powdered form which are produced by processes such as, but not limited to: drying, calcining, incinerating, chemical reaction, catalyzing, drug manufacture, and flue gas scrubbing processes. BACKGROUND OF THE INVENTION The potential hazards of waste disposal have, in recent years, captured the attention of industry, government, and the public. The growth of the chemical processing and power generating industries, in particular, has resulted in the production of a large number of by-product materials (e.g., waste products) which are potentially hazardous to man and his environment. Recognition of these hazards is exemplified by the passage of the Resource Conservation and Recovery Act (RCRA) of 1976, the increased attention applied to the disposal of radioactive wastes, and a variety of legislation and regulations aimed at protecting the environment from such hazards. The necessity for these legislations and regulations was in large part due to inadequate protection of the environment with respect to waste disposal. Accordingly, it is believed that new methods of waste disposal will be required to meet these new, more stringent regulations. The basic objective of the present invention is to provide a process which can reduce the volume of powdered waste and immobilize hazardous wastes in a solid form. It is a further object of the present invention to render the processed waste product resistant to thermal, mechanical and chemical attack mechanisms which might be expected during transporting, storage, or disposal in a hydrogeological environment. Various methods have been suggested and developed for solidifying waste material such as low level radioactive waste materials including solidification with a bonding agent such as cement, borosilicate glasses, urea-formaldehyde resins, and bitumen. In addition, it has recently been suggested to treat nuclear waste by admixing the waste with a ceramic material and then sintering by hot isostatic pressing process (along these lines see Metal Powder Report, Volume 32, No. 3, March 1977, pages 98 and 99, and "Technologies for the Recovery of Transuranium Elements and Immobilization of Non-High-Level Wastes," G. L. Richardson, pages 307-313, Proceedings of the International Symposium on the Management of Wastes from the LWR Fuel Cycle, July 11-16, 1976, Denver, Colo., sponsored by ERDA). This latter publication also suggests a process employing cold pressing and requiring a heat treatment after pressing to effect sintering. The sintering temperature is about 1000.degree. C. On the other hand, the present invention does not require such sintering and still achieves strong solid products. This is believed to be due at least in part to the fact that this prior process suggested requires a ceramic rather than the types of metal employed herein. The "metal matrix" mentioned in FIG. 28 on page 309 of said article refers to the metal surface coating used in the "inertification" step suggested in said article. Additional prior art which is of general interest concerning this subject matter includes U.S. Pat. Nos. 3,213,031 and 4,028,265 which suggest adding various materials to waste products and heating the mixture. In addition, U.S. Pat. No. 3,994,822 suggests coating waste particles with an alpha-silicon carbide, then heating to carbonize the binder. This patent also suggests hot pressing in order to melt silicon and carbonize the carbide in order to enclose the waste material. Moreover, U.S. Pat. Nos. 3,993,579 and 4,010,108 are representative of those disclosures which suggest employing synthetic resins in treatment of waste material. U.S. Pat. No. 3,865,576 is of interest in that it suggests preparing a nuclear fuel by mixing UO.sub.2 -BeO and then hot pressing the mixture. SUMMARY OF THE INVENTION The present invention is concerned with a method for immobilizing, solidifying, and reducing the volume of powdered solid form waste material. The method includes blending waste material with powdered metal. The waste material is substantially anhydrous powdered solid material. The mixture of the waste material and powdered metal is compacted using a pressure of at least about 10 tons per square inch for sufficient time to provide a reduced volume, strong, solid product. The amount of the powdered metal employed is at least sufficient to solidify the waste material when the mixture is subjected to the above pressures. The present invention is also concerned with the solid obtained by the above-described process--one objective being to attain a solidified product whose compressive strength is in excess of 800 pounds per square inch. The compacted solid product of the present invention includes: substantially anhydrous solid waste material, at least about 1.5% by weight of powdered metal, and optionally small amounts of lubricant which may be added for the purpose of reducing wear of pressing machine parts. |
043127053 | description | Referring now to the drawing and first, particularly, to FIGS. 1 to 3 thereof, there is shown a spacer grid according to the invention formed of sheetmetal webs 1 and 2. The spacer grid not only contains the fuel rods 5 but also, in a conventional manner, non-illustrated control rod guidetubes. The latter are insertable into sleeves 6 which are also shown in FIG. 1. Fixed contact elements are formed by ring-shaped tube sections 3 which are inserted into slots 32 and 31, respectively (see FIGS. 2 and 3) at the points of intersection of the webs 1 and 2. They are fastened there by welding; in addition, welded spots can also be provided at the points of intersection of these webs 1 and 2. As shown in FIG. 8, these fixed contact elements 3 are bevelled at the corners 33 thereof. This facilitates insertion thereof into the slots 31 and 32 and facilitates later insertion of fuel rods and guide tubes; furthermore, flow resistance to the coolant, which is normally water, is thereby reduced. The same purpose is served by the "arrow-shaped" construction of the webs 1 and 2 at the intersection points. Since the non-illustrated control rod guide tubes have a greater diameter than that of the fuel rods 5 and, therefore, also the receiving sleeves 6 therefor and the adjacent ring-shaped elements 3 are provided with indentations 36, as shown in FIG. 9 and, in addition, are welded at the locations of the indentations 36 to the sleeve 6 to hold the latter (note FIG. 1). The resilient contact elements 4 are inserted into cutouts 12 formed in the web sheets 1 (see FIG. 3) and are held in this position by the subsequently inserted webs 2. A metallurgical joint is unnecessary. The construction thereof can be seen in detail from FIGS. 5, 6 and 7, wherein FIG. 6 is a side elevational view, FIG. 5 a corresponding top plan view and FIG. 7 a view of the contact element 4 in direction of the web sheet 1. It is apparent especially from FIG. 5 that this contact element 4 can be made by punching or stamping and bending out of a flat metal sheet in conventional manner. The two resilient parts 41 of the contact element 4, which can also be bent differently, of course, connect a head and a base piece 42 of triangular cross section. It is unnecessary to weld these end pieces 42 because short slots 45 are machined or worked into them and, like short slots 43 and 44 formed at the transversely opposed side of the contact element 4, embrace the wall of the web 1 (note FIG. 7) when the end pieces 42 are inserted into the cutout 12 (note FIG. 3) formed in the sheetmetal web 1 and are thereby themselves also held in the intended position thereof. As mentioned hereinbefore at the introduction hereto, these resilient contact elements 4 are made of materials, such as Inconel, for example. The remaining parts of the spacer grid, however, are formed of zirconium alloy. To reduce the expenditure of material further and, thereby, the neutron absorption as well as the pressure loss in the coolant flowing through, the mesh walls 1 and 2 of the spacer grid are furthermore formed with large-area openings 11 and 22. As is evident from FIG. 1, the fuel rods 5, respectively, rest only against the rings 3 which are disposed opposite the resilient contact elements 4. However, a space remains between the fuel rods 5 and the rings 3 which are disposed above and below the spring elements 4. In this way, the respective three-point mounting is provided in each diagonal of a spacer mesh and, moreover, overstressing of the resilient parts 41, if strong lateral forces should occur, is avoided since then, further movement of the fuel rod 5 is prevented by the rings 3 which are fastened above and below the resilient contact elements 4. This meets the requirement for an earthquake-proof construction. As is also apparent from FIG. 1, it is no longer possible for the fuel rod 5 to break out of this mounting, in comparison with the proposals in the state of the art, so that also this is provided as security against lateral forces such as could occur, for instance, due to non-uniform thermal stressing or loading of the fuel rods 5. It may also be seen from the foregoing that the cooling of the fuel rods 5 within the mesh is improved over the proposals in the state of the art since, at the narrowest locations between the fuel rods 5 and the web walls 1 and 2, no bumps or springs interfering with or hindering the flow are provided. Since, due to the geometrical relationships provided there, the flow cross section for the coolant is made more uniform, the behavior of the fuel rods 5 during thermal overloads is also considerably improved. This is achieved in particular also by providing for the coolant to be able to reach the continuously endangered points of a fuel rod just behind the corresponding contact points of the spacers in an unimpeded manner and in greater quantities. It then also follows (and detailed measurements have confirmed this), that the pressure losses are lower than in the spacer constructions which were heretofore conventional. In addition to these functional improvements in spacer construction, the assembly of the thus-improved spacers is also relatively simple to effect. First, the resilient contact elements 4, completed in themselves, are inserted into the openings 11 formed in the sheetmetal webs 1 and slid into the cutouts 12 up to a stop. After all of the places for the resilient contact elements 4 are occupied, the webs 2 are inserted into the slots 21 formed in the webs 1 and surround the latter with the cutouts 22. Thereafter, the rings 3 are inserted on the upper and lower sides of the assembled spacer grid and are automatically fastened by welding. This is, of course, done with due regard being given to those meshes at which the sleeves 6 for the non-illustrated control rod guide tubes are inserted. The contact springs 41 projecting into the latter meshes are first removed from the contact elements 4. A spacer for nuclear reactor fuel assembly which is so constructed is, of course, further held together in a conventional manner by an outer enveloping web. Furthermore, conventional coolant deflection vanes can also be provided for effecting improved turbulence of the coolant and thereby not only improve the cooling effect but also render the coolant outlet temperature more uniform. |
description | This is a continuation of application Ser. No. 10/272,763, filed Oct. 17, 2002 now abandoned. 1. Field of the Invention The present invention relates to scanning electron microscopes used for obtaining topography images of samples. More particularly, the present invention provides a method and system for improving the image obtained by a scanning electron microscope by optimizing the electron yield. 2. Description of the Related Art Conventional scanning electron microscopes (SEM) are used to obtain topographic images of a sample surface to detect, for example, imperfections on the sample surface. This is accomplished by generating a probe current which is directed in a raster pattern at the sample surface. The interaction of the electrons in the probe current with the sample surface produces secondary electrons (which are released from the sample surface due to bombardment by the probe current electrons) and backscattered electrons (which are, in effect, the probe current electrons reflected by the sample surface). The secondary and backscattered electrons are referred to herein as a signal electron beam (or signal current) and is directed to an imaging detector which produces an image of the sample surface. The interaction of the electrons in the probe current with the sample also causes absorption of some of the probe current electrons into the sample or dissipation of sample electrons from the sample surface, which results in the sample becoming negatively or positively charged, respectively. Such charging has an adverse affect on the accuracy of sample surface image detection because, for example, a positively charged sample surface will capture the probe current electrons, thereby causing a dark region to appear on the sample image as a result of the lack of, or a diminished amount of, signal electrons. An analytical tool widely used in categorizing and analyzing samples is a yield curve as shown in FIG. 1. A yield curve is a plot of the ratio of the signal electron beam and probe current with respect to the landing energy of the probe current on the sample. An ideal condition is reached for a yield value of “1” corresponding to equal values of the signal electron beam current and the probe current. As shown in curve A of FIG. 1, two landing energy values correspond to the ideal yield condition, shown as E1 and E2. The shape of the yield curve indicates a more gradual change at E2 relative to E1 such that minor variations of the landing energy proximate the E2 value result in only minor variations of the signal current. For this reason, using a landing energy of E2 to obtain an optimal topographic sample image is more desirable than a landing energy of E1. Prior art techniques for locating the optimal energy E2 for use in irradiating samples with the probe current are qualitative and are typically performed by a microscope technician in programming a microscope so that optimal landing energy values can be preset for a variety of samples to be examined. Such qualitative techniques entail measuring the probe current strength, such as by positioning an electron detector (e.g., a Faraday cup, etc.) in a path of the probe current, and obtaining an image of the sample by receiving the signal electron beam at an imaging detector. By obtaining various images at different landing energies and/or probe currents, the images are visually compared to select the optimal image, which corresponds either to landing energy E1 or E2. By obtaining additional images at landing energies proximate the values of E1 and E2 deduction will lead to distinguishing E1 from E2 using the known characteristics of the yield curve. Once the value of E2 is ascertained, that value will then be used to examine other like samples, such as in a quality control stage of a semiconductor substrate manufacturing facility. A problem of the prior art qualitative approach in locating a desired landing energy E2 is that although the level of the probe current is known from the use, for example, of a Faraday cup positioned in the probe current path, the signal current received by the imaging detector is not known. Thus, an SEM technician trying to locate an optimal landing energy for producing a satisfactory sample image must do so through trial and error by, for example, setting a first landing energy and obtaining an image therefrom, and then repeating the process at other landing energy values to obtain subsequent images. This procedure is not only laborious but results in a subjective determination by the technician as to what is the “best” image. The drawbacks of the prior art techniques used for obtaining topographic images of samples are alleviated by providing a method for obtaining quantitative readings of a signal electron beam produced by irradiating a sample surface with a probe current of a scanning electron microscope (SEM). This is accomplished by measuring the probe current and directing secondary electrons, which are produced from the irradiation of the sample surface, to a current detector for obtaining a current measurement of the signal electrons. The irradiation process is repeated at multiple landing energies of the probe current, and the landing energy corresponding to a value of a ratio of the signal electron beam measurement to the probe current measurement is used to identify a landing energy value for obtaining optimal topographic images of samples. Once the optimal landing energy value is identified, that value is used to irradiate other like samples to obtain optimal images of such sample surfaces. In one embodiment, the landing energy corresponding to a signal electron beam and probe current ratio value of approximately “1” is deemed the optimal landing energy. In another embodiment, the signal electron beam is measured by disposing a current detector coplanar with, and angularly offset from, an imaging detector used to obtain topographic images of samples. In still another embodiment, a current detector is selectively moved to a first position to receive the signal electron beam and to a second position to allow the signal electron beam to be received by the imaging detector. A system is also disclosed for identifying optimal landing energies of a probe current so that topographic images of sample surfaces can be obtained by selecting landing energies of the probe current to be proximate the optimal landing energy value. This is accomplished by a scanning electron microscope having an electron source for generating the probe current along a probe current path in a direction toward the sample plane for producing a signal current when the probe current irradiates a sample positioned on the sample plane. The microscope includes a probe current detector positioned for receiving at least a portion of the probe current for measuring the probe current, and an imaging detector positioned for receiving at least a portion of the signal electron beam. A controller is included for adjusting a landing energy of the probe current, and a current detector is included and is positioned for receiving at least a portion of the signal electron beam. The microscope also includes means for selectively directing at least a portion of the signal electron beam to either the imaging detector or the current detector. Other objects and features of the present-invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein. A scanning electron microscope 10 in accordance with the present invention is depicted in FIG. 2 and includes an electron source 12 for generating a principal beam or probe current 16 for irradiating a sample 24, such as a silicon wafer containing multiple devices (not shown). The sample is positioned at a sample table or sample plane 22. As is well known in the art, electron source 12 is capable of selectively generating probe currents at varying intensities. The generated beam is directed at an aperture 14 for refinement prior to impacting the sample 24 and is also acted upon by electro-optic components, such as a scanner 18, for directing the beam to the sample in a raster pattern, and a lens 20 for focusing the beam onto the sample 24. The probe current 16 is also acted upon by electronic forces and/or components such as sample bias, electron gun voltage and electrostatic elements within the microscope column (generally shown as element 30) which, as is known in the art, adjust or control the acceleration of the electrons in the probe current, thereby allowing user-selection of the probe current landing energy. As explained above, the bombardment or irradiation of a sample surface, e.g. a silicon wafer, with a probe current produces several physical phenomena which are dependent on the landing energy of the probe current. In general, the irradiation will produce backscattered electrons which are reflected from the sample surface, and secondary electrons which are discharged from the sample through collision with the probe current electrons. At certain landing energies and/or for certain types of samples, the sample 24 may become either positively charged or negatively charged, depending on the absorption or desorption of the probe current or the emission of sample electrons that are emitted from the sample due to interaction with the probe current. The backscattered and secondary electrons combine to form a signal electron beam 26. In prior art SEM systems, the signal electron beam would be intercepted by, or be directed to, an imaging detector 28, such as a microchannel plate as is known in the art, for producing a topographic image of the sample. The location or relative position of the imaging detector is dictated by the desired electron collection efficiency as well as by the particular application, such as the type of sample material under investigation and the material surface shape. Although in such prior art systems the intensity of the probe current is typically known—such as by the use of a Faraday cup or other type of current detector 13 positioned in the path of the probe current or on the sample holder 22 to measure the strength of the beam that impacted the sample 24—the strength of the signal electron beam 26 was not known. Rather, only a topographic image produced from receipt of the signal electron beam by the imaging detector 28 was known. As discussed above in connection with FIG. 1, an optimal topographic image of the sample occurs when a yield ratio (the ratio of the signal electron beam to the probe current—the ordinate of the curve of FIG. 1) is proximate the value “1”, and this yield ratio value corresponds to an abscissa coordinate value of landing energy values E1 and E2. Thus, it is desirable for an SEM microscope operator to be able to easily and quickly identify the landing energy values E1 and E2 (or preferably E2) for producing the optimal sample images. Once the optimal landing energies are ascertained, the landing energy E2 can then be programmed to memory, for example, on the SEM, for use in obtaining images of samples. In accordance with the present invention as shown in FIG. 2, a quantitative measurement of the signal electron beam is obtained by providing a current detector 32 located in a position to intercept the signal electron beam 26 to, in effect, obtain a measurement of the signal that will be used to produce an image of the sample 24. Thus, the signal electron beam current 26 that will be used to produce a topographic image when directed at the imaging detector 28, will be measured by the current detector. In this manner, the electron yield can be precisely calculated from the signal electron beam and probe current measurements, and then plotted for different landing energy values to identify the optimal landing energies E1 and E2 and to distinguish these optical landing energies from each other. In other words, the yield ratio at different landing energies will be calculated, such as by use of a processor (not shown) having an operation well known to those of ordinary skill in the art, until the yield ratio having a value approximating “1” is located, whereupon the landing energies corresponding to that yield value is then subsequently used for obtaining images of like samples. The direct measurement of the signal electron beam by the current detector 32 also allows for the generation of yield curves at different probe current values, i.e. at different probe current intensities and/or scan rates, which provides guidance on the characteristics of samples under charge conditions. With reference to FIG. 1, yield curves such as B and C may be obtained at constant probe current and/or scan rate values other than the probe current and/or scan rate value used to produce curve A. Thus, by obtaining yield curves at different constant probe current values, charge characteristics of samples can also be used to select an optimal value for the probe current. To obtain an accurate detection of the signal electron beam, the current detector 32 must be located in a specific position to intercept a level of the signal electron beam that will be received by the imaging detector 28. In a preferred embodiment, this is accomplished through proper alignment of the current detector 32 relative to the imaging detector 28. One technique for obtaining proper alignment is to bias the sample 24 to simulate a reflector, such as by applying a voltage (e.g., 9 keV) to the sample that is equal in magnitude to the voltage of the probe current. Such an applied bias causes the probe current to reflect from the sample surface, and the reflected beam can then be used as a reference for alignment and positioning of the current detector 32 as well as for alignment of other microscope components such as lens 20. In one embodiment, the location of the current detector is preferably coplanar with the imaging detector, as shown in FIG. 2, and angularly offset therefrom, such as at an angle of 180°. For this described embodiment, an electron router, such as a Wien filter 34 operating in a manner that is well known by those in the art, will selectively direct the signal electron beam 26 to the current detector 32 (shown as path 26a), or to the imaging detector 28 (shown as path 26b), depending on the Wien filter polarity. Thus, for a positive operating signal polarity, for example, the Wien filter 34 will direct the signal electron beam to the current detector to ascertain an optimal landing energy (E2), and for a negative operating signal polarity the Wien filter can direct the signal electron beam to the imaging detector for obtaining optimal images of the samples. The current detector 32 may be a solid state current detector of either a surface junction design—for low energy electron detection—or a semiconductor p-n junction design. The detector may be biased with a relatively low positive voltage (e.g. 50V) to ensure that secondary electrons generated during inelastic events are captured by the detector. Alternatively, the current detector may be a Faraday cup, a large conducting plate or an angled array of carbon nanotubes. Turning now to FIG. 3, an alternative to the Wien filter 34 arrangement of FIG. 2 is shown. In this embodiment, a scanning electron microscope 100 includes the components of the microscope 10 shown in FIG. 2 except for the Wien filter. A current detector 132 is movable between a first position (shown as 132a) and a second position (shown in phantom as 132b). An actuator 150, which may be mechanical or electrical, may be used, such as via arm 151, to selectively move the current detector into the position at 132a so that the signal electron beam 26 which would be received by the imaging detector 28 is, instead, received by the current detector 132 for providing a current measurement and, hence, an electron yield calculation when compared with the measurement of the probe current detector 13. Alternatively, the actuator 150 may be used to control the imaging detector 28 to receive the signal electron beam that is directed to the current detector 132. To direct the signal electron beam 26 to either the current detector 132 or the imaging detector 28, a positive voltage field will be applied proximate the imaging detector 28 to attract low voltage signal electrons of the signal electron beam 26 to either the current detector 132 or the imaging detector 28 (i.e. depending on the position of the current detector 132.) In this embodiment, once the optimal landing energy E2 is ascertained, the current detector 132 can be moved to position 132b, wherein the identified landing energy E2 will then be used to obtain optimal images of the sample. Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto. |
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description | Having reference now to the drawings, in FIG. 1A, there is shown a precision focusing x-ray collimator fabricating system in accordance with the present invention generally designated by the reference character 100. It should be understood that precision focusing x-ray collimator fabricating system 100 can also be used for fabricating non-focusing x-ray collimators. Precision focusing x-ray collimator fabricating system 100 includes a highly collimated synchrotron radiation source 102, such as an Advanced Photon Source (APS) at Argonne National Laboratory. Referring also to FIGS. 1B and 1C, synchrotron radiation source 102 is used with a scanner 104 for moving a substrate 106. For a non-focusing collimator, scanner 104 includes a first stage 108 mounted vertically or perpendicular to the beam to move the substrate 106 in the Z-direction while the substrate 106 is scanned vertically in the Z-direction. For a focusing collimator, scanner 104 includes a second stage 110 mounted on the first stage 108 that can rotate in the Y-Z plane about the X-axis, at a varying angle W of inclination of the substrate 106 as a function of the position of the Z-direction during the scan. A scanner controller 112 operatively controls the scanner 104 and stages 108, 110 with precise computer control, such as a multiaxis servo motor controller or with an arrangement of appropriate mechanical linkages. Precision focusing x-ray collimator fabricating system 100 includes a plurality of substrate processing stages including substrate coating stages 114, an exposure stage 116, a substrate x-ray resist development stage 118, a substrate electroplating stage 120, an optional substrate refinishing stage 122, an optional substrate resist removal stage 124, and an optional substrate removal stage 126. Referring to FIG. 1D, there is shown the substrate 106 together with a mask 130 that can be used for exposure to define a pattern of x-ray. The mask 130 is clamped to the substrate as indicated by lines 132 to provide the mask 130 in proximity and fixed to the substrate 106 between the substrate 106 and the highly collimated x-ray radiation source 102. Referring now the FIGS. 2 and 3, there are shown exemplary sequential steps for fabricating precision focusing x-ray collimators in accordance with the present invention. First a substrate 106 that is electrically conductive is used or the substrate 106 is coated with a thin layer of electrically conductive material 302, such as a metal suitable for use as a plating base for subsequent electroforming as indicated in a block 202. The substrate 106 may be x-ray transparent or not. Next, the substrate is coated with a layer of positive or negative x-ray resist, such as positive x-ray resist polymethylmethacrylate (PMMA), or a negative x-ray resist SU-8 epoxy described by U.S. Pat. No. 4,882,245 owned by IBM Corporation, of sufficient thickness such as 100 xcexcm to many mm, with appropriate adhesion promoters as necessary as indicated in a block 204. The x-ray resist is exposed to a pattern of x-ray by way of the synchrotron radiation source 102; the pattern delineating the grid or array of apertures to collimate the x-rays as indicated in a block 206. The exposed parts of the PMMA are removed by development in an appropriate solvent as indicated in a block 208. Metal capable of absorbing x-rays, such as gold, nickel, copper, platinum, zinc, lead, tin and alloys thereof, or another galvanic metal, is electroplated into the regions where the x-ray resist has been removed, starting from the previously deposited plating base as indicated in a block 210. Optionally, the surface is refinished to planarize as indicated in a block 212. Next remaining resist is optionally removed as indicated in a block 214. Finally, an optional substrate removal to release the grid may be provided as indicated in a block 216. During the exposure of the x-ray resist 304 carried by the substrate 106 to a pattern of x-ray by way of the synchrotron radiation source 102 at block 206 in FIGS. 2 and 3 can be varied to fabricate non-focusing or precision focusing x-ray collimators in accordance with the present invention. During exposure for non-focusing x-ray collimators, the substrate 106 is normally kept perpendicular to the impinging x-rays. For example, assume that the x-rays are propagated horizontally in the Y-direction as shown in FIG. 1B. With the synchrotron radiation source 102, the x-rays from the electron storage ring bend magnet, while highly collimated, are confined to a horizontal plane, such as a plane in the X-direction. As a result, to expose a two-dimensional area on the substrate 106, the substrate is scanned vertically in the Z-direction. If the substrate 106 is aligned to the X-Z plane, the x-rays will impinge normal to the substrate surface and the final collimator will provide collimation in the same direction, without focusing. During exposure for precision focusing x-ray collimators, the substrate is scanned in the Z-direction while the angle of inclination of the substrate is varied as a function of the position in the Z-direction during the scan to produce the precision focusing x-ray collimators. In accordance with a feature of the invention, when the substrate 106 is inclined with respect to the Z-direction, while still aligned in the X-direction, the exposure has the same relative angle to the substrate, and the final collimator provides collimation in the inclined direction. A collimator can be formed that focuses in one direction by changing the angle the substrate forms with respect to the exposing x-rays while the substrate 106 is being scanned through the beam in the Z-direction. This is done by placing the substrate 106 on the scanner stage 110 that can rotate in the Y-Z plane about the X-axis, and changing the angle as the substrate 106 is being scanned vertically in the Z-direction. The angle of inclination can be controlled mechanically by fixing an arm to the scanner stage 110 and to the position of the desired focus located in the plane of the exposing x-rays. Alternatively, the angle of inclination can be precisely controlled with the scanner controller 112. It should be understood that the production of a collimator that focuses in two directions can be achieved by first exposing through a grating mask in one direction, then rotating the substrate by 90 degrees in the X-Z plane while keeping the grating mask fixed. Then exposing again so that the sum of the exposures is a two-dimensional grid with a variable angle of inclination with respect to the substrate surface as a function of distance from the center of both the X and Z directions. Also, by selectively varying the relationship of the angle of inclination to the Z-position, a resulting collimator is produced that focuses at different distances for X versus Z, or may provide different focus distance as a function of the distance from the center of the collimator. While the present invention has been described with reference to the details of the embodiments of the invention shown in the drawing, these details are not intended to limit the scope of the invention as claimed in the appended claims. |
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claims | 1. A multi-leaf collimator (MLC) comprising:a driving array comprising a plurality of motors;a leaf array comprising a plurality of leaves; anda plurality of elongated flexible transmission units, each connected to one of the leaves of the leaf array to form a collimator unit such that motors of the driving array are operably connected with leaves of the leaf array through the transmission units to form a MLC array that comprises a plurality of collimator units;wherein in each collimator unit, the motor transmits motion from the motor to the leaf through the transmission unit to adjust the position of each leaf independently, andwherein the transmission unit comprises a transmission line and an elastic piece operably connected to the transmission line, and the transmission line provides the leaf a first force, and the elastic piece provides the leaf a second force. 2. The collimator of claim 1, having a pair of driving arrays and a pair of leaf arrays paired up to form a pair of MLC arrays. 3. The collimator of claim 1, wherein the transmission unit includes a transmission shaft. 4. The collimator of claim 3 further comprising a connection unit configured to connect the transmission unit and the leaf, wherein the leaf has a groove, the connection unit has an expansion bump, and the expansion bump matches the groove. 5. The collimator of claim 1, wherein the MLC is used in a device having a magnetic field and the transmission units are angular and create a distance between the motors and the magnetic field to reduce the interferences between the motor and the magnetic field. 6. The collimator of claim 1, wherein the elastic piece of the transmission unit is a spring having a first end and a second end, the first end of the spring is fixed, the second end of the spring is connected to the leaf, and the spring is in a compressed state. 7. The collimator of claim 1, wherein the leaf has a thickness in a range from 0.8 mm to 2.2 mm. 8. The collimator of claim 1 further comprising a conversion unit configured to change a rotational motion of the motor to a linear motion. 9. The collimator of claim 8, wherein the conversion unit comprises a gear and a worm, the worm is connected to the motor, and the gear is driven by the worm. 10. The collimator of claim 9, wherein the gear and the worm have a self-locking function. 11. The collimator of claim 1 further comprising a guiding unit configured to control a movement path of the transmission unit. 12. The collimator of claim 1 further comprising a feedback module configured to detect a movement of the leaf. 13. A collimator system comprising:a leaf array comprising a plurality of leaves operated by a leaf module;a driving array comprising a plurality of motors operated by a driving module wherein each motor of the driving array is operably connected to one of the leaves of the leaf array through elongated flexible transmission unit to create a distance between the motor and the leaf and form a collimator unit such that the motors of the driving array are connected with leaves of the leaf array to form a MLC array that comprises a plurality of collimator units, with each motor transmitting motion to one of the leaves to adjust the position of each leaf independently; anda processing module to generate a leaf movement profile based on an initial location, a current location, and a target location for each of the leaf such that the motor of the driving module drives each leaf according to the leaf movement profile;wherein the movement profile of the motor includes a first speed of the motor during a first stage, a second speed of the motor during a second stage, and a third speed of the motor during a third stage, the first speed increases with time, the second speed is constant, and the third speed decreases at a variable rate with time, andwherein the transmission unit comprises a transmission line and an elastic piece operably connected to the transmission line, and the transmission line provides the leaf a first force, and the elastic piece provides the leaf a second force. 14. The collimator system of claim 13, wherein the variable rate is determined based on a distance between the leaf current location and the leaf target location. 15. The collimator system of claim 13 further comprising a feedback module configured to detect a movement of the leaf. 16. The collimator system of claim 15, wherein the feedback module comprises a first feedback unit and a second feedback unit, the first feedback unit is configured to detect the movement of the leaf, and the second feedback unit is configured to detect a movement of the motor. 17. The collimator system of claim 16, wherein the processing module detects a status of the leaf based on the movement of the leaf and the movement of the motor. 18. The collimator system of claim 13, wherein the transmission unit is flexible and is in turn connected to a connection unit that is connected to one of the leaves of the leaf array to form the collimator unit. 19. The collimator system of claim 13, further comprising a protection module configured to detect whether the motor is running normally. 20. The collimator system of claim 13, wherein the processing module obtains a trajectory traveled by the leaf based on the initial, current, and target locations of each of the leaves to provide different movement speeds for the leaf during different stages of travel. |
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042591562 | claims | 1. In a device for couping pipelines in a pressure vessel of a nuclear reactor having a first piping section sealingly extending through the pressure vessel-housing wall and fastened thereto, and a second piping section sealingly connected to the first piping section, as well as a core container fastened within the pressure vessel, the core container having a cover, and steam separators forming, together with the core-container cover, a structural unit, the second piping section being also included with the core-container cover and with the steam separators fastened to the cover in the structural unit and, when the pressure vessel is opened, the second piping section together with the core-container cover being liftable out of the pressure vessel and being reinsertable into the pressure vessel; the first and the second piping sections being in mutual contact at coaxial sealing surface portions formed thereon at the sealed connecting location thereof, ball-cylinder seat means forming an axial slide fit for bringing said sealing surface portions of the first and second piping sections into said mutual contact, said sealing surface portions being placeable into a nominal location of sealing connection thereof through the weight per se of the structural unit of the core-container cover and the steam separators as well as through bracing forces for the core container cover, said bracing forces being oriented in axial direction of the pressure vessel, and resilient means foraffording relative motion, dependent upon thermal expansion, of said sealing surface portions within a predetermined tolerance range without impairing sealing action thereof. 2. Device according to claim 1 wherein the cylinder seat of said ball-cylinder seat means is formed as an angle ring, said sealing surface portions of the first and the second piping sections, as well as of said angle ring, having outer layers of material selected from plating material and weldment material. 3. Device according to claim 1 wherein the cylinder seat of said ball-cylinder seat means comprises an angle ring having inwardly directed flanks at the underside thereof held against a support flange of an upwardly directed mouthpiece of the first piping section and outwardly directed flanks surrounding coaxial sealing surface portions of the ball seat of said ball-cylinder seat means of an upwardly directed union of the second piping section. 4. Device according to claim 3 wherein said angle ring has a retaining flange at the outer periphery thereof spring-elastically braced with said support flange of said mouthpiece of the first piping section in a manner that relative movement in at least one of radial and tangential directions between the second piping section and said angle ring with slight tilting disposition of said angle ring within said predetermined tolerance range is afforded. 5. Device according to claim 4 wherein said flanks at the underside of said angle ring are formed with spherical contact surfaces engaging said flange of said mouthpiece. 6. Device according to claim 4 wherein the second piping section has conically inwardly running axial guidepins and said angle ring-retaining flange is formed with corresponding guide bushings for engaging said guide pins whereby said union of the second piping section is centered. 7. Device according to claim 5 including a sheetmetal apron applied to said support flange of said upwardly directed mouthpiece of the first piping section for shielding said angle ring-sealing surface portions from the pressure-vessel wall. 8. Device according to claim 7 wherein said upwardly directed mouthpiece has a tube part, and said tube part of said upwardly directed mouthpiece, said angle ring and said union of the second piping section are flattened in radial direction forming a slot-like cross section. |
summary | ||
description | This application claims priority to U.S. Provisional Patent Application No. 62/000,452 filed on May 19, 2014, the contents of which are incorporated by reference herein. This invention was made with Government support under Contract No. DE-NE0000633 awarded by the Department of Energy. The Government has certain rights in this invention. This disclosure generally relates to systems, devices, structures, and methods for monitoring a nuclear power reactor. In a nuclear reactor, a core of nuclear material may be confined to a relatively small volume internal to the reactor so that a reaction may occur. A controlled nuclear reaction may persist for an extended period of time, which may include several years, before refueling of the reactor core is required. Accordingly, when used as a source of heat for converting water into steam, a properly designed nuclear reactor may provide a carbon-free, stable, and highly reliable source of energy. During operation of a nuclear reactor, one or more sensors may be used to measure a neutron flux associated with a neutron source and/or with neutrons generated through fission events in the reactor core. Similarly, it may be useful to monitor the temperature, pressure, coolant level, power level, and/or coolant flow rate within the reactor module to ensure that all aspects of the reactor's internal operation are maintained within acceptable limits. For example, in the event that the flow of coolant is too low, components within the reactor may undergo excessive heating, which may result in the failure of one or more reactor components. In the event that the flow of coolant is too high, the reactor core may experience an undue level of cooling, which may result in undesirable fluctuations of reactor output power levels. Temperatures and potentially corrosive characteristics of coolant located near the reactor core and/or otherwise located within the reactor module may cause sensors, gauges, and/or other types of measurement devices to fail over a period of time. Additionally, shutting down the reactor to replace and/or repair the failed measurement devices may result in significant operational costs and ultimately a less efficient and less reliable source of energy. Periodically, a reactor module may need to be refueled, serviced, and/or inspected. Certain types of reactor modules may be removed from the reactor bay and replaced with a new reactor module. In addition to the number of sensors that may be used to monitor various characteristics of the reactor module, additional components, fittings, attachments, piping, wiring, supports, etc. that may be attached, connected to, or otherwise placed in communication with the rector module may impede the ability to gain access to and/or to service the reactor module. Similarly, it may take a significant amount of time to connect and disconnect the various components from the reactor module, such as during installation of the reactor module and removal of the reactor module, respectively. Furthermore, any penetrations into a reactor vessel and/or containment vessel that are made to accommodate the various components may provide potential leakage points and/or areas of structural weakness in the reactor module. This application addresses these and other problems. A system for monitoring a reactor module housed in a reactor bay may include a mounting structure and one or more extendable attachment mechanisms connected to the mounting structure. Additionally, one or more monitoring devices may be operably coupled to the one or more extendable attachment mechanism, and the one or more extendable attachment mechanisms may be configured to selectively position the one or more monitoring devices at varying distances from a wall of the reactor bay to place the one or monitoring devices in proximity to the reactor module. One or more monitoring devices may be located in a reactor bay during a monitoring operation. In some examples, the one or more monitoring devices may be completely submerged in a pool of water contained within the reactor bay. The one or more monitoring devices may be extended from a retracted position near a wall of the reactor bay to an extended position near the reactor module. The one or more monitoring devices may be configured to monitor the reactor module in the extended position. Additionally, the one or more monitoring devices may be retracted to the retracted position after completing the monitoring operation. A system comprising a transportable monitoring device may be configured to monitor one or more neutron sources. In other examples, a system comprising a transportable monitoring device may be configured to monitor a flow rate of primary coolant contained within the reactor module. One or more signal path devices may be configured to enhance, augment, multiply, and/or otherwise increase a signal that may be detected at one or more of the monitoring devices. Various examples disclosed and/or referred to herein may be operated consistent with, or in conjunction with, one or more features found in U.S. Pat. No. 8,687,759, entitled Internal Dry Containment Vessel for a Nuclear Reactor, U.S. Pat. No. 8,588,360, entitled Evacuated Containment Vessel for a Nuclear Reactor, U.S. application Ser. No. 14/242,677, entitled Neutron Path Enhancement, and/or U.S. Provisional Application No. 62/021,627, entitled Flow Rate Measurement in a Volume, the contents of which are incorporated by reference herein. FIG. 1 illustrates a cross sectional side view of an example reactor module 100 comprising a reactor vessel 20 housed in a containment vessel 10. A reactor core 30 is positioned at a bottom portion of a cylinder-shaped or capsule-shaped reactor vessel 20. Reactor core 30 may comprise a quantity of fissile material that generates a controlled reaction that may occur over a period of perhaps several years. In some examples, one or more control rods may be employed to control the rate of fission within reactor core 30. The control rods may comprise silver, indium, cadmium, boron, cobalt, hafnium, dysprosium, gadolinium, samarium, erbium, europium, other types of materials, and any combination thereof, including alloys and compounds. Reactor core 30 may be partially or completely submerged within a coolant or fluid, such as water, which may include boron or other additives. The coolant rises after making contact with a surface of the reactor core 30 and removing heat there from. The coolant travels upward through one or more heat exchangers 40 thus allowing the coolant to impart the heat removed from the reactor core 30 to the heat exchangers 40. In some examples, the coolant travels at a flow rate within the reactor vessel due to natural circulation as the coolant is alternately heated and cooled at different elevations as it circulates within the reactor vessel. The flow rate of the coolant may vary during different modes of operation of the reactor module 100, such as reactor initialization, full power, and shutdown. In some examples, coolant within reactor vessel 20 remains at a pressure above atmospheric pressure, thus allowing the coolant to maintain a high temperature without vaporizing (i.e. boiling). As coolant within the one or more heat exchangers 40 increases in temperature, the coolant may begin to boil. As boiling commences, vaporized coolant may be routed from a top portion of heat exchangers 40 to drive one or more of turbines. The turbines may be configured to convert the thermal potential energy of steam into electrical energy. Containment vessel 10 may be approximately cylindrical in shape. In some examples, containment vessel 10 may be cylinder-shaped or capsule-shaped, and/or have one or more ellipsoidal, domed, or spherical ends. Containment vessel 10 may be welded or otherwise sealed to the environment, such that liquids and/or gases are not allowed to escape from, or enter into, containment vessel 10. In various examples, reactor vessel 20 and/or containment vessel 10 may be bottom supported, top supported, supported about its center, or any combination thereof. In some examples and/or modes of operation of the reactor module 100, containment vessel 10 may be partially or completely submerged within a pool of water or other fluid. The volume between reactor vessel 20 and containment vessel 10 may be partially or completely evacuated to reduce heat transfer from reactor vessel 20 to the external environment. However, in other examples and/or modes of operation of the reactor module 100, the volume between reactor vessel 20 and containment vessel 10 may be at least partially filled with a gas and/or a fluid that increases heat transfer between the reactor vessel and the containment vessel. Containment vessel 10 may substantially surround the reactor vessel 20 within a containment region. The containment region may comprise a dry, voided, and/or gaseous environment in some examples and/or modes of operation. The containment region may comprise an amount of air, a noble gas such as Argon, other types of gases, or any combination thereof. Any gas or gasses in containment vessel 20 may be evacuated and/or removed prior to operation of reactor module 100. An inner surface of reactor vessel 20 may be exposed to a wet environment comprising coolant and/or vapor, and an outer surface of reactor vessel 20 may be exposed to a substantially dry environment. The reactor vessel 20 may comprise and/or be made of stainless steel, carbon steel, other types of materials or composites, or any combination thereof. Additionally, reactor vessel 20 may include cladding and/or insulation. Removal of convective heat transfer in air occurs generally at about 50 torr (50 mmHG) of absolute pressure, however a reduction in convective heat transfer may be observed at approximately 300 torr (300 mmHG) of absolute pressure. In some examples, the containment region may be provided with, or maintained below, a pressure of 300 torr (300 mmHG). In other examples, the containment region may be provided with, or maintained below, a pressure of 50 torr (50 mmHG). The containment region may be provided with and/or maintained at a pressure level which substantially inhibits all convective and/or conductive heat transfer between reactor vessel 20 and containment vessel 10. A complete or partial vacuum may be provided and/or maintained by operating a vacuum pump, steam-air jet ejector, other types of evacuation devices, or any combination thereof. By maintaining the containment region in a vacuum or partial vacuum, moisture within the containment region may be eliminated, thereby protecting electrical and mechanical components from corrosion or failure. Neutrons generated at or near reactor core 30 may comprise fast neutrons, slow neutrons, thermal neutrons, or any combination thereof. A neutron source may be used to provide a stable and reliable source of neutrons for the initiation of a nuclear chain reaction, for example when the reactor includes new fuel rods whose neutron flux from spontaneous fission may otherwise be insufficient for purposes of reactor startup. Additionally, the neutron source may be configured to provide a constant number of neutrons to the nuclear fuel during startup or when restarting the reactor after being shutdown (e.g., for maintenance and/or inspection). In some examples, the power level of the reactor may be inferred, at least in part, from the number of neutrons that are emitted from the neutron source and/or additional neutrons that are generated as a result of a subcritical multiplication process in the reactor core 30 that may occur in response to the emission of neutrons by the neutron source. In examples in which containment vessel 10 is at least partially submerged in a pool of water, access to the portion of containment vessel 10 which surrounds reactor core 30 may be under water. For that matter, the entire reactor vessel 20 may be situated under the top surface of the pool of water. Wires, power cords, and/or other devices may penetrate through a top head of containment vessel 10, such that any penetrations through containment vessel are located above the top surface of the pool of water. FIG. 2 illustrates a cross-sectional top view of an example system 200 for monitoring a reactor module, shown in an inactive, or retracted position. In some examples, FIG. 2 may be understood as illustrating a top view of the reactor module 100 of FIG. 1 taken through cross-section 2A-2A at or near the reactor core 30. In other examples, the top view may comprise a cross-sectional view taken at a different elevation, such as at or near steam generator 40 (FIG. 1), above steam generator 40, or between steam generator 40 and reactor core 30. Containment vessel 10 may be placed, at least partially, in a pool of water 55, for example as located below ground level. The pool of water 55 may be stored in a reactor bay 50 comprising a plurality of walls. In some examples, reactor bay 50 may comprise four walls. In other examples, reactor bay 50 may be part of a facility comprising a number of interconnected reactor bays, where each bay may have fewer than four walls so as to provide passageway between adjacent bays and/or for purposes of moving a reactor module during installation, refueling, or maintenance. Containment vessel 10 may be configured to prohibit the release of coolant associated with reactor vessel 20 to escape outside of containment vessel 10 into the pool of water 55 and/or into the surrounding environment. A neutron source 35 may be positioned so that the neutron flux it produces is detectable by reactor monitoring instrumentation. For example, neutron source 35 may be inserted in regularly spaced positions inside the reactor core 30, such as in place of one or more fuel rods of a fuel grid 32. When the reactor module 100 is shutdown, neutron source 35 may be configured to induce signals that may be detected by the reactor monitoring instrumentation. In some examples, the equilibrium level of neutron flux in a subcritical reactor may be dependent on the strength of neutron source 35. Neutron source 35 may be configured to provide a minimum level of neutron emissions to ensure that the reactor level may be monitored, such as during reactor startup. System 200 may comprise one or more transportable apparatus 210. Apparatus 210 may be mounted on a wall of reactor bay 50. In some examples, transportable apparatus 210 may be mounted on a transport system 220 located on the wall of reactor bay 50. Transport system 220 may be configured to allow transportable apparatus 210 to travel within reactor bay 50, such as vertically and/or horizontally. System 200 may comprise one or more additional transportable apparatus and/or transport systems, such as a second transportable apparatus 215 located on an opposite wall of reactor bay 50 from transportable apparatus 210. In some examples, one or more vertical tracks and/or horizontal tracks may be used to allow transportable apparatus 210 to move around the one or more walls of reactor bay 50, and about a circumference of containment vessel 10. Accordingly, transportable apparatus 210 may be moved to a plurality of locations within reactor bay 50 in order to provide for inspection of, and/or access to, some or all of the exterior surface of containment vessel 10. Additionally, transportable apparatus 210 may be connected to a flexible cable and/or wire that moves, coils, retracts, and/or extends while transportable apparatus 210 is moved by transport system 220. Transport system 220 may comprise a track, a hoisting device, a winch, a pulley, a cable, a motor, one or more guide rails, wheels, or rollers, other transportation components, or any combination thereof. Transportable apparatus 210 may comprise one or more monitoring devices, such as monitoring device 250, located on a mounting arm 225. Monitoring device 250 may comprise a sensor, a gauge, a transmitter, a receiver, a detector, a demodulator, a camera, an imaging device, an ultrasound device, other types of measurement devices and/or monitoring devices, or any combination thereof. Monitoring device 250 may be configured to measure, monitor, record, analyze, view, inspect, calculate, estimate, or otherwise determine one or more functions, characteristics, or other type of information associated with reactor module 100. In some examples, monitoring device 250 may be configured to monitor a neutron flux associated with neutron source 35 and/or associated with neutrons generated within or near reactor core 30. In other examples, monitoring device 250 may be configured to measure a flow rate of coolant within reactor vessel 20. Other types of information that monitoring device 250 may be configured to monitor, measure, or determine include: temperature, pressure, humidity, chemical concentration levels, coolant levels, reactivity, power, heat, vibration, sound, toxicity, material hardness, images, or any combination thereof. In some examples, one or more cameras or imaging devices may be used to scan all or a portion of containment vessel 10. Two apparatus, such as transportable apparatus 210 and second transportable apparatus 215, are shown as being located on opposite walls of reactor bay 50. Each transportable apparatus is additionally shown as having two mounting arms and two corresponding monitoring devices located on the ends of the mounting arms. Mounting arm 225 is shown in a retracted position. In the retracted position, monitoring device 250 may be located near the wall of the reactor bay 50, some distance away from containment vessel 10. By selectively locating or moving monitoring device 250 specifically, and transportable apparatus 210 more generally, away from containment vessel 10, access to reactor module 100 may be facilitated, including any operations which may involve repositioning and/or moving reactor module 100 into or out of reactor bay 50. System 200 may comprise a dry disconnect apparatus 230. Dry disconnect apparatus 230 may be connected to one or more transportable apparatus, such as transportable apparatus 210, second transportable apparatus 215, and/or to one or more monitoring devices associated with the transportable apparatus, such as monitoring device 250. In some examples, dry disconnect apparatus 230 may be located above pool of water 55, and configured to provide an electrical connection to the transportable apparatus and/or monitoring device. Additionally, dry disconnect apparatus 230 may be configured to communicatively connect the transportable apparatus and/or monitoring device to a processing device or control panel. In some examples, dry disconnect apparatus 230 may comprise a processing device, a wireless communication device, an alert system, a database, other monitoring devices, or any combination thereof. Information that is measured, monitored, recorded, analyzed, viewed, inspected, calculated, estimated, or otherwise obtained by the monitoring device may be communicated to and/or through dry disconnect apparatus 230. For example, the information may be transmitted through dry disconnect apparatus 230 to a processing device for further evaluation. Each transportable apparatus 210, 215 may be associated with a separate dry disconnect apparatus. In some examples, dry disconnect apparatus 230 may be configured to be electrically and/or communicatively coupled with two or more transportable apparatus and/or monitoring devices. FIG. 3 illustrates an example system 300 for monitoring a nuclear reactor module 100, shown in an active, engaged, or extended position. One or more of the components, apparatus, and/or systems described with respect to system 300 may be configured similarly as system 200 of FIG. 2. System 300 may comprise one or more transportable apparatus such as a first transportable apparatus 311 and a second transportable apparatus 312. First transportable apparatus 311 may be mounted on a first wall of reactor bay 50, and second transportable apparatus 312 may be mounted on a second wall of reactor bay 50. First transportable apparatus 311 may comprise a first monitoring device 351 and a second monitoring device 352. First monitoring device 351 and second monitoring device 352 may be attached to one or more arms, such as a first arm 321 and a second arm 322, respectively. First arm 321 and second arm 322 may be pivotably attached to first transportable apparatus 311 by a hinge, a pivot, a joint, a gate, a swivel, other types of connections, or any combination thereof. In some examples, first arm 321 and second arm 322 may be configured to cause first monitoring device 351 and second monitoring device 352 to move from a retracted position, similar to that shown in FIG. 2, to an extended position as shown in FIG. 3. In the extended position, one or both of first monitoring device 351 and second monitoring device 352 may be located adjacent to, or in contact with, an exterior surface of containment vessel 10. Second transportable device 312, including a third monitoring device 353 and a fourth monitoring device 354, may be configured similarly as first transportable device 311. Reactor bay 50 may be configured as essentially a square or rectangular area comprising a width 376. Additionally, reactor module 100 may comprise a width 372, which may be approximately equal to a diameter of containment vessel 10. Reactor bay 50 may provide a clearance distance 374 between one or more wall of the reactor bay 50 and the reactor module 100. In the retracted position of first transportable device 311 and/or second transportable device 312 (such as illustrated in FIG. 2), the distance between one or more monitoring devices 351, 352, 353, 354 and vessel 10 may be approximately equal to clearance distance 374. In some examples, the clearance distance 374 may equal several feet or several meters. Although four monitoring devices are illustrated in FIG. 3, more or fewer monitoring devices are contemplated herein. In some examples, the number of monitoring devices may be selected according to a corresponding number of components and/or features which are being measured or monitored. For example, first monitoring device 351 may be configured to monitor the neutron flux associated with a first neutron source 301, second monitoring device 352 may be configured to monitor the neutron flux associated with a second neutron source 302, third monitoring device 353 may be configured to monitor the neutron flux associated with a third neutron source 303, and fourth monitoring device 354 may be configured to monitor the neutron flux associated with a fourth neutron source 304. In some examples, the plurality of monitoring devices may be equally spaced around the perimeter of containment vessel 10. As a neutron source ages, the ability to generate neutrons may diminish over time such that the neutron flux during a reactor initialization may be greater than the neutron flux that is present when the reactor is restarted. The proximity or distance of the one or more monitoring devices to containment vessel 10 may be adjusted to accommodate any change or variation in strength of a neutron source. For example, one or more of the monitoring devices may be incrementally moved closer to containment vessel 10 over the life of the respective neutron source in order to adjust for the decreased neutron flux. One or more of the monitoring devices may comprise near-field or wireless communication devices. In some examples, such as with transportable apparatus 311 oriented in the extended position, monitoring devices 351 and/or 352 may be positioned near enough to receive and or exchange information with another wireless device located within containment vessel 10. Positioning the monitoring devices 351, 352 near corresponding wireless communication devices within containment vessel 10 may reduce the likelihood of cross-talk and may also reduce the signal strength required for uninterrupted communication. Additionally, by using near-field and/or wireless communications, the number of penetrations in containment vessel 10 may be reduced or eliminated. By selecting and/or sizing relatively low-powered neutron source(s) as the neutron source to be monitored, neutron cross-talk between monitoring devices may be further minimized and/or eliminated. This may result in more accurate neutron flux measurements at the one or more monitoring devices. In some examples involving a modular reactor design comprising a plurality of reactor modules, the strength of the neutron source and/or the relative position of the monitoring devices may similarly reduce cross-talk between adjacent reactor modules. In still other examples, one or more monitoring devices 351, 352 may be configured to detect and/or communicate with a device located within containment vessel 10 via audible signals. An internal device may be configured to emit a sound or alert in response to detecting and/or otherwise experiencing a particular operating condition. The operating condition may comprise a coolant level, a coolant temperature, a coolant flow rate, a fuel temperature, a containment pressure, a chemical composition, the presence of a gas, other types of operating conditions, or any combination thereof. In some examples, the internal communication device may be integrated with and/or otherwise coupled to a fuel rod for purposes of evaluating the integrity of the fuel. The internal device may be configured to emit a sound that is detectable by the one or more external monitoring devices 351, 352. The sound may indicate a particular operating condition of the fuel such as a fuel temperature. The internal device may comprise a piezoelectric device configured to emit a sound when the fuel temperature exceeds a predetermined threshold. The relative sound level and/or pitch may indicate different ranges of fuel temperature. Transportable apparatus 311 and/or monitoring devices 351, 352 may be located or positioned at an approximate elevation of reactor core 30. Monitoring devices 351, 352 may be configured to detect neutrons generated at or near reactor core 30. In some examples, monitoring devices 351, 352 may be separated from the neutron source(s) and/or from reactor core 30 by a containment region located between containment vessel 10 and reactor vessel 20. Neutrons generated by and/or emitted from the neutron source(s) and/or from the reactor core 30 may pass through the containment region prior to being detected by monitoring devices 351, 352. Locating monitoring devices 351, 352 adjacent to containment vessel 10 may mitigate or eliminate the neutron moderating effects of the pool of water 55 which surrounds containment vessel 10. In still other examples, monitoring devices 351, 352 may be configured to be physically coupled, attached, or plugged into one or more receiving devices associated with containment vessel 10. The receiving devices may comprise a socket or other type of connection which may be configured to provide an electrical connection with the monitoring device. Signals or other types of information may be transmitted to, or from, monitoring devices 351, 352 via the one or more receiving devices. For example, monitoring devices 351, 352 may be configured to receive information indicating the positions of one or more control rods within the reactor pressure vessel. The receiving devices may be configured to detect the presence and/or insertion of at least a portion of the monitoring device to create the connection. The receiving device may comprise a fitting operable to secure the monitoring device in the connected position. In some examples, the receiving device may be configured to lock and/or release in response to detecting the presence of the monitoring device. Additionally, the receiving device may be configured to release the monitoring device in response to receiving a signal that transportable apparatus 311 is preparing to move and/or retract one or both of first arm 321 and second arm 322. A spring force may be applied to first and second arms 321, 322 to move the monitoring devices 351, 352 towards containment vessel 10. Additionally, the spring force may exert a continuous force to maintain contact between monitoring devices 351, 352 and containment vessel 10 in the extended position FIG. 4 illustrates a side view of an example system 400 for monitoring a nuclear reactor module, shown in a raised position. System 400 may comprise one or more monitoring devices 450 mounted on the ends of one or more extendable arms 425. Extendable arm 425 may be pivotably attached to a hinged device 410. System 400 may be mounted to or located next to a wall of reactor bay 50. In some examples, in the raised position system 400 may be located at an elevation which is above the reactor bay 50, e.g., at the top of the wall. In addition to moving to an extended and retracted position, in some examples hinged device 410 may comprise a ball-joint or rotating joint that allow for rotational movement of the one or more monitoring devices 450 and/or extendable arms 425. A hoisting device 460 may be configured to lift and lower system 400 out of and into, respectively, the reactor bay 50. Hoisting device 460 may comprise a track, a hoisting device, a winch, a pulley, a cable, a motor, one or more guide rails, wheels, or rollers, other transportation components, or any combination thereof. Additionally, hoisting device 460 may be configured to electrically and or communicatively couple monitoring device 450 with dry disconnect device 230. Hoisting device 460 may be configured so that it is readily removable, for example after system 400 has been raised out of reactor bay 50. System 400 may comprise a spool 470 operable with a length of retractable cable 475. Cable 475 may comprise, or be co-located with, one or more mediums which may be configured to provide electricity to, and/or receive communication signals from, monitoring device 450. In some examples, system 400 may comprise a self-powered transport apparatus operable with a track, a hoisting device, a winch, a pulley, a cable, a motor, one or more guide rails, wheels, or rollers, other transportation components, or any combination thereof. A track system 480 is illustrated as being attached to a wall of reactor bay 50. In some examples, track system 480 may comprise one or more vertical and/or horizontal sections of track that enable monitoring device 450 to be guided about one or more walls of reactor bay 50. Hinged device 410 may be configured to run along track system 480. Additionally, a motor may be configured to control movement of hinged device in the horizontal and/or vertical directions along the one or more walls of reactor bay 50. In some examples cable 475 may comprise a continuous cable that connects monitoring device 450 to hoisting device 460 and/or to dry disconnect apparatus 230. Using a continuous length cable may reduce the amount of electrical and/or signal interference associated with multiple connections, and also may reduce or eliminate the number of connections that are submerged in water, e.g., that may be stored in reactor bay 50. Cable 475 may be permanently attached to monitoring device 450 within a non-disconnect, water-tight, sealed casing. The casing may comprise a molded plastic or rubberized sealant that is formed at the connection during manufacture so as to remove any potential leak points. In some examples, cable 475 may be attached to monitoring device 450 at an internal sealed location within extendable arm 425. Additionally, by being able to readily relocate system 400 out of reactor bay 50, monitoring device 450 may be calibrated and/or have maintenance performed thereon in a dry environment. FIG. 5 illustrates the example system 400 of FIG. 4, shown in a lowered position within reactor bay 50. In some examples, in the lowered position system 400 may be substantially submerged in the pool of water 55 while hoisting device 460 and/or dry disconnect device 230 (FIG. 4) remain above the pool of water 55. Accordingly, system 400 may be lowered down into reactor bay 50 below a water line 75, such that system 400 is submerged under water. Conversely, system 400 may be raised out of reactor bay above water line 75, such that system 400 may be selectively exposed to air 65 and/or otherwise positioned in a dry location. Cable spool 470, in conjunction with hoisting device 460, may be configured to retract and/or extend a length of cable 475 as system 400 is lowered into or lifted out of reactor bay 50. Extendable arm 425 may be extended after monitoring device 450 has been submerged in the pool of water 55. Similarly, monitoring device 450 may be activated after extendable arm 425 has been extended, e.g., towards a reactor module located within reactor bay 50. Additionally, extendable arm 425 may be retracted prior to raising system 400 out of the pool of water 55. In some examples, extendable arm 425 may be located in the retracted position anytime that system 400 is either being raised or lowered. Furthermore, hinged device 410 and/or hoisting device 460 may be configured to restrict and/or prohibit any vertical movement of system 400 when monitoring device 450 and/or extendable arm 425 is in the extended or active position. FIG. 6 illustrates an example mounting structure 600 for a monitoring system. Mounting structure 600 may comprise a guide pin 650 and a locking mechanism 675. Guide pin 650 may be mounted on a wall of reactor bay 50. Additionally, guide pin 650 may be configured to insert within a hoisting device, such as hoisting device 460 (FIG. 4). Locking mechanism 675 may be configured to secure the hoisting device on to guide pin 650 so that the hoisting device is not inadvertently dislodged from guide pint 650 during operation of the hoisting device. Dry disconnect apparatus 230 is shown for reference, in a disconnected state. That is, the portion of dry disconnect apparatus 230 is shown without being connected and/or mated to a connection device that may be associated with a hoisting device. In some examples, the hoisting device may be removed from mounting structure 600 by disconnecting the hoisting device from dry disconnect apparatus 230, releasing locking mechanism 675, and/or disconnecting the hoisting device from a transportable monitoring system. FIG. 7 illustrates a side view of an example system 700 for monitoring a nuclear reactor module comprising multiple monitoring devices mounted on a transportable apparatus 710. The multiple monitoring devices may comprise a first monitoring device 751 mounted on a first arm 721 and a second monitoring device 752 mounted on a second arm 722. Transportable apparatus 710 may be attached to a cable 730 and/or other device configured to lower or raise transportable apparatus 710 into reactor bay 50. Transportable apparatus 710 may comprise a hinge, a pivot, a joint, a gate, a swivel, other types of connections, or any combination thereof. One or both of first arm 721 and second arm 722 may be extended, retracted, rotated, pivoted, articulated, repositioned, lowered, raised, and/or otherwise moved to position first monitoring device 721 and second monitoring device 722, respectively. First arm 721 may be moved independently of second arm 722. Additionally, first monitoring device 721 may be extended further from the wall of reactor bay 50 than second monitoring device 722. In some examples, two or more sets of arms, may be connected to transportable apparatus 710. For example, a first set of arms and a second set of arms may be positioned on either side of transportable apparatus 710, similarly as first arm 321 and second arm 322, respectively, are shown on opposite sides of first transportable apparatus 311 in FIG. 3. One or more of the multiple monitoring devices may be mounted on a telescoping arm. For example, second arm 722 may comprise multiple sections 723 which may be configured to telescope or retract into each other in order to extend and/or retract second monitoring device 752. A joint may be located intermediate the multiple sections of the arm to allow for a scissor-like motion of the arm. Additionally, one or more of the arms may comprise a pantograph mechanism for controlling a distance of the monitoring devices. A surface of one or more of the monitoring devices may comprise a magnetic device. For example, the end of first monitoring device 751 may comprise a magnetic device configured to providing an attachment force to a metallic surface of the containment vessel. The magnetic device may be configured to maintain contact between first monitoring device 750 and the containment vessel in the event of any relative movement or vibration of the containment vessel or first arm 721 that might otherwise temporarily cause first monitoring device 750 to become temporarily dislodged from the surface of the containment vessel. The magnetic device may be configured to supply a magnetic or electromagnetic force that may be alternately turned on and turned off for attachment and separation, respectively, of the monitoring device to/from the containment vessel. FIG. 8 illustrates a side view of a further example system 800 for monitoring a nuclear reactor module comprising multiple monitoring devices mounted on a transportable apparatus 810. The multiple monitoring devices may comprise a first monitoring device 851 mounted on a first arm 821 and a second monitoring device 852 mounted on a second arm 822. Additionally, first arm 821 and second arm 822 may be connected to a main arm 820 by connection device 840. In some examples, connection device 840 may comprise one or more hinges, pivots, joints, gates, swivels, other types of connections, or any combination thereof, to allow for movement of first arm 821 and second arm 822. In some examples, first arm 821 may be configured to independent movement from second arm 822. Additionally, transportable apparatus 810 may comprise a hinge, a pivot, a joint, a gate, a swivel, other types of connections, or any combination thereof, to provide for extension and/or retraction of main arm 820. In some examples, two or more main arms, similar to main arm 820, may be connected to transportable apparatus 810. For example, two main arms may be positioned similarly as first arm 321 and second arm 322 of FIG. 3. One or more of the monitoring devices, such as a third monitoring device 853, may be self-propelled and/or self-guided. In some examples, monitoring device 853 may comprise a detachable robotic navigation device that may be tethered 855 to connection device 840 or transportable apparatus 810. The tether 855 may be used to retract monitoring device 853 after a monitoring operation has been completed. FIG. 9 illustrates yet a further example monitoring system 900 comprising one or more signal path devices, such as signal path device 975. Signal path device 975 may be configured to enhance, augment, multiply, and/or otherwise increase a signal that may be detected at a monitoring device 925. In some examples, monitoring device 925 may be configured as a neutron detection device. Additionally, signal path device 975 may be configured as a neutron path device, as described in further detail by U.S. application Ser. No. 14/242,677, which is incorporated by reference herein. Signal path device 975 may comprise a box, tube, pipe, and/or other type of container filled with a gas and/or partial vacuum. In some examples, signal path device 975 may be completely evacuated, or may comprise a substantially complete vacuum. In other examples, signal path device 975 may be a substantially solid object constructed of and/or comprising stainless steel, carbon steel, Zirconium, Zircaloy, other types of materials or composites, or any combination thereof. Two or more signal path devices may be associated with two or more other monitoring devices. For example, a second signal path device 976 may be associated with a second monitoring device 926. Signal path device 975 may be located between a neutron source 950 and monitoring device 925. Similarly, second signal path device 976 may be located between a second neutron source 951 and second monitoring device 926. Signal path device 975 may be located in an annular space 955 located between a reactor vessel 920 and a containment vessel 910. Additionally, containment vessel 910 may be at least partially surrounded in the pool of water 55 of reactor bay 50. Signal path device 975 may comprise a material that is a weaker attenuator of neutrons as compared to a medium found in annular space 955 and/or as compared to the pool of water 55. Signal path device 975 may be mounted, attached, or located adjacent to an outer wall of reactor vessel 920 and/or to an inner wall of a containment vessel 910. For example, signal path device 975 is illustrated as being located between and/or intermediate to reactor vessel 920 and containment vessel 910. In some examples, signal path device 975 may be welded to containment vessel 910 and a gap or space may be maintained between signal path device 975 and reactor vessel 920. The gap may be configured to allow for thermal expansion of signal path device 975, reactor vessel 920, and/or containment vessel 910 during operation of the reactor module. Signal path device 975 may be located substantially within annular space 955. In some examples, signal path device 975 may be located entirely within annular space 955, intermediate reactor vessel 920 and containment vessel 910. Signal path device 975 may provide a neutron attenuation path from neutron source 950 through one or both of reactor vessel 920 and containment vessel 910 prior to being detected by monitoring device 925. In some examples, signal path device 975 may be configured to penetrate one or both of reactor vessel 920 and containment vessel 910 to provide a more direct path between neutron source 950 and monitoring device 925. By penetrating into and/or through one or both vessels 910, 920, the attenuating effects of the vessel walls may be reduced and/or eliminated, thus allowing for more of the neutrons being emitted from neutron source 950 to arrive at and/or be detected by monitoring device 925. During a first mode of operation, annular space 955 may substantially comprise a first, or uniform medium. For example, during normal operation of a reactor module, the medium may comprise air or other types of gas maintained at a partial vacuum. In some examples, the first medium initially contained within annular space 955 may have substantially similar neutron attenuation characteristics as the material and/or medium contained in signal path device 975. Neutrons which are emitted from neutron source 950 may therefore be propagated through signal path device 975 in a similar manner as other neutrons which are propagated through the first medium which is initially contained within annular space 955. During a second mode of operation, annular space 955 may comprise a second medium in addition to, or in place of, the first medium. For example, during an emergency mode of operation, such as an over-pressurization or high temperature incident, the reactor vessel 920 may be configured to release vapor, steam, and/or water into annular space 955. In some examples, the second medium may comprise and/or may include substantially similar neutron attenuation characteristics as coolant contained in reactor vessel 920. The neutron attenuation coefficient associated with signal path device 975 may be smaller than the neutron attenuation coefficient associated with the second medium. The relative size and/or value of the neutron attenuation coefficient may be used to determine the overall propensity of the particular medium to scatter and/or absorb neutrons. The pressure in annular space 955 may increase due to released steam, gas, liquid, vapor, and/or coolant, resulting in a greater than atmospheric pressure condition with annular space 955. In some examples, a condensation of steam and/or liquid released by the reactor vessel may cause a fluid level within annular space 955 to rise. The second medium may substantially surround signal path device 975, or at least about the sides of signal path device 975, during the second mode of operation. Signal path device 975 may be sealed. For example, signal path device 975 may be sealed in order to maintain a partial and/or complete vacuum. Under one or both of the first and second operating conditions, signal path device 975 may remain sealed such that the first medium and/or the second medium are not allowed to enter signal path device 975. Similarly, signal path device 975 may be configured to maintain a partial and/or a complete vacuum within signal path device 975 during one or both of the first and second operating conditions. By maintaining a neutron attenuation path with a substantially consistent neutron attenuation characteristics under multiple modes of reactor operation, neutron source 950 and/or signal path device 975 may be configured to provide a substantially continuous, reliable, and/or uniform level of neutron flux to monitoring device 925 regardless of the operating condition and/or regardless of the surrounding medium within annular space 955. Accordingly, neutron source 950 may be selected and/or sized to provide a sufficient number of neutrons that may be detected by monitoring device 925 through signal path device 975. By utilizing a medium and/or evacuated state for a neutron attenuation path which minimizes the amount of neutron attenuation, a smaller and/or less expensive neutron source may be selected. For example, a relatively low power neutron source may continue to generate a sufficient number of neutrons that may be detected by monitoring device 925 under any operating condition of the reactor. Additionally, by selecting and/or sizing neutron source 950 as a relatively low-powered neutron source, neutron cross-talk between adjacent reactor modules and their respective nuclear detectors, such as in a modular reactor design comprising a plurality of reactor modules, may be minimized and/or eliminated, which may result in more accurate neutron flux measurements at each neutron detector. An actuation device 940 may be configured to position monitoring devices 975, 976. For example, actuation device 940 may be configured to extend and/or retract one or more arms, such as a first arm 921 operably coupled to monitoring device 925 and a second arm 922 operably coupled to second monitoring device 926. First and second arms 921, 922 may be actuated by electronic, hydraulic, magnetic, mechanical, or other means. In some examples, actuation device 940 may comprise a manually rotatable wheel configured to move the first and second arms 921, 922 via a mechanical linkage and/or gear system. A manually actuated system may obviate the need for any electrical power to position the monitoring device(s). FIG. 10 illustrates yet another example system 1000 for monitoring a nuclear reactor module. In some examples, FIG. 10 may be understood as providing a top view of an example system for measuring flow rate through an annular volume 1075. The annular volume 1075 may be formed between a riser 1010 and a reactor pressure vessel 1020 of a reactor module. In some examples, riser 1010 may be associated with a radius that is approximately two-thirds of the radius associated with the reactor pressure vessel 1020. System 1000 may comprise one or more monitoring devices, such as a first monitoring device 1050, a second monitoring device 1052, a third monitoring device 1054, and a fourth monitoring device 1056. The one or more monitoring devices may comprise a transponder. In some examples, the one or more monitoring devices may each comprise an emitting device and a receiving device. The one or more monitoring devices may be configured similarly as the emitters and receivers as described in U.S. Provisional Application No. 62/021,627. Distances L1, L2, L3, and L4 represent line-of-sight paths and/or signal paths between the one or more monitoring devices. Additionally, the one or more monitoring devices may be located at different vertical elevations. In some examples, the line-of-sight paths may be associated with an emitter and a corresponding receiver located at a different, such as lower, elevation than the emitter. The one or more monitoring devices may be externally located to an outer surface of containment vessel 1030 of a nuclear reactor module without requiring any physical penetrations through the containment vessel 1030. In some examples, each monitoring device may be positioned at a unique elevation along a flow path of fluid coolant that travels downward between reactor pressure vessel 1020 and riser 1010. One or more of the monitoring devices may be configured to transmit, retransmit, convey and/or propagate an acoustic signal. By locating the one or more monitoring devices on the containment vessel 1030, they do not impede the flow of coolant within the reactor vessel 1020. System 1000 may comprise one or more signal path devices, such as such as a first signal path device 1060, a second signal path device 1062, a third signal path device 1064, and a fourth signal path device 1066. The one or more signal path devices may be configured to enhance, augment, multiply, and/or otherwise increase a signal that may be detected at a corresponding monitoring device. The one or more signal path devices may comprise a box, tube, pipe, and/or other type of container filled with a gas and/or partial vacuum. In some examples, the one or more one or more signal path devices may be completely evacuated, or may comprise a substantially complete vacuum. In other examples, the one or more signal path devices may be a substantially solid object comprising constructed of and/or comprise stainless steel, carbon steel, Zirconium, Zircaloy, other types of materials or composites, or any combination thereof. In some examples, two or more signal path devices may be associated with a line-of-sight path between two or more monitoring devices. For example, first signal path device 1060 and second signal path device 1062 may form at least part of the line-of-sight path between first monitoring device 1050 and second monitoring device 1052. The one or more signal path devices may be located in an annular space 1055 between reactor pressure vessel 1020 and containment vessel 1030. The acoustic signal transmitted along one or more of the line-of-sight paths L1, L2, L3, and/or L4 may comprise an ultrasonic signal having a frequency of between 20.0 kHz and 2.5 MHz, a sonic signal having a frequency of between 20 Hz and 20.0 kHz, an infrasound signal having a frequency of less than 20.0 kHz, other frequency ranges, or any combination thereof. In other examples, one or more of the monitoring devices may be configured to transmit, retransmit, convey and/or propagate vibratory signals, light signals, ultraviolet signals, microwave signals, x-ray signals, electrical signals, infrared signals, other types of signals, or any combination thereof. Additionally, one or more of the signals may be transmitted, retransmitted, conveyed and/or propagated through an intervening rigid medium, such as an external surface of the reactor vessel 1020, and through at least a portion of a fluid located within the annular volume 1075 located internal to the reactor vessel 1020. By positioning two, three, four, or another number of monitoring devices at different elevations along the external surface of reactor vessel 1020, a longer effective signal path may be created. The effective signal path may comprise a plurality of signal paths as between one or more pairs of emitters and receivers. For example, the effective signal path may comprise signal paths associated with distances L1, L2, L3, and L4. Similarly, the length of the effective signal path may comprise a summation of the distances L1, L2, L3, and L4. In some examples, a monitoring device, such as fourth monitoring device 1056, may be configured to receive a response signal in response to a monitoring device, such as first monitoring device 1050, having transmitted an initial signal into the fluid located within annular volume 1075. The initial signal may be transmitted by first monitoring device 1050 to second monitoring device 1052. In response, second monitoring device 1052 may be configured to transmit, retransmit, convey and/or propagate an intermediate signal to third monitoring device 1054. The receipt of the initial signal may act as a trigger to transmit the intermediate signal. Similarly, additional intermediate signals may be transmitted, retransmitted, conveyed and/or propagated between other monitoring devices located around the containment vessel 1030 until the response signal is received by fourth monitoring device 1056. In some examples, one or more of the monitoring devices may be configured as signal repeaters, in which a signal is repeated, reflected, and/or bounced along the perimeter of containment vessel 1030, forming a signal loop of up to 360 degrees or more. The effective signal path may be initiated at a first rotational angle, and may conclude at a second rotational angle. In some examples, the second rotational angle approximately equals the first rotational angle, such that the effective signal path may completely surround riser 1010. FIG. 11 illustrates an example process of monitoring a nuclear reactor module. At operation 1110, a hoisting device may be installed on a wall of a reactor bay. In some examples, the hoisting device may be installed on and secured to a guide pin mounted in the wall of the reactor bay. At operation 1120, the hoisting device may be coupled to a transportable measuring system. In some examples, the hoisting device may be electrically coupled, communicatively coupled, and/or coupled by a cable to the transportable measuring system. At operation 1130, the hoisting device may be coupled to a dry disconnect apparatus. In some examples, the hoisting device may be electrically coupled and/or communicatively coupled to the dry disconnect apparatus. In some examples, the dry disconnect apparatus may comprise a processing device and/or provide a communication link between a processing device or control panel and one or more one or more monitoring devices located on the transportable measuring system. At operation 1140, the hosting device may be configured to lower the transportable measuring system into the reactor bay. The transportable measuring system may be lowered from an initial position above a pool of water, into a lowered position within the pool of water. The hoisting device and the dry disconnect apparatus may remain above the pool of water while the transportable measuring system is submerged in the pool of water. In some examples, the transportable measuring system may be lowered with the one or more monitoring devices located in a retracted transport position. At operation 1150, the one or more monitoring devices may be extended from the retracted transport position to an extended operational position. In some examples, the extended operational position may comprise locating the one or more monitoring devices adjacent to or in contact with a containment vessel. The elevation of the one or more monitoring devices may be selected according to what is being measured. In addition to adjusting the elevation of the transportable measuring system to accommodate different measurements, the extended position of the one or more monitoring devices may also be adjusted. At operation 1160, the one or more monitoring devices may measure, monitor, record, analyze, view, inspect, calculate, estimate, or otherwise determine one or more functions, characteristics, or other type of information associated with a reactor module. The information may be communicated to and/or through the dry disconnect apparatus. Additionally, the information may be processed by a processing device and/or displayed on a control panel. At operation 1170, the one or more monitoring devices may be retracted to a transport position. The one or more monitoring devices may be retracted after the information has been obtained from the reactor module. Additionally, the one or more monitoring devices may be temporarily retracted or extended depending on information that may only be intermittently evaluated. The one or more monitoring devices may be located and/or stored in the retracted position when not in use, and then extended to the operational position for some predetermined period of time during a measurement operation. For example, the one or more monitoring devices may be extended prior to and during reactor initialization when neutron flux may be considerably low, and then the one or more monitoring devices may be retracted and/or stored during full power of the reactor module. At operation 1180, the hosting device may be configured to raise the transportable measuring system out of the reactor bay. The transportable measuring system may be raised from the lowered position within the reactor bay to a raised position above the reactor bay. The transportable measuring system may be raised with the one or more monitoring devices located in a retracted transport position. In some examples, the transportable measuring system may be raised out of the reactor bay when the reactor module is being installed, refueled, moved, replaced, and/or having maintenance performed. In other examples, the transportable measuring system may be raised out of the reactor bay after a measuring operation has been completed. Although the examples provided herein have primarily described a pressurized water reactor and/or a light water reactor, it should be apparent to one skilled in the art that the examples may be applied to other types of power systems. For example, the examples or variations thereof may also be made operable with a boiling water reactor, sodium liquid metal reactor, gas cooled reactor, pebble-bed reactor, and/or other types of reactor designs. It should be noted that examples are not limited to any particular type of reactor cooling mechanism, nor to any particular type of fuel employed to produce heat within or associated with a nuclear reaction. Any rates and values described herein are provided by way of example only. Other rates and values may be determined through experimentation such as by construction of full scale or scaled models of a nuclear reactor system. Additionally, while various examples described lowering the transportable measuring system into a pool of water, the system will work equally well in the absence of water. For example, the transportable measuring system may also be lowered into a substantially dry reactor bay or containment building, and operate in air or an otherwise gaseous environment, or in a containment structure that is partially or completely evacuated. Having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail. We claim all modifications and variations coming within the spirit and scope of the following claims. |
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054835615 | summary | TECHNICAL FIELD This invention relates to devices for inspecting the internal structure of a nuclear reactor and more particularly to a device for inspecting the internal reactor structure during disassembly. BACKGROUND A core of a nuclear reactor is composed of a plurality of fuel assemblies which require periodic removal for refueling or repair. These fuel assemblies are typically composed of a group of fuel rods incorporated with plates which maintain the fuel rods in proper proximity to allow a cooling fluid to flow around the rods to maintain the rods at a proper temperature. Consequently, the fuel assemblies are usually surrounded by various auxiliary structures such as baffles, which direct cooling flow for optimum efficiency to cool the fuel rods. It is typical for the reactor core fuel assemblies to be aligned in the reactor vessel by lower and upper assemblies known as internals packages. During refueling, the upper reactor internals are lifted out of the reactor housing. Presently, it is difficult to determine if one of the fuel assemblies, during lifting, has become entangled with the reactor upper internals structures. If this occurs, a fuel assembly may be pulled out of the core and dropped. Thus, the fuel assembly or upper internals may be damaged, requiring costly and time consuming repairs. Prior attempts to inspect the upper internals package during lifting utilized a video camera. The distance of lift required to perform the inspection, generally above the reactors upper flanges, could cause damage before the entanglement was detected. Consequently, other inspection methods and apparatus are required. SUMMARY OF THE INVENTION It is an object of the present invention to avoid damage during refueling. It is a further object to provide apparatus for inspecting the reactor internals during removal to detect potential entanglements and thus halt the operation prior to damaging the fuel assembly. These and other objects of the present invention are achieved by an inspection assembly comprising: an inspection means sized for insertion into a partially raised reactor internals package, and having a radially oriented opening at a distal end thereof; PA1 detecting means located within the inspection tube adjacent the opening; PA1 means for lowering the inspection tube to a position where the opening is below the internals package; PA1 rotating means for rotating the inspection tube in a complete circle while inserted within the internals package, such that the detection means translate in a full circle below the package to detect any entangled articles. In a preferred embodiment, the inspection means is a tube having an ultrasonic transmitter located adjacent to the radial opening. After the internals package is partially lifted, the tube is lowered by a cable into a passage with the reactor, with the opening oriented in conformance with a degree wheel located on a rotating device. Once lowered into the reactor, to a point just below the lowermost portion of the internals package, the ultrasonic transmitter is activated and the probe rotated a full 360.degree.. Any anomaly in the reading will indicate that a fuel assembly may be entangled with the internals package, and allow an operator to lower the internals package or take other steps to disengage the fuel assembly before a second attempt is made to raise the internals package out of the reactor. Another option would be to continue with the lift in increments and periodic reinspections before the upper internals raised height exceeds that of the assembly length to determine if the assembly dislodged off the upper internals core plate. In a preferred embodiment, a central drive shaft is removed from the upper internals package to provide the passage for the tube. This provides a central location for the inspection. |
