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	claims	1. An electromagnetic energy spot curing system comprising:a curing unit having a radiation source positioned to irradiate a work piece with radiation energy and having a shutter selectively operable to allow exposure of radiation energy from said source wherein said shutter includes an opening;a light guide positioned to receive the radiation energy from said source and;a processor external to the curing unit for providing an externally output signal to control the movement of the shutter, wherein said movement includes a first position such that the opening of the shutter aligns with the light guide and said movement includes a second position such that the opening of the shutter does not align with the light guide. 2. The system of claim 1 wherein said curing unit further comprises a light guide receptacle positioned opposite the shutter. 3. The system of claim 2 wherein said light guide receptacle includes an opening for supportable receipt of the light guide therein. 4. The system of claim 3 wherein said movement of the shutter to the first position allows the radiation energy from the source to pass through said opening of the shutter to irradiate on said work piece. 5. The system of claim 4 wherein said movement of the shutter to the second position, prevents the radiation energy from the source to pass through said opening of the shutter. 6. The system of claim 1 wherein said curing unit further comprises a solenoid connected to bottom of said shutter for controlling movement of the shutter. 7. The system of claim 6 wherein said curing unit further comprises a transistor power circuit connected to the processor via a switch for receiving externally output signal. 8. The system of claim 7 wherein said transistor power circuit is coupled to the solenoid for activating the solenoid upon receipt of said externally output signal from said processor. 9. The system of claim 8 wherein said source is a UV lamp. 10. A method of spot curing a work piece using radiation in the electromagnetic energy comprising:providing a source of electromagnetic energy using a curing unit, wherein said curing unit includes a shutter having an opening;emanating radiation from said source for exposure of radiation energy to be received by a light guide; andproviding an externally output signal external to the curing unit, thereby causing movement of the shutter to a first position and a second position, wherein said first position includes said opening of the shutter aligning with the light guide and said second position includes said opening of the shutter not aligning with the light guide. 11. The method of claim 10 wherein said movement of the shutter controls the exposure of the radiation energy on said work piece to be cured. 12. The method of claim 11 wherein said movement of the shutter, controls periods of the exposure of the radiation energy on said workpiece to be cured. 13. The method of claim 11 wherein said movement of the shutter to the first position allows the radiation energy to be exposed on said work piece for a period of time. 14. The method of claim 11 wherein said movement of the shutter to the second position prevents the radiation to be exposed to the work piece. 15. The method of claim 10 wherein said externally output signal is provided by a processor. 16. The method of claim 10 wherein said electromagnetic energy source is a UV lamp. 17. The method of claim 10 wherein said work piece includes a curable adhesive.
	claims	1. A radiation source configured to produce extreme ultraviolet radiation, the radiation source comprising:a chamber in which, in use, a plasma is generated to provide the radiation;a heating system configured to maintain an evaporation surface at a temperature to evaporate a material formed as a by-product from the plasma and that is emitted to the evaporation surface; anda vessel having an inner wall and an outer wall, the inner wall comprising the evaporation surface, and the outer wall has a higher emissivity than the inner wall. 2. The radiation source according to claim 1, wherein inner wall comprises a polished metal material. 3. The radiation source according to claim 1, wherein the outer wall comprises a ceramic material. 4. The radiation source according to claim 1, wherein the inner wall is conically-shaped. 5. The radiation source according to claim 1, further comprising a cooler configured to cool the outer wall. 6. The radiation source according to claim 1, wherein the evaporation surface has a RMS roughness of between about 10 nm and about 1 mm, or is porous, or has a plurality of protrusions thereon or therein. 7. A radiation source configured to produce extreme ultraviolet radiation, the radiation source comprising:a chamber in which, in use, a plasma is generated to provide the radiation;a vessel structure within the chamber, the structure configured to receive the radiation in its interior;a gas injector arranged to inject a gas flow in the chamber at an edge of the structure; andan outlet to draw injected gas flow from the edge of the structure towards an interior of the structure. 8. The radiation source according to claim 7, further comprising a heating system configured to maintain an evaporation surface at a temperature to evaporate a material formed as a by-product from the plasma and that is emitted to the evaporation surface, the structure having the evaporation surface. 9. The radiation source according to claim 8, wherein the structure comprises an inner wall and an outer wall, the inner wall having the evaporation surface and the gas injector is configured to feed the gas between the inner and outer walls. 10. The radiation source according to claim 7, wherein a surface of the structure is at least partially conically-shaped. 11. The radiation source according to claim 7, wherein the injector is configured to feed gas along an outer surface of the structure towards and along the edge of the structure. 12. The radiation source according to claim 7, wherein the gas injector is configured to inject a ring-shaped gas curtain in the chamber. 13. The radiation source according to claim 7, wherein the vessel structure has an optical axis and the gas injector is configured to inject the gas flow in a direction substantially parallel to the optical axis. 14. The radiation source according to claim 7, wherein the vessel structure has a first opening to receive the radiation and a second different opening to discharge the received radiation, wherein the outlet is configured to draw injected gas through the first opening and toward second opening. 15. A radiation source configured to produce extreme ultraviolet radiation, the radiation source comprising:a chamber in which, in use, a plasma is generated to provide the radiation; andan outlet conduit to remove debris from the plasma, the outlet conduit having a cooling structure to condense the debris from a gas flow in the outlet conduit. 16. The radiation source according to claim 15, wherein the cooling structure comprises a cooling ring or spiral in a wall of the outlet conduit. 17. The radiation source according to claim 15, wherein an opening of the outlet conduit has a cone-shaped surface and the cooling structure is located at or in the cone-shaped surface. 18. The radiation source according to claim 15, wherein the cooling structure is further configured to capture the condensed debris and remove the condensed debris from the outlet conduit upstream of a pump for the outlet conduit. 19. The radiation source according to claim 15, wherein the cooling structure is further configured to prevent condensed debris from flowing out of the outlet conduit. 20. The radiation source according to claim 15, further comprising a heating system configured to maintain an evaporation surface at a temperature to evaporate the debris.
	description	This application is a continuation application of, and claims priority under 35 U.S.C. § 120 to, U.S. patent application Ser. No. 16/796,787, filed on Feb. 20, 2020, which will issue as U.S. Pat. No. 10,878,972, which in turn claims priority under 35 U.S.C. § 119 to: U.S. Provisional Patent Application Ser. No. 62/808,588, filed on Feb. 21, 2019; U.S. Provisional Patent Application Ser. No. 62/808,545, filed on Feb. 21, 2019; and U.S. Provisional Patent Application Ser. No. 62/833,097, filed on Apr. 12, 2019, the entire contents of each of which are incorporated herein by reference. This disclosure relates to hazardous material repository systems and methods. Hazardous material, such as radioactive waste, is often placed in long-term, permanent, or semi-permanent storage so as to prevent health issues among a population living near the stored waste. Such hazardous waste storage is often challenging, for example, in terms of storage location identification and surety of containment. For instance, the safe storage of nuclear waste (e.g., spent nuclear fuel, whether from commercial power reactors, test reactors, or even high-grade military waste) is considered to be one of the outstanding challenges of energy technology. Safe storage of the long-lived radioactive waste is a major impediment to the adoption of nuclear power in the United States and around the world. Conventional waste storage methods have emphasized the use of tunnels, and is exemplified by the design of the Yucca Mountain storage facility. Other techniques include boreholes, including vertical boreholes, drilled into crystalline basement rock. Other conventional techniques include forming a tunnel with boreholes emanating from the walls of the tunnel in shallow formations to allow human access. In a general implementation, a nuclear waste canister includes a housing that at least partially defines an inner volume sized to enclose a plurality of nuclear waste portions and configured to store the nuclear waste portions in a hazardous waste repository of a directional drillhole formed in a subterranean formation; and a solid or semi-solid granular material enclosed in the inner volume of the housing that at least substantially fills voids within the inner volume and between the plurality of nuclear waste portions. In an aspect combinable with the general implementation, the nuclear waste portions include a plurality of spent nuclear fuel (SNF) rods of an SNF assembly. In another aspect combinable with any of the previous aspects, the inner volume is sized to store a single SNF assembly. In another aspect combinable with any of the previous aspects, the solid or semi-solid granular material includes a solid powder. In another aspect combinable with any of the previous aspects, the solid powder includes silicon-dioxide. In another aspect combinable with any of the previous aspects, the solid or semi-solid granular material includes a neutron-absorbing material. Another aspect combinable with any of the previous aspects further includes an impact absorber positioned within the inner volume or on an exterior surface of the housing. In another aspect combinable with any of the previous aspects, the impact absorber includes a crushable member or spring member. In another aspect combinable with any of the previous aspects, the impact absorber includes a low-corrosion material. Another aspect combinable with any of the previous aspects further includes a friction brake mounted to an end of the housing. In another aspect combinable with any of the previous aspects, the friction brake is mounted to the housing with a pivotable or rotatable connection. In another aspect combinable with any of the previous aspects, the end of the housing includes a downhole end of the housing. In another aspect combinable with any of the previous aspects, the friction brake includes a surface configured to contact a casing installed in the directional drillhole. In another general implementation, a method for storing nuclear waste includes placing a plurality of nuclear waste portions into an inner volume of a housing of a nuclear waste canister configured to store the nuclear waste portions in a hazardous waste repository of a directional drillhole formed in a subterranean formation; substantially filling voids within the inner volume and between the plurality of nuclear waste portions with a solid or semi-solid granular material; and sealing the inner volume of the nuclear waste canister to enclose the plurality of nuclear waste portions and the solid or semi-solid granular material. In an aspect combinable with the general implementation, the nuclear waste portions include a plurality of spent nuclear fuel (SNF) rods of an SNF assembly. In another aspect combinable with any of the previous aspects, the inner volume is sized to store a single SNF assembly. In another aspect combinable with any of the previous aspects, the solid or semi-solid granular material includes a solid powder. In another aspect combinable with any of the previous aspects, the solid powder includes silicon-dioxide. In another aspect combinable with any of the previous aspects, the solid or semi-solid granular material includes a neutron-absorbing material. In another aspect combinable with any of the previous aspects, the nuclear waste canister further includes an impact absorber positioned within the inner volume or on an exterior surface of the housing. In another aspect combinable with any of the previous aspects, the impact absorber includes a crushable member or spring member. In another aspect combinable with any of the previous aspects, the impact absorber includes a low-corrosion material. In another aspect combinable with any of the previous aspects, the nuclear waste canister further includes a friction brake mounted to an end of the housing. In another aspect combinable with any of the previous aspects, the friction brake is mounted to the housing with a pivotable or rotatable connection. In another aspect combinable with any of the previous aspects, the end of the housing includes a downhole end of the housing. In another aspect combinable with any of the previous aspects, the friction brake includes a surface configured to contact a casing installed in the directional drillhole. Another aspect combinable with any of the previous aspects further includes moving the sealed nuclear waste canister into the hazardous waste repository of the directional drillhole. Another aspect combinable with any of the previous aspects further includes mitigating an impact of the sealed nuclear waste canister during a free fall event during movement of the sealed nuclear waste canister through the directional drillhole. Implementations of a hazardous material storage repository according to the present disclosure may include one or more of the following features. For example, a hazardous material storage repository according to the present disclosure may allow for multiple levels of containment of hazardous material within a storage repository located thousands of feet underground, decoupled from any nearby mobile water. As another example, implementations of a hazardous material canister according to the present disclosure may withstand or reduce collisions within a directional drillhole with other objects, including other canisters, to reduce leakage of hazardous material due to such collisions. As another example, implementations of a hazardous material canister according to the present disclosure may be more easily and efficiently loaded with radioactive waste, e.g., without requiring such loading to be completed wholly within a hot room. As another example, a hazardous material storage repository according to the present disclosure may be constructed such that a free-falling hazardous material canister does not damage itself or other objects within a directional drillhole even independently of a construction of the canister, itself. The details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims. FIG. 1 is a schematic illustration of an example implementation of a hazardous material storage repository system 100, e.g., a subterranean location for the long-term (e.g., tens, hundreds, or thousands of years or more), but retrievable, safe and secure storage of hazardous material (e.g., radioactive material, such as nuclear waste which can be spent nuclear fuel (SNF) or high level waste, as two examples). For example, this figure illustrates the example hazardous material storage repository system 100 once one or more canisters 126 of hazardous material have been deployed in a subterranean formation 118. As illustrated, the hazardous material storage repository system 100 includes a drillhole 104 formed (e.g., drilled or otherwise) from a terranean surface 102 and through multiple subterranean layers 112, 114, 116, and 118. Although the terranean surface 102 is illustrated as a land surface, terranean surface 102 may be a sub-sea or other underwater surface, such as a lake or an ocean floor or other surface under a body of water. Thus, the present disclosure contemplates that the drillhole 104 may be formed under a body of water from a drilling location on or proximate the body of water. The illustrated drillhole 104 is a directional drillhole in this example of hazardous material storage repository system 100. For instance, the drillhole 104 includes a substantially vertical portion 106 coupled to a radiussed or curved portion 108, which in turn is coupled to a substantially horizontal portion 110. As used in the present disclosure, “substantially” in the context of a drillhole orientation, refers to drillholes that may not be exactly vertical (e.g., exactly perpendicular to the terranean surface 102) or exactly horizontal (e.g., exactly parallel to the terranean surface 102), or exactly inclined at a particular incline angle relative to the terranean surface 102. In other words, vertical drillholes often undulate offset from a true vertical direction, that they might be drilled at an angle that deviates from true vertical, and inclined drillholes often undulate offset from a true incline angle. Further, in some aspects, an inclined drillhole may not have or exhibit an exactly uniform incline (e.g., in degrees) over a length of the drillhole. Instead, the incline of the drillhole may vary over its length (e.g., by 1-5 degrees). As illustrated in this example, the three portions of the drillhole 104—the vertical portion 106, the radiussed portion 108, and the horizontal portion 110—form a continuous drillhole 104 that extends into the Earth. As used in the present disclosure, the drillhole 104 (and drillhole portions described) may also be called wellbores. Thus, as used in the present disclosure, drillhole and wellbore are largely synonymous and refer to bores formed through one or more subterranean formations that are not suitable for human-occupancy (i.e., are too small in diameter for a human to fit there within). The illustrated drillhole 104, in this example, has a surface casing 120 positioned and set around the drillhole 104 from the terranean surface 102 into a particular depth in the Earth. For example, the surface casing 120 may be a relatively large-diameter tubular member (or string of members) set (e.g., cemented) around the drillhole 104 in a shallow formation. As used herein, “tubular” may refer to a member that has a circular cross-section, elliptical cross-section, or other shaped cross-section. For example, in this implementation of the hazardous material storage repository system 100, the surface casing 120 extends from the terranean surface through a surface layer 112. The surface layer 112, in this example, is a geologic layer comprised of one or more layered rock formations. In some aspects, the surface layer 112 in this example may or may not include freshwater aquifers, salt water or brine sources, or other sources of mobile water (e.g., water that moves through a geologic formation). In some aspects, the surface casing 120 may isolate the drillhole 104 from such mobile water, and may also provide a hanging location for other casing strings to be installed in the drillhole 104. Further, although not shown, a conductor casing may be set above the surface casing 120 (e.g., between the surface casing 120 and the surface 102 and within the surface layer 112) to prevent drilling fluids from escaping into the surface layer 112. As illustrated, a production casing 122 is positioned and set within the drillhole 104 downhole of the surface casing 120. Although termed a “production” casing, in this example, the casing 122 may or may not have been subject to hydrocarbon production operations. Thus, the casing 122 refers to and includes any form of tubular member that is set (e.g., cemented) in the drillhole 104 downhole of the surface casing 120. In some examples of the hazardous material storage repository system 100, the production casing 122 may begin at an end of the radiussed portion 108 and extend throughout the horizontal portion 110. The casing 122 could also extend into the radiussed portion 108 and into the vertical portion 106. As shown, cement 130 is positioned (e.g., pumped) around the casings 120 and 122 in an annulus between the casings 120 and 122 and the drillhole 104. The cement 130, for example, may secure the casings 120 and 122 (and any other casings or liners of the drillhole 104) through the subterranean layers under the terranean surface 102. In some aspects, the cement 130 may be installed along the entire length of the casings (e.g., casings 120 and 122 and any other casings), or the cement 130 could be used along certain portions of the casings if adequate for a particular drillhole 104. The cement 130 can also provide an additional layer of confinement for the hazardous material in canisters 126. The drillhole 104 and associated casings 120 and 122 may be formed with various example dimensions and at various example depths (e.g., true vertical depth, or TVD). For instance, a conductor casing (not shown) may extend down to about 120 feet TVD, with a diameter of between about 28 in. and 60 in. The surface casing 120 may extend down to about 2500 feet TVD, with a diameter of between about 22 in. and 48 in. An intermediate casing (not shown) between the surface casing 120 and production casing 122 may extend down to about 8000 feet TVD, with a diameter of between about 16 in. and 36 in. The production casing 122 may extend inclinedly (e.g., to case the horizontal portion 110) with a diameter of between about 11 in. and 22 in. The foregoing dimensions are merely provided as examples and other dimensions (e.g., diameters, TVDs, lengths) are contemplated by the present disclosure. For example, diameters and TVDs may depend on the particular geological composition of one or more of the multiple subterranean layers (112, 114, 116, and 118), particular drilling techniques, as well as a size, shape, or design of a hazardous material canister 126 that contains hazardous material to be deposited in the hazardous material storage repository system 100. In some alternative examples, the production casing 122 (or other casing in the drillhole 104) could be circular in cross-section, elliptical in cross-section, or some other shape. As illustrated, the vertical portion 106 of the drillhole 104 extends through subterranean layers 112, 114, and 116, and, in this example, lands in a subterranean layer 118. As discussed above, the surface layer 112 may or may not include mobile water. In this example, a mobile water layer 114 is below the surface layer 112 (although surface layer 112 may also include one or more sources of mobile water or liquid). For instance, mobile water layer 114 may include one or more sources of mobile water, such as freshwater aquifers, salt water or brine, or other source of mobile water. In this example of hazardous material storage repository system 100, mobile water may be water that moves through a subterranean layer based on a pressure differential across all or a part of the subterranean layer. For example, the mobile water layer 114 may be a permeable geologic formation in which water freely moves (e.g., due to pressure differences or otherwise) within the layer 114. In some aspects, the mobile water layer 114 may be a primary source of human-consumable water in a particular geographic area. Examples of rock formations of which the mobile water layer 114 may be composed include porous sandstones and limestones, among other formations. Other illustrated layers, such as the impermeable layer 116 and the storage layer 118, may include immobile water. Immobile water, in some aspects, is water (e.g., fresh, salt, brine), that is not fit for human or animal consumption, or both. Immobile water, in some aspects, may be water that, by its motion through the layers 116 or 118 (or both), cannot reach the mobile water layer 114, terranean surface 102, or both, within 10,000 years or more (such as to 1,000,000 years). Below the mobile water layer 114, in this example implementation of hazardous material storage repository system 100, is an impermeable layer 116. The impermeable layer 116, in this example, may not allow mobile water to pass through. Thus, relative to the mobile water layer 114, the impermeable layer 116 may have low permeability, e.g., on the order of nanodarcy permeability. Additionally, in this example, the impermeable layer 116 may be a relatively non-ductile (i.e., brittle) geologic formation. One measure of non-ductility is brittleness, which is the ratio of compressive stress to tensile strength. In some examples, the brittleness of the impermeable layer 116 may be between about 20 MPa and 40 MPa. As shown in this example, the impermeable layer 116 is shallower (e.g., closer to the terranean surface 102) than the storage layer 118. In this example rock formations of which the impermeable layer 116 may be composed include, for example, certain kinds of sandstone, mudstone, clay, and slate that exhibit permeability and brittleness properties as described above. In alternative examples, the impermeable layer 116 may be deeper (e.g., further from the terranean surface 102) than the storage layer 118. In such alternative examples, the impermeable layer 116 may be composed of an igneous rock, such as granite. Below the impermeable layer 116 is the storage layer 118. The storage layer 118, in this example, may be chosen as the landing for the horizontal portion 110, which stores the hazardous material, for several reasons. Relative to the impermeable layer 116 or other layers, the storage layer 118 may be thick, e.g., between about 100 and 200 feet of total vertical thickness. Thickness of the storage layer 118 may allow for easier landing and directional drilling, thereby allowing the horizontal portion 110 to be readily emplaced within the storage layer 118 during constructions (e.g., drilling). If formed through an approximate horizontal center of the storage layer 118, the horizontal portion 110 may be surrounded by about 50 to 100 feet of the geologic formation that comprises the storage layer 118. Further, the storage layer 118 may also have only immobile water, e.g., due to a very low permeability of the layer 118 (e.g., on the order of milli- or nanodarcys). In addition, the storage layer 118 may have sufficient ductility, such that a brittleness of the rock formation that comprises the layer 118 is between about 3 MPa and 10 MPa. Examples of rock formations of which the storage layer 118 may be composed include: shale and anhydrite. Further, in some aspects, hazardous material may be stored below the storage layer, even in a permeable formation such as sandstone or limestone, if the storage layer is of sufficient geologic properties to isolate the permeable layer from the mobile water layer 114. In some examples implementations of the hazardous material storage repository system 100, the storage layer 118 (and/or the impermeable layer 116) is composed of shale. Shale, in some examples, may have properties that fit within those described above for the storage layer 118. For example, shale formations may be suitable for a long-term confinement of hazardous material (e.g., in the hazardous material canisters 126), and for their isolation from mobile water layer 114 (e.g., aquifers) and the terranean surface 102. Shale formations may be found relatively deep in the Earth, typically 3000 feet or greater, and placed in isolation below any fresh water aquifers. Other formations may include salt or other impermeable formation layer. Shale formations (or salt or other impermeable formation layers), for instance, may include geologic properties that enhance the long-term (e.g., thousands of years) isolation of material. Such properties, for instance, have been illustrated through the long term storage (e.g., tens of millions of years) of hydrocarbon fluids (e.g., gas, liquid, mixed phase fluid) without escape of substantial fractions of such fluids into surrounding layers (e.g., mobile water layer 114). Indeed, shale has been shown to hold natural gas for millions of years or more, giving it a proven capability for long-term storage of hazardous material. Example shale formations (e.g., Marcellus, Eagle Ford, Barnett, and otherwise) has stratification that contains many redundant sealing layers that have been effective in preventing movement of water, oil, and gas for millions of years, lacks mobile water, and can be expected (e.g., based on geological considerations) to seal hazardous material (e.g., fluids or solids) for thousands of years after deposit. In some aspects, the formation of the storage layer 118 and/or the impermeable layer 116 may form a leakage barrier, or barrier layer to fluid leakage that may be determined, at least in part, by the evidence of the storage capacity of the layer for hydrocarbons or other fluids (e.g., carbon dioxide) for hundreds of years, thousands of years, tens of thousands of years, hundreds of thousands of years, or even millions of years. For example, the barrier layer of the storage layer 118 and/or impermeable layer 116 may be defined by a time constant for leakage of the hazardous material more than 10,000 years (such as between about 10,000 years and 1,000,000 years) based on such evidence of hydrocarbon or other fluid storage. Shale (or salt or other impermeable layer) formations may also be at a suitable depth, e.g., between 3000 and 12,000 feet TVD. Such depths are typically below ground water aquifer (e.g., surface layer 112 and/or mobile water layer 114). Further, the presence of soluble elements in shale, including salt, and the absence of these same elements in aquifer layers, demonstrates a fluid isolation between shale and the aquifer layers. Another particular quality of shale that may advantageously lend itself to hazardous material storage is its clay content, which, in some aspects, provides a measure of ductility greater than that found in other, impermeable rock formations (e.g., impermeable layer 116). For example, shale may be stratified, made up of thinly alternating layers of clays (e.g., between about 20-30% clay by volume) and other minerals. Such a composition may make shale less brittle and, thus less susceptible to fracturing (e.g., naturally or otherwise) as compared to rock formations in the impermeable layer (e.g., dolomite or otherwise). For example, rock formations in the impermeable layer 116 may have suitable permeability for the long term storage of hazardous material, but are too brittle and commonly are fractured. Thus, such formations may not have sufficient sealing qualities (as evidenced through their geologic properties) for the long term storage of hazardous material. The present disclosure contemplates that there may be many other layers between or among the illustrated subterranean layers 112, 114, 116, and 118. For example, there may be repeating patterns (e.g., vertically), of one or more of the mobile water layer 114, impermeable layer 116, and storage layer 118. Further, in some instances, the storage layer 118 may be directly adjacent (e.g., vertically) the mobile water layer 114, i.e., without an intervening impermeable layer 116. In some examples, all or portions of the radiussed drillhole 108 and the horizontal drillhole 110 may be formed below the storage layer 118, such that the storage layer 118 (e.g., shale or other geologic formation with characteristics as described herein) is vertically positioned between the horizontal drillhole 110 and the mobile water layer 114. In this example, the horizontal portion 110 of the drillhole 104 includes a storage area in a distal part of the portion 110 into which hazardous material may be retrievably placed for long-term storage. For example, a work string (e.g., tubing, coiled tubing, wireline, or otherwise) or other downhole conveyance (e.g., tractor) may be moved into the cased drillhole 104 to place one or more (three shown but there may be more or less) hazardous material canisters 126 into long term, but in some aspects, retrievable, storage in the portion 110. Each canister 126 may enclose hazardous material (shown as material 145). Such hazardous material, in some examples, may be biological or chemical waste or other biological or chemical hazardous material. In some examples, the hazardous material may include nuclear material, such as SNF recovered from a nuclear reactor (e.g., commercial power or test reactor) or military nuclear material. Spent nuclear fuel, in the form of nuclear fuel pellets, may be taken from the reactor and not modified. Nuclear fuel pellet are solid, although they can contain and emit a variety of radioactive gases including tritium (13 year half-life), krypton-85 (10.8 year half-life), and carbon dioxide containing C-14 (5730 year half-life). Other hazardous material 145 may include, for example, radioactive liquid, such as radioactive water from a commercial power (or other) reactor. In some aspects, the storage layer 118 should be able to contain any radioactive output (e.g., gases) within the layer 118, even if such output escapes the canisters 126. For example, the storage layer 118 may be selected based on diffusion times of radioactive output through the layer 118. For example, a minimum diffusion time of radioactive output escaping the storage layer 118 may be set at, for example, fifty times a half-life for any particular component of the nuclear fuel pellets. Fifty half-lives as a minimum diffusion time would reduce an amount of radioactive output by a factor of 1×10−15. As another example, setting a minimum diffusion time to thirty half-lives would reduce an amount of radioactive output by a factor of one billion. For example, plutonium-239 is often considered a dangerous waste product in SNF because of its long half-life of 24,100 years. For this isotope, 50 half-lives would be 1.2 million years. Plutonium-239 has low solubility in water, is not volatile, and as a solid, its diffusion time is exceedingly small (e.g., many millions of years) through a matrix of the rock formation that comprises the illustrated storage layer 118 (e.g., shale or other formation). The storage layer 118, for example comprised of shale, may offer the capability to have such isolation times (e.g., millions of years) as shown by the geological history of containing gaseous hydrocarbons (e.g., methane and otherwise) for several million years. In contrast, in conventional nuclear material storage methods, there was a danger that some plutonium might dissolve in a layer that comprised mobile ground water upon confinement escape. In some aspects, the drillhole 104 may be formed for the primary purpose of long-term storage of hazardous materials. In alternative aspects, the drillhole 104 may have been previously formed for the primary purpose of hydrocarbon production (e.g., oil, gas). For example, storage layer 118 may be a hydrocarbon bearing formation from which hydrocarbons were produced into the drillhole 104 and to the terranean surface 102. In some aspects, the storage layer 118 may have been hydraulically fractured prior to hydrocarbon production. Further in some aspects, the production casing 122 may have been perforated prior to hydraulic fracturing. In such aspects, the production casing 122 may be patched (e.g., cemented) to repair any holes made from the perforating process prior to a deposit operation of hazardous material. In addition, any cracks or openings in the cement between the casing and the drillhole can also be filled at that time. As further shown in FIG. 1, a backfill material 140 may be positioned or circulated into the drillhole 104. In this example, the backfill material 140 surrounds the canisters 126 and may have a level that extends uphole to at or near a drillhole seal 134 (e.g., permanent packer, plug, or other seal). In some aspects, the backfill material 140 may absorb radioactive energy (e.g., gamma rays or other energy). In some aspects, the backfill material 140 may have a relatively low thermal conductivity, thereby acting as an insulator between the canisters 126 and the casings. As further shown in FIG. 1, another backfill material 150 may be positioned or placed within one or more of the canisters 126 to surround the hazardous material 145. In some aspects, the backfill material 150 may absorb radioactive energy (e.g., gamma rays or other energy). In some aspects, the backfill material 150 may have a relatively low thermal conductivity, thereby acting as an insulator between the hazardous material 145 and the canister 126. In some aspects, the backfill material 150 may also provide a stiffening attribute to the canister 126, e.g., reducing crushability, deformation, or other damage to the canister 126. In some aspects, one or more of the previously described components of the system 100 may combine to form an engineered barrier of the hazardous waste material repository 100. For example, in some aspects, the engineered barrier is comprised of one, some, or all of the following components: the storage layer 118, the casing 130, the backfill material 140, the canister 126, the backfill material 150, the seal 134, and the hazardous material 145, itself. In some aspects, one or more of the engineered barrier components may act (or be engineered to act) to: prevent or reduce corrosion in the drillhole 104, prevent or reduce escape of the hazardous material 145; reduce or prevent thermal degradation of one or more of the other components; and other safety measures to ensure that the hazardous material 145 does not reach the mobile water layer 114 (or surface layer 112, including the terranean surface 102). FIG. 2 is a schematic illustration of a hazardous material canister 200 according to the present disclosure. In some aspects, the hazardous material canister 200 may be used as the hazardous material canister 126 shown in the hazardous material storage repository system 100 of FIG. 1. In some aspects, the hazardous material canister 200 may enclose and store nuclear or radioactive waste, such as SNF or high level waste. As described in the example emplacement process of the canisters 126 into the hazardous material storage repository system 100 of FIG. 1, the hazardous material canister 200 may be placed in a human-unoccupiable deep directional drillhole (e.g., drillhole 104) for long term (e.g., hundreds if not thousands of years) storage. During the emplacement process, the hazardous material canister 200 may be moved into the directional drillhole 104 on a conveyance cable, such as, for example, a wireline cable. When the hazardous material canister 200 is lowered through the vertical portion 106 of the directional drillhole 104, there is a possibility that the cable (or a connection between the canister 200 and the cable) that supports the canister 200 may fail. Upon failure, the canister 200 will accelerate downward (e.g., in free fall) in the vertical portion 106 of the directional drillhole 104 (e.g., through a fluid in the drillhole 104). If the directional drillhole 104 has a kickoff point for the transition portion 108 (e.g., a transition to a horizontal or nearly-horizontal drillhole portion from the vertical portion 106), then the canister 200 will slow and eventually stop in the horizontal drillhole portion 110. However, if the hazardous material storage repository system 100 has previously been filled with other hazardous material canisters 200, then the free-falling canister 200 could impact a stationary canister 200 with resulting damage to both hazardous material canisters 200. If the hazardous waste material (e.g., nuclear waste) inside the canister 200 is highly radioactive, there is a danger of release of this material into the drillhole portion 110, which could potentially lead to release into a surrounding subterranean formation 118, and possibly mobile water in such a formation or other formations (e.g., subterranean formation 112). The illustrated implementation of hazardous material canister 200 includes one or more features that, e.g., may reduce or prevent potential damage to the canister 200 due to a free-fall in the deep directional drillhole 104. For example, the hazardous material canister 200 may maintain its structural integrity and its value as an “engineered barrier” to the release of hazardous material during free-fall and/or impact with another object in the drillhole 104. As shown in FIG. 2, the hazardous material canister 200 includes a housing 202 that is comprised of a middle portion 204 to which a top (or lid) 206 and bottom 208 are coupled (e.g., subsequent to enclosing the hazardous waste) to form an inner volume 212. In this example, the hazardous material is one or more SNF assemblies 210 that include SNF rods 214. In an example implementation, a material 216 (e.g., granular or particulate) is emplaced within the inner volume 212 of the canister 200 (surrounding the SNF assembly 210 (or assemblies 210) and even the SNF rods 214). This material 216 may be sand or another granular material (collectively referred to as “sand”) and may be placed into the canister 200 to fill voids that surround the SNF assembly 210 (or rods 214). For example, in the case of the hazardous material being an SNF assembly comprised of SNF rods (in whole or part), then the SNF rods 214 occupy only about ⅓ or less of the inner volume 212 of the canister 200. A sudden impact on the canister 200 (e.g., due to a free-fall event) could cause the SNF rods 214 to buckle and break. Buckling, in some cases, occurs (during a free-fall situation) when a front (bottom or downhole) end of the SNF rod 214 is suddenly stopped (e.g., due to a collision). The rest of the SNF rod 214 initially continues downward due to momentum. If the SNF rod 214 is completely symmetric, then the SNF rod 214 will compress, but slight deviations from symmetry are usually present, and so the SNF rod 214 tends to bend. In this decelerating situation, that bending becomes unstable and the bend increases rapidly until the SNF rod 214 breaks. To prevent buckling, aspects of the hazardous material canister 200 may provide minimal support for the sides of the SNF rods 214. In some cases, the structure of the SNF assembly 210 that holds the SNF rods 214 provides lateral support. But more resistance to buckling can be obtained by filling the voids in the SNF assembly 210 with the material 216 (e.g., sand or other a relatively dense material). In some aspects, the material 216 can be silicon-dioxide, clay, crushed rock, cement, epoxy, or other powder of a solid. The material 216 provides support of the sides of the SNF rods 214 in a collision that prevents or helps prevent the SNF rods 214 from buckling. In some aspects, the prevention of buckling may not require a very strong material since the initial horizontal bucking force is small, so many materials could be used. In alternative aspects, a liquid or gel may be used as the material 216 to fill the voids in the inner volume 212 not occupied by the SNF assembly 210. The liquid or gel may provide less resistance to buckling relative to a solid. The material 216 could achieve other purposes. For example, if the hazardous waste (i.e., SNF assembly 210) has sufficient concentration of fissionable material (e.g., U-235 or Pu-239), then there may be danger of a “criticality accident;” that is, a chain reaction taking place among these isotopes. The presence of water may increase the danger, since water acts as a “moderator” that slows neutrons and increases the likelihood that a neutron will trigger a fission. The material 216 can reduce this risk if it contains suitable amounts of neutron absorbers. Such absorbers are boron, cadmium, and cobalt, as some examples. These can be included (e.g., as part of the granular, solid, or liquid material 216) as metals or as compounds. The material 216 that mitigates or helps mitigate damage to the SNF assembly 210 during transport and emplacement in the directional drillhole 104 may serve additional functions. For example, the material 216 may have thermal conduction qualities that effectively allow heat to be transferred from the SNF 210 to the housing 202 (and ultimately to the geologic environment). Materials like quartz/sand and/or bentonite, or a mixture of the two in some favorable proportion can serve this function as or as mixed in the material 216. Both have suitable thermal conduction characteristics. The thermal conductivity of the quartz/bentonite mixture may maintain lower temperatures inside the hazardous material canister 200. As another example, in some aspects, with bentonite as or mixed with the material 216, the material 216 may include radionuclide sorptive qualities. In addition, by maintaining lower temperatures inside the hazardous material canister 200, such lower temperatures may keep the bentonite from transitioning from a smectite- to an illite-type clay. Such a transition is time and/or temperature dependent, and once it occurs, the bentonite no longer has the capacity to incorporate water into interlayer structures. The bentonite may also lose all or part of a capacity to sorb and retard radionuclides. In some aspects, rather than bentonite being or being part of the material 216, one or more zeolites could be mixed with quartz sand (or replace the sand) of the material 216. For example, zeolites are ring structure silicate minerals that are porous and can be used as molecular sieves. Zeolites can be manufactured and tailored to have structural pores of different sizes to effectively trap different radionuclides. There are zeolites “doped” with (silver) Ag+ ions that are designed specifically to allow I-ions (Iodine ions) to enter the zeolite structure. When the I-ions bond with the Ag+ to form AgI, the larger molecular size irreversibly traps the Iodine in the zeolite, effectively immobilizing the Iodine. Other zeolites could target different radionuclides in a similar fashion. In some aspects, inclusion of the material 216, such as sand, in the inner volume 212 of the hazardous material canister 200 may also prevent collapse of the canister 200 in the event of a rock collapse (e.g., collapse of the horizontal drillhole portion 110, including the casing (if any) by the surrounding subterranean formation). For example, when the hazardous material canister 200 is filled with the material 216, the material 216 may offer extremely strong resistance to crushing. Thus, when a strong force is applied to the canister 200 (e.g., from collapsing rock) the canister 200 may not bend because of the resistance of the material 216 to collapse. As shown in FIG. 2, the example implementation of the hazardous material canister 200 also includes an impact absorber 250 that includes a bumper 252 that is coupled to the housing 202 of the hazardous material canister 200 through a joint 256 connected to the housing (e.g., through an extension 258). As shown, the bumper 252 is positioned at a bottom (downhole) end of the canister 200. In some aspects, the bumper 252 may, alternatively, be built into or part of the bottom 208 of the housing 202. The bumper 252 may absorb impact in a free-fall collision of the canister 200 with, e.g., another hazardous material canister in the drillhole 104, the casing 122 (as shown in this figure) or other object. In some aspects, the bumper 252 may also mitigate acceleration of a free-falling canister 200 from impact at the front (downhole) end. In some aspects, as shown, the impact absorber 252 can be or include a crushable material or a spring 254, either internal to the bumper 252 or surrounding the bumper 252. In some aspects, the impact absorber 252 may assure or help assure safety of the canister 200 during lowering into the directional drillhole 104. For example, when the canister 200 is in place in a repository of the horizontal drillhole portion 110, there may not be a continuing danger of a fall, so the bumper 252 may no longer be needed. When the canister 200 is emplaced, the bumper 252 (and joint 256, and extension 258) may become a liability as a corrosion point that could create hydrogen gas within the casing 122. In a sealed environment such as the drillhole 104, such corrosion could cause an increase in pressure from corrosion volume expansion. For these reasons, in some aspects, the bumper 252 (and other illustrated components) may be made of a low-corrosion material. Possible materials include graphite, titanium, tungsten-carbide cobalt, or nickel-chromium compounds such as Inconel. In some aspects, the impact absorber 252 may also include or act as a friction brake. For instance, when the hazardous material canister 200 is falling freely (as shown by arrow 262) in the fluid-filled casing (with fluid 260 shown in the drillhole portion 106), the canister 200 may be unstable against tipping. In some cases, tipping brings the front (downhole) end of the canister 200 into contact with the casing 122. In a high velocity fall, the friction at this contact point can cause local heating and can apply a force on the canister 200 that could damage the canister integrity. The impact absorber 252 (or separate friction brake attached to the bumper 252) may include a friction brake as shown attached to an exterior of the housing 202 of the canister 200. For example, a section at the front (downhole) end of the canister 200 that is most prone to friction with the casing 122 can include the friction brake to mitigate damage from friction to the canister 200 in the case of a free fall (or otherwise). The friction brake may also utilize friction to slow the acceleration of a falling canister 200. In some aspects, a portion of the impact absorber 252 that acts as the friction brake (or the separate friction brake component of the bumper 252) can be curved (to minimize the friction), or rough or pointed to maximize the friction and provide a stronger limit on the velocity of the falling canister 200. In some aspects, the friction brake could be part of the housing 202 (e.g., on the downhole end). If the brake is rigidly attached to the canister 200, then rotation would be an extension of that of the canister 200. As shown, the friction brake (as part of the impact absorber 252 or otherwise) could also be attached to the canister 200 with the joint 256 that allows relative rotation. FIG. 3A is a schematic illustration of a hazardous material canister 300 according to the present disclosure. In some aspects, the hazardous material canister 300 may be used as the hazardous material canister 126 shown in the hazardous material storage repository system 100 of FIG. 1. In some aspects, the hazardous material canister 300 may enclose and store nuclear or radioactive waste, such as SNF or high level waste. As described in the example emplacement process of the canisters 126 into the hazardous material storage repository system 100 of FIG. 1, the hazardous material canister 300 may be placed in a human-unoccupiable deep directional drillhole (e.g., drillhole 104) for long term (e.g., hundreds if not thousands of years) storage. During the emplacement process, the hazardous material canister 300 may be moved into the directional drillhole 104 on a conveyance cable, such as, for example, a wireline cable. When the hazardous material canister 300 is lowered through the vertical portion 106 of the directional drillhole 104, there is a possibility that the cable (or a connection between the canister 300 and the cable) that supports the canister 300 may fail. Upon failure, the canister 300 will accelerate downward (e.g., in free fall) in the vertical portion 106 of the directional drillhole 104 (e.g., through a fluid in the drillhole 104). Further, although not specifically shown in FIG. 3A, the hazardous material canister 300 may include certain components as described with reference to FIG. 2, such as, for example, the material 216 and the impact absorber 252 (with or without a friction brake). If the directional drillhole 104 has a kickoff point for the transition portion 108 (e.g., a transition to a horizontal or nearly-horizontal drillhole portion from the vertical portion 106), then the canister 300 will slow and eventually stop in the horizontal drillhole portion 110. However, if the hazardous material storage repository system 100 has previously been filled with other hazardous material canisters 300, then the free-falling canister 300 could impact a stationary canister 300 with resulting damage to both hazardous material canisters 300. If the hazardous waste material (e.g., nuclear waste) inside the canister 300 is highly radioactive, there is a danger of release of this material into the drillhole portion 110, which could potentially lead to release into a surrounding subterranean formation 118, and possibly mobile water in such a formation or other formations (e.g., subterranean formation 112). The illustrated implementation of hazardous material canister 300 includes one or more features that, e.g., may reduce or prevent potential damage to the canister 300 due to a free-fall in the deep directional drillhole 104. For example, the hazardous material canister 300 may maintain its structural integrity and its value as an “engineered barrier” to the release of hazardous material during free-fall and/or impact with another object in the drillhole 104. As shown in FIG. 3A, the hazardous material canister 300 includes a housing 302 that is comprised of a middle portion 304 to which a top (or lid) 306 and bottom 308 are coupled (e.g., subsequent to enclosing the hazardous waste) to form an inner volume 312. In this example, the hazardous material is one or more SNF assemblies 310 that include SNF rods (not specifically shown here). As shown, the hazardous material canister 300 also includes two or more centralizers 314 that are attached (e.g., radially around the canister 300) to the housing 302. In some aspects, there may be three centralizers 314 attached to the housing 302 and spaced 120° radially apart. In this example, each centralizer 314 includes spacers (also called “arms”) 316 that are either spring-loaded or deployable to bias against, e.g., the casing 122 as shown. In this example, the centralizers 314 that circumscribe the hazardous material canister 300 operate during deployment of the canister 300 to hold the canister 300 near a radial centerline 318 of the vertical drillhole portion 106 (and other drillhole portions) to provide space between the canister 300 and the casing 122. Thus, during operation, the arms 316 of the centralizers 314 are biased or deployed to contact the casing 122 and align a radial centerline of the canister 300 with the centerline 318. In this example, the centralizer arms 314 may be made of spring steel or otherwise biased by springs outward against the casing 122. The centralizers 314, in some aspects, can reduce the velocity that a falling canister 300 may reach in free-fall through frictional contact with the casing 122, thereby generating a frictional force that opposes the free-fall (caused by the force of gravity) within a fluid 319 in the drillhole portion 106. FIG. 3B is a schematic illustration of a hazardous material canister 320 according to the present disclosure. In some aspects, the hazardous material canister 320 may be used as the hazardous material canister 126 shown in the hazardous material storage repository system 100 of FIG. 1. In some aspects, the hazardous material canister 320 may enclose and store nuclear or radioactive waste, such as SNF or high level waste. As described in the example emplacement process of the canisters 126 into the hazardous material storage repository system 100 of FIG. 1, the hazardous material canister 320 may be placed in a human-unoccupiable deep directional drillhole (e.g., drillhole 104) for long term (e.g., hundreds if not thousands of years) storage. During the emplacement process, the hazardous material canister 320 may be moved into the directional drillhole 104 on a conveyance cable, such as, for example, a wireline cable. When the hazardous material canister 320 is lowered through the vertical portion 106 of the directional drillhole 104, there is a possibility that the cable (or a connection between the canister 320 and the cable) that supports the canister 320 may fail. Upon failure, the canister 320 will accelerate downward (e.g., in free fall) in the vertical portion 106 of the directional drillhole 104 (e.g., through a fluid in the drillhole 104). Further, although not specifically shown in FIG. 3B, the hazardous material canister 320 may include certain components as described with reference to FIG. 2, such as, for example, the material 216 and the impact absorber 252 (with or without a friction brake), as well as certain components as described with reference to FIG. 3A, such as, for example, the centralizers 314. If the directional drillhole 104 has a kickoff point for the transition portion 108 (e.g., a transition to a horizontal or nearly-horizontal drillhole portion from the vertical portion 106), then the canister 320 will slow and eventually stop in the horizontal drillhole portion 110. However, if the hazardous material storage repository system 100 has previously been filled with other hazardous material canisters 320, then the free-falling canister 320 could impact a stationary canister 320 with resulting damage to both hazardous material canisters 320. If the hazardous waste material (e.g., nuclear waste) inside the canister 320 is highly radioactive, there is a danger of release of this material into the drillhole portion 110, which could potentially lead to release into a surrounding subterranean formation 118, and possibly mobile water in such a formation or other formations (e.g., subterranean formation 112). The illustrated implementation of hazardous material canister 320 includes one or more features that, e.g., may reduce or prevent potential damage to the canister 320 due to a free-fall in the deep directional drillhole 104. For example, the hazardous material canister 320 may maintain its structural integrity and its value as an “engineered barrier” to the release of hazardous material during free-fall and/or impact with another object in the drillhole 104. As shown in FIG. 3B, the hazardous material canister 320 includes a housing 322 that is comprised of a middle portion 324 to which a top (or lid) 326 and bottom 328 are coupled (e.g., subsequent to enclosing the hazardous waste) to form an inner volume 332. In this example, the hazardous material is one or more SNF assemblies 330 that include SNF rods (not specifically shown here). In this example, the hazardous material canister 320 also includes a disc (also called a brake) 334 that is coupled to a downhole end of the housing 322. In this example, therefore, a velocity of the hazardous material canister 320 in free-fall may be limited or reduced through the brake 334 driven by a high flow of the liquid 336 in the drillhole 106 relative to the canister movement through the drillhole 106 during free-fall. As shown in FIG. 3B, the brake 334 (which may be made from the same material as the housing 322 or a different material) may have a radial cross-section area that is larger than a radial cross-section area of the canister 320. For example, in some aspects, a diameter of the brake 334 may be smaller than but almost as large as a diameter of the casing 122. In some aspects, however, a size of the brake 334 (and surface finish of the brake 334) may be such that small discontinuities in the inner surface of the casing 122 do not impede the placement (e.g., normal, controlled movement) of the canister. This can be achieved, for example, by having an outer edge of the brake 334 (e.g., a radial circumference edge closest to the casing 122) either flexible (e.g., thinner) or sacrificial, with small sections breaking off if an impediment is encountered. In some aspects, the brake 334 and one or more centralizers (such as centralizers 314) may be employed on the hazardous material canister 320 in order to increase a braking force on the canister 320 in free fall. For instance, with respect to the braking principle, a rapid flow of the liquid 336 may provide a force on the brake 334 and the brake 334 may then cause the arms 316 of the centralizer 314 to be deployed with greater force. In some aspects, one or more of the arms 316 may be connected to the brake 334; thus, a force applied on the brake 334 may urge the arms 316 into contact with the casing 122 or, if already in contact, against the casing 122 with greater force (e.g., normal to the casing 122). In some aspects, the brake 334 may not be rigidly attached to the housing 322 but may retain some movement axially along the housing 322, e.g., to push against arms 316 of the centralizers 314. FIG. 3C is a schematic illustration of a hazardous material canister 340 according to the present disclosure. In some aspects, the hazardous material canister 340 may be used as the hazardous material canister 126 shown in the hazardous material storage repository system 100 of FIG. 1. In some aspects, the hazardous material canister 340 may enclose and store nuclear or radioactive waste, such as SNF or high level waste. As described in the example emplacement process of the canisters 126 into the hazardous material storage repository system 100 of FIG. 1, the hazardous material canister 340 may be placed in a human-unoccupiable deep directional drillhole (e.g., drillhole 104) for long term (e.g., hundreds if not thousands of years) storage. During the emplacement process, the hazardous material canister 340 may be moved into the directional drillhole 104 on a conveyance cable, such as, for example, a wireline cable. When the hazardous material canister 340 is lowered through the vertical portion 106 of the directional drillhole 104, there is a possibility that the cable (or a connection between the canister 340 and the cable) that supports the canister 340 may fail. Upon failure, the canister 340 will accelerate downward (e.g., in free fall) in the vertical portion 106 of the directional drillhole 104 (e.g., through a fluid in the drillhole 104). Further, although not specifically shown in FIG. 3C, the hazardous material canister 340 may include certain components as described with reference to FIG. 2, such as, for example, the material 216 and the impact absorber 252 (with or without a friction brake), as well as certain components as described with reference to FIG. 3B, such as, for example, the brake 334. If the directional drillhole 104 has a kickoff point for the transition portion 108 (e.g., a transition to a horizontal or nearly-horizontal drillhole portion from the vertical portion 106), then the canister 340 will slow and eventually stop in the horizontal drillhole portion 110. However, if the hazardous material storage repository system 100 has previously been filled with other hazardous material canisters 340, then the free-falling canister 340 could impact a stationary canister 340 with resulting damage to both hazardous material canisters 340. If the hazardous waste material (e.g., nuclear waste) inside the canister 340 is highly radioactive, there is a danger of release of this material into the drillhole portion 110, which could potentially lead to release into a surrounding subterranean formation 118, and possibly mobile water in such a formation or other formations (e.g., subterranean formation 112). The illustrated implementation of hazardous material canister 340 includes one or more features that, e.g., may reduce or prevent potential damage to the canister 340 due to a free-fall in the deep directional drillhole 104. For example, the hazardous material canister 340 may maintain its structural integrity and its value as an “engineered barrier” to the release of hazardous material during free-fall and/or impact with another object in the drillhole 104. As shown in FIG. 3C, the hazardous material canister 340 includes a housing 342 that is comprised of a middle portion 344 to which a top (or lid) 346 and bottom 348 are coupled (e.g., subsequent to enclosing the hazardous waste) to form an inner volume 351. In this example, the hazardous material is one or more SNF assemblies 350 that include SNF rods (not specifically shown here). In this example, the hazardous material canister 340 also includes two or more parachutes 352 that are coupled to the housing 342, e.g., through rings 356 that circumscribe a circumference of the housing 342. In this example, therefore, a velocity of the hazardous material canister 340 in free-fall may be limited or reduced through the parachutes 352 driven by a high flow of the liquid 354 in the drillhole 106 relative to the canister movement through the drillhole 106 during free-fall. In this example, the parachutes 352 may be broader on the leading end (e.g., on the downhole end of the canister 340). The broader sections of the parachutes 352, or “wings,” may be subject to a force that pushes the connection point of the parachutes 352 and the ring 356 upward and thus may push the parachutes 352 more tightly against the inner surface of the casing 122 or, generally, spread out the parachutes 352 to create more drag on the canister 340 during a free fall event. The force of the fluid 354 on the parachutes 352 may also provide force to reduce the acceleration of the canister 340 during free-fall. FIG. 3D is a schematic illustration of a hazardous material canister 360 according to the present disclosure. In some aspects, the hazardous material canister 360 may be used as the hazardous material canister 126 shown in the hazardous material storage repository system 100 of FIG. 1. In some aspects, the hazardous material canister 360 may enclose and store nuclear or radioactive waste, such as SNF or high level waste. As described in the example emplacement process of the canisters 126 into the hazardous material storage repository system 100 of FIG. 1, the hazardous material canister 360 may be placed in a human-unoccupiable deep directional drillhole (e.g., drillhole 104) for long term (e.g., hundreds if not thousands of years) storage. During the emplacement process, the hazardous material canister 360 may be moved into the directional drillhole 104 on a conveyance cable, such as, for example, a wireline cable. When the hazardous material canister 360 is lowered through the vertical portion 106 of the directional drillhole 104, there is a possibility that the cable (or a connection between the canister 360 and the cable) that supports the canister 360 may fail. Upon failure, the canister 360 will accelerate downward (e.g., in free fall) in the vertical portion 106 of the directional drillhole 104 (e.g., through a fluid in the drillhole 104). Further, although not specifically shown in FIG. 3D, the hazardous material canister 360 may include certain components as described with reference to FIG. 2, such as, for example, the material 216 and the impact absorber 252 (with or without a friction brake), as well as certain components as described with reference to FIG. 3A, 3B, or 3C, such as, for example, the centralizers 314, the brake 334, and/or the parachutes 352. If the directional drillhole 104 has a kickoff point for the transition portion 108 (e.g., a transition to a horizontal or nearly-horizontal drillhole portion from the vertical portion 106), then the canister 360 will slow and eventually stop in the horizontal drillhole portion 110. However, if the hazardous material storage repository system 100 has previously been filled with other hazardous material canisters 360, then the free-falling canister 360 could impact a stationary canister 360 with resulting damage to both hazardous material canisters 360. If the hazardous waste material (e.g., nuclear waste) inside the canister 360 is highly radioactive, there is a danger of release of this material into the drillhole portion 110, which could potentially lead to release into a surrounding subterranean formation 118, and possibly mobile water in such a formation or other formations (e.g., subterranean formation 112). The illustrated implementation of hazardous material canister 360 includes one or more features that, e.g., may reduce or prevent potential damage to the canister 360 due to a free-fall in the deep directional drillhole 104. For example, the hazardous material canister 360 may maintain its structural integrity and its value as an “engineered barrier” to the release of hazardous material during free-fall and/or impact with another object in the drillhole 104. As shown in FIG. 3D, the hazardous material canister 360 includes a housing 362 that is comprised of a middle portion 364 to which a top (or lid) 366 and bottom 368 are coupled (e.g., subsequent to enclosing the hazardous waste) to form an inner volume 372. In this example, the hazardous material is one or more SNF assemblies 370 that include SNF rods (not specifically shown here). In this example, the hazardous material canister 360 also includes a foam (e.g., a porous material that naturally expands to fill a space) cover 374 that is formed around or attached (e.g., adhesively) around all, most, or some of the housing 362 of the canister 360. In this example, the foam cover 374 covers most of the exterior of the housing 362, e.g., all but the lid 366. In alternative implementations, the foam cover 374 may cover less of the housing 362 (e.g., only a downhole end or portion) or as much as the whole housing 362. In some aspects, the foam cover 374 may be flexible enough that small discontinuities in the casing 122 may compress the foam and allow the canister 360 to be emplaced in the horizontal drillhole portion 110. The foam cover 374 may also offer resistance to fluid flow of the drillhole fluid 376. Since the force of a liquid on an object (in the high Reynold's number limit) is proportional to the square of the velocity of the object through the liquid, the fluid 376 may flow through and/or around the foam cover 374 with little resistance when the canister 360 is being slowly lowered into the vertical drillhole portion 106. However, if the canister 360 falls freely, the resistance of the foam cover 374 increases rapidly, and that increases the force of the flowing liquid 376 on the foam cover 374, which in turn acts to reduce the acceleration of the canister 360. The limiting velocity of the canister 360 surrounded by the foam cover 374 may be substantially less than the limiting velocity of a hazardous material canister that does not include the foam cover 374. The foam cover 374, in some implementations, may be made of the same (or similar) corrosion-resistant material as the housing 362 (all or part). For example, a metal material, such as a metal foam, may be used for the foam cover 374. In some aspects, other components described with respect to the example implementations of the hazardous material canister can also be made of the foam material (e.g., a metal foam). For instance, all or part of the impact absorber 252 and/or the brake 334 may be made of the foam material (as with the foam cover 374). FIGS. 4A-4B are schematic illustration of a hazardous material canister 400 according to the present disclosure. FIG. 4A shows a schematic illustration of the canister 400, while FIG. 4B shows a detail of a portion of the canister 400. In some aspects, the hazardous material canister 400 may be used as the hazardous material canister 126 shown in the hazardous material storage repository system 100 of FIG. 1. Further, in some aspects, the features described with reference to FIGS. 2 and 3A-3D may also be implemented in the hazardous material canister 400 shown in FIG. 4A. As described in the example emplacement process of the canisters 126 into the hazardous material storage repository system 100 of FIG. 1, the hazardous material canister 400 may be placed in a human-unoccupiable deep directional drillhole (e.g., drillhole 104) for long term (e.g., hundreds if not thousands of years) storage. In some aspects, the hazardous material canister 400 may enclose and store nuclear or radioactive waste, such as SNF or high level waste. For example, when hazardous material (e.g., nuclear waste such as spent nuclear fuel or high level waste) is loaded into the hazardous material canister 400 (e.g., for storage in a human-unoccupiable, deep directional drillhole), the canister seal must be made secure against even miniscule leakage. Conventionally, this is done by welding the lid, followed by both visual and radiographic inspection, and a repair of the welding if needed. In the cases of nuclear waste, if all this is done in a “hot cell” (e.g., a room in which any escaped radionuclides can be collected and safely removed without escaping