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abstract | An X-ray multi-layer mirror having a reflection characteristic with a wider incident angle range is realized by conducting optimization processing on an Mo/Si alternate layer having a constant thickness. Film thickness distributions of Si layers and Mo layers in the Mo/Si alternate layer are determined by optimization processing for widening the angle reflection characteristic of the Mo/Si alternate layer having the constant thickness, which is a fundamental structure. |
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claims | 1. An exposure method for transferring a pattern of a mask onto a member to be exposed, said method comprising the steps of: preparing for exposure while a protection cover is attached to the mask; executing alignment between the member to be exposed and the mask while the protection cover is detached from the mask; and executing exposure with X-rays while the protection cover is detached from the mask. 2. A method according to claim 1 , wherein the protection cover is detached at a position for the exposure. claim 1 3. A method according to claim 1 , wherein the mask has a multilayered film reflection type mirror and the pattern is formed on the multilayered film reflection type mirror, and wherein the pattern absorbs the X-rays. claim 1 4. A device manufacturing method comprising the steps of: preparing for exposure while a protection cover is attached to the mask; executing alignment between the member to be exposed and the mask while the protection cover is detached from the mask; and transferring a pattern of the mask onto the member to be exposed with X-rays while the protection cover is detached from the mask, to manufacture a device using the member. 5. A method according to claim 4 , wherein the protection cover is detached from the mask at a position for exposure. claim 4 6. A method according to claim 4 , wherein the mask has a multilayered film reflection type mirror and the pattern is formed on the multilayered film reflection type mirror, and wherein the pattern absorbs the X-rays. claim 4 7. An exposure method for transferring a pattern of a mask onto a member to be exposed, said method comprising the steps of: attaching a protection cover to the mask at an attaching position; detaching the protection cover from the mask at a position different from the attaching position; executing alignment between the member to be exposed and the mask from which the protection cover has been detached; and executing exposure with X-rays, by using the mask from which the protection cover has been detached. 8. A method according to claim 7 , wherein the protection cover is detached from the mask at a position for exposure. claim 7 9. A method according to claim 7 , wherein the mask has a multilayered film reflection type mirror and the pattern is formed on the multilayered film reflection type mirror, and wherein the pattern absorbs the X-rays. claim 7 10. A device manufacturing method comprising the steps of: attaching a protection cover to a mask at an attaching position; detaching the protection cover from the mask at a position different from the attaching position; executing alignment between a member to be exposed and the mask from which the protection cover has been detached; and transferring a pattern onto the member to be exposed by exposure with X-rays by using the mask from which the protection cover has been detached, to manufacture a device using the member. 11. A method according to claim 10 , wherein the protection cover is detached from the mask at a position for exposure. claim 10 12. A method according to claim 10 , wherein the mask has a multilayered film reflection type mirror and the pattern is formed on the multilayered film reflection type mirror, and wherein the pattern absorbs the X-rays. claim 10 13. An exposure method for transferring a pattern of a mask onto a member to be exposed, said method comprising the steps of: providing the mask, which includes (i) a multilayered film reflection type mirror, (ii) a pattern, formed on the multilayered film reflection type mirror, which absorbs X-rays, and (iii) a protection cover covering at least a portion of the multilayered film reflection type mirror, and structured to be detachable from the multilayered film reflection type mirror; executing alignment between the member to be exposed and the mask while the protection cover is detached from the mask; and executing exposure with X-rays while the protection cover is detached from the mask. 14. An exposure apparatus comprising: means for holding a mask that includes (i) a multilayered film reflection type mirror, (ii) a pattern, formed on the multilayered film reflection type mirror, which absorbs X-rays, and (iii) a protection cover covering at least a portion of the multilayered film reflection type mirror, and structured to be detachable from the multilayered film reflection type mirror; means for holding a member to be exposed; and means for detaching the protection cover from the mask, wherein alignment between the mask and the member is executed while the protection cover is detached from the mask, and exposure with X-rays is executed while the protection cover is detached from the mask. 15. A device manufacturing method comprising the steps of: providing a mask which comprises (i) a multilayered film reflection type mirror, (ii) a pattern, formed on the multilayered film reflection type mirror, which absorbs X-rays, and (iii) a protection cover covering at least a portion of the multilayered film reflection type mirror, and structured to be detachable from the multilayered film reflection type mirror; executing alignment between a member to be exposed and the mask while the protection cover is detached from the mask; and transferring the pattern onto the member to be exposed with X-rays while the protection cover is detached from the mask, to manufacture a device using the member. 16. An exposure method for transferring a pattern of a mask onto a member to be exposed, said method comprising the steps of: preparing for exposure while the mask is attached with a protection member; executing alignment between the member to be exposed and the mask while the protection member is detached from the mask; and executing exposure with X-rays while the mask is detached from the protection member. 17. A method according to claim 16 , wherein the mask has a multilayered film reflection type mirror and the pattern is formed on the multilayered film reflection type mirror, and wherein the pattern absorbs the X-rays. claim 16 18. A device manufacturing method comprising the steps of: preparing for exposure while a mask is attached with a protection member; executing alignment between a member to be exposed and the mask while the protection member is detached from the mask; and transferring a pattern of the mask onto the member to be exposed while the mask is detached from the protection member, so as to manufacture a device using the member. 19. A method according to claim 16 , wherein the mask has a multilayered film reflection type mirror and the pattern is formed on the multilayered film reflection type mirror, and wherein the pattern absorbs the X-rays. claim 16 20. An exposure apparatus comprising: means for holding a mask; means for holding a member to be exposed; and means for detaching a protection cover from the mask, wherein alignment between the mask and the member is executed while the protection cover is detached from the mask, and exposure with X-rays is executed while the protection cover is detached from the mask. 21. An exposure apparatus comprising: means for holding a mask; means for holding a member to be exposed; and means for detaching the mask from a protection member, wherein alignment between the mask and the member to be exposed is executed while the mask is detached from the protection member, and exposure with X-rays is executed while the mask is detached from the protection member. 22. A method for exposing a member to be exposed with a pattern on a mask, said method comprising steps of: performing preparation for and exposure operation by covering the pattern with a protection member; and performing an alignment of the member to be exposed and the mask without covering the pattern with the protection member and performing the exposure operation by using X-rays. 23. A device manufacturing method comprising steps of: performing preparation for an exposure operation by covering the pattern with a protection member; performing an alignment of the member to be exposed and the mask without covering the pattern with the protection member and performing the exposure operation by using X-rays; and developing the member to be exposed. 24. An exposure apparatus for exposing a member to be exposed with a pattern on a mask, said apparatus comprising: a mirror for guiding X-rays to the mask; a first state for holding the mask; a second state for holding the member to be exposed; and means for separating the mask and a protection member which covers the pattern on the mask, wherein an alignment of the member to be exposed and the mask is performed without covering the pattern with the protection member and the member to be exposed is exposed by the X-rays. |
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description | This application is a filing under 35 U.S.C. 371 of international application number PCT/US2010/04173, filed Jul. 12, 2010, which claims priority to U.S. application No. 61/224,614 filed Jul. 10, 2009, the entire disclosure of which is hereby incorporated by reference. The present invention is related to the production of tracers useful for positron emission tomography (PET) and single photon emission computed tomography (SPECT). More specifically, the present invention is directed to methods and devices for transferring radioisotopes utilizing electrochemical methods. Furthermore, methods and devices for the integration of the present invention into microfluidic synthesis systems for radiopharmaceutical production are described. In the process of producing radiotracers for PET, a medical molecular imaging method, radionucleids, such as 18F must be extracted from the cyclotron target content and transferred into a solvent for the radiochemical labeling reaction. Besides ion exchangers, an electrochemical method can be applied. In a first step, the 18F ions in a solution with a first solvent, e.g. 18O-enriched water, flows past a pair of graphite or glassy carbon electrodes across which a potential is applied. The 18F ions are deposited on the positively-charged capture electrode (the anode). In a second step, the first solvent is exchanged with a suitable solvent, e.g. DMSO, and a reverse potential is applied to release the ions from the capture electrode back into the solution. The second solution is then transferred to a separations system for labeling. If a release voltage is applied during the second step, fluoride gets trapped on the counter electrode (i.e., the anode after reversing the potential or the cathode during the first step) while the fluoride is released into solution from the first electrode by application of the reverse potential. The fluoride is electrophoretically driven to the counter electrode and readsorbed thereon. In order to prevent counter trapping of 18F on the cathode, platinum electrodes have been used, as platinum is known for its low fluoride adsorption. Known processes and structures for trapping and release of 18F− do trap and release 18F− but do not ensure that the released 18F− is suitable for a labeling reaction. Specifically, the labeling yield may be low or zero in some cases. One reason could be that high voltages applied during the process create other ions which later then compete with the released 18F ions to bind to the provided precursor. To limit counter trapping, the prior art methods employ one carbon capture electrode and a noble metal counter electrode. The prior art counter electrode is typically formed from a metal, e.g. platinum, to prevent re-adsorption of the radionucleids during the release process applying a reverse potential. Platinum has poor absorption/adsorption properties for fluoride ions. Whether formed from platinum or solid graphite or glassy carbon plate, the electrodes of the prior art provide several challenges. They are very expensive, hard to machine and hard to integrate into a mass manufacturable process such as injection molding. For example, the prior art has used monolithic glassy carbon plates for the electrodes. However, these are very expensive, costing about $250 for a 25×25×3 mm3 piece, and are also difficult to machine and complex to integrate into a disposable product. WO 2009/015048 A2 describes coin-shaped and long-channel shaped electrochemical cells utilizing metal, graphite, silicon, and polymer composites of these materials. The document describes that the precursor is introduced into the cell and that gas drying is achieved with heating and acetonitrile drying. The operation is described as employing potentials up to 500V. WO 2008/028260 A2 describes electrochemical phase transfer devices consisting of a fine network of carbon filaments. An electrical double layer is used for capture, making it possible to trap 18F− without applying an external voltage. Cold Acetonitrile is listed as a method for drying. No or low externally applied voltage minimizes REDOX reactions. Heating is described for improving release of the trapped ions. Both WO 2008/028260 A2 and WO 2009/015048 A2 describe the use of alternating currents during the step of releasing of the fluoride. There is therefore a need for a disposable electrochemical phase transfer reactor which may be easily produced while still providing sufficient operating efficiencies. The integration of solid glassy carbon plates into a disposable phase transfer unit is complex due to the high cost of the glassy carbon, the need to CNC machine the glassy carbon, the poor ability of the glassy carbon to bond to plastics, and the difficulty of maintaining the glassy carbon microstructures free of leaks. There is also a need for a method of performing electrochemical phase transfer which provides an acceptable yield of a labeling ion which will attach to a precursor. In view of the needs of the art, the present invention is a device and a process that performs electrochemical phase transfer. Desirably, the present invention is a device and process for electrochemical phase transfer of 18F− from [18F]H218O to an aprotic solvent, and for preparation of the radionuclide for a PET tracer nucleophilic substitution labeling reaction. The present invention allows a synthesis process to be performed on a microfluidic device without requiring azeotropic drying. This is important as drying on a closed microfluidic chip can be challenging to implement since it requires 1) integration of solvent resistant, semi-permeable membranes and 2) re-solution of solid or semi-solid particles and material after azeotropic drying. This means that the invention results in a simplification of the microfluidic device, resulting in lower manufacturing cost to the chip producer due to the need to combine fewer different materials and/or processes. Furthermore, the invention enables all-liquid processing to be performed, reducing the need for radioactive gas handling capabilities in the surrounding instrumentation. This reduces the infrastructure burden on the customer and enables a simpler, and lower cost, instrument. The present invention describes the construction and operation of key components of a phase transfer method which may be used in conjunction with a microfluidic synthesizer for the production of single-patient dose PET and SPECT tracers. Moreover, the invention provides devices and processes for electrochemical phase transfer of 18F− from [18F]H218O to an aprotic solvent, and for preparation of the radionuclide for a PET (positron emission tomography) tracer nucleophilic substitution labeling reaction. The present invention provides the ability to dry the cell, to operate at low voltages, and to manufacture the cell using standard high-volume techniques such as injection molding. In one embodiment, the present invention described herein employs an injection moldable composite material as an electrode material for the extraction of 18F from water and transfer into a solvent. The composite material consists of a blend of a chemically compatible polymeric material such as Cyclic Oleofinic Copolymer (COC) and carbon particles, e.g. glassy carbon particles. The electrodes may be made using known molding techniques, including injection molding. It is contemplated that the electrode surface area may be selected for its carbon/polymer ratio as a means for ‘fine tuning’ the performance of the electrode, although the electrode desirably has a carbon content of at least 30%. Alternatively, the electrodes of the present invention my be formed by glassy carbon (GC). The electrodes of the present invention may then be incorporated into a microfluidic structure by known means, including by, but not limited to, multishot injection molding. As platinum electrodes are not required, and the same material may be used for both electrodes, manufacturability is eased and costs reduced. Particularly, when both electrodes are made using the same material, microintegration of the components and method are simplified. Obviating the need for noble metal electrodes by carbon or other suitable low-cost materials is possible through the present invention. The electrodes of the present invention are separated by a small gap through which a fluid may flow. The electrodes may thus desirably be spaced between 5 μm and 1000 μm apart. Additional sidewalls along the fluidpath may be formed by a gasket or separation layer which thus encloses the fluidpath between opposed inlet and outlet ports. The electrodes thus form a portion of the fluidpath. The fluidpath desirably has a ratio of radiolabeling reaction volume to trapping/desorption [active] electrode surface area to equal to or larger than 30 μl/mm2. Additionally, the methods of the present invention can avoid counter-trapping of the activity during release of the fluoride from the capture electrode, or at least reduce countertrapping to acceptable levels. In one embodiment, the release solvent and phase transfer catalyst can be selected so as to minimize the occurrence of counter-trapping by neutralizing the charge of the activity, thus allowing greater freedom in the selection of the electrode material. The present invention thus provides the ability to dry the phase transfer device between steps, to operate at low voltages while maintaining high electrical field strengths (>5V/mm) between the electrodes, and to manufacture the device using standard high-volume techniques such as injection molding. The capture and counter electrodes may be formed either in-plane within a device, or in a stacked configuration. The counter electrodes used may be non-metallic while both electrodes may be made of the same material, including glassy carbon or blends of glassy carbon and polymer. The devices and methods of the present invention thus allow successful electrochemical trapping, release and subsequent radio labeling on a chip Prior work in this field has not overcome the technical issues that prevent the device from performing phase transfer in an efficient and reproducible manner. The present invention thus provides both devices and processes for electrochemical phase transfer of 18F− from [18F]H218O to an aprotic solvent, and for preparation of the radionuclide for a PET tracer nucleophilic substitution labeling reaction. A first aspect of the present invention employs a carbon material capture electrode, e.g. glassy carbon (GC), graphite, carbon composites or a thin film deposited carbon species. In particular, GC sold under the brandname SIGRADUR® by HTW HochtemperaturWerkstoffe GmbH, Gemeindewald 41, 86672 Thierhaupten Germany (see http://www.htw-gmbh.de/technology.php5?lang=en&nav0=2) has been found suitable for the present invention. The use of graphite powder instead of GC is also contemplated by the present invention, although experiments have shown less 18F desorption yield when using graphite powder as compared to GC. The electrode of the present invention may be formed from an injection moldable composite material so as to enable the extraction of 18F from water and transfer into a solvent. The composite material consists of a blend of a chemically compatible polymeric material such as Cyclic Oleofinic Copolymer (COC) and carbon particles, e.g. glassy carbon particles. Examples of composite materials include GC-COC (Cyclic Olefin Copolymer), GC-PP (Polypropylene), and GC-PE (Polyethylene). A filler such as carbon fibres or carbon nanotubes can be added to reduce the volume fraction of GC while maintaining electrical conductivity, thus making the composite injection moldable. The electrodes may then be made using known molding techniques, including injection molding. It is contemplated that the electrode surface area may selected for its carbon/polymer ratio as a means for ‘fine tuning’ the performance of the electrode, although the electrode desirably has a carbon content of at least 30%. As the carbon/polymer blend electrodes are easy to manufacture using state of the art multishot injection molding techniques, it is therefore possible to monolithically integrate the phase transfer into a polymeric microfluidic synthesizer chip. With reference to FIGS. 1 and 2, the present invention further provides a electrochemical phase transfer device 10 employing a capture electrode 12 of the present invention. The device includes a pair of electrodes, 12 and 14, separated by a gasket 16. Electrode 12 and 14 are desirably separated between about 5 μm-1000 μm by gasket 16. To better assist drying, the capture electrode is desirably formed of a non-porous carbon structure or a low-porous structure such as glassy carbon (GC) or a GC-COC composite. Gasket 16 is formed from a suitable material, such as polytetraflouroethylene (PTFE). Gasket 16 may alternatively be formed from COC, or other suitable material, and bonded to electrodes 12 and 14 by known techniques so as to provide separation between the electrodes while defining the flow channel in a manner that may be easily manufactured by bonding the COC gasket to the electrodes. Electrode 12 includes a planar body 18 providing opposed major surfaces 20 and 22 and is bounded by perimetrical edge 24. Electrode 14 includes a planar body 36 providing opposed major surfaces 28 and 30 and is bounded by perimetrical edge 32. Gasket 16 includes a planar sheet body 34 and defines an elongate channel aperture 36. Channel aperture 36 desirably has a serpentine shape extending from a first end 38 to opposed second end 40. Second electrode body 18 defines an inlet port 42 and an outlet port 44, each port extending in open fluid communication between major surfaces 28 and 30. Gasket 16 is sandwiched between electrodes 12 and 14 so that first end 38 of channel aperture 36 is positioned in registry with inlet port 42 and second end 40 of channel aperture 36 is positioned in registry with outlet port 44. When assembled, device 10 forms a fluid flow channel 46 extending along channel aperture 36 in fluid communication between inlet port 42 and outlet port 44 and bounded between major surfaces 22 and 28. Referring now to FIGS. 3 and 4, electrochemical phase transfer device 10 may be incorporated into an electrochemical cell 50. Electrochemical cell 50 positions a copper plate 52 upon major surface 30 of electrode 14, and the copper plate/device assembly between a first and second opposed insulation layers 54 and 46, respectively. Second insulation layer 56 provides an inlet and outlet aperture 58 and 60, respectively, which are positioned in registry with inlet and outlet ports 42 and 44, respectively, of device 10. This entire sub-assembly is compressed between first and second plate 62 and 64. Second plate includes opposed first and second major faces 66 and 68 and defines inlet port 70 and outlet port 72 extending in open fluid communication between major faces 66 and 68. Inlet port 70 and outlet port 72 are positioned in fluid registry with inlet and outlet apertures 58 and 60, respectively, of second insulation layer 56. Second major face 68 accommodates first fitting 74 and second fitting 76 with inlet port 70 and outlet port 72, respectively. Fittings 74 and 76 enable easier connection to fluid conduits and other hardware used to drive fluid through electrochemical cell 50. Both plates 62 and 64 include elongate passages therein to accommodate positive positioning rods 78a-c about device 10. Plate 62 defines through apertures 80a-d therethrough to accommodate screws 82a-d therethrough. Major face 66 of plate 64 defines inwardly-threaded recesses 84a-d for threadingly mating to screws 82a-d. Each screw 82a-d is affixed to an elongate washer 84a-d, the outer surface of which supports a fixed washer 86a-d. A spring 88a-d is positioned with each screw so as to provide compressive force between its respective washer and plate 64 when the screw is tightened into its associated recess 84a-d. The present invention contemplates that electrode 14 of electrochemical phase transfer device 10 may also be formed from a carbon-based material. In one embodiment, counter electrode 14 may also be formed of a similar composition to the capture electrode 12, thus facilitating miniaturization and production. Miniaturization will overcome the current infrastructure burden associated with the synthesis of PET and SPECT tracers. It will allow that more hospitals can manufacture PET and SPECT tracers and thereby also purchase PET and SPECT scanners while at the same time offer a larger variety of tracers. The device described can be produced by low-cost manufacturing techniques to include two electrodes. The working electrode, capture electrode 12, can be of GC, a GC composite, or a non-porous nano-structured carbon material or its composite. The counter-electrode, electrode 14, can thus be of the same material, or alternatively the counter-electrode can be of a different material from the capture electrode, selected either from the same family of materials used for the capture electrode, or from a completely different family of materials. An example of a completely different family of materials is metals such as platinum. The electrodes are arranged in an opposing configuration where they can be parallel but need not be parallel. The present invention may be integrated into or combined with other microfluidic systems such as “Lab-on-Chip” systems, micro- or mesofluidic synthesis or analysis devices, micro Total Analytic System (μTAS) and conventional (large scale) synthesizer devices for production of radiopharmaceuticals. The present invention may be used as or combined with reactors, storage vessels, purification systems such as HPLC, MPLC, UHPLC, SEP-Pak® (sold by Waters GmbH, Helfmann-Park 10, 65760 Eschborn, Germany), subsequent drying units (evaporators), valves, mixers, channel structures, tubing, capillaries and capillary-based fluidic systems. FIGS. 5 and 6 depict a microfluidic chip 200 having a chip body 202 incorporating an electrochemical phase transfer device 210 of the present invention therein. Device 210 is similar in structure to device 10, desirably using an insert or multiple inserts formed of GC and/or a GC-COC composite for the electrodes 212 and 214. A gasket 216 (or any other separation device as taught by the present invention) is compressed between electrodes 212 and 214 such that a fluid passageway 218 is defined between electrodes 212 and 214. Electrode 214 defines a fluid inlet port 220 and a fluid outlet port 222 such that fluid passageway extends in fluid communication therebetween. Inlet port 220 and outlet port 222 are desirably placed in fluid communication with other features of chip 200, as defined by chip body 202, as may be useful in the synthesis process (such as reservoirs, reactors, feeding channels, etc.). Device 210 can be assembled and compressed into a leak-tight arrangement at the point of use, or can be permanently bonded during fabrication. The separation between the electrodes can be defined by the assembly/bonding process, or can be defined by a gasket arrangement as in device 10, or by a structure using stand-off features. Microchip 200 provides reactors for labeling and hydrolysis reactions, as well as chambers for reagent storage and valves (not shown). The electrodes as shown in and described for FIGS. 1, 5 and 6 are stacked out-of-plane (a sandwich structure) and substantially parallel. Alternatively, an in-plane (an extruded and/or machined-type structure relative to the plane of the device) arrangement is possible, as shown in and described for microchip 100 of FIG. 7. Microchip 100 incorporates an electrochemical phase transfer device 110 comprising first electrode 112 and second electrode 114. An elongate flowpath 118 is defined between opposed parallel undulating edges 113 and 115 of co-planar anode 112 and cathode 114, respectively. Alternatively still, as shown in and described for FIGS. 9 and 10, the cathode may be oriented with respect to one or more anodes so as to be in tapering, non-parallel alignment for defining the flowpath therebetween. With additional reference to FIG. 7, microchip 200 includes a lower planar body 102 and an upper planar body 104 between which electrodes 112 and 114 are positioned so that flowpath 118 extends in fluid-tight communication between inlet port 120 and outlet port 122. The present invention contemplates that electrodes 112 and 114 may be formed from an original electrode body which has been milled, cut, or otherwise machined along the path of flowpath 118 such that the resulting two portions of the original electrode body now form electrodes 112 and 114. Flowpath 118 is thus in the same plane as inlet port 120 and outlet port 122. As will be appreciated by those of skill in the art, microchip 100 may include additional molded portions. In the embodiment of FIG. 7, it is contemplated that electrodes 112 and 114 are formed flush with the mating surface 102a of body 102. Body 104 thus acts as a cover for the all of the fluid flowpaths and storage areas of chip 100. Chip 100 also includes reservoirs 150, reactors 155, and valves 160, defined between bodies 102 and 104, some of which may be in fluid communication with flowpath 118 of device 110. Planar body 104 defines various access ports which extend in fluid communication with various of the flow channels and fluidpaths of chip 100. For example, port 170 extends through body 104 so as to be in fluid communication with feeding channel 182 and inlet port 120. Body 104 also defines access ports 180 and 190 opening in registry with electrodes 112 and 114, respectively. Access ports 180 and 190 allow electrical connection to electrodes 112 and 114 through body 104. FIGS. 8-10 depicts flow between electrodes of the present invention, with representative performance graphs thereabove. In FIG. 8, the cathode 312 and anode 314 include elongate planar surfaces, 312a and 314a, respectively, which extend in parallel to one another and define an elongate flowpath 318 therebetween. Fluid 315 flows in the direction of Arrow A. As seen in FIG. 8, when a constant voltage is applied between cathode and anode, gas bubbles 325 will form in the fluid due to electrolysis which can then collect in the downstream portion of the flowpath. The gas bubbles 325 deleteriously affect the electric field in the fluid, so that the further along the fluidpath, the greater the collection of bubbles and the weaker the field strength. Additionally, the gas bubbles form obstacles which the fluid must flow past, resulting in an increase in bulk fluid velocity the farther down the flowpath the fluid 315 travels. The gas bubbles 325 may be compensated for by the geometric structure of device or increased system pressure that compresses bubbles and reduces impact on the electrochemical process. Gas bubbles may also be compensated by electric discharge elements, catalysts or gas permeable structures/membranes. FIG. 9 depicts flow between a pair of electrodes of the present invention in non-parallel alignment, with representative performance graphs thereabove. In FIG. 9, cathode 412 and anode 414 are placed in tapering, non-parallel alignment. Cathode 412 and anode 414 include opposed planar faces 412a and 414a, respectively, which define a tapering flowpath 418 therebetween. Fluid 415 flows in the direction of Arrow A. As flowpath 418 tapers outwardly with respect to the flow direction, gas bubbles 425 formed by electrolysis have more room to flow and will not as readlily bunch together as was the case in FIG. 8. However, the field strength will decrease as distance between cathode and anode grows. But as the gas bubbles are not as constricted within flowpath, the bulk velocity can remain near constant. FIG. 10 depicts yet another arrangement of electrodes of the present invention, with representative performance graphs thereabove. In FIG. 10, cathode 512 is opposed by multiple anodes 514, 524, 534, and 544. Anodes 514, 524, 534, and 544 are positioned adjacent one another so as to provide faces 514a, 524a, 534a, and 544a in substantially co-planar alignment. Cathode 512 provides face in opposition to faces so as to form flowpath therebetween. Similar to FIG. 9, flowpath 518 is thus formed between electrodes 512, 514, 524, 534, and 544 in tapering, non-parallel alignment, such that flowpath 518 gets wider in the direction of fluid travel. Fluid 515 travels in the direction of Arrow A. As shown in the accompanying performance graphs, anodes can each apply a stepped-up voltage along flowpath. The increased voltage in succeeding anodes helps maintain the electric field within the fluid while the bulk velocity is also maintained as described for FIG. 9. Gas bubbles 525 provide sufficient separation that the bulk velocity of fluid 515 therepast is maintained. It is desirable that the shape of the electrodes and the microfluidic channel facilitates drying (e.g., no dead-corners or gas-trapping pores), and facilitates the transport and removal of gas generated in the device by electrolysis. Gas bubbles can be pinned on single surfaces or between multiple surfaces. Gas bubbles shield the active trapping surface on the anode from target ions, and increase the local fluid velocity by reducing the effective cross-section area of the flow channel for fluids. Gas bubbles can be compressed and reduced in volume by increasing the pressure of the system. The pressure can be increased by various methods including flow-restrictions on the output of the flow-channel. A further feature of the device is the possibility to shape the electric fields by geometric variations in the electrode design or the electrode separation, to control the inter-play between the drift velocity of ions in the bulk, outside of the electrical double layer, and the bulk velocity of the fluid. This is shown in FIGS. 8-10, where different configurations are illustrated side by side. In general, it has been found that the fluid flow passages, or flowpaths, of the continuous flow structures of the present invention should be long, rather than wide. The electrodes may be parallel or non-parallel, and employ a uniform electric field or employ a field gradient along the flowpath. The electrodes of the present invention desirably provide a surface area exposed to the flowpaths of 0.5 mm2-1000 mm2, depending on the fluid volumes. The electrodes of the present invention are separated by a small gap through which a fluid may flow. The electrodes may thus desirably be spaced between 5 μm and 1000 μm apart. Additional sidewalls along the fluidpath may be formed by a gasket or separation layer which thus encloses the fluidpath between opposed inlet and outlet ports. The electrodes thus form a portion of the fluidpath. The fluidpath desirably has a ratio of radiolabeling reaction volume to trapping/desorption [active] electrode surface area to equal to or larger than 30 μl/mm2. Desirably, the present invention employs low voltages at the electrodes while maintaining high fields (eg, by using small separations between the electrodes along the flowpath). Additionally, the electrodes of the present invention may be realized by mechanically pressed on or in a flow device. GC may be sputtered into an electrode body of the present invention. The electrodes of the present invention may be formed from composite materials be screen printed into shape, formed by injection molding (including in two- or multi-shot molding). The components may be ultrasonically welded or bonded, thermally bonded, or bonded using solvents. The gap or separation between the electrodes may be formed by placing a gasket or spacer between the electrodes or employing thick film techniques. Additionally, a single electrode body may be machined, etched, imprinted, or milled to separate the body into two electrode bodies which may be separated across the gap and serve as a cathode and anode of the present invention. Sacrificial materials may be positioned between the electrodes and then removed (eg, by burning). Alternatively, as described hereinabove, gasket 16 may be provided in the form of an insert that can be assembled into the substrate during manufacture and sealed by joining techniques or by pressure on a sealing feature. Joining techniques include polymer-polymer bonds such as welding, high temperature bonding, solvent bonds and over molding, or GC to polymer bonds such as O2 plasma surface activation or surface sputtering for cleaning, followed by pressure and heat. Pressure sealing alone refers to configurations where a high pressure is applied to a sealing surface, such that a fluid tight seal is created without bonding. The pressure can be applied externally at the point of use, or can be generated on the device by stressing materials during fabrication. In the general stacked or out-of-plane configuration, the sandwich of materials can be assembled using gasket layers such as PTFE gaskets, and sealed at the point of use using external pressure. Alternatively the stack can be bonded together, where gasket 16 is replaced by thin or thick film coatings of suitable materials such as COC. In operation, as target ions flow through flow channel or fluid path of the present invention during the adsorption process, they are pulled to the exposed major surface of the anode. In this way the length of the anode, or the fluid channel, is related to the trapping efficiency, where a longer anode is useful to trap more ions and thus increase the trapping efficiency, for a given electric field strength. However, side-effects during adsorption and desorption lead to reduced yields for the subsequent radiolabeling process. To improve the labelling process it can be advantageous to reduce the total anode surface area. In order to satisfy the requirement of a reduced electrode surface area while maintaining a sufficient adsorption efficiency, the width of the channel can be reduced while keeping the length as desired. Working with 10V trapping potential and 127 μm electrode separation, trapping lengths in the range of 10 mm-100 mm give good results, with 15 mm resulting in 75% trapping and 55 mm resulting in 85-90% trapping efficiency. Starting water volumes of 500 μl-1000 μl have been utilised with an anode surface area of 7 mm2 to 140 mm2, and a width to length ratio of between 1:30 and 1:5. Under certain conditions it is preferred to have the maximum length to width ratio, in order to increase the length with the minimum overall surface area. The device materials and structure are selected such that the drying process (elimination of water) and the cleaning process (elimination of unwanted species for labeling) is reproducible and can achieve water concentrations less than a target value e.g. 1500 ppm for NITTP/FMISO. Furthermore the protocol for using the device must maintain critical parameters such as the phase transfer catalyst (PTC) concentration. The addition of the PTC during the desorption process is also shown to influence the radiolabelling process. An increase in the PTC concentration by a factor of 4 over the conventional value (e.g. 16 mg/ml K222 at 3.5% K2CO3(aq) is superior to 4 mg/ml K222 at 3.5% K2CO3) is shown to give improvements to the subsequent labelling process. It has been confirmed through experimentation that counter trapping can be minimized so as not to play a significant role, e.g., less than 4% reabsorption/readsorption was observed. The reason for this phenomenon lies in the formation of neutral pairs within the solvent solution during the release process. Because of the aprotic character of the solvent into which the ions are released, the 18F fluoride anions bind themself to a cation, often provided in the solution. Upon formation of this ion pair, there is no net-charge that would cause the fluoride ions to migrate in an electric field to the counter electrode. Only diffusion could provide that transport. Additionally, the potentials applied by the present invention during the release of the radionucleids are not high enough to provide an efficient reabsorption/re-adsorption on the counter electrode. Therefore, the low potentials applied and the solvent employed can result in a low reabsorption/re-adsorption of the fluoride. Our experiments have shown that the application of a complexation agent, e.g. Kryptofix K222, used as a phase transfer catalyst in the labeling step, prevents the adsorption on the cathode by forming an ion pair, that is electrically neutral towards the outside. Electrophoretic transport towards the counter electrode and consequent readsorption is suppressed. However, in some embodiments the suppression of counter-trapping by additives such as K222 maybe supported by a release potential that is alternated during the release process. That is, the potentials on the two electrodes are reversed multiple times during the release process so as to thwart counter-trapping. This method leads to a release of the counter-trapped ions in each voltage cycle, thus increasing the overall release efficiency. Therefore one can use a carbon electrode as the counter electrode. This electrode can be made from the same material as the trapping electrode therefore simplifying manufacturing and omitting the use of noble metals. In order to further save cost, a cheap graphite based material can be employed for one or both electrodes. The application of the complexation agent allows to use of any electrode material for the counter electrode, that can withstand the chemical environment it is used in. Others may claim other materials than carbon based materials, such as conductive polymers or other metals. Phase transfer is performed by applying a trapping voltage between 0.8V and 50V while pumping [18F]H218O through the device at flow rates between 0 μl/min and 1000 μl/min. Operating at the lower end of the voltage range minimizes undesirable REDOX reactions. The trapping voltage can be pulsed or alternated in polarity to reduce nucleation of gas generated by electrolysis and to increase efficiency. After trapping, the device is dried and cleaned by any or all of the following techniques: heating at temperatures up to 170° C. under dry N2 or Argon flow, heat to 90° C. while pumping dry Acetonitrile through the device, pump Kryptofix 222+DMSO through the cell at temperatures between room temperature and 90° C. The cell is dried until the residual water in the eluent is below a target value, e.g. 1500 ppm for FMISO labeling using NITTP as the precursor. Side-effects that are disadvantegeous for radiolabeling are also connected to the heating profile utilized during the release process. Hence, the electrochemical phase transfer needs to be heated gradually between 60° C. and up to 120° C. (depending on the solvent that the ions are released into and the sensitivity of the pre-cursor labeling process to species resulting from electrochemical phase transfer side-effects) during the desorption process, leading to a controlled release of 18-fluoride over time. A temperature profile can apply temperature gradients in the range of 1° C./min up to 60° C./min are useful, and good results have been demonstrated with gradients around 3° C./min-8° C./min. The trapped 18F− may thus released from the electrode surface by heating the cell to temperatures between room temperature and 120° C., while applying an electrical potential in the range of 0.1-10V, of the opposite polarity as during trapping. To minimize counter trapping on the counter-electrode during release and/or increase the release efficiency, the release potential can be continuous, pulsed, or sequentially reversed. The release liquid is an aprotic solvent and a phase transfer catalyst, such as Kryptofix 222 with a potassium counter-ion. The K+/k222 concentration desirably exceeds the sum of 18F− and all other anions' concentration to minimize 18F absorption on counter electrode. It is also possible to release directly into the precursor. The feasibility of the methods has experimentally been proven. Trapping of fluoride on the counter electrode accounted for only about 4% of the total activity. During the release process the phase transfer solvent can flow continuously through the structure or the flow can be stopped. While the particular embodiment of the present invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the teachings of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. For example, the fluid paths formed by the electrodes of the present invention go by different names: passageways, flowpaths, fluid paths, etc., but each connote the same meaning of a fluid tight flow channel (achieved with or without other structures) that extend between opposed inlet and outlet ports. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art. |
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044514280 | claims | 1. A method of producing a control rod comprising the steps of: producing by a zone melting process a second neutron absorbing material causing an (n, .UPSILON.) reaction to take place by continuously reducing the ratio of a material of large neutron absorption cross section to a material of small neutron absorption cross section in going from at least a predetermined position along a major portion of said second neutron absorbing material toward one end thereof; and arranging said second neutron absorbing material in an end portion of the control rod at which the control rod is inserted in a reactor core, said second neutron absorbing material being located nearer to said inserting end of the control rod than a plurality of poison tubes having a charge of a first neutron absorbing material causing an (n, .alpha.) reaction to take place filled therein and sealed, said second neutron absorbing material extending in the insertion direction of the control rod and having a volume which exhibits substantially no decrease along the extent of said second neutron absorbing material in the insertion direction and said first and second neutron absorbing materials have substantially the same neutron absorbing capacity in an area between the poison tubes and the second neutron absorbing material. 2. A method according to claim 1, wherein said second neutron absorbing material is in the form of neutron absorbing plates extending in the insertion direction of the control rod. 3. A method according to claim 2, wherein the step of arranging includes arranging said neutron absorbing plates to contact an end portion of at least a portion of said plurality of poison tubes with said neutron absorbing plates extending forwardly therefrom, said neutron absorbing plates and said poison tubes having substantially the same absorption cross section in the region of contact therebetween. 4. A method according to claim 1, wherein said second neutron absorbing material is an all solid solution type alloy. 5. A control rod for a nuclear reactor comprising an absorber rod means extending in the direction of insertion of the control rod in a reactor core, said absorber rod means being charged with a material having a large neutron absorption cross section for causing an (n, .alpha.) reaction to take place upon absorbing neutrons, and neutron absorbing plates extending in the insertion direction of the control rod and being arranged at a forward end portion of the control rod, said neutron absorbing plates being formed of an alloy of a material of a large neutron absorption cross section and a material of a small neutron absorption cross section for causing an (n, .UPSILON.) reaction to take place upon absorbing neutrons, the mixing ratio of said material of small neutron absorption cross section to said material of large neutron absorption cross section in said alloy being continuously varied in the insertion direction from at least a predetermined position along the extent of a major portion of said neutron absorbing plates and becoming increasingly higher toward the forward end of the control rod, said neutron absorbing plates having a volume which exhibits substantially no decrease along the extent of said neutron absorbing plates in the insertion direction and said material charged in said absorber rod means and said material of said neutron absorbing plate have substantially the same neutron absorbing capacity in an area between the absorber rod means and the neutron absorbing plate. 6. A control rod according to claim 5, wherein said neutron absorbing plates contact an end portion of at least a portion of said absorber rod means and extend forwardly therefrom, said neutron absorbing plates and said absorber rod means having substantially the same absorption cross section in the region of contact therebetween. 7. A control rod according to claim 5 or 6, wherein the material with which said absorber rod means is charged is boron carbide and the alloy forming said neutron absorbing plates is an Hf-Zr alloy. 8. A control rod according to claim 7, wherein said absorber rod means comprises a plurality of poison tubes. 9. A control rod according to claim 5, wherein the variation in the mixing ratio of the materials of said alloy forming said neutron absorbing plates is obtained by a zone melting process. 10. A control rod according to claim 9, wherein said alloy forming said neutron absorbing plates is an all solid solution type alloy of an Hf-Zr alloy. 11. A method according to claim 1, wherein the ratio is continuously reduced in a linear manner. 12. A method according to claim 1, wherein the volume of said second neutron absorbing material is substantially constant along the extent thereof. 13. A method according to claim 1, wherein the volume of said second neutron absorbing material increases along the extent thereof in the insertion direction. 14. An apparatus according to claim 5, wherein the mixing ratio continuously varies in a linear manner. 15. A control rod according to claim 5, wherein the volume of said neutron absorbing plates is substantially constant along the extent thereof. 16. A control rod according to claim 5, wherein the volume of said neutron absorbing plates increases along the extent thereof in the insertion direction. |
abstract | Materials and methods of synthesizing mixed-layered bismuth oxy-iodine materials, which can be synthesized in the presence of aqueous radioactive iodine species found in caustic solutions (e.g. NaOH or KOH). This technology provides a one-step process for both iodine sequestration and storage from nuclear fuel cycles. It results in materials that will be durable for repository conditions much like those found in Waste Isolation Pilot Plant (WIPP) and estimated for Yucca Mountain (YMP). By controlled reactant concentrations, optimized compositions of these mixed-layered bismuth oxy-iodine inorganic materials are produced that have both a high iodine weight percentage and a low solubility in groundwater environments. |
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048636380 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention provides a process for the containment of hazardous waste materials such as radiation solids, toxic soils and asbestos wastes or solids and other similar hazardous wastes. The hazardous waste material 10 is initially encased into a plurality of containment vessels 12 which preferably may be in the form of generally cylindrical drums or barrels 14. Drums 14 are preferably of a metal configuration to facilitate retainment of the hazardous waste therein. Lead lining 34 may be applied about the inside of the drum 14 or about the exterior of drum 14 to minimize radiation from low level radioactive wastes. To facilitate knowledge as to the specific type of waste within a particular containment vessel a coding means 16 may be applied to the exterior of the individual containment vessels. Preferably this coding means can be a color coding means, or can be any other coding means such as alphabetic or numeric or symbolic characters. The containment vessels 12 are organized into a grouping 18 thereof which may be anywhere from two to eight such vessels. This grouping 18 is then secured with respect to one another by a securement means such as a steel banding to facilitate retainment of the individual containment vessels with respect to one another. This steel banding means 26 extend in any direction as long as the individual containment vessels 12 are fixedly secured with respect to one another. The banded grouping 18 of containment vessel 12 is then entombed within a plastic casing 20. This entombment is performed by a molding operation which preferably is steam heated but can be formed by any convenient means in order to provide preferably a seamless clear plastic casing completely entombing the grouping 18 of containment vessel 12. To facilitate handling of the plastic casing 20 a handling means 22 may be secured to the plastic casing 20 or to the waste material itself. Handling means 22 can be secured to the lower surface 28. This handling means 22 may take the form of a pallet 24 or any other convenient type handling means. To facilitate stability of placement of the entombed grouping 18 of containment vessel 12 a plurality of casing support means 30 may be secured to the lower surface 28 of plastic casing 20. This support means may take the form of a plurality of cylindrical legs 32 which are preferably approximately eight inches in height and hollow thereby providing an extremely stable means of mounting upon any type of floor area and specifically with respect to the under ocean floor area. As shown best in FIG. 2 and in the bottom view shown in FIG. 3 the cylindrical legs 32 can provide overall stability by placement of one each adjacent each corner of the bottom surface 28 of transparent plastic casing 20. The finally entombed grouping of containment vessels 12 can be placed in any convenient location for storage without fear of any leakage or leaching of the hazardous waste 10 outwardly into the surrounding environment. This is made possible by the combination of the seamless transparent plastic casing 20 and the steel banded and possibly lead lined containment vessels 12 or drums 14. This combination of sealing means will prevent leakage or leaching of hazardous waste 10. The configuration shown in FIG. 4 is particularly usable for landfill waste wherein such waste can be compressed into modules 36 which can be cubical or of other shapes. A plurality of such compressed modules 36 can be banded together utilizing the banding means 26. These modules can then be entombed within a seamless transparent plastic coating in a similar manner to the process described above for encasing drums 14. The plastic transparent casing 20 will provide easy identification and seamless sealing of the hazardous landfill waste with respect to the surrounding environment. While particular embodiments of this invention have been shown in the drawings and described above, it will be apparent, that many changes may be made in the form, arrangement and positioning of the various elements of the combination. In consideration thereof it should be understood that preferred embodiments of this invention disclosed herein are intended to be illustrative only and not intended to limit the scope of the invention. |
abstract | A vacuum assembled along a centerline axis used to collect fissile material. The vacuum includes a housing having internal chamber, a top end having a top opening, a bottom end having a bottom opening, and a radial intake port opening. The vacuum includes a suction apparatus having an intake disposed at the intake opening and having a hose connection means for mating with a vacuum hose assembly. The suction apparatus also includes a flow-through fan disposed in the top opening. The fan intakes and exhausts the airflow in a direction parallel with the centerline axis. The suction apparatus also includes a container connection means disposed at the bottom opening for connecting an external container to bottom end of the housing. There is also provided a first cylindrical free space having a center point disposed along the centerline axis and a diameter passing through the center point. The diameter of the first cylindrical free space is less than or equal to the safe diameter for the fissile material of interest. The vacuum cleaner apparatus is sized to fit entirely within the diameter of the first free space. Therefore, the vacuum apparatus constitutes a single fissile unit that is safe by passive geometry control to prevent the potential for a nuclear criticality in the vacuum. |
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039309410 | abstract | The outer surface of a cladding tube of a nuclear fuel element is -- for the purpose of improving the heat exchange between the cladding tube and a surrounding coolant -- provided with a plurality of parallel fin rows extending normal to the cladding tube axis. Each row is constituted by a plurality of spaced, individual fins; the fins of any one row are offset with respect to the fins of an immediately adjacent row. |
039322165 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS For a more complete appreciation of the invention, attention is invited to FIG. 1, which shows a typical grid structure 10. The grid 10 is formed from a group of equidistantly spaced parallel grid members or plates. In the plane of the drawing, however, only a grid plate 11 is shown. Almost identical plates 12, 13, 14, and 15 are arranged perpendicularly to the plane of the plate 11. All of the plates in the grid structure 10 have mutually engaging slits (not shown in FIG. 1) that enable the interlocking members to mesh with each other and thus form an array of cells. Detents or stops 16 and 17 are provided in the longitudinal edges of the plates. These detents engage the adjacent surfaces of the individual fuel rods that are lodged within the cells, as illustrated by the portion of a fuel rod 18 that is shown in broken lines. Detents or stops 19 also are formed in the middle portion of some of the grid plates. These detent-bearing middle portions, moreover, in at least one embodiment of the invention are warped or bowed slightly to add to the depth to which each of these stops protrude in toward the center of a respective cell. The plates 11 through 15 are joined at the intersections by spot welding, brazing, or the like in order to produce a sturdy rigid structure. In accordance with the invention, the corners of the grid plate 11 and the plates 12 through 15 are beveled by chamfering, stamping, grinding or the like to provide sloping surfaces 20, 21, 22, and 23. The length of the inclination that characterizes these surfaces should extend at least from the outermost edge of the fuel rod 18 to a band 25 that circumscribes the perimeter of the grid structure 10. As described subsequently in more complete detail, the sloping surfaces 20, 21, 22, and 23 act as cams or inclined planes that aid the relative movement of two adjacent grids. The band 25 that encircles the grid structure 10 has stops or detents, of which detent 24 is typical, that help to retain the outer or peripheral ranks of fuel rods, exemplified by the fuel rod 18, in the grid structure. The band 25, joined to the terminal edges of the grid plates, also tends to enhance the physical integrity of the grid structure 10. As shown in the drawing, the band 25 is not as wide as the maximum width of the plates 11 and 12 through 25. The sloping surfaces 20 through 23 thus form transition sections that match the greater width of the grid plates to the lesser width of the band 25. Because in plan view (not shown), the illustrative embodiment of the grid 10 is generally rectangular, the band 25 forms right angle corners. Further in accordance with the invention, the corner edges are finished by means of sloping portions 26 that meet at a corner crease 27. As shown in FIG. 2, these sloping portions 26 meet to provide generally vee shaped edges 30 and 31, which also function as cams or inclined planes. Generally, the beveled, vee-shaped edges 30 and 31 prevent the corners of adjacent fuel element grid structures from locking together during reactor core assembly or refueling. In operation, a typical fuel element 32 shown in FIG. 3 is moved in the direction of an arrow 37. Adjacent fuel element 33 is stationary within the reactor core (not shown). The outer surface of a band 34 on the grid structure for the fuel element 32 is in sliding engagement with a side of the fuel rod 35 that is lodged in the fuel element 33. The fuel rod 35 tends to guide the band 34 into physical contact with a corresponding portion of band 42 on the fuel element 33. Sloping surfaces 40 and 40A that characterize the plates which form the grid structure engage the adjacent portions of the opposite grid. The sloping character of the surfaces 40 and 40A respond to the movement of the fuel element 32 in the direction of the arrow 37 by forcing the element to shift away from the fuel rod 35, in the direction shown by an arrow 44. Thus, the sloping surfaces 40 and 40A act as cams or inclined planes that ease the fuel element 32 into proper relative alignment in which the bands 34 and 42 abut. Although not shown in the drawing, in a similar manner, a vee shaped edge 45, formed at the corner of the band 34, guides the fuel element 32 past the fuel element 33, because the edge 45 prevents corner edges of the grids from becoming temporarily engaged or locked together. An additional feature of the invention resides in the physical structure of the individual grid plates. Turning to FIG. 4 of the drawing, for instance, a generally planar grid plate 46 has parallel longitudinal edges 47 and 50. The edge 50, moreover, is interrupted at regular intervals by slits 51 that terminate in paddle shaped cut-outs 52, which are formed in the mid-portion of the plate 46. As described in more complete detail in F. S. Jabsen U.S. patent application Ser. No. 774,148, filed Nov. 7, 1968, now U.S. Pat. No. 3,665,586; Ser. No. 105,388, filed Jan. 11, 1971; and Ser. No. 193,383, filed Oct. 28, 1971, now U.S. Pat. No. 3,795,040, all assigned to the assignee of the instant invention, the slits 51 enable the grid plate 46 to mesh with other grid plates (not shown in FIG. 4) that are perpendicularly oriented relative to the plane of the drawing. This meshed arrangement establishes the desired cellular structure. Also as described in the foregoing applications for patent, keys (not shown) are inserted into the cellular structure in order to force protruding detents away from the center of the respective cells. This temporary deflection provides a sufficient clearance for fuel rods (not shown in FIG. 4) to pass through the cell structure without being scored, abraded, or gouged by the stops of which detents 53 are typical. After the fuel rods have been lodged within the respective cells, the keys are withdrawn from the cell structure and the detents 53 engage the rod surfaces. As shown in FIG. 4, the detents 53 are formed in bent or warped portions 54 of the plate 46. This is a characteristic of the embodiment shown in the drawing that is not essential, however, to the practice of the invention. The detents 53, for example, can be provided on a flat surface that has not been warped. The detents, moreover, in the mid-portions of at least some of the plates can be omitted, as shown in connection with the plate 14 in FIG. 1 of the drawing. The plate 46 terminates in two parallel transverse edges 55 and 56. In accordance with a feature of the invention, the longitudinal edges 47 and 50 are joined to the adjacent segments of the transverse edges by means of sloping surfaces 57, 60, 61, and 62. These sloping surfaces form obtuse angles with the respective adjacent transverse and longitudinal edges. The relationship between these surfaces and edges provides the inclined planes or cam surfaces that facilitate reactor core assembly and disassembly in the manner that was described in connection with FIG. 3. Considered from another viewpoint, the longitudinal distance that the sloping surfaces 57 and 60 can extend away from the adjacent transverse edge should be about equal to the distance to which the detents protrude into the cell structure (not shown in FIG. 4). This distance is typified by the height to which the detents 53 extend above the warped portions 54 of the plate 46. With this generalization as a guide, there is an assurance that no sharp angles or edges on the plate 46 will protrude beyond the outer rank of fuel rods in a given fuel element. Accordingly, the invention is a simple and efficient technique that enables the nuclear reactor cores to be assembled, rearranged and disassembled without incurring the penalties that have characterized the prior art. |
description | This application claims priority to Taiwanese Application Serial Number 108116969 filed May 16, 2019, which is herein incorporated by reference. The present disclosure relates to heat dissipation structures and neutron beam generating devices using these heat dissipation structures. To be specific, the principle of Boron Neutron Capture Therapy (BNCT) is as follows: boron-containing medicines are combined with tumor cells via blood circulation. A neutron beam is then used to irradiate the location of the tumor tissue as a center. Lithium and helium ions are then produced after boron absorbs the neutrons, which accurately destroy cancer cells without destroying other normal tissues. For patients, boron neutron capture therapy causes only minimal damage and does not require surgery and anesthesia. Furthermore, in the treatment of brain tumors, if boron neutron capture therapy uses thermal neutrons with lower penetrating ability, the cranium of the patient has to be opened additionally. In contrast, if boron neutron capture therapy uses epithermal neutrons, the cranium of the patient is not required to be opened. In this regard, the way of generating a neutron beam can be using a neutron beam generator of accelerator-type to bombard on a target with the ionic beam. However, in the process of generating a neutron beam, the target bombarded by the ionic beam may be unexpectedly damaged due to poor heat dissipation. Therefore, how to effectively solve the heat dissipation of the target in the process of generating neutron beams has become one of the directions in the research and development in the related fields. According to an embodiment of the present disclosure, a heat dissipation structure includes a housing. The housing has a bottom surface, a liquid inlet channel, a liquid outlet channel and a protruding portion. The liquid inlet channel and the liquid outlet channel are located at two opposite ends of the housing and above the bottom surface. The liquid inlet channel and the liquid outlet channel extend along a first direction. The protruding portion is located between the liquid inlet channel and the liquid outlet channel and above the bottom surface. The protruding portion protrudes towards a direction away from the bottom surface. The protruding portion has a protruding surface facing away from the bottom surface. A distance between the protruding surface and the bottom surface is increased first and then decreased along the first direction. In one or more embodiments of the present disclosure, the protruding surface is a convex surface. In one or more embodiments of the present disclosure, the protruding surface has a symmetric line extending along the first direction, and the protruding surface is symmetric relative to the symmetric line. In one or more embodiments of the present disclosure, the distance between the protruding surface and the bottom surface is substantially the same along a second direction, and the second direction is perpendicular to the first direction. In one or more embodiments of the present disclosure, the housing has a first opening, and the protruding portion extends and enters into the first opening. In one or more embodiments of the present disclosure, the housing has a second opening. The second opening communicates with the first opening and is farther away from the protruding portion than the first opening. A dimension of the second opening is larger than a dimension of the first opening. In one or more embodiments of the present disclosure, the housing has a pair of buffering grooves. The buffering grooves are respectively located at two opposite ends of the protruding portion and located between the liquid inlet channel and the liquid outlet channel. In one or more embodiments of the present disclosure, a highest position of the protruding surface is higher than a highest position of the liquid inlet channel and the liquid outlet channel. In one or more embodiments of the present disclosure, a lowest position of the protruding surface is higher than a highest position of the liquid inlet channel and the liquid outlet channel. According to an embodiment of the present disclosure, a neutron beam generating device includes a heat dissipation structure as described above, a tubular body and an accelerator. The tubular body is disposed on the heat dissipation structure and has a channel. The accelerator is connected with the tubular body and is configured to emit an ionic beam towards a target disposed between the heat dissipation structure and the tubular body through the channel. With regard to the configurations as described above, since the distance between the protruding surface of the protruding portion and the target disposed in the housing changes along the first direction, the flowing speed of the cooling fluid flowing through the protruding surface also changes. Therefore, the cooling fluid has a faster flowing speed with respect to the center of the target, leading to a better cooling effect at the center of the target. Through this mechanism, the heat dissipation structure is suitable to be applied in the neutron beam generating device. Drawings will be used below to disclose embodiments of the present disclosure. For the sake of clear illustration, many practical details will be explained together in the description below. However, it is appreciated that the practical details should not be used to limit the claimed scope. In other words, in some embodiments of the present disclosure, the practical details are not essential. Moreover, for the sake of drawing simplification, some customary structures and elements in the drawings will be schematically shown in a simplified way. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. The heat dissipation structure of the present disclosure can control the flowing speed of the cooling fluid though the structural topography. Since the flowing speed of the cooling fluid and its cooling effect are related, different cooling effects can be provided according to different regions of the object to be cooled down (such as a target). Reference is made to FIGS. 1-2. FIG. 1 is a top view of a heat dissipation structure 100 according to some embodiments of the present disclosure. FIG. 2 is a cross-sectional view along the section line 2-2′ of FIG. 1. In order to prevent FIG. 1 from being over-complicated, the target 130 of FIG. 1 is not drawn with hatching lines as shown in FIG. 2. In addition, for the sake of convenient illustration, a first direction D1 and a second direction D2 are drawn in FIG. 1 and FIG. 2, in which the first direction D1 is different from the second direction D2. For example, the first direction D1 can be a transverse direction of FIG. 1, and the second direction D2 can be a longitudinal direction of FIG. 1, while the first direction D1 is perpendicular with the second direction D2. The heat dissipation structure 100 includes a housing 110, in which the material of the housing 110 can be metal, such as aluminum. The housing 110 can be integrally formed and can also be formed from assembly. The housing 110 has a protruding portion 112, a bottom surface 114, a first opening 122, a second opening 124, a liquid inlet channel 140 and a liquid outlet channel 150, in which the bottom surface 114 can be regarded as the bottommost surface of the housing 110. The first opening 122 and the second opening 124 are communicated with each other and are both located above the bottom surface 114. The second opening 124 is farther away from the bottom surface 114 than the first opening 122. The housing 110 can be used to carry a target 130, in which the target 130 can be of a plate-shaped target. A dimension of the second opening 124 can be larger than a dimension of the first opening 122. Through this difference in dimensions, the positioning of the target 130 can be facilitated. In this regard, the dimension as mentioned above can be the length or the width. Taking FIG. 2 as an example, the width of the second opening 124 is larger than the width of the first opening 122. Moreover, since the housing 110 has the first opening 122, after the target 130 is disposed on the housing 110, the target 130 and the housing 110 can together form an accommodation space S therebetween. The liquid inlet channel 140 and the liquid outlet channel 150 are located at two opposite ends of the housing 110 and also located above the bottom surface 114. The liquid inlet channel 140 and the liquid outlet channel 150 can extend along the same direction, such as the first direction D1, and respectively connect with the accommodation space S. In some embodiments, a pressure device (not shown) can be used to deliver a cooling fluid 160 from the liquid inlet channel 140 to the inside of the heat dissipation structure 100, as shown by the arrow A1, such that cooling fluid 160 can flow through the accommodation space S and contact with the target 130, providing a cooling effect to the target 130. Afterwards, the cooling fluid 160 can leave from the heat dissipation structure 100 through the liquid outlet channel 150, as shown by the arrow A2. The protruding portion 112 is located between the liquid inlet channel 140 and the liquid outlet channel 150, and is also located above the bottom surface 114. The protruding portion 112 protrudes towards a direction away from the bottom surface 114. The protruding portion 112 extends by protruding and enters into the first opening 122. The second opening 124 is farther away from the protruding portion 112 than the first opening 122. The protruding portion 112 has a protruding surface 116 facing away from the bottom surface 114. In other words, the protruding surface 116 faces to the first opening 122 and the second opening 124. A distance between the protruding surface 116 and the bottom surface 114 is increased first and then decreased along the first direction D1. For example, the protruding surface 116 is a convex surface, such that the distance between the protruding surface 116 and the bottom surface 114 is increased first and then decreased along the first direction D1. Through the design of the distance between the protruding surface 116 and the bottom surface 114 to be increased first and then decreased, after the target 130 is disposed on the housing 110, the distance between the target 130 and the protruding surface 116 of the housing 110 is decreased first and then increased. Through this configuration, when the cooling fluid 160 flows through the protruding surface 116 in a direction from the liquid inlet channel 140 to the liquid outlet channel 150, the flowing speed of the cooling fluid 160 changes with the change of the distance between the target 130 and the protruding surface 116 of the housing 110. To be specific, with regard to the cooling fluid 160 flowing through the former half region R1 of the protruding surface 116 in the direction from the liquid inlet channel 140 to the liquid outlet channel 150, since the distance between the target 130 and the protruding surface 116 of the housing 110 is gradually decreased, the flowing speed of the cooling fluid 160 is gradually increased. In this regard, since the flowing speed of the cooling fluid 160 is directly proportional to the cooling effect the cooling fluid 160 can provide, the increase in the cooling speed of the cooling fluid 160 can increase the cooling effect. In other words, within the former half region R1 of the protruding surface 116, the cooling effect provided by the cooling fluid 160 gradually increases with the protruding terrain of the protruding surface 116. Subsequently, with regard to the cooling fluid 160 flowing through the latter half region R2 of the protruding surface 116 in the direction from the liquid inlet channel 140 to the liquid outlet channel 150, the distance between the target 130 and the protruding surface 116 of the housing 110 is gradually increased such that the flowing speed of the cooling fluid 160 is gradually decreased. Since the flowing speed of the cooling fluid 160 is decreased, the pressure exerting on the center of the target 130 by the cooling fluid 160 is decreased, such that the stress produced on the target 130 is decreased. In other words, the heat dissipation structure 100 makes the cooling fluid 160 have a faster flowing speed with respect to the center of the target 130, and leads to a better cooling effect at the center of the target 130 by the cooling fluid 160. It also means that the cooling effect provided by the cooling fluid 160 to the target 130 is decreased gradually from the highest position of the protruding surface 116 to the liquid inlet channel 140/the liquid outlet channel 150. Through this mechanism, the heat dissipation structure 100 is suitable to carry out heat dissipation to the target 130 with heat distribution in the pattern of “gradual decrease to the two sides from the center”, in which “gradual decrease to the two sides from the center” can be, for example, of Gaussian distribution, normal distribution or bell-shaped distribution. On the contrary, if the distance between the protruding surface 116 and the bottom surface 114 is not structurally designed to be first increased and then decreased, i.e., under the condition that the gap of the channel of the cooling fluid is constant, the flowing speed of the cooling fluid from the liquid inlet channel to the liquid outlet channel is constant. Moreover, when the overall flow rate remains unchanged, the smaller the width of the constant gap, the faster the flowing speed will be, causing a larger pressure gradient. Thus, the structure with a constant gap of the channel is not suitable to carry out heat dissipation to the target with heat distribution in the pattern of “gradual decrease to the two sides from the center”. On the other hand, the magnitude of the gradual increase and the magnitude of the gradual decrease of the protruding surface 116 can be designed to be the same or different, in order to facilitate the control of the flowing direction of the cooling fluid 160. To be specific, the magnitude of the gradual increase and the magnitude of the gradual decrease of the protruding surface 116 can be equal. Under such condition, the protruding surface 116 has a first symmetric line L1 (as shown in FIG. 1) extending along the second direction D2, and the protruding surface 116 is symmetric relative to the first symmetric line L1. However, this does not intend to limit the present disclosure. In other embodiments, the magnitude of the gradual increase and the magnitude of the gradual decrease of the protruding surface 116 are different from each other. For example, a distance between the an end of the protruding surface 116 close to the liquid inlet channel 140 and the bottom surface 114 can be larger than a distance between the an end of the protruding surface 116 close to the liquid outlet channel 150 and the bottom surface 114, such that the magnitude of the gradual increase of the protruding surface 116 is less than the magnitude of the gradual decrease. The protruding surface 116 can also be designed to have a protruding change in only the first direction D1, in order to facilitate the control of the flowing direction of the cooling fluid 160. For example, the accelerating effect of the cooling fluid 160 in the direction from the liquid inlet channel 140 to the liquid outlet channel 150 is larger than the accelerating effect in other directions. To be specific, the distance between the protruding surface 116 and the bottom surface 114 is substantially the same along the second direction D2. Under such condition, the protruding surface 116 has a second symmetric line L2 (as shown in FIG. 1) extending along the first direction D1, and the protruding surface 116 is symmetric relative to the second symmetric line L2. Moreover, the housing 110 can have a pair of buffering grooves 118A & 118B. The buffering grooves 118A & 1186 are respectively located at two opposite ends of the protruding portion 112 and are located between the liquid inlet channel 140 and the liquid outlet channel 150. The lowest position and the highest position of the protruding surface 116 is higher than the highest position of the liquid inlet channel 140 and the liquid outlet channel 150. Through this mechanism, when the cooling fluid 160 flows from the liquid inlet channel 140 into the heat dissipation structure 100, the cooling fluid 160 can be prevented from entering into the accommodation space S between the target 130 and the protruding surface 116. To be specific, the cooling fluid 160 flowing from the liquid inlet channel 140 into the heat dissipation structure 100 flows into the accommodation space S between the target 130 and the protruding surface 116 after at least two occasions of direction changes, facilitating the control of the flowing speed of the cooling fluid 160. On the other hand, the heat dissipation structure 100 can further includes two sealing gasket 170A & 170B, in which the housing 110 can have two grooves 126A & 126B. The sealing gasket 170A & 170B are respectively disposed with the grooves 126A & 126B. The sealing gasket 170A & 170B can provide air tightness and water-proof effect. In some embodiments, the difference in value between the shortest distance between the protruding surface 116 and the target 130 and the longest distance between the protruding surface 116 and the target 130 can be within 0.3 mm and 0.7 mm. For example, the shortest distance between the protruding surface 116 and the target 130 can be 0.5 mm, and the longest distance between the protruding surface 116 and the target 130 can be 1 mm. In some embodiments, the length of the protruding surface 116 in FIG. 1A along the first direction D1 can be within 160 mm and 200 mm, and the length of the protruding surface 116 in FIG. 1A along the second direction D2 can be within 60 mm and 70 mm. In some embodiments, the distances between the bottom of the buffering grooves 118A & 1186 and the target 130 can be within 25 mm and 35 mm, and the widths of the buffering grooves 118A & 118B can be within 8 mm and 12 mm. In some embodiments, the liquid inlet channel 140 and the liquid outlet channel 150 can be circular channels, and the diameters of these circular channels can be within 18 mm and 22 mm. As mentioned above, since the heat dissipation structure 100 is suitable to carry out heat dissipation to the target 130 with heat distribution in the pattern of gradual decrease to the two sides from the center, the heat dissipation structure 100 is suitable to be applied to device which would cause the target 130 to have this pattern of heat distribution during operation, such as a neutron beam generating device. A neutron beam generating device is taken as an example to be described below. Reference is made to FIG. 3. FIG. 3 is a schematic view of a neutron beam generating device 200 according to some embodiments of the present disclosure. In order to prevent FIG. 3 from being over-complicated, the proportional relation between each of the layers shown in FIG. 3 is not necessary to be the same as the actual proportion. The structures drawn are used to assist for description only, but are not intended to limit the relation of the relative positions of the layers in the structure. In other embodiments, some of the layers can be omitted while other layers can be added. As shown in FIG. 3, a neutron beam generating device 200 includes the heat dissipation structure 100, a tubular body 210 and an accelerator 220. The tubular body 210 is disposed on the heat dissipation structure 100. The target 130 can be disposed between the heat dissipation 100 and the tubular body 210. To be specific, the target 130 can be secured inside the second opening 124 of the housing 110 of the heat dissipation structure 100. In some embodiments, the material of the target 130 can include beryllium (Be), and the thickness of the target 130 can be within 1.5 mm and 2.5 mm. The tubular body 210 has a channel 212, and the accelerator 220 can be connected with the tubular body 210. The accelerator 220 can be configured to emit an ionic beam I towards the target 130 through the channel 212. In other words, the ionic beam I produced from the accelerator 220 can pass through the channel 212 and bombard on the target 130, such that a neutron beam N suitable to be used in boron neutron capture therapy can be stimulated. Reference is made to both FIG. 3 and FIG. 4. FIG. 4 is a schematic view of heat distribution of the target 130 of FIG. 3. When the accelerator 220 emits the ionic beam I towards the target 130 through the channel 212, the density distribution of the ionic beam I emitted is in the form of Gaussian distribution, just like the heat distribution 270 as shown in FIG. 4. In other words, the target 130 can be regarded as a heat source with Gaussian distribution. Since the heat dissipation structure 100 is suitable to carry out heat dissipation to this kind of heat source, the heat dissipation structure 100 can prevent the neutron beam generating device 200 from experiencing unexpected damage during operation, such as the burst of the target 130 due to overheat. In conclusion, the heat dissipation structure in the present disclosure includes housing. The housing has the protruding portion, and the distance between the protruding surface of the protruding portion and the target disposed in the housing changes along the first direction, such that the flowing speed of the cooling fluid flowing through the protruding surface also changes. Therefore, the cooling fluid has a faster flowing speed with respect to the center of the target, leading to a better cooling effect at the center of the target. Through this mechanism, the heat dissipation structure is suitable to be applied in the neutron beam generating device. Although the present disclosure has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. It will be apparent to the person having ordinary skill in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the present disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of the present disclosure provided they fall within the scope of the following claims. |
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abstract | The invention relates to an optical substance manipulator capable of continuing to apply a continued force of action to moving substances without being limited by the flowing conditions for the substances yet with a wide manipulation margin and with efficiency, thereby continuously carrying out various manipulations such as separation, concentration, mixing, and deflection. Specifically, the invention provides an optical substance manipulator capable of manipulating microscopic particles dispersed in a flowing fluid by means of light pressure, characterized by comprising an optical system that forms multiple linear light-collective areas simultaneously with respect to a fluid that flows on a subject surface (5), and further comprising, in optical paths forming the respective linear light-collective areas, means (CL1), (CL2) adapted to adjust directions of the linear light-collective areas on the subject surface and means (M1), (M2) adapted to adjust positions of the linear light-collective areas. |
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061480622 | abstract | A filter having compensating plates, each having a first plate element which can be moved translationally with respect to a frame and a second plate element which can be moved relative to the first plate element so that, when the plates are in an active position, the thickness of absorbent material through which the X-ray beam passes is constant. |