description | In the present invention, a decontamination formulation and means for use are provided which incorporates the known active ingredient, hypochlorite, in a uniquely buffered solution designed to be incorporated into a foam for maximal and stable coating, including vertical surfaces, for a prolonged period including NATO prescribed periods of 30 minutes. Active Ingredient The formulation contains as an active ingredient, sodium dichloroisocyanurate. Other chloroisocyanuric acids, their alkali metal salts or a combination of acids including trichloroisocyanuric acid are also suitable for use as the active ingredient. As an example, alkali metal salts of monochloroisocyanuric or dichloroisocyanuric acid or a combination of any of the above salts with cyanuric acid may be used. The formulation of the present invention contains from about 1% to about 15%, and preferably from about 3% to about 9%, by weight, of the hydrated dichloroisocyanuric acid salt. The formulation may additionally comprise lithium hypochlorite to enhance the activity of the dichloroisocyanuric acid salt. Co-Solvent The formulation further comprises a co-solvent consisting of from about 1% to about 10% and preferably 8% to about 10% by volume, of propylene glycol, polyethylene glycol, or derivatives or mixtures thereof. The glycol co-solvent improves the solubilization of the CW agents, particularly the relatively water-insoluble mustards, and thickeners, in otherwise aqueous solutions. Typically, efficient solubilization is obtained in the range from about 8% upwards, whereas lower amounts will provide some solubilization properties to the formulation. In one preferred embodiment of the invention, the polypropylene glycol has the chemical formula R1xe2x80x94(OCH(CH3)CH2)nxe2x80x94OR2 where R1 and R2 are independently H, an alkyl, or an ester group and n greater than 1. The alkyl group may consist of a methyl, ethyl, propyl, butyl or a mixture thereof. In one example, both R1 and R2 are hydrogens. Alternatively, the polypropylene glycol is a partially etherified polypropylene glycol derivative having the same formula R1xe2x80x94(OCH(CH3)CH2)nxe2x80x94OR2, but where only one of R1 or R2 is independently H, or an alkyl group and n greater than 1. Again the alkyl group representing R1 or R2 may be a methyl, ethyl, propyl, butyl group or a mixture thereof. Use of certain higher molecular weight co-solvents avoids subsequent false positive detection of the co-solvent as residual contaminant. Surfactant The formulation further comprises from about 1% to about 15% and preferably from about 1.5% to about 10%, by volume, of a surfactant. The surfactant is soluable in an aqueous medium and, when aerated, creates a foam. The amount of surfactant used varies with the amount of co-solvent, active ingredient and buffer present. In the presence of optimum levels of co-solvent, the preferred amount of surfactant is from about 6% to about 10%, by volume. On the other hand, when no co-solvent is added and relatively low amounts of active ingredient are present, the preferred amount of surfactant can be as low as 1.5% by volume. The surfactant wets the surfaces to be decontaminated and creates foam on dispensing, suitable for covering and adhering to vertical surfaces. In the case of radioactive dusts, the surfactant encapsulates the dusts for removal from the subject surface. Briefly, the surfactant consists of a composition of either the formula [R(OCH2CH2)nX]aMb, where R is an alkyl group having from eight to eighteen carbon atoms, n is an integer from 1 to 10; X is selected from the group of SO32xe2x88x92, SO42xe2x88x92, CO32xe2x88x92 and PO43xe2x88x92: M is an alkali metal, alkali earth metal, ammonium or amine derivative; a is the valence of M and b is the valence of [R(OCH2CH2)nX] or more preferably, the formula [Rxe2x80x94CHxe2x95x90CH(CH2)mxe2x80x94X]aMb where R is an alkyl group having from eight to eighteen carbon atoms; m is an integer from 0 to 3; X is selected from the group of SO32xe2x88x92, SO42xe2x88x92, CO32xe2x88x92 and PO43xe2x88x92, M is an alkali metal, alkaline earth metal, ammonium or amine derivative, a is the valence of M and b is the valence of [Rxe2x80x94CHxe2x95x90CH(CH2)mxe2x80x94X] or a mixture thereof and an alkyl alcohol, Rxe2x80x94OH, where R is an alkyl group having from eight to sixteen carbons. One such suitable surfactant is Silv-Ex(trademark) made by Ansul Fire Protection described in U.S. Pat. No. 4,770,794 issued to Cundasawmy et al. Sep. 13, 1988. More specifically, the Silv-Ex surfactant consists of 20% by weight of C10H21(OCH2CH2)2-3SO4xe2x88x92Na+, 20% by weight of C14H29(OCH2CH2)3SO4xe2x88x92NH4+, 5% by weight of C12H25OH, 20% by weight of diethylene glycol monobutyl ether, 0.5% of corrosion inhibitors and 34.5% by weight of water. Alternatively, surfactants which do not contain diethylene glycol monobutyl ether are preferable as residuals, as this low molecular weight constituent can be detected by some conventional decontamination monitoring equipment (such as Graseby Ionics(trademark) Chemical Agent Monitor or CAM) and are thus interpreted falsely as positive detection of residual contaminant. A suitable surfactant consists of a composition of alkyl ether sulphate salt, an alkyl alcohol, an alpha olefin sulfonate, a co-solvent and water. More specifically the surfactant is a composition having the component formulas of [RnH2n+1(OCH2CH2)mSO42xe2x88x92M], where R is an alkyl group having from eight to fourteen carbon atoms, m is an integer from 2 to 3, and M is Na+ or NH4+, in mixture with Rxe2x80x94OH where R=C10-C14, in mixture with CH3(CH2)nCHxe2x95x90CHCH2SO3Na, in mixture with HO(CH2(CH3)CHO)nH (polypropylene glycol of MW about 425) where n=5-49 and most preferably 7. The components are in water. In addition, corrosion inhibitors can be added in very small quantities. Accordingly, a preferred composition of a suitable non-residual surfactant (or NR-surfactant) consists of 30% weight/volume i.e., 300 g/L of all ingredients except water, of the sodium salt of an ether sulphate of the formula CH3(CH2)11(OCH2CH2)3OSO3Na; 15.5% weight/volume of a sodium olefin sulphonate of the formula CH3(CH2)nCHxe2x95x90CHCH2SO3Na where n=10 to 12; 50% weight/volume of polypropylene glycol solvent of the formula H(OCH(CH3)CH2)nOH where n=5 to 9; 2% weight/volume of an alcohol CH3(CH2)nOH where n=8 to 16; about 0.3% by weight of corrosion inhibitors such as sodium tolyltriazole, ammonium dimolybdate and sodium pentahydrate silicate and the balance being water, with additional water being added to dissolve other components. Further, this NR-surfactant is capable of generating foam of uniform bubble size, is capable of coating vertical surfaces, is compatible with water, gray water and seawater as the main solvent, and is readily removed following decontamination by rinsing with water. To lower the thixotropic gelling point of the surfactant, useful in a wider range of environments, it has been found that the alcohol component preferably comprises more C12 than C14 (i.e. n=11). It has been found that diluting the surfactant 1:1 with water for storage and transport further lowers the gelling point. Alternatively, a combination of surfactants can be used for the preparation of the decontamination formulation. For example, Silv-Ex may be combined with the NR-surfactant, or an alternative formulation or a combination of them with other surfactant ingredients such as sodium laureth sulfate, having the formula CH3(CH2)10CH2(OCH2CH2)3OSO3Na, sodium C14-16 alpha olefin sulfonate having the formula RCHxe2x95x90CHCH2xe2x80x94SO3Na, and ammonium alcohol ethoxysulfate having the formula C8-10H17-21(OCH2CH2)2.3OSO3xe2x88x92NH4+. Buffer The decontamination formulation of the present invention further comprises a buffer that temporarily maintains an initial pH in the range of 10 to 11, sufficient to enable hydrolysis of G-agents and mustards and favor oxidation of the V-agents so as to produce non-toxic products. An initial pH in the range of 10 to 11 is sufficient to provide adequate hypochlorite ions for decontamination. Subsequently, it is desirable that the buffer fail, allowing the pH to decrease eventually to a more neutral pH to enable more efficient destruction of the BW agents. As the buffer fails and the pH drops to a more neutral pH, hypochlorous acid becomes more prevalent as hypochlorite ions react with available hydrogen ions. Hypochlorous acid is the more active species with respect to the destruction of BW agents as neutral species are able to enter the cell more easily. Should BW agent survive the initial decontamination, the BW agent and decontamination formulation may continue to co-reside over time, perhaps after rinsing, and, as the pH falls, BW agent decontamination continues at an even more effective pH. Further, from an environmental standpoint, a more neutral final pH of the decontamination formulation is less hazardous. It is important to maintain the initial high pH over a prescribed duration (such as a NATO designated duration of 30 minutes), to provide sufficient hypochlorite ions to effect decontaminationxe2x80x94favoring oxidation of VX agent which avoids the formation of toxic hydrolysis byproducts, favoring hydrolysis of G-agents, and favoring oxidation of HD agents and avoiding HD reformation. Accordingly, the buffer must be capable of buffering the release of HCl due to hydrolysis of the chloroisocyanuric salts by water. Most preferably, the pH is maintained above 8.5 during the duration available for decontamination. It has been determined that the most suitable buffering system is an inorganic buffering system, adjusted to an initial pH in the range of 10 to 11. Sodium salts, such as a mixture of sodium tetraborate decahydrate and anydrous sodium carbonate, are preferable since quaternary ammonium compounds result in depletion of hypochlorite through reaction with the hydrolysis product of hypochlorite, chloride ion. The preferred solvent for the decontamination formulation of the present invention is water, including gray and seawaters. The decontamination formulation may further optionally include small amounts (preferably less than 0.03%) of corrosion inhibitors such as sodium tolyltriazole, ammonium dimolybdate and sodium pentahydrate silicate to improve compatibility with use on metals. Augmented Active Ingredients The decontamination formulation may further optionally include lithium hypochlorite to augment the active hypochlorite content of the solution over a short term, thus providing a higher level of active species in the initial stages after the addition of water. Preferably, lithium hypochlorite is present in amounts in the range of from about 5 to about 10% by weight of the active ingredient dichloroisocyanuric acid salt and taking into account that commercially available lithium hypochlorite is normally only available as 30% pure. Alternatively, small amounts of Super Tropical Bleach (STB) or High Test Hypochlorite (HTH), below their solubilisation limits so that no solid or slurry results, could serve somewhat the same function as the addition of lithium hypochlorite. The decontamination formulation of the present invention may further optionally include inorganic/organic bromide to increase the reactivity of the chloroisocyanuric acid and generate low levels of hypobromite and bromine chloride. Optional Embodiments Three embodiments are briefly described as follows and are more specifically disclosed in the following examples. In a first embodiment of the present invention the decontamination formulation contains 9% sodium dichloroisocyanurate, a buffer mixture containing 0.0125M sodium tetraboratedecahydrate and 0.1M anhydrous sodium carbonate adjusted to a pH from about 10 to 11, using NaOH (full strength buffer), 9% surfactant and a total of 8% co-solvent, including co-solvent contained in the surfactant mixture. This formulation provides for maximal decontaminationxe2x80x94capable of decontaminating the broad spectrum of CW and BW agents, in the liquid phase, in under 7 minutes, and provides foam production capable of coating vertical surfaces. The concentration of active ingredient of this first embodiment tends to compromise the performance of the resulting foam as a suppressant of dispersion or blast devices, likely due to the higher co-solvent and salt content. In a second embodiment of the present invention, the decontamination formulation contains 6% dichloroisocyanuric acid salt, full strength buffer, 9% surfactant and a total of 8% co-solvent. This formulation provides for good decontamination and increased foam stability for decontamination of any agents or for clean up after a blast. In a third embodiment of the present invention, the decontamination formulation contains 3% dichloroisocyanuric acid salt, a buffer in which the concentrations of the components have been reduced by ⅓ that described for full strength buffer (⅔ strength buffer), 3% surfactant and no extra added co-solvent. This embodiment, while it provides excellent blast suppression, provides slower reacting decontamination capability. Method of Application The decontamination formulation can be prepared either as a liquid or as foam. The preferred form is to create foam due to its ability to effectively coat surfaces, including vertical surfaces and to suppress vapor emissions. Having reference to FIG. 1a, the decontamination formulation of the present invention can be prepared by first combining in a single source solution in a plastic drum, water bladder or plastic container, at approximately the final percentages, the active ingredient, co-solvent, buffer, the surfactant and fresh or seawater. The source solution is then pumped to the contamination site. For foam application, the formulation is applied using high to medium pressure pumping equipment equipped with appropriate aeration nozzles. Referring to FIG. 1b, in an alternate and staged method the active ingredient and buffer are made up separately from the co-solvent and surfactant/foam. This staged approach provides improved storage life after preparation. The active ingredient can be made up in a single solution concentrate of the highest achievable percentage soluble in water, about 30% by weight total in water. It follows that the higher the weight percent of soluble active ingredient, the less concentrate is required to be aspirated into the main stream to achieve maximum decontamination. This solution is stable for several hours. The buffer mixture is prepared in a second solution at or near the solubility limits of each of the buffer salts and the pH adjusted to provide an initial pH of 10 to 11. This concentrate is stable for long periods of time. The active ingredient and buffer can then be introduced, into a stream of co-solvent, surfactant and water for completing the formulation and initiating decontamination. The concentrations of co-solvent and surfactant are dependent on one another and on the type of decontaminant applicator or inductor used. A synergistic effect can exist between these two ingredients. As well, the ambient temperature can influence the concentration of surfactant required. Therefore, one must consider these factors and adjust the concentration of the surfactant to suit the particular situation in which the formulation is to be used. Regardless of the method of formation, most preferably, the decontamination formulation is prepared by adding into a stream of water, the ingredients in the following order; co-solvent and surfactant, active ingredient, and buffer. The ingredients are pumped through an appropriate aeration nozzle to provide a relatively stable and thick foam. The nozzle should entrain sufficient air into the stream to create the foam without causing excessive back pressure. The active ingredient and the buffer are added as concentrates to the stream of water and are diluted during the application process. The surfactant can be added simultaneously with the buffer, however it may be advantageous to add them separately (FIG. 1b) as the amount of surfactant required depends upon the ambient temperature, the surface being treated and the incident sunlight. By adding the surfactant separately, wholly or as an optimizing addition to a solution already containing most of the decontamination ingredients, one can beneficially adjust the foam properties to the ambient conditions. One further advantage to the staged approach is that hypochlorite or buffer are introduced to the stream after the pump and before the nozzle so that the pump is only exposed to water or possible pump-friendly co-solvent and surfactant. Greater pump life can be expected as it is not degraded or corroded by long-term exposure to potentially corrosive or abrasive ingredients. In the alternative approach, all ingredients are combined in the source container (FIG. 1a). While this approach is simpler, it must be noted that the presence of the buffer mixture will immediately initiate degradation of the active ingredient so the lifetime of the formulation using this method of preparation may be more limited from the time at which they are mixed. Additionally, the pump will be exposed to the complete formulation and could corrode substantially faster, depending upon the materials of construction. In contrast, the lifetime of the active ingredient in water without the addition of the buffer mixture (FIG. 1b) is considerably longer. Modifications to the above methods are possible. For example, the solutions could be mixed off-line in a series of drums or tanks and, when dissolved, the contents could be pumped to source containers permanently attached to the pumps or aspirators. Kit For field use, a practical approach is to provide appropriate quantities of each component in kit form and obtain a local source of water. Separate, lightweight containers such as plastic pouches or pails facilitate transport of the components to the decontamination site. For example, the active ingredient, which is in the form of a powder, can be weighed out in specific amounts and heat-sealed in a plastic pouch to keep it dry. Similarly, the buffer components, also available as solids, could be packaged individually or as a mixture with the active ingredient if moisture can be excluded. The co-solvent can likewise be measured out in appropriate quantity, diluted slightly if necessary and stored in large plastic pails with tightly sealed lids. The surfactant can likewise be supplied in its original shipping pail or, if prepared locally, stored in pails in pre-measured amounts similar to the co-solvent. Alternatively, the co-solvent and surfactant can be provided as a mixture and packaged together. The solid ingredients are then dissolved into solution in water or seawater, which are subsequently added to a pumping system as described above to obtain the decontamination formulation of the present invention at the decontamination site. The following examples are illustrative of the preferred embodiments of the present invention and are not to limit the scope of the invention. Example 1 illustrates typical preparation of a decontamination formulation. Example 2 illustrates the application and effectiveness of the formulation of Example 1 as applied in a field trial for destruction of a mustard chemical agent. More generally, examples 3 through 5 illustrate various formulations and results for liquid phase reaction-decontamination of CB agents. Specifically, examples 3 and 4 illustrate liquid phase reaction-decontamination of G-Type Nerve and Mustard Agents and VX Nerve Agent. Example 5 similarly illustrates liquid phase reaction-decontamination of a known nerve agent simulant, di-isopropyl fluorophosphate (DFP). Example 6 illustrates the foam phase-detoxification of viable anthrax spores on military-spec painted metal coupons. Examples 7 and 8 demonstrate field trial results for the decontamination of a military vehicle, particularly the destruction of mustard chemical agent and foam phase removal of radioactive dusts. The following decontamination formulation was prepared for the vehicle decontamination according to Example 2. A source solution of water, buffer, co-solvent and surfactant was prepared. Separately, a solution of active ingredient was prepared. Separate preparation of the active ingredient postpones the initiation of the degradation of the hypochlorite precursor until mixed. More particularly, a concentrate of the active ingredient was prepared from 72 liters of tap water and 18.6 kg of anhydrous sodium dichloroisocyanurate. The solid active ingredient was added to the water in a plastic waste overpack container and vigorously stirred with an industrial stirrer/homogenizer. The solution turned into an off-white milky liquid which, when gently warmed with the introduction of steam for less than five minutes turned into a translucent amber-colored fluid. Mechanical constraints for this particular experiment limited the solution concentration to a maximum of 5.6% active ingredient, 9% being achievable using different equipment as demonstrated in Examples 3-5. The source solution was prepared with 303 liters of tap water, 16.73 liters of surfactant, 26.35 liters of polypropylene glycol 425 as co-solvent and inorganic buffer salts, more particularly, sodium tetraborate decahydrate and anhydrous sodium carbonate in sufficient amounts to provide concentrations of 0.0125M and 0.1000M respectively in the final solution. Sodium hydroxide was added in sufficient amounts to provide an initial pH of approximately 11, which would, after addition of the active ingredient, cause the resulting pH after stabilization to be from about 9.3 to about 9.7. An NR-surfactant, modified from the Silv-Ex formulation, was used. Generally the composition of the NR-surfactant was, all referenced by weight, 30% C8-10H17-21(OCH2CH2)2.3OSO3xe2x88x92NH4+, 15.5% C11-13H23-27CHxe2x95x90CHCH2xe2x80x94SO3xe2x88x92Na+, 20% polypropylene glycol 425, 5% alcohol mixture (of about 2% CH3(CH2)11OH and 3% CH3(CH2)13OH, and the balance being water. Note that the NR-surfactant already contained 20% by weight of co-solvent and thus only sufficient additional co-solvent (26.35 liters) was added to the source solution to obtain an 8% overall solution (29.75 liters). The source solution and concentrate were separately stored in two plastic storage vessels. The source solution was pumped at 24 liters/min through pressure hose to a foam nozzle. The concentrate was introduced into the flow of source solution immediately downstream of the pump, through two eductors backed by small centrifugal pumps whose flow rates were constantly monitored. The combined eduction of the two units amounted to a total of 18.6% of the overall exit flow of foamed effluent from the nozzle. This combination provided a final active ingredient concentration of approximately 5.6% by weight equivalent of sodium dichloroisocyanurate dihydrate. Two eductors were provided in anticipation of alternate operation wherein each eductor would draw in a separate concentrate; one containing active ingredient, the other containing the buffer, co-solvent, and possibly, the surfactant components. In operation, the combined effluent was fed through 40 m of standard high-pressure hose to a spray lance. Dissemination was achieved through attachment of a foam nozzle (9 US Gal/min) to the spray lance discharge. As a result, foam was readily generated by pumping the formulation through the system and applying the spray from the nozzle to the sides of the target vehicle. Using the formulation as set forth in Example 1, neutralization of mustard agent applied to a vehicle surface was evaluated in the field as follows. Approximately 150 ml of mustard was applied to the surface of a vehicle using a paintbrush. The presence of mustard agent was assessed and verified using a portable gas chromatograph/mass spectrometer (GC/MS). The decontamination formulation of Example 1 was applied to the contaminated side of the vehicle using the lance and nozzle followed by manual scrubbing of the surface using long-handled brushes. After a 30 minute wait period, the foam was washed away with water and the vehicle surface was re-surveyed using the GC/MS. FIG. 2 illustrates that an air sample taken near the contaminated vehicle before decontamination contained mustard agent, the top trace is the total ion current as recorded by a portable GC/MS which shows two large peaks due to internal standards (IS) and two lower peaks. The second trace (FIG. 2b) is an ion chromatogram set at m/z 109 and the bottom trace (FIG. 2c) is a separate ion chromatogram set at m/z 115 to detect a simulant, diethyl malonate, also present in the atmosphere from an earlier contamination. As shown in FIG. 3, a mass spectral analysis of the m/z 109 sample component of FIG. 2b confirmed that this component was mustard chemical agent with a 85.7% probability as compared to the bottom trace, which is an authentic mass spectrum of mustard stored in the search library. Turning to FIG. 4, once the vehicle was treated with the decontamination formulation, no further mustard was detected in air samples taken near the vehicle. In each of Examples 3-5, quantitative analyses for residual agents were performed on a high pressure liquid chromatography (HPLC) system for separation of the reaction components, equipped either with a HPLC-UV detector in series with a commercially available dual flame gas chromatographic flame photometric detector (FPD) from Varian Associates, or, where possible, on a Hewlett-Packard 1100 LC-MS system equipped with a diode-array UV-VIS spectrophotometer and mass selective detector (MSD). The water used in the reactions, prepared solutions, and in the HPLC was distilled and deionized. The formulation for the surfactant/foam was first warmed to 32xc2x0 C. to ensure homogeneity. CB agents and simulant DFP were provided by the Canadian Single Small Scale Facility at the Canadian Defence Research Establishment Suffield (DRES) in southern Alberta, Canada and Aldrich Chemical Company, respectively. GB stock calibration solution was prepared by weight in acetonitrile (AcCN) and several dilutions were prepared ranging from 25 to 900 ng/xcexcL for calibration of the FPD, UV, and MSD responses. Stock solutions of the other CW agents were prepared volumetrically in AcCN and similarly diluted for calibration. Unless otherwise specified, in a typical experiment, samples were prepared in 2.0 mL autosampler vials. The first addition was a water solution containing the surfactant and, if necessary, the co-solvent. This was followed by buffer concentrate, then the decontaminant concentrate which had been separately prepared by adding the active ingredient, anhydrous sodium dichloroisocyanuric acid (SD), to water and heating to 29xc2x0 C. with stirring for 15-30 minutes. Finally, the CB agent was added defining time zero, and aliquots, at noted elapsed times, were directly injected into the LC. The temperature of the vial holder was maintained at 25.0xc2x0 C. and a mini stirbar in the vial mixed the components. Fresh samples were prepared for each FPD analysis to obtain residual agent concentration profiles over time and these same solutions were subsequently analyzed by LC-MS. Having reference also to FIG. 5, the effectiveness of several decontaminant formulations against selected G-type nerve gases GB, GA and GD and mustard gas, HD, was determined. The formulations tested consisted of an active ingredient, a surfactant, an inorganic buffer mixture and, optionally, co-solvent, in excess of that already present in the surfactant mixture. The co-solvent values in FIG. 5 represent added co-solvent and that contained in the surfactant. Three decontamination formulations were assessed for effectiveness against typical G-nerve agents; the mildest formulation, using 3% w/w SD, a ⅔ strength buffer, and 1.3% w/w surfactant; an intermediate strength formulation with 6% w/w SD, full strength buffer, 4.6% w/w surfactant and an additional 6.9% w/w to 7.8% w/w co-solvent, and a full strength formulation with 9% w/w SD, full strength buffer, 4.8% w/w surfactant and 6.9% w/w additional co-solvent. Although anhydrous SD was used in preparation of the solution, percentages are quoted in terms of the equivalent amount of dihydrate. Percentages (w/w) quoted for surfactant represent double-strength surfactant. In order to standardize concentrations between experiments, the effectiveness was calculated as a percentage of residual agent. Using 0.29% w/w GB, there was no evidence of residual agent in any of the LC-FPD or LC-MS analyses for the mildest and intermediate strength formulations (3% w/w and 6% w/w SD). GB was destroyed in each case before the first sample could be taken (0.43 and 1.13 minutes respectively). For the most potent formulation (9% w/w SD), only LC-FPD analysis was performed at 1.78 minutes elapsed time and no agent was detected indicating complete destruction of the agent within 1.78 minutes. Using 0.29% w/w GA, only the mildest and intermediate strength formulations (3% w/w and 6% w/w SD) were evaluated. The mildest formulation was tested in two separate experiments. In the first, containing xcx9c1.6% w/w surfactant, LC-FPD analysis indicated that GA was destroyed within 1.33 minutes. In the second, containing xcx9c1.8% w/w surfactant, there was no evidence of GA in 1.07 minutes elapsed time (LC-FPD) or 3.43 minutes (LC-MS). For the intermediate strength formulation containing an additional 7.5% w/w co-solvent, there was no evidence of GA in 1.07 minutes elapsed time by LC-FPD or 3.35 minutes by LC-MS. Using 0.29% GD, again only the mildest and intermediate strength formulations were each evaluated. The full strength formulation was not tested due to the success with the two milder formulations. The mildest formulation was tested and, in contrast to the other two G-agents examined, small amounts of residual GD appeared to be observed for the shortest reaction time sample. Specifically, as analyzed by LC-FPD, 5.0% residual agent appeared to be present at 1.07 minutes and 0.5% appeared to remain at 4.77 minutes, and the agent was completely gone by 10 minutes, as determined by LC-MS analysis. Similar results were observed using the intermediate solution containing 7.8% co-solvent. Complete LC-MS characterization of the peak eluting at GD in a stock solution of GD suggests that a trace of a GD-related impurity, methylpinacolylmethylphosphonate also eluted at this point, possibly contributing to the residual peak observed at short reaction times. Thus, although GD appears to be more difficult to destroy than GB or GA, the mildest formulation is still very effective against GD within acceptable time limits. Using 0.27% w/w HD, again due to their success, only the mildest and intermediate strength formulations were evaluated. The mildest formulation was tested for effectiveness against HD in three separate tests. In the first test, there was no evidence of residual HD after 2.67 or 4.92 minutes (reaction solutions had to be mixed more vigorously than the other agents due to limited solubility of HD so earlier sampling was not possible). In the second test, no residual agent was detected after 3.0 or 62.1 minutes, however 6.2% of residual HD appeared to be present after 5.4 minutes assuming that the eluting peak was indeed HD. As a confirmatory test, an third experiment was performed and no HD was detected after 3.65 or 4.97 minutes. It is therefore concluded that the mildest formulation is completely effective against this level of HD in less than 2.7 minutes. The intermediate formulation also tested for effectiveness against HD and demonstrated no residual HD after 2.47, 5.27, or 53.3 minutes. Verification by LC-MS could not be performed as HD cannot be detected using positive API-ES under these conditions. Having reference also to FIG. 6, the effectiveness of several formulations against the nerve agent VX was determined. Samples were prepared as described in Example 3. Two decontaminant formulations were assessed for effectiveness against VX-nerve agent: the mildest formulation (MILD) with 3% w/w SD, ⅔ strength buffer, and 1.3% w/w surfactant, and the full strength formulation (FS*) with 9% w/w SD, full strength buffer, 4.8% w/w surfactant and 6.9% w/w additional co-solvent. As with example 3, percentages quoted for surfactant represent double-strength surfactant. Control formulations were also examined. These included a formulation containing only full strength buffer and surfactant (Buffer/Surf) and a formulation containing all ingredients of the full strength decontaminant but without active ingredient (FS*wo/SD). In order to standardize concentrations between experiments, effectiveness was calculated as percentage of residual agent. In addition, an authentic sample of a known potential toxic product (Toxic Product), of hydrolysis of VX, S-(2-diisopropylaminoethyl) methylphosphonothioic acid was synthesized and characterized by LC-MS to be used as an indicator of unsuccessful detoxification of VX. All reaction mixtures were examined for the presence of this compound; the presence of significant quantities would be sufficient evidence to disallow the formulation as a possible decontaminant candidate. The results are summarized in FIG. 6. In the first evaluation, the control formulation of buffer and surfactant (Buffer/Surf) was tested at a low concentration of VX (4 xcexcL/mL). After six days, 42% of the VX remained and toxic product in significant quantity was detected. The control formulation of full strength formulation without active ingredient (FS*wo/SD) was tested against a concentration of 12 xcexcL/mL of VX. Again, significant quantities of VX and toxic product were found at 125 minutes and 6 days. Additionally, there was evidence of VX droplets in the solution at 125 minutes indicating that saturation levels of VX were present in solution and that removal of VX from the system was slow. When full strength formulation with SD was employed in excess (18.2:1 active species/VX), all VX was destroyed in less than 7 minutes with no evidence of toxic product. A more extensive examination of the temporal effectiveness of the mildest formulation was undertaken in which the stoichiometric ratios of concentrations of VX to active chlorine present in solution were varied. For the lowest ratio (xcx9c6:1), effective decontamination of VX was not achieved although only small traces of toxic product were observed. On the other hand, if the ratio was xcx9c16-18:1, complete decontamination without significant production of toxic product was achieved. As shown in FIG. 6, the mildest formulation at a ratio of 18.2:1 is completely effective in less than eleven minutes. A similar formulation reacting at a ratio of 29:1 resulted in similar effectiveness, however this is most likely due to the fact that the trace recorded by the LC-MS is at its detection limit using this procedure. An analysis of the mild formulation without added VX did not register any response for VX eliminating the possibility of a false positive VX result due to the formulation itself. In conclusion, even the mildest formulation is highly effective against VX provided that the ratio of reactant to agent is maintained over at least 17:1. This finding is in accordance with statements made in Y-C Yang, J. A. Baker, and J. R. Ward, Chem Rev., 1992, 92, p1731, in which the authors state that greater than 10 moles of active chlorine are required to oxidize 1 mole of VX. Having reference also to FIG. 7, the effectiveness of several decontaminant formulations was tested against diisopropylfluorophosphate (DFP), a compound often employed as a simulant for G-type nerve gases. Formulations in which the active ingredient, sodium dichloroisocyanurate (SD), was augmented by lithium hypochlorite (30% LiOCl) and potassium bromide (KBr) were also tested. As with the previous examples, the percentages quoted for surfactant represent double-strength surfactant. Following introduction of surfactant and, if applicable, co-solvent, active ingredient (SD) was added as a 30% concentrate prepared in distilled, deionized water by adding solid SD to a measured amount of water which was then heated to 29xc2x0 C., with stirring, for 20-30 minutes. When SD/LiOCl combinations were used, a concentrate was prepared and added to the reaction solution in a similar manner. Constant pH was maintained at 9.5 using an automatic titrator adding dilute NaOH. As a final step, the DFP was weighed out and added to the solution, defining time zero for the reaction. At timed intervals (5, 10, 15, 30, 60 and 120 minutes), aliquots were taken from the reaction solution, delivered into a quench vial containing aqueous hydrogen peroxide in methanol or isopropanol, and the aliquot weight recorded, along with the exact time of the quenching. Each quenched sample was then analyzed by HPLC. In order to standardize concentrations between experiments, the effectiveness was calculated as percentages of residual DFP. The results and experimental parameters are summarized in the table of FIG. 7 and the graphs of FIGS. 8-10. The table of FIG. 7 is divided top down into three sections representing the three formulations of SD, SD+KBr, or SD+LiOCl respectively. In the first formulation (SD) and having reference to FIGS. 7 and 8, the results of a control containing no active ingredient, surfactant or co-solvent and various formulations of SD, co-solvent and surfactant, at pH 9.5, are illustrated. As a control for comparison purposes, and entitled test 7-115, the disappearance of DFP in aqueous solution at pH 9.5 by unaided hydrolysis was monitored. The % of DFP remaining over time is plotted on FIG. 8 as line 81 wherein the control indicated an apparent initial increase in the DFP followed by a decrease over time to a value of 68% at 107 minutes. The calculated percentage of DFP remaining at 30 minutes was 87%. The DFP response for a similar test 7-97 at pH 9.5, in which only SD was added, is plotted on FIG. 8 as line 82 and illustrates a rapid drop over time to a value of zero at approximately 30 minutes. In two additional tests, 7-123 and 7-137, co-solvent polypropylene glycol 425 (7.2% w/w and 7.9% w/w respectively) was added to the water, held at pH 9.5 in the reaction vessel and stirred. SD (7.97% w/w and 7.42% w/w respectively) and finally DFP (1.34% w/w and 1.25% w/w respectively) were added. Test 7-137 was performed with the addition of surfactant (3.5% w/w) along with the co-solvent. Plotted as lines 83 and 84 respectively, there was an exponential decrease of the percentage of residual DFP with time. However, the curve is shifted upwards from that of the reaction of SD alone with DFP at pH 9.5, and, in fact, the DFP was not destroyed in two hours. At the 30-minute mark, 25% of the DFP remained in the reaction solution with co-solvent alone and 21% with the addition of surfactant and co-solvent. It is clear that the addition of SD, whether alone or in the presence of co-solvent and surfactant significantly increases the rate of hydrolyses of DFP but that both of these other additives has a negative effect on reaction rate. In the second formulation and having reference to FIGS. 7 and 9, the results for controls and the effect of augmenting the active ingredient with the addition of KBr to SD with co-solvent and surfactant is demonstrated. Since the addition of co-solvent and NR-surfactant demonstrated a retarding effect on the rate of hydrolysis of DFP, the ability of KBr when added to the SD to offset this effect was investigated. As a control, the results from a test 7-143, plotted as line 91, with both co-solvent (6.3% (w/w)) and surfactant foaming agent (3.4% (w/w)) in the reaction solution were compared to a similar reaction at pH 9.5 involving added KBr. In the control case, there was residual DFP after two hours and 23% remained after 30 minutes. In test 7-147, a KBr (0.1 M) solution held at pH 9.5 was substituted in place of water and the disappearance of DFP was determined. As plotted line 92 shows, although the initial value at five minutes appears to be anomalously low (12% DFP) since the DFP appears to increase to 26% at 10 minutes then gradually decrease with time, it is clear that the rate of hydrolysis of DFP has increased relative to the control formulation. The DFP did not reach zero within one hour and the calculated percentage of DFP remaining at 30 minutes was 8%. Clearly, addition of KBr assists in the rate of hydrolysis of DFP in the presence of surfactant and co-solvent. In the third formulation and having reference to FIGS. 7 and 10, the results of a control and a formulation augmented by the addition of LiOCl to the SD are illustrated. As an alternative to adding relatively insoluble KBr for increasing overall hydrolytic reactivity, a soluble hypochlorite, LiOCl, was substituted. As a comparison, a first test, plotted as line 101, was performed in which the reactivity of SD (11.32%(w/w)) in a solution containing surfactant (1.5% (w/w)) and being held at pH 9.5 was examined. The DFP decreased with time until it was undetectable after 0.5 hours. The calculated percentage of DFP at 30 minutes was 2%. In a second test 8-23, plotted as line 102, LiOCl at 0.19% w/w was added to a solution with SD (6.52%) and the surfactant (1.5% (w/w)) and maintained at pH 9.5. The weight of the LiOCl was 3.0% of the SD. The DFP at five minutes was less than 20% of the initial value and continues to decrease with time. The calculated percentage of DFP remaining at 30 minutes is only 0.5%. Clearly, the substitution of LiOCl to a lower concentration of SD leads to a solution with more reactivity toward DFP than one with SD as the only active ingredient. Also, when compared to Example 3 above, it is apparent that DFP is much more resistant to hydrolysis in this system than are the G-agents it was proposed to simulate. The effectiveness of foam phase-detoxification of anthrax spores was determined. A suspension of Bacillus anthracis (Ames strain) was heat shocked to kill the vegetative cells, leaving only the viable spores. Small metal coupons, painted as per in-service military vehicles, were cleaned with ethanol wipes and sterilised by autoclaving. Each coupon to be used was spotted with 200 xcexcL spore suspension, distributed over the surface of the coupon as 60-70 small droplets and allowed to dry overnight in a biosafety cabinet in a Level 3 Biocontainment laboratory. Two trials were performed on two separate days using freshly prepared foam formulations. Each trial used two of these coupons, one to test the decontamination formulation and one to act as a control. Each coupon was placed in a 100 mm petri dish, supported to keep it from coming in contact with the bottom of the dish and covered with either the decontamination foam of the present invention or a control foam not containing the decontaminant active ingredients. The lid of the petri dish was replaced and twisted to ensure that the foam contacted the entire coupon. After 30 minutes each coupon was removed from the petri dish using forceps, rinsed with sterile PBS, then swabbed twice over its entire surface with a sterile sampling swab. The swab was placed in 5 ml of Heart Infusion broth and vortexed. In both trials, 200 xcexcL of neat broth from the decontamination foam-treated coupon and 200 xcexcl of a 1xc3x9710xe2x88x924 dilution (in PBS) of the broth from the control foam-treated coupon were plated onto each of four Blood Agar plates. The plates were incubated overnight at 37xc2x0 C. and the Colony Forming Units (CFU) observed the following day, are given in Table II. The Control foam results are shown multiplied by 104 to adjust for the 10xe2x88x924 dilution. Trial 1 and Trial 2 indicate, respectively, that, on average, only 0.0108% and 0.00109% of the original material on the decontamination foam-treated coupons remained viable, translating into a 99.989% and 99.999% kill for simple contact with the decontamination foam for a period of 30 minutes. Having reference to FIGS. 11-13, the neutralization of mustard chemical agent on a military vehicle surface was evaluated in a field trial using a formulation comprising of a mixture of sodium dichloroisocyanurate and LiOCl as active ingredients. The vehicle used was a U.S. M113A armored personnel carrier subsequently coated with Canadian Forces specification Chemical Agent Resistant Coating (an agent-resistant two-pot polyurethane paint). In this decontamination trial approximately 75 mL of munitions-grade mustard agent was painted onto the side and end of the vehicle. The vehicle was located inside a plastic-lined containment pit. In FIG. 11, a mass spectral analysis of the total ion and reconstructed m/z 109 chromatograms confirmed that the contaminant in the bottle and painted onto the vehicle was, indeed, mustard by reference to an authentic mass spectrum of mustard stored in the search library (FIGS. 11, 12). Handheld Chemical Agent Monitors (CAMs) exhibited strong H-mode mustard responses and 3-Way Detector Paper displayed the characteristic red colour response indicative of blister agents when pressed onto the contaminated surface of the vehicle. Referring to FIG. 13a, the decontamination formulation was then applied to the contaminated vehicle using a high capacity pump and two hoses fixed with foam nozzles. The vehicle was then scrubbed using long-handled brushes. During and following these steps, readings were made of the air around and downwind of the vehicle. Immediately, Chemical Agent Monitor (CAM) and air sample surveys conducted around the vehicle during the scrubbing procedure failed to detect the presence of mustard vapour, as shown by the GCMS results of FIG. 13a (total in chromatogram) and FIG. 13b (m/z 109 reconstructed mass chromatogram characteristic of mustard) compare to the corresponding traces in FIG. 11. Following a short ( less than 30 min) rest period, the foam was washed away with water and the air near the vehicle surface surveyed against using CAMs and the GCMS. Once the vehicle had been treated, CAM surveys conducted close to the vehicle surface showed no response, indicating mustard vapour was not present. Having reference to FIG. 14, the combined responses. from four Chemical Agent Detection Systems Mark II (CADS II) stations deployed around the vehicle are illustrated. Each CADS II station comprises two CAMs. In this figure, the readings of all eight CAMs (four CADS II stationsxc3x972) were summed and displayed. The vertical bars in the figure denote significant actions on the part of trial personnel. Gross contamination of the vehicle was initiated at point A and decontamination commenced at point B. By point C, the audible alarm from the CADS II central control unit (CCU) had silenced and from point D onward, no further detection or bar reading of mustard vapor was observed. Thus, this formulation applied in this manner is effective in suppressing agent vapor from a freshly contaminated-coated military surface immediately and is effective in decontaminating mustard-contaminated military vehicles within a 30-minute period after application. Having reference to FIG. 15, the effectiveness of the foaming agent by itself to effect decontamination of radioactive dusts from the exterior surface of an armored vehicle was demonstrated. The vehicle, a French AMX-10 Armored Personnel Carrier, was contaminated by spraying the exterior with 140La particles (100-200 xcexcm) to simulate surface contamination as might be caused by driving across contaminated dusty terrain. Decontamination formulation using Silv-Ex surfactant was sprayed over the surface of the vehicle using a powered pressure washer fixed with an air induction foam nozzle of the type normally used in applying fire-fighting foams. Subsequent to the application of decontaminant, the vehicle was towed to a sensing frame where radiation measurements on the exterior could be made. In FIG. 15, the radiation level measured inside the vehicle in the first trial was observed to be in the order of 30 mRem/hr. After towing to the decontamination site and commencing application, the radiation level was observed to drop significantly (to approximately 11 mRem/hr) presumably due to foam layers dropping off the sides of the vehicle during the application stage. The radiation level flattened off over the course of the decontamination probably due to residual particles remaining on the vehicle in areas where the foam could not drop off (top, crevices) readily. On commencement of rinsing of the vehicle with water, the radiation level dropped even further (to approx. 6 mRem/hr) presumably due to flushing off some of the remaining radioactive particles. A map of the radiation emitted from the exterior surface of the vehicle as sampled by a frame of 80 probes confirmed that the radiation had been significantly reduced by decontamination using Silv-Ex-based decontamination foam. In a subsequent trial, the same vehicle was contaminated to a level of approximately 45 mRem/hr. During movement of the contaminated vehicle to the site of decontamination, significant loss in the level of radioactivity was observed. The loss was such that the trial was terminated. It was apparent that the exterior surface, having been previously cleaned in an earlier trial, did not retain radioactive particles sprayed onto it. In other words the surface had been degreased and dust adherence had been significantly decreased, suggesting an additional benefit to the use of the formulation. In a related examination in which paint panels were contaminated and subsequently decontaminated by dry scrubbing, the standard approach for decontamination of radioactive particulate matter was observed to attain a low level of 0.55 mRem/hr whereas decontamination with Silv-Ex-based decontamination foam reduced the radiation to a level of 0.33 mRem/hr after one application and 0.22 mRem/hr after a second decontaminant application, both of which surpass the standard approach for addressing this hazard. |
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042228220 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a schematic representation of a typical pressurized water reactor which can employ the method of this invention to avoid the operating difficulties experienced by the prior art while maintaining a full load follow capability. The reactor of FIG. 1 includes a vessel 10 which forms a pressurized container when sealed by its head assembly 12. The vessel has coolant flow inlet means 16 and coolant flow outlet means 14 formed integral with and through its cylindrical walls. As is known in the art, the vessel 10 contains a nuclear core of the type previously described, consisting mainly of a plurality of clad nuclear fuel elements which generate substantial amounts of heat depending primarily upon the position of the control rods previously described. The heat generated by the reactor core is conveyed from the core by coolant flow entering through inlet means 16 and exiting through outlet means 14. Generally, the flow exiting through outlet means 14 is conveyed through an outlet conduit 26 to a heat exchange steam generator system 28, wherein the heated coolant flow is conveyed through tubes, schematically illustrated by reference character 18, which are in heat exchange relationship with water which is utilized to produce steam. The steam produced by the generator 28 is commonly utilized to drive a turbine 20 for th production of electricity. The flow of the coolant is conveyed from the steam generator 28 by the pump 22 through a cool leg conduit 30 to the inlet means 16. Thus a closed recycling primary or steam generating loop is provided with the coolant piping coupling the vessel 10 and the steam generator 28. The vessel shown in FIG. 1 is illustrated with one such closed fluid flow system or loop though it should be understood that the number of such loops vary from plant to plant and commonly two, three, or four are employed. Though not shown in the loop illustrated in FIG. 1, one loop of each plant includes a pressurizer which is responsive to the onset of a variation in pressure within the primary system due to temperature changes and variations in other operating conditions, to maintain a substantially constant primary pressure. The secondary side of the steam generator is isolated from the primary coolant by the heat exchange tubes 18. In the steam generator the secondary fluid 34 is placed in heat exchange relationship with the primary coolant, where it is heated and converted to a vapor or steam. The vapor flows through a steam conduit 38, as denoted by the arrow 36, to a turbine 20 which is connected via shaft 24 to a load, for example, an electrical generator. The amount of steam exhausted to the turbine is controlled by a throttling valve 40. The steam after passing through the turbine 20 is condensed in a condenser 42. The condensate or water thus formed is returned to the secondary or shell side of the steam generator through conduits 50, condensate pump 44, feedwater heater 46, and feedwater pump 48 as denoted by flow arrow 52. Thus, a recycling secondary electrical generating system is provided with the secondary fluid piping coupling the steam generator 28 to the turbine 20. The coolant temperatures in the reactor outlet conduit 26 and the reactor inlet conduit 30 for each of the primary loops of a typical pressurized water reactor system such as the one illustrated in FIG. 1 is sensed by temperature measuring elements 54 and 56, respectively, each of which may comprise a thermocouple or temperature resistance bulb. The temperature measuring elements 54 and 56 produce output signals T.sub.1 and T.sub.2, respectively, representative of the instantaneous temperature at the measuring location. The T.sub.1 and T.sub.2 signals for each loop are applied to a temperature averaging unit and the respective averages from the several loops are auctioneered to identify the highest instantaneous average operating temperature of the reactor. The identified operating temperature is then compared to a reference which is commonly a programmed function of the load. Presently, when the instantaneous identified temperature of the reactor departs from the programmed reference an error signal is generated which controls movement of the control rods in the direction to minimize the error. Accordingly, a programmed average temperature, reactor following load mode of operation is normally employed such as is described in U.S. Pat. No. 3,423,285 to C. F. Currey et al. Upon an increase in load demand the plant operator opens the throttling valve 40 to the turbine 20 until the desired output is attained. The increased steam flow rate exhausted to the turbine lowers the secondary pressure and enhances heat removal from the primary coolant. The corresponding drop in primary coolant temperature that would otherwise occur is avoided through manipulation of the control rods 58 in response to the control signals obtained from the programmed average temperature control system (i.e., described in the Curry et al patent). Various average temperature control programs have been recognized in the art. For example, one of the early programs maintained the coolant in the primary loop at a constant temperature over the entire load range of the nuclear reactor. For a given nuclear reactor this type of operating program enables the nuclear plant full load rating to be closer to the safe operating limits of the reactor. This results from the fact that one of the limiting parameters of the reactor is the coolant temperature, because thermal-hydraulic considerations require that the permissible power output of the reactor be reduced as coolant temperature is increased. Furthermore, electrical load transients on a nuclear reactor plant, for example, a sudden increase in turbine generator load from 90% to 100%, may readily result in a transient overloading of the reactor up to 5% in excess of the 100% rated load. With a constant average temperature control program, the coolant temperature increase is minimized during such a transient. Thus, the plant full load rating can be specified closer to the safe operating limit of the reactor than for a program temperature type of control which normally permits an increase in temperature during such an overload. With this type of temperature control the primary coolant temperature is independent of plant loading with the result that little or no volume change occurs in the primary coolant with changes in load. Therefore, the pressurizer coupled to the primary loop can be made relatively small, since it may be sized for transient conditions only. However, the disadvantage of using a constant temperature control over the entire load range is that it results in a characteristic rise in secondary loop pressure at light loads. At light loads the mean temperature differential between the tube and shell side of the steam generator falls to a low value as the secondary fluid temperature rises to a value close to that of the primary coolant temperature. This rise in secondary fluid temperature causes a corresponding rise in secondary fluid pressure. Therefore, for a given full load steam pressure the secondary loop must be designed for pressures much higher than the pressures encountered at full load operating level. Obviously the requirement of the higher design pressure results in a large and undesirable increase in the capital cost of the steam generator and other components utilized in and around the secondary loop. Graph A of FIG. 6 illustrates such a constant average temperature program with the corresponding variation in steam pressure versus power illustrated by Graph A in FIG. 7. Alternatively, if a constant steam pressure program is employed as illustrated by Graph B in FIG. 7, large primary temperature excursions are encountered as illustrated by Graph B in FIG. 6, which would necessitate an enlarged pressurizer with its attendent costs and other disadvantages. The variable average temperature program illustrated by Graph C in FIG. 6 and its corresponding steam pressure response identified by Graph C in FIG. 7 is a compromise and provides the most efficient operating condition for normal power operations as is described in the Currey et al patent. Implementation of constant axial offset control without use of part length control rods to maintain the most desirable operating conditions within the reactor to avoid power penalties alters the standard practice of using the full length control rods to achieve the desired rate of reactivity change to maintain the instantaneous average temperature essentially equal to the programmed average temperature. The full length control rods under constant axial offset control without part length rods are employed to maintain the axial offset substantially equal to a target value. Variations in power are now accommodated by varying the concentration of the neutron absorbing element within the coolant. In pressurized light water reactors, the hydrogen within the coolant acts as a moderator to slow down the neutrons created in the fissioning process to an energy level most likely to sustain the fission chain reactions occurring within the core. Boron is commonly employed in such reactors as the neutron absorbing element within the coolant. The boron concentrations are generally controlled through an ion exchange or dilution process which are typically slow and generally deteriorate in effectiveness from the beginning of life to the end of life of the core. However, the system is effective to accommodate most changes in load without disturbing the axial power distribution of the core. FIG. 3 illustrates the ability of both the full-length control rod system and the boron system to accommodate an increase in turbine load as a function of time for both the beginning of life (BOL) and end of life (EOL) of a typical nuclear core. Requirements for faster changes in load have been accommodated in the past by the fossil fuel plants on the electrical grid. This invention provides an improved method of operating a nuclear reactor which maintains the procedure specified by constant axial offset control, but provides an increased capability to respond to load increase requirements and overcomes the limitations of the dilution capabilities of the boron systems. To accomplish this end this invention takes advantage of the negative reactivity moderator temperature coefficient characteristic of light water pressurized reactors to achieve a rapid increase in reactivity by a controlled reduction in the primary loop temperature. Rapid return to power during load follow employing constant axial offset control without part length rods is limited because of the shallow control rod insertion necessitated to maintain the desired axial flux pattern in the core. Considerable improvement in return to power capabilities is obtained by taking advantage of any available excess throttle valve capacity and by reducing primary coolant temperature during load transient increases. The amount of reactivity increase depends upon the size of the temperature drop achieved in the primary loop and on the magnitude of the negative moderator coefficient. Excess throttle valve capacity (available on most reactors) allows higher power levels at reduced steam pressures. FIG. 4 illustrates the power level obtainable at 5%/minute (from 50% power) at BOL and EOL corresponding to the control rod reactivity insertion assumed for FIG. 3. A throttle valve capacity of 105% (typical) of nomial has been assumed in each case. A comparison of the two results illustrates the increase in load follow capability provided by the method of this invention. In accordance with this invention in response to an increase in power output requirement necessitated by an increase in load, the turbine throttle valve 40 is loaded (opened) at the desired rate of increase (e.g., 5%/minute). At the same time boron dilution is effected at the maximum rate available. Loading of the turbine as explained previously will effect a reduction in the average instantaneous core coolant temperature which will effect automatic withdrawal of the full length control rods through the average temperature control system. The axial flux difference, which is the difference in flux monitored in the upper and lower regions of the core, is identified and the automatic withdrawal of the full length control rods are stopped if and when the axial flux difference reaches its upper (most positive) control band limit corresponding to its target value (set by the constant axial offset specifications). The primary coolant temperature will begin to drop as soon as the control rods are stopped or, if the flux difference control limits are not approached, when the control rods reach their withdrawal limit at the top of the core. The instantaneous average primary coolant temperature is constantly monitored. If and when the difference between the instantaneous average primary coolant temperature and the programmed coolant temperature specified by the average temperature control system reaches a maximum pre-established value, typically 20.degree. F., the turbine loading is stopped to prevent further temperature reduction. In practice some rate/lag compensation is employed to allow for the thermal inertia of the system. The maximum temperature limit is set to prevent a reactor trip that would otherwise result from the system interpreting the temperature drop as a steam generator line break. If the pre-established temperature limit is reached and the turbine loading is stopped, then the actual to programmed coolant temperature difference will be reduced as a result of the boron dilution in effect. In most instances a 20.degree. F. drop in temperature will provide the desired power increase. If not, the turbine is loaded and stopped as specified above until the throttle valve is fully opened. From this point the rate of power increase is controlled by the boron dilution rate. This latter phase has assumed that the desired power output has not been reached at some intermediate point. The boron dilution operation is stopped when the turbine is at the desired power and the coolant temperature has reached its program value specified by the average coolant temperature control system. Any excess throttle valve capacity utilized is cut back automatically upon reaching full power by the current turbine controllers. The steps of this method apply to any starting power level during power operation and any set of normal operating conditions. The power level achieved at the accelerated return to power rate depends primarily on the starting power level, core cycle (equilibrium or not), core cycle lifetime, power rate, and temperature reduction permitted. It should be appreciated of course that the values specified are typical but may vary to some degree from plant to plant depending upon the particular plant's operating specifications. The amount of power (reactivity) that can be obtained by reducing the primary coolant temperature is proportional to the drop in temperature permitted. However, there are practical limits to the amount of temperature drop that can be obtained. FIG. 5 shows a typical reduced temperature operating region for a light water pressurized reactor. The left boundary of the operating region is defined by the lower operating limit of the automatic rod control system and by the reactor cool-down protection trips. The right boundary is governed by the throttle valve capacity (a function of steam temperature/pressure). The right boundary shown in FIG. 5 assumes a throttle valve capacity of 105% of full power. Excess throttle valve capacity of 105 to 110% exists in most operating nuclear facilities. The lower boundary of the operating region is defined by reactor cool-down protection trip settings, reactor vessel and other plant component thermal stresses, and by steam generator moisture carry-over considerations. The method of this invention is compatible with the average program temperature control operation described in the aforecited Currey et al patent. For constant axial offset control without part-length control rods the only modification required is that temperature adjustments in the instantaneous average of the core coolant be accomplished by boron dilution rather than control rod movement. The block diagram circuit generally illustrated by reference character 60 in FIG. 2 is capable of implementing the necessary modifications. The target band for the flux limits which is a function of reactor power is programmed into a setpoint circuit 62. The flux difference between the upper and lower regions of the core is monitored by four sets of neutron detectors positioned around the periphery of the reactor. The worst value monitored for the flux difference is identified by an auctioneering unit 64. The worst case flux difference is compared to the setpoint generated by the circuit 62 by a comparator 66. If the setpoint is exceeded an inhibit signal is issued to the full length rod control system to prevent further withdrawal of the control rods. Similarly, the temperature difference limit inhibit is implemented by the block circuitry illustrated by reference character 70. The measured average coolant temperature is compared with the coolant temperature programmed value, which is a function of the load as represented by the turbine impulse pressure input to the programming unit 72. The magnitude of the difference between the measured average coolant temperature and the program temperature is communicated to the comparator 74 which compares the signal to the temperature difference setpoint. If the setpoint is exceeded, further loading of the turbine throttle valve is inhibited by the controller 76. Signal compensation 78 is supplied in the form of rate/lags to compensate for the thermal inertia of the system. Accordingly, the average temperature control system presently in operation is easily modified to perform the steps of this invention to improve load follow capability during constant axial offset operation. FIGS. 14, 15 and 16 illustrate a corresponding change in plant conditions on a rapid return to power employing the reduced average temperature control method of this invention. The dotted portion of the curve illustrated in FIG. 15 identifies the average temperature control program while the solid portion of the curve indicates the departure achieved employing the steps of this invention. The dotted and solid portions of FIG. 16 respectively correspond to the operating conditions identified in FIG. 15. In contrast, FIGS. 8, 9 and 10 correspondingly show an exemplary return to power at a rate of 5%/minute from 50% power, which is equivalent to the full spinning reserve capability from 50% power. The dotted lines in FIGS. 9 and 10 indicate program values and the solid lines correspond to operating conditions. The spinning reserve is the difference between the current operating power level of the plant and the power level that can be achieved in the event of a sudden large demand in power. The transient illustrated in FIG. 8 is not possible without operation with part length rods as the control rods are not inserted into the core far enough to accommodate such a change by their withdrawal. However, if the axial power distribution is not considered, such a transient can theoretically be produced. FIGS. 11, 12 and 13 illustrate the capacity to achieve full power under constant offset control without part length control rods. The dotted and solid portions of the graph correspond respectively to the programmed and actual operating conditions experienced. The operating characteristics illustrated are compatible with the end of life data illustrated in FIG. 3. Only 70% of power is achievable at a load increase rate of 5%/minute. Accordingly, the increase in load follow capability achieved in accordance with this invention can be appreciated. |
description | This application is a divisional application of U.S. application Ser. No. 14/402,325, filed Nov. 20, 2014, which is a national stage application filed under 35 U.S.C. § 371 of International Patent Application No. PCT/EP13/60672, filed May 23, 2013, which in turn claims priority of French Patent Application No. 1254798 filed May 24, 2012, the disclosures of each of which are incorporated herein by reference in their entirety, for all purposes. This invention relates to the field of radionuclide production for medical use. More specifically it relates to a method for producing lead 212 that has a very high degree of radiological, chemical and even bacteriological purity, making it perfectly suited to medical use, as well as to an apparatus specially designed for automated implementation in a closed system of this method. It also relates to lead 212 produced by means of this method and this apparatus. Thus, the invention is especially likely to find applications in the manufacture of radiopharmaceuticals (or radiotracers) based on lead 212, useful in nuclear medicine whether for the treatment of cancers, particularly by α-radio-immunotherapy, or for medical imaging, in both humans and animals. Lead 212 is a rare radioactive isotope of lead. For several years now, it has been the subject of promising research, notably in the treatment by α-radio-immunotherapy of cancers and, in particular, cancer of the pancreas, ovaries, colon, breast and prostate (see for example Milenic et al., Cancer Biotherapy and Radiopharmaceuticals 2005, 20 (5), 557-568, reference [1]). Lead 212 is also a radioelement that has been shown to be of benefit in medical imaging, particularly for monophoton emission tomography coupled to a scan (Azure et al., World Molecular Imaging Congress, 8-11 Sep. 2010, Kyoto, reference [2]). In both cases, the use of lead 212 involves its injection into the patient in the form of a radiopharmaceutical, in other words of a product in which it is bound, typically by the intermediary of a chelating agent, to a molecule capable of highly specific targeting the cells to be destroyed (in the case of radioimmunotherapy) or to be observed (in the case of medical imaging), such as an antibody. To this end, lead 212 must comply with extremely rigorous requirements concerning quality and, especially, radiological (this should ideally be at least equal to 99.95%), chemical and bacteriological purity. As illustrated in FIG. 1 attached in the appendix, which represents the radioactive decay chain of thorium 232, lead 212 belongs to the thorium 232 radioactive family of which it is a daughter product. It is also a daughter product of radium 224 which, in this chain, falls between thorium 232 and lead 212. Lead 212, which is currently being experimented on for medical purposes, is obtained using a radium 224 generator, in other words a device containing a solid medium, typically a cation exchange resin, to which radium 224 is bound, and by means of a method which consists in allowing this radium to produce lead 212 by radioactive decay, recovering the lead 212 by elution, and by submitting the eluate containing this lead to a series of acid digestions in order to reduce the quantity of chemical impurities it contains and, in particular, impurities resulting from radiolysis of the solid medium present in the generator (see for example Horak et al., Journal of Nuclear Medicine 1997, 38, 1944-1950, reference [3]; U.S. Pat. No. 4,663,129, reference [4]). However this method does not systematically guarantee the production of lead 212 with radiological purity consistently greater than 99.50%. It also does not make it possible to carry out true chemical purification of the lead 212. Moreover, the acid digestions applied, which consist in putting lead 212 in a highly concentrated aqueous solution of a strong acid, for example hydrochloric or nitric acid, then evaporating this acid, are carried out manually under a hood and require about an hour-and-a-half of handling. Yet the half-life (also called period) of lead 212 is only 10.6 hours. It would therefore be desirable, within the scope of producing lead 212 for medical use at an industrial or hospital scale (that is to say in nuclear medicine departments), to have a lead 212 production method that: (1) guarantees that the lead 212 produced has radiological purity at least equal to 99.95%; (2) also guarantees that the lead 212 has greater chemical purity than that of lead 212 produced by the methods of the current state of the art; (3) makes it possible to produce lead 212 more quickly than the method of the current state of the art, given its relatively short half life; and (4) can be automated, or at least allows the number of manual operations that need to be carried out to be reduced to a minimum, and can be implemented in a closed system in order to limit the risk of contaminating staff in charge of this production, as well as the products to be administered to the patients. It would also be desirable to have available an apparatus that makes it possible to implement this method in an automated manner and in a closed system. Finally, it would be desirable to have a method and apparatus that can be industrialised. The invention specifically proposes a method for producing lead 212 for medical use which fulfils all these requirements, as well as an apparatus specially designed for automated implementation in a closed system of this method. A first subject-matter of the invention is a method for producing lead 212 for medical use which comprises the production of lead 212 by the decay of radium 224 in a generator containing a solid medium to which radium 224 is bound, and the extraction of this lead from the generator in the form of an aqueous solution A1, and which is characterised in that it further comprises a radiological and chemical purification of the lead 212 contained in said aqueous solution A1 which is carried out by a liquid chromatography on a column. Thus according to the invention, once extracted from the radium 224 generator, the lead 212 is subjected to a liquid chromatography on a column. This makes it possible to eliminate very efficiently both radiological and chemical impurities, which are extracted from the generator jointly with the lead 212, and therefore to obtain lead 212 presenting a radiological purity and a chemical purity that have never been achieved to date, or at least that have never yet been described in the literature. The radiological impurities are the radioelements likely to be present in the radium 224 generator, starting with the latter, whereas the chemical impurities are the organic degradation products resulting from radiolysis of the solid medium onto which the radium 224 is bound in the generator, if this solid medium is organic, as well as the organic and mineral contaminants likely to be introduced into this generator, for example by the solutions that are used to prepare and extract the lead 212. In addition to producing lead 212 that is both radiologically and chemically extremely pure, the use of a liquid chromatography on a column to purify the lead 212 after its extraction from the radium 224 generator also makes it possible to produce lead 212 more quickly than the method of the current state of the art. Moreover, as the liquid chromatography on a column is a technique that can be automated and coupled to the production of lead 212 by a radium 224 generator, which is itself a technique that can be automated, this means it offers a method for the production of lead 212 that can be implemented in an automated mode. In addition, as the liquid chromatography on a column and the production of lead 212 by a radium 224 generator are techniques based on the circulation of liquid media through solid media, they can both be implemented in a closed system. In the preceding and subsequent paragraphs, the term “liquid chromatography on a column” refers to any chromatography in which the mobile phase is a liquid phase and the stationary phase, or immobilized phase, is contained in a column, in other words a tube in which the mobile phase moves under the effect of gravity or under the effect of pressure. Moreover, the term “radiological purity” refers, for a radioelement such as radium 224 or lead 212, to the purity this radioelement presents with regard to the radioelements from which it originates by radioactive decay, as well as with regard to the other radioelements which are not part of its radioactive decay chain, and not to the purity it presents with regard to the radioelements which it generates itself through its own radioactive decay. In accordance with the invention, the liquid chromatography on a column is, preferably, carried out by using a stationary phase which selectively retains the lead 212 present in the aqueous solution A1 when this is contacted with the stationary phase, in other words which retains the lead 212 present in the aqueous solution A1 but which does not retain, or practically does not retain, the radiological and chemical impurities also present in this solution. Moreover, the liquid chromatography on a column is, preferably, an extraction chromatography or a partition chromatography, in other words a chromatography which is based on the distribution of the elements that are to be separated between an organic phase, or extractant, and an aqueous phase, the extractant being bound to an inert support and forming with it the stationary phase, whereas the aqueous phase represents the mobile phase. Indeed, this type of chromatography has the advantage of combining the selectivity of the liquid-liquid extraction with the rapidity of the chromatography. Within the scope of the invention, this extraction chromatography is advantageously carried out using a stationary phase which includes an ether crown as the extractant and, in particular, a dicyclohexano-18-crown-6 or a dibenzo-18-crown-6 whose cyclohexyl or benzyl groups are substituted by one or more C1 to C12 alkyl groups, with a straight or branched chain, in solution in an organic diluent not miscible with water, typically a long hydrocarbon chain alcohol, in other words a C8 chain and above. In particular, a stationary phase is used which comprises 4,4′ (5′)-di-tert-butylcyclohexano-18-crown-6 as the extractant, preferably diluted in octan-1-ol, such a stationary phase presenting the advantage of selectively retaining over 99% of the lead 212 present in an aqueous solution containing from 1.5 to 2.5 moles/L of a strong acid, which typically corresponds to the types of aqueous solutions that are used to extract lead 212 from a radium 224 generator. This type of stationary phase is particularly available, in bottles but also packaged in ready-to-use columns or cartridges for chromatography, from the company TRISKEM International under the commercial name “Pb resin”. It is of course also possible to purify the lead 212 extracted from the generator by liquid chromatography on a column other than extraction chromatography, for example, cation exchange chromatography. Whatever the type of liquid chromatography chosen and the type of stationary phase used, the liquid chromatography on a column preferentially comprises: loading the stationary phase with the aqueous solution A1, to allow the lead 212 present in this solution to be retained by the stationary phase; washing the stationary phase with an aqueous solution A2, to eliminate from the stationary phase the radiological and chemical impurities it contains but without eliminating the lead 212; then eluting the lead 212 from the stationary phase with an aqueous solution A3, to recover this lead in the form of an aqueous solution. Evidently the conditions under which these three steps are carried out and, particularly, the pH values of aqueous phases A1, A2 and A3, are suitably chosen as a function of the stationary phase used. Thus, for example, in the case where the liquid chromatography on a column is carried out using the previously mentioned “Pb resin” as the stationary phase: the aqueous solution A1 advantageously has an acidity corresponding to that of an aqueous solution of a strong acid having a molar concentration ranging from 1.5 to 2.5 and, preferably equal to 2, and corresponds, for example, to an aqueous solution containing from 1.5 to 2.5 moles/L and, even better, 2 moles/L of hydrochloric or nitric acid; the aqueous solution A2 advantageously has an acidity corresponding to that of an aqueous solution of a strong acid of molar concentration ranging from 0.1 to 0.5 and, preferably, equal to 0.5, and corresponds, for example, to an aqueous solution containing from 0.1 to 0.5 mole/L and, even better, 0.5 mole/L of hydrochloric or nitric acid; whereas the aqueous solution A3 advantageously has a pH ranging from 5 to 9 and corresponds, for example, to an aqueous solution of ammonium acetate which preferably contains 0.15 to 1 mole/L and, even better, 0.4 mole/L of ammonium acetate. In accordance with the invention, the loading of the stationary phase with the aqueous solution A1 is carried out preferably without altering the pH that has this solution when it is extracted from the radium 224 generator. Nevertheless, it is also possible to decrease (by addition of a strong acid) or increase (by dilution with water and/or addition of a strong base) the pH of the aqueous solution A1 before it is loaded onto the stationary phase present in the chromatography column in such a way that the retention of lead 212 by this stationary phase is optimal. Advantageously, the method also comprises a bacteriological purification of the lead 212, which is preferably carried out after the liquid chromatography on a column, for example by circulating the aqueous solution having been used to elute the lead 212 through a 0.2 μm pore filter. The production of the lead 212 in the radium 224 generator and its extraction from this generator can be carried out, in a manner known per se, by using as the solid medium a cation exchange resin that can retain the radium 224 but that does not retain the lead 212, for example the resin sold by the company BIO-RAD under the reference AG™ MP50 and which consists of a macroporous matrix of polystyrene/divinylbenzene onto which sulphonic groups —SO3H are grafted, and by: loading this resin with an acid aqueous solution containing radium 224, preferably of radiological purity greater than or equal to 99.5% such as, for example, an aqueous solution containing from 1 to 3 moles/L and, even better, 2 moles/L of hydrochloric or nitric acid; washing the resin with an aqueous acid solution, for example an aqueous solution containing from 0.01 to 2 moles/L and, even better, 0.01 mole/L of hydrochloric or nitric acid; leaving the radium 224 to produce lead 212 by radioactive decay; then eluting the resin with an aqueous acid solution, for example an aqueous solution containing from 1.5 to 2.5 moles/L and, even better, 2 moles/L of hydrochloric or nitric acid. Preferably, the whole process is implemented within a closed system or circuit, that is to say in practice in an apparatus allowing all the aqueous solutions used or produced, from the aqueous solution used for extracting the lead 212 from the radium 224 generator to the aqueous solution containing the lead 212 eluted from the chromatography column, to circulate in a circuit that is totally isolated from the surrounding environment and, notably, from the ambient air and the pollutants contained therein, which contributes to obtaining lead 212 of very high chemical purity. A subject-matter of the invention is also an apparatus specially designed for automated implementation in a closed system of the method as defined earlier, characterised in that it comprises at least: a generator comprising a solid medium onto which is fixed radium 224 to produce lead 212 by decay of this radium; means for extracting the lead 212 from the generator in the form of an aqueous solution A1; means for purifying the lead 212 contained in the aqueous solution A1 from the radiological and chemical impurities that this solution also contains by a liquid chromatography on a column; means for collecting the purified lead 212; means for a selective connection between the generator, the means for extracting the lead 212 from the generator, the means for purifying the lead 212 and the means for collecting the purified the lead 212; and an electronic processor for commanding the means for extracting lead 212 from the generator, the means for purifying the lead 212 and the means for the selective connection. In accordance with the invention, the means for extracting the lead 212 from the generator advantageously comprise means for circulating an aqueous solution in the apparatus in order to circulate said aqueous solution in the generator, which means preferably comprise a first pump for drawing in the aqueous solution from the solution source and for injecting the drawn aqueous solution into the generator. In addition, the means for purifying the lead 212 preferably comprise a chromatography column which contains a stationary phase capable of selectively retaining the lead 212 present in aqueous solution A1, when this is contacted with the stationary phase, as well as means for eluting the lead 212 from the stationary phase in the form of an aqueous solution. In accordance with the invention, the means for eluting the lead 212 from the stationary phase advantageously comprise means for circulating an aqueous solution A3 in the apparatus in order to circulate said aqueous solution A3 in the chromatography column, which means preferably comprise a second pump for drawing in the aqueous solution A3 from the solution source and for injecting the drawn aqueous solution A3 into the chromatography column. Advantageously, the first pump is able to draw in an aqueous solution A2 from the aqueous solution source and to inject the aqueous solution A2 into the chromatography column to wash the stationary phase. The means for collecting the purified lead 212 preferentially comprise a flask in which the solution containing the lead 212 eluted from the stationary phase is collected. Advantageously, the apparatus according to the invention further comprises a bacteriological purification filter which is placed between the flask and the chromatography column. In a particularly preferred embodiment of the apparatus according to the invention, this comprises a chamber inside which the means for extracting the lead 212 from the generator, the means for purifying the lead 212 from the radiological and chemical impurities, the means for the selective connection and the electronic command processor are placed. Preferably this chamber comprises means for connecting the apparatus to aqueous solution sources. Also preferably, this chamber comprises a plurality of inlet ports each of which can be connected to an associated aqueous solution source, and the apparatus includes fail-safe means to prevent connecting an aqueous solution source to a port with which it is not associated. The method and the apparatus which have just been described guarantee the production of lead 212 with a radiological purity at least equal to 99.95% and which can reach and even exceed 99.99%, and even 99.995%. To the best of the inventors' knowledge, lead 212 with such a high degree of radiological purity has never been obtained to date or, in any case, has never been described in the literature. Another subject-matter of the invention is therefore lead 212 which has a radiological purity at least equal to 99.95%, preferably at least equal to 99.99% and, even better, at least equal to 99.995%. Other characteristics and advantages of the invention will become apparent from the additional description given below with reference to the appended drawings. This additional description is, of course, given for the purpose of illustration of the subject-matter of the invention only and in no case constitutes a limitation to this subject-matter. This refers to FIG. 2 which diagrammatically represents an apparatus 20 according to the invention. As can be seen from this figure, this apparatus firstly comprises a radium 224 generator 22 for the production of lead 212 by radioactive decay of this radium. This generator consists of a device containing a solid medium, such as a cation exchange resin previously loaded with radium 224, this radium preferably having a radiological purity greater than or equal to 99.5%. The generator 22 has two ports 24, 26, allowing it to be connected to the other components of the apparatus 20 by ducts (not represented). This connection allows the lead 212 produced in the generator 22 to be extracted in the form of an aqueous solution. The apparatus 20 also comprises a chromatography column 28 for purifying, by a liquid chromatography, the lead 212 extracted from the generator 22, from the radiological and chemical impurities which are extracted from this generator jointly with the lead. This chromatography column can be either a column that has been previously prepared, conditioned and calibrated, or a commercially available ready-to-use column. In all cases, it contains a stationary phase, such as an extraction chromatography stationary phase, which is capable of retaining lead 212 under certain conditions and also capable of releasing lead 212 by elution under other conditions. The chromatography column 28 comprises a first port 30 and a second port 32 to connect it to the other components of the apparatus 20. The apparatus 20 also comprises inlet ports 34 connecting it to the sources 36 of aqueous solutions. According to a preferred embodiment particularly suited to the use of the apparatus 20 in a nuclear medicine department, each aqueous solution source 36 consists of a syringe filled with a predetermined amount of an appropriate aqueous solution which is to be used during the method. Each syringe 36 is suited to use in nuclear medicine: it has no rubber or silicon grease. The apparatus 20 also comprises means for pumping 38 the various aqueous solutions contained in the syringes 36, in order to circulate the aqueous solutions in the generator 22 and in the chromatography column 28. In the embodiment represented in FIG. 2, these pumping means 38 comprise two pumps 40 and 42, a first pump being employed to pump the aqueous solutions used respectively to extract the lead 212 from generator 22 and to wash the stationary phase contained in the chromatography column 28 after it is loaded with the aqueous solution used to extract the lead 212 from the generator 22, whereas the second pump 42 is employed to pump the aqueous solution used to elute the lead 212 from the chromatography column 28. Preferably, each of the pumps 40 and 42 is of the syringe-pump type in order to pump an exact amount of aqueous solution. The pumping means 38 also comprise two activators 52 each of which is associated with one of the two pumps 40 and 42 in order to drive this pump. These activators 52 can be electronically controlled to activate pumps 40 and 42 in a relatively precise manner in order to manage the quantity and flow of the pumped aqueous solutions. The apparatus 20 also comprises outlet ports 44 to collect the aqueous solutions produced by the method according to the invention. A first port 44 is connected to a flask 46 in which the aqueous solution containing the purified lead 212 is collected. A second port 44 opens into a receptacle 48 in which the other aqueous solutions are collected in order to be disposed of. A filter 56 having, for example, a pore size of 0.2 μm is placed at the entrance to the flask 46 to complete the chemical purification of lead 212 by a bacteriological purification. The apparatus 20 also comprises a plurality of multichannel valves 50 as well as a plurality of ducts (not represented) making it possible to selectively connect the components of the apparatus 20 one another for implementation of the method according to the invention. The valves 50 can be electronically controlled in order to optimise circulation of the aqueous solutions in the apparatus 20. The apparatus 20 also includes an electronic processor (not represented) for the command and control of the valves 50 and activators 52. This processor makes it possible to automate the functioning of the apparatus 20, such that the manual operations then consist mainly of connecting certain components of the apparatus 20 prior to implementing the method of the invention and disconnecting these components at the end of the implementation. The apparatus 20 still comprises a chamber 54 within which the chromatography column 28, the pumps 40 and 42, the activators 52, the valves 50 and, if need be, the electronic processor are placed. This chamber is presented here in the form of a parallelepiped in which the ports corresponding to the inlet ports 34 and outlet ports 44 of the apparatus 20 are found. The chamber 54 preferably forms a sealed box preventing access to the elements it contains. The chamber also comprises means of access to its interior volume which can be locked. This makes it possible to prevent any non-qualified persons from accessing the components of apparatus 20, particularly the components having some radiological activity, or the components whose functioning can be damaged. In the embodiment represented in FIG. 2, the radium 224 generator 22 is located outside the chamber 54. The latter therefore has two ports 60 which are crossed by pipes allowing the generator 22 to be connected to the other components of the apparatus 20. The general dimensions of various components of the apparatus 20 are relatively small, which makes it possible to arrange them in a chamber 54 which is also small in size. The apparatus 20 can therefore be a portable apparatus that can be used close to the area of usage of lead 212-based radiopharmaceuticals, for example in a nuclear medicine department. As mentioned previously, the chamber 54 has several inlet ports 34 to which the different sources 36 of aqueous solution are connected to the apparatus. The sources 36 of the aqueous solutions are similar in nature and consist here of predosed syringes. In order to guarantee the efficacy of the method according to the invention, each aqueous solution source 36 is associated with a single inlet port 34 through which the aqueous solution contained in this aqueous solution source supplies the apparatus. In order to avoid any reversal between the aqueous solution sources, as a result of connecting a syringe to an inlet port 34 other than the inlet port 34 with which it is associated, the apparatus 20 comprises so-called failsafe means allowing an operator to correctly connect each aqueous solution source 36 to the inlet port 34 with which it is associated. According to a first embodiment, the failsafe means are of a visual type and consist of colour coding, in other words labelling with a certain colour associated with each inlet port, and each aqueous solution source 36 has the same colour code as the one used to label the associated inlet port 34. According to another embodiment, the failsafe means are mechanical in nature, in other words each inlet port 34 and the associated aqueous solution source have complementary shapes and sizes and the size and/or shape of an inlet port 34 and of the associated solution source 36 are different from the size and/or shape of another inlet port 34 and the associated solution source 36. In this way it becomes impossible to connect a solution source 36 to an inlet port 34 with which it is not associated, thus preventing any human error. According to a preferred embodiment of the apparatus 20, the generator 22 can be disconnected from the rest of the apparatus 20 to be replaced by another similar generator. In fact, given that radium 224 has a half life of 3.66 days, the generator 22 can only be used for a limited period of time, usually for two weeks, after which the generator no longer contains a sufficient amount of radium 224. It therefore has to be replaced by a new generator. In a similar manner, the chromatography column 28 can be disconnected from the rest of the apparatus 20 for replacement by another similar column. The radium 224 generator 22 and the chromatography column 28 are both designed to allow the flow of aqueous solutions without manual intervention. Thus by simply operating the valves 50 and activators 52 by means of the electronic processor, it is possible to circulate the different aqueous solutions from the syringes 36, in which the solutions are stored, through the generator and/or the chromatography column 28, and to direct these aqueous solutions towards the outlet ports of the apparatus 20, according to controlled flow rates. The apparatus 20 thus makes it possible to implement the method of the invention in an automated manner. In addition, the connections are all impermeable, which allows all the aqueous solutions circulating, from the syringes 36 to the flask 46 and to the receptacle 48, in a circuit that is totally isolated from the surrounding environment and, notably, from the ambient air and the pollutants contained therein. The description which follows refers to an example of implementing the method according to the invention using the apparatus 20 which has just been described. In this example, the syringes 36 are considered to be filled with an appropriate amount of an aqueous solution and are connected to the apparatus 20 as well as are the flask 46 and the receptacle 48. Production of the Lead 212 The lead 212 is initially produced in the generator 22. This production consists in leaving the radium 224 retained on the solid medium contained in the generator 22 to produce lead 212 by radioactive decay, for example over a period of one day. Extraction of Lead 212 The lead 212 produced in the generator 22 is then extracted from this generator by elution, in other words by circulation in generator 22 of a first aqueous solution which draws out the lead 212 with it. This extraction consists in taking the first aqueous solution, which is initially contained in a first syringe 36, by the first pump 40 then injecting it into the generator 22, also through this pump. To do so, the valves 50 are directed by the electronic processor to connect the first pump 40 to the first port 24 of the generator 22. Loading of the Stationary Phase of the Chromatography Column The aqueous solution which leaves the generator 22 by the second port 26 of this generator contains lead 212, along with radiological and chemical impurities originating from the solid medium present in the generator 22. This aqueous solution is taken directly into the chromatography column 28. To do so, the valves 50 are adjusted to connect the second port 26 of the generator 22 to the first port 30 of the chromatography column 28. The aqueous solution passes through the chromatography column 28. The lead 212 is retained by the stationary phase contained in this column while some of the radiological and chemical impurities remain in the aqueous solution and therefore leave the column 28 along with the aqueous solution. Once it has left this column, the aqueous solution is directed towards the receptacle 48. To do so, the valves are directed by the electronic processor to connect the second port 32 of the chromatography column 28 to the receptacle 48. Washing of the Stationary Phase of the Chromatography Column After being loaded, the stationary phase contained in the chromatography column 28 is washed with a second aqueous solution to extract the radiological and chemical impurities it contains from this phase but without extracting the lead 212. This washing consists in taking the second aqueous solution, which is contained in a second syringe 36, by means of the first pump 40 then injecting it into the chromatography column 28, also through this pump. The second aqueous solution then passes through the chromatography column 28, drawing with it the radiological and chemical impurities contained in the stationary phase, and is then directed towards the receptacle 48 in which it is collected. To do this, the valves 50 are directed by the electronic processor to connect the first pump 40 to the first port 30 of the chromatography column 28 and to connect the second port 32 of the chromatography column 28 to the receptacle 48. Elution of the Lead 212 The lead 212 retained by the stationary phase of the chromatography column 28 is then extracted from this column by elution, in other words by circulation in the chromatography column 28 of a third aqueous solution which draws out the lead 212 with it. This elution consists in taking the third aqueous solution, which is contained in a third syringe 36, by the second pump 42 then injecting it into the chromatography column 28, also through this pump. To do this, the valves 50 are directed by the electronic processor to connect the second pump 42 to the first port 30 of the chromatography column 28. The third aqueous solution therefore passes through the chromatography column 28 drawing out the lead 212 with it. A volume of aqueous solution leaving the chromatography column 28, which corresponds to the dead volume of the column, is initially directed towards the receptacle 48 in which it is collected. To do this, the valves 50 are directed by the electronic processor to connect the second port 32 of the chromatography column 28 to the receptacle 48. Next, the remaining aqueous solution leaving the chromatography column 28 is directed towards the flask 46 where it is collected after having passed through the filter 56. To do this, the valves 50 are directed by the electronic processor to connect the second port 32 of the chromatography column 28 to the flask 46. Apparatus Purging According to a final step, the apparatus 20 is purged by circulating sterile air through it. This sterile air is obtained by taking ambient air through the first pump 40 then passing this ambient air through a filter 58, having for example a pore size of 0.2 μm, which is placed to the air inlet. Sterile air is then carried to the receptacle 48 to purge the circuit leading to this receptacle then up to the flask 46 to purge the circuit leading to this flask. To do this, the valves 50 are directed by the electronic processor to connect the first pump 40 to the receptacle 48 then to the flask 46. Lead 212 was produced with an apparatus similar to the one that has just been described and using: a radium 224 generator containing 400 mg of a cation exchange resin (company BIO-RAD—reference AG™ MP50) as the solid medium, this resin having been previously loaded with 10 mL of a solution containing 19 MBq of radium 224 of radiological purity greater than 99.5% (such as that determined by γ spectrometry) as well as 2 moles/L of hydrochloric acid (loading rate: 1 mL/min), then washed with 5 mL of an aqueous solution containing 0.01 mole/L of hydrochloric acid (washing rate: 1 mL/min); a ready-to-use chromatography column containing 80 mg of “Pb-resin” (company TRISKEM International) as the stationary phase; 4 mL of an aqueous solution containing 2 mol/L of hydrochloric acid to extract the lead 212 from the generator and to load the stationary phase of the chromatography column (elution and loading rate: 1 mL/min); 2 mL of an aqueous solution containing 0.5 mole/L of hydrochloric acid to wash the stationary phase of the chromatography column (washing rate: 1 mL/min); and 1 mL of an aqueous solution containing 0.4 mol/L of ammonium acetate (pH 6.5) to elute the lead 212 from the stationary phase of the chromatography column (elution rate: 0.5 mL/min). By leaving the radium 224 present in the generator 22 to produce lead 212 for 24 hours, 13 MBq of lead 212 were obtained, presenting: (1) a radiological purity greater than 99.995%, as established from measurement of the radiological purity presented by this lead 212 after 10 decay periods, this measurement being carried out by means of a germanium detector; (2) a chemical purity characterised by the presence, in the lead 212 elution solution, of: less than 11 ppb (parts per billion) of lead (other than lead 212); less than 2 ppb of vanadium, manganese, cobalt, copper, molybdenum, cadmium, tungsten and mercury; less than 20 ppb of iron; and less than 50 ppb of zinc; (3) bacteriological purity characterised by sterility and less than 0.5 endotoxin unit/mL; and this in less than 20 minutes between the start of the extraction of lead 212 from the radium 224 generator and the end of the filling of the flask 46 with purified lead 212. For the purpose of comparison, the radiological purity (established under the same conditions) of the lead 212 produced by a method of the current state of the art ranges from 98 to 99.80%. [1] Milanec et al., Cancer Biotherapy and Radiopharmaceuticals 2005, 20 (5), 557-568. [2] Azure et al., World Molecular Imaging Congress, 8-11 Sep. 2010, Kyoto. [3] Horak et al., Journal of Nuclear Medicine 1997, 38, 1944-1950. [4] U.S. Pat. No. 4,663,129. |
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055132278 | abstract | In order to reduce the time and difficulty of disassembling a seal arrangement in a cramped radioactive environment, a nozzle assembly hub is provided with a step bore which receives a seal arrangement, a compression collar, and a retaining nut which presses the seal arrangement into engagement with an inner wall portion of the hub and an outer wall portion of an ICI (in-core instrument) seal plug assembly. The ICI units remain connected to the seal plug assembly during normal disassembly operations. In this manner, the nozzle assembly may be disassembled by merely removing the retaining nut, compression collar, and seal arrangement and lifting the reactor head, along with the nozzle assembly, over the ICI units. The compression collar extends outside the retaining nut such that the collar can be engaged and compressed by an hydraulic loading tool while threading the retaining nut onto the hub. |
041994035 | claims | 1. In a structure for a water-cooled and water-moderated nuclear reactor that includes fuel assemblies arranged in a core within a reactor vessel, thereby defining a core boundary, and a core barrel disposed around the core for confining coolant entering the vessel to the core barrel exterior until the coolant has reached the lower end of the core, a core shroud within the barrel for directing the coolant flow in a predetermined longitudinally upward direction through the fuel assemblies, comprising: a. a coolant boundary surrounding and spaced from the fuel assemblies, having an integral inner surface generally following the shape and extending the entire longitudinal length of the core boundary, for channeling the coolant through the fuel assemblies; b. a plurality of longitudinally spaced, substantially cylindrical bands positioned inside the core barrel and surrounding the coolant boundary; and c. a plurality of discrete support members for transferring loads from the coolant boundary to bands, including strut means extending between the coolant boundary and each band, the thicknesses of the strut means in the circumferential direction being smaller than the distance between proximate struts, whereby uninterrupted longitudinal flow between the coolant boundary and the core barrel may be maintained for cooling the coolant boundary. 2. A core shroud as recited in claim 1, wherein the support members are longitudinally oriented in the direction of the coolant flow. 3. A core shroud as recited in claim 2, wherein the core shroud is structurally independent of the core barrel. 4. A core shroud as recited in claim 1, wherein the core shroud is structurally independent of the core barrel. |
claims | 1. A method of operating a nuclear core, the method comprising:loading an outer peripheral region extending from an edge of the core toward a center of the core with burnt fuel bundles;loading fuel bundles in a first type of control cell in an inner peripheral region extending from the outer peripheral region toward the center; andloading fuel bundles in a second type of control cell in an inner core region extending from the inner peripheral region toward the center, wherein,the first type and the second type of control cells include only fuel bundles positioned directly adjacent to moveable reactivity control elements, andthe first type of control cell includes,a first fuel bundle having a reactivity that is substantially higher than a reactivity of each fuel bundle of the second type of control cell, anda second fuel bundle having a reactivity that is substantially equal to a fuel bundle of the second type of control cell. 2. The method of claim 1, further comprising:moving control elements in only the second type of control cell to control reactivity in the core for a plurality of operating days while control elements in the first type of control cell remain inserted in the core and stationary. 3. The method of claim 2, further comprising:withdrawing control elements in the first type of control cell only after approximately 3 GWd/ST. 4. The method of claim 1, further comprising:completely withdrawing control elements in only the first type of control cell during the final quarter of the operating cycle. 5. The method of claim 1, wherein the loading the inner periphery creates the first type of control cell including at least two fresh fuel bundles, and wherein the loading the inner core creates the second type of control cell including no fresh fuel bundles. 6. The method of claim 1, wherein the first type of control cell includes a plurality of the first fuel bundles, wherein the first fuel bundles are fresh fuel bundles having different fuel enrichments from each other. 7. The method of claim 1, further comprising:removing approximately half of all fuel bundles in the core before the loadings. 8. The method of claim 1, further comprising:loading the inner core region completely with fuel bundles, wherein adjacent fuel bundles not in the second type of control cell in the inner core region have substantially differing reactivities from each other. 9. The method of claim 8, further comprising:repeating the loading the outer peripheral region and the inner peripheral region until the core is full and so that the core includes more of the second type of control cells than the first type of control cells, wherein the first fuel bundle is a fresh fuel bundle, and wherein the second type of control cells includes no fresh fuel;fully withdrawing all control elements except those in the first and the second type of control cells from the core; andmaintaining all control elements in the core in the first type of control cells while controlling reactivity in the core with only the control elements in the second type of control cells for a plurality of days. 10. The method of claim 8, wherein the first type of control cell is loaded with fuel bundles having a highest reactivity among all fuel bundles in the core. 11. The method of claim 1, wherein the first fuel bundle has a reactivity that is higher by equivalent of approximately 15 to approximately 23 GWd/ST exposure from the second bundle. 12. A method of operating a nuclear core having at least two different types of control cells, with a first type of control cell having a combined reactivity higher than a combined reactivity of the second type of control cell, and with more second type of control cells than the first type of control cells, wherein the first type of control cell includes a fuel bundle having a reactivity that is substantially equal to a fuel bundle of the second type of control cell, the method comprising:moving control elements in only the second type of control cell to control reactivity in the core while control elements in the first type of control cell remain inserted in the core and stationary for a plurality of operating days. 13. The method of claim 12, further comprising:withdrawing control elements in the first type of control cell only after approximately 3 GWd/ST. 14. The method of claim 12, further comprising:completely withdrawing control elements in only the first type of control cell during the final quarter of the operating cycle. 15. The method of claim 12, wherein there are a plurality of the first type of control cells, and wherein all of the first type of control cells are radially outside of the second type of control cells in the core. 16. The method of claim 15, wherein the core is filled with fuel assemblies surrounding the first and the second type of control cells, and wherein adjacent fuel bundles not in the second type of control cell and radially within the first type of control cells in the core have substantially differing reactivities from each other. 17. The method of claim 16, wherein the first type of control cells all include fresh fuel, and wherein the second type of control cells all include only burnt fuel. 18. The method of claim 12, further comprising:fully withdrawing all control elements from the core except for those in the first and the second type of control cells prior to the moving control elements in only the second type of control cell. 19. The method of claim 18, further comprising:partially withdrawing control elements in the first type of control cell only after approximately 3 GWd/ST; andfully withdrawing control elements in the first type of control cell from the core only during the final quarter of the operating cycle. 20. The method of claim 12, wherein the first type of control cells all include fresh fuel, and wherein the second type of control cells all include only burnt fuel. |
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claims | 1. An x-ray optical system comprising:a source that emits an x-ray beam; andan optic that receives the beam from the source and directs the beam toward a sample to characterize the sample, the optic having an optical reflecting surface, the geometry of the optical reflecting surface being defined by revolving a defined contour around an axis that is different than the geometric symmetric axis of the contour. 2. The system of claim 1, wherein the axis is in plane with the geometric symmetric axis in any longitudinal cross section. 3. The system of claim 1, further comprising a detector that characterizes the sample. 4. The system of claim 1, wherein the source has at least a partial circular emission profile. 5. The system of claim 4, wherein the source has a full circular emission profile. 6. The system of claim 4, wherein the source is a large source therefore the at least a partial circular profile is embedded within the source. 7. The system of claim 1, wherein the reflecting surface is a concave surface. 8. The system of claim 7, wherein the source has an emission profile with a semi-circular cross section. 9. The system of claim 7, wherein the source has an emission profile with an at least partial ring cross section. 10. The system of claim 1, wherein the reflecting surface is a convex surface. 11. The system of claim 10, wherein the source has an emission profile with a ring cross section. 12. The system of claim 10, wherein the source has an emission profile with an at least partial circular cross section. 13. The system of claim 1, wherein the reflecting surface includes a convex portion and a concave portion. 14. The system of claim 1, wherein the source is a rotating anode. 15. The system of claim 1, wherein the source is a sealed tube x-ray generator. 16. The system of claim 1, wherein the source is a microfocusing source. 17. The system of claim 1, wherein the optic is a total reflection optic. 18. The system of claim 1, wherein the optic is a multilayer optic. 19. The system of claim 1, wherein the optic is a reflective crystal. 20. The system of claim 1 wherein the x-ray source is segmented into multiple sections of different target materials. 21. The system of claim 20, wherein the optic is a total reflection optic with corresponding sections for different energies. 22. The system of claim 20, wherein the optic is a multilayer optic with corresponding sections for different energies, each section follows Bragg's law with its own contour and coating structure which include coating material combinations, layer thickness and variation of the layer thickness. 23. The optic of claim 22, wherein the optic has the same contour for different sections but different coating structure. 24. The optic of claim 22, wherein the optic has the same coating structure but different contours. 25. The system of claim 20, wherein the optic is a crystal optic with different sections, each of them has its own contour and crystal structure so that Bragg's law can be satisfied for its energy. 26. An x-ray optical element comprising an reflecting surface configured to reflect an x-ray beam, the reflecting surface having a first contour along a first direction defined by a geometric shape, a second direction being perpendicular to the first direction, the reflecting surface having a second contour in the second direction defined by the first contour being revolved about an axis that is different from the geometric symmetric axis of the geometric shape. 27. The system of claim 26, wherein the axis is in plane with the geometric symmetric axis. 28. The system of claim 26, wherein the reflecting surface is a concave surface. 29. The system of claim 26, wherein the reflecting surface is a convex surface. 30. The system of claim 26, wherein the reflecting surface includes a convex portion and a concave portion. 31. A method for analyzing a sample including:generating an x-ray beam;directing the x-ray beam to a sample using an optic with a reflecting surface, the geometry of the reflecting surface being defined by revolving a defined contour around an axis that is different than the geometric symmetric axes of the optic;detecting the x-rays from the sample; andgenerating an electrical signal corresponding to the x-rays detected. |
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claims | 1. An antimatter storage device for electrically neutral excited species of antimatter or exotic matter, said antimatter storage device comprising a three-dimensional or two-dimensional photonic bandgap (PBG) structure containing at least one PBG cavity in said PBG structure, said PBG cavity comprising a cavity wall embedded in said PGB structure and surrounded thereby and containing a quantity of species selected from the group consisting of excited electrically neutral atoms and molecules of antimatter, and excited electrically neutral atoms and molecules of exotic matter. 2. The antimatter storage device of claim 1 wherein said PBG structure comprises materials and geometry that together provide bandgaps at frequencies specific to each species to be stored in said antimatter storage device. claim 1 3. The antimatter storage device of claim 2 wherein said PBG structure has behavior that is dependent on a periodic contrast, wherein said periodic contrast is one-dimensional, two-dimensional, or three-dimensional, in the index of refraction between different constituent elements of said PBG structure, its geometry, and spacing associated with an arrangement of said constituent elements, and shapes of said constituent elements. claim 2 4. The antimatter storage device of claim 3 wherein said material comprising said PBG structure is selected from the group consisting of inverse opal backbone, macroporous silicon, colloidal crystals, woodpile structure, Yablonovite, and the like. claim 3 5. The antimatter storage device of claim 1 wherein said excited electrically neutral species is selected from the group consisting of positronium, antihydrogen, protonium, antimuonium, molecular positronium, molecules containing positronium, positronium molecules bound to ordinary matter, and electrically neutral molecules containing a positron having a single positive charge bound to ordinary matter having a single negative charge. claim 1 6. The antimatter storage device of claim 5 wherein said excited positronium comprises an electron and a positron bound together in orbit, but separated by a first distance, and wherein said excited positronium is separated from said cavity wall by a second distance. claim 5 7. The antimatter storage device of claim 6 wherein said first distance is large enough to prevent self-annihilation but small enough to keep said electron and said positron in orbit about each other, and wherein said second distance is large enough to prevent contact of said excited positronium with said cavity wall. claim 6 8. The antimatter storage device of claim 1 comprising an array of said PBG cavities, each PBG cavity separated from its nearest-neighbor PBG cavities by a third distance. claim 1 9. The antimatter storage device of claim 8 wherein said third distance is less than the photon localization length. claim 8 10. The antimatter storage device of claim 8 wherein said third distance is greater than the photon localization length. claim 8 11. A method of capturing antimatter, said method comprising: providing an antimatter capture device comprising, a three-dimensional or two-dimensional photonic bandgap (PBG) structure containing at least one PBG cavity therein, said PBG cavity capable of containing a quantity of species selected from the group consisting of excited electrically neutral atoms and molecules of antimatter, and excited electrically neutral atoms and molecules of exotic matter; and introducing said species into said at least one PBG cavity. 12. The method of claim 11 wherein said PBG structure comprises materials and geometry that together provide bandgaps at frequencies specific to each species to be stored in said antimatter storage device. claim 11 13. The method of claim 12 wherein said PBG structure has behavior that is dependent on a periodic contrast, wherein said periodic contrast is one-dimensional, two-dimensional, or three-dimensional, in the index of refraction between different constituent elements of said PBG structure, its geometry, and spacing associated with an arrangement of said constituent elements, and shapes of said constituent elements. claim 12 14. The method of claim 13 wherein said material comprising said PBG structure is selected from the group consisting of inverse opal backbone, macroporous silicon, colloidal crystals, woodpile structure, Yablonovite, and the like. claim 13 15. The method of claim 11 wherein said excited electrically neutral species is selected from the group consisting of positronium, antimuonium, antihydrogen, protonium, molecular positronium, molecules containing positronium, positronium molecules bound to ordinary matter, and electrically neutral molecules containing a positron having a single positive charge bound to ordinary matter having a single negative charge. claim 11 16. The method of claim 11 wherein the step of said introducing is selected from one of the following three methods: claim 11 (a) injecting said antimatter from radioactive sources or accelerator sources through a velocity moderator, either located within said PBG material of said PBG structure, or located outside said PBG structure; (b) pair-producing positrons and electrons by high-energy gamma rays generated by electron beams or as a by-product of neutron capture processes, wherein said neutrons impinge on said PBG structure in a collimated beam, or said PBG structure is placed inside a nuclear reactor in which there is an abundance of neutrons; or (c) embedding a radioactive material that emits positrons said PBG structure, resulting in a xe2x80x9cself-chargingxe2x80x9d device, wherein a positron is introduced into said PBG structure, picks up an electron at said wall of said cavity, and becomes a positronium atom within said cavity. 17. A method for exciting antimatter species to an excited state, comprising: providing an antimatter excitation device comprising a three-dimensional or two-dimensional photonic bandgap (PBG) structure containing at least one PBG cavity therein, said PBG cavity containing a quantity of species selected from the group consisting of excited electrically neutral atoms and molecules of antimatter, and excited electrically neutral atoms and molecules of exotic matter; introducing said species into said at least one PBG cavity; and exciting said species. 18. The method of claim 17 wherein said PBG structure comprises materials and geometry that together provide bandgaps at frequencies specific to each species to be stored in said antimatter storage device. claim 17 19. The method of claim 18 wherein said PBG structure has behavior that is dependent on a periodic contrast, wherein said periodic contrast is one-dimensional, two-dimensional, or three-dimensional, in the index of refraction between different constituent elements of said PBG structure, its geometry, and spacing associated with an arrangement of said constituent elements, and shapes of said constituent elements. claim 18 20. The method of claim 19 wherein said material comprising said PBG structure is selected from the group consisting of inverse opal backbone, macroporous silicon, colloidal crystals, woodpile structure, Yablonovite, and the like. claim 19 21. The method of claim 17 wherein said electrically neutral species is selected from the group consisting of positronium, antimuonium antihydrogen, protonium, molecular positronium, molecules containing positronium, positronium molecules bound to ordinary matter, and electrically neutral molecules containing a positron having a single positive charge bound to ordinary matter having a single negative charge. claim 17 22. The method of claim 17 wherein the step of said introducing is selected from one of the following methods: claim 17 (a) injecting said antimatter from radioactive sources or accelerator sources through a velocity moderator, either located within said PBG material of said PBG structure, or located outside said PBG structure; (b) pair-producing positrons and electrons by high-energy gamma rays generated by electron beams or as a by-product of neutron capture processes, wherein said neutrons impinge on said PBG structure in a collimated beam, or said PBG structure is placed inside a nuclear reactor in which there is an abundance of neutrons; or (c) embedding a radioactive material that emits positrons in said PBG structure, resulting in a xe2x80x9cself-chargingxe2x80x9d device, wherein a positron is introduced into said PBG structure, picks up an electron at said wall of said cavity, and becomes a positronium atom within said cavity. 23. The method of claim 17 wherein said method of exciting said species is selected from one or the following methods: claim 17 (a) using a laser tuned to an energetic state outside said PGB structure to place said species in said excited state; (b) creating said excited species in a more highly excited state that cascades down to the proper excited state, from which further decay is inhibited by said surrounding PBG structure; or (c) achieving said excited state directly during formation of Ps*, employing radioactive sources that exhibit xcex2 + -decay embedded in said PBG structure, such that as emitted high-energy positrons traverse said PBG material, they are slowed, and as they pass through said cavity wall, they capture an electron and form positronium in a Rydberg state, which can be said excited slate or which can be a state or higher energy that cascades down to said excited state, or it can be a state of lower energy that is laser pumped up to said excited state or up to a state of higher energy than said excited state and subsequently allowed to cascade down to said excited state. 24. A state of antimatter comprising a three-dimensional or two-dimensional photonic bandgap (PBG) structure containing an array of PBG cavities in said PBG structure, each PBG cavity separated from its nearest-neighbor cavities by a distance that is less than the photon localization length, each cavity containing a quantity of species selected from the group consisting of excited electrically neutral atoms and molecules of antimatter, and excited electrically neutral atoms and molecules of exotic matter. 25. The state of antimatter of claim 24 wherein said PBG structure comprises materials and geometry that together provide bandgaps at frequencies specific to each species to be stored in said antimatter storage device. claim 24 26. The state of antimatter of claim 25 wherein said PBG structure has behavior that is dependent on a periodic contrast, wherein said periodic contrast is one-dimensional, two-dimensional, or three-dimensional, in the index of refraction between different constituent elements of said PBG structure, its geometry, and spacing associated with an arrangement of said constituent elements, and shapes of said constituent elements. claim 25 27. The state of antimatter of claim 26 wherein said material comprising said PBG structure is selected from the group consisting of inverse opal backbone, macroporous silicon, colloidal crystals, woodpile structure, Yablonvite, and the like. claim 26 28. The state of antimatter of claim 24 wherein said electrically neutral species is selected from the group consisting of positronium, antihydrogen, protonium, antimuonium, molecular positronium, molecules containing positronium, positronium molecules bound to ordinary matter, and electrically neutral molecules containing a positron having a single positive charge bound to ordinary matter having a single negative charge. claim 24 29. The state of antimatter of claim 29 wherein said excited positronium comprises an electron and a positron bound together in orbit, but separated by a first distance, and wherein said excited positronium is separated from said cavity wall by a second distance. claim 29 30. The state of antimatter of claim 29 wherein said first distance is large enough to prevent self-annihilation but small enough to keep said electron and said positron in orbit about each other, and wherein said second distance is large enough to prevent contact of said excited positronium with said cavity wall. claim 29 31. A combination of localized photons and partially excited species to form a stationary-state superposition thereof, or a stable photon-species-cavity bound state, formed by an excited electrically neutral species of antimatter or exotic matter interacting with cavity walls of a cavity located within a photonic bandgap (PBG) structure, said interaction being mediated by photons. 32. The combination of claim 31 wherein said species is excited positronium (Ps*), which develops a very long lifetime, because it will remain in an excited state, which prevents self-annihilation from ground state, said lifetime being at least a few seconds. claim 31 33. The combination of claim 32 wherein said lifetime is extendable by proper selection of angular momentum for the excited state Ps*, said lifetime being at least a few seconds. claim 32 34. The combination of claim 32 further including externally applied crossed electric and magnetic fields to substantially enhance said lifetime extension. claim 32 35. A method of releasing gamma ray radiation, comprising: providing an antimatter excitation device comprising a three-dimensional or two-dimensional photonic bandgap (PBG) structure containing at least one PBG cavity therein, said at least one PBG cavity containing a quantity of excited positronium; and perturbing said PBG structure such that the index of refraction contrast, the geometry, the spacing, and/or the shape of the constituent components changes in such a way as to shift or turn off the bandgap that is responsible for maintaining the positronium in an excited state to thereby release said gamma ray radiation. 36. The method of claim 35 , wherein said released gamma rays either have a fixed energy of 511 keV per gamma ray for two gamma rays per positronium atom or have a distribution of energies ranging up to approximately 1 Mev for three gamma rays per positronium atom. claim 35 37. The method of claim 35 wherein said excited positronium decays to its ground state, forming a mixture of spin singlet and spin triplet states, which mixture of states produces self-annihilation from both spin states, resulting in a mixture of atoms producing two 511 keV gamma rays and atoms producing three gamma rays with a total energy of approximately 1 MeV. claim 35 38. The method of claim 37 wherein a 203 GHz pulse is applied to the trapped positronium atoms to de-excite said atoms in said spin triplet state to said spin singlet state, thereby enhancing production of two 511 keV gamma rays per atom and reducing production of three gamma rays with total energy approximately 1 MeV per atom. claim 37 39. A beam of species comprising excited electrically neutral atoms or molecules of antimatter or excited electrically neutral atoms or molecules of exotic matter emitted by a photonic bandgap (PBG) structure containing at least one PBG cavity therein, said at least one PBG cavity containing a quantity of said species, said beam comprising said species channeled out of said PBG structure into a desired direction by opened linear defect waveguides in said PBG structure. 40. A particle beam comprising electrically charged antimatter emitted by a photonic bandgap (PBG) structure containing at least one PBG cavity therein, said PBG cavity containing a quantity of excited electrically neutral atoms or molecules of antimatter or excited electrically neutral atoms or molecules of exotic matter, said excited electrically neutral atoms or molecules then ionized by an electric field, with electric and magnetic fields used to direct the ions out of the PBG device. |