the room in an unwanted manner), then the hot cell must be large and capable of incorporating all the tasks including welding. Such large hot cells can be very expensive, particularly if they are designed to be portable for use at multiple locations. In some aspects, the loading of, e.g., spent nuclear fuel in the hazardous material canister 400 and then the sealing of that canister 400 may proceed in a manner that will provide a barrier to escape of radionuclides that will perform for thousands of years. Most of the spent nuclear fuel of interest is located in either cooling pools or dry casks, large concrete and steel containers that provide safety from the gamma radiation that spent fuel emits. Spent nuclear fuel consists of pellets consisting primarily of uranium dioxide, but containing a large inventory of highly radioactive fission fragments, transuranics such as plutonium and americium, and other radioactive elements created when the fuel was in the nuclear reactor. Removing the fuel assembly from a pool or dry cask and placing the fuel assembly in a canister for disposal may be required to be performed in a hot cell in order to prevent the release of radioisotopes to the environment (e.g., outside of the hot cell). Within the fuel assemblies, the radioisotopes are confined to long tubes known as cladding, typically manufactured out of a metal alloy (such as zircalloy). The cladding provides isolation of the radioisotopes, and the main concern for safely moving the rods into canisters is that the cladding may have lost integrity, e.g., that there may be pinholes or cracks in the cladding that allow radionuclides to escape. For that reason, the transfer is typically done in the hot cell. A tiny hole in the fuel rod could allow radioactive krypton-85, for example, to leak. Other radioisotopes that might leak include tritium gas (hydrogen in which one or both hydrogen atoms are replaced with H3), chlorine-36, and materials that become volatile at high temperature, such as iodine. In addition, small particles of the fuel pellets that could have separated from the pellets and formed a dust could leak if there is a sufficiently large hole or if the cladding has substantial damage. The hazardous material canister 400, for example, provides safety against escape of radioisotopes when the fuel assembly or the fuel pellets are placed in an open housing of the canister while facilitating the sealing of two or more lids (or caps) on the housing. In some aspects, at least one of the lids may be sealed to the housing of the canister outside of a hot cell. For example, as shown, the hazardous material canister 400 includes a housing 402 that is comprised of a middle portion 404 to which tops (or lids) 406a and 406b, as well as a bottom 408 are coupled (e.g., subsequent to enclosing the hazardous waste) to form an inner volume 412. In this example, the hazardous material is one or more SNF assemblies 410 that include SNF rods (not specifically shown here). As shown more specifically in FIG. 4B, the hazardous material canister 400 includes a seal that includes two separate barriers. For example, inner lid 406b may be attached to the housing 402 of the hazardous material canister 400. In some aspects, the inner lid 406b is removably attached to the housing 404, such as by mechanical attachment (e.g., a threaded attachment). For example, as shown, threads 416 may be formed on a portion of an inner radial surface of the middle portion 404 of the housing 402. Threads 420 are also formed on a radial edge of the inner lid 406b to mate (e.g., threadingly) with the housing 402. As shown, a diameter of the inner lid 406b may be less than a diameter of outer lid 406a (and a diameter of the housing 402 at the threads 416). In such examples, the inner lid 406b may not be semi-permanently (e.g., welded) in place in such a way as to require destruction of the inner lid 406b or part of the housing 402 to remove the inner lid 406b. Other example removable attachment techniques include use of a melted metal solder or an adhesive. The inner lid attachment may provide sufficient safety for the canister 400 to be removed from the hot cell but may not provide sufficient safety for the long term requirements for disposal of the nuclear waste 410. In some aspects, the inner lid 406b may stay in place after the hazardous material canister 400 is placed in a hazardous waste repository in a deep, directional drillhole (such as in system 100). In some aspects, the inner lid 406b may not provide a seal that prevents the leakage of radioactive waste for a long time, e.g., hundreds if not thousands of years, but instead may facilitate removal of the hazardous material canister 400 from the hot cell. As shown in FIG. 4B, a seal 418 (e.g., a gasket such as a metal gasket) may be positioned between the inner lid 406b and the middle portion 404 (e.g., at a shoulder 422 of the middle portion 404). In some aspects, the gasket 418 is put under sufficient pressure by the mechanical placement of the inner lid 406b that the gasket 418 provides a seal of the inner lid 406b to the housing 402 that provides a barrier for the escape of radioactive material from the SNF assembly 410. As shown, the shoulder 422 may separate a storage portion of the volume 412 (e.g., below the shoulder 422 toward the bottom 408) from the threaded portion 416. As shown, the storage portion has a smaller diameter than the threaded portion 416 in this example. As shown, outer lid 406a is attached to the housing 402 subsequent to attachment of the inner lid 406b. The outer lid 406a, in some aspects, may provide greater safety against unwanted leakage of the radioactive waste from the SNF assembly 410 by comprising a semi-permanent seal, for example, by welding the outer lid 406a to the housing 402. As shown in this example, a weld 414 is created between the outer lid 406a and a top radial edge of the housing 402, such as by spin welding. Although not required, one or more of the components of the hazardous material canister 400, such as the housing 402 and the lids 406a and 406b, may be made from similar materials (or the same material), such as a corrosion resistant alloy (e.g., CRA-625). In some aspects, the hazardous material canister 400 (with the inner lid 406b attached) may be removed from a hot cell such that the outer lid 406a may be sealed to the housing 404 of the canister 400. In some aspects, the outer lid 406a may be certified as providing an “engineered barrier” as required by a regulatory agency. In an example operation of hazardous material canister 400, the SNF assembly 410 is placed in the inner volume 412 of the housing 402 (e.g., which is open at a top end and may be enclosed with the bottom 408). The placement of the SNF assembly 410 may be in a hot cell. Subsequently, and still in the hot cell, the inner lid 406b may be attached (e.g., threadingly) to the housing 402 to seal the SNF assembly 410 within the volume 412. The hazardous material canister 400 may then leave the hot cell, with only the inner lid 406b in place (i.e., not the outer lid 406a). Outside the hot cell, the outer lid 406a can be attached to the housing 402 (e.g., by spin welding or otherwise). The sealed hazardous material canister 400 may then be transported for emplacement in a hazardous waste repository system, such as system 100. FIG. 5 is a schematic illustration of an example implementation of a hazardous material storage repository 500 that includes a safety runway portion 502. As shown in FIG. 5, certain components of the hazardous material storage repository 500 are the same as the hazardous material storage repository 100 shown in FIG. 1, such as, for example, a deep, human-unoccupiable directional drillhole 104 formed from the terranean surface 102 through subterranean formations 112 through 118. As shown, the directional drillhole (or wellbore) 104 includes a vertical drillhole portion 106 coupled to a transition, or radiussed, drillhole portion 108. The transition drillhole 108 is coupled to a horizontal drillhole portion 110. In this example, the horizontal drillhole portion 110 is inclined relative to “horizontal” such that a first end of the drillhole portion 110 that is coupled to the transition drillhole 108 is deeper (e.g., greater TVD) than a second end of the portion 110 opposite the first end. Alternatively, the horizontal drillhole 110 may be close to or exactly horizontal. In some aspects, all or part of the directional drillhole 104 may include a casing cemented in place. As also described with reference to FIG. 1, hazardous material canisters 126 that enclose hazardous material (e.g., nuclear waste such as SNF or high level waste) may be emplaced in a storage area 504 at the second end of the horizontal drillhole portion 110. As described in the present disclosure, emplacement of hazardous material canisters 126 may include moving the canisters 126 into the storage area 504, e.g., by a downhole conveyance, such as a tractor or by a force applied by coiled tubing or a working string (e.g., of threaded tubulars). In some situations, a particular canister 126 could be accidentally released from the downhole conveyance while the canister 126 is being lowered into the directional drillhole 104. That could be due to a consequence of failure of a latch that holds the canister 126 to the conveyance, or other reason. The canister 126 may then fall at increasing velocity down the vertical portion 106 of the drillhole 104. This presents a danger that the canister 126 may collide with, e.g., a previously-placed canister, and be damaged and will release hazardous material into the drillhole 104 (and surrounding subterranean formations 112-118). In some aspects, one or more features of the canister 126 can mitigate or prevent such damage, e.g., as shown in FIGS. 2 and 3A-3D. The hazardous material storage repository 500 may, in some aspects, be operable based on its design (independent of a design of the hazardous material canisters 126 or other canisters) to bring a released canister 126 to a safe stop, avoiding impacts with any object that could cause damage to the canister 126 (or other objects in the drillhole) or release of hazardous material from a damaged canister 126. As shown, the hazardous material storage repository 500 includes a safety runway 502 that is a portion of the horizontal drillhole portion 110. The safety runway 502 is of sufficient length or inclination away (or both) from horizontal (e.g., toward the terranean surface 102), or both, to safely bring an improperly or accidentally released (and free-falling) canister 126 to rest within the drillhole portion 110 without damagingly contacting one or more hazardous material canisters 126 that are already emplaced within the storage area 504. In some aspects, the sufficient length and/or sufficient inclination may be determined according to one or more test canisters (shown as hazardous material canisters 526) used in a constructed directional drillhole (e.g., the drillhole 104 or a similar “test” drillhole) that includes a storage area (e.g., storage area 504) formed in at least a part of the horizontal portion 110 of the drillhole 104. For example, before any hazardous material in placed in a storage area of a deep, directional drillhole, one or more test canisters 526 may be inserted into the vertical portion of the drillhole from the terranean surface and purposefully allowed to fall freely into and through the vertical portion of the drillhole. The test canister 526 may be identical in all key parameters to that of a hazardous waste canister that encloses waste (e.g., high level radioactive waste or spent nuclear fuel), except that the test canister 526 will enclose non-hazardous material (e.g., with the same or similar weight as proposed hazardous waste). Thus, the test canister 526 may match the disposal canister in weight, weight distribution, and surface properties (such as coefficient of friction and roughness for liquid flow). The drillhole, including the vertical portion, curved portion, and the horizontal or nearly horizontal portion, may be filled with the same fluid or gas that is present when a disposal canister would be inserted therein (if not already filled with such fluid). In some aspects, a “test” drillhole may transition to the directional drillhole 104 based on a successful test of the test canisters 526 (and, in some aspects, meeting other criteria for suitability as a hazardous waste repository). The test canister 526 falls through the fluid in the drillhole, accelerating as it falls, and the test canister 526 may reach a terminal velocity at which time the velocity will remain approximately constant. It may not be possible to calculate that terminal velocity explicitly since the fluid flow around the test canister will likely be in a turbulent range, and insufficient analytic methods may exist to determine such velocity under these conditions. The terminal velocity can be estimated by using approximate methods and/or numerical simulations; these suggest that the terminal velocity for a 1000 kg test canister 526 will be about 10 meters per second (in the example here). However, the actual velocity of the test canister 526 may also be measured during free fall within the vertical portion of the directional drillhole. When the test canister 526 enters the curved portion, and then the horizontal (or nearly-horizontal) portion, it may slow from both fluid resistance and from friction with the walls of the drillhole (or casing). The distance that the test canister 526 may travel depends at least in part on the terminal velocity, the coefficient of friction of the exterior of the canister 526, and the upward tilt (if any) of the horizontal portion of the directional drillhole. A “stopping distance” (also called the safety runway) may be determined that is a distance that the test canister travels in the horizontal portion of the drillhole until the canister comes to zero velocity, i.e., stops from the free fall. As an example, if a terminal velocity of the test canister 526 is 10 meters per second (m/s) and the coefficient of friction, k, is 0.1, a stopping distance will be approximately 25 meters. In some aspects, according to dimensional analysis, the stopping distance will be approximately proportional to the square of the terminal velocity. Thus, a length of the horizontal portion of the drillhole that includes the storage area may be determined as a length of the repository in which hazardous waste canisters (i.e., the storage area) are stored plus the stopping distance (or safety runway). For instance, for a 1 km horizontal portion of the drillhole, 25 meters may be the stopping distance portion (i.e., the safety runway), leaving 975 meters for the repository length. In this example, there is only a 4% loss (i.e., percentage of safety runway length to length of storage area of the horizontal portion of the drillhole). As another example, for a 3 km horizontal portion length and a 25 meter safety runway portion, canister capacity in the storage area is reduced by only 1.33%. As another example, if the terminal velocity of the test canister 526 is 20 m/s, then the length of the safety runway would be about four times greater, and the reduced canister capacity would be increased by approximately four times. Such estimates may be adjusted and determined experimentally by dropping one or more test canisters 526 into a drillhole. As shown and described with reference to FIG. 5, the hazardous material storage repository 500 includes a horizontal drillhole portion 110 that is inclined upward toward the terranean surface 102 (e.g., thereby causing the drillhole 104 to resemble a “j-” or “plumber's” trap). If a part of the horizontal portion 110 is tilted upward, then the stopping distance may be shorter, since the test canister 526 will be slowed by gravity as well as by friction. For example, if the terminal velocity is 10 m/s, then gravity alone may stop the canister with a 5 meter rise. In some aspects, the inclined part of the horizontal portion 110 (and also the transition from the curved portion 108 of the drillhole 104 to the inclined part of the horizontal portion 110) may act along with a hydraulic resistance and frictional force on the test canister 526 to reduce a length of the safety runway 502. In some aspects, a terminal velocity of the test canister 526 may decrease as soon as it enters the curved portion of the directional drillhole. For example, gravity may no longer act on the canister in the direction of motion (i.e., vertically downward), which reduces a gravitational force that is moving the canister 526 through the drillhole. When the canister enters the curved portion, the canister may be directed about 30° from horizontal, and therefore, not vertically downward. The force of gravity may be reduced by about one-half, and the terminal velocity may be reduced by about 30%. When the terminal velocity is reduced by 30%, then the length of the safety runway is reduced, in turn, by 50%. So the slowing of the canister 526 in the curved portion of the drillhole can result in a significant reduction in the length of the safety runway. In some aspects, other techniques may be utilized to shorten a length of the safety runway 502. For example, a surface of the canister 126 (or a casing in the drillhole 104) could be purposefully roughened to increase the coefficient of friction, k; such roughening could also affect the flow of fluids between the canister 126 and the casing (e.g., casing 122) in such a way as to increase the hydrodynamic retarding force. However, in some circumstances, such roughening could decrease the hydrodynamic retarding force by increasing turbulence as well. In some aspects, a canister capacity of the hazardous material storage repository 500 is determined by a number of hazardous material canisters 126 that can be emplaced within the storage area 504. Thus, the horizontal portion 110 may include the storage area 504 (e.g., defined by a volume in which the canisters 126 are emplaced) and the safety runway 502 (e.g., defined by a volume in which no canisters 126 are emplaced). In some aspects, the safety runway portion is located at or near a location of the drillhole in which a curved portion meets the horizontal portion (e.g., near a “heel” of the directional drillhole) while the storage area is located near a “toe” of the directional drillhole (as shown in FIG. 5). In some aspects, a length of the safety runway portion may be determined based at least in part on an estimated terminal velocity of the hazardous waste canister in the drillhole, a friction coefficient between the canister and the drillhole (or a casing in the drillhole), and, in some cases, an inclination deviation from horizontal of at least a part of the horizontal portion of the drillhole. In some aspects, a length of the safety runway portion may be determined based at least in part on a recorded terminal velocity of a test hazardous waste canister in the drillhole, a friction coefficient between the test canister and the drillhole (or a casing in the drillhole), and, in some cases, an inclination deviation from horizontal of at least a part of the horizontal portion of the drillhole. In some aspects, a length of the safety runway portion may be determined based at least in part on a recorded stopping location of a test canister that is allowed to free fall within the drillhole, with such a stopping location being a particular distance (i.e., the safety runway distance) within the horizontal portion of the drillhole from the curved portion of the drillhole. In some aspects, a directional drillhole formed to include the storage area for the storage (or disposal) of canisters that enclose nuclear waste as well as the safety runway may allow for a rapid delivery of multiple canisters into the repository. For example, the safety runway may reduce or eliminate the danger of damage to one or more canisters due to a free falling canister within the drillhole. Thus, an initial hazardous waste canister (or set of canisters) may be emplaced into the storage area of the horizontal portion of the drillhole by releasing the canister(s) from the surface and allowing a quick descent at terminal velocity through much of the drillhole. The initial canister or set of canisters would then come to rest in the horizontal portion of the drillhole. In some aspects of the aforementioned rapid delivery process, a downhole tractor 530 (with power source) may be attached to a canister (or a canister within a set of canisters). The downhole tractor 530 may extend its wheels to make contact with the walls of the drillhole (or casing in the drillhole) only when the canister has come to rest. Alternatively, the tractor wheels may be extended during free fall of the canister(s), and the resistance between the tractor wheels and the drillhole (or casing) may reduce the velocity of the dropped canister(s). Once the canister (or canisters) has come to rest, the tractor 530 would push or pull the canister into a desired position within the hazardous waste repository. For example, a canister that weighs about 1-ton may require a pushing force from the downhole tractor 530 of about 1000 Newtons. The energy to push the canister for a distance of 1 km could be supplied by a small battery weighing less than 2 kg, such as a 1.5 kg Lithium-ion battery. The downhole tractor 530 could be left in place, or it could be programmed to move back to the access hole. In an example implementation, the downhole tractor 530 would then be retrieved to the surface. In other example implementations, the downhole tractor 530 would use the wheels in contact with the drillhole (or the casing) to crawl upward and out of the hole. For a 10 kg tractor, including battery, the additional energy required to climb out would be about 30 kWh, much less than the energy to push the canister one kilometer. In some aspects, the downhole tractor 530 could be attached to a communications cable that would indicate its location at all times. This communications cable would be light in weight, and it would be spun out so that there would be no force on it while the canister falls. In some aspects of the present disclosure in which a safety runway length is determined through test canister 526 drops into the drillhole, after a first test canister 526 is dropped and retrieved, then a set of test canisters 526 is dropped into the drillhole. The set of test canisters 526 may be connected such as railroad cars are connected in a string of cars. The second set of test canisters 526 may be designed (by increased mass and length) to slide deeper into the disposal region. After this test is done, and the set of test canisters 526 is removed (or left in place), sets of canisters 126 containing hazardous material can be dropped into the drillhole and carried by their velocity into more distant parts of the storage area. The distance they travel would be determined by their terminal velocity, which in turn is dependent on their mass, size, shape, and coefficient of friction. While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular implementations of particular inventions. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. A first example implementation according to the present disclosure includes a hazardous material storage system that includes a drillhole extending into the Earth and including an entry at least proximate a terranean surface. The drillhole includes a substantially vertical portion, a curved portion, and a horizontal portion that includes a hazardous waste repository formed within a first portion of the horizontal portion of the drillhole, the hazardous waste repository vertically isolated, by a rock formation, from a subterranean zone that includes mobile water, and a safety runway formed within a second portion of the horizontal portion exclusive of the hazardous waste repository and adjacent the curved portion, the safety runway defined by a particular length. The system further includes at least one hazardous waste canister positioned in the hazardous waste repository. The canister is sized to fit from the drillhole entry through the vertical, the curved, and the horizontal portions of the drillhole, and into the hazardous waste repository. The hazardous waste canister includes an inner cavity sized to enclose hazardous material. In an aspect combinable with the first example implementation, the hazardous waste includes nuclear waste. In another aspect combinable with any of the previous aspects of the first example implementation, the nuclear waste includes at least one of spent nuclear fuel or high level radioactive waste. In another aspect combinable with any of the previous aspects of the first example implementation, the particular length is determined based at least in part on a travel distance of the hazardous waste canister or a test canister into the horizontal portion from the vertical portion and through the curved portion in a free fall event. In another aspect combinable with any of the previous aspects of the first example implementation, the travel distance is based at least in part on a terminal velocity of the hazardous waste canister or the test canister during the free fall event and a coefficient of friction between the hazardous waste canister or the test canister and the drillhole. Another aspect combinable with any of the previous aspects of the first example implementation further includes an inclined portion of the drillhole coupled between the curved portion and the horizontal portion. In another aspect combinable with any of the previous aspects of the first example implementation, the particular length is determined based at least in part on a travel distance of the hazardous waste canister or a test canister into the horizontal portion from the vertical portion and through the curved and inclined portions in a free fall event. In another aspect combinable with any of the previous aspects of the first example implementation, the travel distance is based at least in part on a terminal velocity of the hazardous waste canister or the test canister during the free fall event, a coefficient of friction between the hazardous waste canister or the test canister and the drillhole, and an angle of inclination of the inclined portion. In another aspect combinable with any of the previous aspects of the first example implementation, the inclined portion is angled toward the terranean surface from the curved portion. In another aspect combinable with any of the previous aspects of the first example implementation, the at least one hazardous waste canister is positioned exclusively in the hazardous waste repository and externally to the safety runway. In another aspect combinable with any of the previous aspects of the first example implementation, the at least one hazardous waste canister includes a plurality of hazardous waste canisters. In another aspect combinable with any of the previous aspects of the first example implementation, each of the plurality of hazardous waste canisters is positioned exclusively in the hazardous waste repository and externally to the safety runway. Another aspect combinable with any of the previous aspects of the first example implementation further includes a seal positioned in the drillhole that isolates the hazardous waste repository from the entry of the drillhole. A second example implementation according to the present disclosure includes a method for storing hazardous waste that includes moving a hazardous waste canister through an entry of a drillhole that extends into a terranean surface. The entry is at least proximate the terranean surface, and the hazardous waste canister includes an inner cavity that encloses hazardous waste. The method further includes moving the hazardous waste canister through a vertical portion of the drillhole and through a curved portion of the drillhole; moving the hazardous waste canister from the curved portion through a first part of a horizontal portion of the drillhole that includes a safety runway defined by a particular length; and moving the hazardous waste canister from the first part of the horizontal portion of the drillhole into a second part of the horizontal portion of the drillhole that includes a hazardous waste repository. The hazardous waste canister is sized to fit from the drillhole entry through the vertical, the curved, and the horizontal portions of the drillhole. The hazardous waste repository is vertically isolated, by a rock formation, from a subterranean zone that includes mobile water. In an aspect combinable with the second example implementation, the hazardous waste includes nuclear waste. In another aspect combinable with any of the previous aspects of the second example implementation, the nuclear waste includes at least one of spent nuclear fuel or high level radioactive waste. In another aspect combinable with any of the previous aspects of the second example implementation, the particular length is determined based at least in part on a travel distance of the hazardous waste canister or a test canister into the horizontal portion from the vertical portion and through the curved portion in a free fall event. In another aspect combinable with any of the previous aspects of the second example implementation, the travel distance is based at least in part on a terminal velocity of the hazardous waste canister or the test canister during the free fall event and a coefficient of friction between the hazardous waste canister or the test canister and the drillhole. Another aspect combinable with any of the previous aspects of the second example implementation further includes an inclined portion of the drillhole coupled between the curved portion and the horizontal portion. In another aspect combinable with any of the previous aspects of the second example implementation, the particular length is determined based at least in part on a travel distance of the hazardous waste canister or a test canister into the horizontal portion from the vertical portion and through the curved and inclined portions in a free fall event. In another aspect combinable with any of the previous aspects of the second example implementation, the travel distance is based at least in part on a terminal velocity of the hazardous waste canister or the test canister during the free fall event, a coefficient of friction between the hazardous waste canister or the test canister and the drillhole, and an angle of inclination of the inclined portion. In another aspect combinable with any of the previous aspects of the second example implementation, the inclined portion is angled toward the terranean surface from the curved portion. In another aspect combinable with any of the previous aspects of the second example implementation, the at least one hazardous waste canister is positioned exclusively in the hazardous waste repository and externally to the safety runway. In another aspect combinable with any of the previous aspects of the second example implementation, the at least one hazardous waste canister includes a plurality of hazardous waste canisters. In another aspect combinable with any of the previous aspects of the second example implementation, each of the plurality of hazardous waste canisters is positioned exclusively in the hazardous waste repository and externally to the safety runway. Another aspect combinable with any of the previous aspects of the second example implementation further includes positioning a seal in the drillhole that isolates the hazardous waste repository from the entry of the drillhole. A third example implementation according to the present disclosure includes a nuclear waste canister that includes a housing that includes a closed end and an open end opposite the closed end. The housing defines an inner volume sized to hold at least one nuclear waste portion. The housing is configured to store nuclear waste in a human-unoccupiable directional drillhole. The canister includes a first lid attachable to the housing between the closed end and the open end to create a first seal of the inner volume; and a second lid attachable to the housing at or near the open end to create a second seal of the inner volume. In an aspect combinable with the third example implementation, the nuclear waste portion includes a spent nuclear fuel assembly. In another aspect combinable with any of the previous aspects of the third example implementation, the outer housing includes a corrosion resistant alloy. In another aspect combinable with any of the previous aspects of the third example implementation, the corrosion resistant alloy includes CRA 625. In another aspect combinable with any of the previous aspects of the third example implementation, the first lid is configured to mechanically attach to the housing. In another aspect combinable with any of the previous aspects of the third example implementation, the first lid is configured to threadingly attach to the housing. In another aspect combinable with any of the previous aspects of the third example implementation, the housing includes an inner surface that includes a threaded portion between the open end and the closed end. In another aspect combinable with any of the previous aspects of the third example implementation, the inner surface includes a smooth portion between the closed end and the threaded portion. In another aspect combinable with any of the previous aspects of the third example implementation, the inner volume includes a first cross-sectional dimension at the smooth portion of the inner surface and a second cross-sectional dimension greater than the first cross-sectional dimension at the threaded portion of the inner surface. Another aspect combinable with any of the previous aspects of the third example implementation further includes a gasket positioned between a portion of the housing and the first lid. In another aspect combinable with any of the previous aspects of the third example implementation, the gasket includes a metal gasket. In another aspect combinable with any of the previous aspects of the third example implementation, the second lid is attachable to the housing at the open end. In another aspect combinable with any of the previous aspects of the third example implementation, the second lid is attachable to the housing at or near the open end with a weld. In another aspect combinable with any of the previous aspects of the third example implementation, the weld includes a spin weld. In another aspect combinable with any of the previous aspects of the third example implementation, the first lid is attachable to the housing within a hot cell, and the second lid is attachable to the housing outside of the hot cell. A fourth example implementation according to the present disclosure includes a method for containing nuclear waste that includes placing at least one nuclear waste portion into an inner volume of a housing of a nuclear waste canister. The housing includes a closed end and an open end opposite the closed end. The housing is configured to store nuclear waste in a human-unoccupiable directional drillhole. The method further includes attaching a first lid to the housing between the closed end and the open end to create a first seal of the inner volume; and attaching a second lid to the housing at or near the open end to create a second seal of the inner volume. In an aspect combinable with the fourth example implementation, the nuclear waste portion includes a spent nuclear fuel assembly. In another aspect combinable with any of the previous aspects of the fourth example implementation, the outer housing includes a corrosion resistant alloy. In another aspect combinable with any of the previous aspects of the fourth example implementation, the corrosion resistant alloy includes CRA 625. In another aspect combinable with any of the previous aspects of the fourth example implementation, attaching the first lid includes mechanically attaching the first lid to the housing. In another aspect combinable with any of the previous aspects of the fourth example implementation, mechanically attaching the first lid includes threadingly attaching the first lid to the housing. In another aspect combinable with any of the previous aspects of the fourth example implementation, threadingly attaching the first lid to the housing includes screwing the first lid to an inner surface that includes a threaded portion between the open end and the closed end. In another aspect combinable with any of the previous aspects of the fourth example implementation, the inner surface includes a smooth portion between the closed end and the threaded portion. In another aspect combinable with any of the previous aspects of the fourth example implementation, the inner volume includes a first cross-sectional dimension at the smooth portion of the inner surface and a second cross-sectional dimension greater than the first cross-sectional dimension at the threaded portion of the inner surface. Another aspect combinable with any of the previous aspects of the fourth example implementation further includes a gasket positioned between a portion of the housing and the first lid. In another aspect combinable with any of the previous aspects of the fourth example implementation, the gasket includes a metal gasket. In another aspect combinable with any of the previous aspects of the fourth example implementation, attaching the second lid to the housing at or near the open end includes attaching the second lid to the housing at the open end. In another aspect combinable with any of the previous aspects of the fourth example implementation, attaching the second lid includes welding the second lid to the housing at or near the open end. In another aspect combinable with any of the previous aspects of the fourth example implementation, welding the second lid includes spin welding the second lid to the housing. In another aspect combinable with any of the previous aspects of the fourth example implementation, the step of attaching the first lid occurs within a hot cell, and the step of attaching the second lid occurs outside of the hot cell. A fifth example implementation according to the present disclosure includes a nuclear waste disposal system that includes a nuclear waste canister including a housing that defines an interior volume sized to enclose nuclear waste. The nuclear waste canister is configured to store the nuclear waste in a human-unoccupiable directional drillhole in a subterranean formation beneath a terranean surface. The system further includes a free-fall limiting device mounted on the nuclear waste canister configured to slow a velocity of the canister during free-fall movement of the canister in the drillhole. In an aspect combinable with the fifth example implementation, the nuclear waste includes spent nuclear fuel. In another aspect combinable with any of the previous aspects of the fifth example implementation, the spent nuclear fuel includes at least one spent nuclear fuel assembly. In another aspect combinable with any of the previous aspects of the fifth example implementation, the free-fall limiting device includes a centralizer mounted on the nuclear waste canister. In another aspect combinable with any of the previous aspects of the fifth example implementation, the centralizer includes a plurality of expandable arms configured to adjust radially away from the housing to contact the drillhole during free-fall movement of the canister in the drillhole. In another aspect combinable with any of the previous aspects of the fifth example implementation, the plurality of expandable arms are configured to adjust radially away from the housing based at least in part on a fluid force acting on the arms during free-fall movement of the canister in the drillhole. Another aspect combinable with any of the previous aspects of the fifth example implementation further includes a disc mounted on a downhole end of the canister. In another aspect combinable with any of the previous aspects of the fifth example implementation, the disc is configured to increase a fluid force acting on the arms during free-fall movement of the canister in the drillhole. In another aspect combinable with any of the previous aspects of the fifth example implementation, the free-fall limiting device includes one or more parachute arms mounted on a downhole end of the canister. In another aspect combinable with any of the previous aspects of the fifth example implementation, the parachute arms are configured to increase a fluid force acting on the arms during free-fall movement of the canister in the drillhole. In another aspect combinable with any of the previous aspects of the fifth example implementation, the free-fall limiting device includes a foam member mounted on the canister. In another aspect combinable with any of the previous aspects of the fifth example implementation, the foam member is configured to increase a fluid force acting on the foam member during free-fall movement of the canister in the drillhole. Another aspect combinable with any of the previous aspects of the fifth example implementation further includes at least one impact absorber mounted on the canister. In another aspect combinable with any of the previous aspects of the fifth example implementation, the impact absorber is mounted on a downhole end of the canister. A sixth example implementation according to the present disclosure includes a method for impeding a free-falling nuclear waste canister that includes moving a nuclear waste canister through a directional drillhole from a terranean surface toward a subterranean zone on a cable, the nuclear waste canister configured to store nuclear waste; and based on the nuclear waste canister experiencing a free-fall event upon being detached from the cable, limiting a free-fall velocity of the canister in the drillhole with a free-fall limiting device mounted on the nuclear waste canister. In an aspect combinable with the sixth example implementation, the nuclear waste includes spent nuclear fuel. In another aspect combinable with any of the previous aspects of the sixth example implementation, the spent nuclear fuel includes at least one spent nuclear fuel assembly. In another aspect combinable with any of the previous aspects of the sixth example implementation, the free-fall limiting device includes a centralizer mounted on the nuclear waste canister. In another aspect combinable with any of the previous aspects of the sixth example implementation, limiting the free-fall velocity of the canister in the drillhole includes radially adjusting a plurality of expandable arms on the centralizer to contact the drillhole during free-fall movement of the canister in the drillhole. In another aspect combinable with any of the previous aspects of the sixth example implementation, the plurality of expandable arms are configured to adjust radially away from the housing based at least in part on a fluid force acting on the arms during free-fall movement of the canister in the drillhole. Another aspect combinable with any of the previous aspects of the sixth example implementation further includes a disc mounted on a downhole end of the canister. In another aspect combinable with any of the previous aspects of the sixth example implementation, the disc is configured to increase a fluid force acting on the arms during free-fall movement of the canister in the drillhole. In another aspect combinable with any of the previous aspects of the sixth example implementation, the free-fall limiting device includes one or more parachute arms mounted on a downhole end of the canister. In another aspect combinable with any of the previous aspects of the sixth example implementation, limiting the free-fall velocity of the canister in the drillhole includes increasing a fluid force acting on the arms during free-fall movement of the canister in the drillhole. In another aspect combinable with any of the previous aspects of the sixth example implementation, the free-fall limiting device includes a foam member mounted on the canister. In another aspect combinable with any of the previous aspects of the sixth example implementation, limiting the free-fall velocity of the canister in the drillhole includes increasing a fluid force acting on the foam member during free-fall movement of the canister in the drillhole. Another aspect combinable with any of the previous aspects of the sixth example implementation further includes at least one impact absorber mounted on the canister. In another aspect combinable with any of the previous aspects of the sixth example implementation, the impact absorber is mounted on a downhole end of the canister. A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, while many example implementations of a hazardous material canister according to the present disclosure include a cross-section that is circular or oval, other shapes are contemplated, such as square or rectangular. Also, example operations, methods, or processes described herein may include more steps or fewer steps than those described. Further, the steps in such example operations, methods, or processes may be performed in different successions than that described or illustrated in the figures. Accordingly, other implementations are within the scope of the following claims.
062263439	abstract	A water rod for a fuel assembly of a boiling water nuclear reactor has a first end and a second end, wherein at least one of the first and second ends is directly attachable to a tie plate of the fuel assembly without an end plug. The structure of the present invention simplifies the manufacturing process and reduces the cost of the fuel assembly in the boiling water nuclear reactor. The water rod according to the invention has one or both of its ends configured to be directly attachable to the tie plate of the fuel assembly.
	summary
	description	The present disclosure is generally related to nuclear reactors and, more particularly, embodiments of the present disclosure are related to methods and systems for reactor lattice depletion. In a typical nuclear reactor, energy is produced from fissionable material located in fuel assemblies or bundles within a reactor core. Depletion of the fissionable material occurs throughout the operational life of a nuclear reactor. Operational and refueling cycles are dependent upon fuel depletion in the reactor core. Reactor core depletion is tracked using lattice depletion estimations. A lattice represents the spatial distribution of fissionable and non-fissionable materials within a portion of the reactor. Lattice depletion estimations incorporate eigenvalue calculations preformed with defined boundary condition. In an operating reactor, a reactor eigenvalue (kreactor) represents the ratio of neutron production to neutron loss (absorption and leakage) within the reactor. Thus, the reactor eigenvalue is one for a self-sustaining reactor, less than one for a subcritical reactor, and greater than one for a supercritical reactor. Current industry methods assume a fixed reflective boundary condition and solve an auxiliary equation with some simplification (e.g. homogenization) of the lattice to match the operating reactor eigenvalue. However, use of the fixed boundary condition and simplification of the lattice produces a neutron energy spectrum that does not properly account for the actual lattice heterogeneity and boundary effects. Thus, lattice depletion estimations using these methods result in errors in the calculated depletion within the reactor core. These errors can adversely affect fuel utilization, plant availability, operating margins, and fuel damage probabilities. Briefly described, embodiments of this disclosure, among others, include methods and systems for reactor lattice depletion. One exemplary method, among others, comprises the steps of defining a reactor eigenvalue, the reactor eigenvalue being a specified ratio of actual neutron production to loss in the reactor; producing a lattice eigenvalue, the lattice eigenvalue being an estimated ratio of neutron production to loss in the lattice; and adjusting a boundary condition of the lattice to cause convergence of the lattice eigenvalue and the reactor eigenvalue in order to produce at least one physics parameter. Systems are also provided. One exemplary system, among others, comprises means for defining a reactor eigenvalue, the reactor eigenvalue being a specified ratio of actual neutron production to loss in the reactor; means for producing a lattice eigenvalue, the lattice eigenvalue being an estimated ratio of neutron production to loss in the lattice; and means for adjusting a boundary condition of the lattice to cause convergence of the lattice eigenvalue and the reactor eigenvalue in order to produce at least one physics parameter. Another exemplary embodiment, among others, comprises a computer readable medium having software code configured to perform the steps of defining a reactor eigenvalue, the reactor eigenvalue being a specified ratio of actual neutron production to loss in the reactor; producing a lattice eigenvalue, the lattice eigenvalue being an estimated ratio of neutron production to loss in the lattice; and adjusting a boundary condition of the lattice to cause convergence of the lattice eigenvalue and the reactor eigenvalue in order to produce at least one physics parameter. Other structures, systems, methods, features, and advantages will be, or become, apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional structures, systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims. Reactor lattice depletion methods solve transport theory to determine the neutron distributions within a lattice. The Boltzmann neutron transport equation, [ Ω ⋒ · Δ → + σ ⁡ ( r → , E ) ] ⁢ ϕ ⁡ ( r → , Ω ⋒ , E ) = ∫ ⅆ E ′ ⁢ ∫ ⅆ Ω ′ ⁢ σ s ⁡ ( r → , Ω ′ → Ω , E ′ → E ) ⁢ ϕ ⁡ ( r → , Ω ⋒ ′ , E ′ ) + χ ⁡ ( E ) k ⁢ ∫ ⅆ E ′ ⁢ v ⁢ ⁢ σ f ⁡ ( r → , E ′ ) ⁢ ∫ ⅆ Ω ′ ⁢ ϕ ⁡ ( r → , Ω ⋒ ′ , E ′ ) , ( Equation ⁢ ⁢ 1 ) provides a description of the distribution of neutrons in space, energy and direction (of motion) and is required for depletion estimation. Lattice depletion methods apply neutron transport theory to relatively small portions of the reactor defined by a lattice with defined boundary conditions. A lattice typically represents the spatial distribution of fissionable and non-fissionable materials in a section of the reactor. Each lattice is defined by the user and is dependent upon the reactor design. Predefined lattices are available from manufactures for commercially available fuel assemblies or bundles. Lattices can also be individually generated for new designs. A lattice eigenvalue (klattice) represents the ratio of neutron production to neutron loss within the lattice. Current industry methods solve the neutron transport eigenvalue equation using a reflective boundary condition. Reflective boundary conditions equate the lattice transport problem to one involving an infinitely large core composed of a single type of assembly or bundle. The reflective condition represents the assumption that all neutrons that reach the boundary of the lattice are either reflected back into the lattice or replaced by incoming neutrons, i.e. no leakage. The largest positive eigenvalue for a lattice with reflective boundary conditions represents the infinite medium neutron multiplication factor (k∞), the ratio of neutron production to neutron absorption, since the boundary condition does not allow for any neutron leakage. In an operating reactor, a reactor eigenvalue (kreactor) represents the actual neutron production to loss ratio within the reactor. Since the lattice boundary condition is not known a priori, current industry methods match the lattice eigenvalue to the reactor eigenvalue by simplifying or spatially homogenizing the lattice and then iteratively adjusting the leakage though the buckling term in the transport equation. The resulting neutron energy spectrum from these calculations does not properly account for the lattice heterogeneity and the boundary conditions in the operating reactor. As a result, subsequent lattice depletion estimations may not be accurate. To obtain improved results, the lattice boundary condition must simulate the environment within the nuclear reactor core. Embodiments of a boundary condition adjustment method and system are described below. It should be emphasized that the described embodiments are merely possible examples of implementations, and are set forth for clear understanding of the principles of the present disclosure, and in no way limit the scope of the disclosure. FIG. 1 illustrates a boundary condition adjustment (BCA) method. The boundary condition adjustment method adjusts the boundary conditions causing the lattice eigenvalue to converge to the reactor eigenvalue, while maintaining the heterogeneity of the lattice. The boundary condition adjustment method 100 receives input data from a user (110). Input data can include, but are not limited to, the reactor eigenvalue, initial boundary conditions, and a specified lattice. For source driven reactors, the reactor eigenvalue is replaced with a multiplicity constant (k). Boundary conditions can be defined as, but are not limited to, constants, spatially dependent functions, and functions in terms of reflection coefficients. Determination of a lattice eigenvalue (120) is carried out utilizing the input data. This determination can be accomplished using either deterministic or stochastic methods to solve the neutron transport problem. Deterministic methods include, but are not limited to, collision probability method (CPM), method of characteristics (MOC), discrete-ordinate methods, even-parity methods, response matrix methods, and finite element methods. Stochastic methods include, but are not limited to, Monte Carlo methods (either continuous energy or multigroup), Markov methods, and Stochastic Mesh methods. Convergence of the lattice eigenvalue to the reactor eigenvalue is then evaluated (130). If the lattice eigenvalue has not converged, then the initial boundary condition is adjusted to determine an adjusted boundary condition (140). The adjusted boundary condition is then used to adjust the lattice eigenvalue by repeating the lattice eigenvalue determination (120). Evaluation of the convergence (130) of the adjusted lattice eigenvalue to the reactor eigenvalue is performed. This sequence of determining the adjusted boundary condition (140), adjusting the lattice eigenvalue (120), and evaluating convergence (130) is continued until convergence of the lattice eigenvalue to the reactor eigenvalue is achieved to within a preset limit. When the lattice eigenvalue converges, the solution including all ensuing parameters or quantities resulting from the solution itself, such as, but not limited to, physics parameters, are provided (150) for use in reactor design, optimization, simulation and monitoring. Physics parameters can include, but are not limited to, neutron flux and current, neutron absorption, neutron fission, neutron scattering kernel, fission spectrum, neutron spectrum, and the adjusted boundary condition. Because adjustments are performed directly on the boundary condition without any simplification of the geometry or the material distribution in the lattice, estimates of spatial and spectral distributions of the neutrons are improved. It is possible to perform critical (kreactor=1) as well as fixed multiplicity constant (user defined k) lattice depletion estimations using the BCA method 100. FIG. 2 is an alternative embodiment of the boundary condition adjustment (BCA) method utilizing a stochastic method in the lattice eigenvalue determination. In this non-limiting embodiment of the BCA method 100, input data provided by the user (210) includes, but is not limited to, a reactor eigenvalue 212 and an initial boundary condition 214. The initial boundary condition is defined in terms of reflection coefficients. In this non-limiting embodiment, the reflection coefficients are designated α and β. The α coefficient is defined such that for each neutron that reaches an external boundary an α-fraction of this neutron will leak out of or into the lattice and (1−α) fraction will respectively be reflected back into or out of the lattice with a user defined distribution, such as, but not limited to, specular reflection, mirror reflection, white reflection, and isotropic reflection. The sign of α determines the leakage direction—out of (positive) or into (negative) the lattice. The α coefficient can be constant or spatially vary based on segment or point on the lattice boundary. The α coefficient is a function of the β coefficient. The function can be the same for all α coefficients or can spatially vary with each boundary segment. A reflective boundary condition is described when the values of α and β coefficients are zero. The initial choice of α and β is entirely up to the user. If one has prior knowledge of the problem, these variables can be adjusted to minimize convergence iterations. Determination of the lattice eigenvalue (220) can begin once the boundary conditions are defined for the lattice. In this non-limiting embodiment, the lattice has been specified prior to the data input (210) being completed. The lattice eigenvalue is produced by solving the neutron transport problem stochastically using a Monte Carlo method. Deterministic methods may also be utilized to determine the lattice eigenvalue. Such stochastic and deterministic methods are well known to those skilled in the art. Convergence of the lattice eigenvalue (klattice) to the reactor eigenvalue (kreactor) is then checked (230). Convergence occurs when the lattice eigenvalue approaches to within a preset limit of the reactor eigenvalue. Appropriate choice of the preset limit can minimize convergence iterations. In this non-limiting embodiment, the lattice eigenvalue is directly compared to the reactor eigenvalue. Convergence can also be evaluated using other variables, such as, but not limited to, the refection coefficients α and β since these converge simultaneously with the lattice eigenvalue. If the lattice eigenvalue has not converged, then the initial boundary condition is adjusted to determine an adjusted boundary condition (240). In this non-limiting embodiment, the β coefficient is adjusted (242) using the following equation.βu+1=C1,u(klattice,u−kreactor)+C2,uβu (Equation 2)In this equation, C1 and C2 are arbitrary variables and an index u indicates the iteration or cycle number (e.g., source iteration). The values of C1 and C2 can be determined based on the physics of the current problem or randomly chosen from within a user defined range. This user defined range can be based on the relevant physics of the problem at hand. Values of C1 and C2 that are too high will result in strong oscillations in the lattice eigenvalue hindering its convergence. Values that are too small will result in slow convergence to the reactor eigenvalue. Once the β coefficient is adjusted, the a coefficient is then updated (244) using the following equation.αi,u+1p=ƒip(βu+1), ∀iε∂V (Equation 3)In this equation, an index i refers to a boundary segment or point on the surface ∂V, p represents remaining phase space variables, and ƒ is the function describing the relationship between the α and β coefficients. Equation 3 allows the α coefficient values to vary for different segments or points on the boundary and the remaining phase space. The function ƒ can also vary for different segments or points on the boundary and the remaining phase space. In a non-limiting embodiment where all α coefficient values are the same and are equal to the β coefficient, then β can be directly replaced in Equation 2.αu+1=βu+1=C1,u(klattice,u−kreactor)+C2,uβu=C1,u(klattice,u−kreactor)+C2,uαu (Equation 4) The adjusted boundary condition is then used to adjust the lattice eigenvalue by repeating the lattice eigenvalue determination (220). This sequence of evaluating convergence (230), determining the adjusted boundary condition (240), and adjusting the lattice eigenvalue (220) is continued until convergence of the lattice eigenvalue to within the preset limit of the reactor eigenvalue is achieved. The variables C1 and C2 can be estimated based on the physics of the neutron transport problem at hand. In this non-limiting example, the estimation of C1 and C2 is based on the neutron balance. The lattice eigenvalue can be calculated as the ratio of neutron production to neutron loss given by the following equation. k lattice , u = ∫ S ⁢ Fϕ u ⁢ ⅆ s ∫ S ⁢ H ⁢ ⁢ ϕ u ⁢ ⅆ s + L u ( Equation ⁢ ⁢ 5 ) In this equation, φu is the lattice neutron flux distribution as a function of the phase space s, the numerator represents total production (integrated over the entire phase space s) in the lattice, the first term in the denominator represents total absorption (integrated over the entire phase space s) in the lattice, and Lu is net neutron leakage from the lattice. The net neutron leakage is zero for a fully reflective boundary condition. The reactor eigenvalue can be represented using the same relationship in terms of reactor neutron flux distribution (φreactor) and reactor neutron leakage (Lreactor). k reactor = ∫ S ⁢ F ⁢ ⁢ ϕ reactor ⁢ ⅆ s ∫ S ⁢ H ⁢ ⁢ ϕ reactor ⁢ ⅆ s + L reactor ( Equation ⁢ ⁢ 6 ) Since the reactor flux distribution (φreactor) is not known a priori, it is approximated using lattice neutron flux distribution (φu). This allows an approximation of the lattice neutron leakage (Lu+1) for use in an iteration process as follows where u indicates the iteration or cycle number. L u + 1 = ( k lattice , u - k reactor ) ⁢ ∫ S ⁢ H ⁢ ⁢ ϕ u ⁢ ⅆ s k reactor + k lattice , u k reactor ⁢ L u ( Equation ⁢ ⁢ 7 ) This lattice neutron leakage term can be used to estimate C1 and C2. Using different approximations will yield different expressions for the C1 and C2 variables. In the non-limiting embodiment where all α coefficient values are the same and equal to the β coefficient, as shown in Equation 4, the α coefficient can be estimated using the ratio of the lattice neutron leakage term (Lu+1) to the term accounting for the neutrons reaching the lattice surface (Ju). Substituting for the neutron leakage term, allows Equation 7 to be rewritten as follows. α u + 1 = ( k lattice , u - k reactor ) ⁢ ∫ S ⁢ H ⁢ ⁢ ϕ u ⁢ ⅆ s J u · k reactor + k lattice , u k reactor ⁢ J u - 1 ⁢ α u J u ⁢ = C 1 , u ⁡ ( k lattice , u - k reactor ) + C 2 , u ⁢ α u ( Equation ⁢ ⁢ 8 ) This iterative process is then used to provide an adjusted boundary condition. As can be seen from Equation 8, the leakage term and α coefficient converge as the lattice eigenvalue converges to the reactor eigenvalue. This process can be utilized in either deterministic or stochastic methods. Since one must compute the total absorption term and Ju on all boundaries, implementation of this method can be complicated. Further simplifications in deterministic or stochastic codes, such as, but not limited to, Monte Carlo N-Particle transport code (MCNP), can improve solution times. In a non-limiting implementation using MCNP code, an average lattice eigenvalue (kave) is estimated by a stochastic process. Since MCNP code normalizes the solution in such a way that the production term in the numerator of Equation 5 is equal to the average lattice eigenvalue, the integrated absorption term in the denominator of Equation 5 can be approximated by (1−Lu). This normalization also allows approximating Ju by kave. Equation 8 can be rewritten as the following since C2,u converges to unity (one) as the eigenvalues and leakage converge. α u + 1 = ( k ave - k reactor ) ⁢ ( 1 - L u ) k ave ⁢ k reactor + α u = C 1 , u ⁡ ( k ave - k reactor ) + α ( Equation ⁢ ⁢ 9 ) Application of this model does not take into account the random nature of the stochastic process. This introduces a bias in the eigenvalue calculations that can cause strong oscillations. Introducing a random factor (ρ) to Equation 9 can be used to control the attributed contribution to the leakage such that Equation 9 becomes the following. α u + 1 = ρ ⁢ ( k ave - k reactor ) ⁢ ( 1 - L u ) k reactor ⁢ k ave + α u ( Equation ⁢ ⁢ 10 ) Introduction of the random factor (ρ) mitigates, but does not eliminate oscillations in the eigenvalue calculations. Trends can still persist because the α coefficient depends only on kave and does not take into account the eigenvalue of the previous cycle. This can be incorporated by replacing kave with a weighted sum of kave and the previous lattice eigenvalue (ku).knew=wavgkave+wuku (Equation 11)In this equation, the weights attributed to each respective eigenvalue (wave and wu) are normalized to sum equal to one. A simple averaging of wave=wu=0.5 can greatly improve the trend of the eigenvalue. Incorporating the random factor (ρ) and weighted sum (knew) in this non-limiting implementation, the C1,u variable can be expressed as the following. C u , 1 = ρ ⁢ ( 1 - L u ) k reactor ⁢ k new ( Equation ⁢ ⁢ 12 ) Using different approximations can yield different expressions for the C1,u variable. When the lattice eigenvalue has converged within a preset limit to the reactor eigenvalue, user selected physics parameters determined from the adjusted boundary condition are provided (250). If the lattice eigenvalue converged using the initial boundary condition, then adjustment of the boundary condition is not necessary and user selected physics parameters produced using the initial boundary condition are provided to the user. The boundary condition adjustment (BCA) system of the invention can be implemented in software (e.g., firmware), hardware, or a combination thereof. In the currently contemplated best mode, the BCA system is implemented in software, as an executable program, and is executed by a special or general purpose digital computer, such as a personal computer (PC; IBM-compatible, Apple-compatible, or otherwise), workstation, minicomputer, or mainframe computer. An example of a general purpose computer that can implement the BCA system of the present invention is shown in FIG. 3. In FIG. 3, the BCA system is denoted by reference numeral 310. Generally, in terms of hardware architecture, as shown in FIG. 3, the computer 311 includes a processor 312, memory 314, and one or more input and/or output (I/O) devices 316 (or peripherals) that are communicatively coupled via a local interface 318. The local interface 318 can be, for example but not limited to, one or more buses or other wired or wireless connections, as is known in the art. The local interface 318 may have additional elements, which are omitted for simplicity, such as controllers, buffers (caches), drivers, repeaters, and receivers, to enable communications. Further, the local interface may include address, control, and/or data connections to enable appropriate communications among the aforementioned components. The processor 312 is a hardware device for executing software, particularly that stored in memory 314. The processor 312 can be any custom made or commercially available processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the computer 311, a semiconductor based microprocessor (in the form of a microchip or chip set), a macroprocessor, or generally any device for executing software instructions. Examples of suitable commercially available microprocessors are as follows: a PA-RISC series microprocessor from Hewlett-Packard Company, an 80×86 or Pentium series microprocessor from Intel Corporation, a PowerPC microprocessor from IBM, a Sparc microprocessor from Sun Microsystems, Inc, or a 68xxx series microprocessor from Motorola Corporation. The memory 314 can include any one or combination of volatile memory elements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM, etc.) and nonvolatile memory elements (e.g., ROM, hard drive, tape, CDROM, etc.). Moreover, the memory 314 may incorporate electronic, magnetic, optical, and/or other types of storage media. Note that the memory 314 can have a distributed architecture, where various components are situated remote from one another, but can be accessed by the processor 312. The software in memory 314 may include one or more separate programs, each of which comprises an ordered listing of executable instructions for implementing logical functions. In the example of FIG. 3, the software in the memory 314 includes the BCA system in accordance with the present invention and a suitable operating system (O/S) 322. A nonexhaustive list of examples of suitable commercially available operating systems 322 is as follows: (a) a Windows operating system available from Microsoft Corporation; (b) a Netware operating system available from Novell, Inc.; (c) a Macintosh operating system available from Apple Computer, Inc.; (e) a UNIX operating system, which is available for purchase from many vendors, such as the Hewlett-Packard Company, Sun Microsystems, Inc., and AT&T Corporation; (d) a LINUX operating system, which is freeware that is readily available on the Internet; (e) a run time Vxworks operating system from WindRiver Systems, Inc.; or (f) an appliance-based operating system, such as that implemented in handheld computers or personal data assistants (PDAs) (e.g., PalmOS available from Palm Computing, Inc., and Windows CE available from Microsoft Corporation). The operating system 322 essentially controls the execution of other computer programs, such as the BCA system 310, and provides scheduling, input-output control, file and data management, memory management, and communication control and related services. The BCA system 310 is a source program, executable program (object code), script, or any other entity comprising a set of instructions to be performed. When a source program, then the program needs to be translated via a compiler, assembler, interpreter, or the like, which may or may not be included within the memory 314, so as to operate properly in connection with the O/S 322. Furthermore, the BCA system 310 can be written as (a) an object oriented programming language, which has classes of data and methods, or (b) a procedure programming language, which has routines, subroutines, and/or functions, for example but not limited to, C, C++, Pascal, Basic, Fortran, Cobol, Perl, Java, and Ada. In the currently contemplated best mode of practicing the invention, the BCA system 310 can be implemented using Monte Carlo N-Particle transport code (MCNP). The I/O devices 316 may include input devices, for example but not limited to, a keyboard, mouse, scanner, microphone, etc. Furthermore, the I/O devices 316 may also include output devices, for example but not limited to, a printer, display, etc. Finally, the I/O devices 316 may further include devices that communicate both inputs and outputs, for instance but not limited to, a modulator/demodulator (modem; for accessing another device, system, or network), a radio frequency (RF) or other transceiver, a telephonic interface, a bridge, a router, etc. If the computer 311 is a PC, workstation, or the like, the software in the memory 314 may further include a basic input output system (BIOS) (omitted for simplicity). The BIOS is a set of essential software routines that initialize and test hardware at startup, start the O/S 322, and support the transfer of data among the hardware devices. The BIOS is stored in ROM so that the BIOS can be executed when the computer 311 is activated. When the computer 311 is in operation, the processor 312 is configured to execute software stored within the memory 314, to communicate data to and from the memory 314, and to generally control operations of the computer 311 pursuant to the software. The BCA system 310 and the O/S 322, in whole or in part, but typically the latter, are read by the processor 312, perhaps buffered within the processor 312, and then executed. When the BCA system 310 is implemented in software, as is shown in FIG. 3, it should be noted that the BCA system 310 can be stored on any computer readable medium for use by or in connection with any computer related system or method. In the context of this document, a computer readable medium is an electronic, magnetic, optical, or other physical device or means that can contain or store a computer program for use by or in connection with a computer related system or method. The BCA system 310 can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “computer-readable medium” can be any means that can store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a nonexhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic) having one or more wires, a portable computer diskette (magnetic), a random access memory (RAM) (electronic), a read-only memory (ROM) (electronic), an erasable programmable read-only memory (EPROM, EEPROM, or Flash memory) (electronic), an optical fiber (optical), and a portable compact disc read-only memory (CDROM) (optical). Note that the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory. In an alternative embodiment, where the BCAS system 310 is implemented in hardware, the BCA system can implemented with any or a combination of the following technologies, which are each well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc. It should be emphasized that the above-described embodiments of the present invention, particularly, any “preferred” embodiments, are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiment(s) of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.