039986934 | claims | 1. In a thermal damage protection system for a nuclear steam supply system, said steam supply system including a reactor core having channels therein through which a coolant is circulated, said steam supply system further including sensors for generating signals commensurate with the coolant temperature and means for measuring and providing a signal commensurate with core power as a function of measured neutron flux, the nuclear steam supply system also including means for sensing and generating signals commensurate with neutron flux at a plurality of locations adjacent the core, the improvement comprising: means responsive to signals commensurate with coolant temperature upstream and downstream of the reactor core for generating a signal commensurate with core power as a function of the thermal energy added to the coolant; first comparator means responsive to said signal commensurate with core power as a function of added thermal energy and to a signal commensurate with core power as a function of measured neutron flux for selecting the power signal commensurate with the higher power level; means responsive to the power signal selected by said selecting means for generating a first compensation signal which varies as a function of core radial peaking factor; means responsive to signals commensurate with neutron flux sensed at a plurality of locations adjacent the core for generating a second compensation signal which varies as a function of the axial distribution of power in the core; means responsive to said selected power and first and second compensation signals for generating a core power signal compensated for axial and radial peaking factors; and means responsive to said compensated power signal and to a signal commensurate with the coolant temperature upsteam of the reactor core for generating a signal commensurate with the core thermal limit as a function of a coolant pressure. means responsive to said signal commensurate with power as a function of added thermal energy and to a signal commensurate with core downstream coolant temperature for generating a signal commensurate with the coolant pressure at which temperature saturation will occur; and second comparator means responsive to said signal commensurate with saturation pressure and to said signal commensurate with core thermal limit as a function of coolant pressure for providing a pressure trip point signal commensurate with the instantaneously maximum one of the compared signals. means for correcting the upstream coolant temperature signal to compensate for stratification effects before applying said temperature signal to said thermal limit signal generating means. means for correcting the upstream coolant temperature signal to compensate for stratification effects before applying said temperature signal to said thermal limit signal generating means. means responsive to said signal commensurate with power as a function of added thermal energy for generating a stratification compensation signal; means responsive to said stratification compensation signal and a signal commensurate with core downstream coolant temperature for adjusting said temperature signal as a function of said stratification compensation signal; and means for varying said adjusted downstream temperature signal in accordance with the relationship between temperature and the known reactor cooling system pressure at which temperature saturation occurs to generate a saturation pressure signal. means third comparator responsive to a plurality of signals commensurate with coolant temperature downstream of the reactor core for selecting a signal commensurate with maximum coolant temperature for application to said stratification compensation signal generating means. first function generator means; and means for adjusting said first function generator means in accordance with the circulator pump operating configuration whereby a radial peaking factor signal which varies with coolant flow rate is generated. means for generating a signal commensurate with average control rod position; first function generator means responsive to said average rod position signal for generating a first variable bias signal; and means responsive to said variable bias signal and to said selected power signal for generating said first compensation signal. means responsive to signals commensurate with measured neutron flux for generating a signal commensurate with axial power offset; function generator means, said function generator means being responsive to said axial power offset signal for generating said second compensation signal; and means for adjusting the output of said function generator means in response to the circulator pump operating configuration. means responsive to signals commensurate with measured neutron flux for generating a signal commensurate with axial power offset; second function generator means, said second function generator means being responsive to said axial power offset signal for generating said second compensation signal; and means for adjusting the output of said second function generator means in response to the circulator pump operating configuration. means responsive to signals commensurate with measured neutron flux for generating a signal commensurate with axial power offset; function generator means, said function generator means being responsive to said axial power offset signal for generating said second compensation signal; and means for adjusting the output of said function generator means in response to the circulator pump operating configuration. means responsive to said signal commensurate with power as a function of added thermal energy and to a signal commensurate with core downstream coolant temperature for generating a signal commensurate with the coolant pressure at which temperature saturation will occur; and second comparator means responsive to said signal commensurate with saturation pressure and to said signal commensurate with core thermal limit as a function of coolant pressure for providing a pressre trip point signal commensurate with the instantaneously maximum one of the compared signals. means responsive to said signal commensurate with power as a function of added thermal energy and to a signal commensurate with core downstream coolant temperature for generating a signal commensurate with the collant pressure at which temperature saturation will occur; and second comparator means responsive to said signal commensurate with saturation pressure and to said signal commensurate with core thermal limit as a function of coolant pressure for providing a pressure trip point signal commensurate with the instantaneously maximum one of the compared signals. means for modifying said signal commensurate with upstream coolant temperature in accordance with a constant which changes with the circulator pump configuration; means for modifying said compensated core power signal in accordance with a constant which changes with the circulator pump configuration; means for combining said modified upstream temperature and selected power signals to generate said core thermal limit signal. means for modifying said signal commensurate with upstream coolant temperature in accordance with a coolant which changes with the circulator pump configuration; means for modifying said compensated core power signal in accordance with a constant which changes with the circulator pump configuration; means for combining said modified upstream temperature and selected power signals to generate said core thermal limit signal. means for generating a minimum coolant pressure signal; and means for applying said minimum coolant pressure signal as a third input to said second comparator means. means for generating a minimum coolant pressure signal; and means for applying said minimum coolant pressure signal as a third input to said second comparator means. means for generating a minimum coolant pressure signal; and means for applying said minimum coolant pressure signal as a third input to said second comparator means. means for correcting the upstream coolant temperature signal to compensate for stratification effects before applying said temperature signal to said thermal limit signal generating means. means for correcting the upstream coolant temperature signal to compensate for stratification effects before applying said temperature signal to said thermal limit signal generating means. means for generating a signal commensurate with the thermal energy added to the circulating fluid in the system; means responsive to said signal commensurate with added thermal energy for generating a variable stratification bias signal; means for generating a signal commensurate with maximum system circulating fluid temperature; means responsive to said generated bias and temperature signals for generating a temperature signal calibrated for stratification effects; and means for varying said calibrated temperature signal in accordance with the relationship between temperature and the system pressure at whih temperature saturation occurs to provide a saturation pressure signal. means for sensing and generating signals proportional to the temperature of the circulating fluid upstream and downstream of the heat source of the steam supply system; and means responsive to said temperature signals for generating a signal commensurate with power as a function of added thermal energy. means for varying said power signal as a function of the selected fluid flow rate prior to application to said bias signal generating means. adjusting a measured value of core power to compensate for core radial peaking factor and the axial distribution of power in the core; computing the thermal margin set point as a function of the temperature of a coolant circulated through the reactor core as measured upstream of the core and core power compensated for radial peaking factor and axial power distribution, the computed thermal margin set point being indicative of the core thermal limit as a function of coolant pressure; and comparing the computed thermal margin set point with the actual coolant pressure. adjusting a measure of core power in accordance with a known radial peaking factor versus power curve; calculating an axial power off-set factor as a function of the power distribution in the upper and lower halves of the reactor core; and further adjusting the measure of core power in accordance with a point on a known axial peaking factor versus axial off-set curve corresponding to the calculated axial off-set factor. calculating the core power as a function of coolant temperature rise across the reactor core; measuring core power as a function of neutron flux; and selecting the measure of core power indicative of the highest power level for adjustment in accordance with radial peaking factor and axial power distribution. choosing the radial peaking factor versus power and axial peaking factor versus axial off-set curves as a function of the instantaneous coolant mass flow conditions for the reactor core. correcting the computed thermal margin set point for the effects of coolant stratification. correcting the computed thermal margin set point for the effects of coolant stratification. calculating the pressure at which core coolant temperature saturation will occur; and selecting the maximum of the computed thermal margin set point and temperature saturation pressure signals for comparison with the actual coolant pressure. calculating a stratification bias factor as a function of the thermal energy added to the coolant circulating through the reactor core; adjusting a measured value of maximum coolant temperature in accordance with the stratification bias factor; and determining an adjustable saturation pressure corresponding to the adjusted maximum temperature, said pressure being determined in accordance with a known relationship between temperature and the system pressure at which temperature saturation occurs. adjusting a measure of core power in accordance with a known radial peaking factor versus power curve; calculating an axial power off-set factor as a function of the power distribution in the upper and lower halves of the reactor core; and further adjusting the measure of core power in accordance with a point on a known axial peaking factor versus axial off-set curve corresponding to the calculated axial off-set factor. calculating the core powr as a function of coolant temperature rise across the reactor core; measuring core power as a function of neutron flux; and selecting the measure of core power indicative of the highest power level for adjustment in accordance with radial peaking factor and axial power distribution. choosing the radial peaking factor versus power and axial peaking factor versus axial off-set curves as a function of the instantaneous coolant mass flow conditions for the reactor core. correcting the computed thermal margin set point for the effects of coolant stratification. calculating the pressure at which core coolant temperature saturation will occur; and selecting the maximum of the computed thermal margin set point and temperature saturation pressure signals for comparison with the actual coolant pressure. 2. The apparatus of claim 1 further comprising: 3. The apparatus of claim 1 further comprising: 4. The apparatus of claim 2 further comprising: 5. The apparatus of claim 2 wherein said means for generating a signal commensurate with saturation pressure comprises: 6. The apparatus of claim 5 wherein said means for generating a signal commensurate with saturation pressure further comprises: 7. The apparatus of claim 1 wherein said reactor system includes a plurality of coolant circulator pumps and wherein said protection system further comprises: means for varying the signal commensurate with core power as a function of added thermal energy in accordance with the circulator pump operating configuration prior to application to said selecting means. 8. The apparatus of claim 7 wherein said first compensation signal generating means comprises: 9. The apparatus of claim 7 wherein said means for generating a first compensation signal comprises: 10. The apparatus of claim 7 wherein said means for generating a second compensation signal comprises: 11. The apparatus of claim 8 wherein said means for generating a second compensation signal comprises: 12. The apparatus of claim 9 wherein said means for generating a second compensation signal comprises: 13. The apparatus of claim 11 further comprising 14. The apparatus of claim 12 further comprising: 15. The apparatus of claim 13 wherein said core thermal limit signal generating means comprises: 16. The apparatus of claim 14 wherein said core thermal limit signal generating means comprises: 17. The apparatus of claim 2 further comprising: 18. The apparatus of claim 15 further comprising: 19. The apparatus of claim 16 further comprising: 20. The apparatus of claim 18 further comprising: 21. The apparatus of claim 19 further comprising: 22. Apparatus for generating a signal commensurate with the pressure at which temperature saturation will occur in a steam supply system comprising: 23. The apparatus of claim 22 wherein said means for generating a signal commensurate with added thermal energy comprises: 24. The apparatus of claim 23 wherein said means for generating a signal commensurate with added thermal energy further comprises: 25. A method for predicting whether the core thermal limits of a nuclear reactor are in danger of being violated comprising the steps of: 26. The method of claim 25 wherein the step of compensating a measured value of core power for radial peaking factor and axial power distribution includes: 27. The method of claim 26 wherein the step of compensating a measured value of core power for radial peaking factor and axial powr distribution further includes: 28. The method of claim 27 further comprising: 29. The method of claim 26 further comprising: 30. The method of claim 27 further comprising: 31. The method of claim 26 further comprising: 32. The method of claim 31 wherein the step of calculating the pressure at which temperature saturation will occur includes: 33. The method of claim 32 wherein the step of compensating a measured value of core power for radial peaking factor and axial power distribution includes: 34. The method of claim 33 wherein the step of compensating a measured value of core power for radial peaking factor and axial power distribution further includes: 35. The method of claim 34 further comprising: 36. The method of claim 35 further comprising: 37. The method of claim 36 further comprising: |
062020382 | description | DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS A system 10 constructed in accordance with the invention is set forth in general in the flow chart of FIG. 1A. In describing various preferred embodiments, specific reference will be made throughout to application of the surveillance methodologies to specific industrial systems, such as nuclear reactors; however, the inventions are equally applicable to any system which provides signals or other data over time which describe attributes or parameters of the system. Therefore, the inventions herein are, for example, applicable to analysis, modification and termination of processes and systems involving physical, chemical, biological and financial sources of data or signals. The system 10 is made up of three methodologies which, as appropriate, can be used separately, and possibly together, to monitor or validate data or signals. A series of logical steps can be taken to choose one or more of the methods shown in detail in FIGS. 1B-1D. Initialization of the system 10 is shown in FIG. 1A. The first step in the initialization is to obtain the user specified parameters; the Sample Failure Magnitude (SFM), the false alarm probability (.alpha.), and the missed alarm probability (.beta.). The next step in the initialization is to query the monitored system to obtain the sensor configuration information. If the system has a single sensor the method selected for monitoring will be the MONOSPRT approach described immediately hereinafter. For the single sensor case, that is all that needs to be done to complete the initialization. If the system has exactly two sensors, then information about the relationship between the two sensors is required. First, are the two sensors linearly related? If so, the regression SPRT algorithm is selected for monitoring, and this will be discussed in detail hereinafter. If the two sensors aren't linearly related, the next step is to check to see if they are non-linearly related. If so, the BART algorithm (described hereinafter) is used for monitoring. Otherwise, each sensor is monitored separately using the MONOSPRT method. In a first preferred embodiment (MONOSPRT) involving surveillance and analysis of systems having only one source of signals or data, such as, non-safety grade nuclear reactors and many industrial, biological and financial processes, a highly sensitive methodology implements a sequential analysis technique when the decision process is based on a single, serially correlated stochastic process. This form of the invention is set forth in detail in FIG. 1B on the portion of the flow diagram of FIG. 11A directed to "one sensor" which activates a MONOSPRT methodology. Serial correlation can be handled by a vectorized type of SPRT (sequential probability ratio test) method which is based on a time series analysis, multivariate statistics and the parametric SPRT test (see, for example, U.S. Pat. Nos. 5,223,207; 5,410,492; 5,586,066 and 5,629,872 which describe details of various SPRT features and are incorporated by reference herein for such descriptions). The MONOSPRT method is described in FIG. 1B. The method is split into two phases, a training phase and a monitoring phase. During the training phase N samples are collected from the single sensor (or data source) that are representative of normal operation. Next, a covariance matrix is constructed from the representative data that is p.sub.x p, where p is the user specified number of lags to consider when characterizing the autocorrelation structure of the sensor signal. The final steps in the training phase of the MONOSPRT method are to calculate the SPRT parameters; SDM, L and U. The SDM (System Disturbance Magnitude) is calculated by multiplying the standard deviation of the sensor signal with the SFM specified during the system initialization. The standard deviation of the sensor signal is the square root of the diagonal elements of the covariance matrix. L and U are the lower and upper thresholds used for to compare the MONOSPRT indexes to in order to make a failure decision. Both L and U are functions of .alpha. and .beta. specified during system initialization. During the monitoring phase of MONOSPRT a data vector of length p is acquired at each time step t and is used in the calculation of the MONOSPRT index .lambda.. The index is then compared to L and H. If the MONOSPRT index is greater than or equal to U, then the sensor signal is not behaving normally and a failure alarm is annunciated. If the MONOSPRT index is less than or equal to L then the decision that the sensor is good is made. In either case, after a decision is made in the MONOSPRT index is reset to zero and the process continues. In this vectorized SPRT methodology, (hereinafter "MONOSPRT"), suppose there exists the following stationary, a periodic sequence of serially correlated random variables: {X'}.sub.t where t=1, 2, 3 . . . , N. It is conventional that a periodic sequence can be handled by removing the periodic component of the structural time series model, and a non-stationary sequence can be differenced to produce a stationary sequence. The stationary assumption provides constant mean, constant variance and covariances that depend only on the separation of two variates in time and not the actual times at which they were recorded. The mean, .mu., is given by EQU .mu.=E[X'.sub.t ] where E[.] is the expectation operator. If we let EQU X.sub.t =X'.sub.t -X PA1 where, ##EQU1## PA1 Decision Rule: if .lambda..sub.t <L, then ACCEPT H.sub.0 : PA1 where S is either 0 or A. Therefore: ##EQU7## PA1 H.sub.0 : D.sub.1,D.sub.2, . . . have Gaussian distribution with mean M.sub.0 and variance .sigma..sup.2 PA1 H.sub.F : X.sub.1,X.sub.2, . . . have Gaussian distribution with mean M.sub.F and variance .sigma..sup.2 PA1 A) The similarity between the maximum and minimum values in the similarity domain is 0, and PA1 B) the similarity between equal values is 1. PA1 if x.sub.1 =[X.sub.11 X.sub.12 X.sub.13 . . . X.sub.1n ]and x.sub.2 =[X.sub.21 X.sub.22 X.sub.23 . . . X.sub.2n ] and n.sub.s is the sample size, then E[X.sub.t ]=0. The autocovariance of two time points, X.sub.t and X.sub.s is .sigma..sub..Arrow-up bold.t-s.Arrow-up bold. =E[X.sub.t X.sub.s ], where s and t are integers in the set {[1, N]} and .sigma..sub.0 is the variance. Suppose there exists p<N such that for every m.gtoreq.p: .sigma..sub.n <.delta., where .delta.is arbitrarily close to 0. ##EQU2## Therefore, we have constructed a stationary sequence of random vectors. The mean of the sequence {{character pullout}}.sub.t is {character pullout}.sub.p where {character pullout}.sub.p is the zero vector with p rows. The variance of the sequence is the covariance matrix .SIGMA..sub.y. ##EQU3## The SPRT type of test is based on the maximum likelihood ratio. The test sequentially samples a process until it is capable of deciding between two alternatives: H.sub.0 :.mu.=0; and H.sub.A :.mu.=M. It has been demonstrated that the following approach provides an optimal decision method (the average sample size is less than a comparable fixed sample test). A test statistic, .lambda..sub.t, is computed from the following formula: ##EQU4## where 1n(.) is the natural logarithm, .function..sub.H.sub..sub.s ( ) is the probability density function of the observed value of the random variable Y.sub.i under the hypothesis H.sub.s and j is the time point of the last decision. In deciding between two alternative hypotheses, without knowing the true state of the signal under surveillance, it is possible to make an error (incorrect hypothesis decision). Two types of errors are possible. Rejecting H.sub.0 when it is true (type I error) or accepting H.sub.0 when it is false (type II error). We would like to control these errors at some arbitrary minimum value, if possible. We will call the probability of making a type I error, .alpha., and the probability of making a type II error .beta.. The well-known Wald's Approximation defines a lower bound, L, below which one accepts H.sub.0. and an upper bound, U beyond which one rejects H.sub.0. ##EQU5## else if .lambda., <U, then REJECT H.sub.0 : PA2 otherwise, continue sampling. To implement this procedure, this distribution of the process must be known. This is not a problem in general, because some a priori information about the system exists. For our purposes, the multivariate Normal distribution is satisfactory. Multivariate Normal: ##EQU6## The equation for .lambda..sub.t can be simplified into a more computationally efficient form as follows: ##EQU8## For the sequential test the equation is written as ##EQU9## In practice, we implement two separate tests. One test is for M greater than zero and the second test for M less than zero. Here, M is chosen by the evaluating, EQU M=[1 1 1 . . . 1]'.sigma..sub.0 k (11) where k is a user specified constant that is multiplied by the standard deviation of y. M is then used in equation (10) to determine the amount of change in the mean of y that is necessary to accept the alternative hypothesis. FIGS. 2A-2F show results after applying the MONOSPRT embodiment to a sinusoid containing no disturbance, a step disturbance, and a linear drift. In these examples the noise added to the sinusoid is Gaussian and white with a variance of 2. The sinusoid has an amplitude of 1, giving an overall signal-to-noise ratio ("SNR" hereinafter) of 0.25 (for a pure sinusoid SNR=0.5A.sup.2.sigma..sup.2, where .sigma..sup.2 is the variance of the noise and A is the amplitude of the sinusoid). The autocorrelation matrix used in MONOSPRT for these examples were calculated using 30 lags. The false alarm probability .alpha. and missed alarm probability .beta. are both specified to be 0.0001 for MONOSPRT, and the sample failure magnitude (SFM) is set to 2.5. FIG. 2A shows the sinusoid with noise without any disturbance being present. FIG. 2B is the resulting MONOSPRT when applied to the signal. FIGS. 2C and 2D illustrate the response of MONOSPRT to a step change in the sinusoid. The magnitude of the step is 2.sigma..sub.s, where .sigma..sub.s is the standard deviation of the sinusoid plus the noise. The step begins at time 500 seconds. Due to the low SNR, MONOSPRT takes 25 samples to alarm, indicating that the signal is not at a peak in the sinusoid but rather that the mean of the overall signal has changed. In FIGS. 2E and 2F analogous MONOSPRT results are shown for a linear drift introduced into the noisy sinusoid signal. Here, the drift starts at time 500 seconds at a value of 0 and increases linearly to a final value of 4.sigma..sub.s at 1000 seconds. MONOSPRT detects the drift when it has reached a magnitude of approximately 1.5.sigma..sub.s. In FIGS. 3A-3F the results of running the same experiment are shown except this time the SNR is 0.5 and the SFM is changed to 1.5. The degree of autocorrelation is much higher in this case, but MONOSPRT can detect the disturbances more quickly due to the increased SNR. To test MONOSPRT on an actual sensor signal exhibiting non-white characteristics a sensor signal was selected from the primary pump #2 of the EBR-II nuclear reactor at Argonne National Laboratory (West) in Idaho. The signal is a measure of the pump's speed over a 1000 minute interval. FIG. 4A shows the sensor signal under normal operating conditions. The MONOSPRT results are shown in FIG. 4B. For this example .alpha. and .beta. are specified to be 0.0001 and the SFM is 2.5. The autocorrelation matrix was calculated using 10 lags. In FIGS. 5A and 5B MONOSPRT results are shown when a very subtle sensor drift is simulated. FIG. 5A is the sensor signal with a linear drift starting at time 500 min and continuing through the rest of the signal to a final value of -0.10011% of the sensor signal magnitude. MONOSPRT detects this very small drift after about only 50 min, i.e. when the drift has reached a magnitude of approximately 0.01% of the signal magnitude. The MONOSPRT plot is shown in FIG. 5B with the same parameter settings as were used in FIG. 4B. FIG. 5B illustrates the extremely high sensitivity attainable with the new MONOSPRT methodology. In another preferred embodiment (the regression SPRT method of FIG. 1C), a methodology provides an improved method for monitoring redundant process signals of safety- or mission-critical systems. In the flow diagram shown in FIG. 1C, the method is split into two phases, a training phase and a monitoring phase. During the training phase N data samples are collected from both sensors when the system is operating normally. The two data sets are then used to calculate the regression coefficients m and b using the means of both sensor signals (.mu..sub.1 and .mu..sub.2), the autocorrelation coefficient of one of the sensors (.sigma..sub.22), and the cross-correlation coefficient (.sigma..sub.12) between both sensors. The SPRT parameters are also calculated in the same manner as was calculation of the SDM is from the regression difference function. During the monitoring phase of the regression SPRT method, a regression based difference (D.sub.t) is generated at each time point t. The regression based difference is then used to calculate the SPRT index and to make a decision about the state of the system or sensors being monitored. The logic behind the decision is analogous to the decision logic used in the MONOSPRT method. Further details are described hereinafter. In this method, known functional relationships are used between process variables in a SPRT type of test to detect the onset of system or sensor failure. This approach reduces the probability of false alarms while maintaining an extremely high degree of sensitivity to subtle changes in the process signals. For safety- or mission-critical applications, a reduction in the number of false alarms can save large amounts of time, effort and money due to extremely conservative procedures that must be implemented in the case of a failure alarm. For example, in nuclear power applications, a failure alarm could cause the operators to shut down the reactor in order to diagnose the problem, an action which typically costs the plant a million dollars per day. In this preferred embodiment shown schematically in flow diagram FIG. 1C (two sensors, linearly related), highly redundant process signals can be monitored when the signals have a known functional relationship given by EQU X.sub.t =f(X.sub.2) (12) where f( ) is some function determined by physical laws or by known (or empirically determined) statistical relationships between the variables. In principle, if either of the process signals X.sub.1 or X.sub.2 have degraded (i.e. fallen out of calibration) or failed, then (12) will no longer hold. Therefore, the relationship (12) can be used to check for sensor or system failure. In practice, both monitored process signals, or any other source of signals, contain noise, offsets and/or systematic errors due to limitations in the sensors and complexity of the underlying processes being monitored. Therefore, process failure cannot be detected simply by checking that (12) holds. More sophisticated statistical techniques must be used to ensure high levels of noise or offset do not lead to false and missed failure alarms. This preferred embodiment involves (a) specifying a functional relationship between X.sub.1 and X.sub.2 using known physical laws or statistical dependencies and linear regression when the processes are known to be in control, and (b) using the specified relationship from (a) in a sequential probability ratio test (SPRT) to detect the onset of process failure. For example, in many safety- or mission-critical applications, multiple identical sensors are often used to monitor each of the process variables of interest. In principle, each of the sensors should give identical readings unless one of the sensors is beginning to fail. Due to measurement offsets and calibration differences between the sensors, however, the sensor readings may be highly statistically correlated but will not be identical. By assuming that the sensor readings come from a multivariate normal distribution, a linear relationship between the variables can be specified. In particular, for two such sensor readings it is well-known that the following relationship holds EQU E[X.sub.1.vertline.X.sub.2 ]=.sigma..sub.12 /.sigma..sub.12 (X.sub.2 -u.sub.2)+u.sub.1 (13) where E[X.sub.1.vertline.X.sub.2 ] is the conditional expectation of the signal X.sub.1 given X.sub.2, .sigma..sub.12 is the square root of the covariance between X.sub.1 and X.sub.2. The .sigma..sub.22 is the standard deviation of X.sub.2, and u.sub.1 and u.sub.2 are the mean of X.sub.1 and X.sub.2 respectively. Equation (13) is simply a linear function of X.sub.2 and can therefore be written EQU X.sub.1 =mX.sub.2 +b (14) In practice, the slope m=.sigma..sub.12 /.sigma..sub.22 and intercept b=-.sigma..sub.12 /.sigma..sub.22 u.sub.2 +u.sub.1 can be estimated by linear regression using data that is known to have no degradation or failures present. Once a regression equation is specified for the relationship between X.sub.1 and X.sub.2, then the predicted X.sub.1 computed from (14) can be compared to the actual value of X.sub.1 by taking the difference EQU D.sub.1 =X.sub.1 -(mX.sub.2 +b) (15) Under normal operating conditions, D.sub.1, called the regression-based difference, will be Gaussian with mean zero and so me fixed standard deviation. As one of the sensors begins to fail or degrade, the mean will begin to chance. A change in the mean of this regression-based difference can be detected using the SPRT methodology. The SPRT approach is a log-likelihood ratio based test for simple or composite hypothesis (also see the incorporated patents cited hereinbefore). To test for a change in the mean of the regression-based difference signal D.sub.1, D.sub.2, . . . , the following two hypotheses are constructed: where H.sub.0 refers to the probability distribution of the regression-based difference under no failure and H.sub.F refers to the probability distribution of the regression-based difference under system or process failure. The SPRT is implemented by taking the logarithm of the likelihood ratio between H.sub.0 and H.sub.F. In particular, let f.sub.0 (d.sub.i) represent the probability density function for D.sub.1, D.sub.2, . . . under H.sub.0, and f.sub.1 (d.sub.i) represent the probability density function for D.sub.1, D.sub.2, . . . under H.sub.F. Let Z.sub.i =log [.function..sub.1 (X.sub.i)/.function..sub.0 (X.sub.i)] the log-likelihood ratio for this test. Then ##EQU10## Defining the value S.sub.n to be the sum of the increments Z.sub.i up to time n where S.sub.n =.SIGMA..sub.1.ltoreq.i.ltoreq.n Z.sub.i, then the SPRT algorithm can be specified by the following: If S.sub.n .ltoreq. B terminate and decide H.sub.0 If B < S.sub.n < A continue sampling If S.sub.n .gtoreq. A terminate and decide H.sub.F The endpoints A and B are determined by the user specified error probabilities of the test. In particular, let .alpha.=P{conclude H.sub.F.vertline.H.sub.0 true} be the type I error probability (false alarm probability) and .beta.=P{conclude H.sub.0.vertline.H.sub.F true} be the type II error probability (missed alarm probability) for the SPRT. Then ##EQU11## For real time applications, this test can be run repeatedly on the computed regression-based difference signal as the observations are collected so that every time the test concludes H.sub.0, the sum S.sub.n is set to zero and the test repeated. On the other hand, if the test concludes H.sub.F, then a failure alarm is sounded and either the SPRT is repeated or the process terminated. An illustration of this preferred form of bivariate regression SPRT method can be based on the EBR-II nuclear reactor referenced hereinbefore. This reactor used redundant thermocouple sensors monitoring a subassembly outlet temperature, which is the temperature of coolant exiting fuel subassemblies in the core of the reactor. These sensors readings are highly correlated, but not identical. The method of this embodiment as applied to this example system was performed using two such temperature sensors; X.sub.1 =channel 74/subassembly outlet temperature 4E1, and X.sub.2 =channel 63/subassembly outlet temperature 1A1. For 24 minutes worth of data during normal operation on Jul. 7, 1993, a regression line is specified for X.sub.1 as a function of X.sub.2 according to equation (14). The predicted X.sub.1 from (14) is then compared to the actual X.sub.1 by taking the regression-based difference (15) in our new regression-SPRT algorithm. The results of this experiment are then compared to the results of performing a prior-art SPRT test on the difference X.sub.2 -X1 according to U.S. Pat. No. 5,410,492. Plots of subassembly outlet temperature 1A1 and 4E1 under normal operating conditions are given in FIG. 7A. The relationship between the two variables when no failure is present is illustrated in FIG. 8. In FIG. 8, the slope and intercept of the regression line from equation (14) are given. FIGS. 9A and 9B illustrate the regression-based difference signal along with the difference signal of the prior art proposed by U.S. Pat. No. 5,223,207. It is easy to see that the regression-based difference signal tends to remain closer to zero than the original difference signal under normal operating conditions. FIGS. 9A and 9B plot the results of a SPRT test on both the regression-based difference signal and the original difference signal. In both cases, the pre-specified false- and missed-alarm probabilities are set to 0.01, and the threshold for failure (alternate hypothesis mean) is set to 0.5.degree. F. In both subplots, the circles indicate a failure decision made by the SPRT test. Note that under no failure or degradation modes, the new regression-based SPRT gives fewer false alarms than the original difference. The calculated false alarm probabilities are given in Table I for these comparative SPRT tests plotted in FIGS. 9A and 9B. TABLE I Empirical False Alarm Probability for the SPRT test to Detect Failure of an EBR-II Subassembly Outlet Temperature Sensor Regression-Based Original Difference Difference False Alarm Probability 0.025 0.0056 The empirical false alarm probability for the SPRT operated on the regression-based difference (see FIG. 9A) is significantly smaller than the for the SPRT performed on the original difference signal (see FIG. 9B), indicating that it will have a much lower false-alarm rate. Furthermore, the regression-based difference signal yields a false alarm probability that is significantly lower than the pre-specified false alarm probability, while the original difference function yields an unacceptably high false alarm probability. To illustrate the performance of the regression-based difference method in a SPRT methodology under failure of one of the sensors, a gradual trend is added to the subassembly outlet temperature 4E1 to simulate the onset of a subtle decalibration bias in that sensor. The trend is started at 8 minutes, 20 seconds, and has a slope of 0.005.degree. F. per second. The EBR-II signals with a failure injected in the 4E1 sensor are plotted in FIGS. 10A and 10B. The regression-based difference signal and the original difference signal are plotted in FIGS. 11A and 11B. FIGS. 12A and 12B plot the results of the SPRT test performed on the two difference signals. As before, the SPRT has false and missed alarm probabilities of 0.01, and a sensor failure magnitude of 0.5.degree. F. In this case, the regression-based SPRT annunciated the onset of the disturbance even earlier than the conventional SPRT. The time of failure detection is given in Table II. TABLE II Time to Detection of Gradual Failure of EBR-II Subassembly Outlet Temperature Regression-Based Original Difference Difference Time to Failure Detection 9 min. 44 sec. 9 min. 31 sec. These results indicate that the regression-based SPRT methodology yields results that are highly sensitive to small changes in the mean of the process. In this case, using the regression-based SPRT gave a failure detection 13 seconds before using the prior art method. A problem that is endemic to conventional signal surveillance methods is that as one seeks to improve the sensitivity of the method, the probability of false alarms increases. Similarly, if one seeks to decrease the probability of false alarms, one sacrifices sensitivity and can miss the onset of subtle degradation. The results shown here illustrate that the regression-based SPRT methodology for systems involving two sensors simultaneously improves both sensitivity and reliability (i.e. the avoidance of false alarms). It is also within the scope of the preferred embodiments that the method can be applied to redundant variables whose functional relationship is nonlinear. An example of this methodology is also illustrated in FIG. 1 branching off the "sensors are linearly related" to the "monitor separately" decision box which can decide to do so by sending each signal to the MONOSPRT methodology or alternatively to the BART methodology described hereinafter. In particular for a nonlinear relation, if the monitored processes X.sub.1 and X.sub.2 are related by the functional relationship EQU X.sub.1 =f(X.sub.2) (18) where f( ) is some nonlinear function determined by physical laws (or other imperical information) between the variables, then the relationship (18) can be used to check for sensor or system failure. In this case, the relationship (18) can be specified by using nonlinear regression of X.sub.1 on X.sub.2. The predicted X.sub.1 can then be compared to the actual X.sub.1 via the regression-based SPRT test performed on the resulting nonlinear regression-based difference signal. In another form of the invention shown in FIG. 1D in systems with more than two variables one can use a nonlinear multivariate regression technique that employs a bounded angle ratio test (hereinafter BART) in N Dimensional Space (known in vector calculus terminology as hyperspace) to model the relationships between all of the variables. This regression procedure results in a nonlinear synthesized estimate for each input observation vector based on the hyperspace regression model. The nonlinear multivariate regression technique is centered around the hyperspace BART operator that determines the element by element and vector to vector relationships of the variables and observation vectors given a set of system data that is recorded during a time period when everything is functioning correctly. In the BART method described in FIG. 1D., the method is also split into a training phase and a monitoring phase. The first step in the training phase is to acquire a data matrix continuing data samples from all of the sensors (or data sources) used for monitoring the system that are coincident in time and are representative of normal system operation. Then the BART parameters are calculated for each sensor (Xmed, Xmax and Xmin). Here Xmed is the median value of a sensor. The next step is to determine the similarity domain height for each sensor (h) using the BART parameters Xmed, Xmax and Xmin. Once these parameters are calculated a subset of the data matrix is selected to create a model matrix (H) that is used in the BART estimation calculations. Here, H is an NxM matrix where N is the number of sensors being monitored and M is the number of observations stored from each sensor. As was the case in both the MONOSPRT and regression SPRT method, the last steps taken during the training phase are the SPRT parameters calculations. The calculations are analogous to the calculations in the other methods, except that now the standard deviation value used to calculate SDI is obtained from BART estimation errors from each sensor (or data source) under normal operating conditions. During the BART monitoring phase a sample vector is acquired at each time step t, that contains a reading from all of the sensors (or data sources) being used. Then the similarity angle (SA) between the sample vector and each sample vector stored in H is calculated. Next an estimate of the input sample vector Y is calculated using the BART estimation equations. The difference between the estimate and the actual sensor values is then used as input to the SPRT. Each difference is treated separately so that a decision can be made on each sensor independently. The decision logic is the same as is used in both MONOSPRT and the regression SPRT methods. This method is described in more detail immediately hereinafter. In this embodiment of FIG. 1D of the invention, the method measures similarity between scalar values. BART uses the angle formed by the two points under comparison and a third reference point lying some distance perpendicular to the line formed by the two points under comparison. By using this geometric and trigonometric approach, BART is able to calculate the similarity of scalars with opposite signs. In the most preferred form of BART an angle domain must be determined. The angle domain is a triangle whose tip is the reference point (R), and whose base is the similarity domain. The similarity domain consists of all scalars which can be compared with a valid measure of similarity returned. To introduce the similarity domain, two logical functional requirements can be established: Thus we see that the similarity range (i.e. all possible values for a measure of similarity), is the range 0 to 16) inclusive. BART also requires some prior knowledge of the numbers to be compared for determination of the reference point (R). Unlike a ratio comparison of similarity, BART does not allow "factoring out" in the values to be compared. For example, with the BART methodology the similarity between 1 and 2 is not necessarily equal to the similarity between 2 and 4. Thus, the location of R is vital for good relative similarities to be obtained. R lies over the similarity domain at some distance h, perpendicular to the domain. The location on the similarity domain at which R occurs (Xmed) is related to the statistical distribution of the values to be compared. For most distributions, the median or mean is sufficient to generate good results. In or preferred embodiment the median is used since the median provides a good measure of data density, and is resistant to skewing caused by large ranges of data. Once Xmed has been determined, it is possible to calculate h. In calculating h, it is necessary to know the maximum and minimum values in the similarity domain. (Xmax and Xmin respectively) for normalization purposes the angle between Xmin and Xmax is defined to be 90.degree.. The conditions and values defined so far are illustrated in FIG. 13. From this triangle it is possible to obtain a system of equations and solve for h as shown below: EQU c=Xmed-Xmin EQU d-Xmax-Xmin EQU a.sup.2 -c.sup.2 +h.sup.2 EQU b.sup.2 -d.sup.2 +h.sup.2 (19) EQU (c+d(.sup.2 -.sup.2 +b.sup.2 EQU (c+d).sup.2 c.sup.2 -d.sup.2 +2h.sup.2 EQU h.sup.2 =cd EQU h=cd Once h has been calculated the system is ready to compute similarities. Assume that two points: X.sub.0 and X.sub.1 (X.sub.0.ltoreq.X.sub.1) are given as depicted in FIG. 14 and the similarity between the two is to be measured. The first step in calculating similarity is normalizing X.sub.0 and X.sub.1 with respect to Xmed. This is done by taking the euclidean distance between Xmed and each of the points to be compared. Once X.sub.0 and X.sub.1 have been normalized, the angle .angle.X.sub.0 RX.sub.1 (hereinafter designated .theta.) is calculated by the formula: EQU .theta.=Arc Tan(X.sub.1.vertline.h)=Arc Tan(X.sub.0.vertline.h) (20) After .theta. has been found, it must be normalized so that a relative measure of similarity can be obtained that lies within the similarity range. To ensure compliance with functional requirements (A) and (B) made earlier in this section, the relative similarity angle (SA) is given by: ##EQU12## Formula (21) satisfies both functional requirements established at the beginning of the section. The angle between Xmin and Xmax was defined to be 90.degree., so the similarity between Xmin and Xmax is 0. Also, the angle between equal values is 0.degree.. The SA therefore will be confined to the interval between zero and one, as desired. To measure similarity between two vectors using the BART methodology, the average of the element by element SAs are used. Given the vectors x.sub.1 and x.sub.2 the SA is found by first calculating S.sub.i for i=1,2,3 . . . n for each pair of elements in x.sub.1 and x.sub.2 i.e., The vector SA .GAMMA. is found by averaging over the S.sub.i 's and is given by the following equation. ##EQU13## In general, when given a set of multivariate observation data from a process (or other source of signals), we could use linear regression to develop a process model that relates all of the variables in the process to one another. An assumption that must be made when using linear regression is that the cross-correlation information calculated from the process data is defined by a covariance matrix. When the cross-correlation between the process variables is nonlinear, or when the data are out of phase, the covariance matrix can give misleading results. The BART methodology is a nonlinear technique that measures similarity instead of the traditional cross-correlation between variables. One advantage of the BART method is that it is independent of the phase between process variables and does not require that relationships between variables be linear. If we have a random observation vector y and a known set of process observation vectors from a process P, we can determine if y is a realistic observation from a process P by combining BART with regression to form a nonlinear regression method that looks at vector SAs as opposed to euclidean distance. If the know observation vectors taken from P are given by, ##EQU14## where H is k by m (k being the number of variables and m the number of observations), then the closest realistic observation vector to y in process P given H is given by EQU y=Hw (24) Here w is a weighting vector that maps a linear combination of the observation vectors in H to the most similar representation of y. The weighting vector w is calculated by combining the standard least squares equation form with BART. Here, .theta.stands for the SA operation used in BART. EQU w=(H'.sym.H).sup.-1 H'.sym.y (25) An example of use of the BART methodology was completed by using 10 EBR-II sensor signals. The BART system was trained using a training data set containing 1440 observation vectors. Out of the 1440 observation vectors 129 were chosen to be used to construct a system model. The 129 vectors were also used to determine the height h of the angle domain boundary as well as the location of the BART reference point R for each of the sensors used in the experiment. To test the accuracy of the model 900 minutes of one minute data observation vectors under normal operating conditions were run through the BART system. The results of the BART system modeling accuracy are shown in FIGS. 15A-15E and FIGS. 16A-16E (BART modelled). The Mean Squared Errors for each of the sensor signals is shown in Table III. TABLE III BART System Modeling Estimation Mean Squared Errors for EBR-II Sensor Signals MSE of Normalized Normalized Sensor Estimation MSE MSE Channel Sensor Description Error (MSE/.mu..sub.3) (MSE/.sigma..sub.3) 1. Primary Pump #1 0.0000190 0.0000002 0.0002957 Power (KW) 2. Primary Pump #2 0.0000538 0.0000004 0.0004265 Power (KW) 3. Primary Pump #1 0.0000468 0.0000001 0.0005727 Speed (RPM) 4. Primary Pump #2 0.0000452 0.0000001 0.0004571 Speed (RPM) 5. Reactor Outlet 8.6831039 0.0009670 0.1352974 Flowrate (GPM) 6. Primary Pump #2 0.0571358 0.0000127 0.0163304 Flowrate (GPM) 7. Subassembly Outlet 0.0029000 0.0000034 0.0062368 Temperature 1A1 (F) 8. Subassembly Outlet 0.0023966 0.0000027 0.0052941 Temperature 2B1 (F) 9. Subassembly Outlet 0.0025957 0.0000029 0.0050805 Temperature 4E1 (F) 10. Subassembly Outlet 0.0024624 0.0000028 0.0051358 Temperature 4F1 (F) A second example shows the results of applying BART to ten sensors signals with three different types of disturbances with their respective BART estimates superimposed followed by the SPRT results when applied to the estimation error signals. The first type of disturbance used in the experiment was a simulation of a linear draft in channel #1. The drift begins at minute 500 and continues through to the end of the signal, reaching a value of 0.21% of the sensor signal magnitude and the simulation is shown in FIG. 17A. The SPRT (FIG. 17B) detects the drift after it has reached a value of approximately 0.06% of the signal magnitude. In FIG. 17C a simulation of a step failure in channel #2 is shown. Here the step has a height of 0.26% of the signal magnitude and begins at minute 500 and continues throughout the signal. FIG. 17D shows the SPRT results for the step failure. The SPRT detects the failure immediately after it was introduced into the signal. The last simulation was that of a sinusoidal disturbance introduced into channel #6 as shown in FIG. 17E. The sinusoid starts at minute 500 and continues throughout the signal with a constant amplitude of 0.15% of the sensor signal magnitude. The SPRT results for this type of disturbance are shown in FIG. 17F. Again the SPRT detects the failure even though the sinusoid's amplitude is within the operating range of the channel #6 sensor signal. In further variations on the above described embodiments a user can generate one or more estimated sensor signals for a system. This methodology can be useful if a sensor has been determined to be faulty and the estimated sensor signal can be substituted for a faulty, or even degrading, sensor or other source of data. This methodology can be particularly useful for a system having at least three sources of data, or sensors. While preferred embodiments of the invention have been shown and described, it will be clear to those skilled in the art that various changes and modifications can be made without departing from the invention in its broader aspects as set forth in the claims provided hereinafter. |
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046438459 | claims | 1. A method for cutting a high activity solid waste of used nuclear reactor fuel channel boxes and control rods, each having a generally uniform cross-sectional shape along its axial length formed by four angularly oriented plates, comprising: providing at least one cart mounted for movement in an axial direction; holding a used channel box or a used control rod on the cart with its axis aligned with the cart axial direction; axially driving the cart and used channel box or a used control rod; providing at least one cutting torch secured in a predetermined position adjacent the cart; and axially cutting, as the torch and cart move relative to each other, the channel box through opposed corners thereof or the used control rod through a central portion thereof and thereby producing two L-shaped portions; commonly orienting the thus formed L-shaped portions and nesting the two together in a space saving manner; storing the nested L-shaped portions; and performing said steps of holding and cutting in a closed atmosphere environment having radiation protection. 2. The method of claim 1, further including moving the used control rod with means supporting the used control rod on the cart, in a direction perpendicular to the longitudinal axis thereof. 3. The method of claim 1, further including locating the cart and cutting torch in a space defined by a partition wall during said steps. 4. The method of claim 2, further including locating the cart and cutting torch in a space defined by a partition wall during said steps. 5. The method of claim 3, further including collecting gases generated when cutting is performed and diluting the collected gases with air by means provided to the partition wall. 6. The method of claim 4, further including collecting gases generated when cutting is performed and diluting the collected gases with air by means provided to the partition wall. 7. The method of claim 1, further including the preliminary step of cutting off a velocity limiter from the used control rod before cutting said used control rod to product the L-shaped potions. 8. The method of claim 1, wherein said step of cutting is performed underwater. |
abstract | A pressure-relief system for the containment of a nuclear power facility allows reliable operation of a wet scrubber for the pressure relief flow with a simultaneously compact structural design. The pressure relief system has a pressure relief line guided through the containment and can be closed by a shut-off valve, a wet scrubber arranged in a portion of the pressure relief line located inside the containment, for the pressure relief flow which forms in the pressure-relief mode when the shut-off valve is open, a reservoir arranged inside the containment and is fluidically connected to the remaining inner space of the containment such that any overpressure, with respect to the surroundings outside the containment, prevailing in the containment is transferred at least in part to the reservoir, and a supply line leading from the reservoir to the wet scrubber for supplying the wet scrubber with fluid from the reservoir. |
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053713630 | abstract | A device for detecting radiation within a pipe having one or more carriages adapted for movement through the pipe. A set of radiation sensors is mounted on each carriage for detecting radiation on the interior of the pipe. The radiation sensors are positioned to cover a complete circumferential strip on the pipe interior while maintaining the geometry required to meet U.S. government criteria for the unconditional release of the pipe. Readings from the radiation sensors are transmitted out of the pipe and recorded to establish a detailed radiological survey of the pipe interior. |
summary | ||
abstract | Modular cathode assemblies are useable in electrolytic reduction systems and include a basket through which fluid electrolyte may pass and exchange charge with a material to be reduced in the basket. The basket can be divided into upper and lower sections to provide entry for the material. Example embodiment cathode assemblies may have any shape to permit modular placement at any position in reduction systems. Modular cathode assemblies include a cathode plate in the basket, to which unique and opposite electrical power may be supplied. Example embodiment modular cathode assemblies may have standardized electrical connectors. Modular cathode assemblies may be supported by a top plate of an electrolytic reduction system. Electrolytic oxide reduction systems are operated by positioning modular cathode and anode assemblies at desired positions, placing a material in the basket, and charging the modular assemblies to reduce the metal oxide. |
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abstract | According to one embodiment, a method for producing a directed neutron beam includes producing a voltage of negative polarity of at least −100 keV on a surface of a deuterated or tritiated target in response to a temperature change of a pyroelectric crystal of less than about 40° C., the pyroelectric crystal having the deuterated or tritiated target coupled thereto, pulsing a deuterium ion source to produce a deuterium ion beam, accelerating the deuterium ion beam to the deuterated or tritiated target to produce a neutron beam, and directing the ion beam onto the deuterated or tritiated target to make neutrons using at least one of a voltage of the pyroelectric crystal, and a high gradient insulator (HGI) surrounding the pyroelectric crystal. The directionality of the neutron beam is controlled by changing the accelerating voltage of the system. Other methods are presented as well. |
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048045160 | claims | 1. In a nuclear reactor having a vessel for containment of a moderating and cooling pressurized water, a core in said vessel, arranged to be upwardly traversed by said water and comprising a plurality of mutually adjacent upstanding nuclear fuel assemblies, a nuclear fuel assembly comprising: 2. A nuclear fuel assembly according to claim 1, wherein the upper grids of the upper set of grids are provided with flow mixing fins, the lower grids of the lower set of grids are devoid of fins, and said nuclear fuel assembly further comprises a top grid located between the upper set of grids and the upper end piece of the nuclear fuel assembly and devoid of fins. 3. A nuclear fuel assembly according to claim 1, wherein the first predetermined distance between the upper grids has a value within the range of 15 to 30 cm. 4. A nuclear fuel assembly according to claim 1, wherein the upper grids comprise a peripheral belt and at least two series of parallel plates, the plates of one serie being of an angle with the plates of the other so that the series define passage cells for the fuel elements, said parallel plates being distributed in at least two beds spaced in the longitudinal direction of the assembly, and being provided with fins having different orientations. |
051397331 | claims | 1. Transfer cupboard for a fuel assembly extracted from the core of a nuclear reactor cooled by a liquid metal, said transfer cupboard comprising (a) a solid body (2) of elongate shape made of radiation-absorbing material; (b) an axially directed receptable (3) for said fuel assembly (4), opening out at an axial end of said body (2) via a sealingly closable orifice; (c) at least one lifting means (12) for displacing said fuel assembly (4) in an axial direction in relation to said body (2); (d) at least one circuit (15) for cooling said fuel assembly (4) by gas, completely integrated in said body (2) and comprising at least one main substantially axially directed gas-circulation channel (16) formed in said body (2) and arranged over a substantial part of a length of said body; (e) at least one means (18) for circulation of gas (18); (f) a device (17) for purifying circulating gas disposed adjacent one end of said main channel (16); and (g) first and second secondary channels (20, 21) connecting respective ends of said main channel (16) to a corresponding end of said receptacle (3) for said fuel assembly (4), by means of which secondary channels said cooling circuit is closed again. 2. Transfer cupboard according to claim 1, further comprising a capacity (30) for recovering liquid metal carried along by said cooling gas, connected by means of a channel (28) formed in said body (2) to a zone adjacent to the end of said main channel (16) connected to said circulating gas purification device (17). 3. Transfer cupboard according to claim 1, wherein said liquid-metal recovery capacity (30) is arranged at one end of said body (2) within a support (8) in which is fastened a valve (9) for sealing closure of said orifice of said receptacle (3) opening out at said axial end of said body (2). 4. Transfer cupboard according to claim 1, wherein said device (17) for purifying said circulating gas consists of a separator of the cyclone type. 5. Transfer cupboard according to claim 1, wherein said device (17) for purifying said circulating cooling gas is arranged in a receptacle (22) provided in said body (2) and communicating with one end of said main channel (16). 6. Transfer cupboard according to claim 1, wherein said means (18) for circulation of gas in said cooling circuit (15) consists of a blower (18) having an inlet and suction port communicating with an outlet of said gas purification device (17) and a port for delivering and blowing purified cooling gas into a secondary connecting channel (20) connected to said receptacle (3) for said fuel assembly (4), so as to cause said cooling gas to circulate and ensure closed-circuit purification of said cooling gas. 7. Transfer cupboard according to claim 1, wherein said main channel (16) has a diameter sufficiently small to cause said cooling gas in turbulent flow in said main channel (16) to cool in contact with said body (2) in which said main channel (16) is formed. 8. Transfer cupboard according to claim 1, comprising, around said body (2), a tubular casing (26) ensuring that said body (2) is cooled by thermosiphon. 9. Transfer cupboard according to claim 1, wherein said lifting means (12, 13, 14, 7) for said fuel assembly (4) comprises a tubular hollow grab (7) having an inner bore communicating with one of said secondary channels (20) of said cooling circuit when said fuel assembly (4) is in transfer position within said receptacle (3) and is fastened to an end of said grab (7), blowing of cooling gas into contact with said fuel assembly (4) being carried out by means of said hollow grab (7). 10. Transfer cupboard according to claim 1, wherein said body (2) comprises four cooling circuits arranged substantially at 90.degree. relative to one another about an axis of said body (2). |
description | This invention refers to a floor cleaner specially designed to be used in critical areas with difficult accessibility or restricted access, such as the pools used for housing a reactor vessel at a nuclear power station, in which human presence must be avoided as far as possible or only be for the shortest possible time, when this is absolutely necessary. According to the invention, the floor cleaner comprises: A casing or housing provided with a suction mouth; A set of inner drive rollers; A set of outer rollers with permanent opposite rotation; At least one elastic hinge of at least one axle carrying the rollers; Gear motor assemblies for the roller movement A set of sealed connections and a first control body; Lighting systems; At least one camera for taking pictures. The pools in which the reactor of a nuclear power station is housed are made up of a compartment which may be in a regular or irregular shape and have dimensions that can range from one or two dozen meters on the smaller horizontal side to several dozen meters on the larger side, with a height of several meters, able to temporarily house a large number of the components of the reactor in the dismantling stage. The base of these pools tends to be of irregular shape. On one hand there are small-sized recesses which have to be cleaned preferably before emptying the pool, as these could contain radioactive material, and there are also uneven parts of the floor, due to the bolts for holding the vessel of the reactor, amongst other reasons. A device is thus required for cleaning the floors of the pools in which reactors of nuclear power stations are housed which is able to clean narrow spaces, to the maximum width of the apparatus and which is able to get over any small obstacles which it might come up against. There are different types of floor cleaners. First of all there are manual cleaners, in which a rod is used to guide the cleaning head; this head is connected by means of a suction hose to a pump and normally to a filter to be returned to the pool. EP 1472425 describes an independent floor cleaner for pools which comprises a set of support wheels and is provided with filtration and pumping means. It does not have means of controlling the movement. A robot device known on the market as “ZODIAC Sweepy M3”, comprises a pair of lateral drive chains driven by motors and also comprises a motor for pumping water through a filter. The cleaning width is nevertheless interior, between the drive chains, for which reason it is far from the outer edges. Furthermore, since this is conceived for cleaning swimming pools, it is not designed to get over obstacles. In the nuclear industry, the “WEDA N600” device is also a compact device able to be handled in remote control or in automatic mode, which has, like the previous one, a pair of drive chains, in this case with front and rear brushes of a width approximately equal to that of the body of the device and in which the extraction system installed in the apparatus itself expels the water through filter bags. The “ATOX underwater bottom cleaner” device has a structure similar to the previous ones, in that this is provided with lateral drive chains, with a filtration body operated with an exterior pump. One major disadvantage of this device is its weight, apart from the difficulties of cleaning the side zones, for the reasons given above. Other devices, even whilst meeting some of the characteristics described in the devices mentioned, are machines of greater size, weight, cost and with the disadvantages also described above, without the manoeuvring capacity which is intended to be solved with this invention. Furthermore, any of these can be held up by a small obstacle, such as a bolt head two or three centimeters high, when said obstacle is not directly confronted by one of the drive chains. The invention being proposed consists of a floor cleaner which comprises a casing or housing carrying the other items, which forms a suction bell. This is moved by drive wheels or chains (belts); it is preferable for the movement to take place by means of belts, as the possibility of the device being held up on an obstacle, such as a bolt head, is lower if this option is used. It is driven by means of independent motors, with variable speed and rotation direction, meaning that, depending on the rotation direction of the motors, the cleaner can move forward when both belts rotate at the same speed in one direction, move in reverse when they rotate inversely in respect of the above or rotate on its own axis if the belt movements are mutually inverse or with displacement when the speeds of the belts are different. For proper cleaning of the floor, there are interior rollers and exterior rollers. In particular, according to the preferred embodiment, two interior rollers are used, with the suction bell between them, and two rollers (two geometrical axles carrying the rollers). The interior set of these rollers has a smaller size than the width of the cleaner, insofar as these are driven from at least one of its sides. As was already seen, however, the cleaning has to be done without being able to leave any zones uncleaned, for example beside the walls. The outer rollers are thus divided into two portions, and driven from the centre, so that the free end of each side reaches the width required; in particular the length of the rollers is greater than the width of the cleaner casing. The rollers are made up of a core and a sheath. It has been found that an ideal sheath for proper cleaning is made up of rubber strips, arranged radially (in a transversal direction to the movement). Hence, at least some of the strips will have to be positioned radially in respect of the roller axis. These transversal strips may be joined to strips arranged on a plane perpendicular to the axle of the roller without impairing their operation. The exterior rollers (and preferably also the interior ones) rotate towards the interior of the suction bell (they drag the dirt along the floor towards the interior of the suction bell). The movement of the rollers and especially that of the interior rollers in respect of the exterior ones may be mutually independent (with different motors and mechanical systems) or can be synchronised with each other (driven by a single motor) but is always independent from the displacement movement of the cleaner, driven by two independent motors. For the movement of the rollers and the drive belts, there are respectively motors and mechanical transmission assemblies, each formed of a plurality of pinions engaging each other. As has already been stated, the exterior rollers are driven from the central part; this central drive is made up of an arm or support which houses a mechanism, and sustains the corresponding parts of the lateral rollers projecting outward. This means that the exterior rollers do not properly clean a central zone, which is why this zone has to be cleaned by the interior rollers. The sheath of the interior rollers must therefore be continuous on the longitudinal plane on which the mechanism for driving the exterior rollers is located, especially the front rollers. Throughout the cleaning process different obstacles may come up, such as screw heads, bolt covers, etc. These obstacles do not tend to be over 2 or 3 cm in height but no compact conventional system is able to get over them without becoming jammed. If the arm carrying the front or rear rollers is rigidly fixed to the housing of the cleaner, this makes it jam, since on rising up the obstacle, it also undesirably raises the drive belts, and the device loses traction. For this reason it has been designed for the front arm to be hinged, and to be subject to an elastic retaining tension, so that the elevation tension is lower than the cleaner's effective weight in the water and so that when an obstacle is reached said arm rises over the obstacle and the cleaner continues its displacement and after the obstacle is reached by the drive belts, these are indeed able to get over this with no further problems, the arm returning to the normal working position when the elastic tension caused on reaching the obstacle has been released. Sometimes small obstacles are nevertheless located in the centre of the cleaner and are not reached by the drive belts. To solve this drawback, at least one of the rollers, normally the front interior roller, has been provided with a set of wheels joined to its axle, so that when the cleaner comes up against an obstacle, these wheels continue to pull. The wheels have a smaller diameter than that of the corresponding brush, so that they will not be in contact with the floor unless an obstacle with sufficient height is found. This guarantees that the cleaning is correct in routes with no obstacles. For the proper support of the rear interior rollers, which rotate inversely to the front interior rollers, said rollers are also designed to be fitted with wheels. However, in the event of both wheels (those of the front rollers and the rear rollers) coming into contact with an obstacle and their inverse movements being compensated, blocking the device, said wheels are designed to be freely rotating, constituting only a support which does not force any inverse movement because of the movement of the corresponding brush. The alignment of the support wheels of the interior rollers with the position of the arm holding the mechanism for driving the exterior rollers should be avoided. The suction head forming the external casing or housing comprises an upper suction mouth which is connected to a suction pump; the element for connection to the pump is designed to be freely rotating at both mouths and obliquely at 45° in its central zone allowing positioning with no restriction both from the upper end and from any lateral position. The casing is made up of lateral elements and an upper cover closed at the front and rear by the relevant rollers According to one option each of the lateral elements is formed of separate parallel plates which define a chamber housing mechanical transmission assemblies. As a means of adhesion to the floor, to maximise the cleaning capacity, the casing comprises a turbine which takes the water from the inside of the bell, and ejects this outwards in the opposite direction, upwards when the cleaner is on the floor. Since the device may be used in a dark zone, such as the pool of reactor vessel at a nuclear power plant, the cleaner is designed to have lighting means, at least in the forward motion direction, but possibly also for reverse movement. It is also designed for this to have at least one camera and possible two, one at the front and one at the rear, so that the state of cleaning achieved can be known at all times as well as the directions to be taken. The cleaner comprises an electronic control system. The electronic control system determines the actions of speeds and movement directions of each of the motors for driving the displacement or movement of the rollers and the turbine, of the lighting and picture-taking elements, or indicates any fault which might arise in the device. The electronic system comprises a sealed connection box for connecting the electric supply and control cables of the device. The control body is preferably formed of at least two elements, one of these constituting the actual electronics of the device, and the control system is normally placed in a remote unit, this remote unit normally being a computer. It could possibly have an intermediate unit, for example in a float which minimises the requirements of control cable sections, when the distances are excessively long, and which allows control by means of wireless means, where applicable. The invention being proposed consists, as stated in the heading, of a floor cleaner, governed by remote control, which is suitable for use in cleaning the floors and walls of the pools housing the vessel of nuclear power stations, which comprises: A casing (1) provided with a suction mouth; the casing (1) is mainly made up of components of stainless steel; this casing consists of lateral elements (11) and a top cover (12) on one of the sides (rear) and according to a specific configuration, an oblique cover (13) on the opposite side (front); in one option the side elements are made up of a double wall which houses transmission elements; it was nevertheless preferred to replace the double wall with a single thick wall which simplifies the operations for assembling the different transmissions, keeping the whole assembly rigid; A traction device; the traction device is preferably made up of a belt (552) normally housed on a pair of pulleys (551), set on each side of the cleaner and driven by independent drive motors and transmission mechanisms on each of the sides so that the speed of the movement and the rotation direction can be regulated simply by moving both motors in one direction, in another or in different directions at the required speed; a motor with adjustable speed located in the body of the casing (1) moves an axle transferring the rotation movement to one of the sides and a mechanical system of gears transmits this to at least one set of pulley wheels placed on each side; the belt (552) may have a toothed interior matching the outside of the pulleys (551), so as to guarantee absolute control of the movement with no unwanted sliding; A set of cleaning rollers: the rollers are made up of a core (518, 528, 538) and a sheath; the sheath is made according to a preferred option of a strip (56) an elastic material, such as rubber, formed of or comprising in its outer surface at least one set of lamellae (561) arranged in a radial position, i.e. transversal in respect of the rotation direction; said lamellae (561) may be complemented by others arranged in planes transversal to the roller axis (51,52,53,54), or in other directions; there are exterior cleaning rollers (51,52) which are located at the front and rear edges of the casing and interior cleaning rollers (53,54) which are located inside the casing, between the drive belts or between the lateral elements (11) which sustain these; the cleaning rollers (51, 52, 53, 54) can be driven by means of a single motor which transmits the movement to the motor axles of both of these by means of the corresponding transmission mechanisms, or by means of more than one motor, independently for each roller, or with each motor driving a set of rollers; hence, the movement of the interior rollers (53,54) can for example be independent from that of the exterior cleaning rollers (51,52), and thus also be independent from the drive motors and the transmission mechanisms; the roller movement is such that these will always drag any dirt found at the bottom towards the inside of the casing, and particularly towards the suction zone; the width of the interior rollers is thus limited by the width of the casing; it is nevertheless a requisite for the cleaning to be carried out at the maximum width of the devices, without a wall or any other similar obstacle being able to limit the lateral cleaning capacity; for this reason the exterior cleaning rollers (51,52) reach the required width on the outside, at the limit of or outside the width of the device; for this purpose they are fitted on respective central arms (510, 520) which support these, and which have the corresponding transmission mechanisms, with the cleaning roller (51,52) being formed of two separate portions and sustained only by its central part (by one end of each of the portions); in accordance with one option, the separate portions may be independently supported, so that the corresponding arm (510,520) is independent for each side, and in the event of there being any type of hinge of said arm (510,520) the axle of the two portions could become out of alignment; said option is not nevertheless considered preferential due to its mechanical complexity, even though it is considered within the scope of the invention; it is designed for at least one of the arms (520), to be elastically hinged so that it can pivot on an axle (521) located in the body of the casing (1); when an obstacle is reached the elastic retaining of the arm (520), which keeps this in a position aligned with the floor (as for the rest of the rollers), is overcome. This means that the arm allows the cleaning roller (52) which this sustains to rise, thus preventing the cleaner from becoming jammed on said obstacle; FIG. 5 shows a configuration of the fixed arm (510) without elastic retention; FIG. 6 shows a configuration of the hinged arm (520) with elastic retention by means of a spring (526); the power shafts (515,525) for the movement in the fixed and hinged arms are respectively represented in FIGS. 5 and 6; the interior rollers (53,54) are continuous and have a core made up of a single rigid body, and their drive mechanism is placed on at least one of their sides; on the other hand, the exterior rollers (51,52) are divided so as to present two external portions, with a central drive mechanism in the arms (510,520) which constitute the single support of each of said portions; the inner rollers (53,54) are provided with one or more support wheels, with movement linked to the roller on which these are located, or free in respect of this. It is specifically designed for the movement to be linked in the rollers which turn in the movement direction and free in the opposite direction. For proper cleaning, the support wheels (539) of the interior rollers are intended not to be aligned with the arms (510, 520) and drive mechanisms for the exterior rollers, in which there is no exterior cleaning; The casing (1) also comprises a suction bell (3) which is a chamber defined by the housing or casing (1) between the two inner rollers (53,54), with the function to confine the dirt collected from the surface to be sucked by the suction mouth. The casing (1) also comprises at least one gripping turbine (4); the gripping turbine (4) takes the water from the outside of the casing and drives this in normal direction (perpendicular) and in the opposite direction to the support surface of the rollers (normally horizontal); the greater the discharge force (flow, speed), the greater the adherence to the surface will be; According to a preferred option, the casing (1) also comprises a suction turbine or pump (8); the internal suction turbine (8), integrated in the cleaner, allows independent operation with no need for any external suction source; The casing (1) comprises a suction mouth (2); said suction mouth will be provided with a rotating element joined to the casing (or to the suction turbine (8)); according to an option with connection to an exterior suction source. this will also comprise a body for rotation at 45° (21) with a lower element (24) and an upper element (23), in turn provided with a rotating mouth (22). In the event of connecting a filter directly to the suction mouth (2) of the suction turbine (8), the first rotating element will be sufficient; The casing (1) also comprises at least one light source and a camera for taking pictures; The casing (1) is provided with a sealed connection box (6) and a control and governing body; due to the sensitivity of the semi-conductors to radiation, it is intended to have an external control body, apart from the cleaner's internal control body, for providing remote control for each of the elements controlled, such as stop-start and speeds and rotation direction of each of the motors, as well as the light, camera, turbines, etc. In the event of the internal control body ceasing to work, the external control body's connections can simply be made to take over for this, so there is no loss in functionality of the device. In this configuration, the drive and cleaning body has a maximum width of roughly 32 cm and a length of roughly 41 cm, with a height up to the suction mouth under 30 cm, which allows great manoeuvring capacity and can reach recesses which would be impossible for other devices due to their dimensions and structure. |
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abstract | A method for the production of spherical combustible or fertile material particles from an oxide of the group of the heavy metals uranium, plutonium, or mixtures thereof. For this purpose, the process steps of producing a base solution of the nitrates of the heavy metal(s), adding at least one first reagent in order to adjust the viscosity of the solution, dropping the solution to form microspheres, at least superficially solidifying the microspheres in an atmosphere containing ammonia, collecting the microspheres in a solution containing ammonia, and subsequent washing, drying and thermal treatment are carried out, where at least one of urea, ammonium carbonate, ammonium hydrogen carbonate, ammonium cyanate, and biuret are added to the base solution before adding the first reagent. The solution thus prepared is heated to a temperature T where 80° C.≦T<Ts and where Ts=boiling temperature of the solution, and is maintained at the temperature over a time period t where 2 h≦t≦8 h. |