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039363503 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT This invention utilizes support members formed from preselected materials with different rates of thermal expansion to compensate for the different temperature gradients encountered during reactor operation. The accompanying drawing shows a schematic illustration of a nuclear reactor 10, illustrating the relative positions of various reactor components such as the top plug 12 (top closure with control rod drive mechanisms 14), the core bottom support plate 16, which positions the core fuel assemblies 18 and a coretop hold down plate or core bundling 20. It may be seen from the figure that the aforementioned reactor components provide lateral support to the fuel sub-assembly 18 and control rod drive mechanism 14. However it is to be noted that this invention need not be limited to the specific components shown and described herein, but may be applied to any arrangement of reactor components that experience thermal gradients at reactor operation. Thus, the aforementioned components will be used as an illustration of the principles of this invention and the scope of the invention is not meant to be limited thereby. The reactor components, such as, the fuel rod and the control rod supports, are constructed out of materials having thermal expansion rates such that the total expansion of each component, under the environmental operating conditions at its respective location, substantially equals the thermal expansion of every other reactor component which functions to provide support in a parallel plane within the reactor, thus balancing the thermal expansions of the various supports to retain alignment. The balancing of the thermal expansions is achieved as illustrated in the following example. The top plug 12 is to be maintained at, for example, 400.degree.F, the bottom support plate 16 at 750.degree.F and the top "hold down" plate or "core bundling device" 20 at 1000.degree.F. These are the anticipated temperature gradients for the fast breeder reactor. The following equation is then used to calculate the per unit length thermal expansion of each component: EQU E = .alpha. (T.sub.2 - T.sub.1); where "E" equals the per unit length thermal expansion of the reactor component; PA1 ".alpha." equals a constant called the coefficient of thermal expansion, which is readily obtainable in precalculated tables; and PA1 "(T.sub.2 - T.sub.1 )" is the temperature gradient experienced by the reactor component, which is the difference between room temperature or the temperature at which alignment is originally obtained and the operating temperature. PA1 where ".DELTA.W" is the change in width of the sub-assembly 18; PA1 ".alpha." is the coefficient of thermal expansion of the sub-assembly 18; PA1 "(T.sub.2 - T.sub.1)" is the thermal gradient, which is the operating temperature of the sub-assembly 18 (i.e., 1000.degree.F), minus the loading temperature (i.e., 400.degree.F); and PA1 "W" is the width of the sub-assembly 18. PA1 where ".DELTA.S" is the change in spacing; PA1 ".alpha." is the coefficient of thermal expansion of the core bundling device 20 which would effect the change in spacing of the fuel-assemblies 18, (in this example it is assumed, the core bundling device 20 is constructed out of vanadium as calculated above); "(T.sub.2 - T.sub.1)" is the thermal quadrant of the core bundling device 20 (1000-400); and PA1 "S" is the spacing between the centers of the fuel sub-assemblies 18 at loading temperatures (approximately 5 inches). The materials to be used for the individual components may then be determined by first specifying the material to be used in the construction of one of the aforementioned reactor components. This choice is arbitrary and is only limited to a material which will satisfy the components characteristics. Thus, specifying type 304 stainless steel as the material used in the construction of the top plug 12, the coefficient of thermal expansion (.alpha.) for Type 304 stainless steel is then found to be 10 .times. 10.sup.-.sup.6 in/in. The temperature gradient as defined above is then (400-70). Substituting these values in the equation we obtain: EQU E = 10 .times. 10.sup.-.sup.6 (400-70) = 3300 .times. 10.sup.-.sup.6 = 0.0033 in./in. Then to balance the thermal expansion of the bottom support plate 16, with the thermal expansion of the top plug 12, we use this value of per unit length thermal expansion and the thermal gradient for the bottom support plate 16, which is (750-70 ) and substitute it into the equation: ##EQU1## Using this coefficient of thermal expansion we then consult the tables of coefficients of thermal expansion and select a material that has an .alpha. approximately equal to 4.86 .times. 10.sup.-.sup.6 and the other desired characteristics necessary for constructing the bottom support plate 16. Such a material is vanadium, which has a coefficient of thermal expansion equal to 5.0 .times. 10.sup.-.sup.6 in./in. The same procedure is followed in selecting a material for the top core bundling plate 20: ##EQU2## Molybdenum is an example of a material which satisfies this criteria with a coefficient of thermal expansion of 3.2 .times. 10.sup.-.sup.6 in./in. If the alignment dimensions are based on a heated assembly, for a hot sodium with a temperature of 400.degree.F and a top plug 12 at room temperature, the stainless steel plug 12 expansion will remain 3300 .times. 10.sup.-.sup.6 in./in. For the bottom support plate 16: ##EQU3## Therefore Type 304 stainless steel with a coefficient of thermal expansion of 10 .times. 10.sup.-.sup.6 may also be used for the bottom support plate 16. For the top core bundling plate 20: ##EQU4## Therefore Vanadium with a coefficient of thermal expansion of 5.0 .times. 10.sup.-.sup.6 could be used for the top core bundling plate 20. In addition to balancing the thermal expansions to retain alignment, the present invention permits the reduction of the gap between fuel sub-assemblies 18, wherein thermal bowing occurs. Some nominal gap is required at reloading temperatures (approximately 400.degree.F) so that the sub-assemblies 18, can be inserted and removed. This gap may be selected to be about 0.030 inches for a fuel sub-assembly 18 about 5 inches wide wherein the structural components of the subassembly are formed from Type 304 stainless steel. Then of a 0.030 gap exists at 400.degree.F this would be reduced at operating conditions as follows. The change in width of a fuel sub-assembly 18 is: EQU .DELTA.w = .alpha. (T.sub.2 - T.sub.1) W; Thus substituting the aforementioned values in the equation we obtain: EQU .DELTA. W = .alpha. (T.sub.2 - T.sub.1) W = 10 .times. 10.sup.-.sup.6 (1000-400) 5 = .030 inches. The change in the spacings between sub-assemblies 18 is then calculated from the equation: EQU .DELTA. S = .alpha. (T.sub.2 - T.sub.1) S; Substituting these values in the equation we obtain: EQU .DELTA.S =.alpha. (T.sub.2 - T.sub.1) S = 5.0 .times. 10.sup.-.sup.6 (750-400) 5 = 0.0084. The gap between fuel sub-assembies 18 at operating conditions is then: EQU gap = (the gap at loading temperature) - .DELTA.W + .DELTA.S EQU gap = 0.030 - 0.030 + 0.0084 = 0.0084 inches. Thus, the reduction in the gap between fuel sub-assemblies 18 reduces the amount of bow which can develop from 0.030 to 0.0084 inches per sub-assembly 18. If the gap between sub-assemblies 18 is reduced, as shown above, then the "jump movement" problem is also reduced by the same amount . |
description | This application claims the benefit of U.S. Provisional application 61/990,642, titled “Two-Color Radiography System and Method with Laser-Compton X-Ray Sources”, filed on May 8, 2014 and incorporated herein by reference. This is a continuation-in-part of U.S. patent application Ser. No. 14/274,348 titled “Modulated Method for Efficient, Narrow-Bandwidth, Laser Compton X-Ray and Gamma-Ray Sources,” filed May 9, 2014, incorporated herein by reference. U.S. patent application Ser. No. 14/274,348 claims the benefit of U.S. Provisional Patent Application No. 61/821,813 titled “Modulated, Long-Pulse Method for Efficient, Narrow-Bandwidth, Laser Compton X-Ray and Gamma-Ray Sources,” filed May 10, 2013, incorporated herein by reference. U.S. patent application Ser. No. 14/274,348 claims the benefit of U.S. Provisional application 61/990,637, titled “Ultralow-Dose, Feedback Imaging System and Method Using Laser-Compton X-Ray or Gamma-Ray Source”, filed May 8, 2014 and incorporated herein by reference. U.S. patent application Ser. No. 14/274,348 claims the benefit of U.S. Provisional application 61/990,642, titled “Two-Color Radiography System and Method with Laser-Compton X-Ray Sources”, filed on May 8, 2014 and incorporated herein by reference. The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344 between the U.S. Department of Energy and Lawrence Livermore National Security, LLC, for the operation of Lawrence Livermore National Laboratory. Field of the Invention The present invention relates to x-ray and gamma-ray generation via laser Compton scattering and more specifically, it relates to subtraction radiology utilizing laser-Compton x-ray sources. Description of Related Art In conventional 2-D x-ray/gamma-ray imaging, the patient or object is illuminated with a flat field of x-rays or gamma-rays and the transmitted signal is recorded on a 2D film or array of detectors. Variations of material density within the object cause variations in beam transmission for the penetrating radiation and these variations appear as shadows on film or a detector array. The dynamic range of this imaging technique is determined by the response function of the detector system and by the object thickness and secondary x-ray scattering by the object. In addition, all parts of the object see the same input flux (photons per unit area) and the total dose impinging upon the object is set by the area of the object and by the flux required to penetrate the densest region of the object, i.e., the flux required to resolve the structures of interest within the object. In this imaging modality, the entire object sees a high dose. For some imaging procedures in which the desired object is either small or low density, a higher atomic number contrast agent is injected or ingested to provide specific information about targeted structures. For example in coronary angiography the goal is to image the blood vessels and in particular to locate areas of reduced blood vessel aperture or blockages. Because the blood and the blood vessels are soft tissue and small in size, the total x-ray attenuation by them is small compared to the background matrix in which they are present and thus it is hard if not impossible to sufficiently resolve them in a conventional, whole body x-ray image. To overcome this issue, a dense material generally of higher atomic number than the surrounding biological material is injected into the blood stream to increase the x-ray attenuation in the areas of interest and in doing so improve contrast. Contrast agents used in human imaging tasks must of course be certified as being biologically inert or at least relatively so. For coronary angiography, iodine-containing compounds have been used as contrast agents. It should be noted that while this procedure does improve contrast and provide the required spatial information, the dose received by the patient can be very high. Some coronary angiography procedures can expose the patient to a full year's allowable dose. In order to increase the contrast and/or reduce the required dose for an image at a desired contrast level, two-color subtraction imaging has been suggested and demonstrated. In this modality, the patient is illuminated twice with a tunable, quasi-mono-energetic x-ray source. In one case the x-ray source has its energy set slightly above the k-shell absorption edge of the contrast agent and in the other case it is set slightly below. As shown in FIG. 1, the absorption cross section for the contrast material varies dramatically around the k-shell absorption region while the absorption cross section for the surrounding material can be relatively unchanged. If the two images are normalized to have the same signal in regions not containing the contrast agent, then a subtraction of the normalized images will be an image whose content is due primarily to the contrast agent. While early experiments conducted with filtered light from synchrotron x-ray sources demonstrated that this procedure could dramatically increase image contrast and/or reduce dose to the patient, its implementation in real-world clinical environments has been relatively limited due to the lack of clinically-compatible, quasi-mono-energetic x-ray sources. Synchrotron sources are expensive (>$100M), large (>100 m in diameter) and relatively uncommon. In addition the output from a synchrotron source is constant and not rapidly adjustable nor easily scanned across the object. It should also be noted that some have attempted to use conventional bremsstrahlung sources for k-edge imaging by changing the end point energy of the electron beam impinging upon the rotating anode so that the highest energy photons are either above or slightly below the desired k-edge absorption. In practice this, however, does not work very well as the total x-ray content of a bremsstrahlung source extends from the end point energy of the electron beam to DC, thus the fraction of the beam spectrum that is above the k-edge is relatively small compared to the total x-ray production and the image is thus dominated by background absorption. The dose to the patient is also high in this mode as it predominantly comes from the low energy tail of the bremsstrahlung spectrum of the source. To some extent this issue can be minimized by attenuating the beam with a low atomic number material that preferentially reduces the low energy portion of the spectrum relative to the high-energy portion but this of course reduces the total x-ray flux available for imaging, increases the proportion of image-degrading, scattered x-ray content within the illuminating x-ray beam and requires a higher current anode device to create the same number of useful above and below k-edge photons at the object. Note that the k-shell edge and not the outer shell absorption edges, i.e. L and M is generally used for two color clinical imaging as the x-ray energy required to remove a k-shell electron generally falls in the x-ray region of interest to clinical radiography while the outer shell absorptions occur at lower x-ray energies. The same two-color image subtraction scheme can be implemented, however, at lower energies using outer shell absorption edges if object and source are compatible. A new method for creation of high-contrast, subtraction, x-ray images of an object via scanned illumination by a laser-Compton x-ray source is described. The invention utilizes the spectral-angle correlation of the laser-Compton scattering process and a specially designed aperture and/or detector to produce/record a narrow beam of x-rays whose spectral content consists of an on-axis region of high-energy x-rays surrounded by a region of slightly lower-energy x-rays. The end point energy of the laser-Compton source is set so that the high-energy x-ray region contains photons that are above the k-shell absorption edge (k-edge) of a specific contrast agent or specific material within the object to be imaged while the outer region consists of photons whose energy is below the k-edge of the same contrast agent or specific material. Illumination of the object by this beam will simultaneously record the above k-edge and below k-edge absorption response of the object for the regions illuminated by the respective portions of the beam. By either scanning the beam or scanning the object relative to the beam, one may build up the full above and below k-edge spatial response of the object. These spatial responses when properly-normalized and subtracted from one another create a map that is sensitive to the presence or absence of the specific contrast agent or special material within the object and as such the subtraction image represents a high-contrast radiograph of the presence of the contrast agent or special material within the object. The technique may be used for a variety of x-ray imaging tasks to either increase image contrast at a fixed x-ray dose to the object or to reduce the x-ray dose required to obtain an x-ray image of a desired contrast. Of particular note is that this method obtains both the above and below k-edge maps of the object without requiring any adjustment of the end-point energy of the x-ray source or any whole beam filtering of the x-ray source and can do so without illuminating the object with lower-energy, non-penetrating x-rays that are typically present from conventional rotating anode, x-ray sources. Possible applications include but are not limited to coronary angiography in which the blood is doped with iodine as a contrast agent and used to provide an image of arterial blockages or low-dose mammography in which the breast is injected with a gadolinium based contrast agent and used to image the vascularization associated with pre-cancerous material. In both cases, subtraction x-ray images of the contrast agents can provide vital information and do so with equivalent or better image quality and/or significantly lower dose than conventional x-ray radiography. The invention has a wide variety of uses including high-contrast x-ray imaging, medical x-ray imaging, e.g., angiography and mammography, subtraction x-ray imaging of specific atomic species in an object or patient and non-destructive evaluation of multi-component parts with x-rays e.g., element specific radiography of computer chips and components. In this invention, the laser-Compton scattering process is used to create a beam of x-rays that consists of two distinct spatial regions with two distinct x-ray spectra; one region on axis having higher energy photons and another region surrounding it having lower energy photons. This beam is then used in a scanning imaging modality to produce a 2-color, subtraction, x-ray image of an object. For appropriate settings of the laser-Compton x-ray beam energy, this subtraction image will be highly sensitive only to the presence of specific materials within the radiographed object. This high-contrast, low-dose image is obtained without adjustment to the laser-Compton x-ray source end point energy, i.e., without tuning the x-ray source. Laser-Compton scattering (sometimes also referred to as inverse Compton scattering) is the process in which an energetic laser pulse is scattered off of a short duration bunch of relativistic electrons. This process has been recognized as a convenient method for production of short duration bursts of quasi-mono-energetic, x-ray and gamma-ray radiation. When interacting with the electrons, the incident laser light induces a transverse motion of the electrons within the bunch. The radiation from this motion when observed in the rest frame of the laboratory appears to be a forwardly directed, Doppler upshifted beam of high-energy photons. For head on collisions, the full spectrum of the laser-Compton source extends from DC to 4 gamma squared times the energy of the incident laser, where Gamma is the normalized energy of the electron beam, i.e., gamma=1 when Electron energy?=511 keV. The end point energy of the laser-Compton source may be tuned, by changing the energy of the electron bunch and/or the energy of the laser photons. Beams of high-energy radiation ranging from a few keV to greater than a MeV have been produced by this process and used for a wide range of applications. The spectrum of the radiated Compton light is highly angle-correlated about the propagation direction of the electron beam with highest energy photons emitted only in the forward direction. See FIG. 2. With an appropriately designed aperture placed in the path of the laser-Compton beam, one may easily create a quasi-mono-energetic x-ray or gamma-ray beam whose bandwidth (DE/E) is typically 10% or less. Laser-Compton x-ray sources are also highly collimated especially in comparison with conventional rotating anode x-ray or gamma-ray bremsstrahlung sources. The cone angle for emission of the half-bandwidth spectrum of a laser-Compton source is approximately 1 radian on gamma or of order of milliradians and the cone angle for narrowest bandwidth, on-axis portion of the spectrum may be of order of 10's of micro-radians. Typical rotating anode sources have beam divergences of ˜0.5 radians. This high degree of collimation makes laser-Compton x-ray sources ideally suited to pixel by pixel imaging modalities. Furthermore, the output from a laser-Compton x-ray source is dependent upon the simultaneous presence of laser photons and electrons at the collision point (the interaction point). Removal of either eliminates the output of the source completely thus making it easy for one to rapidly turn on or off the x-ray or gamma-ray output. As illustrated in FIGS. 2A-2D, this invention utilizes two regions of the angle-correlated spectral output of a laser-Compton x-ray beam; the on axis portion of the beam containing the highest energy photons and the region immediately around this portion of the beam containing photons of lower energy. The extent of the surrounding region, the spectral content of the surrounding region and the total number of photons in the surrounding region relative to the on axis portion of the beam may be easily set by passing the entire beam through an appropriate aperture and/or beam blocks of fixed size. By operating the laser-Compton x-ray source with fixed laser pulse energy and fixed electron bunch charge, the total output of the laser-Compton x-ray source as well as the ratio of total x-ray photons in the two regions of interest can be held fixed and constant. Specifically, FIG. 2A shows a cross-sectional side view of a diverging output beam 10 from a laser-Compton x-ray source. The cross-section is taken in the plane of the page through the center of the beam 10. In the following discussions, the term “axis” refers to the central optical axis on which beam 10 propagates. The energy of beam 10 is highest in the central on-axis region 12 and falls off with radial distance of the beam relative to the central axis. Thus, region 14 has less energy than region 12 and region 16 has less energy that region 14. Although the regions are shown in FIGS. 2A, 2B and 2C to have distinct lines of separation one to another, in reality, there is a continuous change of energy from the most energetic beam at the very center to the lowest energy at the outer radius. The figure includes a cross-sectional view of a circular aperture 20. In FIG. 2A, aperture 20 has an opening diameter that allows regions 12 and 14 to pass and that blocks a large portion of region 16, although a small portion is allowed through. The area under the curve 40 of FIG. 2D is the loosely-apertured, wide-bandwidth spectrum of light (x-ray energy) of the combination of energies of the portions of beam regions 12, 14 and 16. FIG. 2B illustrates the use of a narrow diameter aperture 22. The area under curve 42 of FIG. 2D represents the on-axis, high-energy narrow-band spectrum of only beam region 12. FIG. 2C illustrates the use of an aperture 24 that has a diameter that allows passage of beam regions 12 and 14 but not region 16. A beam block 26 is positioned to block beam region 12 and thus, only region 14 can propagate toward a target. Note that the beam 14 is shown in side view and the therefore the beam is really circular with a central area that has no energy because beam region 12 has been blocked by aperture 26. Thus, the area under curve 44 of FIG. 2D represents the narrow-band, lower-energy spectrum of only beam region 14. Note that many of the exemplary embodiments described herein utilize circular apertures, but the invention is not limited to a particular aperture shape. The exact transmitted spectrum will depend upon the shape and size of the aperture and/or beam block and the polarization of the laser. To produce a 2-color, subtraction, x-ray image, the narrow-divergence, laser-Compton x-ray beam is either scanned across the object or the object is raster scanned relative to a fixed beam or a combination of scanning the beam and the object. For illustrative purposes (see FIGS. 3A and 3B), it is assumed that the beam is fixed and propagates in the z-direction and that the object is raster scanned in the x-y plane. The goal of a 2-color subtraction image is to detect within this object the presence of a specific atomic material that either occurs naturally or has been artificially added as a contrast agent. The beam energy for the laser-Compton source is chosen so that the on-axis, high-energy x-ray beam photons are above the k-shell absorption edge of the atomic material/contrast agent and the outside, surrounding, low-energy x-ray beam photons are below the k-shell absorption threshold. For each location in the scan, the transmitted x-ray beam impinges upon an electronic x-ray-sensitive detector that is aligned with the x-ray beam and held fixed in space with respect to the x-ray beam. The detector records separately and the number of ballistic photons impinging upon it from the inner and outer portions of the x-ray beam. After fully scanning the object, both the inner and outer portions of the beam will each have exposed the full 2-dimentional extent of the object. The recording by the detector of the x-ray photon number as a function of position of the inner portion of the beam represents the attenuation by the object of photons above the k-edge of the contrast agent while the recording by the detector of the x-ray photon number for the outer portion of the beam represents the attenuation by the object of photons that are below the k-edge of the contrast agent. For materials within the object that are composed of atoms that are different from the absorbing atom of the contrast agent, the relative attenuation of photons contained in the two regions of the x-ray beam are basically identical. Therefore, a suitably-normalized, numerical subtraction of the two images obtained by the scan will be to first order zero everywhere except where the contrast agent is present. This technique provides a highly sensitive and low dose modality for imaging of contrast agents or specific atomic materials within an object provided that they differ significantly in atomic weight from the overall matrix of the object. More specifically, FIG. 3A shows beam region 12 as provided by the system of FIG. 2B. The laser Compton x-ray source is configured so that beam region 12 has an energy that is above the k-edge of a material of interest in the object 50. Note that and example object 50 can be human tissue but of course other object can be placed in the beam. Beam region 12 propagates in the z direction through the object 50 and onto an x-ray detector 52. Such detectors are known in the art. Again, the figure depicts the object to be a person. In such cases, the person may ingest or be injected with a contrast agent containing the material of interest. The person or object can be raster scanned in the x-y plane to collect and obtain an image of the above k-edge x-ray photons that are not absorbed by the contrast agent. FIG. 3B shows the beam 14 as provided by the system of FIG. 2C. In this case, only beam region 14 is allowed to propagate through the object 50 and onto the x-ray detector 52. The person or object can be raster scanned in the x-y plane to collect and obtain an image of the below k-edge photons that pass through the object. As discussed herein, a suitably-normalized, numerical subtraction of the two images obtained by the scans will be to first order zero everywhere except where the contrast agent is present. One specific example is angiography in which an iodine-containing contrast agent is injected into the blood stream. Iodine is atomic number 53 and has a k-edge absorption energy of 33.2 keV. The surrounding tissue is generally composed of lower atomic weight atoms, e.g., carbon, oxygen, hydrogen etc. These atoms do not vary significantly in their attenuation at or around the 33.2 keV k-edge of iodine. Thus a 2-color, subtraction image with a laser-Compton x-ray beam tuned to the iodine k-edge will produce a high contrast map of the location of iodine and consequently a high contrast image of the blood vessels containing the iodine. The following are some exemplary variations of two-color, subtraction imaging with laser-Compton x-ray sources. The invention is not limited to these examples. 1. FIG. 4A illustrates an embodiment of a two pixel modality of the present invention. FIG. 4B illustrates an embodiment of a two pixel detector for use with the two pixel modality of FIG. 4A. In this instantiation, the detector contains only two detection regions; one that subtends the on-axis, high-energy region of the beam (beam region 12) and one that subtends the desired, surrounding, low-energy region of the beam (beam region 14). Such a detector may be constructed by the same micro-fabrication techniques used to create silicon x-ray diodes. Alternatively a 2-D detector such as an x-ray CCD may be used if the pixels of the detector are binned into two groups associated with the two regions. The advantage of this modality is potential simplicity of the detector and data reduction. Spatial resolution of the image however will be limited to the spatial extent of the beam in the two regions. FIG. 4A includes a high Z tube 70 between the object 50 and the two pixel x-ray detector 56. The high Z tube 70 is matched to the diameter of the beam to preclude scattered x-rays from reaching the detector 54. FIG. 4B shows the face of the two pixel x-ray detector 54. The inner, round pixel area 64 records “above” k-edge photons and the outer, annular pixel region 66 records “below” k-edge photons. 2. FIG. 5A illustrates a “many pixel” modality embodiment of the present invention. FIG. 5B illustrates the face of an exemplary detector used with the embodiment of FIG. 5A where the detector consists of a 2-D array of pixels which subtends both the high energy and low energy portion of the beam. The elements of FIG. 5A are identical to those of FIG. 4A, and such elements are identically numbered, except that this embodiment uses the 2-D x-ray detector array 56. In this instantiation, the detector is a high-resolution 2-D detector such as (but not limited to) a 2-D x-ray CCD detector. The spatial resolution of the image will be determined by the spacing of the CCD elements and the source size of the laser-Compton x-ray source. The numerical registration and subtraction of the image will require more computations than variation 1 above. In the embodiments that utilize an array type of detector, only the pixels that are completely within the high energy region are used to calculate the energy level of that region. The same is true of the lower energy region. Only the pixels that are completely within the area of the array that detects the lower energy beam region are used to calculate the lower beam energy level. The pixels that are not completely within the respective beam region are discarded in the calculation. FIG. 5B shows the face of the detector array. The inner pixel area 74 records “above” k-edge photons and the outer pixel region 76 records “below” k-edge photons. 3. In an embodiment utilizing an equal area modality, the area of the two x-ray regions are set to be the same. This is either accomplished by apertures placed in the beam to limit the extent of the outer surrounding beam or by limiting the extent of the detector subtended by the outer region of the beam such that the area illuminated by this portion of the beam is equal to the area illuminated by the inner portion of the beam. This mode reduces the computational overhead associated with image reconstruction and assures that one portion of the beam does not sample the object any more than the other. 4. In an embodiment utilizing an equal flux modality, the size of the surrounding region is set so that the total number of photons contained in this region equals that of the on axis region. The images recorded by the two regions are naturally normalized and thus simplifying the image reconstruction. 5. FIG. 6A illustrates an “equal spatial dimension” modality embodiment of the present invention where the beam is passed through a slit so that either the horizontal or vertical dimensions of the beam portions are equal. FIG. 6B illustrates a detector 56 for use with the embodiment of FIG. 6A. Elements identical to those of FIG. 5A are identically numbered. In this instantiation, the entire beam is passed through a slit aperture 80 so that the surrounding region is limited in either the horizontal or vertical dimension to be the same width as the on-axis high energy x-ray region. This simplifies the scanning and data retrieval algorithm. FIG. 6B shows the face of the detector array. The inner pixel area 84 records “above” k-edge photons and the outer pixel region 86 records “below” k-edge photons. 6. FIG. 7A illustrates a “discontinuous annular beam” modality embodiment of the present invention. Elements identical to the embodiment of FIG. 5A are identically numbered. An annular aperture 90 is placed such that it produces an area 92 of no photons between beam region 12′ and beam region 14′. FIG. 7B illustrates the face of a detector for use with the embodiment of FIG. 7A. The laser-Compton x-ray beam profile for linear polarized laser light is oval in shape. In this modality a round annular obscuration is placed in the beam to create the two distinct spectral regions of the beam. This is the simplest method for physically creating the separate beam areas. 7. FIG. 8A shows a “dithered detector” modality according to the present invention. Elements identical to the embodiment of FIG. 5A are identically numbered. FIGS. 8B-D show various positions of a detector in the beam of the embodiment of FIG. 8A. In this instantiation a single pixel detector 58 which consists of an x-ray diode and collimating aperture/tube subtends an area equal to the high energy portion of the x-ray beam. With the x-ray beam held fixed, the detector is dithered in the plane transverse to the propagation direction of the laser so that it alternatively intercepts the low energy portion and the high energy portion of the beam. FIG. 8B shows the detector 58 in the “up” position so that it intercepts only “below” k-edge photons 14. FIG. 8C shows the detector in the “middle” position so that it intercepts only “above” k-edge photons 12. FIG. 8D shows the detector in the “down” position so that it intercepts only “below” k-edge photons 14. This modality enables use of the fastest possible, simplest possible and/or least expensive detectors to construct an x-ray image. It does, however, increase the dose seen by the object by a factor of 2. 8. FIGS. 9A and 9B show a “dithered aperture” modality according to the present invention. Elements identical to the embodiment of FIG. 5A are identically numbered. In this instantiation a fixed detector 60 that subtends the entire area of both beam regions 12 and 14 is used. After the laser-electron interaction point that produces the x-ray beam and before the object, a movable aperture or beam block 110 is placed in the beam. The role of this aperture is to block in an alternating manner the on-axis high-energy portion of the beam and the surrounding low-energy portion of the beam in synchronism with the pulsed output of the laser-Compton x-ray source. FIG. 9A shows the aperture 110 in the “middle” position so that it passes only beam region 12 which consists of high energy x-rays. FIG. 9B shows the aperture 110 in the “up” position so that it passes only beam region 14 which consists of low energy x-rays. This alternating beam block could be constructed in a number of ways. For example by placing a high-Z material of the appropriate shape on a low-Z disk and rotating the disk in the beam at a rate that places the aperture such that the desired beam portion is blocked and the desired beam portion is allowed to transmit. This modality alternatingly records the above k-edge and below k-edge attenuation of the object. This modality enables use of fast, simple and/or cheap detectors to construct an x-ray image and does not expose the object to any higher dose than instantiations 1 thru 6 above. It does however take 2× longer to accumulate an image with this modality. It should be noted that both the dithered detector and dithered aperture modality could be combined and would enable use of a smaller area x-ray detector. In principle the scatter reduction tube 70 shown in this disclosure could also be dithered in synchronism with the aperture and/or detector and in doing so would allow for a smaller tube diameter and greater discrimination of unwanted, scattered x-ray photons emerging from the back surface of the imaged object. 9. An embodiment of the invention is referred to as a double annulus modality. In this instantiation, the on axis portion of the beam is not used but rather two annular portions of the beam are selected. Because the energy of the spectral content of the beam decreases as a function of angle, it is possible to select an inner annulus that contains higher energy photons than the outer annulus. As described above, these two annuli can be used to construct a 2-color subtraction image. There is no intrinsic advantage to this modality except that the two beams have similar form factors. In this embodiment, although the inner annulus is not centered on the optical axis of the x-ray beam, the source power can be turned up so that the inner annulus has an energy level that is above the k-edge of a material of interest. 10. In another embodiment, no aperture is used to constrain the extent of the laser-Compton beam and the full beam is incident upon the object to be imaged. By removing the object from the beam path, the profile of the full laser-Compton beam may be obtained on the downstream 2-D detector. Pixel location on this detector will be correlated with a specific range of x-ray photon energies and may then be used as described above to produce a 2-color subtraction radiograph. This modality is suited to applications in which the laser-Compton source is scanned across the object and for which a moving aperture to limit the outer beam extent would be impractical. 11. In another modality, a time-gated detector is used to record the ballistic photons above and below k-edge photons that reach the detector and to discriminate against any photons scattered by the object under interrogation that might also reach the detector location. The gate time of the detector must be of order the duration of the laser-Compton x-ray pulse, i.e., a few to a few 10's of picoseconds. The time-gate must be synchronized to the x-ray pulse. This modality not only enables higher contrast for a fixed dose by eliminating the background scattered x-ray photons from the image but also improves the subtracted image by insuring that only the ballistic photons of the correct energy are present in the respective above and below k-edge images. This modality may be accomplished with either a gated 2-D detector or a gated single pixel detector. The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The embodiments disclosed were meant only to explain the principles of the invention and its practical application to thereby enable others skilled in the art to best use the invention in various embodiments and with various modifications suited to the particular use contemplated. The scope of the invention is to be defined by the following claims. |
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043303676 | abstract | A protective control system and method for a nuclear steam supply system for the protection against the violation of safety design limits, the system comprising the combination of two sub-systems. The first sub-system includes a method or system for a continuous calculation of an operating limit which incorporates a margin that allows sufficient time for the initiation and completion of corrective action without the violation of a design limit. The second sub-system includes a method or system for continuously predicting a pending violation of a design limit far enough in advance to allow the initiation and completion of corrective action. The combination of the two systems not only allows operation of the nuclear steam supply system with the assurance of a sufficient margin to take protective action on the occurrence of an accident but also assures that actual protective action is in fact instituted in sufficient time to avoid the violation of a design limit. |
description | The present application claims priority of British patent application Serial No. 0802762.5, filed Feb. 15, 2008, and published in English the content of which is hereby incorporated by reference in its entirety. The present invention relates to a multi-leaf collimator. External Beam Radiotherapy involves the production of a beam of ionising radiation, usually x-rays or a beam of electrons or other sub-atomic particles, which is then directed towards a cancerous region of the patient. This adversely affects the tumour cells, causing an alleviation of the patient's symptoms. Generally, it is preferred to delimit the radiation beam so that the dose is maximised in the tumour cells and minimised in healthy cells of the patient, as this improves the efficiency of treatment and reduces the side effects suffered by a patient. A variety of methods of doing so have evolved. One principal component in delimiting the radiation dose is the so-called “multi-leaf collimator” (MLC). This is a collimator which consists of a large number of elongate thin leaves arranged side to side in an array. Each leaf is moveable longitudinally so that its tip can be extended into or withdrawn from the radiation field. The array of leaf tips can thus be positioned so as to define a variable edge to the collimator. All the leaves can be withdrawn to open the radiation field, or all the leaves can be extended so as to close it down. Alternatively, some leaves can be withdrawn and some extended so as to define any desired shape, within operational limits. A multi-leaf collimator usually consists of two banks of such arrays, each bank projecting into the radiation field from opposite sides of the collimator. An example of an MLC is shown in EP-A-0,314,214. WO 2007/124248 shows an MLC with leaves having ridges along their upper and lower edges, to engage in corresponding formations in a leaf support structure. However, this document teaches that the leaves should be aligned relative to the radiation source, i.e. that the sides of the leaf are aligned with the local direction of the radiation. WO 2007/003925 also shows an MLC leaf having ridges along its upper and lower edges, to engage in corresponding formations in a leaf support structure, but is silent as to the orientation of the leaf relative to the beam. One factor in the design of a high-quality MLC is the leakage of radiation through the collimator. One likely area for leakage is between the leaves; there must obviously be some degree of separation between the leaves in order to allow them to slide easily relative to the adjacent leaf, and this small gap could allow for leakage. To alleviate this, MLC leaves and their supporting structures can be designed so that the leaves are held at a small acute angle to the beam direction. This means that from the point of view of the beam, the gap between adjacent leaves is closed. The present invention provides a multi-leaf collimator for collimating a beam of a radiotherapeutic apparatus, comprising a plurality of elongate narrow leaves arranged side-by side and supported in a frame, the frame having upper and lower formations for guiding each leaf into which extend ridges on the upper and lower edges of the leaves, thereby to allow the leaves to move in a longitudinal direction, the upper and lower formations being aligned so that the sides of the leaves when fitted are at a non-zero angle to the beam direction, the upper and lower ridges being located on the upper and lower edges of the leaves so that a line joining their centres is at a non-zero angle to the sides of the leaf, tilted relative to the sides in a sense opposite to that of the beam. The upper formations and/or the lower formations can comprise channels into which the ridges extend. Given that there will need to be a number of adjacent channels to accept a plurality of adjacent leaves, each channel can be defined between a pair of ridges. An outer face of the upper and/or lower ridges can be aligned with a side face of the leaf, for ease of manufacture. The present invention further comprises a radiotherapeutic apparatus comprising a source of radiation and a multi-leaf collimator for shaping the radiation emitted by the source, the multi-leaf collimator being as set out above. In this description the terms “up” and “down” refer to directions relative to the general disposition of the leaf or leaves of the multi-leaf collimator (MLC). Usually, the rest position for the radiation source of a typical oncology device is at the top of its rotational sweep, and therefore the conventional view of a radiotherapy head is with the beam travelling vertically downward. The leaves will thus be aligned in a generally vertical direction, with their long axis arranged horizontally. As the radiation head rotates around a patient, as is commonly done in order to irradiate the tumour from a variety of directions and thereby minimise the dose that is applied to healthy tissue, the absolute orientation of the leaves (etc) will of course change, relative to a fixed frame of reference such as the room in which the apparatus is located. However, regardless of the actual orientation of the MLC and its leaves, in this description “up” is intended to mean a direction towards the radiation source, and other directions should be interpreted accordingly. FIG. 1 shows an MLC according to the present invention. Two banks of leaves are provided, each facing the other, one on either side of the beam so as to delimit the beam from opposing sides. Thus, a first bank 10 comprises a frame 12 which supports an array of leaves 14, whilst a second bank 20 comprises a frame 22 which supports an array of leaves 24. Each leaf is oriented in a generally upright manner relative to the beam, with most leaves having a small deflection from perfect verticality as will be described shortly. The leaves 14, 24 are held in the frames 12, 22 by ridges running the length of the upper and lower edges of the leaves, which engage in corresponding channels in the frames so that the leaves can slide horizontally backwards (i.e. out of the beam) and forwards (i.e. into the beam). Each leaf is driven by a suitable motor or other drive means (not illustrated) in a generally known manner. FIG. 2 shows the frame 12 of the first bank, which supports the leaves 14. The other frame 22 is substantially identical to this frame, albeit a mirror image thereof. The frame 12 is shown in FIG. 2 from a point of view along the long axis of the leaves 14, with the leaves themselves absent. An aperture 16 is formed within the frame 12 to receive the leaves 14, and has a corrugated upper edge 18 in which a series of small channels 26 are defined between frame ridges 28. Each channel 26 receives a leaf ridge running along the upper edge of the leaf 14; the leaf ridges are narrower than the leaf itself so as to allow space for the frame ridges 28 which define each channel 26, whilst still maintaining a very small separation between each leaf 14. A corresponding array of frame ridges 30 that define channels 32 between them is provided on the bottom edge of the aperture 16. The ridges 28 on the upper edge of the aperture 16 are more closely spaced than the ridges 30 on the bottom edge, and the side faces 34, 36 of the aperture 16 angle outwardly downwards. This allows the leaves 14 to be held in a non-parallel state, with the vertical axes of the leaves converging upwards towards a single convergence point. As a result, the divergent radiation beam emanating from the beam source can be collimated by the leaves with a minimal penumbra. FIG. 3 shows a single leaf 14. This has an elongate upper edge 34 along which is provided a ridge 36. An elongate lower edge 38 has a corresponding ridge 40. A front edge 42 projects into the radiation beam and is gently curved so that the penumbra is minimised regardless of the translational position of the leaf. A rear edge 43 has an inset area 44 to accommodate the drive mechanism, which is by way of a rotatable threaded rod (not shown) which passes into an elongate aperture 46 running along a substantial portion of the length of the leaf, accessed via an internally threaded section 48 which engages with the threaded rod. Thus, as the threaded rod is rotated, it drives the threaded section 48 and hence the leaf 14. FIG. 4 illustrates the alignment of the leaves relative to the radiation source. A set of leaves 14a, 14b, 14c etc are shown, together with a plurality of rays 50a, 50b, 50c etc all of which emanate from the radiation source 51. In practice, of course, the radiation emitted by the source is continuous over the field of illumination, rather than being in the form of discrete narrow rays as illustrated for the purposes of clarity. FIG. 4 also shows a series of lines 15a, 15b, 15c etc which show the alignment of a side of each leaf 14a, 14b, 14c etc. These converge on a point 49 which is set so as to be at the same height as the radiation source 51, but offset slightly therefrom as shown by arrow A. The result is that the radiation beams strike the leaves 14 at a slight angle, thereby avoiding the creation of a thin gap between each leaf through which radiation could pass uninterrupted. FIG. 5 shows a subset of the leaves 14, side by side, together with an individual beam segment 50. As mentioned earlier, the beam 50 is not perfectly parallel to the vertical extent of the leaves 14, in order to minimise the leakage between leaves. However, FIG. 5 illustrates a worst case scenario in which the beam just impinges upon the upper edge of a first leaf 14a and the lower edge of a second leaf 14b, and otherwise passes through the gap between them to the maximum extent possible. It therefore passes for much of its path between the two leaves and hence demonstrates the beam path of minimum attenuation that is possible with this design of MLC. It should be noted that the gaps between the leaves, the thicknesses of the leaves, and the angle of the beam 50 are exaggerated in order to demonstrate the effect more clearly. It will be seen that in this example the beam 50 intersects with and is attenuated by both the upper ridge 36a of the leaf 14a and the lower ridge 40b of the leaf 14b. As a result, the attenuation of this worst-case beam 50 is maximised through careful location of the leaf ridges. Line 52 shows a hypothetical alternative beam 52, in which the relative tilt of the MLC to the beam direction is reversed, hence enabling the beam to miss the upper ridges 36 and the lower ridges 40 and thereby suffer slightly less attenuation. Accordingly, the leakage rate through such a hypothetical MLC would be greater than the leakage rate of the MLC here described. It can be seen from FIG. 5 that a beam just to the right of the illustrated beam 50 may just miss the lower ridge 40b. However, this beam will meet a greater length of the upper ridge 36a and the leaf 14a. Careful design of the dimensions of the leaves and the ridges can ensure that beams will always pass through either the whole of the upper ridge, or the whole of the lower ridge, or a combination of the two that adds up (in total) to the attenuation of one ridge, but never more or less than the equivalent attenuation of one ridge. This means that the leakage profile of the MLC as a whole is smoother (as well as lower) than the leakage profile of an MLC where beams can pass through the leaf without meeting either the upper or the lower ridge. Likewise, if the chosen inclination of the beam relative to the leaves is lesser, then by careful design of the depths and thicknesses of the upper and lower ridges 36 and 40 relative to the general dimensions of the leaves and the gaps therebetween, it is possible to ensure that the beam 50 will always go through either 36a or 40a (or both) but never none. These mean that the leakage profile of the MLC as a whole is smoother than if a beam could pass through the leaf without touching either 36a or 40a. Line 54 has been shown in FIG. 5, joining the centre of the upper ridge 36c of one leaf and the lower ridge 40c of that leaf. It will be seen that, since the upper ridges 36 are offset to one side and the lower ridges 40c are offset to the other side of the leaf 14c, the line 54 joining their centres is likewise offset relative to the vertical extent of the leaf 14c. It will be noted that, in FIG. 5, the angle of offset of α of the line 54 joining the centres of the upper ridges 36c and lower ridges 40c is in a direction opposite to the angle offset β between the local direction of the beam 50 and the vertical extent of the leaves 14. That reversal of the sense of the two angles means that the beam 50 suffers greater attenuation even in the worst-case example illustrated. Where the sense of the offset is the same as, for example, between line 54 and line 52, attenuation is less in this worst-case instance. Accordingly, the overall performance of the MLC in terms of the contrast between areas where the beam is being permitted to pass and areas where it should be blocked, is greater. FIG. 5 illustrates our preferred arrangement. The upper ridges 36 and the lower ridges 40 are fully offset to one side of the leaf, i.e. the sides 56 of the ridges are smooth with the sides 58 of the leaf, with no ridge or undulation present. This maximises the attenuation of a worst-case beam 50. FIG. 5a illustrates this. However, it is still possible to design leaves that take advantage of this principle and have some advantage over existing leaves, albeit not as great an advantage as the arrangement shown in FIG. 4. FIG. 6 illustrates such a set of leaves 14′. The upper ridge 36′ has an edge that is smooth with the relevant side of the leaf 14′, but the lower ridge 40′ is centrally placed relative to the leaf. The line 54′ joining the centres of these ridges 36′ and 40′ is again tilted, although the angle of that tilt relative to the leaves 14 is less than the angle ═ in FIG. 4. Nevertheless, some greater attenuation will be offered by such leaves 14′. FIG. 7 shows a further alternative version of the leaves 14″. In this case, both the upper ridges 36″ and the lower ridges 40″ are offset slightly from the sides of the leaf 14″ and there will be a small step 60, 62 between them. However, a line 54″ joining the centres of the upper ridges 36″ and the lower ridges 40″ is still inclined slightly although again the angle of inclination is less than α. It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. |
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046769455 | abstract | In accordance with the present invention, use is made of the adjacent vertically arranged fuel bundles which surround the empty core position to be filled with the fuel bundle to be inserted. Such use of the adjacent bundles involves the placement upon the top tie plate of each bundle of a separate and individual centering device, each centering device being of a generally box-like cap configuration and engaging the upper tie plate of each fuel bundle. Preferably, each such centering device includes a pair of tapered dowel pins which engage apertures formed in the upper surface of the fuel assembly tie plate so that lateral forces imposed upon the centering device will be transmitted to the upper end of the fuel bundle assembly that may be bowed into the empty core position. Each centering device also preferably includes an elongated handling pole uniquely connected to the top wall of the centering device so that each centering device may be lowered individually onto the upper tie plate of its respective associated fuel bundle. This elongated handling pole engages the top wall of the centering device through a novel ball and socket arrangement which permits the handling of the pole to swing well clear of the fuel insertion operating area after the centering device has been placed on its respective fuel bundle. The unique ball and socket arrangement also allows the centering device to self-align itself on the handling pole when the handling pole is lifted vertically or, alternatively, being lowered down on top of the fuel bundle during installation thereon. |
claims | 1. Method for controlling an exterior aspect of fuel rods (2) for nuclear reactors, each of the fuel rods (2) having an end cap with a truncated surface, comprising the following steps:providing optical means (40) comprising a plurality of primary cameras (42) and a plurality of secondary cameras (42′);inclining said secondary cameras with respect to said primary cameras in order to be able to scan the truncated surface (68) of the end cap (6) of each of the fuel rods (2) to be controlled;providing an electronic and computer assembly (30);linking the plurality of primary cameras (42) and the plurality of secondary cameras (42′) to the electronic and computer assembly (30);acquiring an image of the fuel rods (2) with at least one of the plurality of primary cameras (42) and the plurality of secondary cameras (42′);delivering the image of the fuel rods (2) to the electronic and computer assembly (30);processing the image using the electronic and computer assembly (30);automatically detecting geometric defects present on each rod (2) to be controlled, with the electronic and computer assembly (30);providing a roughness tester (50);automatically controlling the roughness tester (50); andautomatically measuring a depth of each geometric defect detected during the detecting geometric defects steps, with the aid of the roughness tester (50). 2. Method for controlling the exterior aspect according to claim 1, wherein for each rod (2), the geometric defect detection step comprises a scanning operation of the exterior surface (2a) of said rod (2) with the aid of the optical means (40), the scanning operation being carried out by means of a plurality of displacements of the optical means (40) along the whole rod (2) concerned, each displacement being carried out for a given angular position of said rod (2). 3. Method for controlling the exterior aspect according to claim 2, wherein during the scanning operation of the exterior surface (2a) of a rod (2), the optical means (40) deliver a plurality of images to the electronic and computer assembly (30), each image delivered from the rod (2) being associated with an address indicating an angular position of said rod (2) and a position of a trolley (28) on which are mounted the optical means (40), in relation to a displacement stand (8). 4. Method for controlling the exterior aspect according to claim 3, wherein when at least one geometric defect has been detected on a rod (2) by the electronic and computer assembly (30), a displacement of the roughness tester (50) is carried out, thanks to addresses associated with the images delivered by the optical means (40), in such a way that it can measure the depth of each geometric defect detected. 5. Method for controlling the exterior aspect according to claim 1, wherein the measurement of the depth of each geometric defect detected is carried out by bringing closer the roughness tester (50) to the rod (2) concerned. 6. Method for controlling the exterior aspect according to claim 2, wherein said primary (42) and secondary (42′) cameras being cameras with a charge coupled device, and each simultaneously scanning at least two adjacent fuel rods (2). 7. Method for controlling the exterior aspect according to claim 1, further comprising an operation of detecting cleanliness defects present on each fuel rod (2) to be controlled, the operation being capable of being carried out by means of diode detectors (56) and lighting ramps (54). 8. Method for controlling the exterior aspect according to claim 1, comprising a step of delivering, for each rod (2) controlled, a result file of the control carried out. |
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039869776 | description | While only elementary apparatus for use in carrying out the methods of the present invention are shown in the drawing, it will be apparent to those having ordinary skill in the art that other apparatus could be provided without the exercise of invention whereby the methods of the invention could be carried out semi-automatically or fully automatically, and it is to be understood that such alternative apparatus falls within the ambit of the present invention as defined in the claims appended hereto. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings in detail, it is to be understood that the resistance curve 10 of FIG. 1 is derived from an ohmmeter 12 (FIG. 2), ohmmeter 12 being connected by means of two electrical leads 14, 16 to respective ones of a pair of electrical contacts 18, 20 which are partially submerged in a mass 22 of admixed radioactive waste material and the setting agent of said Gablin and Hansen application contained in a receiving container 24 which is itself surrounded by shield 26. Receiving containers and shields of this general kind are shown in and described in connection with FIGS. 12 and 13 of said Gablin and Hansen application, a liquid level sensor of the kind shown in FIG. 2 of the present application, and there designated by the reference numeral 28, being identified in FIG. 12 of said Gablin and Hansen application by the reference numeral 103. Going to FIG. 2, it will be seen that liquid level sensor 28 comprises a hollow cylindrical member 30 received in a second hollow cylindrical member 32. Hollow cylindrical member 30, hereinafter called the electrode support, is affixed within a close-fitting bore 34 in hollow cylindrical member 32, hollow cylindrical member 32 being hereinafter called the plug. As shown in FIG. 2, plug 32 is adapted to loosely fit in bore 36 which passes through shell 28, and thus to rest upon the top surface of container 24 immediately surrounding a hole 38 in the top surface of receiving container 24, hole 38 being of such diameter as to loosely fit electrode support 30. If desired or required by regulation or regulatory authorities plug 32 may be provided with threads on its outer surface adapted to interengage with threads provided in the wall of bore 36, whereby liquid level sensor 28 may be removably fixed in shield 26. As also shown in FIG. 2, the bore 40 of electrode support 30 extends completely from end to end of electrode support 30 and thus mass 22 is not impeded from rising within bore 40 as the admixed radioactive waste material and setting agent are pumped into receiving container 24. Diametrically directed holes 42, 44 are provided in the lower end of electrode support 30 for receiving the shanks of electrical contacts 18 and 20, which may be cotter keys of the well known type commonly used in mechanical applications. As shown in FIG. 2, the heads 46 and 48 of electrical contacts 18 and 20 are located inside bore 40, while the legs of electrical contacts 18 and 20 are passed through holes 42 and 44, respectively, and then headed over on the outside surface of electrode support 30, whereby heads 46 and 48 are maintained at a fixed distance from each other by electrode support 30. Connection from electrical contacts 18 and 20 to the exterior of the receiving tank is provided by means of insulated leads 50 and 52, which are themselves directly connected to heads 46 and 48, respectively, and connected at their upper ends directly to a pair of terminals 54 and 56, insulated leads 50 and 52 passing through bore 40 of electrode support 30 closely adjacent the wall of bore 40, all as shown in FIG. 2. As also shown in FIG. 2, electrical leads 14 and 16 are supplied with connectors 58 and 60, respectively, whereby electrical connection is made between electrical lead 14 and terminal 54 and between electrical lead 16 and terminal 56, and thereby the resistance measuring terminals of ohmmeter 12 are connected directly to the heads 46 and 48 of electrical contacts 18 and 20, respectively. Typically, receiving container 24 may be of cylindrical configuration, about 48 inches deep and 48 inches (horizontal) in diameter. Further details of such receiving container are given in said Gablin and Hansen application. Electrode support 30 may be fabricated, for instance, from polyvinyl chloride pipe having an outer diameter of about 23/4 inches, and being of such length that contact heads 46 and 48 are located approximately 3 inches below the lower surface of the top of receiving container 24. In some embodiments it may be desired to provide an additional pair of electrical contacts about 2 inches above electrical contacts 18 and 20, as shown in FIG. 2; these additional electrical contacts being provided with separate leads, and being used in connection with an electrical safety system which automatically initiates certain plant safety measures in the event that the filling of container 24 with liquid mass 22 proceeds so far that the upper surface of mass 22 reaches these upper contacts. It is to be understood, however, that in normal operation electrical contacts 18 and 20 only are used, the filling of container 24 with mass 22 being terminated either manually or automatically when the top surface of mass 22 reaches and first comes into contact with electrical contacts 18 and 20, thereby very substantially reducing the resistance measured between heads 46 and 48 by ohmmeter 12, or by automatic resistance sensing means of the kind employed in the radioactive waste material packaging system shown and described in said Gablin and Hansen application. Going to FIG. 1, an example of the carrying out of the method of the present invention will now be described. The vertical axis of the idealized resistance variation plot of FIG. 1 may be thought of as being graduated in magnitude values of resistance in ohms, as measured across the gap between heads 46 and 48 (FIG. 2) by ohmmeter 12 (FIG. 2). The horizontal axis of the idealized resistance change plot of FIG. 1 may be thought of as being graduated in terms of elapsed times, commencing at 0 when the filling of receiving container 24 (FIG. 2) with a mass of admixed radioactive waste material and its setting agent commences, and extending to and beyond C, C being the time when a quantity of hygroscopic surface hardening material is flowed over the surface of mass 22 (FIG. 2) in a relatively thin layer. During the interval OF, as shown in FIG. 1, the liquid or slurry of mass 22 is being pumped into receiving tank 24. At time F, as shown in FIG. 1, the upper surface of mass 24 reaches and comes into contact with electrical contacts 18 and 20, whereupon the resistance indicated by ohmmeter 12 drops from the infinity indication to a very low value, e.g., 200 ohms. In a typical example of the employment of the method of the present invention, mass 22 may consist of premeasured portions of a highly concentrated solution of boric acid and other radioactively contaminated waste material representing the dregs drained from the evaporators utilized to purify the water used in a reactor (see page 13 of said Gablin and Hansen application) and the setting agent of said Gablin and Hansen application, which is made and sold by the assignee of the present application and said Gablin and Hansen application under the trademark TigerLock (see page 5 of said Gablin and Hansen application). Returning to FIG. 1, the interval FG, the duration of which is shown only schematically and not to scale, is the time during which a curing agent (see page 5 of said Gablin and Hansen application), heat, or both of them, is added or applied to mass 22. At about time G (FIG. 1) jelling or solidification of mass 22 begins. It is at this time (immediately to the right of G in FIG. 1) that it is desirable to remove the drive shaft of the mass agitator if one is used (see agitator 181 in FIG. 13 of said Gablin and Hansen application). Thus, it will be seen that one advantage of the present method lies in the fact that the operator of the apparatus of said Gablin and Hansen application is warned by an initial rise in the resistance indicated on ohmmeter 12 to remove the drive shaft of the agitator used to agitate mass 22 if one is employed. It will, of course, be evident to those having ordinary skill in the art that suitable alarm means such as manually positionable photoelectric means actuated by the upward travel of the indicator of ohmmeter 12 may be provided to actuate alarm means for alerting the operator to remove the agitator drive shaft. Returning to FIG. 1, it will be seen that the resistance indicated by ohmmeter 12 rises over the interval GS to a knee or maximum point at time S. It has been observed that when solidifying a mass 22 of the materials of this example, viz., radioactive boric acid waste and TigerLock setting agent, the knee or peak at time S corresponds to a resistance value as measured by ohmmeter 12 of approximately 20,000 ohms. It has also been observed in the reduction to practice of this invention that after reaching the knee or peak at S the resistance measured across contact heads 46 and 48 declines from the knee or peak value as surface water develops on the top of the solidified mass, this decline of the resistivity value being indicated by the segment SC of the resistivity plot of FIG. 1. It will now be understood that by making use of the method of the present invention the operator of the apparatus of said Gablin and Hansen application is able to very accurately determine the time when full solidification of the mass 22 has occurred even though due to protective shielding the operator cannot visually observe the surface of mass 22 or stir or manipulate mass 22. This accurate indication of the time of substantially full solidification is also very advantageous in carrying out the additional step of providing mass 22 with a water absorbing overlayer, which step is a characteristic feature of the novel and inventive process carried out by the apparatus made and sold by the assignee of the present application and said Gablin and Hansen application, this step being known as the "PPI coat process". In accordance with the PPI coat process, a body of TigerLock setting agent is flowed onto the top surface of mass 22, followed by a suitable quantity of its curing agent, producing a hard upper surface which absorbs the surface water occluded from mass 22. The flowing of TigerLock setting agent and curing agent onto the upper surface of mass 22 is indicated in idealized fashion as occurring at time C in FIG. 1. As also shown in FIG. 1, by the rise of the resistance plot occurring immediately to the right of time C, the absorption of surface water by the superposed body of TigerLock setting agent results in the resistance measured across contact heads 46 and 48 rising to a relatively high value. Thus it will be seen that by employing the method of the present invention the operator of apparatus of the type shown and described in said Gablin and Hansen application is provided with a positive indication that the PPI coat process has been carried out to a satisfactory conclusion and that the process of producing a solidified mass of admixed radioactive boric acid and TigerLock setting agent is complete. It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in carrying out the above method without departing from the scope of the invention it is intended that all matter contained in the above description shall be interpreted as illustrative only and not in a limiting sense. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which as a matter of language might be said to fall therebetween. |
description | This patent application is a continuation application of U.S. application Ser. No. 12/919,912, filed Oct. 29, 2010 (to issue as U.S. Pat. No. 9,607,720, which claims priority to PCT International Application No. PCT/US09/35600, filed Feb. 27, 2009, which claims the benefit of U.S. Provisional Patent Application No. 61/031,899, filed Feb. 27, 2008, 61/031,908, filed Feb. 27, 2008, 61/031,912, filed Feb. 27, 2008, 61/031,916 filed Feb. 27, 2008, and 61/031,921, filed Feb. 27, 2008, the contents of which are incorporated herein by reference in their entireties, including any references therein. Radioactive nuclear sources are currently used in industry in a variety of places, including on-line elemental analysis of mining, coal, and cement feedstocks, and sub-surface scanning (e.g. soil composition analysis and landmine detection). The traditional neutron source has been a radioisotope such as 252Cf or Am—Be. Radioisotopes are always on, require shielding, limit types of analysis (e.g. no pulsing or time-of-flight), and pose a personnel hazard during manufacturing and assembly, as well as a security hazard due to threats of so-called “dirty bombs”. Neutrons can also be generated with conventional accelerator technology but these systems have large size and power consumption requirements. Having a compact and efficient fusion neutron generator (FNG) would directly benefit many industries by solving the problems associated with radioactive isotopes while avoiding the complications of large accelerators. The basic layout of a modern compact accelerator neutron source is shown in FIG. 1. The standard hardware consists of: a high-voltage generator 1 (˜100 kV), a metal hydride target material 2 (usually titanium), one or more accelerator grids 3, an ion source assembly 4 (Penning or RF) and a gas-control reservoir 5 that often uses a hydrogen getter. Operation proceeds as follows: either pure deuterium (D-D system) or a deuterium-tritium (D-T system) mix of gas (up to 10 Ci of T) is introduced into the system at pressures around 10 mTorr; a plasma is generated to provide ions that are extracted out of the source region and accelerated to ˜100 keV; these ions bombard the target 2 where they can undergo fusion reactions with other hydrogen isotopes embedded in the target 2. DD fusion reactions generate 2.45 MeV neutrons and the DT reaction makes 14 MeV neutrons. Exemplary systems can be operated continuously or in pulsed operation for time-of-flight measurements. There are several major suppliers of non-radioactive neutron generators, all using accelerator-target configurations. List prices range between $85-350 K with the highest cost components being the high-voltage power supply, electrical feeds, and interconnects. Lifetime is typically limited by the degradation of the target material and the coating of insulators with best suppliers reporting ˜1000 hours for nominal output levels of 1×1.06 DD n/s and 1×108 DT n/s, and replacement target units range from $5-50 K each. Currently, no suppliers have cost-effective high output (>1E8 n/s) DD systems. Neutron generators for industrial radioisotope replacement often use the DD fusion reaction because the 2.45-MeV DD neutrons are more easily applied to existing applications that use Cf252, which has an average neutron energy of 2.1 MeV. On the basis of fusion cross section and reaction branching alone, a DT generator has a neutron production rate ˜100 times that of a DD generator, however, the shielding and moderation requirements for 14.1-MeV DT-generated neutrons compared to 2.45-MeV neutrons are much more severe, making DD more attractive for many market applications. Aspects of the invention include a highly-innovative approach for a compact, high-efficiency, long-life fusion neutron generator (FNG) for applications such as enhanced neutron radiography, non-destructive testing, bulk material scanning using the testing process known as Prompt Gamma Neutron Activation Analysis (PGNAA), other NAA methods, and other analytical methods utilizing neutrons. Radioisotopes, such as 252Cf, are currently used in the academic and industrial markets, but are under increasing scrutiny due to homeland security concerns. Several FNG technologies are available in the marketplace, but are hampered by high cost, large size, low efficiency, and short lifetime, typically making them unsuitable for broad use. As summarized in FIG. 2, an innovation for the device as a whole results from the combination of a regenerable low-Z (low atomic number) target for long life and high efficiency with an RF ion source that allows compact and easy thermal management with long life. These factors combine to increase yield and decrease cost. Improved efficiency and better thermal properties allow the source size to be decreased, allowing its use in applications that require small sources, such as small-diameter boreholes (<2 inches). Such a compact and inexpensive source could also be used in laboratory and academic settings for geoscience and other non-destructive testing applications, such as online bulk materials analysis (such as for coal and cement mining), soil analysis, borehole logging analysis, and security screening systems, and others. These innovations would allow for radioactive neutron sources in industry to be replaced with FNGs in a wide variety of applications, improving safety and broadening the types of analysis that can be accomplished. Additionally, innovative designs have been made to combine the necessary components and subsystems of an FNG in highly efficient and cost-effective ways. Traditional ion sources such as a Penning ion source use active filaments or multiple plasma-contacting electrodes to create ionizations. These components eventually wear out, causing a system failure and limiting lifetime. Aspects of the present invention include a radio frequency (RF) or microwave ion source which uses no electrodes and has the advantage of generating high fractions of monatomic ions. An RF ion source uses a coiled, or shaped ribbon, antenna on the outside of the system wall/insulator that deposits electromagnetic power into the gas, causing ionizations, dissociations and plasma sustainment. While current FNGs bias their target to a large negative voltage to create the acceleration field, aspects of the invention use another inherent advantage of the RF ion source and raise the voltage of the plasma while maintaining the RF hardware and the target at or near ground potential. This is possible because the RF couples its energy through electromagnetic fields instead of physical electrodes in contact with the plasma. Using a grounded target resolves several design concerns, such as thermal control of the target and target diagnostics. This has the additional benefit of allowing the neutron source—the target—to be closer to the materials being analyzed due to lack of the necessary high-voltage standoff hardware, resulting in higher neutron fluxes at the material of interest for the same source output. The RF or microwave ion source also allows for relatively easy multi-source configurations where multiple ion beams can be extracted from a common plasma region to produce a multi-point neutron source. In addition to continuous operation, several options exist for pulsed operation. One option is to pulse an extraction electrode. This has the benefit of requiring relatively low voltage pulses, but would still require a high-voltage pulse forming network. Another option is to use a pulse transformer to directly pulse the high-voltage power. A simple schematic of a transformer-based pulsing system is shown in FIG. 7. This exemplary method has the advantage of allowing low-voltage pulse forming network elements and a low-voltage (lower cost) DC power supply. The use of beam-bunching electrodes can further shorten pulses of a system down to the nanosecond range. The choice of pulsing technique depends on the cost, size and the needs of the end-user. All of these techniques are capable of achieving pulse lengths in the range of 0.1-10,000 μs with a corresponding broad range of repetition rates, depending on the duty factor of the pulse system. Further exemplary systems described herein can be integrated with associated particle imaging (API) techniques. FIG. 3 shows the layout for the “neutron tube” core of a generic embodiment of the invention. A vacuum vessel 10 forms the main structure. Inside are the three primary electrodes: the ion source (anode) 11, neutron-producing target (cathode) 12, and electron suppressor electrode 13. The ion source power supply 14 creates AC, DC, or radio frequency/microwave power depending on the type of ion source 11 used. A non-evaporable getter 15 is used to control gas pressure via heating. In one possible embodiment shown in FIG. 4, the vacuum vessel 10 is a sealed tube made of a combination of conductor and insulator. If one end of the neutron tube is at low voltage, it can easily be made of conductive material facilitating fabrication and installation of electrical feedthroughs. Conductors used include primarily aluminum, stainless steel, copper, and kovar. Stainless steel and iron are minimized to reduce gamma signature in NAA applications. Glass, quartz, or alumina (or similar ceramic) can be used for insulated, high voltage areas. The outer diameter for this style of vacuum vessel 10 can range from 0.25″ to 12″. As seen in FIG. 4, attached to the vacuum vessel 10, auxiliary to the neutron tube, can be a diagnostic pressure gauge 30, for example an ionization gauge. Electrical feedthroughs 31, 32, 33, 34, 35 allow voltages to be applied to or read from to the ion source 37, suppressor 13, target 12, diagnostic thermocouple 37 and getter 15, and also control other diagnostics and internal systems. To evacuate the vessel, a pump-out port 16 is included made of copper pinch-off tube, glass tube, or a mechanical valve 38. To fit these features within space constraints, vacuum-compatible tubing 39 may be used. Pump-out port 15 can be attached to metal or insulator sections of the vessel. In the case of systems assembled completely in a vacuum environment, a pump-out port may not be needed. The body of the vacuum vessel 10 is comprised of pre-made glass to metal or ceramic to metal seals that can be brazed or welded together using standard metalworking or glass working techniques, and/or have two sections affixed to each other with vacuum flanges 40 for easy assembly/disassembly, typically ranging in diameter from 1-⅓″ to 12″. During assembly the vessel 10 is pre-loaded with an appropriate amount of deuterium and/or tritium gas. For systems in output and lifetime configurations where helium buildup is a concern from the plurality of neutron-producing reactions, an ion pump style of device can also be attached to the vessel to pump away helium and other contaminants after the getter 15 has temporarily pumped away the working gas. The ion source 36 is the anode 11 of the system that produces a plurality of ions that are accelerated into the target 12. The ion beam 43 is extracted from the ion source 36, goes through an opening in suppressor 13, and finally impinges on the target 12. The amount of extracted current should be from 10 nA/cm2 to 1 kA/cm2. At the front of the ion source 36 is an extraction plane 41 with an open diameter typically between 1 mm and 80% of the ion source 36 diameter combined with electrode shapes 42 that customize the focusing of the extracted ion beam 43 to cover most or all of target 12. The extraction plane 41 may or may not contain a gridded extraction screen with a high percentage open area and grid spacing typically between 20 in-1 and 150 in-1, dependent on plasma properties. The system may or may not have an extraction bias electrode (not shown) positioned between the ion source 36 and the suppression electrode 13 to aid in extracting ion current. The ion beam 43 is shaped such that the energy density impinging on the target 12 is substantially uniform. This is beneficial for power/heat handling, neutron production efficiency, and target 12 lifetime. The type of ion source 36 used can be, but is not limited to, radio frequency (RF) using an RF antenna 44 and matching network system 45, electron-cyclotron resonance (ECR) using microwave generator 70 to make microwave energy 71, Penning (cold cathode) 4, field ionization, or spark gap. The anode 11 region in vacuum may range from 1″ to 12″ long, filling either partially or completely the diameter of the vacuum vessel 10 containing it. In the case of the RF ion source, the ion source 36 is comprised of a glass container 46 (to increase monatomic species fraction relative to quartz or alumina) inside of vacuum vessel 10 (to reduce the amount of sputtering, contamination, and ion-electron recombination compared to a steel or alumina container), RF antenna 44 (wrapped cylindrically around vacuum vessel 10 with 0.5 to 10 turns), magnets 47 (to make a strong, substantially uniform axial magnetic field of strength 10 Gauss to 10000 Gauss inside ion source 36 to minimize power losses from plasma-wall interactions), and RF matching network 45. Glass container 46 may be integral to vacuum vessel 10 (for example, see vacuum vessel 72). RF power input to the ion source 36 can range from 0.1 W to 10,000 W. The RF frequency can be in the range of 0.1 MHz to 1 GHz. Matching network 45 contains capacitors and/or inductors that can be of fixed and/or adjustable values, arranged in an “L” or “pi” configuration. The components can have the values fixed at the factory or be adjustable during operation with a stepper motor or similar system. To further fine-tune matching conditions in an assembled system, the frequency at which the RF generator 14 operates can be adjusted in sufficiently small increments. The components are chosen, arranged, tuned, and fixed in place in a relative arrangement similar to what is shown in FIG. 4 to excite one or more modes to form and maximize plasma density and amount of extractable current, maximize monatomic species fraction in the ion beam 43, and optimize usage of RF power. The use of an ECR ion source (see FIG. 6) can accomplish these objectives even more effectively. Typical values of frequency can range from 200 MHz to 20 GHz. Microwave energy can be applied to ion source with an external applicator including, but not limited to, a waveguide, dielectric window, or antenna launching structure. The magnetic field is shaped to create a zone of electron cyclotron resonance. The ion source 11 can be raised to a positive voltage or run at ground potential. The configuration is chosen to be appropriate for the requirements of pulsing, power level, size, and lifetime. For the embodiment in FIG. 4, the target 12 is near ground potential while the ion source 36 is raised to a high positive DC voltage. The electron suppressor electrode 13 works with the ion source extraction optics 41, 42 to shape the ion beam 43. It should be biased negative with respect to the target (cathode) electrode 12 by an amount ranging from 0 V to 10,000 V. It can be biased with a separate power supply 21, or be biased using a resistor or zener diode system attached to the target 12. It is sized and shaped such that field emission from the high voltage gradients is avoided. The outer diameter of the suppressor 13 should substantially fill the inner diameter of vacuum vessel 10; the opening at the center should be large enough to allow the ion beam 43 to pass through unobstructed, while not being so large so as to require a prohibitively large voltage difference between it and the target 12 to effectively suppress secondary electrons emitted from the target due to impinging ions. The one or more electrodes are arranged to shape an electric potential to cause a substantial fraction of ions from the ion source to collide with the target, to reduce electron losses to an anode electrode. The solid target (cathode) electrode 12 consists of a cooled metal substrate via coolant connections 33 (also used as an electric feed if a bias voltage is applied), usually stainless steel, nickel, copper or molybdenum, that is coated with a layer of hydrogen-absorbing material, such as lithium, titanium, or others to achieve useful neutron-producing reactions. Low-Z materials are often preferable to increase efficiency. A target material may have at least one of the following properties: the average or effective atomic number of the target material is between 1 and 21; the target material can be regenerated in situ; the target material can be deposited in situ; the target material has the capability of causing secondary neutron-producing reactions with cross sections greater than 1 microbarn. The target may include hydrogen isotopes, lithium, lithium isotopes, lithium compounds including LiD, LiAlD4, and LiBD4, lithium alloys, and any mixture or combinations thereof. The target 12 can be maintained at ground potential or biased negative with an external power supply 17. Furthermore, the bias voltage between the suppressor and the target can be maintained by either connecting the suppressor to a negative voltage, or grounding it, and connecting the target to the suppressor through a zener diode, resistor, or other voltage regulation device. The size of the target 12 can be chosen appropriately for the application, power load, and lifetime needed. A substantially flat, circular shape is preferred, but other shapes, such as slanted, conical, or cylindrical, can be used to control sputtered material amounts and locations (both of source and destination) and to provide for unique neutron source emission areas/volumes. A circular target 12 for this style of device can range from 0.1″ to 12″ in diameter. A neutron tube 10 with two or more targets on either side of an ion source can be made so that two or more sources of neutrons are located inside of one device. Use of intentional sputtering and evaporation inside the vacuum vessel 10, 72 can have many benefits for system lifetime and efficiency. An attached thermocouple 37 or other means of measuring temperature can be used as a diagnostic while in operation. The cooling system 18 of the target 12 can be electrically isolated from the vacuum vessel 10, 72 in order to measure beam 43 current landing on the target 12 and for other diagnostic purposes. Active liquid cooling through channels 33 embedded in the target can be used for high power applications with either ambiently or actively cooled fluids. It is also possible to use a heat sink, exhausting to the surroundings. The location of the target can be anywhere beyond the suppressor electrode 13 in the path of the ion beam 43, viz. near the extreme end of the system to increase neutron flux on adjacent materials under test. The surface material of the target 12 can be deposited and/or refreshed in situ 3. Target 12 lifetime can be extended through use of regeneration. The target 12 material can also be chosen carefully to dictate the neutron output energy spectrum while still using deuterium and/or tritium as the working fuel. This includes making the system a source of fast (>2.5 MeV) neutrons without using radioactive tritium gas. The gas reservoir 15 can be a simple titanium filament or a non-evaporable getter pump for increased vacuum vessel 10, 72 vacuum quality. It can be located in a low-voltage area, such as behind the target 12, to the side of the target 12, or behind or in the ion source region 36. An external power supply 19 runs ac or dc current through the device through an electrical feedthrough 35 to heat and control the gas reservoir's 15 temperature, thus controlling the pressure of the working gas in the vacuum vessel 10, 72. It is loaded with an appropriate amount of deuterium and or tritium gas to achieve operating pressures between 10−5 Torr and 10−2 Torr while maintaining enough of a reserve amount of gas to compensate for the effects of contamination and radioactive decay over time. High voltage power supplies 17, 20 are used to separate the ion source (anode) 11, 36 and target (cathode) 12 by fusion-relevant voltages, from 10 kV to greater than 500 kV. This can be accomplished with a positive voltage supply 20 connected to the anode 11, 36, a negative voltage supply 17 connected to the cathode 12, or both. The high voltages can be generated though a variety of means, such as with a traditional Cockcroft-Walton voltage multiplier 73, piezoelectric crystal transformer, or with pyroelectric crystal technology. The high voltage generation can be done in the generator system next to the neutron tube 10 or the high voltage can be transmitted to the neutron tube via an umbilical cable 48. To help stabilize the system and reduce the effects of accidental high-voltage arcing, over-currenting, or other problems, ballast resistance 49 may be used, which can range in value from 10 kΩ to 10 MΩ. The external enclosure 50 contains the neutron tube 10 and associated feedthroughs, electronics, and power supplies. It is constructed from a conducting structural material such as aluminum or stainless steel to provide a ground shield around the entire system for safety and to prevent RF noise from affecting other equipment. The grounded enclosure 50 is filled with an insulating fluid 51 for high voltage standoff and cooling, such as mineral oil, transformer oil, SF6 gas, or a fully fluorinated insulating fluid such as Fluorinert, which is sealed around the neutron tube 10 with seal 52. A control console may be included in the exemplary system that contains most or all of the needed support equipment in an enclosure or rack that protects the equipment and makes it accessible to the user for setting and monitoring operational parameters. The system controller should be housed here, which may be comprised of a personal computer, field-programmable gate array (FPGA), or other custom or standard circuitry. Analog and digital inputs and outputs allow the control system to communicate with the other pieces of equipment, viz. the ion source power supply (RF or microwave amplifier) 14, other power supplies as diagrammed in FIG. 3, gas reservoir 15, and any applicable coolant systems 18. Aspects of invention may include a plurality of diagnostic sensors selected from the group consisting of a particle detector, a current detector, a voltage detector, a resistivity monitor, a pressure gauge, a thermocouple, and a sputtering meter. In addition, for a grounded target, the electrode area can maximized for a given neutron tube diameter to improve longevity and tube life. The control station is connected to the neutron tube 10 via a bundle of coaxial cables, wires, and tubing. A preferred embodiment is detailed in FIG. 5. The vacuum envelope is a small diameter insulating tube 72 utilizing an RF-powered ion source 36 with magnet material 47. The ion source 36 is raised to high voltage with power supply 20 (depicted as a custom-built and sized Cockcroft-Walton voltage multiplier 73 located adjacent to the neutron tube 10 so that no high voltage umbilical cables 48 are required, and fed into vacuum vessel 72 with feedthrough 74 embedded in vacuum vessel 72 to bias beam-shaping electrodes (41, 42)) and the flat, circular target 12 is at ground potential. The suppressor 13 is biased via feedthrough 75 embedded in vacuum vessel 72. An advanced getter material 15 is loaded with D and/or T and uses a closed-loop control system 19 to maintain stable gas pressure in the vacuum vessel 72. The target 12, comprised of a thin layer of lithium to maximize efficiency 2 and customize the neutron energy spectrum 5, is located on a cooled substrate made of a material such as nickel or molybdenum and can be regenerated 4 with heat from the ion beam 43 and through an in-situ evaporation process 3 that does not require the neutron tube 72 to be opened. The target 12 is located near the extreme end of the system to place maximum neutron flux on the objects under test. For demanding applications where target thermal management is a necessity, such as borehole oil well logging, a grounded target 12 can be directly heatsinked to the external enclosure 50 to efficiently transport heat generated by the ion beam interaction with the target to the surrounding environment. The external enclosure 50 is made of aluminum to minimize NAA signals; similarly, use of carbon steel and stainless steel in general is minimized. The external enclosure 50 is filled and sealed with a fully fluorinated insulating and cooling fluid to avoid neutron moderation and absorption by hydrogen. FIG. 6 shows a preferred embodiment modified to use an ECR-type ion source 36 using microwave generator 70 to make microwave energy 71, exciting gas molecules to create ionizations. Basic layouts of components auxiliary to neutron tube (10, 72) can be readily adjusted for the device to fit within the size and shape constraints of a given application. Aspects of the invention include a neutron generator having an RF ion source. To achieve high atomic fractions in such neutron generators (e.g. >50%) inductively coupled plasma discharges are often used. Traditionally these require kilowatt-level power for hydrogen discharges due to the high mobility of hydrogen ions in the plasma. As a result intense heating and thermal cooling issues make compact devices difficult and expensive to engineer. For example, the prior art uses sapphire windows with specialized cooling structures to manage multi-kilowatt levels and molybdenum surfaces to sustain high thermal loads. Aspects of the invention include an approach to design the plasma source cavity to encourage dissociation of molecular hydrogen gas through plasma interaction while maintaining a high degree of atomic hydrogen trapping or confinement within the plasma region for subsequent ionization. This can be accomplished by using a low recombination rate surface materials exposed to the plasma and high geometric trapping design of the plasma source region. Additionally, surfaces can be treated to reduce their surface recombination properties by a variety of techniques including but not limited to, chemical etch, material deposition, baking, coating, and plasma treatment. In an embodiment, the plasma source region is crafted with low-recombination material surfaces and an exit aperture such that dissociated hydrogen atoms will bounce around within the plasma source volume with a high degree of confinement until ionization near the exit aperture for ion beam extraction. Optimization of this neutral atomic trapping can be done by shaping the ion source. Using a magnetic mirror configuration, RF energy can be efficiently transferred into the plasma near the exit aperture using the magnetic mirror effect. RF plasma pumping can drive electrons into a high magnetic field location and transfer axial energy into radial energy. Electrons with high radial energy ionize and dissociate hydrogen rapidly while low axial velocity increases local density in the high B field region and produce a high-quality ion beam. The RF antenna is located in the region of lower magnetic field such that electrons are accelerated into the higher B section with the RF or electromagnetic field. The applied RF frequency can be adjusted to maximize plasma power deposition into the high field region in relation to the electron bounce frequency between the RF antenna region and the high field region. The ion source exit aperture is located near this region to source high currents. Combined with low-recombination materials and geometric trapping, high atomic hydrogen ion fractions and beam currents can be obtained with low input power levels. For a 1-inch diameter tube, currents in excess of 1 mA have been obtained for power levels of less than 5 W with good atomic to molecular fractions. The design of the magnetic mirror, B field shape and plasma source volume and ion beam extraction aperture can be optimized for different neutron generator applications, e.g. small diameter for oil-well logging applications, high current for neutron radiography or cargo inspection applications, etc. Adjusting the source profile affects the beam profile projected onto the target. This is important for heating purposes and it is desired to have a uniform target loading. In one embodiment, the magnetic mirror is adjusted such that the ion source exit aperture magnetic field is close to that of the field in the RF source region to produce a highly-uniform beam at the target location. Another embodiment of invention may include one ion source that generates ions that are accelerated and collide with one or more target materials each at a different target location. A further embodiment may include a negative ion source. A state-of-the-art high-efficiency ion source using a helicon RF plasma produces 8.1 mA of ion current using 1.24 kW of RF power for an efficiency of 6.5 microamperes per Watt of RF power. An aspect of the invention produces at least 10 microamperes of ion current per Watt of RF power. By enhancing the neutral atomic species trapping in the ion source, 10 microamperes of atomic ion current per Watt of RF power can also be attained. All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. |
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046997601 | claims | 1. In a fuel assembly including a top nozzle, a plurality of longitudinally-extending guide thimbles having upper ends and means interconnecting said top nozzle and said upper ends of said guide thimbles, said interconnecting means comprising: (a) a plurality of structural joints each being composed of means rigidly interconnecting a selected one of said guide thimble upper ends to said top nozzle; and (b) at least one non-structural joint being composed of a hollow sleeve rigidly connected to said top nozzle and extending between said top nozzle and said upper end of one of said guide thimble being spaced below said top nozzle, said sleeve being disposed in a slip fit relationship to said guide thimble upper end, said sleeve having an upper portion of outside and inside diameter sizes substantially the same as that of said guide thimble upper end and a lower portion of an inside diameter size slightly larger than the outside diameter size of said guide thimble upper end for receiving said guide thimble upper end therein in a close fitting relationship. (a) a top nozzle; (b) a plurality of longitudinally-extending guide thimbles having upper ends; (c) a plurality of fuel rods; (d) a plurality of support grids axially spaced along and supported by said guide thimbles and in turn supporting said fuel rods in a spaced apart array, an uppermost one of said grids being spaced below said top nozzle; and (e) a plurality of joints interconnecting said top nozzle and said upper ends of said guide thimbles, all but at least one of said joints being structural joints providing rigid connections between all but at least one of said guide thimble upper ends and said top nozzle, said one joint being a non-structural joint; (f) said non-structural joint being composed of a member rigidly connected to said top nozzle and being disposed in a spaced nonattached relationship to, and above, said uppermost grid and in a slip fit relationship to said upper end of one of said guide thimbles being spaced below said top nozzle and above said uppermost grid. 2. The fuel assembly as recited in claim 1, wherein said upper portion of said sleeve is rigidly joined to said top nozzle and said lower portion of said sleeve slidably receives said guide thimble upper end portion therein in said close fitting relationship. 3. The fuel assembly as recited in claim 2, wherein said sleeve is bulge fitted in a passageway defined in said top nozzle. 4. In a fuel assembly, the combination comprising: 5. The fuel assembly as recited in claim 4 wherein the number of structural joints constitutes at least a substantial majority of said joints. 6. The fuel assembly as recited in claim 4, wherein the number of structural joints is at least three times the number of said non-structural joints. 7. The fuel assembly as recited in claim 4, wherein said member of said non-structural joint is a sleeve having an upper portion joined to said top nozzle and of a diameter size substantially the same as that of said guide thimble upper end and a lower portion of a diameter size slightly larger than that of said guide thimble upper end for slidably receiving said guide thimble upper end therein in a close fitting relationship and being disposed in spaced relationship to, and above, said uppermost grid. 8. The fuel assembly as recited in claim 7, wherein said sleeve is bulge fitted in a passageway defined in said top nozzle. |
048141364 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT This invention provides an process for producing liner material for zircaloy reactor fuel cladding similar to the lined cladding described in the aforementioned U.S. Pat. Nos. 4,372,817 and 4,200,492, except the liner material, rather than being pure or ultrapure zircoium, is, in the invention hereindescribed, produces a zirconium alloy. While so-called crystal bar material has been proposed for lining of fuel element cladding, such material is generally too expensive for commercial use, and so-called "sponge" zirconium has generally been used for such lined cladding. The sponge material is typically selected from the lower oxygen containing batches of normal zirconium production, and generally contains 500-600 ppm of oxygen. Such material is referred to as "sponge" or "selected sponge" as there is practically no purification of the metal after reduction (the distillation and vacuum melting are generally viewed as the separation of magnesium chloride by-product and excess magnesium left over from reduction, rather than as purification, although the double or triple vacuum melting also removes some small amount of manganese). Thus the purity the metal in the final product in such material is generally the same as the purity of the metal in the sponge configuration produced by reduction (the reduction product, although metallic, has a sponge-like appearance). Recently, so-called "EB" material has been used to line cladding (as noted in the aforementioned copending applications Ser. Nos. 871,182 and 871,183). This EB material has been significantly further purified by melting in an electron beam furnace at about 4-16 inches per hour, generally to reduce the iron content. Typically, the iron content of sponge is in the 500-800 ppm range, and EB melting in one or two passes at such speeds is utilized to lower the iron content to the 200-300 ppm range. In addition to crystal bar, sponge, and EB melted zirconium, it has also been proposed that zirconium alloyed with 0.5-1.5 percent tin be utilized for liner material. A zirconium alloy liner is also described in the aforementioned U.S. Pat. No. 4,675,153, which alloy contains about 0.2-0.6 weight percent tin, about 0.03-0.11 percent iron, and up to about 350 ppm oxygen. The process of this invention can be used to produce the improved alloy of that patent. In particular, typical sponge has an aluminum content of 40-50 ppm (the ASTM Spec B349-80, cited in that patent prescribes a 75 ppm maximum). The process of this invention will give aluminum of less than 5 ppm (our experimental runs produced zirconium containing less than 2 ppm of aluminum). In addition, this invention will reduce the chromium content from typically about 100 ppm (the aforementioned specification calls for 200 ppm chromium max) to less than 10 ppm chromium (typical measured numbers were about 5 ppm chromium). While chromium, unlike aluminum, is not generally considered detrimental in many alloys, reducing the chromium reduces lot-to-lot property variability due to second phase formation. The aluminum reduction reduces solid solution strengthening. Preferably, the reduced aluminum is combined with low oxygen content, as produced, for example, by the aforementioned copending application Ser. Nos. 871,182 and/or 017,301, such that the hardening produced by the alloying agents is at least partially compensated by the softening effect of the lesser oxygen and lesser aluminum. This can provide a material which is softer and more ductile than other zirconium alloys to substantially impede crack propagation. The so-called "pellet-cladding-interaction" has caused crack initiation on the inside surface of cladding, and while the zirconium lined cladding of the prior art greatly reduces such cracking, such a zirconium liner is susceptible to steam corrosion. The alloys of the process of this invention combine the resistance of crack propagation with resistance to steam corrosion. In particular, this process provides for very low metallic impurity content (especially aluminum), preferably combined with low oxygen content. In a preferred embodiment, zirconium tetrachloride is reduced to metallic zirconium utilizing low oxygen magnesium (e.g., magnesium treated by the process described in copending application Ser. No. 017,301) and, after distillation, the low oxygen sponge is prebaked to remove absorbed water (generally the process of the aforementioned copending application Ser. No. 871,182) and the material is electron beam melted and then double or triple vacuum arc melted (generally EB and vacuum arc melting as taught in copending application Ser. No. 871,183, except that an alloying charge is added to the vacuum arc melting electrode). The alloying charge added during vacuum arc melting contains 0.1-2.0 weight percent of alloying agent selected from tin or iron or a combination of the two, and may in addition, contain 0.02-1.0 weight percent of additional alloying element, the additional alloying element being selected from the group consisting of niobium, chromium, molybdenum, copper, and combinations thereof. Preferably the alloying elements are either tin and niobium or 0.1-0.6 tin and 0.03-0.30 iron. The ingot of vacuum arc melted zirconium alloy can then be fabricated into the liner of reactor fuel element cladding, providing an essentially aluminum-free (as used herein, the term "essentially aluminum-free" means having less than 5 ppm aluminum), and preferably less than 400 ppm oxygen, material. More preferably, the process is controlled to provide material containing less than 300 ppm oxygen. In addition, when iron is not used as an alloying agent, the material preferably contains less than 300 ppm iron (and most preferably less than 100 ppm iron). When chromium is not used as an alloying agent, the material also preferably contains less than 10 ppm chromium and most preferably less than about 5 ppm chromium. Other than iron and oxygen, the material preferably contains less than 100 ppm of impurities. Thus, it can be seen that the process of this invention produces an alloy liner (rather than a liner of unalloyed zirconium) having an extremely low metallic impurity level (especially aluminum and also preferably a low oxygen level) and provides a consistent and low corrosion liner. The invention is not to be construed as limited to the particular examples described herein as these are to be regarded as illustrative, rather than restrictive. The invention is intended to cover all processes which do not depart from the spirit and the scope of the invention. |
052689425 | claims | 1. In combination with a nuclear power generating facility including: a composite fuel pool including a reactor cavity and a spent fuel pool fluidly connectable to said reactor cavity, said composite fuel pool at least partially containing a primary fluid; a nuclear reactor vessel positioned in said reactor cavity; a residual heat removal system installed in said facility and fluidly connectable to said reactor vessel; and a spent fuel pool cooling system installed in said facility and fluidly connectable to said spent fuel pool; a primary heat exchange means for transferring heat from a primary fluid to a secondary cooling fluid, said primary heat exchange means being temporarily positioned in said facility and having a primary inlet and a primary outlet, and a secondary inlet and a secondary outlet, said secondary inlet being fluidly connectable to a secondary cooling fluid supply line and said secondary outlet being fluidly connectable to a secondary cooling fluid return line; a primary pump being temporarily positioned in said facility and having an inlet and an outlet; a primary pump suction line having an inlet end and an outlet end, said inlet end removably and fluidly connected to said composite fuel pool and said outlet end fluidly connected to said inlet of said primary pump; a primary pump discharge line having an inlet end and an outlet end, said inlet end fluidly connected to said outlet of said primary pump and said outlet end fluidly connected to said primary inlet of said primary heat exchange means; and a primary return line having an inlet end and an outlet end, said inlet end fluidly connected to said primary outlet of said primary heat exchange means and said outlet end removably and fluidly connected to said composite fuel pool. a secondary heat exchange means for cooling said secondary cooling fluid, said secondary heat exchange means having a secondary cooling fluid inlet and a secondary cooling fluid outlet, said secondary cooling fluid inlet being fluidly connected to a secondary cooling fluid return line, and said secondary cooling fluid outlet being fluidly connected to a secondary cooling fluid supply line; a secondary cooling fluid return line having an inlet end and an outlet end, said inlet end being fluidly connected to said secondary outlet of said primary heat exchange means, and said outlet end being fluidly connected to said secondary cooling fluid inlet of said secondary heat exchange means; and a secondary cooling fluid supply line having an inlet end and an outlet end, said inlet end being fluidly connected to said secondary cooling fluid outlet of said secondary heat exchange means, and said outlet end being fluidly connected to said secondary inlet of said primary heat exchange means. a composite fuel pool including a reactor cavity and a spent fuel pool fluidly connectable to said reactor cavity; a nuclear reactor vessel positioned in said reactor cavity, said nuclear reactor vessel containing a primary fluid at an operating level; a residual heat removal system installed in said facility and fluidly connectable to said reactor vessel; and a spent fuel cooling system installed in said facility and fluidly connectable to said spent fuel pool; temporarily and fluidly connecting a primary heat exchange system to said composite fuel pool, said primary heat exchange system being adapted to cool said primary fluid at a faster rate than said spent fuel pool cooling system; raising said primary fluid from said operating level to a refueling level, at least partially filling said composite fuel pool with said primary fluid; circulating said primary fluid in said primary heat exchange system in order to reach and maintain a desired temperature of said primary fluid; and removing said primary heat exchange system from said facility. 2. A temporary cooling system according to claim 1, further comprising a secondary heat exchange system, including: 3. A temporary cooling system according to claim 2, wherein said secondary heat exchange system further comprises a regulator means, connected to said secondary heat exchange system, for maintaining an operating pressure of said secondary cooling fluid higher than an operating pressure of said primary fluid. 4. A temporary cooling system according to claim 3, wherein said regulator means includes a backpressure valve, fluidly connected in said secondary cooling fluid return line between said primary heat exchange means and said secondary heat exchange means. 5. A temporary cooling system according to claim 1, wherein said primary heat exchange system further includes a particulate filter, fluidly connected in said temporary cooling system between said composite fuel pool and said primary heat exchange means. 6. A temporary cooling system according to claim 1, wherein said primary heat exchange system further includes a demineralization means for removing minerals from said primary fluid, fluidly connected in said temporary cooling system between said composite fuel pool and said primary heat exchange means. 7. A temporary cooling system according to claim 5, wherein said primary heat exchange system further includes a demineralization means for removing minerals from said primary fluid, fluidly connected in said temporary cooling system between said particulate filter and said primary heat exchange means. 8. A temporary cooling system according to claim 1, wherein said primary heat exchange system further comprises a regulator means, fluidly connected to said secondary cooling fluid outlet, for maintaining an operating pressure of said secondary cooling fluid higher than an operating pressure of said primary fluid. 9. A temporary cooling system according to claim 2, wherein said primary heat exchange system further includes a particulate filter, fluidly connected in said temporary cooling system between said composite fuel pool and said primary heat exchange means. 10. A temporary cooling system according to claim 3, wherein said primary heat exchange system further includes a particulate filter, fluidly connected in said temporary cooling system between said composite fuel pool and said primary heat exchange means. 11. A temporary cooling system according to claim 3, wherein said primary heat exchange system further includes a demineralization means for removing minerals from said primary fluid, fluidly connected in said temporary cooling system between said composite fuel pool and said primary heat exchange means. 12. A temporary cooling system according to claim 3, wherein said primary heat exchange system further includes a demineralization means for removing minerals from said primary fluid, fluidly connected in said temporary cooling system between said composite fuel pool and said primary heat exchange means. 13. A temporary cooling system according to claim 9, wherein said primary heat exchange system further includes a demineralization means for removing minerals from said primary fluid, fluidly connected in said temporary cooling system between said particulate filter and said primary heat exchange means. 14. A temporary cooling system according to claim 10, wherein said primary heat exchange system further includes a demineralization means for removing minerals from said primary fluid, fluidly connected in said temporary cooling system between said particulate filter and said primary heat exchange means. 15. A temporary cooling system according to claim 1, wherein said primary heat exchange means includes a plate-type heat exchanger. 16. A temporary cooling system according to claim 2, wherein said secondary heat exchange means includes a cooling tower. 17. In a nuclear power generating facility including: 18. A method for cooling according to claim 17, further comprising the step of filtering particulate matter from said primary fluid during said step of circulating said primary fluid. 19. A method for cooling according to claim 17, further comprising the step of demineralizing said primary fluid during said step of circulating said primary fluid. 20. A method for cooling according to claim 18, further comprising the step of demineralizing said primary fluid during said step of circulating said primary fluid. 21. A temporary cooling system according to claim 1, further comprising a flow distribution means, connected to a portion of said primary return line which is submersible in said composite fuel pool, for distributing return flow of said primary fluid into said composite fuel pool. 22. A temporary cooling system according to claim 21, wherein said flow distribution means comprises a plurality of flow distribution holes provided in said primary return line, positioned so as to evenly distribute flow of said primary fluid so as to minimize turbulence within said composite fuel pool. 23. A temporary cooling system according to claim 1, further comprising an antisiphon means, connected to a portion of said primary pump suction line which is submersible in said composite fuel pool, for preventing siphoning of said primary fluid out of said composite fuel pool when said primary fluid in said composite fuel pool falls below an undesirable level. 24. A temporary cooling system according to claim 23, wherein said anti-siphon means comprises at least one anti-siphon hole provided in said primary pump suction line, positioned at said undesirable level within said composite fuel pool. |