	description	This application is a continuation of U.S. patent application Ser. No. 13/373,899, filed Dec. 5, 2011 hereby incorporated by reference. This invention was made with government support under DE-NA-00007520 awarded by the US Department of Energy. The government has certain rights in the invention. The present invention relates to a system for generating isotopes useful for medical purposes, such as Mo-99, I-131, Xe-133, Y-90, Cs-137, I-125, and others and in particular to a system employing an annular aqueous fissile solution vessel. Medical isotopes are employed in nuclear medicine where they may be administered to a patient in a form that localizes to specific organs or cellular receptors where they may be imaged with special equipment. Medical isotopes may also be used in the treatment of disease exploiting the tissue-destructive power of short-range ionizing radiation after such localization. Today, most radioisotopes used in nuclear medicine are produced in nuclear reactors employing highly enriched uranium (HEU). The reactors used for the production of Mo-99 for the United States are outside of the United States requiring the export of HEU and an attendant risk of nuclear proliferation associated with such out-of-country shipments. It has been proposed to generate medical isotopes using low enriched uranium (LEU) which cannot be used directly to manufacture nuclear weapons. Systems for this purpose are described in US patent applications: 2011/0096887 entitled: “Device and Method for Producing Medical Isotopes” and 2010/0284502 entitled: “High Energy Proton or Neutron Source” hereby incorporated by reference. In these systems, ions are directed through a target volume holding a gas to generate neutrons. The neutrons may expose a parent material held in solution near the target volume in a fissile solution vessel. In one embodiment the target volume is annular and placed around a cylindrical fissile solution vessel holding the parent material solution. Ions are injected in a spiral through the target volume producing neutrons directed inwardly toward the parent material and outwardly toward a reflector. Neutrons received in the neutron rich parent material (such as LEU uranium) experience a multiplication in which neutrons striking the parent material generate additional neutrons which strike additional neutron rich material in a chain reaction. In a nuclear reactor, at steady power, the effective neutron multiplication factor (keff) is equal to 1. In a subcritical system, keff is less than 1. One problem with aqueous reactors is that it can be difficult to maintain a stable power level. This is because there exists strong feedback mechanisms in the neutron multiplication factor as the temperature of the fissile solution rises and as voids are generated (gas bubbles caused by radiolysis breaking water into hydrogen and oxygen). The rapid reduction in the neutron multiplication factor results in a decrease power, which causes the neutron multiplication factor to increase again. In particular, a control system that is trying to maintain constant power in the reactor may not be able to react sufficiently fast to adequately control the system. The result is a system with an unstable power level and potential safety impacts. The present invention provides an improved geometry for a fissile solution vessel used to generate medical isotopes. Specifically, the fissile solution vessel is a limited thickness annulus holding an aqueous suspension of a parent material. By controlling the aspect ratio of the annulus, improved reaction stability may be obtained over a conventional cylindrical chamber. In addition, enhanced cooling is possible by employing a cooling jacket on the inner wall of the annular solution vessel. Specifically then, one embodiment of the present invention provides a nuclear reaction system having an annular solution vessel for holding an aqueous suspension of nuclear material having an inner wall defining a central opening extending along an axis. A first and second cooling jacket are in thermal communication with the inner wall of the annular solution vessel and an opposed outer wall of the annular solution vessel. It is thus an object of at least one embodiment of the invention to provide improved stability to a reaction vessel by increasing the heat transfer area to volume through the use of an annular configuration. The annular reaction container may contain low enriched uranium. It is thus a feature of at least one embodiment of the invention to provide an apparatus for producing medical isotopes without the risks attendant to handling HEU. The annular solution vessel may contain a mixture of water and at least one of uranyl nitrate, uranyl sulfate, uranyl fluoride or uranyl phosphate. It is thus a feature of at least one embodiment of the invention to provide a system that may use a variety of different fissile solutions. The nuclear reaction system may include a particle source positioned to direct charged particles into a target material proximate to the annular solution vessel for generation of neutrons from the target material to be received in the annular reaction container; and the target material may be contained within a target chamber centered within the central opening and receiving particles along the axis. It is thus a feature of at least one embodiment of the invention to provide a target that may be wholly contained within the fissile solution vessel and that will readily produce neutrons passing into the annular fissile solution vessel after excitation by ions generated externally. The medical isotope generator may include a neutron multiplier and or moderator material positioned between the target chamber and the inner wall. It is thus a feature of at least one embodiment of the invention to convert excess neutron energy obtainable with the ion collision mechanism into additional neutrons. It is another feature of at least one embodiment of the invention to provide for moderation of neutron speeds through a collisional process and thus better control the reaction rate within the annular chamber. The medical isotope generator may further include a reflecting material concentrically outside of the annular solution vessel. It is thus a feature of at least one embodiment of the invention to permit placement of a reflector outside of the annular fissile solution vessel at a location that allows an arbitrary thickness of material to be employed. The aspect ratio defined by a radial thickness of the annular solution vessel perpendicular to the axis to a height of the annular solution vessel along the axis may be substantially greater than 0.1 or between 0.1 and 0.3 or between 0.12 and 0.25. It is thus a feature of at least one embodiment of the invention to provide dimensions to the annular chamber realizing an improvement over a cylindrical chamber or other aspect ratio annular chambers. The nuclear material may be low enriched uranium having a concentration between 10 and 450 grams of low enriched uranium per liter solution. It is thus an object of the invention to provide a reaction system that may work with low concentrations of nuclear materials. These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. Referring now to FIG. 1, a medical isotope generator 10 of the present invention may provide a set of nested annular elements including an outer annular reflector chamber 12 surrounding and coaxial with an annular reactor assembly 14. A cylindrical target chamber 16 fits within the annular reactor assembly 14 so that all three elements of the annular reflector chamber 12, annular reactor assembly 14, and target chamber 16 share a common central axis 18. The outer annular reflector chamber 12 may be taller than the annular reactor assembly 14 to provide a substantially equal thickness of reflecting material around the annular reactor assembly 14 in a direction perpendicular to central axis 18, and above and beneath the annular reactor assembly 14 in directions along central axis 18. In this embodiment, the annular reactor assembly 14 may be substantially equal in height to the target chamber 16. The target chamber 16 may be a vertically oriented cylindrical shell extending along axis 18 and defining a cylindrical volume that will be charged with a target gas 20, for example tritium. The cylindrical volume of the target chamber 16 communicates through a vertically extending conduit 22 upward through the outer annular reflector chamber 12 to an ion injector 24 positioned above the target chamber 16 and outside of the outer annular reflector chamber 12. The ion injector 24 is positioned to direct a beam of ions 26, for example deuterium (D+), vertically along axis 18 through the conduit 22 into the target chamber 16. The height of the target chamber 16 along axis 18 and the pressure of the target gas 20 are adjusted to ensure substantially complete collision of the ions with the tritium in the target chamber 16. In one embodiment the target gas 20 may have a pressure of approximately 10 Torr and having a height within the target chamber 16 along axis 18 of approximately 1 meter. The ion injector 24 incorporates an ion source 28 which, in one embodiment, is a cavity receiving deuterium gas through valve 30 to be ionized, for example, by microwave emissions, ion impact ionization, or laser ionization. A generated beam of ions 26 (for example at a rate of approximately 50 milliamperes) passes into an accelerator 32 accelerating the ion beam along the axis 18. The accelerator, for example, may be an electrostatic accelerator providing 300 kilovolts of acceleration of the ions. The beam of ions 26 then passes through a set of baffle chambers 38 bridged by differential pumps 34. The differential pumps 34 operate to preserve a low-pressure of approximately 50 micro-Torr in the accelerator 32 while permitting the higher 10 Torr pressure in the target chamber 16. In one embodiment this system employees three pumps 36 each drawing gas from a higher baffle chamber 38 (toward the accelerator 32) and pumping it to a lower baffle chamber 38 (toward the target chamber 16). The baffle chambers 38 communicate through relatively small openings along axis 18, for example one centimeter in diameter, to allow passage of the beam of ions 26 while reducing leakage of the tritium in the target chamber 16 The gas streams through the pumps 36 may be cooled by a moderator fed by chilled water (not shown). The upper pumps may, for example, be turbo pumps operating at less than 5×10−5 Torr and 5-10 milliTorr respectively, for example, commercially available from Varian, Inc. having offices in Lexington, Mass. The lower pump may be a roots blower, for example, of a type commercially available from Leybold Vacuum Products Inc. having offices in Export, Pa. Cold traps, getter traps and palladium leaks may be used to remove atmospheric and/or hydrocarbon contaminants from the pump gases. The beam of ions 26 strikes target gas 20 in the target chamber 16 to produce neutrons 40 that pass radially and axially outward from the target chamber 16, for example, with deuterium (D+) striking the tritium to produce 4He and a 14.1 MeV neutron. This reaction is predicted to produce approximately 5×1013 neutrons per second for a 50 milliampere beam of ions 26. Contamination of the target gas 20 by the ions of the beam of ions 26 and helium may be reduced by a purification system 42 such as the Thermal Cycling Absorption Process (TCAP) system developed by the Savanna River National Laboratory (SRNL). In an alternate embodiment, the ions may be replaced by electrons and the target chamber may contain a bremsstrahlung converter and photonuclear material such as uranium from which neutrons are produced. Referring now to FIG. 2, the beam of neutrons 40 from the target chamber 16 may pass into the annular reactor assembly 14. The annular reactor assembly 14 includes an initial one-centimeter thick (in a radial direction) annular water jacket 44 receiving circulated chilled light water provided through one or more conduits 51 from an external water chiller, recycler. The annular water jacket 44 is followed by a coaxial annular neutron multiplier/moderator 46, the latter being in one embodiment an aluminum-clad beryllium metal that multiplies fast neutrons passing outward from the target chamber 16 and moderates fast neutrons traveling inward from the annular fissile solution vessel 50 (to be described) by “cooling” those neutrons, a process that reduces their speed in exchange for an increasing of the temperature of the neutron multiplier/moderator 46. The excess heat of the neutron multiplier/moderator 46 is removed by water jackets 48 and 44 which allow control the temperature of the neutron multiplier/moderator 46 to ensure the escape of sufficient neutrons from the target chamber 16 while moderating neutrons received from the annular fissile solution vessel 50. Alternatively, the neutron multiplier/moderator 46 may be constructed of depleted uranium or other similar material. The neutron multiplier/moderator 46 may provide 1.5-3.0 multiplication factor such as may be adjusted by adjusting its thickness. Neutrons emerging from the neutron multiplier/moderator 46 pass through a second annular chilled water jacket 48 similar to water jacket 44 and then into annular fissile solution vessel 50, the latter having walls comprised, in one embodiment, of zircaloy-4. The annular fissile solution vessel 50 includes a solution 52 of a parent material such as Uranyl Nitrate or Uranyl Sulfate in a light water solution. The solution 52 contains nominally 19.75 percent 235U and thus is low enriched uranium (LEU). Production of the desired 99Mo isotope occurs by fission of 235U in the solution 52 which also produces additional neutrons. Solution 52 may be extracted from the annular fissile solution vessel 50 via one or more conduits 54 where the desired isotopes may be chemically extracted from the fissile solution. These isotopes may be purified via the LEU-modified Cintichem process to provide a source of the desired medical isotopes, particularly 99Mo. The fissile solution may be cleaned using the UREX process to extend the useable lifetime of the solution. Access conduits 54 also allow control of the height of the solution 52 for control of the reaction as well as initial filling, subsequent drainage, and flushing of the annular fissile solution vessel 50. The access conduits 54 also allow introduction and removal of nitrogen for space filling and for feed makeup for water, fissile solution, and pH control (when using uranyl nitrate). Concentrically surrounding the annular fissile solution vessel 50 is another water jacket 56 similar to water jackets 48 and 44 having chilled light water circulating therein. Outside of the annular reactor assembly 14 is the annular reflector chamber 12, for example being an aluminum walled chamber filled with a reflector material 60 which in one embodiment may be heavy water having a volume, for example, of 1000 liters. The reflector material 60 increases the generation efficiency by reflecting neutrons back into the annular fissile solution vessel 50 and therefore may also permit reaction control by draining the annular reflector chamber 12 and thus reducing the neutron reflection into the annular fissile solution vessel 50. Control of the reaction rate may also be had by changing the height of solution 52 in the annular fissile solution vessel 50. Referring now to FIGS. 2 and 6, during operation, thermal energy generated by the fission reactions causes solution 52 to rise in temperature, for example, from 20 degree Celsius to 60 degrees Celsius and can promote the generation of voids formed by radiolysis of hydrogen or oxygen or from other gases such as ammonia and NOx (in the case of use of uranyl nitrate) as well as krypton and xenon produced by fission. Generally, these gases are diluted by nitrogen fill and drawn off for processing. The increase in temperature and the formation of voids can significantly reduce the neutron multiplication factor keff in the chamber 50. This effect, however, is reduced by the annular form of the annular fissile solution vessel 50 as compared to cylindrical chamber of similar volume. As shown generally in FIG. 6, a calculated reactivity curve 70 as a function of aspect ratio for the annular chamber 50 shows a lower magnitude reactivity change (values closer to zero in the chart) for the annular volume 50 then a comparable reactivity curve 72 for a cylindrical volume at aspect ratios above approximately 0.11. Lower magnitude of reactivity change equates to a desirable improved stability of the reaction system. The aspect ratio is the radial thickness of the volume 50 divided by the height of the volume 50. Reactivity change is change in neutron multiplication factor k (i.e., Δk) divided by k. Generally it will be therefore desirable that the volume 50 have an aspect ratio of between 0.1 and 0.3 and alternatively between 0.12 and 0.25 or substantially greater than 0.15. Referring now to FIG. 7, a calculated reactivity curve as a function of concentration of low enriched uranium shows an improved stability within the range of 102-450 grams of low enriched uranium per liter of solution when compared to a cylindrical chamber, finding acceptable operating concentration within this range. It is believed that this data can be extrapolated to indicate an acceptable operating range from 10-450 grams of low enriched uranium per liter of solution. Referring now to FIG. 3, the top and bottom of the target chamber 16 also may be surrounded by the neutron multiplier/moderator 46 and portions of the annular chamber 50 for improved efficiency in capturing neutrons 40. It will thereby be understood that the term annular should be understood to include an annulus having an upper and lower solid base. Referring now to FIG. 4, it will further be appreciated that the annular chamber 50 need not be a cylindrical annulus but may take on other annular shapes such as a polygonal annulus 80 having an inner and outer periphery providing a polygonal cross-sectional such as a hexagon. Further, the solution 52 within the annular fissile solution vessel 50 need not be homogenously distributed, but may be, for example, contained within separate reactant columns 84, for example, passing in a serpentine path through the water bath of the annular fissile solution vessel 50. Such reactants columns can further provide reduced thermal resistance and moderate the effect of voids. Referring now to FIG. 5, the neutron multiplier/moderator 46 of FIG. 2 may desirably be split into two components, the first being primarily a neutron moderator 92, for example, constructed of beryllium or the like as described above, and positioned coaxially inside the water jacket 48 and coaxially outside the water jacket 44 both previously described. In this embodiment, a separate neutron multiplier 90 may be positioned coaxially within the water jacket 44, constructed, for example, of and cooled both by its contact with water jacket 44 coaxially surrounding the neutron multiplier 90 and a water jacket 94 coaxially within the neutron multiplier 90 and surrounding the target chamber 16. The separation of functions allows independent temperature control of the neutron moderator 92 and the neutron multiplier 90 as well as constructing these components of different materials (if desired) and tailoring their thicknesses to the particular roles they play. The temperature of the water jacket 44 and 94 may be monitored by temperature probes 96 and 98 and provided to a feedback control system 100 controlling intake valves 102 and 104 for the water jackets 44 and 94 respectively (outlet valves not shown). The valves 102 and 104 may control the circulation of chilled water within the water jackets 44 and 94 thereby controlling the temperature of the neutron moderator 92 and its effect in moderating the nuclear reaction. The feedback controller 100 may control the temperature of the water jackets 44 and 94 to a predetermined value or to a dynamic value based on a monitoring of the general reaction rate by other means. In addition the feedback controller 100 may manage other control variables such as control of height of the solution 52 to moderate the reaction rate. Generally, the medical isotope generator 10 will be further shielded with concrete and water according to standard practices. Other isotopes such as 131I, 133Xe, and 111In may also be produced by a similar structure. Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.
	summary
	claims	1. An assembly for converting radiation to electrical energy, comprising:a host matrix of inorganic semiconducting material defining a first surface and a second surface and a thickness disposed between the first and second surfaces;a plurality of nanoparticles interspersed within the thickness of the host matrix, the plurality of nanoparticles in combination with the host matrix generating at least one charge carrier upon interaction with the radiation;a first electrode disposed adjacent to the first surface of the host matrix; anda second electrode disposed adjacent to the second surface of the host matrix,wherein, the generated electrical energy is output from the pair of the first and second electrodes. 2. The assembly of claim 1, wherein the assembly is configured to convert at least one of the following types of radiation to electrical energy: infrared, visible, ultraviolet, x-ray, gamma, beta, cosmic rays, neutrons, and geothermal. 3. The assembly of claim 1, wherein the thickness between the first and second surfaces is in the range of 1 micrometer and 10 centimeters. 4. The assembly of claim 1, wherein at least a portion of host matrix is made of porous silicon. 5. The assembly of claim 4, wherein the thickness of porous silicon is in the range of 1 micrometer and 10 centimeters. 6. The assembly of claim 1 wherein at least one of a resistor, a capacitor, and a transistor is formed using the same substrate as was used to form the host matrix or a suitable material added to the same substrate as was used to form the host matrix. 7. The assembly as of claim 6, wherein thickness between first and second surface is in the range of 1 micrometer and 10 centimeters. 8. An assembly for converting radiation to electrical energy, comprising:a host matrix defining a first surface and a second surface and a thickness disposed between the first and second surfaces;a plurality of nanoparticles interspersed within the thickness of the host matrix, the plurality of nanoparticles in combination with the host matrix generating at least one charge carrier upon interaction with the radiation;a first electrode disposed adjacent to the first surface of the host matrix; anda second electrode disposed adjacent to the second surface of the host matrix,wherein, the generated electrical energy is output from the pair of the first and second electrodes, andwherein the plurality of nanoparticles enables charge transport from particle to particle in at least one particle network within the host matrix. 9. The assembly of claim 8, wherein the assembly is configured to convert at least one of the following types of radiation to electrical energy: infrared, visible, ultraviolet, x-ray, gamma, beta, cosmic rays, neutrons, and geothermal. 10. The assembly of claim 8, wherein the thickness between first and second surface is in the range of 1 micrometer and 10 centimeters. 11. The assembly of claim 8, wherein at least a portion of host matrix is of porous silicon. 12. The assembly of claim 11, wherein the thickness of porous silicon is in the range of 1 micrometer and 10 centimeters. 13. The assembly of claim 8, wherein at least one of a resistor, a capacitor, and a transistor is formed using the same substrate as was used to form the in the host matrix or a suitable material added to the same substrate as was used to form the host matrix. 14. A radiation detector, comprising:a plurality of assemblies for converting radiation to electrical energy, disposed adjacent to one another in a stacked fashion, each of the assemblies comprising:a host matrix of inorganic semiconducting material defining a first surface and a second surface and a thickness disposed between the first and second surfaces,a plurality of nanoparticles interspersed within the thickness of the host matrix, the plurality of nanoparticles in combination with the host matrix generating at least one charge carrier upon interaction with the radiation,a first electrode disposed adjacent to the first surface of the host matrix, anda second electrode disposed adjacent to the second surface of the host matrix,wherein, the generated electrical energy is output from the pair of the first and second electrodes. 15. The radiation detector of claim 14, wherein the detector is configured to detect at least one of the following types of radiation: infrared, visible, ultraviolet, x-ray, gamma, beta, cosmic rays, neutrons, and geothermal. 16. The detector of claim 14, wherein at least a portion of host matrix is made of porous silicon. 17. The detector of claim 16, wherein the thickness of porous silicon is in the range of 1 micrometer and 10 centimeters. 18. The detector of claim 14, wherein at least one of a resistor, a capacitor, and a transistor is formed using the same substrate as was used to form the host matrix or a suitable material added to the same substrate as was used to form the host matrix. 19. A radiation detector; comprising:a plurality of assemblies for converting radiation to electrical energy, disposed adjacent to one another in a stacked fashion, each of the assemblies comprising:a host matrix defining a first surface and a second surface and a thickness disposed between the first and second surfaces,a plurality of nanoparticles interspersed within the thickness of the host matrix, the plurality of nanoparticles in combination with the host matrix generating at least one charge carrier upon interaction with the radiation,a first electrode disposed adjacent to the first surface of the host matrix, anda second electrode disposed adjacent to the second surface of the host matrix,wherein, the generated electrical energy is output from the pair of the first and second electrodes, andwherein at least one outer coating encapsulating at least one of the plurality of nanoparticles, the coating changing the electrical behavior of the at least one nanoparticle. 20. The detector of claim 19 wherein, the detector is configured to detect at least one of the following types of radiation: infrared, visible, ultraviolet, x-ray, gamma, beta, cosmic rays, and neutrons, geothermal. 21. The detector of claim 19, wherein the detector is configured to detect neutrons, wherein at least one of the host matrix and the nanoparticles contained therein contain at least one atom of Hydrogen, Helium, Lithium, and/or Boron. 22. The detector of claim 19, wherein the detector is configured to detect neutrons, wherein at least one of the host matrix, the nanoparticles and the at least one outer coating contain at least one atom of Hydrogen, Helium, Lithium, and/or Boron. 23. The detector of claim 19, wherein at least a portion of host matrix is made of porous silicon. 24. The detector of claim 23, wherein at least one of a resistor, a capacitor, and a transistor is formed using the same substrate as was used to form the host matrix. 25. The detector of claim 24, wherein the thickness of porous silicon is in the range of 1 micrometer and 10 centimeters.
	abstract	Motion artifacts and patient dose during 4D CT imaging are reduced by adaptive control of data acquisition. The respiration signal (310) and CT data acquisition (340) are linked, such that ‘bad’ data from erratic breathing cycles that cause artifacts is not acquired by pausing CT data acquisition (360) when erratic breathing is detected, and not resuming CT data acquisition until steady-state respiration is resumed. Training data is used to develop a tolerance envelope for a respiratory signal such that for erratic breathing cycles the respiratory signal is not within the tolerance envelope (330).
	summary
046876200	claims	1. The method of closely controlling the reactor water coolant temperature of an operating spectral-shift nuclear reactor, said reactor comprising a core formed of a plurality of fuel assemblies through which said reactor water coolant flows; different types of elongated elements operable to be controllably moved into and out of said core; one type of said elongated elements comprising control rods formed of neutron absorbing material and operable to decrease reactivity through neutron absorption when inserted into said core; another of said types of elongated elements comprising displacer rods formed of material which has a low absorption for neutrons and which have overall neutron-absorbing and moderating characteristics essentially not exceeding those of hollow tubular Zircaloy members with a filling zirconium oxide or aluminum oxide, said displacer rods operating to displace an equivalent volume of water coolant fluid from said core when inserted therein to decrease reactivity and to increase reactivity when moved from said core; which method comprises: establishing the reactor coolant temperature set point at which said water coolant is desired to be maintained in an operating reactor; establishing first temperature band limits which are a first temperature amount above and below said temperature set point and which are water-coolant-initiating temperatures for initiating movement of said displacer rods; establishing second temperature band limits which are a second temperature amount above and below said temperature set point and within which the temperature of said reactor coolant is desired to be maintained, and said first temperature band limits falling within said second temperature band limits; and when measured reactor coolant temperature approaches a deviation from said temperature set point by an amount as established by said first temperature band limits, inserting or withdrawing a sufficient number of displacer rods with respect to the core to shift water coolant temperature toward the desired temperature set point; and movement of said reactor control rods is initiated when said reactor coolant temperature differs from said temperature set point by said second temperature amount. establishing the reactor coolant temperature set point at which said water coolant is desired to be maintained in an operating reactor; establishing first temperature band limits which are a first temperature amount above and below temperature set point and which are water-coolant-initiating temperatures for initiating movement of said displacer rods; establishing second temperature band limits which are a second temperature amount above and below said temperature set point and within which the temperature of said reactor coolant is desired to be maintained, and said first temperature band limits falling within said second temperature band limits; and when measured reactor coolant temperature approaches a deviation from said temperature set point by an amount as established by said first temperature band limits, inserting or withdrawing a sufficient number of displacer rods with respect to the core to shift water coolant temperature toward the desired temperature set point; and movement of said reactor control rods is initiated when said reactor coolant temperature differs from said temperature set point by said second temperature amount. 2. The method as specified in claim 1, wherein said reactor coolant displacer rods are inserted into said core when the measured reactor coolant temperature is greater than said temperature set point by said first temperature amount. 3. The method as specified in claim 1, wherein said reactor coolant displacer rods are moved from said core when the measured reactor coolant temperature is less then said temperature set point by said first predetermined amount. 4. The method as specified in claim 1, wherein said second temperature band limits are established to be 2.degree. F. greater and lesser than said temperature set point. 5. The method as specified in claim 1, wherein said first temperature band limits are established to be 11/2 F. greater and lesser than said temperature set point. 6. The method as specified in claim 1, wherein said reactor coolant displacer rods are grouped in separately movable clusters. 7. The method as specified in claim 1, wherein said control-rod-initiating reactor coolant temperature is measured as the reactor coolant average temperature. 8. The method as specified in claim 1, wherein said control-rod-initiating reactor coolant temperature is measured as the average cold leg temperature. 9. The method as specified in claim 1, wherein a third type of said elongated elements is operable to be moved into and out of said core, said third type of elongated elements comprise gray rods formed of an intermediate neutron absorbing material which has an overall neutron absorptivity approximately that of hollow stainless steel tubes, and during operation of said reactor said gray rods are moved in conjunction with said displacer rods when measured reactor coolant temperature approaches a deviation from said temperature set point by an amount as established by said first temperature band limits to shift water coolant temperature toward said desired temperature set point. 10. The method of closely controlling the reactor water coolant temperature of an operating spectral-shift nuclear reactor, said reactor comprising a core formed of a plurality of fuel assemblies through which said reactor water coolant flows; different types of elongated elements operable to be controllably moved into and out of said core; one type of said elongated elements comprising control rods formed of neutron absorbing material and operable to decrease reactivity through neutron absorption when inserted into said core; another of said types of elongated elements comprising displacer rods formed of material which has a low absorption for neutrons and which have overall neutron-absorbing and moderating characteristics essentially not exceeding those of hollow tubular Zircaloy members with or without a filling of zirconium oxide or aluminum oxide, said displacer rods operating to displace an equivalent volume of water coolant fluid from said core when inserted therein to decrease reactivity and to increase reactivity when moved from said core; which method comprises:
	claims	1. A method for co-solidifying sulfate solution and spent ionexchange resins, comprising the steps of: converting the sodium sulfate solution into a slurry of sodium hydroxide and barium sulfate; removing water from the slurry by evaporation; mixing the slurry with the ion-exchange resins to form mixed wastes; and homogeneously mixing a powdery solidification agent prepared from cement, pozzolanic materials and at least one species of oxides or salts of divalent metals into the mixed wastes to form a mixture of mixed wastes and solidification agent and leaving the mixture of mixed wastes and solidification agent for setting and hardening; wherein after the removal of water, water content of the slurrv is less than 50%. 2. The method as claimed in claim 1 , wherein the solidification agent includes oxides or salts selected from the group consisting of borates, silicates, carbonates, and phosphates. claim 1 3. The method as claimed in claim 1 , wherein the solidification agent includes oxides or salts selected from the group consisting of oxides and salts of calcium, silicon, magnesium, aluminum, iron, and zirconium. claim 1 4. The method as claimed in claim 1 , wherein the pozzolanic materials in the solidification agent are selected from the group consisting of silica fume, blast furnace slag powders and fly ash. claim 1 5. The method as claimed in claim 4 , wherein a weight ratio of the solidification agent to the mixed wastes is less than 1 . claim 4 6. The method as claimed in claim 4 , wherein the mixed wastes and the solidification agent are mixed at a temperature below 90xc2x0 C. claim 4
	summary
	summary
	abstract	At least one system for eluting a radioactive material and a method of eluting a radioactive material is provided. The system for eluting a radioactive material may include an elution column configured to enclose an radioactive material, a first sealing member sealing a first end of the elution column, a second sealing member sealing a second end of the elution column, an elution supply source connected to the first end of the elution column via a first needle, a collection system connected to the second end of the elution column via a second needle, and a filter in the elution column, the filter being configured to support the radioactive material and prevent the radioactive material from contacting the second needle.
050650335	abstract	A coupling apparatus for connecting a separable control cable assembly to a camera storage unit in a radiographic system, having a connector assembly fixed to the camera storage unit and a separable control cable assembly. The separable control cable assembly is attached the camera storage unit via the fixed connector assembly for controlling movement of radioactive material attached to a source cable to a desired location outside of the camera storage unit. The camera storage unit stores the source cable and attached radioactive material in an aperture where the two are locked against removal. Proper connection of the separable control cable assembly to the camera storage unit releases the source cable and radioactive material from their lock position. Upon releasing the source cable and radioactive material from their lock position, the control cable assembly is prevented from being removed from ther camera storage unit. The control cable assembly, with a control cable, guides the source cable and radioactive material to a desired location and returns the soure cable and radioactive material to their storage position within the camera storage unit, at which time the two are automatically locked in position and releasing of the control cable assembly is enabled.
	abstract	Optical proximity correction methods and apparatus are disclosed. A simulated geometry representing one or more printed features from a reticle is generated using an optical proximity correction (OPC) model that takes into account a reticle design and one or more parameters from a process window of a stepper. An error function is formed that measures a deviation between the simulated geometry and a desired design of the one or more printed features. The error function takes into account parameters (p0 . . . pJ) from across the process window in addition to, or in lieu of, a best focus and a best exposure for the stepper. The reticle design is adjusted in a way that reduces the deviation as measured by the error function, thereby producing an adjusted reticle design.
043572090	claims	1. A nuclear divisional reactor including: (a) a reactor core having side and top walls (b) a closed nuclear reactor coolant circulating system for said reactor core and forming a part of said reactor core (c) a heat exchanger substantially surrounding said core (d) said heat exchanger including a plurality of separate fluid holding and circulating chambers each in contact with a portion of said core (e) said closed nuclear reactor coolant circulating system for said reactor core being separate and independent from said plurality of separate fluid holding and circulating chambers of said heat exchanger surrounding said core (f) control rod means associated with said core and external of said heat exchanger including control rods and means for moving said control rods (g) each of said chambers having separate means for delivering and removing fluid therefrom (h) separate means associated with each of said delivering and removing means for producing usable energy external of said chambers (i) each of said means for producing usable energy having variable capacity energy output (j) thereby making available a plurality of individual sources of usable energy of varying degrees. (a) said reactor core includes a base, and (b) said closed nuclear reactor coolant circulating system for said reactor core includes means at said reactor core base only for delivering and removing reactor coolant from said reactor core. (a) each of said plurality of holding and circulating chambers extend outwardly from said core a distance at least approximately the width of said core. (a) each of said plurality of holding and circulating chambers contact a portion of said side and top walls. (a) each of said plurality of holding and circulating chambers contact a porton of said side walls. (a) at least one of said plurality of holding and circulating chambers contact a portion of said side walls. (a) least one of said plurality of holding and circulating chambers contacts a portion of said top and side walls. (a) said holding and circulating chambers including different heat transfer compositions. (a) one of said chambers includes H.sub.2 O and the other of said chambers another fluid. (a) one of said chambers includes an organic fluid composition. (a) one of said chambers includes an inorganic fluid. (a) each of said means for producing useable energy includes a heat exchanger. (a) each of said means for producing useable energy includes a turbine. (a) each of said heat exchangers includes variable capacity energy control means. (a) each of said turbines includes variable capacity energy control means. (a) said core includes a bottom opening. (a) said control rod means is associated with said bottom opening. (a) means for cooling said core. (a) said plurality of chambers includes four equal chambers radiating from about the central axis of said core. 2. A nuclear divisional reactor as in claim 1 and wherein: 3. A nuclear divisional reactor as in claim 1 and wherein: 4. A nuclear divisional reactor as in claim 1 and wherein: 5. A nuclear divisional reactor as in claim 1 and wherein: 6. A nuclear divisional reactor as in claim 1 and wherein: 7. A nuclear divisional reactor as in claim 1 and wherein: 8. A nuclear divisional reactor as in claim 1 and wherein: 9. A nuclear divisional reactor as in claim 8 and wherein: 10. A nuclear divisional reactor as in claim 8 and 11. A nuclear divisional reactor as in claim 8 and wherein: 12. A nuclear divisional reactor as in claim 1 and wherein: 13. A nuclear divisional reactor as in claim 1 and wherein: 14. A nuclear divisional reactor as in claim 12 and wherein: 15. A nuclear divisional reactor as in claim 13 and wherein: 16. A nuclear divisional reactor as in claim 1 and wherein: 17. A nuclear divisional reactor as in claim 16 and wherein: 18. A nuclear divisional reactor as in claim 1 and including: 19. A nuclear divisional reactor as in claim 1 and wherein:
	summary
	description	The porous glass crystalline blocks of the invention, molded from glass crystalline hollow microspheres (specifically cenospheres), are characterized by high values of open-cell porosity of about 40 vol. % up to about 90 vol. %, a homogenous porous structure, significant interglobular pore sizes (voids) in the range of 20-100 micrometers, thermal stability and high stability in most acids, which makes it possible to provide very effective solidification of waste in a wide range of pH, temperatures and radionuclide compositions. It is believed that the concentration, solidification and immobilization of radionuclides and the mineral component of radioactive and other hazardous waste in porous glass crystalline blocks are made possible due to the following functional processes: Absorption of solutions into the block volume by means of capillary forces and high wetting capability of the internal surface; Water evaporation and its intensive release with the aid of a dry carrier gas at low temperatures (about 25xc2x0 C.-60xc2x0 C.), by static heating in a conventional furnace, by hot air heating in an oven, or by microwave heating. Repeated absorption of the waste solution with a low salt content to achieve the required loading capacity; Binding of radionuclides and other hazardous wastes by incorporating stable oxides with a high specific surface into the block; Complete decomposition of salts directly in the internal voids of the block at temperatures which are lower than the melting point of the block material; Reliable immobilization of radionuclides and other hazardous wastes, as well as their associated salts, inside the block at the final stage of the process by calcination of the saturated glass-ceramic matrix; Further consolidation of the blocks containing the oxides at high temperatures and high pressures; Further encapsulation of the blocks with glass or ceramic coating. In the embodiment of the invention useful for liquid radioactive waste solidification, it is possible to microencapsulate radionuclides in glass crystalline blocks formed from microspheres. The radionuclides are microencapsulated in internal cavities of the microspheres as well as in the interglobular voids between the microspheres. The hollow microspheres, obtained from fly ash and known as cenospheres, are separated according to their size, bulk density and magnetic properties. The properties of these porous glass crystalline blocks make it possible to provide especially reliable immobilization of long-lived radionuclides with significant minimization of liquid waste volume that, depending on the salt content, can reach 1:40 ratio of solid to liquid. Compared to known processes, an advantage of the use of the porous glass-ceramic blocks made of glass crystalline cenospheres in this invention is their thermal stability and high stability in most acids, thereby making it possible to use with waste in a wide range of pH, temperatures and radionuclide compositions. The cenospheres used to prepare the glass crystalline blocks used for this invention were obtained from fly ash from several power plants in Russia. For an example of the composition of the cenospheres, the following data are for the magnetic and non-magnetic cenospheres from the Novosibirskaya power plant: The following ranges of composition for magnetic and non-magnetic products accordingly are respectively as follows: SiO2xe2x80x9458.0-61.0 wt. % and 64.9-66.3 wt. %; Al2O3xe2x80x9418.2-20.4 wt. % and 20.1-21.1 wt. %; Fe2O3xe2x80x949.7-12.3 wt. % and 3.1-4.6 wt. %; MgOxe2x80x941.4-3.0 wt. % and 1.9-2.2 wt. %; CaOxe2x80x942.3-3.8 wt. % and 1.8-2.7 wt. %; Na2Oxe2x80x940.4-1.3 wt. % and 0.3-0.6 wt. %; K2Oxe2x80x941.8-2.7 wt. % and 1.9-2.9 wt. %; TiO2xe2x80x940.3-0.8 wt. % and 0.2-0.5 wt. %. The porous glass crystalline material of high open-cell porosity used in the invention is characterized by two types of openings, interglobular voids (voids between cenospheres) and through-flow wall pores or perforations in the cenosphere walls. This material and the methods of making it are described in greater detail in U.S. patent application Ser. No. 09/721,962, filed on Nov. 27, 2000, which is incorporated herein by reference. In summary, the material is produced by separating and selecting cenospheres of fixed sizes and composition, molding the cenospheres and agglomerating the cenosphere array under sintering conditions. The cenospheres are sintered to each other at their points of contact either with or without a binder. The separation steps include a density separation step to remove the broken cenospheres and accessory particles such as unburned carbon material, and one or more of the following steps, depending on the required parameters of the product, performed in any order: dry magnetic separation, separation by grain size, gravity concentration (which is separation by density) and recovery of perforated and non-perforated cenospheres. However, to achieve the maximum open-cell porosity of 90 vol %, the gravity concentration step is always required in order to separate and use the least dense cenospheres. To enhance the interglobular void of the sintered cenosphere array and to obtain openings of a predicted size, the cenospheres having diameters in a narrow range of values are preferable. The lightest fraction with an accessible interglobular void produced total open-cell porosity up to 90 vol. %, which is as high as porosity of the cellular porous bodies. It is also desirable to have through-flow pores in the cenosphere walls (the perforated cenospheres), which make the internal void of cenospheres accessible. In one preferred embodiment for making the glass crystalline blocks the cenospheres are separated into size groups, into perforated and non-perforated, and into magnetic and non-magnetic. The non-perforated non-magnetic cenospheres of size xe2x88x92400+50 micrometers (greater than 50 but less than 400 micrometers) are selected and mixed with a wetting agent, such as water, and a binder, such as a liquid silicate glass, in a weight ratio of cenospheres:wetting agent:binder of about 1:(0.012-0.29):(0.18), followed by compaction of the obtained plastic mixture in a press form to reduce the mixture volume by 10-20%. The molded blocks are dried at 160xc2x0 C. for 2 hours and sintered for 0.5-1 hour at a temperature above 800xc2x0 C. but below the softening temperature of the cenospheres. (Glasses are characterized by a melting temperature range: the lower limit of this range is the softening temperature and the high limit of the range is the liquidity temperature. The liquidity temperature for non-magnetic cenospheres of Novosibirskaya power plant is about 1400xc2x0 C. and the softening temperature is about 1100xc2x0 C. However, these temperature values depend on the cenosphere composition and, consequently, on the power plant). The same process can be used starting with only perforated cenospheres, or a mixture of perforated and non-perforated cenospheres. In another preferred embodiment, the non-perforated cenospheres are placed in a refractory mold of a predetermined shape and the mold is placed in a muffle and held at a sintering temperature below the liquidity temperature for 20-60 minutes. The sintering causes most of the non-perforated cenospheres to become perforated. However, to cause additional perforation, the cenosphere agglomerate can be treated with acid to perforate further the cenospheres. The acid reagents are selected from the group consisting of 3-6 M hydrochloric acid; NH4Fxe2x80x94HFxe2x80x94H2O with content of Fxe2x88x92 about 15-30 gram-ions per liter at a molar ratio NH4F/HF of about 0.1-1.0; and NH4Fxe2x80x94HClxe2x80x94H2O with content of Fxe2x88x92 about 1-10 gram-ions per liter at a molar ratio Fxe2x88x92/Clxe2x88x92 of about 0.1-1.0. The cenospheres used in this invention generally have a diameter in the range of 40-800 micrometers, preferably in the range of 50-400 micrometers, a softening temperature above about 1000xc2x0 C., a temperature of liquidity about 1400xc2x0 C., and a bulk density above about 0.25 g/cm3. The resulting porous material is characterized by open-cell porosity in the range of 40-90 vol. %, interglobular openings in the range of 20-100 micrometers, through-flow wall pore size of 0.1-30 micrometers, an apparent density in the range of 0.3-0.6 g/cm3 and a compressive strength in the range of 1.2-3.5 MPa.. The invention is illustrated by the following non-limiting examples. The porous crystalline blocks used in these examples were made by two of the processes disclosed in U.S. patent application Ser. No. 09/721,962, referenced previously. The two methods of block preparation used were as follows: (a) Separation of cenospheres by magnetic properties, and separation of the non-magnetic product by size. This process was applied to make the porous blocks of 40-50 vol. % open-cell porosity used in examples 1-5: About 100 g of cenospheres from Novosibirskaya power plant were separated into magnetic and non-magnetic products by applying a magnetic field. After that, the non-magnetic product was classified by grain sizes selecting a fraction of xe2x88x92200+50 micrometers for examples 1 and 2, and xe2x88x92400+50 for examples 3, 4 and 5. 75 g of the selected cenospheres were mixed with 13.5 g of a liquid silicate glass and 15 ml of water. The plastic mixture by portions was compacted by one-side pressing in cylinder molds of 16 mm in diameter (the diameter can be, 35, 40 and 56 mmxe2x80x94it depends on the size of the sample) to reduce the mixture volume by up to 20%. The formed block was removed from the mold and dried in an oven at 160xc2x0 C. for 1 hour. After drying, the block was placed in a muffle on a ceramic support and sintered by heating from room temperature to 850xc2x0 C. at about 10xc2x0 C./min and holding at 850xc2x0 C. for 0.5 hour. Thereafter, the furnace was switched off and allowed to cool prior to removing the block. (b) Separation of cenospheres by magnetic properties, separation of the non-magnetic product by size, and separation by perforation. This process was applied to make the porous blocks of 40-70 vol. % open-cell porosity used in examples 6-9: About 800 g of cenospheres from Novosibirskaya power plant were separated into magnetic and non-magnetic products by applying a magnetic field. After that, about 500 g of the non-magnetic product was classified.by grain sizes selecting a fraction of xe2x88x92400+50 micrometers (about 450 g), and another part of the non-magnetic product (about 260 g) was classified by grain sizes selecting a fraction of xe2x88x92160+100 micrometers (about 100 g) and of xe2x88x92400+200 micrometers (about 60 g). Every fraction was then packed in a textile bag and subsequently placed into a glass vessel which was pumped down by a water jet pump to 8.0 kPa and kept at the reduced pressure for 20-30 minutes. Then the vessels containing the cenospheres were filled with water by suction and left for 20-30 minutes until degassing was completed. The cenospheres were held under the water layer by a metallic net. After this procedure, the pressure in the vessels was returned to atmospheric pressure resulting in the injection of water into the cavities of perforated cenospheres. The wet cenospheres were removed from the textile bag and placed in a glass beaker with water so that the cenospheres separated into a floating layer (non-perforated product) and a sinking layer (perforated product). The layers were drained in a Buechner funnel and dried at 110-150xc2x0 C. The output of different products was as follows: 50 g of the selected perforated cenospheres of xe2x88x92400+50 microns were mixed with 9 g of a liquid silicate glass and 10 ml of water. 75 g of the selected non-perforated cenospheres of xe2x88x92160+100 microns were mixed with 13.5 g of a liquid silicate glass and 15 ml of water. 45 g of the selected non-perforated cenospheres of xe2x88x92400+200 micrometers were mixed with 8 g. of a liquid silicate glass and 9 ml. of water. The plastic mixtures by portions were compacted by one-side pressing in cylinder molds of 16 mm in diameter (for xe2x88x92400+50 and xe2x88x92160+100 micrometers) and in cone molds of 35xc3x9740 mm in diameter (for cenospheres of xe2x88x92400+200 micrometers) to reduce the mixture volume by up to 20%. The blocks formed from perforated and non-perforated cenospheres respectively were removed from the molds and dried in an oven at 160xc2x0 C. for 1 hour. After drying, the blocks were placed in a muffle on a ceramic support and sintered by heating from room temperature to 850xc2x0 C. at about 10xc2x0 C./min and holding at 850xc2x0 C. for 0.5 hour. Thereafter, the furnace was switched off and allowed to cool prior to removing the block. The average open-cell porosity of the blocks is 40-50 vol. % and 60-70 vol. % for the non-perforated and perforated blocks, respectively. A simulant for the raffinate of the first extraction cycle of a typical spent nuclear fuel reprocessing operation is used, having the following composition: HNO3, g/l: 30; Fe (3), g/l: 20; Cr (3), g/l: 15; Ni, g/l: 15; Pu, mg/l: 15. The porous block that was used for this experiment consisted of glass crystalline microspheres recovered from fly ash, resulting from Kuznetskii (Russia) coal incineration, with the following properties: 150 ml of the simulated solution was added to the porous glass crystalline block by multiple loading cycles alternating with drying in an oven at about 50-150xc2x0 C. for approximately 120 minutes. Each loading/drying cycle was carried out by saturation of the block with liquid solution by absorption of about 20 ml, followed by drying. About 8 cycles were required to load the block with salt components of the solution. After the final drying stage, the block saturated with the salts was calcined in the muffle furnace at 800xc2x0 C. for 120 minutes. No encapsulation of the block was performed. The Pu immobilization reliability in the porous glass crystalline compound without the encapsulation shell has been tested in accordance with the procedure described in GOST 29114-91 (a well-known state standard procedure used in Russia for the leaching measurement of solidified radioactive waste). The following results were obtained: Degree of loading the block with the waste oxides, %: 42.2 Pu content in the block, mg: 2.3 Pu average leach rate in water during 93 days, g/cm2xc3x97days: 5.9xc3x9710xe2x88x926 For solidification the simulant for the raffinate of the first extraction cycle of a typical spent nuclear fuel reprocessing operation is used, as in Example 1, wherein the Pu content is 43 mg/l. The chemical composition of the porous glass crystalline block subject to loading is identical to that used in Example 1. The properties of the block are as follows: 150 ml of the simulated solution was added into the block by multiple loading cycles, alternating with drying in an oven at about 50-150xc2x0 C. for 120 minutes. After the final stage of dehydration, the block saturated with salts was calcined in the muffle furnace at 800xc2x0 C. for 120 minutes. Then the block was coated with low-melting glass with the following properties: Reliability of Pu immobilization in the glass-ceramic compound has been tested in accordance with the procedure as described above in Ex. 1. The following results were obtained: For solidification, the liquid radioactive waste simulants, such as solutions of NaNO3, CsNO3 and SrNO3 with a concentration of 100 g/l, have been used. The simulants have been loaded into the cylindrical glass crystalline porous blocks made of cenospheres. The characteristics of these blocks are given in Table 1. The loading of the simulated solutions alternated with active ventilation of the loaded blocks at room temperature by dry air, and moisture condensation from the saturated air. Then the blocks were dehydrated for 120 minutes at 150xc2x0 C., and were calcined in the muffle furnace at 850xc2x0 C. No encapsulation of the blocks was performed. The reliability of Na, Cs and Sr immobilization in the glass-ceramic compound was tested in accordance with the procedure as described above in Ex. 1. The results obtained are given in Table 1. The blocks were loaded with liquid radioactive waste simulants, as in Example 3. After calcination, the blocks were coated with a ceramic layer of the following composition (in wt. %): SiO2: 55.5 Al2O3: 6.4 CaO: 28.5 MgO: 9.3 TiO2: 0.3 The reliability of Na, Cs and Sr immobilization in the glass-ceramic compound was tested in accordance with the procedure as described above in Ex. 1. The results obtained are given in Table 2. The solidification of liquid radioactive waste simulants is performed as in Example 3 wherein with the application of Sr(NO3)2 solution, prior to solidification, the internal surface of the porous glass crystalline ceramic block is coated with a metal oxide, selected from ZrO2, TiO2, Fe2O3 or Al2O3, in the amount of 15-30 wt. %. The final calcination of the blocks saturated with SrO is performed at 1,000xc2x0 C. After calcination, all the blocks contain 2.8-3.0 wt. % of SrO. No encapsulation of the generated glass-ceramic compounds was performed. The properties of the solidified products are shown in Table 3. The compounds described in Examples 1, 3 and 5 show that the solidified glass-ceramic compounds immobilize radionuclides fairly well even without the encapsulation shell. The average leach rates for Cs rates from the non-encapsulated samples reach (1.6xe2x88x925.1)xc3x9710xe2x88x925 g/cm2xc3x97days, and for Sr (2.1xc3x9710xe2x88x926 g/cm2xc3x97days)xe2x88x92(1.5xc3x9710xe2x88x924xc3x97g/cm2xc3x97days), while the Pu leach rate is 5.9xc3x9710xe2x88x926 g/cm2xc3x97days. These leach rates are higher than in previous tests disclosed in Russian patent application RF#2091874, but lower than in the Russian High-Level Solidified Waste, Technical Requirements State Standard P 509226-96. Packing the porous glass crystalline ceramic blocks into ceramic or glass-like shells, as well as incorporation of 15-30 wt. % of microencapsulated oxide additives (ZrO2, TiO2 and Al2O3) into the block composition, increase the stability of the solidified products and reduce their leach rates down to the levels allowable for long-term disposal of high-level solidified waste (about 10xe2x88x926 g/cm2xc3x97days for Sr and Cs, and 2.5xc3x9710xe2x88x927 g/cm2xc3x97days for Pu). The non-encapsulated solidified glass-ceramic compounds, including the blocks with Fe2O3, can be used for interim storage or radioactive waste, including its transportation to the site of its further treatment. Two simulated actinide waste solutions, designated dilute actinide/lanthanide solution and actinide solution filtrate, were used to perform waste loading tests on porous glass crystalline ceramic blocks. The blocks used for the experiments in examples 6-9 consisted of non-perforated and perforated, non-magnetic, glass crystalline cenospheres recovered from coal incineration fly ash as described above in the method of block preparation (b). The elemental concentrations in the simulant solutions were: Aliquots of the dilute actinide/lanthanide simulant were added to the blocks made from the non-perforated cenospheres by multiple loading cycles, alternating with drying at 100-130xc2x0 C. for 2 hours in a tube furnace with carrier gas (air) flow at approximately 0.1 m/s. The blocks made from perforated cenospheres were loaded under vacuum with the actinide solution filtrate simulant by multiple loading cycles, alternating with drying in a tube furnace under the same conditions as the blocks made from non-perforated cenospheres. After the final drying stage, the blocks saturated with the salts were weighed to determine the total salt up-take as a percent of the total mass. Block characteristics and results are listed in Table 4. The results of Table 4 show that the salt mass loading of the blocks with perforated cenospheres is roughly 50% and that it is approximately twice that of the non-perforated samples. This is expected since the perforated cenospheres allow deposition inside the cenosphere as well as in the inter-globular voids between cenospheres. In this test, porous glass crystalline blocks of the perforated cenosphere type were loaded under vacuum with the dilute lanthanide and actinide solution filtrate simulants similar to those of the previous example. However, in this test, the drying between loading cycles was done by placing the sample in a microwave oven to decrease drying times. After the last drying cycle, the blocks were weighed to determine the total salt up-take as a percent of the total mass. Block characteristics and results are listed in Table 5. Table 5 shows that the drying times were significantly decreased using the microwave drying technique. Salt loadings for blocks 82-pc and 73-pc were similar to the previous example in the 40 to 50 wt. % range. Loadings for blocks 81-pc and 96-pc were lower because these blocks were loaded with a more dilute solution and the test was terminated before total saturation was reached. This recovery experiment was performed to determine if deposited salts could be leached or recovered from a previously loaded block after calcination of the block. These data are important in the application where a block might be used as a transport medium for radioactive metals to be recovered at a different location and concentrated or placed in a different waste form. The porous glass crystalline block used for the experiment consisted of non-perforated glass crystalline cenospheres that had been previously saturated with the dilute actinide/lanthanide simulant listed in Example 6, by multiple loading and drying cycles. In this case, an Am-241 tracer was also added to the simulant to facilitate kinetic release measurements by gamma spectroscopy. The loaded block was suspended in 6 M HNO3 at 60xc2x0 C. with constant stirring and small aliquots of the acid solution were removed over time to obtain a kinetic release curve. The results of this test are shown in the figure. These data show that the release is essentially complete after 1 hour of contact time. The blocks of glass crystalline porous material made by sintering non-perforated non-magnetic cenospheres of 100-160 micrometers in diameter with the silicate binder (samples #161-54, #161-56 and #161-58) were loaded with components of another simulated actinide solution spiked by plutonium (Table 6). Cerium nitrate doped with Pu-239 was used as a simulant for plutonium. Saturation was performed for 5 cycles with oven drying at 130xc2x0 C. after each cycle for 1 hour followed by calcination at 800xc2x0 C. for 0.5 hour. Under these conditions the loading of blocks with oxides was about 20 wt. %. Two loaded blocks were compacted using hot uniaxial pressing (HUP) under the following parameters: Pressure: 300 kg/cm2 (29.4 MPa); Temperature: 900xc2x0 C.; Time: 0.5 hour; Temperature at pressure release: 400xc2x0 C. The hot-pressed samples were tested by their durability at 90xc2x0 C. in distilled water during 100 days according to the Material Characterization Center MCC-1 test. Parameters of Pu-containing samples and leaching rates are presented in Tables 7 and 8. The data show that the final waste form obtained as a result of hot pressing procedure is a stable glass-ceramic material with low Pu release rates. Other modifications and variations of the above present invention are possible in the light of the above teaching. The changes may be made in the particular embodiments of the invention as defined by the appended claims.