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description | The present application is a National Phase of International Application Number PCT/EP2012/051958, filed, Feb. 6, 2012, and claims priority from, Italian Application Number MI2011A000200, filed Feb. 11, 2011. The present invention relates to a nuclear reactor and a power generating facility. Nuclear reactors are used for electric power generating facilities. Nuclear reactors include fast neutron reactors. Fast neutron reactors are nuclear reactors which mainly use fast neutrons to cause fission of fissionable nuclides to generate power. Sodium, lead-bismuth alloys, and other heavy metals and, further, gas are used to cool the core. In nuclear reactors of the prior art, fission occurs at the core as a whole to generate power. The criticality of the core of a nuclear reactor is maintained and the output is adjusted by for example control rods. The control rods are formed by a material which easily absorbs neutrons. At the start of an operation cycle, when inserting control rods into the core, along with the progress in burning, the control rods are gradually withdrawn so as to maintain the critical state while maintaining output. In this way, in operation of a nuclear reactor, control is necessary for maintaining the criticality of the nuclear reactor. Control is performed for maintaining the criticality on a continuous basis from the start of the operation cycle to the end of the operation cycle. Japanese Patent No. 3463100 discloses a nuclear reactor in which control for maintaining the criticality in the operation cycle is unnecessary. This nuclear reactor employs the burning method called CANDLE (Constant Axial Shape of Neutron Flux, Nuclide Densities and Power Shape During Life of Energy Production) burning. In CANDLE burning, the core can be divided into a generally new fuel part, burning part, and burned up part. The burning part moves toward the new fuel part by a speed proportional to output along with burning. In CANDLE burning, after a single operation cycle is ended, fuel is replaced for the next operation cycle. When replacing the fuel, the burned up fuel can be taken out in the core axial direction and new fuel can be loaded in the end at the opposite side to the end at the taken out side. In CANDLE burning, there is no need for adjustment of criticality. Further, even if not adjusting the power density distribution, the power density distribution is maintained substantially constant. For this reason, there is the feature that from the beginning to the end of the operation cycle, there is no need for control of the reactivity of the core such as manipulation of the control rods. Further, there is the feature that the reactivity coefficient does not change and it is not necessary to change the method of operation together with burning. PLT 1: Japanese Patent No. 3463100 By employing CANDLE burning as the method of burning fuel at a nuclear reactor, it is possible to provide a nuclear reactor in which the core properties can be maintained substantially constant even when burning progresses, control of the operation becomes simple, and the probability of accidents is low. Further, there is no need to arrange control rods in the core, so there is no possibility of accidents where the control rods are mistakenly pulled out during the operating period. Further, the burn-up when taking out the fuel is high, so it is possible to reduce the amount of waste. In CANDLE burning, as the new fuel for the second cycle and on, it is possible to use natural uranium or depleted uranium alone for operation. These fuels are subcritical, so are easy to transport and store. Further, it is possible to utilize about 40% of the uranium as energy without enrichment or reprocessing, so resources can be effectively utilized. Further, since the new fuel of the second cycle and on does not require enrichment, reprocessing, etc., there is the feature of a high prevention of proliferation of nuclear weapons. A nuclear reactor is arranged in a power generating facility, ship, etc. A nuclear reactor is sometimes changed in power in accordance with the amount of heat which is required during its operating period. For example, in a power generating facility, the power of the core is changed in accordance with the generated electric power. In a nuclear reactor of the conventional art, for example, control rods are inserted into and withdrawn from the inside of the core so as to control the power of the core. Even in a nuclear reactor which is provided with a core which employs CANDLE burning, it is possible to arrange control rods which are inserted in the core so as to adjust the power of the core. However, in CANDLE burning, if forming channels for insertion of control rods in the core, sometimes it is difficult to achieve criticality. In the core in the prior art, it was possible to increase the concentration of fissionable uranium or the concentration of plutonium or increase the number of fuel assemblies of new fuel so as to easily achieve criticality. In CANDLE burning as well, concentrated uranium etc. can be included in new fuel, but it is preferable to not use concentrated uranium etc. but to use only natural uranium or depleted uranium as new fuel. Further, to uniformly burn fuel, it is preferable that the power density distribution in the radial direction be substantially constant. In this regard, if forming channels for insertion of control rods in the core, spaces in which fuel is not loaded are formed in the core. The problem arises that in these spaces, the power density ends up becoming smaller and the power density distribution in the radial direction becomes uneven. The present invention has as its object the provision of a nuclear reactor which is provided with a core in which the burning part moves toward the new fuel part along with burning of fuel and which can adjust the power even without using control rods and a power generating facility which is provided with such a nuclear reactor. The nuclear reactor of the present invention is provided with a core which is provided with a new fuel part at which new fuel is loaded and a burning part which is arranged at one side of the new fuel part and which generates neutrons to enable the fuel to burn, wherein the new fuel includes at least one type of uranium from among natural uranium and depleted uranium, the uranium absorbs neutrons to generate plutonium which fissions to generate power, and the burning part moves in a direction toward the new fuel part while maintaining a substantially constant shape from the beginning to end of the operation cycle. The nuclear reactor is provided with a reactivity applying mechanism to apply the reactivity which can change the power of the core when the temperature of the coolant which flows through the inside of the core changes, and the power of the core is adjusted by performing control to change the temperature of the coolant which flows through the inside of the core in accordance with the change of power which is demanded for the core. In the above invention, preferably the reactivity applying mechanism includes fuel members which include fuel rods or fuel assemblies and a gap adjusting member which is arranged in a region which is included in a burning part at the beginning of an operation cycle, supports a plurality of fuel members together, and determines the distance between the fuel members, the gap adjusting member is formed by a material which expands when the temperature rises, and the gap adjusting member expands and the distance between fuel members become larger when the temperature of the coolant in the core rises. In the above invention, preferably the core has a high rise rate region where the temperature of the coolant rises from a core inlet toward a core outlet and a low rise rate region which is arranged downstream from the high rise rate region and has a smaller rate of rise of temperature than the high rise rate region, and the gap adjusting member is arranged in the low rise rate region at the beginning of the operation cycle. In the above invention, preferably the gap adjusting member includes a gap adjusting plate which has holes, and a plurality of fuel members are supported in the holes. In the above invention, preferably the reactor changes the temperature of the coolant which flows inside the core by performing a coolant temperature adjustment control which makes the temperature of the coolant which flows into the core change. In the above invention, preferably the nuclear reactor is formed so that when the flow rate of the coolant which flows into the core changes, the temperature of the coolant which flows through the inside of the core changes and the reactivity which can change the power of the core is applied, and the reactor changes the temperature of the coolant which flows inside the core by performing a coolant flow rate adjustment control which makes the flow rate of the coolant which flows into the core change. In the above invention, preferably the coolant is mainly comprised of lead 208 among the isotopes of lead. The power generating facility of the present invention is provided with the above nuclear reactor, a steam generator which generates steam by heat which is generated by the core, a turbine which turns by the supply of steam which is produced by the steam generator, and a generator which is connected to the turbine. According to the present invention, it is possible to provide a nuclear reactor which is provided with a core which burns fuel and in which the burning part moves toward the new fuel part and which adjusts the power without using control rods and a power generating facility which is provided with this nuclear reactor. Referring to FIG. 1 to FIG. 13, the nuclear reactor and power generating facility in the Embodiment 1 will be explained. The core of the nuclear reactor in the present embodiment is a fast neutron reactor which can use fast neutrons to cause fission of plutonium. The nuclear reactor in the present embodiment is arranged in a power generating facility and generates electric power by the heat of the coolant which flows out from the nuclear reactor. FIG. 1 is a schematic view of a power generating facility in the present embodiment. The electric power generating facility in the present embodiment is provided with a nuclear reactor 1. The nuclear reactor 1 includes a reactor vessel 9 and a core 10 which is arranged at the inside of the reactor vessel 9. The core 10 is loaded with fuel. In the core 10 in the present embodiment, the vertical direction corresponds to the axial direction of the core. Inside of the nuclear reactor 1, coolant is supplied. By the coolant flowing through the inside of the core 10, the heat of the core 10 is transmitted to the coolant. For the coolant in the present embodiment, it is possible to use a material with a small ability to decelerate neutrons and a small ability to absorb neutrons. In the present embodiment, liquid sodium 51 is used as the coolant. As the coolant of the nuclear reactor, in addition to a sodium coolant, it is possible to use a lead-bismuth coolant or other lead-based coolant, helium or another gas coolant, etc. Further, in the present embodiment, liquid sodium 52 is used even as a heat medium which transfers heat from the intermediate heat exchanger 2 to the steam generator 3. The power generating facility is provided with an intermediate heat exchanger 2 and steam generator 3 which use the heat of the coolant which flows through the core 10 to generate steam which turns the turbine 4. The heat of the coolant is transmitted through the intermediate heat exchanger 2 to the steam generator 3. By driving a pump 41, the primary system sodium 51 which functions as the coolant, as shown by the arrow 112, flows into the inside of the reactor vessel 9. The coolant circulates through the inside of the core 10 whereby the temperature rises. The coolant which is raised in temperature, as shown by the arrow 111, is sent to the intermediate heat exchanger 2. The coolant exchanges heat by the intermediate heat exchanger 2, then is supplied by the pump 41 to the inside of the reactor vessel 9. The secondary system sodium 52 which transfers heat from the intermediate heat exchanger 2 to the steam generator 3, as shown by the arrow 114, is supplied to the intermediate heat exchanger 2 by driving the pump 42. The secondary system sodium 52 exchanges heat with the coolant whereby the temperature rises. The secondary system sodium 52 which is raised in temperature, as shown by the arrow 113, is supplied to the steam generator 3. The steam generator 3 in the present embodiment heats water 53 by the heat of the secondary system sodium 52. By driving the pump 43, as shown by the arrow 116, water is supplied to the steam generator 3. In the steam generator 3, the secondary system sodium 52 and water exchange heat whereby steam is generated. The secondary system sodium 52 which performs heat exchange in the steam generator 3 is supplied by the pump 42 to the intermediate heat exchanger 2. The power generating facility in the present embodiment is provided with a turbine 4 and a generator 5. The steam which is generated by the steam generator 3 passes through a flow regulating valve 44 and, as shown by the arrow 115, is supplied to the turbine 4. By adjusting the opening degree of the flow regulating valve 44, it is possible to adjust the flow rate of steam which is supplied to the turbine. The steam makes the turbine 4 turn. The rotational force of the turbine 4 is transmitted to the generator 5 whereby the generator 5 generates power. The steam and condensed water which flow out from the turbine 4 flow into the condenser 6. The condenser 6 includes a heat exchanger 6a. The heat exchanger 6a, as shown by the arrow 118, is supplied with seawater or other cooling water. The steam is returned to water 53 in the condenser 6. The water 53 which flows out from the condenser 6 is supplied by the pump 43 to the steam generator 3. FIG. 2 is a schematic plan view of the core of a nuclear reactor in the present embodiment. FIG. 2 shows one-quarter of the core. The core 10 in the present embodiment is formed so as to become substantially hexagonal in plan view. The core of the nuclear reactor is not limited to this. It may be formed into any geometric shape or circular shape becoming substantially circular when seen by a plan view. The core 10 in the present embodiment includes fuel assemblies 21 as fuel members. In the present embodiment, the plurality of fuel assemblies 21 are regularly arranged. The plurality of fuel assemblies 21 in the present embodiment are loaded with the same new fuel. In the present embodiment, depleted uranium is loaded as new fuel. In the present embodiment, no reflecting material is arranged around the core 10, but the invention is not limited to this. A reflecting material may also be arranged around the core 10. FIG. 3 is a schematic perspective view of a fuel assembly in the present embodiment. Each fuel assembly 21 includes a plurality of fuel rods 22. The fuel rods 22 are supported by nozzles 27 at their longitudinal direction ends. Alternatively, the fuel rods 22 are supported by fastening members which are arranged inside of the fuel assemblies 21 and are fastened to the nozzles 27. Further, the fuel rods 22 are supported by a plurality of support grids 25a and 25b. The support grids 25a and 25b support the fuel rods 22 to be separated from each other. The coolant flows between the fuel rods 22 and cools the fuel rods 22. In the present embodiment, the support grids are used to maintain the distance between the fuel rods, but the invention is not limited to this. Instead of support grids, it is also possible to use wire spacers etc. FIG. 4 is a schematic perspective view of a fuel rod in the present embodiment. FIG. 4 shows a fuel rod which burns from the top side toward the bottom side. Part of the cladding material is shown cut away. The fuel rod 22 in the present embodiment includes a cladding material 23. The cladding material 23 is formed in a tubular shape. The cladding material 23 is, for example, formed by stainless steel. The fuel rod 22 contains fuel pellets 24a, 24b, and 24c. The fuel pellets 24a, 24b, and 24c are arranged inside the cladding material 23. The fuel rod 22 is sealed by a cap 29. The fuel pellets 24a, 24b, and 24c are pushed down by a coil spring 28. The fuel rod shown in FIG. 4 shows the state at the beginning of an operation cycle. A plurality of fuel pellets 24a, 24b, and 24c are arranged in the order of fuel pellets 24a containing new fuel, fuel pellets 24b in the middle of burning, and fuel pellets 24c fully burned up. The new fuel part of the core is defined by the part of the fuel pellets 24a containing new fuel. The burning part of the core is defined by the part of the fuel pellets 24b in the middle of burning. The burned up part of the core is defined by burned up fuel pellets 24c. In this way, in the fuel rod 22 in the present embodiment, fuel pellets 24a, 24b, 24c of different burn-ups are arranged. After the end of one operation cycle, for example, the cladding material 23 is stripped off and the fuel pellets of the burned up part are separated from the other fuel pellets. Next, fuel pellets containing new fuel and the recovered fuel pellets are arranged inside a new cladding material, whereby it is possible to form a fuel rod for the next operation cycle. Further, as the method of recovering fuel pellets, it is also possible to cut the fuel rod at each part, then strip off the cladding material 23. This method may also be used to recover fuel pellets which were arranged at the burning part and burned up part. Referring to FIG. 2 to FIG. 4, the fuel pellets which are arranged in the new fuel part of the fuel assemblies 21 in the present embodiment include depleted uranium. The fuel in the present embodiment is a metal fuel, but the invention is not limited to this. For example, it is also possible to use a nitride fuel etc. Next, power operation of the core in the present embodiment will be explained. In the present embodiment, an example where the power is maintained substantially constant during power operation will be explained. FIG. 5 is a schematic view for explaining the state of progress of burning of the core in the present embodiment. FIG. 5 is a schematic cross-sectional view when cutting the core along the axial direction. FIG. 5 shows a core at the beginning (BOC) of the n-th cycle and a core of the end of (EOC) of the n-th cycle after a plurality of operation cycles. Further, it shows a core after a plurality of cycles of operation by the same cycle length and same fuel replacement method. The axis where the position “r” in the radial direction is zero is the core axis. In the core 10 of the nuclear reactor in the present embodiment, the burning part 12 moves toward the new fuel part 11 from the beginning to end of the operation cycle. That is, the core of the present embodiment performs CANDLE burning. The velocity of movement of the burning part 12 is roughly proportional to the power density and is inversely proportional to the fuel atomic number density. The power density of the core in the present embodiment becomes higher at the center of the core. At the outer circumference of the core, the leakage of neutrons becomes greater, so the power density becomes smaller the further toward the outside in the radial direction. For this reason, the position of the burning part in the axial direction is a position delayed further the more to the outside in the radial direction. The core 10 in the present embodiment includes the new fuel part 11, burning part 12, and burned up part 13. The new fuel part 11 is the part at which new fuel is arranged. The burning part 12 is a part at which neutrons are produced and the fuel burns. At the burning part 12, fission occurs whereby output is substantially produced. The burned up part 13 is a part which has burned up and almost no power is being produced. At the core at the beginning of the n-th cycle, the new fuel part 11 is arranged at the bottom part of the core 10. The burning part 12 is arranged at the upper side of the new fuel part 11. At the burning part 12, fuel which already began burning at the previous cycle is arranged. In the present embodiment, the burning part 12 which is arranged at the beginning of cycle becomes the part where the burning is started. The fuel starts to burn from the burning part 12 and, as shown by the arrow 101, proceeds to burn in a direction toward the new fuel part 11. When the burning of the n-th cycle proceeds and the end of cycle is reached, the burning part 12 proceeds down to the bottom end of the core 10. In the present embodiment, the burning is continued until the new fuel part 11 is consumed. At the end of the operation cycle, the new fuel part 11 may remain. FIG. 6 is a graph which explains the relationship between the neutron fluence of fuel and infinite neutron multiplication factor in the present embodiment. The abscissa indicates the neutron fluence obtained by integrating the neutron flux over time, while the ordinate indicates the infinite neutron multiplication factor kinf. The neutron fluence is a quantity corresponding to the burnup of fuel for example. In the present embodiment, depleted uranium is used as fuel. Depleted uranium contains about 99.8% of uranium 238 and about 0.2% of uranium 235. Uranium 238 absorbs neutrons whereby nuclear transformation occurs as shown in the following formula 1. Uranium 238 is transformed to plutonium 239. In the vicinity of zero neutron fluence, uranium 238 absorbs neutrons whereby plutonium 239 is produced. Due to this, the infinite neutron multiplication factor rises. When reaching a predetermined neutron fluence, the ratio of the amount of plutonium 239 etc. to the amount of uranium 238 approaches a constant one, the fission products (FP) build up, and the infinite neutron multiplication factor is gradually reduced. In this way, the fuel in the present embodiment has the property that the infinite neutron multiplication factor increases at the beginning of burning and then the infinite neutron multiplication factor gradually decreases after that. Further, the subcriticality of depleted uranium is large, so to make part of the core critical or more, a large amount of neutrons have to be made to be absorbed at the uranium 238. In the present embodiment, the core size is selected and the fuel assemblies and fuel rods are designed so as to satisfy these conditions. By employing such a core configuration, it is possible to perform CANDLE burning. That is, it is possible to form a core wherein output is produced over the entire radial direction of the core and wherein a burning part is formed in part of the region in the axial direction of the core. FIG. 7 shows a graph of the infinite neutron multiplication factor when burning fuel by an infinite core height. The abscissa indicates the core height, while the ordinate indicates the infinite neutron multiplication factor of fuel. In the present embodiment, as shown by the arrow 101, the burning part moves toward the new fuel part. The burning part includes a region with an infinite neutron multiplication factor of over 1. The height of a core of an actual nuclear reactor is finite. In this case, the infinite neutron multiplication factor at the end of the core is slightly off from the graph shown in FIG. 7. FIG. 8 is a graph which explains the state of progress of burning of the core and fuel replacement in the present embodiment. FIG. 8 shows a graph of a core at the beginning and end of the n-th cycle and a graph of a core at the beginning and end of the (n+1)th cycle. In the graphs, the power density at the core axis, the number density of uranium 238, and the number density of fission products are shown. Referring to FIG. 7 and FIG. 8, the maximum point of the power density, as shown by the arrow 101, moves toward the bottom of the core where the new fuel part 11 is arranged. The burning part in the present embodiment moves in a direction from the top end to the bottom end of the core. The velocity at which the burning part moves, that is, the velocity at which the maximum point of the power density moves, is, for example, several cm a year. In this way, the burning part slowing moves. The number density of uranium 238 is made smaller at the downstream side of the burning part due to nuclear transformation. Further, the number density of the fission products becomes larger at the downstream side of the burning part due to fission. In the present embodiment, the fuel finishes burning when the burning part reaches the substantial bottom end of the core. If the n-th cycle ends, the fuel of part of the burned up part is taken out. At the core at the beginning of the (n+1)th cycle, as shown by the arrow 117, the burning part which is arranged at the bottom part of the core at the n-th cycle is arranged at the top part of the core and is used as the part for starting burning. At the core at the (n+1)th cycle, a new fuel part 11 is newly arranged at the bottom of the core. By replacing the fuel in this way, it is possible to burn fuel in the same way as the n-th cycle in the core at the (n+1)th cycle as well. FIG. 9 is a schematic partial cross-sectional view of a core in the present embodiment. In the present embodiment, the core 10 is arranged at the inside of the baffle plate 34. The fuel assemblies 21 are arranged so that their longitudinal directions become substantially parallel to the axial direction of the core 10. The nuclear reactor 1 in the present embodiment is provided with a reactivity applying mechanism to apply the reactivity which can change the power of the core 10 when the temperature of the coolant which flows through the inside of the core changes. At the bottom end of the core 10, an assembly bottom end support member 32 is arranged. The bottom ends of the fuel assemblies 21 are fastened to the assembly bottom end support member 32. The assembly bottom end support member 32 need only fasten the fuel assemblies 21, so it is possible to employ a material excellent as a structural member. At the top end part of the core 10, an assembly top end support member 33 is arranged. The assembly top end support member 33 is formed so as to support the top ends of the fuel assemblies 21 in a movable manner. The top ends of the fuel assemblies 21 are supported by the assembly top end support member 33 to be able to move toward the outside. The core in the present embodiment 10 is provided with a gap adjusting plate 31 serving as a gap adjusting member which supports the plurality of fuel assemblies 21. The gap adjusting plate 31 is arranged at the part of the support grids 25a among the plurality of support grids 25a and 25b (see FIG. 3). At the part where the gap adjusting plate 31 is not arranged, a clearance is formed between the support grids 25b of the adjoining fuel assemblies 21. FIG. 10 is a schematic plan view of a gap adjusting plate in the present embodiment. Referring to FIG. 9 and FIG. 10, the gap adjusting plate 31 has holes 31a in which the fuel assemblies 21 are inserted. The holes 31a of the gap adjusting plate 31 are formed so as to match with the support grids 25a of the fuel assemblies 21. The gap adjusting plate 31 in the present embodiment is formed so as to support all fuel assemblies 21 which are contained in the core 10. By arranging the support grids 25a of the fuel assemblies 21 at the holes 31a, the adjoining fuel assemblies 21 can be constrained with respect to each other. The gap between the plurality of fuel assemblies 21 is set. In the present embodiment, the gap adjusting plate 31 is formed by a material which expands when the temperature rises. The gap adjusting plate 31 is formed by a material with a large coefficient of thermal expansion. Further, the gap adjusting plate 31 in the present embodiment is formed by a material with a higher coefficient of thermal expansion than the assembly bottom end support member 32. As a material with a large coefficient of thermal expansion, stainless steel may be illustrated. For example, stainless steel SUS304 which contains nickel in 8 to 10.5% and chromium in 18 to 20% (based on Japanese Industrial Standard (JIS)) or stainless steel SUS316 which contains nickel in 10 to 14%, chromium in 16 to 18%, and molybdenum in 2 to 3% (based on Japanese Industrial Standard (JIS)) may be employed. FIG. 9 shows the power density and the coolant temperature in the axial direction of the core in addition to a schematic view of the core. The solid lines show the state at the beginning of the operation cycle (BOC), while the broken lines show the state at the end of the operation cycle (EOC). The distribution of the power density and the distribution of the coolant temperature move toward the bottom end of the core from the beginning to end of the operation cycle as shown by the arrows 101. The temperature of the coolant rises from the bottom end to the top end of the core 10. In the present embodiment, the gap adjusting plate 31 is arranged in the region of the burning part at the beginning of the operation cycle. In particular, in the present embodiment, it is arranged at the region of the burning part throughout the operation cycle. That is, the gap adjusting plate 31 is arranged at the inside of the region of the burning part both at the beginning and at the end of the operation cycle. The gap adjusting plate 31 is arranged at a region where the temperature of the coolant becomes high throughout the period of the operation cycle. Furthermore, the gap adjusting plate 31 in the present embodiment is arranged at a position in the axial direction of the core where the power density becomes substantially maximum at the beginning of the operation cycle. Alternatively, the gap adjusting plate 31 in the present embodiment is arranged at a position where the rise in the temperature of the coolant becomes gentle in the direction from the core inlet to the core outlet at the beginning of the operation cycle. FIG. 11 is another schematic partial cross-sectional view of the core in the present embodiment. At the core 10, the coolant contacts the gap adjusting plate 31. For this reason, along with the rise of the temperature of the coolant, the temperature of the gap adjusting plate 31 also rises. The gap adjusting plate 31 expands toward the outside in the radial direction as shown by the arrows 120 when the temperature rises. The fuel assemblies 21 are constrained by the gap adjusting plate 31. Further, in the core 10 of the present embodiment, the bottom ends of the fuel assemblies 21 are fastened to the assembly bottom end support member 32. If the gap adjusting plate 31 expands, as shown by the arrows 121, the top ends of the fuel assemblies 21 head to the outside in the radial direction. The distances of movement of the top ends of the fuel assemblies 21 gradually increase the more to the outside of the radial direction about the core axis (r=0). In this way, when the temperature of the coolant rises, the distance between the fuel assemblies 21 increases, so the leakage of neutrons increases. The effective neutron multiplication factor of the core 10 can be made less than 1 and the reactivity which is applied to the core 10 can be made negative. That is, in the core 10 in the present embodiment 10, a negative reactivity is applied when the temperature of the coolant rises. Further, when the temperature of the coolant falls, the distance between fuel assemblies 21 becomes smaller, so the leakage of neutrons becomes smaller. The core 10 is given a positive reactivity. In this way, the core in the present embodiment 10 can be applied a negative temperature coefficient relating to the coolant. The temperature coefficient of the fuel easily becomes a negative value due to the Doppler effect, but the absolute value is small. The temperature coefficient relating to the coolant in the present embodiment can be made negative value which has a large absolute value. The temperature coefficient relating to the coolant of the present embodiment can be made a negative value much larger than the temperature coefficient of the fuel. For this reason, even if the temperature coefficient of the other structural members etc. is positive, the temperature coefficient of the core as a whole easily becomes negative. Further, in the core in the present embodiment, the shape of the core is changed to make the temperature coefficient relating to the coolant more negative, but even with a large-sized core with a large number of fuel assemblies, the temperature coefficient relating to the coolant can be made negative. Referring to FIG. 9, the gap adjusting plate 31 in the present embodiment is arranged in the region which is included in the burning part at the beginning of the operation cycle. Due to this configuration, when the power and the coolant flow rate etc. change and the temperature of the coolant changes, it is possible to arrange the gap adjusting plate 31 in the region with a large extent of change of the temperature of the coolant and increase the amount of expansion of the gap adjusting plate 31. The distance between fuel assemblies 21 when the gap adjusting plate 31 expands can be enlarged and the temperature coefficient relating to the coolant can be made a more negative value. For example, when arranging the gap adjusting plate 31 near the bottom end of the core 10, the gap adjusting plate 31 is arranged at the outside of the burning part at the beginning of the operation cycle. Near the bottom end of the core 10, heat due to nuclear fission is not transferred to the coolant, so the extent of change of the temperature of the coolant becomes smaller. For this reason, the gap adjusting plate 31 cannot be made to sufficiently expand. By arranging the gap adjusting plate 31 in the region of the burning part like in the present embodiment, the gap adjusting plate 31 can be arranged in the region with a relatively high temperature of the coolant. In this region, the extent of change of the temperature of the coolant becomes larger, so the gap adjusting plate 31 can be made to greatly expand. The temperature coefficient relating to the coolant can be made a more negative value. Further, by arranging the gap adjusting plate 31 in the region of the burning part, the extent of temperature change of the coolant becomes larger, so the speed of change of the volume of the gap adjusting plate 31 becomes faster. It is possible to increase or reduce the distance between fuel assemblies 21 with a good response while tracking changes in the temperature of the coolant. That is, the reaction speed of the reactivity with respect to changes in the temperature of the coolant can be improved. Furthermore, the gap adjusting plate 31 in the present embodiment is arranged at a position in the axial direction of the core where the coolant temperature becomes a value close to the coolant temperature at the core outlet at the beginning of the operation cycle. The coolant temperature greatly rises from the core inlet to the core outlet mainly in the region where the power density of the burning part becomes high. Referring to FIG. 9, the core has a high rise rate region 131 where the temperature of the coolant rises from the core inlet toward the core outlet and a low rise rate region 132 where the rate of rise of temperature becomes smaller than the high rise rate region 131. The low rise rate region 132 is arranged downstream from the high rise rate region 131. FIG. 9 shows the high rise rate region 131 and the low rise rate region 132 at the beginning of the operation cycle. The gap adjusting plate 31 in the present embodiment is arranged at the low rise rate region 132 where the temperature of the coolant rises gently at the beginning of the operation cycle. By employing this configuration, it is possible to arrange the gap adjusting plate 31 in the low rise rate region 132 from the beginning to end of the operation cycle. Even if the burning part moves during the period of the operation cycle, the coolant temperature at the gap adjusting plate 31 does not change that much and the amount of expansion does not change either. For this reason, it is possible to suppress changes in the effective neutron multiplication factor accompanying burning of fuel and possible to realize ideal CANDLE burning. Further, it is possible to reduce the change in temperature coefficient relating to the coolant accompanying burning of fuel. Furthermore, the gap adjusting plate 31 is preferably arranged at a position near to the assembly bottom end support member 32 where the distance between fuel assemblies 21 does not change in the range where the coolant temperature becomes a value close to the coolant temperature at the core outlet. In the present embodiment, it is preferably arranged at a position near the core inlet. For example, the gap adjusting plate 31 is preferably arranged at the core inlet side end of the low rise rate region 132 at the beginning of the operation cycle. By adopting this configuration, the distance between fuel assemblies can be increased when the gap adjusting plate 31 expands and the temperature coefficient relating to the coolant can be made a more negative value. Note that, the position of the gap adjusting plate 31 is not limited to this. For example, it may also be arranged at the core outlet. Further, when the power of the core rises, the temperature of the coolant which flows through the inside of the core rises. When the power of the core falls, the temperature of the coolant which flows through the inside of the core falls. The coolant proceeds from the core inlet toward the core outlet through a channel in the core. When the coolant proceeds through the channels, heat is transferred from the fuel members. For this reason, when the power of the core changes, the amount of change of the coolant temperature at the inlet of the core is small. The amount of change of the coolant temperature becomes larger the more toward the outlet of the core. For example, when the power of the core rises, the extent of change of the coolant temperature becomes smallest at the inlet of the core and becomes largest at the outlet of the core. For this reason, referring to FIG. 9, from another viewpoint, at the core 10, it is possible to set a low change region 133 where the extent of change of the coolant temperature becomes smaller when the power changes and a high change region 134 where the extent of change of the coolant temperature becomes larger than the low change region. The low change region 133 in the present embodiment becomes a region which is arranged at the upstream side from the high change region 134. By arranging the gap adjusting member in the high change region 134, it is possible to increase the amount of deformation of the gap adjusting member when the power of the core changes. Further, when the positions of the bottom ends of the fuel members are fixed, by arranging the gap adjusting member in the low change region 133, it is possible to increase the amount of movement of the top ends of the fuel members. That is, even if the amount of deformation of the gap adjusting members is small, the distance between the bottom ends of the fuel members and the gap adjusting member is small, so the amount of deformation of the distance between fuel members can be increased. In the core in the present embodiment, the bottom ends of the fuel assemblies are fastened by the assembly bottom end support member, but the invention is not limited to this. The bottom ends of the fuel assemblies may also be supported to be able to move in the radial direction like the top ends of the fuel assemblies. For example, the assembly bottom end support member may also be formed so as to expand by heat according to the temperature of the coolant. The assembly bottom end support members which are arranged at the bottom ends of the fuel assemblies may also be formed by materials similar to the gap adjusting members. In the present embodiment, the fuel members which are adjusted in distance by the gap adjusting member include fuel assemblies, but the invention is not limited to this. Fuel rods may also be employed as fuel members. The fuel rods need not be bundled to form fuel assemblies. The fuel rods may also be supported directly by the gap adjusting member so that the channels of the coolant are secured. Further, the gap adjusting member in the present embodiment is formed so as to support all of the fuel members among the plurality of fuel members which are contained in the core, but the invention is not limited to this. It is also possible that it be formed so as support part of the fuel members. The gap adjusting member in the present embodiment includes a gap adjusting plate which is formed in a plate shape, but the invention is not limited to this. The gap adjusting member may be any which is formed so as to adjust the distance between adjoining fuel members in accordance with the temperature. For example, the gap adjusting member may include wires or other members formed into wire shapes. Alternatively, the gap adjusting member may also be block shaped members which are attached to the fuel assemblies and expand with heat. For example, the gap adjusting member may include block shaped members which are attached to the outer surfaces of the support grids, and the fuel assemblies may be formed so that when loaded into the core, the block shaped members of the adjoining fuel assemblies contact each other. Further, in the present embodiment, the gap adjusting plate was arranged at a position of one location in the axial direction of the core, but the invention is not limited to this. The gap adjusting member may also be arranged at a plurality of positions. In the present embodiment, the power of the core 10 is adjusted by performing control to change the temperature of the coolant which flows through the inside of the core in accordance with the change in the power demanded for the core 10. The nuclear reactor 1 in the present embodiment can apply a large absolute value reactivity when the temperature of the coolant which flows through the inside of the core 10 changes. The nuclear reactor 1 in the present embodiment adjusts the power of the core by performing the coolant temperature adjustment control in which the temperature of the coolant which flows into the core 10 is changed. In the core 10 of the present embodiment, the temperature coefficient relating to the coolant is a negative value which has a large absolute value. For this reason, by raising the temperature of the coolant which flows into the core 10, it is possible to apply the negative reactivity which has a large absolute value to the core 10 and lower the power of the core 10. Alternatively, by lowering the temperature of the coolant which flows into the core 10, it is possible to apply a large positive reactivity to the core 10 and raise the power of the core 10. In particular, in the present embodiment, it is possible to not only finely adjust the power of the core to several %, but also, for example, roughly adjust the power of the core by several tens of %. In the present embodiment, to change the temperature of the coolant which flows into the core 10, control is performed to change the load of the apparatus which is connected to the nuclear reactor. Referring to FIG. 1, in the power generating facility in the present embodiment, control is performed to change the generated electric power. For example, when raising the temperature of the coolant which flows into the core 10, the generated electric power is made smaller to reduce the load. By reducing the opening degree of the flow regulating valve 44, the steam flow rate which is supplied to the turbine 4 becomes smaller and the generated electric power becomes smaller. The amount of heat exchanged at the steam generator 3 becomes smaller. The temperature of the secondary system sodium 52 which circulates through the intermediate heat exchanger 2 and the steam generator 3 rises. By the rise of the temperature of the secondary system sodium 52, the temperature of the primary system sodium 51 (coolant) which flows out from the intermediate heat exchanger 2 also rises. The temperature of the coolant which flows into the core 10 rises and the temperature of the coolant which flows through the inside of the core 10 rises. Alternatively, the core outlet becomes higher in temperature of the coolant than the core inlet, but the average temperature of the coolant in the core rises. As the average temperature of the coolant, the temperature of the coolant which is averaged in the direction of the core axis may be mentioned. At the core 10, the temperature coefficient relating to the coolant is a negative value, so if the temperature of the coolant rises, the core 10 is given a negative reactivity. As a result, the power of the core 10 can be lowered. Further, when lowering the temperature of the coolant which flows into the core 10, the generated electric power is increased to increase the load. By increasing the opening degree of the flow regulating valve 44, the flow rate of the steam which is supplied to the turbine 4 increases and the generated electric power increases. The amount of heat which is exchanged at the steam generator 3 becomes greater. For this reason, the secondary system sodium 52 and primary system sodium 51 (coolant) fall in temperature. The coolant which flows into the core 10 falls in temperature and a positive reactivity is applied to the core 10. As a result, the power of the core 10 can be raised. In this way, in the present embodiment, by reducing the amount of heat which the apparatus which is connected to the nuclear reactor 1 consumes, it is possible to raise the temperature of the coolant which flows into the core 10 and lower the power of the core 10. Further, by increasing the amount of heat which the apparatus which is connected to the nuclear reactor 1 consumes, it is possible to lower the temperature of the coolant which flows into the core 10 and raise the power of the core 10. In this way, the nuclear reactor in the present embodiment can change the power of the core even without using control rods. Note that, the nuclear reactor is not limited to this. Control rods may be used to adjust the reactivity at the same time. In the present embodiment, the flow rate of the steam which is supplied to the turbine is adjusted to change the temperature of the coolant which flows into the core, but the invention is not limited to this. It is possible to employ any apparatus which can adjust the temperature of the coolant which is supplied to the nuclear reactor. For example, referring to FIG. 1, a heat exchanger etc. may be arranged to adjust the temperature of the heat medium at the channel of at least one of the channel for circulation of the primary system sodium 51, the channel for circulation of the secondary system sodium 52, and the channel for circulation of water and steam. FIG. 12 is a time chart of the coolant temperature adjustment control in the present embodiment. FIG. 12 illustrates the control for lowering the power of the core. The nuclear reactor in the present embodiment is operated so that in ordinary operational control, the power of the core becomes substantially constant. FIG. 12 shows the case of raising the coolant temperature at the core inlet in steps by the solid lines. Up to the time t1, the reactor operates steadily. Further, the flow rate of the coolant which flows into the core is held substantially constant even during the period of change of the power of the core. At the time t1, control is performed to reduce the generated electric power. The coolant temperature at the core inlet rises in steps. The fuel temperature and the coolant temperature at the core outlet rise along with the rise of the coolant temperature at the core inlet. The temperature of the fuel gradually rises from the core inlet toward the core outlet along with the rise of the temperature of the coolant, but the fuel temperature which is shown in FIG. 12 shows the average temperature in the core 10. As the average temperature of the fuel, it is possible to illustrate the value of the fuel temperature averaged in the direction of the core axis in the same way as the average temperature of the coolant. The coolant temperature at the core inlet rises, so the average temperature of the coolant in the core rises. In the core in the present embodiment, the temperature coefficient relating to the coolant is a negative value which has a large absolute value, so a negative reactivity is applied to the core. For this reason, the core changes from a state where criticality is maintained to a subcritical state and the power of the core falls. Along with the fall of the power of the core, the temperature of the fuel which temporarily rose falls and becomes substantially constant at a predetermined temperature. Further, along with a drop in the power of the core, the coolant temperature at the core outlet which temporarily rose also falls and becomes substantially constant at a predetermined temperature. The reactivity which is given to the core temporarily falls, but becomes substantially zero along with the drop in temperature of the coolant outlet and the fuel temperature. That is, the core returns from the subcritical state to the critical state. In the state where the power of the core falls, the critical state is again shifted to. In this way, by raising the cooling temperature at the core inlet, the power of the core can be reduced. FIG. 12 illustrates the case where the coolant temperature at the core inlet is gradually raised by broken lines. To gradually raise the coolant temperature at the core inlet, for example, it is possible to gradually lower the generated electric power. When gradually raising the coolant temperature at the core inlet, the power of the core can be made to gradually fall. The reactivity which is applied to the core continues to be substantially constant in state. That is, the core can be maintained in the substantially critical state while changing the power of the core. The fuel temperature and the coolant temperature at the core outlet also do not rapidly change, but gradually change. In this way, as coolant temperature adjustment control for changing the coolant temperature which flows into the core, it is possible to change the temperature of the coolant which flows into the core in steps or to change it gradually. When raising the power of the core, opposite to the above example of control, it is possible to lower the temperature of the coolant at the core inlet in steps or to lower it gradually. The reactivity applying mechanism of the present embodiment is formed so that a change in the temperature of the coolant causes the gap adjusting member to expand or contract whereby the temperature coefficient relating to the coolant becomes a large absolute value negative value. The reactivity applying mechanism is not limited to this. Any mechanism to apply reactivity by which the power of the core can be changed may be employed. For example, the reactivity applying mechanism preferably employs a coolant mainly comprised of 208Pb among the isotopes of lead so as to make the temperature coefficient relating to the coolant a larger absolute value negative value. Lead is suitable as a coolant of a fast reactor since the scattering cross-section of fast neutrons is large and the capture cross-section is small. Lead has four isotopes: lead 204, lead 206, lead 207, and lead 208. Lead 208 is suitable as a coolant since, even among these isotopes, the capture cross-section of the neutrons becomes smaller than other isotopes of lead. Furthermore, lead 208 can be given a temperature coefficient relating to the coolant more to the negative side value than the other isotopes of lead. FIG. 13 is a graph of the inelastic scattering cross-sections of isotopes of lead. The abscissa and ordinate are shown by log gradations. The inelastic scattering cross-sections of isotopes of lead have predetermined threshold values. For example, lead 204 and lead 206 have threshold values of neutron energies of around 106 eV. If energy of a neutron is higher than these threshold values, the neutron is inelastically scattered and decelerated. The neutron spectrum of a fast reactor has a peak at a neutron energy slightly lower than 106 eV. For example, when using lead 204 and lead 206 as the coolant, numerous neutrons are inelastically scattered and decelerated by the coolant. For this reason, when the coolant temperature rises and the density of the coolant is reduced, the effect of deceleration by inelastic scattering of neutrons becomes extremely small. The neutron spectrum hardens and the reactivity changes to the positive side. As opposed to this, when using lead 208 as the coolant, the threshold value of the neutron energy of the inelastic scattering cross-section is high, so the effect of causing inelastic scattering of neutrons is smaller than lead 204 etc. For this reason, even if the temperature of the coolant rises and the density of the coolant is reduced, the action of hardening of the neutron spectrum is smaller than that of lead 204 etc. The action of the reactivity shifting to the positive side is smaller than that of lead 204 etc. For this reason, when using lead 208 as the coolant, compared by using another lead 204 etc. as the coolant, the temperature coefficient relating to the coolant can be made a value more to the negative side. For this reason, as the coolant, it is preferable to employ a coolant mainly comprised of lead 208 which is raised in content of lead 208 by separation of lead into isotopes etc. Furthermore, substantially all of the lead which is contained in the coolant is preferably lead 208. Due to this configuration, the temperature coefficient relating to the coolant can be made a larger absolute value negative value. Further, the power of the core can be easily changed. The fuel in the present embodiment was explained with reference to the example of depleted uranium as the new fuel which is charged into the core, but the invention is not limited to this. At least one of natural uranium and depleted uranium may be used to realize CANDLE burning. Alternatively, the present invention can be applied to any fast neutron reactor able to perform CANDLE burning. In the present embodiment, the burning part of the previous cycle is arranged at the upper side of the new fuel part at the beginning of the operation cycle, but the invention is not limited to this. The new fuel part can be arranged at least at one end of the burning part in the axial direction of the core. Furthermore, the new fuel part may be arranged at the two sides of the burning part. Further, in the present embodiment, for the part which starts burning at the beginning of the operation cycle, the fuel which is arranged at the bottom of the core at the end of the previous operation cycle is used, but the invention is not limited to this. The part which starts burning at the beginning of the operation cycle need only be formed so that neutrons are emitted in it. For example, fuel which contains a predetermined concentration of plutonium or concentrated uranium etc. may also be arranged. Furthermore, the burning may be started by neutrons being supplied from the outside as well. Further, the core in the present embodiment is arranged with the axial direction of the core parallel to the vertical direction, but the invention is not limited to this. The axial direction of the core may also be parallel to the horizontal direction. That is, the core in the present embodiment may also be arranged horizontally. In the present embodiment, the explanation was given with reference to the example of a core of a nuclear reactor which is used for a power generating facility, but the invention is not limited to this. The present invention can be applied to the nuclear reactor of any facility. For example, the nuclear reactor of the present invention can be used as the power source of a ship etc. Referring to FIG. 14, the nuclear reactor and power generating facility in the Embodiment 2 will be explained. The structures of the nuclear reactor and power generating facility in the present embodiment are similar to the Embodiment 1. In the present embodiment, the reactivity which is applied to the core is changed and the power of the core is changed by performing a coolant flow rate adjustment control in which the flow rate of the coolant which flows into the core is changed. In the present embodiment as well, in the same way as the Embodiment 1, control is performed to change the temperature of the coolant which flows through the inside of the core in accordance with the change in the power which is demanded for the core. In the present embodiment, the flow rate of the coolant which flows into the core is changed to change the temperature of the coolant which flows through the inside of the core. Referring to FIG. 1, when the temperature of the coolant which flows into the core 10 is constant, it is possible to change the flow rate of the coolant which flows into the core 10 so as to change the temperature of the coolant at the core outlet. In this case, the average temperature of the coolant in the core 10 changes. For example, the value of the temperature of the coolant which is averaged in the axial direction of the core from the core inlet to the core outlet changes. As a result, it is possible to give a positive or negative reactivity to the core 10. For example, by reducing the flow rate of the coolant which flows into the core 10, it is possible to raise the coolant temperature in the core 10. The core of the nuclear reactor in the present embodiment has a negative temperature coefficient relating to the coolant which has a large absolute value, so by raising the coolant temperature inside of the core 10, it is possible to apply a negative reactivity to the core 10. As a result, it is possible to lower the output of the core 10. Further, by increasing the flow rate of the coolant which flows into the core 10, it is possible to give a positive reactivity to the core 10 and possible to raise the power of the core 10. In the present embodiment, by changing the output of the pump 41 which supplies coolant to the core 10, the flow rate of the coolant which flows into the core 10 is changed. Further, in the present embodiment, the load which is connected to the nuclear reactor is adjusted so that even if changing the flow rate of the coolant which flows into the core 10, the temperature of the coolant which flows into the core 10 becomes substantially constant. That is, the generated electric power is adjusted. FIG. 14 is a time chart of the coolant flow rate adjustment control in the present embodiment. FIG. 14 illustrates control for reducing the power of the core. FIG. 14 describes the case of changing the flow rate of the coolant which flows into the core in steps by solid lines. Up to the time t1, a steady operation is performed. At the time t1, the flow rate of the coolant which flows into the core 10 is reduced in steps. The coolant temperature at the core outlet temporarily rises since the flow rate of the coolant which flows through the inside of the core 10 is reduced. The average temperature of the coolant inside the core also rises. The fuel temperature temporarily rises along with the rise of average temperature of the coolant. The fuel temperature which is shown in FIG. 14 shows the average temperature inside the core. In the core 10 in the present embodiment, the temperature coefficient relating to the coolant is a negative value which has a large absolute value, so the core 10 is applied a negative reactivity and the power of the core 10 falls. Along with the drop in output of the core 10, the coolant temperature and fuel temperature at the core outlet fall and the temperatures become substantially constant. The reactivity shifts to the positive side along with the drop in coolant temperature and the drop in the fuel temperature in the core and becomes substantially zero. That is, the core temporarily becomes a subcritical state, then returns to the critical state. The power of the core falls from the time t1 and becomes substantially constant at a predetermined power. In this way, the core of the nuclear reactor in the present embodiment can be reduced in the power of the core by reducing the flow rate of the coolant which is supplied to the core. FIG. 14 shows the case of gradually changing the flow rate of the coolant by the broken lines. When gradually changing the flow rate of the coolant, the reactivity of the core is held at a substantially zero value. It is possible to keep the core at a substantially critical state while lowering the power of the core. By gradually changing the coolant flow rate, the coolant temperature and fuel temperature at the core outlet are gradually changed. In this way, even if gradually changing the flow rate of the coolant which flows into the core, the power of the core can be changed. When raising the power of the core, in the opposite manner as the above example of control, it is possible to increase the flow rate of the coolant which flows into the core in steps or gradually increase it. In the present embodiment, the output of the pump which supplies coolant to the core is changed to change the flow rate of the coolant which flows into the core, but the invention is not limited to this. Any mechanism can be used to change the flow rate of the coolant which flows into the core. For example, it is possible to arrange an apparatus which adjusts the flow rate of the coolant at the inside of the reactor vessel or arrange an apparatus which adjusts the flow rate of the coolant at the end of the fuel assemblies. The rest of the configuration, action, effects, etc. are similar to those of Embodiment 1, so the explanations will not be repeated here. The control for adjustment of the coolant temperature of the Embodiment 1 and the control for adjustment of the coolant flow rate of the Embodiment 2 can be combined. For example, control for adjustment of the coolant flow rate can be performed as main control to change the power of the core during which auxiliary control comprised of control for adjustment of the coolant flow rate is performed. In the above figures, the same or corresponding parts are assigned the same reference numerals. Note that, the above embodiments are illustrations and do not limit the invention. Further, in the embodiments, changes included in the claims are intended. 1 nuclear reactor 2 intermediate heat exchanger 3 steam generator 4 turbine 5 generator 6 condenser 10 core 11 new fuel part 12 burning part 13 burned up part 21 fuel assembly 22 fuel rod 25a, 25b support grids 31 gap adjusting plate 32 assembly bottom end support member 33 assembly top end support member 41 to 43 the pump 44 flow regulating valve 51, 52 sodium |
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claims | 1. A device for centering a temperature measurement device inside a reactor tube that will be filled with catalyst, comprising multiple inflatable bladders mechanically and fluidically attached to a centering ring, wherein when inflated, the multiple inflatable bladders are configured to comprise multiple open regions though which catalyst passes through. 2. The device of claim 1, wherein the multiple inflatable bladders comprise three inflatable bladders. 3. The device of claim 1, wherein a pressurized gas conduit is fluidically attached to a compressed gas source. 4. The device of claim 1, wherein the multiple inflatable bladders are configured to center the centering ring within reactor tube when inflated. 5. A device for centering a temperature measurement device inside a reactor tube that will be filled with catalyst, comprising:a centering ring with an interior and an exterior, configured to accommodate a temperature measurement device and a pressurized gas conduit in the interior,multiple inflatable bladders mechanically and fluidically attached to the exterior of the centering ring,the pressurized gas conduit fluidically attached to the centering ring such that a flow of pressurized gas exiting the pressurized gas conduit passes through a gas passage into the multiple inflatable bladders,wherein when inflated, the multiple inflatable bladders are configured to comprise multiple open regions though which catalyst passes through. 6. The device of claim 5, wherein the multiple inflatable bladders comprise three inflatable bladders. 7. The device of claim 5, wherein the pressurized gas conduit is fluidically attached to a compressed nitrogen source. 8. The device of claim 5, wherein the pressurized gas conduit is fluidically attached to a compressed air source. 9. The device of claim 5, wherein the multiple inflatable bladders are configured to center the centering ring within a reactor tube when inflated. 10. The device of claim 5, further comprising a temperature measurement device, wherein the temperature measurement device comprises a distal end, and the distal end is attached to a distal end mesh disk. |
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claims | 1. A system comprising:(i) a capsule holder having a lower end and an upper end wherein said capsule holder comprises a solid base positioned at said lower end, a solid body extending upwardly from said solid base, and a well extending downwardly within said solid body wherein said well opens at the upper end of said capsule holder and ends prior to said solid base and is configured to receive a lower half of a capsule, wherein said capsule holder is formed from a radiation-shielding material; and(ii) a shielded needle positioner having a lower end and an upper end wherein said shielded needle positioner comprises a solid body defining a bore extending substantially linearly and centrally therethrough, said bore comprising a lower section opening onto said lower end and configured to be fitted over and contain the solid body of said capsule holder, and an upper section opening onto said upper end and configured to receive an upper half of a capsule, wherein said shielded needle positioner is formed from a radiation-shielding material. 2. The system of claim 1, wherein said shielded needle positioner further comprises a cap configured to fit over the upper end thereof wherein said cap comprises a bore therethrough having a similar width to the upper section of the bore of the shielded needle positioner, wherein said cap is formed from a radiation-shielding material. 3. The system of claim 1, wherein the radiation-shielding material comprises lead, steel or tungsten. 4. The system of claim 1, further comprising:(iii) a preliminary needle positioner having a lower end and an upper end wherein said preliminary needle positioner comprises a body defining a bore extending substantially linearly and centrally therethrough, said bore comprising a lower section opening onto said lower end and configured to be fitted over and contain the solid body of said capsule holder, and an upper section opening onto said upper end and configured to contain an upper half of a capsule, wherein said shielded needle positioner is formed from a rigid material. 5. The system of claim 4, wherein said rigid material comprises a rigid plastic. 6. The system of claim 4, wherein said rigid material comprises Perspex™. 7. The system of claim 4, wherein said body of said preliminary needle positioner is solid. 8. The system of claim 4, wherein said body of said preliminary needle positioner is a scaffold. 9. The system of claim 4, further comprising securing means configured to support a needle within the bore of said preliminary needle positioner. 10. The system 9, wherein said securing means comprises a spring or a screw. 11. The system of claim 1, wherein each of the components is substantially cylindrical. 12. A method for filling a capsule with radioactivity wherein said capsule comprises an inner shell and an outer shell wherein said outer shell comprises a lower diameter body and a greater diameter cap and wherein said method comprises the following steps:(a) providing the system as defined in claim 1;(b) placing said lower diameter body into the well of the capsule holder;(c) placing said inner shell into said lower diameter body;(d) placing the shielded needle positioner over the capsule holder containing the lower diameter body and the inner shell so that the solid body of the capsule holder is contained within the lower section of the bore of the shielded needle positioner and an upper half of the inner shell is contained within the upper section of the bore of the shielded needle positioner;(e) introducing a first needle attached to a shielded syringe containing a solution of radioactivity into the upper section of the bore at the upper end of said shielded needle positioner;(f) injecting the solution of radioactivity into the inner shell(g) removing the shielded needle positioner; and(h) fixing said greater diameter cap to said lower diameter body so that said inner shell is securely contained within said outer shell. 13. The method of claim 12, wherein steps (a)-(h) are carried out sequentially. 14. The method of claim 12, wherein said capsule is suitable for oral administration. 15. The method of claim 12, wherein said capsule is made from a material comprising gelatine or polymer formulated from cellulose. 16. The method of claim 15, wherein said capsule is made from hard gelatine. 17. The method of claim 12, wherein said inner shell contains an absorbing buffer. 18. The method of claim 17, wherein said absorbing buffer comprises a hydroscopic crystalline powder. 19. The method of claim 17, wherein said absorbing buffer is dibasic sodium phosphate anhydrous USP. 20. The method of claim 12, wherein said inner shell contains a stabiliser. 21. The method of claim 20, wherein said stabiliser is disodium edetate dehydrate. 22. The method of claim 12, wherein said inner shell contains a reducing agent. 23. The method of claim 22, wherein said reducing agent is sodium thiosulfate pentahydrate. 24. The method of claim 12, wherein at the end of said method, the pH of the contents of said inner shell is in the range 7.5-9.0. 25. The method of claim 12, wherein said solution of radioactivity comprises a radioactive isotope suitable for use as an orally-administered radiopharmaceutical. 26. The method of claim 25, wherein said radioactive isotope is radioiodine or 99mTc. 27. The method of claim 26, wherein said radioiodine is selected from the group comprising 123I, 131I and 124I. 28. The method of claim 12, wherein said solution of radioactivity is a solution of sodium iodide. 29. The method of claim 12, wherein said solution of radioactivity is a solution of 99mTc pertechnetate. 30. The method of claim 12, wherein the system further comprising:(iii) a preliminary needle positioner having a lower end and an upper end wherein said preliminary needle positioner comprises a body defining a bore extending substantially linearly and centrally therethrough, said bore comprising a lower section opening onto said lower end and configured to be fitted over and contain the solid body of said capsule holder, and an upper section opening onto said upper end and configured to contain an upper half of a capsule, wherein said shielded needle positioner is formed from a rigid material,wherein said method further comprising between steps (c) and (d) steps of:(c-i) placing the preliminary needle positioner over the capsule holder;(c-ii) introducing a second needle into the upper section of the bore at the upper end of said preliminary needle positioner wherein said second needle has a smaller gauge compared to said first needle;(c-iii) optionally securing said second needle into place in said needle positioner;(c-iv) piercing a hole in the top of the inner shell with said second needle; and,(c-v) removing the preliminary needle positioner. 31. The method of claim 30, wherein said securing step (c-iii) is achieved by means of securing means supported within said preliminary needle positioner. 32. The method of claim 31, wherein said securing means comprises a screw or a spring. 33. The method of claim 12, wherein the method is automated. |
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040627241 | summary | BACKGROUND OF THE INVENTION This invention relates to nuclear reactors and to collecting trays for molten nuclear fuel debris. In one form of nuclear reactor a nuclear fuel mass constituting a reactor core is submerged within a pool of liquid coolant which serves as a vehicle for the transfer of heat from the reactor core to steam generating equipment. Examples of reactors of this form are the liquid metal cooled fast breeder reactor, boiling and pressurised water reactors. In the event of loss of coolant from the core, or restricted flow of coolant through the core, the nuclear fuel could melt down and fall to the floor of the coolant containing vessel. Because of the high heat content of the fuel debris supplemented by fission produce decay heat and, possibly, by criticality of the nuclear mass, serious damage could be caused to the floor of the vessel and its environment. For a liquid metal cooled fast breeder reactor several proposals have been made for retaining molten fuel debris before it reaches the floor of the vessel one such proposal including the provision of a plurality of layers of collecting trays disposed beneath the core, trays in the upper layers being arranged to overlap trays in the lower layers. However, the trays would be subject to such high heat flux that serious distortion could occur. SUMMARY OF THE INVENTION According to the invention, in a nuclear reactor construction comprising a reactor core submerged in a pool of coolant in a containing vessel and a collecting tray for core debris submerged in the pool of coolant below the core and spaced from the floor of the containing vessel, the wall of the vessel has an internal skirt arranged to overlap a peripheral wall of the tray to direct core debris into the tray, and the collecting tray has a plurality of cooling tubes extending between a base plate and the peripheral wall and through which coolant from the lower regions of the pool can be circulated upwardly. In use, coolant is circulated through the cooling tubes so that the heat flux into the base of the tray is maintained at a tolerable level. Preferably, circulation of coolant through the tubes is by natural convection to provide a completely passive system but, alternatively, the coolant could be pumped through the tubes. The tubes of the complex are arranged to be evenly distributed within the tray so that, in the event of an emergency resulting in melt down of fuel, cooling is substantially uniform throughout the mass of fuel debris. Bends in the tubes provide adequate flexibility to accommodate thermal linear expansion. The invention also resides in a collecting tray for a nuclear reactor construction according to the preceding paragraph, the collecting tray comprising a base plate in which one open end of each tube of a complex of cooling tubes is received and a peripheral wall in which the other open end of each tube of the complex of cooling tubes is received. |
claims | 1. Process for separating, in an aqueous medium, at least one actinide element from one or more lanthanide elements by using, in combination, at least one molecule which sequesters the at least one actinide element to be separated and membrane filtration, the process successively comprising:a) bringing the at least one molecule which sequesters the at least one actinide element in contact with the aqueous medium, the at least one molecule not being retained in a non-complexed state by the membrane and being capable of forming a complex with the at least one actinide element to be separated, the complex comprising the at least one actinide element and at least two of the at least one sequestering molecules, which complex is capable of being retained by the membrane; andb) passing the aqueous medium over the membrane in order to form a permeate on one side, the permeate comprising an aqueous effluent depleted of the at least one actinide element, and a retentate comprising the complex,wherein the at least one sequestering molecule is a monoaromatic compound carrying at least two sequestering functions on its ring, which are selected from —COOH, —CONHOH, —SO3H, —PO3H2, —P(O)OHQ with Q representing an alkyl, hydroxyalkyl or oxoalkyl group, andwherein the monoaromatic compound corresponds to the following formula:wherein:A, B, D independently represent a carbon atom or a nitrogen atom;X1 and X2 independently represent a —COOH, —CONHOH, —SO3H, —PO3H2 or —P(O)OHQ group, with Q representing an alkyl, hydroxyalkyl or oxoalkyl group; andZ1, Z2 and Z3 are selected independently from the group consisting of —H, —F, —Cl, —Br, —I, —OH, —OR, —SR, —NHR, —CHO, —COOR, —CONR1R2, —NR1R2, —NR1—NR2R3, —R′—SO2R, —SO3R, when A, B and/or D represents a carbon atom, with:R, R1, R2, R3 independently representing H, an alkyl or hydroxyalkyl group comprising from 1 to 6 carbon atoms; andR′ representing an alkene or hydroxyalkene group comprising from 1 to 6 carbon atoms. 2. Process according to claim 1, wherein the at least one actinide element to be separated is americium. 3. Process according to claim 1, wherein step b) is carried out by ultrafiltration or nanofiltration. 4. Process according to claim 1, wherein the contacting step a) is carried out with a predetermined pH. 5. The process of claim 1,wherein the monoaromatic compound corresponds to the following formula: 6. Process according to claim 5, wherein the at least one actinide element to be separated is americium. 7. Process according to claim 5, wherein step b) is carried out by ultrafiltration or nanofiltration. 8. Process according to claim 5, wherein the contacting step a) is carried out with a predetermined pH. 9. Process for separating, in an aqueous medium, at least one actinide element from one or more lanthanide elements by using, in combination, at least one molecule which sequesters the at least one actinide element to be separated and membrane filtration, the process successively comprising:a) bringing the at least one molecule which sequesters the at least one actinide element in contact with the aqueous medium, the at least one molecule not being retained in a non-complexed state by the membrane and being capable of forming a complex with the at least one actinide element to be separated, the complex comprising the at least one actinide element and at least two of the at least one sequestering molecules, which complex is capable of being retained by the membrane; andb) passing the aqueous medium over the membrane in order to form a permeate on one side, the permeate comprising an aqueous effluent depleted of the at least one actinide element, and a retentate comprising the complex,wherein the at least one sequestering molecule is a monoaromatic compound carrying at least two sequestering functions on its ring, which are selected from —COOH, —CONHOH, —SO3H, —PO3H2, —P(O)OHQ with Q representing an alkyl, hydroxyalkyl or oxoalkyl group, andwherein the monoaromatic compound corresponds to one of the following formulae:wherein:X1 and X2 independently represent a —COOH, —CONHOH, —SO3H, —PO3H2 or —P(O)OHQ group, with Q representing an alkyl, hydroxyalkyl or oxoalkyl group; andZ1, Z2 and Z3 are selected independently from the group consisting of —H, —F, —Cl, —Br, —I, —OH, —OR, —SR, —NHR, —CHO, —COOR, —CONR1R2, —NR1R2, —NR1—NR2R3, —R′—SO2R, —SO3R, with:R, R1, R2, R3 independently representing H, an alkyl or hydroxyalkyl group comprising from 1 to 6 carbon atoms; andR′ representing an alkene or hydroxyalkene group comprising from 1 to 6 carbon atoms. 10. Process according to claim 9, wherein the at least one actinide element to be separated is americium. 11. Process according to claim 9, wherein step b) is carried out by ultrafiltration or nanofiltration. 12. Process according to claim 9, wherein the contacting step a) is carried out with a predetermined pH. 13. Process for separating, in an aqueous medium, at least one actinide element from one or more lanthanide elements by using, in combination, at least one molecule which sequesters the at least one actinide element to be separated and membrane filtration, the process successively comprising:a) bringing the at least one molecule which sequesters the at least one actinide element in contact with the aqueous medium, the at least one molecule not being retained in a non-complexed state by the membrane and being capable of forming a complex with the at least one actinide element to be separated, the complex comprising the at least one actinide element and at least two of the at least one sequestering molecules, which complex is capable of being retained by the membrane; andb) passing the aqueous medium over the membrane in order to form a permeate on one side, the permeate comprising an aqueous effluent depleted of the at least one actinide element, and a retentate comprising the complex,wherein the at least one sequestering molecule is a monoaromatic compound carrying at least two sequestering functions on its ring, which are selected from —COOH, —CONHOH, —SO3H, —PO3H2, —P(O)OHQ with Q representing an alkyl, hydroxyalkyl or oxoalkyl group, andwherein the monoaromatic compound is a 5-membered ring. 14. Process according to claim 13, wherein the monoaromatic compound comprises one or more oxygen, sulphur and/or nitrogen atoms in its ring. 15. Process according to claim 13, wherein the monoaromatic compound comprises one or more nitrogen atoms in its ring. 16. Process according to claim 13, wherein the at least one actinide element to be separated is americium. 17. Process according to claim 13, wherein step b) is carried out by ultrafiltration or nanofiltration. 18. Process according to claim 13, wherein the contacting step a) is carried out with a predetermined pH. 19. Process for separating, in an aqueous medium, at least one actinide element from one or more lanthanide elements by using, in combination, at least one molecule which sequesters the at least one actinide element to be separated and membrane filtration, the process successively comprising:a) bringing the at least one molecule which sequesters the at least one actinide element in contact with the aqueous medium, the at least one molecule not being retained in a non-complexed state by the membrane and being capable of forming a complex with the at least one actinide element to be separated, the complex comprising the at least one actinide element and at least two of the at least one sequestering molecules, which complex is capable of being retained by the membrane; andb) passing the aqueous medium over the membrane in order to form a permeate on one side, the permeate comprising an aqueous effluent depleted of the at least one actinide element, and a retentate comprising the complex,wherein the at least one sequestering molecule is a monoaromatic compound carrying at least two sequestering functions on its ring, which are selected from —COOH, —CONHOH, —SO3H, —PO3H2, —P(O)OHQ with Q representing an alkyl, hydroxyalkyl or oxoalkyl group, andwherein the monoaromatic compound corresponds to the following formula:wherein:A represents a sulphur or oxygen atom;X1 and X2 are selected independently from the group consisting of —COOH, —CONHOH, —SO3H, —PO3H2, —P(O)OHQ with Q representing an alkyl, hydroxyalkyl or oxoalkyl group; andZ1 and Z2 are selected independently from the group consisting of —H, —F, —Cl, —Br, —I, —OH, —OR, —SR, —NHR, —CHO, —COOR, —CONR1R2, —NR1R2, —NR1—NR2R3, —R′—SO2R, —SO3R with:R, R1, R2, R3 independently representing H, an alkyl or hydroxyalkyl group comprising from 1 to 6 carbon atoms; andR′ representing an alkene or hydroxyalkene group comprising from 1 to 6 carbon atoms. 20. Process according to claim 19, wherein the at least one actinide element to be separated is americium. 21. Process according to claim 19, wherein step b) is carried out by ultrafiltration or nanofiltration. 22. Process according to claim 19, wherein the contacting step a) is carried out with a predetermined pH. |
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abstract | The present invention relates to an optical module, in particular facet mirror, comprising an optical element and a supporting structure for supporting the optical element, wherein the supporting structure comprises a positioning device for actively setting a position and/or orientation of the optical element in at least one degree of freedom. The supporting structure comprises a selectively activatable contacting device having at least one contacting unit having a first contact section, wherein the first contact section, in an activated state of the contacting device, contacts a second contact section of the optical element in order to exert a contact force on the optical element, while the first contact section, in a deactivated state of the contacting device is removed from the second contact section. |
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summary | ||
abstract | A background reduction system may include, but is not limited to: a charged particle source configured to generate a charged-particle beam; a louvered structure including one or more apertures configured to selectively transmit charged particles according to their angle of incidence; and a charged-particle detector configured to receive charged particles selectively transmitted by the louvered structure. |
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claims | 1. A scattered ray removal grid formed in an overall shape of constant spherical curvature, prepared by a process comprising: forming a substantially flat-shaped grid having thermoplastic resin interposed between grid elements; placing the grid between a set of dies having surfaces of complementary spherical curvature of prescribed radii, and causing the set of dies to form the grid into a shape having spherical curvature of a prescribed radius by pressing and heating the grid to its softening temperature, wherein the step of forming the substantially flat-shaped grid includes: forming a laminate by alternately stacking and bonding layers of scattered ray absorbers and spacers; slicing an end portion of the laminate perpendicularly to a stacked direction of the layers so that the scattered ray absorbers lie parallel to one another; forming a second laminate by alternately layering the sliced end portions of the laminate with radiation absorption plates to form a lattice structure; and slicing an end portion of the second laminate perpendicularly to a stacked direction of the layers to form the substantially flat-shaped grid. 2. The scattered ray removal grid according to claim 1 , wherein the scattered ray absorbers are formed of a lead compound or a bismuth compound. claim 1 3. The scattered ray removal grid according to claim 1 , wherein the spacer is formed of a polymer resin. claim 1 |