claims | 1. A method of testing a subsea electronics module (SEM) for an underwater well installation, comprising the steps of:providing test equipment configured for testing an SEM, the test equipment comprising a plurality of processors and a first Local Area Network (LAN) switch, such that the processors may communicate with the first LAN switch;providing an SEM for an underwater well installation, the SEM comprising a data acquisition means and a second LAN switch, such that the data acquisition means may communicate with the second switch;separately passing packages of test data from each of the processors of the test equipment, in parallel, to the data acquisition means of the SEM undergoing testing via the first and second LAN switches to thereby reduce testing time, performed separately from normal operations of the SEM in the underwater well installation; andmonitoring for a corresponding response of the SEM in response to the test data passed to the SEM, the monitoring performed by the test equipment to evaluate operation of the SEM. 2. A method according to claim 1, further comprising the step of:evaluating operation of the SEM for fault location performed by the test equipment responsive to the response of the SEM in response to the test data passed to the SEM. 3. A method according to claim 1, wherein the SEM response comprises response data sent from the SEM to the test equipment via the second and first LAN switches. 4. A method according to claim 1, wherein the first and second LAN switches comprise Ethernet switches. 5. A method according to claim 1, wherein the data acquisition means of the SEM comprises a plurality of Data Acquisition and Control (D&C) cards, and wherein the step of separately passing packages of test data from each of the processors of the test equipment, in parallel, to the data acquisition means of the SEM undergoing testing, includes:each of the, plurality of processors providing the test data in parallel to a separate one of the plurality of D&C cards. 6. A. method according to. claim 1, wherein the test conditions include vibration testing of the SEM. 7. A method according to claim 1, which is performed prior to deployment of the SEM at the well installation. 8. A testing system for a subsea electronics module (SEM) for use at a well installation, comprising:test equipment comprising a plurality of processors for outputting test data to an SEM at a well installation and a first Local Area Network (LAN) switch, configured such that each of the plurality of processors communicate with the first LAN switch, the test equipment further configured to separately communicate packages of the test data from each of the plurality of processors, in parallel, to a data acquisition means of the SEM via the first LAN switch of the test equipment and a second LAN switch of the SEM to thereby reduce testing time, and to receive a response to the test data from the SEM to thereby evaluate operation of the SEM; andthe SEM comprising the data acquisition means and the second LAN switch, the SEM configured such that the data acquisition means communicates with the second LAN switch to provide the test equipment a response to test data in response thereto to so that the test equipment evaluates operation of the SEM. 9. A method according to claim 1, wherein the SEM is an operationally deployed SEM, the method further comprising the step of:performing time-limited vibration testing when performing the steps of separately passing packages of test data from each of the processors of the test equipment, in parallel, to the data acquisition means of the SEM undergoing testing and monitoring for a corresponding response of the SEM in response to the test data passed to the SEM. 10. A method according to claim 9, wherein the data acquisition means comprises a plurality of D&C cards, and wherein the step of separately passing packages of test data from each of the processors of the test equipment, in parallel, to the data acquisition means of the SEM undergoing testing, includes:each of the plurality of processors providing the test data in parallel to a separate one of the plurality of D&C cards to thereby minimize testing time. 11. A method according to claim 7,wherein test conditions include vibration testing of the SEM; andwherein the vibration testing is time-limited vibration testing. 12. A testing system as defined in claim 8, wherein the test equipment is further configured to perform the following operations:monitoring for a corresponding response of the SEM in response to the test data passed to the SEM; andevaluating, operation of the SEM for fault location responsive to the response of the SEM in response to the test data passed to the SEM. 13. A testing system as defined in claim 8, wherein the data acquisition means of the SEM comprises a plurality of Data Acquisition and Control (D&C) cards, and wherein the operation of separately communicating packages of the test data from each of the plurality of processors, in parallel, to the data acquisition means of the SEM undergoing testing, includes:each of the plurality of processors providing the test data in parallel to a separate one of the plurality of D&C cards. 14. A method according to claim 1, wherein the data acquisition means of the SEM comprises a plurality of Data Acquisition and Control (D&C) cards. |
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048511552 | summary | BACKGROUND OF THE INVENTION This invention relates to an apparatus for treating radioactive materials by solidifying them, and more particularly to a solidification processing apparatus for solidifying radioactive waste materials in powdery, granular or indefinite forms in a treating vessel to form stable solidified bodies suitable for keeping, storing or disposing. Various kinds of radioactive waste materials produced in nuclear power installations such as nuclear power stations are usually stored in the respective installations. Various kinds of solidification processing methods have been proposed or actually used for reducing volume of the waste materials and ensuring their stability in consideration of saving storage spaces as well as safety, transportation and future disposal of the waste materials. There have been known solidification processing methods for the radioactive waste materials, such as solidifying them with cement or solidifying them by mixing with melted asphalt or plastic material or the like. As an improved method of the above methods, it has been recently proposed to melt radioactive waste materials so as to be solidified in glass or together with melted glass or to solidify radioactive waste materials by cement glass. In the method of solidifying radioactive waste materials with cement, asphalt or plastic material, however, it is necessary to knead the radioactive waste materials with the solidifying agent such as the cement, asphalt or plastic material after the waste materials have been crushed or pulverized. In the solidification method by the cement glass, moreover, it is necessary to make the radioactive waste materials into pellet forms or to knead the materials with the solidifying agent after crushing or pulverizing the materials. These operations are not preferable as handling operations for the radioactive waste materials, because for example crushers, kneading extruders or pellet forming machines are needed. In the method of solidifying the radioactive waste materials together with glass, the materials are once melted and solidified in glass, or the materials are mixed with melted glass and then solidified together with the glass. Therefore, melting installations required for melting the materials and the glass are very expensive in operation. Moreover, in the case of waste material apt to thermally decompose, an additional installation is needed for treating gases produced in the decomposition. SUMMARY OF THE INVENTION It is a principal object of the invention to provide a solidification processing apparatus for radioactive waste materials, which eliminates all the disadvantages of the prior art and which is able to simply solidify radioactive waste materials in a vessel such as a drum can without any pretreatment by pouring a solidifying agent into the materials and heating and curing the materials at low temperatures. In order to achieve the object the solidification processing apparatus for radioactive waste materials according to the invention comprises a tank for a solidifying agent for solidifying the radioactive waste materials, a waste material vessel connected to said tank for the radioactive waste materials, pouring control means for controlling pouring of said solidifying agent into said vessel, and a heating and curing chamber for heating said vessel by indirect heating means after pouring said solidifying agent onto said waste materials in said vessel to polymerize and set said solidifying agent, thereby solidifying said radioactive waste materials. With this arrangement, the solidifying agent superior in impregnation is poured into a vessel filled with radioactive waste materials, whose poured amount is controlled by the pouring control means. After completion of pouring the solidifying agent into the vessel, it is heated indirectly by indirect heating means in order to avoid deflagration if the solidifying agent is combustible. The solidifying agent is polymerized and set in a relatively short time by promoting the polymerization reaction of the agent to solidify the radioactive waste materials with stability. In a preferred embodiment, the pouring control means comprises valve means provided in a pipe connecting the tank and the vessel, and a vacuum deaerating unit connected to the vessel for promoting the pouring of the solidifying agent. With this arrangement, the pouring of the solidfying agent into the vessel is controlled by the valve means, while gases in the vessel are removed by the vacuum deaerating unit to bring the vessel into a negative pressure, thereby enabling the solidifying agent to be poured into the vessel with high efficiency. The pouring control means preferably comprises impregnation detecting means for controlling the valve means in response to signals from a sensor in the vessel. In this manner, the amount of the solidifying agent impregnated in the radioactive waste materials in the vessel is able to be detected. At a moment when a predetermined amount of the solidifying agent has been impregnated, the valve means is closed to stop the pouring of the solidifying agent. In another embodiment, the apparatus further comprises a recovery unit for recovering gases exhausted from the tank for the solidifying agent, the vacuum deaerating unit and the heating and curing chamber to recover vaporized solidifying agent in the gases, and a filter for purifying gases after recovering the vaporized solidifying agent. With the arrangement, the vaporized solidifying agent is adsorbed and condensed in the recovery unit for reuse, thereby reducing the running cost and preventing the contamination of environment due to exhausted agent. In a further embodiment, the indirect heating means comprises control means for controlling polymerization reaction by controlling heating temperature in response to detected temperatures of outer surfaces of the vessel and in the heating and curing chamber. The atmosphere for heating and curing is controlled in a substantially constant condition. Moreover, the condition of the polymerization reaction of the solidifying agent in the vessel is detected from the outside of the apparatus. The invention will be more fully understood by referring to the following detailed specification and claims taken in connection with the appended drawings. |
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claims | 1. Method of ventilating a device for electron beam irradiation of at least one side of a web, the device for electron beam irradiation being comprised of a first chamber and a second chamber, the second chamber extending inside the first chamber in separated relation to the first chamber, the first chamber comprising a web inlet opening and a web outlet opening, the second chamber comprising a web inlet opening, a web outlet opening, and an electron exit surface through which electrons are adapted to be emitted into the second chamber, the method comprising:passing the web through the second chamber,creating a flow of a gaseous fluid through both the first and second chambers in a direction opposite the direction of travel of the web by supplying said fluid into the web outlet opening of the first chamber, anddischarging the gaseous fluid in at least the second chamber through at least one discharge outlet. 2. Method of ventilating a device for electron beam irradiation of at least one side of a web, the device for electron beam irradiation being comprised of a first chamber and a second chamber, the second chamber extending inside the first chamber in separated relation to the first chamber, the first chamber composing a web inlet opening and a web outlet opening, the second chamber comprising a web inlet opening, a web outlet opening, and an electron exit surface through which electrons are adapted to be emitted into the second chamber, the method comprising:passing the web through the second chamber,providing fluid connection between the web outlet opening of the second chamber and the web outlet opening of the first chamber,preventing fluid connection between the first chamber and the web outlet opening of the first chamber,creating a flow of a gaseous fluid through both the first and second chambers in a direction opposite the direction of travel of the web by supplying said fluid into the first chamber and into the web outlet opening of the first chamber, anddischarging the gaseous fluid in at least the second chamber through at least one discharge outlet. 3. The method according to claim 1, comprising fluidly connecting the web inlet opening of the first chamber and both the first chamber and the web inlet opening of the second chamber. 4. The method according to claim 1, comprising fluidly connecting the web outlet opening of the first chamber and both the first chamber and the web outlet opening of the second chamber. 5. The method according to claim 1, wherein the web outlet opening of the second chamber is located at a distance from and substantially in line with the web outlet opening of the first chamber. 6. The method according to claim 1, wherein the discharge outlet is located in vicinity of the web inlet opening of the second chamber. 7. The method according to claim 1, wherein the discharge outlet is located inside the second chamber in the vicinity of the web inlet opening. 8. The method according to claim 1, wherein the discharge outlet is located in the vicinity of the web inlet opening of the first chamber. 9. The method according to claim 1, comprising controlling the flow of gaseous fluid so that a first overpressure is created inside the first chamber, and a second overpressure is created inside the second chamber. 10. The method according to claim 9, whereby the overpressures are chosen so that the first overpressure and the second overpressure are the same. 11. The method according to claim 9, whereby the overpressures are chosen so that the first overpressure and the second overpressure are different. 12. Device for electron beam irradiation of at least one side of a web, the device comprising:a first chamber comprising a web inlet opening and a web outlet opening,a second chamber extending inside the first chamber in separated relation to the first chamber, the second chamber comprising a web inlet opening, a web outlet opening, and being adapted to receive an electron beam emitter provided with an electron exit window through which electrons are adapted to be emitted into the second chamber,the web being adapted to pass the second chamber, andthe web outlet opening of the first chamber being adapted to be in communication with a gaseous fluid supply and both chambers being in communication with an outlet, the supply and the outlet are adapted to create a flow of the gaseous fluid through both the first and second chambers in a direction opposite the direction of travel of the web. 13. Device for electron beam irradiation of at least one side of a web, the device comprising:a first chamber comprising a web inlet opening and a web outlet opening,a second chamber extending inside the first chamber in separated relation to the first chamber, the second chamber comprising a web inlet opening, a web outlet opening and being adapted to receive an electron beam emitter provided with an electron exit window through which electrons are adapted to be emitted into the second chamber,the web being adapted to pass the second chamber,a fluid connection is adapted to be provided between the web outlet opening of the second chamber and the web outlet opening of the first chamber,a fluid connection is adapted to be prevented between the first chamber and the web outlet opening of the first chamber,the web outlet opening of the first chamber being adapted to be in communication with a first gaseous fluid supply,the first chamber being adapted to be in communication with a second gaseous fluid supply,both chambers being in communication with a discharge outlet through which is discharged the gaseous fluid from at least one of the first and second gaseous fluid supplies, andthe first and second supplies and the discharge outlet are adapted to create a flow of the gaseous fluid through both the first and second chambers in a direction opposite the direction of travel of the web. 14. Device for electron beam irradiation of at least one side of a web, the device comprising:a first chamber comprising a web inlet opening and a web outlet opening,a second chamber extending inside the first chamber in separated relation to the first chamber, the second chamber comprising a web inlet opening, a web outlet opening, and an electron beam emitter provided with an electron exit window through which electrons are to be emitted into the second chamber,the web being adapted to pass through the second chamber, andthe web outlet opening of the first chamber is in communication with a gaseous fluid supply and both chambers are in communication with a discharge outlet through which the gaseous fluid in the chambers is discharged, the supply and the discharge outlet are adapted to create a flow of the gaseous fluid through both the first and second chambers in a direction opposite the direction of travel of the web. 15. Device for electron beam irradiation of at least one side of a web, the device comprising:a first chamber comprising a web inlet opening and a web outlet opening,a second chamber extending inside the first chamber in separated relation to the first chamber, the second chamber comprising a web inlet opening, a web outlet opening, and an electron beam emitter provided with an electron exit window through which electrons are emitted into the second chamber,the web being adapted to pass through the second chamber,a fluid connection is provided between the web outlet opening of the second chamber and the web outlet opening of the first chamber,the first chamber is prevented from being in fluid connection with the web outlet opening of the first chamber,the web outlet opening of the first chamber being in communication with a first gaseous fluid supply,the first chamber is in communication with a second gaseous fluid supply, both chambers being in communication with a discharge outlet through which the gaseous fluid in the chambers is discharged, andthe first and second supplies and the discharge cutlet are adapted to create a flow of the gaseous fluid through both the first and second chambers in a direction opposite the direction or travel of the web. 16. The method according to claim 1, wherein the first chamber through which the flow of The gaseous fluid is created is located inside an outer housing, and the second chamber through which the gaseous flow is created is located inside an inner housing which is separate from and positioned inside the outer housing, the first chamber being between the outer housing and the inner housing. 17. The device according to claim 12, wherein the first chamber is located inside an outer housing, and the second chamber is located inside an inner housing which is separate from and positioned inside the outer housing, the first chamber being between the outer housing and the inner housing. 18. The device according to claim 13, wherein the first chamber is located inside an outer housing, and the second chamber is located inside an inner housing which is separate from and positioned inside the outer housing, the first chamber being between the outer housing and the inner housing. 19. The device according to claim 14, wherein the first chamber is located inside an outer housing, and the second chamber is located inside an inner housing which is separate from and positioned inside the outer housing, the first chamber being between the outer housing and the inner housing. 20. The device according to claim 15, wherein the first chamber is located inside an outer housing, and the second chamber is located inside an inner housing which is separate from and positioned inside the outer housing, the first chamber being between the outer housing and the inner housing. |
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043550029 | summary | BACKGROUND OF THE INVENTION The present invention relates to a nuclear fuel assembly which is loaded with nuclear fuel elements in which a burnable poison is incorporated and more particularly it concerns a nuclear fuel assembly having little possibility of nuclear fuel elements within which burnable poison is added failing. A nuclear fuel assembly used in a boiling water reactor comprises nuclear fuel elements, an upper tie-plate, a lower tie-plate, a channel box and a spacer. The nuclear fuel element is formed by loading plural UO.sub.2 pellets within a fuel cladding, providing an end plug at both ends of the fuel cladding and sealing them by welding. The UO.sub.2 pellets are formed by molding powders of uranium dioxide and sintering it. Zircaloy-2 is used for the fuel cladding. Within the nuclear fuel assembly, roughly classified, two kinds of nuclear fuel elements are loaded. One of them is a nuclear fuel element which comprises UO.sub.2 pellets to which gadolinium oxide (Gd.sub.2 O.sub.3), a burnable poison, is added (which is referred to as gadolinium-nuclear fuel element hereinafter). Another one is a nuclear fuel element which comprises UO.sub.2 pellets to which no gadolinium oxide is added (which is referred to as non-gadolinium-nuclear fuel element hereinafter). Addition of gadolinium oxide to UO.sub.2 pellets is for controlling excess reactivity of the nuclear fuel assembly at the beginning of burning of the nuclear fuel assembly and smoothing the power of nuclear fuel assembly in the horizontal direction. About 2-5 gadolinium-nuclear fuel elements are loaded within the nuclear fuel assembly. As the results of various researches on characteristics of a nuclear fuel assembly constructed as mentioned above, it has been found that the gadolinium-nuclear fuel element more easily fails than the nongadolinium-nuclear fuel element. When nuclear fuel elements fail, fissionable material present therein, and fission products accumulated therein by nuclear fission, leak out of the nuclear fuel element. This is apt to cause environmental contamination and markedly reduces the safety of nuclear reactor. The nuclear fuel assembly containing failed nuclear fuel element must be substituted with fresh nuclear fuel assembly. This causes prolongation of shut-down periods of nuclear reactors and reduction in operation rates of the nuclear reactors. SUMMARY OF THE INVENTION It is an object of the present invention to improve the safety of a nuclear reactor. It is another object of the present invention to reduce the possibility of failure of nuclear fuel elements loaded with fissionable materials in which burnable poison is incorporated. It is another object of the present invention to adjust the content of fissionable material in the nuclear fuel element loaded with fissionable material in which a burnable poison is incorporated. The characteristic of the present invention resides in making the content of fissionable material in the first nuclear fuel element containing a burnable poison smaller than that of fissionable material in the second nuclear fuel element which is adjacent to the first nuclear fuel element and which contains no burnable poison. Preferably, the content of the fissionable material in the first nuclear fuel element is less than about 72% of the content of the fissionable material in the second nuclear fuel element. Thus, possibility of failure of the first nuclear fuel element is markedly decreased. |
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039716970 | summary | BACKGROUND OF THE INVENTION This invention is concerned with the production of high purity radioiodine for thyroid measurements and as a general radionuclide. The invention is particularly directed to the utilization of a heat pipe in the production of radioisotopes using very intense particle accelerators. Radioactive iodine is used for medical diagnostic studies. The isotope .sup.131 I has been used for this purpose because of its availability. The radioisotope .sup.123 I is considered much superior to the .sup.131 I in studies where the amount of radiation exposure to a patient is of prime concern. Because of the shorter half-life and the decay by electron capture, the radiation exposure received by the patient from .sup.123 I is about one-fortieth that of an equal amount of .sup.131 I. .sup.123 I is also superior to .sup.131 I because the gamma ray energy of .sup.123 I is 159 KEV compared to 364 KEV of .sup.131 I. Collimators operate more effectively with this lower energy. Also the collimators used with .sup.123 I are less bulky. A method of .sup.123 I production is disclosed in U.S. Pat. No. 3,694,313. The method disclosed in this patent has been quite successful in terms of freedom from radioactive impurities. However, the method is not capable of handling the power densities involved in using high energy, high current machines. SUMMARY OF THE INVENTION According to the present invention cesium is used both as the working fluid of a heat pipe and as the target material for high energy protons. A spallation reaction produces .sup.123 Xe and many radioactive contaminants which pass from the heat pipe to low temperature traps where the undesirable contaminants are removed. The xenon is held for a period of time sufficient for it to decay to .sup.123 I. OBJECTS OF THE INVENTION It is, therefore, an object of the invention to produce the radioisotope .sup.123 I with high energy particles from very intense particle accelerators. Another object of the invention is to produce .sup.123 I using a heat pipe that is bombarded with high energy particles. These and other objects of te invention will be apparent from the specification which follows and from the drawing wherein like numerals are used throughout to identify like parts. |
description | The present application is related to, claims the priority benefit of, and is a U.S. §371 national stage entry of, International Patent Application Serial No. PCT/US2010/000290, filed Feb. 2, 2010, which is related to, claims the priority benefit of, and is a continuation of U.S. Patent Application Serial No. 12/378,273, filed Feb. 13, 2009, which issued as U.S. Patent No. 7,917,971 on Apr. 5, 2011. The contents of the patent and each of these applications are hereby incorporated by reference in their entirety into this disclosure. The present invention relates generally to protective equipment for an individual's body, for protecting against blows imparted upon the body during athletic competition. Body protective equipment is commonly worn by participants of contact sports for the purpose of preventing injuries. In these contact sports, various situations may cause injuries. Examples of these situations include tackling or otherwise bumping into other players, falling to the ground, being struck by another player's equipment, or being struck by a game ball itself. Of course, body protective equipment may reduce or prevent injuries resulting from various other circumstances, including those not associated with contact sports. Existing body protective equipment utilize a relatively significant amount of foam padding for absorbing the energy of blows delivered to the body. Moreover, a rigid hard shell cover typically made of hard plastic, usually overlays the foam padding so as to distribute the force of the blow across a larger area of the foam padding. As is known in the art, distributing the force in this manner permits the foam padding to absorb only a portion of the energy associated with the blow. A drawback of using a rigid hard shell cover is its limited ability to absorb and displace energy and its lack of flexibility to the user. Another drawback is that the combined use of the foam padding and the rigid hard shell cover adds relatively significant weight to the protective equipment. Since absorbing and displacement of energy is needed to prevent injury and flexible lightweight athletic equipment are known for allowing players freedom of movement, the ridged hard shell cover and its lack of energy absorbing and displacing properties and its lack of flexibility and the added weight are all undesirable results. Therefore, a need exists for body protective equipment that can absorb and displace the energy from a powerful blow, is flexible, and is relatively lightweight. Protective equipment also exists to protect other parts of the body from injury during contact athletic events. Such protective equipment includes shin guards, shoulder pads, kneepads, elbow pads, and hip pads. This protective equipment like the athletic shin-guard described above, is typically comprised of foam padding with a plastic cover and thus suffers from the same deficiencies discussed above. Therefore, a need also exists for protective equipment for any part of the body that can absorb and displace the energy from a powerful blow, is flexible, and is relatively lightweight. It is therefore an object of the present invention to provide protective equipment with improved protection for the body of an athlete. It is another object of the present invention to provide protective equipment that is durable and can withstand a substantial number of blows over a significant period of time. It is another object of the present invention to provide protective equipment that can absorb and displace the energy from blows. It is yet another object of the present invention to provide protective equipment that is flexible, lightweight, and allows a user greater freedom of movement and to expend less energy carrying the equipment. In accordance with the above and other objects of the present invention, a protective athletic shin-guard is provided for protection of blows imparted upon the body of a user. The protective athletic shin-guard includes an inner rigid band-shaped member that follows the curve of the shin bone and provides protection thereto and a outer flexible web-shaped body made of a softer rubber like material and works as a locator and supporter of the rigid band-shaped member, combined the structure works like a spring keeping the inner, rigid band-shaped member, in proper location away from the user allowing for compression. The combination of these elements allows for the absorption and displacement of the energy of a blow delivered to an individual's body. One advantage of the present invention is that a user is protected from harmful forces that may injure his shin, knee, and elbow, as well as other parts of the body. Another advantage of the present invention is that it has a minimized weight for permitting a user to expend more energy participating in an ongoing activity. Yet another advantage of the present invention is that it is flexible and allows a user greater freedom of movement. Other advantages of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims. This description relates to the general comments herein, as well as the figures referred to above. As noted, FIG. 1 is a front perspective view of the energy absorbing and displacing structure for athletic protective equipment therein. In FIG. 1, the structure is incorporated into an athletic shin-guard (1). The structure includes a rigid band-shaped member over molded with a flexible web-shaped body. FIG. 2 is yet another perspective view there of. Next, consistent with all of the foregoing, FIG. 3 is a cross-sectional view of the shin guard, illustrating the impact and energy absorbing structure. The rigid band shaped member (2) over-molded with the flexible web-shaped body (1) to provide enhanced impact and energy absorption. As depicted, the structure is pre-formed with the rigid band shaped member (2) made of a hard resilient material like polycarbonate, and the flexible web-shaped body (1) made of a rubber like material, each is combined in an over mold process to make a complete structure. The webbed like structure (1) is utilized to locate and support the rigid band shaped member (2), also unlike the prior art. As noted, this configuration provides the utmost in impact and energy absorption. In the preferred mode, a flexible web-shaped body (1) is used to hold a rigid band-shaped member (2) in the desired location. The inner rigid band-shaped member (2) follows the contour of the desired area to protect. The outer flexible web-shaped body (1) is made of a flexible rubber like material and works as an exoskeleton to hold the inner rigid band-shaped member (2), in the desired location. In an effort to make the most efficient use possible of the rigid band shaped member (2). In addition, FIG. 4 illustrates that the rigid band shaped member (2) is kept to a minimum and is only as big as the area it is to protect. The length and width will very in size and is dictated by the desired area to protect. For the purposes of example, a flexible web-shaped body (1) together with the rigid band shaped member (2) works like a spring and provides absorption and dissipation. Combined as an assembly it creates a system for great distribution and spreading of forces, thereby reducing the adverse effects of impact in a manner previously unattained. Importantly, the flexible web-shaped body (1) with its spring like design and rubber like properties working in conjunction inhibits the structure from bottoming out, or reaching their full capacity of energy absorption. Furthermore, the assembly provides for complete memory, which is instantaneous upon release of the force exerted. In addition, the structure functions to allow the outer portion of the assembly to receive primary forces, the flexible web-shaped body (1) directs and distributes forces to the user. As such, the assembly compresses in a unique manner to absorb the force and displace the energy of impact received. FIG. 4 illustrates the assembly separated into its components. The combined structure allows for the rigid band shaped member (2) and the flexible web-shaped body (1) to work in unison, as opposed to a single rigid structure attempting to absorb all forces received. This simply allows for a far greater amount of energy absorbed by the assembly of the present invention. Thus, regarding the present invention embodied within an athletic shin-guard, the webbed structure will mitigate the incidence of pain and injuries. The depiction of the invention within an athletic shin-guard is for example purposes only, as the impact and energy absorbing structure may also be utilized on items such as shoulder pads, knee pads, elbow pads, hip pads and other athletic protective equipment. It should be noted that when two separate devices, each incorporating the assembly of the present invention, collide with one another, the level of energy absorbed and dissipated by the present invention is even greater than the already beneficial result received through usage of just a single such device. Knee to knee or elbow-to-elbow type collisions are common in many contact sports such as lacrosse, soccer, football and hockey, and usage of the present invention by all players within a game will only reduce the incidence of injury by that much more. Regarding the present invention and its applications of usage, it is important to distinguish the present invention from prior art structures wherein athletic protective equipment, rather than providing for flexibility and freedom of movement, are rigid, restrictive, and hinder movement. It is the purpose of the present invention to absorb and displace energy for the purpose of injury prevention and user safety while allowing for uninhibited freedom of movement. As such, the present system meets all rules and regulations of all major sports, rendering the same available for any physical activity. In all such cases, the rigid band shaped member is manufactured in a variety of materials and sizes previously determined to render them effective for multiple previously determined sporting events and hazardous activities. Thus, the assembly may be utilized for protective devices in activities such as diving, swimming, ice hockey, roller hockey, roller skating, skateboarding, field hockey, soccer, lacrosse, football, arena football, gymnastics, baseball, auto racing, motorcycle racing, cycling, and track and field events. It is imperative to note that the rigid band shaped member of the present invention may be tailored to absorb and dissipate foreseeable forces of humans and objects coming in contact with the assembly. As such, allowing for far greater adaptability to particular needs than traditional pads constructed of hard shell and foam and the like. It is intended that the rigid band shaped member width also be variable according to particular needs. In all instances, the rigid band shaped member will vary in size in accordance to the area of desired protection, constantly allowing for a secure fit for each application. Moreover, the impact and energy absorbing structure may be manufactured in a variety of previously determined sizes, functioning to render the assembly effective for multiple previously determined sporting events and hazardous activities. In any such instance, the use of the impact and energy absorbing structure will significantly reduce the quantity of padding and material needed, thus reducing weight to achieve the desired protection. With regards to all descriptions and graphics, while the present invention has been illustrated and described as embodied, it is not intended to be limited to the details shown herein, since it will be understood that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated, and in its operation, can be made by those skilled in the art without departing in any way from the spirit of the invention. Without further analysis, the foregoing will so reveal the gist of the present invention that others can readily adapt it for various applications without omitting features that from the standpoint of prior art, constitute characteristics of the generic or specific aspects of this invention. What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims. |
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abstract | A telescoping guide for extraction and reinsertion support handling of in-core instrument thimble assemblies in the area above the upper support plate in the upper internals of a pressurized water reactor. The telescoping guides extend between the upper ends of the upper internals support columns and an axially movable instrumentation grid assembly which is operable to simultaneously raise the telescoping guides and extract the in-core instrument thimble assemblies from the reactor fuel assemblies. |
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056278721 | abstract | A stationary exit window for an X-ray lithography beamline having a shape and thickness such that the exit window can withstand a pressure differential of 14.7 psi and allows an X-ray beam as passed through the window to have X-rays above and below a desired energy band substantially attenuated. The exit window includes a thin material having a window section disposed within an opening of a frame. The window section has a cylindrical sector shape to capitalize on the pressure load bearing ability of hoop stress to keep the thin material from tearing apart. A method of scanning the X-ray beam through a stationary exit window and onto an exposure field on a wafer is also disclosed. |
052375951 | summary | BACKGROUND OF THE INVENTION This invention generally relates to an improved guide plate of the type used to guide the control rodlets through the guide tubes of a nuclear reactor. The guide plate includes a plurality of vent openings for reducing turbulence in the flow of coolant through the guide plate, which in turn reduces both fretting and frictional engagement between the control rodlets and the guide holes in such guide plates. The core of a modern nuclear reactor of the type used to generate electrical power generally includes an upper internals assembly disposed over a lower core barrel. The lower core barrel houses an array of fuel assemblies which generate heat as a result of a controlled fission reaction that occurs in the uranium oxide pellets present within the individual fuel rods. Water is constantly circulated from the lower core barrel through the upper internals and out through the outlet ports provided in the walls of an upper core barrel in order to transfer the heat generated by the fuel rod assemblies to heat exchangers which ultimately convert this heat into usable, non-radioactive steam. The upper internals assembly includes an upper core barrel arrangement in tandem with the lower core barrel of the reactor. The ceiling of the upper core barrel is formed from an upper support plate. The peripheral edge of this support plate is seated around the upper edge of the upper core barrel. Both the support plate and the upper core plate which underlies it include a plurality of apertures for conducting the stream of hot, pressurized water exiting the fuel assemblies to the heat exchangers, as well as for conducting what are known in the art as rod cluster control assemblies into the fuel assemblies. The rate of the fission reaction taking place within the fuel assemblies is regulated by means of the rod cluster control assembly. Each of the control rod assemblies is formed of a neutron absorbing substance, such as an alloy of silver, indium and cadmium, that is clad in a tube of stainless steel. The stainless steel tubes (known as "rodlets" in the art) are suspended from a spider-like bracket formed from a plurality of interconnected vanes which in turn interconnect the top end of all of the rodlets. A reciprocable drive rod is connected to the spider-like bracket for either inserting or withdrawing the rodlets either deeper into or farther out of each of the fuel assemblies in order to modulate the amount of heat generated within the fuel assemblies. As they reciprocate, the rodlets of the rod cluster control assemblies are guided into their respective fuel assemblies by guide tubes. The bottom end of each of these guide tubes is bolted onto the upper core plate which forms the ceiling of the lower core barrel, while the upper portion of each of these guide tubes is laterally supported within an aperture in the upper support plate which forms the ceiling of the upper core barrel of the reactor. While the lower end of each of the guide tubes includes a plurality of guide sheaths having round holes interconnected by slots which guide the rodlets in much the same fashion as a sword is guided into proper alignment within its sheath, the intermediate and upper portion of each guide tube includes a plurality of guide plates for this purpose. Similar to the guide sheaths, each of these guide plates includes a plurality of guide holes interconnected by slots for slidably receiving both the rodlets and the control rod vanes of the rod cluster control assembly. Each of the guide plates further includes a central orifice for conducting coolant through the guide tube. However, while the guide sheath may be 30 to 35 inches (76.2-88.9 cm) long, each of the guide plates is only about one inch (2.54 cm) thick. Hence, the guide plate provides guidance to the rodlets of the rod cluster control assembly with far less frictional engagement than the guide sheath provided at the very ends of each of the guide tubes, which is advantageous in view of the fact that such lowered frictional contact reduces the minimum drop time required to completely insert the rodlet into the fuel assemblies. Such a lowered drop time in turn allows the reactor operators to slow down or stop the nuclear reaction within the fuel assemblies in a shorter period of time in the event of an emergency situation. While the performance of such prior art guide plates has generally proven to be satisfactory, the applicant has noted a number of areas in which the performance of these guide plates might be improved. For example, over a period of time, it has been observed that the flow of coolant water through the central orifice of these guide plates can induce vibrations in the rodlets which can cause them to rub against the guide holes in the plates and ultimately wear down the stainless steel cladding which forms the outer surface of such rodlets. Additionally, the applicant has observed that the flow of coolant through the central orifice in these guide plates also creates a low pressure area just above the upper surface of the plate which tends to radially pull each of the rodlets into frictional engagement with the guide holes that slidably receive them. Such frictional engagement, in combination with the periodic reciprocable movements of these rodlets during the operation of the reactor, can also cause the stainless steel cladding that forms the outer surface of the rodlets to wear down. The resulting fretting and wear caused by the flow patterns of coolant through such prior art guide plates reduces the life of the rodlets, thereby causing them to be replaced at shorter time intervals than would otherwise be the case. Such rodlet maintenance and replacement is expensive, since it increases reactor down time, and necessitates the opening up of the upper internals assembly of the reactor, which is in itself an expensive operation that exposes maintenance workers to potentially hazardous radiation. Clearly, there is a need for an improved guide plate that eliminates or at least reduces unwanted fretting and frictional engagement between the rodlets of the rod cluster control assembly and the guide holes in the guide plate so as to minimize wear between these plates in the outer cladding of the rodlets. Ideally, the reduction in fretting and frictional engagement would result in an even faster minimum drop time for the rodlet to be inserted completely into the respective fuel assemblies, which in turn would enhance the safety capabilities of the reactor by allowing the reactor operators to more quickly reduce or stop the nuclear reaction within the fuel assembly in the event such reduction becomes necessary. SUMMARY OF THE INVENTION The invention is an improved guide plate of the type used in guide tubes of nuclear reactors which overcomes or at least ameliorates the problems associated with the prior art by the provision of at least one vent opening which reduces the turbulence in the coolant flow through the central orifice of the plate. The resulting reduction in turbulence results in less fretting and frictional engagement between the control rodlets and the guide holes in the guide plate. The improved guide plate preferably includes a plurality of such vent openings, at least some of which may be in the form of vent holes provided between every two adjacent slots in the guide plate. Each of these vent holes may be chamfered at both ends to further reduce turbulence in the coolant which flows through the openings. Moreover, each of the vent openings is preferably located adjacent to the midpoint of each of the two slots that it is positioned between to uniformly relieve turbulence-causing pressure differentials between the stream of coolant flowing through the central orifice of the vent plate, and the coolant circulating around the periphery of this stream. While the vent holes may assume a variety of shapes, circular holes are preferred due to their relative ease of manufacture. Additionally, the total cross sectional area of the vent holes is preferably between about 50 and 60 per cent of the cross sectional area of the central orifice, although the benefits of the invention may be realized with a greater or a lesser ratio of cross sectional area. Finally, to compensate for any mechanical weakening that the vent holes may have caused in the guide plate, the thickness of the guide plate is increased from 50 to 100 per cent over the of a prior art guide plate. The vent openings may further assume the form of annular gaps between the peripheral edges of the guide plate and the inner wall of the guide tube. Such gaps may be between 0.125 and 0.375 inches (0.3175 and 0.9525 cm) wide, and the total combined area of these vent gaps may be 50 to 60 per cent of the area of the central orifice. Preferably, the vent openings include both vent holes and vent gaps so that the total additional fluid venting area is increased from 100 to 120 per cent. The vent openings in the improved guide plate not only reduce fretting and frictional engagement between the rodlets of the rod cluster control assembly and the guide holes in the guide plate; they also advantageously reduce the minimum rod drop time through the guide tube by as much as 0.20 seconds, which allows the operator of the reactor to rapidly slow down the nuclear reaction within the fuel assemblies in the event of an emergency condition. As a final improvement, the guide holes of the guide plate may be chrome plated. Such plating not only further reduces friction between the stainless steel cladding of the control rodlets and the guide holes; it also renders the surface of the guide holes more corrosion resistant, which helps to prevent binding between the rodlets and the holes during the lifetime of the reactor. |
claims | 1. A method of at least one of processing and removing radioactive materials from an underwater environment comprising:a) submerging a container having a top, a bottom, and a cavity in a body of water having a surface level, the cavity filling with water;b) positioning radioactive material within the cavity of the submerged container;c) raising the submerged container until the top of the container is above the surface level of the body of water while a major portion of the container remains below the surface level or the body of water, wherein water from the body of water can no longer flow into the cavity; andd) removing bulk water from the cavity while the top of the container remains above the surface level of the body of water and a portion of the container remains submerged. 2. The method of claim 1 wherein step c) further comprises positioning a lid having one or more openings atop the submerged container so as to substantially enclose the cavity. 3. The method of claim 1 wherein the container provides both gamma radiation shielding and neutron shielding. 4. The method of claim 1 wherein the container comprises a cask and a canister positioned within the cask. 5. The method of claim 4 wherein step b) comprises positioning radioactive material within the canister. 6. The method of claim 5 wherein step d) comprises removing bulk water from the canister while a top of the cask remains above the surface level of the body of water and a portion of the cask remains submerged. 7. The method of claim 1 wherein step c) comprises raising the submerged container until the top of the container is between 1 to 12 inches above the surface level of the body of water. 8. The method of claim 7 wherein step d) comprises removing the bulk water from the cavity while at least a major portion of the container remains submerged. 9. The method of claim 1 wherein the radioactive material is spent nuclear fuel rods, and wherein:step a) further comprises submerging the container in the body of water in a substantially vertical orientation;step b) further comprises lowering the spent nuclear fuel rods into the cavity of the submerged container; andstep c) further comprises raising the submerged container in the vertical orientation with a crane until the top of the container is above the surface level of the body of water while a major portion of the container remains below the surface level of the body of water. 10. The method of claim 1 wherein the radioactive material is spent nuclear fuel rods. 11. The method of claim 1 wherein step b) further comprises positioning a lid having one or more openings atop the submerged container so as to substantially enclose the cavity, the method further comprising:e) upon the bulk water being removed from cavity, lifting the container entirely out of the body of water;f) setting the container down in a staging area;g) filling the cavity back up with water; andh) securing the lid to the container. 12. The method of claim 11 wherein step h) comprises welding the lid to the container. 13. A method of at least one of processing and removing high level radioactive materials from an underwater environment comprising:a) providing a container having a cavity having an open top end and closed bottom end, the container having a top;b) positioning a canister having an open top end and a closed bottom end in the cavity of the container to form a container assembly;c) submerging the container assembly in a body of water;d) positioning high level radioactive material in the canister;e) placing a lid atop the canister that substantially encloses the top end of the canister, the lid having one or more holes;f) raising the submerged container assembly until the top of the container is above a surface level of the body of water while a major portion of the container remains below the surface level of the body of water, wherein water from the body of water can no longer flow into the canister; andg) removing bulk water from the canister while the top of the container remains above the surface level of the body of water and a portion of the container remains submerged. 14. The method of claim 13 wherein the high level radioactive material is spent nuclear fuel. 15. The method of claim 13 wherein the container is a cask that provides both neutron and gamma radiation shielding and the canister is hermetically scalable. 16. The method of claim 13 further comprising:h) upon the bulk water being removed from canister, lifting the container assembly entirely out of the body of water;i) setting the container assembly down in a staging area;j) filling the canister back up with water;k) securing the lid to the canister;l) draining the bulk water from the canister;m) drying an interior of the canister and the radioactive materials to a desired dryness level; andn) backfilling the canister with a non-reactive gas and hermetically sealing the canister. 17. A method of removing spent nuclear fuel from an underwater environment and preparing the spent nuclear fuel for dry storage, the method comprising:a) providing a cask having both gamma radiation and neutron shielding properties, the cask having a top, a bottom and a cavity having an open top end and a closed bottom end;b) positioning a canister having an open end in the cavity;c) submerging the cask and canister into an underwater environment, the canister filling with water;d) positioning spent nuclear fuel within the canister;e) placing a lid atop the open canister thereby substantially enclosing the open end of the canister;f) raising the cask and canister until the top of the cask is above a water level of the underwater environment while a major portion of the cask remains below the water level, wherein water from the body of water can no longer flow into the canister;g) removing bulk water from the canister while a portion of the cask remains below the water level utilizes the buoyancy of the water itself to minimize the load experienced by a crane and/or other lifting equipment; andh) raising the entire cask above the water level of the underwater environment. 18. The method of claim 17 further comprising:i) placing the cask and canister in a staging area;j) filling the canister with a neutron absorbing fluid; andk) securing the lid to the canister. 19. The method of claim 18 further comprising:l) drying the spent nuclear fuel within the canister to a desired level of dryness; andm) backfilling the canister with a non-reactive gas and hermetically sealing the canister. 20. A method of at least one of processing and removing radioactive materials from an underwater environment comprising:a) submerging a container having a cavity in a body of water having a surface level, the cavity filling with water;b) positioning radioactive material within the cavity of the submerged container;c) raising a submerged container until a top of the container is above the surface level of the body of water while a major portion of the container remains below the surface level of the body of water; andd) removing bulk water from the cavity while the top of the container remains above the surface level of the body of water and a portion of the container remains submerged, wherein a buoyancy force exerted by the body of water on the container is increased as a result of the removal of bulk water from the cavity. |
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description | The present application claims the benefit of U.S. Provisional Patent Application 60/652,363, filed Feb. 11, 2005, the entirety of which is hereby incorporated by reference in its entirety. The present invention relates generally to the field of storing high level waste, and specifically to systems and methods for storing spent nuclear fuel in ventilated vertical modules that utilize passive convective cooling. In the operation of nuclear reactors, it is customary to remove fuel assemblies after their energy has been depleted down to a predetermined level. Upon removal, this spent nuclear fuel is still highly radioactive and produces considerable heat, requiring that great care be taken in its packaging, transporting, and storing. In order to protect the environment from radiation exposure, spent nuclear fuel is first placed in a transportable canister. An example of a typical canister used to transport, and eventually store, spent nuclear fuel is disclosed in U.S. Pat. No. 5,898,747 to Krishna Singh, issued Apr. 27, 1999. Such canisters are commonly referred to in the art as multi-purpose canisters (“MPCs”) and are hermetically sealable to effectuate the dry storage of spent nuclear fuel. Once the canister is loaded with the spent nuclear fuel, the loaded canister is transported and stored in large cylindrical containers called casks. A transfer cask is used to transport spent nuclear fuel from location to location while a storage cask is used to store spent nuclear fuel for a determined period of time. In a typical nuclear power plant, an open empty canister is first placed in an open transfer cask. The transfer cask and empty canister are then submerged in a pool of water. Spent nuclear fuel is loaded into the canister while the canister and transfer cask remain submerged in the pool of water. Once fully loaded with spent nuclear fuel, a lid is typically placed atop the canister while in the pool. The transfer cask and canister are then removed from the pool of water, the lid of the canister is welded thereon and a lid is installed on the transfer cask. The canister is then properly dewatered and back filled with inert gas. The canister is then hermetically sealed. The transfer cask (which is holding the loaded and hermetically sealed canister) is transported to a location where a storage cask is located. The canister is then transferred from the transfer cask to the storage cask for long term storage. During transfer from the transfer cask to the storage cask, it is imperative that the loaded canister is not exposed to the environment. One type of storage cask is a ventilated vertical overpack (“VVO”). A VVO is a massive structure made principally from steel and concrete and is used to store a canister loaded with spent nuclear fuel. Existing VVO stand above ground and are typically cylindrical in shape and extremely heavy, weighing over 150 tons and often having a height greater than 16 feet. VVO typically have a flat bottom, a cylindrical body having a cavity to receive a canister of spent nuclear fuel, and a removable top lid. In using a VVO to store spent nuclear fuel, a canister loaded with spent nuclear fuel is placed in the cavity of the cylindrical body of the VVO. Because the spent nuclear fuel is still producing a considerable amount of heat when it is placed in the VVO for storage, it is necessary that this heat energy have the ability to escape from the VVO cavity. This heat energy is removed from the outside surface of the canister by passively ventilating the VVO cavity using natural convective forces. In passively ventilating the VVO cavity, cool air enters the VVO chamber through bottom ventilation ducts, flows upward past the loaded canister, and exits the VVO at an elevated temperature through top ventilation ducts. The bottom and top ventilation ducts of existing VVO are located circumferentially near the bottom and top of the VVO's cylindrical body respectively, as illustrated in FIG. 1. While it is necessary that the VVO cavity be vented so that heat can escape from the canister, it is also imperative that the VVO provide adequate radiation shielding and that the spent nuclear fuel not be directly exposed to the external environment. The inlet duct located near the bottom of the overpack is a particularly vulnerable source of radiation exposure to security and surveillance personnel who, in order to monitor the loaded overpacks, must place themselves in close vicinity of the ducts for short durations. Additionally, when a canister loaded with spent nuclear fuel is transferred from a transfer cask to a storage VVO, the transfer cask is stacked atop the storage VVO so that the canister can be lowered into the storage VVO's cavity. Most casks are very large structures and can weigh up to 250,000 lbs. and have a height of 16 ft. or more. Stacking a transfer cask atop a storage VVO/cask requires a lot of space, a large overhead crane, and possibly a restraint system for stabilization. Often, such space is not available inside a nuclear power plant. Finally, above ground storage VVO stand at least 16 feet above ground, thus, presenting a sizable target of attack to a terrorist. FIG. 1 illustrates a traditional prior art VVO 1. The prior art VVO 1 comprises a flat bottom 7, a cylindrical body 2, and a lid 4. The lid 4 is secured to a cylindrical body 2 by a plurality of bolts 8. The bolts 8 serve to restrain separation of the lid 4 from the body 2 if the prior art VVO 1 were to tip over. The cylindrical body 2 has a plurality of top ventilation ducts 5 and a plurality of bottom ventilation ducts 6. The top ventilation ducts 5 are located at or near the top of the cylindrical body 2 while the bottom ventilation ducts 6 are located at or near the bottom of the cylindrical body 2. Both the bottom ventilation ducts 6 and the top ventilation ducts 5 are located around the circumference of the cylindrical body 2. The entirety of the prior art VVO 2 is positioned above grade and, therefore, suffers from a number of the drawbacks discussed above and remedied by the present invention. It is therefore an object of the present invention to provide a system and method for storing high level waste, such as spent nuclear fuel, that reduces the height of the stack assembly during canister transfer procedure. Another object of the present invention to provide a system and method for storing high level waste, such as spent nuclear fuel, that requires less vertical space. Yet another object of the present invention is to provide a system and method for storing high level waste, such as spent nuclear fuel, that utilizes the radiation shielding properties of the subgrade during storage while providing adequate passive ventilation of the high level waste. A further object of the present invention is to provide a system and method for storing high level waste, such as spent nuclear fuel, that provides the same or greater level of operational safeguards that are available inside a fully certified nuclear power plant structure. A still further object of the present invention is to provide a system and method for storing high level waste, such as spent nuclear fuel, that decreases the dangers presented by earthquakes and other catastrophic events and virtually eliminates the potential damage from a World Trade Center or Pentagon type of attack on the stored canister. It is also an object of the present invention to provide a system and method for storing high level waste, such as spent nuclear fuel, that allows an ergonomic transfer of the high level waste from a transfer cask to a storage VVO. Another object of the present invention is to provide a system and method for storing high level waste, such as spent nuclear fuel, below grade. Yet another object of the present invention is to provide a system and method of storing high level waste, such as spent nuclear fuel, that reduces the amount of radiation emitted to the environment. Still another object of the present invention is to provide a system and method of storing a plurality of canisters containing high level waste in separate below grade cavities while facilitating adequate passive ventilated cooling of each canister. These and other objects are met by the present invention which in one aspect is a system for storing high level waste emitting a heat load, comprising: an air-intake shell forming a substantially vertical air-intake cavity; a plurality of storage shells, each storage shell forming a substantially vertical storage cavity; a hermetically sealed canister for holding high level waste positioned in each of the storage cavities so that a gap exists between the storage shell and the canister, the horizontal cross-section of each storage cavity accommodating no more than one canister; a removable lid positioned atop each of the storage shells so as to form a lid-to-shell interface, the lid containing an outlet vent forming a passageway between an ambient environment and the storage cavity; and a network of pipes forming a passageway between a bottom portion of the intake cavity and a bottom portion of each of the storage cavities. Preferably, the system of the present invention is used to store spent nuclear fuel in a below grade environment. In such an embodiment, the storage shells are positioned so that at least a major portion of their height is located below grade (i.e., below the surface level of the ground). The network of pipes are also located below grade while the lids positioned atop the storage shells are located above grade. A radiation absorbing material preferably surrounds the storage shells and covers the network of pipes. The radiation absorbing material can be concrete, an engineered fill, soil, and/or a combination thereof. It is further preferable that the storage shells, the air-intake shell, the network of pipes, and all connections therebetween be hermetically constructed so as to prohibit the ingress of below grade liquids. The air-intake shell, the storage shells and the network of pipes are preferably constructed of a metal or alloy. All connections can be achieved by welding or other suitable procedures that result in an integral hermetic structure. In this below grade embodiment of the system, the air-intake cavity forms an air passageway between the above grade air and the network of pipes. Similarly, the vents in the lids positioned atop the storage shells form passageways between the storage cavities and the above grade air. As a result of this design, when the hermetically sealed canisters (which are loaded with the hot high level waste) are loaded in the storage cavities, cool ambient air will enter the air-intake cavity, travel through the network of pipes, and enter the bottom portion of the storage cavities. Heat from the high level waste within the canisters will warm the cool air causing it to rise through the gap that exists between the storage shell and the canister. Upon continuing to rise, the heated air will then exit the storage cavities via the vents in the lids. The chimney effect of the heated air escaping the storage cavities siphons additional cool air into the air-intake cavity, through the network of pipes, and into the storage cavities. Thus, the below grade storage of multiple spent nuclear fuel canisters can be achieved while affording adequate ventilation for cooling. As in typical overpack systems, the canisters are preferably non-fixedly positioned within the storage cavities in a substantially vertical orientation. In other words, the canisters are positioned within the storage cavities free of anchors and are free-standing. As a result, the canisters can be easily inserted, removed and transferred from the storage cavities, as necessary. A lid can also be positioned atop the air-intake shell so as to form a lid-to-shell interface with the air-intake shell. This lid preferably contains an inlet vent that forms a passageway between the ambient environment and the air-intake cavity. As a result, cool air can be siphoned into the air-intake cavity while prohibiting the entrance of debris and/or rain water. The network of pipes preferably comprises one or more headers that couple the storage shells to the air-intake shell. The headers act as a manifold and assist in evenly distributing the incoming cool air to the storage cavities. A layer of insulating material can also be provided to circumferentially surround the storage shells. The insulation facilitates in prohibiting the incoming cool air from becoming heated prior to entering the storage cavities. In other words, the insulation prohibits the heat emanated by the canisters from conducting into the radiation absorbing material surrounding the storage shells, thereby keeping the air-intake cavity and the network of pipes cool. Preferably, the system further comprises means for supporting the canisters in the storage cavities so that a first plenum exists between a bottom of the canister and a floor of the storage cavity. It is further preferable that a second plenum exists between a top of the canister and a bottom surface of the lid that encloses the storage cavity. In this embodiment, the network of pipes form passageways between the air-intake cavity and the first plenums while the outlet vents within the lids form passageways between the ambient environment and the second plenums. In one embodiment, the support means can comprise a plurality of circumferentially spaced support blocks. It is further preferable that the gaps that exist between the storage shells and the canisters be a small annular gap. In one embodiment, the storage shells can surround the air-intake shell so as to form an array of shells, arranged in side-by-side relation. The dimensions of the array can vary as desired. In another aspect, the invention can be a ventilated system for storing high level waste having a heat load, the system comprising: an array of substantially vertically oriented shells arranged in a side-by-side relation, each shell forming a cavity a hermetically sealed canister for holding high level waste positioned in one or more of the cavities, the cavities having a horizontal cross-section that accommodates no more than one of the canisters; a removable lid positioned atop each of the shells so as to form a lid-to-shell interface, each lid containing a vent forming a passageway between an ambient environment and the storage cavity; a network of pipes forming air passageways between bottoms of all of the cavities; and wherein at least one of the cavities is empty so as to allow cool air to enter the network of pipes. In yet another aspect, the invention is a method of storing and passively ventilating high level waste comprising: providing a system comprising an array of substantially vertically oriented shells arranged in a side-by-side relation, each shell forming a cavity, and a network of pipes forming air passageways between bottom portions of all of the cavities; positioning the system in a below grade hole so that a major portion of the height of the shells is below grade; filling the below grade hole with a radiation absorbing material so as to surround the shells and cover the network of pipes, the cavities being accessible from above grade; lowering a hermetically sealed canister containing high level waste into the cavity of one or more of the shells so that a gap exists between the canister and the shell, the cavity having a horizontal cross-section that accommodates no more than one of the canisters; positioning a removable lid atop the shell containing the canister so as to form a lid-to-shell interface, the lid containing a vent forming a passageway between an above grade atmosphere and the cavity containing the canister; maintaining at least one of the cavities empty; and cool air entering the empty cavity, the cool air being draw into the network of pipes and into the cavity containing the canister, the cool air being warmed by heat from the canister, the warm air rising in the gap and exiting the cavity through the vent of the lid. Referring first to FIG. 2, a manifold storage system 100 is illustrated according to an embodiment of the present invention. As illustrated in FIG.2, the manifold storage system 100 is removed from the ground. However, as will be discussed in greater detail below, the manifold storage system 100 is specifically designed to achieve the dry storage of multiple hermetically sealed canisters containing spent nuclear fuel in a below grade environment. The manifold storage system 100 is a vertical, ventilated dry spent fuel storage system that is fully compatible with 100 ton and 125 ton transfer casks for spent fuel canister transfer operations. The manifold storage system 100 can be modified/designed to be compatible with any size or style transfer cask. The manifold storage system 100 is designed to accept multiple spent fuel canisters for storage at an Independent Spent Fuel Storage Installation (“ISFSI”) in lieu of above ground overpacks (such as prior art VVO 2 in FIG. 1). All canister types engineered for the dry storage of spent fuel in above-grade overpack models can be stored in the manifold storage system 100. Suitable canisters include multi-purpose canisters and thermally conductive casks that are hermetically sealed for the dry storage of high level wastes, such as spent nuclear fuel. Typically, such canisters comprise a honeycomb grid-work/basket, or other structure, built directly therein to accommodate a plurality of spent fuel rods in spaced relation. An example of a canister that is suitable for use in the present invention is disclosed in U.S. Pat. No. 5,898,747 to Krishna Singh, issued Apr. 27, 1999, the entirety of which is hereby incorporated by reference in its entirety. The manifold storage system 100 is a storage system that facilitates the passive cooling of storage canisters through natural convention/ventilation. The manifold storage system 100 is free of forced cooling equipment, such as blowers and closed-loop cooling systems. Instead, the manifold storage system 100 utilizes the natural phenomena of rising warmed air, i.e., the chimney effect, to effectuate the necessary circulation of air about the canisters. In essence, the manifold storage system 100 comprises a plurality of modified ventilated vertical modules that can achieve the necessary ventilation/cooling of multiple canisters containing spent nuclear in a below grade environment. The manifold storage system 100 comprises a vertically oriented air-intake shell 10A and a plurality of vertically oriented storage shells 10B. The storage shells, 10B surround the air-intake shell 10A. Structurally, the air-intake shell 10A is identical to the storage shells 10B. However, as will be discussed below, the air-intake shell 10A is intended to remain empty (i.e., free of a heat load and unobstructed) so that it can act as an inlet passageway for cool air into the manifold storage system 100. The storage shells10B are adapted to receive hermetically sealed canisters containing spent nuclear fuel and to act as storage/cooling chamber for the canisters. However, in some embodiment of the invention, the air-intake shell 10A can be designed to be structurally different than the storage shells 10B so long as the internal cavity of the air-intake shell 10A allows the inlet of cool air for ventilating the storage shells 10B. For example, the air-intake shell 10A can have a cross-sectional shape, cross-sectional size, material of construction and/or height that can be different than that of the storage shells 10B. While the air-intake shell 10A is intended to remain empty during normal operation and use, if the heat load of the canisters being stored in the storage shells 10B is sufficiently low such that circulating air flow is not needed, the air-intake shell 10A can be used to store a canister of spent fuel. Both the air-intake shell 10A and the storage shells 10B are cylindrical in shape. However, in other embodiments the shells 10A, 10B can take on other shapes, such as rectangular, etc. The shells 10A, 10B have an open top end and a closed bottom end. The shells 10A, 10B are arranged in a side-by-side orientation forming a 3×3 array. The air-intake shell 10A is located in the center of the 3×3 array. It should be noted that while it is preferable that the air-intake shell 10A be centrally located, the invention is not so limited. The location of the air-intake shell 10A in the array can be varied as desired by simply leaving one or more of the storage shells 10B empty. Moreover, while the illustrated embodiment of the manifold storage system 100 comprises a 3×3 array of the shells 10A, 10B, other array sizes and/or arrangements can be implemented in alternative embodiments of the invention. The shells 10A, 10B are preferably spaced apart in a side-by-side relation. The horizontal distance between the vertical center axis of the shells 10A, 10B is in the range of about 10 to 20 feet, and more preferably about 15 feet. However, the exact distance between shells will be determined on case by case basis and is not limiting of the present invention. The shells 10A, 10B are preferably constructed of a thick metal, such as low carbon steel. However, other materials can be used, including without limitation metals, alloys and plastics. Examples include stainless steel, aluminum, aluminum-alloys, lead, and the like. The thickness of the shells 10A, 10B is preferably in the range of 0.5 to 4 inches, and most preferably about 1 inch. However, the exact thickness of the shells 10A, 10B will be determined on a case-by-case basis, considering such factors as the material of construction, the heat load of the spent fuel being stored, and the radiation level of the spent fuel being stored. The manifold storage system 100 further comprises a removable lid 12 positioned atop each of the shells 10A, 10B. The lids 12 are positioned atop the shells 10A, 10B, thereby enclosing the open top ends of the cavities formed by the shells 10A, 10B. The lids 12 provide the necessary radiation shielding so as to prevent radiation from escaping upward from the cavities formed by the storage shells 10B when the loaded canisters are positioned therein. The lids are secured to the shells 10A, 10B by bolts or other connection means. The lids 12 are capable of being removed from the shells 10A, 10B without compromising the integrity of and/or otherwise damaging either the lids 12 or the shells 10A, 10B. In other words, each lid 12 forms a non-unitary structure with its corresponding shell 10A, 10B. Each of the lids 12 comprises one or more inlet ducts that form a passageway from the ambient air into the cavity formed by the shells 10A, 10B. The structural details of the lids 12 will be discussed in greater detail below with respect to FIGS. 6A and 6B. The interaction of the lids 12 with the shells 10A, 10B will described in greater detail below with respect to FIG. 7. Referring still to FIG. 2, the manifold storage system 100 further comprises a network 50 of pipes/ducts that fluidly connect all of the storage shells 10B to the air-intake shell 10A. The network 50 comprises two headers 51, a plurality of straight pipes 52, and a plurality of curved expansion joints 53. The headers 51 are used as manifolds to fluidly connect all of the storage shells 10B to the air-intake shell 10A in order to more evenly distribute the flow of incoming cool air to the storage shells 10B as needed. The curved expansion joints 53 provide for thermal expansion/extraction of the network as needed. The straight pipes complete the network 50 so that all shells 10A, 10B are hermetically and fluidly connected. The piping network 50 connects at or near the bottom of the shells 10A, 10B to form a network of fluid passageway between the internal cavities of all of the shells 10A, 10B. More specifically, the piping network 50 provides passageways from the internal cavity of the air-intake shell 10A to all of the internal cavities of the storage shells 10B via the headers 51. As a result, cool air entering the air-intake shell 10A can be distributed to all of the storage shells 10B via the piping network 50. It is preferable that the incoming cool air be supplied to at or near the bottom of the internal cavities of the storage shells10B to achieve cooling of the canisters positioned therein. The piping network 50 is designed so that a direct line of sight does not exist between any two internal cavities of the storage shells 10B. While one embodiment of a plumbing/layout for the piping network 50 is illustrated, the invention is not limited to any specific layout. Those skilled in the art will understand that an infinite number of design layouts can exist for the piping network 50. Furthermore, depending on the ventilation and air flow needs of any given manifold storage system, the piping network may or may not comprise headers and/or expansion joints. The exact layout and component needs of any piping network will be determined on a case-by-case design basis. The internal surfaces of the piping network 50 and the shells 10A, 10B are preferably smooth so as to minimize pressure loss. Similarly, ensuring that all angled portions of the piping network are of a curved configuration will further minimize pressure loss. The size of the pipes/ducts used in the piping network 50 can be of any size. The exact size of the ducts will be determined on case-by-case basis considering such factors as the necessary rate of air flow needed to effectively cool the canisters. In one embodiment, a combination of steel pipes having a 24 inch and 36 inch outer diameter are used. The components 51, 52, 53 of the piping network 50 are seal joined to one another at all connection points. Moreover, the piping network 50 is seal joined to all of the shells 10A, 10B to form an integral/unitary structure that is hermetically sealed to the ingress of water and other fluids. In the case of weldable metals, this seal joining may comprise welding or the use of gaskets. In the case of welding, the piping network 50 and the shells 10A, 10B will form a unitary structure Moreover, as shown in FIG. 7, each of the shells 10A, 10B further comprise an integrally connected floor 11. Thus, the only way water or other fluids can enter any of the internal cavities of the shells 10A, 10B or the piping network 50 is through the top open end of the internal cavities. An appropriate preservative, such as a coal tar epoxy or the like, is applied to the exposed surfaces of shells 10A, 10B and the piping network 50 to ensure sealing, to decrease decay of the materials, and to protect against fire. A suitable coal tar epoxy is produced by Carboline Company out of St. Louis, Mo. under the tradename Bitumastic 300M. Referring now to FIGS. 2 and 3, it can be seen that a layer of insulating material 20 circumferentially surrounds each of the storage cavities 10B. Suitable forms of insulation include, without limitation, blankets of alumina-silica fire clay (Kaowool Blanket), oxides of alumina and silica (Kaowool S Blanket), alumina-silica-zirconia fiber (Cerablanket), and alumina-silica-chromia (Cerachrome Blanket). The insulation 20 prevents excessive transmission of heat from spent fuel canisters within the storage shells 10B to the surrounding structure/material, such as the concrete monolith 60 (FIG. 7), the air-intake shell 10A and the piping network 50. Insulating the storage shells 10B serves to minimize the heat-up of the incoming cooling air before it enters the cavities of the storage shells 10B. This facilitates in maintaining adequate ventilation/cooling of the spent fuel canisters stored therein. The insulating process can be achieved in a variety of ways, none of which are limiting of the present invention. For example, in addition to adding a layer of the insulating material 20 to the exterior of the storage shells 10B, insulating material can also be added to surround the components of the piping network 50 and/or the air-intake shell 10A. Furthermore, in addition to or instead of an insulating material, it may be possible to provide the necessary insulation of the incoming cool air by providing gaps in the concrete monolith 60 (FIG. 7) at the appropriate places. These gaps may be filled with an inert gas or air if desired. Referring now to FIG. 4, the manifold storage system 100 is illustrated with the lids 12 removed from the shells 10A, 10B. As can be seen, each of the shells 10A, 10B comprise a container ring 13 at or near their top. The container rings 13 are thick steel ring-like structures. The container rings 13 circumferentially surround the periphery of the shells 10A, 10B and are secured thereto by welding or another connection technique. In addition to adding structural integrity to the shells 10A, 10B, the container rings 13 also interface with the shear rings 23 (FIGS. 6A, 6B) on the lids 12 to provide resistance to lateral forces. Referring to FIGS. 6A and 6B, the lid 12 is illustrated in detail according to an embodiment of the present invention. In order to provide the requisite radiation shielding for the spent fuel canisters stored in the storage shells 10B, the lid 12 is constructed of a combination of low carbon steel and concrete. More specifically, in constructing one embodiment of the lid 12, a steel lining is provided and filled with concrete (or another radiation absorbing material). In other embodiments, the lid 12 can be constructed of a wide variety of materials, including without limitation metals, stainless steel, aluminum, aluminum-alloys, plastics, and the like. In some embodiments, the lid may be constructed of a single piece of material, such as concrete or steel for example. The lid 12 comprises a flange portion 21 and a plug portion 22. The plug portion 22 extends downward from the flange portion 21. The flange portion 21 surrounds the plug portion 22, extending therefrom in a radial direction. A plurality of outlet vents 28 are provided in the lid 12. Each outlet vent 28 forms a passageway from an opening 29 in the bottom surface 30 of the plug portion 22 to an opening 31 in the top surface 32 of the lid 12. A cap 33 is provided over opening 31 to prevent rain water or other debris from entering and/or blocking the outlet vents 28. The cap 33 is secured to the lid 12 via bolts or through any other suitable connection, including without limitation welding, clamping, a tight fit, screwing, etc. The cap 33 is designed to prohibit rain water and other debris from entering into the opening 31 while affording heated air that enters the vents 28 via the opening 29 to escape therefrom. In one embodiment, this can be achieved by providing a plurality of small holes (not illustrated) in the wall 34 of the cap 33 just below the overhang of the roof 35 of the cap. In other embodiments, this can be achieved by non-hermetically connecting the roof 35 of the cap 33 to the wall 34 and/or constructing the cap 33 (or portions thereof) out of material that is permeable only to gases. The opening 31 is located in the center of the lid 12. In order to further protect against rain water or other debris entering opening 31, the Top surface 32 of the lid 12 is sloped away from the opening 31 (i.e., downward and outward). The top surface 32 of the lid 12 (which acts as a roof) overhangs beyond the side wall 135 of the flange portion 21. The outlet vents 28 are curved so that a line of sight does not exist therethrough. This prohibits a line of sight from existing from the ambient environment to a canister that is loaded in the storage shell 10B, thereby eliminating radiation shine into the environment. In other embodiments, the outlet vents may be angled or sufficiently tilted so that such a line of sight does not exist. The lid 30 further comprises a shear ring 23 secured to the bottom surface 37 of the flange portion 31.The shear ring 23 may be welded, bolted, or otherwise secured to the bottom surface 37. The shear ring 23 is designed to extend downward from the bottom surface 37 and peripherally surround and engage the container ring 13 of the shells 10A, 10B, as shown in FIG. 7. While not illustrated, it is preferable that duct photon attenuators be inserted into all of vents 28 of the lids 12 for both the storage shells 10B and the air-intake shell 10A, irrespective of shape and/or size. A suitable duct photon attenuator is described in U.S. Pat. No. 6,519,307, Bongrazio, the teaching of which are incorporated herein by reference in its entirety. It should be noted that in some embodiments, the air-intake shell 10A may not have a lid 12. Referring now to FIG. 7, the cooperational relationship of the elements of the lid 12 and the elements of the shells 10A, 10B will now be described. In order to avoid redundancy, only the interaction of the lid 12 with a single storage shell 10B will be described in detail with the understanding that those skilled in the art will appreciate that the below discussion applies to all of the storage shells 10B and the air-intake shell 10A. In order to further protect against rain water or other debris entering opening 31, the top surface 32 of the lid 12 is sloped away from the opening 31 (i.e., downward and outward). The top surface 32 of the lid 12 (which acts as a roof) overhangs beyond the side wall 135 of the flange portion 21. At this point, the shear ring 23 of the lid 12 engages and peripherally surrounds the outside surface of the container ring 13. The interaction of the shear ring 23 and the container ring 13 provides enormous shear resistance against lateral forces from earthquakes, impactive missiles, or other projectiles. The lid 12 is secured in place via bolts (or other fastening means) that can either extend into holes in the concrete monolith 60 or into the storage shell 10B itself. While the lid 12 is secured the storage shell 10B and/or the concrete monolith 60, the lid 12 remains non-unitary and removable. While not illustrated, one or more gaskets can be provided at some position at the lid-to-shell interface so as to form a hermetically sealed interface. When the lid 12 is properly positioned atop the storage shell 10B as illustrated in FIG. 7, the vents 28 are in spatial cooperation with the cavity 24 formed by the storage shell 10B. In other words, each of the vents 28 form a passageway from the ambient atmosphere to the cavity 24 itself. The vents in the lid positioned atop the air-intake shell 10A provide a similar passageway. With respect to the air-intake shell 10A, the vents 28 act as a passageway that allows cool ambient air to siphoned into the cavity 24 of the air-intake shell 10A, through the piping network 50, and into the bottom portion of the cavities 24 of the storage shells 10B. When a canister containing spent fuel (or other HLW) having a heat load is positioned within the cavities 24 of one or more of the storage shells 10B, this incoming cool air is warmed by the canister, rises within the cavity 24, and exits the cavity 24 via the vents 28, in the lids 12 atop the storage shells 10B. It is this chimney effect that creates the siphoning effect in the air-intake shell 10A. Referring now to FIGS. 7 and 8, the shells 10A, 10B form vertically oriented cylindrical cavities 24 therein. While the cavities 24 are cylindrical in shape, the cavities 24 are not limited to any specific shape, but can be designed to receive and store almost any shape of canister without departing from the spirit of the invention. The horizontal cross-sectional size and shape of the cavities 24 of the storage shells 10B are designed to generally correspond to the horizontal cross-sectional size and shape of the spent fuel canisters 80 (FIG. 8) that are to be stored therein. The horizontal cross-section of the cavities 24 of the storage shells 10B accommodate no more than one canister 80 of spent fuel. The horizontal cross-sections of the cavities 24 of the storage shells 10B are sized and shaped so that when spent fuel canisters 80 are positioned therein for storage, a small gap/clearance 25 exists between the outer side walls of the canisters 80 and the side walls of cavities 24. When the shells 10B and the canisters 80 are cylindrical in shape, the gaps 25 are annular gaps. In one embodiment, the diameter of the cavities 24 of the storage shells 10B is in the range of 5 to 7 feet, and more preferably approximately 6 feet. Designing the cavities 24 of the storage shells 10B so that a small gap 25 is formed between the side walls of the stored canisters 80 and the side walls of cavities 24 limit the degree the canisters 80 can move within the cavities 24 during a catastrophic event, thereby minimizing damage to the canisters 80 and the cavity walls and prohibiting the canisters 80 from tipping over within the cavities 24. These small gap 25 also facilitates flow of the heated air during spent nuclear fuel cooling. The exact size of the gap 25 can be controlled/designed to achieve the desired fluid flow dynamics and heat transfer capabilities for any given situation. In one embodiments, the gap 25 has a width of about 1 to 3 inches. Making the width of the gap 25 small also reduces radiation streaming. Support blocks 42 are provided on the floors 11 of the cavities 24 of the storage shells 10B so that the canisters 80 can be placed thereon. The support blocks 42 are circumferentially spaced from one another around the floor 11. When the canisters 80 are loaded into the cavities 24 of the storage shells 10B, the bottom surfaces 81 of canisters 80 rest on the support blocks 42, forming an inlet air plenum 27 between the bottom surfaces 81 of the canisters 80 and the floors 11 of the cavities 24. The support blocks 42 are made of low carbon steel and are preferably welded to the floors 11 of the cavities 26 of the storage shells 10B. Other suitable materials of construction include, without limitation, reinforced-concrete, stainless steel, and other metal alloys. The support blocks 42 also serve an energy/impact absorbing function. The support blocks 32 are preferably of a honeycomb grid style, such as those manufactured by Hexcel Corp., out of California, U.S. When the canisters 80 are positioned atop the support blocks 32 within the storage shells 10B, outlet air plenums 26 are formed between the top surfaces 82 of the canisters 80 and the bottom surfaces 30 of the lids 12. The outlet air plenums 36 are preferably a minimum of 3 inches in height, but can be any desired height. The exact height will be dictated by design considerations such as desired fluid flow dynamics, canister height, shell height, the depth of the cavities, the canister's heat load, etc. The cavity 24 of the air-intake shell 10A is deeper than the cavities 24 of the storage shells 10B and serves as a sump for ground water or rain water (if there is a leak and/or debris). The cavity 24 of the air-intake shell 24 is typically empty and, therefore, can be readily cleared of debris. Additionally, the piping network 50 is preferably sloped toward the air-intake shell 10A and away from the storage shells 10B so that any water seepage collects in the bottom of the cavity 24 of the air-intake shell 10A. If desired, a drain can be included at the bottom on the cavity 24 of air-intake shell 10B. In FIGS. 7 and 8, the illustrated embodiment of the manifold storage system 100 further comprises a concrete monolith 60 surrounding the shells 10A, 10B and piping network 50. The concrete monolith 60 provides the necessary radiation shielding for the spent fuel canisters 80 stored in the storage shells 10B. The concrete monolith 60 provides non-structural protection for shells 10A, 10B and the piping network 50. The entire height of the shells 10A, 10B are surrounded by the concrete monolith 60 with only the lids 12 protruding therefrom and resting atop its top surface. While the vents 28 that allow the warmed air to escape the storage shells 10B are illustrated as being located within the lids 12, the present invention is not so limited. For example, the vents 28 can be located in the concrete monolith 60 itself. In such an embodiment, the openings of the vents to the ambient air can be located in the top surface of the monolith 60 and a line of sight should not exist to the ambient. Similar to when the outlet vents are located in the lid, the outlet vents can take on a variety of shapes and/or configurations, such as S-shaped or L-shaped. In all embodiments of the present invention, it is preferred that the outlet openings of the vents 28 from the storage shells 10B be azimuthally and circumferentially separated from the intake openings of the vents 28 into the air-intake shell 10A to minimize interaction between inlet and outlet air streams. As discussed above, a layer of insulating material 20 is provided at the interface between storage shells 10B and the concrete monolith 60 (and optionally at the interface between the concrete monolith 60 and the piping network 50 and the air-intake shell 10A. The insulation 20 is provided to prevent excessive transmission of heat decay from the spent fuel canisters 80 to the concrete monolith 60, thus maintaining the bulk temperature of the concrete within FSAR limits. The insulation 20 also serves to minimize the heat-up of the incoming cooling air before it enters the cavities 24 of the storage shells 10B. As mentioned above, the manifold storage system 100 is particularly suited to effectuate the storage of spent nuclear fuel and other high level waste in a below grade environment. Referring to FIG. 8, the manifold storage system 100 is positioned so that the entire concrete monolith 60 (including the entire height of the storage shells 10B) is entirely below the grade level 73 at an ISFSI. The entire piping network 50 is also located deep underground. By positioning the manifold storage system 100 below grade level 73, the system 100 is unobtrusive in appearance and there is no danger of tipping over. The low profile of the underground manifold storage system 100 does not present a target for missile or other attacks. Additionally, the underground manifold storage system 100 does not have to contend with soil-structure interaction effects that magnify the free-field acceleration and potentially challenge the stability of an above ground free-standing overpack. While the entire height of the storage shells 10B is illustrated as being below grade level 73, in alternative embodiments a portion of the storage shells 10B can be allowed to protrude above the grade level 73. In such embodiments, at least a major portion of the height of the storage shells 10B are positioned below grade level 73. Any portion of the storage shells 10B that protrude above the grade level 73 must be surrounded by the necessary radiation shielding structure. In all embodiments, the storage shells 10B are sufficiently below grade level so that when canisters 80 of spent fuel are positioned in the cavities 24 for storage, the entire height of the canisters are below the grade level 73. This takes full advantage of the shielding effect of the surrounding soil at the ISFSI. Thus, the soil provides a degree of radiation shielding for spent fuel stored that can not be achieved in aboveground overpacks. With reference to the manifold storage system 100, a method of constructing the underground manifold storage system of FIG. 7 at an ISFSI or other location, will be discussed. First, a hole is dug into the ground at a desired position at the ISFSI having a desired depth. Once the hole is dug and its bottom properly leveled, a base foundation is placed at the bottom of the hole. The base can be a reinforced concrete slab designed to satisfy the load combinations of recognized industry standards, such as ACI-349. However, in some instances, depending on the load to be supported and/or the ground characteristics, the use of a base may be unnecessary. Once the foundation/base is properly positioned in the hole, the integral structure of FIG. 2 (which consists of the storage shells 10B, the air-intake shell 10A, and the piping network 50) is lowered into the hole in a vertical orientation until it rests atop the base. The integral structure then contacts and rests atop the top surface of the base. If desired, the integral structure can be bolted or otherwise secured to the base at this point to prohibit future movement of the integral structure with respect to the base. Once the integral structure is resting atop the base in the vertical orientation, the hole is filled with concrete to form the concrete monolith 60 around the integral structure. The concrete monolith also acts a moisture barrier to the below grade components. Alternatively, soil or an engineered fill can be used instead of concrete to fill the hole. Suitable engineered fills include, without limitation, gravel, crushed rock, concrete, sand, and the like. The desired engineered fill can be supplied to the hole by any means feasible, including manually, dumping, and the like. The concrete is supplied to the hole until it surrounds the integral structure and fills hole to a level where the concrete reaches a level that is approximately equal to the ground level 73. When the hole is filled, the concrete monolith 60 is formed. The shells 10A, 10B protrude slightly from the top surface of the concrete monolith 60 so that the cavities 24 of the shells 10A, 10B are accessible from above grade. Additionally, the lids 12 can be positioned atop the shells 10A, 10B as described above. Because the integral structure is hermetically sealed at all below grade junctures, below grade liquids can not enter into the cavities 24 of the shells 10A, 10B or the piping network 50. An embodiment of a method of using the underground manifold system 100 of FIGS. 7 and 8 to store a spent nuclear fuel canister 80 will now be discussed. Upon being removed from a spent fuel pool and treated for dry storage, the spent fuel canisters 80 is hermetically sealed and positioned in a transfer cask. The transfer cask is then carried by a cask crawler to an empty storage shell 10B for storage. Any suitable means of transporting the transfer cask to a position above the storage shell 10B can be used. For example, any suitable type of load-handling device, such as without limitation, a gantry crane, overhead crane, or other crane device can be used. In preparing the desired shell 10B to receive the canister 80, the lid 12 is removed so that the cavity 24 of the storage shell 10B is open and accessible from above. The cask crawler positions the transfer cask atop the storage shell 10B. After the transfer cask is properly secured to the top of the storage shell 10B, a bottom plate of the transfer cask is removed. If necessary, a suitable mating device can be used to secure the connection of the transfer cask to storage shell 10B and to remove the bottom plate of the transfer cask to an unobtrusive position. Such mating devices are well known in the art and are often used in canister transfer procedures. The canister 80 is then lowered by the cask crawler from the transfer cask into the cavity 24 of the storage shell 10B until the bottom surface 81 of the canister 80 contacts and rests atop the support blocks 42 on the floor 11 of the cavity 24. The canister 80 is free-standing in the cavity 24, free of anchors or other securing means. When resting on the support blocks 42 within the cavity 24 of the storage shell 10B, the entire height of the canister 80 is below the grade level 73. Once the canister 80 is positioned and resting in the cavity 24, the lid 12 is positioned atop the storage shell 10B, substantially enclosing the cavity 24. The lid 12 is then secured to the concrete monolith 60 via bolts or other means. When the canister 80 is so positioned within the cavity 24 of the storage shell 10B, an inlet air plenum 27 exists between the floor 11 and the bottom surface 81 of the canister 80. An outlet air plenum 27 exists between the bottom surface 30 of the lid 12 and the top surface 82 of the canister 80. A small annular gap 25 also exists between the side walls of the canister 80 and the wall of the storage shell 10B. As a result of the chimney effect caused by the heat emanating from the canister 80, cool air from the ambient is siphoned into the cavity 24 of the air-intake shell 10A via the vents 28 in its lid 12. This cool air is then siphoned through the piping network 50 and into the inlet air plenum 27 at the bottom of the cavity 24 of the storage shells 10B. This cool air is then warmed by the heat emanating from the spent fuel canister 80, rises in the cavity 24 via the annular gap 25 around the canister 80, and into the outlet air plenum 26 above the canister 80. This warmed air continues to rise until it exits the cavity 24 as heated air via the vents 28 in the lid 12 positioned atop the storage shell 10B. While the invention has been described and illustrated in sufficient detail that those skilled in this art can readily make and use it, various alternatives, modifications, and improvements should become readily apparent without departing from the spirit and scope of the invention. Specifically, in one embodiment, the shells 10A, 10B and/or the piping network 50 can be omitted. In this embodiment, the cavities of the shells and the passageways of the piping network can be formed directly into the concrete monolith if desired. |
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summary | ||
048797359 | abstract | An improved X-ray baggage inspection device having an input port with a baffle pivotally suspended from an upper edge to substantially occlude an upper selected region of the input port, leaving an open space adjacent to a baggage conveyor having a configuration suited for the passage of briefcase type baggage horizontally disposed upon the conveyor, but which will pivot inward in response to all types of baggage having a height exceeding a preselected distance between the conveyor and the lower edge of the baffle. |
claims | 1. A method for accelerated hydriding of a metallic substrate comprising:supplying a metallic substrate wherein said metal substrate has an activation energy for hydrogen adsorption (Easubstrate);cleaning the substrate surface by etching with an acid;coating at least a portion of a substrate surface of the metallic substrate with a metal having an activation energy for hydrogen adsorption (Eametal) that is lower than Easubstrate; hydriding the coated substrate at a temperature of less than or equal 500°C. and for a period of less than or equal to 24 hours;wherein said hydriding occurs in said metallic substrate. 2. The method of claim 1 wherein the metallic substrate comprises a metal selected from the group consisting of Ag, Au, Co, Cr, Cu, Fe, Ir, Mo, Nb, Ni, Os, Pd, Pt, Re, Rh, Su, Sc, Ta, Ti, V, W Y or Zr. 3. The method of claim 1 wherein the metallic substrate comprises a Zr alloy comprising containing tin, iron, chromium, nickel, and oxygen. 4. The method of claim 1 wherein said metallic substrate consists of a single metal having an activation energy for hydrogen adsorption and said metal in said coating has an activation energy for hydrogen adsorption that is less than said activation energy of said single metal substrate. 5. The method of claim 1 wherein said metallic substrate comprises a metal alloy where each metal in said alloy has an activation energy for hydrogen adsorption and said metal in said coating having an activation energy for hydrogen adsorption (Eametal)having an activation energy for hydrogen adsorption that is lower than any one of the metals in said metal alloy substrate. 6. The method of claim 1 wherein the coating of said metallic substrate surface with a metal having an activation energy for hydrogen adsorption (Eametal) that is lower than Easubstrate comprises treatment of the metallic substrate surface with a metal P-diketonate complex of the following formula:wherein M is a transition metal having said Eametal that is less than Easubstrate. 7. The method of claim 1 wherein the coating of said metallic substrate with a metal having an activation energy for hydrogen adsorption (Eametal) that is lower than Easubstrate comprises treatment of the metallic substrate surface with (1,5-cyclooctadiene) dimethyl platinum (II). 8. The method of claim 1 wherein the coating of said metallic substrate with a metal having an activation energy for hydrogen adsorption (Eametal) that is lower than Easubstrate comprises treatment of the metallic substrate surface with bis (1,5-cyclooctadiene) nickel (0). 9. The method of claim 6 wherein said metallic substrate comprises a Zr alloy comprising containing tin, iron, chromium, nickel, and oxygen. 10. The method of claim 9 wherein said coating containing a metal having an activation energy for hydrogen adsorption (Eametal) that is less than Easubstrate comprises a metal selected from Co, Cu, Ni, Pd or Pt. 11. The method of claim 1 wherein said portion of said substrate surface that is coated with said metal comprises 1-90% of said substrate surface. 12. The method of claim 1 wherein said portion of said substrate surface that is coated with said metal comprises 1-80% of said substrate surface. 13. The method of claim 1 wherein said portion of said substrate surface that is coated with said metal comprises 1-70% of said substrate surface. 14. The method of claim 1 wherein said portion of said substrate surface that is coated with said metal comprises 1-60% of said substrate surface. 15. The method of claim 1 wherein said portion of said substrate surface that is coated with said metal comprises 1-50% of said substrate surface. 16. The method of claim 1 wherein said hydriding of said substrate is carried out at a temperature of 50° C. to 500° C. 17. The method of claim 1 wherein said hydriding of said substrate is carried out at a temperature of 50° C. to 300° C. 18. The method of claim 1 wherein said hydriding of said substrate is carried out at a temperature of 50° C. to 300° C. for a period of 2-24 hours. |
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claims | 1. A specimen enclosure assembly for use in an electron microscope and comprising:a specimen enclosure dish having an aperture and defining an enclosed specimen placement volume;an electron beam permeable, fluid impermeable, cover scaling said specimen placement volume at said aperture from a volume outside said specimen enclosure assembly; anda pressure controller communicating with said enclosed specimen placement volume, said pressure controller being configured for maintaining said enclosed specimen placement volume at a pressure which exceeds a vapor pressure of a sample in said specimen placement volume and is greater than a pressure of a volume outside said specimen enclosure assembly, wherein a pressure differential across said cover does not exceed a threshold level at which rupture of said cover would occur. 2. A specimen enclosure assembly according to claim 1 and wherein said specimen enclosure dish is a rigid specimen enclosure dish. 3. A specimen enclosure assembly according to claim 1 and wherein said pressure controller comprises a passageway communicating with said enclosed specimen placement volume. 4. A specimen enclosure assembly according to claim 3 and wherein said passageway comprises a fluid conduit having a lumen whose cross section is sufficiently small so as to maintain said pressure, which exceeds said vapor pressure of said sample in said specimen placement volume and is greater than said pressure of said volume outside said specimen enclosure assembly. 5. A specimen enclosure assembly according to claim 4 and wherein said fluid conduit comprises a tube. 6. A specimen enclosure assembly according to claim 4 and wherein said lumen of said fluid conduit has a circular cross section having a diameter in the range of 50–150 micrometers. 7. A specimen enclosure assembly according to claim 4 and wherein said fluid conduit communicates with a fluid reservoir. 8. A specimen enclosure assembly according to claim 7 and wherein said fluid reservoir comprises at least one fluid channel in fluid communication with said fluid conduit and a passageway formed in said fluid reservoir for fluid communication with said volume outside said specimen enclosure assembly. 9. A specimen enclosure assembly according to claim 8 and wherein said fluid channel of said fluid reservoir comprises at least one tube. 10. A specimen enclosure assembly according to claim 8 and wherein said passageway formed in said fluid reservoir comprises a fluid conduit having a lumen whose cross section is sufficiently small so as to maintain a pressure, which exceeds said vapor pressure of said sample in said specimen placement volume and is greater than said pressure of said volume outside said specimen enclosure assembly and said fluid reservoir. 11. A specimen enclosure assembly according to claim 1 and also comprising a fluid ingress and egress assembly permitting supply and removal of fluid from said enclosed specimen placement volume. 12. A specimen enclosure assembly according to claim 11 and wherein said fluid ingress and egress assembly comprises at least two fluid conduits. 13. A specimen enclosure assembly according to claim 12 and wherein at least one of said at least two fluid conduits of said fluid ingress and egress assembly comprises at least one tube. 14. A method for constructing a specimen enclosure assembly for use in a scanning electron microscope comprising:providing a specimen enclosure dish having an aperture and defining an enclosed specimen placement volume;attaching an cicetion beam permeable, fluid impermeable, cover to said specimen placement volume at said aperture for sealing said aperture from a volume outside said specimen enclosure assembly; andproviding a pressure controller communicating with said enclosed specimen placement volume, said pressure controller being configured for maintaining said enclosed specimen placement volume at a pressure, which exceeds a vapor pressure of a sample in said specimen placement volume and is greater than a pressure of a volume outside said specimen enclosure assembly, wherein a pressure differential across said cover does not exceed a threshold level at which rupture of said cover would occur. 15. A method according to claim 14 and wherein said providing said pressure controller comprises forming in said specimen enclosure assembly a passageway communicating with said volume outside said specimen enclosure assembly. 16. A method according to claim 15 and wherein said providing said pressure controller comprises sealingly attaching to said passageway a fluid conduit having a lumen whose cross section is sufficiently small to maintain said pressure, which exceeds said vapor pressure of said sample in said specimen placement volume and is greater than said pressure of said volume outside said specimen enclosure assembly. 17. A method according to claim 16 wherein said fluid conduit comprises at least one tube. 18. A method according to claim 16 and wherein said lumen of said fluid conduit has a circular cross section having a diameter in the range of 50–150 micrometers. 19. A method according to claim 16 and also including providing a fluid reservoir in fluid communication with said specimen enclosure assembly. 20. A method according to claim 19 and wherein said fluid reservoir comprises at least one fluid channel in fluid communication with said fluid conduit and a passageway formed in said fluid reservoir for communicating with said volume outside said specimen enclosure assembly. 21. A method according to claim 20 and wherein said fluid channel of said fluid reservoir comprises at least one tube. 22. A method according to claim 20 and wherein said passageway formed in said fluid reservoir comprises a fluid conduit having a lumen whose cross section is sufficiently small so as to maintain a pressure, which exceeds said vapor pressure of said sample in said specimen placement volume and is greater than said pressure of a volume outside said specimen enclosure assembly and said fluid reservoir. 23. A method according to claim 20 and wherein said passageway formed in said fluid reservoir also comprises a tube with a circular cross section having a diameter in the range of 50–150 micrometers. 24. A method according to claim 14 and also comprising providing a fluid ingress and egress assembly communicating with said enclosed specimen placement volume for permitting supply and removal of fluid from said enclosed specimen placement volume. 25. A method according to claim 24 and wherein said fluid ingress and egress assembly comprises at least two fluid conduits. 26. A method according to claim 25 and wherein at least one of said at least two fluid conduits of said fluid ingress and egress assembly comprises at least one tube communicating with said specimen placement volume. |