054401879	abstract	An electric battery comprises: a nuclear source of relatively high energy radiation fluence; a semiconductor junction characterized by a curve for this fluence relating minority carrier diffusion length and a damage constant and; an enclosure having a sufficiently low thermal impedance for dissipation of sufficient heat from the nuclear source to permit predetermined degradation of the minority carrier diffusion length initially and predetermined maintenance of the minority carrier diffusion length thereafter; the nuclear source being a radionuclide selected from the class consisting of alpha, gamma and beta emitters; and the curve being substantially logarithmic.
	abstract	The invention pertains to a nuclear fuel assembly grid or a portion or a part of the grid, such as a grid strap and/or an integral flow mixer that is at least partially constructed of a composition containing one or more ternary compounds of the general formula I:Mn+1AXn (I) wherein, M is a transition metal, A is an element selected from the group A elements in the Chemical Periodic Table, X is carbon or nitrogen, and n is an integer from 1 to 3.
056549920	summary	BACKGROUND OF THE INVENTION The present invention relates to a method of repairing a structure or a component composing internals of a nuclear reactor pressure vessel in a nuclear power plant in service and, more particularly, to a method of repairing a structure or a component irradiated with neutrons and having a crack defect by covering the defect portion of the structure with a cover plate and welding the structure and the cover plate to realize a high reliable repair for the integrity after the repair. It is worried to occur a crack defect such as a stress corrosion cracking in a structure or a component under a high temperature and high pressure environment in a reactor pressure vessel as time passes. The stress corrosion cracking occurs in a superposed condition of a deterioration factor such as local change in the composition of a material itself, a stress factor of tensile remaining stress applied to the structure due to welding or the like and a corrosion environment factor under a high temperature and high pressure environment, and the crack grows. When the crack grows through the structure or the component, a serious accident may occur in the nuclear plant by some possibility. Therefore, a repairing technology to prevent a through-crack in the structure having the crack is necessary. As for such a repairing technology to prevent a through-crack, there is a repairing method shown in FIG. 19a, wherein the growth of crack is prevented by covering a region containing a crack 1 with a plate 3 and by filler-welding the edge portion of the plate 3 and the structure 2 utilizing heat input generated by arc or welding arc 6 while a filler metal 5 is being added to isolate the crack 1 from the corrosion environment. However, the structure irradiated with high energy particle rays such as .alpha.-rays, .beta.-rays, neutron rays or the like contains He generated by nuclear transformation of the component elements of the structure. In a case wherein a structure of such a material containing He is covered with a plate and the edge of the plate and the structure are filler-welded as described above, heat is inevitably input large enough to melt the filler material, a part of the base material and a part of the plate in a conventional welding technology such as arc welding. Therefore, when the structure 2 irradiated with neutrons and having a crack 1 is repaired by filler-welding the cover plate 3 and the structure 2 as shown in FIG. 19a, the heat affected zone 8 due to the weld in the structure around the filler-welded portion 7 of the repaired portion possibly may become a new heat affected zone to produce a crack 9, as shown in FIG. 19b. The above problem for austenitic stainless steel is described in, for example, Journal of Material Science, Vol. 26(1991), pp 2063-2070. The mechanism of occurrence of a crack is that when welding work is performed with adding heat on the above material of an alloy containing generated He and having a cumulative total amount of neutron irradiation more than 1.0.times.10.sup.20 n/m.sup.2, the He easily diffuses to the crystal grain boundaries of the material by thermal activation due to heating of the welding heat affected zone near the welded portion, and the He voids collected in the grain boundaries gathers to form bubbles having sizes of .mu.m order to decrease the strength of grain boundaries of the material. Further when a tensile stress due to solidification and shrinkage is added to the material after the welding, cracks occur in the grain boundaries in the heat affected zone of non-melted portion. As for repairing of a structure with a crack which is the object of the present invention, in the repairing method according to the conventional technology of covering the structure with a plate and filler-welding it to the structure, the plate and the structure are closely contacted so that the side surface of the edge portion of the plate and the surface of the structure are in a face-contact state, and the filler wire, the side surface of the edge portion of a plate and the surface of the structure are melted to be welded while the filler wire is being fed and thermal energy is being input. Therefore, there are some cases where the amount of heat input added to the structure becomes locally high. Under such a welding condition, there is a possibility that the He easily diffuses to the crystal grain boundaries of the material by thermal activation due to heating of the welding heat affected zone, and the heat affected zone in the structure becomes a new crack generating portion. There are various disclosures concerning relations between welding of steel containing He and cracking. They are as follows: Metallurgical Transaction A. Vol. 21A (1990/9) pp. 2585-2596 [H. T. Lin etc.], which discloses that when GTA arc welding is applied to He containing stainless steel, intergranular cracking occurs in a welding heat affected zone; decrease in welding heat input tends to decrease in cracking sensibility. Welding Journal (1991/5) pp. 123-132 [S. H. Goods etc.], which discloses relations between He amount and cracking property when large heat input GMA welding is applied to 304 stainless steel containing He, wherein as the heat input becomes smaller, scale of cracking becomes small, as in FIG. 12. Metallurgical Transaction A Vol. 23A (1992/5) pp. 1021-1032 [S. H. Goods etc.], which discloses welding cracking of irradiated material is due to formation/growth/joining of He bubbles, and wherein mechanism of cracking caused by He is discussed. Welding Journal (1992/4) pp. 43-51 [E. A. Franco-Ferreira etc.], which discloses relations between welding heat input and cracking in case various He amounts are taken in GTA/GMA welding. DP-MS-89-41 (DE90-001312) Herium Induced Weld Cracking In Irradiated 304 Stainless Steel (U) by A. K. Birchenall, which discloses a relation between welding heat input and cracking in case various He amount are taken. SUMMARY OF THE INVENTION The object of the present invention is to provide a repairing method securing the integrity of repaired portion with considering the problems in the conventional repairing method described above when repairing is performed on a crack such as a stress corrosion cracking occurred in a structure or a component made of stainless steel, a Ni based alloy or low alloy steel inside a reactor pressure vessel. The above object of the present invention can be attained by providing a method of repairing a structural material such as stainless steel, a Ni based alloy or low alloy steel of a nuclear reactor internals having a crack and irradiated with .alpha.-rays, .beta.-rays and neutron rays to the irradiation amount of 0 to 5.0.times.10.sup.27 n/m.sup.2 in a nuclear power plant in service, the method of repairing a structural material of a nuclear reactor internals comprising the steps of covering a region of the structural material having a crack defect with a plate to cover, welding the plate and the structural material to be repaired by locally applying pressure on the surface of the plate and adding energy to the portion to which the pressure is applied thereby to generate thermal energy in the contact surface between the plate and the structural material. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized, as the above step of welding the plate and the repaired structural material, by welding the plate and the structural material by heating with ohmic heat generated, by allowing current to flow the portion to be repaired while applying pressure on the surface of the plate. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized, as the above step of welding the plate and the structural material by heating with ohmic heat generated, by seam-welding the cover plate to the structural material using a roller electrode. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized, as the above-mentioned welding of the plate and the structural material by heating with ohmic heat generated, by resistance-spot-welding the cover plate to the structural material using a roller electrode. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized in that the above-mentioned resistance-spot-welding of the plate and the repaired structural material by heating with ohmic heat generated is carried out by welding the structure and the cover plate at a plurality of positions at a time by allowing current to flow in a plurality of electrodes. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized in that the above mentioned welding of the plate and the repaired structural material is performed by generating thermal energy caused by frictional resistance by mechanically rubbing the contact surface between the structural material and the cover plate. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized in that the above mentioned welding of the plate and the repaired structural material by generating thermal energy caused by frictional resistance is performed by giving mechanical vibration while applying pressure on the portion to be welded to mechanically rub the contact surface. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized in that the above mentioned welding of the plate and the structural material by generating thermal energy caused by frictional resistance by giving mechanical vibration is performed by mechanically rubbing the contact surface by giving mechanical vibration obtained by converting high frequency energy into mechanical vibration through magneto-striction to the portion to be welded. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized, in the above repairing work, by providing convex projections on the surfaces of the cover plate as welding surfaces. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized by providing concave notches on the positions of the structural material contacting to the convex projections on the cover plate, the cover plate being placed and welded to the structural material by engaging the convex projections on the welding surface of the cover plate with the concave notches. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized, in the above repairing work, by using a reactor internal structure or component as a supporting portion for means for offsetting the reaction force produced when the pressure is applied. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized, as means for offsetting the reaction force produced when the pressure is applied, by introducing a supporting pillar between an upper grid plate and a core support plate of a light water reactor internals, the pillar supported with the upper grid plate and the core support plate being used as a supporting portion for means for offsetting the reaction force produced when the pressure is applied. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized, as means for offsetting the reaction force produced when the pressure is applied, by introducing a supporting pillar between a pressure vessel and a core shroud, the pillar supported with the inner surface of the pressure vessel being used as a supporting portion for means for offsetting the reaction force produced when the pressure is applied. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized, in repairing work performing the above work to a structure of reactor internals contacting to the reactor water, by performing the above welding work by removing the oxide layer existing on a region including the weld surface of the position of the structural material to be repaired with the cover plate before placing the cover plate on a position of the structural material to be repaired, and then placing the cover plate. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized, in repairing work performing the above work to a structure of reactor internals contacting to the reactor water, by performing the work for removing the oxide layer existing on a region including the weld surface of the position of the structural material to be repaired with the cover plate, performing surface finishing of the region including the weld surface of the position of the structural material to an average roughness of 0.2 to 10 .mu.m, after performing the surface finishing, placing the cover plate and welding the plate to the position of the structural material. The present invention provides a method of repairing a structural material of a nuclear reactor internals, which is characterized, in the above repairing work, by metallurgically welding a part of the outer periphery or the whole periphery in the contact surface of the cover plate and the repaired structural material. The present invention provides an apparatus of repairing a structural material of a nuclear reactor internals, which is characterized by comprising means for offsetting the reaction force produced when the pressure is applied in order to perform the above work. The present invention provides an apparatus of repairing a structural material of a nuclear reactor internals, as means for offsetting the reaction force produced when the pressure is applied in order to perform the above work, which is characterized by comprising pressure supporting mechanism supported by an upper grid plate and a core support plate of a light water reactor internals as a means for applying the pressure. The present invention provides an apparatus of repairing a structural material of a nuclear reactor internals, as means for offsetting the reaction force produced when the pressure is applied in order to perform the above work, which is characterized by comprising a pressure supporting mechanism supported by the inner surface of a pressure vessel as a means for applying the pressure.
044435657	summary	The present invention relates to a resin composition containing metal foil fragments in a high concentration. In recent years, electric apparatus and devices equipped with an electromagnetic wave generating source, such as microwave ovens, televisions or micro-computors, have become popular. There are accordingly an increasing number of instances where such apparatus and devices give electromagnetic wave interferences against communication or measuring devices, or they receive electromagnetic wave interferences from outside. In order to avoid such interferences by electromagnetic waves, it is common to use a metal casing for the assembly of these apparatus or devices. However, the metal casing requires a number of process steps for its shaping or coating. Therefore, it has been desired to develop a thermoplastic resin material which can be readily shaped and which is highly effective to attenuate the electromagnetic waves to pass therethrough. Thermoplastic resins can easily be shaped. However, if a substantial amount of metal foil fragments such as aluminum or copper foil fragments which are effective for attenuation of the electromagnetic waves, is incorporated to provide an adequate shielding effect against the electromagnetic waves, it would be difficult to adequately knead the mixture by a single shaft extruder as the mixture tends to be hardly processable by the screw of the single shaft extruder. Further, it is difficult to adequately disperse the metal foil fragments in the resin by mere mechanical kneading, and the resin composition thereby obtained does not have adequate strength. Accordingly, it is an object of the present invention to provide such a resin composition which is highly effective to attenuate electromagnetic waves. Another object of the present invention is to overcome the abovementioned difficulties in the conventional technique and to provide a resin composition containing metal foil fragments in a high concentration and yet having good dispersibility and adequate strength. A further object of the present invention is to provide a process for preparing such a resin composition. The present invention provides a composition comprising 100 parts by weight of metal foil fragments, from 1 to 10 parts by weight of a first polymer covering the surfaces of the metal foil fragments and obtained by polymerizing at least one of monomers selected from the group consisting of acrylic acid, methacrylic acid, an alkylacrylate, an aminoalkylacrylate, an alkylmethacrylate and an aminoalkylmethacrylate in the presence of the metal foil fragments, and from 5 to 33 parts by weight of a second polymer obtained by polymerizing a mixture of an aromatic vinyl monomer and a monomer copolymerizable with the aromatic vinyl monomer. The present invention also provides a process for preparing a thermoplastic resin composition containing metal foil fragments, which comprises suspension-polymerizing from 1 to 10 parts by weight of at least one of monomers selected from the group consisting of acrylic acid, methacrylic acid, an alkylacrylate, an alkylmethacrylate, an aminoalkylacrylate and an aminoalkylmethacrylate in the presence of 100 parts by weight of metal foil fragments and then adding and suspension-polymerizing from 5 to 33 parts by weight, based on 100 parts by weight of the metal foil fragments, of a mixture of an aromatic vinyl monomer and a monomer copolymerizable with the aromatic vinyl monomer. Now, the present invention will be described in detail with reference to the preferred embodiments. The metal foil fragments used in the present invention are preferably made of a metal which is stable and does not fuse or evaporate at a temperature for shaping the thermoplastic resin (usually from 230.degree. to 260.degree. C.) and which has good electric conductivity, such as aluminum, zinc, copper, iron, tin, gold, silver or an alloy thereof. Further, in order to obtain greater effectiveness for attenuation of electromagnetic waves, it is preferred to use a combination of at least two different types of metal foil fragments. In such a case, a combination of metals belonging to different Groups in the Periodical Table is preferred since it is thereby possible to minimize the specific resistance of the resin composition thereby obtained. For instance, good results will be obtained by a combination of aluminum and zinc or aluminum and tin. In the case of the combination of aluminum and zinc foil fragments, the mixing ratio is preferably from 3 to 70% by weight of zinc foil fragments, the rests being aluminum foil fragments, more preferably from 5 to 20% by weight of zinc foil fragments, the rest being aluminum foil fragments. When the proportion of zinc foil fragments is less than 3% by weight or more than 70% by weight, no improvements in the reduction of the specific resistance and the attenuation effect against electromagnetic waves are observed as compared with the case where aluminum foil fragments or zinc foil fragments are used alone. The metal foil fragments preferably have a thickness of from 5 to 50 .mu.m and a quadrilateral shape of 0.5-5 mm.times.0.5-5 mm, more preferably 1-2 mm.times.1-2 mm. They may have any other shapes so long as they have a size similar to the above size. These metal foil fragments are covered on their surfaces with a polymer obtained by polymerizing at least one of monomers selected from the group consisting of acrylic acid, methacrylic acid, an alkylacrylate, an aminoalkylacrylate, an alkylmethacrylate and an aminoalkylmethacrylate. Such a polymer is suitable because it has good adhesion to the metal foil fragments. The amount of the polymer is from 1 to 10 parts by weight per 100 parts by weight of the metal foil fragments. If the amount is less than 1 part by weight, no adequate coating effectiveness will be obtained. On the other hand, if the amount exceeds 10 parts by weight, there will be an excess amount of the polymer which does not attach to the surfaces of the metal foil fragments and which gives an adverse effect to the physical properties of the composition thereby obtained. The polymer to be used for coating the metal foil fragment may be a homopolymer of one of the above-mentioned monomers or copolymer of at least two such monomers. For instance, there may be used a homopolymer of methylmethacrylate or a copolymer of methylmethacrylate with from 10 to 30% by weight of acrylic acid. However, a copolymer of methylmethacrylate with from 30 to 70% by weight of an aminoalkylacrylate or an aminoalkylmethacrylate is particularly preferred since it is superior in the coatability on the metal foil fragments and the compatibility with other resins. In such a case, the aminoalkyl group in the aminoalkylalkylate or the aminoalkylmethacrylate is preferably a dimethylaminoethyl group ((CH.sub.3).sub.2 NCH.sub.2 CH.sub.2 --). However, other groups such as a diethylaminoethyl group and a dimethylaminopropyl group are also useful as the aminoalkyl group. As the alkyl group, a straight chain, branched chain or alicyclic alkyl group having from 1 to 10 carbon atoms is used. However, a methyl group or an ethyl group is preferred in view of the physical properties such as tensil strength of the polymer thereby obtained. The mixing ratio of the monomers in a mixture is not restricted to the above-mentioned range. However, if the mixing ratio is in the above-mentioned range, good results are obtainable in the coatability on the metal foil fragment surfaces, the dispersibility and the physical properties. The metal foil fragments may be coated with the above-mentioned polymer by dipping the metal foil fragments in a solution prepared by dissolving the polymer in a suitable organic solvent. However, it is preferred to suspension-polymerize the above-mentioned monomer or monomer mixture in the presence of the metal foil fragments, whereby the coating can readily be done. When a combination of two different types of metal foil fragments is used, it is preferred preliminarily mix the two types of the metal foil fragments and then to suspension-polymerize the monomer or monomer mixture in the presence of the metal foil fragment mixture. Then, from 5 to 33 parts by weight, based on 100 parts by weight of the metal foil fragments, of a polymer obtained by polymerizing a mixture of an aromatic vinyl monomer and a monomer copolymerizable with the aromatic vinyl monomer is incorporated so that total amount of the polymers, i.e. this polymer and the polymer covering the surfaces of the metal foil fragments, is brought to from 6 to 43 parts by weight per 100 parts by weight of the metal foil fragments. If the amount of the polymer obtained by the polymerization of the aromatic vinyl polymer and the monomer copolymerizable therewith, is less than 5 parts by weight, the bulk density of the composition thereby obtained tends to be small, whereby the composition tends to be hardly mixed with e.g. an ABS resin. On the other hand, if the amount exceeds 33 parts by weight, the concentration of the metal foil fragments tends to be insufficient when the composition is mixed with an ABS resin or other thermoplastic resin. As the aromatic vinyl monomer to be used in the present invention, there may be mentioned styrene, .alpha.-methylstyrene, vinyl toluene and a halogenated styrene. As the copolymerizable monomer, acrylonitrile, methacrylonitrile or an alkylester of acrylic acid or methacrylic acid is suitable. The concentration of the copolymerizable monomer in the monomer mixture is preferably from 20 to 50% by weight. If the concentration is outside this range, the composition thereby obtained tends to have poor compatibility with other resins. In the preparation of the composition of the present invention, it is preferred that the above-mentioned monomers are suspension-polymerized in the presence of the metal foil fragments. Namely, 100 parts by weight of the metal foil fragments and from 1 to 10 parts by weight of at least one of the monomers selected from the group consisting of acrylic acid, methacrylic acid, an alkylacrylate, an aminoalkylacrylate, an alkylmethacrylate and an aminoalkylmethacrylate are suspended in water and the suspension is suspension-polymerized in accordance with a usual method. As the polymerization initiator, a water soluble initiator such as a persulfate is preferably used to obtain a good coating on the foil surfaces. Upon completion of the polymerization, from 5 to 33 parts by weight of a mixture of the aromatic vinyl monomer and the monomer copolymerizable therewith is added and further suspension-polymerized. The composition thereby obtained is in the form of pellets in which some tens metal foils are laminated. The composition has a great bulk density and good compatibility with e.g. an ABS resin. The composition of the present invention can be used by itself. However, it may also be used as a mixture with other resin such as an ABS resin or an AS resin. In such a case, the mixing can be done by a single shaft extruder. The mixture thereby obtained has good physical properties and good electroconductivity. Especially when two types of the metal foil fragments are used in combination, particularly good reduction of the specific resistance and electromagnetic wave attenuation characteristics are obtainable. Further, the metal foils in the composition are hardly susceptible to peeling even when an outer force is applied. Now, the present invention will be described in further detail with reference to Examples, Comparative Examples and Application Examples.
043057870	abstract	A rack for storing spent radioactive fuel is disclosed in which a set of cells, consisting of self-supporting metal tubes arranged in a staggered fashion with respect to each other, and joined to each other along their longitudinal edges, forms a rigid spatial structure. The tubular hole defined by each of four tubes has a larger cross-sectional area than said tubes and is provided with neutron-absorbing material. This material is independent of the tubes and may be removed and re-inserted in the tubular hole as often as necessary. Various tubular structures are also disclosed.
	description	This application is a continuation of U.S. Non-Provisional application Ser. No. 14/174,630 filed Feb. 6, 2014 and titled “CRDM WITH SEPARATE SCRAM LATCH ENGAGEMENT AND LOCKING”. This application claims the benefit of U.S. Provisional Application No. 61/792,235 filed Mar. 15, 2013 and titled “CRDM DESIGNS WITH SEPARATE SCRAM LATCH ENGAGEMENT AND LOCKING”. U.S. Provisional Application No. 61/792,235 filed Mar. 15, 2013 and titled “CRDM DESIGNS WITH SEPARATE SCRAM LATCH ENGAGEMENT AND LOCKING” is hereby incorporated by reference in its entirety into the specification of this application. This invention was made with Government support under Contract No. DE-NE0000583 awarded by the Department of Energy. The Government has certain rights in this invention. DeSantis et al., U.S. Pub. No. 2011/0222640 A1 published Sep. 15, 2011 and incorporated herein by reference in its entirety discloses (among other subject matter) a CRDM for a nuclear reactor employing a lead screw (sometimes referred to as a ball screw herein denoting specific lead screw embodiments employing ball nuts disposed between the screw and nut threadings) engaged by a motor to provide controlled vertical translation, in which a separate latch assembly connected with the lead screw latches to the lifting rod of a control rod (or to the lifting rod of a control rod assembly comprising plural control rods connected by a yoke or spider to the lifting rod). The latch is actively closed to connect the translating assembly comprising the lifting rod and the control rod(s) so that the translating assembly translates with the lead screw under control of the CRDM motor. Upon removal of the closing force, e.g. during a SCRAM, the latch opens to release the lifting rod and SCRAM the control rod(s), while the lead screw remains engaged with the CRDM motor and does not fall. In some illustrative embodiments, the latches are actively closed by cam bars that are lifted by a hydraulic piston, solenoid, or other lifting mechanism, where each cam bar is part of a four-bar linkage that moves the cam bar horizontally in response to the lifting in order to cam the latches shut. In DeSantis et al., U.S. Pub. No. 2011/0222640 A1, the four-bar linkage is arranged such that under gravity the four-bar linkage operates to move the cam bars outward so as to release the latch. By way of non-limiting illustrative example, FIGS. 1 and 2 correspond to drawing sheets 1 and 16, respectively, of DeSantis et al., U.S. Pub. No. 2011/0222640 A1. With reference to FIG. 1, an illustrative nuclear reactor vessel of the pressurized water reactor (PWR) type is diagrammatically depicted. An illustrated primary vessel 10 contains a reactor core 12, internal steam generator(s) 14, and internal control rods 20. The illustrative reactor vessel includes four major components, namely: 1) a lower vessel 22, 2) upper internals 24, 3) an upper vessel 26 and 4) an upper vessel head 28. A mid-flange 29 is disposed between the lower and upper vessel sections 22, 26. Other vessel configurations are also contemplated. Note that FIG. 1 is diagrammatic and does not include details such as pressure vessel penetrations for flow of secondary coolant into and out of the steam generators, electrical penetrations for electrical components, and so forth. The lower vessel 22 of the illustrative reactor vessel 10 of FIG. 1 contains the reactor core 12, which can have substantially any suitable configuration. The illustrative upper vessel 26 houses the steam generator 14 for this illustrative PWR which has an internal steam generator design (sometimes referred to as an integral PWR design). In FIG. 1, the steam generator 14 is diagrammatically shown. In a typical circulation pattern the primary coolant is heated by the reactor core 12 and rises through the central riser region 32 to exit the top of the shroud 30 whereupon the primary coolant flows back down via the downcomer region 34 and across the steam generators 14. Such primary coolant flow may be driven by natural convection, by internal or external primary coolant pumps (not illustrated), or by a combination of pump-assisted natural convection. Although an integral PWR design is illustrated, it is also contemplated for the reactor vessel to have an external steam generator (not illustrated), in which case pressure vessel penetrations allow for transfer of primary coolant to and from the external steam generator. The illustrative upper vessel head 28 is a separate component, but it is also contemplated for the vessel head to be integral with the upper vessel 26. While FIG. 1 illustrates an integral PWR, in other embodiments the PWR may not be an integral PWR, that is, in some embodiments the illustrated internal steam generators may be omitted in favor of one or more external steam generators. Still further, the illustrative PWR is an example, and in other embodiments a boiling water reactor (BWR) or other reactor design may be employed, with either internal or external steam generators. With reference to FIG. 2, a control rod system embodiment is described, e.g. suitably part of the upper internals 24 of the nuclear reactor of FIG. 1, which provides electromagnetic gray rod functionality (i.e. continuously adjustable control rod positioning) and a hydraulic latch system providing SCRAM functionality (i.e. in an emergency, the control rods can be fully inserted in order to quickly quench the nuclear reaction, an operation known in the art as a SCRAM). The control rod system of FIG. 2 allows for failsafe SCRAM of the control rod cluster without scramming the lead screw. A motor/ball nut assembly is employed, such that a lead screw 40 is permanently engaged to a ball-nut assembly 42 which provides for axial translation of the lead screw 40 by driving a motor 44. The illustrative motor 44 is mounted on a standoff 45 that positions and bottom-supports the motor 44 in the support structure of the upper internals 24; other support arrangements are contemplated. A control rod cluster (not shown) is connected to the lead screw 40 via a lifting/connecting rod or lifting/connecting rod assembly 46 and a latch assembly 48. The lead screw 40 is substantially hollow, and the lifting/connecting rod 46 fits coaxially inside the inner diameter of the lead screw 40 and is free to translate vertically within the lead screw 40. The latch assembly 48, with spring loaded latches, is attached to (i.e. mounted on) the top of the lead screw 40. When the latches of the latch assembly 48 are engaged with the lifting rod 46 they couple the lifting/connecting rod 46 to the lead screw 40 and when the latches are disengaged they release the lifting/connecting rod 46 from the lead screw 40. In the illustrated embodiment, latch engagements and disengagements are achieved by using a four-bar linkage cam system including two cam bars 50 and at least two cam bar links 52 per cam bar 50. Additional cam bar links may be added to provide further support for the cam bar. When the cam bars 50 move upward the cam bar links 52 of the four-bar linkage also cam the cam bars 50 inward so as to cause the latches of the latch assembly 48 to rotate into engagement with the lifting/connecting rod 46. In the illustrated embodiment, a hydraulic lift assembly 56 is used to raise the cam bar assemblies 50. In an alternative embodiment (not illustrated), an electric solenoid lift system is used to raise the cam bar assemblies. When a lift force is applied to the cam system, the upward and inwardly-cammed motion of the cam bars 50 rotates the latches into engagement thereby coupling the lifting/connecting rod 46 to the lead screw 40. This causes the control rod cluster to follow lead screw motion. When the lift force is removed, the cam bars 50 swing down and are cammed outward by the cam bar links 52 of the four-bar linkage allowing the latches of the latch assembly 48 to rotate out of engagement with the lifting/connecting rod 46. This de-couples the lifting/connecting rod 46 from the lead screw 40 which causes the control rod cluster to SCRAM. During a SCRAM, the lead screw 40 remains at its current hold position. After the SCRAM event, the lead screw 40 is driven to the bottom of its stroke via the electric motor 44. When the lift force is reapplied to the cam system via the hydraulic lift assembly 56, the latches of the latch assembly 48 are re-engaged and the lifting rod 46 is re-coupled to the lead screw 40, and normal operation can resume. Other latch drive modalities are contemplated, such as a pneumatic latch drive in which pneumatic pressure replaces hydraulic pressure in the illustrated lift assembly 56. In FIG. 2, the lead screw 40 is arbitrarily depicted in a partially withdrawn position for illustration purposes. The latching assembly 48 is attached to (i.e. mounted on) the top of the lead screw 40. The ball nut 42 and motor 44 are at the bottom of the control rod drive mechanism (CDRM), the latch cam bars 50 extend for the full length of mechanism stroke, and the hydraulic lift system 56 is located at the top of the mechanism. In some embodiments, the CRDM of FIG. 2 is an integral CDRM in which the entire mechanism, including the electric motor 44 and ball nut 42, and the latching assembly 48 are located within the reactor pressure vessel 10 (see FIG. 1) at full operating temperature and pressure conditions. Further illustrative embodiments of CRDM designs employing the cam bars with four-bar linkages are described in DeSantis et al., U.S. Pub. No. 2011/0222640 A1, which is incorporated herein by reference in its entirety. In some illustrative embodiments, a control rod drive mechanism (CRDM) comprises: a lifting rod configured to support a control rod configured to be inserted into a nuclear reactor core to quench a nuclear reaction in the nuclear reactor core; a holding mechanism comprising an electromagnetic circuit with magnetic poles configured to be drawn together when the electromagnetic circuit is energized to hold the lifting rod and to release the hold on the lifting rod upon de-energizing the electromagnetic circuit; and a translation mechanism configured to linearly translate the lifting rod held by the holding mechanism toward and away from the nuclear reactor core. The holding mechanism includes a non-magnetic spacer between the magnetic poles that defines a gap between the drawn together magnetic poles. In some embodiments the spacer is disposed around a perimeter of the drawn-together magnetic poles. In some embodiments the spacer is attached to one of the magnetic poles of the electromagnetic circuit. In some embodiments the spacer is effective to define the gap between the drawn-together magnetic poles of at least 0.010 cm. In some embodiments the spacer is effective to define the gap between the drawn-together magnetic poles of at least 0.025 cm. In some embodiments the holding mechanism includes a plurality of latches, a latch engagement mechanism configured to engage the latches to an upper end of the lifting rod, and a latch holding mechanism separate from the latch engagement mechanism, wherein the electromagnetic circuit with the magnetic poles is part of the latch holding mechanism and is not part of the latch engagement mechanism. In some embodiments the holding mechanism includes a screw on which the lifting rod is mounted and a separable ball-nut including the electromagnetic circuit with magnetic pole pieces, wherein the electromagnetic circuit is configured to magnetically hold the separable ball-nut together engaged with the screw and to allow the separable ball-nut to separate upon de-energizing the electromagnetic circuit. In some embodiments as set forth in the immediately preceding paragraph, the translation mechanism comprises a screw and a motor configured to linearly translate the screw, and the CRDM further comprises a plurality of latches mounted on the screw and configured to engage an upper end of the lifting rod, wherein the holding mechanism is configured to draw the magnetic poles together when the electromagnetic circuit is energized to hold the latches engaged with the upper end of the lifting rod and to release the hold on the latches upon de-energizing the electromagnetic circuit to disengage the latches from the upper end of the lifting rod. In some such embodiments the CRDM further includes a latch engagement mechanism that is separate from the holding mechanism, the latch engagement mechanism configured to close the latches to engage the upper end of the lifting rod. Some embodiments further include a cam assembly comprising cam bars and cam bar links interconnected to define a four-bar linkage that urges the cam bars laterally inward to cam the latches closed in response to a vertical actuation force applied to the cam bars, and the holding mechanism is configured to draw the magnetic poles together when the electromagnetic circuit is energized to hold the cam bars in their inward position and to release the hold on the cam bars upon de-energizing the electromagnetic circuit. In some illustrative embodiments, a pressurized water nuclear reactor (PWR) comprises a pressure vessel, a reactor core disposed in the pressure vessel, and a CRDM as set forth in the preceding two paragraphs. Some such PWR embodiments further comprise coolant water filling the pressure vessel, and the spacer does not completely fill the gap between the drawn-together magnetic poles and the portion of the gap not filled by the spacer is filled by coolant water. In some illustrative embodiments, a control rod drive mechanism (CRDM) comprises: a lifting rod configured to support a control rod configured to be inserted into a nuclear reactor core to quench a nuclear reaction in the nuclear reactor core; a translation mechanism comprising a translating element including latches configured to engage an upper end of the lifting rod and a motor configured to linearly translate the translating element so as to linearly translate the lifting rod engaged by the latches; a cam assembly comprising cam bars and cam bar links interconnected to define a four-bar linkage that urges the cam bars laterally inward to cam the latches closed in response to a vertical actuation force applied to the cam bars; and a holding mechanism comprising an electromagnetic circuit with a fixed magnetic pole and a movable magnetic pole. The movable magnetic pole is connected with the cam bars, and the holding mechanism is configured to draw the movable magnetic pole to the fixed magnetic pole when the electromagnetic circuit is energized to hold the cam bars connected with the movable magnetic pole in their inward position and to release the hold on the cam bars upon de-energizing the electromagnetic circuit. In some embodiments the four-bar linkage is configured to urge the cam bars laterally inward to cam the latches closed in response to gravitational actuation force comprising the weight of the cam bars. In some such embodiments the lifting rod includes: a cam surface configured to cam the latches open in response to the translation mechanism lowering the latches of the translating element over the upper end of the lifting rod; and a recess with which the latches engage in response to the translation mechanism further lowering the latches past the cam surface and in response to the four-bar linkage urging the cam bars laterally inward to cam the latches closed in response to the gravitational actuation force comprising the weight of the cam bars. In some embodiments the movable magnetic pole is arranged above the fixed magnetic pole so as to be drawn downward when the electromagnetic circuit is energized and to release the downward hold on the connected cam bars upon de-energizing the electromagnetic circuit. In some embodiments the translating element comprises a hollow screw, and the latches are mounted at an upper end of the hollow screw, and the lifting rod passes through the hollow screw with the upper end of the lifting rod protruding from the upper end of the hollow screw. In some illustrative embodiments, a pressurized water nuclear reactor (PWR) comprises a pressure vessel, a reactor core disposed in the pressure vessel, and a CRDM as set forth in the immediately preceding paragraph. Disclosed herein are improvements upon CRDM designs of DeSantis et al., U.S. Pub. No. 2011/0222640 A1 employing the cam bars with four-bar linkages. In one aspect, the CRDM is improved by separating the latch engagement and latch holding functions. This may entail increasing the number of CRDM components since a separate latch engagement mechanism and latch holding mechanism are provided. However, it is recognized herein that this increase in parts is offset by improved energy efficiency. This is because the latch engagement is a momentary event that occurs very infrequently (possibly only once per fuel cycle). In contrast, the latch holding operation is performed over the entire fuel cycle (barring any SCRAM events). By employing separate latch engagement and holding mechanisms, the latch holding mechanism is not required to perform the relatively higher-energy operation of moving the latches from the unlatched position to the latched position. Accordingly, the latch holding mechanism can be made more energy efficient. In another aspect, the latch engagement mechanism, which no longer needs to perform the latch holding function, can be substantially improved. In one embodiment (see FIGS. 3-6), the latch engagement mechanism comprises a lower camming link built into the lower portion of the CRDM, which is engaged by the latch box or housing as it is lowered toward the lifting rod (which, due to its not currently being latched, is typically located at its lowermost position corresponding to maximum insertion of the control rods into the nuclear reactor core). The lowering latch housing engages the lower camming link which is curved and mounted pivotally so that an end distal from the end cammed by the latch housing is caused to drive the cam bars inward, into the latched position. Once in the latched position, the separate latch holding mechanism is engaged, and thereafter when the latch housing is raised by the CRDM motor and lead screw the lower camming link disengages but the latch remains closed by action of the separate latch holding mechanism. In another aspect, the latch engagement mechanism is implemented as a self-engaging cam/latch system (see FIGS. 7-18). This approach is achieved by modifying the four-bar linkage such that under gravity the four-bar linkage operates to move the cam bars inward so as to engage the latch. Similar to the latch engagement of FIGS. 3-6, this latch engagement activates upon lowering the latch housing over the upper end of the lifting rod. In the self-engaging approach, the latch is normally closed due to the four-bar linkage defaulting to moving the cam bars inward under force of gravity, and the upper end of the lifting rod includes a camming surface that cams the latch open as the latch housing is lowered over the upper end of the lifting rod. Once over the camming surface of the upper end, the latch again closes under force of gravity due to the orientation of the four-bar linkage. The separate latch holding mechanism is then activated to hold the cam bars in the inward position to keep the latch closed. Surprisingly, this embodiment is capable of reliable SCRAM even though the four-bar linkage is biasing the latch closed under gravity. This is because the four-bar linkage is designed with its links at large angles and of relatively long length so that the force necessary to open the latches against the gravitational closing bias of the four-bar linkage is quite modest. (See FIGS. 7-18 and related discussion for details). Accordingly, the weight of the translating assembly (i.e. the lifting rod and the attached control rod or rods and optional spider or yoke) is sufficient to easily overcome the closing bias of the four-bar linkage. In further disclosed aspects, various embodiments of the latch holding mechanism are disclosed. See FIG. 19 and following. In the CRDM system of FIG. 2, the lift system 56 (hydraulic as shown, or alternatively an electric solenoid) supports both latch actuation and long term engagement during hold and translational operations. In the variant embodiments described in the following, features of like functionality to the CRDM of FIG. 2 (for example, the cam bars 50 and the cam bar links 52 of the four-bar linkage) are labeled with like reference numbers. With reference to FIGS. 3-6 and with contextual reference to FIG. 2, a CRDM embodiment is described in which latch activation and long term hold/translation functions are separated, resulting in reduction of operational power requirements. The CRDM comprises a mechanically actuated latching device. FIG. 3 shows an isometric view of the CRDM with the control rod (not shown) fully inserted. FIGS. 4 and 5 show isometric and side cutaway views, respectively, with the latching device disengaged. FIG. 6 shows a side cutaway view with the latch engaged. The latching mechanism utilizes the CRDM motor 44, the lead screw 40 (e.g. threadedly engaged with the CRDM motor 44 via the ball screw 42 as shown in FIG. 2) and a latch box 102 to engage the latches 104 to the top of the connecting (i.e. lifting) rod 46. Springs 106 bias the latches 104 open. The latch box 102 and spring-biased latches 104 form a latch assembly corresponding to the latch assembly 48 of FIG. 2. In FIGS. 3-6, a mounting feature 108 is shown via which the latch box 102 is mounted to the top of the lead screw 40, but the lead screw itself is omitted in FIGS. 3-6. Similarly, only the top of the lifting rod 46 is shown in FIGS. 3-6, but it is to be understood that the lifting rod 46 extends downward as shown in contextual FIG. 2.) In this operation, the control rod or rods are initially fully inserted and the upper end of the lifting rod 46 is disengaged from the latches 104. The CRDM motor 44 is then operated to cause the lead screw 40 to translate downward, thus lowering the latch box 102 toward the upper end of the lifting rod 46. The downward force supplied by the CRDM motor 44 through the ball screw 42 moves the latch box 102 into contact with a lower camming link 110 built into a lower portion 112 of the CRDM. FIGS. 4 and 5 show isometric cutaway and side cutaway views, respectively, of the state in which the latch box 102 is just beginning to contact the lower camming link 110 at a contact area 114. As seen in FIG. 6, the continued application of motor torque forces the latch box 102 downward so as to press the lower camming link 110 downward resulting in a rotary action about a pivot point 116. This rotary action lifts and translates the cam bars 50 into the engaged position so as to cam against and close the latches 104 in the latch box 102. A separate holding mechanism (not shown in FIGS. 3-6 but embodiments of which are disclosed elsewhere in this application) keeps the cam bars 50 engaged as the latch box 102 is translated back upward after the latch engagement so as to lift the lifting rod 46 and attached control rod(s) upward. (Note that the control rods are not shown in FIGS. 3-6). This approach of the embodiment of FIGS. 3-6 separates latch activation and long term hold/translation functions of the CRDM, resulting in reduction of operational power requirements. (Again, FIGS. 3-6 illustrate only the latch activation—suitable embodiments of the long term hold/translation component are described elsewhere in this application.) The separation of latch activation and long term hold/translation functions simplifies the latching assembly making it easier to manufacture and less expensive. The mechanically actuated latching device described with reference to FIGS. 3-6 is electrically operated (assuming the lead screw 40 is driven by the electric CRDM motor 44 as per FIG. 2). In combination with an electrically operated holding mechanism (again, disclosed elsewhere in this application), this constitutes an all-electric CRDM. With reference to FIGS. 7-18, a CRDM embodiment with self-engaging cam/latch system and electromagnetic holding is described. In these CRDM embodiments, the four-bar linkage is modified such that under gravity the four-bar linkage operates to move the cam bars 50 inward so as to engage the latch. These CRDM embodiments also include a holding mechanism that only holds the latch and does not perform the engagement. With reference to FIG. 7, the CRDM is shown in combination with a control rod assembly 140 connected by the lifting/connecting rod 46 via the lead (or ball) screw 40 to the CRDM which includes the motor assembly 44, a modified cam assembly 144 (with a modified four-bar linkage) and latch assembly 148. With reference to FIG. 8, an enlarged view of the CRDM of FIG. 7 is shown, including the motor 44 mounted on the standoff 45, the cam assembly 144 with modified four-bar linkage, the latch assembly 148, and an optional position sensor 149. The illustrative CRDM also includes an electromagnet holding system 150 at the top of the cam assembly 144. With reference to FIGS. 9 and 10, which show cutaway perspective view of the CRDM in SCRAM mode (fully inserted) and in normal operating mode (translating or holding the control rods), respectively, the CRDM allows for failsafe SCRAM of the control rod (or control rod cluster) 140 without the need to SCRAM the lead screw 40. The lead screw/ball nut assembly is permanently attached to the electric motor 44 (only the top of which is visible in FIG. 9) which provides for its axial translation. The control rod cluster 140 is connected to the lead screw 40 via a connecting (i.e. lifting) rod 46 and the latch assembly 148 (see FIG. 7). As seen in FIG. 9, the lead screw 40 is hollow, and the lifting rod 46 fits inside the lead screw inner diameter (ID) and is free to translate vertically within the lead screw 40. The latch assembly, with two latches 154 (although three or more latches are contemplated), is secured to the top of the lead screw 40 by a lead screw/latch assembly coupling 156 (e.g., a latch housing mounted to the upper end of the lead screw). When the latches 154 are engaged with the lifting rod 46 they couple the lifting rod 46 to the lead screw 40 (normal operation) so that the lead screw 40 and lifting rod 46 move together. When the latches 154 are disengaged they release the lifting rod 46 from the lead screw 40 (an event referred to as SCRAM). Latch engagements and disengagements are achieved by using the four-bar linkage cam system 144 with a cam bar assembly provided for each latch including a cam bar 160 and cam bar links 162. However, unlike the embodiment of FIG. 2, in the CRDM embodiments of FIGS. 7-18 the cam bar links 162 are oriented such that when gravity causes the cam bars 160 to move downward the four-bar linkage action rotates the cam bars 160 inward thereby causing the latches 154 to rotate into engagement with the lifting rod 46. Because of this self-engaging feature, there is no action required to engage the latches 154 to the lifting rod 46 (other than operating the CRDM motor 44 to lower the latch assembly 148 over the upper end of the lifting rod 46) and there are no springs for biasing the latches 154 (compare with springs 106 of the embodiment of FIGS. 3-6). Thus, force of gravity is sufficient to cause the cam bars 160 to cam the latches 154 to engage the lifting rod 46 when the lifting rod is in its lowermost position (corresponding to the control rods being fully inserted). However, force of gravity is not capable of keeping the latches 154 engaged when the CRDM of FIGS. 7-18 is operated to lift the control rod assembly 140 via the lifting rod 46. Thus, the separate holding mechanism 150 is provided, which includes electromagnets 170 and magnetic couplers 172 each connected with the upper end of a respective one of the cam bars 160. In the embodiments described herein with reference to FIGS. 7-18, the illustrative electromagnet holding system 150 is incorporated to hold the cam bars 160, and thus the latches 154, in full engagement for long term hold and translational operations. When power is removed from the electromagnets 170 (as per FIG. 9) the weight of the translating assembly 140, 46 is sufficient to rotate the latches 154 and cams bars 160 out of engagement thereby causing the CRDM to SCRAM. (The term “translating assembly” or similar phraseology refers to the combination of the lifting rod 46 and the control rod assembly 140 including a set of control rods connected with the lifting rod 46 by a yoke or spider.) While the electromagnet holding mechanism embodiment 150 is described for illustrative purposes in FIGS. 7-18, elsewhere in this application other holding mechanism embodiments are disclosed that may be substituted for the holding mechanism 150. After the SCRAM event the lead screw 40 is driven back to the bottom of its stroke via the electric CRDM motor. As the latch assembly nears the bottom of the stroke it automatically re-engages with the lifting rod 46 by cam action against the conical surface 176 of the upper end of the connecting rod 46. The same automatic re-engagement action could also be used to re-engage in the event that a control rod becomes stuck and the SCRAM does not complete. The overall CRDM assembly is shown in FIGS. 7-8. Note that the lead screw 40 may also be referred to as a “ball screw”, which is an equivalent term when the threaded engagement employs a ball nut (that is, a threaded nut/screw coupling with ball bearings disposed in the threads). The layout of the CRDM of FIGS. 7-18 is similar to illustrative CRDMs described with reference to FIG. 2. However, in the CRDM of FIGS. 7-18 the electromagnet holding system 150 at the top of the CRDM has replaced the hydraulic (or solenoid) lift assembly 56 of CRDM embodiments of FIG. 2. FIG. 9 illustrates the CRDM of FIGS. 7-18 in full SCRAM mode with the ball screw 40 and control rod assembly fully inserted. In FIG. 9 only the upper end of the lifting rod 46 (also sometimes called a connecting rod) is visible. The reversed (as compared with embodiments of FIG. 2) cam link orientation causes the four-bar linkage action under downward gravitational weight of the cam bars 160 to rotate the cam bars 160 inward into full engagement thereby causing the latches 154 to be fully engaged with (the upper end of) the lifting rod 46 of the translating assembly. This is the normal self-engaged cam bar position with no load on the latches from the translating assembly and no electromagnet holding force applied by the electromagnet holding system 150. FIG. 10 illustrates normal CRDM operation (either long term hold mode or translation of the control rod assembly under control of the CRDM motor). For this operating condition the electromagnets 170 are powered on to hold the cam bars 160, and thus the latches 154, in full engagement so that they can carry the maximum translating assembly weight force. As seen in FIG. 10, the cam bars 160 extend above the top plate of the cam housing where the magnetic couplers 172 are attached. These couplers 172, made of 410 SS magnetic material in a suitable embodiment, complete the magnetic circuit for optimum electromagnet holding force. FIG. 11 shows the CRDM of FIGS. 7-18 at the start of SCRAM. The latches 154 have been rotated out of engagement by the downward force due to the weight of the translating assembly. The latch heels, which are in contact with the cam bars 160, push the cam bars outward thereby allowing the connecting rod to SCRAM. This action is designated by the force annotation 180 in FIG. 11. FIG. 11 shows the latches 154 in the land-on-land (LOL) position just riding over the outside diameter of the upper end of the connecting rod 46. FIG. 12A illustrates the CRDM of FIGS. 7-18 with the latches 154 and cam bars 160 in the fully disengaged position. This orientation is a non-operational position that could occur if the latches 154 are “kicked” outward by the downward movement of the translating assembly during SCRAM. Although this is a non-operational position with the self-engaged cam bar design of FIGS. 7-18, it illustrates that there is ample clearance between the inside surface of the latches 154 and the connecting rod 46 for SCRAM reliability. This is shown in the inset, FIG. 12B, where the clearance dclearance is indicated. FIGS. 13A and 13B illustrate the force balance for SCRAM operation. In FIGS. 13A and 13B, the weight of the translating assembly is denoted WTA, the force pushing the cam bars outward is denoted Fpush, and the weight of the cam bars is denoted WCam Bar. In the illustrative design, the maximum force needed to push each cam bar assembly outward for SCRAM (that is, the maximum required Fpush) is only a few pounds. This lateral force component of the cam bar assembly weight WCam Bar can be minimized by increasing the orientation angle of the cam link 162, e.g. to a minimum angle of about 70° in some calculated designs. In general, making the cam link 162 longer or at a larger angle (relative to the horizontal) reduces the maximum force needed to push out the cam bars. The minimum force available to push each cam bar 160 outward is produced by latch rotation due to the downward weight force of the translating assembly. This minimum available force is based on the translating assembly weight WTA minus worst-case assumed mechanical friction drag in the control rod channel and worst-case friction at all contact surfaces. SCRAM reliability is assured since the minimum available force Fpush for SCRAM is significantly larger than the force needed for SCRAM. Advantageously, the SCRAM is totally driven by gravity with no other loads required. FIGS. 14A and 14B illustrate the force balance for normal operation. Sufficient lateral force Fhold must be applied at the heel of each latch 154 to hold the translating assembly weight WTA for various modes of operation. In the illustrative embodiment of FIGS. 7-18, this force is provided by the electromagnet holding system 150 at the top of the CRDM. Since the cam bars 160 are self-engaged, the cam bar side load reduces the needed electromagnetic force. The minimum holding force FMag needed at the holding magnet 170 to maintain latch engagement during translation of the control rod assembly is computed based on translating assembly weight WTA plus worst-case assumed mechanical friction drag in the control rod channel. In calculated designs, there is ample holding force margin for all normal operating conditions. FIGS. 15A, 15B, and 15C illustrate isometric views of the electromagnet holding system 150 at the top of the CRDM. FIG. 15A shows the fully engaged operational configuration (power to magnet 170 either on or off), FIG. 15B the SCRAM operational configuration (power to magnet 170 off) and FIG. 15C the fully disengaged operational configuration (power to magnet 170 off). In the fully engaged mode (top view), either with or without electromagnet holding force, the magnetic couplers 172 are seated against the electromagnet housings 170. This seat provides the inward stop for the cam bars 160 and for the latches for full operational engagement. FIGS. 16A, 16B, and 16C show plan views corresponding to the isometric views of FIGS. 15A, 15B, and 15C. It is seen from FIGS. 16A, 16B, and 16C that for all operating modes the electromagnet holding system 150 fits well within the CRDM space envelope. FIG. 17 illustrates an enlarged cutaway view of the electromagnet holding system 150 for the fully engaged condition. The electromagnets 170 are suitably hermetically sealed by welding and potted for high temperature use inside the reactor pressure vessel. Some suitable materials for the components are as follows: for the electromagnet 170, the electromagnet housing may be alloy 625 non-magnetic material, the electromagnet core may be 410 stainless steel magnetic material, and the electromagnet winding may be 24 gauge copper wire; and the magnet couplers 172 may suitably be 410 stainless steel magnetic material. Designs with these materials are estimated to provide a calculated 310 lbs of holding force. These are merely illustrative examples, and other materials and/or design-basis holding force may be employed depending upon the reactor design. FIG. 18 illustrates the latch re-engagement action. The views are labeled: (1) top left view; (2) top middle view; (3) top right view; (4) bottom left view; (5) bottom middle view; and (6) bottom right view. After a SCRAM event, when re-engagement is desired, the ball screw is driven back to the bottom by the CRDM motor. The latches 154 automatically re-engage with the lifting/connecting rod 46 as the latching assembly reaches bottom. For this purpose, a conical cam surface 176 is incorporated into the configuration of the upper end of the connecting rod 46. As the latch assembly is driven back down, the inboard surfaces of the latches 154 slide down over the top of the connecting rod 46, being cammed open by the conical cam surface 176 against the gravitational bias toward closure driven by the four-bar linkage, until the self-engaged latches 154 snap back into the normal engagement pocket. Normal operation can then resume. The same latch auto re-engagement action, as illustrated in FIG. 18, can also be used to re-engage a control rod (or bank of control rods) that becomes stuck during SCRAM. The latch assembly is driven down over the upper end of the connecting rod 46 of the stuck rod (or rod bank) until the latches 154 snap into the normal engagement pocket. If it is desired to fully insert the rods into the reactor core (as is typically the case in the event of a SCRAM), then the latching assembly is driven downward by the ball screw and motor with the latches 154 pushing downward on the stuck rod. In that scenario, the bottom surfaces of the latches 154 contact the flat portion of the engaging pocket in the connecting rod 46. As load is applied, the eccentricity of the contact surfaces causes the latches 154 to remain engaged without any additional holding system. As the motor drives the ball screw down, the latches drive the stuck rod in. With reference to FIGS. 19-22, another holding mechanism embodiment for a CRDM is described. In this regard, FIGS. 3-6 and 7-18 illustrate embodiments in which latch activation and long term hold/translation functions are separated, resulting in reduction of operational power requirements. FIGS. 3-6 illustrate an embodiment of the latch activation, while FIGS. 7-18 illustrate an embodiment of the latch activation (the self-engaging cam/latch system) in combination with an embodiment 150 of the long term hold/translation function. FIGS. 19-22 illustrate another embodiment of the long term hold/translation function, which may be used in combination with the embodiment of FIGS. 3-6 or substituted for the holding mechanism 150 of the embodiment of FIGS. 7-18. FIG. 19 shows an isometric view of the latch hold mechanism of FIGS. 19-22 operating in conjunction with the cam assembly of FIGS. 2-6, i.e. with cam bars 50. FIGS. 20 and 21 show side view and cutaway side views, respectively, of the latch hold mechanism in its disengaged position. FIG. 22 shows a side cutaway view of the latch hold mechanism in its engaged position. The holding mechanism illustrated in FIGS. 19-22 utilizes a large electromagnet 200, coupled with a magnetic hanger 202 connected with the upper ends of the cam bars 50 by pins 204, as shown in FIG. 19. The electromagnet 200 is spaced apart from the hanger 202 by support posts 206 extending from a base plate 208 secured to (or forming) the top of the cam bar assembly 144. With the CRDM engaged by an engagement mechanism (such as that described with reference to FIGS. 3-6, in illustrative FIGS. 19-22), the electromagnet 200 is activated, causing a magnetic attraction between the hanger 202 and the electromagnet 200 that holds the hanger 202 in contact with the electromagnet 200 as shown in FIG. 22 (or, in alternative embodiments, into contact with a landing surface interposed between the electromagnet and the hanger). The raised hanger bar 202 holds the cam bars 50 in their raised (i.e. engaged) position via the pins 204. When power is cut to the electromagnet 200 the attractive force between the magnet 200 and the hanger 202 is severed, causing the hanger 200 and cam bars 50 to fall to the disengaged position shown in FIGS. 20 and 21. Pin slots 210 in the hanger 202 accommodate the lateral motion of the cam bars 50 due to the four-bar linkage. The sectional views of FIGS. 21 and 22 illustrate the copper windings 212 of the electromagnet 200. By separating latch activation and long term hold/translation functions of the latch of the CRDM, it is recognized herein that the operational power requirements can be reduced, since the holding mechanism is not required to actually lift the cam bars, but merely maintains the cam bars