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048428124 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS By providing a removable ZrO.sub.2 surface of large area relative to the surface area of the fuel elements, much of the colloidal crud can be removed before it deposits on the core or on other plant surfaces. In essence, a ZrO.sub.2 surface is introduced into the coolant stream to serve as a getter or scavenger for colloidal crud particles. The resulting aggregate particles are then easily separated from the reactor coolant stream by an appropriate filtration process. The present method involves the introduction of a relatively large, removable ZrO.sub.2 surface into the reactor coolant system (RCS) for the purpose of seeding the RCS with appropriately sized scavenger particles having a large ZrO.sub.2 surface area. These particles will be dispersed throughout the reactor coolant and will come into close proximity with the circulating nickel ferrite and magnetite colloids. The crud particles will tend to agglomerate onto the ZrO.sub.2 surface and can be removed along therewith. Manifestly, although the present invention is described in terms of zirconium oxide particles and/or zirconium oxide coated particles, in its broad sense the present invention contemplates the use of any sort of particle which is suspensible in the coolant and which has active surfaces that possess surface characteristics which are attractive of the crud. ZrO.sub.2 is particularly valuable since it inherently may compete with the ZrO.sub.2 coating on the core elements in attracting crud deposition. Another advantage in selecting ZrO.sub.2 is that its addition to the Reactor Coolant System (RCS) introduces, no chemical species not already present there. While the colloidal and near-colloidal crud particles are difficult to filter by conventional means, the larger aggregated crud particles are easily filterable by any one of a number of conventional filtration devices which may be included in the coolant circulation system. For a more thorough understanding of the coolant system, reference is made to FIGS. 1 and 2 which illustrate preferred systems with which the present invention may be utilized. In FIG. 1, a typical three-loop PWR reactor coolant system (RCS) is schematically illustrated. In FIG. 1, the reactor vessel is designated by the reference numeral 10. The three-loops are designated generally by the reference numerals 12a, 12b and 12c and each includes a respective pump 14a, 14b and 14c which causes the coolant to flow through respective steam generators 16a, 16b and 16c. Coolant is circulated by the pumps 14a, 14b and 14c through the reactor 10 where it is heated by the nuclear reactor core. The coolant then circulates through the steam generators 16a, 16b and 16c where some of its sensible heat is used to boil water on the secondary side of each generator. The coolant then returns to each pump suction in a continuous manner. The loops 12a, 12b and 12c are equivalent and coolant mixes between the three-loops internally of the reactor vessel 10. All of the internal surfaces of the plant corrode to some extent, releasing crud to the coolant as both soluble and particulate material. The major contribution, by far, comes from the steam generator tubes which represent the bulk of the wetted surface. The crud circulates with the coolant through the core in reactor 10, where, depending on several parameters, it deposits on the core surfaces for a time and is irradiated. The irradiated crud is then released to the coolant and freely circulates through the loops 12a, 12b and 12c until it deposits on relatively cooler plant surfaces, particularly in the steam generators 16a, 16b and 16c. This process continues indefinitely resulting in activation of plant surfaces which are external to the core. The reactor coolant system (RCS) is designated broadly by the reference numeral 20 in FIG. 1. The RCS is provided with a Chemical and Volume Control System (CVCS) which is designated broadly by the reference numeral 22 in FIG. 1. The CVCS performs several known functions necessary for proper plant operation. As can be seen in FIG. 1, coolant is continually removed from loop 12c via line 24 and is returned to loop 12a via line 26. Heat is exchanged between the coolant being returned to loop 12a via line 26 and the coolant in line 24 which has been withdrawn from the reactor coolant system 20. This heat exchange occurs in a heat exchanger 28 where the coolant in line 24 is relatively cooled and the coolant in line 26 is relatively heated. After passing through the regenerative heat exchanger 28, coolant from line 24 is directed through a letdown orifice 30 and a control valve 32 and the same is further cooled in a letdown heat exchanger 34. Heat exchanger 34 is provided with cooling water entering through line 36 and exiting by way of a line 38. The cooled stream is then directed through a mixed anion/cation bed demineralizer 40 where the coolant stream is chemically conditioned in a conventional manner. The conditioned coolant is filtered in a conventional filter 41 and the filtered coolant is directed into a volume control tank 42 which again operates in a conventional manner. In this regard, those of ordinary skill in the art to which the present invention pertains will recognize that tank 42 may generally be provided with auxiliary and accessory devices and mechanisms for controlling the volume of coolant in system 20. Moreover, mixed bed demineralizer such as the demineralizer 40 are generally provided in pairs and installed in such a manner that one can be taken out of operation for maintenance and/or restocking with active ingredients while the other continues to treat the coolant. The auxiliary and accessory devices for the volume control tank 42 and the second demineralizer are not shown in FIGS. 1 and 2 for enhanced clarity and simplicity. The chemical and volume control system 22 may also include a chemical mixing tank 44 where chemical additives may be prepared for addition to CVCS 22 through line 46. After the coolant exits from tank 42 and after additives have been inserted into the coolant through line 46, the treated coolant is pumped by pump 48 back through exchanger 28 and reintroduced into system 20 via line 26. CVCS 22 thus operates to remove soluble and particulate impurities by filtration and ion exchange in the mixed bed demineralizer 40 in a generally conventional fashion and by conventional filtration on the reactor coolant filter 41. Manifestly, CVCS 22 serves as the makeup system and chemical addition system for RCS 20. In operation, a fraction of the reactor coolant is bled off from RCS 20 through line 24 and is cooled in exchangers 28 and 34 and depressurized in orifice 30 and valve 32. The cooled and depressured coolant from line 24 is then transported to the demineralizer 40. The demineralized coolant flows through filter 41 and into volume control tank 42 and then back to the suction of charging pump 48. The coolant is pumped by pump 48 through heat exchanger 28 where it is heated and returned to RCS 20 through line 26. Losses in reactor coolant and/or required chemical additive materials are introduced via chemical mixing tank 44 and line 46 where the makeup joins the main flow at the suction of charging pump 48. This is the preferred injection point for the zirconium oxide scavenger material, which may be provided as a slurry in reactor makeup water introduced through line 51. In operation, colloidal and near-colloidal crud particles are difficult to filter by conventional means; however, the larger ZrO.sub.2 /crud aggregates may easily be filtered using any one of a number of conventional filtration schemes. The zirconium oxide/crud aggregates may be filtered utilizing the conventional plant letdown filter 41 and the conventional CVCS mixed-bed demineralizer 40. Alternatively, a zirconium oxide filled deep-bed filter may be utilized in place of or in addition to CVCS demineralizer 40. Moreover, with particular reference to FIG. 2, an electromagnetic filter 50 might be employed for removing the zirconium oxide-crud aggregates from the coolant stream since the particles will have magnetic properties, either because the seeding particle is so designed as to be magnetically susceptible or because of the attracted coating of crud particles on the ZrO.sub.2 particle surface. In FIG. 2, the schematic diagram illustrates an electromagnetic filter 50 disposed between heat exchanger 34 and demineralizer 40. Otherwise the diagram is the same as shown in FIG. 1. FIG. 2 simply is used in place of the equipment shown to the right of the dashed line A--A in FIG. 1. With regard to the electromagnetic filter 50 illustrated in FIG. 2, reference is made to the '215 patent mentioned above and to a publication entitled Study of Magnetic Filtration Applications to the Primary and Secondary Systems of PWR Plants, M. Troy, et al., EPRI Final Report, NP 514, (May, 1978). the disclosures of which are specifically incorporated herein by reference. The suspensible particles having active surfaces in accordance with the present invention should be prepared so as to have a large specific surface area and an appropriate particle size. Suitable zirconium oxide particles may be prepared using any one of a number of different methods. Moreover, while known demineralizers useful in connection with CVCS methodology are generally effective in removing colloidal and near-colloidal crud, the agglomerating effect of zirconium oxide will enhance the removal efficiencies available using conventional plant systems. Zirconia has been shown to have ion exchange properties for certain fission products, and to capitalize on this factor and provide an appropriate filter for the zirconium oxide agglomerate particles, a deep-bed zirconium oxide filter could be substituted for one of the two conventional mixed bed ion exchangers normally installed in the CVCS and used in parallel with the deep-bed ion exchanger 40. Alternatively, a separate zirconium oxide deep-bed filter could be placed in series with and upstream from the demineralizer 40. This latter arrangement would protect the mixed bed from being plugged by particulates since the deep-bed zirconia filter would also serve as a filter for the agglomerated particulates. Useful methods for production of scavenger particles suitable for employment in connection with the present invention include oxidation of zirconium metal sponge with subsequent sizing; vacuum sputtering of zirconia onto a prepared particulate substrate of high specific surface area which, in the application using an electromagnetic filter as the removal technique, might preferably be magnetite; oxidation of zirconium salts under appropriate conditions such as, for example, atomization of salt solution into an air atmosphere at high temperature; and sizing of zirconium hydride, a brittle solid, followed by oxidation. Magnetite particles may also be coated with zirconium oxide using a chemical adsorption technique. In such technique, a zirconium salt is pre-adsorbed onto the surface of magnetite particles and then the coated particles are subjected to controlled surface oxidation to produce a layer of zirconium oxide on the magnetite particles. In this regard, there are many known procedures for coating the surfaces of particles with a surface layer of another substance and thus provide coated particles that are useful for purposes of the present invention. Such procedures are known and are not part of the present invention. The total zirconium oxide surface area should be relatively large compared to the total area of the clad surface of the fuel elements. The larger the specific surface of the zirconia the better, since less zirconium oxide will then be required. A useful system might employ 10 micron spherical zirconia particles having a typical porous particle specific surface area of 200 sq. meters per gram. A one pound batch of such particles would have a surface area of about 1.times.10.sup.6 ft.sup.2 whereas the typical core surface area in a conventional reactor is about 6.times.10.sup.4 ft.sup.2. Accordingly, a 6.times.10.sup.-2 lb batch of particles will have a surface area which is equivalent to a typical core surface area. The volume of coolant in a typical RCS application is about 1.3.times.10.sup.4 ft.sup.3, and accordingly, the concentration of zirconia particles to provide a surface area which is 20 times larger than the core area is approximately 2 ppm. Moreover, a 1.2 lb batch of zirconia particles will thus provide a surface area which is about 20 times as large a the surface area of the core. As will be apparent to those skilled in the pertinent art, zirconia coated magnetite particles having comparable surface area characteristics may generally be slightly lighter than solid zirconia particles. Although, in the practice of the present invention, the point where the particles are added to the coolant is not critical, a convenient point is simply to add the particles to tank 44 as a concentrated suspension. Such suspension may then be flushed by makeup water directly into the suction of pump 48. Agglomeration of the crud particles onto attracting scavenger particles will enhance the ability to filter the crud using any of the methods discussed above. Moreover, the use of a high-flow high-temperature filtration process may one day be particularly attractive since the removal rate should be significantly greater than that which is available through the use of the CVCS 22 circuit. Such high-flow high-temperature filtration processes employing an electromagnetic filter (EMF) to remove small nickel ferrite and magnetite crud particles directly has been previously proposed by M. Troy et al., Effects of High-Temperature Filtration on PWR Plant Radiation Fields, supra and by Moskal et al. (E. J. Moskal and W. T. Bourns, High-Flow, High Temperature Magnetic Filtration on the Primary Heat Transport Coolant of the CANDU Power Reactors, Paper No. 37, in Proceedings of Conference on Water Chemistry of the Nuclear Reactor System, Bournemouth, England (October, 1978)). The zirconium oxide particle seeding process of the present invention should not only enhance the effectiveness of the EMF, but should make the use of any high-temperature backflushable mechanical filter practical. Although hightemperature high-pressure filtration might one day prove to be the best procedure, today the use of such procedure would require expensive retrofitting of existing plants and generally is therefore contraindicated. Thus, at present, filtration in the CVCS may offer a more practical solution. The PWR plant letdown filter 41, as utilized in conventional application, is generally designed to filter particles larger than 25 microns in size. Accordingly, such filters are not effective for removing typical crud particles. The agglomerating action of the zirconium oxide particles, in accordance with the present invention, will thus enhance the effectiveness of filters such as filter 41. With regard to electromagnetic particle trapping, Oberteuffer (J. A. Oberteuffer, Magnetic Separation: A Review of Principles, Devices and Applications, IEEE Transactions on Magnetics, Vol. Mag-10, No. 2, (June, 1974)) has shown that to obtain the optimum effect of a magnetic filter on small paramagnetic particles, the EMF matrix element radius should be approximately three times the particle radius. Obviously for practical magnetic filter matrices, the approach to optimum design falls off as the radius of the target particles decreases. For submicron (near-colloidal) fractions of the primary corrosion product, magnetic filters tend to become less effective. Particles with strongly positive magnetic susceptibility, for example, magnetite, nickel ferrite, etc., are acted upon by the EMF magnetic gradient to produce an attractive magnetic force which competes with the fluid drag forces. If the magnetic force is dominant, the particle will be trapped. Since hydraulic drag is a function of the second power of the particle radius, whereas magnetic attractive force depends on the third power of the radius (i.e, particle volume), a point will be reached, as particle size is reduced, where drag force becomes dominant. By collecting the small crud particles on the surfaces of larger coated magnetic particles, the effective critical trapping particle radius may thus be considerably reduced and magnetic attractive force caused to become dominant. Magnetite has a saturation magnetization of approximately 90 emu/gm. Zirconium dioxide is diamagnetic (i.e., repulsed by a magnetic gradient) with a magnetic susceptibility of -1.times.10.sup.-7 emu/gm. Under a magnetic field of 4.times.10.sup.3 oersteds (sufficient to saturate magnetite) the magnetization of zirconia would be -4.times.10.sup.-4 emu/gm. Accordingly, since the duplex magnetite/ZrO.sub.2 particle will be mostly magnetite, the attraction of the magnetite particle by the EMF will be essentially unaffected by the zirconia coating. Furthermore, since the crud particles themselves have magnetic characteristics, even the simple zirconia particles, once coated with agglomerated crud, will have acquired sufficiently strong magnetic characteristics to be trapped by a magnetic filter. Periodically a magnetic filter will be isolated from the coolant system to allow off-loading of the collected corrosion products to waste disposal. When the filter has been isolated, the matrix is demagnetized and the filter backflushed. Without the magnetic forces on the particles the fluid drag is sufficient to entrain the particles thus removing them from the matrix. |
abstract | An electron beam apparatus, in which an electron beam emitted from an electron gun having a cathode and an anode is focused and irradiated onto a sample, and secondary electrons emanated from the sample are directed into a detector, the apparatus further comprising means for optimizing irradiation of the electron beam emitted from the electron gun onto the sample, the optimizing means may be two-stage deflectors disposed in proximity to the electron gun which deflects and directs the electron beam emitted in a specific direction so as to be in alignment with the optical axis direction of the electron beam apparatus, the electron beam emitted in the specific direction being at a certain angle with respect to the optical axis due to the fact that, among the crystal orientations of said cathode, a specific crystal orientation allowing a higher level of electron beam emission out of alignment with the optical axis direction. |
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054105773 | claims | 1. A core-melt source reduction system which is supported within a nuclear reactor containment structure for catching and stopping the progression of a molten core during a core meltdown accident such that the containment structure of the reactor does not deteriorate, the core-melt source reduction system comprising: a plurality of layers of a first material for chemically reacting with the molten core to absorb the molten core, and; a plurality of layers of lead, one each of said plurality of layers of said lead being disposed between each consecutive pair of said plurality of layers of said first material, each of said plurality of layers of said lead being substantially thinner than each of said plurality of layers of said first material, said plurality of layers of said lead for slowing the progression of the molten core such that the molten core can sufficiently react with said plurality of layers of said first material. a plurality of layers of a glass material for chemically reacting with the molten core to absorb the molten core, said glass material having a density, said glass material having a softening point lower than 1200.degree. C., said glass material dissolving a portion of the molten core, and; a plurality of layers of a second material, one each of said plurality of layers of said second material being disposed between each consecutive pair of said plurality of layers of said glass material, each of said plurality of layers of said second material being substantially thinner than each of said plurality of layers of said glass material, said plurality of layers of said second material for slowing the progression of the molten core such that the molten core can sufficiently react with said plurality of layers of said glass material. a plurality of layers of a glass material for chemically reacting with the molten core to absorb the molten core, said glass material having a density, said glass material having a softening point lower than 1200.degree. C., said glass material dissolving a portion of the molten core, and; a plurality of layers of lead, one each of said plurality of layers of lead being disposed between each consecutive pair of said plurality of layers of said glass material, each of said plurality of layers of lead being substantially thinner than each of said plurality of layers of said glass material, said lead having a density more than said density of said glass material, said plurality of layers of lead for slowing the progression of the molten core such that the molten core can sufficiently react with said plurality of layers of said glass material. a plurality of layers of a glass material for chemically reacting with the molten core to absorb the molten core, said glass including lead oxide for chemically reacting with the molten core such that the reaction products are stable in the presence of air and water and; a plurality of layers of a second material, one each of said plurality of layers of said second material being disposed between each consecutive pair of said plurality of layers of said glass material, each of said plurality of layers of said second material being substantially thinner than each of said plurality of layers of said glass material, said plurality of layers of said second material for slowing the progression of the molten core such that the molten core can sufficiently react with said plurality of layers of said glass material. a plurality of layers of a glass material for chemically reacting with the molten core to absorb the molten core, said glass material being comprised of 1 to 4 moles of lead oxide and 1 mole of boron oxide, and; a plurality of layers of a second material, one each of said plurality of layers of said second material being disposed between each consecutive pair of said plurality of layers of said glass material, each of said plurality of layers of said second material being substantially thinner than each of said plurality of layers of said glass material, said plurality of layers of said second material for slowing the progression of the molten core such that the molten core can sufficiently react with said plurality of layers of said glass material. 2. The core-melt source reduction system of claim 1 wherein said first material is glass. 3. The core-melt source reduction system of claim 2 wherein said glass has a softening point lower than 1200.degree. C. said glass having a density less than a density of said second material, said glass being able to dissolve a portion of the molten core. 4. The core-melt source reduction system of claim 2 wherein said glass includes a sacrificial metal oxide for reacting with the molten core such that the reaction products are stable in the presence of air and water. 5. The core-melt source reduction system of claim 4 wherein said sacrificial metal oxide is lead oxide. 6. The core-melt source reduction system of claim 2 wherein said glass is comprised of 1 to 4 moles of lead oxide and 1 mole of boron oxide. 7. The core-melt source reduction system of claim 1 wherein said system includes thermal insulation surrounding said system and resting on the containment structure, said insulation for protecting the containment structure from high temperatures. 8. A core-melt source reduction system which is supported within a nuclear reactor containment structure for catching and stopping the progression of a molten core during a core meltdown accident such that the containment structure of the reactor does not deteriorate, the core-melt source reduction system comprising: 9. The core-melt source reduction system of claim 8 wherein said glass material includes a sacrificial metal oxide for reacting with the molten core such that the reaction products are stable in the presence of air and water. 10. The core-melt source reduction system of claim 9 wherein said sacrificial metal oxide is lead oxide. 11. The core-melt source reduction system of claim 8 wherein said density of said glass material is less than a density of said second material. 12. The core-melt source reduction system of claim 8 wherein said glass material is comprised of 1 to 4 moles of lead oxide and 1 mole of boron oxide. 13. The core-melt source reduction system of claim 8 wherein said second material is lead. 14. The core-melt source reduction system of claim 8 wherein said system includes thermal insulation surrounding said system and resting on the containment structure, said insulation for protecting the containment structure from high temperatures. 15. A core-melt source reduction system which is supported within a nuclear reactor containment structure for catching and stopping the progression of a molten core during a core meltdown accident such that the containment structure of the reactor does not deteriorate, the core-melt source reduction system comprising: 16. The core-melt source reduction system of claim 15 wherein said glass material includes a sacrificial metal oxide for reacting with the molten core such that the reaction products are stable in the presence of air and water. 17. The core-melt source reduction system of claim 16 wherein said sacrificial metal oxide is lead oxide. 18. The core-melt source reduction system of claim 15 wherein said glass material is comprised of 1 to 4 moles of lead oxide and 1 mole of boron oxide. 19. The core-melt source reduction system of claim 15 wherein said system includes thermal insulation surrounding said system and resting on the containment structure, said insulation for protecting the containment structure from high temperatures. 20. A core-melt source reduction system which is supported within a nuclear reactor containment structure for catching and stopping the progression of a molten core during a core meltdown accident such that the containment structure of the reactor does not deteriorate, the core-melt source reduction system comprising: 21. The core-melt source reduction system of claim 20 wherein said glass has a softening point lower than 1200.degree. C., said glass having a density less than a density of said second material, said glass being able to dissolve a portion of the molten core. 22. The core-melt source reduction system of claim 20 wherein said glass is comprised of 1 to 4 moles of lead oxide and 1 mole of boron oxide. 23. The core-melt source reduction system of claim 22 wherein said second material is stainless steel. 24. The core-melt source reduction system of claim 20 wherein said second material is lead. 25. The core-melt source reduction system of claim 20 wherein said system includes thermal insulation surrounding said system and resting on the containment structure, said insulation for protecting the containment structure from high temperatures. 26. A core-melt source reduction system which is supported within a nuclear reactor containment structure for catching and stopping the progression of a molten core during a core meltdown accident such that the containment structure of the reactor does not deteriorate, the core-melt source reduction system comprising: 27. The core-melt source reduction system of claim 26 wherein said glass has a softening point lower than 1200.degree. C., said glass having a density less than a density of said second material, said glass being able to dissolve a portion of the molten core. 28. The core-melt source reduction system of claim 26 wherein said glass includes a sacrificial metal oxide for reacting with the molten core such that the reaction products are stable in the presence of air and water. 29. The core-melt source reduction system of claim 28 wherein said sacrificial metal oxide is lead oxide. 30. The core-melt source reduction system of claim 26 wherein said second material is stainless steel. 31. The core-melt source reduction system of claim 21 wherein said second material is lead. 32. The core-melt source reduction system of claim 26 wherein said system includes thermal insulation surrounding said system and resting on the containment structure, said insulation for protecting the containment structure from high temperatures. |
054024579 | abstract | In a fuel assembly, rods are disposed in meshes of a grid. Crossing points of the grid are distributed in a checker-board-like manner, partly in an upstream crossing plane and partly in a downstream crossing plane. Webs of the grid run in zigzag form between the two planes. As a result, flow resistance which is produced by the webs and/or by mixing vanes disposed thereon and by flow turbulences is shifted into different axial planes and is considerably reduced. |
048184713 | claims | 1. In the combination of at least one Local Power Range Monitor (LPRM) string and a plurality of fuel assemblies arranged in side-by-side spaced positions about said string, said LPRM string having a hollow tube and a plurality of neutron detectors located therein at spaced axial locations for providing local power monitoring information, said hollow tube of said string for receiving a neutron flux sensitive probe to calibrate said detectors, each of said fuel assemblies having a plurality of spaced fuel rods, an outer hollow tubular channel surrounding said fuel rods and a plurality of fuel rod spacers disposed within and axially along said channel and about said fuel rods so as to maintain them in side-by-side spaced relationship, all of said spacers of at least one of said fuel assemblies being composed solely of a material incapable of producing a localized change in neutron flux, the improvement which comprises: a plurality of elements attached to the exterior of said channel of said at least one fuel assembly so as to be spaced from and in non-contacting relation with said channels of adjacent fuel assemblies and with said fuel rods of said one fuel assembly, located axially at different preselected positions therealong at each of which position it is desired to produce a localized change in netruon flux and located adjacent to and spaced from said hollow tube of said string, each of said elements being composed of a material capable of producing a localized change in neutron flux such that the sole function of said each element is to produce such localized change in neutron flux upon passage of the probe through said hollow tube of said string and past said elements, whereby the probe will sense the neutron flux change being produced by each of said elements and thereby the position of the probe can be tracked as it is moved through said string tube. said channel of said at least one fuel assembly is rectangular in cross-section and has a corner located adjacent to said string tube; and each of said plurality of elements is arranged about said corner of said channel. a plurality of elements attached to the exterior of said channel of each of said fuel assembly so as to be spaced from and in non-contacting relation with said channels of adjacent fuel assemblies and with said fuel rods of said each fuel assembly, located axially at different preselected positions therealong at each of which position it is desired to produce a localized change in neutron flux and located adjacent to and spaced from said hollow tube of said string, each of said elements being composed of a material capable of producing a localized change in neutron flux such that the sole function of said each element is to produce such localized change in neutron flux upon passage of the probe through said hollow tube of said string and past said elements, whereby the probe will sense the neutron flux change being produced by each of said elements and thereby the position of the probe can be tracked as it is moved through said string tube. each of said channels of said fuel assemblies is rectangular in cross-section and has a corner located adjacent to said string tube; and each of said plurality of elements is attached about said corner of said each channel. a plurality of angle-shaped metal strips attached to and extending about the exterior of said corner on each of said fuel assembly channels so as to be spaced from and in non-contacting relation with said channels of adjacent fuel assemblies and with said fuel rods of said each fuel assembly, located axially at different preselected positions therealong at each of which position it is desired to produce a localized change in neutron flux and located adjacent to and spaced from said hollow tube of said string, each of said strips being composed of a material capable of producing a localized change in neutron flux such that the sole function of said each strip is to produce such localized change in neutron flux upon passage of the probe through said hollow tube of said string and past said strips, whereby the probe will sense the neutron flux change being produced by each of said strips and thereby the position of the probe can be tracked as it is moved through said string tube. 2. The combination as recited claim 1, wherien each of said elements is a strip of said material. 3. The combination as recited in claim 1, wherein: 4. In the combination of at least one local Power Range Monitor (LPRM) string and a plurality of fuel assemblies arranged in side-by-side spaced positions about said string, said LPRM string having a hollow tube and a plurality of neutron detectors located therein at spaced axial locations for providing local power monitoring information, said hollow tube of said string for receiving a neutron flux sensitive probe calibrate said detectors, each of said fuel assemblies having a plurality of spaced fuel rods, an outer hollow tubular channel surrounding said fuel rods and a plurality of fuel rod spacers disposed within and axially along said channel and about said fuel rods so as to maintain them in side-by-side spaced relationship, each of said spacers of said fuel assemblies being composed solely of a material incapable of producing a localized change in neutron flux, the improvement which comprises: 5. The combination as recited in claim 4, wherein each of said elements is a strip of said material. 6. The combination as recited in claim 4, wherein: 7. In the combination of at least one Local Power Range Monitor (LPRM) string and a plurality of fuel assemblies arranged in side-by-side spaced positions about said string, said LPRM string having a hollow tube and a plurality of neutron detectors located therein at spaced axial locations for providing local power monitoring information, said hollow tube of said string for receiving a neutron flux sensitive probe to calibrate said detectors, each of said fuel assemblies having a plurality of spaced fuel rods, an outer hollow tubular channel surrounding said fuel rods and a plurality of fuel rod spacers disposed within and axially along said channel and about said fuel rods so as to maintain them in side-by-side spaced relationship, each of said channels of said fuel assemblies being rectangular in cross-section and having a corner located adjacent to and spaced from said string tube, each of said spacers of said fuel assemblies being composed solely of a material incapable of producing a localized change in neutron flux, the improvement which comprises: |
abstract | In space, a linear accelerator firing charged pellets can be situated at a large distance from a target at which the pellets are aimed. The accelerator can fire a graduated-speed train of pellets over a period of seconds or longer which arrive at the target simultaneously, and impart a large pulse of energy. An accelerator of modest power can thus provide a pulse in the megajoule range, sufficient to ignite fusion. It is necessary to provide course corrections to the pellets, to bring them together with very high precision as they approach the target. An ideal siting is to place the accelerator at the Earth-Moon L1 or L2 Lagrange point, and the fusion target at a point on the surface of the Moon where the pellets will strike at grazing incidence, i.e. on a great circle intersecting the lunar poles. Length of the particle trajectory is over 60000 km. |
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description | The following is a detailed description of an embodiment of an X-ray apparatus of this invention, with reference of FIGS. 1-3. FIG. 1 shows a state of an X-ray flux 19a rotating about a focal point 3a of an X-ray tube 3 along a plane which is perpendicular to the body axis of a person 2. FIG. 2 is a plane view of a flat panel detector 6 with which the X-ray apparatus is equipped. FIG. 3 is a schematic view for explanation of an operation of an X-ray apparatus in the embodiment of this invention. In FIG. 1, a supporting arm 35 supports an X-ray tube 3 and the flat panel detector 6 which oppose to each other across the person 2. A supporting base 36 supports all structures of the X-ray apparatus. An X-ray tube rotation driver 26 rotates the X-ray tube about the focal point 3a along a plane, which is perpendicular to the body axis of the person 2. The X-ray tube 3 has an aperture, through which X-rays come out, where an X-ray limiting device 4a is attached. The X-ray tube 3 rotates with the X-ray limiting device 4a. The flat panel detector 6 detects X-rays transmitted through the person 2. In FIG. 3, a control part 31 controls the X-ray tube rotation driver 26 to rotate the X-ray tube 3 about the focal point 3a in the right and left direction. A control panel 100 has a handle 101, which is used to instruct rotation of the X-ray tube 8 through the control part 31 and the X-ray tube rotation driver 26. An operator can move the X-rays flux center 19c to the right or left target part of the person 2 by inclining a handle 101 on the control panel 100 on the control panel 100 in the right or left direction as watching a photofluorography image on a monitor. The rotation center of the X-ray tube 3 is set at the focal point 3a of the X-ray tube 3 in this embodiment. However, the rotation center may be set at a point other than the focal point 3a. One of ordinary skill in the art would appreciate that, in this embodiment; the focal point 3a is positioned on a stationary axis that is disposed above the patient and extends parallel with the patient""s body axis. However, in any event, the driver rotates the X-ray tube and the X-ray limiting device about the stationary axis in an arc defining a plane oriented perpendicularly to the patient""s body axis. The X-ray limiting device 4a, which is attached to the aperture of the X-ray tube 3, has R shield blades 30 corresponding to the right, blades of the lower blades 10 and upper blades 7, as shown in FIG. 8. The X-ray limiting device 4a is structured so that the R shield blades 30 and L shield blades 29 move independently from each other. A control part 31, receiving signals from the edge detector 6a, controls a R shield blade driver 28 and L shield blade driver 27 which drive the R shield blades 30 and L shield blades 29 in the X-ray limiting device 4a, respectively. The control panel 100 also has a handle 102 and a handle 103, in addition of the handle 101. The handle 102 and handle 103 are used to instruct the movement of the R shield blades 30 and L shield blades 29 through the control part 31, respectively. As shown in FIG. 2, the flat panel detector 6 is a solid state flat plate detector on which semiconductor elements are arranged in a matrix. The flat panel detector 6 has an image detecting part 32 which is formed with an image detecting area 32a. The flat panel detector 6 also has an edge detector 6a along four edge sides thereof. When X-rays are irradiated onto the area of the edge detector 6a, the edge detector 6a detects the X-rays and outputs signals corresponding to the X-rays to the control part 31. The flat panel detector 6 may have the edge detector 6a along two edge sides thereof along the width of the person 2. The edge detector 6a consists of the X-ray semiconductor elements in a part of four edge sides among the whole X-ray semiconductor elements on the flat panel detector 6. The edge detector 6a may also be a separate X-ray detector from the whole X-ray semi-conductor elements on the flat panel detector 6. The following is a detailed description of an operation of the embodiment, with reference of FIG. 3 and FIG. 4 with a flow diagram of operation of the control part 31. The person 2 rests on the table 1 and then a bronchoscope or endoscope is inserted in the mouth to observe the inside thereof. Then, radioscopy is performed to recognize the target part of the person 2 with the person 2 standing still. When the target part is in either of the left or right side of the person 2, the operator rotates the X-ray tube 3 by inclining the handle 101 so that the X-ray flux center 19c comes to the target part. The control part 31 controls the X-ray tube rotation driver 26 to rotate the X-ray tube 3 by the amount in proportion to the signal value provided by a sensor, not shown in the figures, which detects the amount of inclination of the handle 101. In the above operation, as shown in the FIG. 4, first, the control part 31 monitors if there is an indication for rotating the X-ray tube 3 through the handle 101, an indication for moving the R shield blades 30 through the handle 102, and an indication for moving the L shield blades 29 through the handle 108 (S11, S12, S14). When recognizing an indication for rotating the X-ray tube 3, the control part 31 rotates, through the X-ray tube rotation driver 26, the X-ray tube 3 by the rotation amount indicated with the handle 101 (S16). Then, the control part 31 judges if the X-ray flux 19a reaches the edge detector 6a by receiving signals from the edge detector 6a (S17). When the control part 31 judges that the X-ray flux 19a reaches the edge detector 6a, it moves either of the R shield blades 30 or L shield blades 29 by the certain amount which places in the side of the edge detector 6a which detected X-ray through the R shield blade driver 28 or L shield blade driver 27 (S18), then the control part 31 reiterates this operation until the edge detector 6a does not detect X-ray (S17, S18). When the edge detector 6a does not become to detect X-ray, the control part 31 monitors the indications from the handle 101, the handle 102, or the handle 103 again (S11, S12, S14). The above operation makes it possible to move the center of the X-ray irradiation field without moving the body of the person and also to prevent the X-ray irradiation field from going outside of the image detecting part 32. The operation of the handle 102 or handle 103 make it possible to move one of the R shield blades 30 or L shield blades 29 independently, for example, depending on the size of the target part (S12, S13, S14, S15). This operation makes it possible to perform an X-ray imaging with the necessary and sufficient size of the X-ray irradiation field. In this case, since the control part 31 also judges if the edge detector 6a detects X-rays (S17), when the control part 31 judges that the edge detector 6a detects X-rays, it moves either of the R shield blades 30 or L shield blades 29, by the certain amount. This shifts the X-rays from the edge detector 6a, through the R shield blade driver 28 or L shield blade driver 27 (S18), and the control part 31 reiterates this operation until the edge detector 6a does not detect X-rays (S17, S18). Therefore, in spite of possible over operation of the handle 102 or the handle 103, the control part 31 makes it possible to prevent the X-ray irradiation field, formed by X-ray flux 19a, from going outside of the image detecting part 32. In the above embodiment, the R shield blades 30 and the L shield blades 29 of the X-ray limiting device 4a are controlled based on signals provided by the edge detector 6a placed along the edges of the flat panel detector 6. However, it is also possible to control the R shield blades 30 and the L shield blades 29 for the X-ray irradiation field, formed by the X-ray flux 19a not to go out of the image detecting part 32 of the flat panel detector 6 by a calculation with the rotation angle of the X-ray tube 3 and the size of the X-ray irradiation field limited by the X-ray limiting device 4a. The following is a detailed description of an operation of this embodiment, with reference of FIG. 5 and FIG. 6 with a flow diagram of operation of the control part 31. The control part 31 monitors if there is an indication for rotating the X-ray tube 3 through the handle 101, an indication for moving the R shield blades 30 through the handle 102, and an indication for moving the L shield blades 29 through the handle 103 (S1, S2, S4). Recognizing an indication for rotating the X-ray tube 3, the control part 31 calculates the permissible aperture size AP after rotating the X-ray tube 3 by the rotation amount indicated with the handle 101 (S6). The permissible aperture size AP is defined as the distance from the X-ray flux center 19c to the edge of the flat panel detector 6. In FIG. 5, the permissible aperture size AP is calculated from the following formula: AP=the center-edge distance (34)xe2x88x92Xxe2x80x83xe2x80x83(1) Where X={the focal pointxe2x88x92panel distance (33)}xc3x97tan xcex8 In the above formula, xcex8 is defined as the X-ray tube rotation angle, which shows the amount of the rotation degree of the X-ray tube 3 from the center of the flat panel detector 6. X is defined as the distance from the center of the flat panel detector 6 to the x-ray flux center 19c. The center-edge distance 34 is defined as the distance from the center of the flat panel detector 6 to the edge of the image detecting part 32 of the flat panel detector 6. The focal pointxe2x80x94panel distance 33 is defined as the distance from the focal point 3a to the center of the flat panel detector 6. When the permissible aperture size AP is smaller than the distance, on the flat panel detector 6, of the outer half defined as the part between the outer edge of the X-ray flux 19a and the X-ray flux center 19c, the control part 31 controls the L shield blade driver 27 or the R shield blade driver 28 to move either the R shield blades 30 or the L shield blades 29, so that the distance from the X-ray flux center 19c becomes the permissible aperture size AP (S7, S8), then rotates the X-ray tube 3 by the rotation amount indicated (S9). When the permissible aperture size AP is larger than the distance of the outer half on the flat panel detector 6, the control part 31 rotates the X-ray tube 3 by the rotation amount indicated (S7, S9). Then the control part 31 monitors the indications from the handle 101, the handle 102, or the handle 103 again (S1, S2, S4). The R shield blades 30 and the L shield blades 29 can be controlled independently with the handle 102 and handle 103 depending on the size of the target part of the person 2, as the operation shown in FIG. 4. In the above embodiment, the permissible aperture size AP is defined as the distance between the X-ray flux center 19c and the edge of the image detecting part 32 of the flat panel detector 6. However, the permissible aperture size may be defined as the angle from the X-ray flux center 19c to the edge of the image detecting part 32 of the flat panel detector 6. In this case, the permissible aperture size AP can be obtained with the following formula. AP=xcex8Fxe2x88x92xcex8,xe2x80x83xe2x80x83(2) with tan xcex8F=(the center-edge distance (34))/(the focal pointxe2x80x94panel distance (33)). In the embodiment shown in FIG. 3, the control part 31 receives signals from the edge detector 6a and only provides signals for controlling the R shield blade driver 28 and the L shield blade driver 27. In the embodiment shown in FIG. 5, the edge detector 6a is not needed, but the controller 31 needs a calculation function. in the embodiments shown in FIGS. 3-6, the R shield blades 30 and the L shield blades 29 are structured to move independently with the operation of the handle 102 and the handle 103. However, the R shield blades 30 and the L shield blades 29 may be structured to move by the same distance dependently in the opposite direction from each other. This embodiment makes it possible to operate both of them with a single handle. In the above mentioned X-ray apparatus, since an X-ray tube rotates about its focal point along a plane which is perpendicular to the body axis, X-ray irradiation field can be changed without moving the table. Therefore, when an examination with a brouchoscope, endoscope and so on is carried out, the examination can continue without moving the person into whom the hardware is inserted. Furthermore, in this invention, when X-rays are irradiated onto any edge area on the flat panel detector, the X-rays do not go outside of the edge of the flat panel detector. Therefore, unnecessary X-rays for imaging can be cut out. |
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description | 1. Field of the Invention The present invention relates to a position measurement system and a lithographic apparatus. 2. Description of the Related Art A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. In order to accurately transfer the pattern onto the target portion of the substrate, the relative position of the pattern and the target portion should be known. Therefore, the lithographic apparatus is in general equipped with one or more measurement systems to determine the position of, e.g., the substrate or the patterning device. Examples of such measurement systems are interferometer systems or encoder systems. Both systems can be designated as incremental systems. Using such a position measurement system, the position of an object can be determined relative to a chosen reference as an integer number of increments (or periods) of a predefined length. Using an interferometer, this increment may, e.g., correspond to a quarter of the wavelength of the interferometer laser. In case of an encoder system, the increment may, e.g., correspond to a quarter of the period of the encoder grating. In order to improve the resolution of such an incremental measurement system, methods are developed to provide an interpolation within one increment (or period). Such a position measurement system usually comprises an incremental measurement unit comprising a first part comprising a sensor and a second part co-operating with the sensor of the first part. In case of an interferometer system, the second part may comprise a mirror for reflecting a beam originating from the interferometer laser to the sensor. In case of an encoder system, the second part may comprise a one- or two-dimensional grating co-operating with the sensor (in this case, the sensor usually comprises an encoder head). Because of the limited size of, e.g., the mirror or the grating, the operating range of the measurement system is limited. In order to increase the operating range, the measurement system can be equipped with more that one sensor arranged on different locations along a required operating range ensuring that the position measurement can be performed over the entire required operating range. In such a multi-sensor measurement system, problems may arise during the transition of the position measurement by a first sensor to the position measurement by a second sensor. Conventionally, one (or more) measurement values of the first sensor are used to initialize the second sensor during the transition (such initialization may be required because the initial measurement by the second sensor may not be related to a reference). Because this initialization is based upon measurements of both the first sensor and the second sensor, measurements that may contain a measurement error, this initialization may result in an increased measurement error for the second sensor. During a next transition (either a transition of a measurement by the second sensor to a measurement by a third sensor or a transition of a measurement by the second sensor to a measurement by the first sensor) a further increase in the measurement error may occur. As such, the accuracy of a multi-sensor measurement system used in a conventional way may deteriorate due to transition from a measurement by one sensor to a measurement by another sensor. Embodiments of the invention include an improved position measurement system. In embodiments of the invention, the accuracy of the position measurement system is improved during a take over process between two sensors of the measurement system. According to an embodiment of the invention, there is provided a position measurement system for measuring a position of an object, comprising: a first incremental measurement unit for measuring a first number of first distance steps in a distance between a reference frame and the object, wherein the first number equals a first integer value plus a first fraction, a second incremental measurement unit for measuring a second number of second distance steps in a distance between the reference frame and the object, wherein the second number equals a second integer value plus a second fraction, wherein the position measurement system is constructed and arranged to initialize the second incremental measurement unit on the basis of the first number and the second fraction. According to a further embodiment of the invention there is provided a lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate, wherein the apparatus further comprises a position measurement system according to the present invention. FIG. 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., UW radiation or EUV radiation). a support structure (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g., a wafer table) WT constructed to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. The support structure supports, i.e., bears the weight of, the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.” The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit. The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix. The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system.” As here depicted, the apparatus is of a transmissive type (e.g., employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g., employing a programmable mirror array of a type as referred to above, or employing a reflective mask). The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure. Referring to FIG. 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system. The illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may comprise various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section. The radiation beam B is incident on the patterning device (e.g., mask MA), which is held on the support structure (e.g., mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g., an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in FIG. 1) can be used to accurately position the mask MA with respect to the path of the radiation beam B, e.g., after mechanical retrieval from a mask library, or during a scan. In general, movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the mask table MT may be connected to a short-stroke actuator only, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies. The depicted apparatus could be used in at least one of the following modes: 1. In step mode, the mask table MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. 2. In scan mode, the mask table MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the mask table MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single, dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. 3. In another mode, the mask table MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above. Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed. In order to project a pattern onto a predefined target portion of the substrate, the lithographic apparatus requires an accurate measurement system for determining the position of the substrate table and the patterning device. Interferometer systems and encoder systems are found to be suitable for accurately determining the position of an object (e.g., a substrate table or a mask table). Both measurement systems can be designated as incremental position measurement systems. In both systems, the position of an object can be determined relative to a chosen reference as an integer number of distance steps (or periods or increments) of a predefined length. Within one increment or distance step, the position can be determined by means of interpolation in order to improve the resolution of the measurement. As such, an output signal Xout of the position measurement system, representing the position of an object (e.g., an X-position) can be described by the following equation (1):Xout=IC+(N+φ+ε)·p (1) wherein p=distance step of the measurement system IC=initialization constant N=integer number representing a number of distance steps p φ=fraction between 0 and 1 ε=measurement error. Fraction φ in equation (1) is also referred to as the phase of the position measurement. In general, an incremental position measurement comprises an incremental measurement unit comprising a first part comprising a sensor and a second part co-operating with the sensor of the first part. In case of an interferometer system, the second part may comprise a reflective surface (e.g., a mirror) for reflecting a beam originating from the interferometer laser to the sensor. In case of an encoder system, the second part may comprise a one- or two-dimensional grating co-operating with the sensor. Either the first part or the second part can be mounted to the object of which the position is to be determined (as an example, the object may be an object table for holding a substrate or a patterning device of a lithographic apparatus). In general, an incremental position measurement system does not provide an absolute position measurement but provides information about a distance traveled between a first position and a second, by counting the number of distance steps p that are detected during the displacement from the first position to the second and by an interpolation within one period. Therefore, in order to provide an output signal Xout representing the position of an object, e.g., relative to a reference or in order to define a reference position such as a zero reference, a calibration may be required. As an example, starting from a known position of the object (e.g., a position relative to a frame), the initialization constant IC can be set during a calibration sequence such that the output signal of the measurement system correspond to that known position. Alternatively, the initialization constant IC may also be used to define a zero reference for the measurements. It should also be noted that the calibration may be based on another position measurement. The measurement range of the position measurement system is, in general, limited by the size of the second part, i.e., the reflective surface in case of an interferometer system or the grating in case of an encoder system. In case the operating range of the object of which the position is to be determined is larger that the measurement range, one can opt to increase the size of the second part (e.g., increase the length of the reflective surface or the grating) or one can choose to position multiple sensors along the required operating range. The latter is illustrated in FIG. 2a. FIG. 2a schematically depicts a measurement setup for measuring the X-position of an object 20 provided with a linear grating 22. As an example, the object may be a mask table of a lithographic apparatus. The linear grating 22 is schematically depicted as an array of black and white squares representing the periodicity of the grating with a period p. The measurement setup further comprises an array of sensors 30 (comprising sensors 30.1, 30.2, 30.3 and 30.4) arranged to co-operate with the grating 22. In order to perform a measurement, the optical sensor should be able to see the grating 22. As such, it will be clear that the range of X-positions that allow a position measurement of the object is determined by the length of the grating in the X-direction and therefore would be limited to the length of the grating in the X-direction incase only one sensor would be applied. By a proper arrangement of an array of sensors, the position measurement by a first sensor can be taken over by a neighboring second sensor when the first sensor reaches the end of its measurement range. FIG. 2b schematically an X-position of the object 20 wherein the grating is in front of two sensors 30.1 and 30.2 (it is assumed that the output signal of sensor 30.1 represents the position of the object). In such a position, both sensors could be used to provide a signal representing the position of the object. However, as discussed, the signal generated by sensor 30.2 initially does not represent the position of the object; an initialization is required. This initialization may result in sensor 30.2 providing a signal representing the position of the object such that sensor 30.2 may take over the position measurement of sensor 30.1. FIGS. 3a, 3b and 3c schematically illustrate the take over process from one sensor to another in a more detailed manner. FIG. 3a schematically depicts an initial position of an object 20 provided with a grating 22 having a period p. It is further assumed that the X-position of the object relative to a reference frame 32 is known in the initial position (X0) as depicted. This position reference (X0) can be applied to calibrate the measurement system such that the output signal of the sensor 30.1 substantially equals X0 in the initial position. This can be achieved as follows: When the measurement system is brought online in the initial position, the sensor 30.1 may produce an output signal X1out—0, prior to initializationX1out—0=IC0+(N10φ10+ε)·p (2) Equation (2) comprises an initialization constant IC0. Initially, the initialization constant may have an arbitrary value or can be set equal to zero. Initially, N10, representing the number of periods traveled between two positions, can be set to zero or may have any arbitrary value. φ10 represents the phase determined by the measurement system in the initial position. Referring to FIG. 3a, φ10 may correspond to a fraction of period 28. ε·p represents the error of the actual measurement. It should be noted that the measurement error is a stochastic variable that can be characterized by a standard deviation σε. As such, the subtraction of two signals comprising the error may, in general, not result in a cancellation of the error because the errors of both signals can be considered to be independent. Rather, the standard deviation (defined by its probability distribution) of the result of the subtraction yields in a larger standard deviation than σε. The addition (or subtraction) of two independent signals having a standard deviation a and b results in a signal having a standard deviation equal to a √{square root over (a2+b2)}. In order to provide an output signal corresponding to X0, a value ICa can be added to the initial value of the initialization constant IC0:ICa=X0−X1out—i (3) By doing so, the output signal corresponds to X0. Once the measurement system is calibrated, a measurement of the X-position within the measurement range of the sensor 30.1 can be performed. In case the object 20 is to be displaced beyond the measurement range of the sensor 30.1, a take over of the position measurement by sensor 30.2 may be required. Such a take over can be performed in a position as schematically indicated in FIG. 3b. Designating the X-position by Xt in the position as indicated, the output signal of sensor 30.1 in this position (X1out—t) can be described as:X1out—t=IC0+(N1t+φ1t+ε)·p=Xt (4) IC0 in equation (4) represents the initialization constant of the sensor 30.1 after calibration. When sensor 30.2 is brought online in the position as depicted in FIG. 3b, it may generate an output signal X2out—t, prior to initialization:X2out—t=IC2+(N2t+φ2t+ε)·p (5) As indicated, the output signal comprises an initialization constant IC2 initially having an arbitrary value prior to the initialization. Also N2t may initially have an arbitrary value. In general, X2out—t, shall not correspond to Xt, because no initialization has been done yet. In order to obtain this correspondence (i.e., a correspondence between the output signal of sensor 30.2 and the X-position Xt), an initialization constant ICa can be added to the initial value of the initialization constant IC2:ICa=Xt−X2out—t (6) Once initialized, the position measurement can be obtained from the output signal of sensor 30.2. As such, a take over process between sensor 30.1 and sensor 30.2 can be established. As a result, a position measurement of the object 20 may be performed by sensor 30.2 in a position as indicated in FIG. 3c, i.e., a position wherein sensor 30.1 can no longer perform the position measurement thereby increasing the operating range of the object. The process as described in FIGS. 3a to 3c can be summarized as follows: At first, a first measurement sensor is calibrated based upon, e.g., a reference position. In order to take over the position measurement from the first sensor, a second sensor is initialized using the output signal from the first sensor in a position wherein both sensors are able to perform a position measurement. When the object 20 is in a position as depicted in FIG. 3c, it may be required to reposition it again to a position wherein the position can only be measured using sensor 30.1. Conventionally, such a take over from a position measurement using sensor 30.2 back to a position measurement using sensor 30.1 is done in a similar manner as the take over from a position measurement using sensor 30.1 to a position measurement using sensor 30.2, i.e., in order to take over the position measurement from the sensor 30.2, sensor 30.1 is initialized using the output signal from the sensor 30.2 in a position wherein both sensors are able to perform a position measurement. It should be noted that such an approach may have an important impact on the positional accuracy of the measurement. This can be illustrated as follows: Assuming a first sensor arranged to measure the position of an object, the sensor being initialized in a reference position as described above. The output signal of the sensor can in general be described by equation (1) and contains a certain measurement error ε·p (note that the measurement error may also be described as a separate error rather than as a fraction of the period p). Because the initialization constant IC (see eq. (3)) is based upon a measurement, this constant also comprises a measurement error ε·p. (It is assumed that the measurement error ε·p made by a sensor on different positions or by different sensors in an array of sensors is substantially equal for all measurements and that those errors are independent of each other). As a result, a position measurement with the first sensor at an arbitrary position after initialization may have a measurement error that is larger than ε·p because the initialization constant is subject to a measurement error ε·p and the actual measurement is subject to a measurement error ε·p . Characterizing the error of the measurements by the standard deviation σε, the standard deviation of the position measurement of the first sensor substantially equals σε·√{square root over (2)} (because the addition (or subtraction) of two signals which are independent and having a standard deviation a and b results in a standard deviation equal to √{square root over (a2+b2)}). During the take over process of the position measurement by a second sensor, the second sensor is initialized using the position measurement of the first sensor. The initialization constant of the second sensor can be determined according to equation (6). The initialization constant according to equation (6) is a function of the measurement of the first sensor (having an standard deviation of σε·√{square root over (2)}) and the initial measurement of the second sensor (having a standard deviation σε). As a result, the initialization constant of the second sensor may have a standard deviation equal to σε·√{square root over (3)}. As a result, a position measurement with the second sensor at an arbitrary position after initialization may result in a further increase in the measurement error because of the initialization that is subject to a standard deviation of σε·√{square root over (3)} and because of the actual measurement that is subject to an standard deviation of σε. In case both errors are independent, the standard deviation of the output signal of the second sensor equals σε·√{square root over (4)}. In case the same procedure is repeated during a subsequent take over take over from a position measurement using the second sensor back to a position measurement using the first sensor, the standard deviation of the first sensor may have increased to σε·√{square root over (6)}. As can be seen, in case a larger number of take over processes are to be expected, the take over process may cause a built up of take over errors and may result in significant reduction in the accuracy of the measurement. It should be noted that the built up of take over errors can be mitigated to some extend by calculating the initialization constant on the basis of an average of multiple measurement samples. However, in order for this method to be effective, the averaging should be performed over a comparatively large period in time because in general, the dominant part in the measurement error ε·p may be low frequent. As an example, the frequency spectrum may comprise an important so-called 1/f component implying that the size of the error in the frequency domain is proportional to one over the frequency f. Significantly reducing the take over error by averaging would require sampling over several tenth of a second. In most cases this would cause an unacceptable throughput penalty. In the measurement system according to the present invention, a different approach is adopted during the take over process in order to reduce or mitigate the built up of take over errors. The approach adopted in the present invention uses the insight that the measurement systems as described can be considered deterministic with respect to the measured phase φ: a repeated object position, measured with a specific sensor, will result in the same phase φ or, the measured phase φ can be considered to represent an absolute position within one period p (apart from the measurement error). In case the relative position between different sensors of an array of sensors remains substantially constant, one can easily acknowledge that the difference between the measured phase of one sensor and the measured phase of an other sensor also remains substantially constant in a repeated object position. This can be illustrated as follows: FIG. 4a schematically depicts an object 40, a grating 44 mounted to the object (the grating is represented as an array of alternating black and white squares (44.1, 44.2, 44.3 and 44.4) having a period p). FIG. 4a further depicts two sensors 46.1 and 46.2 mounted on a reference frame 42 and arranged to co-operate with the grating 44 for measuring the X-position of the object. Assuming that sensor 46.1 has been initialized (e.g., by equating the sensor output signal to a predefined value in a reference position), the position of the object 40 (i.e., the X-position X1) can be obtained from output signal of sensor 46.1. When the object 40 is displaced to a position as depicted in FIG. 4b (X-position equal to X2), sensor 46.1 may provide an output signal representing the X-position of the object, the output signal can be characterized by an initialization constant IC1, an integer number N1 representing a number of distance steps (or increments) traveled from the reference position and a phase φ1 (describing the position within the period of the actual position, i.e., the period with reference number 44.1. In order for sensor 46.2 to take over the position measurement of sensor 46.1, an initialization can be performed based on the difference between the output signal of sensor 46.1 (representing the X-position X2) and the output signal of sensor 46.2. When sensor 46.2 is brought online, it may generate an arbitrary output signal Xa that, in general, can be described as:Xa=IC2+(N2φ2+ε)·p (7) wherein IC2 denotes an initialization constant. Subscript 2 in eq. 7 refers to variables/constants of sensor 46.2. φ2 in equation (7) corresponds to the phase measurement of sensor 46.2 in the X-position as depicted in FIG. 4b (as such, φ2 may represent a fraction of the period 44.4 of the grating 44). When sensor 46.2 is brought online, IC2 and N2 may have an arbitrary, but known, value (both may, as an example, be set equal to zero). The X-position of the object as depicted in FIG. 4b (X2) can be described by:X2=IC1+(N1+φ1+ε)·p (8) IC1, N1 and φ1 are known and are related to the X-position as shown in FIG. 4b. The difference Δ between the output signal of sensor 46.1 (representing the X-position X2) and the output signal of sensor 46.2 (Xa) can therefore be written as:Δ=X2−Xa=(IC1−IC2)+(N1−N2)·p+(φ1−φ2)·p+ε″·p (9) Note that Equation 9 introduces an error ε″·p for the difference Δ that may be larger than the error error ε·p of the output signals Xa and X2. The standard deviation of the difference Δ can be represented by σε·√{square root over (2)}, wherein σε corresponds to the standard deviation the error ε·p of the output signals Xa and X2 Equation 9 provides a relationship between the variables N1, N2, φ1 and φ2 and the initialization constants IC1 and IC2. It may further be observed that, the phase difference ((φ1−φ2) is substantially constant for a given position and determined by the geometry of the measurement system. As a consequence, a repeated object position can result in the same phase measurements φ1 and φ2 and in the same phase difference (φ1−φ2). The difference Δ can be applied to initialize the sensor 46.2 in order for sensor 46.2 to take over the position measurement of the object. This may be obtained by adding the difference Δ to the output signal Xa, e.g., by setting the initialization constant IC2 to the initial value of IC2+Δ. (note that this corresponds to the conventional approach as described above). Once sensor 46.2 is initialized, an X-position of the object as indicated in FIG. 4c can be measured using sensor 46.2. Note that in the situation as depicted, sensor 46.1 may not provide an output signal corresponding to the X-position of the object. In case the object is to return subsequently to the position as indicated in FIG. 4b, the conventional approach would be to initialize sensor 46.1 based upon the output signals of sensor 46.2 and sensor 46.1. However, as indicated above, this would lead to an increase in the measurement error. In the measurement system according to the present invention, a previously established relation between the sensors 46.1 and 46.2 (as described by equation 9) is used to initialize the sensor 46.1 in the following manner (rather than adding the difference Δ to the output signal Xa, e.g., by setting the initialization constant IC2 to the initial value of IC2+Δ): In order to calibrate sensor 46.1 such that its output signal represents the position of the object 40, IC1, N1 and φ1 are required (see equation 8). Because the phase measurement φ1 is deterministic, it can be obtained from the measurement system. IC1 can also be considered known from the initial calibration of the sensor 46.1. As such, the only unknown to be determined is N1. According to the present invention, N1 is calculated from the previously established relationship between the sensor parameters (e.g., equation (9)). This calculation may, e.g., be accomplished by rounding off to the nearest integer value. By doing so, the measurement errors can be eliminated, provided that they are smaller than half a period p (which is usually the case). As a result, sensor 46.1 can be calibrated substantially without introducing an additional error. It should be noted that the take over from sensor 46.2 back to sensor 46.1 can be performed in a different position than the position in which the relationship according to equation 9 is determined. Equation 9, in general, provides a relation between N1, N2, φ1 and φ2 that can be summarized as:(N1−N2)+(φ1−φ2)=C (10) wherein C is a constant. Equation 10 can, e.g., be applied to determine N1 when N2, φ1 and φ2 are known or to determine N2 when N1, φ1 and φ2 are known according to the following equations 11a and 11b:N1=round(C+N2−(φ1−φ2)) (11a)N2=round(−C+N1+(φ1−φ2)) (11b) wherein ‘round( )’ is used to designate the well-known round off function to the nearest integer. As such, a subsequent take over from a position measurement using sensor 46.1 to a position measurement using sensor 46.2 can be performed in a similar manner, substantially without introducing an additional measurement error. It will be clear that in case more than two sensors are present, similar relationships can be determined between, e.g., a second sensor and a third sensor in order to perform a take over from a position measurement using the second sensor to a position measurement using the third sensor. It should be noted that the round-off process may also be applied during the initialization process of the second sensor. This can be illustrated as follows: Assuming the first sensor 46.1 being calibrated at a known object position such that IC1, N1 and φ1 are known. When sensor 46.2 is brought online, IC2, N2 should be determined. φ2 is available from measurement of sensor 46.2. In order to initialize N2, one may set IC2 equal to zero and initialize N2 using equation 11b. When the value of N2, as found is used to generate an output signal, the output signal shall, in general, not correspond to the actual position, due to the round off function that is applied to obtain N2. In order for the output signal to correspond to the actual position, IC2 can be calibrated by equating it to the actual position (e.g., corresponding to the output signal of the first sensor 46.1) minus the output signal of sensor 46.2 (after introduction of the calculated N2). The measurement system may comprise a control unit for processing the output signals of the sensors of the array of sensors. The control system can be arranged to select and/or process one or more of the output signals in order to generate an output signal suitable for use in e.g. a position controller. When a relationship between the sensor parameters N1, N2, φ1 and φ2 is established (see e.g., equations 9 or 10), it can be applied, for example, in the control unit of the measurement system or in a separate unit in order to perform the take over process according to the present invention. The control unit of the measurement system may further be arranged to perform the round off process in order to determine the integer number representing a number of periods traveled from the reference position of the sensor to be initialized. It should be noted that the take over process according to the present invention may also be applied in a homodyne or a heterodyne interferometer measurement system. Such a measurement system may also require a take over from a position measurement using a first sensor to a position measurement using a second sensor. FIG. 5a schematically depicts an interferometer measurement system for measuring the Y-position of an object 50 (e.g., a substrate table of a lithographic apparatus) relative to a reference frame 60. The measurement system comprises an array of sensors 62 comprising a first sensor 62.1 and a second sensor 62.2 mounted on the reference frame 60. A mirror (in general a reflective surface) 64 is mounted to the object 50 in order to reflect laser beams 66 and 68 to the sensors 62.1 and 62.2. The Y-position of the object can be determined by the interferometer measurement system by counting a number of periods (each period corresponding, for example, to a quarter of the wavelength of the laser beam) that is detected and by interpolation within one period. By using an array of sensors, the objects Y-position can be determined over a range of motion in the X-direction that is larger than the length of the mirror in the X-direction. FIGS. 5b and 5c schematically depict two X-positions of the object 50. In the X-position as depicted in FIG. 5b, the Y-position of the object can be determined using sensor 62.1. In the X-position as depicted in FIG. 5c, the Y-position can be determined using sensor 62.2. In order to displace the object from a position as depicted in FIG. 5b to a position as depicted in FIG. 5c while maintaining a Y-position measurement, a take over process according to the present invention between sensors 62.1 and 62.2 can be performed. In case of a heterodyne interferometer system, counting the number of increments and the interpolation to determine the phase can be done relative to a reference signal. In general, both sensors may use the same reference signal or a fixed offset may exist between the reference signals. As such, a relationship between the sensor parameters as described in eq. 10 can be established in order to apply the take over process of the present invention. It should be noted that the laser beams 66 and 68 may originate from the same laser source or from a different laser source. In the latter case, the Y-measurement performed with sensor 62.1 may have a different period (or increment) than the period of a Y-measurement performed with sensor 62.2. In general, when a different period is applicable for two sensors, the take over process according to the present invention can be applied in a similar manner. In such an arrangement, the relationship established between the parameters N1, N2, φ1 and φ2 (representing the measurement of the phase and the integer number of periods passed of the sensors) may be expanded to include the period p1 of the first sensor and the period p2 of the second sensor. This can be done as follows. Assuming an incremental position measurement system such as an interferometer system or an encoder system (e.g., a Y-measurement) comprising a first (index 1) and a second (index 2) sensor operating with a different period, the output signal Yout—1 of the first sensor and the output signal Yout—2 of the second sensor can be described by:Yout—1IC1+(N1+φ1+ε)·p1Yout—2IC2+(N2+φ2+ε)·p2 (12) wherein p1, p2=period of the incremental measurement system of the resp. sensors IC1, IC2=initialization constant of the resp. sensors N1, N2=integer representing a number of periods of the resp. sensors φ1, φ2=fraction between 0 and 1 representing the interpolation within a period of the resp. sensors ε=measurement error. A difference Δ′ between the output signal of both sensors may take the following form:Δ′=(IC1−IC2)+(N1·p1−N2·p2)+(φ1·p1−φ2·p2)+(ε·p1−ε·p2) (13) and can be used to derive the following relationship between the parameters N1, N2, φ1, φ2, p1 and P2:(N1·p1−N2·p2)+(φ1·p1−φ2·p2)=C′ (14) wherein C′ is a constant. Note that, regarding the error as indicated in eq. 13, the considerations as made for eq. 9 are valid, i.e., the standard deviation of the difference Δ′ may be larger than the standard deviation of the output signals of eq. 12. Equation 14 can be applied to determine N1 when N2, φ1 and φ2 are known or to determine N2 when N1, φ1 and φ2 are known according to the following equations 15a and 15b: N 1 = round ( C + N 2 · p 2 - ( φ 1 · p 1 - φ 2 · p 2 ) p 1 ) ( 15 a ) N 2 = round ( - C + N 1 · p 1 - ( φ 1 · p 1 - φ 2 · p 2 ) p 2 ) ( 15 b ) wherein ‘round( )’ is used to designate the well-known round off function to the nearest integer. Using equations 15a and 15b, the take over process as used in the present invention can be perform when the sensors involved are operating with a different period. The take over process according to the present invention may also be applied in a measurement system comprising multiple gratings and multiple sensors. FIG. 6a schematically depicts such an arrangement comprising two gratings 80, 82 mounted to a reference frame 84, an object 86 displaceable along the X-direction relative to a frame 88 and two sensors 90, 92 arranged to co-operate with the gratings 80, 82, the two sensors being arranged adjacent to each other in the X-direction and mounted to the object 86. In such an arrangement, the take over process as applied in the present invention can be applied in order transfer from a position measurement using the first grating to a position measurement using the second grating. Departing from an initial position as depicted in FIG. 6b wherein the position measurement is performed by sensor 92 in co-operation with the grating 80, the object may be displaced to a position as depicted in FIG. 6c. In case the object is to be displaced to a position as depicted in FIG. 6d the position measurement should first be taken over by the sensor 90 co-operating with grating 80. This can be done using the take over process applied in the present invention and explained in FIG. 4b. Once the position measurement is taken over by sensor 90 co-operating with grating 80, the object 86 can displace to the position as indicated in FIG. 6d. In the position as depicted in FIG. 6d the position measurement by sensor 90 in co-operation with grating 80 can be changed to a position measurement by sensor 92 in co-operation with grating 82 by a take over process as applied in the present invention. Note that grating 82 may have a period that is different from the period of grating 80. Once the position measurement by sensor 92 in co-operation with grating 82 is established, the object may, e.g., displace to a position as indicated in FIG. 6e. It should be noted that the described invention may also be applied to monitor certain drift components in the measurement system such as the distance from sensor to sensor or the length of the grating. The take over process according to the present invention applies a previously established relationship between parameters obtained from different sensors (see e.g., eq. 10 or 14). This relationship can, e.g., be established during calibration of the measurement system. In case of a relative slowly drifting measurement system, the relationship between the sensor parameters may change over time. This change can be monitored because the relationship between the sensor parameters can be determined each time a take over process is performed resulting in a actualized value of C. Comparing the actualized value to the initially established value provides information on the drift of the measurement system over time. By monitoring C as a function of time and correcting for it, the take over process according to the present invention can also be applied in relative slow drifting systems. It should be noted that the present invention may equally be applied in a measurement system arranged to measure a position in more than one degree of freedom. As an example, the present invention can be applied in a 2D encoder measurement system. Such a system may comprise a plurality of sensors constructed and arranged to co-operate with a two-dimensional grating in order to determine the position of an object in both X-direction and Y-direction. In order to perform the take over process according to the present invention, a relationship as described in eq. 9 or 10 can be established for both directions. Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion,” respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers. Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured. The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g., having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams. The term “lens,” where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components. While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g., semiconductor memory, magnetic or optical disk) having such a computer program stored therein. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below. |
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claims | 1. A gripper mechanism for moving an object having a surface cavity, the gripper mechanism comprising:an actuation end moveable in an axial direction;a rotary body;a first mechanism configured such that movement of the actuation end in an axial direction rotates the rotary body;a gripper moveable between an engaged position and a disengaged position, wherein in the engaged position the gripper is capable of engaging an object and in the disengaged position the gripper is capable of being received into and removed from a cavity of an object,wherein the gripper is connected to the rotary body by a second mechanism configured such that rotary motion of the body moves the gripper between the engaged position and the disengaged position; anda latching arrangement comprising an internal latch enclosed within the gripper mechanism, wherein:the latching arrangement is configured to prevent the gripper moving from the engaged to the disengaged position before the actuation end is moved by a predetermined distance; andthe latching arrangement is configured such that axial movement of the actuation end in a direction opposite to a desired direction of motion of the gripper mechanism at least partially unlatches the latching arrangement. 2. The gripper mechanism according to claim 1 comprising a linear actuator, wherein the actuation end is defined at one end of the linear actuator. 3. The gripper mechanism according to claim 2, wherein the first mechanism is provided between the linear actuator and the rotary body. 4. The gripper mechanism according to claim 1 wherein the internal latch is configured such that axial movement of the actuation end in the direction opposite to the desired direction of motion of the gripper mechanism unlatches the internal latch. 5. The gripper mechanism according to claim 1 wherein the first mechanism comprises a pin and a curved pathway, the pin being arranged to move along the curved pathway. 6. The gripper mechanism according to claim 5, wherein the curved pathway has a tick shape arranged so that when the gripper is in the engaged position the pin is at a tip of the tick, and arranged such that axially downward movement of the actuation end by a predetermined distance is required before the pin and actuation end can move axially upward. 7. The gripper mechanism according to claim 1 wherein the latching arrangement comprises an external latch, and wherein at least a portion of the external latch is positioned external to a volume defined by a remainder of the gripper mechanism such that the latch can be actuated by a component external to the gripper mechanism. 8. The gripper mechanism according to claim 1, wherein a biasing element is arranged to resist axial movement of the actuation end. 9. The gripper mechanism according to claim 1, wherein the gripper is configured such that in the engaged position at least a portion of the gripper is positioned more radially outward from a central longitudinal axis of the gripper mechanism than in the disengaged position. 10. The gripper mechanism according to claim 1 comprising an indicator configured to indicate the position of the gripper. 11. The gripper mechanism according to claim 1, wherein the gripper mechanism is a nuclear fuel rod gripper mechanism, and in the engaged position the gripper is capable of engaging a cavity in a plug end of a fuel rod and in the disengaged position the gripper is capable of being received into and removed from a cavity in a plug end of a fuel rod. 12. A gripper mechanism for moving an object having a surface cavity, the gripper mechanism comprising:an actuation end moveable in an axial direction;a rotary body;a first mechanism configured such that movement of the actuation end in an axial direction rotates the rotary body;a gripper moveable between an engaged position and a disengaged position, wherein in the engaged position the gripper is capable of engaging an object and in the disengaged position the gripper is capable of being received into and removed from a cavity of an object,wherein the gripper is connected to the rotary body by a second mechanism configured such that rotary motion of the body moves the gripper between the engaged position and the disengaged position;a latching arrangement configured to prevent the gripper moving from the engaged to the disengaged position before the actuation end is moved by a predetermined distance,wherein the latching arrangement comprises an external latch and at least a portion of the external latch is positioned external to a volume defined by a remainder of the gripper mechanism such that the latch can be actuated by a component external to the gripper mechanism; anda housing wherein the external latch comprises one or more latch arms engageable with the housing. 13. The gripper mechanism according to claim 12, wherein the latch arms comprise one or more engagement features and the housing comprises one or more complimentary engagement features. 14. The gripper mechanism according to claim 13, wherein the engagement feature of the housing comprises circumferential grooves provided at two axial locations on the housing; a first groove corresponding to a position where the gripper is in the disengaged position and a second groove corresponding to a position where the gripper is in the engaged position. 15. The gripper mechanism according to claim 12, wherein the latch arms are biased to a position of engagement with the housing. 16. The gripper mechanism according to claim 12, wherein the gripper mechanism is a nuclear fuel rod gripper mechanism, and in the engaged position the gripper is capable of engaging a cavity in a plug end of a fuel rod and in the disengaged position the gripper is capable of being received into and removed from a cavity in a plug end of a fuel rod. 17. The gripper mechanism according to claim 12, wherein the latching arrangement comprises an internal latch enclosed within the gripper mechanism. 18. A gripper mechanism for moving an object having a surface cavity, the gripper mechanism comprising:an actuation end moveable in an axial direction;a rotary body;a first mechanism configured such that movement of the actuation end in an axial direction rotates the rotary body;a gripper moveable between an engaged position and a disengaged position, wherein in the engaged position the gripper is capable of engaging an object and in the disengaged position the gripper is capable of being received into and removed from a cavity of an object,wherein the gripper is connected to the rotary body by a second mechanism configured such that rotary motion of the body moves the gripper between the engaged position and the disengaged position, and the gripper is configured such that in the engaged position at least a portion of the gripper is positioned more radially outward from a central longitudinal axis of the gripper mechanism than in the disengaged position; anda guide plate at a position axially beneath the gripper, wherein the guide plate is configured to guide the gripper between the engaged and the disengaged position. 19. The gripper mechanism according to claim 18, wherein the gripper mechanism is a nuclear fuel rod gripper mechanism, and in the engaged position the gripper is capable of engaging a cavity in a plug end of a fuel rod and in the disengaged position the gripper is capable of being received into and removed from a cavity in a plug end of a fuel rod. |