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summary | ||
claims | 1. A spherical fusion reactor, comprising:a spherical solid target formed of a material that is disposed to provide an impact surface for fusion reactions of ions impacting the outer surface of this target and,a spherical shell of insulating material enclosing a space coaxially centered upon the centrally located target electrode and,an electrically insulated stalk suspending said spherical target fixedly and concentrically within said spherical shell and,a rarefied fusion reactive gas contained within spherical shell and,an insulating and cooling medium within which the spherical shell is suspended and,a thermally and electrically insulated enclosure whose partial radius is concentrically centered on spherical target and spherical shell containing said insulating and cooling medium and,a radiation absorbing and cooling medium within which said thermally and electrically insulated enclosure is suspended and,a heat absorbent container for containing said radiation absorbing and cooling medium and;a high voltage, high frequency alternating current, AC, power supply and,electrical interconnections for connecting said high voltage, high frequency AC power supply between the spherical solid target and earth ground. 2. The spherical fusion reactor of claim 1 wherein the spherical solid target is a titanium sphere which provides an impact surface for fusion reactions. 3. The spherical fusion reactor of claim 1 wherein the spherical solid target is composed of a material capable of permitting and surviving nuclear reactions. 4. The spherical fusion reactor of claim 1 wherein the enclosed space is defined as a space between the central spherical target and the inner surface of the enclosing spherical electrically insulated envelope. 5. The spherical fusion reactor of claim 4 wherein the defined space provides a location for the generation of an alternating electric field. 6. The spherical fusion reactor of claim 5 wherein the alternating electric field provides for the ionization of gases contained therein. 7. The spherical fusion reactor of claim 5 wherein the alternating electric field provides for the alternately radial outward acceleration and the alternately radial inward acceleration of ionized gases contained therein. 8. The spherical fusion reactor of claim 7 wherein the radial inward acceleration of ionized gases provides for ions impacting the spherical target, for the impact of ions with one another, and for such impacts to occur at fusion reactive velocities. 9. The spherical fusion reactor of claim 7 wherein the radial outward acceleration of ionized gases provides for a period of time during operation in which gas distribution allows for gas exchange. 10. The spherical fusion reactor of claim 1 wherein the fusion reactive gas is composed of the following gases: fusion reactive isotopes of Hydrogen or Helium, singularly or combination. 11. The spherical fusion reactor of claim 1 wherein the spherical shell of insulating material provides for the following: a sealed space containing gas at a predetermined pressure, an insulating surface providing a location for the stopping of the outward movement of electrons, a location of a equipotential of electric charge accumulation, and the development of a spherically symmetrical electric field. 12. The spherical fusion reactor of claim 1 wherein the fusion reactive gas is at a predetermined pressure from about 0.0001 to about 0.1 Torr. 13. The spherical fusion reactor of claim 1 wherein the insulating and cooling medium separates and distances RF, radio frequency, ground potential from locations: within the reactor chamber, along the inner surface of the reactor chamber, along the outer surface of the reactor chamber, and to places external to the thermally and electrically insulated enclosure. 14. The spherical fusion reactor of claim 13 wherein the separation and distancing of RF ground potential provides for: a symmetrically developed field within the reactor, an electric field of evenly developed intensity radially outward from the target to the ground plane, the prevention of internal arcing, and the reduction of capacitive reactance loading of the power supply. 15. The spherical fusion reactor of claim 1 wherein the high voltage, high frequency AC potential provided by the power supply is at a predetermined voltage from 100,000 volts AC RMS, root mean square to 500,000 volts AC RMS. 16. The spherical fusion reactor of claim 1 wherein the high voltage, high frequency AC potential provided by the power supply is at a predetermined frequency from 20,000 Hertz to 100,000 Hertz. 17. The spherical fusion reactor of claim 1 wherein the thermally and electrically insulated enclosure provides for the electrical isolation of RF ground potential to a location external to the space enclosed by said thermally and electrically insulated enclosure. 18. The spherical fusion reactor of claim 1 wherein the thermally and electrically insulated enclosure provides for: the outward passage of particulate and waveform radiations, and the restriction of the inward passage of thermal energy from the surrounding radiation absorbing and cooling medium. 19. The spherical fusion reactor of claim 1 wherein the absorbing and cooling medium provides for the absorption of emitted radiations released by the fusion reactor. 20. The spherical fusion reactor of claim 19 wherein the absorption of emitted radiations released by the reactor provides for: the harnessing of said radiations to do work, the shielding of the external environment of the reactor from radiations, and the cooling of the contained reactor and it's associated internal components. |
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047132132 | abstract | A nuclear reactor plant housed in a steel pressure vessel comprises a small high temperature reactor and a He/He heat exchanger located above the reactor, preferably followed by two circulating blowers connected in parallel. The installation further comprises at least one decay heat removal system, following in line the He/He heat exchanger in the direction of flow and with the entire flow of primary helium constantly flowing through it. In a preferred embodiment, the He/He heat exchanger is made up of two concentrically arranged coil bundles connected in succession, through which both the primary and the secondary helium are flowing in opposing directions. |
summary | ||
claims | 1. An illumination system comprising: a reflection type integrator having cylindrical surfaces, for reflecting light from a light source; and a condensing optical system for reflecting the light reflected by said cylindrical surfaces, and for illuminating an object, with the light, in an oblique direction with respect to a surface of the object. 2. An illuminating system comprising: a reflection type integrator having plural cylindrical surfaces, each cylindrical surface having a function for transforming light from a light source into light having a section of an arcuate shape; and a condensing optical system for superposing lights having arcuate sectional shapes, from said reflection type integrator, one upon another on an object. 3. An X-ray exposure apparatus comprising: an X-ray illumination optical system having (i) a reflection type integrator, with cylindrical surfaces, for reflecting an X-ray beam and (ii) a concave mirror arranged so as to reflect the X-ray beam reflected by said cylindrical surfaces and to illuminate a reflection type mask with the X-ray beam in an oblique direction with respect to a surface of the reflection type mask; and an X-ray projection optical system arranged so as to project a pattern of the reflection type mask with an X-ray beam reflected obliquely by the reflection type mask, onto a surface of a piece onto which the pattern is to be transferred. 4. An apparatus according to claim 3 , further comprising a scanning mechanism for relatively and scanningly moving the mask and the piece relative to said X-ray projection optical system. claim 3 5. An apparatus according to claim 3 , further comprising another concave mirror for projecting a parallel X-ray beam onto said integrator. claim 3 6. An apparatus according to claim 3 , wherein said reflection type integrator provides a secondary light source of X-rays, and said concave mirror has a focal point disposed at the position of said secondary light source. claim 3 7. An apparatus according to claim 3 , further comprising a stage for holding the reflection type mask thereon, wherein said stage, said reflection type integrator, and said concave mirror are arranged so that the X-ray beam is projected to the reflection type mask held by said stage, via said reflection type integrator and said concave mirror such that an illumination region of the X-ray beam defined on the reflection type mask has a rectangular shape. claim 3 8. An apparatus according to claim 3 , wherein said reflection type integrator has a reflection surface having a multilayered film formed thereon. claim 3 9. An apparatus according to claim 3 , further comprising a laser plasma X-ray source for emitting an X-ray beam. claim 3 10. An X-ray illumination apparatus, comprising: a reflection type integrator, having cylindrical surfaces, for reflecting an X-ray beam; and a concave mirror arranged so as to reflect the X-ray beam reflected by said cylindrical surfaces and to illuminate an object with the X-ray beam in an oblique direction with respect to a surface of the object. 11. An apparatus according to claim 10 , further comprising another concave mirror for projecting a parallel X-ray beam onto said integrator. claim 10 12. An apparatus according to claim 10 , wherein said reflection type integrator provides a secondary light source of X-rays, and said concave mirror has a focal point disposed at the position of said secondary light source. claim 10 13. An apparatus according to claim 10 , wherein said reflection type integrator has a reflection surface having a multilayered film formed thereon. claim 10 14. An apparatus according to claim 10 , further comprising a laser plasma X-ray source for emitting an X-ray beam. claim 10 15. A device manufacturing method, comprising the steps of: setting a reflection type mask having a pattern and a piece with respect to an X-ray exposure apparatus, wherein the X-ray exposure apparatus includes (1) an X-ray illumination optical system having (i) a reflection type integrator with cylindrical surfaces, for reflecting an X-ray beam and (ii) a concave mirror arranged so as to reflect the X-ray beam reflected by the cylindrical surfaces and to illuminate a reflection type mask with the X-ray beam in an oblique direction with respect to a surface of the reflection type mask, and (2) an X-ray projection optical system arranged so as to project the pattern of the reflection type mask with an X-ray beam reflected obliquely by the reflection type mask, onto a surface of the piece; and projecting the pattern onto the piece via the projection optical system, such that a circuit pattern is defined on the piece. 16. An illumination system comprising: a reflection type integrator having plural cylindrical surfaces, each cylindrical surface having a function for transforming an X-ray beam from an X-ray source into an X-ray beam having a section of an arcuate shape; and a concave mirror for superposing X-ray beams having arcuate sectional shapes from said reflecting type integrator, one upon another on an object. 17. An illumination system according to claim 16 , wherein the object is a reflection type mask, and the mask is illuminated obliquely. claim 16 18. An illumination system according to claim 16 , wherein a plane of incidence for incidence of the X-ray beam from the X-ray source upon said reflection type integrator is parallel to a generating line of each cylindrical surface. claim 16 19. An illumination system according to claim 16 , wherein said concave mirror comprises a rotational parabolic surface mirror. claim 16 20. An illumination system according to claim 16 , further comprising another concave mirror for projecting a parallel X-ray beam onto said integrator. claim 16 21. An illumination system according to claim 16 , wherein said reflection type integrator provides a secondary light source of X-rays, and said concave mirror has a focal point disposed at the position of said secondary light source. claim 16 22. An illumination system according to claim 16 , wherein said reflection type integrator has a reflection surface having a multilayered film formed thereon. claim 16 23. An illumination system according to claim 16 , wherein the X-ray source comprises a laser plasma X-ray source. claim 16 24. An illumination system according to claim 16 , wherein the X-ray beam is a soft X-ray beam. claim 16 25. An X-ray exposure apparatus comprising: an illumination system including (i) a reflection type integrator having plural cylindrical surfaces, each cylindrical surface having a function for transforming an X-ray beam from an X-ray source into an X-ray beam having a section of an arcuate shape, and (ii) a concave mirror for superposing X-ray beams having arcuate sectional shapes, from said reflection type integrator, one upon another on a reflection type mask; and a projection optical system for projecting a pattern of the reflection type mask onto a wafer, by use of X-rays reflected, by the reflection type mask, obliquely with respect to the surface of the refection type mask. 26. An apparatus according to claim 25 , further comprising a scanning mechanism for relatively and scanningly moving the mask and an object relative to said projection optical system. claim 25 27. An apparatus according to claim 25 , further comprising another concave mirror for projecting a parallel X-ray beam onto said integrator. claim 25 28. An apparatus according to claim 25 , wherein said reflection type integrator provides a secondary light source of X-rays, and said concave mirror has a focal point disposed at the position of said secondary light source. claim 25 29. An illumination system according to claim 25 , wherein said reflection type integrator has a reflection surface having a multilayered film formed thereon. claim 25 30. An illumination system according to claim 25 , wherein the X-ray source comprises a laser plasma X-ray source. claim 25 31. A device manufacturing method, comprising the steps of: exposing a wafer with a pattern of a reflection type mask, by use of an exposure apparatus which includes (i) an illumination system having (a) a reflection type integrator having plural cylindrical surfaces, each cylindrical surface having a function for transforming an X-ray beam from an X-ray source into an X-ray beam having a section of an arcuate shape, and (b) a concave mirror for superposing X-ray beams having arcuate sectional shapes, from the reflection type integrator, one upon another on the reflection type mask, and (ii) a projection optical system for projecting the pattern of the reflection type mask onto the wafer, by use of X-rays reflected, by the reflection type mask, obliquely with respect to the surface of the reflection type mask; and developing the exposed wafer. |
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claims | 1. A data management and networking system for automatically retrieving and storing data from a machine tool for distribution to a remote terminal over a network, the machine tool being operable to perform at least one machining operation on a workpiece and having at least one sensor operatively connected thereto for sensing a machine operation parameter, the at least one sensor having a first processing unit operatively connected thereto for receiving machine operation parameter data related to the machine operation parameter, the machine tool further having a controller operatively connected thereto and configured to output machining operation data related to the at least one machining operation to the first processing unit, the system comprising:a data storage unit for storing data for subsequent retrieval; anda second processing unit configured to automatically collect the machining operation data and the machine operation parameter data from the first processing unit and to apply an algorithm to the machine operation parameter data to generate at least one parametric representation of the machine operation parameter data, the second processing unit being further configured to:associate the at least one parametric representation with respective machining operation data and to send the associated parametric representation and machining operation data to the data storage unit, andautomatically collect alarm data from the first processing unit and associate the alarm data with the at least one parametric representation and respective machining operation data such that the associated parametric representation and machining operation data sent to the data storage unit includes the alarm data. 2. The system of claim 1, wherein the at least one parametric representation includes at least one of a maximum, a minimum, an average, an average root mean square, a maximum root mean square, a minimum root mean square, a root mean square summation, a kurtosis, a kurtosis average, a kurtosis maximum, a kurtosis minimum, a kurtosis standard deviation, energy band values, and frequency band amplitudes. 3. The system of claim 1, the at least one machining operation including machining time and non-machining time, wherein the second processing unit is further configured to separate out at least some data related to non-machining time before the associated parametric representation and machining operation data is sent to the data storage unit, thereby reducing the amount of data sent to the data storage unit. 4. The system of claim 3, wherein the data related to non-machining time is sampled at a predetermined frequency and the sample is sent to the data storage unit, thereby providing data related to operation of the machine tool when the workpiece is not being machined. 5. The system of claim 1, wherein the data related to the machine operation parameter is at least one of machine tool vibrations, machine tool current draw, machine tool temperature, machine tool torque, machine tool speed, and machine tool feed. 6. The system of claim 1, wherein the second processing unit is further configured to automatically collect, from the first processing unit, data related to operation of the machine tool under predetermined conditions, the predetermined conditions including the machine tool selecting a cutting tool and operating at a predetermined speed without work being performed on a workpiece, thereby providing information related to the machine tool independent of workpiece machining. 7. The system of claim 1, wherein the second processing unit includes a data bridge application configured to verity the validity of the machining operation data collected by the second processing unit. 8. The system of claim 1, wherein the data storage unit resides in a network server, the system further comprising a terminal linked to the server by a network, the terminal being configured for remote retrieval of the associated parametric representation and machining operation data. 9. The system of claim 8, a second machine tool being operable to perform at least one machining operation on a workpiece and having at least one sensor operatively connected thereto for sensing a machine operation parameter, the at least one sensor on the second machine tool having a third processing unit operatively connected thereto for receiving data related to the machine operation parameter of the second machine tool, the second machine tool further having a controller operatively connected thereto and configured to output data related to the at least one machining operation of the second machine tool to the third processing unit, the system further comprising:a fourth processing unit configured to automatically collect the machining operation data and the machine operation parameter data from the third processing unit and to apply an algorithm to the collected data to generate at least one parametric representation of the machine operation parameter data of the second machine tool, the fourth processing unit being further configured to associate the at least one parametric representation of the machine operation parameter data of the second machine tool with respective machining operation data of the second machine tool and to send the associated data of the second machine tool to the data storage unit, andwherein the network server is configured to associate the data sent from the second processing unit with respective data sent from the fourth processing unit, thereby facilitating analysis of a specific machining operation performed on different machine tools. 10. A data management and networking system for automatically retrieving and storing data from a machine tool for distribution to a remote terminal over a network, the machine tool being operable to perform at least one machining operation on a workpiece, the at least one machining operation including machining time and non-machining time, the machine tool having at least one sensor operatively connected thereto for sensing a machine operation parameter and for outputting signals related to the machine operation parameter to a first processing unit, the signals related to the machine operation parameter providing the first processing unit with machine operation parameter data, the machine tool further having a controller operatively connected thereto and configured to output signals related to the at least one machining operation to the first processing unit, the signals related to the at least one machining operation providing the first processing unit with machining operation data the system comprising:a data storage unit for storing data for subsequent retrieval; anda second processing unit configured to automatically collect the machining operation data and the machine operation parameter data from the first processing unit at a predetermined frequency greater than a cycle time for the at least one machining operation, and to separate out at least some data related to non-machining time, thereby leaving remaining machine operation parameter data, the second processing unit being further configured to apply an algorithm to the remaining machine operation parameter data to generate at least one parametric representation of the remaining machine operation parameter data, and to associate the machining operation data and the at least one parametric representation and to send the associated parametric representation and machining operation data to the data storage unit. 11. The system of claim 10, wherein the data related to non-machining time is sampled at a predetermined frequency and the sample is sent to the data storage unit, thereby providing data related to operation of the machine tool when the workpiece is not being machined. 12. The system of claim 10, wherein the at least one parametric representation includes at least one of a maximum, a minimum, an average, an average root mean square, a maximum root mean square, a minimum root mean square, a root mean square summation, a kurtosis, a kurtosis average, a kurtosis maximum, a kurtosis minimum, a kurtosis standard deviation, energy band values, and frequency band amplitudes. 13. The system of claim 10, wherein the data related to the machine operation parameter is at least one of machine tool vibrations, machine tool current draw, machine tool temperature, machine tool torque, machine tool speed, and machine tool feed. 14. The system of claim 10, wherein the data storage unit resides in a network server, the system further comprising a terminal linked to the server by a network, the terminal being configured for remote retrieval of the associated parametric representation and machining operation data. 15. The system of claim 14, a second machine tool being operable to perform at least one machining operation on a workpiece and having at least one sensor operatively connected thereto for sensing a machine operation parameter and for outputting signals related to the machine operation parameter to a third processing unit, the second machine tool further having a controller operatively connected thereto and configured to output signals related to the at least one machining operation of the second machine tool to the third processing unit, the system further comprising:a fourth processing unit configured to automatically collect the machining operation data and the machine operation parameter data from the third processing unit and to apply an algorithm to the collected data to generate at least one parametric representation of the machine operation parameter data of the second machine tool, the fourth processing unit being further configured to associate the at least one parametric representation of the machine operation parameter data of the second machine tool with respective machining operation data of the second machine tool and to send the associated data of the second machine tool to the data storage unit, andwherein the network server is configured to associate the data sent from the second processing unit with respective data sent from the fourth processing unit, thereby facilitating analysis of a specific machining operation performed on different machine tools. 16. A method for managing and networking data for a machine tool, comprising:performing a machining operation on a first workpiece and on a second workpiece, the machining operations on the first and second workpieces each including machining time and non-machining time;sensing a machine operation parameter while the machining operations are being performed on the first and second workpieces;capturing machine operation parameter data related to the sensed machine operation parameter for the machining operations performed on the first and second workpieces;capturing machining operation data related to the machining operations performed on the first and second workpieces;separating out at least some data related to the non-machining time from the captured machine operation parameter data for the machining operations performed on each of the first and second workpieces, thereby leaving remaining machine operation parameter data for each of the first and second workpieces;applying an algorithm to the remaining machine operation parameter data for each of the first and second workpieces to generate at least one parametric representation of the remaining machine operation parameter data for each of the first and second workpieces;associating the at least one parametric representation for each of the first and second workpieces with respective machining operation data; andstoring the associated parametric representation and machining operation data for each of the first and second workpieces for subsequent retrieval by a remote terminal over a network, thereby facilitating analysis of the machining operation performed on two workpieces. 17. The method of claim 16, wherein the first and second workpieces are machined on the same machine tool. 18. The method of claim 16, wherein the first and second workpieces are machined on different machine tools. |
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description | The invention relates to an irradiation device for proton and/or ion beam therapy according to claim 1. Such devices are known and are referred to as therapy facilities. Normally, they have a radiation source, which is implemented on base of a cyclotron or a synchrotron, with a beam guiding device as well as at least one therapy room, into which a treatment beam is directed. This beam is guided towards a treatment site, at which a patient to be treated may be placed. When accelerating beams and using them in patient treatment, secondary radiation is generated. In the energy range to be considered herein of up to some 100 MeV per nucleon, neutrons, protons, light ions and gamma radiation are generated in nuclear reactions (spallation reactions or fragmentations of projectile or target nuclei), when decelerating ions. Shielding the secondary radiation is primarily dominated by the generated neutron radiation. It is known that the largest part of an accelerated treatment beam is deposited in the tissue and generates there an highly forward-oriented—as seen in the direction of the treatment beam—cone of neutron radiation. Most of the generated neutrons exit the patient without interaction. Since the neutron radiation may have very high energies and the tenth value layer thickness equals one meter in standard concrete for example, particularly in the forward-direction of the incoming treatment beam, a substantial shielding effort is necessary. The constructional radiation protection design has to allow for those radiation-physical and geometric basic conditions. When planning treatment centres, especially clinical facilities for particle therapy, in which irradiation devices of the type addressed herein are used, often the problem arises that this facility has to be built in an existing infrastructure close to or inside of a larger treatment centre. Due to the complex accelerator technology and the associated beam guiding devices, particle therapy facilities with cyclotrons and synchrotrons have a large floor space required. For providing treatment beams, a branched system of beam guidings is often needed in order to direct the beams of the radiation source into therapy rooms. Thus, the access to these rooms is often limited. Often, it cannot be avoided that the access to a therapy room is arranged in the region of the neutron radiation so that often heavy shielding doors have to be installed, which on the one hand increase the space required, and on the other hand, delay the access to the patient. Therefore, it is an object of the invention to provide an irradiation device, which avoids the disadvantages stated herein. For solving this object, an irradiation device for proton and or ion beam therapy with a radiation source, having the features stated in claim 1 is proposed. It comprises a beam guiding device and at least one treatment site and a therapy room with an access, into which therapy room a treatment beam for treating a patient is directed. The irradiation device is characterized by several planes being provided. Thereby, the therapy room is arranged in a first plane. The treatment beam is directed from a second plane located above or below this plane into the therapy room and is directed towards the treatment site so that the treatment beam is directed away from the access. The space required can be reduced considerably, because parts of the irradiation device are arranged on different planes. Furthermore, the beam guiding device can be displaced out of the plane, in which the therapy room is arranged. Therewith, the access to the therapy room can be chosen independently of the beam guiding. With the irradiation device according to the invention it is provided that in the therapy room, there is provided a shielding being open to the treatment site. The shielding protects the further regions of the therapy room against the radiation. The access to the therapy room is arranged on the side of the shielding which faces away the treatment site so that at least one labyrinth leading from the access to the treatment site can be provided laterally offset in relation to the treatment beam proceeding in the therapy room and to the shielding. This labyrinth is not hit by the treatment beam. The neutron radiation, which may be generated downstream of the treatment site, does not hit the labyrinth, too. Therefore, the access to the therapy room can be protected against reflected radiation by the labyrinth solely, particularly, heavy shielding doors can be omitted. Therewith, an easy and fast access to the treatment site results. The shielding effort can be reduced, because the neutron radiation generated in the therapy room in the region of the treatment site just does not hit the access and the labyrinth between the access and the treatment site, as it is the case with the therapy room according to DE 102 35 116 A1. This decreases the space required by the irradiation device. With a preferred embodiment of the irradiation device, it is provided that a labyrinth is provided between the access and the treatment site on both sides of the shielding. One of the two can be used as access, and the other one as exit, so that using the therapy room can be optimized: The removal of patients does not hinder the access so that exchanging the patients is possible quickly. A further preferred embodiment of the irradiation device is characterized in that rooms serving for the pre-treatment and for the after-treatment of patients and for the stay of further persons respectively may also be arranged on the first plane, in which the therapy room is located. This enables an optimization of the course of the therapy preparation (computer tomography, x-raying for verification of position etc.) and of the therapy procedure. A further embodiment of the irradiation device is characterized in that the treatment beam entering the therapy room is directed towards the treatment site but not towards the rooms mentioned. Therefore, these rooms are in any case not be contaminated by the treatment beam and by the neutron radiation generated during treatment. Thereby, a special shielding between the entrance region and the mentioned rooms is not even necessary, because the therapy room may be arranged in such a manner that the neutron is directed into the soil for example, where a contamination of patients, treatment staff and persons, who operate and maintain the irradiation device is avoided. With a further preferred embodiment of the irradiation device, it is provided that the radiation source is arranged in a third plane. The individual elements like radiation source, beam guiding device and therapy rooms may quasi be nested one upon the other to minimize the space required, because the irradiation device is distributed over several planes and because a further plane is opened here. Though, it remains provided that the beam directed towards the treatment site is directed away from the rooms, in which patients and further persons may stay. Further embodiments result from the remaining subordinate claims. The schematic diagram according to FIG. 1 shows an irradiation device 1, which comprises a radiation source 3, beam guiding device 5 and a therapy room 7 with a treatment site 9, at which a patient can be exposed to a treatment beam 13. The schematic diagram shows that the therapy room is located on a first plane E1, while the beam guiding device 5 is arranged on an second plane E2 and the radiation source 3 is arranged on a third plane E3, wherein here the planes E2 and E3 are arranged below the first plane E1. But it is very well imaginable that the beam guiding device 5 and the therapy room 7 are arranged below the radiation source 3. From the schematic diagram according to FIG. 1 it is apparent that the beam exiting the beam guiding device 5 enters the therapy room 7 in an entrance region E. FIG. 1 shows further that a beam deflecting device SU as well as a beam forming device SF are provided in the therapy room 7 above the beam guiding device 5. Next to the therapy room 7 a room 15 is indicated, which may serve the preparation of patients and in which operating staff for the irradiation device may stay. The illustration shows that the radiation source 3, the beam guiding device 5 and the therapy room 7 as well as further rooms associated with the irradiation device 1, here room 15, may be arranged on top of each other, which results in a considerable saving of space. Moreover it appears that here the beam guiding device 5 is arranged below the therapy room 7 and thus does not disturb the access to the therapy room 7. With the irradiation device according to FIG. 1 it is provided that the access 17 is located in the transit region between the room 15 and the therapy room 7. In the illustration according to FIG. 1 one therefore enters the therapy room 7 from room 15 by going from left to right through the access 17. In the illustration according to FIG. 1, one accordingly reaches from therapy room 7 from right to left into the room 15. The entrance region E is located inside the therapy room 7 in a distance to the right of the access 17 and in a distance in the left of the treatment site 9. In no case the access 17 is affected by the treatment beam 13, because the treatment beam 13 starting at the entrance region E passes through the therapy room 7 from left to right, Also, neutron radiation given beyond the treatment site 9 hits the access 17 in no case. As seen from the entrance region E, it proceeds to the right and is rather guided into the soil following the therapy room 7, the soil which is also provided above the therapy room 7. Therefore, it will become apparent that—seen in the direction of the treatment beam 13—no special shielding has to be provided beyond the treatment site 9, because, as mentioned, the neutron radiation 19 is guided into the soil 21 and therefore might not reach the room 15 in no case, which—seen in the direction of the treatment beam 13—is arranged at the side of the therapy room 7 opposite to the treatment site 9. Also, the figure shows clearly that the access 17 is stressed neither by the treatment beam 7 nor by the neutron radiation 19. The lateral view shows that the beam guiding device 5 is constructed such that a partial beam T of the radiation source 3 is directed into the therapy room 7 in the entrance region E from below through the floor of the therapy room 7 and is there deflected in such a manner that it proceeds parallel to the floor B, thus horizontally towards the treatment site 9. Deflecting the partial beam T may also be chosen in such a manner that it enters the therapy room 7 in an angle, or in such a manner, however, that it is deflected inside the therapy room 7 in such a way that it does not proceed parallel to the floor B, but in angle to the floor. Therewith, the treatment beam 13 proceeds in an angle to the floor B in the treatment site 9 also. Therefore, it is apparent that the irradiation device 1 may variably be designed concerning this aspect also. Thereby, it is also possible that the treatment beam 13 enters the therapy room 7 in an angle through the ceiling of the therapy room 7 or that there it is deflected in such a manner that it hits the treatment site 9 not parallel to the floor B, but transversely from above. This radiation path has the advantage that the treatment beam 13 and the neutron radiation 19 are guided into the soil 21 from above so that an optimal absorption is ensured. With a radiation path transversely upwards, it would have to be ensured that the soil 21 above the therapy room 7 is thick enough or that a shielding is there provided additionally. In some cases, a gantry can be set aside, because here it is made possible to direct the partial beam T and particularly the treatment beam 13 onto the treatment site 9 in an angle. The illustration also shows that the entrance region E into the therapy room 7 of the partial beam T is located in a distance to access 17 into the therapy room 7 and in a distance to the treatment site 9. Thereby, it becomes particularly apparent that region between the access 17 and the entrance region E is free, because here the beam guiding device 5 is arranged below the floor B. In FIG. 1, it is indicated that the room 15 may be part of a treatment centre, a research centre or a hospital 23. Also above the therapy room 7, there is soil 21. By the arrangement below the ground level 25, the shielding by concrete and other materials may be reduced to a minimum above the therapy room 7 also. Overall, voluminous shielding masses may be avoided inside the irradiation device 1 and the hospital 23, because natural shielding materials, namely soil 21, may be used, which additionally brings down costs of installation, but of deconstruction also. Overall, the following advantages result: By arranging the elements of the irradiation device 1 on different planes E1, E2, and E3 it is particularly possible to provide the beam guiding device 5 in another plane than the therapy room 7 so that the access 17 to this room and the rooms 15, which are necessary in conjunction with using the therapy room 7, may be optimally arranged and that the course of therapy preparation and of therapy procedure is undisturbed. Furthermore, the constructional radiation protection for the radiation source 3, the beam guiding device 5 and for the therapy room 7 is guaranteed. Shielding materials are used very efficiently. Particularly, expensive materials like concrete and the like may be substituted by soil. Furthermore, the individual elements of the irradiation device 1 may be arranged compactly and the space usage may be optimized. Incidentally, the linking to existing treatment or research centres, particularly to hospitals, is possible without additional radiation exposure by treatment beams or neutron radiation arising there. In top view, FIG. 2 shows the irradiation device 1 depicted in FIG. 1. Here, the radiation source 3 may clearly be seen, which comprises a pre-accelerator V, also referred to as LINAC, and a synchrotron S. The radiation source 3 is located in the lowest plane E3. Above this plane, the beam guiding device 5 with several beam branchings 27, 29 and 31 is located in the plane E2. Above the plane E2, here there are four indicated therapy rooms 7/1, 7/2, 7/3, and 7/4. From the illustration according to FIG. 2, it becomes apparent that, seen from the radiation source 3, beyond the beam branchings 27, 29, and 31, partial beams T are given, which are fed into the therapy rooms 7/1 to 7/4. Because here the therapy rooms are identically constructed, only the therapy room 7 will be described in the following. The further explanations will be given by means of the therapy room 7/1 rightmost depicted in FIG. 2; in the following, this room will generally be referred to as therapy room 7. The access 17 to the therapy room 7 is oriented in such a manner that it points in the direction of the partial beam T, wherein it will be apparent from the comments on FIG. 1 that the partial beam T proceeds below the floor B of a therapy room 7 and in the first place enters—here from below—the therapy room 7. It is self-explanatory that such a beam leading-in may also occur from above. In the illustration according to FIG. 2, the isocentre at the treatment site 9 is indicated by a point. The treatment beam 13 entering the therapy room 7 in the entrance region E is directed towards this isocentre. Neutron radiation given beyond the treatment site 9 is directed away the access 17 and enters the soil 21 surrounding the therapy room 7. Here, it becomes apparent also that the access 17 is stressed neither by the treatment beam 13 nor by the neutron radiation 19. The entrance region E is surrounded by a quasi U-shaped shielding 33 being open towards the treatment site 9. As seen from the access 17 towards the treatment site 9, there is at least one labyrinth L beside the shielding 33. With the embodiment depicted in FIG. 2, a labyrinth is provided each to the right and to the left of the shielding 33. One of those labyrinths may be used as access, the other as exit, in order to optimize the therapy procedure. In larger scale, FIG. 3 shows a therapy room 7 being apparent from FIG. 2. Same parts are referred to by same referrals so that it is insofar referred to the preceding description. The therapy room 7 is surrounded by a conventional shielding wall 35, for example by a concrete wall with a thickness of one meter. The thickness of the wall 35 may be fitted to the different use cases; as well the shielding material. So it is known for example from DE 103 12 271 A1 to use gypsum for shielding. Outside the therapy room 7, there is the soil 21. With the illustration according to FIG. 3, the access 17 of the therapy room 7 is given on the left side. Inside this room, the entrance region E of the partial beam T depicted in the FIGS. 1 and 2 may be seen in a distance to the access 17. The partial beam is surrounded by a shielding 33 being practically located in the middle of the therapy room 7. From the schematic diagram according to FIG. 3 it is, as already from FIG. 1, apparent that one may enter the therapy room 7 via the access 17 without being exposed to any hazard by the treatment beam 13. Therefore, one may reach the shielding 33 from a room 15, mentioned in FIG. 1, which room is arranged left to the access 17. The treatment beam 13 exits the beam tube being apparently here with the usual deflecting and scanning components, which are here arranged in the therapy room 7. The treatment beam is directed onto the treatment site 9, at which a couch for the patient is provided. By the double-headed arrow 39 it is indicated that the couch may be rotatable. The treatment beam 13 exits the beam tube 37 and the shielding 33, which is open towards the treatment site 9, and hits the treatment site 9. Neutron radiation 19 given beyond the treatment site 9 is directed away from the access 17 and enters the soil 21 through the wall 35. With the embodiment depicted in FIG. 3, a labyrinth is provided each to the right and to the left of the shielding 33—seen in the direction of the treatment beam 13. Those labyrinths serve to absorb radiation reflected by the treatment site 9. Thereby, it is possible to implement the access 17 without a heavy shielding door, what facilitates and accelerates the accessibility to the treatment site 9. With the embodiment depicted here, it is further provided that the shielding 33 comprises a shielding reinforcement 41 preferably made from iron in its region, which also points to the access 17, opposite to the treatment site 9. The labyrinths L located to the right and to the left of the entrance region E and of the shielding 33 inside the therapy room 7 are here implemented by steps 43 and 45 provided at the inside of the wall 35 and at the out side of the shielding 33. But it is also imaginable here to provide wall sections projecting into the aisles of the labyrinths L. From the top view according to FIG. 3, it is apparent that the therapy room 7 is constructed symmetrically, wherein also the shielding 33 surrounds the entrance region E symmetrically. The shielding 33 provides two wall regions 33a and 33b located opposite to each other, between which the entrance region E is arranged. At the end of the shielding facing the access 17, the wall regions 33a and 33b are connected with each other by a base section 33c so that the essentially U-shaped form of the shielding 33 is implemented. On the side facing the base section 33c, the wall regions 33a and 33b diverge substantially funnel-shaped towards the treatment site 9. With other words: The region of the shielding 33 being between the wall regions dilate, seen downstream the entrance region E, towards the treatment site 9 so that a funnel-shaped absorbing region for neutron radiation reflected by the treatment site 9 results. Therefore, this radiation is optimally absorbed by the shielding 33 so that the radiation exposure is reduced to a minimum on the side of the shielding facing the treatment site 9, thus in the region of the access 17 and of rooms 15 following thereto. With the embodiment depicted in FIG. 3, the shielding 33 is free-standing in the therapy room 7 so that on both sides, an aisle results between the wall 35 of the therapy room 7 and the outside of the shielding 33, namely the labyrinths L mentioned above. With this embodiment of the therapy room 7, it is provided that the limiting wall of the therapy room 7 facing away the access 17 and located to the right of the treatment site 9 has a region protruding into the soil 21 so that operating staff may easily compass the treatment site 9 or a couch respectively provided there for the patient provided. Concerning its dimensions, this protrusion is fittable to the space required. FIG. 4 shows an embodiment of a therapy room 7, which is modified in comparison with the one depicted in FIG. 3. Same parts are referred to by same referrals so that it is insofar referred to the description of FIG. 3. The therapy room 7 according to FIG. 4 is constructed a little bit easier than the one depicted in FIG. 3: The limiting wall of the therapy room 7 facing the access 17 may be arranged in a slightly larger distance to the shielding 33 than provided in FIG. 3 so that there is enough space to encompass a patient couch on the side facing the entrance site E. For that purpose, here the limiting wall of the therapy room is constructed straightly; thus the protrusion depicted in FIG. 3 is set aside, what reduces the manufacturing costs of the therapy room 7. But here, the same basic principle is implemented, too: The mean neutron radiation cone, which is directed from the treatment site 9 to the right, is guided through the wall 35 of the therapy room 7 into the soil 21. Neutron radiation reflected by the treatment site 9 is absorbed by the shielding 33 and therefore reaches the access extremely attenuated, if at all. Incidentally, the interior construction of the therapy room, particularly of the shielding 33, identical to the embodiment shown in FIG. 3 so that it is referred to the preceding comments to avoid repetitions. FIG. 5 shows a modified embodiment of a therapy room 7. Same parts are referred to by same referrals. Insofar, it is referred to the preceding comments to avoid repetitions. It becomes apparent that the second embodiment is constructed asymmetrically. But the basic structure is identical: The therapy room 7 is surrounded by a wall 35, which may consist of usual shielding concrete or the like. Outside the therapy room 7, there is soil 21. Left in FIG. 5, the access 17 to the therapy room 7 can be seen. In a distance to this, there is the entrance region E, in which a partial beam T, as explained in the FIGS. 1 to 3, enters the interior of the therapy room 7 through the floor of the therapy room 7 and is there deflected as well as formed. Since in the region of the access 17, the partial beam T proceeds below the floor of the therapy room 7 or above the ceiling, the region between the access 17 and the shielding 33 is not disturbed and accessible without danger. The treatment beam 13 is guided by an usual beam tube 37 towards the treatment site 9, wherein the treatment beam 13 exits to the right, as seen from the beam tube 37, so that the access 17 is not exposed in any way. Neutron radiation generated in the region of the treatment site 9 is directed to the right and enters the soil 21 through the wall 35, so that here a specially powerful shielding made from concrete or the like can be omitted here. The entrance region E is surrounded by a shielding 33 being open towards the treatment site 9, wherein in FIG. 4 above the shielding a labyrinth L is made, which has wall section 47 protruding into the aisle of the labyrinth. But it is imaginable here to provide steps, as explained by means of FIG. 3. The therapy room 7 is constructed very compactly, because a labyrinth located below the shielding 33 is omitted and a part of the shielding is formed by a region of the wall 35. Therefore, concerning its basic design, the shielding 33 is identical to the one described by means of FIG. 3: it has an upper wall region 33a and a facing lower wall region 33b. The entrance region E is located between these wall sections. Here, the beam deflecting device SU and the beam forming device SF are arranged, too. The two wall regions 33a and 33b are connected with each other by a base section 33c, so that again the U-shaped shielding 33 is formed as described above. Also here, a shielding reinforcement 41 is provided in the region of the base section 33c, as it was described above. Therefore, the shielding 33 is closed towards the access 17 and open towards the treatment site 9. Also here, it is provided that the wall regions 33a and 33b dilate towards the treatment site 9 on the side facing away the base section 33c, so that a region absorbing reflected neutron radiation is formed, as it is also given with the embodiments according to the FIGS. 3 and 4. In comparison with the embodiments according to the FIGS. 3 and 4, a difference has to be seen in the fact that a wall section of the shielding 33, here the lower wall region 33b, is part of the wall 35 surrounding the therapy room 7, while the opposite wall region 33a is free-standing in the therapy room 7. With the embodiment depicted in FIG. 5 also, as may be seen from the embodiments depicted in the FIGS. 1 to 4, the therapy room 7 is freely accessible via the access 17. No special shielding door is needed here. The treatment beam 13 reaches the therapy room 7 via the entrance region E, is there deflected and formed and exits via the beam tube 37 and therefore reaches the treatment site 9. Thereby, the beam direction is away from the access 17. Neutron radiation 19 generated at the treatment site 9 is also directed away from the access 17, thereby also away from regions located in the left of the access 17. Radiation reflected by the treatment site 9 is optimally shielded against the access 17 by the shielding 33, particularly, also due to its funnel-shaped dilation towards the treatment site 9. It is common to all embodiments that a limited part of the therapy room 7 from the entrance region E to the treatment site 9 and a region located downstream of the treatment site, exposed to neutron radiation 19 is shielded against radiation very well. The shielding 33 being used for this purpose surrounds the entrance region E on both sides, furthermore the beam deflecting device SU and the beam forming device SF. Moreover, the shielding device 33 protects against reflected neutron radiation, so that the remaining regions of the therapy room are exposed to a very highly reduced radiation level. By the fact that the treatment beam 13 reaches the therapy room from above or from below in the entrance region E, on the side of the shielding facing the treatment site 9, there are free regions, namely the access 17, via which the therapy room can be entered unhindered. Therefore, the therapy room 7 may optimally be used, because no disturbing structural elements are present from the access 17 till the shielding 33. Incidentally, it is ensured that the treatment beam 13 is, as seen from the access 17, directed away towards the treatment site 9. The shielding 33 is located on an imaginary connecting line between the access 17 and the treatment site 9, wherein just the treatment beam 13 and therewith neutron radiation emanating from the treatment site 9 is directed away from the access. Therefore, no further special shielding measures are needed in the region of the access 17 and of rooms following there to the left. Radiation generated in the entrance region E and neutron radiation reflected by the treatment site 9 are optimally absorbed by the shielding 33. Therefore, also with the embodiment depicted in FIG. 5, the treatment beam 13 does not enter the therapy room 7 through a side wall but through the floor. In principle, a leading-in through the ceiling would be possible, too. Beam guiding devices as described by means of the FIGS. 1 and 2 are therefore arranged below or above of the therapy room 7 and do therefore not disturb the access 17, which is hit neither by the treatment beam 13 nor by the neutron radiation 19. Scattered radiation being generated in the region of the treatment site 9 is caught by the shielding 33 and by the labyrinth L so effectively that heavy shielding doors can be omitted in the region of the access 17. By means of the FIGS. 6 to 9, different alternatives for arranging the therapy rooms shall be discussed: FIG. 6 shows a number of symmetrically arranged therapy rooms 7, as they were already discussed in the FIGS. 2, 3, and 4. Preferably, they are formed identically and have labyrinths L arranged symmetrically to the middle axis of the therapy room 7. The labyrinths form a connection between the access 17 and the treatment site 9, and are routed past in the right and in the left of the shielding 33. In all cases, depicting the beam tube 37 was omitted, because in this context the arrangement of the therapy rooms is important only. They are placed as close as possible, so that touch points and common wall regions result quasi. The accesses of all therapy rooms 7 lead to a room 15, which serves for preparing and medically caring patients, and may comprise X-ray regions 49 and bedding rooms for patients as well as central control rooms for assistant medical technicians, who operate and monitor the irradiation device 1, particularly the devices assigned to the several therapy rooms 7. The X-ray regions 49 particularly serve to verify the positions of the patients. In this context, it is explicitly pointed out that X-ray diagnostics for verifying the position may be carried out in the therapy rooms 7, too. According to FIG. 6, the therapy rooms 7 are arranged in a curved manner, in order to be able to use the common space 15 optimally, and to limit the total space-required for the therapy rooms 7 to a minimum. Also here, the therapy rooms 7 are, as indicated by a line, surrounded by soil 21, so that neutron radiation 19 given downstream of the treatment site 9 is absorbed by the soil 21, and expensive shieldings for that purpose can be omitted. FIG. 7 shows another embodiment of an arrangement of therapy rooms 7. Here, therapy rooms, as they were described by means of FIG. 5, are arranged in a curved manner. Therefore, here, in contrast to FIG. 6, asymmetrical therapy rooms are arranged in a curved manner, wherein their accesses lead to a common room 15, in which patients may be subject to precaution and aftercare and may lie. Furthermore, X-ray regions 49 may be provided here as well as central control rooms not depicted here in detail for operating the irradiation device 1 and for carrying out the treatment of patients in the therapy rooms 7. Also with the embodiment depicted here, as in FIGS. 2 and 6, the therapy rooms 7 are arranged in such a manner that the treatment beams 13 and the neutron radiation 19 are directed away outward and hit the soil 21 surrounding the therapy rooms 7. The room 15 is exposed neither to the treatment beam 13 of the several therapy rooms nor to the neutron radiation, which may be generated in the region of the treatment sites 9. Finally, FIG. 8 shows an irradiation device 1 with a number of therapy rooms 7, as they were discussed by means of FIG. 5. Therefore, here it is a matter of asymmetrical therapy rooms 7 with one labyrinth only. As from FIG. 5, it is apparent from the illustration according to FIG. 8 that quasi a bulge is given in the region of the treatment site 9, but that incidentally the therapy rooms 7 have side walls proceeding in parallel to each other. With the illustration according to FIG. 8, the therapy rooms 7 are arranged in parallel to each other and are offset in longitudinal direction to each other, so that the parallel wall regions of two adjacent therapy rooms rest with each other, and therefore a minimal space-required is given. Also here, the accesses 17 of the therapy rooms 7 lead to a room 15, which may comprise X-ray regions 49 or central control rooms not depicted here in detail. Also here, the arrangement and the alignment of the therapy rooms 7 are chosen in such a manner that the treatment beams 13 and the neutron radiation 19 are directed away from the access 17 and the room 15 and are shielded by the soil 21 surrounding the therapy rooms. Since the treatment beams 13 and the neutron radiation 19 do not expose the access 17 here, too, shielding doors can be omitted, so that an easy and quick access to the treatment sites 9 is possible. But with the asymmetrical therapy rooms 7, one has to assume that the labyrinth L may only be used alternatively as entrance or as exit, respectively. Finally, in FIG. 9 yet an embodiment is depicted, with which four therapy rooms 7 of an irradiation device 1 are illustrated. These are arranged in a mirrored manner with respect to an indicated middle plane M, wherein also the therapy rooms are formed in a mirrored manner to the right and to the left of the middle plane M: In case of the therapy rooms located to the right of the middle plane M, the labyrinth is in the left of the shielding 33 of the entrance region E, in case of the therapy rooms located in the left of the middle plane, in the right thereof. The accesses 17 of the therapy rooms again lead to a common room 15, in which patients may be pre-treated and after-treated. Here, X-ray regions may be seen, too. Also here, central control rooms may be provided, which, however, are not depicted. Also here, the therapy rooms 7 are arranged in a space-saving, close-packed manner, wherein it is ensured in each case that the treatment beams 13 and the neutron radiation 19 do not hit the accesses 17 and the common room 15. In each case, the neutron radiation 19 is rather directed outwards, and is absorbed by the soil 21 surrounding the therapy rooms 7. In total, it is apparent that the irradiation device 1 may provide different therapy rooms 7, which may be arranged to each other in different ways. When doing so, symmetrically constructed therapy rooms with two labyrinths and asymmetrically constructed therapy rooms with one labyrinth each may be employed. As necessary, it is very well possible to combine symmetrical and asymmetrical therapy rooms in order to ensure an optimal space utilization. In any case it is guaranteed that at least the therapy rooms 7 and the beam guiding devices 5 are arranged on different planes, so that the accesses 17 to the therapy rooms 7 may be arranged optimally. The beams each are leaded into the interior of a therapy room in a distance to the limiting walls thereof, so that inside the therapy rooms 7 in each case, an entrance region E may be surrounded by an own shielding, and the access 17 is protected against the treatment beam 13 and the neutron radiation 19. In total, it is apparent that the irradiation device 1 is constructed very compactly and that the distribution of therapy room 7, radiation source 3 and/or beam guiding device 5 on different planes quasi allows nesting the elements of the irradiation device 1, what results in a very compact design. Moreover, the therapy rooms are constructed in such a manner that the beam might not be guided through a side wall of the therapy room 7, but through the ceiling thereof into the interior and may be directed to the treatment site 9. By doing so, it is possible to position the access 17 in such a manner that it is exposed neither by the treatment beam 13 nor by the neutron radiation 19, and that a labyrinth may be formed between the access 17 and the treatment site 9. The labyrinth may be formed symmetrically to the entrance region E of the beam into the therapy room 7, and has an entrance and an exit. The therapy rooms will become yet more compact, if only one single labyrinth is provided, which serves as entrance as well as exit. The irradiation device 1 may be positioned closely to a treatment or research centre as well as to a hospital 23, because the treatment beams 13 and particularly the neutron radiation 19 is directed away from the access 17 and away from the rooms 15 preceding the access 17. When doing so, expensive shielding measures are omitted, because the treatment beam 13 and the neutron radiation 19 penetrate the soil 21 surrounding the therapy room 7, and are caught by it. Therapy rooms constructed in such a manner may be arranged closely to each other in a curved manner or in parallel to each other, wherein an offset stringing together of therapy rooms 7 is possible, too. By doing so, a common room 15 may also be associated with several therapy rooms 7, what further optimizes the space use. Particularly from the FIGS. 8 and 9, it becomes apparent that with the arrangement of therapy rooms shown here, wall sections may be formed thinner or may be omitted totally, in order to save shielding material and space. Particularly, this applies in regions, in which wall sections of adjacent therapy rooms are adjoin. Here, in case of usual devices, often a wall thickness results, which exceeds the thickness being desired for shielding purposes. |
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description | Impurities are implanted into semiconductor devices for a variety of reasons, including introducing electrons and holes into the semiconductor substrate in order to locally change the conductive properties of the substrate. For example, silicon has four electrons in the outer ring. Phosphorus has five electrons in its outer ring, one more than silicon. Boron has three electrons in its outer ring, one fewer electron than silicon. Boron can be used to introduce holes into the substrate. Phosphorous can be used to introduce electrons into the substrate. To enable implantation, the impurities are implanted as ions having one fewer electron than the neutral species. During the implantation process, the electron deficit can be used to determine how much impurity has been implanted. Specifically, it is not possible to accurately count the number of ions (or atoms) leaving the ion gun. Therefore, a predetermined portion of the ions is directed to an ion counter instead of the semiconductor wafer(s). The ion counter may be embodied has a disk faraday. When an ion strikes the disk faraday, an electron is pulled to the disk faraday in order to neutralize the ion. The number of electrons pulled to the disk faraday is counted using a current meter. It is presumed that the number of ions striking in the disk faraday is proportional to the number of ions striking and entering the semiconductor wafer. The current (electrons per second) represents the rate at which impurities are introduced into the wafer. If the implanter detects that one area of the wafer is receiving impurities at a slower rate than other areas of the wafer, then the implanter spends more time implanting on the deficient area. In this manner, the implanter can work to achieve uniform total dosing across the surface of the wafer. When the ions hit the semiconductor wafer, they may destroy a portion of a resist layer formed on the wafer. This process releases an outgas into the implant chamber, which would otherwise kept at a very low pressure. Electrons from the outgas can neutralize a portion of the ions, before the ions reach the disk faraday or the semiconductor wafer. Although the ions are neutralized by the resist outgas (rather than being neutralized at the disk faraday or within the semiconductor wafer), the neutral species is still implanted and still causes the desired change to the substrate. However, because the neutral species contains the correct number of electrons, there is not disk faraday current flow for neutralization. Therefore, the neutral species are not counted. In order to count the impurities implanted as atoms, rather than ions, a pressure sensor is used. As the pressure increases from resist outgassing, it is presumed that a larger percentage of the impurities are introduced into the wafer as atoms rather than ions. The following equation represents how pressure is taken into consideration to determine the number of ions implanted.IDISK=IDOSE·e−KP In the above equation, IDISK is the current flowing to the disk faraday. This current is proportional to the number of ions implanted. IDISK is the rate at which impurities (ions+atoms) are implanted. P is the pressure as sensed by the ion gauge/pressure sensor within the device. K is a factor determined by the engineer and input into the implanter. K represents how a pressure change is presumed to effect ion neutralization. Instead of, or in addition to, the K-factor shown above, a pressure compensation factor P-COMP can be used. The mathematical relationship between K and P-COMP is as follows: P - COMP = 100 ( ⅇ K / 10000 - 1 ) or K = ln ( 1 + P - COMP 100 ) ( 10000 ) Because K and P-COMP are interchangeable through simple math, the term “pressure compensation factor” is used hereinafter to represent both K and P-COMP with the understanding that the two parameters are interchangeable through the above mathematical relationships. The process chamber is kept at a very low pressure. By detecting pressure increases, the ion gauge is able to calculate the number of ions within the chamber. The chamber is held at a near-vacuum through cryogenic pumps. The conventional ion gauge is located outside of the process chamber, near a cryogenic pump. However, this location reduces the accuracy of the pressure reading for two reasons. First, resist outgassing causes dramatic increase of pressure near the wafer. This high pressure is localized and drops with distance. At the location of the ion gauge, the pressure has dropped significantly, causing an artificially low pressure reading. Second, the ion gauge is in close proximity to the cryogenic pump, which reduces chamber pressure. The cryogenic pump also reduces the pressure reading of the ion gauge. With high energy implants, the pressure increase is sufficiently high that the implanter can accommodate the pressure inaccuracies. At the outside chamber location, the ion gauge can accurately sense pressure changes produced by implanting high energy impurities, such as arsenic. That is, the high energy of arsenic causes a lot of resist outgassing, and hence a large pressure increases. By positioning the pressure sensor away from the chamber, near the cryogenic pump, pressure changes are reduced to a range where the ion gauge operates efficiently. While the conventional position is acceptable for high energy impurities, more recent technologies require lower energy implants that work well with the present system. For example, when nitrogen is implanted, the ion gauge detects very little pressure increase. However, nitrogen implantation causes a substantial amount of resist outgassing and beam neutralization, which are not detected by the ion gauge in its current location. One way to address this deficiency is to use a large K value in calculating pressure compensation. The large K value effectively amplifies the pressure readings of the ion gauge. For example, typical P-COMP values for a high energy impurities such as arsenic range from 8 to 60, depending on the beam current, species and energy. For low energy nitrogen beams, a significantly higher P-COMP value is necessary. Perhaps P-COMP would be in excess of 150. The above high P-COMP values make ion gauge inaccuracies critical in terms of dose accuracy. A high pressure compensation value exposes the process to a non-acceptable risk of dose error. The risk stems from the pressure read out variability and instability that are inherent in any ion gauge. Unstable pressure readings lead to varying dose, even when all other variables are perfectly stable. Experience has shown that for very high P-COMP values, it is difficult to repeatedly produce wafers with the same dosing. High P-COMP values introduce wafer-to-wafer variations. Another approach to addressing the problem is to reduce the beam current until resist outgassing does not significantly affect the process. Specifically, the beam current is reduced to a point that free electrons produced by resist outgassing are consumed by the cryogenic pump(s) as soon as they are released. In this manner, there are not enough electrons to appreciably neutralize the ion beam. However, reducing the beam current lowers the throughput of the implanter and reduces the tool capacity. To address these and/or different concerns, the inventors propose a device to implant impurities into a semiconductor wafer. The device has a process chamber having a wall, a pressure compensation unit, a disk to support a plurality of semiconductor wafers within the process chamber. The disk has a radialy extending slot arranged among the wafers. A beam gun is positioned within the process chamber to shoot an ion beam at the semiconductor wafers. A cryo pump minimizes the pressure within the process chamber. A first ion gauge is positioned between the process chamber and the cryo pump. A second ion gauge extends through the wall of the process chamber. A switching device selectively connects the first or second ion gauge to the pressure compensation unit. A faraday receives ions from the ion gun after the ions travel through the slot in the disk. A current meter counts the number of electrons flowing to the disk faraday to neutralize the ions. Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. FIG. 1A is a schematic side view of an ion implanter 10. The implanter may be an Axcelis GSD™ platform implanter. The implanter has a chamber 105, which is kept at a very low pressure by cryo pumps, one of which is represented by reference numeral 115. Within the chamber 105, a beam gun 125 produces an ion beam 120 which is focused on wafers 210. The wafers 210 are placed around a disk 200. A faraday 100 is provided under the disk 200 to sense beam current. A first pressure sensor 135 is provided outside of the chamber 105 in the vicinity of the cryo pump 115. This location corresponds with a conventional location and is useful for implanting ions that produce a large pressure response during resist outgassing. A second pressure sensor 145 is provided within the chamber 105. The second pressure sensor (an ion gauge) 145 is useful for the implanting impurities that exhibit a smaller pressure response with resist outgassing. Both the first and second pressure sensors 135, 145 are connected to a pressure sensor controller 155. The pressure sensor controller 155 is in turn connected to a user interface 165. On the user interface 165, the pressure from one of the pressure sensors 135, 145 is displayed together with an indication of which pressure sensor or gauge is being used. FIG. 1B is a schematic side view of the pressure sensor controller 155. Connectors 175, 185 are provided respectively for the first and second pressure sensors 135, 145. Through these connectors 175, 185, the pressure sensors 135, 145 communicate with the pressure sensor controller 155. A user interface input 190 receives information regarding the recipe from the user interface 165. A connector 195 allows various signals within the pressure sensor controller 155 to be manipulated. An output 198 supplies information regarding the detected pressure (or detected number of ions) and information regarding which pressure sensor is active. The information regarding the detected pressure may be provided as an analog output. The information from the output 198 may be provided to the user interface 165 or to a separate display on the implanter 10. In FIG. 1A an additional ion gauge 145 is added to the implanter 10. This ion gauge 145 is located to close to the wafer 210 such that it can more accurately determine pressure changes. In the process chamber 105, the ion gauge 145 is closer to where resist outgassing, pressure increases and beam neutralization occurs. This placement works well for recipes having a high ratio of beam neutralization to pressure increase. In order to place the ion gauge 145 within the process chamber 105, a hole is drilled in the process chamber 105. The ion gauge mounting hardware is installed. The ion gauge 145 is installed and connected to the ion gauge controller 155. Under resist outgassing conditions, the beam current drops due to recombination. Recombination is when an ion is combined with an electron and becomes a neutral atom. The neutral atom is still implanted into the wafer but not counted by the disk faraday of the implanter. Therefore, for every neutralized ion at a specific wafer area, the implanter focuses the beam on the wafer for an additional time long enough to implant one additional ion. This causes an overdose of one ion. The amount of resist exposed to the beam is greatest at the vertical center of the wafer. If pressure compensation is not used, the vertical center of the wafer is overdosed relative to the top and bottom areas of the wafer. FIG. 2A is a schematic side view of a disk faraday used to determine beam current, which is in turn used to count the number of implanted ions. FIG. 2B is a top view of a disk holding a plurality of wafers for implantation. In FIG. 2B, a plurality of wafers 210 are arranged on the disk 200. A disk slot 220 is positioned among the wafers 210. An ion gun focuses a beam spot at one point on the wafers 210 as the disk 200 rotates. FIG. 2C is an enlarged top view of the disk shown in FIG. 2B. In FIG. 2C, reference numeral 230 represents a beam spot, where the beam is currently being focused. If the disk 200 is being rotated in a clockwise direction with the beam spot 230 focused as shown, the beam spot 230 will move from wafer to wafer, implanting impurities toward the top of each wafer 210. According to one embodiment, the disk rotates at approximately 1200 rpm. As the disk rotates, a portion of the beam will extend through the disk via the disk slot 220. At this point, the beam spot 230 is directed through the disk 200 to the disk faraday 100 shown in FIG. 2A. The beam 120 contains ions. The disk faraday 100 is grounded. Electrons flow into the disk faraday 100 through a current meter 110 to thereby neutralize each of the ions. The current meter 110 counts the number of electrons, producing a current reading. FIG. 3 is a side view of the disk faraday 100 shown in FIG. 2A and the disk 200 shown in FIGS. 2B and 2C. The disk 200 moves vertically up and down with respect to a horizontally traveling beam 120. This ensures that the beam 120 strikes the complete area of each wafer 210 mounted on the disk. Referring to FIG. 2C, the vertical travel path of the beam is such that the beam travels slightly past the top of the wafer 212 (where it is shown in FIG. 2C). When the beam is slightly above wafer 212, the beam changes direction to travel toward the bottom of the wafer 212. After traveling slightly paste the bottom of the wafer 212, the beam again changes direction so as to head toward the top of the wafer 212. The beam therefore stops and changes directions when the beam is not on the wafer. The amount of outgassing is proportional to the amount of time that the beam is on the resist, which can be translated to the time the beam spends on the wafer. The beam spends time on the wafer, on the disk slot and the on the disk between, above and below the wafers. FIG. 4 is a schematic representation of the time spent on the wafers during the beam travel path. When the beam is above or below the wafer, there is no time spent on the wafers. All of the time during the disk rotation is spent on the disk or possibly on the disk slot. When the beam is at the top and bottom of the wafer, there is a minimum time spent on the wafer. During each revolution of the disk 200, the beam 220 spends most of its time on the disk 200, rather than on a wafer 210. At the middle of the wafer, the beam spends the maximum time on the wafer. FIG. 5 shows the correlation between the time the beam spends on the wafer at various disk positions (FIG. 4), the amount of outgassing, the number of neutral species implanted and the amount of overdose if the neutral species are ignored in the calculations. When the beam is at the center of the wafer, there is more outgassing and beam neutralization. The current meter 110 detects fewer implanted ions. Without accounting for the neutralized atoms, the disk moves more slowly when the beam is focused at the center of the wafer. This allows the beam to implant more ions on the center of the wafer. Because the implanted neutralized atoms are ignored, this results an overdose in the center of the wafer. At the beginning of the implantation process, there is more resist to be burnt. There is therefore more resist outgassing at the beginning of the implantation process than at the end of the implantation process. Pressure is proportional to the amount of outgassing. FIG. 6 is an X-Y plot of outgassing as a function of disk radius. As can be seen, the largest pressure increase happens on the first pass of the ion beam over the wafer. There is less of a pressure increase with each succeeding pass. For each pass, the pressure increase is greatest at the center of the wafer. It should be noted that the beam may be traveling in opposite directions for each succeeding pass. For example, the first pass may be a downward pass, the second pass may be an upward pass, the third pass may be a downward pass, and so on. The outgassing is reduced with the each pass due to the decreasing availability of hydrogen and resist solvents in the organic resist. This is known as resist conditioning. FIG. 7 shows an X-Y plot of the uncompensated beam current IDISK as a function of disk radius. FIG. 7 represents the current detected by the disk faraway. Comparing FIGS. 6 and 7, it can be seen that when there is maximum outgassing, the disk faraday detects the minimum current. This is because the outgassing causes the ions to recombine before implantation. The dose system controls the vertical disk speed. It attempts to minimize vertical dose non-uniformity by changing the vertical disk speed in response to changes in the measured beam current IDISK. A drop in measured beam current causes the vertical disk speed to decrease at that vertical position so that an underdosing situation does not occur. The vertical disk speed may be varied while maintaining the same disk rotational speed. If the beam current drop is “legitimate” meaning it is caused by something that effects the number of implanted impurities (ions plus atoms), then dose uniformity is optimized by the vertical speed reduction. If the beam current drops due to beam neutralization, then overdosing occurs at the vertical position on the wafer that is being hit by the beam when the speed reduction occurs. Pressure changes are considered in order to differentiate between legitimate current drops and neutralization current drops. With the following equation, IDISK to control vertical disk speed:IDISK=IDOSE·e−KP For one revolution of the disk, the relative area struck by the beam spot is related to the circumference. That is, the closer the beam is to the center of the disk (not center of the wafer), the less area (wafers plus exposed disk) that is covered by the beam spot during each revolution. As the beam spot gets further towards the outer periphery of the disk, more area (wafers plus exposed disk) is covered during each revolution. Since the area changes for a given disk position and the disk rotational speed does not change, the horizontal speed of the beam over the outer areas disk is greater. Toward the outer portions of the disk, fewer impurities are implanted per area for each rotation. To compensate for this and to ensure dose uniformity, the vertical speed of the disk changes. FIG. 8A is a plot of vertical disk speed versus disk position. The vertical speed is slowest towards the top of the wafer, where the horizontal disk speed is greatest. A slower vertical disk speed effectively allows the beam to implant on a given area for more revolutions the disk. FIG. 8B is a plot of vertical disk speed versus disk position when outgassing causes a drop in beam current. The flat portion of the curve shown in FIG. 8B demonstrates that when there is outgassing toward the middle of the wafer, the vertical disk speed is slower than would otherwise be necessary. FIG. 9 is a sheet resistance map for a non-uniformly dosed wafer. Towards the middle of the wafer, the sheet resistance is less than the average sheet resistance. This indicates that there is overdosing toward the middle of the wafer. The sheet resistance of FIG. 4 can be obtained through testing, by placing probes at different positions on the wafer. Some implanters minimize dose non-uniformity by ignoring beam current fluctuations. This can be done, for example, by not monitoring the beam current during “beam-on-wafer” time periods. That is, a disk faraday is not used during implanting. However, if there is a problem upstream from the wafer during implanting, which cases fewer impurities to enter the wafer, then this problem cannot be recognized. Alternatively, non-uniformity can be minimized by increasing the capacity of the cryo pumps. With more powerful pumps, the resist outgassing electrons are sucked into the cryo pumps as they are released. The inventors, however, are avoiding non-uniformities with pressure compensation and the formula below.IMEASURED=IDOSE·e−KPIMEASURED is also referred as IDISK, and is current detected by the disk faraday. IDOSE is the corrected dose current. The K-factor, which is input by the operator, either magnifies or diminishes the effect of pressure on the corrected dose current IDOSE. If K is large, then an inaccuracy in IMEASURED produces a large inaccuracy in the compensated beam current IDOSE While K should be high enough to assure cross wafer dose uniformity, a small K is better in terms of dealing with noise from the pressure sensor and avoiding inaccuracies. FIGS. 10A and 10B are plots of beam current and pressure versus disk position for a higher energy implant. The pressure readings for FIG. 10B were produced by an ion gauge at the conventional position. In FIG. 10A, the uncorrected beam current is plotted versus disk position. The uncorrected beam current is the current that is detected through the disk faraday. The bottom curve in FIG. 10A shows that for the first pass across the wafer, there is the greatest drop in beam current. This can be explained by reviewing FIG. 10B which shows that the pressure increase is greatest on the first pass over the wafer. On the first pass, there is maximum resist outgassing, which causes the pressure increase and introduces free electrons into the chamber in the vicinity of the wafer. The electrons cause ion beam neutralization and hence a drop in the detected current. Because of the significant pressure response detected, a smaller P-COMP value is sufficient to compensate for beam neutralization. FIGS. 11A and 11B are plots of uncorrected beam current and pressure versus disk position for a lower power implant such as nitrogen. Again, the beam current is the beam current detected by a disk faraday. Like FIG. 10B, the pressure readings for FIG. 11B were produced by an ion gauge at the conventional position. As can be seen, significant beam neutralization (current drop) only produces small changes in the pressure reading. A very high P-COMP value is necessary in order to flatten out the beam current (IDOSE) versus disk position curve. The reason for this phenomenon is not yet fully understood. It could be that, under similar process conditions other than impurity species, low energy implants, such as N+, are much more likely to accept an electron (neutralization) than BF2+, P+, or AS+. This would result in excessive/greater beam current drop, as a function of pressure. Conditional P-COMP systems and ion gauges, while being very accurate for other (high energy) implant processes, are not sufficient for N+. One solution to this problem is to increase the ion gauge response in order to bring it up to the magnitude with which the implanter works. In order to achieve this, pressure must be monitored close to where the resist outgassing occurs. Conventional ion gauges resides upstream of the beam gate, outside of the process chamber, next to the cryo pump. This location is too far from the outgassing source (and too close to the cryo) to detect more subtle pressure fluctuations. Placing the pressure monitor in the process chamber results in the pressure response shown in FIG. 11C, which is another plot of pressure versus disk radius. Unlike FIGS. 10B and 11B, the pressure readings for FIG. 11C were produced by an ion gauge located within the process chamber. Comparing FIG. 11C with FIG. 11B, it can be seen that if the ion gauge is located within the process chamber for low energy implants, a sufficient pressure response is produced. Placing an ion gauge in the process chamber results in much smaller P-COMP values than an ion gauge placed at the conventional location. For example, a P-COMP of 7 is possible instead of a P-COMP in excess of 150. This is a dramatic improvement as it drastically reduces dose inaccuracies/functuations and increases dose repeatability by reducing the affect of ion gauge inaccuracies. Placing an ion gauge in the process chamber, while desirable for low energy impurities, such as N+, makes the pressure readings unacceptable for the other processes such as high energy implants. Therefore, the ion gauge within the process chamber does not replace the ion gauge located downstream, toward a cryo pump. Both ion gauges should be installed. Depending on the process/recipe, the operator should switch between the ion gauges. An alternate solution is to place two ion gauges within the process chamber. The first ion gauges should be a highly sensitive ion gauge, which accurately detects pressures below a given threshold, perhaps 1×10−4 Torr. A second ion gauge is positioned within the process chamber, perhaps at the same general location as the first pressure gauge. The second ion gauge is less sensitive than the first ion gauge. For example, the second ion gauge can detect pressures above the given threshold, perhaps 1×10−4 Torr. The first ion gauge is used for low energy implants, and the second ion gauge is used for high energy implants. FIG. 12 is a schematic view of a switching circuit to switch between the first and second ion gauge (pressure sensors) shown in FIG. 1A. FIG. 12 shows the connector 195 of the pressure sensor controller 155 shown in FIGS. 1 and 2. Pin number 9 is a beam line gas signal. Beam line gas is a parameter that serves to focus the beam on the wafer. The beam line gas is a parameter that may not be used for either high energy implants, such as BF2+, P+, As+, and low energy implants such as nitrogen. Although beam line gas is shown in FIG. 12, any recipe parameter that is unused for both high and low energy implants could be used for the circuit shown in FIG. 12. The beam line gas is part of the recipe, which may be developed through the user interface shown in FIG. 1A. Because beam line gas is not used for either high or low energy implants, the recipes would normally call for beam line gas to be off. However, the inventors propose using the beam line gas parameter to select an ion gauge. Thus, the beam line gas recipe parameter now serves an important function. Pin number 8 is a digital interface signal. The digital interface signal is low when one of the pressure sensors is to be on and high when both of the pressure sensors are to be off. Pin number 7 is the controller input for pressure sensor 2. Pin number 6 is the controller input for pressure sensor 1. If only one of the two pressure sensors (ion gauges) were to be used, the digital interface signal could simply be jumped from pin number 8 to either pin number 7 or pin number 6. The circuit shown in FIG. 12 allows the user to select between either the first or second pressure sensor and allows the operator to select the appropriate pressure sensor automatically. The circuit shown in FIG. 12 has two delay circuits and two relays. Delay circuit 1210 is connected to relay circuit 1215, and delay circuit 1220 is connected to relay circuit 1225. Both of the delay circuits 1210 and 1220 have two inputs, for a total of four inputs. Each of these four inputs is connected to the beam line gas signal. The delay circuits 1210 and 1220 are substantially the same. However, inverters U3A and U3B cause the delay circuits to operate at different times. Transistor T2 is similar to transistor T5. However, transistor T2 is connected to a resistor R8, and transistor T5 is connected to an inverter U3A. Transistor T3 is similar to transistor T6. However, transistor T3 is connected to an inverter U3B, and transistor T6 is connected to a resistor R15. With these connections, transistor T2 is on when transistor T5 is off. Transistor T3 is off when transistor T6 is on. Because of the similarities between the two delay circuits 1210, 1220, only one will be described in detail. Transistor T2 through the capacitor C2 and resistor R5 form a delay circuit together with the associated components. The RC time constant of C2 and R5 determines how long transistor T2 must be on before a signal is received at U5B. U5B together with R9 and T4 assure that an accurate voltage signal is output even if the input to U5B fluctuates. They also serve to control the timing of the delay circuit such that the delay does not change with changing temperature, for example. When transistor T2 is on and a signal is eventually output through U5B, and R9 and T4, the second pressure sensor is turned on through pin 7 of the ion gauge controller. When transistor T2 is on, transistor T3 is off. Thus, transistor T3 has no effect when the delay circuit is working to activate the second pressure sensor. However, when transistor T2 is off, transistor T3 is on. The purpose of transistor T3 is to discharge the capacitor C2. In this manner, when transistor T2 is again turned on, the RC time constant will not be altered by any charge stored from a previous operation. The delay circuit 1220 operates substantially the same as the delay circuit 1210 with the exception that the components U5A, R10 and T7 produce an on signal when the components U5B, R9 and T4 produce an off signal. The delay circuits 1210 and 1220 are connected to the pressure sensor controller through respective relay circuits 1215 and 1225. Both relay circuits 1215 and 1225 receive the digital input signal from pin 8. When the relay circuit 1215 or 1225 receives a high signal from the delay circuit 1210 or 1220, the relay circuit 1215 or 1225 effectively passes the digital input signal from pin 8 to pin 7 or 6. The relay circuits 1215 and 1225 are used instead of a direct connection in order to provide insulation from the rest of the device. In some applications, it is certainly possible to eliminate the relay circuits 1215 and 1225. The devices labeled U5A and U5B together form a hex buffer between each delay circuit and the associated relay circuits. The hex buffer is a logic device which outputs a predetermined voltage when an input voltage is greater than or equal to a certain voltage. For example, referring to hex buffer U5A, when pin 3 reaches a voltage greater than or equal to five volts, a five-voltage signal will be output on pin 2. FIG. 12 shows an indicator light LED2. This indicator light can be used to inform the operator which pressure sensor is operating. Alternatively, this can be done through the user interface shown in FIG. 1A. Although the pressure gauge controller has inputs for two ion gauges, it is not designed to switch between the two ion gauges. Thus, an instantaneous digital switching signal is ineffective. With the circuit shown in FIG. 12, sufficient delay is provided. The delay emulates an operator mechanically changing a jumper between pins 6 and 7. This jumper would connect one of pins 6 and 7 to pin 8. When the pressure sensor/ion gauge controller is instructed to operate either the first or second pressure sensor, the pressure sensor controller communicates with the appropriate pressure sensor through the connector 175 or the connector 185 (see FIG. 1B), as described previously. The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. |
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047044136 | description | DESCRIPTION OF THE INVENTION The present invention will be described in detail hereinbelow. The matrix resin for the resin composition having an electromagnetic wave shielding effect, according to the present invention, is a copolymer of an ethylenic unsaturated nitrile, a diene rubber and an aromatic vinyl compound or a mixture thereof with another copolymer of an ethylenic unsaturated nitrile and an aromatic vinyl compound. The ethylenic unsaturated nitrile used in the invention includes, for example, acrylonitrile, methacrylonitrile, ethacrylonitrile and methyl methacrylonitrile. The particularly preferred are acrylonitrile and methacrylonitrile. The diene rubber used in the invention includes one or more of conjugated 1,3-dienes, such as butadiene, isoprene, 2-chloro-1,3-butadiene, 1-chloro-1,3-butadiene and piperylene, which form rubbery polymers, the particularly preferred being butadiene. The aromatic vinyl compound used in the invention includes, for example, styrene, .alpha.-methylstyrene, vinyltoluene, divinylbenzene and chlorostyrene, which may be used singly or in combination. A favorable result can be obtained, in the present invention, when styrene is used singly as the aromatic vinyl compound. A more favorable result may be obtained when the copolymer of the ethylenic unsaturated nitrile, the diene rubber and the aromatic vinyl compound is a graft copolymer prepared by graft-copolymerizing 20 to 75 parts, preferably 20 to 60 parts, by weight of a diene rubber or a diene-containing polymer containing not less than 50 wt% of diene rubber with 80 to 25 parts, preferably 80 to 40 parts, by weight of a mixture of an ethylenic unsaturated nitrile and an aromatic vinyl compound. If a mixture of a copolymer of ethylenic unsaturated nitrile, a diene rubber and an aromatic vinyl compound with another copolymer of an ethyleneic unsaturated nitrile and an aromatic vinyl compound is used, the mixing ratio of the former to the latter may range within 25 to 99 parts by weight of the former to 1 to 75 parts by weight of the latter, preferably within 35 to 65 parts by weight of the former to 65 to 35 parts by weight of the latter. If the mixing ratio is out of the aforementioned range, the moldability and the properties of the resultant composition are deteriorated. The process for the preparation of the copolymers and the mixture thereof are well-known in the art, and disclosed, for example, in the specification of Japanese Patent Publication No. 37675/1976. The description of the prior publication referred to above will be incorporated herein as a reference. Specific examples of the plasticizers used in the composition of the invention include phthalic acid esters, such as dibutyl phthalate and di-2-ethylhexyl phthalate; fatty acid esters, such as di-2-ethylhexyl adipate, dibutyl sebacate, di-2-ethylhexyl sebacate and di-2-ethylhexyl azelate; epoxides, such as epoxidized fatty acid monoesters, epoxidized soybean oil and epoxidized linseed oil; phosphoric acid esters, such as tricresyl phosphate, tri-2-ethylhexyl phosphate and tributoxyethyl phosphate; ethers, such as triethyleneglycol di-2-ethyl butylate, dibutylcarbitol adipate and dibutylcarbitol formal; polyesters, such as adipic acid polyesters, sebacic acid polyesters and azelaic acid polyesters; and chlorinated plasticizers, such as chlorinated aliphatic esters and chlorinated paraffins. Particularly preferred plasticizers are phthalic acid esters, phosphoric acid esters and fatty acid esters. When it is desired to provide the resin composition of the present invention with the flame-retarding property, a plasticizer selected from phosphoric acid derivatives and ethylene/propylene terpolymers is used. Specific examples of the flame-retarding plasticizers of phosphoric acid derivatives are tri(2-ethylhexyl) phosphate, 2-ethylhexyl diphenyl phosphate, tributoxyethyl phosphate, triphenyl phosphate, cresyl diphenyl phosphate, isodecyl diphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, mixed aryl phosphates, phenyl/isopropyl phenyl phosphate, mixed triaryl phosphates and tris(chloroethyl) phosphate. Particularly preferred results can be obtained by using 2-ethylhexyl diphenyl phosphate and tricresyl phosphate singly or in combination. The best flame-retarding property may be obtained by using the ethylene/propylene terpolymer as the plasticizer in the resin composition of the invention. The ethylene/propylene terpolymer used as the plasticizer include copolymers of ethylene and propylene polymerized with a small amount of unsaturated compound as the third component. The terpolymer may be composed of 50 to 80 mol% of ethylene, 20 to 50 mol% of propylene and 0.5 to 10 mol% of an unsaturated third compound, and the most preferable composition contains 60 to 70 mol% of ethylene, 30 to 40 mol% of propylene and 0.5 to 5 mol% of an unsaturated third compound. Dienes and/or trienes may be generally used as the third unsaturated compound, inter alia 1,4-hexadiene, dicyclopentadiene and ethylidene norbornene are particularly preferred because of their excellent copolymerizability and low cost. The content of the plasticizer in the resin composition of the invention may range within 1 to 25 wt%, preferably within 2 to 15 wt%. If the content of the plasticizer is less than 1 wt%, the viscosity of the molten resin composition at the kneading step becomes so high as to cause breakdown of the carbon fibers and to result in insufficient dispersion of the fibers, thereby to lower the electromagnetic wave shielding effect and to deteriorate the moldability of the resultant resin composition. On the contrary, if the content of the plasticizer is more than 25 wt%, the physical properties including the resistance to heat of the resin composition are lowered and the molded products become sticky due to bleeding of the plasticizer. When the flame-retarding plasticizer is used, satisfactory flame-retarding effect cannot be expected if the content thereof is less than 1 wt%. When a phosphoric acid derivative is used as the flame-retarding plasticizer, particularly preferable content thereof ranges within 2 to 8 wt%. On the other hand, when the ethylene/propylene terpolymer is used as the plasticizer, particularly preferable content thereof ranges within 5 to 10 wt%. One or a mixture of two or more of carbonized polyacrylonitrile fibers, carbonized pitch fibers and carbonized phenolic compound fibers may be used in the resin composition of the invention. Superior electromagnetic wave shielding effect can be attained by using the carbonized polyacrylonitrile fibers singly. It is desirable that the length of individual carbon fiber be preferably in the range of from 0.5 to 20 mm, most preferably in the range of from 2 to 10 mm. If the length of individual fiber is less than 0.5 mm, the conductivity of the resin composition is lowered to an unsatisfactory level due to excessively small aspect ratio of the fibers. On the contrary, if the length of individual fiber is longer than 20 mm, the fluidity of the resin composition is extremely lowered to deteriorate the moldability thereof significantly with attendant deterioration of the appearance and mechanical properties of the molded products. In addition, the conductivity of the resin composition is rather lowered, since the fibers are not evenly dispersed throughout the composition. The carbon fibers may preferably have the diameters ranging within 3 to 25.mu., more preferably within 5 to 12.mu.. The fibers are apt to be broken under the shearing action at the kneading step to lessen the aspect ratio of the fibers or to be entangled with each other to form fiber balls to lessen the dispersibility thereof, resulting in unsatisfactory conductivity of the resin composition, if the diameter of individual fibers is less than 3.mu.. On the contrary, if the diameter of individual fibers is more than 25.mu., the conductivity of the resin composition becomes unsatisfactory since the aspect ratio of the fibers is too small. The bundle count of the carbon fibers may range preferably within 1,000 to 20,000, more preferably within 3,000 to 15,000. If the bundle count is less than 1,000, the bundled fibers are apt to be entangled with each other to form fiber balls to lessen the dispersibility thereof and to result in unsatisfactory conductivity of the resultant resin composition. On the contrary, if the bundle count is more than 20,000, the fiber bundles cannot be cloven effectively even by the shearing action at the kneading step, leading to uneven dispersion of the fibers to result in inferior conductivity of the resin composition. When it is desired to provide the resin composition with especially high conductivity thereby to improve the electromagnetic shielding effect, carbon fibers with metallized surfaces may be used as the carbon fibers added to the matrix resin. Such carbon fibers may be produced by coating the surfaces of the carbon fibers with a metal, such as Ni, Cu or Al, by the plating, vacuum evaporation coating or spattering processes. The content of the carbon fibers in the resin composition should range within 5 to 40 wt%, preferably 10 to 25 wt%. If the content thereof is less then 5 wt%, substantial electromagnetic wave shielding effect cannot be provided. On the contrary, if the content thereof exceeds 40 wt%, the resultant resin composition is hardly molded through extrusion or injection molding and the physical properties of the molded products are deteriorated. In the present invention, a conductive carbon black may be added to the composition in addition to the aforementioned carbon fibers. Specific examples of the conductive carbon black include furnace black, channel black and the like such as S.C.F. (Super Conductive Furnace) black, E.C.F. (Electric Conductive Furnace) black, a by-product black such as "Ketchen Black" available from Nippon E.C. Co., Ltd. and acetylene black. It is preferred that the carbon black satisfies at least one of the following features of: (1) having highly developed structure; PA1 (2) having small particle size; PA1 (3) having large specific surface area; PA1 (4) Containing only a small amount of impurities which capture electrons; and PA1 (5) having high degree of graphitization. The preferable quantity of the carbon black added to the composition varies depending on the kind of the carbon black used, particularly on the specific surface area thereof, and may range within 2 to 30 wt%, more preferably 3 to 15 wt%. If the added amount of the carbon black is less than 2 wt%, the volume resistivity of the molded product becomes uneven to result in inferior electromagnetic wave shielding effect. On the contrary, if the added amount of the carbon black exceeds 30 wt%, the resin composition is hardly molded by extrusion or injection molding and the physical properties of the molded product become inferior. An alkylamine antistatic agent may also be added to the resin composition. Preferable antistatic agents are amine compounds having hydroxyethyl groups and represented by the following formula of: ##STR1## wherein R.sub.1 is an alkyl or alkenyl group having 8 to 22 carbon atoms, and m and n are integers of 1 to 10. The compounds set forth above are well-known in the art, and it is preferred to use those represented by the aforementioned formula wherein 2.ltoreq.m+n.ltoreq.10. Representative amine compounds having hydroxyethyl groups are N,N-bis(hydroxyethyl) tallow amine, polyoxyethylene lauryl amine and fatty acid esters of polyoxyethylene lauryl amine. Amongst them, N,N-bis(hydroxyethyl) tallow amine is the most preferred. The amount of the added alkyl amine antistatic agent may range within 0.5 to 10 wt%, preferably 1 to 5 wt%. The effect of lowering the volume resistivity of the molded product cannot be expected when the added amount of alkyl amine antistatic agent if less than 0.5 wt% so that the electromagnetic wave shielding effect is not improved. On the contrary, if the amount of the added alkyl amine antistatic agent is more than 10 wt%, the resin composition is excessively lubricated to affect adversely the dispersibility of the carbon fibers at the compounding step so that the resin composition becomes hardly molded through extrusion or injection molding with attendant undesirable results that the physical properties and the electromagnetic wave shielding effect of the molded product become inferior. A halogen-containing organic flame retarder and an auxiliary flame-retarding agent may also be added to provide the resin composition with potent resistance to catching fire. Specific examples of halogen-containing organic flame retarder include chlorinated paraffins, tetrabromobisphenol-A and oligomers thereof, decabromobiphenyl ethers, hexabromobiphenyl ethers, pentabromobiphenyl ethers, pentabromotoluene, pentabromoethylbenzene, hexabromobenzene, pentabromophenol, tribromophenol derivatives, perchloropentanecyclodecane, hexabromocyclododecane, tris(2,3-dibromopropyl-1)isocyanurate, tetrabromobisphenol-S and derivatives thereof, 1,2-bis(2,3,4,5,6-pentabromophenoxy)ethane, 1,2-bis(2,4,6-tribromophenoxy)ethane, brominated styrene oligomers, 2,2-bis-(4(2,3-dibromopropyl)-3,5-dibromophenoxy)propane, tetrachlorophthalic anhydride and tetrabromophthalic anhydride. The auxiliary flame-retarding agents which may be used in the resin composition of the invention include antimony trioxide, sodium antimonate, zinc borate, and oxides and sulfides of zirconium and molybdenum, the most favourable result being obtained by the use of antimony trioxide. The amount of the halogen-containing organic flame retarder added to the resin composition varies depending on the required degree of flame resistant property and also on the content of the flame-retarding plasticizer, and ranges generally from 2 to 35 wt%, preferably from 5 to 25 wt%. The flame-retarding effect becomes insufficient if the amount of the added halogen-containing organic flame retarder is less than 2 wt%, whereas the thermal and mechanical properties of the molded product become inferior if the amount of added halogen-containing organic flame retarder exceeds 35 wt%. The added amount of the auxiliary flame-retarding agent may be within 0.4 to 21 wt% and the ratio thereof to the halogen-containing organic flame retarder should be within the range of from 6/10 to 2/10, preferably from 5/10 to 3/10. Satisfactory synergistic effect of retarding the propagation of flame cannot be obtained if the added amount of the auxiliary flame-retarding agent is less than 0.4 wt%, whereas the mechanical properties of the molded product are deteriorated if the added amount of the auxiliary flame-retarding agent exceeds 21 wt%. If the ratio of the auxiliary flame-retarding agent to the halogen-containing organic flame retarder is less than 2/10, synergistic flame-retarding effect cannot be realized to result in unsatisfactory flame-retarding function, whereas the mechanical properties of the molded product becomes inferior if the ratio of the former to the latter exceeds 6/10. In order to further improve the properties of the resin composition of the invention, antioxidants, internal or external lubricants and stabilizers may be added thereto. Antioxidants which may be added to the resin composition of the invention include phenolic antioxidants, sulfur base antioxidants and phosphor base antioxidants. Specific examples of the phenolic antioxidants are 2,6-di-tert-butyl-p-cresol, 2,2'-methylenebis(4-methyl-6-tert-butyphenol), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), 4,4'-thiobis(3-methyl-6-tert-butylphenol), butylhydroxyanisole and tetrakis[methylene-3(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane; the specific examples of the sulfur base antioxidants are dilauryl thiodipropionate, distearyl thiodipropionate, lauryl stearyl thiodipropionate, dimyristyl thiodipropionate and distearyl .beta.,.beta.'