in the lifted position after the (different) engagement mechanism operates. The separation of features simplifies the holding feature making it easier to manufacture and less expensive. With reference to FIGS. 23-32, another holding mechanism embodiment for a CRDM is described, which may be used in combination with the embodiment of FIGS. 3-6 or substituted for the holding mechanism 150 of the embodiment of FIGS. 7-18. FIGS. 23-25 show two isometric views and a plan view, respectively, of the holding mechanism in the fully engaged position. FIGS. 26-28 show two isometric views and a plan view, respectively, of the holding mechanism in the SCRAM position. FIGS. 29-31 show two isometric views and a plan view, respectively, of the holding mechanism in the fully disengaged position. The isometric view of FIGS. 23, 26, and 29 show the top region of the CRDM including the holding mechanism at a viewing angle of approximately 45°. The isometric view of FIGS. 24, 27, and 30 show the top region of the CRDM including the holding mechanism at a more oblique viewing angle than 45°. FIG. 32 illustrates a plan view of the holding mechanism with annotations of the electromagnet holding force FElect for applying a force FCam Bar sufficient to hold the cam bars 160. The holding mechanism of FIGS. 19-28 utilizes horizontal holding arms 230 that have slots 232 into which pins 234 at the tops of the cam bars 160 (e.g. cam bar pins 234) fit. When the cam bars 160 are moved to the engaged position by an engagement mechanism (e.g. such as the one described with reference to FIGS. 3-6, or the self-engaging cam/latch system of the embodiment of FIGS. 7-18), the cam bar pin 234 in each pin slot 232 pushes the holding arm 230 to rotate to a point where it is in close proximity with an electromagnet 240. The rotation is about an arm pivot point 242, and the various components of the holding mechanism are mounted on a baseplate 244 that is secured to (or forms) the top of the cam bar assembly 144. When power is applied to the electromagnets 240 they attract and hold the arms 230 which are made of magnetic material. The restrained arms, in turn, hold the cam bars 160 in the engaged position via the cam bar pins 234 in the pin slots 232 and thereby maintain latch engagement. FIGS. 23-25 shows two alternative isometric views and a top view, respectively, of the holding mechanism in this fully engaged position. With reference to FIGS. 26-28 (SCRAM mode) and FIGS. 29-31 (fully disengaged mode), when power is cut to the electromagnets 240, the attractive force between the electromagnets 240 and the arms 230 is severed, allowing the arms 230 to rotate out of engagement. The weight of the translating assembly is sufficient to disengage the latches and move the cam bars 160 away (i.e. outward) for SCRAM. During this action, the holding arms 230 freely move out of the way. With particular reference to FIG. 32, the holding mechanism of FIGS. 23-32 provides a mechanical advantage due to the configuration of the holding arms 230. This is accomplished by the relative positions of the arm pivot point 242, the cam bar contact point (i.e. the engagement between the cam bar pin 234 and the pin slot 232) and the electromagnet holding force contact point (corresponding to the location of the electromagnet 240), suitably quantified by the distance dmag between the magnet 240 and the pivot point 242 and the distance dpin between the cam bar contact point (approximately the cam bar pin 234) and the pivot point 242. Because of this mechanical advantage, the holding force FElect provided by the electromagnets 240 can be reduced to provide a given force FCam Bar for holding the cam bars 160. This facilitates the use of smaller, less complex electromagnets as the electromagnets 240, as well as lower power demands for operation. The configuration of the electromagnetic holding mechanism of FIGS. 23-32 will vary somewhat depending on the configuration of the cam bars 160 and the four bar linkage. The pin slot 232 is arranged to accommodate the horizontal cam bar travel while providing the appropriate engagement to rotate the horizontal holding arms 230. In a variant embodiment, magnets are embedded into the holding arms to provide added holding strength. In some embodiments, this added force is expected to be enough to enable the holding mechanism of FIGS. 23-32 to perform both the engagement and holding operations, and could, for example, be used in place of the hydraulic lifting assembly 56 of the embodiment of FIG. 2. By way of review, FIGS. 23-25 show the cam bars 160 and holding arms 230 in the fully engaged position, either held by the electromagnets 240 or engaged by an outside means (e.g. such as the one described with reference to FIGS. 3-6, or the self-engaging cam/latch system of the embodiment of FIGS. 7-18) prior to powering the electromagnets 240. FIGS. 26-28 show the SCRAM mode, in which the arms 230 and thus the cam bars 160 have moved sufficiently for the latches to completely release the connecting (i.e. lifting) rod and control rod assembly. FIGS. 29-31 show the fully disengaged position. Due to the 4-bar linkage action, the cam bars 160 rise and fall as they are moved laterally from engaged to disengaged positions. This action is best seen in the isometric view of FIGS. 24, 27, and 30. Since the holding arms 230 pivot about fixed support posts (the pivot arm points 242), the pin slots 232 are incorporated into the holding arms 230 to accommodate the rise and fall of the cam bars 160. These slots 232 should be sized and positioned to accommodate both the rise and fall of the cam bars 160 and the lateral motion of the cam bars 160 due the four-bar linkage action responding to the rise/fall of the cam bars 160. When used in conjunction with the self-engaging cam/latch system described herein with reference to FIGS. 7-18, the direct mechanical advantage for the illustrated locations of the holding arm pivot points 242 has been estimated to be approximately 4.5:1 (corresponding to the ratio dmag/dpin in FIG. 32). However, there is not a direct relationship between this mechanical advantage and the holding force needed since the holding arms 230 do not pull in line with the plane of collapse of the cam bars 160. A force correction is needed that is proportional to the cosine of the holding arm angle. The net effect for the configuration shown herein is an effective mechanical advantage of 2.4:1. This force balance, along with the effective mechanical advantage, is diagrammatically illustrated in FIG. 32. The holding mechanism of FIGS. 23-32 has the benefit of a mechanical advantage provided by the configuration of the holding arms. With reference to FIGS. 33-38, another holding mechanism embodiment for a CRDM is described, which may be used in combination with the embodiment of FIGS. 3-6 or substituted for the holding mechanism 150 of the embodiment of FIGS. 7-18. FIGS. 33-35 show two isometric views at different viewing angles and a top view, respectively, of the top of the CRDM (and more particularly the top of the cam assembly and the holding mechanism) with the cam system in the unlatched position. FIGS. 36-38 show two isometric views at different viewing angles and a top view, respectively, of the top of the CRDM including the holding mechanism with the cam system in the latched position. Illustrative FIGS. 33-38 show the holding mechanism in combination with the embodiment of FIGS. 3-6, and hence the cam bars are labeled cam bars 50 in FIGS. 33-38. Once the cam system is in the engaged (i.e. “latched”) position the holding mechanism of FIGS. 33-38 holds the cam bars 50 such that they engage the latches and maintain latching of the connecting (i.e. lifting) rod. The holding mechanism of FIGS. 33-38 includes two high temperature magnets 260 and magnetic links 262 attached to the upper end of each of the two cam bars 50 at the top end of the CRDM. The two canned high temperature electromagnets are suitably wired in a parallel fashion. When the cam system transitions from the unlatched position (FIGS. 33-35) to the engaged (latched) position (FIGS. 36-38), the upper ends of the cam bars 50 engaging the magnetic links 262 rotate the magnetic links 262 about pivots 264 so that the ends 270 of the magnetic links 262 distal from the cam bar/magnetic link joint 272 are moved by the inward movement of the cam bars 50 to be in close proximity to the electromagnets 260. When the electromagnets 260 are energized these distal ends 270 of the magnetic links 262 are held against the magnets 270, and the cam bar 50 at the opposite end of the link 262 is prevented from moving. This holds the latch in the latched position. The holding power of the electromagnets 260 is adequate to hold the weight of the cam bars 50 as well as the force exerted on the cam bars 50 by the latches. The latched state is shown in alternative isometric views (FIGS. 36 and 37) and a plan view (FIG. 38). Slots 276 in a base plate 278 secured to (or forming) the top of the cam bar assembly and supporting the hold mechanism components accommodate the lateral motion of the cam bars 50 during unlatched/latched transitions. When used in conjunction with the embodiment of FIGS. 3-6 (as illustrated in FIGS. 33-38), operation is as follows. When the electromagnets 260 are de-energized the magnetic links 262 are decoupled from the electromagnets 260 and the cam bars 50 are free to fall under their own weight and swing into the unlatched position. In the unlatched position the cam bars 50 are disengaged from the latches and the latches can then rotate out of engagement with the connecting rod. When the cam bars 50 are disengaged from the latches, the latches can be rotated out of engagement with the connecting rod by the latch springs 106 (for the embodiment of FIGS. 3-6). Therefore, in the unlatched position the cam bars 50 are not engaged with the latches, the latches are not engaged with the lifting rod and the translating assembly (including the lifting rod and the attached control rod or rods) can then fall under its own weight (SCRAM). The holding mechanism of FIGS. 33-38 is fail-safe in the sense that if power is lost to the electromagnets 260 the connecting rod will SCRAM due to gravity. Operation of the holding mechanism of FIGS. 33-38 in conjunction with the cam arrangement of FIGS. 7-18 (self-latching) is similar, except that when the electromagnets 260 are de-energized the cam bars 160 do not open under gravity, but rather are cammed open by the cam surface at the upper end of the lifting rod 46 of the falling translating assembly. (See description of FIGS. 7-18 for details). Again, the de-energizing of the electromagnets 260 allows the magnetic links 262, and hence the cam bars 160, to freely move to perform the SCRAM. With reference to FIGS. 39-48, another holding mechanism embodiment for a CRDM is described, which may be used in combination with the embodiment of FIGS. 3-6 or substituted for the holding mechanism 150 of the embodiment of FIGS. 7-18. The embodiment of FIGS. 39-48 is illustrated in conjunction with a four-bar linkage with cam bars and cam bar links oriented as in the embodiments of FIGS. 2-6; accordingly, in FIGS. 39-48 the cam bars and cam bar links are labeled as cam bars 50 and cam bar links 52, respectively. The embodiment of FIGS. 39-48 illustrates a variant latching mechanism located beneath the cam assembly, in which a hydraulic cylinder 300 (or, alternatively, an electric solenoid) raises a lift plunger or piston 302 upward to engage cam bar lift rollers 304 at the bottom ends of the cam bars 50 so as to raise the cam bars 50—by action of the four-bar linkage provided by cam bar links 52 this raising of the cam bars 50 simultaneously moves the cam bars 50 inward to engage the latch. (By comparison, in the embodiment described with reference to FIG. 2, the hydraulic lift assembly 56 located above the cam assembly lifts the upper ends of the cam bars 50 to engage the latches). The embodiment of FIGS. 39-48 also illustrates a holding mechanism located above the cam assembly, where a base plate 308 secured to (or forming) the top of the cam bar assembly supports the hold mechanism components. FIG. 39 shows a diagrammatic side view of the cam assembly, in which the lift system (comprising electric solenoid or hydraulic cylinder 300 and piston 302 in conjunction with cam bar lift rollers 304) is deactivated and the hold mechanism (diagrammatically shown in a tilted view) is also deactivated. FIG. 40 shows a top view of the deactivated hold mechanism corresponding to FIG. 39. FIG. 41 shows a diagrammatic side view of the cam assembly in which the lift system is activated and the hold mechanism is still deactivated. FIG. 42 shows a top view of the deactivated hold mechanism corresponding to FIG. 41. FIG. 43 shows a diagrammatic side view of the cam assembly in which both the lift system and the hold mechanism are activated, and FIG. 44 shows a corresponding top view of the activated hold mechanism. FIG. 45 shows a diagrammatic side view of the cam assembly in which the lift system is deactivated and the hold mechanism is still activated, and FIG. 46 shows a corresponding top view of the activated hold mechanism. FIGS. 47 and 48 illustrate geometric aspects of the hold mechanism. The hold mechanism of the embodiment of FIGS. 39-48 keeps the four-bar linkage cam system 50, 52 in the engaged position during rod translation and hold functions, and provides the SCRAM functionality when subsequently deactivated. It also structurally internalizes the majority of the cam bar retention force required to hold the latches in the engaged position, and utilizes mechanical advantage to minimize the remaining hold force, resulting in a structurally efficient unit. FIGS. 39 and 40 illustrate the holding mechanism (and associated lift system in FIG. 39) both in the deactivated state. The holding mechanism including a rotary hold bar 310, a hold-solenoid 312 (where the housing of the solenoid 312 is visible), a hold-solenoid plunger 314, and hold-bar rollers 316, is located at the top or base plate 308 of the cam bar assembly. FIGS. 39 and 40 illustrate the hold mechanism deactivated at startup. Prior to startup, the lift system (electric solenoid or hydraulic), which includes the electric solenoid or hydraulic cylinder 300 and the lift plunger or piston 302, is also deactivated. Therefore, the latches are not engaged by the four-bar cam system 50, 52, rendering the connecting rod and attached control rods in the fully inserted position. As best seen in the top view of FIG. 40, in the unlatched state of the four-bar linkage 50, 52 the cam bars 50 are in their outboard positions (i.e., moved outward and away from the latches). Also note that the base plate 308 includes slots to accommodate movement of the upper ends of the cam bars 50 between their inboard (i.e. moved in) and outboard (i.e. moved out) horizontal positions. With reference to FIGS. 41 and 42, upon activation of the lift system (shown in FIG. 41), the lift plunger or piston 302 raises the cam bars 50 into the latch engagement position by contact with the cam bar lift rollers 304. At initial engagement of the lift mechanism, the hold mechanism is still deactivated as depicted in FIGS. 41 and 42. Because of activation of the lift system, the latches are now engaged with the connecting rod which is resting with the attached control rods at the fully inserted position. As best seen in FIG. 42, the lifting of the cam bars 50 also moves the cam bars 50 into their inboard positions by action of the four-bar linkage, and this inward movement is what engages the latches, as described in more detail with reference to the embodiments of FIGS. 2-6. With reference to FIGS. 43 and 44, subsequently following activation of the lift system, the hold solenoid 312 of the hold mechanism is activated, resulting in extension of the solenoid plunger 314, which rotates the hold bar 310 about a pivoting engagement 318 of the hold bar 310 with the base plate 308. At full extension of the solenoid plunger 314, the hold-bar rollers 316 are rotated into position behind the upper extremity (i.e. upper ends) of the cam bars 50 (note again that the upper ends of the cam bars 50 protrude through the slots in the base plate 308), so as to function in the hold capacity. It is noted that the hold solenoid 312 is free to pivot about a post mount 320 that secures the solenoid 312 on the base plate 308. It is also noted that the solenoid plunger 314 is pin-connected to the hold bar 310, which provides rotational freedom for operation. The relative orientations of all the pertinent components at this phase of operation are illustrated in FIGS. 43 and 44. With reference to FIGS. 45 and 46, with the hold mechanism activated the lift system can be deactivated, with the hold system thereafter keeping the latches engaged. Upon deactivation of the lift system, the lift plunger or piston 302 is released, and therefore, no longer (bottom) supports the cam bars 50. At this point, the cam bars 50 are retained in the engaged position solely by the hold mechanism. The four-bar cam system 50, 52 is now being retained for long-term retention of the connecting rod by the hold mechanism. With reference to FIG. 47, there exists an eccentricity Econtact between the center of rotation of the hold bar 310 and the line of action of the contact force between (the upper end of) the cam bar 50 and the hold-bar roller 316. This eccentricity Econtact results in a force-moment imbalance on the hold bar 310 when the force applied by the hold solenoid 312 is removed. This moment imbalance at power loss to the hold solenoid 312 is the driving mechanism for rapidly rotating the hold bar 310 and the attached rollers 316 out of contact with the cam bars 50—resulting in SCRAM (rapid release of connecting rod). In order to create a smooth rolling action of the hold-bar rollers 316 on the contact surface of the cam bars 50, the contact surface is contoured to the arc of the rolling-contact point. With continuing reference to FIG. 47 and with further reference to FIG. 48, the desired lower power consumption of the hold mechanism is a product of the significant mechanical advantage of the unit. The moment arm Eplunger of the hold solenoid plunger 314, relative to the pivot center of the hold bar 310, is significantly larger than the moment arm of the contact force of the cam bar 50 at the hold-bar roller 316, as illustrated in FIGS. 47 and 48. Therefore, the force required by the hold solenoid 312 is significantly less than the latch-to-cam bar contact force required to support the connecting rod load. Of further advantage, internalization of the majority of the cam bar retention forces as equal and opposite loads reacted through the hold bar 310 eliminates force reaction through the remainder of the hold mechanism, resulting in a structurally efficient unit. As previously stated, the hold mechanism described with reference to FIGS. 39-48 separates latch activation and long term hold/translation functions, resulting in reduction of operational power requirements. The hold mechanism keeps the four-bar linkage cam system in the engaged position during rod translation and hold functions, and provides the SCRAM functionality when subsequently deactivated. It also structurally internalizes the majority of the cam bar retention force required to hold the latches in the engaged position, and utilizes mechanical advantage to minimize the remaining hold force, resulting in a structurally efficient unit. With reference to FIGS. 49-52, another holding mechanism embodiment for a CRDM is described, which may be used in combination with the embodiment of FIGS. 3-6 or substituted for the holding mechanism 150 of the embodiment of FIGS. 7-18. FIG. 49 shows an isometric view of the top region of the CRDM including the holding mechanism with the vertical linkage engaged to raise the cam bars. FIG. 50 shows a corresponding isometric view with the vertical linkage disengaged to allow the cam bars to fall. FIG. 51 corresponds to the engaged view of FIG. 49 but includes a partial cutaway, and similarly FIG. 52 corresponds to the disengaged view of FIG. 50 but includes the partial cutaway. The latch holding mechanism of FIGS. 49-52 utilizes a vertical linkage system including vertical links 340 connected to a hanger 342 disposed between (the upper ends of) the cam bars 160 of FIGS. 7-18 (as shown; or, alternatively, the cam bars 50 of FIGS. 2-6) and (in the engaged position shown in FIGS. 49 and 51) held in the engaged position by electromagnets 344. When the cam bars 160 are moved to the engaged position by the separate latch engagement mechanism (e.g. as in the embodiment of FIGS. 3-6, or the embodiment of FIGS. 7-18), it causes the hanger 342 to move up which, in turn, raises the vertical links 340 to a position where horizontal drive members 348 are in close proximity with the electromagnets 344. When power is applied to the electromagnets 344 they attract and hold magnets that are embedded into the horizontal drive members 348. (Alternatively, the horizontal members 348 may be made of steel or another ferromagnetic material but not include magnets). The restrained vertical links 340, in turn, hold the hanger 342, and thus the cam bars 160, in the engaged position and thereby maintain latch engagement. When power is cut to the electromagnets 344, the attractive force between the electromagnets 344 and the horizontal drive members 348 is severed, allowing the vertical links 340 to drop out of engagement, as seen in FIGS. 50 and 52. The weight of the translating assembly is sufficient to disengage the latches and move the cam bars 160 away for SCRAM. During this action, the linkage system freely moves downward out of the way. To recap, FIGS. 49 and 50 show isometric views of the top region of the CRDM at a viewing angle of approximately 45° for the engaged and disengaged states, respectively. FIG. 49 shows the vertical linkage system in the fully engaged (full up) position, either held by the electromagnets 344 or engaged by an outside means prior to powering the electromagnets. For the SCRAM mode, shown in FIG. 50, the linkage system has moved full down for the latches to completely release the connecting rod and control rod assembly. FIGS. 51 and 52 show isometric cutaway views of the top region of the CRDM for the engaged and disengaged states, respectively. FIG. 51 shows the vertical linkage system in the fully engaged (full up) position, either held by the electromagnets 344 or engaged by an outside means prior to powering the electromagnets 344. FIG. 52 shows the linkage system in the full down (SCRAM) position. In the illustrative embodiment, the minimum angle of the vertical links 340, in the fully engaged position (FIGS. 49 and 51), is set to about 10° which is expected to assure an adequate SCRAM reliability margin. In the disengaged position (FIGS. 50 and 52) the vertical links 340 collapse to a maximum angle of about 40° in the illustrative embodiment. The latch holding mechanism described with reference to FIGS. 49-52 provides a mechanical advantage due to the configuration of the linkage system. This is due to the relative positions and size of the vertical link 340 lengths compared to the horizontal drive member 348. In addition, the permanent magnet that is embedded in the horizontal arm 348 provides added holding force. The true mechanical advantage for this disclosed vertical linkage system is calculated to be 2.9:1 at the minimum link angle. However, the effective mechanical advantage is higher, estimated to be closer to 4.0:1, when an assumed permanent magnet force per link assembly is added. Because of this mechanical advantage, the required holding force needed by the electromagnets is reduced. This results in smaller, less complex electromagnets, as well as lower power demands for operation. Referring back to FIGS. 19-22, that illustrated latch holding mechanism embodiment operates vertically (i.e. axially) insofar as the electromagnet 200 draws the hanger 202 upward to hold the latch, and releases the hanger 202 to fall so as to allow the latch to open. Raising the hanger 202 to hold the latch closed is appropriate for the four-bar linkage cam system 50, 52 of FIGS. 2-6 since the cam bar links 52 are oriented to move the cam bars 50 inward (to latch) in response to the cam bars 50 being raised upward, and to move the cam bars 50 outward (to unlatch) in response to the cam bars 50 falling downward under gravity. On the other hand, in the four-bar linkage cam system 160, 162 of FIGS. 7-18 the cam bar links 162 are oriented to move the cam bars 160 inward (to latch) in response to the cam bars 160 falling downward under gravity (thus providing a “self-latching” arrangement). This is seen in FIG. 10, for example. When the hold is released, the orientation of the cam bar links 162 drives the cam bars upward in response to the cam bars 160 being pushed outward by the latches 154 under the weight of the translating assembly via the upper end of the lifting rod 46, as per the “start of SCRAM” configuration shown in FIG. 11. Thus, the hold mechanism for the four-bar linkage cam system 160, 162 of FIGS. 7-18 should apply a downward force to the cam bars 160 to retain them in the “hold” position, and this downward force should be sufficient to hold against the weight of the translating assembly comprising the control rods 140 and lifting rod 46. With reference to FIGS. 53-56, a variant of the hold mechanism of FIGS. 19-22 is illustrated, which is configured to apply the requisite downward holding force to the cam bars 160 so as to operate in conjunction with the four-bar linkage cam system 160, 162 of FIGS. 7-18. FIGS. 53 and 54 show perspective cutaway and side sectional views, respectively, of the hold mechanism in its engaged position, with the lifting rod 46 also raised such that the upper end of the lifting rod 46 and the engaged latches 154 are also visible in FIG. 53. FIG. 55 shows a perspective cutaway view during SCRAM with the hold mechanism disengaged and at the point where the latches 154 have been driven open by the weight of the translating assembly so as to allow the translating assembly to fall under gravity. FIG. 56 shows a perspective cutaway view of the holding mechanism and the latches 154 after the SCRAM, with the lifting rod having fallen out of view and with the cam bars 160 having fallen back down under force of gravity to reclose the latches 154. As in previous embodiments, the lead screw 40 does not fall down during the SCRAM, and the latches 154 remain mounted to the upper end of the lead screw 40. The holding mechanism includes an electromagnet comprising electromagnet windings 400, a fixed annular pole piece 401 secured with the windings 400, and a movable annular pole piece 402 arranged above the electromagnet windings 400 and fixed pole piece 401 such that energizing the electromagnet windings 400 draws the movable pole piece 402 downward toward the fixed pole piece 401. Connecting links 404 connect the upper ends of the cam bars 160 to the movable pole piece 402. The assembly including the electromagnet windings 400 and the fixed pole piece 401 is secured in a fixed position to a base plate 406 that in turn is secured to (or forms) the top of the cam bar assembly. In some embodiments, an axial adjusting ring 408 is disposed between the base plate 406 and the assembly 400, 401, and the thickness of the axial adjusting ring 408 is chosen to precisely position its height. FIGS. 53 and 54 show the holding mechanism in its energized position, with the movable pole piece 402 drawn down to the fixed pole piece 401. As labeled in the side sectional view of FIG. 54, each connecting link 404 is angled at an angle Alink such that the downward force exerted by the electromagnet on the movable pole piece 402 is transmitted as both downward and inward force components onto the upper end of the connected cam bar 160. This keeps the cam bars 160 in their lower and inward (latched) positions so as to hold the latches 154 closed against the opposing outwardly oriented force exerted on the cam bar 160 by the weight of the translating assembly transmitted through the upper end of the lifting rod 46 and specifically at a heel 412 of the latch 154 labeled in FIG. 54 (this opposing outwardly oriented force is the denoted force annotation 180 in the “start of SCRAM” configuration shown in FIG. 11). Note that due to the angle Acam (labeled in FIG. 54) of the cam bar links 162, the outward force acting on the cam bar 160 also produces an upward force by action of the four-bar linkage 160, 162. The angle Alink of the connecting link 404 provides the downward and inward opposing force components when the electromagnet 400 is energized to keep latches 154 closed. With reference to FIG. 55, when the electromagnet windings 400 are deenergized, this removes the attractive force between the pole pieces 401, 402 which is the downward latch-holding force acting on the movable pole piece 402. With this downward holding force removed, the outward and upward oriented force components acting on the cam bar 160 via the heel 412 of the latch 154 and by action of the four-bar linkage 160, 162 is no longer opposed by the holding mechanism, and these force components drive the cam bar 160 outward and upward so as to allow the latches 152 to be cammed open by the upper end of the lifting rod 46 under the weight of the translating assembly. Note that the upward movement of the cam bars 160 lifts the movable pole piece 402 upward and away from the fixed pole piece 401, as seen in FIG. 55. With reference to FIG. 56, once the translating assembly (no longer held up by the latches 154) falls, this removes the outward force acting on the latches 154. With this force removed, the weight of the cam bars 160 causes the cam bars to fall downward. The four bar linkage action leads to the falling cam bars 160 also moving the cam bars 160 inward so as to re-close the latches 154 (albeit not onto the upper end of the lifting rod, which has fallen away during the SCRAM), as seen in FIG. 56. This action is attributable to the “self-latching” nature of the four-bar linkage cam system 160, 162 of FIGS. 7-18. It is noteworthy that the weight of the movable pole piece 402 adds to the downward force to reinforce the self-latching action (that is, even with the electromagnet windings 400 de-energized so that there is no magnetic downward force, there is still gravitational downward force acting on the movable pole piece 402). In the system of FIGS. 53-56, the holding force must be sufficient to hold against the opposing force imparted by the combined weight of the control rods 140 and lifting rod 46, along with the added weight of the movable pole piece 402 and the connecting links 404. This translates to electrical current flowing through the electromagnet windings 400, that is, as the weight driving the opposing force increases, a greater current must flow through the windings 400 to provide sufficient holding force. Higher winding current in turn requires a larger electromagnet and consumes more electrical power. To reduce these requirements, the movable pole piece 402 is preferably made thin and light in weight; however, if the movable pole piece 402 is too small this also will reduce the holding force. Another consequence of a larger electromagnet driven at higher electrical current is that the residual magnetic force is increased. It is recognized herein that this has the effect of increasing the SCRAM time, since the residual magnetic force produces a force that opposes the opening of the latches 154. With continuing reference to FIGS. 53-56 and with further reference to FIGS. 57 and 58, this effect of the residual magnetic force can be mitigated by imposing a gap between the pole pieces 401, 402 in the latched or holding configuration of FIGS. 53-54. With further reference to FIG. 57, this gap is suitably introduced by interposing a spacer made of non-magnetic material between the pole pieces 401, 402. In the illustrative embodiment, the spacer is configured as inner and outer annular spacer rings 420, 422 secured to the movable pole piece 402 at the inside and outside perimeters, respectively, of the pole piece 401. Alternatively, the spacer rings 420, 422 can be attached to the fixed pole piece 401. The spacer rings 420, 422 introduce an “air gap” 424 between the pole pieces 401, 402 when the holding mechanism is engaged, as shown in FIG. 57. (While the term “air gap” is sometimes used herein as shorthand, during reactor operation the gap 424 is actually filled with coolant water as the reactor pressure vessel is filled with said coolant water, see FIG. 1 and related text herein). The reduction in residual magnetic force provided by the gap 424 depends on the gap distance d and on the permeability (μ) of the material filling the gap 424. However, a larger gap distance d also reduces the electromagnetic holding force provided by the energized holding mechanism, and so the gap distance d cannot be made too large. In the illustrative example, the gap 424 ideally is filled with coolant water at reactor operating pressure and temperature, which advantageously has low magnetic permeability. However, if magnetic debris such as steel particles collects in the gap 424, this increases the effective magnetic permeability of the gap 424 and counteracts the reduction in residual magnetic force provided by the gap 424. The use of annular spacer rings 420, 422 advantageously provides a barrier to ingress of debris into the gap 424. Alternatively, annular spacer rings 420, 422 can be replaced by a single-piece annular element (not shown) that is coextensive with the annular area of movable pole piece 402 (or, equivalently, coextensive with the annular area of fixed pole piece 401). In such an embodiment, the single-piece non-magnetic annular element is preferably a non-porous material or is otherwise configured to avoid entrapping steel particles. Depending upon the materials at the interfaces between the movable pole piece 402 and the spacer element, a possible difficulty is the potential to develop adhesive forces in the engaged state due to the large area of the single-piece annular spacer element and the compression applied by the electromagnetic force. Such an adhesive force can increase SCRAM time in the same way that the residual magnetic force increases SCRAM time, by delaying the disengagement and lifting of the movable pole piece 402 upon de-energizing the magnetic windings 400. FIG. 58 shows a view analogous to that of FIG. 57, but with the magnetic windings 400 de-energized and the latches opened (corresponding to the “start of SCRAM” view of FIG. 55). In this state the raising of the cam bars 160 operating on the connecting links 404 has raised the movable pole piece 402 upward and away from the fixed pole piece 401, so that the gap between the pole pieces 401, 402 is now much larger than the gap 424 defined by the spacers 420, 422 in the engaged (or holding) state shown in FIG. 57. The increased volume between the pole pieces 401, 402 must be filled by coolant water; to this end, flow holes or passages 430 are optionally formed in the movable pole piece 402 to admit water and reduce any “suction-type” drag on the raising of the pole piece 402. While the air gap 424 is shown only for the embodiment of FIGS. 53-58, more generally it is expected that such an air gap between magnetic poles may be useful in any holding mechanism that employs a magnetic holding circuit. Even more generally, such an air gap is expected to be useful in any SCRAM mechanism that employs a magnetic circuit, whether the “latch” and “hold” operations are separate or integrated into a single unit. By way of illustrative example, such an air gap is expected to be useful in conjunction with a CRDM employing a separable ball-nut that is magnetically held together and SCRAMs by de-energizing the magnets holding the separable ball-nut together to allow it to separate and release the engaged lead (i.e. ball) screw to fall toward the reactor core. The air gap reduces the residual magnetic force and accordingly increases SCRAM speed (i.e. reduces SCRAM time). To verify this, experiments were performed using the lateral electromagnetic latch holding mechanism described herein with reference to FIGS. 7-18. In one set of experiments, the magnetic couplers 172 were made of 1002 steel, while in another set of experiments the magnetic couplers 172 were made of 410 steel. In both sets of experiments, the electromagnets 170 were made of 1002 steel. FIGS. 59 and 60 show the measured current (in amperes) versus holding force (in pounds) curves for air gaps of 0.005 inches, 0.010 inches, and 0.015 inches. The vertical line in these plots represents a design holding force of 375 lbs. As expected, the required current in the electromagnet windings to achieve the design 375 lbs increases with increasing air gap distance. FIG. 61 diagrammatically plots current versus time during a SCRAM event, along with three time metrics: T1, T2, and T3. The tests were performed for a translating assembly weight of 75 lbs (in general, SCRAM time decreases, i.e. SCRAM speed increases, with increasing weight of the translating assembly; 75 lbs is expected to be a low-end weight for the translating assembly in the case of a compact nuclear reactor having relatively short control rods). As diagrammatically shown in FIG. 61, the time interval T1 is the time from which the current in the electromagnet 170 begins to decay to the time when the cam bars 160 begin to show separation. The time T2 is the time from which the current in the electromagnet 170 begins to decay to the time when a SCRAM is able to occur (i.e. to the time shown in FIG. 11 at which latches 154 have been rotated out of engagement by the downward force due to the weight of the 75 pound translating assembly allowing the connecting rod 46 to SCRAM). The time T3 is the time from which a SCRAM is initiated by sending the control signal to de-energize the holding mechanism electromagnet to the time when a SCRAM is able to occur. The most relevant of these times for testing the holding mechanism itself is T2, and this is plotted in FIGS. 62 and 63 for the experiments with 1002 steel couplers and with 410 steel couplers, respectively. As seen in FIGS. 62 and 63, SCRAM time decreases rapidly (i.e. SCRAM speed increases rapidly) with increasing air gap. The effect is especially pronounced for the 410 steel coupler experiments between gaps of 0.005-inch and 0.010-inch, for which SCRAM time (T2) decreases from 925-1260 milliseconds for the 0.005-inch gap to 315-355 milliseconds for the 0.010-inch gap. This factor-of-three reduction in SCRAM time is achieved for only about 50% increase in electromagnet current. Without being limited to any particular theory of operation, theses observed results are believed to be due to the reduction in residual magnetism with increasing air gap being proportional to an exponential of the air gap distance; whereas, the power increase with increasing air gap is not exponential in nature. While the experiments reported with reference to FIGS. 59-63 are for the holding mechanism of FIGS. 7-18, similar benefit of an air gap is expected to be achieved for other types of CRDMs having holding mechanisms comprising an electromagnetic circuit with magnetic poles that are drawn together when the electromagnetic circuit is energized to hold the lifting rod and that release the hold on the lifting rod when the electromagnetic circuit is de-energized to initiate SCRAM. Such CRDMs include illustrative examples herein in which the holding mechanism is separate from the latch engagement mechanism. Such CRDM's also include designs with integrated latch activation and hold functions, such as CRDM designs that employ a separable ball-nut that is energized to simultaneously engage and hold the ball-screw and that is de-energized to release the hold. Providing a non-magnetic spacer between the magnetic poles to maintain a gap between the drawn-together magnetic poles advantageously reduces residual magnetic force when the magnetic circuit is de-energized to initiate SCRAM, thus reducing SCRAM time (i.e. increasing SCRAM speed). Design of the air gap distance between the drawn-together magnetic poles in such a magnetic circuit is readily performed empirically as described with reference to FIGS. 59-63, by testing several air gap distances to determine an optimal air gap that optimally balances holding power (e.g., as measured by electromagnet current) and SCRAM speed or time (e.g. as measured by the time T2 described herein). Alternatively, the design can employ electromagnetic computer modeling, assuming that accurate material parameters (e.g. permeability, conductivity, et cetera) are available for the material(s) under consideration. While the optimal gap distance between the magnetic poles in the energized (hold) configuration is expected to be CRDM design-specific, some general principles can be applied. The holding current required to provide a given holding force is expected to be roughly linear with increasing gap distance d (cf. FIGS. 59 and 60). By contrast, the residual magnetic force is expected to scale with gap distance d in a roughly negative-exponential fashion (e.g., roughly of the form e−αd where d is the gap distance, α is a fitted parameter, and e is the base of the natural logarithm). It follows that there is an optimal gap distance d given design constraints on the holding current and SCRAM speed (controlled in part by the residual magnetic force). Based on the experiments reported herein with reference to FIGS. 59-63, it is expected that an air gap of between 0.01 cm to 0.16 cm (i.e. 0.004-inch and 0.063-inch) should provide a useful reduction in SCRAM time while keeping the holding current reasonable for typical CRDM designs. For more significant SCRAM time reduction, an air gap of between 0.025 cm to 0.16 cm (i.e. 0.010-inch and 0.063-inch) is preferable. In general, the spacer between the drawn-together magnetic poles should be effective to define the gap between the drawn-together magnetic poles having a gap distance of at least 0.010 cm (0.004 inch), and is more preferably at least 0.025 cm (0.010 inch) to provide significant SCRAM time reduction. Illustrative embodiments including the preferred embodiments have been described. While specific embodiments have been shown and described in detail to illustrate the application and principles of the invention and methods, it will be understood that it is not intended that the present invention be limited thereto and that the invention may be embodied otherwise without departing from such principles. In some embodiments of the invention, certain features of the invention may sometimes be used to advantage without a corresponding use of the other features. Accordingly, all such changes and embodiments properly fall within the scope of the following claims. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the present disclosure be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
	summary
061480541	summary	TECHNICAL FIELD The present invention relates to fluid separation devices for use in vent volumes within a nuclear fuel bundle and particularly to devices insertable into and removable from the fuel bundle for flowing liquid laterally outwardly into the interstices between and onto adjacent surrounding fuel rods. BACKGROUND OF THE INVENTION A typical boiling water nuclear reactor has a reactor core comprised of a plurality of fuel bundles in side-by-side relation to one another. Coolant/moderator flows upwardly within the fuel bundles and about the fuel rods within the fuel bundles and is converted to steam to produce power. In U.S. Pat. No. 5,112,570, there is illustrated a fuel bundle having a plurality of part-length fuel rods (PLR). These PLR's are supported on the lower tie plate of each bundle and extend upwardly toward the upper tie plate. The rods, however, terminate short of the upper tie plate and typically between a pair of spacers along the fuel bundle. Between the upper end of each PLR and the upper tie plate, there is defined in the upper two-phase region of the fuel bundle a vent volume. This vent volume preferentially receives vapor from the two phase mixture of liquid and vapor in the upper region of the fuel bundle during power producing operations. There are many advantages associated with the use of PLR's including the increased vapor fraction within the vent volume and the pressure drop reduction in the upper two phase region of the bundle. These advantages include increased stability from thermal hydraulic and nuclear instabilities. It will be appreciated that the mechanical hardware associated with fuel rod spacers causes local reduction in the flow area available for the vapor and liquid flowing through the fuel bundle. This causes significant pressure drops to occur as the flow passes each spacer. By using PLR's, the associated flow blockage effects of one or more of the full-length fuel rods extending through these spacers above the PLR is substantially eliminated. That is, because of the absence of a fuel rod at a lattice location above one or more PLR's, additional flow area through the spacer is obtained with consequent reduction in pressure drop across such spacer. As a consequence, significant flow diversion occurs into the lower pressure drop paths or vent volumes above the upper ends of the PLR's. Increased vapor and liquid are therefore pumped from surrounding flow passages, i.e., the interstitial regions around the adjacent fuel rods, into these vent volumes. The creation of vent volumes above PLR's, and flow diversions resulting therefrom, however, can cause some reduction in critical power performance in the fuel bundle. Additional water may accumulate in the vent volume region above the PLR and thus be shunted out of the vent volume without heat generating contact with the remainder of the full-length fuel rods. Separation devices have been utilized to drive the dense liquid or water out of the vent volumes in generally lateral directions onto the surfaces of and into the interstitial regions between the full-length fuel rods to improve heat transfer performance. Such separation devices have generally taken the form of swirlers disposed in the vent volumes. These swirlers create a helical flow pattern causing the dense liquid to be driven laterally outwardly of the vent volume by centrifugal force. Such separation devices have been located within the spacers and have extended therefrom above or below the spacers. However, the separation devices are typically connected to the spacers, at least in part closing off the opening through the spacer, preventing access to a part-length rod in the registering opening or openings below the closed opening(s) of the superposed spacer(s). This complicates bundle assembly because typically the separation devices are not separate entities which can be removed and then reinstalled into the bundle assembly at the assembly site or in the field. For example, in the case of a failed part-length rod underlying one or more superposed spacers containing separation devices, the part-length rod cannot be removed from the bundle without disassembly of the bundle. BRIEF SUMMARY OF THE INVENTION According to the present invention, and in one aspect thereof, there is provided a fuel bundle for a nuclear reactor having a vent volume above a part-length fuel rod wherein one or more separation devices are carried by a support structure, e.g., a rod which can be inserted through and removed from the one or more registering openings of the spacers in registration above a part-length rod. The support rod carries at its lower end a connecting structure for engagement and connection with a mating connecting structure on the upper end of the part-length rod. The separation devices are preferably in the form of swirlers, which are located within the vent volumes between adjacent spacers when the support rod is connected to the part-length rod. Particularly, the swirlers are spaced just above the underlying spacer. The separation device and spacer opening or openings are sized relative to one another to enable withdrawal of the support rod and separation device through the spacer opening or openings upon disconnection of the upper and lower connecting structures of the support rod and the part-length fuel rod, respectively. This facilitates assembly of the fuel bundle and permits withdrawal in the field of a failed part-length rod by removal of the overlying support rod and separation device(s). In another aspect of the present invention, it will be appreciated that the part-length fuel rod is typically coupled to the lower tie plate, for example, by a threaded connection. By coupling the support rod for the swirler to the upper end of the part-length rod prior to assembly in the bundle, the support rod with attached swirlers, together with the part-length rod, may be inserted into the bundle through the registering openings of the spacers upon assembly of the fuel bundle. The support rod may then be used to screwthread the part-length rod into the tie plate, thus facilitating assembly of the fuel bundle. The support rod and part-length rod likewise can be removed from the bundle as a unit on-site, by unthreading the part-length rod from the lower tie plate and withdrawing the combined support rod, part-length rod and separation device(s) through the registering openings of the spacers. In both of the preceding aspects, and when using a ferrule-type spacer, the ferrule(s) of the spacer(s) in the vent volume above the part-length rod may be omitted. The swirler above each spacer may then comprise multiple blades having tips extending laterally to overlie the corners of the vent volume portion within the spacer. Thus, substantial portions of the entire vent volume area within the spacer are vertically aligned with the blades of the swirler. This requires substantially the entirety of the flow through the spacer opening left by the omitted ferrule to flow against the swirler blades for deflection laterally outwardly onto adjacent fuel rods. Moreover, the thickness of the spacer and the pitch of the swirler blades, in another form, can be such that the bladed swirler can be rotated, i.e., threaded past the spacer upon axial insertion and removal of the support rod carrying the swirlers. In this manner, an even larger area of the vent volume can lie in axial alignment with an overlying swirler. In another aspect of the present invention, the support rod may extend the full length of the fuel bundle, passing through the registering openings of the spacers between the upper and lower tie plates. One or more separation devices, e.g., swirlers, may be disposed at discrete locations along the support rod or, alternatively, the support rod may carry a separation device substantially along its full length. For example, a continuous helical swirler can extend about substantially the full length of the support rod for flowing a liquid laterally outwardly onto the surfaces and into the interstices of the surrounding full-length fuel rods. In this form, the support rod and swirler(s) may extend through the ferrules at those lattice locations in the spacers. In a preferred embodiment according to the present invention, there is provided a fuel bundle for a nuclear reactor comprising a plurality of fuel rods spaced laterally from one another in a matrix thereof enabling flow of liquid about the rods from a lower end of the fuel bundle toward an upper end thereof, a plurality of spacers spaced one from the other along the fuel bundle, each spacer having openings for receiving the fuel rods and maintaining the rods spaced from one another in the matrix thereof, at least one of the rods being a part-length fuel rod terminating in an upper end below upper ends of surrounding fuel rods and below at least one of the plurality of spacers, the part-length rod defining with respect to the surrounding rods a vent volume overlying the part-length rod and having a connecting structure adjacent an upper end thereof, a support structure extending through an opening in one spacer in registration with the part-length rod and having a connecting structure adjacent a lower end thereof, the support structure carrying a separation device disposed in the vent volume when the upper and lower connecting structures are connected to one another for flowing liquid laterally outwardly onto surfaces and into interstices of the surrounding fuel rods, the separation device and the opening of the one spacer being sized relative to one another to enable withdrawal of the support structure and the separation device through the opening of the one spacer. In a further preferred embodiment according to the present invention, there is provided a fuel bundle for a nuclear reactor comprising a tie plate, a plurality of rods including fuel rods spaced laterally from one another in a matrix thereof and connected to the tie plate, enabling flow of liquid about the rods from a lower end of the fuel bundle toward an upper end thereof, a plurality of spacers spaced one from another along the fuel bundle and having openings for receiving the fuel rods and maintaining the rods spaced from one another in the matrix thereof, a support structure extending through registering openings in the spacers and having a coupling structure adjacent a lower end thereof for releasably coupling the support structure and the tie plate to one another, the support structure carrying a separation device for flowing liquid laterally outwardly onto the surfaces and into the interstices of surrounding fuel rods, the separation device and the registering spacer openings being sized relative to one another to enable withdrawal of the support structure and the separation device through the registering spacer openings upon disconnecting the support structure and the tie plate relative to one another. In a still further preferred embodiment according to the present invention, there is provided in a fuel bundle for a nuclear reactor having (i) a plurality of fuel rods spaced laterally from one another in a matrix thereof enabling flow of liquid about the rods from a lower end of the fuel bundle toward an upper end thereof, (ii) a plurality of spacers spaced one from the other along the fuel bundle, each spacer having openings for receiving the fuel rods and maintaining the rods spaced from one another in the matrix thereof and (iii) at least one of the rods being a part-length fuel rod terminating in an upper end below upper ends of surrounding fuel rods and below at least one of the plurality of spacers, comprising the steps of providing a support structure extending through an opening in the one spacer in vertical registration with the part-length rod, providing a separation device on the support structure, locating the support structure in the fuel bundle with the separation device below the one spacer, withdrawing the support structure and the separation device through the opening of the one spacer enabling removal of the support structure and the separation device from the fuel bundle. Accordingly, it is a primary object of the present invention to provide removable separation devices for the vent volumes of nuclear fuel bundles enabling insertion and removal of support rods carrying separation devices as well as part-length rods relative to the fuel bundle.
	description	This application claims the benefit of U.S. Provisional Application No. 60/779,498, filed on Mar. 7, 2006. The entire teachings of the above application are incorporated herein by reference. In order to treat cancer with radiation, it is necessary to deliver the dose prescribed to the target volume, while minimizing the dose to other areas. Many mechanical configurations of radiation therapy machines and the associated radiation sources have been developed since Roentgen discovered X-Rays. Modern radiation therapy systems use relatively high energy beams of radiation from radioactive isotopes or electron beam X-Ray generators. The X-Ray generators can employ either high voltage direct current or RF driven linear accelerators (LINACs). A mainstream radiation therapy system uses a LINAC to generate an electron beam with between 4 and 22 MeV of energy at low current. The electron beam strikes a high-atomic number target, typically tungsten, and generates penetrating x-rays. The beam is shaped and delivered to the target volume from one or more directions. The overlapping dose at the target volume is generally higher than the dose at the surface from any one delivery angle. The skin is sensitive to radiation, so it is desirable to limit the skin dose to minimize complications. If more fixed beam angles or continuous rotation are used, the surface dose can be spread out more and minimized with respect to the dose delivered to the target volume. It is also desirable to minimize the stray radiation dose to the rest of the patient. Low levels of radiation delivered to a large volume can trigger cancer growth in patients that survive the primary disease for a long time. A significant fraction of all radiation therapy treatments is employed to treat breast cancer with very good success. A typical general purpose radiation therapy system is designed to treat virtually all anatomical sites with some trade-offs being made in the design in order to make a universally applicable machine. A machine designed specifically for a limited range of anatomical sites can be designed with different trade-offs to more fully optimize the treatment for a limited range of circumstances. This invention relates to the optimization of machine and patient positioning geometry to deliver a clinically better treatment for a limited range of anatomical target volumes. By using a novel patient positioner and source geometry, the target anatomy can be separated from the non-target areas of the patient and treated effectively. This invention can be used for many extremities, but for the purposes of illustration of the salient features, and the most probable use of the machine, breast treatments will be discussed. A substantially horizontal table with an aperture is provided for the patient to lie on in a prone position. The breast to be treated is positioned through the aperture for alignment and treatment. In this position, gravity is an assist in elongating the breast and maximizing the separation between the target volume and the critical structures within the patient such as the chest wall, lung, and heart. By making the table from a shielding material, the unwanted dose from stray radiation to the rest of the patient can be greatly reduced or eliminated. Any source of radiation can be accommodated as part of this invention, and the energy required to treat small volumes such as the breast or other extremities is lower than a general purpose machine designed to treat target volumes deep in a large patient's abdomen, for example. A compact LINAC, cobalt 60 isotopic source, or ortho- or supervoltage x-ray generator may be employed, depending on the clinician's preference for dose delivery. Lower energy, simpler systems may be preferred in remote areas where maintenance is limited. The design of the system employs a positionable, rotational element. The radiation source or the patient positioner can be rotated about a substantially vertical axis, the motions being geometrically equivalent. In the case of a configuration employing a rotating radiation source, the rotating element may also include an optional diagnostic energy imaging source and detector system for localizing the target volume in situ at the time of treatment. As can be appreciated by one of skill in the art, a source assembly and associated shielding will typically weigh many times the weight of patient plus patient positioner. The invention can consist of only the patient positioning and radiation source systems, or also employ a diagnostic energy x-ray source and imaging system. If the radiation therapy source can also produce diagnostic energy and quality beams, only one radiation source is required if imaging is desired. The imaging system can be optical or use ionizing radiation. Utilizing a high energy portal imager in the path of the therapy beam after the treated anatomy is also a possible configuration. The rotational movement combined with an ionizing radiation imaging source and detector can be used to generate plane orthogonal x-rays, cone beam CT, or digitally reconstructed radiographs to assist in anatomical positioning. The position of the anatomy with respect to the radiation beam size, shape, and position can be adjusted to locate the therapy beam in the desired position with respect to the anatomy. Alternatively, the radiation beam size, shape, and or position can be adjusted with respect to the anatomy to provide alignment for the planned treatment. The rotational movement of the patient positioner or the beam in conjunction with the radiation source and a multileaf collimator or other beam modulation device can be used to deliver a highly optimized, pre-planned dose distribution to the treatment volume. The gravity assist of a prone patient position and optional anatomy fixation device maximize the separation of the target volume with respect to critical structures and other areas not intended to receive radiation. By making the patient support table from a shielding material such as lead, and extending the beam block to surround the radiation source(s) entirely, the system can be made self-shielding. General purpose radiation therapy machines that use higher energy beams for treating deep targets in the abdomen, for example, operate at up to and sometimes exceeding 21 MeV. This requires extensive shielding as the primary beam is very penetrating. Above 8 MeV, an x-ray beam produces neutrons which require additional thick shielding. A typical concrete bunker for a LINAC has walls on the order of 4 feet thick, leading to substantial construction costs and a large installation footprint. By optimizing the design of the machine for smaller anatomical targets, the energy of the therapy beam does not need to approach the neutron production threshold, significantly reducing the neutron shielding requirements. A self shielded machine can be installed in a room with minimal shielding, such as employed for CT or diagnostic x-ray rooms. This approach reduces the cost of installation substantially and also makes mobile operation feasible, bringing standard-of-care treatment options to smaller hospitals and rural areas with a low population density. This invention relates to the devices and methods for delivering an accurately located dose of radiation to a predetermined target volume within an anatomical site such as a breast. The following description and figures illustrate both a machine configuration where the patient positioner is non-rotating, and a machine configuration where the patient positioner rotates around a non-rotating radiation source and optional imaging system, which is geometrically equivalent. Referring to FIGS. 1A and 1B, a radiation therapy system of the present invention comprises a patient interface surface shown as a patient table 1 with an aperture 2 above a rotational assembly 3 carrying a radiation source 4 with beam shaping collimator 5, a diagnostic x-ray source 6, and an imaging detector 7, which can have a moveable position. An optional anatomy fixation device 8 holds the extremity of interest in a fixed position during the imaging and therapy phases of machine operation and is mounted to the patient interface surface. A beam block 9 (also referred to as a shielded base) intercepts unwanted energy from the primary beam of the radiation source 4 which escapes the treatment volume. Beam block 9 may include a portal imaging device which creates an image from the therapy beam passing through the treated anatomy. Positioning the rotational axis of the radiation source with respect to the anatomy is provided by either moving the source assembly relative to the table or the table relative to the source assembly. As can be appreciated by one of skill in the art, positioning the anatomy to be treated with respect to the therapy beam 6 is provided by either moving the table with respect to the rotational axis of the table or by selecting an offset portion of the beam by controlling the beam collimator 5. A diagnostic energy x-ray source and imager can be incorporated into the shielded base. The shielded base 3 can encompass the entire radiation source assembly 4 as shown in FIG. 5, providing full shielding from the radiation sources 4 and 6. This optional construction feature would allow the system to work in a room without primary shielding (typically a concrete bunker with walls several feet thick) for the radiation source, decreasing the cost of the installation substantially. This embodiment of the invention could preferably employ a shielded rotating patient table 10, reducing the complexity and cost of the rotating system as shown in FIGS. 5, 6A, 6B, 7 and 8. The rotating patient table 10 can optionally be raised with respect to the fixed shielded base 3 for positioning the patient's anatomy with respect to the therapy beam 6. When the patient table 10 is lowered into the treatment position, the gap between the high radiation zone within the surrounding shielded base 3 and the rotating patient table 10 is shielded by one of several means such as a labyrinth seal or dense brushes or wipers. The shielded table can be provided with interchangeable shielded apertures to accommodate differing size and shape anatomical targets. As an alternative to the elevating table, a shielded door can be provided in the surrounding shielded base 3 for access to the patient during initial positioning. Either the fixed or rotating table versions of the fully shielded embodiment of the invention can be mounted in a mobile enclosure such as an over-the road trailer with extensible sides to accommodate the rotating parts of the invention during operation. When in the stow position, the moveable extensions of the trailer can be retracted for transport to another medical facility. The fully shielded nature of the device provides for flexibility in siting the invention on fixed or mobile applications. At least some of these features are encompassed by one or more of the appended claims. In order to minimize the installed footprint of the system, it is possible to fold the electron beam trajectory as shown in FIG. 4. The LINAC radiation source 4 can be mounted horizontally below the patient table 1 and the electron beam 13 transported to the X-ray target 11 by employing bending magnets 12. If short enough, the LINAC radiation source 4 can also be mounted vertically in a position along the axis shown between bending magnets 12, allowing the use of only one bending magnet 12. Each of these mounting arrangements has positive and negative implications for the overall system design including overall size, servicing ease and radiation shielding requirements. By employing a bending magnet 12 it may be possible to get the electron beam axis closer to the bottom of the patient table 1 before it strikes the X-ray target 11, allowing better therapy photon beam 14 trajectories for treating anatomical targets closer to the patient table 1 bottom surface. FIG. 4 does not illustrate the fully shielded with rotating shielded patient table version of the invention for clarity, but the fully shielded rotating shielded patient table version is fully contemplated by this description. Many variations and combinations of the main elements of the invention are possible.