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abstract | A method and system for determining the overall performance of a power plant are provided. The system includes a plurality of components including a processor configured to generate a first reference model of the power plant and generate a first measured model of the power plant. The processor is further configured to determine the performance impact of the at least one of the plurality of components of the power plant on the overall thermal performance of the power plant, normalize the performance impact to design conditions, and output at least one of the normalized performance impact on overall plant performance. |
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description | The United States Government has rights in this invention pursuant the terms of Department of Energy contract number DE-AC09-96SR18500. The present invention relates to a method for decontamination of radioactive waste, and in particular, a method employing an electrolyte for decontamination of metals that have been contaminated by exposure to radioactive materials. Nuclear industry equipment and structural materials are subjected to radioactive contamination during use. The equipment, which is usually constructed from stainless steel or other metal, must therefore be routinely cleaned or otherwise treated to render it safe for further use or disposal. Such treatments include scrubbing, washing or abrading of the surface of the material in an effort to remove the deposits. One such decontamination technology involves immersing the contaminated material in a carbonate solution and subjecting it to electrolysis sufficient to cause stripping or separating of the contaminants from the surface of the metal. Representative examples include the following U.S. patents; U.S. Pat. No. 3,873,362 to Mihram et al., U.S. Pat. No. 4,217,192 to Lerch et al., U.S. Pat. No. 4,537,666 to Murray et al., U.S. Pat. No. 4,663,085 to Edna et al., U.S. Pat. No. 5,102,511 to Suwa et al., U.S. Pat. No. 5,322,644 to Dunn et al. and U.S. Pat. No. 5,340,505 to Hanulik et al. In each of the above cases, the chemical decontaminate comprises various acidic and/or alkaline reagents, with or without oxidizing agents. In these chemical-only decontamination methods, the electrolytic cell is employed solely for the purpose of regenerating the decontamination reagent. Accordingly, these methods do not teach use of the electrolytic cell as the primary mechanism for decontamination. Further, the reagents are in and of themselves hazardous or dangerous, particularly the acidic reagents. Finally, prior art acidic or alkaline reagents are destructive to the metal equipment being treated since they invariably erode or etch the surface of the metal during treatment. Other prior art decontamination methods include the following: U.S. Pat. No. 4,193,853 to Childs et al. teaches a metal decontamination system employing an electrolyte comprising nitrate salts, borate, fluoride or oxalate individually and at a basic pH. In a preferred embodiment, the electrolyte contains a combination of nitrate, borate, fluoride and oxalate ions and a pH between 7 and 11. U.S. Pat. No. 4,481,089 to Izumida et al. teaches a metal decontamination system employing a neutral salt electrolyte with an alternating electrolysis method. Contamination is removed by applying a current to the electrochemical cell and at programmed intervals the current is reversed thereby causing loosening or shaking off of the contaminant from the surface of the metal. As is apparent, programmed current fluctuations requires the system be equipped with appropriate controls which adds to the cost of the system. U.S. Pat. No. 4,481,090 to Childs teaches an improved system wherein a more efficient acidic electrolyte, which may include high concentrations of nitrate, is substituted for a prior art alkaline nitrate, borate, fluoride and oxalate electrolyte. U.S. Pat. No. 4,615,776 to Sasaki et al. discloses an electrochemical metal decontamination method having a highly concentrated phosphoric acid solution for the electrolyte. The pH of the electrochemical cell is approximately 2. U.S. Pat. No. 5,439,562 to Snyder et al. discloses a nickel recovery process employing electrochemical metal decontamination and in particular method a nickel recovery process directed toward removal of actinide radionuclides and technetium. U.S. Pat. No. 5,614,077 to Wittle et al. discloses an electrochemical decontamination system including a reaction chamber where the pH and electrical current may be varied as required to precipitate out any radionuclide contamination. There is no disclosure of a specific electrolyte nor is contact provided between the anode or cathode and the item being decontaminated. In view of the above, a need has existed in the art for a decontamination method that will not corrode or otherwise damage the metal equipment being treated thereby allowing the decontaminated equipment to be reused. It is an object of the present invention to provide a method for decontaminating radioactive contaminated metal including application of a moderately acidic carbonate/bicarbonate electrolyte solution adapted to be non-corrosive to the metal being decontaminated. Another object of the present invention is to provide a method for decontaminating metal contaminated by cesium, strontium or actinides, such as plutonium and uranium. A further object of the present invention is to provide a method for decontaminating metal contaminated by radioactive materials that are strongly adhered to the surface of the metal and therefore cannot otherwise be removed by washing of the metal or the like. Yet another object of the present invention is to provide a method for decontaminating metal that has been contaminated by radioactive material wherein following treatment the decontaminated metal may be rinsed and then properly disposed of or reused. Yet another object of the present invention is to provide an efficient and economical method for decontaminating radioactive scrap metal to thereby reduce the disposal and storage costs normally associated with contaminated scrap metal. A still further object of the present invention is to provide an electrolyte solution for decontaminating radioactive contaminated metals wherein following treatment, the electrolyte solution may be distilled to remove excess water and the remaining volume readily disposed of in an efficient and economical manner. And another object of the present invention is to provide an electrolyte solution adapted to strip off radionuclides that have been plated or adhered to the surface of the metal being treated. These and other objects are achieved by a decontamination method for removing radionuclides plated or otherwise adhered to the surface of stainless steel or aluminum materials, the method comprising the steps of contacting the metal with a moderately acidic carbonate/bicarbonate electrolyte solution containing sodium or potassium ions and thereafter electrolytically removing the radionuclides from the surface of the metal whereby radionuclides are caused to be stripped off of the material without corrosion of or etching to the material surface. The method according to the present invention employs an acidic carbonate and/or bicarbonate electrolyte solution. The electrolyte solution promotes efficient and safe electrochemical stripping of radionuclides from the surface of a contaminated metal. The method is especially adapted for treatment of aluminum or stainless steel materials since they will not be damaged during electrolysis. In the preferred embodiment, the electrolyte solution is moderately acidic i.e. having a pH of about 4, which renders the electrolyte uniquely non-corrosive to the stainless steel or aluminum metal being decontaminated. The electrolyte solution must readily provide the flow of free ions in solution during electrolysis sufficient to promote conduction of the applied current between the cathode and the anode while at the same time remove radionuclides without damage or corrosion to the surface of the material being decontaminated. Representative electrolyte solutions include, potassium or sodium carbonate and/or bicarbonate solutions having a moderately acidic pH of about 4. In embodiments employing carbonate and bicarbonate in the electrolyte, the carbonate concentration is preferably about 2% by weight of the bicarbonate in water. FIG. 1 is a schematic diagram illustrating a separation apparatus A. As is apparent, it is within the scope of the present invention to modify the separation apparatus for commercial or other specific applications. The apparatus A comprises a tank or vessel 2 appropriately adapted to receive and retain an electrolyte solution 8. A DC current power source 4 is provided, the power source including appropriate controls for regulating current density, voltage and the like. The power source 4 is electrically connected to a negative electrode or cathode 6 shown disposed in the interior of vessel 2 and shown immersed in the electrolyte. The positive electrode or anode comprises the object being decontaminated and is identified in the drawing as reference numeral 10. The object 10 is suspended in the tank 2 and electrically connected to the power source by appropriate means. The object 10 may comprise any of a variety of metals but is preferably constructed from stainless steel. Application of the DC current between the electrodes causes radionuclides attached to the surface of the anode; namely, cesium, strontium and actinides (such as plutonium and uranium) to be electrochemically stripped off of the metal object and into solution without damaging erosion of the metal surface. The decontaminated metal may then be rinsed and disposed of or reused, while the electrolyte solution containing the removed radionuclides disposed of as liquid waste or further distilled to concentrate the radioactive nuclides for further treatment or disposal. While this invention has a preferred design that has been illustrated and described, it will be apparent to those skilled in the art that various changes, modifications or adaptations may be easily made without deviating from the scope of the invention or the limits of the claims appended hereto. |
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abstract | A filter which includes a stack of deformable foils which are locally attached to one another, and also includes comparatively rigid members which are situated to both sides of the stack of foils, extend parallel to the surface of the foils and each of which is attached to an outer surface of the stack of foils by way of a buffer member. The foils can be moved away from one another in a main direction by means of the rigid members, which main direction extends transversely of the surface, in order to form ducts between the foils. The buffer member is then contractible mainly in a direction which extends parallel to the surface and transversely of the ducts. |
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claims | 1. A method for the extraction of americium comprising:providing a first immobilized liquid membrane including a metal oxide separating layer, a supporting layer formed of a separate material than the separating layer, and an immobilized solvent retained in the separating and supporting layers, the separating layer defining a core, the supporting layer extending around the separating layer;directing an aqueous feed solution containing Am(VI) through the core and along a surface of the separating layer distal from the supporting layer; anddirecting a receiving solvent along a surface of the supporting layer distal from the separating layer to transfer Am(VI) from the aqueous feed solution, through the immobilized solvent, and into the receiving solvent. 2. The method of claim 1 including introducing ozone in the aqueous feed solution to oxidize Am(III) to Am(VI). 3. The method according to claim 1 further including recirculating the aqueous feed solution along the separating layer. 4. The method of claim 1 wherein the immobilized solvent and the receiving solvent include tributyl phosphate. 5. The method according to claim 1 further including extracting Am(VI) from the receiving solvent and recycling the receiving solvent at the first immobilized liquid membrane. 6. The method of claim 5 wherein the extracting step includes treating the receiving solvent at a second immobilized liquid membrane containing an immobilized dilute acid solvent. 7. The method of claim 6 wherein the first and second immobilized liquid membranes are cylindrical, the first immobilized liquid membrane being concentric with and spaced apart from the second immobilized liquid membrane. 8. The method of claim 1 including pressuring the aqueous feed solution to between approximately 0 psig and approximately 50 psig. 9. The method of claim 1 further including maintaining a concentration gradient of Am(VI) across the first immobilized liquid membrane. 10. An immobilized liquid membrane comprising:a metal oxide separating layer adjacent a feed flow containing Am(VI), the separating layer defining a cylindrical core to receive the feed flow; anda supporting layer extending around the separating layer and being adjacent a receiving flow, the supporting layer formed of a separate material than the separating layer, wherein the separating and supporting layers retain an immobilized solvent adapted to extract Am(VI) from the feed flow for transfer to the receiving flow. 11. The immobilized liquid membrane of claim 10 wherein the immobilized solvent includes tributyl phosphate. 12. The immobilized liquid membrane of claim 10 wherein separative and supporting layers are cylindrically shaped. 13. The immobilized liquid membrane of claim 10 wherein the separating layer includes a thickness of between approximately 0.5-50 μm and an average pore size of between approximately 2-200 nm. 14. The immobilized liquid membrane of claim 10 wherein the supporting layer includes a thickness of between approximately 400-4000 μm and an average pore size of between approximately 0.5-50 μm. 15. A system for the extraction of americium from spent nuclear fuel comprising:a feed flow containing oxidized americium;a receiving flow containing an organic receiving solvent; andan immobilized liquid metal oxide membrane including a metal oxide separating layer, a supporting layer, and an interface therebetween, the separating layer defining a core that includes a major surface, the supporting layer extending around the separating layer and including a major surface, wherein the separating layer and the supporting layer retain the organic receiving solvent therein, wherein the direction of the feed flow is parallel to the major surface of the separating layer, and wherein the direction of the receiving flow is parallel to the major surface of the supporting layer. 16. The system of claim 15 wherein the immobilized liquid membrane defines a decreasing concentration gradient of oxidized americium from the feed flow to the receiving flow. 17. The system of claim 15 wherein the separating and supportive layers define a cylinder. 18. The system of claim 17 wherein the feed flow is directed through a core of the cylinder defined by the separative and supporting layers. 19. The system of claim 17 wherein the receiving flow is directed along the exterior of the cylinder defined by the separative and supporting layers. 20. The system of claim 15 wherein the separating layer defines an average pore size less than the average pore size of the supportive layer. 21. A method comprising:providing an metal oxide membrane including an immobilized solvent retained therein, the inorganic membrane including a metal oxide separating layer defining a core, a supporting layer extending around the separating layer, and an interface between the separating layer and the supporting layer; andapplying a concentration gradient of oxidized americium across the inorganic membrane to transfer americium from a feed flow to a receiving flow, the feed flow and the receiving flow being in a direction generally parallel to the separating layer and the supporting layer, respectively. 22. The method of claim 21 wherein the immobilized solvent is operable to extract oxidized americium solutes from an aqueous feed solution. 23. The method of claim 21 wherein the applying step includes directing the feed flow along a first major surface of the inorganic membrane and directing the receiving flow along a second major surface of the inorganic membrane. 24. The method of claim 21 including applying a pressure differential across the inorganic membrane. 25. The method of claim 21 including providing a hydrophobic layer on a surface of the inorganic membrane. |
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045004870 | summary | BACKGROUND OF THE INVENTION This invention relates to a system for suppressing and absorbing pressure surges in piping and other systems, especially piping and systems part of liquid metal nuclear reactors. Nuclear reactors often contain a large volume of liquid which is used to cool the reactor fuel. This liquid may be water, molten salt, or liquid metal, particularly liquid sodium. Because various reactor accidents may result in pressure surges in this liquid coolant, it is desired to provide a passive, reliable system for the suppression of such surges. It is desired to accomplish such suppression without loss of the integrity of the coolant-containing boundary such that no coolant is permitted to escape or spill. SUMMARY OF THE INVENTION Sections of piping are provided with fluted, thin walls surrounded by foam metal. Upon a coolant pressure surge, the fluted wall deforms by expansion, crushing the foam metal which absorbs the energy of deformation thereby attenuating the original pressure surge. Pressure surges may also be attenuated by installation of metal foam below the head of a nuclear reactor and surrounding a reactor vessel itself. |
052316556 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A radiation imager system 10, such as a medical computed tomography (CT) system incorporating the device of the present invention, is shown in schematic form in FIG. 1. CT system 10 comprises a radiation point source 20, typically an x-ray source, and a radiation detector 30 comprising a plurality of radiation detector modules or panels 40 and a plurality of collimators 50 disposed between radiation source 20 and detector panels 40. Each detector panel comprises a plurality of detector elements (not shown) which produce an electrical signal in response to the incident radiation. The detector elements are typically arranged in a one- or two-dimensional array on each detector plate 40. The radiation detector elements are coupled to a signal processing circuit 60 and thence to an image analysis and display circuit 70. Detector plates 40 are mounted on a curved supporting surface 80 which is positioned at a substantially constant radius from radiation point source 20. This arrangement allows a subject 90 to be placed at a position between the radiation source and and the radiation detector for examination. Collimators 50 are positioned over radiation detector panels 40 to allow passage of radiation beams that emanate directly from radiation source 20, through exam subject 90, to radiation detector panels 40, while absorbing substantially all other beams of radiation that strike the collimator. The details of steps in the fabrication, and the resulting structure, of collimators 50 are set out below. In accordance with this invention, material is selectively removed from each of a plurality of collimator plates to form a plurality of passages in each plate. Two representative plates, 210a and 210b, are illustrated in FIGS. 2(a) and 2(b) respectively. Passages 215 extend between openings in opposite surfaces of each plate. Preferably the shape of the sidewalls (e.g., vertical or slanted) in each individual plate is substantially the same, and each plate has sidewalls shaped similarly to those in adjoining plates. In one embodiment of this invention, the collimator plates comprise relatively thin (i.e., having a thickness less than about 0.25 mm) sheets of radiation absorbent material. The radiation absorbent material is selected to exhibit good absorption characteristics for radiation having the wavelength distribution emitted by radiation source 20, and typically comprises a material having a relatively high atomic number, i.e. about 72 or greater. Examples of such material include tungsten, gold, and lead. Conventional photolithographic techniques are advantageously used to selectively remove material from collimator plates 210 to shape passages 215. For example, a mask 220a is formed on collimator plate 210a and a mask 220b is formed on collimator plate 210b, each mask having a selected pattern chosen to result in the formation of passages in the respective plates so that when the plates are assembled or stacked together the adjoining passages in the plates will form channels through the assembled collimator with respective axes having a respective selected orientation. If the photoresist used in the photolithographic processes does not adhere well to the radiation absorptive material, a transfer mask may be used in order to form a mask of a material that does adhere well to the material to be etched. The pattern of the mask is selected for each collimator plate and typically results in the passages being positioned in slightly different places on each respective plate. The desired positions of the passages on the plate are dependent on the location of the plate with respect to the underlying radiation detector elements in the assembled collimator device, the arrangement of detector elements in the detector array, and the path along which radiation emanating from the radiation point source passes to the detector element. After the mask is formed, the collimator plates are etched to form a plurality of passages 215 (portions of the collimator plates that are removed in the etching process are shown in dotted cross hatching in FIGS. 2(a) and 2(b)). Known etching processes are used to form the passages, such as wet etching of tungsten. Alternatively, masks can be formed on both sides of the collimator plate and the plate then etched simultaneously from both sides. To assist with alignment of the collimator plates, an alignment hole 217 may advantageously be formed in each collimator plate at the time passages 215 are formed. One or more alignment holes are positioned in the same respective positions on each collimator plate to be used as a reference point so that the plates can be properly positioned with respect to one another when they are stacked together to form the collimator. In an alternative embodiment of the present invention, collimator plates comprise collimator substrates 310 coated with radiation absorbent material 330, as illustrated in FIGS. 3(a) and 3(b) respectively. Substrate 310 comprises photosensitive material, i.e., a material that will react to exposure to light in a manner similar to photoresist. Such a material may lose its photosensitive characteristics once it has been exposed and processed. One example of this type of substrate material is the Corning, Inc. product known as Fotoform.RTM. glass. Collimator substrate 310 is selectively exposed through a mask to a light source so that the light exposes areas of the photosensitive substrate corresponding to a selected pattern for each collimator plate. For example, an optically opaque mask 312 is formed by conventional methods on a first surface 310a of collimator substrate 310. The pattern of openings in mask 312 corresponds to the pattern of detector elements in radiation detector panel 40 (FIG. 1). For example, mask 312 has a pattern mimicking the arrangement, i.e., rows and columns, and the cross-sectional shape of detector elements at the interface between radiation detector panel 40 and collimator 50 (FIG. 1). Alternatively, mask 312 need not be on the surface of the collimator substrate but can be positioned with respect to the substrate in accordance with known photolithographic techniques to provide the desired exposure of the photosensitive material in substrate 310. In any event, the pattern of the mask is selected to expose areas of photosensitive collimator substrate 310 of sufficient size and orientation so that upon completion of fabrication of collimator 50, the surface of each radiation detector element for receiving the radiation is exposed to radiation passing along the desired paths from the radiation source. Collimator substrate 310 is then etched using conventional techniques appropriate for the substrate photosensitive material to remove the exposed photosensitive material and thus create a plurality of passages 320 through the substrate, as illustrated in FIG. 3(a). Portions of the photosensitive material that are removed in the etching are shown in dotted cross hatching in the figure. Each of these passages extends between openings in opposite surfaces of the collimator plate. Preferably the sidewalls of the passages on each individual plate have substantially the same shape and orientation, and are of substantially the same shape and orientation as the passage sidewalls in other plates used in the assembled imager system. A radiation absorbent material layer 330 (FIG. 3(b)) is then applied on collimator substrate 310 so as to cover at least the surfaces of the substrate which will be exposed to radiation when assembled in an imager device. The radiation absorbent material applied on the far interior wall of the channel is shown in dotted cross hatching. For example, many types of radiation absorbent material can be applied through known vapor deposition techniques. Radiation absorbent material 330 is selected to absorb radiation of the energy level and wavelength emitted by radiation source 20 (FIG. 1). The radiation absorbent material typically has a relatively high atomic number, e.g., greater than about 72, and advantageously comprises tungsten, gold or lead when the radiation used in the imager device is x-ray. The thickness of the radiation absorbent material layer is selected to provide, when the collimator is assembled, efficient absorption of radiation. This selected thickness depends on the nature of the radiation and the energy level of the radiation when it strikes the collimator. For example, in a CT system using an x-ray point radiation source of about 100 KeV positioned approximately one meter from the detector array, the collimator plates would need to present a collective tungsten thickness in a range of between about 30 to 40 mils along the path of the radiation to be absorbed. After application of the radiation absorbent material, the cross-sectional area of the opening or the void space in the passage is substantially the same as the area for receiving radiation on the detector element which it adjoins so as to allow substantially all radiation rays emanating along direct paths from the radiation source to strike the detector element. The collimator plates are then stacked, i.e., assembled one over the other as shown in FIG. 4(a), to form a collimator body 455 and aligned so that respective passages in the collimator plates form a plurality of respective channels 420 through the collimator body. The collimator plates are advantageously aligned in the stacking process by positioning an alignment hole 417 about an alignment rod 430. Alternatively, optical alignment devices aimed through alignment holes 417 or alignment of the edges of the plates can be used to provide correct alignment of the passages when stacking the collimator plates. In the assembled collimator 50 of FIG. 1, shown in a detailed view in FIG. 4(a), each collimator plate 410 comprises a patterned sheet of radiation absorbent material or alternatively comprises a photosensitive material substrate coated with a radiation absorbent material. Each channel is defined by sidewalls 418 of the respective passages in each collimator plate. The sidewalls of each respective passage in adjoining collimator plates form a step-shaped boundary 422 of channel 420 in collimator body 455. As illustrated in FIG. 4(b), a longitudinal axis 424 of each channel is substantially equidistant from a pair of longitudinal tangent lines 423 passing along the portions of sidewalls 418 which extend furthermost into the channel. The orientation of the tangent lines towards a convergence point above the collimator (i.e., the radiation point source) is exaggerated for illustration purposes. The longitudinal axis for each channel will have a unique selected orientation angle, varying in magnitude and orientation (i.e., displacement in an x or y direction, or a combination of those directions, in the plane of the radiation detector array). For example, in the plane of the cross-sectional view presented in FIG. 4(a), axis 424' has a selected orientation angle .beta. and axis 424" has a selected orientation angle .differential., each of which are in the plane of the drawing but which differ in magnitude and in direction of displacement with respect to the radiation source. With a two-dimensional array of radiation detectors 42, the various selected orientation angles would also be displaced in a plane normal to the plane of the cross-sectional illustration of FIG. 4(a). The magnitudes of the selected orientation angles typically range between about 0.degree. and 10.degree.. In accordance with the present invention, each longitudinal axis of each respective channel in the collimator body is aligned with a respective selected orientation angle, which angle corresponds to the direct path between radiation point source 20 and radiation detector element 42 adjoining the channel (FIG. 4(a)). The radiation beams spread out from the point source so as to strike each radiation detector element disposed on a planar array at a slightly different angles respectively, the magnitude and orientation of which depend on the position of the detector in the array. The pattern of the passages in each collimator plate is selected so that when the plates are stacked together each of the channels formed has an axis oriented along a selected orientation angle that corresponds with the path of a radiation beam from the point source to the radiation detector in the assembled imager. The number of collimator plates used in the assembly of the collimator body is dependent on the energy level and wavelength of the radiation to be collimated and hence the overall thickness of radiation absorptive material necessary to absorb radiation striking the collimator. As illustrated in FIG. 4(a), in the assembled device, collimator body 455 is disposed to adjoin radiation detector panel 40. Radiation detector elements 42 are positioned in an array on detector panel 40 and each typically comprises a scintillator coupled to a photodetector. Collimator body 455 is positioned to allow incident radiation on a direct path between the radiation source and each one of the radiation detector elements 42 to pass through the channels in the collimator. Beams of radiation that are not aligned with such a direct path strike the collimator body and are absorbed. The collimator of the present invention is readily used with either a one-dimensional or a two-dimensional array of radiation detector elements. A plan view of a collimator fabricated in accordance with the present invention and showing a representative number of channels 420 appears in FIG. 5. The figure has been marked to show left, right, upper, and lower edges solely to provide a reference for ease of discussion, and the selection and positioning of such references is not meant to constitute any limitation on the structure or positioning of the device of the invention. Channel openings 425 in the surface of the collimator closest to the radiation source are shown in dark outline and channel openings 425' on the opposite surface of collimator body 455 are shown in phantom. In the two-dimensional array the center channel is in substantial vertical alignment with the radiation source, and the opening 425' of the channel on the side of the collimator body opposite the radiation source is aligned with the opening in the surface closest to the radiation source. As the radiation beams spread out as they emanate from the point source, each of the openings 425' has a slightly larger cross-sectional area than its respective opening 425 in the surface of the collimator closest to the radiation source. Openings 425' for channels on the left, right, top, or bottom are also slightly offset from being in vertical alignment with their respective openings 425. The direct path from the radiation source to a radiation detector in the upper left hand corner, for example, is offset both to the left and to the upper side of the array. The selected orientation angle of the axis of the channel is substantially aligned with this direct path, and the channel thus extends through the collimator body at this angle. The selected orientation angle for each channel is different from any other channel in the collimator. Such a structure, which would be extremely difficult and time consuming to construct with conventional collimator fabrication techniques, is readily produced in accordance with this invention. While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. |
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description | This application claims priority to and benefit of U.S. Provisional Application No. 62/414,507, filed Oct. 28, 2016, the contents of which are incorporated herein by reference in their entirety. The present invention relates generally to the field of thermal energy. More specifically, the present invention relates to a Low Temperature Thermal Energy Converter (LTTEC) for use with spent nuclear fuel rods. Of the various issues with storing spent nuclear fuel rods, cost is a major issue. Instead of spending tens of billions to store and deplete a valuable energy resource for 10-20 years, it is recognized herein that this waste could be sent to secondary nuclear facilities, where a specifically designed LTTEC could be used to produce electric power and even revenue from this nuclear waste. Some LTTECs are described in U.S. Pat. No. 8,915,083, issued to this inventor on Dec. 23, 2014 and titled “Vapor Powered Engine/Electric Generator.” The contents of U.S. Pat. No. 8,915,083 are incorporated herein in their entirety. The present solution would involve technological improvements to an LTTEC. One such modification of an LLTEC would include the addition of a thermally conductive coiled tube or other similar device, where the LTTEC is designed such that working fluid fills the coil/device from the lowest point of a working liquid chamber of the LTTEC. In so doing, a thermal reaction takes place, which draws and condenses the water from the surrounding air onto the outer surfaces of the coil. It is also recognized herein that due to the chemical characteristics of the LTTEC working liquid, when the working fluid is taken from the lowest point of the working liquid chamber and routed through a radiator/exchanger separating a vapor chamber from the working liquid chamber, this creates a condenser that can be used to eliminate the separate cold thermal supply that all other Rankine Cycle systems must have for a successful phase change operation. By removing the separate cold thermal supply from the LLTEC, it allows for a multitude of benefits, including a smaller mass/footprint and the removal of a point of possible failure from the system. Furthermore, the secondary nuclear facilities would be safer than a nuclear reactor-based primary nuclear power plant due to the fact that certain radioactive materials have been spent and there is no reactor. According to some embodiments, a vapor powered apparatus for generating electric power includes a liquid chamber configured to contain a working fluid, a first heat exchanger, in fluid communication with the liquid chamber, configured to transfer heat from fluid coming from a heat source to working fluid coming from the liquid chamber, where the transferred heat vaporizes at least a portion of the working fluid to provide a working pressure of the vaporized working fluid. The apparatus includes a pressure motor, in fluid communication with the heat exchanger, configured to convert the working pressure of the vaporized working fluid into mechanical motion for a power generator operatively connected to the pressure motor. The apparatus includes a vapor chamber configured to capture the vaporized working fluid exiting the pressure motor and a second heat exchanger configured to use working fluid from a bottom portion of a pool of working liquid in the liquid chamber to condense the captured vaporized working fluid, returning the condensed working fluid back to the liquid chamber. The apparatus also includes an exchanger fluid system within the liquid chamber configured to provide the working fluid from the bottom portion of the pool of working liquid in the liquid chamber to the second heat exchanger. The working fluid becomes colder when maintained at a determined depth in the pool of working fluid in the liquid chamber. The first heat exchanger may be configured to be in fluid communication with a liquid pool that is configured to obtain heat transferred from spent nuclear fuel rods. According to some embodiments, a vapor powered apparatus for generating electric power includes a liquid chamber configured to contain a working fluid, a first heat exchanger, in fluid communication with the liquid chamber, configured to transfer heat from fluid coming from a heat source to working fluid coming from the liquid chamber, where the transferred heat vaporizes at least a portion of the working fluid to provide a working pressure of the vaporized working fluid. The apparatus includes a pressure motor, in fluid communication with the heat exchanger, configured to convert the working pressure of the vaporized working fluid into mechanical motion for a power generator operatively connected to the pressure motor. The apparatus includes a vapor chamber configured to capture the vaporized working fluid exiting the pressure motor and a second heat exchanger configured to use working fluid from a bottom portion of a pool of working liquid in the liquid chamber to condense the captured vaporized working fluid, returning the condensed working fluid back to the liquid chamber. The apparatus includes an exchanger fluid system configured to provide the working fluid from the bottom portion of the pool of working liquid in the liquid chamber to the second heat exchanger. The exchanger fluid system includes a conduit entry point at the bottom portion of the pool of working fluid in the liquid chamber and an outside conduit that provides fluid communication between the conduit entry point and the second heat exchanger, where the outside conduit is outside of the liquid and vapor chambers. The outside conduit may be exposed to air outside of the vapor powered apparatus. The outside conduit may include a coil or increased surface area portion. The coil or increased surface area portion may be lower than the conduit entry point. The working fluid and the coil or increased surface area portion may be arranged to cause condensation of air onto the coil or increased surface area portion. Of course, the present invention is not limited to the above features and advantages. Those of ordinary skill in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings. All illustrations of the drawings are for the purpose of describing selected embodiments of the present invention and are not intended to limit the scope of the present invention. There is a mounting problem of growing nuclear waste in the nuclear industry—radioactive waste in the form of spent nuclear fuel rods. Storage is now becoming a growing concern. The industry is actively seeking a solution regarding how to store this nuclear waste. At this point of the spent fuel rods' “half-life,” the spent fuel rods are no longer active enough to produce the thermal energy required by a nuclear electric power plant. However, the spent fuel rods are still active enough to pose threats to human health and the environment. The spent fuel rods, in their state, are no longer beneficial for producing electricity effectively in existing nuclear facilities, even though the spent fuel rods are still emitting energy in vast amounts. The technology to effectively harness this low thermal energy has not yet been developed. Embodiments of the present invention provide what is needed to help manage the ever-growing nuclear waste issue. As storing spent nuclear fuel rods is a very expensive problem, it would be advantageous to harness the majority of the remaining energy so as to pay for the waste issue rectification. Harnessing this energy could also lessen, in some part, the amount of energy required of active fuel rods, alleviating further spent fuel rod storage requirements. In other words, rather than paying to store nuclear waste year after year, this same nuclear waste could be generating energy and possibly revenue. Steam Ranking Cycle (SRC) FIG. 1 illustrates an existing Steam Rankine Cycle (SRC) power system, where very high temperatures and energy are required to create working pressure. By creating high temperature vaporized water (steam) and routing this pressure through a vapor motor/turbine 102, mechanical power is developed to turn an electric generator 104. A cold temperature exchanger 110 is used to condense the vaporized water. The draw-backs to the SRC include the incredible amount of thermal energy that is required to achieve the heat needed to effectively create the pressure required for the process. This is the method used in existing nuclear power plants presently. For the above reasons, SRC is not the solution to be utilized with spent nuclear fuel rods. Organic Ranking Cycle (ORC) There have been attempts to use lower thermal energy or lower temperatures to vaporize chemicals such as Freon. Toluene, Ammonia, etc. to create power with some success. This involves a method known as the Organic Rankine Cycle (ORC). FIG. 2 illustrates an ORC, with a vapor pressure motor 202, generator 204, heat exchanger 220 and cold temperature exchanger 210. The disadvantage of the ORC is that it uses chemicals that are not only hazardous, these chemicals break down over time and lose the original capability of the given chemical. This system is also not the answer for the spent nuclear fuel rod problem due to the ORC limitations and the type of chemicals used. LTTEC Because an LTTEC is able to utilize thermal energy at temperature as low as 98° F. this technology is more appropriate in alleviating the spent fuel rod storage issue. FIGS. 3 and 4 illustrate embodiments of an LTTEC with technical improvements. Such systems utilize much lower thermal energy than an SRC. One difference between the LTTEC and the ORC is the fact that the LTTEC uses environmentally friendly chemicals that are not hazardous, caustic, flammable, explosive, corrosive, or even harmful to the ozone layer. As well, most hydrofluorocarbons (HFCs) and hydrofluoroethers (HFEs) commonly used in the LTTEC have little to no deterioration regarding the phase changing cycles over very long timelines. It is suggested that the spent fuel rods or nuclear waste be placed into a secured facility created with a pool that is re-enforced and redundantly secured and sealed against leakage. This pool would be fitted with a thermostatically controlled valve system that manages and stabilizes the pool at the appropriate temperature required to power the LTTEC electric generator, and as a safety precaution. As shown in FIG. 3, the LTTEC would include a working liquid chamber 306 that holds working liquid. The pool of working liquid in the liquid chamber 306 may be of a certain depth. The LTTEC includes a heat exchanger 320 for transferring heat from liquid from the heat source to the working liquid that is pumped out of the liquid chamber 306. The LTTEC also includes a vapor chamber 308 where heated working liquid vapor is captured after passing through the vapor motor/turbine 302 that is connected to generator 304. The LTTEC includes a radiator/heat exchanger 310 that uses cooled working liquid from the bottom of the pool of working liquid in the liquid chamber 306 to cause the vapor in the vapor chamber 308 to condense and fill the liquid chamber 306. In an example, hot water from the pool that captures the heat from the spent fuel rods is cycled through the heat exchanger 320, which is routed to and through a portion of the LTTEC system. This heated water (or other thermal transfer fluid) would provide the thermal energy to run the LTTEC for many years as it consumes the heat from the spent fuel rods, using the heat to generate electric power. This system can turn a problematic expensive waste into a valuable energy resource, solving multiple issues. First, the storage of the spent fuel rods is now somewhat rectified by their placement in a secondary nuclear facility. Second, the remaining radioactive energy is converted into usable electric power. Third, these secondary nuclear power plants are inherently safer than the primary reactor-based nuclear power plants, providing for additional location opportunities. Fourth, by having secondary nuclear facilities utilize this radioactive waste and convert emitted heat it into electricity, the primary plants could use less new nuclear fuel rods in the future. Fifth, since the spent rods are rated as less hazardous and are far less radioactive, a much smaller facility footprint can be achieved. LTTECs, modified as described herein, may have uses other than only land-based power plants. The LTTEC could be adapted for military applications or container ships. The LTTECs in FIGS. 3 and 4 and their advantages over the SRC and ORC of FIGS. 1 and 2 will be further described. In existing electric power industrial generators, the SRC is the most common system. In SRCs, two thermal masses are required for phase changing a liquid to vapor and back to liquid. This SRC method utilizes a “Hot Temp” thermal supply, usually in the form of nuclear fuel, burning coal or petrol to super-heat water until a pressurized steam vapor is produced. This pressure produces the means for creating mechanical energy to operate the electric generator 104 via the pressure engine or turbine 102, etc., so as to make electricity. The system then requires a “Cold Temp” thermal mass, primarily in the form of cold water supplied by rivers, lakes and even the ocean itself via plumbing, a pump, and a separate cold liquid containment source. This cold water is cycled through a cold exchanger 110. The steam vapor is directed across the cold exchanger 110, which condenses and converts the steam vapor back into liquid form to be phase changed again or to be released as water. With regard to the ORC shown in FIG. 2, chemicals such as Freon, Toluene, or other compounds are used in place of water or other liquids for creating pressurized vapor for means of gaining mechanical energy to turn a pressure motor/turbine 202, which in turn spins an electric generator 204, alternator or other electricity producing device to create electric power. The ORC has several advantages and disadvantages. The process is very similar to the SRC in that the ORC also requires two thermal masses, but the ORC demands far less heat. There must be a hot temperature exchanger 220 as well as a cold temperature exchanger 210 (condenser). Both the SRC and ORC use the same method of utilizing heat to vaporize a liquid to produce mechanical power, which is used to spin a generator, alternator or other electricity producing device, so as to create electric energy. Then, both the SRC and ORC use a cold temperature thermal exchange/condenser system which moves cold water or other thermally conductive liquid through the exchanger/condenser via a pump, plumbing and a separate cold liquid containment source. The vapor is forced through the exchanger/condenser where it is converted back to its liquid form to be phase changed again and again. In one embodiment of the present invention, illustrated by FIG. 3, the LTTEC power system uses an HFC/HFE designer chemical in place of water. The “Hot Temp” thermal supply is needed the same as with other Rankine Cycle systems to provide the vaporizing temperature to create the mechanical energy. However, with the LTTEC Rankine Cycle process, the cold thermal system is eliminated. The LTTEC uses the chemical from the bottom of the liquid chamber 306 of the system and guides it directly through a radiator/exchanger 310. This method allows for a cold thermal exchanger that does not require any separate “Cold Temp” thermal supply, which is required for all other forms of Rankine Cycle systems. With regard to HFC/HFE chemicals (and similar), the compound, when in liquid form, becomes colder when maintained at a determined depth. Because of this phenomenon, the chemical in the lower or bottom section of the liquid chamber 306 is guided through the cold exchanger 310. As the vaporized chemical passes over the cold exchanger 310, it rapidly cools and re-condenses the vapor back into liquid form. The LTTEC has a pump and plumbing system 330 to bring the working liquid from a bottom portion of the pool of the working liquid in the liquid chamber 306. Consistent with certain aspects of the figures and as described in U.S. Pat. No. 8,915,083, the content of which is incorporated herein, an existing LLTEC may be a vapor powered apparatus for generating electric power. The LLTEC may include a hermetically sealed casing, a storage tank containing a working fluid having a boiling point of 150° F. or less. There may be a heating source that vaporizes at least a portion of the working fluid to provide a working pressure of the vaporized working fluid, the heating source being in fluid communication with said storage tank. The LLTEC may include a pressure motor that converts the working pressure of the vaporized working fluid into mechanical motion, where the pressure motor is in fluid communication with a heat source. The LLTEC may include a recapture system configured to capture the vaporized working fluid exiting the pressure motor and return the condensed working fluid back to the storage tank. The pressure motor may be operatively connected to a power generator or alternator. Each of the storage tank, heating source, pressure motor, recapture system, and/or power generator or alternator may be mounted within the hermetically sealed casing. Also, the working fluid may include Methoxy-nonafluorobutane, CF3CF2C(O)CF(CF3)2, or Dodecafluoro-2-methylpentan-3-one. The working fluid may be NOVEC™ 7000 or other engineered working materials (e.g., ethers and ketones with the same low temperature vaporizing characteristics that do not conduct electrical energy). NOVEC™ 649, 7100, and 1230 may also be suitable for use in certain embodiments. The heat exchanger may be configured to transfer heat from the fluid from the heating source at a temperature from 90° F. to 150° F., 93° F. to 150° F., 100° F. to 140° F., or 90° F. to 100° F. In another embodiment illustrated by FIG. 4, the cold working liquid in the LTTEC is routed through a radiator or other form of exchanger 310. However, the working liquid is passed through an external coil system 410 prior to being transferred through the radiator/exchanger 310. The vapor from the pressure motor/turbine 302 exhaust is then directed across-fins or across-tubes of the cold exchanger 310 to be fully reconverted back to liquid form. All other processes may be the same as the LTTEC Rankine Cycle shown in FIG. 3. These two embodiments of the LTTEC Rankine Cycle have several advantages. First, they remove the complexity of the existing separate cold exchanger process of the SRC and ORC. Second, they also eliminate the separate cold temperature containment and simplify the plumbing. Third, they allow the system to be built much smaller, needing less space. Fourth, they eliminate a point of possible failure from the system. Fifth, the possibility of the cold temperature thermal supply failing and mixing chemicals is eliminated as the moving cold thermal transfer liquid is removed. Another advantage of the LTTEC of FIG. 4 is that it creates a very beneficial by-product. When a copper or other material with thermal conductive ability is incorporated as a coil (or other form with a large surface area), with the working liquid at the very bottom of the lower liquid chamber 306 fed into the coil system 410, the coil freezes the humidity in the surrounding air. Ice rapidly forms on the coil and insulates the coil. This causes the coil inner temperature to rise minimally. This causes the ice to quickly melt into a container accumulating water. Once the ice melts off of the coil, the coil temperature again drops, causing it to refreeze and build up ice. This causes the coil to become insulated and then rapidly melt again due to the slight increase in the coil temperature. The cycle continues and repeats over and over, filling the container with distilled water that can be used for certain maintenance purposes. FIG. 5 illustrates an overview of an example system that may involve LTTEC power modules, with a hot supply (e.g., spent fuel rods). While a cold supply is not necessarily needed in certain embodiments of the LTTEC itself, a cold supply can be on hand in a simpler fashion for safety or other maintenance purposes. Multiple LTTEC power modules may combine together to provide electrical power to a power junction output or other component or location. While the LTTEC is described with respect to nuclear waste, the LTTEC embodiments may serve other purposes. In some cases, an LTTEC can be miniaturized and incorporated within a special garment such as a vest or similar clothing to allow the wearer to generate enough electric power so as to charge personal devices such as small radios or cellular phones, etc. It is to be understood that the invention(s) is/are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. |
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053393414 | summary | FIELD AND BACKGROUND OF THE INVENTION The present invention relates in general to the cooling of nuclear reactors and in particular to a new and useful mixer grid for cooling the fuel rods of a nuclear reactor fuel assembly. In the nuclear power field, it is common to use a mixer grid in conjunction with a nuclear reactor fuel assembly for enhancing the heat transfer between the nuclear fuel rods of the assembly and the coolant of the nuclear reactor. U.S. Pat. No. 4,474,730 discloses a nuclear fuel spacer grid comprising a plurality of straps in an egg crate configuration defining a plurality of cells for enclosing the fuel rods for a nuclear reactor fuel assembly. A spring portion is provided on at least one of the straps of each cell and extends into each cell for pushing against the fuel rod contained therein. A back-up spring is positioned transverse to and behind each of the spring portions of the straps and is positioned so as not to touch the fuel rods within the cells. U.S. Pat. No. 3,933,584 discloses a spacer grid for nuclear fuel rods comprising identical metal straps arranged in cross relation in order to define a multiplicity of cells for receiving elongated fuel elements such as rods. Tabs are used at the edges of the cell openings for the deflecting of coolant into the cells. Tabs from adjacent side walls are fixedly secured together in order to provide rigid flanges for the grid. Spring fingers are provided within each cell in order to hold the fuel rods against fixed stops. U.S. Pat. No. 4,692,302 discloses a mixer grid for a nuclear reactor fuel assembly wherein the sole purpose of the grid is to promote cross flow mixing of the coolant of the reactor rather than support the fuel rods. At least one mixing vane is provided in each cell for directing coolant flow. Four dimple protrusions, which are open, extend into each cell and allow the flow of coolant therethrough and prevent damage to the fuel rods within each cell. A major problem of the mixer grids commonly used in the nuclear reactor field is that both a separate stopper and mixing vane are used within the same cell for cooling hot spots within the grid and supporting the nuclear fuel rods. Hard stops used within each cell are aimed at preventing the fuel rods from contacting the mixing vanes of each cell while the mixing vanes are used to direct and channel coolant in each cell. Additionally, it is common in the known mixer grids to use an outer strip around the grid for providing lead-in and coolant flow to hot spots of cells located on the periphery of the grid. Moreover, it is common in the known mixer grids to use mixing vanes in every other peripheral cell of the mixer grid. Presently, there is no known mixer grid which alleviates the need for using both a stopper and a mixing vane within each cell of the grid. SUMMARY OF THE INVENTION The present invention comprises a mixer grid for a nuclear fuel reactor assembly having a plurality of strips arranged in rows and columns and defining a plurality of cells for receiving fuel rods of the nuclear fuel reactor assembly. The present invention also comprises a stopper fixed at each corner of each cell. The stoppers are used to direct and channel coolant flow as well as support the nuclear fuel rods within. The stoppers are cone-shaped or cylindrical-shaped for channeling the coolant throughout the grid for proper heat exchange with the fuel rods. Moreover, each stopper has a smooth, flat chamfered surface for supporting each fuel rod and minimizing fretting or damage to the rod. The present invention also provides for some of the cells to be designated as guide assembly cells for attachment to the nuclear reactor fuel assembly. A plurality of support arches are fixed to the strips of each guide assembly cell for welding to the nuclear reactor fuel assembly. It is an object of the present invention to provide a mixer grid for a nuclear reactor fuel assembly which provides for efficient heat transfer over those mixer grids found in the prior art. It is another object of the proposed invention to provide non-contacting grid allowing for less complicated design and manufacturing. It is another object of the present invention to provide a mixer grid for a nuclear reactor fuel assembly which alleviates the use of both stoppers and mixing vanes within each cell of the mixer grid. It is yet another object of this invention to provide four (4) mixing devices per cell. This is not the case with other designs (FIG. 1) where it is not possible for the strips to provide a vane on two sides. This new design promotes more mixing. It is another object of the present invention to provide a mixer grid wherein each cell of the grid uses a plurality of stoppers which direct coolant flow and may provide an area where the fuel rod may rest against without causing excessive wear on the fuel rods. The stoppers are in each corner of each cell which typically has the greatest flow of coolant through it due to the fact that this is a path of least resistance. 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 disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated. |
abstract | A lightweight cask comprises a barrel body which shields gamma rays. A resin which shields neutrons is provided on the periphery of the barrel body. A basket is made of a plurality of square pipes having neutron absorbing ability. There is a cavity inside the barrel body. This cavity is worked to have a shape corresponding to the outer shape of the basket. The square pipes are inserted in this cavity so as to abut against this inner surface. Furthermore, chamfered portions are provided on the outside surface of the barrel body at 90xc2x0 intervals and space portions are formed between another resin and an outer casing. |
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047028629 | abstract | Method for the final conditioning of radioactive and/or toxic waste by fusing it into thermoplastic matrix material, binding radioactive and/or toxic pollutants contained in the waste from all sides, characterized by the feature that radioactive thermoplastic synthetic material is used as the thermoplastic matrix material. |
047553529 | abstract | A system of generating electricity is disclosed. The system employs a new kind of swimming pool type nuclear reactor which is safe and can be made operable unattended but at the same time raises the mean pool temperature by forcing moderator-coolant-shield circulation. When the reactor is combined with an organic Rankine cycle engine, a significant improvement in efficiency of electricity generation can be obtained, making very small nuclear/electricity units economically viable. |
abstract | A method for chemically decontaminating radioactive material. The method includes reducing-dissolving step for setting surface of radioactive material in contact with reducing decontamination liquid including mono-carboxylic acid and di-carboxylic acid as dissolvent; and oxidizing-dissolving step for setting the surface of the radioactive material in contact with oxidizing decontamination liquid including oxidizer. The method may include repeated pairs of steps, each pair including the reducing-dissolving step and the oxidizing-dissolving step. The mono-carboxylic acid may include formic acid, and the di-carboxylic acid includes oxalic acid. The oxidizer may be ozone, permanganic acid or permanganate. |
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abstract | In one characterization, the present invention relates to a radiation-shielding assembly for holding a container having a radioactive material disposed therein. The assembly may, at least in one regard, be referred to as an elution shield and/or a dispensing shield. The assembly includes a body at least partially defining a cavity. There is at least one opening through the body into the cavity. The assembly may include a cap that at least generally hinders escape of radiation from the assembly through the opening. The cap may be releasably attached to the body in one orientation and may establish non-attached engagement with the body in another orientation. The assembly may include an adjustable spacer system for adapting the assembly for use with containers having different heights. |
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description | The present invention concerns a fuel assembly for a nuclear power boiling water reactor. In a fuel assembly for a nuclear boiling water reactor, there are a number of fuel rods, which comprise a nuclear fuel material. When the fuel assembly is in operation in a nuclear reactor, a cooling medium, usually water, flows up through the fuel assembly. This water fulfils several functions. It functions as a cooling medium for cooling the fuel rods such that they will not be overheated. The water also serves as a neutron moderator, i.e. the water slows down the neutrons to a lower speed. Thereby, the reactivity of the reactor is increased. Since the water flows upwards through the fuel assembly, in the upper part of the fuel assembly, the water has been heated to a larger extent. This has as a consequence that the portion of steam is larger in the upper part of the fuel assembly than in the lower part. Since steam has a relatively low density, the steam in the upper part of the fuel assembly is a poorer moderator than the water in the lower part of the fuel assembly. Furthermore, it is the case that cold water is a better moderator than warm water. This means that the largest moderation is obtained when the reactor is out of operation, i.e. when it is cool. The reactivity of a reactor depends on the amount of nuclear fuel material and on the amount of moderator. The reactivity in a cool reactor is thereby higher than the reactivity in a warm reactor. To enable safe shutdown, there are requirements on a highest allowed reactivity when the reactor is out of operation. An aim is thus that the reactor has a reactivity as high as possible when the reactor is in operation at the same time as the reactivity may not be too high when the reactor is out of operation. It should be mentioned that the water does not only have a moderating function. The water functions in fact also as a neutron absorber. In this context, the expression over-moderation is often used. Thereby is meant that the absorbing function of the water dominates over its moderating function. Such an over-moderation thus leads to a lowered reactivity. This means that the requirement on a highest allowed reactivity when the reactor is out of operation is more easily fulfilled if the amount of water leads to over-moderation. Another requirement is that the cooling of the fuel rods is sufficient such that a so-called dry-out does not occur. Dry-out means that the water film which exists on the surface of the fuel rods disappears or is broken in limited areas. This leads to a locally deteriorated heat transfer between the fuel rod and the water flowing through the fuel assembly. This leads in its turn to an increased wall temperature of the fuel rods. The increased wall temperature may lead to serious damage on the fuel rod. It is desired to achieve a distribution of fission power over the cross-section of the fuel assembly which is more uniform such that the so-called radial peaking factor will be reduced. This means that the assembly can be operated to a higher total power before any individual fuel rod reaches its limits in terms of dry-out margin and other safety related parameters. In order to fulfil the different safety requirements, to obtain a sufficient cooling of the fuel rods, and, at the same time, to obtain a high reactivity during operation, a large number of different technical solutions have been proposed. Examples of different designs of fuel assemblies for a nuclear boiling water reactor can be seen EP 1551034 A2, U.S. Pat. Nos. 5,068,082 and 4,968,479. An object of the present invention is to provide a fuel assembly for a nuclear boiling water reactor with an improved cold shut-down margin, i.e. the reactivity should be sufficiently low when the nuclear reactor is shut down (cold condition). A further object is to provide such a fuel assembly which has a high reactivity when the nuclear reactor is in operation (hot condition). A further object is to provide such a fuel assembly which has a fission power distributed evenly over the cross-section of the fuel assembly. A further object is to provide such a fuel assembly which has a reduced pressure drop in the upper two-phase flow region, in order to improve thermal-hydraulic stability. The above objects are achieved by a fuel assembly for a nuclear power boiling water reactor, comprising: a fuel channel (6) extending in and defining a length direction (L) of the fuel assembly (4) and defining a central fuel channel axis (8) extending in said length direction, fuel rods (10) positioned such that they are surrounded by said fuel channel (6), each fuel rod having a central fuel rod axis (12) extending substantially in said length direction, water channels (14) positioned such that they are surrounded by said fuel channel, the water channels (14) being configured and positioned for, during operation, allowing non-boiling water to flow through the water channels, each water channel having a central water channel axis (16) extending substantially in said length direction, wherein said fuel rods comprise a first group of fuel rods and a second group of fuel rods, wherein each fuel rod in said first group is a so-called full length fuel rod which extends from a lower part of the fuel assembly to an upper part of the fuel assembly, wherein each fuel rod in said second group extends from said lower part of the fuel assembly and upwards, but does not reach as high up as said full length fuel rods, wherein said water channels (14) of the fuel assembly (4) comprises at least 3 water channels (14), each of which has a cross-sectional area which is at least twice as large as the cross-sectional area of each one of said fuel rods (10), or, in case the fuel assembly has fuel rods of different cross-sectional areas, at least twice as large as the average cross-sectional area of the fuel rods, wherein said at least 3 water channels (14) are positioned such that there is no further water channel of the fuel assembly, the central water channel axis (16) of which is closer to the central fuel channel axis (8) than the central water channel axis (16) of each of said at least 3 water channels, characterized in that the fuel assembly (4) comprises at least 5 fuel rods which belong to said second group and which are positioned such that the central fuel rod axis (12) of each of these at least 5 fuel rods is closer to the central fuel channel axis (8) than any of the water channel axes (16) of the water channels (14) of the fuel assembly. Since the fuel assembly comprises a relatively large number of shorter fuel rods in a central position of the fuel assembly, together with at least three, relatively large, water channels, which are positioned “outside” of the central short fuel rods, a large volume of water is created in the central upper region of the fuel assembly, when the nuclear reactor is in the cold condition. This region is then overmoderated and the cold reactivity is reduced. Therefore, an improved shut-down margin is obtained. Furthermore, since at least three, relatively large, water channels are used, and since these water channels are “spread out” in the fuel assembly (since they are positioned outside of the defined central shorter fuel rods), these water channels will be located near many of the fuel rods arranged in the fuel assembly. Therefore a good moderation is obtained in the hot condition, which means that the reactivity of the nuclear reactor will be high. Moreover, because the reactivity is more evenly spread out to more fuel rods, the distribution of fission power over the cross-section of the fuel assembly will be more uniform. Also because of the relatively large number of central shorter fuel rods, a larger volume without any fuel rods is created in the upper part of the fuel assembly. This means that the pressure drop will be reduced in the upper part of the fuel assembly as desired. In an operating boiling water reactor the moderation changes up through the reactor due to the formation of steam and hence the reduced density. This gives a higher conversion in the upper part, i.e. more production of Pu-239 from U-238, with higher reactivity at cold condition as a result. This problem has in the prior art been solved by use of shorter fuel rods. Since the shorter rods have negative side effects, their numbers, lengths and positions are crucial. The large open region above the central shorter fuel rods also enhances natural steam separation which reduces the average steam volume and hence increases moderation at hot conditions. A separation of steam and water where the steam travels upwards through the assembly at a higher speed reduces the average steam volume. This process requires larger open areas than the empty positions above single shorter fuel rods. The fuel assembly thus comprises at least 3 water channels with the cross-sectional area as defined in claims 1. The fuel assembly could also comprise one or more water channels with a smaller cross-sectional area. However, according to a preferred embodiment, the fuel assembly does not comprise any such water channel with a smaller cross-sectional area. Nevertheless, if the fuel assembly comprises one or more water channels with a smaller cross-sectional area, then, as defined in claim 1, none of such possible water channels with a smaller cross-sectional area is positioned such that its central water channel axis is closer to the central fuel channel axis than the central water channel axis of each of said at least 3 water channels with the defined larger cross-sectional area. The following may be noted concerning the expressions used in the claims. A fuel channel can also be called for example a box wall or channel wall. The fuel channel is normally quite long (for example about 4 m) compared to its width (for example about 1.5 dm). It therefore has a length direction. In use in a nuclear reactor, the fuel assembly, and the fuel channel, preferably extend mainly in the vertical direction. The length direction is thus, in use, the vertical direction. The lower and upper parts of the fuel assembly therefore refer to the fuel assembly as seen in the intended use position. The fuel rods could be slightly tilted. Hence, it is specified that the fuel rod axis extends substantially in the length direction. However, preferably the fuel rods are not tilted and therefore the fuel rod axis extends only in the length direction. Preferably the fuel rods are straight. However, the fuel rods may also be somewhat bent. The defined central fuel rod axis would in that case follow the bent shape of the fuel rod, i.e. also the central fuel rod axis would in that case be bent. Similarly for the water channels. The water channels could be slightly tilted. Hence it is specified that the water channel axis extends substantially in the length direction. However, preferably the water channels are not tilted and therefore the water channel axis extends only in the length direction. Also, preferably the water channels are straight. However, the water channels could also be bent. The defined central water channel axis would in that case follow the bent shape of the water channel, i.e. also the central water channel axis would in that case be bent. A water channel in this application thus means an enclosure (for example of a tubular shape) which is positioned in the fuel assembly and which is arranged for allowing non-boiling water to flow therethrough. Furthermore, preferably the water channel has a constant cross-sectional area over at least 80% of its length, preferably over its whole length (the cross-sectional area could change somewhat close to the end(s) of the water channel). However, according to an alternative embodiment, the cross-sectional area of the water channel may vary along its length. For example, the cross-sectional area may become larger at a level above the mentioned at least 5 shorter central fuel rods. When the cross-sectional area of the water channels and the fuel rods are compared with each other, this comparison concerns the same level in the fuel assembly (in case the water channels or, possibly, the fuel rods would have a varying cross-sectional area). In particular, the comparison applies to the lower part of fuel assembly, where the shorter fuel rods are positioned. The cross-sectional area relates to the area defined by the outer periphery of the water channels or the fuel rods. The nuclear reactor is preferably a light water reactor. According to one embodiment of a fuel assembly according to the invention, there is no full length fuel rod, the central fuel rod axis of which is positioned closer to the central fuel channel axis than the central fuel rod axis of any of said at least 5 fuel rods. This fact ensures that there will be a relatively large region above the mentioned centrally located shorter fuel rods. Consequently, a space is provided above these shorter rods for a relatively large volume of water, which will improve the shut-down margin. According to another embodiment of a fuel assembly according to the invention, the fuel assembly comprises at least 7 fuel rods which belong to said second group and which are positioned such that the central fuel rod axis of each of these at least 7 fuel rods is closer to the central fuel channel axis than any of the water channel axes of the water channels. With at least 7 such fuel rods, an even larger central space is created, which means a further improved shut-down margin. According to an embodiment, there are also no more than 8 fuel rods which belong to said second group and which are positioned such that the central fuel rod axis of each of these fuel rods is closer to the central fuel channel axis than any of the water channel axes of the water channels. According to a preferred embodiment there are exactly 8 such fuel rods which belong to said second group and which are positioned such that the central fuel rod axis of each of these fuel rods is closer to the central fuel channel axis than any of the water channel axes of the water channels. By having 8 such fuel rods, an optimized design is achieved. According to another embodiment of a fuel assembly according to the invention, there is no full length fuel rod, the central fuel rod axis of which is positioned closer to the central fuel channel axis than the central fuel rod axis of any of said at least 7 fuel rods. Similarly to above, it is thereby ensured that there will be a large space for water above the short central fuel rods. According to another embodiment of a fuel assembly according to the invention, each of said at least 5 fuel rods or each of said at least 7 fuel rods has a length that is less than 0.50 times the length of said full length fuel rods. Since the fuel rods are that short, it is ensured that there is a large space for water above the fuel rods. According to a preferred embodiment, each of said at least 5 fuel rods or each of said at least 7 fuel rods has a length that is between 0.29 and 0.45 times the length of said full length fuel rods. With such short fuel rods an even larger volume for water is created. According to another embodiment, there is no fuel rod which is such that it is longer than 0.50 times the length of said full length fuel rods and has a central fuel rod axis which is positioned closer to the central fuel channel axis than the central fuel rod axis of any of said at least 5 fuel rods or said at least 7 fuel rods. Similarly to the above explanation, by ensuring that there are no longer fuel rods among the mentioned central shorter fuel rods, a large, undisturbed, space for water is created. According to another embodiment, the fuel assembly comprises no more than 3 of said at least 3 water channels. It has been found that the use of three such, relatively large, water channels is optimal for achieving good moderation in the hot condition, at the same time as there is still sufficient space in the fuel assembly for a relatively large number of fuel rods. According to a preferred embodiment, the fuel assembly does not comprise any other water channels either (i.e. also no water channel with a cross-sectional area which is less than twice as large as the cross-sectional area of each one of said fuel rods, or, in case the fuel assembly has fuel rods of different cross-sectional areas, less than twice as large as the average cross-sectional area of the fuel rods). According to another embodiment, each one of said at least 3 water channels has a cross-sectional area which is between 3.0 and 10.0, preferably between 4.0 and 8.0, times the cross-sectional area of each one of said fuel rods, or, in case the fuel assembly has fuel rods of different cross-sectional areas, between 3.0 and 10.0, preferably between 4.0 and 8.0, times the average cross-sectional area of the fuel rods. With such relatively large water channels, a sufficiently high amount of non-boiling water will flow through the fuel assembly. This ensures a good moderation, i.e. a high reactivity. According to another embodiment, each of said at least 3 water channels has a circular cross-section, at least in the portion of the water channel that is located at the level of said at least 5 fuel rods or said at least 7 fuel rods. From a flow dynamic point of view, it is advantageous to use round water channels. Furthermore, it is easy to manufacture and position such round water channels in the fuel assembly. According to another embodiment, the fuel assembly comprises no more than 19 fuel rods, preferably no more than 16 fuel rods, more preferred no more than 14 fuel rods, each of which fulfils the following criterion: the distance between the central fuel rod axis and the central fuel channel axis is less than the distance between the central water channel axis of at least one of said at least 3 water channels and the central fuel channel axis. It is thereby ensured that the water channels are not positioned too far towards the periphery of the fuel assembly. This means that a good moderation, and a high reactivity, for many fuel rods is achieved, and consequently also an evenly distributed fission power. According to preferred embodiments, the fuel assembly comprises 7-21, preferably 10-18, more preferred 13-15, most preferred 14 fuel rods which fulfil the mentioned criterion. This has appeared to ensure an optimal positioning of the water channels. This means that the water channels are positioned near the central short fuel rods (said at least 5 or at least 7 fuel rods). Preferably, each of the water channels is positioned next to at least two of the central short fuel rods, such that there is no further fuel rod positioned between the respective water channel and said at least two central short fuel rods. According to another embodiment, the fuel assembly comprises a substantially regular pattern of fuel rod positions, wherein each one of said at least 3 water channels is positioned such that it replaces 4 fuel rods in this substantially regular pattern. Such a design is quite easy to implement in a fuel assembly. The concept “substantially regular pattern” is used, since some fuel rods may be slightly displaced from the absolutely regular pattern. Preferably the regular pattern is in the form of rows and columns (when a cross-section of the fuel assembly is viewed). According to another embodiment, the fuel assembly comprises 65-160, preferably 100-120, more preferred 105-113, most preferred 109 fuel rods. Such a relatively high number of fuel rods ensures that the fuel assembly can achieve an efficient heat transfer to the coolant, and because of the arrangement of the fuel rods and the water channels, a good moderation is obtained. According to another embodiment, the fuel assembly comprises 2-8, preferably 4-6 fuel rods, each of which has a length of between 0.59 and 0.79 times the length of said full length fuel rods. The arrangement of such fuel rods contributes to the shut-down margin and to a reduction of the pressure drop in the upper part of the fuel assembly. According to one embodiment, the fuel assembly comprises 8-16, preferably 11-13 fuel rods, each of which has a length that is between 0.29 and 0.45 times the length of said full length fuel rods. With this number of such short fuel rods, the shut-down margin is improved. According to another embodiment, the fuel assembly comprises at least 70, preferably at least 80, or at least 90 full length fuel rods. An efficient heat transfer is obtained by using many full length fuel rods. According to one embodiment, the fuel assembly comprises 5-20, preferably 10-15 fuel rods, each of which has a length of between 0.80 and 0.95 times the length of said full length fuel rods. The arrangement of such fuel rods will reduce the pressure drop in the upper part of the fuel assembly, near the outlet for the water/steam. According to another embodiment, the fuel assembly comprises: a lower tie plate, positioned below the fuel rods, wherein a lower end of each of said at least 3 water channels is attached to said tie plate, an upper lifting device, positioned above the fuel rods, including a handle for gripping and lifting a bundle of fuel rods, a plurality of spacer grids for holding the fuel rods, at least most of the spacer grids being attached to said at least 3 water channels, attachment rods, attached at a lower end to the upper part of said at least 3 water channels and at an upper end attached to said upper lifting device. Such a design will make it easier to handle the bundle of fuel rods. Since the upper handle and lifting device is attached to the attachment rods, which are attached to the water channels, which are attached to the lower tie plate, and since the spacer grids hold the fuel rods and since at least most of the spacer grids are attached to the water channels, it is possible to lift the whole bundle of fuel rods by gripping and lifting the handle. According to one design principle, the fuel channel is permanently fixed to a bottom transition piece, which includes a debris filter, and the whole fuel bundle as described above (including upper handle and lifting device, attachments rods, water channels, lower tie plate, and spacer grids) is lowered into the fuel channel and is resting freely on top of the transition piece. According to an alternative design principle, the whole fuel bundle as described above (including upper handle and lifting device, attachments rods, water channels, lower tie plate, and spacer grids) is permanently fixed to the transition piece, which includes a debris filter, and the fuel channel is placed over the fuel bundle and resting on the handle. An embodiment of the invention will now be described with reference to FIG. 1 and FIG. 2. FIG. 1 shows schematically a side view of a fuel assembly 4 according to an embodiment of the invention. The fuel assembly 4 comprises a number of fuel rods 10 and water channels 14. A lower tie plate 20 is arranged below the fuel rods 10. A lower end of the water channels 14 is attached to the tie plate 20. Above the fuel rods 10 an upper lifting device 22 is arranged. The upper lifting device 22 has a handle 24 for gripping and lifting a bundle of fuel rods 10. The fuel rods 10 are held by a plurality of spacer grids 26. It should be noted that FIG. 1 schematically shows only an upper and lower part of the fuel assembly 4. According to an embodiment, the fuel assembly 4 comprises ten spacer grids 26. The fuel assembly 4 also comprises attachment rods 28, which at a lower end are attached to the upper part of the water channels 14 and which at an upper end are attached to the upper lifting device 22. All spacer grids 26, with one exception, are attached to the water channels 14. The upper spacer grid 26 is positioned at the level of the attachment rods 28. The whole bundle of fuel rods 10 is thus held together with the help of the water channels 14, lower tie plate 20, attachment rods 28, upper lifting device 22 and spacer grids 26. It is therefore possible to lift the whole bundle of fuel rods 10 by gripping and lifting at the handle 24. With reference also to FIG. 2 the fuel assembly 4 will now be described in more detail. The fuel assembly 4 comprises a fuel channel 6 which surrounds the bundle of fuel rods 10. In FIG. 1 the fuel channel 6 has been removed in the viewing direction in order to make it possible to see the components arranged inside the fuel channel 6. The fuel channel 6 extends in a length direction L. The length direction L is normally, when the fuel assembly 4 is in use in a nuclear reactor, the vertical direction. The fuel channel 6 has a central fuel channel axis 8 in said length direction L. In FIG. 2, all the small circles refer to fuel rods 10. Each fuel rod 10 has a central fuel rod axis 12 (shown only for one fuel rod 10), which extends substantially in the length direction L. The larger circles in FIG. 2 show the water channels 14. The water channels 14 are configured and positioned for allowing non-boiling water to flow through the water channels 14, when the fuel assembly 4 is in use in a nuclear reactor. Each water channel 14 has a central water channel axis 16 (shown only for one water channel 14 in FIG. 2), which extends substantially in the length direction L. The fuel assembly comprises a first group of full length fuel rods 10. The full length fuel rods are not marked in FIG. 2 (i.e. they are shown by empty circles). The full length fuel rods 10 extend from a lower part of the fuel assembly 4 to an upper part of the fuel assembly 4, preferably through all the spacer grids 26. It can be noted that in FIG. 1 only full length fuel rods 10 are shown. The fuel assembly 4 also comprises a second group of fuel rods 10. The second group of fuel rods 10 extend from the lower part of the fuel assembly (like the full length fuel rods) but do not reach as high up as the full length fuel rods. The fuel rods 10 in said second group can have different lengths. In the shown embodiment, some fuel rods 10 are marked with one stroke. These fuel rods have a length of about 9/10 of the length of the full length fuel rods. In the shown embodiment, there are ten such fuel rods. When placing these 9/10 fuel rods the most reactive positions next to non-boiling water inside the water channels and outside the fuel channel are avoided. This is to minimize the negative impacts of having 1/10 less uranium in these rods, while serving their purpose of reducing pressure drop near the assembly outlet. The fuel rods 10 marked with two strokes (a cross) have a length of about ⅔ of the length of the full length fuel rods. In the shown embodiment there are four such fuel rods. These ⅔ fuel rods are positioned halfway between the corner rods in the outer rows and columns of the 11×11 fuel rod array. This is to reduce cold reactivity in the upper part of the fuel bundle which improves the shutdown margin late in the fuel cycle when the power distribution has moved towards the top. The fuel rods 10 marked with three strokes (a star) have a length of about ⅓ of the length of the full length fuel rods. In the shown embodiment there are twelve such fuel rods. As shown in FIG. 2, the fuel assembly 4 according to this embodiment has three water channels 14. Each water channel 14 has a cross-sectional area which is about 5.5 times the cross-sectional area of each one of the fuel rods 10 (or, in case the fuel assembly 4 would have fuel rods 10 of different cross-sectional areas, about 5.5 times the average cross-sectional area of the fuel rods 10). In the shown embodiment, there are only three water channels 14, i.e. no further water channels. As shown in FIG. 2, there are eight centrally located fuel rods 10 of the shortest kind. These central short fuel rods 10 are positioned such that for each of these fuel rods 10 it is the case that the distance between the fuel rod axis 12 and the central fuel channel axis 8 is shorter than the distance between any of the water channel axes 16 of the water channels 14 and the fuel channel axis 8. It should be noted that FIG. 2 shows a schematic cross-section of the fuel assembly 4 in the lower part of the fuel assembly (where also all the shorter fuel rods 10 are present). There is no longer fuel rod 10 (no ⅔ fuel rod or 9/10 fuel rod or full length fuel rod) which is positioned closer to the central fuel channel axis 8 than the central fuel rod axis 12 of any of the eight central short fuel rods 10. Above the eight short central fuel rods 10, there is thus an empty space for water in the fuel assembly 4. In addition to the eight central short ⅓ fuel rods, there are a further four such short fuel rods 10 located in the corners of the fuel assembly 4. Each of the water channels 14 has a circular cross-section, at least in the lower part of the fuel assembly 4 where the shorter central fuel rods 10 are arranged. In addition to the mentioned eight central short fuel rods 10, the fuel assembly 4 comprises a further six fuel rods, each of which fulfils the following criterion. The distance between the central fuel rod axis 12 and the central fuel channel axis 8 is less than the distance between the central water channel axis 16 of at least one of the three water channels 14 and the central fuel channel axis 8. In the shown embodiment, there are 14 fuel rods 10 that fulfil the mentioned criterion. These fuel rods 10 are located inside the dashed lines in FIG. 2. Each water channel 14 is positioned next to at least some of the eight centrally located short fuel rods 10. As can be seen in FIG. 2, the fuel assembly 4 comprises a substantially regular pattern of fuel rod positions. Each one of the water channels 14 is positioned such that it replaces four fuel rods 10 in this regular pattern. In the shown embodiment, the fuel assembly 4 thus comprises 83 full length fuel rods 10, ten 9/10 length fuel rods, four ⅔ length fuel rods and twelve ⅓ length fuel rods. The shown embodiment provides an advantageous fuel assembly 4 with which the above described objects and advantages of the invention are achieved. The present invention is not limited to the examples described herein, but can be varied and modified within the scope of the following claims. |