-thiodibutylate; and the specific examples of the phosphor base antioxidants are tridecyl phophite, diphenyl phenyl phosphite, triphenyl phosphite and trinonylphenyl phosphite. These antioxidants may be used singly or in combination. Decomposition or deterioration due to oxidation of the resin composition can be prevented by adding one or more of the aforementioned antioxidants, preferably, in an amount of 0.01 to 4 parts by weight to 100 parts by weight of the resin composition. The internal or external lubricants which may be added to the resin composition of the invention include paraffins and hydrocarbon resins, such as paraffin waxes, liquid paraffins, paraffin base synthetic waxes and polyethylene waxes; fatty acids, such as stearic acid and hydroxystearic acid; fatty acid amides, such as stearoamide, oxystearoamide, oleyl amide, methylenebisstearoamide and methylenebisbehenamide; fatty acid esters, such as n-butyl stearate, methyl hydroxystearate and esters of saturated fatty acids; fatty acid alcohols, such as higher alcohols, and esters of higher alcohols; and partial esters of fatty acids and polyhydric alcohols, such as esters of glycerine and fatty acids, triglyceride of hydroxystearic acid and esters of sorbitan and fatty acids. One or a mixture of two or more of the internal or external lubricants set forth above may be used. The stabilizers which may be added to the resin composition of the invention include metallic soaps, salts of inorgnic acids, organic tin compounds and composite stabilizers. Specific examples of the metallic soaps are zinc stearate, calcium stearate, zinc laurate and cadmium 2-ethylhexoate; examples of the salts of inorganic acids being tribasic lead sulfate, basic lead sulfite and lead-barium compounds; examples of the organic tin compounds being dibutyl tin laurate, dibutyl tin dimaleate, and di-n-octyl tin maleate polymers; and examples of the composite stabilizers are calcium-zinc base stabilizers, barium-lead base stabilizers and cadmium-barium-zinc base stabilizers. These stabilizers may be used singly or in combination. Any one or more of the aforementioned internal and/or external lubricants and/or stabilizers may be added to the resin composition, preferably, in a ratio of 0.01 to 4 parts by weight to 100 parts by weight of the resin composition to improve the fluidity of the resin composition at the molding step and to prevent decomposition or deterioration of the resinous ingredient. The process for the preparation of the resin composition of the invention will now be described. The copolymer of an ethylenic unsaturated nitrile, a diene rubber and an aromatic vinyl compound may be in the form of powder, beads or pellets. The copolymer or mixture thereof with another copolymer of an ethylenic unsaturated nitrile and an aromatic vinyl compound is mixed with the plasticizer and the carbon fibers and optionally with other ingredients. In order to improve the moldability of resin composition and to improve the properties of the molded products, it is preferred that the ethylenic unsaturated nitrile/diene rubber/aromatic vinyl compound copolymer be in the form of powder and the ethylenic unsaturated nitrile/aromatic vinyl compound copolymer be in the form of bead. In order to make uniform or homogenize the resin composition, the mixture is mixed and kneaded using a kneader or extruder, such as a Banbury mixer, cokneader, single spindle extruder or double spindle extruder. The mixture may be subjected to pre-mixing process using a tumbler or high speed mixer prior to the mixing and kneading step. The mixed and kneaded resin composition is then charged in a hopper of an injection molding machine to be melted in a plasticizing cylinder of the injection molding machine, and the molten resin composition is injected into a mold and then cooled to be solidified. Solidified molded mass is removed from the mold to obtain an injection molded article made of the resin composition of the invention. Likewise, the mixed and kneaded resin composition is charged in a hopper of an extuder to be melted in a plasticizing cylinder of the extruder, and the molten resin composition is extruded through a die attached to the end of the extruding cylinder to form an extruded product made of the resin composition of the invention. EXAMPLES OF THE INVENTION The present invention will now be described more specifically by referring to Examples thereof. EXAMPLES 1 to 8 A powder-form ABS resin (acrylonitrile/butadiene/styrene copolymer resin) having a composition composed of 10 wt% of acrylonitrile, 50 wt% of butadiene and 40 wt% of styrene and a bead-form AS resin (acrylonitrile/styrene copolymer resin) having a composition composed of 30 wt% of acrylonitrile and 70 wt% of styrene were used. A plasticizer available from Kao Soap Co., Ltd. under the Trade Name "VYNYCIZER #80" was used as the plasticizer in the resin composition. Carbonized polyacrylonitrile (referred to as "PAN" in the following Tables) chopped strands (Length: 6 mm, Diameter: 7.mu. Bundle Count: 12,000) available from Toho Rayon Co., Ltd. under the Trade Name "BESFIGHT HTAC6S" were used as the carbon fibers. One part, by weight, for each of an antioxidant and zinc stearate were added to 100 parts, by weight, of the resin. The compositions are shown in Table 1. Each of the compositions was put into a Banbury mixter heated to 140.degree. C. to be mixed and kneaded until the temperature of the mixture reached 190.degree. C.. Immediately after the mixture was discharged from the mixer, it was rolled through mixing rollers to form a sheet which was cooled and then crushed into pellets. The thus formed pellets were charged in a hooper of an 8-ounce injection molding machine to be melted in a plasticizing cylinder of the machine, and then injected into a mold. The mold was one provided with a 2 mm direct gate for molding a housing 15 cm square and having an wall thickness of 3 mm. The thus molded products had excellent physical properties, improved resistance to heat and improved electromagnetic wave shielding effect, as shown in Table 1. EXAMPLES 9 to 11 Each of the compositions set forth in Table 1 was pelletized similarly to Example 1, and charged in a hopper of an extruder having a cylinder of 40 mm in diameter (L/D=24) to be melted therein at 200.degree. C. The molten mass was allowed to pass through a die for molding a single layer sheet. The die had a width of 600 mm and the lip gap was adjusted to 3.5 mm. As the result, a single layer sheet having a thickness of 3 mm was formed. The thus formed single layer sheets had excellent physical properties, improved resistance to heat and improved electromagnetic wave shielding effect, as shown in Table 1. EXAMPLES 12 and 13 A powder-form MBS resin (methacrylonitrile/butadiene/styrene copolymer resin) composed of 50 wt% of methyacrylonitrile, 10 wt% of butadiene and 40 wt% of styrene was used in place of the powder-form acrylonitrile/butadiene/styrene copolymer resin. Other ingredients used in the compositions were the same as used in Example 1. The compositions were pelletized similarly to Example 1 and then subjected to injection molding to form molded products. The properties of the molded products were tested to reveal that they were improved in physical properties, resistance to heat and electromagnetic wave shielding effect, as shown in Table 1. EXAMPLE 14 A pellet-form ABS resin (acrylonitrile/butadiene/styrene copolymer resin) composed of 20 wt% of acrylonitrile, 20 wt% of butadiene and 60 wt% of styrene was used in place of the ABS resin as used in Example 1 to prepare the resin composition shown in Table 1. The resin composition was pelletized similarly to Example 1 and subjected to injection molding to form a molded product. The properties of the molded product were tested to reveal that it had excellent physical properties, improved resistance to heat and improved electromagnetic wave shielding effect. COMPARATIVE EXAMPLES 1 and 2 Injection molded products were produced from the compositions set forth in Table 2 in accordance with the procedures similar to Example 1, except in that one composition contained a plasticizer in an amount of less than the range defined in the claims whereas the other composition contained the plasticizer in an amount more than the defined range. The properties of the injection molded products were tested. The results are shown in Table 2. COMPARATIVE EXAMPLES 3 and 4 Injection molded products were produced from the compositions set forth in Table 2 in accordance with the procedures similar to Example 1, except in that one composition contained carbon fibers in an amount of less than the range defined in the claims whereas the other composition contained carbon fibers in an amount more than the defined range. The properties of the injection molded products were tested. The results are shown in Table 2. TABLE 1 __________________________________________________________________________ Example No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 __________________________________________________________________________ Composition Resin Powder-Form ABS Resin (wt %) 32 30 29 31 30 28 30 28 30 30 28 -- -- -- Powder-form MBS Resin (wt %) -- -- -- -- -- -- -- -- -- -- -- 30 29 -- Bead-form AS Resin (wt %) 48 45 44 47 45 42 45 42 45 45 42 45 44 -- Pellet-form ABS Resin (wt %) -- -- -- -- -- -- -- -- -- -- -- -- -- 75 Plasticizer Di-2-ethylhexyl Phthalate (wt %) 5 10 12 -- -- -- 5 10 10 -- 10 10 12 10 Adipic Acid Polyester (wt %) -- -- -- 7 10 15 -- -- -- 10 -- -- -- -- Carbon Fibers 15 15 15 15 15 15 20 20 15 15 20 15 15 15 PAN Chopped Strand (wt %) Property Electromagnetic Wave Shielding 30 40 45 35 40 50 40 50 35 35 40 40 45 20 Effect (dB) Tensile Strength (kg/mm.sup.2) 3.7 3.6 3.5 4.1 4.0 3.9 2.9 2.7 4.0 4.4 3.0 4.0 3.8 3.3 Bending Strength (kg/mm.sup.2) 5.5 5.4 5.3 6.0 5.9 5.8 4.3 4.5 5.9 6.5 5.0 5.9 5.8 4.9 Bending Modulus of 260 240 220 270 260 250 290 280 260 290 310 260 270 240 Elasticity (kg/mm.sup.2) Izod Impact Strength (kg-cm/cm) 18 20 22 17 18 21 16 15 22 20 17 16 18 18 Vicat Softening Point (.degree.C.) 80 75 72 82 80 75 80 75 75 80 75 85 82 80 __________________________________________________________________________ TABLE 2 ______________________________________ Comparative Example 1 2 3 4 ______________________________________ Composition Resin Powder-form ABS Resin (wt %) 33.8 22 35.2 16 Powder-form MBS Resin (wt %) -- -- -- -- Bead-form AS Resin (wt %) 50.7 33 52.8 24 Pellet-form ABS Resin (wt %) -- -- -- -- Plasticizer Di-2-ethylhexyl Phthalate (wt %) 0.5 30 10 10 Adipic Acid Polyester (wt %) -- -- -- -- Carbon Fibers 15 15 2 50 PAN Chopped Strand (wt %) Electromagnetic Wave 12 40 5> 55 Shielding Effect (dB) Property Tensile Strength (kg/mm.sup.2) 4.5 2.7 4.4 1.6 Bending Strength (kg/mm.sup.2) 6.5 4.5 6.5 2.3 Bending Modulus of 300 220 230 280 Elasticity (kg/mm.sup.2) Izod Impact Strength (kg-cm/cm) 12 22 24 10 Vicat Softening Point (.degree.C.) 95 50 75 75 ______________________________________ The properties of the molded products set forth in Tables 1 and 2 and throughout the other Examples and Comparative Examples were determined by the following test methods. (1) Electromagnetic Wave Shielding Effect: PA0 (2) Tensile Strength: PA0 (3) Bending Strength & Bending Modulus of Elasticity: PA0 (4) Izod Impact Strength (with Notch): PA0 (5) Vicat Softening Point: PA0 (1) Thermal Deformation Temperature: PA0 (2) UL-94 Combustion Test: PA0 (3) Oxygen Index: Using the tester for the determination of electromagnetic wave shielding effect as shown in the appended drawing, the effects of respective molded articles were determined through the DENKA method. In detail, a plastic molded article 2 was mounted in a shield box 1 so that the tested article 2 traversed the box 1 to separate the latter into two sections, a high frequency wave emitter antenna 3 being contained in one section and a receiver antenna 4 being contained in the other section. The high frequency wave emitter antenna 3 was connected to a tracking generator 6 which was energized to generate high frequency wave of a predetermined voltage. The wave passing through the traversing article 2 was received by the receiver antenna 4. The voltage of the wave passing through the article 2 and received by the receiver antenna 4 was compared with the voltage of the wave emitted from the emitter antenna 3 to determine the electromagnetic wave shielding effect of the article 2. Tensile strengths of respective molded articles were determined generally in accordance with the JIS K-6871 Method. These values were determined generally in accordance with the ASTM D-790 Method. Izod impact strengths of respective molded articles were determined generally in accordance with the JIS K-6871 Method. Vicat softening points of respective molded articles were determined generally in accordance with the JIS K-7206 Method. EXAMPLES 15 to 29 The powder-form ABS resin (acrylonitrile/butadiene/styrene copolymer resin) as used in Example 1 and the bead-form AS resin (acrylonitrile/styrene copolymer resin) as used in Example 1 were used. The same plasticizer and the same carbon fibers as used in Example 1 were used. The carbon black used was the one available from Cabot Corp. under the Trade Name "VULCAN XC-72" which had a DBP oil absorption of about 180 cm.sup.3 /100 g, an N.sub.2 specific surface area of about 180 m.sup.2 /g and a particle size of about 30 .mu.m. An alkyl amine antistatic agent available from Kao Soap Co., Ltd. under the Trade Name "ELECTRO STRIPPER-EA" was used as the antistatic agent. Each of the compositions set forth in Table 3 was further added with an antioxidant and zinc stearate, and put into a Banbury mixer heated to 140.degree. C. to be melted and kneaded. Immediately after the temperature of the kneaded mixture reached 190.degree. C., the mixture was discharged from the mixer and rolled between mixing rollers into a sheet, which was cooled and then crushed into pellets. The pellets were charged in a hopper of an 8-ounce injection machine to be melted in the plasticizing cylinder of the machine, and the molten mass was injected into a mold. The mold was provided with a 2 mm.phi. direct gate for molding a housing 15 cm square and having a wall thickness of 3 mm. The thus molded products had excellent physical properties, improved resistance to heat and improved electromagnetic wave shielding effect, as shown in Table 3. EXAMPLES 30 AND 34 Each of the compositions as set forth in Table 4 was pelletized in accordance with the procedures similar to Example 1, and charged in a hopper of an extruder having a cylinder of 40 mm in diameter (L/D=24) to be melted in the cylinder. The molten composition in the cylinder was then extruded through a die for molding a single layer sheet, the die being maintained at 200.degree. C. The die had a width of 600 mm and a lip gap of 3.5 mm. As the result of extrusion, a single layer sheet having a thickness of 3 mm was formed. The thus formed single layer sheet had excellent physical properties, improved resistance to heat and improved electromagnetic wave shielding effect, as shown in Table 4. EXAMPLES 35 TO 36 A powder-form MBS resin (methacrylonitrile/butadiene/styrene copolymer resin) composed of 50 wt% of methacrylonitrile, 10 wt% of butadiene and 40 wt% of styrene was used in place of the powder-form acrylonitrile/butadiene/styrene copolymer resin used in Example 1. The composition as set forth in Table 4 were pelletized generally following the procedures as described in Example 1. Injection molded products were produced from the thus prepared pellets. The properties of the molded products were tested to reveal that they had improved physical properties, improved resistance to heat and improved electromagnetic wave shielding effect. EXAMPLE 37 A pellet-form ABS resin (acrylonitrile/butadiene/styrene copolymer resin) composed of 20 wt% of acrylonitrile, 20 wt% of butadiene and 60 wt% of styrene was used. The composition as set forth in Table 4 was pelletized generally following the procedures as described in Example 1. An injection molded product was formed from the pellets and subjected to tests. The results of the tests revealed that the molded product had improved physical properties, improved resistance to heat and improved electromagnetic wave shielding effect. COMPARATIVE EXAMPLES 5 AND 6 Generally following the procedures as described in Example 1, injection molded products were produced from the compositions as set forth in Table 4, one composition containing the plasticizer in an amount less than the range defined in the appended claims whereas the other composition containing the plasticizer in an amount more than the defined range. The properties of the injection molded products are shown in Table 4. As shown, the product of Comparative Example 5 is inferior in electromagnetic wave shielding effect due to inadequate dispersion of carbon fibers, and the product of Comparative Example 6 is inferior in resistance to heat due to excessively high content of plasticizer. COMPARATIVE EXAMPLES 7 AND 8 Generally following to the procedures as described in Example 1, injection molded products were produced from the compositions as set forth in Table 4, one composition containing carbon fibers in an amount less than the range defined in the appended claims whereas the other composition containing carbon fibers in an amount more than the defined range. The properties of the injection molded products are shown in Table 4. As shown, the product of Comparative Example 7 has an inferior electromagnetic wave shielding effect, whereas the product of Comparative Example 8 has a low impact strength. TABLE 3 __________________________________________________________________________ Example No. 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 __________________________________________________________________________ Composition Resin Powder-Form ABS Resin (wt %) 32 30 29 31 30 28 28 26 25 30 29 27 31 29 28 Powder-form MBS Resin (wt %) -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- Bead-form AS Resin (wt %) 48 45 44 47 45 42 42 39 38 45 43 40 47 44 43 Pellet-form ABS Resin (wt %) -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- Plasticizer Di-2-ethylhexyl Phthalate (wt %) 5 10 12 -- -- -- 5 10 12 7 10 15 5 10 12 Adipic Acid Polyester (wt %) -- -- -- 7 10 15 -- -- -- -- -- -- -- -- -- Carbon Fibers 10 10 10 10 10 10 20 20 20 10 10 10 10 10 10 PAN Chopped Strand (wt %) Carbon Black 3 3 3 3 3 3 3 3 3 6 6 6 3 3 3 VULCAN XC-72 (wt %) Antistatic Agent 2 2 2 2 2 2 2 2 2 2 2 2 4 4 4 Alkyl Amine Base (wt %) Electromagnetic Wave Shielding 50 60 65 55 60 65 70 80 85 65 70 75 60 70 75 Effect (dB) Property Tensile Strength (kg/mm.sup.2) 3.8 3.7 3.6 4.2 4.1 4.0 3.2 3.1 3.0 3.5 3.4 3.3 3.8 3.7 3.6 Bending Strength (kg/mm.sup.2) 5.6 5.5 5.4 6.2 6.1 6.0 5.0 4.9 4.8 5.3 5.2 5.1 5.6 5.5 5.4 Bending Modulus of 270 250 230 290 280 270 320 300 280 300 280 260 270 250 230 Elasticity (kg/mm.sup.2) Izod Impact Strength (kg-cm/cm) 17 19 21 15 17 19 13 15 17 15 17 19 17 19 21 Vicat Softening Point (.degree.C.) 80 75 72 82 80 75 80 75 72 77 75 70 80 75 72 __________________________________________________________________________ TABLE 4 __________________________________________________________________________ Comparative Example No. Example 30 31 32 33 34 35 36 37 5 6 7 8 __________________________________________________________________________ Composition Resin Powder-form ABS Resin (wt %) 30 30 26 29 29 -- -- -- 34.2 22 33 14 Powder-form MBS Resin (wt %) -- -- -- -- -- 30 29 -- Bead-form AS Resin (wt %) 45 45 39 43 44 45 44 50.3 33 50 21 Pellet-form ABS Resin (wt %) -- -- -- -- -- -- -- 75 Plasticizer Di-2-ethylhexyl Phthalate (wt %) 10 -- 10 10 10 10 12 10 0.5 30 10 10 Adipic Acid Polyester (wt %) -- 10 -- -- -- -- -- -- -- -- -- -- Carbon Fibers 10 10 20 10 10 10 10 10 10 10 2 50 PAN Chopped Strand (wt %) Carbon Black 3 3 3 6 3 3 3 3 3 3 3 3 VULCAN XC-72 (wt %) Antistatic Agent 2 2 2 2 4 2 2 2 2 2 2 2 Alkyl Amine Base (wt %) Electromagnetic Wave Shielding 50 50 70 60 60 60 65 40 12 60 5> 90 Effect dB Property Tensile Strength (kg/mm.sup.2) 4.1 4.5 3.4 3.7 4.1 4.0 3.9 3.3 4.5 3.7 4.4 1.3 Bending Strength (kg/mm.sup.2) 6.1 6.7 5.4 5.7 6.1 5.9 5.8 4.9 6.6 4.4 6.6 2.2 Bending Modulus of 280 310 330 310 280 260 240 240 310 230 230 290 Elasticity (kg/mm.sup.2) Izod Impact Strength (kg-cm/cm) 21 19 17 19 21 13 17 18 11 22 25 7 Vicat Softening Point (.degree.C.) 75 80 75 75 75 85 82 80 95 50 75 75 __________________________________________________________________________ EXAMPLE 38 Molded products were produced similarly to Example 15 while using the same resins, the same carbon black and the same antistatic agent. However, the length, diameter and bundle count of the carbon fibers used were varied as shown in Table 5. The properties of the molded products were tested similarly to the preceding Examples. The results are shown in Table 5. TABLE 5 __________________________________________________________________________ Example 38 Run Run Run Run Run Run 1 2 3 4 5 6 __________________________________________________________________________ Composition Resin Powder-form ABS Resin (wt %) 32 32 32 32 32 32 Powder-form MBS Resin (wt %) -- -- -- -- -- -- Bead-form AS Resin (wt %) 48 48 48 48 48 48 Pellet-form ABS Resin (wt %) -- -- -- -- -- -- Plasticizer Di-2-ethylhexyl Phthalate (wt %) 5 5 5 5 5 5 Adipic Acid Polyester (wt %) -- -- -- -- -- -- Carbon Fibers 10 10 10 10 10 10 PAN Chopped Strand (wt %) Shape Length (mm) 0.2 30 6 6 6 6 Diameter (.mu.) 7 7 1 50 7 7 Bundle Count 12000 12000 12000 12000 500 30000 Carbon Black 3 3 3 3 3 3 VULCAN XC-72 (wt %) Antistatic Agent 2 2 2 2 2 2 Alkyl Amine Base (wt %) Electromagnetic Wave Shielding Effect (dB) 20 25 20 10 20 25 Property Tensile Strength (kg/mm.sup.2) 1.4 1.9 3.1 3.4 3.4 3.4 Bending Strength (kg/mm.sup.2) 5.0 6.2 4.5 6.2 5.0 6.2 Bending Modulus of Elasticity (kg/mm.sup.2) 240 300 220 300 240 330 Izod Imapct Strength (kg-cm/cm) 15 9 13 15 17 9 Vicat Softening Point (.degree.C.) 70 80 70 70 75 80 __________________________________________________________________________ EXAMPLE 39 (RUN NOS. 1 TO 8) The same resins and the same carbon fibers as used in Example 1 were used with a tetrabromobisphenol-A available from Teijin Kasei Limited under the Trade Name "FIREGUARD 2000", as a halogen-containing flame retarder, and antimony trioxide produced by Nippon Mining Company Limited, as an auxiliary flame-retarding agent. Further added as a flame-retarding plasticizer of phosphoric acid derivative was tricresyl phosphate produced by Daihachi Kagahu K.K. The compositions set forth in the following Table 6 were further supplied with an antioxidant, a stabilizer made of tribasic lead and zinc stearate, and put into a Banbury mixer heated to 140.degree. C. to be melted and kneaded. Each of the kneaded mixture was discharged from the mixer after the temperature thereof reached 190.degree. C., and rolled immediately between mixing rollers to form a sheet, which was cooled and then crushed into pellets. The pellets were charged in a hopper of an 8-ounce injection molding machine to be injected into a mold for molding a housing 15 cm square and having a wall thickness of 3 mm, the mold being provided with a direct gate having a diameter of 2 mm.phi.. As shown in Table 6, the thus molded products were improved in physical properties, resistance to heat and electromagnetic wave shielding effect, as well. EXAMPLE 39 (RUN NO. 9) The composition as set forth in Table 6 was pelletized similarly to Run No. 1 of Example 39, and the pellets were charged in a hopper of an extruder having a cylinder of 40 mm in diameter (L/D=24) to be melted and extruded through a die for forming a single layer sheet, the die being maintained at 200.degree. C. The die had a width of 600 mm and the lip gap was adjusted to 3.5 mm. As a result, a single layer sheet having a thickness of 3 mm was formed. As shown in Table 6, the thus produced single layer sheet had excellent physical properties, improved resistance to heat and improved electromagnetic wave shielding effect. EXAMPLE 39 (RUN NOS. 10 AND 11) A powder-form MBS resin (methacrylonitrile/butadiene/styrene copolymer resin) composed of 50 wt% of methacrylonitrile, 10 wt% of butadiene and 40 wt% of styrene was used in place of the powder-form ABS copolymer resin used in Run Nos. 7 and 8. The compositions as set forth in Table 6 were pelletized similarly to Run No. 1 of Example 39, and injection molded products were produced using the thus prepared pellets. The results of tests showed that the molded products had excellent physical properties, improved resistance to heat and improved electromagnetic wave shielding effect. EXAMPLE 39 (RUN NO. 12) A pellet-form ABS resin (acrylonitrile/butadiene/styrene copolymer resin) composed of 20 wt% of acrylonitrile, 20 wt% of butadiene and 60 wt% of styrene was used. The composition set forth in Table 6 was pelletized similarly to Run No. 1 of Example 39, and an injection molded product was produced using the thus prepared pellets. The results of tests showed that the molded product had excellent physical properties, improved resistance to heat and improved electromagnetic wave shielding effect. EXAMPLE 39 (RUN NO. 13) A composition similar to that of Run No. 2 of Example 39 except in that 2-ethylhexyldiphenyl phosphate was used in place of tricresyl phosphate, was pelletized generally following to the procedures as described in Example 1. An injection molded product was produced using the thus prepared pellets, and subjected to tests. The results of the tests showed that the molded product had excellent physical properties, improved resistance to heat and improved electromagnetic wave shielding effect. TABLE 6 __________________________________________________________________________ Example 39 Run No. 1 2 3 4 5 6 7 8 9 10 11 12 13 __________________________________________________________________________ Composition (wt %) Resin Powder-form ABS Resin 18 20 14 21 15 20 18 20 20 -- -- -- 20 Powder-form MBS Resin -- -- -- -- -- -- -- -- -- 18 20 -- -- Bead-form AS Resin 38 42 29 45 31 44 37 42 42 37 42 -- 42 Pellet-form ABS Resin -- -- -- -- -- -- -- -- -- -- -- 62 -- Flame-Retarding 2-Ethylhexyl Diphenyl -- -- -- -- -- -- -- ---- -- -- -- 5 Phosphate Plasticizer Tricresyl Phosphate 5 5 5 5 5 5 9 2 5 9 2 5 -- Carbon Fibers PAN Chopped Strand 15 15 10 15 35 10 15 15 15 15 15 15 15 Flame Retarder Tetrabromobisphenol-A 15 15 30 10 10 15 15 15 15 15 15 15 15 Antimony Trioxide 9 3 12 4 4 6 6 6 3 6 6 3 3 Property Electromagnetic Wave Shielding 40 40 30 40 60 30 40 40 30 40 40 35 40 Effect (dB) Tensile Strength (kg/mm.sup.2) 2.7 3.0 2.4 3.3 3.3 3.0 3.0 3.0 3.6 3.0 3.0 2.9 3.0 Bending Strength (kg/mm.sup.2) 4.5 5.0 4.5 5.0 6.0 5.0 4.5 5.5 5.0 5.0 5.0 4.5 5.0 Bending Modulus of 500 500 450 500 600 500 450 550 500 500 500 450 500 Elasticity (kg/mm.sup.2) Izod Impact Strength (kg-cm/cm) 8 10 6 12 6 10 12 18 10 10 10 8 10 Thermal Deformation Temperature (.degree.C.) 90 85 75 90 95 85 80 90 85 85 85 85 85 Flame-Retarding UL-94 Combustion Test V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-0 Property (3" bar) Oxygen Index (%) 31 28 34 25 28 29 29 29 28 29 29 28 28 __________________________________________________________________________ The properties of the molded product shown in Table 6 and other Tables were determined by the following test methods. The temperature was determined generally in accordance with the JIS K-7207 Method (Load-Flexure Temperature Determination Test for Rigid Plastics). The test was conducted generally in accordance with the UL-94 Vertical Combustion Test Method. The oxygen index was determined generally in accordance with the JIS K-7201 Method. EXAMPLE 40 (RUN NOS. 1 TO 8) Used as the resinous components were a powder-form ABS resin (acrylonitrile/butadiene/styrene copolymer resin) composed of 10 wt% of acrylonitrile, 50 wt% of butadiene and 40 wt% of styrene, and a bead-form AS resin (acrylonitrile/styrene copolymer resin) composed of 30 wt% of acrylonitrile and 70 wt% of styrene. Further added as an ethylene/propylene terpolymer was an ethylene/propylene/dicyclopentadiene resin produced and sold by Mitsui Petrochemical Industries, Ltd. under the Table Name "EPT-#1045". Used as the carbon fibers were carbonized polyacrylonitrile chopped strands having a fiber length of 6 mm, a fiber diameter of 7.mu. and a bundle count of 12,000 and available from Toho Rayon Co., Ltd. under the Trade Name "BESFIGHT HTAC6S". A tetrabromobisphenol-A available from Teijin Kasei Limited under the Trade Name "FIREGUARD 2000" was used as a halogen-containing organic flame retarder, and antimony trioxide available from Nippon Mining Company, Limited was used as an auxiliary flame-retarding agent. To the compositions as set forth in Table 7 were further added an antioxidant, a stabilizer made of tribasic lead and zinc stearate, and the mixtures were put in a Banbury mixer heated to 140.degree. C. Each of the compositions was discharged from the mixer after the temperature thereof reached 190.degree. C., and processed immediately through mixing rollers to form a sheet, which was cooled and then crushed into pellets. The pellets were charged in a hopper of an 8-ounce injection molding machine to be injected into a mold for molding a housing 15 cm square and having a wall thickness of 3 mm, the mold being provided with a direct gate having a port diameter of 2 mm.phi.. The thus molded products were excellent in mechanical properties, and improved in resistance to heat and electromagnetic wave shielding effect, as well. EXAMPLE 40 (RUN NOS. 9 TO 11) The compositions as set forth in Table 7 were pelletized similarly to Run No. 1 of Example 40, and the thus prepared pellets were charged in a hopper of an extruder having a 40 mm diameter cylinder (L/D=24) to be melted and then extruded through a die for forming a single layer sheet, the die being maintained at 200.degree. C. The die had a width of 600 mm and the lip gap was adjusted to 3.5 mm. By pasing the molten mass through the die, a single layer sheet having a thickness of 3 mm was formed. As shown in Table 7, the formed single layer sheets were excellent in mechanical properties and resistance to heat and improved in flame-retarding property and electromagnetic wave shielding effect. EXAMPLE 40 (RUN NOS. 12 AND 13) A powder-form MBS resin (methacrylonitrile/butadiene/styrene copolymer resin) composed of 50 wt% of methacrylonitrile, 10 wt% of butadiene and 40 wt% of styrene was used in place of the powder-form acrylonitrile/butadiene/styrene copolymer resin used in Run No. 1 of Example 40. The compositions as set forth in Table 7 were pelletized similarly to Run No. 1 of Example 40, and injection molded products were produced from the thus prepared pellets. The test results of the molded products showed that they were excellent in physical properties, resistance to heat, flame-retarding property and electromagnetic wave shielding effect. EXAMPLE 40 (RUN NO. 14) A pellet-form ABS resin (acrylonitrile/butadiene/styrene copolymer resin) composed of 20 wt% of acrylonitrile, 20 wt% of butadiene and 60 wt% of styrene was used to prepare the composition shown in Table 7. The composition was pelletized similarly to Run No. 1 of Example 40 and then molded to form an injection molded product. The properties of the molded product were tested to find that it had high mechanical strengths, excellent resistance to heat, improved flame-retarding property and improved electromagnetic wave shielding effect. EXAMPLE 40 (RUN NOS. 15 AND 16) An ethylene/propylene/ethylidenenorbornene terpolymer resin available from Mitsui Petrochemical Industries, Ltd. under the Trade Name "EPT-#3045" was used in place of the ethylene/propylene/dicyclopentadiene terpolymer resin used in Run No. 1 of Example 40. The compositions as set forth in Table 7 were pelletized similarly to Run No. 1 of Example 40 and then molded to form injection molded products. The properties of the molded products were tested to find that they had high mechanical strengths, excellent resistance to heat, improved flame-retarding property and improved electromagnetic wave shielding effect. COMPARATIVE EXAMPLES 9 AND 10 Injection molded products were produced from the compositions as set forth in Table 8 generally following to the procedures as described in Run No. 1 of Example 40, one composition containing an ethylene/propylene/dicyclopentadiene terpolymer resin in an amount less than the range defined in the claims whereas the other composition containing the same terpolymer resin in an amount of more than the defined range. The results of tests for determining the properties of the molded proucts are shown in Table 8. COMPARATIVE EXAMPLES 11 AND 12 Injection molded products were produced from the compositions as set forth in Table 8 generally following to the procedures as described in Run No. 1 of Example 40, one composition containing carbon fibers in an amount of less than the range defined in the claims whereas the other composition containing the carbon fibers in an amount of more than the defined range. The results of tests for determining the properties of the molded products are shown in Table 8. The ethylene/propylene/DCPD resin appearing in Tables 7 and 8 means a terpolymer of ethylene, propylene and dicyclopentadiene, and the ethylene/propylene/ENB resin appearing in the same Tables mean a terpolymer of ethylene, propylene and ethylidenenorbornene. TABLE 7 __________________________________________________________________________ Example 40 Run No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 __________________________________________________________________________ Composition Resin Powder-form ABS Resin 19 20 13 22 15 21 18 21 20 18 21 -- -- -- 19 20 (wt %) Powder-form MBS Resin -- -- -- -- -- -- -- -- -- -- -- 19 20 -- -- -- (wt %) Bead-form AS Resin (wt %) 40 43 27 46 31 45 38 45 41 38 45 40 43 -- 40 43 Pellet-form ABS -- -- -- -- -- -- -- -- -- -- -- -- -- 59 -- -- Resin (wt %) Ethylene/Propylene Terpolymer Ehthylene/propylene/ 10 10 10 10 10 10 15 5 10 15 5 10 10 10 -- -- DCPD Resin (wt %) Ethylene/prpylene/ -- -- -- -- -- -- -- -- -- -- -- -- -- -- 10 10 ENB Resin (wt %) Halogen-Containing Organic 10 10 25 5 10 10 10 10 10 10 10 10 10 10 10 10 Flame-Retarder Tetrabromobisphenol-A (wt %) Auxiliary Flame-Retarding 6 2 10 2 4 4 4 4 4 4 4 6 2 6 6 2 Agent Antimony Trioxide (wt %) Carbon Fibers 15 15 15 15 30 10 15 15 15 15 15 15 15 15 15 15 PAN Chopped Strand (wt %) Property Tensile Strength (kg/mm.sup.2) 2.7 3.0 2.4 3.3 3.0 3.0 3.0 3.0 3.3 3.3 3.3 3.0 3.3 2.7 2.7 3.0 Bending Strength (kg/mm.sup.2) 4.5 5.0 4.5 5.0 6.0 5.0 4.5 5.5 5.5 5.0 6.0 5.0 5.5 5.0 4.5 5.0 Bending Modulus of 450 500 450 500 600 500 450 550 550 500 600 500 550 500 450 500 Elasticity (kg/mm.sup.2) Izod Impact 12 13 10 14 10 13 14 12 13 13 13 13 14 13 10 11 Strength (kg-cm/cm) Thermal Deformation 90 95 80 95 100 95 90 95 95 90 95 85 90 85 90 95 Temperature (.degree.C.) Flame-Retarding V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-1 V-0 V-0 V-0 V-0 V-0 Property (1/8 inch bar) Oxygen Index (%) 32 29 35 26 26 32 32 26 26 29 23 31 28 31 35 32 Electromagnetic Wave 40 40 40 40 60 30 40 40 35 35 35 40 40 40 40 40 Shielding Effect (dB) Molding Process INJ INJ INJ INJ INJ INJ INJ INJ EXT EXT EXT INJ INJ INJ INJ INJ __________________________________________________________________________ Note: INJ in the Table means injection molding, and EXT in the Table mean extrusion molding. TABLE 8 ______________________________________ Comparative Example 9 10 11 12 ______________________________________ Composition Resin Powder-form ABS Resin (wt %) 13 22.2 10 24 Powder-form MBS Resin (wt %) -- -- -- -- Bead-form AS Resin (wt %) 28 48.3 21 50 Pellet-form ABS Resin (wt %) -- -- -- -- Ethylene/Propylene Terpolymer Ethylene/propylene/DCPD Resin (wt %) 30 0.5 10 10 Ethylene/propylene/ENB Resin (wt %) -- -- -- -- Halogen-Containing Oragnic Flame 10 10 10 10 Retarder Tetrabromobisphenol-A (wt %) Auxiliary Flame-Retarding Agent 4 4 4 4 Antimony Trioxide (wt %) Carbon Fibers 15 15 45 2 PAN Chopped Strand (wt %) Property Tensile Strength (kg/mm.sup.2) 2.3 3.1 3.0 3.0 Bending Strength (kg/mm.sup.2) 3.5 5.5 7.0 5.5 Bending Modulus of Elasticity (kg/mm.sup.2) 340 560 700 550 Izod Impact Strength (kg-cm/cm) 20 8 4 12 Thermal Defromation Temperature (.degree.C.) 65 100 100 95 below below Flame-Retarding Property (1/8 inch bar) V-0 V-2 V-2 V-0 Oxygen Index (%) 32 21 21 32 above below Electromagnetic Wave Shielding 43 37 70 10 Effect (dB) Molding Process INJ INJ INJ INJ ______________________________________ Note: INJ in the Table means injection molding. EXAMPLE 41 (RUN NOS. 1 TO 6) Used as the resin components were a powder-form ABS resin (acrylonitrile/butadiene/styrene copolymer resin) composed of 10 wt% of acrylonitrile, 50 wt% of butadiene and 40 wt% of styrene, and a bead-form AS resin (acrylonitrile/styrene copolymer resin) composed of 30 wt% of acrylonitrile and 70 wt% of styrene. The plasticizer used was a tricresyl phosphate available from Daihachi Kagaku K.K., and the conductive filler used was the nickel-plated carbonized polyacrylonitrile chopped strands having a fiber length of 6 mm, a fiber diameter of 7.mu. and a bundle count of 12,000, available from Toho Rayon Co., Ltd. under the Trade Name "BESFIGHT M.C.". 1 part by weight of an antioxidant and 1 part by weight of zinc stearate were added to 100 parts by weight of the resinous components of each composition to prepare each of the compositions set forth in Table 9. Each of the compositions was put in a Banbury mixer heated to 140.degree. C. to be mixed and kneaded. After the temperature of the mixture reached 190.degree. C., the mixture was discharged from the mixer and then immediately rolled through mixing rollers to form a sheet, which was cooled and then crushed into pellets. The pellets were charged in a hopper of an 8-ounce injection molding machine to be melted and then injected into a mold for molding a housing 15 cm square and having a wall thickness of 3 mm, the mold being provided with a direct gate having a port diameter of 2 mm.phi.. The thus molded products had excellent physical properties, improved electromagnetic wave shielding effect, excellent resistance to heat and good appearance. EXAMPLE 41 RUN NOS. 7 AND 8) The compositions as set forth in Table 9 were pelletized similarly to Run No. 1 of Example 41, and the pellets were charged in a hopper of an extruder having a cylinder of 65 mm in diameter (L/D=25) to be melted and then extruded through a die for forming a single layer sheet. The die had a width of 600 mm and the lip gap was adjusted to 3.5 mm. By passing the molten mass through the die, a single layer sheet having a thickness of 3 mm was produced. The thus formed single layer sheets had excellent physical properties, improved electromagnetic wave shielding effect, excellent resistance to heat and good appearance, as shown in Table 9. EXAMPLE 41 (RUN NOS. 9 AND 10) A powder-form MBS resin (methacrylonitrile/butadiene/styrene copolymer resin) composed of 40 wt% of methacrylonitrile, 20 wt% of butadiene and 40 wt% of styrene was used in place of the powder-form acrylonitrile/butadiene/styrene copolymer resin used in Example 41 Run Nos. 1 and 2 to prepare the compositions as set forth in Table 9. The compositions were pelletized similarly to Run No. 1 of Example 41, and injection molded products were produced from the pellets. Test results revealed that the molded products had excellent physical properties, excellent resistance to heat, improved electromagnetic wave shielding effect and good appearance. EXAMPLE 41 (RUN NO. 11) A pellet-form ABS resin (acrylonitrile/butadiene/styrene copolymer resin) composed of 20 wt% of acrylonitrile, 20 wt% of butadiene and 60 wt% of styrene was used to prepare the composition as set forth in Table 9. The composition was pelletized similarly to Run No. 1 of Example 41, and an injection molded product was produced from the pellets. The test results revealed that the molded product had excellent physical properties, excellent resistance to heat, improved electromagnetic wave shielding effect and good appearance. EXAMPLE 41 (RUN NO. 12) As shown in Table 9, copper-plated carbon fibers were used in place of the conductive filler as used in Run No. 1 of Example 41. An injection molded product was produced from the composition generally following to the procedures as described in Run No. 1 of Example 41. The test results revealed that the molded product had excellent physical properties, excellent resistance to heat, improved electromagnetic wave shielding effect and good appearance. EXAMPLE 41 (RUN NOS. 13 AND 14) Injection molded products were produced similarly to Run No. 1 of Example 41, except in that dioctylphthalate (DOP) produced by Daihachi Kagaku K.K. was used in place of the plasticizer used in Run No. 1 of Example 41. The compositions are shown in Table 9. The test results revealed that the molded products had excellent physical properties, excellent resistance to heat, improved electromagnetic wave shielding effect and good appearance. COMPARATIVE EXAMPLES 13 AND 14 Injection molded products were produced similarly to Run No. 1 of Example 41, except in that one composition contained Ni-plated carbon fibers in an amount of less than the defined range whereas the other composition contained the Ni-plated carbon fibers in an amount of more than the defined range, as shown in Table 10. The properties of the injection molded products are shown in Table 10. COMPARATIVE EXAMPLE 15 An injection molded product was produced similarly to Run No. 1 of Example 41, except in that brass fibers available from Aisin Seiki Co., Ltd. under the Trade Name "AISIN METAL FIBER" were used in place of the conductive filler used in Run No. 1 of Example 41. The properties of the injection molded product are shown in Table 10. TABLE 9 __________________________________________________________________________ Example 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 __________________________________________________________________________ Composition (wt %) Resin Powder-form ABS Resin 30 40 30 25 25 30 30 40 -- -- -- 30 30 30 Powder-form MBS Resin -- -- -- -- -- -- -- -- 30 40 -- -- -- -- Bead-form AS Resin 50 45 45 45 35 30 50 40 50 40 -- 50 45 35 Pellet-form ABS Resin -- -- -- -- -- -- -- -- -- -- 80 -- -- -- Plasticizer Tricresyl Phosphate 5 5 10 15 5 20 5 5 5 5 5 5 -- -- Dioctyl Phthalate -- -- -- -- -- -- -- -- -- -- -- -- 10 20 Conductive Filler Ni--PLated Carbon Fibers 15 10 15 15 35 20 15 15 15 15 15 -- 15 15 Cu--Plated Carbon Fibers -- -- -- -- -- -- -- -- -- -- -- 15 -- -- Carbon Fibers -- -- -- -- -- -- -- -- -- -- -- -- -- -- Brass Fibers -- -- -- -- -- -- -- -- -- -- -- -- -- -- Property Electromagnetic Weave Shielding 65 50 65 70 85 75 55 50 65 60 60 65 55 60 Effect (dB) Tensile Strength (kg/mm.sup.2) 4.0 4.2 3.8 3.7 3.1 3.4 3.7 3.6 4.1 4.3 3.8 3.9 3.9 3.7 Bending Strength (kg/mm.sup.2) 6.0 6.4 5.5 5.4 4.9 5.0 6.1 6.3 6.1 6.2 5.5 5.8 5.4 5.1 Bending Modulus of 500 480 500 540 610 600 490 5000 500 520 480 480 500 490 Elasticity (kg/mm.sup.2) Izod Impact Strength (kg-cm/cm) 10 13 11 13 7 8 9 9 9 10 9 10 9 11 Vicat Softening Point (.degree.C.) 80 78 75 72 74 75 78 75 82 80 78 76 79 77 Appearance o o o o o o o o o o o o o o __________________________________________________________________________ Note: Appearance was visually appraised. The mark o indicates that the surface is excellent in smoothness, the mark .DELTA. indicates that the surface is fairly smooth, and the mark x indicates that the surface is rough or rugged. TABLE 10 ______________________________________ Comparative Example 13 14 15 ______________________________________ Composition (wt %) Resin Powder-form ABS Resin 33 20 30 Powder-form MBS Resin -- -- -- Bead-form AS Resin 60 30 50 Pellet-form ABS Resin -- -- -- Plasticizer Tricresyl Phosphate 5 5 5 Dioctyl Phthalate -- -- -- Conductive Filler Ni--Plated Carbon Fibers 2 45 -- Cu--Plated Carbon Fibers -- -- -- Carbon Fibers -- -- -- Brass Fibers -- -- 15 Property Electromagnetic Wave Shielding Effect 5 90 30 (dB) Tensile Strength (kg/mm.sup.2) 5.0 2.0 2.8 Bending Strength (kg/mm.sup.2) 7.0 3.2 4.3 Bending Modulus of Elasticity (kg/mm.sup.2) 300 500 480 Izod Impact Strength (kg-cm/cm) 20 4 4 Vicat Softening Point (.degree.C.) 82 75 75 Appearance o x x ______________________________________ Note: Appearance was visually appraised. The mark o indicates that the surface is excellent in smoothness, the mark .DELTA. indicates that the surface is fairly smooth, and the mark x indicates that the surface is rough or rugged. Although the invention has been described by referring to specific examples, it should be interpreted that the present invention is not limited only to the specific examples as herein disclosed, but it is intended to embrace all modifications and alternations included in the broad scope of the invention as defined in the appended claims. |
description | This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2011-009812 filed on Jan. 20, 2011 in Japan, the entire contents of which are incorporated herein by reference. 1. Field of the Invention The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method. For example, it relates to an apparatus that transmits deflection data by optical transmission in electron beam writing. 2. Description of Related Art The microlithography technique which advances microminiaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. In order to form a desired circuit pattern on semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high precision is needed. Thus, the electron beam writing technique, which intrinsically has excellent resolution, is used for producing such a highly precise master pattern. FIG. 7 is a schematic diagram explaining operations of a variable-shaped electron beam (EB) writing apparatus. As shown in the figure, the variable-shaped electron beam writing apparatus operates as described below. A first aperture plate 410 has a quadrangular, such as a rectangular, opening 411 for shaping an electron beam 330. A second aperture plate 420 has a variable-shape opening 421 for shaping the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector to pass through a part of the variable-shape opening 421 of the second aperture plate 420, and thereby to irradiate a target workpiece or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g. X direction) during the writing. In other words, a quadrangular shape that can pass through both the opening 411 and the variable-shape opening 421 is used for pattern writing in a writing region of the target workpiece 340 on the stage continuously moving in the X direction. This method of forming a given shape by letting beams pass through both the opening 411 of the first aperture plate 410 and the variable-shape opening 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) method. (For example, refer to Japanese Unexamined Patent Publication No. 2007-043083.) In the electron beam writing, writing is performed per subfield (SF) which is obtained by dividing the writing region of the substrate into meshes. Since the number of SFs increases with the recent miniaturization of patterns, further improvement is required in speed and precision of processing deflection data concerning deflection to SF. For example, when transmitting a deflection signal from a control circuit by optical transmission, there occurs a communication delay. On the other hand, when irradiating with an electron beam an SF in the mask substrate on the stage which is moving, tracking processing needs to be performed in accordance with the movement of the stage, and thereby it needs to perform deflection to the tracked position. When the writing processing in one SF has been completed, tracking of the next SF position is started. Therefore, if there is a communication delay, writing processing for the next SF will be delayed, thereby causing an increase in the writing time, which degrades the throughput of the writing apparatus. In accordance with one aspect of the present invention, a charged particle beam writing apparatus includes an emission unit configured to emit a charged particle beam, a stage on which a substrate serving as a writing target is placed and which is movable, a plurality of tracking calculation units each configured to calculate a deflection amount of the charged particle beam, for following movement of the stage, while having a calculation time difference wherein there exists a mutual overlapping time period, a switching unit configured, for each small region of a plurality of small regions made by virtually dividing a surface of the substrate, to input an end signal indicating that emission of the charged particle beam to a small region concerned has been completed, and to switch, using the end signal as a trigger, from output of one of the plurality of tracking calculation units to output of another of the plurality of tracking calculation units, and a deflector configured, while the stage is moving, to deflect the charged particle beam to an n-th small region, based on a signal output from one of the plurality of tracking calculation units before switching the plurality of tracking calculation units, and to deflect the charged particle beam to an (n+1)th small region, based on a signal output from another of the plurality of tracking calculation units after switching the plurality of tracking calculation units. In accordance with another aspect of the present invention, a charged particle beam writing method includes emitting a charged particle beam, calculating, by a plurality of tracking calculation units, deflection amounts of the charged particle beam, for following movement of a stage on which a substrate serving as a writing target is placed, while having a calculation time difference wherein there exists a mutual overlapping time period, inputting, for each small region of a plurality of small regions made by virtually dividing a surface of the substrate, an end signal indicating that the emitting of the charged particle beam to a small region concerned has been completed, and switching, using the end signal as a trigger, from output of one of the plurality of tracking calculation units to output of another of the plurality of tracking calculation units, deflecting, while the stage is moving, the charged particle beam to an n-th small region, based on a signal output from one of the plurality of tracking calculation units before switching the plurality of tracking deflection amount calculation units, and deflecting, while the stage is moving, the charged particle beam to an (n+1)th small region, based on a signal output from another of the plurality of tracking calculation units after switching the plurality of tracking calculation units. In Embodiment 1, there will be described a structure in which an electron beam is used as an example of a charged particle beam. However, the charged particle beam is not limited to the electron beam, and other charged particle beam, such as an ion beam, may also be used. Moreover, a variable-shaped electron beam writing apparatus will be described as an example of a charged particle beam apparatus. In Embodiment 1, there will be described an apparatus and a method capable of inhibiting throughput degradation due to a communication delay of a deflection signal. FIG. 1 is a schematic diagram showing a structure of a writing apparatus according to Embodiment 1. In FIG. 1, a writing apparatus 100 includes a writing unit 150 and a control unit 160. The writing apparatus 100 (or drawing apparatus 100) is an example of a charged particle beam writing apparatus, and especially, an example of a variable-shaped beam (VSB) writing apparatus. The writing apparatus 100 writes (or draws) a pattern on a target workpiece by using an electron beam. The writing unit 150 includes an electron lens barrel 102 and a writing chamber 103. In the electron lens barrel 102, there are arranged an electron gun assembly 201, an illumination lens 202, a blanking (BLK) deflector 212, a blanking aperture 214, a first shaping aperture 203, a projection lens 204, a deflector 205, a second shaping aperture 206, an objective lens 207, a main deflector 208, and a sub deflector 209. In the writing chamber 103, there is arranged an XY stage 105 movable in at least the X and Y directions. On the XY stage 105, there is placed a target workpiece 101 serving as a writing target. The target workpiece 101 (substrate) is, for example, a mask for exposure, a silicon wafer, etc. used for manufacturing semiconductor devices. The mask is, for example, a mask blank where no patterns are formed. Resist has been applied to the surface of the target workpiece 101. The control unit 160 includes a control computer 110, a memory 112, a deflection control circuit 120, relay units 130 and 132, a stage control circuit 134, a storage device 140 such as a magnetic disk drive, and digital-to-analog conversion (DAC) amplifiers 170, 172, 174, and 176. The control computer 110, the memory 112, the deflection control circuit 120, the stage control circuit 134, and the storage device 140 such as a magnetic disk drive are mutually connected through a bus (not shown). The deflection control circuit 120 is connected to the relay units 130 and 132 by an optical cable 122. The optical cable 122 includes optical cables 124 and 126. The deflection control circuit 120 is connected to the relay unit 132 (first relay unit) by the optical cable 124 (first optical cable). The deflection control circuit 120 is connected to the relay unit 130 (second relay unit) by the optical cable 126 (second optical cable). The relay units 130 and 132 are connected with each other. The relay unit 132 is connected to the blanking deflector 212 through the DAC amplifier 170, to the deflector 205, which is used for shaping purposes, through the DAC amplifier 172, and to the sub deflector 209 through the DAC amplifier 174. The relay unit 130 is connected to the main deflector 208 through the DAC amplifier 176. In the deflection control circuit 120, there are arranged a BLK calculation unit 10, a shaping deflection calculation unit 12, a sub deflection calculation unit 14, a control unit 18, a main deflection calculation unit 20, and two or more (a plurality of) tracking calculation units 22 and 24 (tracking deflection amount calculation units). Each function, such as the BLK calculation unit 10, the shaping deflection calculation unit 12, the sub deflection calculation unit 14, the control unit 18, the main deflection calculation unit 20, and the two or more tracking calculation units 22 and 24 may be configured by software such as a program, or may be configured by hardware such as an electronic circuit. Alternatively, it may be configured by a combination of software and hardware. Input data necessary for the deflection control circuit 120 and a calculated result are stored in the memory (not shown) each time. In the relay unit 130, there are arranged two or more (a plurality of) main deflection I/F circuits 30 and 32 and a switching unit 34. In the relay unit 132, there are arranged a blanking (BLK) I/F circuit 36, a shaping deflection I/F circuit 38, a sub deflection I/F circuit 40, a subfield end (SFE) detection unit 42, and a pre subfield end (PreSFE) calculation unit 44. In the storage device 140, writing data necessary for writing, such as a pattern layout, a figure code, and coordinates, is input from the outside to be stored. FIG. 1 shows a structure necessary for describing Embodiment 1. Other structure elements generally necessary for the writing apparatus 100 may also be included. For example, although the main and sub two stage deflectors, namely the main deflector 208 and the sub deflector 209 are herein used, a one stage deflector or a three (or more) stage deflector may also be used to perform deflection to a predetermined position of the target workpiece. In the pattern input step, the control computer 110 inputs writing data stored in the storage device 140. The control computer 110 performs data conversion processing of a plurality of steps for the writing data input from the storage device 140, and generates shot data unique to the writing apparatus. The control computer 110 functions as a writing data processing unit. The control computer 110 converts a plurality of figure patterns defined in the writing data into shot figures each having the size which can be irradiated (which can be shaped) by a one-time shot of an electron beam 200. Then, shot data is generated in which there are defined a dose, an irradiation position, a type, a size, etc. of each shot figure. Input data necessary for the control computer 110 and a calculated result are stored in the memory 112 each time. Then, the generated shot data is output to the deflection control circuit 120. In accordance with the shot data, in the deflection control circuit 120, the BLK calculation unit 10 performs calculation to generate BLK deflection data which is for alternately producing a beam-ON state and a beam-OFF state so that the beam-ON state may be maintained only for a defined dose (only during a defined deflection time period). The generated BLK deflection data is output to the relay unit 132 through the optical cable 122. Moreover, in accordance with the shot data, the shaping deflection calculation unit 12 performs calculation to generate shaping deflection data which is for variably shaping the beam shape and the beam size of each shot of the electron beam 200 generated in the beam-ON state. The generated shaping deflection data is output to the relay unit 132 through the optical cable 122. The writing region of the target workpiece 101 is virtually divided into a plurality of strip-like stripe regions in the X or Y direction, each having a width deflectable by the main deflector 208. Further, the stripe region is virtually divided into subfields (SFs) deflectable by the sub deflector 209. In accordance with the shot data, the sub deflection calculation unit 14 performs calculation to generate deflection data (sub deflection data) which is for deflecting the electron beam 200 from the reference position of the SF concerned to each shot position in each SF. The generated sub deflection data is output to the relay unit 132 through the optical cable 122. Moreover, in accordance with the shot data, the main deflection calculation unit 20 performs calculation to generate deflection data (main deflection data) which is for deflecting the electron beam 200 to each SF. The generated main deflection data is output to the tracking calculation units 22 and 24. When performing writing onto the target workpiece 101, since the XY stage 105 moves, the two or more tracking calculation units 22 and 24 perform calculation to generate deflection data for tracking, that is tracking data, to be used by the main deflector 208 which performs deflection to follow the movement of the XY stage 105. The position of the XY stage 105 may be input from the stage control circuit 134, for example. According to Embodiment 1, the tracking calculation units 22 and 24 alternately calculate tracking data of each SF, such as calculating tracking data of the n-th SF by the tracking calculation unit 22 and calculating tracking data of the (n+1)th SF by the tracking calculation unit 24. For each SF, main deflection data and tracking data concerned are output to the relay unit 130 through the optical cable 122. Tracking data of each of the tracking calculation units 22 and 24 is: (tracking data)=(main deflection data−stage position data). Since the main deflection data is set up for each SF, the offset of each SF is different. Therefore, it is more preferable to perform tracking calculation for the n-th SF and the (n+1)th SF by a plurality of tracking calculation units 22 and 24. In the relay unit 132, BLK deflection data is output to the DAC amplifier 170 through the blanking I/F circuit 36. Then, the BLK deflection data is converted to an analog signal from the digital signal by the DAC amplifier 170 to be amplified and applied as a deflection voltage to the BLK deflector 212. Moreover, shaping deflection data is output to the DAC amplifier 172 through the shaping deflection I/F circuit 38. Then, the shaping deflection data is converted to an analog signal from the digital signal by the DAC amplifier 172 to be amplified and applied as a deflection voltage to the deflector 205 which is used for shaping purposes. Moreover, sub deflection data is output to the DAC amplifier 174 through the sub deflection I/F circuit 40. Then, the sub deflection data is converted to an analog signal from the digital signal by the DAC amplifier 174 to be amplified and applied as a deflection voltage to the sub deflector 209. On the other hand, in the relay unit 130, the main deflection data and the tracking data output from the tracking calculation unit 22 are output to the main deflection I/F circuit 30, and the main deflection data and the tracking data output from the tracking calculation unit 24 are output to the main deflection I/F circuit 32. The switching unit 34 switches the connection between the DAC amplifier 176 and the main deflection I/F circuits 30 and 32 so that the main deflection data and the tracking data may be output to the DAC amplifier 176 through one of the main deflection I/F circuits 30 and 32. Then, the data of added main deflection data to tracking data is converted to an analog signal from the digital signal by the DAC amplifier 176 to be amplified, thereby being applied as a deflection voltage to the main deflector 208. The writing unit 150 writes a pattern onto the target workpiece 101 by using the electron beam 200. Specifically, the following operation is performed. When passing through the blanking deflector 212, the electron beam 200 emitted from the electron gun assembly 201 (emission unit) is controlled by the blanking deflector 212 to pass through the blanking aperture 214 when the beam is in the ON state, and is deflected so that the entire beam may be blocked by the blanking aperture 214 when the beam is in the OFF state. The electron beam 200 passing through the blanking aperture 214, while changing the state from beam-OFF to beam-ON and lastly again to beam-OFF, serves as one shot of the electron beam. The blanking deflector 212 controls the direction of the passing electron beam 200 to alternately generate the beam-ON state and the beam-OFF state. For example, it is acceptable to apply a voltage to the blanking deflector 212 when in the beam-OFF state and not to apply a voltage when in the beam-ON state. The dose per shot of the electron beam 200 to irradiate the target workpiece 101 is adjusted based on the irradiation time of each shot. As described above, each shot of the electron beam 200, generated by passing through the blanking deflector 212 and the blanking aperture 214, irradiates the whole of the first shaping aperture 203 which has a quadrangular opening such as a rectangular opening by the illumination lens 202. At this time, the electron beam 200 is first shaped to be a quadrangle such as a rectangle. Then, after having passed through the first shaping aperture 203, the electron beam 200 of a first aperture image is projected onto the second shaping aperture 206 by the projection lens 204. The first aperture image on the second shaping aperture 206 is deflection-controlled by the deflector 205 to change the shape and size of the beam, that is, the variable beam shaping is performed. Such variable beam shaping is performed for each shot, and, usually, each of the shots is shaped to have a different shape and size. Then, after having passed through the second shaping aperture 206, the electron beam 200 of a second aperture image is focused by the objective lens 207, and deflected by the main deflector 208 and the sub deflector 209 to reach a desired position on the target workpiece 101 placed on the XY stage 105 which moves continuously. First, the main deflector 208 deflects the electron beam 200 to the reference position in the SF to be shot. Since the XY stage 105 is moving, the main deflector 208 deflects the electron beam 200 such that the movement of the XY stage 105 is followed. Then, each position (shot position) in the SF is irradiated by the sub deflector 209. FIG. 2 shows a time chart of signals in the deflection control circuit and the relay unit according to Embodiment 1. In FIG. 2, for example, for the n-th SF, the main deflection data and the tracking data following the main deflection data are output from the deflection control circuit 120. Then, after waiting for the settling time of the DAC amplifier 176 for the main deflection, the BLK deflection data is output. Since the deflection control circuit 120 and the relay units 130 and 132 are connected by the optical cable 122, a delay (time T1) is generated in the signal transmission. Therefore, the main deflection data and the tracking data from the deflection control circuit 120 are delayed by the time T1 to reach the relay unit 130. Similarly, the BLK deflection data is delayed by the time T1 to reach the relay unit 132. When the settling time of the DAC amplifier 176 has passed and the deflection voltage to be applied to the main deflector 208 is stabilized, the BLK deflector 212 generates an “on” beam for each shot, based on ON or OFF of the deflection voltage from the DAC amplifier 170. Then, a shot figure is written for each shot by shaping the electron beam for the shot concerned by the deflector 205 and emitting the shaped electron beam to the shot position concerned in the SF by the sub deflector 209. By combining such shot figures, a pattern in the SF is written onto the target workpiece 101. When the writing to the n-th SF is completed, the SFE detection unit 42 detects the completion of the writing to the n-th SF and outputs a subfield end (SFE) signal (SFE flag). When the writing to the n-th SF has been completed and writing to the next SF, namely the (n+1)th SF, is going to be performed, if such an SFE signal is waited, the following problem will occur. FIG. 3 is a schematic diagram, for comparing with Embodiment 1, showing a structure in the case there is only one tracking calculation unit and there is no signal switching function in the relay unit for the main deflection. In FIG. 3, a deflection control circuit 320 and relay units 331 and 332 are connected by an optical cable similarly to the case of FIG. 1. In the structure of FIG. 3, the deflection control circuit 320 receives an SFE flag for the n-th SF from the relay unit 332 side, and starts writing processing for the (n+1)th SF. FIG. 4 shows, for comparing with Embodiment 1, an example of a time chart of signals in the deflection control circuit and the relay unit in the case there is only one tracking calculation unit and there is no signal switching function in the relay unit for the main deflection. In FIG. 4, for the n-th SF, the main deflection data and the tracking data following the main deflection data are output from the deflection control circuit 320 side. Then, after waiting for the settling time of the DAC amplifier 176 for the main deflection, the BLK deflection data is output. Since the deflection control circuit 320 and the relay unit 331 are connected by the optical cable, the delay (time T1) is generated in the signal transmission. Therefore, the main deflection data and the tracking data from the deflection control circuit 320 are delayed by the time T1 to reach the relay unit 331. When the settling time of the DAC amplifier 176 has passed and the deflection voltage to be applied to the main deflector is stabilized, the BLK deflector generates an “on” beam for each shot, based on ON or OFF of the deflection voltage from the DAC amplifier 170. Then, a beam is shaped for each shot, and the shaped electron beam is emitted to the shot position concerned. Since it takes a time T2, as a transmission delay of the optical cable, for the SFE flag to reach the deflection control circuit 320 from the relay unit 332, even after the BLK deflection data for the n-th SF is finished, it is still necessary to continue to calculate and output the tracking data for the time period of T1+T2. This is because if tracking is finished before completing the writing to the n-th SF, the writing position will be shifted. Accordingly, in spite of the tracking data for writing the n-th SF being actually enough, it continues to calculate the data, thereby generating a problem of a delay of starting calculation for the next SF. FIG. 5 shows, for comparing with Embodiment 1, another example of the time chart of signals in the deflection control circuit and the relay unit in the case there is only one tracking calculation unit and there is no signal switching function in the relay unit for the main deflection. In the case of FIG. 4, since the SFE flag is waited, calculation start for the next SF is delayed by the time period of T1+T2. Then, in the case of FIG. 5, before the writing to the n-th SF is completed, a pre SFE flag is output to the deflection control circuit 320 from the relay unit 332 in advance anticipating the time delay T1+T2. In the present case, using a margin time Tm, the relay unit 332 outputs a pre SFE flag to the deflection control circuit 320 at the time prior to the completion of the writing by (T1+T2−Tm). Originally, since the SFE is not synchronized with the main deflection data or the tracking data, it is needed to set a margin time Tm that can be obtained by considering a time delay of an optical communication module, jitter, skew, etc. and multiplying by a safety coefficient. Thus, in the deflection control circuit 320, the calculation of tracking data can be finished in response to the pre SFE flag, thereby reducing the unnecessary time. However, according to the method of FIG. 5, there occurs a problem that if making a mistake in estimating the setting of the margin time Tm, tracking data will stop before completing the writing. Then, in Embodiment 1, as shown in FIG. 1, a plurality of tracking calculation units are arranged in the deflection control circuit 120, and a signal switching function is arranged in the relay unit 130 for the main deflection. As shown in FIG. 2, before the writing to the n-th SF is completed, a pre SFE flag is output to the deflection control circuit 120 from the relay unit 130 in advance, anticipating the time delay T1+T2. In the present case, the PreSFE calculation unit 44 in the relay unit 132 generates a pre SFE flag at the time prior to the completion of the writing by T1+T2+T0 by using the margin time T0, and outputs it to the deflection control circuit 120 from the relay unit 132. In other words, the PreSFE calculation unit 44 outputs to each SF (small region) a pre SFE flag, which is a false signal of the SFE flag being an end signal, before the emission of the electron beam to the SF concerned is completed. The PreSFE calculation unit 44 serves as an example of a false signal output unit. In the deflection control circuit 120, in response to the pre SFE flag, the control unit 18 makes the main deflection calculation unit 20 start to calculate main deflection data for the (n+1)th SF. Furthermore, the control unit 18 makes, for example, another tracking calculation unit 24, which is different from the tracking calculation unit 22 currently tracking the n-th SF, start to calculate tracking data for the (n+1)th SF. Then, the main deflection data and the tracking data following the main deflection data are output from the deflection control circuit 120 to the relay unit 130. Since the deflection control circuit 120 and the relay unit 130 are connected by the optical cable 122, a delay (time T1) is generated in the signal transmission. Therefore, the main deflection data and the tracking data are delayed by the time T1 to reach the relay unit 130 from the deflection control circuit 120. At this moment, the writing of the n-th SF has not been completed yet. Therefore, the two or more tracking calculation units 22 and 24 calculate tracking data used as a deflection amount of the electron beam, for following the movement of the XY stage 105, while having a calculation time difference wherein there exists a their mutual overlapping time period. Moreover, in response to the pre SFE flag, the control unit 18 controls the BLK calculation unit 10, the shaping deflection calculation unit 12, and the sub deflection calculation unit 14 to respectively calculate BLK deflection data, shaping deflection data, and subdeflection data for each shot in the (n+1)th SF. Then, the BLK deflection data, the shaping deflection data, and the shaping deflection data are output to the relay unit 132 from the deflection control circuit 120. Since the BLK deflection data, the shaping deflection data, and the subdeflection data are also connected by the optical cable 122, a delay (time T1) is generated in the signal transmission. Therefore, it is delayed by the time T1 to reach the relay unit 132 from the deflection control circuit 120. The switching unit 34 in the relay unit 130 inputs the SFE flag output from the SFE detection unit 42 in the relay unit 132, and, using the SFE flag as a trigger, switches the connection from the output of the tracking calculation units 22 to the output of the tracking calculation unit 24. By this, switching is immediately performed from the main deflection data for the n-th SF and its tracking data to the main deflection data for the (n+1)th SF and its tracking data. After the settling time of the DAC amplifier 176 has passed since the main deflection data for the (n+1)th SF, in the state before switching the connection, reached the relay unit 130, the BLK deflector 212 generates an “on” beam for each shot in the (n+1)th SF, based on ON or OFF of the deflection voltage from the DAC amplifier 170. Then, for each shot, an electron beam for the shot concerned is shaped by the deflector 205, and the shaped electron beam is emitted to the shot position concerned in the (n+1)th SF by the sub deflector 209. Thus, in this way a shot figure is written. By combining such shot figures, a pattern in the (n+1)th SF is written to the target workpiece 101. After completing the writing to the (n+1)th SF, the SFE detection unit 42 detects the completion of the writing to the (n+1)th SF, and outputs an SFE signal (SFE flag). A similar operation will be performed hereafter. The time period since the main deflection data for the (n+1)th SF, in the state before switching the connection, reached the relay unit 130 until the SFE flag reaches the relay unit 130 is several hundreds of nS, which is sufficiently short for the settling time necessary for the DAC amplifier 176 for the main deflection. Therefore, even starting the writing of the (n+1)th SF when the settling time of the DAC amplifier 176 has passed since the main deflection data for the (n+1)th SF, in the state before switching the connection, reached the relay unit 130, the deflection voltage to be applied to the main deflector 208 can be in a stabilized state. FIG. 6 is a schematic diagram explaining an alternate calculation in Embodiment 1. As described above, the two or more tracking calculation units 22 and 24 input the pre SFE flag which serves as a false signal from the PreSFE calculation unit 44, and using the pre SFE flag as a trigger, alternately start tracking calculation. Then, the switching unit 34, for each SF, inputs an SFE flag indicating that emission of the electron beam to the SF concerned has been completed, and using the SFE flag as a trigger, switches the connection with the DAC amplifier 176 from output of one of a plurality of tracking calculation units 22 and 24 to output of another of the units 22 and 24. While the XY stage 105 is moving, the main deflector 208 deflects the electron beam 200 to the n-th SF, based on a signal output from one of the plurality of tracking calculation units 22 and 24 before switching the plurality of tracking calculation units. Then, the sub deflector 209 respectively deflects the beam of a shot concerned to each shot position in the n-th SF. Next, after switching, the main deflector 208 deflects the electron beam 200 to the (n+1)th SF, based on a signal output from another of the plurality of tracking calculation units 22 and 24. Then, the sub deflector 209 respectively deflects the beam of a shot concerned to each shot position in the (n+1)th SF. During the time between receiving the SFE flag for the n-th SF and switching the connection by the switching unit 34, the tracking data for the (n+1)th SF generated in response to the pre SFE flag is not used as being a so-called discard signal. However, it becomes possible to eliminate a unnecessary standby time by having an overlapped time period of the tracking data for the n-th SF and the tracking data for the (n+1)th SF. Therefore, the margin Tm needed in order not to stop the tracking data during the writing, which has been explained with reference to FIG. 5, can also be unnecessary. As described above, according to Embodiment 1, it is possible to inhibit lowering of the deflection processing speed even if there is a communication delay of a deflection signal, such as the case of using an optical cable etc. for connection. Therefore, it is possible to inhibit decrease of the throughput of the writing apparatus. Referring to specific examples, Embodiment has been described above. However, the present invention is not limited to these examples. For example, although the optical cable is used in the example mentioned above, it is not limited to it, and any connection having a communication delay can be applied. While the apparatus structure, control method, etc. not directly necessary for explaining the present invention are not described, some or all of them may be suitably selected and used when needed. For example, although description of the structure of a control unit for controlling the writing apparatus 100 is omitted, it should be understood that some or all of the structure of the control unit is to be selected and used appropriately. In addition, any other charged particle beam writing apparatus and method thereof that include elements of the present invention and that can be appropriately modified by those skilled in the art are included within the scope of the present invention. Additional advantages and modification will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. |
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summary | ||
description | FIG. 1 shows the construction of the X-ray examination apparatus according to the invention. The X-ray source 1 emits X-rays 9. The X-rays pass the absorption means 3 which will also be referred to hereinafter as collimator plates 3. The collimator plates 3 are displaced by the control unit 4. The X-rays 7 transmitted by the collimator plates 3 irradiate the object 8 to be examined and are incident on the X-ray detector 2. The X-ray image is then picked up and converted into an electric image signal. The image signal 20 is applied to the image processing unit 5. The acquired image is displayed on the display unit in the form of a monitor 6. The image processing unit 5 is connected to the control unit 4 in order to adjust the degree of absorption of the collimator plates 3. FIG. 2 shows the construction of the image processing unit 5. The image processing unit 5 receives the image signal 20 from the X-ray detector 2 which is not shown herein. The signal is applied to the image memory 21 for storage and at the same time to the monitor 6 for display. The actual attenuation is calculated in the attenuation calculation unit 22 by means of the adjustment parameter vector pakt stored in the memory 29. The actual attenuation D(pakt) is the value of the attenuation applied to the acquired X-ray image, because absorption means may have been partly slid into the X-ray beam path. The unit 35 forms the reciprocal value of the actual attenuation value D in order to multiply it by the X-ray image stored in the image memory 21 so as to obtain an image wherefrom the attenuation D has been removed. The non-attenuated image is subdivided into image regions N in the unit 23. The unit 23 is succeeded by a parameter extraction unit 24 for calculating the image parameters such as contrast or structure parameters. In the optional attenuation correction unit the attenuation could also be calculated on the basis of the adjustment parameter vector Pakt. The parameter matrix C thus formed is applied to the quality function calculation unit 26. The unit 26 receives from the unit 32 the system parameters in the form of the system parameter vector s and the vector r representing the knowledge base. The knowledge or control base in the form of the vector r is stored in the unit 31 and is applied to the unit 26 for the calculation of the quality function Z as well as to the adaptation unit 30 for the adaptation of the knowledge base. The quality function is optimized in the unit 27. The adjusting parameter vector popt is calculated which contains the optimized adjustment of the absorption means. This adjustment parameter vector popt is applied to a further attenuation correction unit 33 which is similar to the attenuation unit 22 and calculates the adjustment of the attenuation D(p) on the basis of the adjustment parameter vector popt in order to apply it to the calculation of the quality function in the unit 26 again so as to be used for further optimization of the adjustment parameter vector p during the next run, until the optimized adjustment parameter vector popt has been determined. The latter is then applied to the unit 28 in which it is checked or confirmed that the instantaneous adjustment of the plates, also being applied to the monitor 6, is correct. When the instantaneous adjustment in the form of the adjustment parameter vector popt is confirmed by the physician, the adjustment parameter vector pakt is stored in the memory 29 and conducted therefrom to the control unit (not shown). At the same time the adjustment of the absorption means, embodied in the adjustment parameter vector popt, is superposed on the actual X-ray image in the superposition unit 34. The adjustment parameter vector pakt actually used and stored in the memory 29 is applied to the adaptation unit 30 in which the knowledge base is adapted by means of a learning process. The use of the quality function calculation will be illustrated on the basis of a simple example. The image I(x,y) stored in the image memory is subdivided into N non-overlapping, rectangular regions Ii(x,y) of a width of Nx. pixels and a length of Ny pixels. For these regions the structure contained therein is described by the variance and σ i 2 = 1 ( N x N y - 1 ) ∑ x = 1 N x ∑ y = 1 N y ( I i ( x , y ) - 1 N x N y ∑ x = 1 N x ∑ y = 1 N y I i ( x , y ) ) 2 ( 4 ) is calculated as the parameter. Because only one parameter is calculated for all image regions, the parameter matrix C has one row only: C=("sgr"l . . . "sgr"N) For a single absorption means, hereinafter being a semi-transparent plate whose position is characterized by the adjustment parameter vector p=(1, "PHgr"xcfx86), with the angle "PHgr" and the insertion length l, the effect of the radiation attenuation on an image I can be represented by a function D(p,x,y) in such a manner that the attenuated image ID is given by ID(p, x, y)=D(p, x, y)I(x, y)xe2x80x83xe2x80x83(5) D(p,x,y) can be approximated, for example, via simple simulations. For the optimization a quality function Z(r, s, C, D(p)) can be indicated which is dependent on the additional parameter vectors r and s. A simple example of such a quality function can be given by the weighted addition of a plurality of single quality functions; for example, should essentially regions of little structure be removed, a component can penalize the attenuation of diagnostically relevant regions containing structures, that is such structures lead to an increase of the quality function which is then to be minimized. A further component penalizes regions with little structure which are not masked by the inserted diaphragm plate. Such a quality function is, for example, as follows: Z ( r , s , C _ _ , D ( p _ ) ) = xe2x80x83 ∑ n = 1 N ( rU ( D n ( p _ ) ( 1 - c 1 , n / s 2 ) ) + xe2x80x83 U ( ( 1 - D n ( p _ ) ) xe2x80x83 ( c 1 , n / s 2 - 1 ) ) ) ( 6 ) where D n = 1 N x N y ∑ x = 1 N x ∑ y = 1 N y D ( p _ , x , y ) ( 7 ) and the elements of C are in conformity with cl,n={C}l,n. In the present example the control base has only a single component r; the parameter s represents the sole component of the system parameter vector s and provides dose-dependent and radiation quality dependent normalization of the diagnostically relevant contrast. This parameter can be read from a stored table in dependence on the beam quality used. The function U increasingly penalizes positive contributions. It may be given, for example by U ( x ) = { x 2 for xe2x80x83 x greater than 0 0 for xe2x80x83 x ≤ 0 The first term of the quality function (6) thus penalizes unstructured regions which are not attenuated. The second term of the quality function (6) evaluates the effect of the introduced plate on contrasts in the diagnostically relevant region. Both components are contradictory and are weighted relative to one another via r. The larger r is chosen, the more the suppression of unstructured regions is given priority over the preservation of diagnostically relevant information. The optimum diaphragm position is then determined by minimizing the quality function: p _ opt = arg xe2x80x83 min p xe2x80x83 _ xe2x80x83 Z ( r , s , C _ _ , D xe2x80x83 ( p _ ) ) . ( 8 ) This can be performed, for example numerically by way of the Nelder-Mead Simplex algorithm. The diaphragm position thus determined is then graphically superposed on the monitor or adjusted directly by motor. As has already been described, the correction can be used to perform the user-specific or application-specific adaptation of r. |
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claims | 1. A cooling system for a nuclear fuel storage cask, the cooling system comprising:an inner passage extending around and circumscribing an inner perimeter of a nuclear fuel storage cask and extending along a length of the nuclear fuel storage cask, the length being evaluated between a first end and a second end of the nuclear fuel storage cask positioned opposite the first end;an outer passage positioned outward from the inner passage and in fluid communication with the inner passage;a coolant positioned within the inner passage and the outer passage, wherein the coolant is configured to move through the inner passage, absorbing heat from an inner cavity of the storage cask, and the coolant is configured to move through the outer passage, dissipating heat through an outer perimeter of the storage cask, wherein the inner cavity is circumscribed by an outer shell; anda lid to the outer shell, wherein the lid covers the inner cavity of the outer shell and the lid comprises a lid cooling circuit, the lid cooling circuit comprising a vapor passage and a lid outer passage distinct from one another, the lid outer passage positioned outward of the vapor passage, wherein the lid further comprises a lid coolant positioned within the lid cooling circuit, and wherein the lid coolant remains in the lid cooling circuit and circulates between the vapor passage and the lid outer passage. 2. The cooling system of claim 1, wherein the inner passage is an annular inner passage extending circumferentially around the inner perimeter of the nuclear fuel storage cask. 3. The cooling system of claim 1, wherein the outer passage is an annular outer passage extending circumferentially around the inner passage. 4. The cooling system of claim 1, further comprising an exit passage in fluid communication with the inner passage and the outer passage, wherein the exit passage is positioned at the first end of the nuclear fuel storage cask and extends circumferentially around the nuclear fuel storage cask. 5. The cooling system of claim 1, further comprising an exit passage in fluid communication with the inner passage and the outer passage, wherein the exit passage extends radially along the length of the nuclear fuel storage cask. 6. The cooling system of claim 1, further comprising a return passage in fluid communication with the inner passage and the outer passage, wherein the return passage is positioned at the second end of the nuclear fuel storage cask and extends circumferentially around the nuclear fuel storage cask. 7. The cooling system of claim 1, further comprising a return passage in fluid communication with the inner passage and the outer passage, wherein the return passage extends radially along the length of the nuclear fuel storage cask. 8. The cooling system of claim 1, further comprising a central cooling member extending through a center of the nuclear fuel storage cask. |
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06310931& | claims | 1. A fuel assembly for a light-water cooled nuclear reactor, comprising: a first and a second locking member; a plurality of elongated elements wherein each of lower ends of the elongated elements is provided with an end plug, where the end plug is arranged guided or locked in an end plate which comprises at least two adjacently located plug holes for receiving an end plug each; wherein: the second locking member is arranged displaceable in a locking hole arranged extending between two adjacently arranged plug holes and opening out thereinto, the second locking member being made with a length which exceeds the length of the locking hole and having end surfaces with a shape intended for cooperation with the first locking member in a plug hole and an end plug in the adjacently located plug hole. 2. A fuel assembly (1) according to claim 1, characterized in that the first locking member (9a, 9b) is designed so as to extend around the periphery of the end plug (3b). 3. A fuel assembly (1) according to claim 1, characterized in that the first locking member (9a, 9b) has a substantially concave shape. 4. A fuel assembly (1) according to claim 1, characterized in that the first locking member (9a, 9b) has a substantially spherical shape. 5. A fuel assembly (1) according to claim 3, characterized in that the second locking member (10) is designed as a substantially cylindrical body (10a) with two ends where each end has a convex (10b) shape. 6. A fuel assembly (1) according to claim 5, characterized in that at least one end of the second locking member (10) is designed with a substantially spherical shape (10b). 7. A fuel assembly (1) according to claim 1, characterized in that the second locking member (10) is designed as a substantially cylindrical body (10a) with two ends where at least one end has a plane shape (10e). 8. A fuel assembly (1) according to claim 1, characterized in that the second locking member (10) is designed as a substantially cylindrical body (10a) with two ends where at least one end has a bevelled shape (10d). 9. A fuel assembly (1) according to claim 1, characterized in that the second locking member (10) is designed with a smaller diameter of a part (10c) of the cylindrical body (10a) for cooperation with a locking pin (11) for limiting the movement of the second locking member (10) in the locking hole (6c). |
060977906 | summary | FIELD OF THE INVENTION AND RELATED ART This invention relates to a pressure partition for use as an X-ray window in an exposure chamber of an X-ray exposure apparatus, for example, for mutually isolating two ambiences of different pressures, and also to an X-ray exposure apparatus using the same. In X-ray exposure apparatuses to be used with exposure light comprising synchrotron radiation such as synchrotron X-rays from a charged particle accumulation ring, for example, a high vacuum should be maintained in a beam duct extending from a light source to an exposure chamber in order to reduce attenuation of the X-rays by the atmosphere. To this end, an X-ray extracting window (pressure partition) is provided to mutually isolate two ambiences, that is, the high vacuum beam duct and the exposure chamber of an ambience approximately the same as the atmosphere or of a low vacuum or reduced pressure ambience of helium gas, for example. Such an X-ray window comprises a thin film of a material of a high X-ray transmissivity, such as beryllium, silicon nitride, silicon carbide, and diamond, for example. The thin film should have a high X-ray transmissivity in order to avoid loss of X-ray energy, and also it should have mechanical strength sufficient to bear the pressure difference between the beam duct and the exposure chamber. FIG. 6 shows a known type X-ray window E.sub.0 which comprises a beryllium film 111 of a few microns or several tens of microns in thickness and a flange 112 for supporting the outside periphery of the film. The outside periphery of the beryllium film 111 is fixed to the flange 112 by means of a bonding ring 113. The flange 112 is fixedly connected to a flange 102a of a beam duct 102 by means of an O-ring 114 and bolts 115. As described, the beryllium film 111 should have mechanical strength sufficient to bear a pressure difference .DELTA.P between a pressure P.sub.1 of the beam duct 102, being kept in a high vacuum, and a pressure P.sub.2 of the exposure chamber, being kept in a reduced pressure of helium gas. Additionally, it should have a high X-ray transmissivity. Thus, it is desirable to reduce the thickness of the beryllium film 111 as much as possible, within the limit of the required mechanical strength. Generally, when a pressure difference p is applied to a very thin film of a material having a Young's modulus E and a large deflection or flexure is produced, and if the thickness of the film is h, the tension stress .sigma.(r=0) at the center of the film of a circular shape with a radius a and the tension stress .sigma.(r=a) at the outside peripheral edge of that film can be calculated in accordance with the following equations: ##EQU1## Thus, usually, the thickness of the beryllium film 111 is determined so that the tension stress .sigma..sub.1 at the center of the film 111 as the flexure is produced in the film 111 by the applied pressure difference .DELTA.P, does not exceed the breaking stress. More specifically, if the breaking stress of the beryllium film 111 is .sigma..sub.0 and the tolerance for the pressure difference .DELTA.P related to the beryllium film 111, that is, the design pressure, is P.sub.0, then the necessary thickness T can be expressed from equation (1) as follows: EQU T>0.275.multidot.P.sub.0 .multidot.a/.sigma..sub.0 .multidot.(E/.sigma..sub.0).sup.1/2 (3) In practical design of an X-ray window, a safety factor A is taken into account and the thickness T.sub.0 of the beryllium film 111 is determined in accordance with the following equation: EQU T.sub.0 =A.multidot.0.275.multidot.P.sub.0 .multidot.a/.sigma..sub.0 .multidot.(E/.sigma..sub.0).sup.1/2 (4) Actually, however, even if the thickness of a beryllium film is determined in accordance with equation (4), there is a possibility that the beryllium film is broken by a pressure difference lower than the design pressure P.sub.0. It is, therefore, necessary to design the thickness with a larger safety factor A. Breakage of a beryllium film with a pressure difference lower than the design pressure P.sub.0 may appear at its contact portion with the flange which fixes the outside periphery of the film. Such breakage cannot be prevented simply by rounding the corner of the flange. If the safety factor A is made large, the beryllium film should then have a larger thickness and, thus, the X-ray transmissivity cannot be large. This causes a large loss of energy and a reduction of productivity of semiconductor products. SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide a pressure partition which enables a design with sufficient mechanical strength and with a very small thickness. It is another object of the present invention to provide an X-ray exposure apparatus or a device manufacturing method which uses a pressure partition as described above. In accordance with an aspect of the present invention, there is provided a pressure partition, comprising: a thin film for dividing a predetermined space into two spatial zones; and supporting means for supporting said film at an outside peripheral portion thereof, said supporting means having a curvature support for producing curvature in the outside peripheral portion of said film, along a predetermined curvature plane. The curvature support may have a curvature radius which is larger than the value of the curvature radius to be defined when a tension stress .sigma.f to be produced at the outside peripheral portion of said film by flexure thereof along said curvature support becomes equal to a difference between tension stresses .sigma..sub.1 and .sigma..sub.2, to be produced at the center portion and the outside peripheral portion of the film, respectively, by deflection of the film due to a pressure difference between the two spatial zones. Said curvature support of said supporting means may have a curvature radius which increases toward the center of said film. The thickness of the thin film for bisecting the predetermined space may be designed so that, as deflection is produced due to a difference of pressures applied to both faces of the film, it bears the tension stress to be produced at the center of the film. The tension stress produced at the center of the film by flexure of the film due to the pressure difference is larger than the tension stress at the outside peripheral portion of the film. However, since a tension stress produced by bending or flexure of the film, caused by contact with the supporting means, is additionally applied to the outside peripheral portion of the film, there is a possibility that a tension stress larger than that at the center is applied to this portion. In consideration of this, a curvature support for supporting the outside peripheral portion of the film along a curved surface having a large curvature radius may be provided, to reduce the tension stress to be produced by flexure due to contact with the supporting means. If the tension stress to be produced at the outside peripheral portion of the film does not exceed the tension stress at the center thereof and if the largest value of tension stress of the whole film corresponds to the tension stress at the center thereof, it is riot necessary to use an unnecessarily large safety factor in the film thickness design as has been described above. This enables a further reduction of the film thickness and enlargement of the X-ray transmissivity. Where such a pressure partition is used as an X-ray window, the efficiency of X-ray utilization can be improved and the productivity of an X-ray exposure apparatus can be enlarged. |
description | 1. Field of the Invention The invention relates to a trajectory corrector in a charged particle beam optical system and to a charged particle beam apparatus, such as an electron microscope, which includes the charged particle beam apparatus. 2. Background Art Charged particle beam apparatuses fulfill important roles across the broad nanotechnology field. Such apparatuses include scanning electron microscopes (SEM) which converge electrons and scan a surface, detect signal electrons from the specimen surface and convert the signal electrons to a visible image on an image display apparatus, transmission electron microscopes which form images from electrons scattered by a specimen using an electron lens, electron beam exposure devices which irradiate a specimen surface with an electron beam to form patterns, and Focused Ion Beam (FIB) apparatuses which perform processing by irradiating a specimen with a focused ion beam. To bring the charged particle beams into convergence, electron lenses constructed from electrodes or magnetic poles which generally have rotational symmetry are used for reasons of controllability and fabrication properties. One problem which occurs in such electron lens systems is electron optical aberration. For instance, magnetic-field type lenses with rotational symmetry have large convergence effects due to increased magnetic field strength on an off-axis side in proximity to the magnetic pole, and therefore function as convex lenses. Moreover, aberration that is a high-order perturbation component of the lens causes a phenomenon in which charged particle beams emitted from a given point diverge in a manner dependent on conditions of incidence of the beam to the lens, and do not converge to a point. Hence, even when an ideal point source is used, a finite spread dependent on a radiation angle distribution or a central trajectory axis of the point source occurs at image-formation point, in what is known as beam defocusing. Thus, aberration causes deterioration in resolution when observing a specimen using a converged charged particle beam or a serious deterioration in accuracy in micro-fabrication. According to perturbation aberration theory, it is known that, due to the occurrence of spherical aberration proportional to the third power of an incident angle α of a beam and chromatic aberration proportional to a deviation dV relative to accelerating energy V, an amount δ of departure of a beam trajectory on the axis can be expressed as:δ=Csα3+CcΔV/V+ (1)where Cs denotes a spherical aberration coefficient and Cc denotes a chromatic aberration coefficient. Other contributions are generated off the axis. For α-dependent beam current distribution or energy dispersion, beam defocusing occurs in accordance with the above formula. Generally, charged particle beam apparatus requires a large current in order to increase the signal size or micro-fabrication speed, and has to capture, across a wide angle, the charged particle beam generated by a charged particle source. As a result, the trajectory distribution within the convergent lens is widened in a trade-off for an increase in the amount of aberration. This trade-off defines the performance of the lens. Various methods for correcting the aberration have been proposed. The methods include a multipole aberration correction system that involves controlling the divergence and convergence using a multi-stage arrangement of regularly partitioned multipoles (see “Outline of an ultracorrector compensating for all primary chromatic and geometrical aberrations of charged-particle lenses”, H. Rose, Nuclear Instruments and Methods in Physics Research, Section A, 519, 12-27 (2004)), and a multi-beam method that involves disposing a microlens array, splitting the charged particle beam into multiple beams, and performing a trajectory correction on the beams (see JP Patent Publication (Kokai) No. 2006-80155A). Also included is an annular illumination method that involves disposing an annular limiting aperture on the axis with the aim of inhibiting aberration to some extent under a large current and, in particular, lessening the space-charge effect resulting from Coulomb repulsion or scattering within a beam (see JP Patent Publication (Kokai) No. 2000-12454A). An increase in the intensity of the charged particle beam increases the contribution made to the space charge by electrons present on the maximum intensity axis where current density is high. Thus, the concept of the above method is to use an annular of aperture of axis-symmetrical configuration to capture a peripheral electron rather than capture the charged particle beam circularly about the axis, and thereby increase the intensity of an electron source and hence an effective area for beam capture. An annular lens system in which an electrode is placed on the axis, and the charged beam is limited to an annular region to entry to the lens (see U.S. Pat. No. 3,100,260). Multipole systems and multi-beam systems require extremely accurate machine fabrication, positioning, power sources and adjustment method and are therefore expensive and technologically difficult to implement. As such, these systems are still only used in a certain portion of electron microscopes and the like. The annular illumination method is also capable of reducing aberration to a certain extent and increased currents can be anticipated. However, the method has a problem in that aberration-limited off-axis trajectories are captured, and consequently it is not possible to increase acquired current by large amounts, especially in regions where the space-charge effect is not dominant. Moreover, although the annular lens system allows simply some degree of trajectory correction, there are associated technological problems, such as high-order electric field distortion, effects of parasitic aberration, and difficulty in making adjustments. Thus, for charged particle beam convergence, it is necessary to reduce an amount of aberration. This has been an important problem. More specifically, the rotationally symmetrical magnetic potential φ can be subjected to a Taylor expansion using an on-axis potential Φ, to give the following:φ(r,z)=Φ(z)−(¼)Φ(z)″r2+( 1/64)Φ(z)″″r4+ (2)where (r, z, θ) are polar coordinates based at the axis of rotational symmetry. Here, the differential values of magnetic potential, specifically the third and subsequent terms for which the magnetic field B is non-linear are aberration terms. In particular, the third term, which is proportional to the axis separation r3, represents 3rd-order spherical aberration. With a coaxial infinitely-long cylindrical electrode having internal and external dimension of a and b as the annular electrode, formulas for the electric field E can be solved analytically to giveE(r)=V/r log(a/b) (3).From Formula (3), it is clear that the differential of the potential, which is the electric field E, is proportional to 1/r and that the electric field E therefore increases steeply towards the central axis. Further, as the axis is approached, the effect of higher order terms in the Formula (2) increases in a relationship which is inversely proportional to r. Thus, by skillfully using these effects to cancel each other out, it is possible to correct aberration using a coaxially arranged annular electrode in a rotationally symmetrical magnetic lens. However, in conventional coaxial annular electrode, since a very strong deflecting electric field is formed in proximity to the axial electrode according to Formula (2), the electric field distortion is large and the beam incidence angle is restricted. Further, an annular limiting aperture and a supporting portion to support the axial electrode are required in proximity to the beam. These components may be charged as a result of contamination, and thereby introduce the risk of destabilizing the trajectories and causing high-order parasitic aberration. These restrictions and risks are the cause of the above-described difficulty in making adjustments. The invention was conceived after closely studying the above-described circumstances and solves the problems of conventional aberration correction systems, providing a low-cost, high-accuracy, and high-resolution converging optical system for use with a charged particle beam. To solve the above problems, a beam trajectory is given a curved form by rotationally symmetrical, multi-stage, coaxial correction electrodes. Specifically, charged particle beams are caused to form an image on an axis of rotational symmetry and thus to cross obliquely. Rotationally symmetrical axial and off-axis electrodes are provided in multiple stages at intervals along the beam trajectory. With this arrangement, a balance is produced by relaxing the concentrated electric field distortion generated, for instance, at the ends of the electrodes and compounding the actions of an externally provided magnetic lens, and the overall aberration is canceled out. Here, from the theory of symmetry in optical system, it is known to be sufficient to form an aberration-free image on an axis with the rotation direction trajectory and analyze the aberration of the off-axis direction (radial direction) trajectory. (1) More specifically, the charged particle beam trajectory corrector according to the present invention includes a correction electrode group including an axial electrode provided on a straight-line axis which obliquely crosses an emission axis of the charged particle beam from the illumination lens, and off-axis electrodes provided with rotational symmetry so as to surround the axial electrode; and a magnetic lens which generates an electric field between the axial electrode and the off-axis electrodes. The charged particle beam is caused to obliquely intersect the straight-line axis, a voltage is applied between the axial electrode and the off-axis electrodes to relax electric field distortion, and the aberration by an action of the magnetic lens is corrected. Further, an intersection point of the emission axis of the charged particle beam and the straight-line axis matches an image-formation point of the illumination lens. For example, the off-axis electrodes may be configured as an off-axis electrode group which includes a plurality of off-axis electrodes, and voltage values proportional to a voltage input value to a predetermined off-axis electrode of the plurality of off-axis electrodes may be inputted to the other off-axis electrodes of the plurality of off-axis electrodes. Further, the magnetic lens may be compounded so as to be a rotation target that is coaxial with the straight-line axis on which the axial electrode of the correction electrodes is provided. Input values of the correction electrodes may be controlled with a linear function of input values to the magnetic lens. Further, the corrector may include a supporting body to which is fixed one end of the axial electrode and the off-axis electrodes. Then, the axial electrode is configured as a short rod-like electrode or a substantially point-like electrode surrounded by a ground-connected shield electrode. The supporting body may have an annular opening which limits an incident range of the charged particle beam to a periphery of a portion fixed to an end of the rod-like electrode. The off-axis electrodes may be divided in a circumferential direction to form a plurality of portion electrode, and voltages may be independently applied to the each portion electrode. The above-described corrector further includes a movable limiting aperture having differing opening dimensions in a radial direction and a rotation direction from a center of an axis of rotational symmetry of the off-axis electrodes. The above-described corrector may further include an incident astigmatism corrector for correcting convergence towards a radial direction and a rotation direction from a center of an axis of rotational symmetry of an incident charged particle beam; and an emission astigmatism corrector which restores a shape of the charged particle beam emitted from the correction electrodes. (2) The charged particle beam apparatus according to the present invention includes: a charged particle source which generates the charged particle beam; an illumination lens for converging the charged particle beam; a charged particle beam trajectory corrector for modifying a trajectory of the charged particle beam to correct aberration; a corrector having the above-described characteristics, an illumination deflector for illuminating a specimen with a modified-trajectory charged particle beam; and an image generating and processing unit which detects a reflected electron signal from the specimen and displays an image on an image display apparatus. Here, the illumination deflector corrects an incident direction of the charged particle beam. The illumination deflector further includes a function for scanning an upper structure of the correction electrodes, and the image generating and processing unit detects a reflected electron signal from the upper structure of the correction electrodes, generates images of the upper structure of the correction electrodes, and displays the images on the image display apparatus. The charged particle beam apparatus further includes a control unit which controls input voltage values of the correction electrodes with a linear function of input to the illumination deflector. The charged particle beam apparatus further includes a control unit which controls the illumination deflector by measuring shape distortion of an emission beam with respect to a plurality of input values to the illumination deflector, approximating the distortion amounts as a polynomial function, and computing from the polynomial function an input value to the illumination deflector to minimize the distortion amount. Further characteristic of the invention will become clear from the following preferred embodiments of the invention and the accompanying drawings. According to the present invention, a wide-use aberration correction method can be provided at low cost with an apparatus that includes a power source and is extremely compact. The following describes embodiments of the invention with reference to the accompanying drawings. Note, however, that the embodiments are no more that examples for realizing the invention, and do not limit the technological scope of the present invention. Also, although the following describes cases in which the charged particles are electrons, the corrector of the invention can also used when the charged particles are ions. Note also that the common construction elements are denoted using the same reference numerals throughout the drawings. Concept (Principle) of Spherical Aberration Correction First, the concept of spherical aberration correction is described with reference to FIG. 1 and FIG. 2. FIG. 1 and FIG. 2 show electron trajectories with an energy of 300 eV calculated from a central axis across semi-planar electrodes and a magnetic lens. FIG. 1 shows an example of adjusted converging conditions using correction electrodes made up of an axial point-like correction electrode and off-axis electrodes which are substantially aligned along the beam trajectory. The axial electrode has a supporting body which doubles as a ground electrode. The off-axis electrodes are arranged so as to be spread out along the beam trajectory. This arrangement suppresses the effect of electric field distortion in proximity to the electrode. The supporting body, in a sense, absorbs the electric force lines in proximity to the central electrode, and produces a shielding effect which relaxes a point charge field to a dipole field. It is also possible to reduce the distortion that results from electric field relaxation due to interaction among the plurality of the axial electrodes. FIG. 2, on the other hand, shows beam trajectories caused to converge without using correction electrodes by exciting a conventional magnetic lens with an excitation of 200 AT. From a comparison of the two configurations, it can be seen that while the beam emitted from point “A” in FIG. 2 spreads by dZ in the axial direction by the spherical aberration of the magnetic lens, the beam emitted from point “A” in FIG. 1 converges with a spread of 0 to dZ. By using a single or plurality of rotationally symmetrical corrector groups which cause oblique incidence of the beam, it is possible to cancel out electron optical aberrations, to promote convergence/divergence of electrons pulled from the surface of a specimen, thereby supporting the adjustment of conditions of incidence to the detector, signal separation, and the like. In recent years, MEMS (Micro-Electro-Mechanical Systems) fabrication techniques and machine fabrication techniques have progressed, and can be used to fabricate minute electron sources and electron lenses. From electron optical scaling law, it is known that the same beam trajectory can be obtained when electric fields are scaled down by scaling down the voltages and electrodes in an identical manner. Hence, by manufacturing a number of electrodes which are of the order of 10 μm in size using the above-mentioned micro-fabrication techniques, it is possible to finely control the beam trajectories with a low voltage source by simply exchanging the limiting aperture of the conventional art for the corrector of the invention. Example Configuration of Correcting Optical System FIG. 3 is a cross-sectional view showing an outline construction of a correcting optical system according to an embodiment of the invention. As shown in FIG. 3, an axial electrode 2 which includes a coaxial supporting body 3 and off-axis electrodes 4 are arranged with rotational symmetry in a magnetic lens 7. In this structure, the internal part of the supporting body 3 is supported by and forms part of a ground electrode 5, and forms a structure for applying a voltage Vo to the axial electrode 2 via an insulating portion 6. Each of the off-axis electrodes 4 is insulated from the ground electrodes 5, and a voltage Vn is applied to the nth off-axis electrode 4 from the top. Thus, the axial electrode 2 and the off-axis electrodes 4 are divided into a plurality of stages by multistage division or layering, enabling minute combination lens groups to be constructed. Moreover, in the correcting optical system of FIG. 3, the electrode arrangement and adjustment are executed in the following procedure to obtain a desired beam trajectory. The first step of the procedure is to determine the form and excitation of the magnetic lens 7 by simulating the conditions for the desired beam trajectory while taking the inserted electrode arrangement into consideration. The second step is to place the correction electrodes as far as possible from the calculated beam trajectory in order to avoid electric field distortion. For instance, in FIG. 3, the off-axis electrodes 4 are arranged on a substantially rotationally symmetrical curved surface along the beam trajectory. In FIG. 3, two trajectories from the inner and outer parts of the beam 1 incident from the point “A” are shown. As described with reference to FIG. 2, when the magnetic lens 7 is used alone, the trajectories cross at the point “B” due to spherical aberration, causing a spread of dZ on the axis. Next, in a third step, the voltages of the correction electrodes are adjusted to correct the trajectories to the point “B′”. When the corrected trajectory is displaced from the desired axial image-formation point, it is preferable to control so that the excitation adjustment of the magnetic lens 7 and the process to adjust the correction electrodes are repeated so that image formation takes place on the axis. From the focal point correcting voltages for various voltage values between the magnetic lens 7 and the electrodes or between the respective electrodes, it is possible to find in advance a linear relationship between voltage and image formation position on the axis (i.e. a sensitivity), and, through linked control simplify or automate adjustment. In FIG. 3 for instance, when a predetermined voltage is applied to a specific correction electrode (off-axis electrode 4), voltages proportional to the voltage inputted to the specific off-axis electrode are applied to the other electrodes. The input value of the correction electrodes may be controlled using a linear function of the input value to the magnetic lens 7. Note that since the optical system has rotational symmetry in the above example, estimates are also obtained relatively easily by simulation. FIG. 4 is a plan view showing the correcting optical system of FIG. 3 from the direction of incidence of the electron beam, and shows the case in which the beam 1 is incident on one side (upper portion of FIG. 4) of a beam introduction path. The upper portion of supporting body 3 is supported by a crossbar structure of the ground electrode 5 which crosses the center. With this structure, the beam 1 is passed through the central portion that is divided into equiangular portions so as to be as far as possible from the supporting body and the crossbar in particular, and it is thereby possible to reduce unwanted effects such as electric field distortion and contamination. Further, as indicated by the broken line of FIG. 4, it is possible to pass the beam 1 in a similar way on a different beam introduction path (lower side of FIG. 4). Thus, it is possible to cause convergence of a plurality of beams to an arc form based on a number of crossbar divisions and area of the opening. Further, it is also possible to provide electrode support using the crossbar structure located far away from the beam 1 on the lower side of FIG. 4, and thereby reduce the adverse effects of the crossbar structure. In another example of an electrode supporting method, the supporting body 3 of the axial electrode 2 is split into frame shapes which are inserted from outside the lens, thereby allowing exchange and mechanical axis adjustment. Since the internal portion of the electrodes of the optical system has full rotational symmetry, precise fabrication and construction are comparatively simple. However, when the beams are to be accurately converged, greater precision is required in beam trajectories, displacements between the cores of the axial electrode and the off-axis electrodes, and fabrication. As a measure meet this requirement, the correction of the beam trajectories can be performed by placing an aligning deflector on the incident side of the correcting optical system. The displacement between electrode cores, which is present when the centers of the axial electrode 2 and the off-axis electrode 4 are offset, can be effectively corrected by dividing the off-axis electrodes to form a multipole system. FIG. 5 is a plan view of the octa-poles 8 resulting from equal division in a rotation direction. The circular surface of equal potential generated when the same voltage value is uni-directionally applied as each electrode voltage Dn (where n=1, 2, 3, . . . 8) is shown with a broken line. Here, by adjusting Dn, it is desirable that the surface of equal potential shown with the broken line can be moved to the circular surface of equal potential which is shown by the solid line and has an axis which matches the axial electrode 2 which offset in the X-axis direction. As is clear from the symmetry of FIG. 5, voltage addition is performed so that correcting voltage Dx is given by:D1=D8=Dx, D2=D7=aDx,D3=D6=−aDx, D4=D5=−Dx (3)Note that the correction coefficient “a” depends on the form of the electrodes. Here, in the general case in which there is also an offset in the y-axis direction, Dx is replaced with Dy and the addition is performed after rotating the relationships of Formula (3) by 90 degrees. When astigmatism occurs due to some unspecified effect, correction is possible by adding the mutually reversed voltages Ds and Dt which are given byD1=D5=Ds, D3=D7=−Ds, D2=D6=Dt, D4=D8=−Dt (4)Correction is also possible when the magnetic field coil is arranged to have octa-poles. Moreover, it is possible to correct higher order astigmatism by adding more poles. Configuration of Electron Lens System for Simultaneous Reduction of Spherical Aberration and Chromatic Aberration In conventional electron lens systems, energy scattering of the incident electrons results in chromatic aberration (i.e. differences in convergent sensitivity) which increases beam defocusing. For instance, a normal electron lens has smaller convergent angle for higher energy electrons, and chromatic aberration is generated as a result of this different sensitivity. On the other hand, coaxial electric field correctors change the deflection direction according to the divergence and convergence conditions, and systems which include the coaxial correction electrodes can, in principle, have both positive and negative values of chromatic aberration coefficient. Generally, in the field of optics, it is necessary to combine both positive and negative lenses (i.e. concave and convex lenses) to correct chromatic aberration. With the configuration of the example shown in FIG. 3, if the field of the magnetic lens 7 is superimposed with the correction electrodes working as a diverging lens, it is possible to change the trajectories according to the difference in energies, and thereby correct the chromatic aberration. However, in the example of the FIG. 3, the correction electrodes cause the beam trajectory in proximity to the axis to form an image in an upstream position. Thus, if a diverging lens is used under these circumstances without further correction, the trajectory in proximity to the axis will curve outwards, causing an increase in the spherical aberration. For the reasons described above, FIG. 6 shows an example of the use of correctors with divergent conditions in a two-stage combining lens system in order to simultaneously reduce spherical aberration and chromatic aberration. An incident lens 10 adjusts incident angles to the correction electrodes (i.e. the axial electrode 2 and the off-axis electrodes 4) of the electron beam 1 emitted from the object point “A”. Here, the incident beam 1 and the correction electrodes are parallel, and the near-axis side and external-side trajectories of the beam 1 are shown. When trajectories of beam 1 are set to diverging direction using the axial electrode 2 and the off-axis electrodes 4, the near-axis side and external side electrons are seen by an objective lens 11 to have been emitted from Ai and Ao respectively. Thus, from the lens formula, the near-axis side trajectory on the image forming side of the objective lens 11 moves towards the objective lens side, the off-axis trajectory moves away from the objective lens 11. It is therefore possible to reverse deflections of the spherical aberration and cause the trajectories to converge at point “B”. Further, it is possible to cancel out the chromatic aberration by making use of the diverging effect of the electric field corrector and the converging effects of the objective lens 11. Further, a two-stage incident lens 10 and objective lens 11 can be used in a configuration in which they does not superimpose a corrector. An electrostatic lens can also be used. Here, in the configuration shown in FIG. 6, it is important to control the angle of incidence of beam 1. Through placement of the center of an illumination deflector 9 for trajectory correction at an object point position of the incident lens 10, it is possible to perform adjustments without moving the object point position. Note that when spherical aberration alone is to be corrected, a configuration in which the axial electrode 2 and the off-axis electrodes 4 are combined with the objective lens 11 (see FIG. 3) may be used. However, when the chromatic aberration is to be simultaneously corrected, it is preferable that the axial electrode 2 and the off-axis electrodes 4 are not combined with the objective lens 11 and have a configuration of the type shown in FIG. 6. Configuration of Multifunctional Optical System In recent years, the requirements for charged particle beam optical system have diversified including 3-dimensional observation based on oblique observation from multiple directions. FIG. 7 and FIG. 8 are schematic diagrams showing examples of multifunctional electron optical systems which combine the electric field-type corrector of the invention and a deflecting aberration correction system. (1) According to the embodiment of the invention, the bi-directional beam irradiation system shown FIG. 7 can be provided. In the system of FIG. 7, the beam 1 emitted from an electron source 12 is caused to form an image on the correction electrode axis by an illumination lens 13. The image formation position and angle are adjusted using the two-stage illumination deflector 9. An objective lens (magnetic lens) 11 produces a pre-correction curved basic trajectory, and forms an image of a substantially obliquely incident beam at a desired position. Further, through the action of the axial electrode 2 supported by the supporting body 3 in the objective lens 11 (magnetic lens), the corrected trajectory forms an image on the axis downstream of the electrodes. Here, the deflected signal superimposed in the illumination deflector 9 by a deflector circuit 17 is used to 2-dimensionally scan a correction electrode incident surface. A reflected electron signal detected by a detector 14 is passed through a signal processing circuit 18, and a scan image is synchronously constructed on an image display apparatus 19. From this position information it is possible to perform axial adjustments. In this state, with a small deflection superimposed at the illumination deflector 9, it is possible to 2-dimensionally scan the specimen surface and construct a scan image from the reflected electron signal detected by the detector 14. Thus, it is possible to easily perform axially adjustments by minimizing an amount of displacement of an opening portion of a corrector upper portion image obtained from the scan image and minimizing distortion in the image of the specimen surface. With regard to adjustment of the illumination deflector 9, image defocusing can be lessened and adjustments can be facilitated by finding the focal point sensitivity of one of the electrodes in advance, and performing integrated control of the electrode. Thus, an incident position to the correction electrodes changes according to an output of the illumination deflector 9, and the conditions for convergence are not longer present. In this case, a linear relationship between an amount of focus blurring and a correction amount of the correction electrodes is found in advance based on an input signal to the illumination deflector 9 and fed back to the correction electrode to enable automatic correction. If the range deflection is very small, it is possible to find, in advance, scan image distortion amounts and defocusing amounts on the specimen surface with respect to a plurality of input values to the illumination deflector 9 and to approximate the results as a perturbation polynomial function using a least squares method. By setting the minimum value of the function, the incident conditions can be optimized. In charged particle optics, the magnetic-field type objective lens 11 has a focal point position and characteristics of beam-deflecting the rotation/convergent directions of the off-axis beam 1 according to an amount of excitation. As a result, a position displacement to a characteristic focal point is also generated for the correction electrode according to the arrangement thereof. When a 3-dimensional focal point position (x, y, z) is considered, action amounts (dxi, dyi, dzi) of three off-axis electrodes (corrector) of, for instance, the four off-axis electrodes in FIG. 3 are added.dx1+dx2+dx3=x dy1+dy2+dy3=y dz1+dz2+dz3=z (5) From Formula (5), it is clear that 2-dimensional (x, y) scanning while performing a certain degree of dynamic correction of the focal point can be performed using only the correction electrodes in the magnetic field. In the configuration of FIG. 7, since a rotation direction component of the beam 1 within the off-axis electrode 4 converges without aberration for reasons of symmetry, off-axis scattering, which is radial direction scattering, becomes a problem. Hence, by causing the trajectories in the radial direction to converge in advance within the off-axis electrode groups 4, it is possible to obtain an improved correction effect. For instance, if the positive and negative voltages of the same value are applied to opposing electrodes of the octa-poles 8 shown in FIG. 5 to be an astigmatism corrector, it is possible to apply converging and diverging effects to the passing beam. In the configuration of FIG. 7 specifically, such incident astigmatism corrector 15 is positioned before the corrector, the trajectories converge in the substantially radial direction, and diverge in a direction perpendicular to the radial direction (i.e. the rotation direction). Further, an exit astigmatism corrector 16 is placed after the corrector, and has an effect directly opposite to that of the beam incident astigmatism corrector on the incident side. With this arrangement, it is possible to improve the aberration correction effects. Note that, by placing the detector 14 in an upper portion of the correcting optical system, images in proximity to the correction electrodes can be acquired. Consequently, it is possible to find where the beam 1 should be introduced to the correcting optical system. (2) According to the embodiment of the invention, it is possible to mix of electron trajectories of the integrated system shown in FIG. 8. In FIG. 8, scale has been ignored for the purposes of illustration. For instance, the dimensions of the correction electrodes in the center of FIG. 8 can be expected to be extremely small due to the high sensitivity of action shown in FIG. 1. In FIG. 8, beams emitted from a first electron source 12 and a second electron source 20 form an image on a correction electrode axis as a result of the action of a first illumination lens 13 and a second illumination lens 21. Position displacement and angle displacement in the image formation are adjusted by a first illumination deflector 9 and a second illumination deflector 22. Here too, an axial electrode 2 which is supported by a supporting body 3 in the magnetic lens 7 and off-axis electrodes 4 act to form an image on the axis downstream of the electrodes. In this state, a perpendicularly incident beam 24 and an obliquely incident beam 25 in FIG. 8 can form an image of the specimen surface or like via an objective deflector 26 and the objective lens 11. Hence, it is possible to mix beams from different sources. In FIG. 8, the off-axis electrodes 4 are provided in proximity to the beam and the forms of the off-axis electrodes 4 is optimized to control the trajectories. Thus, fringe portions of the off-axis electrodes 4 generate high-order distortion. However, under this way of thinking is that incident angle to the electrodes is suppressed, the electrodes are lengthened, and the resulting controllability is used. Thus, in contrast to the configuration in FIG. 7, the electric field generated in proximity to the axis by the plurality of axial electrode groups 2 is controlled, to control the trajectories. Further, in the configuration of FIG. 8, since the obliquely incident beam 25 passes off-axis of the objective lens 11, a large deflection aberration occurs. However, by arranging the multiple poles shown in FIG. 5 and adjusting the distribution, it is possible to greatly reduce the aberration. With the configuration of FIG. 8, as with the configuration of FIG. 7, it is possible to obtain a larger correcting effect by converging, in advance, the trajectories in the radial direction within the off-axis electrodes 4. In the configuration of FIG. 8, a movable limiting aperture 23 (which changes a form of an aperture in the radial direction and the rotation direction) is placed on the incident side, and the radial direction trajectory of the beams are limited. The result is an arc opening which captures more perpendicular direction trajectories, which is to say rotation direction trajectories. With this arrangement, it is possible to improve the aberration correction effects. When a switch to a plurality of charged particles is desired in the configuration in FIG. 8, the beams can be separately blanked from the limiting aperture 23 of the correction electrode upper portion using the first illumination deflector and 9 and the second illumination deflector 22. Being extremely simple and compact in comparison to conventional aberration correctors, the charged particle beam trajectory corrector according to the invention is, from the point of view of implementation and cost reduction, of great use in scanning electron microscopes and transmission electron microscopes. Further, the charged particle beam trajectory corrector is characterized by a simple structure which easily miniaturized through use of MEMS techniques or the like, and may be included with ease in the multi-beam systems which have been receiving a great deal of attention in recent years. Further, according to the present embodiment, since a configuration which compounds the corrector and a magnetic lens is possible, the overall length of the optical system can be shortened in comparison to conventional multi-stage multipole correction system, and the influence of external disturbances can be reduced. Moreover, a reliable system construction with a surrounding magnetic shield and the like that are easily provided and excellent anti-vibration/anti-noise/spatial properties can be provided (see the configurations of FIG. 6 to FIG. 8). Further, according to the present embodiment (FIG. 6 to FIG. 8), since there is no need to use a multipole electrode, it is possible to reduce the number of electrodes by a factor of approximately ten in comparison to multi-stage multipole correction system, and thereby greatly reduce the number of corresponding power sources. This reduction gives the present embodiment the advantage of a large reduction in cost. Further, since the bright central beam which can cause problems in annular illumination methods is not excluded, the obtained beam current is large and axial adjustment is simple. Also, there is advantage from the point of view of stability in that because the beam incident range is limited, the beam does not directly illuminate the correction electrodes or the like, and contamination deposition is small. The correction system overall is a rotationally symmetrical system, and it is therefore easy to analyze the trajectory magnetic/electric fields and calculate trajectories. Further, there are advantages relating to manufacture. Since the charged particle beam trajectory corrector can be mechanically fabricated and assembled with accuracy and has a high correction sensitivity, miniaturization is possible. Moreover, the number of electrodes in the configuration and thus the number of power sources is reduced, making it easy to realize cost savings. |