047284846	abstract	An apparatus for handling a control rod driving mechanism (CRD) of a nuclear reactor. The apparatus has a turn carriage provided in a space within a reactor container where a pedestal is provided, and is adapted to turn on a rail provided on the inner peripheral wall of the container. The turn carriage carries a truck adapted to run along a rail on the turn carriage. A mast is provided on the truck and is driven by a mast driving means between an upright position and a horizontal position. The mast is designed for accommodating a CRD cart. The apparatus also has a CRD mounting/demounting means secured to the mast and adapted to be moved up and down by the CRD cart such as to mount and demount the CRD in and from a CRD housing.
052020835	claims	1. A nuclear reactor system comprising a reactor core and a main heat transport path containing a first heat removal component, at least one main coolant pump and coolant wherein, during normal operation, the coolant is pumped in the main heat transport path by said main coolant pump through a core of the reactor to said heat removal component and back to the reactor core to transport heat generated in the reactor core to the heat removal component; the system comprising a further decay heat removal path connected in parallel with the heat removal component and main coolant pump, the further decay heat removal path including a heat exchange component located at an elevation such that a natural convection flow will occur in the decay heat removal path from a high temperature outlet for coolant from the reactor core through the heat exchange component and to a low temperature inlet of the reactor core when said main coolant pump is shutdown; the further decay heat removal path includes a means to prevent flow in a direction opposite to the intended natural convection flow and a means to maintain a small flow of coolant from said outlet and through the heat exchange component during normal operation of the main coolant pump. 2. A nuclear reactor system as defined in claim 1, wherein the means to maintain the small flow of coolant is a first high-head low-flow pump and the means to prevent flow in the opposite direction is a check valve in the decay heat removal path. 3. A nuclear reactor system as defined in claim 2, wherein the first heat removal component is a steam generator. 4. A nuclear reactor system as defined in claim 2 wherein a second high-head low-flow pump is connected in parallel to said first high-head low-flow pump. 5. A nuclear reactor system as defined in claim 4, wherein a control valve is located in the decay heat removal path to control said small flow to a suitable value. 6. A nuclear reactor system as defined in claim 4, wherein a speed control for the high-head low-flow pumps provides a control to maintain said small flow at a suitable value. 7. A nuclear reactor system as defined in claim 1, wherein the means to prevent flow in the opposite direction is a check valve in the decay heat removal path and the means to maintain said small flow is a bleed located between an outlet of the heat exchange component and the check valve. 8. A nuclear reactor system as defined in claim 1, wherein the heat exchange component is a heat exchanger located in a large tank of coolant. 9. A nuclear reactor system as defined in claim 7, wherein the heat exchange component is a heat exchanger located in a large tank of coolant. 10. A nuclear reactor system as defined in claim 7, wherein the heat removal component is a steam generator. 11. A nuclear reactor system as defined in claim 10, wherein the bleed from the decay heat removal path is connected to a purification unit. 12. A nuclear reactor system as defined in claim 1, wherein the first heat removal component is connected to a high temperature outlet header of the reactor and said at least one main coolant pump is connected to a low temperature inlet header of the reactor. 13. A nuclear reactor system as defined in claim 12, wherein the heat removal component is a steam generator. 14. A nuclear reactor system as defined in claim 13, wherein the means to maintain the small flow of coolant is a first high-head low-flow pump and the means to prevent flow in the opposite direction is a check valve in the decay heat removal path. 15. A nuclear reactor system as defined in claim 14, wherein a further high-head low-flow pump is connected in parallel to said first high-head low-flow pump. 16. A nuclear reactor system as defined in claim 15, wherein a speed control for the high-head low-flow pumps provides a control to maintain said small flow at a suitable valve. 17. A nuclear reactor system as defined in claim 16, wherein the heat exchange component is a heat exchanger located in a large tank of water. 18. A nuclear reactor system comprising a reactor core through which a coolant flows from a low temperature inlet header to a high temperature outlet header with a primary cooling circulation path being located between the high temperature outlet header and the low temperature inlet header including main circulation pumps and a heat removal component, wherein a decay heat removal path is connected between the high temperature outlet header and low temperature inlet header and includes a heat exchange component located at an elevation such that a natural convection circulation flow can start in the decay heat cooling path from the high temperature outlet header to the low temperature inlet header when the main circulation pumps are shutdown, a high-head low-flow pump being located in the decay heat cooling path for maintaining a small flow of coolant in the decay heat cooling path in the same direction as the natural convection circulation flow during normal operation of the main circulation pumps. 19. A nuclear reactor system as defined in claim 18 wherein a check valve in the decay heat removal path prevents flow in a direction opposite to the intended natural convection circulation flow. 20. A nuclear reactor system comprising a reactor core through which a coolant flows from a low temperature inlet header to a high temperature outlet header with a primary cooling circulation path being located between the high temperature outlet header and the low temperature inlet header including main circulation pumps and a heat removal component, wherein a decay heat removal path is connected between the high temperature outlet header and low temperature inlet header and includes a heat exchange component located at an elevation such that a natural convection circulation flow can start in the decay heat cooling path from the high temperature outlet header to the low temperature inlet header when the main circulation pumps are shutdown, a coolant bleed line being located in the decay heat cooling path for maintaining a small flow of coolant in the decay heat cooling path in the same direction as the natural convection circulation flow during normal operation of the main circulation pumps.
	abstract	Control rod guide tubes for a nuclear reactor having a body with an axial length that defines a lower end portion and an upper end portion and a cavity within a substantial length of the body. Orifices are included at the upper and lower end portions of the body. A control rod chamber is located within the cavity and is configured for receiving a control rod. A plurality of ports is coupled to the cavity and is positioned at a substantial length from the upper end portion of the body. Also included are at least two flow channels within the cavity that extend a substantial portion of the axial length of the body. Each flow channel is fluidly coupled to one or more of the ports for receiving fluid flow from outside the body and an outlet proximate to the upper end portion of the body for providing the received fluid flow.
	summary
059237171	claims	1. A method for identifying a core loading arrangement for loading nuclear reactor fuel bundles into a reactor core, the core loading arrangement being required to satisfy predetermined design constraints, said method comprising the steps of: assigning each bundle a relative reactivity value within a loading range; assigning each core location a relative reactivity value; assigning values to each predetermined constraint; creating rules for each reactor core location to specify a direction in which to move a bundle to maximize the cycle energy or satisfy a predetermined constraint, or both; initially simulating a core loading wherein each bundle is loaded into the core location having a core location reactivity value equal to the bundle relative reactivity value; and determining initial values for cycle energy and design constraints for the initial core loading arrangement. selecting a first core location; determining whether the initial core loading arrangement satisfies the design constraints at the first core location; and if at least one design constraint is not satisfied at the first core location, then searching the rules to determine a direction in which the reactivity value of the first core location should be changed in order to satisfy the constraint. searching the rules to determine a direction in which the reactivity value of the core location should be changed in order to improve cycle energy if all the design constraints are satisfied at the first core location. (i) selecting a core location; (ii) determining whether the initial core loading arrangement satisfies the design constraints at the selected core location; (iii) if at least one design constraint is not satisfied at the selected core location, then searching the rules to determine a direction in which the reactivity value of the selected core location should be changed in order to satisfy the constraint; (iv) if all the design constraints are satisfied at the selected core location, then searching the rules to determine a direction in which the reactivity value of the selected core location should be changed in order to improve cycle energy; (v) if there is no rule for changing the first core location reactivity value, then randomly selecting a reactivity level change for the selected core location; and (vi) determining new constraint values and cycle energy for the core loading arrangement which results from changing the reactivity value of the selected core location. initially simulate a core loading in which each bundle is loaded into the respective core location having a core location reactivity value equal to the bundle relative reactivity value; and determine initial values for cycle energy and the design constraints for the initial core loading arrangement. select a first core location; determine whether the initial core loading arrangement satisfies the design constraints at the first core location; and search the rules to determine a direction in which the reactivity value of the core location should be changed in order to satisfy a design constraint if the design constraint is not satisfied at the first core location. search the rules to determine a direction in which the reactivity value of the core location should be changed in order to improve cycle energy if all the design constraints are satisfied at the first core location. determine new constraint values and cycle energy for the core loading arrangement which results from changing the reactivity value of the first core location. (i) select a core location; (ii) determine whether the initial core loading arrangement satisfies the design constraints at the selected core location; (iii) if at least one design constraint is not satisfied at the selected core location, then search the rules to determine a direction in which the reactivity value of the selected core location should be changed in order to satisfy the constraint; (iv) if all the design constraints are satisfied at the first core location, then search the rules to determine a direction in which the reactivity value of the selected core location should be changed in order to improve cycle energy; (v) if there is no rule for changing the selected core location reactivity value, then randomly select a reactivity level change for the selected core location; and (vi) determine new constraint values and cycle energy for the core loading arrangement which results from changing the reactivity value of the selected core location. 2. A method in accordance with claim 1 wherein each core location is assigned a relative reactivity value based on the acceptable reactivity level of each core location. 3. A method in accordance with claim 1 further comprising the step of identifying an optimum core loading arrangement based on the initial core loading arrangement. 4. A method in accordance with claim 3 wherein identifying the optimum core loading arrangement comprises the steps of: 5. A method in accordance with claim 4 further comprising the step of: 6. A method in accordance with claim 5 further comprising the step of randomly selecting a reactivity level change for the first core location if there is no rule for changing the first core location reactivity value. 7. A method in accordance with claim 5 further comprising the step of determining new constraint values and cycle energy for the core loading arrangement which results from changing the reactivity value of the first core location. 8. A method in accordance with claim 3 wherein identifying the optimum core loading arrangement comprises the steps of: 9. A method in accordance with claim 8 wherein each core location is selected and steps (ii)-(vi) are performed for each such selected core location. 10. A method in accordance with claim 9 wherein each core location is analyzed using a depth mode of operation, the depth mode providing that once a change has been made that results in an improved core loading arrangement, then any subsequent change is made to such alternative arrangement in performing steps (ii)-(vi). 11. The method in accordance with claim 9 wherein each core location is analyzed using a breadth mode of operation, the breadth mode providing that each alternative core loading arrangement is analyzed with respect to the initial core loading arrangement in performing steps (ii)-(iv). 12. The method in accordance with claim 9 further comprising the step of generating random core loading arrangements. 13. The method in accordance with claim 12 further comprising the step of selecting a core loading arrangement which satisfies all design constraints and has the highest cycle energy as a best case core loading arrangement. 14. A system for identifying a core loading arrangement for loading nuclear reactor fuel bundles into a reactor core, the core loading arrangement being required to satisfy predetermined design constraints, said system comprising a computer having a memory storage, said memory storage having stored therein a relative reactivity value within a loading range assigned to each bundle, a relative reactivity value assigned to each reactor core location, values assigned to each predetermined design constraint, and rules for each reactor core location which specify a direction in which to move the core location reactivity level to maximize the cycle energy or satisfy a predetermined constraint, or both, said computer programmed to: 15. A system in accordance with claim 14 wherein to identify an optimum core loading arrangement, said computer is further programmed to: 16. A system in accordance with claim 15 wherein said computer is further programmed to: 17. A system in accordance with claim 16 wherein said computer is further programmed to: 18. A system in accordance with claim 14 wherein to identify an optimum core loading arrangement said computer is programmed to: 19. A system in accordance with claim 18 wherein each core location is selected and steps (ii)-(vi) are performed for each such selected core location. 20. A system in accordance with claim 19 wherein said computer is programmed to select a core loading arrangement which satisfies all design constraints and has the highest cycle energy as a best case core loading arrangement.
	abstract	A system for injecting hydrogen into Boiling Water Reactor (BWR) reactor support systems in operation during reactor startup and/or shutdown. The system the hydrogen injection system includes at least one hydrogen source, flow control equipment, and pressure control equipment. The pressure control equipment being configured to regulate a pressure of a hydrogen flow between the at least one hydrogen source and the at least one first BWR support system based upon an operating pressure of the at least one first BWR support system.
	summary
	summary
	abstract	A pressurized water reactor (PWR) comprises a pressure vessel containing primary coolant water. A nuclear reactor core is disposed in the pressure vessel and includes a plurality of fuel assemblies. Each fuel assembly includes a plurality of fuel rods containing a fissile material. A control system includes a plurality of control rod assemblies (CRA's). Each CRA is guided by a corresponding CRA guide structure. A support element is disposed above the CRA guide structures and supports the CRA guide structures. The pressure vessel may be cylindrical, and the support element may comprise a support plate having a circular periphery supported by the cylindrical pressure vessel. The CRA guide structures suitably hang downward from the support plate. The lower end of each CRA guide structure may include alignment features that engage corresponding alignment features of the upper end of the corresponding fuel assembly.
051596210	claims	1. An X-ray transmitting window structure functioning as a vacuum partition wall device for allowing transmission therethrough of X-rays from a vacuum ambience to a different ambience, said structure comprising: an X-ray transmitting film; an outer frame member for gas-tightly covering peripheral edge portions of opposite sides of said X-ray transmitting film; and a pair of flange means for sandwiching and fastening therebetween said outer frame member, said flange means being made of a material having a Brinell hardness greater than that of said outer frame member. gas-tightly providing an outer frame member on outer peripheral edge portions of opposite sides of the X-ray transmitting film; and sandwiching and fastening the outer frame member between a pair of flanges, wherein the outer frame member has a Brinell hardness smaller than that of the flange. an X-ray transmitting film; and a gasket material gas-tightly provided integrally on opposite surfaces in a peripheral portion of said X-ray transmitting film, said gasket material having a Brinell hardness smaller than that of said X-ray transmitting film. an X-ray transmitting film; and a gasket material gas-tightly provided on at least one of opposite surfaces in a peripheral portion of said X-ray transmitting film, said gasket material having a Brinell hardness smaller than that of said X-ray transmitting film, wherein said gasket material is provided on said X-ray transmitting film by plating. an X-ray transmitting film; and a gasket material gas-tightly provided on at least one of opposite surfaces in a peripheral portion of said X-ray transmitting film, said gasket material having a Brinell hardness smaller than that of said X-ray transmitting film, wherein a pair of gasket materials are provided on opposite surfaces in the peripheral portion of said X-ray transmitting film. an X-ray transmitting film; and a gasket material gas-tightly provided on at least one of opposite surfaces in a peripheral portion of said X-ray transmitting film, said gasket material having a Brinell hardness smaller than that of said X-ray transmitting film, wherein an integral gasket material is provided to cover opposite surfaces in the peripheral portion of said X-ray transmitting film. 2. A structure according to claim 1, wherein said pair of flange means have opposed surfaces each having an inside circumferential recess for receiving said X-ray transmitting film, wherein each recess has a flat bottom surface extending from a central part to an inside circumferential edge, and wherein each recess is formed with a sealing edge at said central part thereof which is defined by a circumferential projection projecting perpendicularly from said flat bottom surface and having a slanted surface inclined from a ridge of said projection toward an outside circumferential edge of said recess. 3. A structure according to claim 1 or 2, wherein the Brinell hardness of said outer frame member is smaller than that of said X-ray transmitting film. 4. A structure according to claims 1 or 2 wherein a total thickness of an outside circumferential edge portion of said X-ray transmitting film and said outer frame member adjoining thereto is in a range of 0.2-10 mm. 5. A structure according to claim 1 or 2 wherein a portion of the surface of said X-ray transmitting film not covered by said outer frame member has one of a rectangular shape, a pentagonal shape, another polygonal shape, a shape without a corner, a circular shape and an elliptical shape, and wherein said portion not covered by said outer frame member has a longitudinal size in a range of 10-60 mm. 6. A method of mounting an X-ray transmission film functioning as a vacuum partition wall for allowing transmission therethrough from a vacuum ambience to a different ambience, said method comprising the steps of: 7. An X-ray transmitting window, for use in X-ray lithography, for allowing transmission therethrough of X-rays from a vacuum ambience to a different ambience, comprising: 8. An X-ray transmitting window for use in X-ray lithography, for allowing transmission therethrough of X-rays from a vacuum ambience to a different ambience, comprising: 9. An X-ray transmitting window for use in X-ray lithography, for allowing transmission therethrough of X-rays from a vacuum ambience to a different ambience, comprising: 10. An X-ray transmitting window for use in X-ray lithography, for allowing transmission therethrough of X-rays from a vacuum ambience to a different ambience, comprising:
	claims	1. An apparatus comprising:a pressure vessel;a nuclear reactor core comprising fissile material disposed in the pressure vessel;a core basket disposed in the pressure vessel and containing the nuclear reactor core;an incore instrumentextending in a guide tube of the nuclear reactor core andhaving a cable extending out of a bottom of the nuclear reactor core and then making a 180° turn inside the pressure vessel; anda bottom support element located inside the pressure vessel,attached to a bottom of the core basket, andincluding a routing tube that routes the cable of the incore instrument through the 180° turn. 2. The apparatus of claim 1 wherein the bottom support element includes flow openings to allow flow of primary coolant water through the bottom support element and into the bottom of the nuclear reactor core. 3. The apparatus of claim 1 wherein the core basket includes a lower core plate and the bottom support element is attached to the lower core plate. 4. The apparatus of claim 1 wherein the bottom support element is attached to the core basket without welds. 5. The apparatus of claim 1 wherein the bottom support element does not include any welds. 6. The apparatus of claim 1 wherein the bottom support element has an egg crate grid structure. 7. The apparatus of claim 1 wherein the bottom support element does not contact the pressure vessel. 8. The apparatus of claim 1 wherein the core basket is suspended within the pressure vessel and the bottom support element is attached to the bottom of the core basket without contacting the pressure vessel. 9. The apparatus of claim 8 wherein the bottom support element has structural strength sufficient to support the core basket and the nuclear reactor core in the event that the core basket suspension fails. 10. The apparatus of claim 1 wherein the cable of the incore instrument extends upward after the 180° turn to a vessel penetration located above the nuclear reactor core and below a top of the pressure vessel. 11. The apparatus of claim 1 wherein:the pressure vessel includes an upper vessel portion and a lower vessel portion, the nuclear reactor core and core basket being disposed in the lower vessel portion, the cable of the incore instrument extending upward after the 180° turn to a vessel penetration through the lower vessel portion that is located above the nuclear reactor core. 12. The apparatus of claim 1 wherein:the pressure vessel includes an upper vessel portion, a lower vessel portion, and a mid-flange joining the upper and lower vessel portions, the nuclear reactor core and core basket being disposed in the lower vessel portion, the cable of the incore instrument extending upward after the 180° turn to a vessel penetration located in the mid-flange or in the lower vessel portion. 13. The apparatus of claim 12 wherein the core basket is suspended from the mid-flange. 14. A method performed in conjunction with a nuclear reactor includinga pressure vessel,a nuclear reactor core comprising fissile material disposed in the pressure vessel,a core basket disposed in the pressure vessel and containing the nuclear reactor core,an incore instrumenthaving a sensor disposed in a guide tube of the nuclear reactor core andhaving a cable extending out of a bottom of the nuclear reactor core and then making a 180° turn inside the pressure vessel, anda bottom support element located inside the pressure vessel,attached to a bottom of the core basket, andincluding a routing tube that routes the cable of the incore instrument through the 180° turn,the method comprising:retracting the cable to move the sensorout of the guide tube of the nuclear reactor core andinto the routing tube of the bottom support element;performing maintenance on the nuclear reactor, including replacing the guide tube with a different guide tube; andre-inserting the cable to move the sensorout of the routing tube of the bottom support element andinto the different guide tube. 15. The method of claim 14 wherein the retracting and the re-inserting are blind operations in which the position of the incore instrument is not visibly observable. 16. The method of claim 15 wherein the re-inserting includes monitoring a signal from the incore instrument to determine placement of the incore instrument in the reactor core.
	description	This patent claims priority to U.S. Provisional Patent Application Ser. No. 62/627,473, filed Feb. 7, 2018, entitled “X-Ray Detectors for Generating Digital Images,” U.S. Provisional Patent Application Ser. No. 62/627,469, filed Feb. 7, 2018, entitled “Systems and Methods for Digital X-Ray Imaging,” U.S. Provisional Patent Application Ser. No. 62/627,464, filed Feb. 7, 2018, entitled “Systems and Methods for Digital X-Ray Imaging,” and U.S. Provisional Patent Application Ser. No. 62/627,466, filed Feb. 7, 2018, entitled “Radiography Backscatter Shields and X-Ray Imaging Systems Including Backscatter Shields.” The entireties of U.S. Provisional Patent Application Ser. No. 62/627,473, U.S. Provisional Patent Application Ser. No. 62/627,469, U.S. Provisional Patent Application Ser. No. 62/627,464, and U.S. Provisional Patent Application Ser. No. 62/627,466 are incorporated herein by reference. This disclosure relates generally to radiography and, more particularly, to systems and methods for digital X-ray imaging. Systems and methods for digital X-ray imaging are disclosed, substantially as illustrated by and described in connection with at least one of the figures, as set forth more completely in the claims. The figures are not necessarily to scale. Wherever appropriate, similar or identical reference numerals are used to refer to similar or identical components. Disclosed example handheld X-ray imaging systems enable real-time generation and/or display of digital images during X-ray radiography. In contrast with conventional systems, disclosed examples provide an all-in-one X-ray radiography unit that does not require extraneous equipment for power, X-ray generation, radiograph capture, radiograph display, or radiograph storage. Disclosed example handheld X-ray imaging systems reduce operator fatigue relative to conventional scanning devices by having a reduced weight (e.g., less than 20 pounds) and/or by providing improved weight distribution that concentrates the weight of the handheld X-ray imaging system near the operator's body. As used herein, the term “real-time” refers to the actual time elapsed in the performance of a computation by a computing device, the result of the computation being required for the continuation of a physical process (i.e., no significant delays are introduced). For example, real-time display of captured images includes processing captured image data and displaying the resulting output images to create the perception to a user that the images are displayed immediately upon capture. As used herein, the term “portable” includes handheld (e.g., capable of being carried and operated by a single person) and/or wheeled (e.g., capable of being transported and operated while wheels are attached and/or placed on wheels). FIG. 1 is a perspective view of an example handheld X-ray imaging system 100 to generate and output digital images and/or video based on incident X-rays. The example handheld X-ray imaging system 100 may be used to perform non-destructive testing (NDT), medical scanning, security scanning, and/or any other scanning application. The system 100 of FIG. 1 includes a frame 102 that holds an X-ray generator 104 and an X-ray detector 106. In the example of FIG. 1, the frame 102 is C-shaped, such that the X-ray generator 104 directs X-ray radiation toward the X-ray detector 106. As described in more detail below, the frame 102 is positionable (e.g., held by an operator, supported by an external support structure and/or manipulated by the operator, etc.) around an object to be scanned with X-rays. The example frame 102 is constructed using carbon fiber and/or machined aluminum. The X-ray generator 104 is located on a first section 108 of the C-shaped frame 102 generates and outputs X-ray radiation, which traverses and/or scatters based on the state of the object under test. The X-ray detector 106 is located on a second section 110 of the frame 102 (e.g., opposite the first section 108) and receives incident radiation generated by the X-ray generator 104. The example frame 102 may be manipulated using one or more handles 112, 114. A first one of the handles 112 is an operator control handle, and enables an operator to both mechanically manipulate the frame 102 and control the operation of the handheld X-ray imaging system 100. A second one of the handles 114 is adjustable and may be secured to provide the operator with leverage to manipulate the frame 102. The example handle 114 may be oriented with multiple degrees of freedom and/or adjusted along a length of a central section 116 of the frame 102. During operation, the handheld X-ray imaging system 100 generates digital images (e.g., digital video and/or digital still images) from the X-ray radiation. The handheld X-ray imaging system 100 may store the digital images on one or more storage devices, display the digital images on a display device 118, and/or transmit the digital images to a remote receiver. The example display device 118 is attachable to the example frame 102 and/or may be oriented for viewing by the operator. The display device 118 may also be detached from the frame 102. When detached, the display device 118 receives the digital images (e.g., still images and/or video) via a wireless data connection. When attached, the display device 118 may receive the digital images via a wired connection and/or a wireless connection. A power supply 120, such as a detachable battery, is attached to the frame 102 and provides power to the X-ray generator 104, the X-ray detector 106, and/or other circuitry of the handheld X-ray imaging system 100. An example power supply 120 that may be used is a lithium-ion battery pack. The display device 118 may receive power from the power supply 120 and/or from another power source such as an internal battery of the display device 118. The example central section 116 of the frame 102 is coupled to the first section 108 via a joint 122 and to the second section 110 via a joint 124. The example joints 122, 124 are hollow to facilitate routing of cabling between the sections 108, 110, 116. The joints 122, 124 enable the first section 108 and the second section 110 to be folded toward the center section to further improve the compactness of the handheld X-ray imaging system 100 when not in use (e.g., during storage and/or travel). FIG. 2 is a block diagram of an example digital X-ray imaging system 200 that may be used to implement the handheld X-ray imaging system 100 of FIG. 1. The example digital X-ray imaging system 200 of FIG. 2 includes a frame 202 holding an X-ray generator 204, an X-ray detector 206, a computing device 208, a battery 210, one or more display device(s) 212, one or more operator input device(s) 214, and one or more handle(s) 216. The X-ray generator 204 includes an X-ray tube 218, a collimator 220, and a shield switch 222. The X-ray tube 218 generates X-rays when energized. In some examples, the X-ray tube 218 operates at voltages between 40 kV and 120 kV. In combination with a shielding device, X-ray tube voltages between 70 kV and 120 kV may be used while staying within acceptable X-ray dosage limits for the operator. Other voltage ranges may also be used. The collimator 220 filters the X-ray radiation output by the X-ray tube 218 to more narrowly direct the X-ray radiation at the X-ray detector 206 and any intervening objects. The collimator 220 reduces the X-ray dose to the operator of the system 200, reduces undesired X-ray energies to the detector 206 resulting from X-ray scattering, and/or improves the resulting digital image generated at the X-ray detector 206. The shield switch 222 selectively enables and/or disables the X-ray tube 218 based on whether a backscatter shielding device 224 is attached to the frame. The backscatter shielding device 224 reduces the dose to the operator holding the frame 202 by providing shielding between the collimator 220 and an object under test. The example backscatter shielding device 224 includes a switch trigger configured to trigger the shield switch 222 when properly installed. For example, the shield switch 222 may be a reed switch or similar magnetically-triggered switch, and the backscatter shielding device 224 includes a magnet. The reed switch and magnet are respectively positioned on the frame 202 and the backscatter shielding device 224 such that the magnet triggers the reed switch when the backscatter shielding device 224 is attached to the frame 202. The shield switch 222 may include any type of a capacitive sensor, an inductive sensor, a magnetic sensor, an optical sensor, and/or any other type of proximity sensor. The shield switch 222 is configured to disable the X-ray tube 218 when the backscatter shielding device 224 is not installed. The shield switch 222 may be implemented using, for example, hardware circuitry and/or via software executed by the computing device 208. In some examples, the computing device 208 may selectively override the shield switch 222 to permit operation of the X-ray tube 218 when the backscatter shielding device 224 is not installed. The override may be controlled by an administrator or other authorized user. The X-ray detector 206 of FIG. 2 generates digital images based on incident X-ray radiation (e.g., generated by the X-ray tube 218 and directed toward the X-ray detector 206 by the collimator 220). The example X-ray detector 206 includes a detector housing 226, which holds a scintillation screen 228, a reflector 230, and a digital imaging sensor 232. The scintillation screen 228, the reflector 230, and the digital imaging sensor 232 are components of a fluoroscopy detection system 234. The example fluoroscopy detection system 234 is configured so that the digital imaging sensor 232 (e.g., a camera, a sensor chip, etc.) receives the image indirectly via the scintillation screen 228 and the reflector 230. In other examples, the fluoroscopy detection system 234 includes a sensor panel (e.g., a CCD panel, a CMOS panel, etc.) configured to receive the X-rays directly, and to generate the digital images. An example implementation of the X-ray detector 206 is described below with reference to FIGS. 5-8. In some other examples, the scintillation screen 228, may be replaced with a solid state panel that is coupled to the scintillation screen 228 and has pixels that correspond to portions of the scintillation screen 228. Example solid state panels may include CMOS X-ray panels and/or CCD X-ray panels. The computing device 208 controls the X-ray tube 218, receives digital images from the X-ray detector 206 (e.g., from the digital imaging sensor 232), and outputs the digital images to the display device 212. Additionally or alternatively, the computing device 208 may store digital images to a storage device. The computing device 208 may output the digital images as digital video to aid in real-time non-destructive testing and/or store digital still images. As mentioned above, the computing device 208 may provide the digital images to the display device(s) 212 via a wired connection or a wireless connection. To this end, the computing device 208 includes wireless communication circuitry. For example, the display device(s) 212 may be detachable from the frame 202 and held separately from the frame 202 while the computing device 208 wirelessly transmits the digital images to the display device(s) 212. The display device(s) 212 may include a smartphone, a tablet computer, a laptop computer, a wireless monitoring device, and/or any other type of display device equipped with wired and/or wireless communications circuitry to communicate with (e.g., receive digital images from) the computing device 208. In some examples, the computing device 208 adds data to the digital images to assist in subsequent analysis of the digital images. Example data includes a timestamp, a date stamp, geographic data, or a scanner inclination. The example computing device 208 adds the data to the images by adding metadata to the digital image file(s) and/or by superimposing a visual representation of the data onto a portion of the digital images. The operator input device(s) 214 enable the operator to configure and/or control the example digital X-ray imaging system 200. For example, the operator input device(s) 214 may provide input to the computing device 208, which controls operation and/or configures the settings of the digital X-ray imaging system 200. Example operator input device(s) 214 include a trigger (e.g., for controlling activation of the X-ray tube 218), buttons, switches, analog joysticks, thumbpads, trackballs, and/or any other type of user input device. The handle(s) 216 are attached to the frame 202 and enable physical control and manipulation of the frame 202, the X-ray generator 204, and the X-ray detector 206. In some examples, one or more of the operator input device(s) 214 are implemented on the handle(s) 216 to enable a user to both physically manipulate and control operation of the digital X-ray imaging system 200. FIG. 3 is a perspective view of the first portion 108 of the handheld X-ray imaging system 100 of FIG. 1, including the X-ray generator 104, the power supply 120, and the operator control handle 112. FIG. 3 is illustrated with a portion of a housing 302, while a second portion of the housing (shown in FIG. 1) is omitted for visibility of other components. The example first portion 108 is further coupled to a computing device 304, such as the computing device 208 of FIG. 2. The computing device 304 is attached to the frame 102 via a printed circuit board 306. An X-ray tube 308 (e.g., the X-ray tube 218 of FIG. 2) is coupled to a collimator 310 (e.g., the collimator 220 of FIG. 2) and controlled by the computing device 304 and/or by an operator input device on the handle 112. As shown in FIG. 3, the handle 112 may include an X-ray trigger 312 (e.g., one of the operator input device(s) 214 of FIG. 2). When actuated (e.g., by the operator of the handheld X-ray imaging system 100), the X-ray trigger 312 activates the X-ray tube 308 to generate X-ray radiation. The X-ray trigger 312 may activate the X-ray tube 308 directly and/or via the computing device 304. The collimator 310 filters X-ray radiation generated by the X-ray tube 308 to reduce the X-ray radiation that is not directed at the X-ray detector 106 and/or to increase the proportion of X-ray radiation that is directed at the X-ray detector 106 (e.g., radiation that ends up being incident on a scintillator of the X-ray detector 106) relative to radiation not directed at the X-ray detector 106. A targeting camera 314 is coupled to the computing device 304 to enable an operator of the handheld X-ray imaging system 100 to determine a target of generated X-rays. The example targeting camera 314 generates and outputs digital images (e.g., digital video, digital still images, etc.) to the computing device 304 for display to the operator via the display device 118. The digital images of the target (e.g., an exterior of the target) may be saved in association with the digital images of the X-ray scanning to provide contextual information about the location or object from which digital X-ray images are captured. Additionally or alternatively, a laser may be projected from the location of the targeting camera 314 toward the X-ray detector 106. The laser illuminates an approximate location on a workpiece that is being scanned by the digital X-ray imaging system 100 and/or output to the display device 118. FIG. 4 is a more detailed view of the first portion 108 of the handheld X-ray imaging system of FIG. 3 including the example handle 112. To improve the handling of the digital X-ray imaging system 100, the handle 112 is capable of attachment to multiple locations on the frame 102. The handle 112 is illustrated at a first location 402 on the frame 102 in FIG. 4. In the example of FIG. 4, the handle 112 is secured to the housing 302 via multiple screws. The handle 112 may be detached from the first location 402 and attached at a second location 404. As illustrated in FIG. 4, the second location 404 on the housing 302 includes multiple screw nuts 406a-406c and a data connector 408, which match screw nuts and a data connector at the first location 402. The example handle 112 may be attached to the second location 404 by connecting a corresponding connector on the handle 112 to the data connector 408 and screwing the handle into the screw nuts 406a-406c. FIGS. 5A and SB illustrate perspective views of the example handle 112 of FIGS. 1 and 3. As mentioned above, the handle 112 includes the trigger 312, which enables and/or activates the X-ray tube 308 to output the X-ray radiation. The handle 112 includes additional input devices 502, 504 (e.g., operator input devices 214 of FIG. 2). The input device 502 is a thumbstick, which can be used to input commands to the computing device 304, such as navigating menus, confirming selections, configuring the X-ray tube 308 and/or the X-ray generator 106, changing views and/or any other type of operator input. The input device 504 is a push button that may be used by an operator to confirm and/or cancel a selection. The computing device 304 controls the X-ray tube 308, the X-ray detector 106 (e.g., the X-ray generator 206 and/or the digital imaging sensor 232 of FIG. 2), the display device 118, and/or any other aspect of the digital X-ray imaging system 100 based on input from the trigger 312, the input devices 502, 504, and/or any other input devices. The handle 112 includes a data connector 506, which mates to the data connector(s) 408 on the housing 302. The data connectors 408, 506 establish a hard-wired connection between the trigger 312 and/or the input devices 502, 504 and the computing device 304 and/or other circuitry. The handle 112 includes input guards 508, which protect the input devices 502, 504 from accidental damage. The input guards 508 extend from the handle 112 adjacent the input devices 502, 504 and farther than the input devices 502, 504. The example handle 112 further includes a trigger lock 510. The trigger lock 510 is a mechanical lock that, when activated, mechanically prevents activation of the trigger 312. The example trigger lock 510 is a push-button safety that locks the trigger 312 against depression by the operator. FIG. 6 is a partially exploded view of the example digital X-ray detector 106 of FIG. 1. FIG. 7 is a perspective view of the example digital X-ray detector 106 of FIG. 1. As illustrated in FIG. 6, the X-ray detector 106 includes a detector housing 602, a scintillation screen 604, and a reflector 606. The scintillation screen 604 and the reflector 606 are held within the housing 602 and are illustrated in FIG. 6 to show the relationship between the shape of the housing 602 and the geometries of the scintillation screen 604 and the reflector 606. The detector housing 602 may be constructed using carbon fiber, aluminum, and/or any other material and/or combination of materials. The example detector housing 602 may function as a soft X-ray filter to reduce undesired X-ray radiation at the scintillation screen 604, thereby reducing noise in the resulting digital image. The scintillation screen 604 and/or the reflector 606 may be attached to the detector housing 602 using adhesive (e.g., epoxy, glue, etc.) and/or any other attachment technique. In some examples, the detector housing 602 is lined with a layer of lead or another backscatter shielding material to lower the dose to the operator in a handheld system. FIG. 8 is a side view of the example digital detector housing, the scintillator, and the reflector. FIG. 9 is a side view of the example digital X-ray detector 106 of FIG. 1, illustrating imaging of incident X-rays by the digital X-ray detector. As illustrated in FIG. 9, a digital imaging sensor 612 is oriented to capture light generated by the scintillation screen 604 in response to incident X-ray radiation. The scintillation screen 604 converts incident X-rays 608 to visible light 610. An example scintillation screen 604 that may be used in a handheld X-ray scanner has a surface area of 4 inches by 6 inches. The size and material of the scintillation screen 604 at least partially determines the size, brightness, and/or resolution of the resulting digital images. The example scintillation screen is Gadox (Gadolinium oxysulphide) doped with Terbium, which emits a peak visible light at a wavelength of substantially 560 nm. The example reflector 606 is a mirror that reflects visible light generated by the scintillation screen 604 to the digital imaging sensor 612 (e.g., via a lens 614). The example reflector 606 has the same surface area (e.g., 4 inches by 6 inches) as the scintillation screen 604, and is oriented at an angle 616 to direct the visible light 610 to the digital imaging sensor 612 and/or the lens 614. An example angle 616 is 30 degrees, which enables a 4 inch by 6 inch scintillation screen and a 4 inch by 6 inch reflector 606 to fit within a housing having a thickness 618 of less than 2.5 inches. In other examples, the angle 616 is an angle less than 45 degrees. Other sizes and/or geometries may be used for the scintillation screen 604 and/or the reflector 606. Additionally or alternatively, the digital X-ray detector 106 may include optics such as prisms to direct the visible light 610 to the digital imaging sensor 612. The example digital imaging sensor 612 is a solid state sensor such as a CMOS camera. In the illustrated example using the scintillation screen 604 and the reflector 606, and a 6 mm lens 614, the digital imaging sensor 612 has a field of view of 143 degrees to capture light from substantially the entirety of the reflector 606. The digital imaging sensor 612 is coupled to an imager bracket 620 via a mounting brackets 622. The detector housing 602 is also coupled to the imager bracket 620. The imager bracket 620 couples both the detector housing 602 and the digital imaging sensor 612 to the frame 102 of the handheld X-ray imaging system 100. The mounting brackets 622 includes slots 624 to which an imaging bracket 626 is adjustably coupled. The digital imaging sensor 612 is attached to the imaging bracket 626 (e.g., via a printed circuit board). The imaging bracket 626 may be adjusted and secured along the length of the slots 624 to adjust an angle of the digital imaging sensor 612 relative to the reflector 606. The field of view of the digital imaging sensor 612 is oriented substantially perpendicularly to the scintillation screen, within the angular limits permitted using the slots 624 and the imaging bracket 626. The example imager bracket 620 may include a data connector 628 (FIG. 8) to enable sufficient data throughput from the digital imaging sensor 612 to a computing device or other image display and/or image storage devices. An example data connector 628 may be a USB 3.0 connector to connect a USB 3.0 bus between the digital imaging sensor 612 and the receiving device. The USB 3.0 bus provides sufficient bandwidth between the digital imaging device 608 and the receiving device for high-definition video or better resolution. While an example implementation of the X-ray detector 106 is described above, other example implementations of the X-ray detector 106 include using a solid state image sensor, such as a CMOS panel or a CCD panel, coupled directly to a scintillator. The CMOS panel produces digital images based on visible light generated by the scintillator, and outputs the digital images to the computing device 304. FIG. 10 is a side view of the handheld X-ray imaging system of FIG. 1, illustrating scanning of an object 1002 under test by directing X-rays 1004 from the X-ray tube 308 to the X-ray detector 106. As mentioned above, the collimator 310 reduces X-ray radiation that is not directed at the X-ray detector 106, so the concentration of the X-ray radiation 1004 that is not scattered by the object 1002 is incident on the X-ray detector 106. FIG. 11 is a flowchart representative of example machine readable instructions 1100 which may be executed by the example computing device 208 of FIG. 2 to perform digital X-ray imaging. The example machine readable instructions 1100 of FIG. 11 are described below with reference to the digital X-ray imaging system 200 of FIG. 2, but may be performed by the digital X-ray imaging system 100 of FIG. 1. At block 1102, the example computing device 208 initializes the X-ray detector 206. For example, the computing device 208 may verify that the X-ray detector 206 is in communication with the computing device 208 and/or is configured to capture digital images of X-ray radiation. At block 1103, an operator of the digital X-ray imaging system 200 may position the frame 202 adjacent on object under test, such that the object under test is located between the X-ray detector 206 and the X-ray tube 218. At block 1104, the computing device 208 determines whether a trigger is activated. For example, the computing device 208 may activate the X-ray tube 218 in response to activation of a trigger (e.g., a physical trigger, a button, a switch, etc.) by an operator. If the trigger has not been activated (block 1104), control returns to block 1104 to await activation of the trigger. When the trigger is activated (block 1104), at block 1105 the computing device 208 determines whether the X-ray tube voltage is at least a threshold voltage. For example, the X-ray tube voltage may be configured to be between 70 kV and 120 kV, in which case the computing device 208 requires the backscatter shielding device 224 to be detected (e.g., via the shield switch 222). If the X-ray tube voltage is at least the threshold (block 1105), at block 1106 the computing device 208 determines whether a backscatter shield is detected. For example, the computing device 208 may determine whether the backscatter shield (e.g., the backscatter shielding device 224, the backscatter shield 300, the backscatter shield 600) is installed using the shield switch 222. If the backscatter shield is not detected (block 1106), at block 1108 the computing device 208 disables the X-ray tube 218 and outputs a backscatter shield alert (e.g., via a visual and/or audible alarm, via the display device 212, etc.). Control then returns to block 1104. If the backscatter shield is detected (block 1106), or if the X-ray tube voltage is less than the threshold (block 1105), at block 1110 the X-ray tube 218 generates and outputs X-ray radiation. At block 1112, the X-ray detector 106 (e.g., via the scintillation screen 228, the reflector 230, and the digital imaging sensor 232, and/or via a solid state panel coupled to a scintillator) captures digital image(s) (e.g., digital still images and/or digital video). The X-ray detector 106 provides the captured digital image(s) to the computing device 208. At block 1114, the computing device 208 adds the auxiliary data to the digital image(s). Example auxiliary data includes a timestamp, a date stamp, geographic data, and/or an inclination of the frame 202, the X-ray detector 206, the X-ray tube 218, and/or any other component of the digital X-ray imaging system 200. At block 1116, the computing device 208 outputs the digital image(s) to the display device(s) 218 (e.g., via a wired and/or wireless connection). In some examples, the computing device 208 outputs the digital image(s) to an external computing device such as a laptop, a smartphone, a server, a tablet computer, a personal computer, and/or any other type of external computing device. At block 1118, the computing device 208 determines whether the digital image(s) are to be stored (e.g., in a storage device). If the digital image(s) are to be stored (block 1118), at block 1120 the example computing device 208 stores the image(s). The example computing device 208 may be configured to store the digital image(s) in one or more available storage devices, such as a removable storage device. After storing the image(s) (block 1120), or if the digital image(s) are not to be stored (block 1118), control returns to block 1104. In some examples, blocks 1110-1120 may be iterated substantially continuously until the trigger is deactivated. FIG. 12 is a block diagram of an example computing system 1200 that may be used to implement the computing device 208 of FIG. 2. The example computing system 1200 may be implemented using a personal computer, a server, a smartphone, a laptop computer, a workstation, a tablet computer, and/or any other type of computing device. The example computing system 1200 of FIG. 12 includes a processor 1202. The example processor 1202 may be any general purpose central processing unit (CPU) from any manufacturer. In some other examples, the processor 1202 may include one or more specialized processing units, such as RISC processors with an ARM core, graphic processing units, digital signal processors, and/or system-on-chips (SoC). The processor 1202 executes machine readable instructions 1204 that may be stored locally at the processor (e.g., in an included cache or SoC), in a random access memory 1206 (or other volatile memory), in a read only memory 1208 (or other non-volatile memory such as FLASH memory), and/or in a mass storage device 1210. The example mass storage device 1210 may be a hard drive, a solid state storage drive, a hybrid drive, a RAID array, and/or any other mass data storage device. A bus 1212 enables communications between the processor 1202, the RAM 1206, the ROM 1208, the mass storage device 1210, a network interface 1214, and/or an input/output interface 1216. The example network interface 1214 includes hardware, firmware, and/or software to connect the computing system 1200 to a communications network 1218 such as the Internet. For example, the network interface 1214 may include IEEE 1202.X-compliant wireless and/or wired communications hardware for transmitting and/or receiving communications. The example I/O interface 1216 of FIG. 12 includes hardware, firmware, and/or software to connect one or more input/output devices 1220 to the processor 1202 for providing input to the processor 1202 and/or providing output from the processor 1202. For example, the I/O interface 1216 may include a graphics processing unit for interfacing with a display device, a universal serial bus port for interfacing with one or more USB-compliant devices, a FireWire, a field bus, and/or any other type of interface. Example I/O device(s) 1220 may include a keyboard, a keypad, a mouse, a trackball, a pointing device, a microphone, an audio speaker, an optical media drive, a multi-touch touch screen, a gesture recognition interface, a display device (e.g., the display device(s) 118, 212) a magnetic media drive, and/or any other type of input and/or output device. The example computing system 1200 may access a non-transitory machine readable medium 1222 via the I/O interface 1216 and/or the I/O device(s) 1220. Examples of the machine readable medium 1222 of FIG. 12 include optical discs (e.g., compact discs (CDs), digital versatile/video discs (DVDs), Blu-ray discs, etc.), magnetic media (e.g., floppy disks), portable storage media (e.g., portable flash drives, secure digital (SD) cards, etc.), and/or any other type of removable and/or installed machine readable media. Example wireless interfaces, protocols, and/or standards that may be supported and/or used by the network interface(s) 1214 and/or the I/O interface(s) 1216, such as to communicate with the display device(s) 212, include wireless personal area network (WPAN) protocols, such as Bluetooth (IEEE 802.15); near field communication (NFC) standards; wireless local area network (WLAN) protocols, such as WiFi (IEEE 802.11); cellular standards, such as 2G/2G+(e.g., GSM/GPRS/EDGE, and IS-95 or cdmaOne) and/or 2G/2G+(e.g., CDMA2000, UMTS, and HSPA); 4G standards, such as WiMAX (IEEE 802.16) and LTE; Ultra-Wideband (UWB); etc. Example wired interfaces, protocols, and/or standards that may be supported and/or used by the network interface(s) 1214 and/or the I/O interface(s) 1216, such as to communicate with the display device(s) 212, include comprise Ethernet (IEEE 802.3), Fiber Distributed Data Interface (FDDI), Integrated Services Digital Network (ISDN), cable television and/or internet (ATSC, DVB-C, DOCSIS), Universal Serial Bus (USB) based interfaces, etc. The processor 202, the network interface(s) 1214, and/or the I/O interface(s) 1216, and/or the display device 212, may perform signal processing operations such as, for example, filtering, amplification, analog-to-digital conversion and/or digital-to-analog conversion, up-conversion/down-conversion of baseband signals, encoding/decoding, encryption/decryption, modulation/demodulation, and/or any other appropriate signal processing. The computing device 208 and/or the display device 212 may use one or more antennas for wireless communications and/or one or more wired port(s) for wired communications. The antenna(s) may be any type of antenna (e.g., directional antennas, omnidirectional antennas, multi-input multi-output (MIMO) antennas, etc.) suited for the frequencies, power levels, diversity, and/or other parameters required for the wireless interfaces and/or protocols used to communicate. The port(s) may include any type of connectors suited for the communications over wired interfaces/protocols supported by the computing device 208 and/or the display device 212. For example, the port(s) may include an Ethernet over twisted pair port, a USB port, an HDMI port, a passive optical network (PON) port, and/or any other suitable port for interfacing with a wired or optical cable. The present methods and systems may be realized in hardware, software, and/or a combination of hardware and software. The present methods and/or systems may be realized in a centralized fashion in at least one computing system, or in a distributed fashion where different elements are spread across several interconnected computing systems. Any kind of computing system or other apparatus adapted for carrying out the methods described herein is suited. A typical combination of hardware and software may include a general-purpose computing system with a program or other code that, when being loaded and executed, controls the computing system such that it carries out the methods described herein. Another typical implementation may comprise an application specific integrated circuit or chip. Some implementations may comprise a non-transitory machine-readable (e.g., computer readable) medium (e.g., FLASH drive, optical disk, magnetic storage disk, or the like) having stored thereon one or more lines of code executable by a machine, thereby causing the machine to perform processes as described herein. As used herein, the term “non-transitory machine-readable medium” is defined to include all types of machine readable storage media and to exclude propagating signals. As utilized herein the terms “circuits” and “circuitry” refer to physical electronic components (i.e. hardware) and any software and/or firmware (“code”) which may configure the hardware, be executed by the hardware, and or otherwise be associated with the hardware. As used herein, for example, a particular processor and memory may comprise a first “circuit” when executing a first one or more lines of code and may comprise a second “circuit” when executing a second one or more lines of code. As utilized herein, “and/or” means any one or more of the items in the list joined by “and/or”. As an example, “x and/or y” means any element of the three-element set {. (x), (y), (x, y)}. In other words, “x and/or y” means “one or both of x and y”. As another example, “x, y, and/or z” means any element of the seven-element set {(x), (y), (z), (x, y), (x, z), (y, z), (x, y, z)}. In other words, “x, y and/or z” means “one or more of x, y and z”. As utilized herein, the term “exemplary” means serving as a non-limiting example, instance, or illustration. As utilized herein, the terms “e.g.,” and “for example” set off lists of one or more non-limiting examples, instances, or illustrations. As utilized herein, circuitry is “operable” to perform a function whenever the circuitry comprises the necessary hardware and code (if any is necessary) to perform the function, regardless of whether performance of the function is disabled or not enabled (e.g., by a user-configurable setting, factory trim, etc.). While the present method and/or system has been described with reference to certain implementations, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present method and/or system. For example, block and/or components of disclosed examples may be combined, divided, re-arranged, and/or otherwise modified. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from its scope. Therefore, the present method and/or system are not limited to the particular implementations disclosed. Instead, the present method and/or system will include all implementations falling within the scope of the appended claims, both literally and under the doctrine of equivalents.
060375175	abstract	A reaction chamber (20) is charged with a reactant metal (18) which is heated to a molten state by a suitable heating arrangement (21). A field generating arrangement (17) generates a unidirectional electromagnetic field through the molten reactant metal (18) and through at least one target area preferably within the molten reactant metal. The electromagnetic field directs beta particles toward the first target area. A radiation absorbing module (15, 16) is positioned in the first target area and includes at least one radiation absorbing material (75, 76). The radiation absorbing material (75, 76) in the modules (15, 16) absorb the beta radiation which has been directed to the target area by the electromagnetic field.