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description | This is a Continuation Application of PCT Application No. PCT/JP2005/005000, filed Mar. 18, 2005, which was published under PCT Article 21(2) in Japanese. This application is based upon and claims the benefit of priority from prior Japanese Patent Applications No. 2004-095449, filed Mar. 29, 2004; and No. 2004-095450, filed Mar. 29, 2004, the entire contents of both of which are incorporated herein by reference. 1. Field of the Invention The present invention relates to a specimen temperature adjusting apparatus that adjusts the temperature of an observation specimen. 2. Description of the Related Art In general, specimen observation using a microscope is performed by moving an object lens close to a specimen placed on a microscope stage and magnifying the observation target portion on the specimen. Regarding the objective lens, which is moved close to the specimen, the larger the magnification, the smaller the depth of focus, and the more difficult alignment of the objective lens and observation specimen. Also, even a small change in distance between the objective lens and specimen blurs the observation image. While the apparent positions of the objective lens and observation specimen are very close to each other, the pass-way of their mechanical connection is very long due to the presence of a large number of mechanical components such as a microscope frame, an objective lens moving mechanism, a revolver, and the like. The mechanical components tend to change their sizes depending on a temperature change. During specimen observation, assume that the objective lens has been focused on the observation specimen. Upon the ON/OFF operation of the illumination and the operations of the internal power supply and air-conditioning facilities, when the ambient temperature changes to change the sizes of the mechanical components, the distance between the objective lens and specimen changes. Accordingly, the focal point is shifted readily. In order to solve this drawback, Jpn. Pat. Appln. KOKAI Publication No. 2001-305432 discloses an apparatus that detects the distance between an objective lens and a specimen stage by a displacement sensor and maintains the distance constant. Recently, vital specimen observation using a microscope has been performed widely, and a vital specimen must be kept alive on the microscope for a long period of time. In view of this, for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-50358 discloses an apparatus that keeps a vital specimen at a predetermined temperature. The present invention is a specimen temperature adjusting apparatus for adjusting a temperature of an observation specimen, the specimen temperature adjusting apparatus comprising a specimen stage that the observation specimen is to be placed on, the specimen stage having a groove surrounding a portion where the observation specimen is to be placed, and a temperature adjustment element that is attached to the specimen stage, the temperature adjustment element being located in the groove of the specimen stage. Advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. The embodiments of the present invention will be described with reference to the views of the accompanying drawing. First Embodiment The first embodiment is directed to an inverted microscopic apparatus incorporating a specimen temperature adjusting apparatus that adjusts the temperature of an observation specimen. FIG. 1 schematically shows the microscopic apparatus according to the first embodiment of the present invention. As shown in FIG. 1, the specimen temperature adjusting apparatus according to the first embodiment is adapted to the use of a culture container 150 containing an observation specimen 162 and comprises a specimen stage 100 that the culture container 150 containing the observation specimen 162 is to be placed on and a temperature adjustment element 103 that is attached to the specimen stage 100. The specimen stage 100 has a groove 102 surrounding a portion where the culture container 150 containing the observation specimen 162 is to be placed. The temperature adjustment element 103 is located in the groove 102 of the specimen stage 100. Preferably, the groove 102 continuously surrounds the portion where the culture container 150 is to be placed. More preferably, the groove 102 symmetrically surrounds the portion where the culture container 150 is to be placed. For this purpose, the groove 102 may be a ring-like groove, for example. The specimen stage 100 preferably comprises a relatively thick disk-like plate. The specimen stage 100 is preferably made of a conductive material having a low thermal expansion coefficient, e.g., Invar. For example, the temperature adjustment element 103 comprises an element that can heat, e.g., a heater. Alternatively, the temperature adjustment element 103 may comprise an element that can both heat and cool, e.g., a Peltier element. The temperature adjustment element 103 may comprise a ring-like element, but may be a plurality of elements circularly located in the groove 102 of the specimen stage 100 preferably symmetrically. The temperature adjustment element 103 is covered with a cover 104. The cover 104 is preferably made of a highly heat-insulating material, e.g., a resin. The specimen temperature adjusting apparatus further comprises a temperature sensor 111 that measures the temperature of the specimen stage 100 and a temperature controller 112 that controls the temperature adjustment element 103 on the basis of the temperature measured by the temperature sensor 111. The temperature sensor 111 is located in contact with the temperature adjustment element 103 and covered with the cover 104. The arrangement of the temperature sensor 111 is not limited to this. The temperature sensor 111 may be located near the central portion of the specimen stage 100, i.e., near the portion where the culture container 150 is to be placed. For example, the temperature controller 112 controls the temperature adjustment element 103 so that the temperature of the specimen stage 100 is kept constant, in other words, so as to keep an output from the temperature sensor 111 constant. Alternatively, the temperature controller 112 controls the temperature adjustment element 103 so that the temperature of the specimen stage 100 changes with a temperature cycle within a temperature range. The specimen stage 100 has an opening 101 at its central portion and is supported by a microscope stage 121. The opening 101 allows optical observation of the observation specimen 162 from below. The observation specimen 162 is cultured in a culture solution 161 contained in the culture container 150. The culture container 150 has an opening at the center of the bottom portion of a container main body 151. The opening of the culture container 150 is closed with a glass plate 154 fixed to the lower surface of the bottom portion of the container main body 151. The container main body 151 has a leg 152 projecting more downward than the bottom surface of the glass plate 154. The leg 152 comprises, e.g., a ring-like projection, but is not particularly limited to this, and may comprise a plurality of projections located on a circumference. The specimen stage 100 further has a recess 105 to receive the leg 152 of the culture container 150. When the leg 152 of the culture container 150 is received in the recess 105, the recess 105 allows the bottom surface of the glass plate 154 of the culture container 150 to be in contact with the specimen stage 100. The recess 105 comprises, e.g., a ring-like groove, but is not limited to this, and suffices as far as it can receive the leg 152 of the culture container 150. Preferably, a weight 155 is placed on the culture container 150 on the specimen stage 100 to further stabilize the contact of the specimen stage 100 with the glass plate 154 of the culture container 150. The observation specimen 162 is positioned in the opening at the center of the bottom portion of the container main body 151, and optically observed from below through the glass plate 154. The microscopic apparatus comprises an objective lens 122 to optically observe the observation specimen 162. The objective lens 122 is positioned below the opening 101 of the specimen stage 100. The objective lens 122 cooperates with an observation optical system (not shown) to optically observe the observation specimen 162 from below through the opening 101 of the specimen stage 100. The objective lens 122 supports a displacement sensor 124 through a sensor support member 123. The displacement sensor 124 cooperates with the specimen stage 100 to constitute an electrostatic capacitive sensor. Both the displacement sensor 124 and specimen stage 100 are connected to a sensor amplifier 125. The sensor amplifier 125 outputs a signal that reflects the distance from the displacement sensor 124 to the lower surface of the specimen stage 100. The position of the objective lens 122 along the optical axis is preferably controlled on the basis of the output from the sensor amplifier 125. For example, the objective lens 122 is moved along the optical axis so that the distance from the displacement sensor 124 to the lower surface of the specimen stage 100 is kept constant. The operation of the microscopic apparatus according to this embodiment will be described. In the following description, the temperature adjustment element 103 is exemplified by a heater. When the power supply of the temperature controller 112 is turned on, the heater 103 generates heat to increase the temperature of the specimen stage 100. As the heater 103 is covered with the cover 104, while the heater 103 generates heat, the culture solution will not wet the heater 103, or the operator's hand will not come into direct contact with the heater 103. As the cover 104 has high heat-insulating properties, the specimen stage 100 is heated efficiently. The temperature of the heater 103 is detected by the temperature sensor 111 and fed back to the temperature controller 112. On the basis of this signal, the temperature controller 112 adjusts the current to the heater 103 to set the specimen stage 100 to a desired temperature. When the temperature of the specimen stage 100 increases, the specimen stage 100 is deformed by the heat. FIG. 4 schematically shows deformation caused by heat of the specimen stage 100. The specimen stage 100 comprises a plate and has the ring-like groove 102 that surrounds the portion where the culture container 150 is to be placed. Thus, as the specimen stage 100 deforms, the portion where the culture container 150 is to be placed moves parallel along the optical axis, as shown in FIG. 4. The displacement of the upper surface and that of the lower surface of the specimen stage 100 are equal. The portion where the culture container 150 is to be placed includes a portion that opposes the displacement sensor 124, in other words, a target portion of the displacement sensor 124. Accordingly, the displacement along the optical axis of the sensor position as the target of the displacement sensor 124 is equal to the displacement along the optical axis of the observation position positioned on the optical axis. Consequently, the displacement along the optical axis detected by the displacement sensor 124 faithfully reflects the displacement along the optical axis of the observation position. When the objective lens 122 is moved along the optical axis to keep the output signal from the displacement sensor 124 constant, the positional relationship between the observation specimen 162 and objective lens 122 is kept constant. As a result, occurrence of image blurring is prevented well. As the specimen stage 100 is made of a material having a low thermal expansion coefficient, its thermal deformation upon temperature change is very small. This also contributes to prevention of image blurring. FIG. 5 schematically shows deformation of a specimen stage caused by heat, and the stage has no ring-like groove to surround a portion where the culture container 150 is to be placed. The closer to the central portion, the larger this specimen stage displaces along the optical axis, as shown in FIG. 5. In other words, the displacement along the optical axis changes depending on the distance from the optical axis. Consequently, the displacement along the optical axis at the sensor position differs from the displacement along the optical axis at the observation position positioned on the optical axis. Therefore, even when the objective lens is moved along the optical axis to keep constant the displacement detected at the sensor position, the positional relationship between the observation specimen and observation specimen is not kept constant. Consequently, image blurring occurs. In contrast to this, according to this embodiment, since the displacement at the observation position and that at the sensor position are equal, as described above, the positional relationship between the observation specimen 162 and objective lens 122 can be kept constant. As a result, image blurring can be prevented. As the specimen stage 100 is heated, heat is conducted from the specimen stage 100 to the culture container 150 through their contact portion, so that the observation specimen 162 is heated. According to this embodiment, the culture container 150 is in contact with the specimen stage 100 at the glass plate 154 as well as at the leg 152. Namely, the contact area of the culture container 150 and specimen stage 100 is enough large. Thus, the observation specimen 162 is heated efficiently. Furthermore, the weight 155 placed on the culture container 150 increases the contact pressure of the glass plate 154 and specimen stage 100 to decrease contact heat resistance. Consequently, heat is more readily conducted from the specimen stage 100 to the glass plate 154. Accordingly, the insulation effectiveness of the observation specimen 162 is improved. According to the experiment conducted by the present inventors, with the surrounding ambient temperature and preset heater temperature being equal, when the weight 155 was placed on the culture container 150, the culture solution temperature increased from 37° C. to 38° C. FIG. 6 shows a specimen stage that has no groove to receive the leg 152 of the culture container 150. With this specimen stage, the culture container 150 is in contact with a specimen stage 500 through only the bottom surface of the leg 152, as shown in FIG. 6. Namely, the contact area of the culture container 150 and specimen stage 500 is small. Accordingly, heat transfer efficiency from the specimen stage 500 to the culture container 150 is low. In contrast to this, according to the present embodiment, the contact area of the culture container 150 and specimen stage 100 is large, as described above, so that the observation specimen 162 can be heated efficiently. In this embodiment, since the heater exemplifies the temperature adjustment element 103, heating is described, but the same discussion applies to cooling as well. The culture solution 161 in the culture container 150 evaporates and is often replenished during the experiment. As the specimen stage 100 comprises a relatively thick plate, it has relatively high rigidity. Hence, when the culture solution 161 evaporates or is replenished to change its weight, the specimen stage 100 does not substantially deform. Various changes and modifications may be made in this embodiment without departing from the spirit and scope of the present invention. For example, in this embodiment, the specimen stage 100 is made of a conductive material. Alternatively, the specimen stage 100 may comprise an insulating plate such as a glass plate and a conductive film formed on the bottom surface of the plate, in which the conductive film is electrically connected to the sensor amplifier 125 through a cable or the like. In this case, since the glass is transparent, an observation window must not be formed at its central portion. In this embodiment, the culture container 150 containing the observation specimen 162 is placed on the specimen stage 100. Alternatively, a slide glass that the observation specimen 162 is placed on may be placed on the specimen stage 100. In this embodiment, the groove 102 in which the temperature adjustment element 103 is to be located continuously surrounds the portion where the culture container 150 is to be placed. Alternatively, the groove 102 may discontinuously surrounds the portion where the culture container 150 is to be placed. More specifically, the groove 102 in which the temperature adjustment element 103 is to be located may comprise a plurality of recesses formed around the portion where the culture container 150 is to be placed. In this case, the plurality of recesses are preferably located symmetrically, e.g., equidistantly on a circumference. If a sufficient number of recesses are formed, the same advantage as in this embodiment can be expected. Second Embodiment The second embodiment is directed to deformation of the position where the temperature sensor is located. FIG. 2 schematically shows a microscopic apparatus according to the second embodiment of the present invention. In FIG. 3, members indicated by the same reference numerals as the members shown in FIG. 1 are identical, and a detailed description thereof will be omitted. As shown in FIG. 2, a specimen temperature adjusting apparatus according to the second embodiment comprises a temperature sensor 211 that measures the temperature of an observation specimen 162 and a temperature controller 212 that controls a temperature adjustment element 103 on the basis of the temperature measured by the temperature sensor 211, in place of the temperature sensor 111 and temperature controller 112 of the first embodiment. The temperature sensor 211 is located in a culture container 150 and dipped in a culture solution 161. For example, the temperature controller 212 controls the temperature adjustment element 103 so that the temperature of the culture solution 161 is kept constant. In other words, the temperature controller 212 controls the temperature adjustment element 103 to keep an output from the temperature sensor 211 constant. Alternatively, the temperature controller 212 controls the heater 103 so that the temperature of the culture solution 161 changes with a constant temperature cycle. The arrangement except for the temperature sensor 211 and temperature controller 212 is the same as that of the first embodiment. The second embodiment has the same advantages as the first embodiment. In particular, in the present embodiment, since temperature control is performed on the basis of the temperature measured by the temperature sensor 211 located in the culture solution 161, the temperature of the observation specimen 162 can be controlled more accurately. In the second embodiment as well, the same changes and modification as those of the first embodiment may be made. Third Embodiment The third embodiment is directed to an upright microscopic apparatus incorporating a specimen temperature adjusting apparatus that adjusts the temperature of an observation specimen. FIG. 3 schematically shows the microscopic apparatus according to the third embodiment of the present invention. In FIG. 3, members indicated by the same reference numerals as the members shown in FIG. 1 are identical, and a detailed description thereof will be omitted. As shown in FIG. 3, the specimen temperature adjusting apparatus according to the third embodiment comprises a specimen stage 300 in place of the specimen stage 100 of the first embodiment. The specimen stage 300 has a ring-like groove 302 surrounding a portion where a culture container 150 containing an observation specimen 162 is to be placed. A temperature adjustment element 103 is located in the groove 302 of the specimen stage 300. The heater 103 is covered with a cover 104. The specimen stage 300 preferably comprises a relatively thick disk-like plate like the specimen stage 100. The specimen stage 300 is preferably made of a conductive material having a low thermal expansion coefficient, e.g., Invar. The specimen stage 300 has an opening 301 at its central portion and is supported by a microscope stage 121. The opening 301 allows the observation specimen 162 to be illuminated from below. The specimen stage 300 further has a recess 105 to receive a leg 152 of the culture container 150. When the leg 152 of the culture container 150 is received in the recess 105, the recess 105 allows the bottom surface of a glass plate 154 of the culture container 150 to be in contact with the specimen stage 300. The recess 105 comprises, e.g., a ring-like groove, but is not limited to this, and suffices as far as it can receive the leg 152 of the culture container 150. According to this embodiment, the ring-like groove 302 in which the temperature adjustment element 103 is located is formed in the lower surface of the specimen stage 300. The recess 105 that receives the leg 152 of the culture container 150 is formed in the upper surface of the specimen stage 300. The microscopic apparatus comprises an objective lens 322 to optically observe the observation specimen 162. The objective lens 322 is positioned above the opening 301 of the specimen stage 300 and cooperates with an observation optical system (not shown) to optically observe the observation specimen 162 from above. The objective lens 322 supports a displacement sensor 324 through a sensor support member 323. The displacement sensor 324 cooperates with the specimen stage 300 to constitute an electrostatic capacitive sensor. Both the displacement sensor 324 and specimen stage 300 are connected to a sensor amplifier 325. The sensor amplifier 325 outputs a signal that reflects the distance from the displacement sensor 324 to the upper surface of the specimen stage 300. The position of the objective lens 322 along the optical axis is preferably controlled on the basis of the output from the sensor amplifier 325. For example, the objective lens 322 is moved along the optical axis so that the distance from the displacement sensor 324 to the upper surface of the specimen stage 300 is kept constant. The third embodiment is directed to an upright microscopic apparatus. The third embodiment is different from the first embodiment in only that the observation specimen 162 is optically observed from above, and has the same advantage as those of the first embodiment. In the third embodiment, the same changes and modifications as in the first embodiment may be made. Fourth Embodiment The fourth embodiment is directed to a manipulation device for an electric stage in a microscope. In the microscope, the manipulation of a rotary handle performed by the observer is transmitted through a mechanical transmission mechanism to move the observation specimen in the X-Y direction and to focus on the observation specimen. Recently, demands for an automatic microscope and fine positioning of an observation specimen and an objective lens increase. Sometimes, electric actuators are used to actuate the focusing mechanism of an objective lens and the X-Y stage. For this reason, a device that converts the rotation angle of the handle into an electric signal has been proposed. Such a device is disclosed in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 2002-182122. According to the device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2002-182122, coarse movement and fine movement are switched by a coarse movement/fine movement selection switch, so that coarse movement and fine movement are performed with one handle. Therefore, when manipulating an X-Y stage while observing the observation specimen, in spite that the coarse movement/fine movement selection switch has been set to the coarse movement state, sometimes the observer may erroneously determine that the microscope is set in the fine movement state and manipulate the handle. Then, the observation target falls outside the visual field. In high-magnification observation using a microscope, vibration should be avoided, and accordingly the microscope is set on an anti-vibration stage for observation. After the observation specimen is set, initial focusing and alignment are performed while looking into the microscope eyepiece lens. After setting is completed or during observation, when the observation position is to be adjusted or the focal position is to be changed, it should be performed from a table separated from the anti-vibration stage, for avoiding adverse affection of vibration during the manipulation to observation. When observing a vital specimen, fluorescence observation is employed often. Disturbance light should be avoided during fluorescence observation. Thus, for observation, a microscope is set in a darkroom. During the observation or the like, if the observation position or focal position is to be changed, switching between the coarse movement and fine movement is difficult to perform because the interior of the darkroom is dark. In the darkroom, it is dark around the microscope, and accordingly note taking and keyboard operation are difficult to perform. Therefore, the microscope is desirably manipulatable outside the darkroom. To keep the vital specimen alive for a long period of time, the temperature and humidity must be kept constant. For this purpose, sometimes the microscope is set in a thermostat/humidistat bath for observation. In this case, alignment and focusing of the observation specimen must be manipulated outside the thermostat/humidistat bath by remote control. This embodiment has been made in view of the above situation, and has as its object to provide a manipulation device that can manipulate an electric stage without performing a switching operation between the coarse movement and fine movement. FIG. 7 shows a manipulation device according to the fourth embodiment of the present invention. As shown in FIG. 7, a manipulation device 1100 comprises an X-Y base 1101 and a Z base 1102. The X-Y base 1101 and Z base 1102 are spatially separable. The X-Y base 1101 has an X-movement coaxial handle 1110 and a Y-movement coaxial handle 1120. The Z base 1102 has a Z-movement coaxial handle 1130. The X-movement coaxial handle 1110 comprises a first rotary knob 1111 and a second rotary knob 1112. The first and second rotary knobs 1111 and 1112 are assigned with X coarse movement and X fine movement. The first and second rotary knobs 1111 and 1112 respectively comprise a rotary resistance adjustment member 1113 and a rotary resistance adjustment member 1114 that adjust rotary resistances. The rotary resistance adjustment member 1113 is provided with a groove 1115. The rotary resistance adjustment member 1114 is provided with a hole 1116. The Y-movement coaxial handle 1120 comprises a first rotary knob 1121 and a second rotary knob 1122. The first and second rotary knobs 1121 and 1122 are assigned with Y coarse movement and Y fine movement. The first and second rotary knobs 1121 and 1122 respectively comprise a rotary resistance adjustment member 1123 and a rotary resistance adjustment member 1124 that adjust rotary resistances. The rotary resistance adjustment member 1123 is provided with a groove 1125. The rotary resistance adjustment member 1124 is provided with a hole 1126. The Z-movement coaxial handle 1130 comprises a first rotary knob 1131 and a second rotary knob 1132. The first and second rotary knobs 1131 and 1132 are assigned with Z coarse movement and Z fine movement. The first and second rotary knobs 1131 and 1132 respectively comprise a rotary resistance adjustment member 1133 and rotary resistance adjustment member 1134 that adjust rotary resistances. The rotary resistance adjustment member 1133 is provided with a groove 1135. The rotary resistance adjustment member 1134 is provided with a hole 1136. The X-, Y-, and Z-movement coaxial handles 1110, 1120, and 1130 have the same structure. Accordingly, the rotary resistance adjustment members 1113, 1123, and 1133 have the same structure. Similarly, the rotary resistance adjustment members 1114, 1124, and 1134 have the same structure. In the following description, the rotary resistance adjustment members 1133 and 1134 of the Z-movement coaxial handle 1130 will be described representatively. FIG. 8 shows a partial section of the Z-movement coaxial handle 1130. As shown in FIG. 8, a rotary shaft 1142 extends inside a stationary shaft 1141, and the rotary shaft 1142 is rotatable with respect to the stationary shaft 1141. The rotary shaft 1142 and first rotary knob 1131 are fixed and rotate integrally. A rotary shaft 1143 extends around the stationary shaft 1141, and the rotary shaft 1143 is rotatable with respect to the stationary shaft 1141. The rotary shaft 1143 and second rotary knob 1132 are fixed and rotate together. The rotary resistance adjustment member 1133 is screwed into the distal end portion of the rotary shaft 1142. A pin 1151 is arranged in the first rotary knob 1131 and movable parallel to the central shaft of the stationary shaft 1141, i.e., longitudinally movable. One end portion of the pin 1151 is in contact with the rotary resistance adjustment member 1133. A frictional member 1152, a spring 1153, and a frictional member 1154 are located between the other end portion of the pin 1151 and the stationary shaft 1141. Both the frictional members 1152 and 1154 have annular shapes and are positioned around the rotary shaft 1142. The frictional member 1152 is in contact with the pin 1151, and the frictional member 1154 is in contact with the stationary shaft 1141. The spring 1153 is located between the frictional members 1152 and 1154 to apply to them forces that increase the distance between them. For example, the spring 1153 is a coil spring and positioned around the rotary shaft 1142. As the rotary resistance adjustment member 1133 rotates with respect to the rotary shaft 1142, the rotary resistance adjustment member 1133 moves longitudinally with respect to the rotary shaft 1142. When the rotary resistance adjustment member 1133 moves longitudinally, the pin 1151 moves longitudinally, and accordingly the frictional member 1152 also moves longitudinally. Consequently, the spring 1153 expands or compresses. The expansion and compression of the spring 1153 change the contact pressure of the frictional member 1152 and spring 1153 and the contact pressure of the frictional member 1154 and stationary shaft 1141. When the first rotary knob 1131 is rotated, the pin 1151 rotates together with it. For example, while holding the first rotary knob 1131, when the first rotary knob 1131 is rotated to move downward, the pin 1151 compresses the spring 1153 through the frictional member 1152. The compression increases the restoration force of the spring 1153. Hence, the contact pressure of the frictional member 1152 and spring 1153 and the contact pressure of the frictional member 1154 and stationary shaft 1141 increase. Consequently, the force required to rotate the first rotary knob 1131 increases to increase the rotary resistance. The rotary resistance adjustment member 1134 is screwed into the outer surface of the rotary shaft 1143. A pin 1161 is arranged in the second rotary knob 1132 and movable parallel to the central shaft of the stationary shaft 1141, i.e., longitudinally movable. One end portion of the pin 1161 is in contact with the rotary resistance adjustment member 1134. A frictional member 1162, a spring 1163, and a frictional member 1164 are located between the other end portion of the pin 1161 and the stationary shaft 1141. Both the frictional members 1162 and 1164 have annular shapes and are positioned around the rotary shaft 1143. The frictional member 1162 is in contact with the pin 1161, and the frictional member 1164 is in contact with the stationary shaft 1141. The spring 1163 is located between the frictional members 1162 and 1164 to apply to them forces that increase the distance between them. For example, the spring 1163 is a coil spring and positioned around the rotary shaft 1143. As the rotary resistance adjustment member 1134 rotates, it moves longitudinally with respect to the rotary shaft 1143. Accordingly, the pin 1161 moves longitudinally, and the frictional member 1162 also accordingly moves longitudinally. Consequently, the spring 1163 expands or compresses. The expansion and compression of the spring 1163 change the contact pressure of the frictional member 1162 and spring 1163 and the contact pressure of the frictional member 1164 and stationary shaft 1141. Consequently, the force required to rotate the second rotary knob 1132 changes to change the rotary resistance. FIG. 9 shows a usage of the manipulation device shown in FIG. 7. As shown in FIG. 9, a microscope 1170 comprises an X-Y stage 1171 that moves an observation specimen in the X-Y direction and a Z stage 1172 that moves an objective lens 1175 in the Z direction. Both the X-Y stage 1171 and Z stage 1172 comprise electric stages respectively. The microscope 1170 is connected to a manipulation device 1100 through a controller 1181 that drives the X-Y stage 1171 and Z stage 1172. The controller 1181 is connected to the manipulation device 1100 through connection cables. The microscope 1170 is set on an anti-vibration stage 1182. The manipulation device 1100 is located on a table 1183 spatially separate from the anti-vibration stage 1182. Thus, vibration caused by manipulating the manipulation device 1100 does not influence observation. The operation of the manipulation device 1100 will be described. When focusing on the observation specimen, the Z-movement coaxial handle 1130 is manipulated. First, the second rotary knob 1132 is rotated to roughly focus on the observation specimen with coarse movement. Subsequently, the first rotary knob 1131 is rotated to focus with fine movement. The Z base 1102 generates an electric signal (manipulation signal) corresponding to the manipulation of the Z-movement coaxial handle 1130. The manipulation signal generated by the Z base 1102 is transmitted to the controller 1181 through the connection cables. On the basis of the transmitted signal, the controller 1181 moves the Z stage 1172. The Z stage 1172 of the microscope 1170 can be manipulated in this manner. The rotary resistance of the rotary knob (first and second rotary knobs 1131 and 1132) is desirably heavy in coarse movement and light in fine movement. The optimal resistance changes depending on the application and operator, and accordingly the operator may adjust a preferred resistance that matches the application. Rotary resistance adjustment is performed in the following manner. First, assume that the rotary resistance of the first rotary knob 1131 is to be adjusted. While holding the first rotary knob 1131, the operator inserts a coin or the like in the groove 1135 of the rotary resistance adjustment member 1133 and turns the coin or the like, thus adjusting the rotary resistance. Assume that the rotary resistance of the second rotary knob 1132 is to be adjusted. The operator inserts a screwdriver or the like in the hole 1136 of the rotary resistance adjustment member 1134 to fix the rotary resistance adjustment member 1134. Then, the operator rotates the second rotary knob 1132, thus adjusting the rotary resistance. The operator can adjust the rotary resistance arbitrarily in the above manner. When positioning the observation specimen in the X direction, the X-movement coaxial handle 1110 is manipulated. First, the second rotary knob 1112 is rotated to roughly align the observation specimen in the X direction with coarse movement. Subsequently, the first rotary knob 1111 is rotated to align the observation specimen in the X direction with fine movement. The X-Y base 1101 generates an electric signal (manipulation signal) corresponding to the manipulation of the X-movement coaxial handle 1110. The manipulation signal generated by the X-Y base 1101 is transmitted to the controller 1181 through the connection cables. On the basis of the transmitted signal, the controller 1181 moves the X-Y stage 1171 in the X direction. The X-Y stage 1171 of the microscope 1170 can be manipulated in the X direction in this manner. The rotary resistance of the rotary knob (first and second rotary knobs 1111 and 1112) is desirably heavy in coarse movement and light in fine movement. The optimal resistance changes depending on the application and operator, and accordingly the operator may adjust a preferred resistance that matches the application. Rotary resistance adjustment is performed in the following manner. First, assume that the rotary resistance of the first rotary knob 1111 is to be adjusted. While holding the first rotary knob 1111, the operator inserts a coin or the like in the groove 1115 of the rotary resistance adjustment member 1113 and turns the coin or the like, thus adjusting the rotary resistance. Assume that the rotary resistance of the second rotary knob 1112 is to be adjusted. The operator inserts a screwdriver or the like in the hole 1116 of the rotary resistance adjustment member 1114 to fix the rotary resistance adjustment member 1114. Then, the operator rotates the second rotary knob 1112, thus adjusting the rotary resistance. The operator can adjust the rotary resistance arbitrarily in the above manner. When positioning the observation specimen in the Y direction, the Y-movement coaxial handle 1120 is manipulated. First, the second rotary knob 1122 is rotated to roughly align the observation specimen in the Y direction with coarse movement. Subsequently, the first rotary knob 1121 is rotated to align the observation specimen in the Y direction with fine movement. The X-Y base 1101 generates an electric signal (manipulation signal) corresponding to the manipulation of the Y-movement coaxial handle 1120. The manipulation signal generated by the X-Y base 1101 is transmitted to the controller 1181 through the connection cables. On the basis of the transmitted signal, the controller 1181 moves the X-Y stage 1171 in the Y direction. The X-Y stage 1171 of the microscope 1170 can be manipulated in the Y direction in this manner. The rotary resistance of the rotary knob (first and second rotary knobs 1121 and 1122) is desirably heavy in coarse movement and light in fine movement. The optimal resistance changes depending on the application and operator, and accordingly the operator may adjust a preferred resistance that matches the application. Rotary resistance adjustment is performed in the following manner. First, assume that the rotary resistance of the first rotary knob 1121 is to be adjusted. While holding the first rotary knob 1121, the operator inserts a coin or the like in the groove 1125 of the rotary resistance adjustment member 1123 and turns the coin or the like, thus adjusting the rotary resistance. Assume that the rotary resistance of the second rotary knob 1122 is to be adjusted. The operator inserts a screwdriver or the like in the hole 1126 of the rotary resistance adjustment member 1124 to fix the rotary resistance adjustment member 1124. Then, the operator rotates the second rotary knob 1122, thus adjusting the rotary resistance. The operator can adjust the rotary resistance arbitrarily in the above manner. In the above manner, the X-Y and Z stages 1171 and 1172 of the microscope 1170 can be manipulated on the table 1183 that is spatially separate from the anti-vibration stage 1182 where the microscope 1170 is set. Namely, the X-Y and Z stages 1171 and 1172 of the microscope 1170 can be manipulated without transmitting to the microscope 1170 vibration caused by manipulating the manipulation device 1100. If the X-Y stage 1171 need not be manipulated in observation, the X-Y base 1101 can be removed from the controller 1181. Then, a wide space can be reserved around the observer's hands. As the X-Y and Z bases 1101 and 1102 are separable, the operator can arrange them at appropriate convenient positions and use them in accordance with the usage. The controller 1181 can be connected to a plurality of X-Y bases 1101 and a plurality of Z bases 1102. When the controller 1181 is connected to the plurality of X-Y bases 1101 and the plurality of Z bases 1102 and the plurality of X-Y bases 1101 and the plurality of Z bases 1102 are located at different positions, the microscope can be manipulated from different positions. Each of the X-Y base 1101 and Z base 1102 has several switches. These switches include a position lock switch, a position memory switch, and a position memory position restoration switch. With the position lock switch being turned on, after focusing or positioning is completed, even if the operator erroneously touches a rotary knob, the rotary knob will not move. With the position memory switch and position memory position restoration switch being turned on, even if the operator should erroneously touch a rotary knob, the rotary knob can be restored to the initial position. The upper surface of the X-Y base 1101 is inclined. Therefore, the observer who places his or her elbows on the table can place his or her hands on the upper surface of the X-Y base 1101 easily. This reduces the fatigue the operator suffers from long-time manipulation. As the X- and Y-movement coaxial handles 1110 and 1120 provided to the X-Y base 1101 are arrayed longitudinally, their rotary knobs can be manipulated with either the left or right hand. The arrangement of the X- and Y-movement coaxial handles 1110 and 1120 is not limited to a longitudinal array, but can be a transverse array. The Z-movement coaxial handle 1130 is arranged on the right side surface to extend horizontally, but its position is not limited to this. The Z-movement coaxial handle 1130 may be provided on the left side surface to extend horizontally, or on the upper surface to extend upward. The four rotary knobs 1111, 1112, 1121, and 1122 may be arbitrarily assigned with the functions of X coarse movement, X fine movement, Y coarse movement, and Y fine movement. More specifically, while the rotary knobs 1111 and 1112 are assigned with X coarse movement and X fine movement in this embodiment, they may be respectively assigned with X fine movement and X coarse movement. Similarly, while the rotary knobs 1121 and 1122 are respectively assigned with Y coarse movement and Y fine movement, they may be respectively assigned with Y fine movement and Y coarse movement. In this embodiment, the coaxial handle 1110 is assigned with X coarse movement and X fine movement, and the coaxial handle 1120 is assigned with Y coarse movement and Y fine movement. Alternatively, the coaxial handle 1110 may be assigned with Y coarse movement and Y fine movement, and the coaxial handle 1120 may be assigned with X coarse movement and X fine movement. In this case, naturally, assignment of Y coarse movement and that of Y fine movement to the rotary knobs 1111 and 1112 of the coaxial handle 1110 are arbitrarily interchangeable. Similarly, assignment of X coarse movement and that of X fine movement to the rotary knobs 1121 and 1122 of the coaxial handle 1120 are arbitrarily interchangeable. Fifth Embodiment The fifth embodiment is directed to another usage of the manipulation device described in the fourth embodiment. FIG. 10 shows a usage of the manipulation device shown in FIG. 7 according to the fifth embodiment. In FIG. 10, members indicated by the same reference numerals as the members shown in FIG. 9 are identical, and a detailed description thereof will be omitted. As shown in FIG. 10, a microscope 1170 is set in a thermostat/humidistat bath 1191 together with a controller 1181 that drives an X-Y stage 1171 and a Z stage 1172. A manipulation device 1100 is located outside the thermostat/humidistat bath 1191 that shields light and radio waves. The controller 1181 is connected to the manipulation device 1100 through connection cables. The manipulation device 1100 of this embodiment is manipulated in the same manner as the manipulation device 1100 of the fourth embodiment. More specifically, when focusing on an observation specimen, a Z-movement coaxial handle 1130 is manipulated. First, a second rotary knob 1132 is rotated to roughly focus on the observation specimen with coarse movement. Subsequently, a first rotary knob 1131 is rotated to focus with fine movement. A manipulation signal generated by manipulating the Z-movement coaxial handle 1130 is transmitted through the connection cables to the controller 1181 placed in the thermostat/humidistat bath 1191. On the basis of the transmitted signal, the controller 1181 operates the Z stage 1172. The Z stage 1172 of the microscope 1170 can be manipulated in this manner. When positioning the observation specimen in the X direction, an X-movement coaxial handle 1110 is manipulated. First, a second rotary knob 1112 is rotated to roughly align the observation specimen in the X direction with coarse movement. Subsequently, a first rotary knob 1111 is rotated to align the observation specimen in the X direction with fine movement. A manipulation signal generated by manipulating the X-movement coaxial handle 1110 is transmitted through the connection cables to the controller 1181 placed in the thermostat/humidistat bath 1191. On the basis of the transmitted signal, the controller 1181 operates the X stage. The X-Y stage 1171 of the microscope 1170 can be manipulated in the X direction in this manner. When positioning the observation specimen in the Y direction, a Y-movement coaxial handle 1120 is manipulated. First, a second rotary knob 1122 is rotated to roughly align the observation specimen in the Y direction with coarse movement. Subsequently, a first rotary knob 1121 is rotated to align the observation specimen in the Y direction with fine movement. A manipulation signal generated by manipulating the Y-movement coaxial handle 1120 is transmitted through the connection cables to the controller 1181 placed in the thermostat/humidistat bath 1191. On the basis of the transmitted signal, the controller 1181 operates the X-Y stage 1171 and Z stage 1172. The X-Y stage 1171 of the microscope 1170 can be manipulated in the Y direction in this manner. According to this embodiment, the X-Y stage 1171 and Z stage 1172 of the microscope 1170 in the thermostat/humidistat bath 1191 can be manipulated by the manipulation device 1100 located outside the thermostat/humidistat bath 1191 that shields light and electric waves, from outside the thermostat/humidistat bath 1191 by remote control. Sixth Embodiment The sixth embodiment is directed to still another usage of the manipulation device described in the fourth embodiment. FIG. 11 shows a usage of the manipulation device shown in FIG. 7 according to the sixth embodiment. In FIG. 11, members indicated by the same reference numerals as the members shown in FIG. 9 are identical, and a detailed description thereof will be omitted. As shown in FIG. 11, a microscope 1170 is set in a darkroom 1192 together with a controller 1181 that drives an X-Y stage 1171 and a Z stage 1172. The microscope 1170 and controller 1181 are set on an anti-vibration stage 1182. The controller 1181 is connected to two manipulation devices 1100A and 1100B through connection cables. The manipulation devices 1100A and 1100B are identical with the manipulation device 1100 described in the fourth embodiment, and their practical manipulation is also identical to that described in the fourth embodiment. One manipulation device 1100A is in the darkroom 1192 and placed on a table 1183. The other manipulation device 1100B is outside the darkroom 1192 and placed on a table 1184. Furthermore, the microscope 1170 is connected to two observation monitors 1185 and 1186 through connection cables. One observation monitor 1185 is located in the darkroom 1192, and the other observation monitor 1186 is located outside the darkroom 1192. According to this embodiment, the X-Y stage 1171 and Z stage 1172 of the microscope 1170 can be driven by using either one of the manipulation devices 1100A and 1100B. In particular, assume that the microscope 1170 is set in a dark environment as in, e.g., fluorescence observation. In this case, when the manipulation device 1100B and observation monitor 1186 that are located outside the darkroom 1192 are used, manipulation such as a change of the observation position or focal position can be performed outside the darkroom 1192. The outside of the darkroom 1192 is bright, or can be lightened if it is dark. Hence, switching between coarse movement and fine movement can be performed easily. Also, note taking and keyboard operation can be performed easily. When focusing on an observation specimen, a Z-movement coaxial handle 1130 is manipulated. First, a second rotary knob 1132 is rotated to roughly focus on the observation specimen with coarse movement. Subsequently, a first rotary knob 1131 is rotated to focus with fine movement. A manipulation signal generated by manipulating the Z-movement coaxial handle 1130 is transmitted through the connection cables to the controller 1181 placed in the darkroom 1192. On the basis of the transmitted signal, the controller 1181 operates the Z stage 1172. The Z stage 1172 of the microscope 1170 in the darkroom 1192 can be manipulated in this manner by remote control. When positioning the observation specimen in the X direction, an X-movement coaxial handle 1110 is manipulated. First, a second rotary knob 1112 is rotated to roughly align the observation specimen in the X direction with coarse movement. Subsequently, a first rotary knob 1111 is rotated to align the observation specimen in the X direction with fine movement. A manipulation signal generated by manipulating the X-movement coaxial handle 1110 is transmitted through the connection cables to the controller 1181 placed in the darkroom 1192. On the basis of the transmitted signal, the controller 1181 operates the X stage. When positioning the observation specimen in the Y direction, a Y-movement coaxial handle 1120 is manipulated. First, a second rotary knob 1122 is rotated to roughly align the observation specimen in the Y direction with coarse movement. Subsequently, a first rotary knob 1121 is rotated to align the observation specimen in the Y direction with fine movement. A manipulation signal generated by manipulating the Y-movement coaxial handle 1120 is transmitted through the connection cables to the controller 1181 placed in the darkroom 1192. On the basis of the transmitted signal, the controller 1181 operates the X-Y stage 1171 and Z stage 1172. According to this embodiment, the X-Y stage 1171 and Z stage 1172 of the microscope 1170 in the darkroom can be manipulated at an arbitrary position in or outside the darkroom by remote control. Seventh Embodiment This embodiment is directed to a modification of the X-Y base described in the fourth embodiment. FIG. 12 shows the X-Y base according to the fourth embodiment of the present invention. As shown in FIG. 12, an X-Y base 1103 comprises an X-movement coaxial handle 1110 and a Y-movement coaxial handle 1120. The X-movement coaxial handle 1110 and Y-movement coaxial handle 1120 have been described in detail in the fourth embodiment, and a detailed description thereof will be omitted. In this embodiment, the X-movement coaxial handle 1110 and Y-movement coaxial handle 1120 are provided to the lower surface of the X-Y base 1103 to face downward. Namely, the X-movement coaxial handle 1110 and Y-movement coaxial handle 1120 extend toward below. The X-Y base 1103 has a flat upper surface and can be attached to, e.g., the lower surface of a table. When the X-Y base 1103 is attached to the lower surface of a table, the operator can manipulate an X-Y stage 1171 and a Z stage 1172 with his hands on the table. This reduces the fatigue the operator suffers from long-time manipulation. So far the embodiments of the present invention have been described with reference to the views of the accompanying drawing. Note that the present invention is not limited to these embodiments, but various changes and modifications may be made without departing from the spirit and scope of the present invention. |
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claims | 1. A cooling system for an extreme ultraviolet (EUV) grazing incidence collector (GIC) having at least one shell with a back surface and a central axis, comprising:a plurality of spaced apart substantially circular cooling lines arranged in substantially parallel planes that are substantially perpendicular to the shell central axis, the cooling lines thermally contacting and running around a corresponding circumference of the back surface; andinput and output cooling-fluid manifolds respectively fluidly connected to the plurality of cooling lines at spaced apart input and output locations to flow a cooling fluid from the input cooling-fluid manifold to the output cooling-fluid manifold over two paths for each cooling line. 2. The cooling system of claim 1, wherein the spaced apart input and output locations are arranged substantially 180° apart so that the two paths for each cooling line are substantially semicircular. 3. The system of claim 1, including a conformal metal layer that covers the shell back surface and at least a portion of the plurality of cooling lines. 4. The system of claim 3, wherein the at least one shell is electroformed, and wherein the conformal metal layer comprises an electroformed layer. 5. The system of claim 1, wherein the at least one shell comprises an electroformed metal or metal alloy, and the plurality of cooling lines comprise said metal or metal alloy. 6. The system of claim 1, wherein the plurality of cooling lines have more than one cooling line diameter. 7. The system of claim 1, wherein at least one pair of adjacent cooling lines have an outside diameter DO and are spaced apart from one another by at least one of:a) a center-to-center distance of at least about 3×DO; andb) a edge-to-edge distance of at least about 2×DO. 8. The system of claim 1, wherein at least one pair of adjacent cooling lines have an outside diameter DO and are spaced apart from one another by at least one of:a) a center-to-center distance of at least about 2×DO; andb) a edge-to-edge distance of at least about 1×DO. 9. The system of claim 1, wherein at least some of the cooling lines have a non-circular cross-section. 10. The system of claim 1, further comprising a flow-control device adapted to control the flow of cooling fluid through a corresponding cooling line. 11. The system of claim 1, wherein the shell has an edge, and wherein a cooling line is arranged immediately adjacent the edge but without shadowing EUV radiation when the shell is operably arranged relative to an EUV radiation source. 12. The system of claim 1, wherein the edge cooling line has a non-circular cross-section. 13. The cooling system of claim 1, further comprising alloy-brazed connections that fluidly connect the plurality of cooling lines and the input and output cooling-fluid manifolds. 14. The system of claim 1, further comprising:a plurality of spaced-apart nested shells each having respective pluralities of cooling lines connected to the input and output cooling-fluid manifolds; anda stand-off device configured to maintain the spaced-apart configuration of the nested shells. 15. The system of claim 1, further comprising:input and output main cooling-fluid manifolds; andinput and output feeder lines that respectively connect the input and output cooling-fluid manifolds to the input and output main cooling-fluid manifolds. 16. The system of claim 1, wherein the input and output cooling-fluid manifolds are configured to control a rate of cooling fluid flow to control a temperature difference between the input and output locations of the plurality of cooling lines. 17. The system of claim 1, wherein the GIC shell includes first and second segments that respectively receive first and second thermal loads from an EUV light source, and wherein the cooling lines on the first and second segment are configured to provide respective first and second amounts of thermal cooling corresponding to the first and second thermal loads. 18. The system of claim 17, wherein the cooling lines on the first and second segments are configured to provide varying amounts of thermal cooling corresponding to a variation in thermal load over the respective segments. 19. An extreme ultraviolet (EUV) lithography system for illuminating a reflective mask, comprising:a source of EUV radiation;a GIC collector having the cooling system of claim 1 and configured to receive the EUV radiation and form collected EUV radiation; andan illuminator configured to receive the collected EUV radiation and form condensed EUV radiation for illuminating the reflective reticle. 20. The EUV lithography system of claim 19 for forming a patterned image on a photosensitive semiconductor wafer, further comprising:a projection optical system arranged downstream of the reflective reticle and configured to receive reflected EUV radiation from the reflective reticle and form therefrom the patterned image on the photosensitive semiconductor wafer. 21. A method of cooling a grazing-incidence collector (GIC) shell having a back surface and a central axis, comprising:providing a cooling fluid to a plurality of cooling fluid input locations adjacent the shell back surface; andguiding the cooling fluid over a portion of the shell back surface via plurality of separate pairs of substantially semicircular paths in substantially parallel planes that are substantially perpendicular to the central axis and in thermal contact with the shell back surface to a corresponding plurality of cooling fluid output locations adjacent the shell back surface and located substantially 180° from the cooling fluid input locations. 22. The method of claim 21, further comprising:defining the plurality of separate pairs of semicircular cooling fluid flow paths with a corresponding plurality of cooling lines in thermal contact with the shell back surface; andelectroforming the plurality of cooling lines onto the shell back surface. 23. The method of claim 22, wherein at least some of the cooling lines have different diameters. 24. The method of claim 22, including providing at least some of the cooling lines with non-circular cross-sections. 25. The method of claim 22, further comprising controlling the flow of cooling fluid in at least one of the cooling lines using at least one flow-control device. 26. The method of claim 21, further comprising:providing the cooling fluid to the input locations via an input cooling-fluid manifold; andcollecting the cooling fluid at the output points at an output cooling-fluid manifold. 27. The method of claim 26, further comprising fluidly connecting the cooling lines to the input and output cooling manifolds using a hydrogen retort and brazing process. 28. The method of claim 21, wherein the GIC shell has an edge and further comprising providing at least one pair of semicircular cooling fluid flow paths immediately adjacent the shell edge. 29. A method of forming a cooled, grazing incident collector (GIC) shell having a backside and a central axis, comprising:providing the shell on a mandrel;providing a cooling assembly having a plurality of substantially circularly configured cooling lines arranged in substantially parallel planes that are substantially perpendicular to the shell central axis, with each cooling line having a pair of substantially semicircular sections defined by cooling fluid input and output locations;disposing the cooling assembly such that the cooling lines contact the shell back surface;electroforming the cooling lines to the shell back surface; andremoving the shell and the attached cooling assembly from the mandrel. 30. The method of claim 29, wherein providing the shell comprises forming the shell by electroforming the shell onto the mandrel, with the mandrel having a separation layer provided thereon to facilitate said removing act. 31. The method of claim 29, wherein providing the cooling assembly includes subjecting the cooling assembly to a firing process that burns off contaminants. 32. The method of claim 29, wherein providing the cooling assembly includes forming alloy joints at the input and output locations using a hydrogen retort and a brazing process. 33. The method of claim 29, further including rotating the cooling assembly and the GIC shell during electroforming. 34. The method of claim 29, further including fluidly connecting the cooling lines to input and output cooling-fluid manifolds using a hydrogen retort and brazing process. 35. A method of collecting extreme ultraviolet (EUV) radiation from an EUV radiation source, comprising:arranging relative to the EUV radiation source a grazing-incidence collector (GIC) mirror system having at least one GIC shell;cooling the at least one GIC shell with the cooling method of claim 29; andusing the GIC mirror system to reflect the EUV radiation from the EUV radiation source to an intermediate focus. |
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claims | 1. Focused ion beam system at least adapted for one of CD-measurements or DR-measurements of a specimen, comprising:a gas field ion source, the gas field ion source having an emitter tip;the emitter tip having a base tip comprising a first material and a supertip comprising a material different from the first material,wherein the supertip is a single atom tip for emitting an ion beam;wherein the base tip is a single crystal base tip;a detector for detection of at least one of the group consisting of backscattered and secondary particles released from the specimen;an analyzer for performing at least one of the group consisting of analyzing, evaluating, and classifying structures on the specimen and being connected to the detector; anda probe current control device comprising a current measurement device and having a control loop adapted to trigger a probe current control action. 2. The focused ion beam device according to claim 1, wherein the supertip is a coating of the base tip. 3. The focused ion beam device according claim 1, wherein the supertip is a metal supertip. 4. The focused ion beam device according to claim 1, wherein the base tip consists of a material selected from the group of: tungsten, tantalum, rhenium, molybdenum, and niobium. 5. The focused ion beam device according to claim 1, wherein the supertip consist of a material selected from the group of platinum, rhodium, and palladium. 6. The focused ion beam device according to claim 1, further comprising a deflector directing the ion beam to the measurement device. 7. The focused ion beam device according to claim 1, wherein the probe current measurement device comprises a Faraday cup. 8. The focused ion beam device according to claim 1, wherein the probe current measurement device comprises a beam limiting aperture. 9. The focused ion beam device according to claim 1, further comprising a sample charge control. 10. The focused ion beam device according to claim 9, wherein the sample charge control comprises a surface charge measurement device. 11. The focused ion beam device according to claim 9, wherein the sample charge control comprises a spectrometer. 12. The focused ion beam device according to claim 9, wherein the sample charge control comprises a retarding field configuration. 13. Method of operating a gas field ion source assembly having an emitter tip with a base tip comprising a first material and a supertip comprising a material different from the first material, wherein the base tip is a single crystal base tip; an electrode for providing an extraction voltage; a single emission center by the supertip; a probe current control device comprising a current measurement device and having a control loop, the method comprising:emitting an ion beam comprising:applying a voltage between the single emission center of the supertip and the electrode, andsupplying a gas to the emitter tip;detecting a signal released from a specimen;performing at least one of the group consisting of analyzing, evaluating and classifying the structure of the specimen with the detected signal, and triggering a probe current control action by the control loop. 14. The method according to claim 13, wherein the single emission center is provided by a single atom supertip. 15. The method according to claim 13, wherein the gas is helium, hydrogen, neon, argon or methane. 16. The method according to claim 13, wherein a probe current is controlled. 17. The method according to claim 16, further comprising controlling the probe current changes when the changes have reached a predetermined limit. 18. The method according to claim 16, wherein the controlling of the probe current comprises measuring the probe current. 19. The method according to claim 17, further comprising using the measurement of the probe current as a signal for changing the beam current. 20. The method according to claim 13, wherein a sample charge is controlled. 21. The method according to claim 20, wherein the sample charge is measured and controlled during operation of the ion beam device. 22. The method according to claim 21, further comprising triggering compensation measures based on the measurement of the sample charge. 23. The method according to any of claim 21, further comprising supplying a control voltage to the sample after measuring the sample charge. |
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claims | 1. A radiation monitor comprising:a shutter installed between a check radiation source and a radiation detector;a calculation section which calculates a radiation dose from a detection signal outputted by said radiation detector;an AC solenoid to be operated by an AC power source;a temperature switch which is attached to said AC solenoid and whose contact is reversed from an opened state to a closed state when temperature thereof is equal to or more than a set value;a circuit protector which has a contact and is connected in series to said AC solenoid; anda mode selection switch connected in series to said AC solenoid,wherein said shutter is maintained in a closed state when said mode selection switch is set to a normal mode;said mode selection switch is changed from the normal mode to a check radiation source mode, thereby flowing an AC current through said AC solenoid to change said shutter from the closed state to an opened state; andthe contact of said temperature switch is reversed from the opened state to the closed state, thereby disconnecting the contact of said circuit protector to interrupt the AC current that flows through said AC solenoid. 2. The radiation monitor according to claim 1,further comprising a relay which has a first contact and a second contact and is disposed in series to said temperature switch,the first contact being connected in parallel to said temperature switch, andthe second contact being connected in series to said AC solenoid. 3. The radiation monitor according to claim 1,wherein said calculation section calculates a net value deviation of said check radiation source when setting of said mode selection switch is changed from the normal mode to the check radiation source mode. 4. The radiation monitor according to claim 3,wherein said calculation section determines that said check radiation source is normal if the calculated net value deviation is kept within an acceptable range, and determines that said check radiation source is abnormal if the calculated net value deviation is out of the acceptable range. 5. A radiation monitor comprising:a check radiation source which moves between a facing position and a shield position;a radiation detector which outputs a detection signal when radiation is made incident;a calculation section which calculates a radiation dose from the detection signal outputted by said radiation detector;an AC solenoid to be operated by an AC power source;a temperature switch which is attached to said AC solenoid and whose contact is reversed from an opened state to a closed state when temperature thereof is equal to or more than a set value;a circuit protector which has a contact and is connected in series to said AC solenoid; anda mode selection switch connected in series to said AC solenoid,wherein said check radiation source is maintained at the shield position when said mode selection switch is set to a normal mode;said mode selection switch is changed from the normal mode to a check radiation source mode, thereby flowing an AC current through said AC solenoid to move said check radiation source from the shield position to the facing position; andthe contact of said temperature switch is reversed from the opened state to the closed state, thereby disconnecting the contact of said circuit protector to interrupt the AC current that flows through said AC solenoid. 6. The radiation monitor according to claim 5,further comprising a relay which has a first contact and a second contact and is disposed in series to said temperature switch,the first contact being connected in parallel to said temperature switch, andthe second contact being connected in series to said AC solenoid. 7. The radiation monitor according to claim 5,wherein said calculation section calculates a net value deviation of said check radiation source when setting of said mode selection switch is changed from the normal mode to the check radiation source mode. 8. The radiation monitor according to claim 7,wherein said calculation section determines that said check radiation source is normal if the calculated net value deviation is kept within an acceptable range, and determines that said check radiation source is abnormal if the calculated net value deviation is out of the acceptable range. 9. A radiation monitor comprising:a shutter installed between a check radiation source and a radiation detector;a calculation section which calculates a radiation dose from a detection signal outputted by said radiation detector;an AC solenoid to be operated by an AC power source;a temperature switch which is attached to said AC solenoid and whose contact is reversed from an opened state to a closed state when temperature thereof is equal to or more than a set value;a fuse connected in series to said AC solenoid; anda mode selection switch connected in series to said AC solenoid,wherein said shutter is maintained in a closed state when said mode selection switch is set to a normal mode;said mode selection switch is changed from the normal mode to a check radiation source mode, thereby flowing an AC current through said AC solenoid to change said shutter from the closed state to an opened state; andthe contact of said temperature switch is reversed from the opened state to the closed state, thereby fusing said fuse to interrupt the AC current that flows through said AC solenoid. 10. The radiation monitor according to claim 9,further comprising a relay which has a first contact and a second contact and is disposed in series to said temperature switch,the first contact being connected in parallel to said temperature switch, andthe second contact being connected in series to said AC solenoid. 11. The radiation monitor according to claim 9,wherein said calculation section calculates a net value deviation of said check radiation source when setting of said mode selection switch is changed from the normal mode to the check radiation source mode. 12. The radiation monitor according to claim 11,wherein said calculation section determines that said check radiation source is normal if the calculated net value deviation is kept within an acceptable range, and determines that said check radiation source is abnormal if the calculated net value deviation is out of the acceptable range. |
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summary | ||
claims | 1. A method of moving a canister of spent nuclear fuel from a first location to a storage cask, comprising steps of: (a) positioning a canister of spent nuclear fuel within a transfer cask; (b) engaging the transfer cask with a first lifting mechanism; (c) engaging the canister with a second lifting mechanisms that is mounted on the said first lifting mechanism, said step of engaging the canister with a second lifting mechanism being performed in no particular order with respect to steps (b) and (d); (d) moving the transfer cask having the canister positioned therein to the vicinity of a storage cask; (e) lowering the canister with respect to the transfer cask with said second lifting mechanism into the storage cask, and wherein said step of lowering the canister with said second lifting mechanism is performed while said first lifting mechanism remains continuously engaged with said transfer cask and (f) disengaging the transfer cask from the first lifting mechanism. 2. A method according to claim 1 , wherein said second lifting mechanism is mounted on said first lifting mechanism, whereby lowering of said second lifting mechanism will be substantially limited to vertical relative movement with respect to said first lifting mechanism. claim 1 3. A method according to claim 2 , wherein said first lifting mechanism comprises a crane having a lower block assembly, and wherein said second lifting mechanism comprises a hoist that is attached to said lower block assembly. claim 2 4. A method according to claim 1 , wherein said first lifting mechanism comprises a crane having a lower block assembly, and wherein said second lifting mechanism comprises a hoist that is attached to said lower block assembly. claim 1 5. A method according to claim 4 , wherein said first lifting mechanism comprises at least two lifting hooks that are suspended from said lower block assembly, said lifting hooks being constructed and arranged to engage corresponding lifting lugs that are located on an outer portion of said transfer cask. claim 4 6. A method according to claim 4 , wherein said canister has a lid portion, and wherein said second lifting mechanism further comprises a grab mechanism that is constructed and arranged to engage said lid portion of said canister. claim 4 7. A method according to claim 1 , wherein said canister has a lid portion, and wherein said second lifting mechanism comprises a grab mechanism that is constructed and arranged to engage said lid portion. claim 1 8. A method according to claim 7 , wherein said grab mechanism is configured so as to be constrained to remain engaged with said lid portion when any substantial amount of weight of said canister is borne by said second lifting mechanism. claim 7 9. A method according to claim 1 , wherein said step (e) of lowering the canister with respect to the transfer cask with said second lifting mechanism into the storage cask is performed without first securing the transfer cask against relative movement with respect to the storage cask by means of a tie-down. claim 1 10. A method according to claim 1 , wherein said step (e) of lowering the canister with respect to the transfer cask with said second lifting mechanism into the storage cask is performed without deployment of human resources in direct proximity to the transfer cask for purposes of immobilizing the transfer cask. claim 1 11. A method of moving a canister of spent nuclear fuel from a first location to a storage cask, comprising steps of: (a) positioning a canister of spent nuclear fuel within a transfer cask; (b) engaging the transfer cask with a first lifting mechanism, said first lifting mechanism comprising a crane having a lower block assembly, said first lifting mechanism further comprising at least two lifting hooks that are suspended from said lower block assembly, said lifting hooks being constructed and arranged to engage corresponding lifting lugs that are located on an outer portion of said transfer cask; (c) engaging the canister with a second lifting mechanism, said second lifting mechanism comprising a hoist that is attached to said lower block assembly, said step of engaging the canister with a second lifting mechanism being performed in no particular order with respect to steps (b) and (d); (d) moving the transfer cask having the canister positioned therein to the vicinity of a storage cask; and (e) lowering the canister with respect to the transfer cask with said second lifting mechanism into the storage cask, and wherein said step of lowering the canister with said second lifting mechanism is performed while said first lifting mechanism remains continuously engaged with said transfer casks. 12. A method of moving a canister of spent nuclear fuel from a first location to a storage cask, comprising steps of: (a) positioning a canister of spent nuclear fuel within a transfer cask; (b) engaging the transfer cask with a first lifting mechanism, said first lifting mechanism comprising a crane having a lower block assembly; (c) engaging the canister with a second lifting mechanism, said second lifting mechanism comprising a hoist that is attached to said lower block assembly, said step of engaging the canister with a second lifting mechanism being performed in no particular order with respect to steps (b) and (d), and wherein said canister has a lid portion, and wherein said second lifting mechanism further comprises a grab mechanism that is constructed and arranged to engage said lid portion of said canister; (d) moving the transfer cask having the canister positioned therein to the vicinity of a storage cask; and (e) lowering the canister with respect to the transfer cask with said second lifting mechanism into the storage cask, and wherein said step of lowering the canister with said second lifting mechanism is performed while said first lifting mechanism remains continuously engaged with said transfer cask. 13. A method of moving a canister of spent nuclear fuel from a first location to a storage cask, comprising steps of: (a) positioning a canister of spent nuclear fuel within a transfer cask, said canister having a lid portion; (b) engaging the transfer cask with a first lifting mechanism; (c) engaging the canister with a second lifting mechanism that comprises a grab mechanism that is constructed and arranged to engage said lid portion, said step of engaging the canister with a second lifting mechanism being performed in no particular order with respect to steps (b) and (d); (d) moving the transfer cask having the canister positioned therein to the vicinity of a storage cask; and (e) lowering the canister with respect to the transfer cask with said second lifting mechanism into the storage cask, and wherein said step of lowering the canister with said second lifting mechanism is performed while said first lifting mechanism remains continuously engaged with said transfer cask. 14. A method according to claim 13 , wherein said grab mechanism is configured so as to be constrained to remain engaged with said lid portion when any substantial amount of weight of said canister is borne by said second lifting mechanism. claim 13 15. A method of moving a canister of spent nuclear fuel from a first location to a storage cask, comprising steps of: (a) positioning a canister of spent nuclear fuel within a transfer cask; (b) engaging the transfer cask with a first lifting mechanism, wherein said first lifting mechanism comprises at least two lifting hooks, said lifting hooks being constructed and arranged to engage corresponding lifting lugs that are located on an outer portion of said transfer cask; (c) engaging the canister with a second lifting mechanism, said step of engaging the canister with a second lifting mechanism being performed in no particular order with respect to steps (b) and (d); (d) moving the transfer cask having the canister positioned therein to the vicinity of a storage cask; and (e) lowering the canister with respect to the transfer cask with said second lifting mechanism into the storage cask, and wherein said step of lowering the canister with said second lifting mechanism is performed while said first lifting mechanism remains continuously engaged with said transfer cask. 16. A method of moving a canister of spent nuclear fuel from a first location to a storage cask, comprising steps of: (a) positioning a canister of spent nuclear fuel within a transfer cask; (b) engaging the transfer cask with a first lifting mechanism; (c) engaging the canister with a second lifting mechanism that is not permanently attached to the transfer cask, said step of engaging the canister with a second lifting mechanism being performed in no particular order with respect to steps (b) and (d); (d) moving the transfer cask having the canister positioned therein to the vicinity of a storage cask; (e) lowering the canister with respect to the transfer cask with said second lifting mechanism into the storage cask, and wherein said step of lowering the canister with said second lifting mechanism is performed while said first lifting mechanism remains continuously engaged with said transfer casks. |