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044420668 | description | DETAILED DESCRIPTION OF EMBODIMENTS FIG. 1 shows the core 1 of a gas cooled high temperature reactor formed by a pile of spherical fuel elements, surrounded by an annular side reflector 2. The side reflector is surrounded in turn by a thermal side shield 3, wherein an annular space 4 is provided between the two structural parts. Several pebble removal tubes (one such tube 16 is shown in FIG. 3) exit through the bottom of the pebble bed. Depending on the size of the nuclear reactor installation, the number of pebble removal tubes may vary between 1 and 7. A conical pebble inlet 17 shown in FIG. 3 is provided for each pebble removal tube, which is formed by a part of the support floor. The portion of the support floor arrangement of the invention shown in FIG. 2 consists of a plurality of graphite blocks 6a, arranged in vertical columns 6. The vertical columns 6 have hexagonal cross sections shown in FIG. 4 and are equipped with numerous bores 7 extending in the longitudinal direction through which the cooling gas heated in the core 1 may exit from the core. The structure shown in FIG. 2 illustrates a single column 6 with cooling gas bores 7. The cooling gas bores 7 are established with respect to number, diameter and distance so that no or only slight non-stationary thermal stresses may be generated in the individual vertical columns. The graphite blocks 6a located at different heights or in different layers may have different configurations with respect to the cooling gas bores 7. In the embodiments shown herein, the uppermost layer of the graphite blocks 6a has a greater number of cooling gas bores 7 than the other layers and a small gas collector space 8 is located at the upper end of the second layer from the top. This space is interconnected with the cooling gas bores in the uppermost and the second layer from the top. The vertical columns 6 of the support floor 5 may be constructed of hexagonal graphite blocks having different widths across the flats in the individual layers. As shown in FIGS. 1 and 2, each vertical column 6 resting on a circular column 9 is in turn supported on the bottom layers 10 of the high temperature reactor. The bottom layers 10 are supported by a floor plate 11. The diameter of the circular columns 9 is smaller than the flat width or end surface of the vertical columns 6. The free space between the circular columns 9 forms the hot gas collector space 12 of the high temperature reactor and is, therefore, interconnected with the cooling gas bores 7 in the graphite blocks 6a in such a manner that the gas freely flows therebetween. Because the vertical columns 6 are placed adjacent to each other as independent single columns without expansion gaps, the support floor arrangement 5 as a whole is not sensitive to thermal stresses and is capable of adjusting without strain to deformations of the bottom layers 10 and the floor plate 11. In order to keep the size of the gaps between the columns within the design parameters under all manufacturing, operational and thermal conditions, retaining means 13 acting inwardly in the radial direction are arranged in the annular space 4 as indicated in FIG. 1 by arrows. The type and layout of the retaining means 13 is determined by the reactor capacity and the core dimensions of the high temperature reactor. In FIG. 3, a support floor 5 for a high temperature reactor of small or intermediate capacity is shown. Identical structural elements are designated by the same reference symbols as in FIGS. 1 and 2. FIG. 3 shows that the side reflector consists of a plurality of stacked graphite blocks 2a and rests by means of roller bearings on the bottom of the reinforced concrete pressure vessel 15 surrounding the high temperature reactor. The restoring elements arranged between the thermal side shield 3 and the side reflector 2 consist of supporting struts 13a, provided with a clearance corresponding to the maximum possible differential radial thermal expansion of the support floor 5 and the thermal side shield 3. In the event that the reactor is designed to utilize absorber balls for the shutdown of the high temperature reactor, the restoring elements consist of spring supports in order to suppress or limit the gaps with respect to size. The reactor core 1 has several pebble outlet tubes 16 passing through the support floor 5, each of them being provided with a conical pebble inlet 17. The surface of the support floor 5 is designed so as to form the said conical pebble inlets. FIG. 4 exhibits another embodiment of the support floor 5 according to the invention, intended for a high capacity, high temperature reactor. A total of seven pebble outlet tubes 16 are provided under the reactor core 1, four of which are shown in the drawing. Toward the side reflector 2, the graphite blocks 6a of the vertical columns 6 have a different configuration in cross section. The shape of the cross sections are varied so that each individual graphite block 6a is radially restrained. FIG. 4 demonstrates the arrangement of the vertical columns 6 directly adjacent to each other. As the restoring elements for this support floor, spring supports 13b are provided; they are arranged in the annular space 4 and hold the vertical columns 6 together in the radial direction. In order to prevent the development of a pressure ring support effect in the side reflector 2, the latter is provided with a series of gaps 18 between the individual graphite blocks 2a. The spring supports 13b are laid out that the gaps developing after an extended period of operation of the high temperature reactor between the vertical column 6, remain under a predetermined maximum size. If in the high temperature reactor absorber balls having diameters substantially smaller than those of the fuel elements are used to affect the reactivity of the reactor, the predetermined maximum size of the gaps is also given by the diameter of the absorber balls. |
summary | ||
description | This invention relates in general to semiconductor devices and in particular to de-embedding semiconductor devices. In the design of semiconductor devices such as high-frequency integrated circuits, it is sometimes desirable that only the intrinsic characteristics of a semiconductor device be incorporated in the design process. The intrinsic characteristics can be determined by characterizing a test device. However, determination of the intrinsic characteristics can be problematic due to unwanted parasitics in the characterization process resulting from the process of fabricating the associated test devices. De-embedding is a process that is utilized to remove the effects of the parasitics from the characteristics of the device under test. FIGS. 1-6 are functional schematics of 2-port test structures typically used in prior art de-embedding processes. FIG. 1 is a schematic representation of test structure 101 that includes a transmission-configured two terminal device under test (DUT) 111, shown as a two-port network. Examples of such devices include capacitors, diodes, inductors, resistors, or any other two terminal devices. In one embodiment, DUT 111 is fabricated on a substrate of a semiconductor wafer with input port 103 and output port 107 located on the wafer surface for radio frequency (rf) characterization. FIG. 2 is a schematic representation of a “through” test structure 201 typically used for de-embedding the electrical characteristics of DUT 111. It is desirable that test structure 201 have the same electrical length and port characteristics as test structure 101 exclusive of DUT 111. FIG. 3 is a schematic representation of a “short” test structure 301 typically used for de-embedding the electrical characteristics of DUT 111. It is desirable that test structure 301 have the same port characteristics and the same electrical length as test structure 101, but with rf “shorts” at locations corresponding to the locations of the input and output ports of DUT 111. FIG. 4 is a schematic representation of an “open” test structure 401 typically used for de-embedding the electrical characteristics of DUT 111. It is desirable that test structure 401 have the same port characteristics and the same electrical length as test structure 101, but with rf “opens” at locations corresponding to the locations of port-1 and port-2 the input and output ports of DUT 111. FIG. 5 is a schematic representation of a “left” test structure 501 typically used for de-embedding the electrical characteristics of DUT 111. It is desirable that test structure 501 have the same port characteristics and the same electrical length as test structure 101, but with an rf “match” at the location corresponding to the location of the input port 103 and an rf “open” at the location corresponding to the location of the output port 107 of DUT 111. FIG. 6 is a schematic representation of a “right” test structure 601 typically used for de-embedding the electrical characteristics of DUT 111. It is desirable that test structure 601 have the same port characteristics and the same electrical length as test structure 101, but with an rf “match” at the location corresponding to the location of the output port 107 and an rf “open” at the location corresponding to the location of the input port 103 of DUT 111. Test structures 201, 301, 401, 501, and 601 (test structures 201-601) are constructed from the same fabrication process as test structure 101 of FIG. 1. A variety of methods can be used with the test structures 201-601 to determine the intrinsic characteristics of DUT 111, such as the open-short method, three-step method, and four-port method. However, these methods individually may not de-embed the DUT 111, particularly for very high frequency semiconductor devices within desired parameters. Accordingly, a new process of de-embedding would be useful. A method of determining the intrinsic electrical characteristics of a device under test (DUT) includes determining a set of test measurements for a test structure including the device and determining test measurements for a number of de-embedding test structures. Based on the test measurements, DUT measurements are determined using both open-short and three-step de-embedding processes. The DUT measurements are combined to determine an imperfection error, which is used to adjust the calculations of a four-port de-embedding method. The adjusted calculations provide for a more accurate measurement of the parasitic elements in the test structure, thereby improving the determination of the intrinsic electrical characteristics of the device. FIG. 7 illustrates a schematic diagram of an equivalent circuit 700 for a DUT test structure. DUT 702 is a device in which it is desired to obtain its intrinsic properties. Examples of such devices include capacitors, diodes, inductors, resistors, or any other two terminal devices in a semiconductor device. In an embodiment, the DUT 702 is a device specified for use in an integrated circuit targeted for high frequency applications. For example, the integrated circuit can be specified for frequencies of operation of 77 GHz or greater. In one embodiment, DUT 702 is fabricated on the substrate of a semiconductor wafer with input port 703 and output port 707 located on the wafer surface for radio frequency (rf) characterization. Element 710 represents the series component and element 720 the parallel component of the parasitics of the structures between input port 703 and DUT 702, while element 712 represents the series component and element 722 the parallel component of the parasitics of the structures between output port 707 and DUT 702. The element 740 represents the parasitics resulting from a short imperfection between the DUT 702 and a ground plane. The intrinsic characteristics of the DUT 702 can be determined by determining the characteristics of one or more test structures as illustrated in FIGS. 1-6, and applying one or more de-embedding processes to determine the characteristics of the parasitic structures. These de-embedding processes can include open-short, three-step, and four-port de-embedding processes, and combinations thereof. As used herein, an open-short method refers to a de-embedding process whereby measurements of the intrinsic characteristics of a device under test are determined based on measurements of an open test structure and a short test structure. The resulting measurements provide an indication of the values of intrinsic parallel parasitics (i.e. intrinsic characteristics that can be modeled as elements connected in parallel to the DUT, sometimes referred to as Y-characteristics) and the values of intrinsic series parasitics (i.e. intrinsic characteristics that can be modeled as elements connected in series to the DUT, sometimes referred to as Z-characteristics). An exemplary open-short method is discussed in Koolen et al., “An Improved De-Embedding Technique for On-Wafer High-Frequency Characterization”, IEEE 1991 Bipolar Circuits and Technology Meeting 8.1, 1991, pp. 188-191. As used herein, a three-step method refers to a de-embedding method based on measurements of an open test structure, a short test structure, and a thru test structure. An exemplary three-step method is discussed at H. Cho and D. E. Burk, “A Three-Step Method For The De-Embedding Of High-Frequency S-Parameter Measurements” IEEE Trans. Electron Devices, vol.38, no.6, pp.1371-1375, June 1991. As used herein, a four-port process refers to a de-embedding process that models parasitics as a four-port system and determines intrinsic characteristics based on measurements of an open test structure, a short test structure, a thru test structure, a left test structure, and a right test structure. An exemplary embodiment of a four-port process is discussed at Q. Liang, J. D. Cressler, G. Niu, et al., “A Simple Four-Port Parasitic Deembedding Methodology For High-Frequency Scattering Parameter And Noise Characterization Of SIGE HBTS,” IEEE Trans. Microwave Theory and Techniques, vol. 51, pp.2165-2174, 2003. In an embodiment, the results of these de-embedding processes can be combined to determine the characteristics of a particular parasitic element. Once these characteristics are known, they can be used to further refine the results from another de-embedding method, thereby improving the accuracy of the results. This can be better understood with reference to FIG. 8, which illustrates a flow diagram of a particular embodiment of a method of determining the electrical characteristics for a device under test. Referring to FIG. 8, at block 802 test data is measured for a test structure including a DUT. In an embodiment, the measured test data includes scatter measurements for the test structure. At block 804, an open test structure, short test structure, and through test structure and the measured test data are used to determine a first set of DUT measurements with a three-step method. At block 806, the open test structure and short test structure together with the measured test data are used to determine a second set of DUT measurements using an open-short method. Moving to block 808, the first and second set of DUT measurements are combined to determine the short imperfection error for the test structure of the device under test. In an embodiment, the first and second sets of DUT measurements each result a matrix of values associated with series imperfections (Z3-step and ZO-S, respectively), and the measurements are combined by subtracting ZO-S from Z3-step to obtain the short imperfection error. At block 810, the short test structure measurements are adjusted using the short imperfection error from block 808 to produce adjusted short test structure measurements. In an embodiment, the short test structure measurements are adjusted by subtracting the short imperfection results from the short test structure measurements. At block 812, the open test structure, the through test structure, a left test structure, a right test structure, adjusted short test structure measurements from block 810, and test data from block 802 are used to perform four-port de-embedding method to determine the intrinsic characteristics of the DUT. Accordingly, at block 812 the four-port method is performed using the adjusted short test structure measurements, rather than measurements obtained directly from the short test structure. For example, in a conventional four-port method, the characteristics of a short test structure would be measured, and those measurements, together with measurements of the characteristics of the open, through, left, and right test structures, would be used in the calculations for the intrinsic characteristics. At block 812, measurements for the open, through, left, and right test structures are obtained normally. Those measurements, together with the adjusted short test structure measurements obtained at block 810, are used to determine the results of the four-port method. By using the adjusted short test structure measurements, rather than measurements directly from the short test structure, the accuracy of the four-port method is increased. In particular, for devices specified for use in high frequency applications, the improved accuracy of the described de-embedding process allows for more accurate integrated circuit designs, as described further below. In addition, the accuracy of the four-port method can be further increased by correcting for load reactance according to conventional methods. The method of FIG. 8 can be better understood with reference to FIGS. 9-11. FIG. 9 illustrates a schematic diagram of one embodiment of an equivalent circuit for the short test structure 301 of FIG. 3. As illustrated, the short test structure includes parasitic elements 910, 912, 920, and 922, corresponding respectively to the parasitic elements 710, 712, 720, and 722 of FIG. 7. In addition, the equivalent circuit for the short test structure includes parasitic elements 930 and 932, each representing the short imperfections. Thus, by determining the values for the parasitic elements 930 and 932, the short imperfection can be determined. In a particular embodiment, these values of the parasitic elements 930 and 932 can be determined using the three-step and open-short de-embedding methods as described below with respect to FIGS. 10 and 11. FIG. 10 illustrates one embodiment of a low-frequency equivalent circuit showing the position of parasitic elements as determined by the three-step method. In the illustrated example, the elements 1010, 1012, 1020, and 1022 correspond to the parasitic elements 910, 912, 920, and 922, respectively, of FIG. 9. Further, element 1040 corresponds to the short imperfection represented by elements 930 and 932 of FIG. 9. Thus, in the three-step method the short imperfection (as shown by element 1040) is represented by a shunt component between the DUT 702 and the ground plane. Further, as a shunt component the short imperfection will have a relatively small impact on the results of the three-step method. Accordingly, the three-step de-embedding method provides a good approximation of the values (labeled Z1, Z2, Y1, and Y2, respectively) for the parasitic elements 1010, 1012, 1020, and 1022. FIG. 11 illustrates one embodiment of a low-frequency equivalent circuit showing the position of parasitic elements as determined by the open-short method. In the illustrated example, the elements 1110, 1112, 1020, and 1022 correspond to the parasitic elements 910, 912, 920, and 922, respectively, of FIG. 9. Further, elements 1140 and 1141 corresponds to the short imperfection represented by elements 930 and 932 of FIG. 9. Thus, in the open-short method the short imperfection (as shown by element 1040) is represented by a series element between the DUT 702 and the element 1110 and a series element between the DUT 1102 and the element 1112. Accordingly, the three-step de-embedding method provides the combined values for the parasitic elements 1110, 1112, 1120, and 1122 (Z1, Z2, Y1, and Y2, respectively) and the parasitic elements 1140 and 1141 corresponding to the short imperfection. Accordingly, as illustrated in FIGS. 9 and 10, the three-step de-embedding method provides a good approximation of the values Z1, Z2, Y1, and Y2, while the open-short de-embedding method provides these values combined with the values for the short imperfection. Thus by removing the values Z1, Z2, Y1, and Y2, as indicated by the results of the three-step method from the results of the open-short method, the parasitic element values associated with the short imperfection can be determined. Further, the four-port de-embedding method provides a good representation of the values for the parasitic elements in the test structure 700 of FIG. 7 over both low and high frequency ranges, but includes some error due to the short imperfection. Accordingly, the results of the four-port de-embedding method can be adjusted to achieve more accurate results by removing the short imperfection value from the short standard measurements during the de-embedding calculation of the four-port de-embedding method. Referring to FIG. 12, a schematic diagram of an equivalent circuit 1200 for a three-terminal DUT 1202. Examples of such devices include transistors, or any other three terminal devices in an integrated circuit. In one embodiment, DUT 1202 is fabricated on the substrate of a semiconductor wafer with port 1203, port 1207, and port 1209 located on the wafer surface for radio frequency (rf) characterization. Element 1210 represents the series component and element 1220 the parallel component of the parasitics of the structures between port 1203 and DUT 1202, while element 1212 represents the series component and element 1222 the parallel component of the parasitics of the structures between port 1207 and DUT 1202. The element 1240 represents the parasitics resulting from a short imperfection between the DUT port 1209 and a ground plane. For relatively low frequency devices, the short imperfection has a minimal effect on the characteristics of the DUT 1202, but in high-frequency devices the effect can become significant, and the accuracy of the de-embedding method improved by removing the short imperfection. The method described above with respect to FIG. 8 can be used to approximate the short imperfection represented by element 1240. However, because the DUT 120 is a three-port device, using test results obtained from the DUT 120 in the open short method will result in measurements that include effects of the short imperfection as a shunt, as well as a series element. Accordingly, extracting the effects of the parasitic values Z1, Z2, Y1, and Y2, as identified by the three-step de-embedding method, from the results of the open short method will not directly indicate the value of the short imperfection. Thus, an additional test structure can be used to determine the short imperfection for a three-terminal DUT. A particular embodiment of such an additional test structure is illustrated in FIG. 13, which shows a test structure 1301, configured similarly to a through test structure, but including a resistive element 1335. The use of the test structure 1301 can be better understood by referring to FIG. 14. At block 1402 test data is obtained for the test structure 1301, treating the resistive element 1335 as the device under test. For purposes of discussion, these test results will be referred to as TDATA1. At block 1404 test data is obtained using the three-port device as the device under test. These test results will be referred to as TDATA2. At block 1406, the three-step method is performed using TDATA1 (i.e. test data from the test structure 1301). Similarly, at block 1408, the open-short method is performed using TDATA1. At block 1410, a short imperfection error is determined by combining the results from blocks 1406 and 1408. In an embodiment, the first and second sets of DUT measurements each result a matrix of values associated with series imperfections (Z3-step and ZO-S, respectively), and the measurements are combined by subtracting ZO-S from Z3-step to obtain the short imperfection error. At block 1412, short test structure measurements are adjusted based on the short imperfection error obtained at block 1410. In particular, the short imperfection error is subtracted from the short test structure measurements to obtain adjusted short measurements. At block 1414, the four-port method is performed using the adjusted short measurements, rather than measurements obtained directly from the short test structure. In addition, at block 1414, TDATA2 (i.e. test data obtained using the three-port device as the DUT) is used for the four port method. Accordingly, for a three-port device, the adjusted short measurements are obtained using the test structure 1301. These adjusted short measurements are then used to perform the four-port method in conjunction with test data obtained from the three-port device itself. This provides for more accurate measurement of intrinsic characteristics of a three-port device. FIG. 15 is a block diagram of one embodiment of a system 1500 for obtaining intrinsic characteristics of a DUT according to the present invention. A DUT is located in a test structure 1505 fabricated on the substrate of wafer 1503. Test structures 1504 are also located on wafer 1503. Probes 1506 and 1507 are used to obtain S parameter data from structures 1504 and structure 1505. The probes are operably coupled to calibrated automatic network analyzer 1509. Network analyzer 1509 is controlled by software running on workstation 1511. The software is downloaded from storage media (e.g. hard drives) of a server 1515 by workstation 1511. In other embodiments, the software may be located on a hard drive of personal computer system or downloaded from a removable media (e.g. CD-Rom). The workstation 1511 executes the software to control the analyzer 1509, thereby executing one or more of the methods described herein. FIG. 16 illustrates a block diagram of a particular embodiment of a workstation 1611, corresponding to the workstation 1511 of FIG. 15. The workstation 1611 includes a processor 1602, a memory 1604, and an analyzer interface 1606. The memory 1604 is accessible to the processor 1602. In addition, the analyzer interface 1606 is connected to the processor 1602. The processor 1602 can be a microprocessor, controller, or other processor capable of executing a series of instructions. The memory 1604 is a computer readable medium such as random access memory (RAM), non-volatile memory such as flash memory or a hard drive, and the like. The memory 1604 stores a program 1605 including a set of instructions to manipulate the processor 1602 to perform one or more of the methods disclosed herein. For example, the program 1605 can manipulate the processor 1602 to control the analyzer interface 1606 and can be used to store data, including test results. Via the analyzer interface 1606, the processor 1602 controls the analyzer 1509 (FIG. 15) to determine the intrinsic characteristics of a device under test, as described herein. The intrinsic characteristics can be stored in the memory 1604. It will be appreciated that other types of systems can be used in other embodiments to execute one or more of the methods described herein. Referring to FIG. 17, a flow diagram of a particular embodiment of a method of designing and producing an integrated circuit device is illustrated. At block 1702, a sample device is produced. In an embodiment, the sample device is an integrated circuit device including a device under test (DUT). The sample device is formed so that the intrinsic characteristics of the DUT will closely match those of the integrated circuit device being designed. At block 1704, the intrinsic characteristics of the DUT are determined using one or more of the methods described herein. At block 1706, the integrated circuit under design is simulated, using the intrinsic characteristics of the DUT. For example, if the DUT is a capacitor, one or more of the capacitors of the integrated circuit is simulated based on the determined intrinsic characteristics. The improved accuracy of the de-embedding results provided by the methods described herein allows for more accurate simulation of the integrated circuit operation. Accordingly, the design process is improved, as the simulations more accurately predict operation of the integrated circuit device, particularly in high-frequency applications. At block 1708, the integrated circuit design is adjusted based on the simulation results. For example, the simulation results can indicate that one or more modules of the integrated circuit device do not function according to a specification. The design of those modules can be adjusted to comply with the specification. At block 1710 an integrated circuit is formed based on the adjusted integrated circuit design. Other embodiments, uses, and advantages of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. The specification and drawings should be considered exemplary only, and the scope of the disclosure is accordingly intended to be limited only by the following claims and equivalents thereof. |
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description | The present invention relates, in particular, among particle beam treatment devices for performing a therapy by radiating a particle beam to a diseased site such as a tumor, to a particle beam treatment device for performing three-dimensional radiation and an operation method therefor. In particle beam treatment devices, a particle beam (particle ray) emitted after being accelerated by a circular accelerator up to a given energy, is transported through a transport pathway to a particle beam irradiation apparatus placed in an irradiation room. In the particle beam irradiation apparatus, the supplied particle beam is radiated after being formed into a shape matched to an irradiation target. In recent years, for reducing an unwanted dose to normal tissues and for effective utilization of radial rays, attention has been paid to three-dimensional radiation. In the three-dimensional radiation, not only the shape in x-y direction (cross-section perpendicular to a beam traveling direction) is formed by scanning electromagnets, but also the shape in z-direction (the beam traveling direction) is formed by changing the energy. Here, the following two ways are conceivable how to change the energy; one of which is to change a destination energy due to acceleration by a synchrotron (circular accelerator), and the other way is to cause deceleration by use of a variable range shifter capable of changing its attenuation amount by adjustment of the water-equivalent thickness of its transmissive plate. In order to achieve the three-dimensional radiation, a number of energy stages with one hundred levels, for example, are required. The pitches of these one hundred stages are determined to be the same pitch as a water-equivalent thickness (depth of Bragg peak in water). If these stages are to be achieved solely by changing the acceleration energy of the synchrotron, this results in performing hundred times of emission-adjustments of the synchrotron and adjustments of the transport system, and thus, there is a problem of spending a lot of time. Meanwhile, according to the variable range shifter, the more the thickness increases, the larger the scattering and/or the beam loss becomes, so that it is not desired that the required number (one hundred levels) of energy stages be all achieved solely by the variable range shifter. In this respect, it is conceivable, for example, that half of the required number of stages (50 stages) are provided by the synchrotron as emission energies, while, with respect to respective intermediate levels therein, they are adjusted by changing the attenuation amount at the variable range shifter. At that time, in order to converge the spread particle beam due to scattering at the time of passing through the variable range shifter, it is conceivable to apply a technology of a particle beam irradiation apparatus in which a four-pole electromagnet is placed (see, for example, Patent Document 1). Patent Document 1: Japanese Patent Application Laid-open No. 2007-185423 (Paragraphs 0008 to 0016, FIG. 1) Patent Document 2: Japanese Patent Application Laid-open No. H03-236862 (Page 2, upper-right column to lower-left column, FIG. 1 to FIG. 3) Patent Document 3: Japanese Patent Application Laid-open No. H08-298200 (Paragraphs 0010 to 0019, FIG. 1 to FIG. 5) However, according to such a configuration, when the energy is changed successively, repetitive increase-decrease occurs in degree of scattering because of increase-decrease in the water-equivalent thickness of the variable range shifter. Thus, it was unable to perform such a control to monotonously decrease (or increase) the strength of the four-pole electromagnet as shown, for example in Patent Document 2 or Patent Document 3, for suppressing an influence of hysteresis of the magnetic member. Accordingly, the state of the particle beam supplied to the scanning electromagnets is unstable, so that it was difficult to perform accurate radiation. The present invention has been made to solve the problem as described above, and an object thereof is to realize a particle beam therapy in which the state of the particle beam becomes stable, so that three-dimensional radiation can be made accurately. A particle beam treatment device of the invention is a particle beam treatment device in which, when an irradiation target is partitioned along a depth direction thereof into a plurality of slices and a particle beam formed for each of the slices is radiated thereto in a depth order, an energy of the particle beam to be emitted from an accelerator is set for every slice group including two or more adjacent ones of the slices, and an attenuation amount is set for each slice in said slice group. The particle beam treatment device is characterized by comprising: a variable range shifter that adjusts the attenuation amount by changing a thickness of its transmissive plate through which the particle beam is transmitted; an irradiation nozzle that has a scanning electromagnet and that makes forming of the particle beam adjusted in the attenuation amount, according to each of the slices; a four-pole electromagnet that is placed between the variable range shifter and the irradiation nozzle, and that operates so as to converge the particle beam having been spread by the transmissive plate; and a control unit that determines set values of the accelerator and the variable range shifter, and that controls an amount of magnetic excitation of the four-pole electromagnet according to the set values; wherein, for said every slice group, the control unit sets higher the energy to be emitted from the accelerator than an energy corresponding to the slice at a deepest location in said slice group so that the transmissive plate has a predetermined thickness for the slice at the deepest location; and wherein, with respect to the thickness of the transmissive plate to be set for said every slice group, the thickness set for the slice group at a deep location is larger than or equal to the thickness set for the slice group at a shallow location, and the thickness set for the slice group at a deepest location is thicker than the thickness set for the slice group at a shallowest location. An operation method of a particle beam treatment device of the invention is an operation method of a particle beam treatment device, which is characterized by comprising: when an irradiation target is partitioned along a depth direction thereof into a plurality of slices and a particle beam formed by an irradiation nozzle for each of the slices is radiated thereto in a depth order, setting an energy of the particle beam to be emitted from an accelerator for every slice group including two or more adjacent ones of the slices; setting an attenuation amount for each slice in said slice group by a variable range shifter; and converging the particle beam incident to the irradiation nozzle, by a four-pole electromagnet placed between the variable range shifter and the irradiation nozzle; wherein, for said every slice group, a set value of the energy of the accelerator is set higher than an energy corresponding to the slice at a deepest location in said slice group so that the variable range shifter has a predetermined attenuation amount for the slice at the deepest location; wherein, with respect to the attenuation amount to be set for said every slice group, the amount set for the slice group at a deep location is larger than or equal to the amount set for the slice group at a shallow location, and the amount set for the slice group at a deepest location is larger than the amount set for the slice group at a shallowest location; and wherein an amount of magnetic excitation of the four-pole electromagnet is controlled according to the set value of the energy of the accelerator and the attenuation amount by the variable range shifter. According to the particle beam treatment device or the operation method of the particle beam treatment device of the invention, when the energy is changed, the spread particle beam can be converged by monotonously changing the strength of the four-pole electromagnet, so that the state of the particle beam becomes stable and thus it is possible to perform a particle beam therapy in which three-dimensional radiation can be made accurately. Hereinafter, description will be made about a particle beam treatment device and an operation method of a particle beam treatment device, according to Embodiment 1 of the invention. FIG. 1 is a schematic diagram of an apparatus arrangement for illustrating a configuration of the particle beam treatment device according to Embodiment 1 of the invention, and FIG. 2 is a schematic diagram showing an irradiation region at the time of performing three-dimensional radiation, that is set by being partitioned in a depth direction into slices each having a predetermined thickness. FIG. 3 is a graph showing a relationship between a thickness of a transmissive plate of a variable range shifter for changing the energy and a spread of scattering angle of a particle beam, and FIG. 4 and FIG. 5 are graphs each for illustrating a relationship between a momentum (a quantity having one-to-one relationship to energy) of a particle beam and a strength of a four-pole electromagnet at the time three-dimensional radiation is performed using a particle beam treatment device of a conventional configuration. Further, FIG. 6 is a graph for illustrating a relationship between a momentum of a particle beam and a strength of a four-pole electromagnet at the time three-dimensional radiation is performed using the particle beam treatment device or the operation method of a particle beam treatment device according to Embodiment 1 of the invention. The particle beam treatment device and the operation method of the particle beam treatment device according to Embodiment 1 of the invention are characterized by a configuration for adjusting energy in three-dimensional radiation or a method of adjusting the energy. However, prior to the description of these configuration and method, a whole configuration of the particle beam treatment device will be described using FIG. 1. In the figure, the particle beam treatment device includes, as a source of supplying a particle beam, a circular accelerator which is a synchrotron (hereinafter, referred to simply as accelerator 1); a particle beam irradiation apparatus 5 capable of performing three-dimensional radiation; and a transport system 2 that connects between the accelerator 1 and the particle beam irradiation apparatus 5 so as to transport the particle beam from the accelerator 1 to the particle beam irradiation apparatus 5. Note that the transport system 2 has transport pathways connected to a plurality of the other unshown particle beam irradiation apparatuses in addition to the particle beam irradiation apparatus 5. Here, the particle beam emitted from the accelerator 1 can be supplied to any requesting one of the particle beam irradiation apparatuses by switching the trajectory using switching electromagnets. Note that, with respect to the other unshown particle beam irradiation apparatuses, they are not necessarily limited to having a function of three-dimensional radiation. Next, description will be turned to the respective configurations. The accelerator 1 includes a vacuum duct 11 that provides a trajectory channel for causing charged particles to go around therethrough; an injection device 12 for injecting the charged particles supplied from a pre-accelerator 18 into the vacuum duct 11; deflection electromagnets 13 for deflecting the trajectory of the charged particles so that the charged particles circulate along the round trajectory in the vacuum duct 11; a four-pole electromagnet 14 that causes the charged particles on the round trajectory to converge so as not to diverge; a high-frequency acceleration cavity 15 that applies to the circulating charged particles, a high frequency voltage synchronous with the particles to thereby accelerate them; an emission device 16 for taking out from the accelerator 1 the charged particles accelerated in the accelerator 1, as a particle beam having a predetermined energy, so as to emit it to the transport system 2; and a six-pole electromagnet 17 that excites resonance in the round trajectory for emitting the particle beam from the emission device 16. Here, the charged particles in the round trajectory are accelerated by a high frequency electric field up to approx. 60% to 80% of the light velocity while being bent by the magnets, and emitted to the transport system 2. The transport system 2 is referred to as HEBT (High Energy Beam Transport) system, and includes a vacuum duct 21 that provides a transport channel of the particle beam; the unshown switching electromagnets that are switching devices for switching the trajectory of the particle beam; and deflection electromagnets 23 that deflect the particle beam by a predetermined angle. The particle beam irradiation apparatus 5 serves to perform three-dimensional radiation in which the particle beam supplied from the transport system 2 is radiated to the diseased site after being formed into an irradiation field matched to the size and depth of the irradiation target. Note that, in the description hereinafter, the traveling direction of the particle beam is defined as z-direction and the directions that determine a plane perpendicular to the traveling direction are defined as x-direction and y-direction. In order to form the shape in the z-direction, the particle beam irradiation apparatus 5 includes a variable range shifter 34, a collimator 35 and a four-pole electromagnet 36, which function as an energy adjustment system 3 for adjusting the energy of the particle beam. Further, it includes a ridge filter for spreading the width of the Bragg peak according to the thickness of the slice, and an irradiation nozzle 4 having a scanning electromagnet that causes scanning in the x-direction and a scanning electromagnet that causes scanning in the y-direction, for forming (scanning) the two-dimensional shape in the x-y plane. The variable range shifter 34 is a device for changing the energy of the particle beam. It has a function of advancing/retracting each transmissive plate adjusted to have a predetermined water-equivalent thickness (for example, in the figure, a base transmissive plate 34b having a water-equivalent thickness tb, and an energy-adjustment transmissive plate 34s having a water-equivalent thickness ts) into/from an incident region of the particle beam. Accordingly, the energy of the incident particle beam is adjusted by being attenuated to the extent of energy corresponding to the water-equivalent thickness. For example in the case of a polyethylene plate having a density of 0.94 to 0.96 g/cm3, an intended water-equivalent thickness can be obtained when the plate is given with a thickness calculated by dividing the water-equivalent thickness by the density. The collimator 35 is a metal block or the like in which a predetermined through-hole is formed, and serves to limit the spread in a planer direction (x-y plane) of the irradiation field, which corresponds to a slit in an optical apparatus. The ridge filter is formed, for example, of many cone-like objects or cross-sectionally triangle plates that are arranged in a plane, so that if the inside of the irradiation field is assumed to be divided into many small regions, there are portions of the beam passing through different thicknesses in each small region. This provides an SOBP (Spread-Out Bragg Peak) in which the Bragg Peak region is spread out. Namely, by means of the ridge filter, the irradiation region in the z-direction (thickness) is adjusted to be matched to the slice that is described later. However, there is a case where no ridge filter is used, although shown in this example is a case where adjustment is made by the ridge filter according to the thickness of the slice. The four-pole electromagnet 36 comprises two N poles and two S poles which are alternately and circularly arranged when viewed from the traveling direction of the particle beam, and functions with respect to one direction in the x-y plane, as if it is a convex lens in an optical apparatus, and functions with respect to the direction perpendicular thereto, as if it is a concave lens. Thus, for example, when a plurality of four-pole electromagnet units 36a, 36b, 36c, 36d are arranged as their poles are shifted to each other in the traveling direction of the beam, the trajectory of the beam is converged in a specified region. Note that, in Embodiment 1, a case is shown where four number of four-pole electromagnet units 36a to 36d are arranged; however, this is not limitative, and the number may be increased or decreased appropriately according to the design condition. Besides, there are provided with a control unit 6 for controlling the accelerator 1, the energy adjustment system 3 and the irradiation nozzle 4 in their cooperative manner, so that the three-dimensional radiation that is described later is executed. Next, the three-dimensional radiation using the particle beam irradiation apparatus 5 with the above-described configuration will be described. On this occasion, as shown in FIG. 2, an irradiation region Vt corresponding to the irradiation target is partitioned along the traveling direction of a particle beam B (z-direction: depth) into slices S1, S2, S3, . . . Sm, . . . (collectively, slice(s) S) each having a predetermined thickness. Further, in the energy adjustment system 3, the energy of the particle beam supplied from the accelerator 1 is adjusted so that the particle beam adjusted to have an energy corresponding to a range of each slice S is provided to the irradiation nozzle 4. At this time, in particular in the case of providing a high quality therapy like three-dimensional radiation, it is important to reproduce a radiation specified in a treatment plan as faithful as possible. Thus, it is required for the energy adjustment system 3 to reduce, in each slice S, variation in width of the particle beam supplied to the irradiation nozzle 4 (evaluated by the standard deviation σ of the spread) and in its beam strength (evaluated by the current value indicative of the dose per hour). Specifically, with respect to the width of the particle beam, it is required that, when the standard deviation 1σ of the particle beam supplied at the time of irradiating a given slice Sm is 5 mm, the standard deviation 1σ at the adjacent slice Sm+1 falls within about 6 mm. Further, with respect to the beam strength, when the current value at the time of irradiating a given slice Sm is 2 nA and the current value at the adjacent slice Sm+1 falls within about 3 nA, this allows a highly accurate radiation. However, it becomes difficult to cause a highly accurate radiation, for example, when, in the case where the standard deviation 1σ of the particle beam supplied at the time of irradiating a given slice Sm is 5 mm, the standard deviation 1σ at the adjacent slice Sm+1 varies to 10 mm; or with respect to the beam strength, when the current value at the time of irradiating a given slice Sm is 2 nA and the current value at the adjacent slice Sm+1 varies up to about 6 nA. Here, when the three-dimensional radiation (layer-stacking conformal irradiation) is to be performed for the irradiation region Vt illustrated in FIG. 2, each slice S is designed to have the same pitch as a water-equivalent thickness, and irradiation is made successively from the deepest slice S1 to a shallower-side one in the traveling direction of the beam. Namely, in the three-dimensional radiation, radiation is performed while being shifted by each one slice S from a high energy to a low energy. Note that there is also a case where radiation is performed while being shifted by each one slice S from a low energy to a high energy. At that time, as described in BACKGROUND ART, emission-energy stages whose number is n-th part of the required number of the stages, are provided by the accelerator 1. Further, with respect to the values corresponding to (n−1) number of intermediates in each stage, they are adjusted by inserting or releasing the transmissive plate of the variable range shifter 34. Namely, the energy of the particle beam to be emitted from the accelerator 1 is set for every slice group F including two or more adjacent slices S and an attenuation value(s) is set for each slice S in the slice group F. In this case, since the intermediate values in each stage are at the same pitch, it suffices to prepare (n−1) number of transmissive plates each corresponding to a water-equivalent thickness of n-th part of the energy in each stage, and to change the thickness of the variable range shifter 34 successively in such a manner that the number of the transmissive plates are decreased in each stage from (n−1) to zero. Note that, for simplifying description, in the following description, such a case is described in which n=2 is given so that the emission-energy stages whose number is a half of the required number of the stages are provided by the accelerator 1, and a single value (intermediate value) is set intermediately in each stage (slice group F) by the variable range shifter 34. Namely, an emission energy of the accelerator 1 is set for every slice group F including two slices S, and with respect to the respective two slices S in the slice group F, they are dealt with by adjusting the thickness of the transmissive plate of the variable range shifter 34. The spread of scattering angle of the particle beam when passed through a physical transmissive plate such as the variable range shifter 34 in that manner, becomes large as the thickness increases, as shown in FIG. 3. Thus, according to the adjustment method as described above, even though the energy is reduced successively and monotonously, switching between causing and not causing to pass through a transmissive plate is done for each emission energy (slice group F) of the accelerator 1, which results in repetitive variation in the scattering amount. In general, in the optical design of HEBT without using a transmissive plate such as the variable range shifter 34, the magnetic field strength (magnetic excitation strength) standardized by a momentum one to one correspondence with the energy, is constant. Meanwhile, in the case of passing through a transmissive plate, the scattering becomes stronger as the energy becomes lower, so that the relationship between the momentum (energy) and the magnetic field strength becomes non-linear; however, such a phenomenon that the smaller the momentum becomes, the lower the strength of the four-pole electromagnet is allowed, remains the same. However, as shown in FIG. 4, a curve (ts) in the case of passing through a transmissive plate is shifted toward the higher side of the four-pole electromagnet in comparison with a curve (N) in the case of not passing through the transmissive plate. Namely, even the momentum is constant, when the thickness of the transmissive plate through which the particle beam passes is made thicker, it is required to increase the magnetic field strength of the four-pole electromagnet 36. As a result, even though the energy is decreased successively and monotonously, the strength of the four-pole electromagnet 36 required for converging the scattered beam becomes stronger and weaker repeatedly. Specifically, when a switching is made from a condition in a given stage (slice group F) that disallows passing through a transmissive plate (in the figure, Δ-mark), to a condition in the next stage that allows passing through the transmissive plate (in the figure, -mark), this results in increase of the strength of the four-pole electromagnet 36. In this respect, it is also conceivable to introduce a technology for reducing variation in the scattering angle at the time of inserting the energy-adjustment transmissive plate 34s for adjustment to an intermediate value, by always inserting the base transmissive plate 34b with a thin water-equivalent thickness, as described for example in Patent Document 1 (Paragraph 0021, FIG. 3). In this case, as shown in FIG. 5, the difference (in the strength of the four-pole electromagnet 36) between a curve (tb) in the case of using the base transmissive plate 34b and a curve (tb+ts) in the case of adding the energy-adjustment transmissive plate 34s (corresponding to the same thickness (ts) in FIG. 4) for adjustment to an intermediate value, becomes smaller than the difference in FIG. 4. In this manner, when the difference in the required strength is made smaller using the base transmissive plate 34b, it is able to adjust not to increase the strength of the four-pole electromagnet 36 in a part of the energy region at the time the water-equivalent thickness of the transmissive plate of the variable range shifter 34 is increased (in the figure, at the transition from σ to ⋄ in a momentum-decreasing direction). However, in all of the energy ranges for forming the SOBP for every patient, it was difficult to adjust the energy without increasing the strength of the four-pole electromagnet 36. Thus, in the particle beam treatment device according to Embodiment 1, the thickness of the base transmissive plate 34b used for the slice group F with a small energy-set value (at a shallow position) is thinner than that of the base transmissive plate 34b used for the slice group F with a large energy-set value (at a deep position). Specific examples of energy adjustment method in Conventional Example 1 corresponding to FIG. 4 described above, Conventional Example 2 corresponding to FIG. 5, and Example of the particle beam treatment device or the operation method of the particle beam treatment device according to Embodiment 1, will be shown in Table 1. TABLE 1Specific Examples of Energy Setting MethodSliceS1S2. . .SmSm + 1. . .SnSn + 1. . .Slice GroupF1. . .Fi. . .Fj. . .Corresponding EnergyE1E2. . .EmEm + 1. . .EnEn + 1. . .AdjustmentConventionalAE1. . .Ei. . .Ej + Eb. . .MethodExample 1RS—ts. . .—ts. . .—ts. . .ConventionalAE1 + Eb. . .Ei + Eb. . .Ej + Eb. . .Example 2RStbtb + ts. . .tbtb + ts. . .tbtb + ts. . .Exampleregiont1-regiont2-regiont3-regionAE1 + Et1. . .Ei + Et2. . .Ej + Et3. . .RSt1t1+ts. . .t2t2 + ts. . .t3t3 + ts. . .A: acceleration energy,RS: thickness of range shifterNotethat, 2 < i < j, Ek = E1 − (k − 1) · ΔE, and t1 > t2 > t3. In Table 1, indicated at the uppermost column is the number of each slice S, at the next column is the number of each slice group F, and at the subsequent column is the energy-set value for each slice S. It is assumed that the energy successively decreases by ΔE through the course along E1, E2, . . . , namely, the energy is changed from going toward the deep side to going toward the shallow side on a same pitch basis. Further, when the all energies are divided into three regions, among these set values, respectively represented by E1 and E2 are set values in a maximum energy range, by E1 and Ei+1 are set values in an intermediate energy range, and by Ej and Ej+1 are set values in a minimum energy range. As to the other set values, their description is skipped here. For example in Conventional Example 1, for two energy-set values (Ek and Ek+1) in a slice group F, a particle beam with a common energy (Ek) is emitted from the accelerator 1 (“A” column). Further, there is shown that the energy is adjusted to that corresponding to the energy-set value for each slice S in the slice group F, by inserting or releasing the energy-adjustment transmissive plate 34s with the water-equivalent thickness is corresponding to ΔE (“RS” column). Besides, in Conventional Example 2, for two energy-set values (Ek and Ek+1) in a slice group F, a particle beam with a common energy (Ek+Eb) that is set higher than the set value (Ek) so as to compensate its portion attenuated by the base transmissive plate 34b, is emitted from the accelerator 1 (“A” column). Further, the energy is adjusted to that corresponding to the energy-set value for each slice S in the slice group F, by inserting or releasing the energy-adjustment transmissive plate 34s with the water-equivalent thickness is corresponding to ΔE (“RS” column). In contrast, in Example, an energy range (region) is divided into three ranges, and in the region of a maximum range (referred to as t1-region), the base transmissive plate 34b having a first water-equivalent thickness t1 is used; in the region of an intermediate range (referred to as t2-region), the base transmissive plate 34b having a second water-equivalent thickness t2 that is thinner than the first water-equivalent thickness is used; and in the region of a minimum range (referred to as t3-region), the base transmissive plate 34b having a third water-equivalent thickness t3 that is thinner than the second water-equivalent thickness. Thus, for each two energy-set values (Ek and Ek+1) in each slice group F, a particle beam whose common energy emitted from the accelerator 1 is (Ek+Et1) for the t1 region, (Ek+Et2) for the t2-region, or (Ek+Et3) for the t3 region, instead of the set energy (Ek), is emitted (“A” column) so that the portion attenuated by the base transmissive plate 34b set for that range is compensated. Further, the energy is adjusted to that corresponding to the energy-set value for each slice S in the slice group F, by inserting or releasing the energy-adjustment transmissive plate 34s with the water-equivalent thickness ts corresponding to ΔE (“RS” column). Namely, as shown in FIG. 6, the energy is adjusted based on a set of curves that is different for each region with respect to the thickness combination of the transmissive plate of the variable range shifter 34, such as, a curve (t1) and a curve (t1+ts) in the t1-region, a curve (t2) and a curve (t2+ts) in the t2-region, and a curve (t3) and a curve (t3+ts) in the t3-region. This makes it possible to adjust the strength of the four-pole electromagnet 36 so that it is not increased but monotonously decreased including also the case where the strength is unchanged, in all of the energy ranges for forming the SOBP for every patient. As a result, it is possible to suppress the influence of the hysteresis to thereby accurately control the magnetic field strength at the four-pole electromagnet 36, so that the state of the particle beam becomes stable, thus making it possible to perform a particle beam therapy in which three-dimensional radiation can be made accurately. Further, in the case of the configuration as described above, if the radiation is performed while being shifted by each one slice S from a low energy to a high energy, it becomes possible to adjust the strength of the four-pole electromagnet 36 so that it is not decreased but monotonously increased including also the case where the strength is unchanged. Accordingly, also in that case, it is possible to suppress the influence of the hysteresis to thereby accurately control the magnetic field strength at the four-pole electromagnet 36, so that the state of the particle beam becomes stable, thus making it possible to perform a particle beam therapy in which three-dimensional radiation can be made accurately. Note that, in the above description, a case of dividing energies into three regions has been described; however, this is not limitative. The energies may be divided by an appropriate number of two or more so long as the magnetic field strength can be controlled to monotonously decrease. In addition, the number may be changed for each of the emission energies of the accelerator 1. Further, in the above description, a case has been described where the base transmissive plates 34b different in water-equivalent thickness are used separately for each region; however, this is not limitative. With respect to the adjustment of a water-equivalent thickness (attenuation amount) as the variable range shifter 34, it is also allowable to provide transmissive plates each adjusted to have the water-equivalent thickness to be intended; instead, the adjustment may be achieved by way of a so-called binary method in which the water-equivalent thickness to be intended is obtained by a combination of a plurality of transmissive plates having a twofold relationship in thickness between the respective transmissive plates. Further, with the particle beam treatment device according to Embodiment 1, a configuration has been shown in which the energy adjustment system 3 is placed as a part of the particle beam irradiation apparatus 5 provided in each irradiation room; however, this is not limitative. For example, it may be placed in the transport system 2 at its portion common to the respective irradiation rooms. Furthermore, with the particle beam treatment device according to Embodiment 1, a case has been described in which the irradiation nozzle 4 for forming an irradiation shape in a plane perpendicular to the traveling direction of the beam performs scanning irradiation for which an accuracy of the supplied beam is required; however, this is not limitative. For example, even in the case of such a wobbler method in which an irradiation field enlarged by a scanning electromagnet is formed into an irradiation shape by the use of a limiter having a physical transmissive shape, such as a multileaf collimator or the like, it is possible to cause irradiation with an accurate dose distribution because the accuracy of the beam supplied scanning electromagnets becomes higher. As described above, in accordance with the particle beam treatment device according to Embodiment 1, when the irradiation target is partitioned along a depth direction thereof into a plurality of slices S and a particle ray (particle beam) formed for each of the slices S is radiated thereto in a depth order, the energy of the particle beam to be emitted from the accelerator 1 is set for every slice group F including two or more adjacent ones of the slices S, and the attenuation amount is set for each slice S in said slice group F. The particle beam treatment device is configured to includes: the variable range shifter 34 that adjusts the attenuation amount by changing the thickness of the transmissive plate through which the particle beam is transmitted; the irradiation nozzle 4 that has a scanning electromagnet and that makes forming of the particle beam adjusted in the attenuation amount, according to each of the slices S; the four-pole electromagnet 36 that is placed between the variable range shifter 34 and the irradiation nozzle 4, and that operates so as to converge the particle beam having been spread by the transmissive plate; and the control unit 6 that determines set values of the accelerator 1 and the variable range shifter 34, and that controls the amount of magnetic excitation of the four-pole electromagnet 36 according to the set values; wherein, for said every slice group F, the control unit 6 sets higher the energy to be emitted from the accelerator 1 than an energy corresponding to the slice S at a deepest location in said slice group F so that the transmissive plate has a predetermined thickness for the slice S at the deepest location; and wherein, with respect to the thickness of the transmissive plate to be set for said every slice group F, the thickness set for the slice group F at a deep location is larger than or equal to the thickness set for the slice group F at a shallow location, and the thickness set for the slice group F at a deepest location is thicker than the thickness set for the slice group F at a shallowest location. Thus, the spread particle beam can be converged by controlling the strength of the four-pole electromagnet 36 to monotonously decrease (or increase), so that the state of the particle beam becomes stable, thus making it possible to perform a particle beam therapy in which three-dimensional radiation can be made accurately. In particular, since the irradiation nozzle 4 serves to perform the forming according to each slice S by use of a scanning method and thus requires, in particular, a stability of the beam incident to the irradiation nozzle 4, the effect of the invention emerges more significantly. Further, since the collimator 35 for limiting passing of the particle beam spread out to a predetermined extent or more is placed between the variable range shifter 34 and the four-pole electromagnet 36, the spread particle beam can be converged more easily by controlling the strength of the four-pole electromagnet 36 to monotonously decrease (or increase). Further, in accordance with the operation method of the particle beam treatment device according to Embodiment 1, when the irradiation target is partitioned along a depth direction thereof into a plurality of slices S and a particle beam formed by the irradiation nozzle 4 for each of the slices S is radiated thereto in a depth order, the energy of the particle beam to be emitted from the accelerator 1 is set for every slice group F including two or more adjacent ones of the slices S; the attenuation amount for each slice S in said slice group F, is set by the variable range shifter 34; and the particle beam incident to the irradiation nozzle 4 is converged by the four-pole electromagnet 36 placed between the variable range shifter 34 and the irradiation nozzle 4. The operation method of the particle beam treatment device is configured so that: for said every slice group F, the set value of the energy of the accelerator 1 is set higher than an energy corresponding to the slice S at a deepest location in said slice group F so that the variable range shifter 34 has a predetermined attenuation amount for the slice S at the deepest location; with respect to the attenuation amount to be set for said every slice group F, the amount set for the slice group F at a deep location is larger than or equal to the amount set for the slice group F at a shallow location, and the amount set for the slice group F at a deepest location is larger than the amount set for the slice group F at a shallowest location; and the amount of magnetic excitation of the four-pole electromagnet 36 is controlled according to the set value of the energy of the accelerator 1 and the attenuation amount by the variable range shifter 34. Thus, the spread particle beam can be converged by controlling the strength of the four-pole electromagnet 36 to monotonously decrease (or increase), so that the state of the particle beam becomes stable, thus making it possible to perform a particle beam therapy in which three-dimensional radiation can be made accurately. 1: accelerator, 2: transport system, 3: energy adjustment system, 4: irradiation nozzle, 5: particle beam irradiation apparatus, 34: variable range shifter, 34b: base transmissive plate, 34s: energy-adjustment transmissive plate, 35: collimator, 36: four-pole electromagnet, F: slice group, S: slice, Vt: irradiation region. |
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054240425 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to methods and devices for processing waste, especially radioactive, toxic, industrial and household waste generated from factories, nuclear power plants, hospitals, institutions and the like. More particularly, the present invention relates to the treatment of wastes from solid and liquid, including both aqueous and nonaqueous, wastes streams to form a stable, final glass waste product. 2. Discussion of Background Economic and regulatory factors require nuclear power utilities and other generators of radioactive waste to develop and evaluate new technologies and methodologies for improving safety and reducing the costs of operations. Also, reducing the volume of waste generated and improving the stability of the disposed waste is of prime interest within our increasingly environmental-conscious society. Improvements in waste processing operations and procedures can significantly reduce waste management costs, waste volume, and the concern associated with storage and permanent disposal of the final waste. Additionally, existing legislation may require all power plants to store on-site the waste each plant generates if centralized storage or disposal facilities are not available. Thus, improvements in waste processing systems should include not only significant reductions in the volume of the final waste form but also the capability of identifying and separating the waste from each generator so that waste can be returned to the generator for storage. Nuclear power plants, which produce much of the radioactive waste, generate a plurality of waste types typically broken down into three classifications: "dry active waste" (DAW), "wet waste" or ion exchange resins and "liquid waste." Dry active waste includes paper, wood, metal scraps, plastic sheeting, clothing and the like. Currently, dry active waste is processed by low and high density compaction, with compaction ratios of approximately 2:1 to 6:1, depending on its particular composition and the force exerted. Some forms of DAW are currently incinerated with a volume reduction of approximately 50:1. Wet waste includes ion exchange resins, typically in granular or powdered form. Wet waste is currently processed by dewatering (drying) to take out interstitial or free water. Usually, drying does not necessarily include removing water from the resin bead itself. Liquid waste includes organic waste (oils, chemical solutions), which is combustible, and inorganic waste such as aqueous wastes and sludges, inorganic acids, and solutions of boron, NaOH and the like. Organic wastes are currently incinerated or stabilized. Inorganic waste, mostly comprised of aqueous salt solutions, is currently being processed by demineralization, ion exchange, membrane technology and evaporation, all of which are well known in the art of waste processing. Also, aqueous waste is processed by evaporator/dryers to yield concentrated and/or dried, solid waste. Numerous processing methods are known for treating and processing waste generated from power plants and the like, including radioactive wastes generated from nuclear power plants. For example, Bardot et al, in U.S. Pat. No. 4,925,566, describe the use of ultrafiltration, hyperfiltration and demineralization for radioactive liquid elements. Also, the notion of ion exchange and the use of ion exchange resins for radioactive waste processing is well known, as described in U.S. Pat. Nos. 3,520,805, issued to Ryan, and 4,415,457, issued to Shirosaki et al. Ryan describes filtration through ion exchange resin-coated fibers. Shirosaki et al absorb ions in power plant filter backwash onto an ion exchange resin. Several U.S. patents combine additional waste processing methods with the use of ion exchange resins. These patents include U.S. Pat. Nos. 3,773,177, issued to Queiser et al, and 5,158,674, issued to Kikuchi et al. Queiser et al follow the use of ion exchange resins with filtration and drying processes. Similarly, Kikuchi et al treat radioactive liquid wastes using membranes to concentrate the wastes, filtration of oils using active silica, and then incineration of the flammable solids on the active silica. Also, in Macedo et al (U.S. Pat. No. 4,737,316), contaminated liquid is purified by passing it through an ion exchange resin then "sintering" the resin. Another procedure known for use in processing radioactive waste is vitrification, that is, the incorporation of the inorganic portion of the waste into a stable, glass matrix having radioactive elements as part of the glass structure. Vitrification has been studied for decades as a way of stabilizing high level radioactive waste, and a number of patents exist that relate thereto. However, more recently, vitrification has been used with other types of radioactive wastes. For instance, Macedo et al (U.S. Pat. No. 4,737,316) state in their specification that it is well known to form borosilicate glass from the processing of ion exchange resin and glass frit. Incineration is used to reduce the volume of radioactive waste but, because the ash produced from combusting the waste contains radioactive material, further processing of the ash is required to stabilize it. Despite the number of waste processing procedures known for use with hazardous or radioactive wastes from power plants and the like, there exists a need for an effective process system that significantly reduces the volume of all types of waste from nuclear power plants, and produces a stable, final waste product that is easily manageable for storage, transporting, disposal and the like. SUMMARY OF THE INVENTION According to its major aspects and broadly stated, the present invention is a device and method for processing all kinds of waste including toxic, industrial, household and the like, but especially the three main radioactive waste streams generated by power plants, hospitals and the like. In particular, it is a system applicable for processing all kinds of waste, especially radioactive waste, both solid and liquid forms, including vitrification to immobilize radioisotopes in a stable, final waste product. This system has several subsystems, including a feed conditioning subsystem for conditioning each type of waste, a feed preparation subsystem for blending all of the waste types, a feed melter chamber with an upper thermal zone and a lower melting zone, a glass handling subsystem for packaging and storing the final product, and an off-gas cleaning and control subsystem. The conditioning subsystem conditions the waste feed by shredding tile dry active waste, drying tile bead and powdered ion exchange resins, and concentrating the aqueous waste. The conditioned waste can then be blended in tile feed preparation subsystem to produce a waste feed having a consistent BTU value per unit mass when combusted and incorporated with glass formers into the waste if necessary. In the feed melter chamber, combustible, organic waste is oxidized and noncombustible waste and decomposition products are incorporated into the melted glass formers. The molten glass is cooled and put into a suitable container. The particulate carried in the off-gas resulting from destruction of the waste is captured in the off-gas cleaning and control subsystem and can be returned to the feed melter chamber to be incorporated into the melt or can be solidified with a blender-dryer in the feed conditioning subsystem. The first component of the feed conditioning subsystem is a feed inventory and handling conveyor and shredder for shredding the dry active wastes. Shredding the dry active wastes promotes better blending of dry active wastes with the other waste types, reduces the size to enable faster and more efficient burning and minimizes potential damage to the melter from large, heavy objects. The second component of the feed conditioning subsystem involves means for drying the resin wastes by removing the interstitial or free water from among the granular and powdered ion exchange resins. Such resin drying can be effected by a number of known methods, including the method disclosed in U.S. Pat. No. 4,952,339, which is commonly assigned. The third component of the feed conditioning subsystem involves means for concentrating aqueous wastes by separating some of the liquid from the dissolved salts and particulate suspended in it. Methods for reducing the liquid volume of aqueous wastes include sophisticated filtering systems based on membrane technology such as microfiltration and hyperfiltration (also known as reverse osmosis). Also, drying systems using a rotary blender-dryer to evaporate water, can be used for liquid volume reduction of aqueous wastes. The feed preparation subsystem mixes conditioned DAW, dried resins and concentrated aqueous waste with glass forming materials prior to feeding them into the reciter chamber. Wastes can be processed separately or as a blended feed depending upon radiation dose levels, BTU value or other criteria. Resin drying and concentrating of the aqueous wastes takes place typically at the generator's facility, but the shredding of DAW generally takes place away from the generator's facility. Accordingly, shredders can be used to assist in mixing the waste types and serve the two functions of blending and shredding. Also, depending on the particular constituency of the waste types, some of the waste can be fed directly into the melter chamber along with glass formers without blending. It is desirable to deliver a waste feed to the melter chamber that has a consistent BTU and radioactivity content when combusted to improve the operational efficiency of the melter chamber operation and ultimately produce a highly stable and more uniform final glass product. Shredders can include a low speed shear type, a high speed impact type, as well as rotary conveyor screws. The melter chamber, which has an upper thermal zone and a lower melting zone, receives the waste feed from the feed preparation subsystem. The thermal zone oxidizes the organic constituents within the waste feed in converting the organic and inorganic constituents into ash and off-gas. The melting zone uses a heated vessel to controllably melt the glass formers and combine them with the ash and the noncombustible material. The melting zone of the melter chamber is connected to the glass handling subsystem. In the preferred embodiment, the glass handling subsystem cools the molten glass received from the melter and packages it accordingly. Alternatively, the molten glass may be cooled as it moves along a conveyor that causes the molten glass to form globules (marbles) as it cools for ease in recycling glass in the future or by a fluid cooled bath prior to being packaged in the appropriate containers. The thermal zone of the melter chamber is connected to the off-gas cleaning and control subsystem. The off-gas cleaning and control subsystem captures a portion of the off-gas for recycling to the melter chamber and scrubs the remainder of the off-gas for stack emitting. An important feature of the present invention is the combination of aqueous waste streams and vitrification. Although vitrification of radioactive waste is known, the feeding of partially concentrated aqueous wastes, wastes that are less than 20% concentrated, is believed to be new. Another important feature of the present invention is the waste feed melter chamber. The melter chamber is dual purpose. Some conventional melters allow for some destruction of organics but are not designed or intended for significant destruction. The present melter is so designed in order to accommodate the large fraction of DAW and organic liquid wastes entering the melter. Furthermore, the heated vessel portion of the melter chamber is designed to be easily replaceable so that processing is not interrupted for long periods of time while the entire melter chamber is replaced. The present invention features a disconnect mechanism that detaches the heating vessel from the melting zone. The heating vessel can be quickly and easily interchanged to optimize waste processing or refractory replacement. All melter types can be adapted for use with the disconnect system, including: refractory lined, Joule heated electrode melters; induction-heated cold wall crucible melters; induction-heated warm wall crucible melters; in-can melters having induction or resistance heating; and slagging cold wall melters. Finally, unlike conventional melters, the heated vessel in the preferred embodiment of the present invention is heated by induction rather than by Joule heater electrodes. An inductively heated melter is simpler in design and easier to maintain and can heat to higher temperatures than one heated with electrodes. In addition, most melters operate in a reducing mode that can generate liquid metals that are not readily incorporated into a glass matrix. Also, a hotter oxidizing melter is better suited for waste having a high metal content because it further reduces the amount liquid metal that forms in the melt. Induction heating allows more efficient, uniform and controlled heating and melting rates than conventional electrode melter chambers. Also, direct heating is possible since the induction field directly heats the melter liner, metal and glass matrix. As a result, any undissolved metal remaining in the melt chamber can be melted or consumed by a short heatup to a higher temperature, thereby minimizing refractory temperature during normal operations and eliminating electrode loss common in Joule heated melters. Also, induction melting has inherent stirring characteristics that provide better glass homogeneity. The depth of penetration of the induction field can be increased by selection of the induction coil power supply frequency. Cold or warm wall induction heated crucibles are preferred, as glass can significantly corrode (dissolve) typical suscepting crucible materials such as silicon carbide, whereas a warm or cold wall crucible uses a solidified layer of glass against the inner wall for optimum corrosion protection. Still another feature of the present invention is the system for feeding of enriched oxygen into the melter chamber. Most melters operate in reducing mode, which can generate liquid materials that are not readily incorporated into the glass matrix. The present invention feeds an air/oxygen mixture into the melter chamber to aid in thermal oxidation and control. Also, the use of an enriched air/oxygen improves combustion kinetics, allows higher temperature operation and greatly reduces off-gas volumes. The improved oxygen atmosphere in the melter of the present invention enhances the production of glass soluble metal oxides instead of liquid metals that can cause catastrophic failure of most melters. Since the air/oxygen mixture has enriched oxygen, approximately half of this feed can be returned to the melter chamber from the off-gas if desired. The recycled gas preheats the fresh oxygen/air mixture but does not dilute the amount of oxygen available for oxidation below appropriate levels. Carbon dioxide and nitrogen in the recycle gas can be removed using conventional cyrogenic or adsorption technology to provide oxygen-enriched recycle gas. The major purpose of recycle gas is to control or moderate melter temperatures and to allow reuse of excess oxygen in the off-gas. Yet another feature is the use of off-gas cleaning and pollution control components within the waste processing system. The off-gas cleaning and pollution control components collectively remove radioactive or undesirable particulate and acid gases from off-gas resulting from combustion during waste processing. The advantage of this feature is that harmful pollutants are removed from the off-gas, thus producing cleaner stack emissions. Another feature is the use of a liquid-cooled conveyor in an alternative embodiment of the present invention. The liquid-cooled metal belt conveyor rapidly transports and cools the glass moving from the melter chamber to the storage containers. The conveyor's movement and rapid cooling cause the molten glass to form globules (marbles) that are eventually placed in the storage containers. Another feature of the present invention is the shredding device for shredding dry active waste and, when desired, mixing DAW with ion exchange resins and concentrated liquid waste. The shredder makes the DAW easier to mix and increases it combustion efficiency. Other features and advantages of the present invention will be apparent to those skilled in the art from a careful reading of the Detailed Description of a Preferred Embodiment presented below and accompanied by the drawings. |
040452867 | description | The molten-salt reactor which is illustrated diagrammatically in FIG. 1 is generally designated by the reference 1. The reactor comprises an outer containment structure 2 having concrete walls of substantial thickness defining an internal cavity or vault 3 and an inner cylindrical vessel 4 having a substantially spherical bottom wall and a vertical axis. Said vessel contains the reactor core and the entire primary circuit which is associated with the core. The external surface of the reactor vessel 4 is advantageously surrounded by a second vessel 4a having parallel walls, the space 4b formed between the two vessels being filled with a suitable conditioning fluid. The open top portions of the vessels 4 and 4a are suspended from a closure slab or vault roof 5 which extends horizontally and rests on a bearing surface or corbel 6 formed in the outer containment structure 2. The reactor core 7 is placed in the axis of the vessel 4 in the lower portion of this latter and rests on a diagrid 8 which is in turn carried on a transverse support structure 9, the peripheral portion of said support structure being rigidly fixed to the bottom wall 10 of the vessel 4. The reactor core 7 is formed of a neutron-moderating mass, especially of graphite, which is pierced by ducts (not shown in the drawings) for the circulation of molten salt. The top portion of the reactor core 7 is surmounted by a reflector 11 and surrounded laterally by another reflector 12, said reflectors being in turn surrounded by a suitable thickness of a mass of material designated respectively by the references 11a and 12a and designed to form a neutron shield. There is formed between these core components and above the reactor core at least one narrow passage 13 through which the molten fuel salt passes and collects in a top region 14 forming a manifold after said fuel salt has been circulated upwards through the reactor by means which will be described later. There is placed beneath the reactor core a bottom reflector 15 which is intended in conjunction with the other reflectors to confine the neutrons in the active portion of the reactor. The reactor core 7 and the lateral reflector 12 are placed within a thin-walled open vessel 16 which is placed within the first vessel 4 and rests on the transverse support structure 9 of this latter. An annular region 17 is formed between said second vessel 16 and the internal wall of the first vessel; the top portion of said annular region communicates with the manifold 14 for the hot molten fuel salt which is discharged from the reactor core via the passage 13, there being placed within said annular region the means for circulating the fuel salt and for extracting the heat gained during circulation of this latter through the reactor core. A number of heat exchangers 18 and circulating pumps 19 are in fact mounted in the annular region 17. These primary circuit components are arranged in suitably spaced relation so as to ensure the most favorable conditions for temperature equilibrium and fluid circulation. The heat exchangers and the pumps are surrounded by cylindrical protective shells or sleeves 20 and 21 respectively which extend to the top portion of the vessel 4 so as to be supported by the roof slab 5 which closes said vessel. The top portions of the sleeves 20 and 21 open into the manifold 14 and the bottom portions thereof communicate with a second manifold 22 in which the cold fuel salt discharged from the heat exchangers is recirculated by the pumps and returned to the reactor core beneath the reactor diagrid 8. The heat exchangers 18 are suspended from seal plugs 23 which serve to close-off openings formed in the vault roof and having suitable dimensions whilst the pumps 19 are in turn suspended from seal plugs 24 which contain the motors for driving said pumps. The vault roof 5 is also provided in the central portion and above the reactor core 7 with a removable seal plug 25 which serves to gain access to the core through the neutron shield 11a and the top reflector 11 by means of handling devices 26 which are controlled from the exterior of the reactor vessel by actuating means 27. In accordance with a characteristic arrangement of the invention, the annular region 17 formed between the vessels 4 and 16 is packed within the free spaces located outside the sleeves 20 and 21 which surround the heat exchangers 18 and the pumps 19 with an inert material 28 which is compatible with the molten fuel salt and preferably consists of expanded graphite. Both the bottom portion of the vessel 4 and the region located at the top portion of this latter beneath the vault roof 5 above and beneath the manifolds 14 and 22 are also filled with molten fuel salt. The circulation of the molten fuel salt within the primary circuit constituted by the reactor core 7, the heat exchangers 18, the pumps 19, the manifolds 14 and 22 takes place as follows. The hot fuel salt discharged from the top portion of the reactor core is collected by the passage 13, then flows within this latter towards the manifold 14 in the direction of the arrows 29. In this region, the fuel salt is fed to the heat exchangers 18 in the direction of the arrows 30 and restitutes the heat gained at the reactor core outlet to a suitable secondary fluid which is circulated within the heat exchangers through pipes 31 and 32 respectively. The cold salt is then collected in the outlet manifold 22 to be recirculated by the impellers 33 of the pumps 19 which return the salt beneath the reactor core for a further passage through this latter. The direction of circulation of the fuel salt in this final portion of its path is shown diagrammatically by the arrows 34. The arrangements contemplated for the outley of the primary circuit within the reactor vessel thus consist in reducing the dimensions of the molten salt flow path to a strict minimum, this result being achieved by judicious packing of the spaces which are left free between the pumps and the heat exchangers within the annular region which surrounds the reactor core and around the hot salt manifolds and cold salt manifolds. In particular, that portion of said flow path in which the fuel salt is brought to its highest temperature, that is, between the core outlet and the heat-exchanger inlet and delimited by the passage 13 and the manifold 13 corresponds to a small length in which the effects of corrosion of the fuel salt on the vessel structures can be limited to a permissible value. In an alternative embodiment illustrated in FIG. 2, the molten-salt flow path between the heat exchangers and the pumps may be reduced to a further extent by making provision directly within the annular region formed between the vessel and the reactor core for pump-exchanger units in which one pump is mounted directly beneath each heat exchanger and in the axis of this latter. From this figure, in which the reference numerals are identical to those adopted in FIG. 1, it is apparent that the fuel salt flow path in the hot portion of the primary circuit between the reactor core 7 and the heat-exchanger inlet 18 can be reduced to radial ducts 35 whilst the return of the cold fuel salt discharged by the impellers 33 of the pumps 19 is carried out by means of further ducts 36 which extend radially from said pumps to the center of the reactor core. The expanded graphite 28 which fills the free spaces around the ducts 35 and 36 is compacted to a suitable density. Positioning of the material can be carried out by introducing a number of formwork elements into the reactor vessel which is still empty. Said formwork elements define the volumes of the reactor core, the heat exchangers, the pumps and the connecting ducts, the expanded graphite being then tamped around these components. On completion of the packing operation, the formwork elements are removed in order to leave the necessary space for mounting the corresponding portions of the installation. In either of the two alternative embodiments contemplated in the foregoing, the molten-salt reactor under consideration has a fully integrated primary circuit within the core containment vessel. By means of this constructional arrangement, the protection of the structures of said primary circuit from neutron radiations need only be considered in relation to the fact that the fuel salt itself is a source of neutrons. This necessarily results in activation of these structures which must be designed and positioned accordingly since their integrated fluence must remain compatible with their mechanical strength. On the other hand, the arrangements provided for limiting the flow path of the hot molten fuel salt between the reactor core outlet and the primary heat exchangers reduce the risks of corrosion to a considerable extent. In fact, the hot molten salt is in contact with only a very small portion of the core structures and the primary circuit whereas the greater part of this latter is in contact with the cold fuel salt. In order to limit the effects of the fuel salt in contact with the core structures, it can be particularly advantageous as illustrated in FIG. 3 to "condition" the reactor vessel so as to carry out external cooling of the vessel wall in the regions which are in contact with the salt. To this end, there can be associated with said wall a separate cooling circuit for a suitable fluid combined within the vessel with a perforated heat-insulating structure 41 of a type which is known per se. By virtue of these arrangements, there is formed in contact with the vessel 4 a zone 42 in which the fuel salt is solidified followed by a phase-change zone 43 and finally by a zone 44 in which the liquid salt is again present, the solid layer thus deposited being such as to insulate the vessel wall from the circulating salt. The corrosive action of the molten salt is therefore reduced even further, with the result that the vessel can be constructed of ordinary steel and not of special steel which is both costly and more difficult to machine. The formation of said solidified salt layer on the internal surface of the reactor vessel can be carried out in the following manner. When the vessel has been completely filled with expanded graphite and fuel salt, the entire assembly is heated to a temperature above that of the melting point of the eutectic compound constituted by the neutral elements of the fuel salt consisting for example of a mixture of lithium and beryllium. This temperature is equal, for example, to 400.degree. C. if the liquidus temperature of the salt is of the order of 350.degree. C. and the neutral constituents of the salt are thus permitted to fill the free spaces which may have been left as a result of differential expansions between the reactor vessel and the expanded graphite which has been compacted within said free spaces. In the following stage, the vessel is cooled to below the point of solidification of the eutectic compound, for example to 300.degree. C. When the entire quantity of salt which fills the spaces between the reactor vessel and the graphite has solidified, the vessel is drainedout, whereupon the reactor core is filled with the active components of the fuel salt which are necessary for the reaction while maintaining the reactor vessel at 300.degree. C. Conditioning of the vessel wall at 300.degree. C. is then maintained by the circuit 40 throughout the operation of the reactor so as to prevent the fuel salt from coming into contact with the reactor vessel whereas this latter is continuously insulated by means of the zones 42 and 43. It is readily apparent that, if it is found desirable for any reason to replace the protective layer, it will only be necessary to increase the conditioning temperature to 400.degree. C. in order to remove all the salt, then again to carry out the operations mentioned above. It should be noted in addition that the conditioning explained in the foregoing does not entail a high degree of fine control since the inertia of this system is in fact particularly high and variations of plus or minus 25.degree. C. are not objectionable. Regulation of the conditioning can in any case be obtained simply by controlling the pressure of steam produced within the heat exchangers which are heated by the conditioning fluid within the circuit 40. In all cases, the integration of the primary circuit within the reactor vessel in conjunction with a volume of fuel salt which is substantially equal to or smaller than that of known external-loop systems permits better accessibility to the different circuit components for both maintenance and possible replacement, these components being grouped together in a single location in which the necessary handling means can more readily be concentrated. It is wholly apparent that the invention is not limited solely to the examples of construction which have been described in the foregoing with reference to the drawings but extends to all alternative forms. |
041636902 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to nuclear reactor fuel element assemblies and, in particular, to a fuel element assembly which utilizes a grid plate arrangement for locating and supporting fuel elements in the form of pins, rods or the like. 2. Summary of the Prior Art In heterogeneous nuclear reactors, nuclear fuel is separated from the moderator and arranged in discrete bodies known as fuel elements. Fuel elements typically utilized in heterogeneous reactors consist of thin-walled, elongated, slender tubes or rods which clad the nuclear fuel contained within the element in order to prevent corrosion of the fuel and the release of fission products into the coolant, and are known in the art as "fuel pins" or "fuel rods". Aluminum or its alloys, stainless steel and zirconium alloys are common cladding materials. Such fuel pins are generally arranged in a carefully designed pattern to form an array which comprises the reactor core that provides the concentration of fissionable material needed to sustain a continuous sequence of fission reactions. In a heterogeneous reactor the fuel pins in the core become depleted at different rates, those in the center usually being subjected to a higher neutron flux and thus becoming depleted before those near the outside of the core where a lower neutron flux prevails. Consequently, all of the fuel elements are not normally replaced at one time but rather in stages. Furthermore, at each refueling, partially depleted elements may be relocated in order to optimize core performance and extend the time between refueling outages. It is advantageous, therefore, to group the fuel elements into movable units, known as fuel assemblies, which may contain hundreds of fuel pins. A fuel assembly is typically arranged in juxtaposition with similar assemblies in the core of a pressurized water reactor. In a boiling water reactor, each fuel assembly is typically encased in a square flow channel, commonly called a "can", which is juxtaposed with similar cans occupying the core. Movement of the fuel elements as fuel assemblies during charging and discharging of a reactor core expedites core reloading operations, thereby increasing the overall availability of the reactor and generally enhancing the economics of nuclear reactor use for functions such as power generation. The design of a fuel assembly requires careful analysis to assure the maintenance of the assembly's geometrical integrity during all phases of reactor operation. Heat generated within the fuel pin is often removed by a fluid coolant which flows through the reactor core generally in a direction which is parallel to the longitudinal axes of the fuel pins. The fluid velocity and flow rate may be very high in order to remove the large quantity of heat generated. The surface area of the individual fuel pins, therefore, must be as fully exposed to the flowing fluid as possible in order to promote heat transfer to the coolant and to prevent the development of hot spots on the fuel element due to poor coolant flow conditions. Moreover, the elongated slender fuel pins may be subjected to harmful vibrations induced by the coolant flow or other sources. Thus, it is desirable to arrange fuel elements in an assembly wherein the elements are spaced in a geometry conducive to proper reactor physics while satisfying a number of conflicting needs, viz., the need to minimize structural restraints in order to promote heat transfer from the fuel pins to the coolant, the need to provide structural support to a large number of fuel pins subjected to thermal, hydraulic and vibratory forces and the like, the need to minimize hydraulic pressure losses, and the need to minimize the presence of material capable of parasitic absorption of neutrons. Some fuel assemblies of the prior art have utilized a grid of plates to space and support the fuel pins. Usually, these grids comprise a cellular structure, commonly characterized as the egg crate design, that is formed through the mutually perpendicular intersections of a group of interlocking metal plates. Bosses, dimples, bowed members and the like protrude from the surface of the portions of these interlocking plates that form the individual cell walls. A fuel pin is inserted into each cell formed in the grid structure. The protrusions engage the outer surface of the fuel pin within a particular cell both restraining and locating the pin. Two types of protrusions are commonly employed. One type of grid plate protrusion is very resilient being essentially spring mounted. The resilient character of these protrusions permits their deflection so that the fuel pins can be inserted into the grid structure with relative ease. Upon removal of the deflecting means the resilient protrusion springs back into position in the cell thus receiving the fuel pin. The other type of grid plate protrusion is a very stiff, rigid member which essentially eliminates relative movement between the fuel pins and the protrusions. Problems have been experienced in grid designs in which either resilient or rigid protrusions alone have been used. Construction of a grid with cells containing a totality of resilient protrusions is difficult. Use of a two-tier arrangement of grids to overcome such difficulties results in the introduction of additional material capable of parasitic absorption of neutrons while increasing costs and complicating fabrication of the fuel assembly. During reactor operation the flexibility of the resilient protrusions permits relative movement at the protrusion to fuel pin contact point. This motion produces an undesirable wearing or "fretting" of the pin that weakens the cladding and can cause its failure. Use of a totality of the rigid type of protrusions, on the other hand, leads to other difficulties. For example, it is difficult to insert a fuel pin through a cell containing a totality of the unyielding rigid protrusions without galling, abrasion, gouging or like damage to the cladding. A grid plate design which utilizes a combination of resilient protrusions and rigid protrusions within a cell can overcome these problems. Deflection of the resilient protrusions allows fuel pin insertion without damage. After removal of the deflecting means, the resilient protrusions spring into position causing the fuel pins to be secured at the contact points of both the resilient and rigid protrusions. It is evident that in each cell a resilient protrusion should be located on the plate wall opposite a plate having a rigid protrusion to facilitate fuel pin insertion and removal and to more positively secure the pins during reactor operation. However, it soon becomes apparent that the peripheral band surrounding the fuel assembly will therefore contain resilient and rigid protrusions, complicating the construction of the band. In addition, locating the resilient protrusions on the peripheral band necessarily results in weakening of the band. This is highly undesirable since the peripheral bands of juxtaposed fuel assemblies abut and lend lateral support to each other, and, in addition to retaining their structural integrity without damage during normal conditions, these bands must withstand impact forces generated during abnormal occurrences, for example, earthquakes. Moreover, when a reactor utilizing a grid assembly described above it utilized to power a mobile unit, such as an ice breaker ship, external vibrations may be transmitted thereto causing additional impact between the peripheral bands or between the band and its sheathing can. Hence, it is highly desirable to develop a fuel element grid plate assembly which does not utilize resilient protrusions in its peripheral band while retaining the advantages inherent in the combination resilient and rigid protrusion cells. Furthermore, such a fuel element support assembly would offer further advantages if it could be adapted to use in a reactor that utilizes "cans" to encase each fuel assembly. SUMMARY OF THE INVENTION According to the present invention, in a fuel assembly a spacer grid of the type described above, two longitudinally paired grid plates, constructed differently in accordance with the preferred embodiments discussed below, intersect with a similar set of paired plates at a generally central point in the grid plate lattice. Each of the paired grid plates is formed with resilient protrusions extending into the cells on either side of these paired plates. The remaining grid plates in the grid structure have resilient protrusions on one face and rigid protrusions on the face on the opposite side of the plate. These grid plates are organized in two groups, each of the groups being parallel with a respective paired plate combination; the individual grid plates in each group, moreover, being spaced from each other and generally intersecting perpendicularly with the grid plates in the other group, in order to form a cellular structure. The rigid protrusions in the plates in each group are orientated toward the paired plates with which each respective grid plate group is parallel. In this way, each of the cells is bounded by two adjacent plate surfaces from which a set of rigid protrusions project into the cell and two adjacent plate surfaces from which a set of resilient protrusions project into that cell, none of the protrusions in either of these two sets being on oppositely disposed surfaces. In these circumstances, the grid can be arranged so that the peripheral band contains only rigid protrusions. In one embodiment, the peripheral band is constructed so that a spring-like member is disposed on the surface farther away from the center of the assembly. The spring-like member assures spring contact force between juxtaposed fuel element assembly spacer grid peripheral bands in a "canless" type reactor core arrangement and between the peripheral band and the inner wall of the can of a "can" type reactor core resulting in a fuel assembly having greater stability under normal and abnormal operating conditions. Other combinations of plates to provide the desired orientation of sets of rigid and resilient protrusions in each cell may be used when the use of resilient protrusions in the peripheral band is desired for a particular application. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention. |