053346297	description	DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the graph of FIG. 1 of the drawings, a polyelectrolyte fiber, or when hydrated, polyelectrolyte gel, such as cross-linked poly-acrylic acid (PAA-PAA), when placed in an aqueous solution or saline solution containing a pH-dependent dye, such as Bromocresol Green, responsively deflects, or changes volume, as select wavelengths of electromagnetic radiation, such as light, visible light, such as (yellow and/or green) impinge upon it. The polyelectrolyte fiber inherently has the property of changing its length or volume in response to changes of the pH of the solution in which it is immersed. The pH dependent dye solution inherently has the property of changing its pH in response to select wavelengths of impinging electromagnetic radiation. By immersing the polyelectrolyte fiber in the solution made up of a suitable pH dependent dye which changes its pH in response to impinging light and radiating it with impinging electromagnetic radiation of select wavelengths, responsive actuation of the fiber results. A condition for the fiber that is termed as a null point A appears on the steep portion of its response curve. This null point A occurs at about a pH of 5.3 for this particular polyelectrolyte fiber. When the pH of a particular pH dependent dye solution varies either way from pH=5.3 in a range, for example, of plus or minus one pH unit, then the length or volume of the particular fiber in the particular solution changes in a rather pronounced manner as compared to the effects produced by somewhat greater pH changes outside of the plus and minus one pH range. It is apparent that the pH of the solution be maintained at a value that is substantially equivalent to the null point of the polyelectrolyte fiber for more acceptable operational results and can be expressed that the acid dissociation constant pKa be within a range that is within plus or minus 1 pH unit of the pH null point of the polyelectrolyte fiber or gel, (pH-1<pKa<pH+1). Another property of a particular pH-dependent dye which is selected for use in accordance with this inventive concept is that the pH-dependent dye changes color on either side of the null point pH value. Bromocresol Green, for instance, is yellow at pH 2 and is blue-green at pH 6.6. By shining an intense yellow light on a pH 6 Bromocresol Green solution, the solution can be made more acidic, thus causing a suitable polyelectrolytic gel or fiber, such as polyvinyl alcohol-polyacrylic acid (PVA-PAA) to appropriately contract. Terminating the radiance causes the fiber to extend to its original dimension. Under acid conditions illumination of the solution containing the fiber with a blue light would shift the pH to a lower value to effect an extension of the fiber. The closer the null point of a fiber matches the pKa of the pH dependent dye, or indicator, the more work that may be done for a certain quality of light. The term pKa is the negative logarithm of the acid dissociation constant and is represented by EQU K.sub.diss =[H.sup.+ ][A.sup.- ]/[HA] where H.sup.+ is the hydrogen ion concentration and A.sup.- is the concentration of the conjugate base. The pH change of the selected solutions is reversible, so that the pH returns to its former state as the light is turned OFF. Therefore, it is not always necessary to switch filters, i.e. radiate a different wavelength of light to change the pH to bring a fiber to its original condition. The use of filters may be preferred when the pH of the solution is at the null point pKa of the fiber to take advantage of the more extreme fiber excursions possible in this region as mentioned above. Activation with a single wavelength may be achieved, for example, if the pH of the saline solution is lightly buffered with common chemical buffering agents to be slightly either to the left or right of the null point of the chosen fiber. Typical chemical buffering agents that may be selected are acidic acid/acetate, phosphoric acid/phosphate and boric acid/borate. With these agents, the pH of the saline solution around the fiber may be set to any pH value between 4 and 10. After the buffering agent has been added to the saline solution, the pH-dependent dye is added. The appropriate dye is chosen to have a good absorption band in the selected pH region. The buffered-pH solution is irradiated with the right electromagnetic wavelength. The fiber responsibly changes volume (contracts or expands), as the case may be. At the end of this part of the cycle (contraction or expansion), a light barrier may be placed in the optical path between a light source and the solution to allow the fiber to return to its former state. Clearly, as it returns to its previous length, the activation light may be reintroduced in the manner described herein. A spring might be added to aid in the restoration of the system. Addition of chemical buffering agents assures that the pH of the solution can be custom-adjusted to suit the chosen fiber. In addition, a particular pH-indicator dye needs to have only one absorption band, e.g., a wavelength absorption band on the "driving" side of the fiber; the other side of a rotatable bracket, to be described below, can be opaque. As a consequence, the system may be inherently simpler. In view of the foregoing, it is well within the purview of the routineer to fabricate a solar operated pump for desalination by reverse osmosis. The "muscle" can be made to contract and expand autonomously using solar energy, thereby driving a pump for a reverse osmosis system. The beauty of such a system is that few mechanical parts are required. For instance, the muscle can be made to contract with yellow light and expand with blue light or to relax with no light. The reaction will be in a sufficient time frame to be effective. A plate, evenly divided in yellow and blue windows is placed between sunlight and the muscle. As the muscle contracts with the yellow light it pushes water through a one-way valve. The motion of the muscle also rotates the disc. At point of maximum contraction, the yellow window is replaced by the blue window, which now causes the muscle to expand. Water is now taken in, again through a one-way valve, until maximum expansion, at which point the filter is switched again, and the muscle begins to contract. The system that seems most suited would be PVA-PAA fiber which has a pH of approximately 5.3 with tetrabromo-m-cresol sulfonphthalein which has a pKa of 4.90. Referring now to FIG. 2 of the drawings, a representative operational embodiment may take the form of a solar operated pump 10 for desalination by reverse osmosis or to pump water to a solar distillation unit or to a solar heater, etc. The solar powered pump has an elongate cylinder 15 closed at opposite ends by a pair of caps 16 and 17. At least one clear window portion 18 is provided which is transparent to predetermined wavelengths of light or other suitable incident electromagnetic radiation. A piston 20, appropriately sized and sealed about its periphery, is fitted within cylinder 15 to permit axial, bidirectional longitudinal travel therein and to define a pair of internal chambers 15a and 15b. Optionally, the piston could be a flexible wall secured about its periphery to the inside of cylinder 15 and having a sufficient resiliency for a responsive flexure to effect the pumping action to be described. A pair of one-way valves 25 and 26 are provided on elongate cylinder 15 to assure the selective flow of a fluid, such as seawater for example, from an inlet duct 27 into internal chamber 15a and from internal chamber 15a to an outlet duct 28. A displacement of piston 20 to the right, for example, causes check valve 25 to close and check valve 26 to open to draw seawater from inlet duct 27 into chamber 15a. Displacement of piston 20 to the left closes check valve 26 and opens check valve 25 to force at least part of the seawater in chamber 15a through outlet duct 28. Typically, this pumping device may be used to feed seawater to a reverse osmosis unit, a solar heater or a wide variety of fluid utilization systems. On the right side of piston 20 internal chamber 15b is filled with an appropriate pH dependent dye 60, having an appropriate acid dissociation constant (pKa). A secondary cylinder 35 is located near elongate cylinder 15 and is hydraulically coupled to internal chamber 15b via a feeder duct 36. The feeder duct permits the exchange of the pH dependent dye to and from internal chamber 15b and secondary cylinder 35 through a passageway 36' that penetrates the wall of the elongate cylinder. A slave piston 37, appropriately sized and sealed about its periphery, is fitted within secondary cylinder 35 to permit axial, bidirectional longitudinal displacement therein. The axial, bidirectional longitudinal displacement of the slave piston is in response to ducted volumes of the pH dependent dye which pass through feeder duct 36 from internal chamber 15b as piston 20 is reciprocally displaced. An elongate push rod 38 from slave piston 37 is pinned 39' to slotted lever 39. The lever also is rotatably coupled via pin 39" to a disc 40 journaled in an appropriate support 41 that may be mounted on elongate cylinder 15. Longitudinal 18 displacement of the push rod effects a rotation of disc and a suitable beveled gear arrangement 45 translates the rotational motion of disc 40 into an orthogonally oriented rotary displacement of an interconnected plate or disc-shaped bracket 46. Slotted lever 39 is depicted in FIG. 2 to provide for a lost motion of the push rod so that a delayed rotation of the associated structure, to be described, will occur. This allows the push rod to turn the beveled gear arrangement and its associated disc-shaped bracket 46 principally at the top and the bottom of a stroke. Also, the push rod may have a cam-shape to impart a selective non-uniform or exponential displacement of the disk-shaped bracket. Such a displacement may be preferred to change the positioning of the filters to create a more gradual or to a more abrupt transition of the select wavelengths. Optionally, the disc is a gear directly coupled to a rack on the push rod via mating teeth to displace the bracket rotationally uniformly as the piston moves. Bracket 46 is configured to provide at least a pair of appropriately shaped windows 46a which may be a semicircular wedge-shape to provide a support for optical filters 50 and 51. The optical filters may be suitably colored plastic or glass, to assure that the electromagnetic radiation emitted from a source 55, such as the sun, is filtered to transmit at least the discrete wavelengths of electromagnetic radiation necessary to effect the desired pH changes in pH dependent dye solution 60 that fills internal chamber 15b. In the case of the Bromocresol Green pH dependent dye solution referred to above, optical filters 50 and 51 are a yellow filter and a blue filter, respectively, to cause the desired pH changes. The pH dependent dye solution fills the volume beneath window 18 to receive the appropriate electromagnetic radiation. Polyelectrolyte fibers or gel 65, such as polyvinyl alcohol-poly-acrylic acid (PVA-PAA), are immersed in pH dependent dye solution 60 to receive electromagnetic radiation through clear window 18 and are appropriately disposed or appropriately coupled by bonding or tying to transfer force to piston 20 and cap 15. The fibers may be simply tied with suitable knots to appropriate appendages provided on the piston and the wall, although other suitable means of affixing the fibers will be apparent to one skilled in the art to which this invention pertains. The electromagnetic radiation source may be the sun, although any other suitable light sources or electromagnetic radiation sources can be provided as appropriate in a given pH dependent dye solution or situation. The selective radiations from a host of laser sources can be drawn upon for appropriate actuation and powering of this inventive concept if a designer so elects. For example, a particular application may call for a more directed and/or selective actuation of fibers and gel such as by using appropriately disposed optical fibers to channel the radiation to more completely derive the benefits of this inventive concept. In either case when electromagnetic radiation from the source impinges on the filters, other light may be absorbed and a predetermined light passes through. In this example, the yellow filter and the blue filter in window 50 and 51 transform impinging sunlight into either yellow or blue light. When yellow filter 50 is interposed between source 55 and window 18, yellow light impinges on a pH dependent dye solution 60 and fiber 65 and the fiber appropriately contracts. This causes a displacement to the left of piston 20 and a drawing-in of seawater to chamber 15a. The pH dependent dye solution 60 is forced from chamber 15b and into secondary cylinder 35 via feeder duct 36 so that slave piston 37 pushes push rod 38 upward, away from cylinder 15. The upward motion of push rod 38 translates a force to disc 40 that rotates interconnected beveled gear arrangement 45. Beveled gear arrangement 45 responsively rotates bracket 46 which interposes blue filter 51 between light source 55 and window 18. Blue light passing through blue filter 51 impinges on pH dependent dye solution 60 to change its pH. This change in pH effects polyelectrolyte gel or fiber 65 to at least relax it to its original dimension. The change in pH could also effect an expansion or extension of fiber 65 and a consequent displacement of piston 20 to the left. The displacement closes check valve 26, opens check valve 25 and pumps seawater from chamber 15a to outlet duct 28 and to the reverse osmosis unit. The leftward displacement of piston 20 also draws-in pH-dependent dye solution 60 from secondary cylinder 35 to chamber 15b via duct 36. Slave piston 37 and push rod 38 are displaced downwardly, oppositely rotating disc 40. This opposite rotation of disc 40 causes bevel gear arrangement 45 to rotate bracket 46 appropriately and realign the yellow filter between light source 55 and clear window 18. Yellow light on the polyelectrolyte gel or fiber 60 causes a repeat of the cycle. Optionally, a tensile or compressive force spring 30 may be included to aid in a displacement of piston 20 one way or the other. Different polyelectrolyte gels or fibers may prove to be more efficient or workable when a suitable spring is utilized to displace piston 20. A different configuration in accordance with this inventive concept provides an additional polyelectrolyte gel or fiber which is immersed in a pH-dependent dye solution in internal chamber 15a and is connected between cap 16 and piston 20. A clear window portion would also be included on this other side of the piston 20 to pass the appropriate wavelengths of actuating electromagnetic radiation. When the electromagnetic radiations pass through the aligned filters, the polyelectrolyte gel or fiber on both sides of piston would expand and contract responsibly in an alternate fashion to additively transfer their tensile and pushing forces to piston 20. The piston could be connected to a push rod, not shown, that extends through cap 16 to displace a slidably sealed follower-piston that functions as a mover in a pump which operates in much the same manner as outlined above. Looking to FIG. 3, another embodiment of this inventive concept is as a fiber optic-controlled manipulator or claw 70 provided with a number of pinned articulated segments 71, 72, 73, 74, 75 and 76. Separate ones or discrete groups of fiber optic cables 77a, 77b, 77c, 77d and 77e are interwoven or otherwise disposed within a polymeric gel (the "muscle") contained in and secured at opposite ends to opposite parts of an inner wall of individual flexible sacs or pods 78a, 78b, 78c, 78d and 78e which are filled with an appropriate pH dependent dye solution. The pods are connected to adjacent pinned segments of the claw on the outside wall of individual flexible sacs or pods at a location at or near the opposite parts by suitable means, such as an adhesive. The necessary light radiation or other suitable electromagnetic radiation is provided by an appropriate source 80, such as lasers for example. The source emits the light or radiations of various wavelengths and intensities to the optical fibers as needed to affect the pH of the pH dependent dye solution. The optical fibers may have a configuration and, perhaps, changed surface properties to bend the radiations away from the core of the fiber at each pod to thereby direct and dissipate the radiations throughout each pod to substantially, uniformly effect the pH changes in the solution. A computer 90 or other suitable controller is suitably programmed by one skilled in the art to provide a desired switching sequence. This switching sequence selectably couples the radiations from source 80 to different ones of the optical fiber cables which transmit the radiations to discrete flexible pods. The selective coupling of the radiations to the pods gives a really fine muscular control and actuation of the claw. Looking to FIG. 4, this fine muscular control is attributed to the fact that the appropriate radiations transmitted to each pod by optical fibers or fiber optic cables 77' affect the pH dependent dye 60'. This causes the immersed polyelectrolyte fibers (or gel) 65' secured at opposite ends to the inner wall of a pod 68' to expand as shown by expanded pod 78' or contract as shown by a contracted pod 78" in FIG. 5. The internal volume of each pod stays, essentially, the same. Optionally, a feedback mechanism is associated with the computer by which the computer knows or provides an indication of exactly how much to change the energy and wavelengths of the radiations going through each optical fiber. This mechanism may be based on muscle force or size of the muscle, etc. using appropriate sensors 95, 95', (piezoelectric), attached to the pods or otherwise suitably located on the articulated segments. In addition, a visual observation could be relied upon to allow a manual command of the computer or light source for control purposes. Actuators of both great strength and tactile sensitivity are within the capabilities of this inventive concept to fabricate working robots or prosthetic devices. Having the aforedescribed examples in mind, a host of other manipulator and actuator applications will readily suggest themselves to one skilled in the art using the disclosed radiation powered fibers (gels) in the appropriate pH dependent dyes with beamed or optical fiber passed radiation. Therefore, the illustrative examples provided herein are not intended to be taken as limiting of this inventive concept. A variety of polyelectrolyte fibers, or when hydrated, polyelectrolyte gels may be chosen by one skilled in the art for selective light actuation and powering in accordance with this inventive concept. For example, this inventive concept can utilize all polyelectrolyte gels which respond to pH changes by significantly changing their volume. However, the greater the optical transmittance of the gel, the more likely that the incident radiant energy will be transmitted to changes of pH rather than heat. Typical polyelectrolyte fibers, or when hydrated, polyelectrolyte gels may be made from poly methacrylic acid, polymerized isopropylacrylamide, polyvinyl alcohol-polyacrylic acid (PVA-PAA), polyvinyl alcohol-polyacrylic acid-polyallylamine or protein polyelectrolytes (ex. collagen). U.S. Pat. No. 4,732,930 entitled "Reversible Discontinuous Volume Changes of Ionized Isopropylacrylamide Cells" by Toyoichi Tanaka et al. also identifies suitable gels. These typical polyelectrolyte fiber substances, (or gels), listed herein are for the purpose of demonstration only and are not to be construed as limiting. A number of pH dependent dyes may be chosen by one skilled in the art for selective light actuation and powering in accordance with this inventive concept. For example, this inventive concept can utilize dyes in solution which change pH for all portions of the practical pH range (1-13). The best dye is the one with an acid dissociation constant (pKa) which coincides with the null point of the polyelectrolyte fiber. The following pH indicators may be selected by one skilled in the art for appropriate pH dependent dye solutions in accordance with this inventive concept. ______________________________________ Name pH Range pKa Wavelength (nm) ______________________________________ Thymolsulfonphthalein 1.2-2.8 1.65 544-430 Tetrabromophenol- 3.0-4.6 4.10 436-592 sulfonphthalein (Bromocresol Green) Dimethylaminoazoben- 3.1-4.4 3.46 522-464 zene-p-sulfonate Tetrabromo-m-cresol- 3.8-5.4 4.90 444-617 sulfonphthalein Dimethylaminoazoben- 4.2-6.3 5.00 444-617 zene-o-carboxylic acid Dibromo-o-cresol- 5.2-6.8 6.40 433-591 sulfonphthalein Dibromothymolsulfo- 6.2-7.6 7.30 433-617 phthalein Phenolsulfon- 6.8-8.4 8.00 433-558 phthalein o-Cresolsulfon- 7.2-8.8 434-572 phthalein Thymolsul- 8.0-9.6 9.20 430-596 fonphthalein Di-p-dioxydiphenyl- 8.3-10.0 553 phthalide ______________________________________ These typical substances for the pH dependent dye solutions listed above are for the purpose of demonstration only and are not to be construed as limiting. A main advantage of this technique is that the actuating and powering electromagnetic radiation, such as light, changes the pH of the solution immediately and reversibly around the fiber. This causes every segment of the fiber to contract at substantially the same time. The need to add acid or base solutions is avoided and there are no delays due to the diffusion of hydrogen or hydroxide ion to the individual fiber sites. As an alternative to this inventive concept, an acid or base solution otherwise would have to be added to the fiber which is very slow and cumbersome. Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.
046876243	abstract	A liquid metal cooled fast breeder reactor which permits a closer installation of a fuel handling mechanism relative to an upper reactor core structure of the reactor. The fuel handling mechanism has a fuel handling body without a housing, and has a rotational driving device on a rotating plug of a shield plug device of a reactor vessel. The fuel handling mechanism has an aseismatic support extending outwardly from the upper reactor core structure. The fuel handling mechanism is supported, at its upper portion, by the rotational driving device, and secured, at its lower protion, by the aseismatic support.
	summary
044656530	abstract	A nuclear reactor of the type which uses liquid metal as primary and secondary coolants, and wherein the reactor vessel contains a core and a plurality of vertically extending cylindrical intermediate heat exchangers for carrying out heat exchange between the primary and secondary coolants; primary coolant circulation pumps disposed outside of the reactor vessel; a pipe for conducting to the circulation pump the primary coolant which has passed through the intermediate heat exchangers after leaving the core; and a pipe for guiding the primary coolant discharged from the circulation pump to the core through the reactor vessel.
	description	Embodiment 1 FIG. 1 schematically depicts a lithographic projection apparatus according to the invention. The apparatus comprises: a radiation system LA, Ex, IN, CO for supplying a projection beam PB of radiation (e.g. UV or EUV radiation); a first object table (mask table) MT provided with a mask holder for holding a mask MA (e.g. a reticle, see FIG. 1A), and connected to first positioning means for accurately positioning the mask with respect to item PL; a second object table (substrate table) WT provided with a substrate holder for holding a substrate W (e.g. a resist-coated silicon wafer, see FIG. 1B), and connected to second positioning means for accurately positioning the substrate with respect to item PL; a projection system (xe2x80x9clensxe2x80x9d) PL (e.g. a refractive or catadioptric system, a mirror group or an array of field deflectors) for imaging an irradiated portion of the mask MA onto a target portion C (die) of the substrate W. As here depicted, the apparatus is of a transmissive type (i.e. has a transmissive mask). However, in general, it may also be of a reflective type, for example. The radiation system comprises a source LA (e.g. a Hg lamp, excimer laser, an undulator provided around the path of an electron beam in a storage ring or synchrotron, or an electron or ion beam source) which produces a beam of radiation. This beam is passed along various optical components comprised in the illumination system,xe2x80x94e.g. beam shaping optics Ex, an integrator IN and a condenser COxe2x80x94so that the resultant beam PB is substantially collimated and uniformly intense throughout its cross-section. The beam PB subsequently intercepts the mask MA which is held in a mask holder on a mask table MT. Having passed through the mask MA, the beam PB passes through the lens PL, which focuses the beam PB onto a target area C of the substrate W. With the aid of the interferometric displacement and measuring means IF, the substrate table WT can be moved accurately, e.g. so as to position different target areas C in the path of the beam PB. Similarly, the first positioning means can be used to accurately position the mask MA with respect to the path of the beam PB, e.g. after mechanical retrieval of the mask MA from a mask library. In general, movement of the object tables MT, WT will be realized with the aid of a long stroke module (course positioning) and a short stroke module (fine positioning), which are not explicitly depicted in FIG. 1. The depicted apparatus can be used in two different modes: In step mode, the mask table MT is kept essentially stationary, and an entire mask image is projected in one go (i.e. a single xe2x80x9cflashxe2x80x9d) onto a target area C. The substrate table WT is then shifted in the x and/or y directions so that a different target area C can be irradiated by the beam PB; In scan mode, essentially the same scenario applies, except that a given target area C is not exposed in a single xe2x80x9cflashxe2x80x9d. Instead, the mask table MT is movable in a given direction (the so-called xe2x80x9cscan directionxe2x80x9d, e.g. the x direction) with a speed "ugr", so that the projection beam PB is caused to scan over a mask image; concurrently, the substrate table WT is simultaneously moved in the same or opposite direction at a speed V=M"ugr", in which M is the magnification of the lens PL (typically, M=xc2xc or ⅕). In this manner, a relatively large target area C can be exposed, without having to compromise on resolution. FIG. 2 illustrates the principle of the scanning illumination method of the present invention. As shown in FIG. 2A, which is a longitudinal cross-section of a mask sub-field (sub-pattern), a sub-field 1 is bounded at each end by struts 2 (the term xe2x80x9cstrutxe2x80x9d as here employed should be construed as referring to any opaque region of the mask). FIGS. 2B to 2F show the beam width along the length of the sub-field. The beam is initially relatively narrow (FIG. 2B) and grows (FIGS. 2C and 2D) in the scan direction 4 to reach its final width (FIG. 2E). As shown in FIG. 2F, the beam is then moved to scan the length of the sub-field, whilst maintaining its width. At the end of the sub-field, the process is reversed (not shown). According to the invention, the rate of growth (and decline) of the beam width and the beam intensity (current) are controlled to ensure that the exposure (dose) is constant along the length of the sub-field, as graphically shown in FIG. 2G. In some embodiments, the beam profile parallel to the scan direction may be trapezoidal rather than stepped. In this case, the present invention can be applied to give a total dose at the substrate which is also trapezoidal but with sloped portions much narrower than the beam width, which is acceptable. If a charged particle beam is used then, during the beam growth and reduction stages at the beginning and end of each sub-field, the projection system can dynamically compensate for the effect of the changing space charge as the beam current changes. If a sub-field is xe2x80x9celectronicallyxe2x80x9d scanned (i.e. the position of the beam is moved using adjustment of the optics) across its width as opposed to along its length, the invention can be used to achieve the same effects as described above. The control of beam width can be combined with beam-shaping control used to stitch sub-fields together. A practical implementation of the invention is illustrated schematically in FIG. 3. The source (or an image of the source) 10 emits an illumination beam 11 whose width is initially controlled by first shaping aperture 12. First shaping aperture 12 generates a rectangular (or square) beam. First condenser lens 13 projects a real image of the first shaping aperture 12 onto the plane of the second shaping aperture 14, as indicated by dashed lines 15. The aperture defined by the second shaping aperture 14 is also rectangular or square. The first condenser lens 13 is also embodied to project an image onto the pivot point of shaping deflector(s) 16 which controllably shifts the image of the first shaping aperture 12 relative to the second shaping aperture 14 whilst maintaining the beam cross-over (source image) on the optical axis 17. Second condenser lens 18 focuses the next beam cross-over into the focal plane of the third condenser lens 19 which images the shaped beam onto the reticle 20. Alignment deflectors 21 are provided in the focal plane of the third condenser lens 19 and control the position of the beam on the reticle. FIG. 4 shows how the shaping deflectors 16 control the beam width. When appropriately energized, the image of the first shaping aperture 12 is shifted so that it no longer coincides with the second shaping aperture 14. Thus part of the beam is blocked and the beam imaged on the reticle 20 is narrowed. At the same time the beam center is shifted, in this case to the right. FIG. 5 shows how the alignment deflectors 21 can be used to bring the beam center back onto optical axis 17: the beam is bent at the pivot point in the same manner as with the shaping deflectors. The shaping deflectors 16 and alignment deflectors 21 can thus be used to control the beam width and position at the reticle 20. It should be noted that FIGS. 3 to 5 omit the source optics and alignment mechanism and show the shaping and alignment deflectors in simplified form. Also, the total beam flux (current) can be controlled by moving the pivot point between the shaping apertures, by introducing an additional condenser lens, or by adjusting the source parameters. The projection system which projects an image of the reticle 20 onto the wafer is also omitted. The components of the illumination system have been described above in functional terms. Their actual physical embodiment will depend on the nature of the illumination beam. In a preferred embodiment of the invention, the illumination beam is an electron beam. In that case the source 10 comprises an electron gun and condenser optics, and the condenser lenses 13, 18 and 19, and deflectors 16 and 21, will comprise appropriate electric and/or magnetic field generators. The shaping apertures will comprise conductive plates. Appropriate components are known from shaped-beam electron beam writers, for example. If the illumination beam is an ion beam, or other charged particle beam, field polarities and strengths will need to be changed appropriately. For an electromagnetic, e.g. ultraviolet or X-ray, beam, appropriate refractive or glancing incidence reflective components can be used. Embodiment 2 FIG. 6 shows a portion of a strutted reticle and the scanning directions that may be used in embodiments of the invention. As shown, the reticle 30 comprises an array of elongate sub-fields 31 (e.g. of length 12 mm) separated by struts 32. The reticle is illuminated by, e.g., a square beam of 1xc3x971 mm2 size. The beam must illuminate each sub-field for a sufficient period to deliver a dose to expose the resist on the substrate wafer. By way of an example, if the resist sensitivity is 10 xcexcC/cm2, the beam current 10 xcexcA and the magnification xc2xc then the time required to expose each (sub-) field is 625 xcexcs. The scanning scheme adopted in the prior art is to scan across the widths of the twelve fields in the direction of arrow 33, stepping across the struts to avoid excessive heating, and then to mechanically scan the wafer and reticle along the lengths of the subfields, in the direction of arrow 34. These schemes may be modified by scanning in direction 33 at a high frequency while keeping the scan in the direction of arrow 34 at the same speed. This is advantageous in that the illumination at the wafer then appears to come from a 0.25xc3x973.0 mm2 (after demagnification at M=xc2xc) stripe rather than a 0.25xc3x970.25 mm2 square. This reduces the localized heating of the wafer. An alternative scanning scheme that the present invention makes possible is illustrated in FIG. 7. The reticle 30 is the same as that shown in FIG. 6. In the alternative scanning scheme of the present invention, the beam position is electronically controlled to scan the length of each sub-field 31 in the direction of arrow 35. Then, the reticle and wafer are (electronically and) mechanically stepped to the next sub-field as shown by arrow 36. The electronic scan frequency can be high so that each sub-field is scanned repeatedly before the reticle and wafer are stepped to the next subfield. Again, this is advantageous with regard to wafer heating. The scanning scheme described in the previous paragraph is advantageous in that it reduces the number of stitching operations required to piece together the full image. A stitching process is described in U.S. Pat. No. 5,260,151, and involves a pair of deflectors downstream of the mask arranged to deflect off-axis beams so that the shadow that would have been caused by a strut is eliminated. With the scanning scheme of FIG. 7, only twelve horizontal stitches are required for each scan in direction 36. In the previous scheme, the number of stitches equals the number of passes times the number of fields plus eleven times the number of passes for horizontal illumination stitches. Thus, the number of stitches rises rapidly with the frequency of the electronic scan. Embodiment 3 FIGS. 8A and 8B illustrate an alternative beam shape and scanning scheme that may be used with the present invention. FIG. 8A illustrates a part of a strutted mask which includes several rows (only two shown) of elongate sub-fields 41 which are projected onto a die 45 on the substrate. The illumination beam 42, which may be hexagonal in shape, is electronically scanned along the length of a sub-field 41, as indicated by arrows 43. At the beginning of the scan, the width of the beam is in a reduced state in the direction parallel to the scan direction (arrows 43) only. As in the other embodiments of the invention, the beam is expanded to its normal width whilst adjacent to one end of the sub-field, before being scanned to the other end of the sub-field, where the process is reversed. As shown in FIG. 8B, the electronic scan of the mask sub-field 41 prints an effective field 46 in the die 45 on the substrate. The mask and substrate are then mechanically scanned in the direction of arrows 44, 47 to print the adjacent sub-field. At the end of a row of sub-fields, the mask and substrate are stepped in the direction perpendicular to the mechanical scan 44, 47 and the mechanical scan direction is reversed, as indicated by arrow 48 to print the next row of sub-fields. This method, whereby within one die the mask and substrate are scanned and then stepped, may be referred to as xe2x80x9cScan and Stepxe2x80x9d in distinction to xe2x80x9cStep and Scanxe2x80x9d techniques in which the mask and substrate are mechanically stepped between sub-fields and are mechanically scanned. The xe2x80x9cScan and Stepxe2x80x9d method enables a die of 25xc3x9725 mm2 to be built up using an effective beam size, at substrate level, of 0.25xc3x970.25 mm2, for example. Whilst we have described above specific embodiments of the invention it will be appreciated that the invention may be practiced otherwise than described. The description is not intended to limit the invention.
042773105	description	DETAILED DESCRIPTION OF THE INVENTION Having reference to the above drawings, FIG. 1 shows a portion of the cylindrical wall 1 of the pressure vessel of a pressurized-water reactor. The portion shown includes the inlet nozzle 2 to which the cold leg pipe 3 is connected by welding 3a. As previously described, this cold leg pipe is part of one of the reactor's main coolant systems, the pipe 3 returning pressurized-water coolant to the pressure vessel, under the force of the main coolant pump, the core heat having been substantially removed from the coolant by its passage through the usual steam generator which received the coolant from the pressure vessel by way of its coolant outlet nozzle and the hot pipe leg of the main coolant loop. Other than for the portion of the cold leg pipe 3, the details just referred to are not illustrated because they are conventionally included as part of any pressurized-water reactor installation. In the present instance, the conventional construction of the pressure vessel is modified to the extent that an annular ring 4 is welded to the inside of the pressure vessel wall around the inner end of the nozzle 2, the inner periphery of this ring being flared as at 4a to provide to some extent streamlining for the incoming flow of pressurized coolant delivered by the cold leg pipe 3. The usual core barrel 5, in a lower portion of which the core (not shown) is mounted, forms the annular space 5a down through which the coolant flows for ultimate upwardly travel within the interior of the core barrel and out from the pressure vessel wall by way of the hot leg pipe nozzle (not shown). The space 5a is separated from the space above the upper portion of the core barrel by being sealed by the flange mounting of the core barrel as previously described, FIG. 1 showing the beginning of this flange at 5b. The axial thickness of the ring 4 is such that its inner face is approximately flush to the cylindrical inside 1a of the pressure vessel extending above the nozzle 2. During servicing of the reactor, it may be desirable to remove the core barrel 5 upwardly, the inside diameter of the surface 1a defining the clearance area above the nozzle 2, through which the core barrel must travel for its removal. In the example of the check valve 6 shown by FIGS. 1 through 4, an annular frame 7 of somewhat larger inside diameter than that of the nozzle 2, mounts the multiplicity of individually swinging flap valves 8, each comprising a plate of rectangular contour supported on a pivot pin 9, the frame 7 being of rectangular x-section and the pivot pins 9 being all mutually parallel with each other and with the axis 12 of the annular frame 7. As shown by FIG. 2, the annular frame 7 provides a large number of radial flow paths which are each provided with one of the flat valves 8, the paths being formed by eight relatively thick radial baffles 14 each having screw holes 15, two thinner guide surfaces or vanes 16 being interposed between each two of the thicker baffles or vanes 14. On their sides facing the swinging ends of the flap valves, the veins or guide elements 14 and 16 each provide a shoulder 17 on which the flap valves can seat when in their closed positions, the opening positions of the flap valves being limited by each being provided with a post 18 proportioned to hold the flap valves from swinging into alignment with the coolant flow indicated by the arrows 10. The flap valves are held diagonally against the coolant flows by the posts or stops 18, the angularity being such that during the normal flow 10, the dynamic force of the flows holds the flap valves rigidly open against chattering. The flap valve angularity need not be great, an example being indicated at X in FIG. 2. The thicker radial vanes 14 provide the annular frame with rigidity in its axial direction and provides for mounting the frame on the core barrel 5, the holes 15 receiving cap screws 15a passed through suitable holes formed in the core barrel. This barrel is, of course, cylindrical, and the frame of the check valve 6 forms a cylindrical segment fitting the side of the core barrel 5. The axial thickness of the frame is dimensioned so that when the core barrel is removed, the check valve can clear the surface 1a previously referred to. During the normal coolant flow shown by the arrows 10, all of the flap valves are held rigidly open by the force of the coolant flow. In the event the pressure drops, as for example there being a break in the weld connection 3a, the flow reverses as indicated by the broken line arrow in FIG. 1. Should this occur, the slight angularities of the flap valves provide surfaces for the reverse flow to cause the flap valve to snap shut substantially immediately. This simplicity and reliability of such flap valves should assure that they all snap shut, but should one or more fail, the multiplicity of valves provided assures that the majority will close so that coolant discharge from the vessel is largely prevented. As shown in FIG. 3a, the check valve 6 can be positioned concentrically with respect to the nozzle 2. However, during the normal operation of the reactor, the coolant flow is downwardly through the annular space 5a. Therefore, to decrease the flow resistance offered by the new check valve, it may be positioned eccentrically with respect to the nozzle 2, as shown by FIG. 3b, and in such a case the annular frame can be elongated in the manner of an oval or its equivalent, thus putting the majority of the flap valves and their radial passages in positions where they pass the downward coolant flow to a major extent. The total flow cross-sectional area is the sum of the areas of the radial passages which are, in turn, determined by the areas of the flap valves 8, and the total cross-sectional flow area of the check valve should substantially equal the cross-sectional area of the nozzle's inside. It is easy to design the construction shown by FIG. 2, to provide it with a total flow passage area substantially equaling that of the nozzle 2. FIG. 4 shows the cylindrically segmental shape of the check valve and it and FIG. 1 both show that although the annular welded ring 4 comes close to sealing the check valve against leakage around the outside of its frame, a small space is left as required to accommodate thermal expansion and contraction movements. FIG. 5 shows that the pivot pins of the flap valves can be mounted in bushings 17, while in broken lines, the cross-sectional contour of the flap valves is represented. It can be seen that the valve plate is thicker in the area of the pivot pin, the plate having a generally streamlined contour, it being possible to make each of the flap valves in the form of a casting or forging, including all of its parts including the post 18. In the example of the invention shown by FIGS. 1 through 4, a separate individual check valve is required for each of the cold leg nozzles of the pressure vessel. However, in the example of FIG. 6, the check valve 6, although composed of substantially the same parts previously described, is made in the form of a large annular ring which completely surrounds or encircles the core barrel 5 at a position slightly below the nozzle 2. Instead of the annular welded ring 4, shown by FIG. 1, a horizontally positioned annular ring 20 is welded to the vessel wall 1 so as to be engaged by the outside of the annular frame 7. This provides the seal preventing bypassing of the flow around the check valve construction, the flow through the check valve in this case being in the axial direction. The spacing between the valve's frame and the ring 20, in this case, also should allow for thermal expansion and contraction, but the dimensions may be chosen so that under the operating conditions of the reactor, the frame 7 engages the ring 20 and thereby braces the core barrel 5 both structurally and to assure maintenance of the proper concentricity of the barrel 5 relative to the pressure vessel's wall. As shown by FIG. 7, the normal coolant flow 10 is axial and downwardly, in this case, normally holding the diagonally positioned flap valves 8 rigidly open and free from chattering, while, at the same time, positioning the flap valves diagonally with respect to an accidentally reversing flow, assuring closing of the flap valves. Substantially the same concept is shown by FIG. 8 as is shown by FIG. 6, excepting that in the interest of economy, the flap valves 8 are, in this case, mounted by brackets 21 fixed to the core barrel 5 by screws 22. In this case, a small ring 20' is welded to the inside of the vessel's wall 1, FIG. 9 showing that the flap valves 8 can be very closely interspaced so that when closed, there can be little leakage between the various flap valves. A check valve enjoying the reliability and protection of the flap valves can even be positioned in the inner end of the nozzle 2. One example is shown by FIG. 10 where the construction is built into the nozzle's inner end. The flat valves 8, in this case, are made like louvers as can be seen from FIG. 11, the horizontally elongated plates forming the flap valves being symmetrically distributed on either side of the horizontal center line 30 of the nozzle. The individual plate area of each of the flap valves may be made large enough to offer little impedance to the normal coolant flow. FIG. 12 shows how a check valve construction similar to that shown by FIG. 1 can be reduced in diameter while still providing an adequate normal flow capacity. This is done by making the frame 7 axially thicker such as would normally prevent withdrawal of the core barrel because the check valve would have a greater thickness than that existing between the surface 1a and the outside of the core barrel, shown by FIG. 1. To permit withdrawal of the core barrel, a cover 23 which positions the check valve, is removably installed in a cutout 24 formed in the core barrel opposite to the inlet end of the nozzle 2. The cover is secured releasably by a lever 26 which bears on a projection 28 holding the cover with the check valve clamped in position. By releasing a pressure screw 27, the lever 26 can be swung to permit removal of the cover 23 and of the check valve 6 inwardly through the core barrel, thus permitting removal of the core barrel even though the check valve is of substantial thickness in its axial direction. Obviously a check valve of any kind cannot be used effectively in connection with the pressure vessel's outlet, or hot leg, nozzle or nozzles, because the normal flow is in that direction. However, a break in the hot leg does not immediately stop the coolant flow which is normally flowing in the same direction. On the other hand, a break in the cold leg results in the coolant discharging reversely from the pressure vessel, and can possibly result in at least momentary immediate emptying of the vessel and possible endangerment of the core.
	abstract	The present invention relates to targets, systems and methods for the cyclotron production of 124I from aluminum telluride (Al2Te3) targets. The systems and methods utilize low energy proton cyclotrons to produce 124I by the 124Te(p,n) reaction from enriched Al2Te3 glassy melts. The 124I is recovered in high yield from the glassy melt by adapted methods of common thermal distillation techniques.
046408126	claims	1. A transportable test simulator for a nuclear power plant, the nuclear power plant including a control panel, a reactor having a plurality of actuated rods for moving into and out of a reactor for causing said plant to operate, and a control rod network extending between said control panel and said reactor rods, said network serially transmitting command words between said panel and rods, said network further having connecting interfaces at preselected points remote from said control panel between said control panel and rods, said test simulator comprising: a test simulator input for transport to and connection into said network at at least one said interface for receiving said serial command words from said network, each said serial command including an identifier portion and a command portion; means for processing interior of said simulator for said serial command words for identifying that portion of said power plant designated in said identifier portion and processing said word responsive to the command portion of said word after said identification; means for generating a response word responsive to said command portion; and output means for sending and transmitting said response word to said nuclear power plant at said interface whereby said control panel responds to said response word. providing a transportable test simulator having inputs and outputs for connection into said network at said interfaces; transporting said test simulator to one of said interfaces; unplugging said interface to deactivate the command path between said control panel and reactor; connecting said simulator interstitially within said interface; processing interior of said simulator of said command words between said rods and control panel, said processing including the steps of identifying that portion of said power plant designated in said identifier portion and responding to the command portion of said word after said identification; generating a response word interior of said simulator responsive to said command portion; and outputting said command word at said interface whereby said control panel responds to said response word. 2. The transportable test simulator of claim 1 wherein said means for processing further includes means for generating an acknowledged word responsive to said identifier portion and said output means further includes means for sending and transmitting said acknowledged word to said nuclear power plant at said interface whereby said control panel responds to the acknowledgement of said identifier portion. 3. The transportable test simulator of claim 1 wherein said response word to said command word comprises an erroneous plant output and wherein said means for processing interior of said simulator includes means for generating a response word which is an erroneous output. 4. The transportable test simulator of claim 1 further including at least a portion of a display on said test simulator for indicating visually to an operator at said test simulator at least a portion of either said command word, or said response word, and wherein said means for processing interior of said simulator includes means for generating said visual display responsive to said command word or said response word. 5. A process for testing a nuclear power plant with a test simulator wherein the nuclear power plant includes a control panel, a reactor having a plurality of actuated rods for moving in and out of a reactor for causing said plant to operate, and a control rod network extending between said control panel and said reactor rods, said network serially transmitting command words between said panel and rods each said serial command including an identifier portion and a command portion, said network including a plurality of connection interfaces at preselected points remote from said control panel within said network, the process of testing said nuclear power plant comprising the steps of: 6. The nuclear power plant testing process of claim 5 wherein said processing interior of said simulator of said command words further includes the steps of generating an acknowledge word responsive to said identifier portion and outputting said acknowledged word at said interface whereby said control panel responds to the acknowledgement of said identifier portion. 7. The nuclear power plant testing process of claim 5 wherein said processing interior of said simulator of said command words includes the step of generating a response word which is an erroneous output. 8. The nuclear power plant testing process of claim 5 wherein the first step therein further includes providing a transportable test simulator having a display for indicating visually to an operator at said test simulator at least a portion of either said command word or said response word and wherein said processing interior of said simulator of said command words further including the steps of generating said visual display responsive to said command or response word and wherein said testing process further includes the step of visually monitoring at said simulator at least a portion of either said command word, or said response word.
	abstract	The invention refers to an X-ray beam device for X-ray analytical applications, comprising an X-ray source designed such as to emit a divergent beam of X-rays; and an optical assembly designed such as to focus said beam onto a focal spot, wherein said optical assembly comprises a first reflecting optical element, a monochromator device and a second reflecting optical element sequentially arranged between said source and said focal spot, wherein said first optical element is designed such as to collimate said beam in two dimensions towards said monochromator device, and wherein said second optical element is designed such as to focus the beam coming from said monochromator device in two dimensions onto said focal spot.
	claims	1. A collimating system for collimating radiation received under different angles for performing tomography, the collimating system comprising:a static collimator including a plurality of collimating apertures, and shutters for selectively and temporarily shutting at least two of said collimating apertures;wherein the shutters have a shutting element for closing said at least two collimating apertures;wherein the collimating system further comprises at least one collimating element distinct from the shutting element for collimating radiation passing through non-shut collimating apertures in a direction so as to prevent overlap between radiation stemming from different non-shut collimating apertures. 2. The collimating system according to claim 1, wherein the static collimator is at least partially ring-shaped and wherein the plurality of collimating apertures is positioned on a same collimator ring. 3. The collimating system according to claim 1, wherein the at least one collimating element is part of one of the shutters. 4. The collimating system according to claim 3, wherein the one of the shutters has a shutting element for shutting a predetermined collimating aperture and the at least one collimating element is shaped for controlling collimation of radiation passing through a collimating aperture neighboring the predetermined collimating aperture. 5. The collimating system according to claim 3, wherein the at least one collimating element comprises a slanted surface of the one of the shutters. 6. The collimating system according to claim 1, wherein the at least one collimating element is part of an additional collimator configured with respect to the static collimator for controlling overlap between radiation stemming from different non-shut collimating apertures. 7. The collimating system according to claim 1, wherein the collimating system comprises a controller programmed for controlling the shutters for opening the collimating apertures in a predetermined manner. 8. The collimating system according to claim 7, wherein the controller is programmed for controlling the shutting elements and the corresponding at least one collimating element to move simultaneously. 9. The collimating system according to claim 7, wherein the controller is programmed for controlling at least a subset of the shutters individually. 10. The collimating according to claim 7, wherein the controller is programmed for alternatingly and temporarily opening the shutting elements for collimating apertures. 11. The collimating system according to claim 7, wherein the controller is programmed for alternatingly and temporarily opening the shutting elements for a subset of collimating apertures such that over a predetermined time period, all collimating apertures have been un-shut. 12. The collimating system according to claim 1, wherein the collimator is ring shaped and for use with a ring shaped detector and wherein the number of apertures fulfills the following equation: number ⁢ ⁢ of ⁢ ⁢ apertures > π acos ⁡ ( R FOV R d ) - a ⁢ ⁢ cos ⁡ ( R FOV R c ) wherein Rd is the radius of the detector, Rc is the radius of the static collimator and RFOV is the transaxional field-of-view radius. 13. An imaging system comprising a detector, a collimating system according to claim 1, and a correlator for correlating signals detected using the detector with collimated apertures un-shut at the moment of detection. 14. The collimating system according to claim 1, wherein the shutting element is formed from a radiation-blocking material, and the at least one collimating element extends from the shutting element at an angle transverse to the shutting element. 15. The collimating system according to claim 1, wherein the shutting elements arranged between the at least one collimating element and the static collimator. 16. The collimating system according to claim 1, wherein the at least one collimating element is coupled to the shutting element. 17. The collimating system according to claim 1, wherein the static collimator, at least one collimating element, and the shutting elements are arranged concentrically, and the at least one collimating element is arranged between the static collimator and the shutting elements. 18. A method for imaging an object, the method comprising the steps of:selectively and temporarily shutting at least two of a plurality of collimating apertures of a static collimator using shutters having a shutting element for closing said at least two collimating apertures, thereby alternatingly and temporarily opening shutting elements for collimating apertures or subsets of collimating apertures;detecting the radiation transmitted through non-shut collimating apertures;correlating the detected radiation with the non-shut collimator apertures during the detecting;deriving therefrom information of the object of interest, andusing collimating elements for collimating radiation passing through the non-shut collimating apertures in a direction so as to prevent overlap between radiation stemming from different non-shut collimating apertures. 19. The method according to claim 18, wherein the step of selectively and temporarily shutting comprises shutting the shutting element having a thickness of at least 0.5 mm over its shutting area for blocking radiation stemming from the object of interest passing through the collimating apertures. 20. A collimating system for collimating radiation received under different angles for performing tomography, the collimating system comprising:a static collimator defining a plurality of collimating apertures;a plurality of shutters, each of the shutters configured to selectively and temporarily shut at least two of said collimating apertures, each of the shutters including a shutting element that blocks said at least two collimating apertures; andat least one collimating element that collimates radiation that passes through non-blocked collimating apertures in a direction that prevents overlap between radiation stemming from different non-shut collimating apertures,wherein the static collimator is provided on a first side of the shutting element and the at least one collimating element is provided on a second side of the shutting element, the first side of the shutting element being opposite from the second side of the shutting element.
045434883	claims	1. An exchangeable basket element for a container for transporting and/or storing spent nuclear fuel elements comprising: a plurality of steel tubes of substantially uniform cross-sectional dimensions throughout their length defining compartments shaped for the reception of spent nuclear fuel elements, said tubes being arranged in a spaced-apart and generally parallel relationship to one another; steel plate means provided at least at each end of said basket element for laterally connecting together said tubes so as to define, together with said steel tubes, an integral steel framework; and a casting of a non-ferrous metallic meterial having high heat conductivity wherein said framework is embedded along its length while leaving at least one end of said tubes open so that fuel elements can be inserted into and withdrawn from said tubes. a plurality of integral steel tubes having top and bottom ends and a substantially uniform cross-section throughout their length thereby defining compartments shaped for the reception of spent nuclear fuel elements, said tubes being arranged in a spaced-apart generally parallel relationship; steel plate means provided at least at each end of said basket element for laterally connecting said tubes together and for maintaining said spaced-apart relationships thereof and to define, together with said tubes, an integral steel framework; a casting of a non-ferrous metallic material, having high heat conductivity, in which said integral steel framework is embedded along its length while leaving the top and bottom ends of said tubes open so that fuel elements can be inserted into and withdrawn from said tubes, and aligning means provided on said basket element for aligning the basket element within the container and with other similar basket elements therein. 2. The basket as claimed in claim 1 wherein the casting material is aluminum. 3. The basket as claimed in claim 1 wherein the casting material is copper. 4. The basket as claimed in claim 1 wherein the casting material is an alloy of aluminum. 5. The basket as claimed in claim 1 wherein the casting material is an alloy of copper. 6. The basket as claimed in claim 1 wherein the casting material includes a neutron absorber. 7. The basket as claimed in claim 6 wherein the neutron absorber is boron. 8. The basket as claimed in claim 6 wherein the neutron absorber is a boron carbide. 9. The basket as claimed in claim 6 wherein the neutron absorber is present in the form of plates embedded in the casting between the tubes. 10. The basket as claimed in claim 1 wherein the connecting means comprise steel plates having apertures in which the steel tubes are received. 11. The basket as claimed in claim 10 wherein the steel plates are shaped to support and center the basket at the inner wall of the container. 12. An exchangeable basket element for use in a container for transporting and/or storing spent nuclear fuel elements comprising:
	abstract	The invention comprises an apparatus and method of use thereof for extracting ions from an ion source, such as for use in cancer treatment or tomographic imaging. The extraction apparatus uses a triode extraction system, with the ion source and/or first electrode held at a first potential; an extraction electrode held at a second potential; and a gating electrode, positioned between the ion source and the extraction electrode, oscillating and/or alternating between a first suppression potential proximate that of the ion source potential and a second extraction potential between the ion source potential and the extraction electrode potential. Optionally, the ion source comprises an electron cyclotron resonance ion source.
	claims	1. An apparatus that acts as a shield for radiopharmaceuticals and protects from radioactivity comprising: a) a first body with a first hollow core that is open on a first edge and a second edge of said first body, said first hollow core for housing a hypodermic syringe; b) a second body with a second hollow core that is open on a first edge of said second body, said second hollow core for housing said hypodermic syringe; c) a third body with a third hollow core that is open on a first edge of said third body, said third hollow core for housing said hypodermic syringe; d) said hypodermic syringe capable of containing a radiopharmaceutical; e) a first connection means wherein said first body releasably communicates with said second body for providing protection from radioactivity emitted by the radiopharmaceutical; f) a second connection means wherein said first body releasably communicates with said third body for providing protection from said radioactivity; g) a does applicator for slidably positioning said hypodermic syringe into and out of said first and third body when said body is removed; and h) a latch for releasably securing said dose applicator in said third body. 2. The apparatus of claim 1 wherein said second body further comprises a means for compressing said hypodermic syringe to eject said radiopharmaceutical from the hypodermic syringe while said first body is in communication with said second body. claim 1 3. An apparatus that acts as a shield for radiopharmaceuticals and protects individuals from radioactivity comprising: a) a first body with a first hollow core that is open on a first edge and a second edge of said first body, said first hollow core for housing a hypodermic syringe; b) a second body with a second hollow core that is open on a first edge of said second body, said second hollow core for housing said hypodermic syringe; c) a third body with a third hollow core that is open on a first edge of said third body, said third hollow core for housing said hypodermic syringe; d) said hypodermic syringe capable of containing a radiopharmaceutical; e) a first connection means wherein said first body releasably communicates with said second body for providing protection from radioactivity emitted by the radiopharmaceutical; f) a second connection means wherein said first body releasably communicates with said third body for providing protection from said radioactivity; g) said third body further comprising means for extending said hypodermic syringe from said first and third bodies to permit measurement of said radiopharmaceutical in said hypodermic syringe and providing protection from said radioactivity; h) wherein said means for extending said hypodermic syringe further comprises means to selectively secure said hypodermic syringe in said third body. 4. The apparatus of claim 3 wherein said second body further comprising means for compressing said hypodermic syringe to eject said radiopharmaceutical from the hypodermic syringe while said first body is in communication with said second body. claim 3 5. The apparatus of claim 3 wherein said means for extending said hypodermic syringe comprises a telescoping rod that slidably communicates with said third body""s second edge, said telescoping rod further comprising: claim 3 means at its first end for releasably securing said hypodermic syringe; a nut at said telescoping rod""s second end for grasping said telescoping rod; a circumferential groove proximate said telescoping rod""s first end; and wherein said means to selectively secure said hypodermic syringe in said third body comprises a yoke for selectively engaging said circumferential groove, said yoke comprising a spring arm and a release arm, wherein said spring arm communicates with a spring for urging said yoke into contact with said telescoping rod and wherein a first end of said release arm extends through a release arm channel formed in said third body, for selectively disengaging said yoke from said circumferential groove. 6. An apparatus that acts as a shield for radiopharmaceuticals and protects individuals from radioactivity comprising: a) a first body with a first hollow core that is open on a first edge of said first body and partially open on a second edge of said first body, said first hollow core for housing a hypodermic syringe with a radiopharmaceutical; b) a second body with a second hollow core that is open on a first edge and closed on a second edge of said first body, said first hollow core for housing said hypodermic syringe; c) a first connection means wherein said first body""s first edge releasably communicates with said second body""s first edge for providing protection from said radioactivity; d) a dose applicator that is extendible and that slidably communicates with said first body""s second edge, for slidably positioning said hypodermic syringe into and out of said first body when said second body is removed; and e) a latch for releasably securing said dose applicator in said first body.
045171548	abstract	A self-test system for a nuclear power plant, nuclear reactor protection system is disclosed. Nuclear protection systems are the electronic controls, typically including circuit cards, located intermediate between sensors (as for detecting core overheat) and a control (as for providing rod injection to shut down a reactor). Constant surveillance of the nuclear system protection system is provided by a microprocessor that serially addresses protection system circuit cards and loads them at pre-determined input points with test commands. The addressed cards are thereafter simultaneously activated by a system-wide command. The test command is a pulse which is so short in duration that its affect is transparent to the system and cannot cause overall system operation. The pulse passes through the actuating electrical components to verify, on the real actuating path, the operating integrity of the system. After an appropriate response interval, the output state of the system is recorded in system-wide resident registers. Thereafter, with response data contained in these registers frozen at the recorded state, the output is read. This result is compared with the expected output in computer memory. If correspondence between memory output and register output is found, the next sequential set of test commands is acted upon. If correspondence is not found, a subroutine search is automatically conducted to locate the error. The disclosed self-test subsystem is duplicated in four separate divisions with each division testing one of the four duplicate protection systems. The three remaining and idle divisions constantly monitor the active subsystem's operation. The end result is an overall system which reduces the mean time to discover error, thus minimizing mean time to repair and maximizing protection system availability and safety. The separation of the protection system into four duplicate divisions is not dependent on the disclosed invention and the invention may be applied to protection systems with a different number of divisions.
046438718	abstract	The invention relates to a standby or emergency cooling device for the core of a pressurized water reactor.. A high pressure reservoir filled with boric acid solution is permanently connected to the reactor vessel via two pipes, preferably arriving at the same level. However, one of these pipes is extended within the vessel by a downwardly directed bend in order to issue below the other pipe. These two pipes have horizontal portions which are intended to prevent any natural circulation under normal operating conditions.. Application to the improvement of the safety of pressurized water nuclear reactors.