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042773610 | summary | RELATED INVENTIONS Reference is made to the patent application of Milton J. Szulinski, Ser. No. 793,658, filed May 4, 1977 concerned with a "Fuel Rod Reprocessing Plant" and Ser. No. 793,660, filed May 4, 1977 concerned with a "Water Seal for Compartment for Reprocessing Fuel Rods" each of said applications being deemed here reiterated and incorporated herein. FIELD OF INVENTION This invention relates to the reprocessing of nuclear fuel rods, and to the plurality of ventilating systems by which air is cleaned prior to being discharged to the atmosphere. PRIOR ART It has long been known that the reprocessing of fuel rods could liberate radioactive gases such as radioactive krypton, tritium and iodine. Mists comprising droplets of solutions containing radioactive components can also be formed in a reprocessing plant. Air cleaning systems intended to remove at least a portion of the radioactive components prior to the discharge of ventilating gas to the atmosphere have long been used. In some nuclear facilities, difficult problems have been encountered in meeting the public health standards relating to the purity of the ventilating gas discharged into the atmosphere. The cost of retrofit modifications of ventilating systems has sometimes been a significant factor leading to the abandonment of nuclear facilities which at the time of the initial design, were thought to be providing adequate health protection. Some radioactive components are so highly dangerous to health that remote control operation has been a preferred mode of operation. The difficulties of coping with emergencies and the restriction upon flexibility of operation inherent in remote control mode, has stimulated engineers to minimize the number of chambers in which remote control processes were conducted. Heretofore there has been a general propensity to minimize the number of TV cameras and/or other systems of control in monitoring remote control operations so that a series of reaction vessels and/or steps of a process might be contained within a single canyon. Shutdowns have thus sometimes been necessary because of malfunctioning of a single vessel in a canyon containing a plurality of vessels operated by remote control. In a conventional chemical plant, it is customary to position a vessel above the floor which provides access to the variety of equipment. In the event of leakage of one vessel, the spill may extend over a significant area affecting a considerable variety of pieces of equipment. In a conventional plant the clean-up from the spill of liquid is a nuisance but significant adaptability has been demonstrated in coping with such emergencies. At a nuclear facility, the contamination of equipment because of the spillage of liquid from a vessel can be significantly more complicated than in the ordinary chemical plant. Prolonged experience with nuclear facilities has shown that the malfunctioning occurs more frequently in the vessels and the processing equipment (e.g. valves) closely related to the vessels rather than in the piping between such operating units. SUMMARY OF THE INVENTION In accordance with the present invention, a nuclear facility such as a plant for reprocessing nuclear fuel rods, is provided with a ventilating system in which the central air cleaner for the zones for remotely controlled units is designed for relatively small flow rates. A manifold duct system supplies ventilating air to such central air cleaning unit from each of a plurality of remotely controlled compartments. Particular attention is directed to the fact that the air in each remotely controlled compartment is locally processed with a high ratio of gas recirculation. The fresh gas injection rate and the stale gas withdrawal rate are low so that the turnover rate of the air in such compartment is longer than a day but less than a year. Such slow turnover rate is designated as quasi-hermetic sealing of compartments. Each compartment is maintained in such quasi-hermetically sealed condition with a significant amount of recirculation and recycling of the inventory of air within such compartment. The air pressure within each compartment is controlled to be slightly lower than the air pressure in the area adjacent (usually above) such compartment. Automatic controls provide for the flow of fresh air or air from such adjacent area into the compartment when necessary to maintain such acceptable range of air pressure within the compartment. Similarly automatic controls provide for the withdrawal of ventilating gas from the compartment into the manifold duct system leading to the central air cleaner for the purpose of preserving such gas pressure in the compartment at the desired range below the air pressure adjacent the compartment. Whatever random variations in the atmospheric pressure in the access zones adjacent the remote control compartment may occur, may lead to withdrawal of the air at a rate corresponding to a replacement rate which for the moment may exceed the average replacement interval of more than one day. However, such random pressure variations are not frequent enough to bring about the turnover of the air inventory more than 365 times per year because the air pressure in such adjacent areas are regulated to maintain a substantially constant air pressure differential. In modifications of the invention, the intake volume and exhaust volume for a compartment are controlled so that the marginal pressure difference between the air adjacent the remote control compartment and the air pressure within the remote control compartment can be broadened or narrowed to preserve an acceptable replacement rate. Supplemental gas injection and supplemental ventilating discharge control desirably are included with such volume monitoring system. In the localized air processing unit, the air from the remote control compartment can be processed in any of the ways deemed appropriate for the processing and purification of air in a radioactive processing zone. For example, heat exchangers can be employed to cool the air inventory in the unit. Filters can be provided for the removal of mists and/or particulate material and for the control of the humidity of the air prior to its recirculation to the principal zone of the compartment. Of particular importance, the gas processing is custom-matched to respond to the problems attributable to the specialized processing conducted in that particular compartment. Thus iodine removal can be very complete close to the source of radioactive iodine evolution. This avoids dealing with iodine contamination of long ducts and decreases the problems of removing extremely diluted iodine from a large gas volume. It is sometimes desirable to employ two duplicate facilities for the recirculation, pumping, cooling and filtering of the air for a compartment so that the compartment can continue to be operated during the time when attention is being given to the change of filters, caring for the maintenance or correcting any kind of malfunction in one of the two swing purifiers for the air recirculated within a remote control compartment. The pumps employed for circulating the air within the remote control compartment and through the purifier and back into the remote control compartment provide a turnover rate for such air which is within a range from a few minutes to a few hours, but is significantly less than a day, whereby the assured circulation of air throughout all portions of the remote control compartment is achieved. The pressure within the remote control compartment is regulated to be within an appropriate narrow range slightly below the reference pressure, that is the pressure in the access zone immediately adjacent the remote control compartment. In some embodiments a stabilized regulated pressure isolated from the fluctuating pressure of the weather-influenced atmosphere is maintained in such access area. Ordinarily it is cheaper to maintain pressure differentials amongst the selected zones and to permit a series of zones to have pressures fluctuating according to a pattern resembling the weather induced fluctuations of atmospheric pressure. Such gas zone or air zone immediately adjacent the remote control compartment is the inside of a factory inasmuch as all portions of a reprocessing plant, including even the piping between processing units, are desirably protected from the atmosphere by appropriate walls and roofs for the fuel rod reprocessing facility. It is conventional to control the pressure of the air in every portion of such reprocessing facilities to be slightly less than the pressure of the exterior atmosphere so that if any air leakage occurs, such leakage will be from the atmosphere into the reprocessing facility rather than routinely permitting any air within the reprocessing facility to flow to the atmosphere except through the air cleaning systems. Thus the general effort is that of controlling the overall combination of ventilating systems so that air discharged to the atmosphere from the reprocessing facilities will be subjected to appropriate cleaners prior to such discharge. An important feature of the use of the localized purifiers is that each local purifier can be adapted to cope with the particular problems of the processing unit which it serves. In some portions of a reprocessing plant, radioactive krypton may be involved. By isolating substantially all of the radioactive krypton in filters at the localized purifier, the degree of removal of krypton can be greater. The problems of dispersion of the radioactivity through the ventilating system can thus be decreased. The cost of operating the central air cleaner system for the remote control compartments of the reprocessing plant thus can be significantly reduced. A crystalline zeolite having silver in the ion exchange position can be employed in filters adapted to capture radioactive iodine vapor in the air circulated through a local purifier. By filtering out a major portion of the radioactive iodine and/or other iodine vapor in the air of a remotely controlled compartment, the concentration and amount of iodine directed to the central air cleaner can be significantly decreased. In most portions of the reprocessing plant in which trace amounts of gas containing tritium might be found, a water synthesis catalyst can be provided for converting all hydrogen, deuterioum, and tritium to water and the water can be directed to a purification system for the recovery of tritium and/or deuterium. Other types of filters adapted to capture radioactive hydrogen, i.e. tritium, can be utilized in the local purification zone. In most portions of the reprocessing plant in which mists of aqueous solutions of radioactive components might exist, the purification zone can utilize appropriate demisting filters adapted for the separation of such mists from the recirculating air. In preferred embodiments of the present invention, each remotely controlled compartment is located in a caisson maintained beneath a standard level at the reprocessing plant. Overhead cranes, rubber tired cranes and/or other appropriate vehicles are adapted to move within a vehicle access zone so that a cover can be removed from a caisson during times of construction, during times of monitoring of operations, or during times of maintenance or replacement of units. All pipe connections, valve manipulations, etc. in the reprocessing unit are remotely controlled, such as by crane operators. Not only the reaction vessels and processing units, but also substantially all valves and/or other components which might malfunction or leak are positioned within the caisson type compartment. A sump pit at the bottom of a compartment is provided with sensors sending emergency warnings in the event of leakage or malfunctioning. Certain compartments can also be provided with annular storage tanks beneath the sump pit. Drainage systems directing liquid from the sump pit toward appropriate storage in a remote area can be provided when desirable. The caisson cover for each compartment is separate from the cover for each of the purification units and/or pair of swing purification units. Thus there can be selective access to whatever processing unit may require attention while retaining the covers on the other compartments. Near the top of the compartments and just below the vehicle access zone a system of a series of pipes and related communication lines are connecting the various compartments. The vehicle access zone includes free space so that the cranes can manipulate the tools, vessels and/or other equipment which might need to be moved after start-up of the reprocessing facility. The general operation of the reprocessing plant is not interrupted by reason of making repairs to one of two swing units of an air purifier for a compartment. The ventilating system for the access zone of the reprocessing plant, including the area about which the vehicles (e.g. overhead cranes) move to the covers giving access to the various air purification units and various processing compartments, can be maintained at a controlled and stabilized pressure differential. Inasmuch as some contaminants and mists may enter such zone at the time of opening a compartment and contamination can occur during periods of malfunctioning, any flow of air from the access zone to the atmosphere would be through the central air cleaner. |
description | This application claims the benefit of U.S. Provisional Patent Application No. 61/373,138, filed Aug. 12, 2010, the entirety of which is incorporated herein by reference. The present invention relates generally to systems for storing high level radioactive waste, and specifically to ventilated systems for storing high level radioactive waste that utilize natural convective cooling. The storage, handling, and transfer of high level waste, (hereinafter, “HLW”) such as spent nuclear fuel (hereinafter, “SNF”), requires special care and procedural safeguards. For example, 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 canister. The loaded canister is then 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 tilled with inert gas. The transfer cask (which is holding the loaded canister) is then transported to a location where a storage cask is located. The loaded 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 (or other HLW). VVOs 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. VVOs 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 a means to escape from the VVO cavity. This heat energy is removed from the outside surface of the canister by ventilating the VVO cavity. In 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 VVOs are located near the bottom and top of the VVO's cylindrical body respectively. 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. Thus, a need exists for a VVO system for the storage of high level radioactive waste that has an inlet duct that reduces the likelihood of radiation exposure while providing extreme radiation blockage of both gamma and neutron radiation emanating from the high level radioactive waste. These, and other drawbacks, are remedied by the present invention. In one embodiment, the invention can be a system for storing high level radioactive waste comprising: an overpack body extending along a vertical axis and having a cavity for storing high level radioactive waste, the cavity having an open top end and a floor; an overpack lid positioned atop the overpack body to enclose the open top end of the cavity; an air inlet vent for introducing cool air into the cavity, the air inlet vent comprising an annular air inlet plenum and an annular air inlet passageway, the annular air inlet plenum extending radially inward from an outer surface of the overpack body to the annular air inlet passageway, the annular air inlet passageway extending upward from the annular air inlet plenum to an opening in the floor; and an air outlet vent in the overpack lid for removing warmed air from the cavity. In another embodiment, the invention can be a system for storing high level radioactive waste comprising: an overpack body extending along a vertical axis and having a cavity for storing high level radioactive waste, the cavity having an open top end and a floor, the overpack body comprising an air inlet vent for introducing cool air into a bottom portion of the cavity; an overpack lid positioned atop the overpack body to enclose the open top end of the cavity, the overpack lid comprising an air outlet vent for removing warmed air from the cavity; and the air inlet vent configured so that aerodynamic performance of the air inlet vent is substantially independent of an angular direction of a horizontal component of an air-stream applied to the outer surface of the overpack body. In still another embodiment, the invention can be a system for storing high level radioactive waste comprising: an overpack body extending along a vertical axis and having a cavity for storing high level radioactive waste, the cavity having an open top end and a floor, the overpack body comprising an air inlet vent for introducing cool air into a bottom portion of the cavity; an overpack lid positioned atop the overpack body to enclose the open top end of the cavity, the overpack lid comprising an air outlet vent for removing warmed air from a top portion of the cavity; and the air inlet vent comprising a first section extending from an outer surface of the overpack body to a first radial distance from the vertical axis and a second section extending from the first radial distance to an opening in the floor at a second radial distance from the vertical axis, the second radial distance being greater than the first radial distance. In an even further embodiment, the invention can be a system for storing high level radioactive waste comprising: an overpack body extending along a vertical axis and having a cavity for storing high level radioactive waste, the cavity having an open top end and a floor, the overpack body comprising an air inlet vent for introducing cool air into a bottom portion of the cavity, the air inlet vent being substantially axisymmetric; and an overpack lid positioned atop the overpack body to enclose the open top end of the cavity, the overpack lid comprising an air outlet vent for removing warmed air from the cavity, the air outlet vent being substantially axisymmetric. Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. Referring to FIGS. 1-4 concurrently, a system for storing high level radioactive waste will be described in accordance with an embodiment of the present invention. The system can be considered a VVO 100. The VVO 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 operations. Of course, the VVO 100 can be modified/designed to be compatible with any size or style transfer cask. The VVO 100 is designed to accept spent fuel canisters for storage. All spent fuel canister types engineered for storage in free-standing and anchored overpack models can be stored in VVO 100. As used herein the term “canister” broadly includes any spent fuel containment apparatus, including, without limitation, multi-purpose canisters and thermally conductive casks. For example, in some areas of the world, spent fuel is transferred and stored in metal casks having a honeycomb grid-work/basket built directly into the metal cask. Such casks and similar containment apparatus qualify as canisters, as that term is used herein, and can be used in conjunction with VVO 100 as discussed below. In certain embodiments, the VVO 100 is a substantially cylindrical containment unit having a vertical axis A-A and a horizontal cross-sectional profile that is substantially circular in shape. Of course, it should be understood that the invention is not limited to cylinders having circular horizontal cross sectional profiles but may also include containers having cross-sectional profiles that are, for example, rectangular, ovoid or other polygon forms. While the VVO 100 is particularly useful for use in conjunction with storing and/or transporting SNF assemblies, the invention is in no way limited by the type of waste to be stored. The VVO cask 100 can be used to transport and/or store almost any type of HLW. However, the VVO 100 is particularly suited for the transport, storage and/or cooling of radioactive materials that have a high residual heat load and that produce neutron and gamma radiation, such as SNF. This is because the VVO 100 is designed to both provide extreme radiation blockage of gamma and neutron radiation and facilitate a convective/no force cooling of any canister contained therein. The VVO 100 of the present invention generally comprises an overpack body 110 for storing high level radioactive waste and a removable overpack lid 120 that is positioned atop the overpack body 110. The overpack body 110 extends along the vertical axis A-A. The overpack lid 120 generally comprises a primary lid 121 and a secondary lid 122. The primary lid 121 is secured to the overpack body 110 by bolts 123 that restrain separation of the primary lid 121 of the overpack lid 120 from the overpack body 110 in case of a tip over situation. Moreover, the secondary lid 122 is secured to the primary lid 121 by bolts 124. The overpack lid 120 is a steel/concrete structure that is equipped with an axisymmetric air outlet vent or passageway 145 for the ventilation/removal of air as will be discussed in more detail below. An annular opening 157 is formed in an outer sidewall surface 178 of the overpack lid 120 that forms a passageway from the air outlet vent 145 to the external environment. More specifically, the annular opening 157 is a 360° opening in the outer sidewall surface 178 of the overpack lid 120. The overpack lid 120 has a quick connect/disconnect joint to minimize human activity for its installation or removal. In certain embodiments, the overpack lid 120 may weigh in excess of 15 tons. The VVO 100 further comprises shock absorber or crush tubes 102 in its top region. The shock absorber tubes 102 are arranged at suitable angular spacings to serve as a sacrificial crush material if, for any reason, the VVO 100 were to tip over. The shock absorber tubes 102 also facilitate guiding and positioning of a canister within a cavity 111 of the VVO 100 in a substantially concentric disposition with respect to the VVO 100. Referring to FIGS. 1, 4 and 6 concurrently, the overpack body 110 comprises a cylindrical wall 112, a bottom enclosure plate 130 and the overpack lid 120 described above. The cylindrical wall 112 has an inner shell 113, an intermediate shell 114 and an outer shell 115. In the exemplified embodiment, each of the inner, intermediate and outer shells 113, 114, 115 are formed of one-inch thick steel. Of course, the invention is not to be so limited and in other embodiments the inner, intermediate and outer shells 113, 114, 115 can be formed of metals other than steel and can be greater or less than one-inch in thickness. The inner shell 113 has an inner surface 116 that defines an internal cavity 111 for containing a hermetically sealed canister that contains high level radioactive waste (FIG. 5). The inner surface 116 of the inner shell 113 also forms the inner wall surface of the overpack body 110. Furthermore, the outer shell 115 has an outer surface 117. The outer surface 117 of the outer shell 115 also forms the outer sidewall surface of the overpack body 110. In the exemplified embodiment, the inner, intermediate and outer shells 113, 114, 115 are concentric shells that are rendered into a monolithic weldment by a plurality of connector plates 105a, 105b. The inner shell 113 is spaced from the intermediate shell 114 by connector plates 105a and the intermediate shell 114 is spaced from the outer shell 115 by connector plates 105b. Of course, in certain other embodiments the connector plates 105a, 105b can be altogether omitted. The space between the inner shell 113 and the intermediate shell 114 is intended for placement of a neutron shielding material. For example, in certain embodiments the neutron radiation shielding material is a hydrogen-rich material, such as, for example, Holtite, water or any other material that is rich in hydrogen and a Boron-10 isotope. In certain embodiments, there is approximately seven inches of Holtite filling the space between the inner and intermediate shells 113, 114. Thus, the space between the inner and intermediate shells 113, 114 serves to prevent neutron radiation from passing through the VVO 100 and into the external environment. An axially intermediate portion of the space between the intermediate shell 114 and the outer shell 115 is filled with a heavy shielding concrete to capture and prevent the escape of both gamma and neutron radiation. The density of the concrete is preferably maximized to increase the radiation absorption characteristics of the VVO 100. In certain embodiments, there is approximately twenty-eight inches of concrete filling the intermediate portion of the space between the intermediate and outer shells 114, 115. In some embodiments, steel plates are placed within the concrete to serve as a supplemental radiation curtain. There are no lateral penetrations in the multi-shell weldment that may provide a streaming path for the radiation issuing from the high level radioactive waste. The top and bottom portions of the space between the intermediate and outer shells 114, 115 (both above and below the concrete) are top and bottom forgings 128, 129 in the form of thick annular rings made of a metal material, such as steel. The top forging 128 comprises machine threaded holes 126 that are sized and configured to receive the bolts 123 of the primary lid 121 therein during attachment of the overpack lid 120 to the overpack body 110. As noted above, the inner surface 116 of the inner shell 113 defines the cavity 111. In the exemplified embodiment, the cavity 111 is cylindrical in shape. However, the cavity 111 is not particularly limited to any specific size, shape, and/or depth, and the cavity 111 can be designed to receive and store almost any shape of canister. In certain embodiments, the cavity 111 is sized and shaped so that it can accommodate a canister of spent nuclear fuel or other HLW. More specifically, the cavity 111 has a horizontal cross-section that can accommodate no more than one canister. Even more specifically, it is desirable that the size and shape of the cavity 111 be designed so that when a spent fuel canister is positioned in the cavity 111 for storage, a small clearance exists between outer side walls of the canister and the inner surface 116 of the inner shell 113, as will be discussed in more detail below with reference to FIG. 5. Referring to FIGS. 4 and 5 concurrently, the present invention will be further described. The cavity 111 comprises a floor 152 and an open top end 151 that is enclosed by the overpack lid 120 as has been described herein above. A plurality of support blocks 153 are disposed on the floor 152 of the cavity 111 to support a canister 200 contained within the cavity 111 above the floor 152. In the exemplified embodiment, four support blocks 153 are illustrated (see FIG. 6). However, more or less than four support blocks 153 can be used in alternate embodiments. Each of the support blocks 153 is a low profile lug that is welded to the inner surface 116 of the inner shell 113 and/or to the floor 152. In the exemplified embodiment, the canister 200 is a hermetically sealed canister for containing the high level radioactive waste. When the canister 200 is positioned within the cavity 111, it rests atop the support blocks 153 so that a space 154 exists between a bottom 202 of the canister 200 and the floor 152. The space 154 is a bottom plenum that serves as the recipient of ventilation air flowing up from an inlet vent as will be described below. Furthermore, when the canister 200 is positioned within the cavity 111, an annular gap 155 exists between the inner surface 116 of the inner shell 113 (i.e., the inner wall surface of the overpack body 110) and an outer surface 201 of the canister 200. The annular gap 155 is an uninterrupted and continuous gap that circumferentially surrounds the canister 200. In other words, the canister 200 is concentrically spaced apart from the inner shell 113, thereby creating the annular gap 155. As described in more detail below, the annular gap 155 forms an annular air flow passageway between an annular air inlet passageway 142 and the air outlet vent 145. The VVO 100 is configured to achieve a cyclical thermosiphon flow of gas (i.e., air) within the cavity 111 when spent nuclear fuel emanating heat (i.e., the canister 200) is contained therein. In other words, the VVO 100 achieves a ventilated flow by virtue of a chimney effect. Such cyclical thermosiphon flow of the gas further enhances the transmission of heat to the environment external to the VVO 100. The thermosiphon flow of gas is achieved as a result of an air inlet vent 140 that introduces cool air into the bottom of the cavity 111 of the overpack body 110 from the external environment and an air outlet vent 145 for removing warmed air from the cavity 111. Thus, as a result of thermosiphon flow, cool external air can enter into the space 154 of the cavity 111 between the bottom 202 of the canister 200 and the floor 152 via the air inlet vent 140, flow upward through the cavity 111 within the annular gap 155 between the canister 200 and the inner surface 116 of the inner shell 113, and flow back out into the external environment as warmed air via the air outlet vent 145. The newly entered air will warm due to proximity to the extremely hot canister 200, which will cause the natural thermosiphon flow process to take place whereby the heated air will continually flow upwardly as fresh cool air continues to enter into the cavity 111 via the air inlet vent 140. Thus, the air inlet vent 140 provides a passageway that facilitates cool air entering the cavity 111 from the external environment and the air outlet vent 145 provides a passageway that facilitates warm air exiting the cavity back to the external environment. In the exemplified embodiment, the air outlet vent 145 is formed into the overpack lid 120. The air outlet vent 145 provides an annular passageway from a top portion of the cavity 111 to the external environment when the overpack lid 120 is positioned atop the overpack body 110 thereby enclosing the top end 151 of the cavity 111. Specifically, the air outlet vent 145 has a vertical section 174 that extends from the cavity 111 upwardly into the overpack lid 120 in the vertical direction (i.e., the direction of the vertical axis A-A) and a horizontal section 175 that extends from the vertical section 174 to the annular opening 157 in the horizontal direction (i.e., the direction transverse to the vertical axis A-A). More specifically, the vertical section 174 of the air outlet vent 145 extends from an annular opening 176 in a bottom surface 177 of the overpack lid 120 and the horizontal section 175 extends from the vertical section 174 to the annular opening 157 in the outer sidewall surface 178 of the overpack lid 120. As described above, the annular opening 157 is a circumferential opening that extends around the entirety of the overpack lid 120 in a continuous and uninterrupted manner and circumferentially surrounds the vertical axis A-A. The overpack body 110 additionally comprises a bottom block 160 disposed within the cylindrical wall 112, and more specifically within the inner shell 113 of the cylindrical wall 112, and a base structure at a bottom end 179 of the cylindrical wall 112. The base structure comprises a base plate 161 and an annular plate 162. The air inlet vent 140 is formed directly into the bottom block 160, which is a thick sandwich of steel and concrete. The bottom block 160 is positioned below the floor 152 of the cavity 111. More specifically, the bottom block 160 extends between the floor 152 of the cavity 111 and the base plate 161, which forms the bottom end of the VVO 100. The bottom block 160 has a columnar portion 163 and a horizontal portion 164. The annular plate 162 is a donut-shaped plate having a central hole 181. The annular plate 162 is axially spaced from the base plate 161, thereby creating a space or gap in between the annular plate 162 and the base plate 161. Moreover, the annular plate 162 extends from the outer surface 117 of the overpack body 110 inwardly towards the vertical axis A-A a radial distance that is less than the radius of the overpack body 110. More specifically, the annular plate 162 extends from the outer surface 117 of the overpack body 110 to the columnar portion 163 of the bottom block 160. Thought of another way, the columnar portion 163 of the bottom block 160 extends through the central hole 181 of the annular plate 162 and rests atop the base plate 161. Referring to FIGS. 1, 4, 6 and 8 concurrently, the air inlet vent 140 will be described in more detail. In the exemplified embodiment, the air inlet vent 140 is formed into the bottom closure plate 130 and extends into the bottom block 160 and comprises an annular air inlet plenum 141 and an annular air inlet passageway 142. The annular air inlet plenum 141 is formed in the space/gap between the annular plate 162 and the base plate 161. Thus, the annular air inlet plenum 141 is substantially horizontal and extends radially inward from the outer surface 117 of the overpack body 110. More specifically, the annular air inlet plenum 141 extends horizontally from the outer surface 117 of the overpack body 110 at an axial height below the floor 152 of the cavity 111. An opening 143 is formed in the outer surface 117 of the overpack body 110 that forms a passageway from the external environment to the annular air inlet plenum 141 to enable cool air to enter into the annular air inlet plenum 141 from the external environment as has been described above. The opening 143 circumferentially surrounds the vertical axis A-A around the entirety of the outer surface 117 of the overpack body 110 in an uninterrupted and continuous manner. In other words, the opening 143 is a substantially 360° opening in the outer surface 117 of the overpack body 110. The annular air inlet passageway 142 extends upward from a top surface 144 of the annular air inlet plenum 141 to the floor 152 of the cavity 111. More specifically, the annular air inlet passageway 142 extends upwardly from an opening 147 in the top surface 144 of the annular air inlet plenum 141 to an opening 146 in the floor 152. The annular air inlet passageway 142 is wholly formed within the bottom block 160. The opening 147 in the top surface 144 of the annular air inlet plenum 141 is proximate an end of the annular air inlet plenum opposite the opening 143 in the outer surface 117 of the overpack body 110. The opening 146 in the floor 152 is an annular opening that extends 360° around the floor 152. The annular air inlet plenum 141 circumferentially surrounds the vertical axis A-A. In the exemplified embodiment, the annular air inlet passageway 142 also circumferentially surrounds the vertical axis A-A and has an inverted truncated cone shape. Thus, the annular air inlet passageway 142 extends upward from the air inlet plenum 141 to the opening 146 in the floor 152 of the cavity 111 at an oblique angle relative to the vertical axis A-A. Thought of another way, the annular inlet passageway 142 extends from the air inlet plenum 141 at a first end 183 to the floor 152 at a second end 184. The first end 183 is located a first radial distance R1 from the vertical axis A-A and the second end 184 is located a second radial distance R2 from the vertical axis A-A. The second radial distance R2 is greater than the first radial distance R1. Of course, the invention is not to be so limited and in certain other embodiments the annular air inlet passageway 142 can take on other shapes as desired. Referring to FIGS. 1, 4, 7 and 8 concurrently, the annular air inlet plenum 141 will be further described. The annular air inlet plenum 141 comprises a plurality of plates 148 therein. Each of the plates 148 extends from a first end 149 to a second end 159. The first ends 149 of the plates 148 are proximate the outer surface 117 of the overpack body 110 and the second ends 159 of the plates 148 are proximate the columnar portion 163 of the bottom block 160. A line connecting the first ends 149 of the plates 148 forms a first reference circle 171 having a diameter D1 and a line connecting the second ends 159 of the plates 148 forms a second reference circle 172 having a diameter D2, wherein the first diameter D1 is greater than the second diameter D2. Each of the plates 148 in the annular air inlet plenum 141 extend along a reference line 169 that is tangent to a third reference circle 170. Although the reference line 169 is only illustrated with regard to two of the plates 148, it should be understood that each of the plates has a reference line that is tangent to the third reference circle 170. The circumference of the third reference circle 170 is formed by an outer surface 165 of the columnar portion 163 of the bottom block 160. The third reference circle 170 has a center point that is coincident with the vertical axis A-A. In the exemplified embodiment, the plates 148 are thin steel plates that facilitate transferring the weight of the VVO 100 to the base plate 161 and also provide a means to scatter and absorb any errant gamma radiation that may attempt to exit the air inlet plenum. Furthermore, in the exemplified embodiment sixty plates 148 are illustrated. However, the invention is not to be so limited and in certain other embodiments more or less than sixty plates 148 may be disposed within the annular air inlet plenum 141. Due to the axisymmetric configuration of the air inlet plenum 141, the annular air inlet vent 140 is configured so that aerodynamic performance of the air inlet vent 140 is independent of an angular direction of a horizontal component of an air-stream applied to the outer surface 117 of the overpack body 101. Similarly, due to the axisymmetric configuration of the air outlet vent 145, the air outlet vent 145 is configured so that the aerodynamic performance of the air outlet vent 145 is independent of an angular direction of a horizontal component of an air-stream applied to the outer surface 117 of the overpack body 110. As used throughout, ranges are used as shorthand for describing each and every value that is within the range. Any value within the range can be selected as the terminus of the range. In addition, all references cited herein are hereby incorporated by referenced in their entireties. In the event of a conflict in a definition in the present disclosure and that of a cited reference, the present disclosure controls. While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention. Thus, the spirit and scope of the invention should be construed broadly as set forth in the appended claims. |
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claims | 1. A thin-film target for DT neutron production, comprising:an iron substrate having a high D permeability,a tungsten permeation barrier layer having a low D permeability on the iron substrate to inhibit D permeation from the iron substrate therethrough, anda front-surface tritide layer on the tungsten permeation barrier layer that reacts with an incident D beam to produce DT neutrons,wherein the combined thickness of the tritide layer and the tungsten permeation barrier layer is less than the range of an incident D beam having an energy. 2. The thin-film target of claim 1, wherein the combined thickness of the tritide layer and the tungsten permeation barrier layer if less than 50% of the range of the incident D beam. 3. The thin-film target of claim 2, wherein the combined thickness is less than approximately 10% of the range of the incident D beam. 4. The thin-film target of claim 1, wherein the tritide comprises a metal tritide. 5. The thin-film target of claim 4, wherein the metal tritide comprises titanium tritide. |
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abstract | An apparatus for processing a plurality of semiconductor wafers, the apparatus including a spallation chamber, a neutron producing material mounted in the spallation chamber, a neutron moderator, and an irradiation chamber coupled to the spallation chamber, wherein the neutron moderator is disposed between the spallation chamber and the irradiation chamber, wherein the irradiation chamber is configured to accommodate the plurality of semiconductor wafers, wherein each of the plurality of semiconductor wafers has a first surface and a second surface opposite the first surface, wherein the plurality of semiconductor wafers are positioned so that a first surface of one semiconductor wafer faces a second surface of another semiconductor wafer. |
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claims | 1. An apparatus, comprising:an ionization chamber for providing ions during a process of ion implantation; andan electron beam source device inside the ionization chamber, the electron beam source device comprising a field emission array having a plurality of emitters for generating electrons in vacuum under an electric field, wherein the field emission array contains an opening in its middle portion; and a cathode inside the electron beam source device configured so that the electrons from the field emission array collide with the cathode, wherein a portion of the cathode goes through the opening in the middle portion of the field emission array in a direction normal to a top surface of the field emission array. 2. The apparatus of claim 1, wherein the field emission array has a cross-section shape selected from a group consisting of a circle, a square and a regular polygon. 3. The apparatus of claim 1, wherein each of the plurality of emitters in the field emission array is a nanogap of at least one metal. 4. The apparatus of claim 3, wherein each of the plurality of emitters in the field emission array is disposed on a dielectric film. 5. The apparatus of claim 1, wherein each of the plurality of emitters in the field emission array comprises at least one carbon nanotube disposed in a void on a dielectric film. 6. The apparatus of claim 1, wherein each of the plurality of emitters in the field emission array is a Spindt array structure, the Spindt array structure comprising a plurality of metal cones, each disposed in a respective cylindrical void on a dielectric film. 7. The apparatus of claim 1, wherein the cathode is configured to emit secondary electrons. 8. The apparatus of claim 1, wherein the ionization chamber is configured to receive at least one dopant gas, and the electrons emitted from the field emission array and the secondary electrons emitted from the cathode collide with the at least one dopant gas for generating plasma comprising ionized dopants. 9. The apparatus of claim 8, further comprising an extraction apparatus for extracting the ionized dopants and forming an ion beam for ion implantation, wherein the extraction apparatus is connected with the ionization chamber. 10. An ion implantation equipment system, comprising:an ion source apparatus for generating an ion beam during a process of ion implantation, the ion source apparatus comprising:an ionization chamber configured to receive at least one dopant gas; andan electron beam source device inside the ionization chamber, the electron beam source device comprising a field emission array having a plurality of emitters for generating electrons in vacuum under an electric field, wherein the field emission array contains an opening in its middle portion; and a cathode inside the electron beam source device configured so that the electrons from the field emission array collide with the cathode, wherein a portion of the cathode goes through the opening in the middle portion of the field emission array in a direction normal to a top surface of the field emission array. 11. The ion implantation equipment system of claim 10, wherein the field emission array has a cross-section shape selected from a group consisting of a circle, a square and a regular polygon. 12. The ion implantation equipment system of claim 10, wherein each of the plurality of emitters in the field emission array is a nanogap of at least one metal disposed on a dielectric film. 13. The ion implantation equipment system of claim 10, wherein each of the plurality of emitters in the field emission array comprises at least one carbon nanotube disposed in a void on a dielectric film. 14. The ion implantation equipment system of claim 10, wherein each of the plurality of emitters in the field emission array is a Spindt array structure, the Spindt array structure comprising a metal cone disposed in a cylindrical void on a dielectric film. 15. The ion implantation equipment system of claim 10, wherein the cathode emits secondary electrons. 16. The ion implantation equipment system of claim 10, wherein the field emission array and cathode are configured so that during use, electrons emitted from the field emission array and the secondary electrons emitted from the cathode collide with the at least one dopant gas for generating plasma comprising ionized dopants. 17. The ion implantation equipment system of claim 10, further comprising an extraction apparatus for extracting the ionized dopants and forming an ion beam for ion implantation, wherein the extraction apparatus is connected with the ionization chamber. 18. An ion generation method in a process of ion implantation, comprising:feeding at least one dopant gas into an ionization chamber; andgenerating electrons from an electron beam source device comprising a field emission array having a plurality of emitters in vacuum under an electric field, wherein the field emission array contains an opening in its middle portion; and a cathode inside the electron beam source device configured so that the electrons from the field emission array collide with the cathode, wherein a portion of the cathode goes through the opening in the middle portion of the field emission array in a direction normal to a top surface of the field emission array. 19. The ion generation method of claim 18, further comprising generating secondary electrons from a cathode in the electron beam source device by directing the electrons emitted from the field emission array toward the cathode; and generating plasma comprising ionized dopants by directing the secondary electrons from the cathode into the ionization chamber. 20. The ion generation method of claim 19, further comprising extracting the ionized dopants in the ionization chamber and forming an ion beam. |
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abstract | An irradiation target positioning device and method for creating radioisotopes utilizing linear particle beam accelerators or cyclotron accelerators. The device positions a target proximate to a liquid reservoir and vapor expansion chamber. The target may be in a solid phase. Heat produced within the target during irradiation can be absorbed by the liquid. The liquid may be heated to its vaporization temperature and vapor emitted into the vapor chamber. The vapor chamber may utilize a cooling mechanism, allowing the vapor to condense (second phase change). The radioactive product may diffuse into the liquid, thereby allowing the irradiated product to be conveyed out of the target structure in a liquid, solution or slurry. Multiple radioisotopes may be produced simultaneously out of the target material and liquid and separated later. The target material and irradiated product may be removed from the target surface by acid. |
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claims | 1. A reflective-type soft X-ray microscope, comprising: an image-focusing optical system including a concave mirror and a convex mirror; an illumination optical system that has a light source, a filter, and a focusing optical element for transmitting a illumination light beam; and a stage mechanism that carries and moves a sample under observation, wherein the concave mirror has at least one opening part for transmitting the illuminating light beam that illuminates the sample and at least one other opening part for transmitting reflected light from the sample, and a reflected image of the sample is focused on a soft X-ray image detector by the image-focusing optical system. 2. The reflective-type soft X-ray microscope according to claim 1 , wherein a surface of the sample is positioned to be substantially perpendicular to the optical axis of the image-focusing optical system. claim 1 3. The reflective-type soft X-ray microscope according to claim 1 or 2 , wherein in the concave mirror of the image-focusing optical system, a diaphragm is installed in the position on which the illuminating light beam that has passed through the opening part is incident after being reflected by the sample. claim 1 2 4. The reflective-type soft X-ray microscope according to claim 3 , wherein the diaphragm is formed by forming a light-blocking film on a reflective film formed on a surface of the concave mirror, while leaving an opening part that acts as a diaphragm. claim 3 5. The reflective-type soft X-ray microscope according to claim 3 , wherein the diaphragm is formed by forming a reflective film only in an opening part that acts as said diaphragm. claim 3 6. The reflective-type soft X-ray microscope according to claim 3 , wherein the diaphragm is disposed between the sample and the surface of the concave mirror, and is formed by one of a substrate made of a light-blocking material and a substrate covered by a light-blocking material, which has an opening part that acts as a diaphragm. claim 3 7. The reflective-type soft X-ray microscope according to claim 1 or 2 , further comprising a supporting column for supporting the convex mirror of the image-focusing optical system, the supporting column being disposed such that neither the illuminating light beam illuminating the sample nor the reflected light beam reflected by the sample is blocked by the supporting column. claim 1 2 8. A reflective-type soft X-ray microscope, comprising: an image-focusing optical system including a concave mirror and a convex mirror; an illumination optical system including a light source, a filter and a focusing optical element for transmitting an illumination light beam; and a stage mechanism that carries and moves a sample under observation, wherein at least one opening part used to transmit the illuminating light beam that illuminates the sample is formed in the concave mirror, and at least one other opening part used to transmit scattered or diffracted light from the sample is formed in the concave mirror, an image of the sample formed by the scattered light or diffracted light being focused on a soft X-ray image detector by the image-focusing optical system. 9. The reflective-type soft X-ray microscope according to claim 8 , wherein the surface of the sample is positioned to be substantially perpendicular to the optical axis of the image-focusing optical system. claim 8 10. The reflective-type soft X-ray microscope claimed in claim 8 or 9 , wherein in the concave mirror of the image-focusing optical system, a reflective film is formed on a surface of the concave mirror, and a light-blocking film is formed of a substance that absorbs the reflected light beam only in the position on which the illuminating light beam that has passed through the opening part is incident after being scattered or diffracted by the sample. claim 8 9 11. The reflective-type soft X-ray microscope claimed in claim 8 or 9 , wherein in the concave mirror of the image-focusing optical system, a reflective film is formed on the mirror except in the position on which the illuminating light beam that has passed through the opening part is incident after being scattered or diffracted by the sample. claim 8 9 12. The reflective-type soft X-ray microscope claimed in claim 8 or 9 , wherein in the image-focusing optical system, one of a substrate made of a light-blocking material or a substrate covered by a light-blocking material is disposed between the concave mirror and the sample for blocking the scattered or diffracted light beam from the sample,. claim 8 9 13. The reflective-type soft X-ray microscope according to claim 8 or 9 , further comprising a supporting column for supporting the convex mirror of the image-focusing optical system, the supporting column being disposed such that the illuminating light beam illuminating the sample is not blocked. claim 8 9 14. The reflective-type soft X-ray microscope according to claim 8 or 9 , wherein the illumination optical system comprises: claim 8 9 a light source that is one of a laser plasma light source, a discharge plasma light source, and an X-ray laser light source; a filter that selectively transmits soft X-rays of a specified wavelength; and a focusing optical element that focuses the light beam emitted from the light source. 15. The reflective-type soft X-ray microscope according to any one of claims 1 , 2 , 8 , and 9 , wherein the illumination optical system includes a selector that switches the illuminating light to one of soft X-rays, visible light and ultraviolet light. 16. The reflective-type soft X-ray microscope according to any one of claims 1 , 2 , 8 , and 9 , wherein a plurality of the illumination optical systems are installed, and a plurality of illuminating light beams that have different wavelengths are respectively caused to be incident on the sample via a plurality of different opening parts formed in the concave mirror of the image-focusing optical system. 17. The reflective-type soft X-ray microscope according to any one of claims 1 , 2 , 8 , and 9 , wherein the image-focusing optical system is a Schwarzschild optical system. 18. A mask inspection device for inspecting a reflective mask to be used in a soft X-ray reduction projection exposure, comprising the reflective-type soft X-ray microscope of any one of claims 1 , 2 , 8 , and 9 using soft X-rays having the same wavelength as that to be used in the soft X-ray reduction projection exposure. 19. A mask inspection device for inspecting a reflective mask to be used in a soft X-ray reduction projection exposure, comprising: the reflective-type soft X-ray microscope of any one of claims 1 , 2 , 8 , and 9 using soft X-rays having the same wavelength as that to be used in the soft X-ray reduction projection exposure; and a scanner that causes the surface of the sample to be scanned while the intensity of reflected light, diffracted light or scattered light is detected, the scanner further causing an image to be acquired in areas where the detected intensity varies. 20. A method for manufacturing a reflective mask having a pattern on a substrate, the method comprising: a first step of forming a reflective film having a multi-layer film for reflecting soft X-rays on a substrate; a second step of forming a light-blocking film that absorbs soft X-rays on the reflective film; a third step of forming a resist layer on the light-blocking film; a fourth step of exposing portions of the resist layer for forming a latent image corresponding to a desired reflective or light-blocking pattern in the resist layer; a fifth step of developing the resist layer to form the desired reflective or light-blocking pattern; and a sixth step of etching the light-blocking film using the developed resist layer as a protective layer, wherein at least one of the first, fifth, and sixth steps includes the step of inspecting the reflective film, the light-blocking film, the resist layer, or the reflective or light-blocking pattern formed in the resist layer or the reflective mask using the mask inspection device of claim 19 . claim 19 21. A method for manufacturing a reflective mask having a pattern on a substrate, the method comprising: a first step of forming a reflective film having a multi-layer film for reflecting soft X-rays on a substrate; a second step of forming a resist layer on the reflective film; a third step of exposing portions of the resist layer to form a latent image corresponding to a reflective or light-blocking pattern in the resist layer; a fourth step of developing the resist layer to form the reflective or light-blocking pattern; and a fifth step of forming a light-blocking film formed of one of an inorganic compound, an organic compound, and an organic and inorganic compound, which absorbs soft X-rays in areas not covered by the developed resist layer, using the resist layer as a protective layer, wherein at least one of the first, fourth, and fifth steps includes the step of inspecting the reflective film, the light-blocking film or the reflective or light-blocking pattern formed in the resist layer or the reflective mask using the mask inspection device of claim 19 . claim 19 22. A reflective-type soft X-ray microscope, comprising: an image-focusing optical system including a concave mirror and a convex mirror; an illumination optical system that has a light source, a filter, and a focusing optical element for transmitting an illumination light beam; and a stage mechanism that carries and moves a sample under observation, wherein the concave mirror has at least one opening part for transmitting the illuminating light beam that illuminates the sample, and a reflected image of the sample is focused on a soft X-ray image detector by the image-focusing optical system, and wherein in the concave mirror of the image-focusing optical system, a diaphragm is installed in the position on which the illuminating light beam that has passed through the opening part is incident after being reflected by the sample. 23. The reflective-type soft X-ray microscope according to claim 22 , wherein a surface of the sample is positioned to be substantially perpendicular to the optical axis of the image-focusing optical system. claim 22 24. The reflective-type soft X-ray microscope according to claim 22 or 23 , wherein the diaphragm is formed by forming a light-blocking film on a reflective film formed on a surface of the concave mirror, while leaving an opening part that acts as a diaphragm. claim 22 23 25. The reflective-type soft X-ray microscope according to claim 22 or 23 , wherein the diaphragm is formed by forming a reflective film only in an opening part that acts as said diaphragm. claim 22 23 26. The reflective-type soft X-ray microscope according to claim 22 or 23 , wherein the diaphragm is disposed between the sample and the surface of the concave mirror, and is formed by one of a substrate made of a light-blocking material and a substrate covered by a light-blocking material, which has an opening part that acts as a diaphragm. claim 22 23 27. A reflective-type soft X-ray microscope, comprising: an image-focusing optical system including a concave mirror and a convex mirror; an illumination optical system including a light source, a filter and a focusing optical element for transmitting an illumination light beam; and a stage mechanism that carries and moves a sample under observation, wherein at least one opening part used to transmit the illuminating light beam that illuminates the sample is formed in the concave mirror, and an image formed by scattered light or diffracted light is focused on a soft X-ray image detector by the image-focusing optical system, and wherein in the concave mirror of the image-focusing optical system, a reflective film is formed on a surface of the concave mirror, and a light-blocking film is formed of a substance that absorbs the reflected light beam only in the position on which the illuminating light beam that has passed through the opening part is incident after being scattered or diffracted by the sample. 28. The reflective-type soft X-ray microscope according to claim 27 , wherein the surface of the sample is positioned to be substantially perpendicular to the optical axis of the image-focusing optical system. claim 27 29. A reflective-type soft X-ray microscope, comprising: an image-focusing optical system including a concave mirror and a convex mirror; an illumination optical system including a light source, a filter and a focusing optical element for transmitting an illumination light beam; and a stage mechanism that carries and moves a sample under observation, wherein at least one opening part used to transmit the illuminating light beam that illuminates the sample is formed in the concave mirror, and an image formed by scattered light or diffracted light is focused on a soft X-ray image detector by the image-focusing optical system, and wherein in the concave mirror of the image-focusing optical system, a reflective film is formed on the mirror except in the position on which the illuminating light beam that has passed through the opening part is incident after being scattered or diffracted by the sample. 30. The reflective-type soft X-ray microscope according to claim 29 , wherein the surface of the sample is positioned to be substantially perpendicular to the optical axis of the image-focusing optical system. claim 29 31. A reflective-type soft X-ray microscope, comprising: an image-focusing optical system including a concave mirror and a convex mirror; an illumination optical system including a light source, a filter and a focusing optical element for transmitting an illumination light beam; and a stage mechanism that carries and moves a sample under observation, wherein at least one opening part used to transmit the illuminating light beam that illuminates the sample is formed in the concave mirror, and an image formed by scattered light or diffracted light is focused on a soft X-ray image detector by the image-focusing optical system, and wherein in the image-focusing optical system, one of a substrate made of a light-blocking material or a substrate covered by a light-blocking material is disposed between the concave mirror and the sample for blocking the scattered or diffracted light beam from the sample. 32. The reflective-type soft X-ray microscope according to claim 31 , wherein the surface of the sample is positioned to be substantially perpendicular to the optical axis of the image-focusing optical system. claim 31 33. A reflective-type soft X-ray microscope, comprising: an image-focusing optical system including a concave mirror and a convex mirror; an illumination optical system that has a light source, a filter, and a focusing optical element for transmitting an illumination light beam; and a stage mechanism that carries and moves a sample under observation, wherein the concave mirror has at least one opening part for transmitting the illuminating light beam that illuminates the sample, and a reflected image of the sample is focused on a soft X-ray image detector by the image-focusing optical system, and wherein a plurality of the illumination optical systems are installed, and a plurality of illuminating light beams that have different wavelengths are respectively caused to be incident on the sample via a plurality of different opening parts formed in the concave mirror of the image-focusing optical system. 34. The reflective-type soft X-ray microscope according to claim 33 , wherein a surface of the sample is positioned to be substantially perpendicular to the optical axis of the image-focusing optical system. claim 33 35. A reflective-type soft X-ray microscope, comprising: an image-focusing optical system including a concave mirror and a convex mirror; an illumination optical system including a light source, a filter and a focusing optical element for transmitting an illumination light beam; and a stage mechanism that carries and moves a sample under observation, wherein at least one opening part used to transmit the illuminating light beam that illuminates the sample is formed in the concave mirror, and an image formed by scattered light or diffracted light is focused on a soft X-ray image detector by the image-focusing optical system, wherein a plurality of the illumination optical systems are installed, and a plurality of illuminating light beams that have different wavelengths are respectively caused to be incident on the sample via a plurality of different opening parts formed in the concave mirror of the image-focusing optical system. 36. The reflective-type soft X-ray microscope according to claim 35 , wherein the surface of the sample is positioned to be substantially perpendicular to the optical axis of the image-focusing optical system. claim 35 37. A mask inspection device for inspecting a reflective mask to be used in a soft X-ray reduction projection exposure, comprising: a reflective-type soft X-ray microscope using soft X-rays having the same wavelength as that to be used in the soft X-ray reduction projection exposure, the reflective-type soft X-ray microscope comprising: an image-focusing optical system including a concave mirror and a convex mirror; an illumination optical system that has a light source, a filter, and a focusing optical element for transmitting an illumination light beam; and a stage mechanism that carries and moves a sample under observation, wherein the concave mirror has at least one opening part for transmitting the illuminating light beam that illuminates the sample, and a reflected image of the sample is focused on a soft X-ray image detector by the image-focusing optical system; and a scanner that causes the surface of the sample to be scanned while the intensity of reflected light, diffracted light or scattered light is detected, the scanner further causing an image to be acquired in areas where the detected intensity varies. 38. The mask inspection device according to claim 37 , wherein the surface of the sample is positioned to be substantially perpendicular to the optical axis of the image-focusing optical system. claim 37 39. A mask inspection device for inspecting a reflective mask to be used in a soft X-ray reduction projection exposure, comprising: a reflective-type soft X-ray microscope using soft X-rays having the same wavelength as that to be used in the soft X-ray reduction projection exposure, the reflective-type soft X-ray microscope comprising: an image-focusing optical system including a concave mirror and a convex mirror; an illumination optical system including a light source, a filter and a focusing optical element for transmitting an illumination light beam; and a stage mechanism that carries and moves a sample under observation, wherein at least one opening part used to transmit the illuminating light beam that illuminates the sample is formed in the concave mirror, and an image formed by scattered light or diffracted light is focused on a soft X-ray image detector by the image-focusing optical system; and a scanner that causes the surface of the sample to be scanned while the intensity of reflected light, diffracted light or scattered light is detected, the scanner further causing an image to be acquired in areas where the detected intensity varies. 40. The mask inspection device according to claim 39 , wherein the surface of the sample is positioned to be substantially perpendicular to the optical axis of the image-focusing optical system. claim 39 41. A method for manufacturing a reflective mask having a pattern on a substrate, the method comprising: a first step of forming a reflective film having a multi-layer film for reflecting soft X-rays on a substrate; a second step of forming a light-blocking film that absorbs soft X-rays on the reflective film; a third step of forming a resist layer on the light-blocking film; a fourth step of exposing portions of the resist layer for forming a latent image corresponding to a desired reflective or light-blocking pattern in the resist layer; a fifth step of developing the resist layer to form the desired reflective or light-blocking pattern; and a sixth step of etching the light-blocking film using the developed resist layer as a protective layer, wherein at least one of the first, fifth, and sixth steps includes the step of inspecting the reflective film, the light-blocking film, the resist layer, or the reflective or light-blocking pattern formed in the resist layer or the reflective mask using the mask inspection device of any one of claims 37 , 38 , 39 , and 40 . 42. A method for manufacturing a reflective mask having a pattern on a substrate, the method comprising: a first step of forming a reflective film having a multi-layer film for reflecting soft X-rays on a substrate; a second step of forming a resist layer on the reflective film; a third step of exposing portions of the resist layer to form a latent image corresponding to a reflective or light-blocking pattern in the resist layer; a fourth step of developing the resist layer to form the reflective or light-blocking pattern; and a fifth step of forming a light-blocking film formed of one of an inorganic compound, an organic compound, and an organic and inorganic compound, which absorbs soft X-rays in areas not covered by the developed resist layer, using the resist layer as a protective layer, wherein at least one of the first, fourth, and fifth steps includes the step of inspecting the reflective film, the light-blocking film or the reflective or light-blocking pattern formed in the resist layer or the reflective mask using the mask inspection device of any one of claims 37 , 38 , 39 , and 40 . |
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description | The embodiments of the present invention will be described below with reference to the views of the accompanying drawing. (First Embodiment) FIG. 4 schematically shows the internal structure of the gantry of an X-ray computed tomography apparatus according to the first embodiment of the present invention. FIG. 5 is a block diagram showing the circuit arrangement of the X-ray computed tomography apparatus according to the first embodiment of the present invention. The same reference numerals as in FIG. 4 denote the same parts in FIG. 5. A gantry 7 is the main structure of the X-ray computed tomography apparatus for acquiring multi-directional projection data about an object. The gantry 7 has a stationary portion 8 and ring-like rotating ring 10. The rotating ring 10 is supported on the stationary portion 8 so that it can rotate about a rotation axis RA. A motor (not shown) is used to rotate the rotating ring 10 at a speed as high as less than one sec per rotation. With this operation, the rotating ring 10 undergoes displacement relative to the stationary portion 8. An X-ray tube 12 for generating X-rays in the form of a fan is mounted on the rotating ring 10. In addition, an X-ray detector 16 is mounted on the rotating ring 10 to detect X-rays that are generated by the X-ray tube 12 and transmitted through an object 14. Typically, the X-ray detector 16 complies with multichannel specifications. A DAS (Data Acquisition System) 18 is also mounted on the rotating ring 10. The DAS 18 amplifies a weak electrical signal output from the X-ray detector 16 and converts the amplified electrical signal into a binary (1 and 0) digital signal. Note that a signal output from the DAS 18 will be referred to as projection data. This projection data is transmitted to the stationary portion 8 side through a noncontact type signal transmission device 19. An image data generating unit 25 reconstructs tomographic data about the object on the basis of the transmitted projection data. A monitor 27 visualizes the tomographic data. The noncontact type signal transmission device 19 is configured to perform noncontact transmission of projection data from the rotating ring 10 side to the stationary portion 8 side by using light. For this purpose, the noncontact type signal transmission device 19 includes a plurality of light-emitting diodes 1 and a plurality of light-receiving devices 5. Typically, the light-emitting diode 1 is a light-emitting diode, and the light-receiving device 5 is a photodiode. As shown in FIG. 6, the light-emitting diodes 1 are arranged at predetermined intervals on the outer surface of the rotating ring 10. This interval is set such that the irradiation area from one light-emitting diode 1 overlaps that from another adjacent light-emitting diode 1. The photodiodes 5 are arranged at predetermined intervals on the inner surface of the ring of the stationary portion 8 to oppose the light-emitting diodes 1. The noncontact type signal transmission device 19 also includes a plurality of LED drivers 23 for driving the light-emitting diodes 1 to simultaneously turn them on/off in accordance with projection data, and a data distributor 20 for distributing projection data to the LED drivers 23. The LED drivers 23 and data distributor 20 are mounted on the rotating ring 10. Each LED driver 23 turns on the light-emitting diode 1 when, for example, projection data is xe2x80x9c1xe2x80x9d, and turns it off when the projection data is xe2x80x9c0xe2x80x9d. The light emitted from the light-emitting diode 1 is incident on the photodiode 5. The photodiode 5 detects the incident light and generates an electrical signal having an amplitude corresponding to the amount of light received. The noncontact type signal transmission device 19 further includes a circuit (not shown) for binarizing the electrical signal output from the photodiode 5 and reconstructing the projection data. This reconstruction circuit is mounted on the stationary portion 8. The noncontact type signal transmission device 19 also has a plurality of beam condensing devices 3. The beam condensing devices 3 are respectively provided for the pairs of light-emitting diodes 1 and photodiodes 5. The beam condensing devices 3 are cylindrical lenses, Fresnel lenses, or curved mirrors, typically cylindrical lenses each having a shape concentrically curved with respect to the rotating ring 10. FIG. 7 shows the optical mechanism of the cylindrical lens 3. The cylindrical lens 3 has the function of condensing light from the light-emitting diode 1 in a direction (Zxe2x80x2-axis) substantially perpendicular to the rotational orbit (Yxe2x80x2-axis). The cylindrical lens 3 does not have a function of condensing light from the light-emitting diode 1 or it has the function of diffusing light in a direction substantially parallel to the rotational orbit (Yxe2x80x2-axis). When the light sent onto the lens 3 is viewed from the rotation axis direction of the ring 10, the light from the light-emitting diode 1 diverges in the form of a fan. This light also diverges in the form of a fan after passing through the lens 3. That is, when the traveling direction of light from the light-emitting diode is considered with respect to the Yxe2x80x2 direction and Zxe2x80x2 a direction, respectively, the traveling direction of light from the light-emitting diode 1 does not change with respect to the Yxe2x80x2 direction regardless of the lens 3. With respect to the Zxe2x80x2 a direction, however, the traveling direction of light from the light-emitting diode 1 changes in the direction in which the light is condensed by the lens 3. Therefore, the light from the light-emitting diode 1 is not condensed to one point but is condensed in a linear or belt-like form along the orbit of the photodiode 5. The condensing function of the cylindrical lens 3 makes it possible to ensure a relatively large light reception amount even if the photodiode 5 is located relatively far from the light-emitting diode 1. With the cylindrical lens 3, therefore, even light that does not strike the effective light-receiving surface of the photodiode 5 without the cylindrical lens 3 can be sent onto the effective light-receiving surface of the photodiode 5. The positional relationship between the light-emitting diode 1, the cylindrical lens 3, and the photodiode 5 is set as follows. For example, as shown in FIGS. 7 and 8A, the positional relationship between these three components is set such that the photodiode 5 is irradiated with light from the light-emitting diode 1 within an area CL1 having a width smaller than the effective light-receiving surface (EW) of the photodiode 5. In this case, the photodiode 5 is positioned at or close to a point F to which light is condensed by the cylindrical lens 3. With this positioning, almost all light is received by the photodiode 5 in the Zxe2x80x2-axis direction. Therefore, the amount of light received increases. As showing FIG. 8B, if some mechanical error (a mounting error and displacement in the rotational orbit in the Zxe2x80x2 direction) or some photodiode position variation in the Zxe2x80x2 direction (in this case, photodiode 5 are mounted in a inclined line to the light emitting diode line) occurs, the irradiation area CL1 may fall outside the effective light-receiving surface of the photodiode 5 and may receive no light. For example, in FIG. 8B, photodiode 5c can""t receive light, in this case, the communication is broken. The positional relationship between the three components which is set to solve this problem will be described next. As shown in FIGS. 9 and 10, the positional relationship between the three components is set such that the photodiode 5 is irradiated with light from the light-emitting diode 1 within a belt-like area BL1 having a width BW substantially equal to or larger than the width EW of the effective light-receiving surface of the photodiode 5. In this case, the point F is positioned farther from the light-emitting diode 1 than the photodiode 5. The positional relationship between the three components is set such that the width of the belt-like irradiation area BL1 becomes larger than, for example, the width of the effective light-receiving surface of the photodiode 5 by a mechanical error (a mounting error or displacement in the rotational orbit in the Zxe2x80x2 direction) or a photodiode position variation in the Zxe2x80x2 direction. In this case, the cylindrical lens 3 is preferably mounted on the ring of the stationary portion 8. With this positional relationship, allowance with respect to a mechanical error such as a mounting error or rotation displacement or a photodiode position variation in the Zxe2x80x2 direction increases as compared with the case shown in FIG. 7. In FIG. 7, photodiodes 5a, 5b can receive light, in FIG. 10, photodiodes 5a, 5b, 5c, 5d and 5e can receive light. As shown in FIG. 11, the positional relationship between the three components may be set such that the photodiode 5 is irradiated with light within the above belt-like area BL1. In this case, the point F is positioned between the lens 3 and the photodiode 5. With this positional relationship, a certain amount of light received can be ensured even with some mechanical error such as a mounting error or rotation displacement or a photodiode position variation in the Zxe2x80x2 direction. In this case, the cylindrical lens 3 is preferably mounted on the rotating ring 10. As described above, according to this embodiment, the light reception amount can be increased (the occurrence ratio of transmission errors can be decreased) within the allowable ranges of photodiode position variation in the Zxe2x80x2 direction and rotation offsets of the rotating ring 10. That is, a reduction in the amount of light received by each photodiode 5 can be suppressed by substantially condensing light emitted from the light-emitting diode 1 onto the orbit of the photodiode 5, even if the amount of light emitted from the light-emitting diode 1 decreases. Even if, therefore, the amount of light emitted from the light-emitting diode 1 decreases due to an increase in the frequency of a transmission signal, an increase in communication error ratio can be suppressed. In addition, since light from the light-emitting diode 1 is not condensed to one point on the orbit but is condensed to the entire orbit, each photodiode 5 can always receive light while moving on the orbit. This makes it possible to continuously transmit signals with small numbers of light-emitting diodes 1 and photodiodes 5. (Second Embodiment) FIG. 13 shows the arrangement of a noncontact type signal transmission device according to the second embodiment of the present invention. The same reference numerals as in FIG. 6 denote the same parts in FIG. 13. In the first embodiment, the light-emitting diodes 1 are arranged on the rotating ring 10, and the photodiodes 5 are arranged on the stationary portion 8. In the second embodiment, light-emitting diodes 1 are mounted on a rotating ring 10, and photodiodes 5 are mounted on a stationary portion 8. Fresnel lenses 33 are used as beam condensing devices. The Fresnel lenses 33 are mounted on the stationary portion 8, together with the light-emitting diodes 1. FIG. 14A is a sectional view of the Fresnel lens 33 used in this embodiment. FIG. 14B is a front view of this lens. A general Fresnel lens is made up of a plurality of annular lenses. In this embodiment, however, each Fresnel lens 33 is made up of a plurality of belt-like lenses each having a linear shape instead of an annular shape. As shown in FIG. 14A, each Fresnel lens 33 has a sawtooth-like cross-sectional shape (the oblique portions of the respective teeth are not linear but have the same curvature). In addition, as shown in FIG. 14B, when viewed from the front side of each Fresnel lens, strips each having a predetermined width are arranged parallel. This Fresnel lens 33 is thinner than the cylindrical lens 3 in the first embodiment and has a similar beam condensing function. With the Fresnel lenses, therefore, the same effects as those of the first embodiment can be obtained. In addition, since the Fresnel lenses are thinner than the lenses in the first embodiment, a reduction in weight and improvement in heat dissipation characteristics can be attained. As shown in FIG. 15, the Fresnel lenses 33 may be mounted on the rotating ring 10, together with the photodiodes 5. (Third Embodiment) As beam condensing means, curved mirrors, e.g., elliptic mirrors, are used instead of lenses. The elliptic mirrors are not disposed between light-emitting diodes and photodiodes but are disposed behind the light-emitting diodes or photodiodes. FIG. 16 is a perspective view showing the shape of an elliptic mirror and the position of a light-emitting diode. A light-emitting diode 1 is disposed in an elliptic mirror 35 and emits light toward the mirror surface of the elliptic mirror 35. A shielding plate 55 is disposed to be perpendicular to the generatrix of the elliptic mirror 35. FIG. 17 shows the positions of the light-emitting diode 1 and a photodiode 5 with respect to the elliptic mirror 35. The light-emitting diode 1 is positioned at one focal point of the elliptic mirror 35, and the photodiode 5 is disposed at a position slightly farther from the light-emitting diode 1 than the other focal point of the elliptic mirror 35. Light emitted from the light-emitting diode 1 is reflected by the elliptic mirror 35 and condensed to the other focal point. The reflected light converges first to the focal point and then diverges to reach the photodiode 5. FIG. 18 shows the light condensed to the belt-like irradiation area when viewed from the rear side of the elliptic mirror. In this embodiment using the elliptic mirrors 35, light emitted from each light-emitting diode 1 is condensed onto one line before the orbit of the photodiode 5, and then diverges to be condensed, as light having a belt-like irradiation area 75, onto the orbit of the photodiode 5 as in the first embodiment using the cylindrical lenses. Note that the shielding plates 55 perpendicular to the generatrix of the elliptic mirror 35 are disposed on the right and left ends of the elliptic mirror 35 to suppress the diffusion of light in the generatrix direction, thereby preventing crosstalk. Each elliptic mirror may be disposed behind the corresponding photodiode when viewed from the light-emitting diode. In this case, the light-emitting surfaces of the light-emitting diodes and the light-receiving surfaces of the photodiodes are located in the opposite directions to those in the third embodiment. By substantially condensing light emitted from the light-emitting diode 1 onto the orbit of the photodiode 5 by using the elliptic mirror, the same effects as those of the first embodiment can be obtained. The elliptic mirror is disposed behind the light-emitting diode when viewed from the photodiode, or behind the photodiode when viewed from the light-emitting diode. For this reason, the interval between the light-emitting diode and the photodiode can be reduced as compared with the first and second embodiments in which the lens is disposed between the light-emitting diode and the photodiode. This makes it possible to reduce the size of the apparatus. In the use of elliptic mirrors, as in the first and second embodiments, the light-emitting diodes or photodiodes can be arranged on the rotating portion or stationary portion. In addition, the elliptic mirrors can be arranged on the rotating portion or stationary portion like the cylindrical lenses and Fresnel lenses used in the first and second embodiments. If light emitted from each light-emitting diode is substantially condensed onto the orbit of a corresponding photodiode, the same effects as those of the first embodiment can be obtained, regardless of the positions of light-emitting diodes, photodiodes, and elliptic mirrors. In each embodiment described above, light emitted from a light-emitting means is substantially condensed onto the orbit of a light-receiving means by using one beam condensing means. However, the present invention is not limited these embodiments. Light may be condensed by using two or more beam condensing means. For example, light emitted from a light-emitting means light may be collimated by the first beam condensing means, and this collimated beam is sent onto the second beam condensing means to make the second beam condensing means substantially condense the collimated beam onto the orbit of the light-receiving means. The present invention can be applied to a case wherein both the light-emitting means and the light-receiving means move as well as a case wherein only one of the light-emitting means and the light-receiving means moves. The case in which both the light-emitting means and the light-receiving means move includes not only a case wherein the light-emitting means and light-receiving means move in different directions but also a case wherein they move in the same direction at different moving speeds. Furthermore, these means may move on a straight line or circumference. Each light-emitting means may be formed by only an electrooptic conversion element for generating light modulated in accordance with a signal obtained by coding information to be transmitted or may be made up of a combination of an element that keeps emitting light regardless of the signal and an element for modulating the luminance or the like of the transmitted light in accordance with the signal. The electrooptic conversion element includes a laser diode in addition to a light-emitting diode. The element for modulating transmitted light includes a liquid crystal polarizing plate. Modulated light may be sent onto the light-receiving means through a medium that transmits light instead of being directly sent onto the light-receiving means. The medium for transmitting light includes an optical fiber. The light-receiving means may be formed by only an element (optoelectric conversion element) for detecting the modulation of received light and converting the light into an electrical signal, or may be made up of an optoelectric conversion element and a medium for transmitting received light to the optoelectric conversion element. The optoelectric conversion element includes a phototransistor and photocell in addition to a photodiode. The beam condensing means includes a curve mirror other than an aspherical lens and elliptic mirror as well as a cylindrical lens, Fresnel lens, and elliptic mirror. The case wherein the position of the light-receiving means changes relative to the light-emitting means and beam condensing means includes a case wherein the moving directions and speeds of the light-emitting means and beam condensing means differ from those of the light-receiving means. Likewise, the case wherein the position of the light-emitting means changes relative to the light-receiving means and beam condensing means includes a case wherein the moving directions and speeds of the light-receiving means and beam condensing means differ from those of the light-emitting means. When the number of light-emitting means differs from that of light-receiving means, the beam condensing means are preferably disposed on the minority side. This arrangement requires a smaller number of beam condensing means, and hence makes it possible to facilitate design and manufacture and attain a reduction in cost and the like. Additional advantages and modifications 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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claims | 1. An apparatus, comprising:a material source configured to provide a quantity of a material;a radiation source configured to emit a radiation beam along an axis that strikes the quantity of material, causing substantially all of the quantity of material to evaporate; anda structure having first and second surface portions and configured to rotate the first and second surface portions about the axis, the structure having first and second operational modes, wherein in the first operational mode the structure rotates the first and second surface portions about the axis such that the first surface portion is positioned on a first side of the radiation beam and receives a greater quantity of a byproduct of the evaporation impinges than the second surface portion positioned on a second side of the radiation beam, and in the second operational mode the structure rotates the first and second surface portions about the axis such that the second surface portion is positioned on the first side of the radiation beam and receives a greater quantity of the byproduct impinges than the first surface portion positioned on the second side of the radiation beam. 2. An apparatus according to claim 1,wherein the radiation beam strikes the quantity of material at an impact location;wherein the radiation beam travels along a path that extends to the impact location; andwherein the structure supports the first and second surface portions for movement relative to the impact location. 3. An apparatus according to claim 2,wherein each of the first and second surface portions are reflective;wherein upon striking the quantity of material, a portion of the radiation beam transforms into a radiation portion;wherein in the first operational mode, the radiation portion radiates toward the first surface portion, and the first surface portion reflects the radiation portion; andwherein in the second operational mode, the radiation portion radiates toward the second surface portion, and the second surface portion reflects the radiation portion. 4. An apparatus according to claim 3,wherein the first surface portion is shaped so that in the first operational mode, the first surface portion focuses the reflection of the radiation portion toward a focal point; andwherein the second surface portion is shaped so that in the second operational mode, the second surface portion focuses the reflection of the radiation portion toward the focal point. 5. An apparatus according to claim 3, wherein in the radiation beam has a first wavelength, and the radiation portion has a second wavelength that is different from the first wavelength. 6. An apparatus according to claim 2, wherein the first and second surface portions are spaced from the path. 7. An apparatus according to claim 2, wherein the structure further has a continuous surface that includes the first and second surface portions. 8. An apparatus according to claim 7,wherein the continuous surface includes an aperture; andwherein the path passes through the aperture of the continuous surface. 9. An apparatus according to claim 8, wherein the structure supporting the first and second portions for movement is configured to rotate the continuous surface about the axis that is coincident with the path, the rotation being the movement relative to the impact location. 10. An apparatus according to claim 2, wherein the structure further has separate first and second surfaces that respectively include the first and second surface portions. 11. An apparatus according to claim 10,wherein each of the first and second surfaces includes an aperture;wherein in the first operational mode, the path passes through the aperture of the first surface, and the second surface is spaced from the path; andwherein in the second operational mode, the path passes through the aperture of the second surface, and the first surface is spaced from the path. 12. An apparatus according to claim 11, wherein the structure supporting the first and second portions for movement is configured to rotate the first and second surface portions about an axis that is transverse to the path, the rotation being the movement relative to the impact location. 13. An apparatus according to claim 1, wherein the apparatus includes an extreme ultraviolet (EUV) lithography system having an EUV laser that includes the material source, the radiation source, and the structure. 14. A method, comprising:emitting a radiation beam along an axis toward a quantity of material;striking the quantity of material with the radiation beam, causing substantially all of the quantity of material to evaporate;operating a structure having first and second surface portions in a first operational mode, wherein the first operational mode includes rotating the first and second surface portions about the axis such that the first surface portion is positioned on a first side of the radiation beam and receives a greater quantity of a byproduct of the evaporation impinges than the second surface portion positioned on a second side of the radiation beam; andthereafter operating the structure in a second operational mode, wherein the second operational mode includes rotating the first and second surface portions about the axis such that the second surface portion is positioned on the first side of the radiation beam and receives a greater quantity of the byproduct impinges than the first surface portion positioned on the second side of the radiation beam. 15. A method according to claim 14,wherein the emitting is carried out in a manner that directs the radiation beam along a path that extends to an impact location;wherein the striking is carried out in a manner that causes the striking of the quantity of material with the radiation beam at the impact location; andfurther including transitioning between the first and second operational modes, the transitioning including moving the first and second surface portions relative to the impact location. 16. A method according to claim 15,wherein each of the first and second surface portions are reflective;wherein the striking is carried out in a manner that includes transforming the radiation beam into a radiation portion;further including reflecting the radiation portion using the first surface portion in the first operational mode; andreflecting the radiation portion using the second surface portion in the second operational mode. 17. A method according to claim 16, wherein the reflecting includes:focusing the travel of the radiation portion toward a focal point using the first surface portion in the first operational mode; andfocusing the travel of the radiation portion toward the focal point using the second surface portion in the second operational mode. 18. A method according to claim 16,wherein the emitting is carried out in a manner such that the beam has a first wavelength; andwherein the transforming is carried out in a manner such that the radiation portion has a second wavelength that is different from the first wavelength. 19. A method according to claim 15,wherein the structure further has a continuous surface that includes the first and second surface portions; andwherein the moving includes rotating the continuous surface about the axis that is coincident with the path. 20. A method according to claim 15,wherein the structure further has separate first and second surfaces that respectively include the first and second surface portions; andwherein the moving is carried out in a manner that includes rotating the first and second surface portions about an axis that is transverse to the path. |