abstract | High aspect ratio micromachined structures in semiconductors are used to improve power density in Betavoltaic cells by providing large surface areas in a small volume. A radioactive beta-emitting material may be placed within gaps between the structures to provide fuel for a cell. The pillars may be formed of SiC. In one embodiment, SiC pillars are formed of n-type SiC. P type dopant, such as boron is obtained by annealing a borosilicate glass boron source formed on the SiC. The glass is then removed. In further embodiments, a dopant may be implanted, coated by glass, and then annealed. The doping results in shallow planar junctions in SiC. |
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description | In the present invention, a beta cell is provided comprising a semiconductor junction device made of an icosahedral boride semiconductor, a radioisotope source of beta radiation, and means for transmitting electrical energy to an outside load. Because of the use of the icosahedral boride semiconductor, the beta cell of the present invention does not suffer the long-term conventional radiation-induced damage to a degree to significantly degrade the performance of the beta cell. Carrard et al. (M. Carrard, D. Emin; and L. Zuppiroli, Physical Review B, 1995, 51, 270-274) demonstrated that some boron compounds do not suffer accumulating damage from high-energy electron bombardment even at temperatures as low as 91K. These solids are called icosahedral borides. Icosahedral borides are solids primarily composed of boron atoms that form clusters whose atoms reside at the twelve vertices of icosahedra. Carrard et al. thus find that beta-induced damage to icosahedral borides spontaneously self-heals. The present invention relates to the use of icosahedral boride semiconductors in beta cells. In particular, the self-healing of beta-induced damage in icosahedral boride semiconductors permits beta cells based on icosahedral boride semiconductors to utilize sources that emit high-energy beta particles such as 90Sr or 170Tm. Because of self-healing, the lifetimes of icosahedral boride beta cells are limited by the rate of decay of the radioisotope energy source rather than by radiation damage to the semiconductor. Examples of icosahedral boride semiconductors include B12As2, B12P2, elemental boron in both its xcex1-rhombohedral and xcex2-rhombohedral structures, and boron carbides, B12-xC3-x, where 0.15 less than x less than 1.7 (the single phase region of B12-xC3-x). Room-temperature carrier mobilities in several icosahedral boride semiconductors, B12As2, B12P2, and xcex1-rhombohedral boron, are comparable to those of semiconductors that are commonly utilized in solar cells. These mobilities are high enough for these icosahedral borides to operate efficiently in beta cells. Sources of beta radiation include the radioisotopes 90Sr, 147Pm, 170Tm, 3H, 63Ni, 137Cs, 141Ce, and 204Tl, and compounds containing these radioisotopes. One embodiment of the present invention, shown in FIG. 1, comprises a Schottky-barrier junction device 10, a beta-emitting radioisotope stratum 21 that emits beta radiation 22, and means 31 for transmitting the produced,electrical energy to a load. The Schottky-barrier device can be formed by depositing a thin metal contact 11 that serves as a Schottky barrier (a non-Ohmic contact), for example Au, on an icosahedral boride semiconductor 12. The thickness of the metal contact, typically 0.1 to 0.5 microns, is kept small to minimize loss of beta-particles"" energy 22 as it passes through the metal. The icosahedral boride semiconductor may be a film of typical thickness 0.1 to 100 microns deposited on a substrate such as SiC or a metal diboride (such as NbB2, TiB2, ZrB2, HfB2, TaB2) or a free-standing icosahedral boride semiconductor. Another, Ohmic, metal contact 13 on the unirradiated back side of the sandwich completes the electrical circuit. The layer of the beta-emitting radioisotope, for example 90Sr or compounds containing 90Sr such as 90SrTiO3, is typically of thickness 0.1 to 50 microns. The maximum thickness of the beta-emitting radioisotope stratum will be fixed for each radioisotope by the self-absorption depth of the radioisotope, beyond which no beta particles can escape the stratum. Another embodiment of the invention, a variation of the beta cell illustrated in FIG. 1, comprises a p-n junction icosahedral boride semiconductor device and a beta-emitting radioisotope stratum (see FIG. 2). Boron carbides and xcex2-rhombohedral boron are intrinsically p-type and native defects in both B12As2 or B12P2 frequently render them p-type. The p-type region 15 can also be established by incorporating a p-dopant, for example substituting Si, Ge, or C, for As or P in B12As2 or B12P2. The n-type region 16 is established by incorporating an n-dopant, for example S, Se, or Te for P or As in B12As2 or B12P2. The thickness of the n- and p-type regions are typically between 0.1 and 100 microns. The beta-emitting radioisotope is selected from for example 90Sr, 147Pm, and 170Tm. As with the prior embodiment, the optimal thickness of the radioisotope stratum is determined by its self-absorption length. Electrical leads from the p-type region and the n-type region connect the p-n junction device with the rest of the electrical system. Another embodiment of the invention, illustrated in FIG. 3, comprises a 3-dimensional stack 40 incorporating alternate strata (generally approximately uniform layers) of beta-emitting radioisotope 41 and icosahedral boride junction devices that can comprise both p-type regions 42 and n-type regions 43. As illustrated in FIG. 3, a 3-dimensional stack utilizes beta particles 44 emitted from both faces of radioisotope strata. Furthermore, beta particles emitted from radioisotope layers can have ranges that allow them to traverse several semiconductor junction devices in the stack. The 3-dimensional stack thus permits more efficient collection of beta-particles energies. Individual junction devices within this stack can be either Schottky-barrier or p-n junction devices as described in the prior embodiments. The means for transmitting the produced electrical energy are not shown in FIG. 3. The beta cell is generally enclosed within a metal shield (case), as illustrated in FIG. 4. The thickness and type of material of the shield. 53 is such that radiation produced by the beta cell is attenuated to desired levels outside the case. The electrical output of the stack (such as the stack 40 illustrated in FIG. 3) is established across a positive terminal 51 and a negative terminal 52. In general, at least one terminal projects through an opening in an electrically insulating cap 54 in the shield. The shield material and its thickness is selected based on the beta source and the application. For example, for when minimal or no shielding is required, an aluminum case could be appropriate. For other embodiments that require shielding, the shield could be made from such metals as lead or depleted uranium. The beta cell of the present invention can be utilized in a variety of configurations, including both series and parallel combinations to achieve the desired output currents and voltages. Additionally, the type of beta source and the configuration of the beta source with respect to the type of icosahedral boride material and layer thickness and number of layers of icosahedral bride material can be varied to achieve the desired electrical energy output. One embodiment of the present invention is specifically illustrated by a configuration of the cell of FIG. 5. A Schottky-barrier device 60 was created by depositing separate gold contacts 61 onto the surface of a film of semiconducting B12As2 64, which was layered on top of a SiC substrate 65. Electrical leads 66 were attached to the Au contacts to transmit the produced electrical energy to a load. In this example, the B12As2 was a p-type semiconductor. In this example, the thickness of the B12As2 film was approximately 0.1 micron. A beam of energetic electrons 63, from a source 62, was caused to impinge upon one of the Au contacts. The thickness of this Au contact was approximately 0.1 micron. When the energy of the impinging electrons was insufficient to penetrate this thickness of Au, less than about 10 keV, no emf was measured across the bombarded junction. When the energy of the incident electron beam was sufficient to penetrate through the Au contact, an emf was produced. This emf was caused by the separation of the electron-beam induced electron-hole pairs in the B12As2 semiconductor. The open-circuit emf of the Schottky-barrier device was measured relative to the non-bombarded junction. A 40 keV beam generated an open circuit emf of 800 mV. The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
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abstract | To provide a technique of reducing the costs for maintenance work and also the downtime of products. There is provided a maintenance system that calculates a timing to make a visit for maintenance work for consumable parts of a machine to be maintained. The maintenance system includes: a visit-interval calculating section for calculating a visit interval to make a visit for maintenance work for each consumable part on the basis of a failure rate distribution; a replacement-interval calculating section for calculating a replacement interval to replace the consumable parts for each consumable part on the basis of the failure rate distribution; and a visit-timing calculating section for calculating a timing to actually visit the machine to be maintained on the basis of the visit interval calculated by the visit-interval calculating section and the replacement interval calculated by the replacement-interval calculating section. |
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summary | ||
058870440 | abstract | A uranium-free fuel for a fast nuclear reactor comprising an alloy of Pu, Zr and Hf, wherein Hf is present in an amount less than about 10% by weight of the alloy. The fuel may be in the form of a Pu alloy surrounded by a Zr--Hf alloy or an alloy of Pu--Zr--Hf or a combination of both. |
abstract | A nuclear engineering plant has a containment, whose interior chamber is subdivided by a wall into a systems chamber and an operating chamber which is accessible during normal operation. The containment ensures a particularly high operational reliability, in particular also in incident situations, in which hydrogen is released in the systems chamber. For this purpose, a number of overflow openings are provided in the partition wall, the respective overflow opening is closed by a closure element of a closure apparatus which opens automatically when a trigger condition associated with the respective overflow opening is reached. Closure apparatuses are provided which open both as a function of pressure and independently of pressure. The closure apparatus furthermore has a closure element containing a bursting film or a bursting diaphragm. The closure apparatus is configured such that it frees the overflow opening automatically when a predetermined environment-side trigger temperature is reached. |
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abstract | A radiation-attenuation garment system having a plurality of radiation-attenuating material panels adapted to conform to the contours of a body. The radiation-attenuation garment system includes a shirt and underwear shorts formed by compression material. A plurality of radiation-attenuating material panels are removably disposed within the shirt and underwear shorts to protect the wearer from radiation exposure in the areas having the radiation attenuation panels. |
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claims | 1. Microstructured nuclear fuel adapted for use in a nuclear power system, comprising fissile material structures comprising spherical fuel particles of up to 5 micrometers in diameter for each fuel particle of said fuel particles, and the fuel particles are dispersed in an inert matrix, said inert matrix enabling most of the fission product atoms to escape from the particle and become lodged in the matrix during use of the fuel in said nuclear power system and thereby enabling most of the fission products to be readily separated from the fissile material. 2. The microstructured nuclear fuel of claim 1, wherein the inert matrix is carbon. 3. The microstructured nuclear fuel of claim 1, wherein the inert matrix material is selected from the group consisting of MgO, Al2O3, Y2O3, ZrO2, CeO2, NbO2, and TaO2. 4. The microstructured nuclear fuel of claim 1, wherein the inert matrix material is selected from the group consisting of Mg3N2, AlN, Si3N4, YN, ZrN, and CeN. 5. The microstructured nuclear fuel of claim 1, wherein the inert matrix material is selected from the group consisting of SiC and ZrC. 6. The microstructured nuclear fuel of claim 1, wherein the inert matrix material is selected from the group consisting of MgAl2O4, ZrSiO4, YPO4, and CePO4. 7. The microstructured nuclear fuel of claim 1, wherein the inert matrix material is 1-5 micrometers thick. 8. Microstructured nuclear fuel adapted for use in a nuclear power system, comprising fissile material structures comprising fuel cylinders of up to 5 micrometers in diameter for each fuel particle of said fuel particles, and the fuel particles are dispersed in an inert matrix, said inert matrix enabling most of the fission product atoms to escape from the particle and become lodged in the matrix during use of the fuel in said nuclear power system and thereby enabling most of the fission products to be readily separated from the fissile material. 9. The microstructured nuclear fuel of claim 8, wherein the inert matrix is carbon. 10. The microstructured nuclear fuel of claim 8, wherein the inert matrix material is selected from the group consisting of MgO, Al2O3, Y2O3, ZrO2, CeO2, NbO2, and TaO2. 11. The microstructured nuclear fuel of claim 8, wherein the inert matrix material is selected from the group consisting of Mg3N2, AlN, Si3N4, YN, ZrN, and CeN. 12. The microstructured nuclear fuel of claim 8, wherein the inert matrix material is selected from the group consisting of SiC, and ZrC. 13. The microstructured nuclear fuel of claim 8, wherein the inert matrix material is selected from the group consisting of MgAl2O4, ZrSiO4, YPO4, and CePO4. 14. The microstructured nuclear fuel of claim 8, wherein the inert matrix material is 1-5 micrometers thick. |
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abstract | The invention relates to an X-ray device with an X-ray radiation source and with a preferably digital detector, which is placed in the beam path of the radiation source behind the object, particularly behind a patient. Scattered-rays are suppressed by means of a scanning device that scans the object and the detector only in sections. During a half-scanning process, the X-ray image is composed of half images, one image half being faded out. |
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050230468 | claims | 1. A drive unit for use in inspecting nuclear fuel rods, comprising: a. a housing; b. a drive motor mounted at the first end of said housing; c. a spindle directly coupled to said drive motor and rotatably mounted in said housing; and d. means mounted in said spindle adjacent the second end of said housing for gripping a fuel rod, comprising: a. a housing; b. a drive motor mounted at the first end of said housing; c. a spindle directly coupled to said drive motor rotatably mounted on bearings in said housing and having a recess at its end adjacent the second end of said housing; and d. means received in the recess of said spindle for gripping a fuel rod, comprising: a. a housing; b. a drive motor mounted at the first end of said housing; c. a spindle directly coupled to said drive motor rotatably mounted on bearings in said housing and having a recess at its end adjacent the second end of said housing; d. a substantially donut shaped rubber bladder received in said recess and having its longitudinal axis coaxial with that of said spindle whereby said bladder rotates in conjunction with said spindle in response to driving rotation by said drive motor; and e. a flanged port extending radially from said bladder and in fluid communication with the interior thereof whereby said bladder may be pressurized, causing radial internal expansion thereof for gripping a fuel rod. 2. The drive unit of claim 1, wherein said spindle is rotatably mounted on bearings in said housing. 3. The drive unit of claim 1, further comprising a plunger slidably received in a longitudinal bore in said spindle and biased toward said gripping means. 4. A drive unit for use in inspecting nuclear fuel rods, comprising: 5. The drive unit of claim 4, further comprising a plunger slidably received in a longitudinal bore in said spindle and biased toward said gripping means. 6. A drive unit for use in inspecting nuclear fuel rods, comprising: 7. The drive unit of claim 6, further comprising a plunger slidably received in a longitudinal bore in said spindle and biased toward said rubber bladder. |
041815718 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT The bracing grid shown in FIG. 1 has a right hexagonal boundary and comprises 325 unit cells 1 arranged in honeycomb pattern. The cells are of generally hexagonal shape all except the outer row of cells being right hexagonal. The cell at each corner of the complex is adapted to receive a corner post 6 of a sub-assembly to be described hereinafter. Each unit cell 1 is formed from strip material the edge-to-edge ends being spaced apart. In the outer row of the unit cells designated 1b in FIG. 1 the edge-to-edge ends of the strips occur in the middle of one side as shown in FIG. 2 whilst the inner unit cells designated 1a in FIG. 1 have the edge-to-edge ends at a corner of the hexagonal cell as shown in FIG. 3. Three alternate sides of each cell have a rectangular window 3 whilst the remaining sides each have an elongate embossment or dimple forming a guide pad for a fuel pin. In an alternative construction the windows in the outermost sides of the outermost cells are omitted. There is a pair of smaller embossments 5 disposed one beyond each end of each of the elongate embossments to form linear groups extending parallel to the longitudinal axis of the cells. The smaller embossments provide additional bracing pads or backstops for a fuel pin in the event that bowing of the pin occurs during irradiation of the fuel sub-assembly. Each pair of abutting sides of the cells are secured together by a pair of spot welds disposed in opposed end regions of the sides. The grid has across flats dimension 134.6 mm the cells 1 being formed from stainless steel strip 25.5 mm wide by 0.20 mm thick with windows 12.5 mm long and extending laterally acorss the full width of the side. The embossments 4 define a cell diameter nominally of 5.8 mm whilst the cell diameter bounded by the embossments or pads 5 is 6.1 mm. The fuel sub-assembly shown in FIG. 3 comprises a central fuel section 11, a lower end locating section 12 and an upper end neutron shielding section 13. The fuel section 11 comprises a bundle of spaced elongate fuel pins 14 enclosed within a tubular wrapper 15. The pins are supported at their lower ends by a grid 16 and are braced intermediate their lengths by cellular grids 1 of honeycomb form. The grids 1 are disposed at intervals along the wrapper being secured thereto by engagement of the corner cells with notched posts 6 (FIG. 1) secured in the corners of the wrapper. The lower end locating section comprises a spike 18 for engaging a socket in a fuel assembly support structure 37 and has apertures 19 through which coolant can flow from within the diagrid. A conical mesh filter 20 and gag means 21 are provided for the coolant between the spike 18 and the bundle of fuel pins 14. The gag means 21 comprises a plurality of apertured plates 22 spaced apart by woven wire mesh discs 23. The upper section 13 is of massive steel and comprises a massive steel tubular member 24 which has an internal lip 25 for engagement by lifting means. On assembly the bundle of fuel pins is threaded through successive grids 17 the grids being sufficiently compliant to enable the pins to deflect the unit cell structures to allow the pins to penetrate successive unit cells without causing scoring of the pins. After irradiation the fuel sub-assembly may be readily dismantled for reprocessing by withdrawing the bundle of fuel pins from the bracing grids and wrapper 15 combination thereby reducing the contaminated waste to be processed. The process of withdrawal of the pins is facilitated because of the compliancy of the grid and the reduced bowing of the fuel pins. By constructing the grids of unit cells manufacture is facilitated because the strips can be preformed by a jig to provide a multiplicity of identical cells which can then be assembled in honeycomb array on a second jig to maintain the cells in accurate geometrical relationship and they can be finally joined together by edge welds applied easily from each face of the grid. A plurality of sub-assemblies is used to form a fuel assembly 31 shown in the reactor construction of FIG. 5. The fuel assembly 31 forming the reactor core is submerged in a pool 32 of liquid sodium coolant in a primary vessel 33. The primary vessel is suspended from the roof of a containment vault 34 and there is provided a plurality of coolant pumps 35 and heat exchangers 36 only one each of the pumps and heat exchangers being shown. The fuel assembly 31 mounted on a structure 37 is housed with the heat exchangers in a core tank 38 whilst the pumps 35, which deliver coolant to the diagrid, are disposed outside of the core tank. The core or fuel assembly 31 comprises a plurality of the described fuel sub-assemblies which upstand from the diagrid 37 in closely spaced side-by-side array. Control rods 39 and instrumentation 40 penetrate the roof of the vault of the core tank. In operation of the nuclear reactor coolant is flowed from the pump 35 to the fuel assembly by way of the diagrid 37 which distributes the coolant flow throughout the fuel assembly. Flow is upwardly through the fuel sub-assemblies by way of the tubular wrappers 25 and in heat exchange with the fuel pins. Flow is thence from the upper region of the core tank 38 back to the outer region of the pool by way of the heat exchangers 36. |
claims | 1. A charged particle beam irradiation device comprising:an accelerator configured to accelerate charged particles and emit a charged particle beam;an irradiation unit configured to irradiate a body to be irradiated with the charged particle beam;a duct configured to transport the charged particle beam emitted from the accelerator to the irradiation unit;a tubular body that is arranged on a propagation path of the charged particle beam within the irradiation unit, has inert gas filled thereinto, and has particle beam transmission films transmitting the charged particle beam therethrough at an inlet and an outlet thereof;a gas supply unit configured to supply the inert gas into the tubular body; anda leak valve configured to leak the inert gas inside the tubular body to the outside when the internal pressure of the tubular body is equal to or higher than a set pressure; anda leak line that connects the tubular body and the leak valve;wherein the gas supply unit comprises:an inert gas container configured to supply the inert gas;a plurality of supply lines having different amounts of supply of inert gas; andan inert gas container side line that connects the inert gas container and each of the supply lines;wherein the plurality of supply lines include a pressure-maintaining supply line configured to maintain the pressure inside the tubular body at a predetermined value, an adjusting supply line configured to adjust the pressure within the tubular body, and a substituting supply line configured to substitute an air inside the tubular body with the inert gas, andwherein the amount of supply of the inert gas of the adjusting supply line is larger than the amount of supply of the inert as of the pressure-maintaining supply line, and the amount of supply of the inert gas of the substituting supply line is larger than the amount of supply of the inert gas of the adjusting supply line. 2. The charged particle beam irradiation device according to claim 1, further comprising:a suction pump configured to suction air inside the tubular body,wherein the suction pump suctions the air inside the tubular body, using at least one supply line among the plurality of supply lines. |
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abstract | In a particle therapy treatment planning system for creating treatment plan data, the movement of a target (patient's affected area) is extracted from plural tomography images of the target, and the direction of scanning is determined by projecting the extracted movement on a scanning plane scanned by scanning magnets. Irradiation positions are arranged on straight lines parallel with the scanning direction making it possible to calculate a scanning path for causing scanning to be made mainly along the direction of movement of the target. The treatment planning system can thereby realize dose distribution with improved uniformity. |
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045253234 | summary | BACKGROUND OF THE INVENTION This invention relates to targets for implosion by an energy source, and more particularly to a fusion target compatible with ion beam implosion techniques. In recent years much effort has been directed to inertial confinement fusion involving the development of implosion apparatus and targets for implosion by energy sources, such as lasers and electron beam machines. More recently, development efforts have been directed toward ion beam implosion of fusion targets, thus establishing a need for targets compatible with ion beam technology. While development efforts in the field of magnetic confinement have been carried on for at least two decades to develop a fusion power reactor, inertial confinement fusion (implosion of a fusion target be an energy source) efforts are relatively recent. For example, U.S. Pat. No. 3,378,446 to J. R. B. Whittlesey represents an early effort in inertial confinement to develop apparatus using lasers to trigger thermonuclear reactions whereby laboratory testing of fusionable materials in small quantity could be carried out. U.S. Pat. No. 3,489,645 issued Jan. 13, 1970 to J. W. Daiber et al is directed to a method of creating a controlled nuclear fusion reaction by repeatably imploding fusion targets by laser energy within an explosion chamber. U.S. Pat. No. 3,624,239 issued Nov. 30, 1971 to A. P. Fraas is directed to a pulsed laserignited thermonuclear reactor in which a fusion fuel target is imploded by a laser within a void in liquid lithium contained within a pressure vessel. U.S. Pat. No. 3,723,246 issued Mar. 27, 1973 to M. J. Lubin is directed to a plasma production apparatus having target production means and laser implosion means. U.S. Pat. No. 3,762,992 issued Oct. 2, 1973 to J. C. Hedstrom involved a DT target imploded by a laser wherein the neutron energy is dissipated in a lithium blanket to produce tritium, with the heat transferred to a thermodynamic plant as known in the art. U.S. Pat. No. 3,899,681 issued Aug. 12, 1975 to E. H. Beckner et al teaches an electron beam device for imploding hollow targets. In addition, various papers have been presented in this field as exemplified by "Fusion Power By Laser Implosion" by J. L. Emmett et al, Scientific American, June 1974; "Laser-Induced Thermonuclear Burn" by J. Nuckolls et al, Physics Today, August 1973; and "Laser Compression of Matter to Super-High Densities: Thermonuclear (CTR) Applications" by J. Nuckolls et al, Nature, Vol, 239, No. 5368, pp. 139-142, Sept. 15, 1972. Also substantial effort has been directed to various components of the implosion system as evidenced by U.S. Pat. No. 3,723,703 issued Mar. 27, 1973 to K. W. Ehlers et al directed to a laser alignment and firing system for creating and heating a plasma by imploding targets; U.S. Pat. No. 4,017,163 issued Apr. 12, 1977 to A. J. Glass directed to angle amplifying optics for directing laser energy onto a target located within an explosion chamber; and U.S. Pat. No. 3,892,970 issued July 1, 1975 to J. R. Freeman et al directed to a realivistic electron beam device for producing a plasma therein; and a paper "Laser Fusion Target Illumination System" by C. E. Thomas, Applied Optics, Vol. 14, No. 6, June 1975. Various target designs have been proposed for laser, electron beam, and ion beam implosion techniques as exemplified by "A 1964 Computer Run On A Laser-Imploded Capsule" by R. E. Kidder, UCID-17297 dated Mar. 25, 1973; "Implosion, Stability, And Burn Of Multishell Fusion Targets" by G. S. Fraley et al presented at The Fifth I.A.E.A. Conference on Plasma Physics and Controlled Nuclear Fusion Research, Tokyo, Japan, Nov. 11-15, 1974 as Paper IAEA-CN-33/F55 (LAUR-5783-MS); "Structured Fusion Target Designs" by R. C. Kirkpatrick et al, Nuclear Fusion 15, April 1975, pp. 333-335; "Target Compression With One Beam" by G. H. McCall et al, Laser Focus, December 1974, pp. 40-43; "Electrically Imploded Cylindrical Fusion Targets" by W. S. Varnum, Nuclear Fusion 15, December 1975, pp. 1183-1184; "The Calculated Performance Of Structured Laser Fusion Pellets" by R. J. Mason, Nuclear Fusion 15, December 1975, pp 1031-1043; "Low Power Multiple Shell Fusion Targets for Use With Electron And Ion Beams" by J. D. Lindl et al, International Topical Conference on Electron Beam Research, Albuquerque, New Mexico, Nov. 3-6, 1975 (UCRL-77042); "Stability and Symmetry Requirements of Electron and Ion Beam Fusion Targets" by R. O. Bangerter et al, International E-Beam Conference, Albuquerque, N.M., Nov. 3-6, 1975 (UCRL-77048); and "Fusion Targets Designed to Match Present Relativistic Electron Beam Machine Parameters" by D. J. Meeker et al, The American Physical Society Meeting, Plasma Physics Division, St. Petersburg, Fla., Nov. 10-14, 1975 (UCRL-77045). The production of fusion neutrons by inertial confinement (implosion) techniques have been experimentally verified, thus verifying the accuracy of computer codes used, as exemplified by "Thermonuclear Fusion Research With High-Power Lasers" by R. R. Johnson et al, Vacuum Technology, May 1975, pp. 56-61 and 64; "Laser Fusion Experiments At The Lawrence Livermore Laboratory" by H. G. Ahlstrom, Gordon Research Conference On Laser Plasma Interaction With Matter, Tilton, N.H., Aug. 18-23, 1975 (UCRL-77094); "Status of Laser Fusion" by J. H. Nuckolls, American Physical Society Meeting, St. Petersburg, Fla., Nov. 10-14, 1975 (UCRL-77056); "Laser Fusion Overview" by J. Nuckolls, Ninth International Quantum Electronics Conference, June 14-18, 1976, Amsterdam, the Netherlands (UCRL-77725); "Electron Beam Fusion Pellets" by W. P. Gula et al, Proceedings of the International Topical Conference on Electron Beam Research and Technology, Nov. 3-6, 1975, Albuquerque, N. Mex. pp. 158-170 (SAND76-5122); and "Behavior of Double Shelled Electron Beam Fusion Targets" by W. P. Gula, Bulletin of the APS, 21, 1195, 1976 (LAUR76-2343). Target fabrication techniques are at an advanced state of development with numerous mechanisms and processes having been developed, as exemplified by above-referenced U.S. Pat. No. 3,723,246 to M. J. Lubin; as well as U.S. Pat. No. 3,907,477, issued Sept. 23, 1975 to T. R. Jarboe et al; U.S. Pat. No. 3,953,617 issued Apr. 27, 1976 to W. H. Smith et al; U.S. Pat. No. 3,985,841 issued Oct. 12, 1976 to R. J. Turnbull et al; and U.S. Pat. No. 4,012,265 issued Mar. 15, 1977 to J. A. Rinde et al. In addition numerous publications such as paper "Fabrication and Characterization of Laser Fusion Targets" by C. D. Hendricks et al, American Physical Society, Division of Plasma Physics, Nov. 10-14, 1975, St. Petersburg, Fla. (UCRL-76679); and report UCRL-50021-75 "Laser Program Annual Report-1975", Lawrence Livermore Laboratory, Univ. of Cal., Section 7 "Target Fabrication", pp. 343-368, have been prepared in the field of target fabrication. Thus, while commercial fusion power reactors are still some distance away, the inertial confinement technology has rapidly advanced such that 10.sup.9 fusion neutrons are being produced by existing implosion systems which systems currently provide an excellent source of neutrons, X-rays, alpha particles which has not been previously available to the scientific community for physics studies, radiography, synthetic fuel production, fissile fuel production, tritium production, and radioisotope production, etc. In addition, the energy produced by the implosion of the targets via inertial confinement techniques can be utilized for propulsion applications, process heat production, burning of actinide wastes, etc. Therefore, while fusion power for electrical production has not yet been accomplished, the inertial fusion techniques developed thus far have greatly advanced the state of the art. With the recognition by the scientific community that inertial fusion has been accomplished, substantial effort is now being directed towards a prototype inertial confinement fusion reactor wherein various systems (laser, e-beam, ion-beam, etc.) are being developed to produce the energy required to implode the targets required for these forthcoming inertial fusion reactor systems. In addition substantial effort is being directed toward development of targets compatible with these energy systems. In designing ion beam targets suitable for commercial power production, the following criteria are of importance: 1. The target should be cheap; hence, it should be of inexpensive materials, it should be simple to fabricate, and it should be relatively insensitive to fluid instabilities to minimize the precision required in its construction. 2. The target should produce minimum residual radioactivity. 3. The target should have a high gain (energy yield/beam energy) to minimize recirculating power costs in the power plant. 4. The target should have low beam-power and energy requirements. 5. The target should have a large tolerance to irradiation asymmetries. 6. The target should be insensitive to preheat effects. However, many of the above-listed criteria impose contradictory constraints on target design. For example, power requirements can be lowered by using high-aspect-ratio (radius/shell thickness) shells or multiple-shell designs; but, such targets are relatively unstable and usually have high irradiation symmetry requirements. SUMMARY OF THE INVENTION The present invention is directed to an ion-beam target that satisfies many of the above requirements. The principal feature of this target is the low-density, low-Z pusher material or layer that is located between the high-Z tamper and the fuel. In addition this target is made of inexpensive material and can be readily fabricated by existing technology. The high density tamper serves as a confinement shell to increase the efficiency of the implosion. The pusher shell is seeded with some high-Z material which serves to inhibit energy transport into the fuel and thus prevents preheat thereof. The low-density, low-Z pusher enables one to achieve the following conditions: The pusher can be relatively thick to decrease the fluid instability problem and yet contain relatively little mass. The problem of fluid instabilities causing pusher-fuel mixing during the final stages of the implosion is ameliorated relative to a high density pusher because of the small density difference between fuel and pusher. Therefore, it is an object of this invention to provide a target for implosion by at least one ion beam. A further object is to provide an ion-beam inertial confinement fusion target which utilizes a low-density, low-Z pusher shell. Another object of the invention is to provide a fusion target which overcomes the problems associated with similar targets using a high density pusher. Another object of the invention is to provide a target for inertial confinement fusion applications by ion-beam energy which utilizes a low-density, low-Z pusher located between a high-Z tamper and the fuel. Another object of the invention is to provide a target for implosion by ion beams which utilizes a low-density, low-Z pusher seeded with high-Z material. Other objects of the invention will become readily apparent to those skilled in the art from the following description and accompanying drawings. |
052232107 | description | DETAILED DESCRIPTION OF THE INVENTION Pool-type liquid-metal cooled reactors have sufficient surface area to accommodate dissipation of residual heat during reactor shutdown events. Overall, the reactor system has a relatively small heat capacity. The problem remaining is to dissipate the residual heat without significantly damaging the containment structures. A completely passive cooling system eliminates reliance on energy driven pumps and fans and the need for operator intervention. At the same time, the containment vessel itself must not be structurally modified due to the size constraints on modular reactors, and the necessity of a smooth, unperforated tank structure to prevent any areas where stresses might accumulate. Strict inspection requirements also require that the containment vessel be simple to inspect both during manufacture and erection of the structure. Referring to FIG. 1 of the drawings, an embodiment of a pool-type, liquid metal cooled nuclear reactor plant 10, comprises a reactor vessel 12, typically consisting of an cylindrical tank positioned with its longitudinal axis extending vertically upright, and having an open upper end provided with a removable cover. Reactor vessel 12 contains a pool of liquid metal coolant 14, such as sodium metal, with a heat producing core of fissionable fuel 16 substantially immersed within the liquid metal coolant pool 14 for heat transfer. Fission action of the fuel and the rate thereof is governed by neutron absorbing control rods 18 moving out from or into the fuel core 16. The reactor vessel 12 is enclosed within a concentrically surrounding containment vessel 20 in space apart relation. A baffle cylinder 22 encircles substantially the length of the containment vessel 20 in spaced apart relation. A guard vessel 24 concentrically surrounds the baffle cylinder 22 with the containment vessel 20 and reactor vessel 12, in spaced apart relation. A concrete silo 26 houses the concentrically combined and spaced apart arrangement of the guard vessel 24, the baffle cylinder 22, the containment vessel 20 and the reactor vessel 12. Preferably the concrete silo 26 is substantially buried into the ground to the extent that its contained reactor vessel 12 and adjoining vessels and cylinder are located at least below the ground surface, shown in the drawings as 28. Locating the liquid metal containing reactor vessel below ground surface precludes the escape of any liquid metal regardless of any loss of integrity of the plant. A containment dome covers the open top of the concrete silo to prevent any escape of radioactive contamination from the reactor plant out into the atmosphere. This arrangement of these combined components in surrounding or encircling and spaced apart positions, provides for their respective side walls forming a series of partitions with intermediate spaces. Specifically, a space 30 between the partitions comprising the side walls of the reactor vessel 12 and containment vessel 20; a space 32 between the partitions comprising side walls of the containment vessel 20 and the baffle cylinder 22; a space 34 between the partitions comprising the side walls of the baffle cylinder 22 and the guard vessel 24; and a space 36 between the partitions compressing the inside wall of the guard vessel 24 and the concrete silo 26, which in turn is divided by a second baffle cylinder. In a preferred embodiment of the invention wherein the above combined components are circular in cross-section and concentrically surround or encircle one another, the intermediate space 30, 32, 34, 36 and 37 are each substantially annular in cross-section. The containment vessel 20, the baffle cylinder 22, guard vessel 24 and concrete silo 26 are each provided with at least one upward projection or continuing wall extending above the uppermost portions of the reactor vessel 12, and up beyond the ground level 28. Thus the annular spaces 32, 34, and 36 formed intermediate the partitions are continued or in fluid communication with a corresponding space between projections or continuing walls extending above the heat producing reactor and its enclosing vessel 12. Specifically projection or continuing wall 38 extends from or adjoins the containment vessel 20, the projection or continuing wall 40 extends from or adjoins the baffle cylinder 22, the projection or continuing wall 42 extends from or adjoins the guard vessel 24, and projection or continuing wall 44 extends from or adjoins the concrete silo 26. These projections or continuing walls extending from or adjoining these vessels and cylinder which define the spaces 32, 34, and 36, with space 36 being divided into subspaces 62 and 64 by baffle cylinder 60 provide corresponding continuations or ducts extending upward from each of said spaces. The projections or extension wall 38 continuing from or adjoining the containment vessel 20 and the projections or extension wall 40 continuing from or adjoining the baffle cylinder 22 form a channel or at least one duct 46 in fluid communication with space 32 and extends therefrom upward opening out into the ambient atmosphere. The projections or extension wall 40 continuing from or adjoining the baffle cylinder 22 and the projections or extension wall 42 continuing from or adjoining the guard vessel 24 form a channel or at least one duct 48 in fluid communication with space 34 and extends therefrom upward opening out into the ambient atmosphere. The projections or extension wall 42 continuing from or adjoining the guard vessel 24 and the projections or extension wall 44 continuing from or adjoining the concrete silo 26 form a channel or at least one duct 50 in fluid communication with space 36 and extends therefrom upward opening out into the ambient atmosphere. The space 30 intermediate the reactor vessel 12 and containment 20 is typically filled with an inert gas, such as argon or nitrogen, and sealed. The containment vessel 20 and intermediate inert gas serves as a protective measure against the occasion of a breach of the reactor vessel 12 and in turn leaking of liquid metal coolant such as sodium. The channel or duct(s) 46 and channel or duct(s) 48, are provided with isolation valves 52 and 54, respectively, for closing off the spaces 32 and 34 along with their adjoining channels or ducts from the atmosphere. In operation, heat produced by the fuel core 16 is conveyed to the reactor vessel 12 by natural convection of the surrounding liquid metal coolant 14, then transferred mainly by thermal radiation across the inert gas containing space 30 from the reactor vessel 12 to the containment vessel 20. The heat is absorbed by the air in space 32 which is in contact with the outer surface of the containment vessel 20 and is carried along in the air rising upward due to its decreased density from heating thereby inducing a natural draft in space 32. The heat induced air flow continues upward from space 32 through channel or duct(s) 46 and out into the atmosphere where the heat is vented. This heat induced air flow up and out through space 32 and duct 48 draws air in from the atmosphere down into channel or duct(s) 48 and through space 34. From space 34 the cool atmospheric air flow continues passing beneath the lower edge of the baffle cylinder 22 and up into space 32 where it is heated from the hot outer surface of the containment vessel 20 to perpetuate the circulating cooling flow through the auxiliary safety cooling system for venting the carried heat out into the atmosphere. This heat motivated cooling course of through channels or ducts and/or spaces 48, 34, 32 and 46 comprises auxiliary safety cooling circuit or loop 56. Continued emissions of heat from the fuel core and transfer to the air within space 32 perpetuates the cooling air flow through the auxiliary safety cooling circuit or loop 56, and dissipation of heat out into the ambient atmosphere. Thermal performance studies of the system indicate that the maximum average core sodium outlet temperature for a decay heat removal transient is about 1140 degrees F. which is well below the current ASME service level temperature limit of 1200 degrees F. based on nominal calculations. An extreme and improbable postulated event proposed for safety considerations is the unlikely rupturing of both the reactor and the containment vessels 12 and 20. Such an event would permit the leakage of the liquid metal coolant, typically sodium, contents from the reactor vessel 12 and through the containment vessel 20 out into spaces 32 and 34, possibly blocking the cooling air flow therethrough, as well as imperiously reducing the level of coolant remaining in the reactor vessel for conveying heat away from the fuel core 16. Hot liquid metal coolant such as the commonly used sodium escaping out from the confines of the reactor and containment vessels could result in exothermic chemical reactions, sodium fires and/or a severe release of radioactive material out into the ambient atmosphere. Such an event and coolant leakage which obstructs the cooling air circulation through spaces 32 and 34 prevents the operation of the passive cooling safety system for the removal of decay and sensible heat whereby resultant overheating can cause significant damage to structural components of the reactor plant which propagates further destruction and hazards. In accordance with the invention, a backup or secondary auxiliary safety cooling course or system 58 is provided to coupe with significant liquid metal coolant leaks due to a breach of both the reactor and containment vessel 12 and 20. Referring to the drawing, a baffle cylinder 60 is provided extending down between the concrete silo 26 and the guard cylinder 24 substantially surrounding the length of the guard cylinder. The baffle cylinder 60, which does not extend down to the floor of the concrete silo, divides space 36 into two annular subspaces, subspace 62 between the concrete silo 26 and baffle cylinder 60, and subspace 64 between the baffle cylinder 60 and the guard vessel 26. Subspaces 62 and 64 are in fluid communication below the lower end of baffle cylinder 60. The backup safety cooling course 58 comprises at least one upward projecting or continuing wall 44 continuing outward and upward above the ground level 28 extending from or adjacent to the concrete silo 26. Wall 44 and wall 42 form an annular area which can be divided into sections by radial-like partitions extending from one wall to the other to provide several ducts or flues leading from the atmosphere down into the space 36 between the concrete silo 28 and the guard vessel 24. At least one section forming duct(s) 66 makes fluid communication with subspace 62 between the concrete silo 28 and baffle cylinder 60, and at least one section forming duct(s) 68 makes fluid communication with subspace 64 between the baffle cylinder 60 and the guard vessel 24. Thus both subspaces 62 and 64 are in communication with the outer atmosphere and are in fluid communication with each other in the area beneath the lower end of the baffle cylinder 60. A seal 70 can be provided between the upper portion of the guard vessel 24 and wall 42. Accordingly, in the event of a double breach of the reactor and containment vessels 12 and 20 resulting in substantial leakage of liquid metal coolant into spaces 32 and 34, the valves 52 and 54 in ducts 46 and 48 are closed to prevent radioactive containments escaping out into the atmosphere. Moreover, the heat of the leaked liquid metal into spaces 32 and 34 carries to space 36 and thus induces air in subspace 64 to rise upward carrying heat entrained therein and out into the atmosphere through duct(s) 68 venting the heat. This heat induced air flow from subspace 64 draws air in from the atmosphere down through duct(s) 66 into subspace 62 and then under baffle cylinder 60 and reversing direction into subspace 60 whereby a circulating cooling air flow through the backup safety cooling course 58 is perpetuated and continues as long as heat is generated and transferred to space 36 or subspace 64. Thus, this backup safety cooling course or system 58 is separate from the primary auxiliary safety cooling course 56, and the cooling air subspaces 62 and 64 and ducts 68 and 66 are not closed off when the isolation valves 52 and 54 are closed. Moreover there is no direct contact between the cooling air and the liquid metal coolant typically comprising sodium. Reactor heat is removed by this backup course 58 at all times, including normal reactor operating and auxiliary safety cooling 56 decay heat removal operating conditions. However, heat removal by the backup course 58 increases significantly when the guard vessel 24 is partially filled with hot liquid metal coolant following a postulated double vessel 12 and 20 leak event and the normal operating liquid metal coolant level 80 of the reactor vessel 12 has dropped to the double vessel leak level 82 within the reactor vessel 12. Analysis demonstrate that heat removal by this backup system will maintain maximum bulk liquid metal coolant temperatures below a design limit for precluding destructive and/or hazardous results. An embodiment of this invention comprises a design to cope with the effects of earthquakes. This design comprises a composite of the reactor vessel 12 and its enclosing containment vessel 20 being suspended from an overlying superstructure 72 which includes other seismic sensitive plant components. The vessel carrying superstructure 72 is mounted on and supported with seismically isolating means resting on a fixed structure foundation 74 comprising an upper structural portion of the earth embedded concrete silo 26. Thus the superstructure 72 carrying the reactor and containment vessels 12 and 20 can be mounted and supported on shock absorbers 76, such as springs, rubber pads, hydraulic absorbers and the like which are fixed to an upper annular surface or flange 78 extending around the earth embedded silo 26 comprising the fixed structure 74. |
claims | 1. A nuclear device, comprising:a plurality of heat pipes;a first fuel configured to surround respective of the plurality of heat pipes coaxially with respect to a central axis of each of the respective heat pipes, the first fuel containing a fissile material at a first enrichment level;a second fuel configured to directly abut the first fuel on the outside of the first fuel and farther than the first fuel from the respective heat pipes surrounded by the first fuel, the second fuel containing the fissile material at a second enrichment level less than the first enrichment level; anda core including the heat pipes arranged in parallel with each other. 2. The nuclear device according to claim 1, wherein a enrichment level of the fissile material in a first area is greater than that in a second area, and a heat transferred from the second area to the heat pipes is less than the heat transferred from the first area to the heat pipes. 3. The nuclear device according to claim 2, wherein the first area contains more heat pipes than the second area per unit area in a cross section of the core perpendicular to a central axis of the heat pipe. 4. The nuclear device according to claim 1, further comprising:a first layer that includes the heat pipes arranged in parallel to a central axis of each heat pipe with each first fuel surrounding respective heat pipes surrounded by second fuel;a first heat conductor along a side surface of the first layer and parallel to the central axis, thermal conductivity of the first heat conductor being greater than that of the second fuel. 5. The nuclear device according to claim 4, wherein the first heat conductor contains beryllium. 6. The nuclear device according to claim 4, further comprising:a layer that includes heat pipes arranged next to each other and in parallel to the central axis of each heat pipe, the second fuel configured to surround the first fuel surrounding respective of the heat pipes next to each other; anda second heat conductor disposed in the second fuel. 7. The nuclear device according to claim 1, further comprising:two overlapping layers, each layer including heat pipes arranged next to each other in parallel to a central axis of each heat pipe, the second fuel configured to surround the first fuel surrounding respective of the heat pipes next to each other; anda heat conductor connecting the two overlapping layers, wherein a first end of the heat conductor is closer to the heat pipe than a second end. 8. The nuclear device according to claim 1, further comprising:a first layer that includes heat pipes arranged in parallel to a central axis of each heat pipe, the second fuel configured to surround the first fuel surrounding the heat pipes of the first layer;a second layer that includes heat pipes arranged in parallel to the central axis of each heat pipe, the second fuel configured to surround the first fuel surrounding respective of the heat pipes of the second layer;wherein a heat pipe of the second layer is located between two heat pipes next to each other in the first layer when viewed in a direction parallel to the central axis of each heat pipe. 9. The nuclear device according to claim 1, further comprising a metal layer between the heat pipes and the first fuel, including a metal,wherein a melting point of the metal is such that the metal layer is solid at a temperature before the nuclear reactor starts operating, and melts at a temperature after the nuclear reactor starts operating. 10. The nuclear device according to claim 1, wherein the core includes a plurality of cylinders arranged concentrically,wherein each of the cylinders is made of a layer including heat pipes arranged next to each other in parallel to a central axis of each of the heat pipes, the first fuel surrounding the heat pipes arranged next to each other, and the second fuel surrounding the first fuel which surrounds the heat pipes. 11. The nuclear device according to claim 10, wherein the enrichment level of the fissile material in the core differs along the axis of each heat pipe. 12. The nuclear device according to claim 10, wherein the core includes multiple sections arranged in the central axis direction of the core, wherein the enrichment level of the fissile material in each section varies according to a position of the section. 13. The nuclear device according to claim 10, wherein a point outputting a maximum heat in one layer does not overlap a point outputting a maximum heat in a next adjacent layer. 14. The nuclear device according to claim 10, wherein the enrichment level of the fissile material in the core differs in a radial direction in a cross section of the core perpendicular to the central axis of the heat pipes. 15. The nuclear device according to claim 14, further comprising a control rod arranged in a central part of the core,wherein the enrichment levels of the fissile material in the center part of the core, adjacent a side surface of the core parallel to a central axis of the core, and in a at a half point of a length of the core parallel to the center axis, are lower than that of other parts in the core. |
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summary | ||
claims | 1. A reactor water-level measurement system comprising:a core bottom water-level measuring device that includes a heating element, a heat insulating element installed by surrounding part of the heating element in a height direction of the heating element, and a temperature difference measuring element that measures a temperature difference between an insulated portion of the heating element surrounded by the heat insulating element and a non-insulated portion not surrounded by the heat insulating element;a water-level evaluation device that evaluates a water level of a reactor based on the temperature difference,wherein the core bottom water-level measuring device measures at least a water level from a lower end of a reactor core contained in a reactor pressure vessel to a bottom of the reactor pressure vessel, andwherein the reactor pressure vessel includes a neutron detector that monitors neutron fluxes in the reactor core and a protective tube that contains the neutron detector, and wherein the core bottom water-level measuring device is contained in the protective tube together with the neutron detector. 2. The reactor water-level measurement system according to claim 1, further comprising an in-core water-level measuring device that includes a heating element, a heat insulating element installed by surrounding part of the heating element in a height direction of the heating element, and a temperature difference measuring element that measures a temperature difference between an insulated portion of the heating element surrounded by the heat insulating element and a non-insulated portion not surrounded by the heat insulating element, and measures a water level within a vertical range of the reactor core. 3. The reactor water-level measurement system according to claim 2, wherein the in-core water-level measuring device is contained in the same protective tube together with the neutron detector. 4. The reactor water-level measurement system according to claim 1, wherein the core bottom water-level measuring device is arranged in an outer peripheral portion of the reactor core. 5. The reactor water-level measurement system according to claim 1, wherein a plurality of the core bottom water-level measuring devices are arranged in different sections obtained by dividing an area inside the reactor core into monitoring zones. 6. The reactor water-level measurement system according to claim 2, wherein one of both the a plurality of the core bottom water-level measuring devices and a plurality of the in-core water-level measuring devices are installed, and wherein one of both the temperature difference measuring elements of the core bottom water-level measuring devices and the temperature difference measuring elements of the in-core water-level measuring devices are respectively installed in a vertical direction at locations differing among the water-level measuring devices. 7. The reactor water-level measurement system according to claim 2, wherein one of both the core bottom water-level measuring device and the in-core water-level measuring device further includes a temperature measuring device that measures temperatures. 8. The reactor water-level measurement system according to claim 7, wherein the temperature measuring device measures temperatures at a plurality of locations along a vertical direction in the reactor. 9. The reactor water-level measurement system according to claim 7, wherein the temperature measuring device is arranged in a horizontal central portion of the reactor core. |
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abstract | There is provided a method for selecting and configuring spent nuclear fuel bundles for casks so that the heat load for each of the casks is about the average heat load for all of the casks. The spent nuclear fuel bundles are disposed in the casks as low as reasonably achievable regarding the heat load. |
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050358537 | abstract | A nuclear reactor fuel assembly includes at least one uprightly disposed spacer having a grid of intersecting sheet-metal struts defining meshes therebetween. Mutually parallel rods are each disposed in a respective one of the meshes. Strip-like contact springs are parallel to the rods and each have a side facing toward and a side facing away from a respective one of the struts. Each of the contact springs are disposed in a respective one of the meshes and have two strip ends both being retained on the one strut. Each of the contact springs have a contact location being resilient relative to the one strut for contacting a rod. The contact location is spaced apart from both of the strip ends. Each of the contact springs has an undulatory transverse curve disposed at the contact location on the side of the contact spring facing toward the one strut. The contact springs are continuously smooth and flat from the contact location to the strip ends resting on the one strut. |
abstract | Acquiring sets of test data on amounts of foreign matter passed through a recirculation sump screen when different amounts of foreign matter are input; forming a passed foreign matter amount approximate line that approximates the amounts of passed foreign matter with respect to the amounts of input foreign matter on the basis of the sets of test data on the amounts of passed foreign matter; forming a passed foreign matter amount envelope tangent to the passed foreign matter amount approximate line; and estimating a total passed foreign matter amount with respect to the amounts of input foreign matter on the basis of the passed foreign matter amount envelope to evaluate the recirculation sump screen are provided. |
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description | This application is a Continuation-in-Part of, and claims priority to, International Patent Application Serial No. PCT/EP2015/054737, filed Mar. 6, 2015, and entitled IMAGING SYSTEM AND METHOD WITH SCATTER CORRECTION, the entirety of which is incorporated herein by reference. The subject matter disclosed herein relates generally to the field of non-invasive imaging and more specifically to the field of computed tomography (CT) imaging and inspection systems. In particular, the subject matter disclosed herein relates to a technique for correcting scatter from digital radiographs acquired via volumetric computed tomography (VCT) systems. Inspection of objects is of vital importance in manufacturing and repair industries. Various types of inspection systems, such as computed tomography (CT), coordinate measuring machines (CMM), laser-based profilometry, light gauge, infrared and others, are used in industrial inspection processes for a wide variety of applications. For example, these inspection systems may be used for measuring dimensions or for identifying defects in manufactured parts, such as turbine blades. Each of these inspection systems has its advantages and disadvantages. Modalities such as CMM and laser-based profilometry typically measure external surfaces with high accuracy, but cannot measure internal features unless the object is cut open. To date, CT is the most versatile of the measurement/inspection systems for revealing both the internal and external structures of industrial parts in a non-destructive manner. Because of their ability to provide internal as well as external measurements, CT based techniques may facilitate processes such as reverse engineering, rapid prototyping, casting simulation and validation, tire development, first article inspection, ceramic porosity inspection, process validation, parts qualification and defect detection, among others. However, CT based techniques may also have certain limitations, which may deter their widespread use. For example, volumetric computerized tomography (VCT) imaging for industrial applications (e.g., imaging of metallic parts) typically provides unsatisfactory images having image artifacts due to radiation-matter interaction based artifacts, scanner based artifacts, reconstruction techniques based artifacts, and so forth. The radiation-matter interaction based artifacts may further include beam hardening artifacts and artifacts due to x-ray scatter radiations. Scatter radiation in the projection images reduces the contrast of the projection images, produces degradation of or blurs sharp features of the object in the generated volume images, and reduces the accuracy of metrology applications and the detectability of smaller features. Scatter radiation is a strong function of the imaging parameters such as the object under imaging, beam spectrum used, geometrical distances, and the surrounding medium. Due to various dependencies in the imaging parameters, an accurate estimation of the scatter signal content in projection imaging is challenging. Physics-based models are often used for predicting scatter content in x-ray images, however they are time consuming and predict only scatter arising out of the object under scanning, provided the material properties are known. There exist different techniques for scatter measurement and scatter correction in acquired projection images. For example, one popular scatter measurement technique employs a beam stopper located between the radiation source and the object being scanned in a VCT system to measure the scatter at a corresponding location. However, most currently known techniques primarily address the object scatter and involve time-consuming computer simulations. As manufacturing tolerances become tighter, there is a corresponding increase in the demands for metrology techniques for maintaining the tolerances. The need for quality and performance testing has become an integral part of the production or manufacturing process. Thus, in order to improve CT inspection accuracy and efficiency, more effective methods are needed for removing scatter radiation related artifacts. In order to improve image quality, a scatter rejecting aperture plate can be positioned between the object being imaged and the detector. This aperture plate reduces scatter and thus improves quality of the generated images. However, fine structures on the object between the apertures of the aperture plate can produce artifacts after scatter correction. A method and system for imaging an object are described herein. A scatter image of the object is generated at a projection angle. In generating the scatter image, a non-grid image of the object is acquired using a radiation source and a detector. A scatter rejecting aperture plate is positioned between the object and the detector and a first grid image of the object is acquired. The scatter rejecting aperture plate includes a plurality of apertures positioned on a grid. The scatter rejecting aperture plate is moved to a second position and a second grid image of the object is acquired. A scatter image of the object is generated based on the non-grid image, the first grid image, and the second grid image and stored. In an embodiment, a method for generating a scatter image of an object at a projection angle in an imaging system is described. The method includes acquiring a non-grid image of the object using a radiation source and a detector and positioning a scatter rejecting aperture plate between the object and the detector at a first position. The scatter rejecting aperture plate includes a plurality of apertures, said apertures being positioned on a grid. A first grid image of the object is acquired with the scatter rejecting aperture plate disposed between the object and the detector at the first position. The scatter rejecting aperture plate is moved to a second position between the object and the detector and a second grid image of the object is acquired with the scatter rejecting aperture plate disposed between the object and the detector at the second position. A scatter image of the object is generated based on the non-grid image, the first grid image, and the second grid image and is stored. In another embodiment, a method for generating a three-dimensional image of an object is described. The method includes acquiring a plurality of projection images of the object using a source and a detector oriented at a plurality of projection angles relative to the object. The plurality of projection angles is realized by relatively rotating the object and the radiation source in a common plane of rotation. A scatter image is acquired at each of the plurality of projection angles. Acquiring each scatter image includes acquiring a non-grid image of the object using a radiation source and a detector, positioning a scatter rejecting aperture plate between the object and the detector at a first position, and acquiring a first grid image of the object with the scatter rejecting aperture plate disposed between the object and the detector at the first position. The scatter rejecting aperture plate includes a plurality of apertures, the aperture being positioned on a grid. The scatter rejecting aperture plate is moved to a second position between the object and the detector and a second grid image of the object is acquired with the scatter rejecting aperture plate disposed between the object and the detector at the second position. The scatter image of the object is generated based on the non-grid image, the first grid image, and the second grid image. A plurality of scatter free projection images is generated by correcting the plurality of projection images based on respective ones of a plurality of stored scatter images by subtracting the scatter images from the respective projection images in a single process step and reconstructing a three-dimensional image of the object based on the scatter free projection images. In a further embodiment, a volumetric CT system for imaging an object is described. The CT system is configured to generate a scatter free image of an object for use in generating a three-dimensional image of the object. The system includes a source and a detector configured to move with respect to the object, the detector configured to acquire a plurality of images of the object. A scatter rejecting aperture plate is configured to be positioned at a plurality of positions between the object and the detector. The scatter rejecting aperture plate includes a plurality of apertures, the aperture positioned on a grid. A processor is configured to acquire a non-grid image of the object without the scatter rejecting aperture plate and a grid image of the object with the aperture plate at each of the plurality of positions between the object and the detector and generate the scatter image of the object based on the non-grid image and the grid images acquired at each of the plurality of positions. The above embodiments are exemplary only. Other embodiments are within the scope of the disclosed subject matter. The present techniques are generally directed to computed tomography (CT) imaging resulting in improved image quality. Such imaging techniques may be useful in a variety of imaging contexts, such as medical imaging, industrial metrology and inspection, security screening, baggage or package inspection, and so forth. Moreover, such imaging techniques may be employed in a variety of imaging systems, such as CT systems, tomosynthesis systems, X-ray imaging systems, and so forth. Though the present discussion provides examples in an industrial inspection context with respect to CT systems resulting in improved measurement and inspection accuracy, one of ordinary skill in the art will readily apprehend that the application of these techniques in other contexts and in other systems is well within the scope of the present techniques. Referring now to FIG. 1, an imaging system 10 for use in accordance with the present technique is illustrated. In the illustrated embodiment, the imaging system 10 can be a volumetric computed tomography (VCT) system designed both to acquire image data and to process the image data for display and analysis in accordance with the present technique. In the illustrated embodiment, the imaging system 10 can include a radiation source 12, such as an X-ray source. A collimator may be positioned adjacent to the radiation source 12 for regulating the size and shape of a stream of radiation 14 that emerges from the radiation source 12. In typical operation, the radiation source 12 projects a stream of radiation 14, such as an X-ray beam, towards a detector array 16 placed on the opposite side of the radiation source 12, relative to the imaged object. The stream of radiation 14 passes into an imaging volume in which an object 18, such as a turbine blade or other item to be imaged may be positioned. Non-limiting examples of the object 12 include industrial parts, including but not limited to turbine airfoils, blades, disks, and shafts. It should be noted that a particular region of the object 18 may be chosen by an operator for imaging so that the most useful scan of the region may be acquired. A portion of the radiation 20 passes through or around the object 18 and impacts the detector array 16. The detector array 16 may be an area detector and can be generally formed as a two-dimensional array of detection elements. In one implementation, the detector array 16 may be a flat-panel detector formed as rows and columns of detector elements that may be individually read out. Each detector element produces an electrical signal that represents the intensity of the incident radiation 20 at the detector element when the radiation 20 strikes the detector array 16. Typically, signals can be acquired at one or more view angle positions around the object 18 so that a plurality of radiographic views may be collected. These signals can be acquired and processed to reconstruct an image of the features internal as well as external to the object 18. The object 18, the radiation source 12, and the detector array 16 can be typically displaced relative to each other, allowing projection data to be acquired at various views relative to the object 18 if desired. For example, in one implementation, the object 18 may be positioned on a table, such as a turntable, so that the object 18 may be rotated in a common plane of rotation 100 during the examination process to expose the object 18 to the stream of radiation 14 from all sides. Alternatively, the radiation source 12 and/or the detector array 16 may be disposed on a gantry, which may be rotated around the object 18 placed on a table during the examination process. Further, in certain embodiments, components of the imaging system as well as the imaged object may be moved during the examination process to acquire projection images at different views. As the object 18 and the radiation source 12 rotate relative to each other in a common plane of rotation 100, the detector array 16 collects data of radiation attenuation at the various view angles relative to the object 18. Data collected from the detector array 16 then typically undergoes pre-processing to condition the data to represent the line integrals of the attenuation coefficients of the scanned objects 18. The processed data, commonly called projections, can then be reconstructed to formulate a volumetric image of the scanned area, as discussed in greater detail below. Operation of the source 12 can be controlled by a system controller 22, which furnishes both power, and control signals for examination sequences. Moreover, the detector array 16 can be coupled to the system controller 22, which commands acquisition of the signals generated in the detector array 16. The system controller 22 may also execute various signal processing and filtration functions, such as for initial adjustment of dynamic ranges, interleaving of digital image data, and so forth. In general, the system controller 22 commands operation of the imaging system 10 to execute examination protocols and to process acquired data. In the present context, system controller 22 may also include signal processing circuitry and other circuitry, typically based upon a general purpose or application-specific digital computer, with associated memory circuitry. The associated memory circuitry may store programs and routines executed by the computer, configuration parameters, image data, and so forth. For example, the associated memory circuitry may store programs or routines for implementing the present technique. In the embodiment illustrated in FIG. 1, the system controller 22 can be coupled to a linear positioning subsystem 24 and a rotational subsystem 26. In particular, the system controller 22 may include a motor controller 28 that controls the operation of the linear positioning subsystem 24 and the rotational subsystem 26. The rotational subsystem 26 enables the X-ray source assembly and/or the detector assembly to be rotated around the object or the patient 18. It should be noted that the rotational subsystem 26 may include a gantry. Thus, the system controller 22 may be utilized to control the rotational speed and position of the gantry. Alternatively, the rotational subsystem 26 may include a motorized turntable and the system controller 22 may be configured to rotate the motorized turntable, thereby rotating the object 18 one or multiple turns during an examination. The linear positioning subsystem 24 enables the object 18 to be displaced linearly, such as by moving a table or support on which the object 18 rests. Thus, in one embodiment, the table may be linearly moved within a gantry to generate images of particular areas of the object 18. In another embodiment (e.g., in a tomosynthesis system), the X-ray source may be moveable using a linear positioning subsystem. The detector position may be variable, but not be controlled using a positioning subsystem. It should be noted that other configurations may also be used. Additionally, as will be appreciated by those skilled in the art, the radiation source 12 may be controlled by a radiation controller 30 disposed within the system controller 22. Particularly, the radiation controller 30 may be configured to provide power and timing signals to the radiation source 12. Further, the system controller 22 may include data acquisition circuitry 32. In this exemplary embodiment, the detector array 16 can be coupled to the system controller 22, and more particularly to the data acquisition circuitry 32. The data acquisition circuitry 32 typically receives sampled analog signals from the detector array 16 and converts the data to digital signals for subsequent processing by a processor 34. Such conversion, and indeed any preprocessing, may actually be performed to some degree within the detector assembly itself. The processor 34 can be typically coupled to the system controller 22. Data collected by the data acquisition circuitry 32 may be transmitted to the processor 34 for subsequent processing and reconstruction. Reconstruction of the image may be done by general or special purpose circuitry of the processor 34. Once reconstructed, the image produced by the imaging system 10 reveals internal as well as external features of the object 18. Alternatively, an image reconstruction that can be coupled to or can be a part of a processor 34, may receive sampled and digitized data from the data acquisition circuitry 32 and may perform high-speed image reconstruction to generate one or more images of the scanned object 18. The processor 34 may include or be in communication with a memory 36. It should be understood that any type of computer accessible memory device suitable for storing and/or processing such data and/or data processing routines may be utilized by such an exemplary imaging system 10. Moreover, the memory 36 may comprise one or more memory devices, such as magnetic or optical devices, of similar or different types, which may be local and/or remote to the system 10. The memory 36 may store data, processing parameters, and/or computer programs comprising one or more routines for performing the processes described herein. Furthermore, memory 36 may be coupled directly to system controller 24 to facilitate the storage of acquired data. The processor 34 can be typically used to control the imaging system 10. The processor 34 may also be adapted to control features enabled by the system controller 22, i.e., scanning operations and data acquisition. Indeed, the system controller 22 may be implemented as hardware and software components of the depicted processor 34. In addition, the processor 34 may be configured to receive commands and scanning parameters from an operator via an operator workstation 38. For example, the operator workstation 38 may be equipped with a keyboard and/or other input devices by which an operator may control the imaging system 10. Thus, the operator may observe the reconstructed image and other data relevant to the system from processor 34, initiate imaging and so forth. Where desired, other computers or workstations may perform some or all of the functions of the present technique, including post-processing of image data simply accessed from memory device 36 or another memory device at the imaging system location or remote from that location. A display 40 may be coupled to one of the operator workstation 38 and the processor 34 and may be utilized to observe the reconstructed image and/or to control imaging. Additionally, the scanned image may also be printed by a printer 42 which may be coupled to the processor 34 and/or the operator workstation 38, either directly or over a network. It should be further noted that the processor 34 and/or operator workstation 38 may be coupled to other output devices that may include standard or special purpose computer monitors and associated processing circuitry. Furthermore, additional operator workstations may be further linked in the imaging system 10 for outputting system parameters, requesting inspection, viewing images, and so forth, so that more than one operator may perform operations related to the imaging system 10. For example, one operator may utilize one operator workstation to image acquisition while a second operator utilizes a second operator workstation to reconstruct and/or review the results of the imaging routines. In general, displays, printers, workstations, and similar devices supplied within the imaging system 10 may be local to the data acquisition components, or may be remote from these components linked to the imaging system 10 via one or more configurable networks, such as the Internet, virtual private networks, and so forth. The exemplary imaging system 10, as well as other imaging systems based on radiation attenuation, may employ a variety of scatter mitigation and/or correction techniques for improving the image quality. For example, the present technique employs a scatter rejecting aperture plate, depicted in FIG. 2 and represented generally at reference numeral 46, for rejecting the scatter radiation resulting from object as well as those resulting from the background in accordance with aspects of the present technique. The aperture plate 46, as illustrated in FIG. 2, can include a plurality of sub-centimeter sized circular apertures 48 drilled in a plate 50. It is to be understood that the apertures 48 are shown to be circular by way of example only as circular apertures can be easily manufactured by conventional mechanical drilling. However, using other manufacturing methods like laser drilling apertures with different shapes can be produced. More particularly apertures with regular geometric shapes like triangular, rectangular, hexagonal or octagonal become available. Further even less regular shapes like elliptic or even freely formed apertures become available. The circular apertures 48 of the preferred embodiment shown in FIGS. 2 and 3 can be positioned on a two-dimensional hexagonal grid to optimize the packaging density of the apertures 48 whilst keeping the distance between next neighbors at a level which has been found best suited in the imaging system known from U.S. Pat. No. 8,184,767 B2. The grid lines (dotted lines) have been indicated for reason of clarity. In certain embodiments, the circular apertures 48 may be about 1-2 millimeters in diameter spaced apart at about 5 millimeters from each other (center-to-center). In general terms the apertures 48 have a diameter and a next-neighbor distance. It has been found as a general rule that preferably the ratio between next-neighbor distance and diameter can be in the range of 2 and 3. In a particular embodiment the ratio can be about 2.5. By way of example, circular apertures 48 having a diameter of 1 millimeter can be preferably placed on a hexagonal grid with a next-neighbor distance of about 2.5 millimeters. The exact ratio depends on a number of parameters including, but not limited to, the features of the x-ray flat panel detector. Therefore it is to be understood that the ratio of 2.5 may need some adjustment to meet the requirements of the equipment that causes the unwanted x-ray scattering. The enhanced density of the apertures 48 placed on a hexagonal grid with unaltered next-neighbor distance minimizes the area in images acquired with the aperture plate 46 in place in which image information cannot be acquired by x-ray but needs to be computed based on a suited interpolating algorithm. This results in a higher quality of the images acquired with the aperture plate 46 in place compared to prior art. Typically, the plate 50 can be thick and made of high-density material. The high-density material may be, for example, lead, tungsten or a tungsten alloy, molybdenum, tantalum or rhenium. In certain embodiments, the plate can be about 10 to 20 millimeters in thickness. In certain embodiments, the plate 50 can be made of lead and can be about 19 millimeters in thickness. FIG. 3 shows an enlarged view of the aperture plate 46 as shown in FIG. 2. From FIG. 3 the two-dimensional hexagonal grid is apparent. Again the grid lines (dotted lines) have been indicated for reason of clarity. Additionally surface normal 102 of the common plane of relative rotation 100 of object 18 and the radiation source 12 has been indicated in FIG. 3. Whilst the x-ray inspection method according to U.S. Pat. No. 8,184,767 B2 allows for minimizing the effect of x-ray radiation scattered in the x-ray detection equipment the method at the same time can induce artifacts in scatter corrected images. These artifacts can also negatively affect the quality of volume data reconstructed from scatter corrected images by means of VCT. I.e. if a rectangular grid is employed for the method and the orientation of the rectangular grid relative to the common plane of relative rotation of object 18 and the radiation source 12 is such that one of the grid lines is parallel to the surface normal of the common plane of rotation specific areas of object 18 can be covered by the aperture plate 46 for all acquisition angles. Thus no X-ray attenuation information relating to these areas can be collected by direct measurement but needs to be calculated by appropriate interpolating methods. These methods however cannot account for small structures located in said areas. In fact in this case these structures can be partly to fully masked in the acquired images. Hence they cannot properly appear in any scatter corrected images or, consequently, in any volumetric image reconstructed therefrom. The inventors recognized that even worse the same effect can also cause severe artifacts in volumetric image data reconstructed from scatter corrected images generated pursuant to the teaching of U.S. Pat. No. 8,184,767 B2. This effect is illustrated by means of FIG. 4. FIGS. 4A to 4D which depict, for a turbine fan blade, two uncorrected images acquired at two different acquisition angles A (FIG. 4A) and B (FIG. 4B), the image acquired at acquisition angle B with scatter correction applied employing the method pursuant to U.S. Pat. No. 8,184,767 B2 (FIG. 4C) and finally volumetric image data of the turbine fan blade reconstructed from the multiple acquired and scatter corrected images (FIG. 4D). A fine structure of the object which is indicated in FIGS. 4B to 4D by a circle can be positioned such that it can be covered by the aperture blade 46 for all acquisition angles. Although this fine structure is not visible in FIG. 4B it leaves a footprint in scatter corrected image of FIG. 4C. In the reconstructed volumetric data of FIG. 4D it causes severe artifacts. The impact of this problem can be effectively reduced by making the distances between holes smaller or by choosing an appropriate orientation for a given aperture plate 46. The orientation needs to be chosen such that for a given feature of the object under inspection regardless of its actual position there is a high probability that of this feature coincides not only once but as often as possible with any one of the apertures 48 when varying the projection angle. Hence identifying an appropriate orientation for a given aperture plate 46 means optimizing before mentioned probability. This approach not only applies to an aperture plate 46 with hexagonal geometry but to any given geometry of the aperture plate 46. In particular this approach could also be applied to an aperture plate 46 with rectangular geometry. By way of example this effect can be addressed by the proposed preferred embodiment illustrated by means of FIG. 3. However as said before it can be addressed for any type of aperture plate. The preferred embodiment according to FIG. 3 comprises a specific orientation of the hexagonal grid relative to the common plane of relative rotation 100 of object 18 and the radiation source 12. In this embodiment one of the grid lines of the hexagonal grid can be inclined against the surface normal 102 of the common plane of rotation 100 by a defined inclination angle. Said inclination angle generally lies in the range of 0 to 15 degrees. In a more preferred embodiment the inclination angle can be in the range of 0 to 5 degrees. In certain embodiments the inclination angle can be equal to 0 degrees. This particular embodiment is shown in FIGS. 2 and 3. Further, various other scatter rejection plates may be designed based on the specific imaging applications and requirements, so as to optimize scatter rejection performance. In certain embodiments, if the geometry of an x-ray setup can be fixed, focally aligned apertures 48 may be designed. This provides that no primary x-ray beam deflects at wide angles. In other words, the apertures 48 may be drilled at an angle parallel to the angle of incidence of the X-ray beam, so as to maximize the rejection of scatter radiation. Similarly, the aperture plate may be optimized for a particular X-ray energy application. Further, it should be noted that the spacing of the apertures 48 may be based on specific applications depending on cost and image quality requirements. The flat panel VCT system 10 employs the scatter rejection plates 46 for generating initial scatter image of the object 18 in accordance with aspects of the present technique. For example, as illustrated in the schematic of FIG. 5, the VCT system 10 acquires a first projection image 56 of the object 18 without the scatter rejection plate 46. This first projection image 56 can include a primary (non-grid) image of the object as well as a scatter image of the object. The VCT system 10 then acquires a second projection image 58 of the object with the scatter rejection plate 46 positioned between the object 18 and the detector 16. This second projection image 58 can include only the primary image of the object 18. As will be appreciated by those skilled in the art, the primary image is free from any artifacts caused due to scatter radiation. Further, it should be noted that, in the second projection image, the primary image of the object 18 can be formed only at certain discrete locations where measurements can be obtained through the apertures 48 and can be therefore dependent on the type of scatter rejection plate 46 employed to acquire the image. The illustrated embodiment depicts the primary image acquired by using aperture plate 46. The first image 56 and the second projection image 58 may also be referred as non-grid image 56 and grid image 58 respectively. The VCT system 10 then generates the scatter image of the object at the respective one of the projection angles based on the first projection image 56 and the second projection image 58. In particular, the processor 34 subtracts the second projection image 58 from the first projection image 56 to generate a scatter grid image 60. It should be noted that acquisition of the first projection image 56 and the second projection image 58, and the generation of scatter grid image 60 can be performed for each of the projection angles. The generated scatter grid image 60 can then be interpolated to generate a complete scatter image. FIG. 6 depicts an example schematic for interpolating a scatter grid image obtained by the technique of FIG. 5 to generate a complete scatter image in accordance with aspects of the present technique. As illustrated, all aperture points or centroids for the scatter grid image can be first detected at step 62. It should be noted that, for the scatter grid image acquired by employing an aperture plate, the aperture points may be detected based on the required pixel resolution. The scatter grid image can then be interpolated based on the detected aperture points to generate a full or complete scatter image of the object at step 64. In other words, the data points can be first mapped to a regular grid and then interpolated using shape factors. As will be appreciated by those skilled in the art, any type of interpolation techniques may be employed to generate the scatter image from the scatter grid image. Non-limiting examples of the interpolation techniques include bi-linear interpolation, piecewise constant interpolation, bi-cubic interpolation, multivariate interpolation, and so forth. As will be appreciated by those skilled in the art, a scatter image of the object can be generated for each of the projection angles. The generated scatter images can be stored in the memory for subsequent imaging. As will be appreciated by those skilled in the art, subsequent imaging can include acquiring projection images of the object from various projection angles and generating scatter free projection images for each projection angle based on the projection images and respective stored scatter images. The scatter free projection images can be generated by correcting the projection images based on respective ones of stored scatter images. In certain embodiments, the scatter free projection images may be corrected by subtracting the respective pre-stored scatter images from the acquired projection image for each of the projection angle. It should be noted that the orientation of the object during subsequent imaging should be substantially same as it was during generation of scatter image for each projection angles. The scatter free projection images may be further processed to normalize and correct for any bad pixels in the scatter free projection images. The generated or processed scattered free projection images may then be reconstructed to generate a three-dimensional image of the object. As will be appreciated by those skilled in the art, any suitable reconstruction technique may be employed for the image reconstruction. Non-limiting examples of the reconstruction techniques include filtered back projection (FBP), iterative filtered back projection (IFBP), iterative reconstruction and/or statistical reconstruction techniques. The exemplary imaging system 10 may generate images of the object under examination by the techniques discussed herein. In particular, as will be appreciated by those of ordinary skill in the art, control logic and/or automated routines for performing the techniques and steps described herein may be implemented by the imaging system 10 of FIG. 1, by hardware, software, or combinations of hardware and software. For example, suitable code may be accessed and executed by the processor 34 to perform some or all of the techniques described herein. Similarly application specific integrated circuits (ASICs) configured to perform some or all of the techniques described herein may be included in the processor 34 and/or the system controller 22. For example, referring now to FIG. 7, exemplary control logic for inspecting an object by employing scatter measurement and correction technique on the imaging system such as flat panel VCT system 10 is depicted in accordance with aspects of the present technique. As illustrated in the flowchart 66, a non-grid image and a grid image may be acquired for a given object at multiple projection angles via the VCT system at steps 68 and 70 respectively. As discussed above, the grid image may be acquired by employing the scatter rejection plate positioned between the object and the detector. A scatter grid image can then be generated based on the non-grid image and the grid image at step 72. The scatter grid image can then be processed to detect multiple aperture points or centroids at step 74. Based on the detected centroids, the scatter grid image can then be interpolated to generate a full scatter image of the given object at step 76. The process can be repeated for each of the multiple projection angles and the generated scatter images for the respective projection angles can be stored for subsequent imaging applications at step 78. During subsequent imaging, the VCT system images the object at step 80 and acquires projection images of the object from various projection angles at step 82. It should be noted that, the projection images can be acquired for same projection angles for which the scatter images have been generated. The scatter free projection images can then be generated based on the projection images and corresponding scatter images at step 84. In one embodiment this can be done by subtracting the corresponding scatter images from the acquired projection images. The scatter free projection images can then be post processed at step 86. The post processing may involve normalization and correction for bad pixels. The processed scatter free projection images can then be reconstructed to generate a three-dimensional image of the object at step 88. FIG. 8 illustrates, for a turbine fan blade, uncorrected image and scatter corrected images by employing control logic of FIG. 7. Image 90 is the uncorrected image obtained by a typical VCT system, while images 92 and 94 are scatter corrected images obtained by employing the scatter rejection plate and the control logic described via the flowchart 66. Further, it should be noted that image 92 is the scatter corrected image obtained by employing an aperture plate. It should be noted that one or more imaging parameters should be substantially maintained (that is, maintained at substantially similar values) for a particular imaging application and inspection requirement. Non-limiting examples of the imaging parameters include a type of object being imaged, a shape and an orientation of the object being imaged, projection angles from which the scatter images and subsequent projection images are acquired, an x-ray technique being employed, a geometry and one or more settings of the source and the detector, distance of the scatter rejection plates from the source and the detector, and so forth. For example, the above process may be set for imaging similar objects (e.g., turbine blades). The objects should be mounted on the turntable at substantially similar orientations. Further, the distance of the scatter rejection plate from the source and the detector should be substantially maintained while acquiring and storing the scatter images for each of the predetermined projection angles. In one embodiment, this may be achieved by coupling or attaching the scatter rejection plate to the two-dimensional flat panel detector array. Additionally, projection images should be acquired for projection angles for which the scatter images have been generated and stored. Moreover, the x-ray technique employed, the geometry and other settings for the source and the detector should be maintained at substantially similar values, such that the beam shape and intensity can be same for various image acquisitions. Referring now to FIGS. 9A-9B, another imaging system 200 for use in accordance with an imaging technique to produce a high resolution image described herein is illustrated. In the illustrated embodiment, the imaging system 200 can be a volumetric computed tomography (VCT) system designed both to acquire image data and to process the image data for display and analysis in accordance with a present technique. In the illustrated embodiment, the imaging system 200 can include a radiation source 202, such as an X-ray source 202. A collimator 205 may be positioned adjacent to the radiation source 202 for regulating the size and shape of the stream of radiation 204 that emerges from the radiation source 202. The stream of radiation 204 can be projected toward a detector array 206 placed on the opposite side of the radiation source 202, relative to an object 208 that is to be imaged. The stream of radiation 204 passes into an imaging volume in which the object 208 to be imaged, such as a turbine blade or other item to be imaged, may be positioned. A portion of the radiation 204 passes through or around the object 208 and impacts the detector array 206. The detector array 206 can be generally formed as a two-dimensional array of detection elements. The object 208, radiation source 202, and detector array 206 can be typically displaced relative to each other, allowing projection data to be acquired at various views relative to the object 208 if desired. In an example, the object 208 can be positioned on a table, such as a turntable, so that the object 208 may be rotated about a rotation axis 210. Data collected from the detector array 206 typically undergoes pre-processing to condition the data to represent the line integrals of the attenuation coefficients of the scanned object 208. The processed data or projections can then be reconstructed to formulate a volumetric image of the scanned area, as discussed in greater detail above. The imaging system 200 may employ a variety of scatter mitigation and/or correction techniques for improving the image quality and resolution. For example, as discussed above, a scatter rejecting aperture plate 212 for rejecting the scatter radiation resulting from the object 208 as well as those resulting from the background can be employed. As illustrated in this embodiment, in order to further improve the resolution and image quality, the aperture plate 212 can be movable between a plurality of positions. These positions will be described further below with regard to FIGS. 10A-10D. By moving the aperture plate 212 between the plurality of positions, smaller structures on the object 208 can be recognized and artifacts can be better avoided. As discussed above with regard to FIGS. 2-3, the aperture plate 212 can include a plurality of sub-centimeter sized apertures 48, such as circular apertures, drilled in a plate. The apertures 48 can be positioned on a two-dimensional grid. The two-dimensional grid in this embodiment can have any geometric shape, such as a circular shape, rectangular shape, or hexagonal shape, among others. In certain embodiments, the circular apertures 48 may be about 1-2 millimeters in diameter spaced apart at about 5 millimeters from each other (center-to-center). Referring now to FIGS. 10A-D, as discussed above, the aperture plate 212 can be movable between a plurality of positions in order to increase the resolution and quality of the generated image. As illustrated in FIG. 10A, the aperture plate 212 can initially be placed in a first position 211. After a first grid image is gathered, the aperture plate 212 can be repositioned to a secondary position 213, 214 and a second grid image gathered. In an embodiment, the aperture plate 212 can be moved uni-directionally. For example, the aperture plate 212 can be moved vertically from the first position 211 to the second position 213, as illustrated in FIG. 10B, and a second image gathered or the aperture plate 212 can be moved horizontally from the first position 211 to the third position 214, as illustrated in FIG. 10C, and the second image gathered. In another embodiment, the aperture plate 212 can be moved bi-directionally. For example, the aperture plate 212 can be moved both vertically and horizontally, as illustrated in FIG. 10D. In this embodiment, the aperture plate 212 can be placed in a first position 211 and a first image gathered, moved to a second position 213 and a second image gathered, moved to a third position 214 and a third image gathered, and moved to a fourth position 215 and a fourth image gathered. In another embodiment, the aperture plate 212 can be rotated relative to the object 208. An image can be gathered at each position 211, 213, 214, 215 of the aperture plate 212. In another embodiment, resolution of the image can also be increased by moving the object 208 in front of the grid of the aperture plate 212. Similar to repositioning the aperture plate 212, discussed above, in this embodiment the sample can be moved uni-directionally, bi-directionally, or rotated, for example. By repositioning the apertures 48 of the aperture plate 212 relative to the object 208, the resolution of the image can be increased. The aperture plate 212 and/or object 208 can be repositioned manually or automatically. The resolution of the image can be determined by the number of positions at which the aperture plate 212 and/or object 208 can be placed. As the number of positions increases, the resolution of the image also increases. For example, using bi-directional movement of the aperture plate 212, positioning the aperture plate 212 in four positions increases the image resolution by a factor of two (2). In another example, positioning the aperture plate 212 in sixteen positions increases the image resolution by a factor of four (4). This improvement in image resolution by repositioning the aperture plate 212 is illustrated by FIGS. 11A-11B. FIG. 11A illustrates an image 216 of the object 208 generated in which the aperture plate 212 was placed in a single position. FIG. 11B illustrates an image 219 of the object 208 in which the aperture plate 212 was placed in four positions during gathering of the data. As illustrated by the first 217 and second 218 location indicated in these figures, the additional positions of the aperture plate 212 results in an image in FIG. 11B in which additional details are visible at each of the first location 217 and the second location 218 as compared to FIG. 11A. Referring now to FIG. 12, a flowchart illustrating an exemplary method 220 of imaging an object, such as the object 208, by employing an advanced scatter measurement and correction technique on the imaging system 200 is depicted. This method is exemplary only and the blocks may be altered, added, removed, and/or rearranged. As illustrated in the flowchart, at block 68, a primary, non-grid image can be acquired for the object 208 at multiple projection angles via the imaging system 200. At block 222, a first grid image can be acquired. The first grid image can be acquired by employing the scatter rejection aperture plate 212 positioned between the object 208 and the detector 206. Following acquisition of the first grid image, the apertures 48 of the aperture plate 212 can be repositioned relative to the object 208 and an additional image can be acquired at block 224. For example, the aperture plate 212 can be moved to a second position and the additional grid image can be acquired with the aperture plate 212 at the additional position. In another example, the object 208 can be moved between positions while the aperture plate 212 remains stationary. The aperture plate 212 and/or the object 208 can be moved to a plurality of positions and a grid image acquired at each of the plurality of positions. The number of positions can be determined based on the level of resolution desired in the final image. As discussed above, the aperture plate 212 can be moved uni-directionally (e.g., horizontally or vertically), bi-directionally (e.g., horizontally and vertically), rotated, etc. The aperture plate 212 and/or the object 208 can be moved manually or automatically between the positions. Following acquisition of the plurality of grid images, at block 72, a scatter grid image can be generated based on the non-grid image and the plurality of grid images. The scatter grid image can then be processed to detect multiple aperture points or centroids at block 74. Based on the detected centroids, the scatter grid image can then be interpolated to generate a full scatter image of the object 208 at block 76. The process can be repeated for each of the projection angles and the generated scatter images for the respective projection angles can be stored for subsequent imaging applications at block 78. At block 80, the imaging system 200 images the object 208 and acquires projection images of the object from various projection angles at block 82. At block 84, the scatter free projection images can be generated based on the projection images and corresponding scatter images. In an embodiment, this can be done by subtracting the corresponding scatter images from the acquired projection images. At block 86, the scatter free projection images can be post processed. The post processing may involve normalization and correction for bad pixels. At block 88, the processed scatter free projection images can then be reconstructed to generate a three-dimensional image of the object 208. As will be appreciated by those skilled in the art, the scatter correction techniques described in the various embodiments discussed above permit a measurement of the scatter content in the projection images used for VCT imaging and correct the projection images, thereby improving the VCT image quality. The technique permits measurement of scatter content in x-ray images for a given geometry, scanning orientation, and x-ray technique prior to a VCT scan and use it during an actual imaging scan. This improves the throughput of the VCT system since scatter correction for the projection images is then a simple image subtraction process. Further, as will be appreciated by those skilled in the art, it is easier to measure primary radiation than the scatter radiation and positioning the scatter rejection plate between the object and the detector makes the measurement of primary radiation substantially convenient. Additionally, the use of narrow collimators permits the imaging of the higher spatial frequency content of the scatter images. Moreover, the technique permits capture and correction of the beam scatter (scatter due to the imaged object) as well as the background radiation scatter (scatter due to external object). Further, as will be appreciated by those skilled in the art, the technique may be employed as a part of the system calibration process prior to the actual imaging application. Typically, prior to performing VCT imaging for metrology or inspection, an operator has to perform a few system calibration steps such as, flat field calibration of the detector, bad pixel test and calibration of the detector, geometrical alignment and calibration of the system. The scatter correction technique described in the embodiments discussed above may similarly become a part of the calibration process where the scatter images will be obtained for a specific object and stored prior to the performance of an actual metrology or inspection process. This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. |
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abstract | A nozzle seal structure hermetically seals an instrumentation nozzle provided in a manner penetrating a reactor vessel from inside to outside and has a support post inserted therethrough. The instrumentation nozzle includes a flange portion projecting outward in a radial direction orthogonal to a nozzle axis direction at an end portion on an outer side of the reactor vessel. |
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claims | 1. A radioactive waste solidification method comprising steps of:supplying a radioactive waste including a radioactive nuclide, a glass raw material, and graphite into a first vessel;disposing the first vessel in which the radioactive waste, the glass raw material, and the graphite exist, in an adiabatic area in a second vessel;heating the radioactive waste and the glass raw material existing in the first vessel disposed in an adiabatic area in the second vessel by heat generated by radiation emitted from the radioactive nuclide and melting the glass raw material in the first vessel; andproducing a vitrified radioactive waste by the melt of the heated glass raw materials. 2. The radioactive waste solidification method according to claim 1, wherein in the disposal of the first vessel, in which the radioactive waste, the glass raw material, and the graphite exist, into the adiabatic area, this first vessel is disposed in an adiabatic area formed in an adiabatic vessel being the second vessel. 3. The radioactive waste solidification method according to claim 1, wherein in the disposal of the first vessel, in which the radioactive waste, the glass raw material, and the graphite exist, into the adiabatic area, this first vessel is disposed in a pressure reducing vessel being the second vessel, and a pressure in a space in which the first vessel is disposed is reduced to form the adiabatic area, the space being formed in the sealed pressure reducing vessel. 4. The radioactive waste solidification method according to claim 1, wherein a temperature of the first vessel disposed in the adiabatic area in the second vessel is measured, and a flow rate of gas to be supplied to the adiabatic area in the second vessel is adjusted based on the measured temperature. 5. The radioactive waste solidification method according to claim 3, wherein a temperature of the first vessel disposed in the adiabatic area in the second vessel is measured, and a pressure in the adiabatic area in the second vessel is controlled. 6. The radioactive waste solidification method according to claim 2, wherein a temperature of the first vessel disposed in the adiabatic area in the second vessel is measured, and a flow rate of gas to be supplied to the adiabatic area in the second vessel is adjusted based on the measured temperature. 7. The radioactive waste solidification method according to claim 3, wherein a temperature of the first vessel disposed in the adiabatic area in the second vessel is measured, and a flow rate of gas to be supplied to the adiabatic area in the second vessel is adjusted based on the measured temperature. 8. A radioactive waste solidification method comprising steps of:supplying a radioactive waste including a radioactive nuclide, and a glass raw material into each of a plurality of waste filling areas, the plurality of waste filling areas being formed with thermally conductive members in a first vessel;disposing the first vessel in which the radioactive waste and the glass raw material exist, in an adiabatic area in a second vessel;heating the radioactive waste and the glass raw material existing in each waste filling area in the first vessel disposed in the adiabatic area in the second vessel by heat generated by radiation emitted from the radioactive nuclide and melting the glass raw material in the first vessel; andproducing a vitrified radioactive waste by the melt of the heated glass raw materials. |
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047298553 | claims | 1. A method of decontaminating metal surfaces contaminated with a radioactive deposit, comprising circulating between said deposit and a cationic ion exchange column an aqueous solution of a water soluble condensation reaction product of (1) a hydrazine compound having the general formula ##STR3## where each R is independently selected from hydrogen and alkyl to C.sub.4 ; and (2) a water-soluble aliphatic polycarboxylic acid selected from the group consisting of oxalic acid, tartaric acid, citric acid, succinic acid, and mixtures thereof. (1) preloading a cationic ion exchange column with N.sub.2 H.sub.5.sup.+ ; (2) circulating between said deposit and said cationic exchange column, an aqueous solution iof dihydrazine oxalate, at a concentration of about 0.05 to about 10% by weight, based on solution weight, heated to about 870.degree. to about 125.degree. C.; (3) passing an oxidizing solution over said deposit; (4) repeating step (2); and (5) adding an oxidant to said aqueous solution, whereby said dihydrazine oxalate is oxidized to nitrogen, carbon dioxide, and water. 2. A method according to claim 1 wherein said water-soluble aliphatic polycarboxylic acid is oxalic acid. 3. A method according to claim 1 wherein one mole of said hydrazine compound is reacted with one equivalent of said polycarboxylic acid. 4. A method according to claim 1 wherein the concentration of said condensation reaction product in said aqueous solution is about 0.05 to about 10% by weight, based on total solution weight. 5. A method according to claim 1 wherein the temperature of said aqueous solution is about 80.degree. to about 125.degree. C. 6. A method according to claim 1 including the additional last step of adding an oxidant to said aqueous solution. 7. A method according to claim 1 wherein said R group is H and said cationic exchange resin is loaded with N.sub.2 H.sub.5.sup.+. 8. A method according to claim 1 wherein said cationic ion exchange column is preloaded with the cationic moiety of said condensation reaction product. 9. A method according to claim 1 wherein said water-soluble aliphatic polycarboxylic acid is citric acid. 10. A method according to claim 1 wherein said water-soluble aliphatic polycarboxylic acid is tartaric acid. 11. A method according to claim 1 wherein said water-soluble aliphatic polycarboxylic acid is succinic acid. 12. A method according to claim 1 wherein each R is hydrogen. 13. A method according to claim 12 wherein said water-soluble aliphatic polycarboxylic acid is oxalic acid. 14. A method according to claim 1 including the additional last steps of passing an aqueous oxidizing solution over said deposit, followed by passing said aqueous solution iover said deposit a second time. 15. A method according to claim 14 wherein said oxidizing solution is a solution of an alkali metal hydroxide and an alkali metal permanganate. 16. A method of decontaminating a metal surface having a deposit thereon that contains radioactive elements, comprising 17. A method according to claim 16 wherein said oxidant is hydrogen peroxide. |
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