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description | The present invention relates to a terahertz-gigahertz system (THz system) housing capable of minimizing at least the interference of undesired stray terahertz-gigahertz waves. In particular, the present invention describes a terahertz-gigahertz system housing made of foam material with conductive additives, wherein the foam materials may be the widely used Expanded Polypropylene (EPP) and the widely used Styrofoam, wherein the conductive additives may be the widely used graphite particles and carbon particles. Terahertz-gigahertz waves have been used in some applications during the past years. For example, it has been used in security screening tools because of its unique transmission properties that identifies concealed objects, such as a metal weapon hidden under the fiber clothing. The terahertz-gigahertz system requires housing to hold and/or connect the part(s) of the THz system. The development of high performance Terahertz-Gigahertz (THz) systems, such as THz image systems and THz communication systems, relies upon that both external electromagnetic (EM) noise and internal stray Terahertz-Gigahertz waves are negligible. These considerations are crucial because the wavelength of the THz waves (a few mm) is comparable to the dimensions of elements of the THz system itself. Therefore, a suitable THz system's housing that can effectively reduce reflection from the system interior and absorb EM waves from the exterior at the same time is critical. Till now, some well-known skills use the non-smooth surface to reduce the reflection of incident EM waves. Just for examples, a non-smooth surface having many pin-like or wedge-like structures whose geometrical configurations may significantly modify the propagation of the incident EM waves. Some other well-known skills use specific material(s) to reduce reflection and enhance absorption of the incident EM waves, even other EM noise. Just for example, electrically insulating and silicone-based elastomer which comprises room temperature polymerizing aromatic/aliphatic hydrocarbon substituted polysiloxane with an inert, electrically insulating, powdered siliceous filler and a curing agent. Just for reference, U.S. Pat. No. 7,940,204, U.S. Pat. No. 6,674,609, U.S. Pat. No. 5,208,299 and U.S. Pat. No. 4,942,402 are some of these well-known skills. However, all these well-known skills are not preferable to form a scalable (in terms of its size and its structural complexity), lightweight, compact, robust, and inexpensive THz system's housing capable of minimizing at least the interference of undesired stray terahertz-gigahertz waves. Therefore, there is a need to provide a housing for the terahertz-gigahertz system to minimize both the external noise and internal stray EM waves for THz system application such as imaging, communicating or future-developed applications. The present invention proposes a terahertz-gigahertz system housing to minimize noise and internal interference. The present invention achieves such housing by using specific material(s) to form the housing with the desired electromagnetic properties such that the housing may effectively absorb as much THz wave as possible in all directions while minimizing internal reflection. Some embodiments are related to a Terahertz-Gigahertz system housing by introducing absorptive particles/dyes, such as conductive carbon and conductive graphite, into a foam material, which have low relative dielectric constant (close to 1.0). The conductive particles/dyes with high absorption absorb stray EM waves entering from either the exterior or interior of the housing, especially stray THz waves, which penetrate into the housing through some finite amount of distance. In addition, the low relative dielectric constant of the used foam material prevents harmful Fresnel reflection at the interior of the housing that causes unwanted stray EM waves, especially stray THz waves. The proposed THz system housing is advantageous over other aforementioned well-known skills in some ways. First, the absorptive particles/dyes may be introduced into the material either prior or after the formation of the housing, which means the size, the shape, and the formation of the housing are not limited by the usage of the absorptive particles/dyes. Further, the percentage of the introduced absorptive dyes/particles may be precisely and flexibly controlled to adjust the housing properties. Additionally, because the absorptive particles/dyes are integrated in the housing, both the external anti-reflection and absorption layers/structures which may complicate the housing are not required. Reference will now be made in details to specific embodiment of the present invention. Examples of these embodiments are illustrated in the accompanying drawings. While the invention will be described in conjunction with these specific embodiments, it will be understood that the intent is not to limit the invention to these embodiments. In fact, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without at least one of these specific details. In other instances, the well-known portions are less or not described in detail in order not to obscure the present invention. Terahertz-gigahertz systems (THz system) in general require a specific housing designed to hold and/or connect their element(s). In general, the housing encloses a space and has at least one opening connecting the enclosed space and the exterior space, where different openings are separated from each other. For example, as shown in FIG. 1A, a THz image system 100 may have a cylindrical housing 101 and two lens 102/103 positioned separately inside the cylindrical housing 101. Hence, the THz waves 110 may be reflected off or transmitted through an object positioned on the left side of the cylindrical housing 101 then propagated through the left opening 104, the lens 101, the lens 102 and the right opening 105 in sequence to the image sensor 1002 positioned on the right side of the cylindrical housing 101, which means a THz image is formed by the THz waves 110 reflected off or transmitted through the object may be formed on the right side of the cylindrical housing 101. In another example, as shown in FIG. 1B, a THz communication system 106 may have two separated housings 107 which enclose an emitter 108 and a receiver 109 respectively. Hence, the operation of the emitter 108 and the receiver 109 may be protected from the interference and noise by the two housings 107 respectively, and the THz waves 110 emitted by the emitter 108 may propagate through the space between the two housing 107 and then into the receiver 109. The present invention greatly reduces both external and internal THz noise. More specifically, the present invention forms the housing by using the material(s) capable of reflecting almost none of the incident THz waves (even other EM waves) and absorbing almost all of the incident EM waves (including THz waves). The invention achieves the aforementioned desired properties by using at least one material which has a real part of the relative dielectric constant at about 1.0 and a non-negligible imaginary part of the relative dielectric constant. In this way, the Fresnel reflection at the housing surface is greatly reduced. In other words, the reflection of the THz waves (or other EM waves) incident to the housing may be negligible, but the absorption of the THz waves (and other EM waves) is significant. Therefore, the housing may effectively absorb the THz waves (and other EM waves) with minimal reflection, so that the THz waves propagating in the housing interior is not affected by external or internal noise. The absorption in the housing sidewall is a function of both the absolute value of the imaginary part of the relative dielectric constant of the housing material and the thickness of the housing sidewall, where the former defines the absorption rate and the latter determines the accumulative absorption. Therefore, to achieve the same attenuation amount, the higher the absolute value of imaginary elements of the relative dielectric constant, the less the required housing thickness. The reverse is also true. Just for example, an exemplary standard is that 30 dB attenuation may be achieved when the EM waves (or THz waves) propagate through a housing sidewall with thickness of several centimeters. Some embodiments achieves the aforementioned desired properties of the THz system housing by using foam materials because of its relatively low relative dielectric constant. One benefit of the usage of the foam material is that there are many kinds of commercial foam material having low relative dielectric constant close to about 1.0. Just for example, both the Expanded Polypropylene (EPP) and Styrofoam are two commercial materials having lower relative dielectric constant, and some special kinds of EPP and some special kinds of Styrofoam have relative dielectric constant about 1.0. Particularly, the invention only requires the low relative dielectric constant feature but not limits what kind of the foam material is used. Any existed, on-developed and to be appeared foam material may be used by the invention. Some embodiments achieves the aforementioned desired properties of the THz system housing by using the foam material doped with conductive additives, where the details of the foam material are equal to those discussed above. The benefit of the usage of the conductive additives is that these conductive additives may increase the absorption of the THz waves and/or other EM waves. Just for example, the conductive additives may be made of graphite or carbon, even may be made of sliver or other conductive material(s). Also just for example, the conductive additives may be the absorptive particles or the absorptive dyes, especially, the absorptive dyes and the absorptive particles have higher dielectric loss. Of course, not only both the size and the shape of the conductive additives are adjustable, also the ratio between the conductive additives and the foam material is adjustable to fine tune its absorption/reflection properties. Moreover, as discussed above, the adsorption coefficient and the thickness of the housing are dependent to each other, and the introduced amount of the conductive additives has a flexible range. In practice, the proposed invention is also related to the method of minimizing both the interference and the noise of a THz system housing, the method of minimizing both the noise and the interference of undesired stray of a THZ wave of a THz system housing, or other method(s) of the similar application(s). As shown in FIG. 2, each of these methods includes the following basic steps. First, as shown in block 210, identify the frequency range of the THz waves that the THz system housing is designed correspondingly. Then, as shown in block 220, select at least one material that is capable of effectively absorbing the THz waves with less reflections of the THz waves. Finally, as shown in block 230, form the THz system housing by using the selected material. The selection is essentially based on the electromagnetic property of the selected material(s). It should be able to fully absorb the THz waves and other EM waves from the outside environment, to absorb the noise generated inside the material, and to have lower relative dielectric constant for reducing reflection. Of course, whenever more than one kind of material is qualified, it is popular to form the THz system housing by using one only kind of the qualified materials, although it is also acceptable to form the THz system housing by using the mixture of at least two kinds of the qualified materials. Besides, although not necessary but beneficial, it is better that the selected material(s) possesses both higher mechanical strength and higher chemical stability. The higher mechanical strength allows the housing to hold and protect element(s) in the housing interior, and to have a solid structure with smaller deformation after the impact. Just for example, the elements may be the lens(es) and/or the sensors of the THz image system, also may be the emitter and/or the receiver of the THz communication system. The higher chemical stability allows the housing to be used in the more extreme environments. Just for example, the environmental variations include at least temperature, humidity, and others. In addition, when the housing material is a mixture of the foam material and the conductive particles/dyes, whether the conductive particles/dyes may be simply and uniformly introduced into the foam material is also a factor of the selection of the material(s) for forming THz system housing. One example of the present invention is a housing material which may effectively absorb at least the THz waves on the frequency range about from 90 to 96 GHz. This exemplary material is a conductive EPP which is the mixture of the EPP and the carbon particles, wherein the weight percentage of the carbon particles is about 13%˜15%. FIG. 3 illustrates the performance testing result of such exemplary material. As shown in FIG. 3, the absorption strength of such exemplary material is about 15 dB/cm for the three different frequencies: 90 GHz, 93 GHz and 96 GHz. Obviously, by using the exemplary material, the thickness of the housing may be reduced to only 3˜4 centimeters for about 50 dB attenuation. Of course, higher thickness of the housing is also acceptable to enhance the mechanical strength. Moreover, although not yet particularly illustrated herein, other experiments/simulations show that the mixture of the foam material (especially Expanded Polypropylene and Styrofoam) and the conductive particles (especially carbon particles and graphite particles) also may have essentially similar absorption strength over a large frequency range, such as 80˜300 GHz, 100˜500 GHz and 300˜550 GHz. These non-illustrated experiments/simulations also show that the weight percentage of the carbon particles also may be about from 0.1% to 3%, about from 1% to 5%, about from 3% to 9%, about from 7% to 13% or about from 10% to 15%. Indeed, the acceptable weight percentage of the absorptive dyes/particles is a function of some parameters, such as the density of the foam material, the relative dielectric constant of the foam material, and the thickness of the foam material, even the frequency range of the THz waves that a THz housing is designed for. Just for example, the higher the weight percentage of the carbon particles, the more the absorption of the THz waves (even other EM noise). And then, for achieving the same amount of attenuation, the required thickness of the housing is reduced. Furthermore, to further minimize the harmful Fresnel reflection at the interior sidewall of the housing, one more option of the present invention is that the interior sidewall of the housing may have no exposed elements that may introduce extra internal noise through scattering and reflection off sharp corners or high reflection surfaces. The interior sidewalls of the housing may also be either smooth or textured, and the only limitation is that the geometrical configuration of the interior sidewall will not cause extra internal noise through the interaction between the propagated THz waves and the interior sidewall. In addition, the details of the elements, such as pipelines and joints, are dependent on the details of the THz system, but the invention is nothing about such details. Note that the density of the foam material, such as EPP, is also adjustable. In general, the higher the density of the foam material, the less the air filled inside the foam material and then the higher the reflectivity and weight of the foam material. Hence, for some foam materials having higher density, the reflection of the THz waves may be increased. In such situation, a textured (or viewed as rough) interior sidewall of the THz system housing may increase the effective number of bounces (or viewed as the probability of multiple reflections) of the THz waves at the material interface, then causing both an increase in the absorption and a reduction in THz reflection simultaneously. Again, this also means that both the internal or external noise and interference may be reduced. Furthermore, although the above discussions are focused on the materials which may be used to form the Thz system housing to minimize the interference and the noise, the required electro-magnetic properties of such materials in order to minimize interference and noise are independent on the geometrical features of the THz system housing. In other words, the shape, size, and positioning of the present THz system housing are not limited in this invention. Therefore, in addition to the situation discussed above that the housing encloses a space where the THz waves may be propagated through, in other situations not particularly discussed hereabove, the present THz system housing also may be positioned in proximity to (but not enclosing) the THz waves, or even may be integrated with any element in the THz system. Hence, no matter how the THz system housing is configured, by using the materials discussed above to form the THz system housing, both the noise and the interference of a THZ wave may be minimized. Just for example, the contour of the THz system housing may be a hollow shell with opening(s), a cylindrical shell with opening(s), a polygon shell with opening(s), a columnar shell with opening(s), a curved surface with opening(s), a planer surface without opening, and other contours with/without opening(s). As a short summary, the present invention propose a THz system housing with particular material(s) being able to at least absorb the stray THz waves and to minimize reflection of the stray THz waves simultaneously. As shown in FIG. 4, the general concept of the proposed material(s) is that the real part and the absolute value of the imaginary part of relative dielectric constant is about 1.0 and large enough to induce high absorption, respectively; the general composition of the proposed material(s) is foam material, especially foam material with conductive additives; and some exemplary compositions of the proposed material(s) is the mixture of Expanded Polypropylene and carbon particles, the mixture of Expanded Polypropylene and graphite particles, the mixture of Styrofoam and carbon particles, and the mixture of Styrofoam and graphite particles. Variations of the methods, the devices, the systems and the applications as described above may be realized by one skilled in the art. Although the methods, the devices, the systems, and the applications have been described relative to specific embodiments thereof, the invention is not so limited. Many variations in the embodiments described and/or illustrated may be made by those skilled in the art. Accordingly, it will be understood that the present invention is not to be limited to the embodiments disclosed herein, can include practices other than specifically described, and is to be interpreted as broadly as allowed under the law. |
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summary | ||
053435087 | claims | 1. In a nuclear reactor fuel assembly having top and bottom nozzles and nuclear fuel rod spacer grids therebetween for supporting at least one nuclear fuel rod and at least one guide tube fastened to the top and bottom nozzles, a device for retaining a nuclear fuel rod spacer grid on the guide tube and the top and bottom nozzles comprising: a tubular retainer means having a first end and a second end and a lumen extending longitudinally therethrough; said retainer means having an upper portion located at said first end for retaining said spacer grid, and a lower portion located at said second end for retaining at least one of said guide tubes; said lower portion having an aperture communicating with said lumen whereby said guide tube is inserted through said lumen of said retainer means and a shoulder portion on said guide tube extends through said aperture to retain said lower portion of said retainer means between the shoulder of said guide tube and a surface of said bottom nozzle when said guide tube is attached to said nozzle, thereby retaining said spacer grid on said guide tube and bottom nozzle, said lower portion having a flattened portion and an enlarged portion, said flattened portion mating with the guide tube, and said enlarged portion being retained between the shoulder portion and a surface of said bottom nozzle. a bottom nozzle; at least one guide tube wherein a lower end of said guide tube has an attachment portion for attachment to said bottom nozzle and a shoulder positioned between the attachment portion and an upper end of said guide tube; a spacer grid assembly for supporting at least one nuclear fuel rod and said at least one guide tube; a tubular retaining means having a first end and a second end wherein said first end retains said spacer grid and said second end has an aperture for receiving and retaining said shoulder of said guide tube; and a top nozzle for attachment to an upper portion of said guide tube, wherein said second end of said tubular retaining means has a flattened portion and an enlarged portion, said flattened portion mates with said guide and said enlarged portion is retained between said shoulder and a surface of said bottom nozzle. 2. The device according to claim 1 wherein said upper portion comprises a plurality of leg segments. 3. The device according to claim 2 wherein said legs retain said spacer grid by means of spot welding. 4. The device according to claim 4 wherein said plurality of legs is four legs. 5. The device according to claim 2 wherein said lower portion has two flattened sections opposite each other and two enlarged sections interposed there between. 6. The device according to claim 6 wherein said aperture comprises two apertures located one each on said flattened sections. 7. The device according to claim 2 wherein said retaining means is made from Inconel. 8. The device according to claim 2 wherein said retaining means is made from steel. 9. A skeleton structure for a nuclear reactor fuel assembly comprising in combination: 10. The device according to claim 9 wherein said first end comprises a plurality of leg segments. 11. The device according to claim 10 wherein said legs retain said spacer grid by means of spot welding. 12. The device according to claim 11 wherein said plurality of legs is four legs. 13. The device according to claim 9 wherein said second end has two flattened sections opposite each other and two enlarged sections interposed therebetween. 14. The device according to claim 13 wherein said aperture comprises two apertures located one each on said flattened sections. 15. The device according to claim 9 wherein said retaining means is made from Inconel. 16. The device according to claim 7 wherein said retaining means is made from steel. |
claims | 1. A charged particle beam apparatus comprising:a charged particle beam column configured to irradiate a charged particle beam to a first region and a second region of a sample, the second region included in the first region;a controller configured to control the charged particle beam column to irradiate the charged particle beam to the first region and the second region of the sample, the first region including a plurality of first pixels at a first pixel interval, each of the first pixels including a first predetermined number of first sub-pixels, the second region including a plurality of second pixels at a second pixel interval different from the first pixel interval, each of the second pixels including a second predetermined number of second sub-pixels, wherein the controller is configured to control the charged particle beam column to irradiate the charged particle beam to each of the first sub-pixels at the first pixel interval for the first region and to irradiate the charged particle beam to each of the second sub-pixels at the second pixel interval for the second region;a secondary electron detector configured to detect first secondary electrons for each of the first sub-pixels generated by irradiating the charged particle beam to each of the first sub-pixels at the first pixel interval for the first region, to generate a first signal of the first secondary electrons for each of the first sub-pixels, to detect second secondary electrons for each of the second sub-pixels generated by irradiating the charged particle beam to each of the second sub-pixels at the second pixel interval for the second region, and to generate a second signal of the second secondary electrons for each of the second sub-pixels; andan image forming unit configured to form first sub-pixel images by using the first signal, the number of the first sub-pixel images being the first predetermined number, to generate a first image by synthesizing the predetermined number of the first sub-pixel images, and to form second sub-pixel images by using the second signal, the number of the second sub-pixel images being the second predetermined number, to generate a second image by synthesizing the predetermined number of the second sub-pixel images. 2. The charged particle beam apparatus according to claim 1, wherein the second region is a correction mark detection region that includes a position at which a correction mark is provided. 3. The charged particle beam apparatus according to claim 1, wherein the controller controls the charged particle beam column to perform an irradiation process of irradiating the charged particle beam once for each pixel region designated in a bitmap for multiple times while displacing an irradiation position of the charged particle beam within each pixel region for each of the irradiation process for each pixel. 4. The charged particle beam apparatus according to claim 3,wherein the controller operates to:control the charged particle beam column to perform scanning of a drift correction region with a first pixel pitch that is smaller than a second pixel pitch of the bitmap;calculate a first amount of drift correction based on information obtained through the scanning; andperform drift correction by converting the first amount of drift correction into a second amount of drift correction for the second pixel pitch of the bitmap. 5. The charged particle beam apparatus according to claim 3, wherein when a field of view of the bitmap is set to FOV_A and a field of view having an amount, by which the irradiation position is displaced, the same with a pixel size is set to FOV_B, the controller controls the charged particle beam column to perform the irradiation process for at least (FOV_A/FOV_B) by (FOV_A/FOV_B) times in total within the first region. 6. A processing method of a sample including a first region and a second region, the second region included in the first region, the method comprising:controlling a charged particle beam column to irradiate a charged particle beam to the first region and the second region of the sample, the first region including a plurality of first pixels at a first pixel interval, each of the first pixels including a first predetermined number of first sub-pixels, the second region including a plurality of second pixels at a second pixel interval different from the first pixel interval, each of the second pixels including a second predetermined number of second sub-pixels;irradiating the charged particle beam to each of the first sub-pixels at the first pixel interval for the first region by controlling the charged particle beam column;irradiating the charged particle beam to each of the second sub-pixels at the second pixel interval by controlling the charged particle beam column;detecting first secondary electrons for each of the first sub-pixels generated by irradiating the charged particle beam to each of the first sub-pixels at the first pixel interval for the first region;generating a first signal of the first secondary electrons for each of the first sub-pixels by detecting first secondary electrons;detecting second secondary electrons for each of the second sub-pixels generated by irradiating the charged particle beam to each of the second sub-pixels at the second pixel interval for the second region;generating a second signal of the second secondary electrons for each of the second sub-pixels by detecting second secondary electrons;forming first sub-pixel images by using the first signal, the number of the first sub-pixel images being the first predetermined number;generating a first image by synthesizing the predetermined number of the first sub-pixel images;forming second sub-pixel images by using the second signal, the number of the second sub-pixel images being the second predetermined number; andgenerating a second image by synthesizing the predetermined number of the second sub-pixel images. |
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043705553 | description | Referring now to the drawings, FIG. 1 shows an irradiation device which may advantageously be used in radiotherapy. This apparatus comprises a fixed support 1, an arm 2 movable about an axis X--X, an irradiation device 3 removably mounted on the mobile arm 2, a precollimator 13 and a secondary collimation device 4 of axis Y--Y. The collimator 4 is removably fixed on the mobile arm 2 by means of a support plate 15 fixed by screws 16. FIG. 2 shows a transverse section through the irradiation device 3 of FIG. 1. This irradiation device comprises a bowl-shaped container 5 provided with a flange 6. This container 5 may be removably fixed on the arm 2 by means of screws passing through said flange 6. A fixed shielding 7 for biological protection is placed inside the container 5. The shielding 7 at least partly surrounds a biological protection disc 8 rotatable about an axis passing through its centre C. The disc 8 is provided with a housing 9 adapted to receive a radioactive source. This housing 9 opens outwardly of the disc 8 so as to allow the beam of photons delivered by the radioactive source 10 to pass. The fixed shielding 7 is composed of a block 7a of depleted uranium, embedded in a block 7b of lead. The block 7a of depleted uranium surrounds the source of photons when the latter is in storage position shown in dashed and dotted lines in FIG. 2. The capacity of the uranium to absorb the radiation being about twice that of lead, the use of a block of depleted uranium ensures a satisfactory biological protection, whilst reducing the weight and size of the irradiation device according to the invention. In the embodiment shown in FIG. 2, an optical fibre 11, adapted to transmit a light flux, is disposed in the disc 8. The optical fibre 11 opens at one of its ends 11a, so-called receiver end, opposite a light source 12 fixed outside the container 5 and at its other end 11b, called emitter and, along axis Y--Y. Each of the receiver and emitter ends is held via means for adjusting their positioning. The optical device 12 focuses a ray of light on the receiver end of the optical fibre 11, this optical device 12 consisting for example of a light source associated with a reflector for focusing its light beam. Light ray should be understood in the present specification to mean an electromagnetic radiation in the visible part of the spectrum. The passage provided in the disc 8 for the optical fibre 11 is substantially rectilinear in shape, except for its ends. The emitter and receiver ends of the fibre 11 preferably determine an angle at the centre equal to 90.degree.. Such an arrangement renders the irradiation of the optical fibre in the course of functioning of the apparatus minimum. In FIG. 2, .alpha. designates the angle of rotation of the disc 8 which makes it possible to pass from the position of irradiation of the radioactive source 10 shown in solid lines, to the storage position of this same source, shown in dashed and dotted lines. The value of this angle .alpha. is 110.degree.. This value makes it possible to limit the rate of radiation leaks when the radioactive source 10 is in storage position, as well as the height of the biological protection body 7 surrounding the disc 8. FIG. 3 shows a longitudinal section through the irradiation device shown in FIG. 2. This view particularly shows the positionings of the disc 8 ensuring a rapid alternance of the positions of irradiation and of storage, with locking of the disc in position of irradiation and return thereof into storage position in case of a safety action or an electrical failure. The disc 8, mounted on bearings 15, rotates with the shaft 16. A clutch disc 18 is mounted at the end of the shaft 16. A pinion 20, mounted to rotate freely on the shaft 16, may be coupled to this shaft by means of the electromagnetic clutch 22. When the electromagnetic clutch 22 is supplied, the shaft 16 is rotated by the pinion 24 of the gear-down motor 26. On the other hand, the shaft 16 rotates, for example by means of a keying, with a pinion 30 driving a rack 32 which is intended to define the positions of irradiation and of storage of the disc 8. Also shown schematically in dashed and dotted lines is the mobile arm 2 on which the device of the invention is mounted, as well as the device for maintaining the position of the disc 8, designated by reference 36 and, finally, the device 38 for displaying the position of the disc. These devices will be described in greater detail with reference to FIGS. 4, 5 and 6. FIG. 4a shows a view in the direction of arrow IV of FIG. 3 of the device shown therein. This Figure particularly shows the device 41 for detecting the position of the disc 8. The rack 32 may be displaced by a gear-down motor between a first position, shown in solid lines in FIG. 4a, for which it is in abutment against an electro-magnetic suction member 36 whose position is adjustable by means of a nut 39, and a second position, shown in dashed and dotted lines in FIG. 4a, for which the rack 32 is in the vicinity of a buffer unit 40 whose action is adjusted by the positioning of rod 42. An electrical contact 41 controls the stoppage of the electro-magnetic clutch 22, when the rack 32, by being displaced in the direction of arrow f, comes to a short distance from the electro-magnetic member 36. Furthermore, to allow the disc 8 to return automatically into storage position, a spring 44 is interposed between a wall of the rack 32 and a fixed wall fast with the container 5, so that the disc automatically passes in the direction of arrow F from the position of irradiation to the position of storage if a safety device is triggered off or if there is an electrical failure. A second electrical contact 46 actuated by finger 45 enables the end-of-stroke position of the rack 32 when it is in the vicinity of the buffer device 40 to be determined. Finally, a third electrical contact 48 enables the beginning of irradiation to be determined. In fact, the beginning of irradiation is determined by the moment when the radioactive source 10 begins to appear in the precollimator. This position of the source, designated by reference 10a, has been shown in FIG. 4b. Finally, FIG. 4a shows in dashed and dotted lines a second position 10b of the radioactive source, which corresponds to the radioactive source 10 going slightly beyond the position of the axis Y--Y of the collimation device. The purpose of this arrangement is to allow compensation of the inevitable clearance of the rack and drive pinion. In FIG. 4b, reference 5 represents the precollimation device with, in addition, shown in dashed and dotted lines, a secondary collimation device 50 associated with the irradiation head. FIGS. 5 and 6 show in detail the system allowing the return by force of the disc 8 in the case of incident. This device, generally designated by reference 38, is composed of a dog 60 made fast with the shaft 16 by means of a keying. The dog 60 bears a dog finger 62. The rotation of the dog 60 is limited by two stops 64 and 66. The stop 64, which is made of rubber, corresponds to irradiation position. The stop 66 corresponds to the position of storage of the radioactive source 10. Furthermore, a disc 68 is fast with the dog 60. The disc 68 comprises coloured zones corresponding to the different positions of the disc. Zone 68a corresponding to storage position is green and zone 68c corresponding to the position of irradiation is red. A lever 70, whose angular movement is limited, is idly mounted on the end of the shaft 16. This lever allows the control by force of the disc 8 by means of the dog 60. It will be noted that the shaft 16 can be driven by this device only in one direction, this direction corresponding to the passage from the position of irradiation to the position of storage. FIG. 5 shows in dashed and dotted lines the positions 70a and 70b of the lever 70 which correspond respectively to the positions of irradiation and of storage. An outer indexing means 72 located opposite the disc 68 makes it possible to determine the position of this disc due to the coloured zones thereof. The irradiation device which has just been described has the important advantage of also serving as radioprotection cask for transporting the radioactive source. This makes it possible to adjust the source in the factory, at the moment of manufacture and to change the radioactive source simply, without calling upon specialised man-power. To this end, an irradiation device provided with a previously adjusted new source, ready for use, is transported to the site of use, the irradiation device acting as a radioprotection cask. |
041815726 | abstract | A closure head for a nuclear reactor includes a stationary outer ring integral with the reactor vessel with a first rotatable plug disposed within the stationary outer ring and supported from the stationary outer ring by a bearing assembly. A sealing system is associated with the bearing assembly to seal the annulus defined between the first rotatable plug and the stationary outer ring. The sealing system comprises tubular seal elements disposed in the annulus with load springs contacting the tubular seal elements so as to force the tubular seal elements against the annulus in a manner to seal the annulus. The sealing system also comprises a sealing fluid which is pumped through the annulus and over the tubular seal elements causing the load springs to compress thereby reducing the friction between the tubular seal elements and the rotatable components while maintaining a gas-tight seal therebetween. |
abstract | A steam generator for a nuclear reactor comprises plenums proximate with a first plane, wherein the first plane intersects a bottom portion of a riser column of a reactor vessel. The steam generator may further comprise plenums proximate with a second plane, approximately parallel with the first plane, wherein the second plane intersects a top portion of the riser column of the reactor vessel. The steam generator may further include a plurality of steam generator tubes that convey coolant from a plenum located proximate with the first plane to one of the plenums proximate with the second plane. |
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042696593 | abstract | A neutron generator utilizing relatively small plasma pulses which are constantly re-created in the reaction chamber in a conventional manner by injecting pulses of a fuel such as deuterium or deuterium and tritium, in either a gaseous or small solid pellet form, ionizing the same and compressing the same to form a plasma, while surrounding the plasma with a working gas such as hydrogen under pressure moving longitudinally through the chamber and carrying the plasma with it. As each pulse of plasma is dissipated into the working gas and carried out of the chamber, this completes its life cycle. New cycles are initiated in an appropriate manner to maintain an orderly and nearly continuous energy addition and extraction to and through the background gas. |
051805421 | summary | This invention relates to a container, and more particularly to a container for material contaminated with a toxic substance or with a radionuclide. In the nuclear industry, material such as mechanical components, rubber gloves, or liquids such as oils can become contaminated with radionuclides, for example, iodine 129, uranium, radium 226, and thorium 232. It is the normal practice to place such material in suitable containers, and subsequently to store the containers in specially designed vaults or caves. In order to make more effective use of the space in the vaults or caves a high packing of the contaminated material is desirable. According to one aspect of the present invention, in a container for material contaminated with at least one toxic material or a radionuclide, there is provided highly absorbent cementitious material for absorbing liquid in the container. The container may be adapted to receive compacted receptacles containing the contaminated material, and the liquid may be leakage from said compacted receptacles. Preferably, the cementitious material has a voidage of at least 40% by volume. Desirably, the cementitious material comprises cement hydrated beyond 25% thereof. The cementitious material may be made by a method comprising forming a cement slurry and a bentonite clay slurry, subsequently mixing together the cement slurry and the clay slurry, and heating the resulting mixture at a temperature such as to remove capillary water from the mixture without to a substantial extent dehydrating any hydrated cement. Preferably, the temperature is at least 50.degree. C. Advantageously, the mixed cement slurry and clay slurry has a water/solids ratio of about 1.5/1. The cement may comprise typical Portland cement (OPC). The water absorption capacity of cementitious material depends inter alia on the internal porosity of the material. Hence, to produce a cementitious material having a relatively high absorption capability it is necessary to use a high water content in its preparation. Whilst the maximum water/cement ratio that can be achieved using a low shear system is about 0.45, a water/solids ratio up to about 1.5/1 can be achieved by the addition of a suitable clay, viz: bentonite clay. When such a clay/cement/water mixture is heated to drive out the capillary water without dehydrating any hydrated cement to a substantial extent, an internal porosity of up to 75% by volume may be achieved. Provided that the cement has hydrated beyond 25% thereof, the ratio of hydrated to unhydrated cement should have little influence on the absorption capacity of the dried cementitious material in the short term, on the assumption that the water in the setting cement material is evenly distributed. |
05999889& | claims | 1. An antenna performance monitor comprising: an antenna sensor for coupling to an antenna radiating a radio frequency signal, wherein said antenna sensor generates signals Vm and Im representative of an input voltage and an input current respectively of said antenna; an A/D converter coupled to said antenna sensor for digitizing samples of said signals Vm and Im; and a data processor coupled to said A/D converter for generating outputs representative of an impedance magnitude and an impedance phase angle of said antenna substantially concurrently for each frequency of said radio frequency signal. a bandpass filter coupled to said A/D converter having a center frequency substantially equal to a midpoint of said radio frequency signal for bandpass filtering said samples of said signals Vm and Im; a mixer coupled to said bandpass filter for forming a complex product of said samples of said signals Vm and Im with a signal representative of each frequency respectively in said radio frequency signal; a lowpass filter coupled to said mixer for generating a filtered complex baseband of said complex product; a decimator coupled to said lowpass filter for generating a resampled complex baseband of said filtered complex baseband at a reduced sample rate; a complex FFT transform coupled to said decimator for generating complex spectral coefficients of said signals Vm and Im from said resampled complex baseband; an averager coupled to said complex FFT transform for generating averaged complex spectral coefficients of said signals Vm and Im from said spectral coefficients; a voltage magnitude function coupled to said averager for generating a voltage magnitude of said averaged complex spectral coefficients for said samples of said signal Vm; a current magnitude function coupled to said averager for generating a current magnitude of said averaged complex spectral coefficients for said samples of said signal Im; a magnitude divide function coupled to said voltage magnitude function and said current magnitude function for generating the quotient of said voltage magnitude divided by said current magnitude for a plurality of frequencies within said radio frequency signal; a voltage divide function coupled to said averager for generating a voltage quotient of each real part of said averaged complex spectral coefficients for said signal Vm divided by its corresponding imaginary part; a current divide function coupled to said averager for generating a current quotient of each real part of said averaged complex spectral coefficients for said signal Im divided by its corresponding imaginary part; a voltage arctangent function coupled to said voltage divide function for generating a voltage phase signal from each said voltage quotient; a current arctangent function coupled to said current divide function for generating a current phase signal from each said current quotient; and a difference function coupled to said voltage arctangent function and said current arctangent function for generating the difference of said voltage phase signal minus said current phase signal for said plurality of frequencies in said radio frequency signal. 2. The antenna performance monitor of claim 1 wherein said antenna sensor comprises a capacitive voltage divider and a current transformer. 3. The antenna performance monitor of claim 1 wherein said A/D converter comprises anti-aliasing filters. 4. The antenna performance monitor of claim 1 wherein said A/D converter comprises a digitizer having a sampling rate of at least twice a highest frequency of said radio frequency signal. 5. The antenna performance monitor of claim 1 wherein said antenna sensor is coupled to said A/D converter by a double shielded coaxial cable. 6. The antenna performance monitor of claim 1 wherein said antenna sensor is coupled to said A/D converter by a fiber optic link. 7. The antenna performance monitor of claim 1 wherein said data processor comprises the following functions: |
claims | 1. A mechanism for inspecting a surface of a sample, comprising:an electro-optical inspection apparatus comprising:an electromagnetic wave source for irradiating the sample surface with electromagnetic waves;an electron source consisting of an electron gun for emitting an electron beam in a direction which is not perpendicular to the sample surface; andan EXB deflector for deflecting the electron beam emitted from the electron source to irradiate the sample surface therewith in a direction which is perpendicular to the sample surface, and passing photoelectrons emitted from the sample surface when it is irradiated with the electromagnetic waves, and electrons from the sample surface when it is irradiated with the electron beam;a detector for detecting the photoelectrons and electrons, respectively which are passed through the EXB deflector to output electric signals associated with the detected photoelectrons and electrons, respectively; anda processing unit for processing the signals output from the detector and forming an image associated with the sample surface. 2. A mechanism according to claim 1, wherein the electro-optical inspection apparatus further comprises an objective lens system comprising at least two lenses located between the sample surface and the EXB deflector, and an enlarging lens system comprising at least two lenses and located between the EXB deflector and the detector. 3. A mechanism according to claim 1, wherein the electro-optical inspection apparatus further comprises an objective lens system comprising at least two lenses located between the sample surface and the FXB deflector, and two enlarging lens systems each comprising at least two lenses and located between the EXB deflector and the detector. 4. A mechanism according to claim 1, wherein the electro-optical inspection apparatus is an image projection type inspection apparatus. 5. A mechanism according to claim 1, wherein a diameter of the electromagnetic waves irradiated on the sample surface is in a range of about 10 μm-10 mm. 6. A mechanism according to claim 1, a diameter of a field of view of the electron beam is about 10 μm-10 mm. 7. A mechanism according to claim 1, further comprising a control electrode to supply a voltage to control a field strength on the sample surface, to thereby reduce aberration of the photoelectrons or electrons emitted from the sample surface. 8. A mechanism according to claim 1, wherein the sample is at least one of a semiconductor wafer with a resistive film thereon, a photo-mask and reticle-mask. 9. A mechanism according to claim 1, wherein the electromagnetic wave source irradiates the sample surface with the electromagnetic waves in a direction which is not perpendicular to the sample surface. 10. A method of inspecting a surface of a sample, comprising:actuating one or both of the electromagnetic wave source and the electron source in accordance with a kind of the sample;irradiating the sample surface with one or both of the electromagnetic waves and the electron beam which are/is emitted from the actuated source;detecting either of photoelectrons and electrons emitted from the sample surface by the detector to output the signal; andprocessing the signal by the processing unit to obtain an image of the sample surface. 11. A method according to claim 10, wherein the sample surface is coated with a resistive film. |
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description | The invention relates to an apparatus and method for inspecting a sample of a specimen by means of an electron beam. In particular, the invention relates to an apparatus and method for inspecting a thin slice of a semiconductor wafer. For progress in microelectronics, it is important to have tools for inspecting microelectronical structures on a chip or wafer with ever increasing spatial resolution. At the same time, it is important to decrease the costs of such inspections in order for the industry to fabricate devices of ever increasing complexity at low costs. A prominent tool for such inspections is the scanning electron microscope (SEM). The SEM uses a primary electron beam as a means to probe the surface structure of a given specimen. An interaction of the primary electron beam with the specimen causes electrons to be released into a backward direction with respect to the primary electron beam where they are detected by an electron detector. By scanning the primary electron beam across the specimen and determining the rate of the released electrons at each scan position, an image of the surface of the specimen with high spatial resolution is obtained. The spatial resolution of the image is essentially given by the size of the beam focus. Due to the progressing miniaturization of integrated circuits, it has become important to study the crystal and layer structure of an integrated circuit structure below the surface of the wafer. This is usually done by inspecting a cross sectional thin slice (membrane) from the wafer or chip by means of a transmission electron microscope (TEM). With a TEM, a spatial resolution down to the atomic scale can be achieved, which is sufficient to analyze crystal structures and layers which may be only a few atomic layers thick. The TEM is characterized in that it detects electrons which have been transmitted through the specimen. Therefore, the detector of a TEM is positioned behind the specimen. Further, instead of using a scanning unit for generating an image, a TEM comprises a complex electron beam optics between the detector and the specimen to project and magnify an image of the specimen structure onto the detector. In order to capture the image of the specimen structure with high precision, the TEM detector needs to be highly segmented e.g. like a CCD. The preparation and manipulation of a membrane of a wafer or chip for a TEM inspection represents a major complication because the use of a TEM requires that the membrane is sufficiently thin (typically 10 to 100 nm thickness) in order for the primary electrons to be transmitted through the sample. Fabrication and handling of such thin membranes is no easy task. In recent years, however, the use of focussed ion beam devices (FIB) for etching a membrane from a wafer has been established which significantly simplifies the sample preparation, see e.g. U.S. Pat. No. 6,188,068 by F. Shaapur and R. Graham, or B. Köhler and L. Bischoff “Entwicklung einer neuen Technologie zur Probenpräparation für die Transmissions-Elektronenmikroskopie (TEM) auf der Basis der Ionenfeinstrahlbearbeitung” from “Wissenschaftlich-Technische Berichte”, FZR-329, August 2001, ISSN 1437-322X, Forschungszentrum Rossendorf. Despite the progress in TEM sample preparation and TEM inspection, it is still complicated, expensive and time-consuming to carry out a TEM inspection because of the many steps needed for each measurement. For example, for a TEM integrated circuit failure analysis, it is required to (a) determine the position of the defect on the wafer or chip surface; this step is usually performed by an SEM inspection; (b) preparing a cross sectional membrane from the wafer at the defective position; this step is usually performed by a FIB; the FIB may be combined with a second SEM in order to observe and control the etching of the wafer; (c) moving the membrane into the TEM, and (d) inspecting the membrane by means of the TEM. Each of the steps is time-consuming and has its own pitfalls. E.g., step (b) is highly critical because of the mechanical fragility of the very thin membrane; step (c) is critical because of a possible pollution of the membrane in the atmospheric environment during transport; and step (d) is expensive because the TEM itself is an expensive device, is difficult to operate which requires experts that can operate the TEM and evaluate the measurements. Further, to carry out the steps (a) through (d) for a TEM membrane inspection requires an SEM, a FIB or FIB/SEM system, and a TEM, which together are expensive. Further, SEM, FIB and TEM each require a high quality vacuum for operation. Providing such a vacuum each time when a wafer is taken in and out of the respective device is time-consuming. For these reasons, inspections of cross sectional thin slices of a specimen, in particular the inspection of membranes of a wafer or chip, are expensive. Cross sectional inspections for a failure analysis of integrated circuits on a regular basis are therefore not possible. It is therefore a first aspect of the present invention to provide an apparatus and method for inspecting a sample of a specimen which does not have the above mentioned disadvantages. It is a further aspect of the present invention to provide an apparatus for inspecting a cross sectional slice (membrane) of a wafer in a cost- and time-saving way, to make it available in high-throughput production lines. It is a further aspect of the present invention to provide an apparatus for inspecting a membrane which reduces wafer handling problems and exposure of the membrane to an atmospheric environment. It is a further aspect of the present invention to provide an apparatus for inspecting a membrane of a wafer which can be integrated into existing semiconductor fabrication lines in an efficient way. These and other problems are solved by the apparatus according to claim 1 and by the method disclosed in claim 15. Further aspects and improvements of the invention are disclosed in the description, the dependent claims and the drawings. The present invention includes an apparatus for inspecting a sample of a specimen by means of an electron beam comprising a vacuum chamber, an ion beam device for generating an ion beam used for etching a sample from the specimen within said vacuum chamber; an electron beam device having a scanning unit for scanning the electron beam across said specimen within said vacuum chamber; said electron beam device having a first detector positioned to detect electrons that are released from the specimen in a backward direction with respect to the direction of the electron beam; said electron beam device having a second detector positioned to detect electrons that are released from the sample in a forward direction with respect to the direction of the electron beam; and separation means within said vacuum chamber to separate the sample from the specimen for the inspection of the sample by means of the second detector. With the apparatus according to claim 1, it is possible to inspect the surface of a specimen by means of the electron beam device and the first detector (SEM mode), to etch a sample from the specimen by means of the ion beam device (FIB mode) and to inspect the sample of the specimen by means of the second detector (transmission mode), all within the same vacuum chamber. This way, it is possible that the sample of the specimen remains in a vacuum until its inspection is finished. As a consequence, measurements of the sample are not distorted by a pollution layer which otherwise, during transport in an atmospheric environment, would have been formed on the sample. Further, with a common vacuum chamber, time-consuming venting and evacuation procedures between a SEM inspection, FIB etching and transmission mode inspection are eliminated. Further, with the apparatus according to claim 1, no expensive TEM with its complex magnification optics and imaging detector is needed for a transmission imaging. Instead, the inspection of the sample in the transmission mode is carried out by the electron beam device in combination with the second detector. The electron beam device according to claim 1 in combination with the second detector may not achieve a spatial resolution as high as a TEM. However, depending on the electron beam spot size and the thickness of the sample, a spatial resolution of 1 nm is still achievable, which often is sufficient for a failure analysis. (see e.g. L. Reimer: “Scanning Electron Microscopy, Physics of Image Formation and Microanalysis”, Chapter 8.4, Springer Verlag; E. Coyne “A working Method for adapting the (SEM) Scanning Electron Microscope to Produce (STEM) Scanning Transmission Electron Microscope Images” Proceedings from the 28th International Symposium for Testing and Failure Analysis, 3-7 Nov. 2002, Phoenix, Ariz.; or W. E. Vanderlinde “STEM (scanning transmission electron microscopy) in a SEM (scanning electron microscope) for Failure Analysis and Metrology”, Proceedings from the 28th International Symposium for Testing and Failure Analysis, 3-7 Nov., 2002, Phoenix Ariz.). In addition, even though a TEM may achieve a higher spatial resolution than a scanning transmission electron microscope, scanning of the electron beam makes it possible to create an X-ray image of the sample of the specimen by providing an additional X-ray detector which detects X-rays during the scan. The X-ray image carries information not only about the structural shape but also about the atomic material distribution in the sample of the specimen. This information can be important for many applications, in particular for an integrated circuit analysis. Further, through the presence of the first and the second detector, it is possible to perform a high resolution imaging of the sample of the specimen with electrons released in a backward direction (i.e. secondary or backscattered electrons) in parallel to a transmission mode measurement. Due to the thin sample thickness, the spatial resolution of the “backward released electron” image is superior to the spatial resolution of the inspection on the specimen. Further, the apparatus according to claim 1 dramatically saves costs compared to the previously known equipment needed for an inspection of a membrane of a wafer, which had to include an SEM, a FIB with an SEM and a TEM. With the apparatus according to claim 1, the same operations can be performed having only an SEM with an additional second detector and a FIB. The multiple use of the electron beam device saves considerable purchasing costs. Further, for the apparatus according to claim 1, vacuum equipment for only one vacuum chamber instead of two or three vacuum chambers is needed. In particular, the operation of an SEM and its second detector is much easier than a TEM with its sophisticated imaging beam optics and imaging detector. The easy handling of the apparatus according to claim 1 facilitates a high degree of automation, which is especially useful in a high-throughput semiconductor fabrication line. Further, the apparatus according to the invention is characterized in that it is easily integrated into a given semiconductor processing line where SEMs are needed anyway for non-destructive inspections during the fabrication. By substituting such an SEM by the apparatus according to the invention, an inspection of membranes of wafers being processed in the production line is made available at comparably low costs. Low costs and high throughput facilitate cross sectional sample inspections in the fabrication line on a regular basis which helps to dramatically improve the quality control. The present invention further includes a method for inspecting a sample of a specimen by means of an electron beam comprising the steps as described in claim 15, that is: a) providing an apparatus having a vacuum chamber, an ion beam device to generate an ion beam and an electron beam device to generate an electron beam; b) introducing the specimen into the vacuum chamber; c) irradiating the specimen in the vacuum chamber by means of the electron beam; d) etching the sample from the specimen in the vacuum chamber by means of the ion beam; and e) irradiating the sample of the specimen in the vacuum chamber by means of the electron beam. With the method, it is possible to locate a defect on a wafer (SEM mode), to fabricate a membrane from the wafer (FIB mode) and inspect the membrane by means of transmitted electrons (transmission mode) with only one electron beam device and only one ion beam device. This way, a surface image and a complementary cross sectional image of a defective region of a integrated circuit can be obtained in a time and cost efficient way. In addition to the low costs, compared to previously known TEM inspection systems, the method according to claim 15 can be used to save time by carrying out the inspection cycle of the steps c) to e) of claim 15 in vacuum. This eliminates delays due to the repeated venting and evacuation procedures which are required for loading and unloading previously known SEMs, FIBs and TEMs. In the description of the detailed embodiments below, the numbers refer to the enclosed FIGS. 1a to 1d, 2 and 3. However, the figures only represent particular, non-limiting embodiments of the invention which only have the purpose of being illustrative examples. The description below, even though it makes reference to the figures, is to be understood in a broad sense and includes any deviation from the described embodiments which is obvious to a person skilled in the art. Generally, the apparatus 10 according to the invention is meant to be used for the inspection of any sample 12 of a specimen 14 which is suitable for transmission microscopy inspection. Preferably, the specimen 14 is a solid substrate like, e.g., a semiconductor wafer or chip, and, preferably, the sample 12 thereof is a cross sectional thin slice of the wafer or chip. For such an inspection, the inspection of the wafer 14 with the electron beam device 30 using the first detector 36 results in an image of the surface of the wafer 14 (SEM mode), e.g. to locate a defect on the structured surface of the wafer, while an inspection of the cross sectional thin slice 12 with the electron beam device 30 using the second detector 40 results in an image of the cross sectional structure of the wafer 14 (transmission mode). For the sake of simplicity, below, without being limited to such samples, the cross sectional thin slice 12 will be named “membrane” because of its elasticity and its fairly thin sheet-like shape. Preferably, the membrane 12 is fabricated from the wafer 14 in a region where the wafer has been inspected by a previous electron beam surface inspection with the first detector 36. This way, the image obtained from the membrane and the image obtained from the wafer surface can be combined to a have complementary information of that region of the wafer. Preferably, the membrane has a thickness in the range of 5 to 500 nm and even more preferred, in the range of 10 nm to 100 nm. This way, the membrane 12 can be inspected by the electron beam device by means of the second detector 40 (transmission mode) at typical SEM electron beam energies of 5 to 50 keV (typically, energies up to 30 keV are used, but some manufacturers offer devices with 50 keV). The vacuum chamber according to the invention is intended to provide a continuous vacuum during the irradiation of the wafer 14 by means of the electron beam device 30 (SEM mode), during the etching the membrane 12 from the wafer 14 by means of the ion beam device 20 (FIB mode) and during the irradiation of the membrane 12 by means of the electron beam device 30 (transmission mode). Preferably, the vacuum is maintained during the time between the three operational modes. In this case, the inspection of the membrane 12 and the wafer 14 is carried out without any of the two having to be in contact with the external environment. This greatly improves the reliability of the measurements. Typically, the vacuum chamber is made to provide a vacuum in the region of the specimen which is better than 10−3 mbar, preferably better than 10−5 mbar. The better the vacuum, the better the imaging performance of the electron beam device 30 and the less the pollution of the membrane 12. Further, preferably, the vacuum chamber is connected with the ion beam device 20 and/or electron beam device 30 in order to provide a hermetic vacuum for the electron beam 34 and the ion beam 22 on their way to from their respective beam sources to the common vacuum chamber 18. The ion beam device 20 is used to generate an ion beam 22 for etching a sample 12 from the specimen 14. Severing a sample 12 from a specimen 14 by means of an ion beam 22 has become a standard procedure (see e.g. U.S. Pat. No. 6,188,068 B1, column 3, line 49 to column 5, line 12). The focussed ion beam of the focussed ion beam device (FIB), as described in U.S. Pat. No. 6,188,068, is used to remove wafer material with high lateral spatial resolution in order to “chisel” a thin cross sectional membrane from the wafer. Preferably, the ion beam device 20 according to the invention is equipped with a mechanism, e.g. an ion beam deflector, to adjust the landing angle on the specimen. This greatly improves the flexibility for using the ion beam as a knife that shapes the membrane and cuts it off from the wafer in a desired shape. Alternatively, the specimen holder 50, which holds the specimen or wafer, is tiltably connected underneath the ion beam device in order to provide adjustable landing angles for the ion beam 22 on the wafer to chisel the membrane 12 from the wafer 14. Preferably, the ion beam source 56 generates an Ga-ion beam. The electron beam device 30 according to the invention preferably comprises at least one electron beam source 54 to generate an electron beam 34. The electron beam source 54 may be any of the electron beam sources usually used for electron microscopes, e.g. a thermionic tungsten hairpin gun, or one of the many types of field emission electron guns known in the art. Preferably, the electron beam device 30 includes beam optical components to focus the electron beam onto the specimen 14 in order to increase the spatial resolution for both the SEM-inspection mode and the transmission mode. The electron beam device 30 further, preferably, includes at least one anode to accelerate the electrons of the electron beam 34 to a predetermined energy and/or to define the landing energy on the specimen. For typical SEM applications on a silicon wafer, the landing energy is in the range of 100 eV to 30 keV. Also, preferably, the electron beam device 30 includes a focussing lens 33 to focus the electron beam 34 onto the specimen 14 or onto the sample 12 of the specimen 14 with a spot size down to 1 nm. The electron beam device 30 further includes a scanning unit 32 for scanning the electron beam 34 across the specimen 14 and/or the sample 12 of the specimen 14. This way, the electron beam device 30 can be operated as an SEM to inspect the surface of the specimen using the first detector 36 to detect the electrons 38 that are released from the specimen 14 in a backward direction with respect to the direction of the electron beam 34. Further, with the scanning unit 32, the electron beam device 30 can be operated as a scanning transmission electron microscope to inspect the sample 12 of the specimen 14 in the transmission mode by using the second detector 40. The second detector is meant to detect the electrons 42 that are released from the specimen 14 in a forward direction with respect to the direction of the electron beam 34. The first detector 36 is meant to cover at least some of the area of the upper hemisphere of the specimen 14. The term “upper hemisphere” refers to the hemisphere into which electrons 38 are directed which are released from the specimen 14 in a backward direction with respect to the electron beam 34. The first detector 36 may be enclosed within the electron beam column 31 as shown in the FIGS. 1a) to 1d); however it is also possible to position the first detector 36 outside of the emitter beam column 31, e.g. at the side of the electron beam column 31 for backward electrons 38 detection. The size and design of the first detector 36 depends on the design of the electron beam device 30, in particular on the available space and the electric field distribution in the electron beam region. In the FIGS. 1a to 1d, the first detector 36 surrounds the electron beam axis with a circular symmetry in order to detect backwards directed electrons 38 which have entered the electron beam device 30 through the focussing lens 33. Preferably, the first detector 36 is a semiconductor detector, or a scintillation-photomultiplier detector (Everhart-Thornley detector). Both detectors are preferably capable of detecting secondary electrons having an energy of typically 0 to 50 eV, and backscattered electrons having an energy up to the full primary electron beam energy. The second detector 40 is meant to cover at least some area of the lower hemisphere of the sample 12 of the specimen 14. The term “lower hemisphere” refers to the hemisphere into which electrons 42, which are released from the sample 12 in a forward direction with respect to the electron beam 34, are directed. The size and design of the second detector 40 can be quite freely chosen, since below the sample there is more space and fewer electric field constraints for the second detector. However, the larger the area of the lower hemisphere covered by the second detector, the better the signal-to-noise ratio of the transmission image. Preferably, the first detector 36 and/or the second detector 40 are essentially non-imaging detectors, i.e. detectors which are not segmented to obtain a pixel image. Rather, it is preferred that first detector 36 and/or the second detector 40 are each one-channel detectors, which are significantly easier to operate than an imaging detector like, e.g. a CCD or any other multi-pixel detector. An imaging detector is not required for the apparatus according to the invention since the imaging is preferably performed by scanning the electron beam across the specimen or the sample of the specimen. There are several options regarding the type of detector to take as second detector 40. In one preferred embodiment of the invention, the second detector 40 is a semiconductor detector. In another preferred embodiment, the second detector 40 is a Everhart-Thornley detector. In a third preferred embodiment, the second detector 40 is a scintillator detector using a photomultiplier to amplify the scintillator signal. In this case, preferably, a light guide is used to transfer the scintillator signal to the photomultiplier. Further, it is preferred that the distance between the focussing lens 33 and the second detector 40 is smaller than 10 cm and even more preferred smaller than 5 cm. A close distance of the second detector 40 to the focussing lens 33 may be used to have the sample 12 close up to the second detector 40. This makes it easier to detect a large solid angle of the “lower hemisphere” with a small detector area. The apparatus according to the invention further includes separation means 50, 52 for separating the sample 12 from the specimen 14. Preferably, the separation means 50, 52 includes a specimen holder 50 to hold the specimen 14. It is further preferred that the specimen holder 50 is capable of moving the specimen from the inspection position below the electron beam device 30 to the etching position below the ion beam device 20, and retour. This way, the specimen holder 50 can be used to position the specimen 14 for the surface inspection by the electron beam device (SEM mode) as well as for the ion beam treatment (FIB mode) for the preparation of a sample from the specimen. In the case that the specimen 14 is a semiconductor wafer or a chip, the specimen holder 50 may be a movable wafer chuck. Preferably, the specimen holder 50 also includes some mechanical means to tilt the specimen with respect to the ion beam axis. This way, the landing angle of the ion beam 22 onto the specimen is adjustable to “chisel” a desired sample from the specimen with higher flexibility. Preferably, the separation means 50, 52 further include a sample holder 52 to hold the sample 12. Preferably, the sample holder 52 is movable in order to pick up the sample 12 from the specimen and move it away from the specimen 14. Preferably, the sample holder 52 is capable of moving the sample to the electron beam device 30 for the inspection in transmission mode, i.e. by means of the second detector 40. It is further preferred that the sample holder 52 moves the sample 12 to the electron beam device 30 in a vacuum. This way, the sample 12 is not exposed to the atmosphere. The particular shape and functionality of the sample holder 52 depends on the application and the kind of specimen. The technology to pick up and move a thin membrane is known in the art, e.g. U.S. Pat. No. 6,188,068 B1 discloses an example of such a sample holder in column 5, lines 12 to 62, where a sample holder with a glass tip is used to pick up a membrane from a wafer to carry it to a TEM for TEM inspections. A similar sample holder 52 can be used for the present invention if the specimen 14 is a wafer and the sample 12 is a membrane (see FIG. 1a to 1d). In this case the sample holder 52 is designed to carry and position the sample into the electron beam 34 of the electron beam device 30. As an alternative, it is preferred that the apparatus 10 includes a support structure which is formed and positioned to hold the sample 12 into the electron beam 34 of the electron beam device 30. In this case, the sample holder 52 is to move the sample 12 to the sample holder to lay it thereon. Such a procedure provides a good stability of the specimen during inspection in the transmission mode. The support structure preferably holds the sample 12 between the focussing lens 33 and the second detector 40. Further, the support structure is preferably shaped in a way that it leaves a free passage for the electrons 42 released from the sample 12 in a forward direction to the second detector 40. Preferably, the electron beam column 31 of the electron beam device 30 is essentially in parallel to the ion beam column 21 of the ion beam device 20. In this way, the electron beam 34 and the ion beam 22 can be made to have the same landing angle on the specimen 14 in order to inspect or etch the specimen. However, it is also preferred that the electron beam device 30 has a tilting mechanism in order to inspect the specimen 14 under different landing angles. Similarly, it is also preferred for the ion beam device 30 to have a tilting mechanism in order to etch the specimen at different angles. A tiltable ion beam device 20 provides more flexibilty to etch a membrane or any other sample 12 from a given specimen 14 in any desired shape. In addition, or alternatively, the ion beam device 30 is provided with beam optical components, e.g. a beam deflector or a beam shifter, to move the ion beam 22 across the specimen 14 at various angles to obtain a desired sample 12 from the specimen 14. Preferably, the sample holder 52 and/or the support structure are made to be electrically connectable to a DC voltage source V1 in order to be able to adjust the landing energy of the electron beam 34 on the sample 12 of the specimen. This way, the electron beam device 30 can be operated at higher landing energies during the transmission mode than without the first voltage source V1. During the transmission mode, a higher energy is preferred for a higher spatial resolution. Typically, the DC voltage source V1 is capable of providing a voltage of up to 10 keV and preferably up to 50 keV to the sample 12. In the SEM mode, the landing energy on the specimen 12 is preferably between 5 keV to 50 keV or, more preferred, between 0.1 to 30 keV. FIG. 1a to 1d illustrate a preferred method for inspecting a sample of a specimen according to the invention. In the figures, the specimen 14 is a silicon wafer having an integrated circuit ingrained. The apparatus 10 is preferably integrated in a integrated circuit production line. FIG. 1a to 1d disclose an electron beam device 30 with an electron beam column 31 having an electron beam source 54, a scanning unit 32 to deflect the electron beam 34 across the wafer 14, a focussing lens to focus the electron beam 34 down to a focus spot size of less than 10 nm. The electron beam device 30 further includes an electron detector 36 (first detector) to detect the electrons 38 which are released backwards into the upper hemisphere due to an interaction of the electron beam 34 with the wafer 14. FIG. 1a further discloses an ion beam device 20, which in FIG. 1a is a focussed ion beam device (FIB). The FIB 20 includes a Ga-ion beam source 56 and an ion beam scanning unit 66 to scan the ion beam 22 across the wafer 14 to etch a membrane 12 out of the wafer. The focus of the ion beam 22 on the wafer 14 is typically 5 to 100 nm wide. With the ion beam 22, the FIB 20 is capable of etching a membrane 12, which has to be only a few tens of nanometers thick, out of the wafer 14. The ion beam column 21 of the FIB 20 and the electron beam column 31 of the electron beam device 30 are oriented parallel to each other. FIG. 1a further discloses a stage 68 on whose surface the specimen holder 50 can be moved from the inspection position 62 to the etching position 64. The stage 68 also carries the sample holder 52 which can be moved along the stage surface. The sample holder 52 has a handling arm 70 to move the tip 72 for picking up and positioning the membrane 12 at a desired position. Stage 68, sample holder 52 specimen holder 50 and the second detector 40 (which in FIG. 1a is partially covered by specimen holder 50) are all enclosed by the vacuum chamber 18 in order to provide a vacuum better than 10−5 mbar. The high vacuum is necessary to minimize electron beam spreading. The common vacuum chamber 18 makes it possible that the apparatus can be operated in the SEM mode, the FIB mode or the transmission mode without ever having to break the vacuum when switching from one mode to the other. This way, the membrane 12 is never exposed to environmental pollution during the inspection procedure. FIG. 1a shows the apparatus 10 during SEM mode operation, i.e. the wafer 14 is being scanned by the electron beam 34 using the scanning unit 32 while the FIB 20 is switched off. The landing energy of the electron beam 34 on the wafer 14 is 0.1 to 30 keV. The electron beam 34 impinges on the wafer 14 because of which electrons 38 are released in a backward direction. The first detector 36, which in this embodiment is a scintillation detector, detects and counts the number of backwards directed electrons 38 for each scanning position. This way, an image of the surface structure of the wafer is generated with a spatial resolution of close to 1 nm. The image of the surface of the wafer 14 is used to determine whether and which region of interest should now be inspected in the transmission mode. In the case that no region of interest for a transmission mode inspection is found on the wafer, the wafer 14 is forwarded to the next processing unit of the semiconductor production line for completing the processing. However, in the case that the SEM image of the wafer indicates a region of interest for further inspection in the transmission mode, the specimen holder 50 is moved on the stage 68 from the inspection position 62 to the etching position 64 in order to start the FIB mode to etch a membrane 12 from the wafer 14. To etch the membrane at the determined region of interest of the wafer 14, it is important that a communication unit (not shown) communicates the coordinates of the region of interest as measured by the electron beam device in the SEM mode to the specimen holder 14 and/or FIB. This way, the specimen holder 50 can be moved into the correct etching position 64 in order to etch the wafer 14 at the position where the region of interest is. FIG. 1b shows the apparatus of FIG. 1a during the FIB mode operation. In the FIB mode, the electron beam device 30 is switched off and the FIB 30 generates an ion beam 22 to etch the membrane 12 out of the wafer 14 by scanning the ion beam in the region of interest. The method of etching a membrane 12 from a wafer 14 by means of a FIB ion beam has been discussed earlier and is known in the art. Once the membrane 12 has been etched, the specimen holder 50 with the etched wafer 14 and the membrane 12 still lying on it is moved back into the inspection position 62. There, the specimen holder 50 is tilted in order to allow for an easy extraction of the membrane 12 from the wafer 14. During this process, the electron beam device 30 can help to determine the exact position of the membrane 12 within the wafer 14. With the information of the membrane position, the sample holder 52 is moved on the stage 68 towards the wafer 14 to pick up and lift the membrane 12 away from the wafer 14. The picking of the membrane 12 is performed by means of an electrostatic force generated between the tip 72 of the sample holder 52 and the membrane 12. FIG. 1c illustrates the scenario at the moment when the tip 72 of the specimen holder 52 comes into contact with the membrane 12 on the wafer 14. Once the membrane 12 has been lifted by the arm 70 of the sample holder 52, the specimen holder 50 is moved away from the inspection position 62 to make space for the inspection of the membrane 12 in the transmission mode. Then, the membrane 12 is positioned by the sample holder 52 between the focussing lens 33 and the second detector 40 for the inspection in the transmission mode. FIG. 1d illustrates the scenario during the inspection of the membrane 12 in the transmission mode. The second detector 40, a scintillation detector, is used to detect the electrons 42 which have been released from the membrane 12 in a forward direction with respect to the electron beam 34 while the electron beam 34 is scanned across the membrane 12. By evaluating the electron signal of the scintillation detector 40 with respect to the according scanning position, a transmission image of the membrane is generated. Even though the spatial resolution of such a scanning image may not be sufficient to reveal the crystal structure of the membrane, the spatial resolution is usually high enough to image very thin layers and details of interface regions between the layers. It should be mentioned that during the transmission mode it is also possible to detect electrons 38 which are released from the membrane 12 in a backward direction with respect to the electron beam 34 by means of the first detector 36. The image generated by the first detector 36 can help to obtain complementary information about the surface of the membrane (which corresponds to a cross section of the wafer from which the membrane has been formed). FIG. 2 illustrates the same apparatus like in FIG. 1a to 1d, with the difference that a first voltage of the first voltage source V1 and a second voltage of the second voltage source V2 are applied between the sample holder 52 and vacuum chamber 18, and the scintillation detector 40 and vacuum chamber, respectively. The first voltage source V1 is mainly used in the transmission mode to apply a positive voltage to the membrane 12 in order to increase the transmission energy of the electrons of the electron beam 34 when they pass through the membrane 12. With a higher transmission energy, the spatial resolution of the transmission mode image can be increased to see even more details of the membrane structure. In the SEM mode, the voltage of the first voltage source V1 is usually decreased in order to make sure that low energy secondary electrons can reach the first detector 36. A low voltage of the first voltage source V1 also keeps the landing energy low to obtain a higher spatial resolution in the SEM mode. The second voltage source V2 is used to adjust the voltage of the second detector 40 to make sure that the transmitted electrons 42 have enough energy to reach the detector even when the membrane is lifted to a more positive potential. FIG. 3 illustrates a further embodiment of the invention. The apparatus 10 of FIG. 3 is the same as the apparatus 10 of FIG. 1a to 1d, with the difference that the FIB 20 is tilted with respect to the electron beam device 30. The tilting angle of the FIB 20 is such that the ion beam 22 and the electron beam 34 can be directed onto the same region on a wafer 14. This way, it is possible to inspect the wafer 14 during the etching of the wafer 12 by means of the FIB 20, i.e. SEM mode and FIB mode can be carried out at the same time. In this case, it is not necessary to move the specimen holder 50 to the FIB after inspection in the SEM mode. This might help to increase the precision for etching the membrane 12 at the desired region of interest. |
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