050900374	claims	1. A method of acquiring tomographic projection data of an imaged object comprising: supporting and translating the imaged object concurrently along a translation axis; projecting a beam of x-rays from an x-ray generator through the imaged object and alternately sweeping the beam along the translation axis in a first direction with translation of the imaged object during a first period, and in a second direction along the translation axis but counter to the translation of the imaged object during a second period; receiving the beam from the x-ray generator with an x-ray detector array after it passes through the imaged object; and holding the x-ray generator and x-ray detector in opposition around the imaged body and concurrently rotating the same around a center of rotation and the imaged object, in an gantry plane substantially perpendicular to the translation axis. a fixed x-ray source; and a collimator having an aperture movable along the translation axis. C.sub.z is the distance along the translation axis between the center of the collimator and the gantry plane; l.sub.1 is the distance between the x-ray source and the collimator; and l.sub.2 is the distance between the collimator and the translation axis. V.sub.z is the distance along the translation axis between the predetermined volume element and the gantry plane; C.sub.z is the distance along the translation axis between the center of the collimator and the gantry plane; .alpha. is the angle, with respect to the center of rotation, between the volume of interest and gantry angle .theta.=O; .DELTA. is the distance between the volume of interest and the center of gantry rotation; l.sub.1 is the distance between the x-ray source and the collimator; and l.sub.2 is the distance between the collimator and the translation axis. F.sub.z is the distance along the translation axis between x-ray source and the gantry plane; C.sub.z is the distance along the translation axis between the center of the collimator and the gantry plane; l.sub.1 is the distance between the x-ray source and the collimator; l.sub.2 is the distance between the collimator and the translation axis; and l.sub.3 is the distance between the translation axis and the x-ray detector. and where .theta. is the gantry angle; .alpha. is the angle, with respect to the center of rotation, between the volume of interest and gantry angle .theta.=O; .DELTA. is the distance between the volume of interest and the center of gantry rotation; V.sub.z is the distance along the translation axis between the predetermined volume element and the gantry plane; F.sub.z is the distance along the translation axis between x-ray source and the gantry plane; C.sub.z is the distance along the translation axis between the center of the collimator and the gantry plane; l.sub.1 is the distance between the x-ray source and the collimator; l.sub.2 is the distance between the collimator and the translation axis; and l.sub.3 is the distance between the translation axis and the x-ray detector. where V.sub.z is the distance along the translation axis between the predetermined volume element and the gantry plane; F.sub.z is the distance along the translation axis between x-ray source and the gantry plane; and C.sub.z is the distance along the translation axis between the center of the collimator and the gantry plane. V.sub.z is the distance along the translation axis between the predetermined volume element and the gantry plane; l.sub.1 is the distance between the x-ray source and the collimator; and l.sub.2 is the distance between the collimator and the translation axis. and where .theta. is the gantry angle; .alpha. is the angle, with respect to the center of rotation, between the volume of interest and gantry angle .theta.=O; .DELTA. is the distance between the volume of interest and the center of gantry rotation; F.sub.z is the distance along the translation axis between x-ray source and the gantry plane; V.sub.z is the distance along the translation axis between the predetermined volume element and the gantry plane; l.sub.1 is the distance between the x-ray source and the collimator; and l.sub.2 is the distance between the collimator and the translation axis. 2. The method as recited in claim 1 wherein the x-ray exposure of the imaged object by the x-ray beam during the first period is greater than the x-ray exposure of the imaged object by the x-ray beam during the second period. 3. The method as recited in claim 2 wherein the intensity of the x-ray beam is reduced during the second period. 4. The method as recited in claim 1 wherein the sweeping of the x-ray beam during the first period is such as to maintain the beam centered on a predetermined volume element on the translation axis. 5. The method recited in claim 4 wherein the x-ray generator comprises: 6. The method recited in claim 5 wherein the aperture of the collimator is controlled according to the following equation: ##EQU5## where V.sub.z is the distance along the translation axis between the predetermined volume element and the gantry plane; 7. The method recited in claim 5 wherein the aperture of the collimator is controlled according to the following equation gantry angle .theta. as follows: ##EQU6## where EQU l.sub.2 '=l.sub. -cos(.theta.+.alpha.) (.DELTA.) 8. The method recited in claim 4 wherein the x-ray generator comprises an x-ray source having a focal point movable along the translation axis and collimator having a aperture movable along the translation axis. 9. The method recited in claim 8 wherein the focal point and aperture of the collimator are controlled according to the following equations: ##EQU7## where V.sub.z is the distance along the translation axis between the predetermined volume element and the gantry plane; 10. The method recited in claim 8 wherein the focal point and the aperture of the collimator are controlled according to the following equations: ##EQU8## where EQU l.sub.2 '=l.sub.2 -cos(74 +.alpha.) (.DELTA.) EQU l.sub.3 '=l.sub.3 +cos(.theta.+.alpha.) (.DELTA.) 11. The method recited in claim 8 wherein the focal point and the aperture of the collimator are controlled according to the following equation: EQU F.sub.z =C.sub.z =V.sub.z 12. The method recited in claim 4 wherein the x-ray generator comprises an x-ray source having a focal point movable along translation axis and a fixed collimator aperture. 13. The method recited in claim 12 wherein the focal point is controlled according to the following equation: ##EQU9## where F.sub.z is the distance along the translation axis between x-ray source and the gantry plane; 14. The method recited in claim 10 wherein the focal point is controlled according to the following equation: ##EQU10## where EQU l.sub.2 '=l.sub.2 -cos(.theta.+.alpha.) (.DELTA.)
	summary
	abstract	A device and a method in processing, such as pharmaceutical processing, is provided. At least one signal is transmitted in a processing structure which is adapted to receive materials. The propagated signal is received and a parameter value thereof is compared with a reference value. The presence of materials or any other geometrical change in the processing structure is evaluated based on the comparison. The signal may be in the form of an electromagnetic wave, e.g. a microwave. Also, a use of a processing vessel, or a pipe connected to such a vessel, is provided.
	summary
052271277	abstract	A filtered venting system located in association with a reactor containment vessel installed in a reactor building comprises a filter device disposed in the reactor building and including filter means, a first venting line disposed on an upstream side of the filter device and having one end connected to the reactor containment vessel and another end connected to the filter device, a stand-by gas treatment system including outlet fan means or pump means and connected to the first venting line at the downstream side of the fan or pump means, and a second venting line disposed at a downstream side of the filter device and another end connected to an outlet means/ The filter device being utilized for the stand-by gas treatment system for treating and removing a radioactive substance contained in an atmosphere delivered from the reactor containment vessel.
	summary
	claims	1. A method comprising:installing a CRDM in a nuclear reactor by operations including:attaching the CRDM to a top plate of a standoff and connecting a mineral insulated cable between the CRDM and an electrical connector disposed in or on a bottom plate of the standoff to form a CRDM/standoff assembly; andmounting the bottom plate of the CRDM/standoff assembly to a distribution plate wherein the mounting connects an electrical power line disposed on or in the distribution plate with the electrical connector disposed in or on the bottom plate of the standoff. 2. The method of claim 1 wherein the mounting includes:lowering the CRDM/standoff assembly onto the distribution plate until the bottom plate of the standoff engages a connection site of the distribution plate; andsecuring the bottom plate engaged with the connection site of the distribution plate using a plurality of fasteners;wherein the electrical power line disposed on or in the distribution plate is connected with the electrical connector disposed in or on the bottom plate of the standoff by one or both of (1) the weight of the CRDM/standoff assembly and (2) tension provided by the secured fasteners. 3. The method of claim 1 wherein the installing further comprises:after the mounting, purging water from the connection between the electrical power line disposed on or in the distribution plate and the electrical connector disposed in or on the bottom plate of the standoff. 4. The method of claim 1, further comprising:removing the installed CRDM from the nuclear reactor by operations including:dismounting the bottom plate of the CRDM/standoff assembly from the distribution plate wherein the dismounting disconnects the electrical power line disposed on or in the distribution plate from the electrical connector disposed in or on the bottom plate of the standoff.
	claims	1. A fuel rod support insert for connecting to interlaced straps of a nuclear fuel assembly spacer grid, the interlaced straps defining a lattice of cells for receiving fuel rods, the fuel rod support insert comprising:a first end portion and a second end portion, the first end portion and the second end portion configured for abutting the straps, the fuel rod support insert extending axially along an insert axis between first end portion and the second end portion, the fuel rod support insert being configured such that the insert axis is positioned parallel to a center axis of at least one of the cells when the fuel rod support insert is connected to the straps; andat least one spring extending axially with respect to the insert axis between the first and second end portions, the at least one spring being defined in part by at least one slot extending axially with respect to the insert axis, the at least one spring being configured for transversely abutting a fuel rod when the fuel rod support insert is connected to the straps, the fuel rod support insert being configured for extending in at least one of the cells when the fuel rod support insert is connected to the straps, the spring extending axially through planes perpendicular to the insert axis and radially away from the first end portion and the second end portion to define an apex configured for contacting the fuel rod when the fuel rod is inserted into one of the cells, the spring having a non-rectilinear cross-section in each of the planes perpendicular to the insert axis,wherein the spring comprises a contact wing and a lateral wing adjacent to each other and extending side-by-side along the insert axis, the contact wing and the lateral wing each including an inner surface facing the straps and an outer surface facing away from the straps, the outer surfaces of the contact wing and the lateral wing being inclined relative to each other, the contact wing being configured for contacting the fuel rod and the lateral wing extending laterally from the contact wing towards one of the straps. 2. The fuel rod support insert as recited in claim 1 wherein the outer surface of the lateral wing is flat. 3. The fuel rod support insert as recited in claim 1 wherein the outer surface of the contact is convex. 4. The fuel rod support insert as recited in claim 1 wherein the lateral wing extends along a length thereof between the first end portion and the second end portion axially with respect to the insert axis, the lateral wing extending along a width thereof between a first longitudinally extending edge and second longitudinally extending edge laterally with respect to the insert axis, the width of the lateral wing varying along the length thereof. 5. The fuel rod support insert as recited in claim 1 wherein the contact wing extends along a length thereof between the first end portion and the second end portion axially with respect to the insert axis, the contact wing extending along a width thereof between a first longitudinally extending edge and second longitudinally extending edge laterally with respect to the insert axis, the width of the contact wing substantially constant along the length thereof. 6. The fuel rod support insert as recited in claim 1 wherein the contact wing extends along a length thereof between the first end portion and the second end portion axially with respect to the insert axis, the contact wing being arched away from the insert axis along the length. 7. The fuel rod support insert as recited in claim 1 further comprising one contact wall, a first connection wall and a second connection wall, the first and second connection walls being connected by the contact wall, the at least one spring including a first spring and a second spring, the first spring being formed by the one contact wall and the first connection wall, the second spring being formed by the one contact wall and the second connection wall. 8. The fuel rod support insert as recited in claim 1 further comprising at least two walls extending longitudinally between the first end portion and the second end portion, the at least two walls inclined one relative to the other when viewed along the insert axis, the at least two walls including a contact wall and a first connection wall adjacent to the contact wall, the spring being at a junction between the contact wall and the adjacent connection wall with the contact wing formed by the contact wall and the lateral wing formed by the adjacent connection wall. 9. The fuel rod support insert as recited in claim 8 wherein the at least one spring includes a first spring and a second spring, the at least two walls including a second connection wall adjacent to the contact wall such that the contact walls is laterally between the first connection wall and the second connection wall with respect to the insert axis, the first spring having a first contact wing formed by the contact wall and first lateral wing formed by the first connection wall, the second spring having a second contact wing formed by the contact wall and a second lateral wing formed by the second connection wall. 10. The fuel rod support insert as recited in claim 1 wherein the insert is tubular and includes a plurality of walls defining a polygonal cross-section, the at least one spring including a pair of springs located at each corner of the polygonal cross-section. 11. The fuel rod support insert as recited in claim 1 wherein the at least one spring includes a pair of springs defined by three slots each having a length extending axially with respect to the insert axis, the three slots including one central slot and two lateral slots, the length of the one central slot being greater than the length of each of the two lateral slots. 12. The fuel rod support insert as recited in claim 11 wherein the central slot has a width decreasing from axial ends of the central slot towards a middle of the central slot. 13. A spacer grid for a nuclear fuel assembly, the spacer grid comprising:interlaced straps defining a lattice of cells for receiving fuel rods; andsupport inserts provided at intersections of the straps for supporting the fuel rods which extend through the cells, the support inserts each comprising:a first end portion and a second end portion, the first end portion and the second end portion configured for abutting the straps, the fuel rod support insert extending axially along an insert axis between first end portion and the second end portion, the fuel rod support insert being configured such that the insert axis is positioned parallel to a center axis of at least one of the cells when the fuel rod support insert is connected to the straps; andat least one spring extending axially with respect to the insert axis between the first and second end portions, the at least one spring being defined in part by at least one slot extending axially with respect to the insert axis, the at least one spring being configured for transversely abutting a fuel rod when the fuel rod support insert is connected to the straps, the fuel rod support insert being configured for extending in at least one of the cells when the fuel rod support insert is connected to the straps, the spring extending axially through planes perpendicular to the insert axis and radially away from the first end portion and the second end portion to define an apex configured for contacting the fuel rod when the fuel rod is inserted into one of the cells, the spring having a non-rectilinear cross-section in each of the planes perpendicular to the insert axis,wherein the spring comprises a contact wing and a lateral wing adjacent to each other and extending side-by-side along the insert axis, the contact wing and the lateral wing each including an inner surface facing the straps and an outer surface facing away from the straps, the outer surfaces of the contact wing and the lateral wing being inclined relative to each other, the contact wing being configured for contacting the fuel rod and the lateral wing extending laterally from the contact wing towards one of the straps. 14. The spacer grid as recited in claim 13 wherein connection walls of each of the support inserts are inserted in connection slots provided on lower edges of the interlaced straps. 15. The spacer grid as recited in claim 13 wherein each of the inserts is secured to the straps by spot-welds. 16. A nuclear fuel assembly comprising:a bundle of fuel rods; andan armature for supporting the fuel rods, the armature comprising at least one spacer grid for a nuclear fuel assembly, the spacer grid comprising:interlaced straps defining a lattice of cells for receiving fuel rods; andsupport inserts provided at intersections of the straps for supporting the fuel rods which extend through the cells, the support inserts each comprising:a first end portion and a second end portion, the first end portion and the second end portion configured for abutting the straps, the fuel rod support insert extending axially along an insert axis between first end portion and the second end portion, the fuel rod support insert being configured such that the insert axis is positioned parallel to a center axis of at least one of the cells when the fuel rod support insert is connected to the straps; andat least one spring extending axially with respect to the insert axis between the first and second end portions, the at least one spring being defined in part by at least one slot extending axially with respect to the insert axis, the at least one spring being configured for transversely abutting a fuel rod when the fuel rod support insert is connected to the straps, the fuel rod support insert being configured for extending in at least one of the cells when the fuel rod support insert is connected to the straps, the spring extending axially through planes perpendicular to the insert axis and radially away from the first end portion and the second end portion to define an apex configured for contacting the fuel rod when the fuel rod is inserted into one of the cells, the spring having a non-rectilinear cross-section in each of the planes perpendicular to the insert axis,wherein the spring comprises a contact wing and a lateral wing adjacent to each other and extending side-by-side along the insert axis, the contact wing and the lateral wing each including an inner surface facing the straps and an outer surface facing away from the straps, the outer surfaces of the contact wing and the lateral wing being inclined relative to each other, the contact wing being configured for contacting the fuel rod and the lateral wing extending laterally from the contact wing towards one of the straps. 17. The nuclear fuel assembly as recited in claim 16 further comprising at least one intermediate mixing grid comprising interlaced straps provided with mixing vanes and defining a lattice of cells for receiving the fuel rods, the support inserts being tubular and each being provided around the intersection of two of the straps of the mixing grid for preventing contact between the fuel rods extending through the cells and the mixing vanes. 18. The nuclear fuel assembly as recited in claim 17 wherein the support inserts are secured to the straps of the mixing grid by at least one spot weld.
	summary
	claims	1. Apparatus for providing X-ray energy to irradiate a product comprising:a) an elongated X-ray tube providing X-ray energy;b) a wheel structure having a defined axis of rotation being mounted to rotate about said X-ray tube;c) a plurality of containers for receiving the product to be irradiated mounted equidistant from said axis and in spaced relation to each other on said wheel structure;d) cradles for said containers being mounted to said wheel structure by mounting elements be swingable and have free rotation about the mounting elements with said mounting elements being offset from the center of said cradles thereby allowing said cradles to utilize gravity to maintain an initial horizontal orientation as said cradles are moved in a circle around said X-ray tube by said wheel structure; ande) said elongated X-ray tube being mounted in relatively an offset axial position with reference to the axis of rotation of said wheel structure;f) said tube as mounted, allowing the distance between said tube and said containers to remain relatively uniform throughout the rotation of said containers,whereby as the wheel structure is rotated, the energy provided by said X-ray tube uniformly irradiates the product contained in each of said containers.
	summary
	abstract	Embodiments in accordance with the invention provide respectively for auto-focus, auto-contrast, and auto-correction of astigmatism in both x and y directions, are independent of focus-induced-image-rotation, sample feature orientation and image deformation, and focus-induced-image magnification change, and are insensitive to various kinds of noise. Poor image contrast is handled by an auto-contrast capability. Embodiments in accordance with the invention can achieve high reliability and repeatability, while providing for faster operation than most prior-art methods.
	description	This application claims priority to currently U.S. Provisional Patent Application No. 61/492,258 filed Jun. 1, 2011 and 61/537,988 filed Sep. 22, 2011, which are hereby incorporated by reference as if fully set forth herein. N/A The invention relates to a suction strainer for use on suction lines. More particularly, the invention relates to a suction strainer for use in an emergency core cooling system of a nuclear power plant. All nuclear power plants have some form of emergency core cooling system (ECCS) in the event that normal operation is lost and a major break occurs in the reactor cooling system. There are two phases to most ECCS—The injection phase when the pumps suction water from a large tank and pump that water into the reactor cooling system or reactor, and the recirculation phase when the pumps take water from the containment sump after all of the water has been pumped into the containment. An ECCS has one major function and that is to provide makeup water to cool the reactor in the event of a loss of coolant from the reactor cooling system. This cooling is needed to remove the decay heat still in the reactor's fuel after the reactor is shutdown. ECCS in some plants may have a second major function and that is to provide chemicals to the reactor and reactor cooling system to ensure the reactor does not produce power. The major components of an ECCS are water supplies (tanks), pumps, interconnecting piping, high pressure pumps, low pressure pumps, water storage tanks, accumulators, and a containment sump used to circulate the water through the reactor once the storage tanks are empty. In a nuclear reactor, a suction strainer is located in the containment area and its purpose is to keep loose materials and debris, such as insulation, from getting to the suction of the ECCS pumps during the recirculation phase. The pumps perform an important and vital function at nuclear power plants. Again, a purpose of the strainers is to protect the downstream components, such as pumps and nuclear fuel assemblies, from being adversely affected by such debris. Suction strainers, by their nature, have a tendency to build up debris layers. In use, as water is circulated through the strainer, solid debris builds on the outer surfaces of the strainer. The recirculation continues until the ECCS is no longer needed in cold shutdown. Structural considerations, hydrodynamic loading, and space constraints limit the size and shape of suction strainers in nuclear containment buildings. One existing suction strainer design utilizes nested tubes which are produced from a perforated metal sheet. Ends of the sheet are butted together and welded to form a tube. In the nuclear power industry welding is highly regulated. It is, therefore, advantageous to reduce or eliminate welding in any nuclear application. The present invention is provided to solve the problems discussed above and other problems, and to provide advantages and aspects not provided by prior strainers of this type. A full discussion of the features and advantages of the present invention is deferred to the following detailed description, which proceeds with reference to the accompanying drawings. One aspect of the present invention is directed to a high capacity suction strainer for an emergency core cooling system in a nuclear power plant. The high capacity suction strainer comprises a frame, a flow-through plenum, and a filter array. The flow-through plenum is mechanically mounted to the frame and comprises a plurality of inlets and an outlet. The filter array is also mechanically mounted to the frame and comprises a plurality of filter groupings. Each filter grouping is in fluid communication with a corresponding inlet on the plenum. This aspect of the present invention may include one or more of the following a additional features, alone or in any reasonable combination. Each filter grouping may comprise a plurality of nested tubes. Each nested tube may comprise an inner perforated tube disposed within a corresponding outer perforated tube such that an interstitial space is created between the inner and outer perforated tubes. The nested tubes may be arranged in a plurality of columns and rows and extend outwardly from the plenum such that each nested tube has a nested tube outlet forming a fluid communication between each interstitial space and an inlet on the plenum. Each filter grouping may comprise a flow-through top plate. Each filter grouping may comprise a flow-through bottom plate. Each filter grouping may comprise a plurality of top grates located at a proximal end of the nested tubes. Each flow-through top plate may comprise a plurality of top grates located at a proximal end of the nested tubes. Each flow-through bottom plate may comprise a plurality of bottom grates located at a distal end of the nested tubes. The plurality of top grates may comprise a first top grate comprising a plurality of first apertures corresponding in size and shape to the outer circumference of each outer perforated tube wherein a proximal end of each outer perforated tube is inserted within and supported by a corresponding first aperture and a plurality of second apertures located between and about the first apertures to allow a fluid flow therethrough. The plurality of top grates may comprise a second top grate comprising a plurality of first apertures aligned with the first apertures in the first top grate, each having a smaller cross-sectional area than an opening at the proximal end of the outer perforated tube such that the interstitial space between the inner and outer tubes is at least substantially sealed against a surface of the second grate and such that a proximal end of each inner perforated tube is inserted within and supported by a corresponding first aperture, and a plurality of second apertures aligned with the second apertures on the first top grate and located between and about the first apertures to allow a fluid flow therethrough. The plurality of top grates may comprise a third top grate comprising a plurality of first apertures aligned with the first apertures in the second top grate, each having a smaller cross-sectional area than an opening at the proximal end of the inner perforated tube such that the proximal end of the inner perforated tube abuts a surface of the third top grate forming the nested tube inlet, and a plurality of second apertures aligned with the second apertures on the second top grate and located between and about the first apertures to allow a fluid flow therethrough. The plurality of bottom grates may comprise a first bottom grate comprising a plurality of first apertures corresponding in size and shape to the outer circumference of each outer perforated tube wherein a distal end of each outer perforated tube is inserted within and supported by a corresponding first aperture. The plurality of bottom grates may further comprise a second bottom grate comprising a plurality of first apertures, each aligned with a corresponding interstitial space between an inner perforated tube and an outer perforated tube, a plurality of second apertures, each aligned with an opening at a distal end of a corresponding inner perforated tube forming the nested tube outlet aligned with an inlet on the plenum, a central webbing about each second aperture substantially sealing the opening at the distal end of the corresponding inner perforated tube, and a plurality of mechanical fasteners, each fastener passing through a corresponding second aperture and engaging the distal end of the corresponding inner perforated tube to maintain the corresponding inner perforated tube in a desired position in the nested tube. The first top grate and the third top grate may sandwich the second top grate therebetween such that surfaces of the first top grate and the third top grate engage opposite surfaces of the second top grate. The first top grate, the second top grate, and the third top grate may be mechanically attached to the frame. The first bottom grate and a surface of the plenum may sandwich the second bottom grate therebetween such that surfaces of the first bottom grate and the plenum engage opposite surfaces of the second bottom grate. The first bottom grate and the second bottom grate may be mechanically attached to the frame. Each top plate may be mechanically joined to a corresponding bottom plate by a tie rod and each top plate may be separated from the corresponding bottom plate by the plurality of nested tubes. Each top plate may be mechanically joined to a corresponding bottom plate by a pair of cross members joined to the top plate by a mechanical fastener and to the corresponding bottom plate at an opposing end by a mechanical fastener. Each filter grouping maybe attached to the flow-through plenum by a mechanical fastener. Each top plate may be mechanically joined to a corresponding bottom plate by a tie rod and each top plate may be separated from the corresponding bottom plate by the plurality of nested tubes. The interstitial spaces between the inner perforated tubes and the outer perforated tubes may be adapted to receive a filtered fluid flow as a contaminated fluid passes from outer surfaces to inner surfaces of the outer perforated tubes and from inner surfaces to outer surfaces of the inner perforated tubes. The bottom plates may be adapted to act as outlets feeding a filtered fluid to the inlets on the flow-through plenum. The nested tubes may be oriented between 0 degrees and 90 degrees relative to an upper surface of a fluid in a containment area. The nested tubes may be substantially vertically oriented relative to an upper surface of a fluid in a containment area. The nested tubes are substantially horizontally oriented relative to an upper surface of a fluid in a containment area. Another aspect of the present invention is directed to a high capacity suction strainer for an emergency core cooling system in a nuclear power plant. The high capacity suction strainer comprises a frame, a flow-through plenum, and a filter array. The flow-through plenum is mounted to the frame and comprises a plurality of inlets and an outlet. A filter array is also mounted to the frame and comprises a plurality of filter groupings. Each filter grouping has a plurality of nested tubes. Each nested tube comprises a cylindrical inner perforated tube formed from a metal sheet having complimentary mechanically formed seaming members formed along opposing edge portions wherein the cylindrical inner perforated tube is formed by interlocking the complimentary mechanically formed seaming members to form a mechanical seam. The cylindrical inner perforated tube is disposed within a corresponding cylindrical outer perforated tube such that an interstitial space is created between the inner and outer perforated tubes. The cylindrical outer perforated tube is also formed from a metal sheet having complimentary mechanically formed seaming members formed along opposing edge portions wherein the cylindrical outer perforated tube is formed by interlocking the complimentary mechanically formed seaming members to form a mechanical seam. This aspect may include one or more of the following features, alone or in any reasonable combination. The mechanical seam of the cylindrical inner perforated tube may form a helical structure winding about a longitudinal length of the cylindrical inner perforated tube. The mechanical seam of the cylindrical outer perforated tube may form a helical structure winding about a longitudinal length of the cylindrical outer perforated tube. The nested tubes are arranged in a plurality of columns and rows and extend outwardly from the plenum such that each nested tube has a nested tube outlet forming a fluid communication between each interstitial space and an inlet on the flow-through plenum. The high capacity suction strainer may further comprise a flow-through top plate comprising a plurality of top grates and a flow-through bottom plate comprising a plurality of bottom grate located opposite the plurality of top grates relative to the nested tubes. The plurality of top grates may comprise a first top grate comprising a plurality of first apertures corresponding in size and shape to the outer circumference of each cylindrical outer perforated tube wherein a proximal end of each cylindrical outer perforated tube is inserted within and supported by a corresponding first aperture and a plurality of second apertures located between and about the first apertures to allow a fluid flow therethrough. The plurality of top grates may comprise a second top grate comprising a plurality of first apertures aligned with the first apertures in the first top grate, each having a smaller cross-sectional area than an opening at the proximal end of the cylindrical outer perforated tube such that the interstitial space between the inner and outer tubes is at least substantially sealed against a surface of the second grate and such that a proximal end of each cylindrical inner perforated tube is inserted within and supported by a corresponding first aperture, and a plurality of second apertures aligned with the second apertures on the first top grate and located between and about the first apertures to allow a fluid flow therethrough. The plurality of top grates may comprise a third top grate comprising a plurality of first apertures aligned with the first apertures in the second top grate, each having a smaller cross-sectional area than an opening at the proximal end of the cylindrical inner perforated tube such that the proximal end of the cylindrical inner perforated tube abuts a surface of the third top grate forming the nested tube inlet, and a plurality of second apertures aligned with the second apertures on the second top grate and located between and about the first apertures to allow a fluid flow therethrough. The first top grate and the third top grate may sandwich the second top grate therebetween such that surfaces of the first top grate and the third top grate engage opposite surfaces of the second top grate. The first top grate, the second top grate, and the third top grate may be mechanically attached to the frame. The plurality of bottom grates may comprise a first bottom grate comprising a plurality of first apertures corresponding in size and shape to the outer circumference of each cylindrical outer perforated tube wherein a distal end of each cylindrical outer perforated tube is inserted within and supported by a corresponding first aperture. The plurality of bottom grates may comprise a second bottom grate comprising a plurality of first apertures, each aligned with a corresponding interstitial space between a cylindrical inner perforated tube and a cylindrical outer perforated tube, a plurality of second apertures, each aligned with an opening at a distal end of a corresponding cylindrical inner perforated tube forming the nested tube outlet aligned with an inlet on the plenum, a central webbing about each second aperture substantially sealing the opening at the distal end of the corresponding cylindrical inner perforated tube, and a plurality of mechanical fasteners, each fastener passing through a corresponding second aperture and engaging the distal end of the corresponding cylindrical inner perforated tube to maintain the corresponding cylindrical inner perforated tube in a desired position in the nested tube. The first bottom grate and a surface of the plenum may sandwich the second bottom grate therebetween such that surfaces of the first bottom grate and the plenum engage opposite surfaces of the second bottom grate. The first bottom grate and the second bottom grate may be mechanically attached to the frame. Another aspect of the present invention is directed to a high capacity suction strainer for an emergency core cooling system in a nuclear power plant. This suction strainer comprises a flow-through plenum comprising an inlet and an outlet and a filter array. The filter array comprises a plurality of nested tubes, each comprising an inner perforated tube disposed within a corresponding outer perforated tube such that an interstitial space is created between the inner and outer perforated tubes, the inner and outer tubes comprising a radially extending slot adjacent to a radially extending segment of the inner and outer tubes wherein the radially extending slot and the radially extending segment extend in an identical radial direction relative to a center axis of the inner and outer tubes. Another aspect of the present invention is directed to a high capacity suction strainer for an emergency core cooling system in a nuclear power plant. This suction strainer comprises a flow-through plenum comprising an inlet and an outlet and a filter array. The filter array comprises a plurality of nested tubes, each comprising an inner perforated tube disposed within a corresponding outer perforated tube such that an interstitial space is created between the inner and outer perforated tubes, the inner and outer tubes comprising a helical mechanically-formed seam extending a length of each tube. Another aspect of the present invention is directed to a high capacity suction strainer for an emergency core cooling system in a nuclear power plant. This suction strainer comprises a flow-through plenum comprising an inlet and an outlet and a filter array. The filter array comprises a plurality of nested tubes. Each comprises an inner perforated tube disposed within a corresponding outer perforated tube such that an interstitial space is created between the inner and outer perforated tubes. The inner and outer tubes comprise a plurality of radially extending slots adjacent to a corresponding plurality of radially extending segments of the inner and outer tubes. The plurality of radially extending slots form a first helical pattern having a first orientation about a surface of the inner and outer tubes and a second helical pattern having a second orientation opposite the first orientation about the surface of the inner and outer tubes. Another aspect of the present invention is directed to a high capacity suction strainer for an emergency core cooling system in a nuclear power plant. This suction strainer comprises a flow-through plenum comprising an inlet and an outlet and a filter array. The filter array comprises a plurality of nested tubes. Each comprises an inner perforated tube disposed within a corresponding outer perforated tube such that an interstitial space is created between the inner and outer perforated tubes. The inner and outer tubes comprise a radially extending slot adjacent to a radially extending segment of the inner and outer tubes wherein the radially extending slot and the radially extending segment extend in an identical radial direction relative to a center axis of the inner and outer tubes. The previous four aspects of the present invention may include one or more of the following features, alone or in any reasonable combination. The nested tubes may be arranged in a plurality of columns and rows and extend outwardly from the plenum such that each nested tube has a nested tube outlet forming a fluid communication between each interstitial space and an inlet on the plenum wherein the filter array forms a filter grouping and the high capacity suction strainer comprises a plurality of filter groupings. Each filter grouping may comprise a flow-through top plate. Each filter grouping may comprise a flow-through bottom plate. Each filter grouping may comprise a plurality of top grates located at a proximal end of the nested tubes. Each flow-through top plate may comprise a plurality of top grates located at a proximal end of the nested tubes. Each flow-through bottom plate may comprise a plurality of bottom grates located at a distal end of the nested tubes. The plurality of top grates may comprise a first top grate comprising a plurality of first apertures corresponding in size and shape to the outer circumference of each outer perforated tube wherein a proximal end of each outer perforated tube is inserted within and supported by a corresponding first aperture and a plurality of second apertures located between and about the first apertures to allow a fluid flow therethrough. The plurality of top grates may comprise a second top grate comprising a plurality of first apertures aligned with the first apertures in the first top grate, each having a smaller cross-sectional area than an opening at the proximal end of the outer perforated tube such that the interstitial space between the inner and outer tubes is at least substantially sealed against a surface of the second grate and such that a proximal end of each inner perforated tube is inserted within and supported by a corresponding first aperture, and a plurality of second apertures aligned with the second apertures on the first top grate and located between and about the first apertures to allow a fluid flow therethrough. The plurality of top grates may comprise a third top grate comprising a plurality of first apertures aligned with the first apertures in the second top grate, each having a smaller cross-sectional area than an opening at the proximal end of the inner perforated tube such that the proximal end of the inner perforated tube abuts a surface of the third top grate forming the nested tube inlet, and a plurality of second apertures aligned with the second apertures on the second top grate and located between and about the first apertures to allow a fluid flow therethrough. The plurality of bottom grates may comprise a first bottom grate comprising a plurality of first apertures corresponding in size and shape to the outer circumference of each outer perforated tube wherein a distal end of each outer perforated tube is inserted within and supported by a corresponding first aperture. The plurality of bottom grates may comprise a second bottom grate comprising a plurality of first apertures, each aligned with a corresponding interstitial space between an inner perforated tube and an outer perforated tube, a plurality of second apertures, each aligned with an opening at a distal end of a corresponding inner perforated tube forming the nested tube outlet aligned with an inlet on the plenum, a central webbing about each second aperture substantially sealing the opening at the distal end of the corresponding inner perforated tube, and a plurality of mechanical fasteners, each fastener passing through a corresponding second aperture and engaging the distal end of the corresponding inner perforated tube to maintain the corresponding inner perforated tube in a desired position in the nested tube. The first top grate and the third top grate may sandwich the second top grate therebetween such that surfaces of the first top grate and the third top grate engage opposite surfaces of the second top grate. The first top grate, the second top grate, and the third top grate may be mechanically attached to the frame. The first bottom grate and a surface of the plenum may sandwich the second bottom grate therebetween such that surfaces of the first bottom grate and the plenum engage opposite surfaces of the second bottom grate. The first bottom grate and the second bottom grate may be mechanically attached to the frame. Each top plate may be mechanically joined to a corresponding bottom plate by a tie rod and each top plate may be separated from the corresponding bottom plate by the plurality of nested tubes. Each top plate may be mechanically joined to a corresponding bottom plate by a pair of cross members joined to the top plate by a mechanical fastener and to the corresponding bottom plate at an opposing end by a mechanical fastener. Each filter grouping may be attached to the flow-through plenum by a mechanical fastener. Each top plate may be mechanically joined to a corresponding bottom plate by a tie rod and each top plate may be separated from the corresponding bottom plate by the plurality of nested tubes. The interstitial spaces between the inner perforated tubes and the outer perforated tubes may be adapted to receive a filtered fluid flow as a contaminated fluid passes from outer surfaces to inner surfaces of the outer perforated tubes and from inner surfaces to outer surfaces of the inner perforated tubes. The bottom plates may be adapted to act as outlets feeding a filtered fluid to the inlets on the flow-through plenum. Another aspect of the present invention is directed to a high capacity suction strainer for an emergency core cooling system in a nuclear power plant as shown and described. Another aspect of the present invention is directed to a filter array for a high capacity suction strainer for an emergency core cooling system in a nuclear power plant as shown and described. Another aspect of the present invention is directed to a filter grouping for a high capacity suction strainer for an emergency core cooling system in a nuclear power plant as shown and described. While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated. An embodiment of the present invention will now be described in which, at least: Reference number 1 is a template plate; Reference number 2 is a bottom grate; Reference number 3 is a bottom grate; Reference number 4 is an aperture in the second bottom grate for receiving a fastener and a centering means; Reference number 5 is an outer perforated conduit; Reference number 6 is an inner perforated conduit; Reference number 7 is a first top grate; Reference number 8 is a second top grate; Reference number 9 is a third top grate; and Reference number 10 is a reinforcement cross member of a frame. Referring to the figures, a high capacity suction strainer 100 for an emergency core cooling system (ECCS) in a nuclear power plant comprises a frame 104, a flow-through plenum 108, and a filter array 112. In order to increase filter surface area within a given cube volume, filter tubes 5,6 are nested tubes inside the one another with alternating “dirty” water and “clean” water flow paths. The strainer of the present invention may be used with pressurized water reactors, boiling water reactors, or generally any nuclear power plant system comprising an ECCS. The invention also absolutely minimizes (if not entirely eliminates) welding using, instead, mechanical fasteners. Thus, it is very economical to produce and very easy to assemble. The flow-through plenum 108 is mechanically mounted to the frame and comprises a plurality of inlets 116 located on a template plate 1 and an outlet 120. The plenum 108 is generally an enclosed housing. The filter array 112 is also mechanically mounted to the frame 104 and comprises a plurality of filter groupings 124, each in fluid communication with an inlet 116 on the plenum 108. The filter groupings 124 are attached to the flow-through plenum 108 by a mechanical fastener. Each filter grouping 124 comprises a plurality of nested tubes 128. Each nested tube 128 has an inner perforated tube 6 disposed within a corresponding outer perforated tube 5 such that an interstitial space 132 is created between the inner and outer perforated tubes 6,5. The nested tubes 128 are arranged in a plurality of columns and rows and extend outwardly from the plenum 108 such that each nested tube 128 has an outlet forming a fluid communication between each interstitial space 132 and an inlet 116 on the plenum 108. Each filter grouping 124 also has a flow-through to top plate 136. Each top plate 136 has a plurality of top grates 7,8,9 at a proximal end of the nested tubes 128. A first top grate 7 has a plurality of first apertures 140 corresponding in size and shape to the outer circumference of each outer perforated tube 5 wherein a proximal end of each outer perforated tube is inserted within and supported by a corresponding first aperture 140. One or more second apertures 144 are located between and about the first apertures 140 to allow a fluid flow therethrough. A second top grate 8 has a plurality of first apertures 148 aligned with the first apertures 140 in the first top grate 8. Each such aperture 148 has a smaller cross-sectional area than an opening at the proximal end of the outer perforated tube 5 such that the interstitial space 132 between the inner and outer tubes 6,5 is at least substantially sealed against a surface of the second grate 8 and such that a proximal end of each inner perforated tube 6 is inserted within and supported by a corresponding first aperture 148. One or more second apertures 152 are aligned with the second apertures 144 on the first top grate 7 and located between and about the first apertures 148 to allow a fluid flow therethrough. A third top grate 9 has a plurality of first apertures 156 aligned with the first apertures 148 in the second top grate 8. Each such aperture 156 has a smaller cross-sectional area than an opening at the proximal end of the inner perforated tube 6 such that the proximal end of the inner perforated tube 6 abuts a surface of the third top grate 9 forming the nested tube inlet. One or more second apertures 160 are aligned with the second apertures 152 on the second top grate 8 and located between and about the first apertures 156 to allow a fluid flow therethrough. The first top grate 7 and the third top grate 9 sandwich the second top grate 8 therebetween. Surfaces of the first top grate 7 and the third top grate 9 engage opposite surfaces of the second top grate 8. The first top grate 7, the second top grate 8, and the third top grate 9 are mechanically attached to the frame 104. Each filter grouping 124 also has a flow-through bottom plate 164. Each bottom plate 164 has a plurality of bottom grates 2,3 at a distal end of the nested tubes 128. The bottom plates 164 are adapted to act as outlets feeding a filtered fluid to the inlets 116 on the flow-through plenum 108. A first bottom grate 3 has a plurality of first apertures 168 corresponding in size and shape to the outer circumference of each outer perforated tube 5 wherein a distal end of each outer perforated tube 5 is inserted within and supported by a corresponding first aperture 168. A second bottom grate 2 has a plurality of first apertures 172. Each such aperture 172 is aligned with a corresponding interstitial space 132 between an inner perforated tube 6 and an outer perforated tube 5. The second bottom grate 2 also has a plurality of second apertures 176. Each second aperture 176 is aligned with an opening at a distal end of a corresponding inner perforated tube 6, which forms the nested tube 128 outlet aligned with an inlet on the plenum 108. A central webbing 180 about each second aperture 176 substantially seals the opening at the distal end of the corresponding inner perforated tube 6. A mechanical fastener 180 passes through each second aperture 176 and engages the distal end of the corresponding inner perforated tube 6 to maintain the corresponding inner perforated tube 6 in a desired position in the nested tube 124. Typically, a washer or other substantially donut-shaped member is attached to the mechanical fastener and is located within the inner perforated tube 6 to center the inner perforated tube 6. The first bottom grate 3 and a surface of the plenum 108 sandwich the second bottom grate 2 therebetween such that surfaces of the first bottom grate 3 and the plenum 108 engage opposite surfaces of the second bottom grate 2. The first bottom grate 3 and the second bottom grate 2 are mechanically attached to the frame 104. Accordingly, the interstitial spaces 132 between the inner perforated tubes 6 and the outer perforated tubes 5 are adapted to receive a filtered fluid flow as a contaminated fluid passes from outer surfaces to inner surfaces of the outer perforated tubes 5 and from inner surfaces to outer surfaces of the inner perforated tubes 6. Each top plate 136 is mechanically joined to a corresponding bottom plate 164 by a tie rod. Each top plate 136 is separated from the corresponding bottom plate 164 by the plurality of nested tubes 124. Each top plate 136 is further mechanically joined to a corresponding bottom plate 164 by a pair of cross members 10, which are joined to the top plate 136 by a mechanical fastener and to the corresponding bottom plate 164 at an opposing end by a mechanical fastener. The template plate 1 forms the plurality of inlets on the plenum 108. Accordingly, the template plate 1 has a plurality of openings. Each opening is aligned with a filter grouping to provide the inlets to the plenum. The template plate is mechanically attached to the plenum 108, to each of the groupings 124 and the frame 104. As illustrated in FIGS. 24-26, the tubes are generally produced from a stainless steel 184 strip that is rolled, perforated, and cut in a continuous process. Opposing edges of the perforated strip are brought into engagement and joined by a mechanical seam 186. The opposing edges are brought together by twisting or rotating a terminal end of the strip such that the strip forms a tube having a helical seam, one edge a receiving a portion of the opposing edge into a receiver to form the mechanical seam. The perforations 188 are formed in a fluted fashion. Longitudinal recesses are formed on a surface of the metal sheet 184 forming slotted opposing parallel openings 192 separated by a segment 194 of the metal sheet 184. It should be understood that the segment 194 is recessed relative to an outer surface of the tubes 5,6. When viewed from an inner surface of the tubes 5,6, the segments 194 will appear as protrusions or extensions. This will be explained in more detail below. The structure of the tubes with mechanical seam lends itself to repetition and changes in length and the tube diameter as will be understood from the description below taken in combination with structure so far explained. Again, a tube is formed by twisting the sheet 184 to form a helical orientation and draw the opposing edges together. The opposing edges have complimentary mechanically formed seaming members which are interlocked to form the mechanical seam 186. The resulting mechanical seam 186 forms a helical structure winding about a length of the tubes. Among other things, the mechanical seam 186 eliminates the need for welding of the tube in order for it to achieve structural integrity, which is an improvement over prior designs. As can be seen on, for example, FIGS. 13-18, the openings 192 create a double helix pattern in the finished nested tubes. A first helix pattern of the openings is parallel to the seam 186. A second helix pattern of the openings 192 extends generally transverse to the seam 186 in an opposite direction. In one embodiment, the first helix pattern is a right-handed helix, and the second helix pattern is a left-handed helix. It should be understood that the patterns 300,302 can be reversed without departing from the spirit of the invention. A pitch of the first helix pattern is generally substantially less than a pitch of the second helix pattern. In one embodiment, the pitch of the second helix pattern is 6 times greater than the pitch of the first helix pattern. In another embodiment, the pitch of the second helix pattern is 7 times greater than the pitch of the first helix pattern. In one preferred embodiment, the outer tube 5 of the nested tubes has a second helix pattern having a pitch 6 times greater than a pitch of the first helix pattern, and an inner tube 6 of the nested tubes has a second helix pattern having a pitch 7 times greater than a pitch of the first helix pattern. The ratio of the respective pitches of the second helix pattern and the first helix pattern may be greater than 3, between about 3 to about 10, between about 4 to about 8, between about 6 to about 8, or any range or combination of ranges therein. An improvement over the prior art nested tubes is believed to be the flow angle of the fluid entering the tubes 5,6. In a prior art configuration shown in FIGS. 27-29, tubes 200 are formed from a metal sheet having opposing edge portions welded to form a longitudinal welded seam 204 which forms a tube. The metal sheet is stamped or pierced with round apertures 208 to form a perforated tube 200. A fluid flow entry angle 210 is typically about 90 degrees in this configuration, as shown in FIG. 29. It is believed that an undesired turbulent flow is established at knife edges of each aperture. As illustrated in FIG. 30, a fluid flow 214 enters the interstitial area 132 of the nested tubes at an angle less than 90 degrees, rather than a 90 degree angle as experienced in the prior art tubes. This results in a reduction or elimination of turbulent flow at the knife edge of the openings. As shown in FIG. 30, fluid flow 214 enters the interstitial area 132 through the outer tube 5 via negative, depressed, or recessed portions 194 from an outer space surrounding the tube 5 to the interstitial area 132 within an interior space of the tube 5. Because the openings 192 are slotted, angled greater than 0 degrees relative to the recessed portions 194, generally perpendicular to an outer cylindrical surface of the tube 5, insulation fibers, which can be long and thin in structure, are less likely to enter the interstitial area 132 and/or clog or otherwise obstruct flow at the openings 192 than if the openings were stamped apertures parallel to the cylindrical outer surface of the tube as is prevalent in the prior art. Thus, the slotted openings 192 may have an entrance to the interstitial area 132 which is radially outwardly of the recessed portion 194 and radially inwardly of a radially outermost surface of the tube 5 as shown on FIG. 30. As also shown in FIG. 30, fluid flow 214 enters the interstitial area 132 through the inner tube 6 via positive, extended, or protruding segments 194 from an interior space of the inner tube 6 to the interstitial area 132. Similar to the openings 194 on the outer tube 5, the openings 192 on the inner tube 6 are slotted, angled greater than 0 degrees relative to the segments 194 between the slots, generally perpendicular to an inner cylindrical surface of the tube 6. Thus, the slotted openings 192 may have an entrance to the interstitial area 132 which is radially outwardly of the segment 194 and which extends radially inwardly from a cylindrical surface of the tube 6 into the interior space of the tube 6 as shown on FIG. 30. The orientations of the openings 192 described above on the tubes 5,6 may be reversed. Here, the outer tube 5 has slotted openings extending radially outwardly from the cylindrical surface of the tube 5 and the segments 194 are protruding radially outwardly on the cylindrical surface. The inner tube 6 has slotted openings extending radially outwardly characterized by segments 194 also protruding radially outwardly from the cylindrical surface. See FIG. 31. Alternatively, the orientations can be mixed such that one tube has radially outwardly projecting segments 194, and the other tube has radially inwardly projecting segments 194. See FIG. 32. Alternatively still, the orientations of the projecting segments 194 can be mixed on each tube 5,6. In this embodiment, a single tube can exhibit both radially inwardly and outwardly projecting segments 194. The nested tubes 5,6 with radially extending slotted openings provide at least the following improvements over prior designs. By-pass is reduced. By-pass is amount of material that passes through the nested tube medium and beyond the suction strainer, i.e. not filtered. Additionally, head loss is reduced. Head loss, in this case, is a pressure drop across the filter medium. In another embodiment illustrated in FIG. 34, the high capacity suction strainer 100 according to the present invention is outfitted with nested tubes 5,6 as in the previous example with the exception that the nested tubes 5,6 have conventional perforations similar to the prior art tubes 200 illustrated in FIGS. 27-29. It should be understood that the nested tubes 5,6 may be oriented substantially horizontally to horizontally relative to an upper surface of the fluid within a containment area as illustrated in FIGS. 20-23 and 36 or substantially vertically to vertically as illustrated in FIGS. 33 and 35. Alternatively, the nested tubes 5,6 may be oriented at any angle or angles therebetween, specifically angles between 0 degrees and 90 degrees relative to the upper surface of the fluid in the containment area. When the nested tubes 5,6 are oriented 0 degrees relative to the upper surface of the fluid in the containment area, the tubes are substantially parallel to the upper surface of the fluid, i.e. substantially horizontally oriented. When the nested tubes 5,6 are oriented 90 degrees relative to the upper surface of the fluid in the containment area, the tubes are substantially perpendicular to the upper surface of the fluid, i.e. substantially vertically oriented. Factors that influence the orientation of the nested tubes 5,6 may be required strength of the assembly and/or the available space within the containment area for accommodating the suction strainer 100. The suction strainers described herein may also be outfitted with single tubes rather than nested tubes. See FIG. 37. The terms “first,” “second,” “upper,” “lower,” “top,” “bottom,” etc., when used, are for illustrative purposes relative to other elements only and are not intended to limit the embodiments in any way. The term “plurality” as used herein is intended to indicate any number greater than one, either disjunctively or conjunctively as necessary, up to an infinite number. The terms “joined,” “attached,” and/or “connected” as used herein are intended to put or bring two elements together so as to form a unit, and any number of elements, devices, fasteners, etc. may be provided between the joined or connected elements unless otherwise specified by the use of the term “directly” and/or supported by the drawings. The pitch of a helix is the width of one complete helix turn, measured parallel to the axis of the helix. If the movement away from the observer is clockwise, then the helix is right-handed. Most hardware screw threads (a screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement and force) are right-handed helices. If the movement is in the anti-clockwise direction, then a left-handed helix is being observed. The term “substantially” as used to modify the angle of the nested tubes encompasses ±10 degrees. While the specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying Claims.
	abstract	A fuel assembly includes a plurality of fuel rods placed in a square lattice array of 9-rows/9-columns and at least one water rod. In this fuel assembly, the fuel rod pitch of the plurality of fuel rods is in a range of 14.15 mm to 14.65 mm, and means for offsetting and holding a fuel bundle composed of the fuel rods and the water rod is provided in such a manner that the center in a cross section of the fuel bundle is offset from the center in a cross section of the lower tie plate toward the channel fastener side. With this configuration, it is possible to provide a fuel assembly for a D-lattice core, which is capable of achieving the fuel economy comparable to that of a C-lattice core without reducing the thermal margin, and of using the existing fuel spacers.
	claims	1. An apparatus comprising:a pressurized water reactor (PWR) including:a pressure vessel configured to contain primary coolant water,a nuclear reactor core disposed in the pressure vessel and including a plurality of fuel assemblies,a control system including a plurality of control rod assemblies wherein each control rod assembly is guided by a corresponding control rod assembly guide structure, anda support element disposed above the control rod assembly guide structures,wherein the support element spans an interior of the pressure vessel; a top end of each control rod assembly guide structure is secured directly to the support element; the support element supports the control rod assembly guide structures; and the control rod assembly guide structures are anchored to each other only at their top ends. 2. The apparatus of claim 1, wherein the pressure vessel is a cylindrical pressure vessel, the support element comprises a support plate having a circular periphery supported by the cylindrical pressure vessel, and each fuel assembly includes a plurality of fuel rods. 3. The apparatus of claim 2, wherein the control rod assembly guide structures hang downward from the support plate. 4. The apparatus of claim 2, wherein the lower end of each control rod assembly guide structure includes alignment features that engage corresponding alignment features of the upper end of the corresponding fuel assembly. 5. The apparatus of claim 4, wherein there is a gap between the lower end of each control rod assembly guide structure and the upper end of the corresponding fuel assembly. 6. The apparatus of claim 5, wherein the fuel assemblies are supported from below. 7. The apparatus of claim 2, wherein the control rod assembly guide structures are not supported from below. 8. The apparatus of claim 2, wherein flow of primary coolant water in the pressure vessel in the operational state of the PWR is not sufficient to lift the fuel assemblies upward. 9. The apparatus of claim 1, wherein the control rod assembly guide structures hang downward from the support element. 10. The apparatus of claim 1, wherein the lower end of each control rod assembly guide structure includes mating structures that mate with an upper end of the corresponding fuel assembly. 11. The apparatus of claim 1, wherein there is a gap between the lower end of each control rod assembly guide structure and the upper end of the corresponding fuel assembly. 12. The apparatus of claim 1, wherein the control rod assembly guide structures are not supported from below. 13. The apparatus of claim 1, wherein flow of primary coolant water in the pressure vessel in the operational state of the PWR is not sufficient to lift the fuel assemblies upward. 14. The apparatus of claim 1, wherein there are no hold-down springs disposed on the tops of the fuel assemblies. 15. An apparatus comprising:a pressurized water reactor (PWR) including:a pressure vessel,a nuclear reactor core disposed in the pressure vessel and including a plurality of fuel assemblies,a control system including a plurality of control rod assemblies wherein each control rod assembly includes control rods selectively inserted into the nuclear reactor core and wherein each control rod assembly is guided by a corresponding control rod assembly guide structure, anda support element disposed within the pressure vessel above the control rod assembly guide structures,wherein a top of each control rod assembly guide structure is anchored directly to the support element; the control rod assembly guide structures are suspended from the support element and anchored to each other only at their top ends; and there is a gap between the bottoms of the control rod assembly guide structures and the top of the nuclear reactor core. 16. The apparatus of claim 15, wherein the control rod assembly guide structures are not supported from below the control rod assembly guide structures and each fuel assembly includes a plurality of fuel rods. 17. The apparatus of claim 15, wherein:there is a one-to-one correspondence between the control rod assembly guide structures and the fuel assemblies of the nuclear reactor core, andthe lower end of each control rod assembly guide structure includes alignment features that engage corresponding alignment features of the upper end of the corresponding fuel assembly. 18. The apparatus of claim 15, wherein flow of primary coolant water in the pressure vessel in the operational state of the PWR is not sufficient to lift the fuel assemblies upward.
050646079	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to nuclear reactors and, more particularly, to grey rods having a required reactivity worth for reactivity control of the reactor, such as during and following a period of lower power demand. 2. Description of the Prior Art In a typical nuclear reactor, such as a pressurized water reactor (hereinafter PWR), the reactor core includes a large number of fuel assemblies. Each fuel assembly is composed of a plurality of elongated fuel rods transversely spaced apart from one another. The fuel rods, each containing fissile material, generate a neutron flux in the core sufficient to support a high rate of nuclear fission and thus the release of a large amount of energy in the form of heat. A liquid coolant (usually water) is pumped upwardly through the core in order to extract some of the heat generated in the core for the production of useful work. One type of PWR fuel assembly, to which the present invention is particularly suited, is known as a "17.times.17" fuel assembly design. In this type of design, the fuel assembly includes a square lattice with 17 fuel rods along each side. This fuel assembly has 264 fuel rods, 24 guide thimbles (for control rods or grey rods discussed below) and one instrument thimble. The outer diameters of the rods are usually on the order of 0.4". See, e.g., co-assigned U.S. Pat. NO. 4,642,216, issued to ORR et al. (hereinafter the "'216 patent") for a further discussion of this type of fuel assembly. Since the rate of heat generation in the reactor core is proportional to the nuclear fission rate, which, in turn, is determined by the neutron flux in the core, control of heat generation at reactor startup, during its operation and at shutdown is achieved by varying the neutron flux. Generally, this has been done by absorbing excess neutrons using clusters of control rods in combination with a soluble neutron absorber. Initially, the level of neutron flux and thus the heat output of the core is regulated by the movement of the control rods into and from the guide thimbles. The ability of a control rod to absorb neutrons is measured by its relative "reactivity worth." The reactivity worth of a rod can be determined by calculations well known in the art. The basis for calculating the relative value of total and individual rod worths can be an all uranium core or an assumed mixed oxide and uranium core having uranium fuel rods. Hafnium, silver-indium cadmium, boron carbide, and other materials are known to be strong absorbing or high worth materials. These materials are also termed black absorbers because they are relatively opaque to neutrons. In contrast, stainless steel, zirconium, INCONEL (The trademark for a nickel-based alloy containing 16% chromium and 7% iron and characterized by marked resistance to aqueous corrosion and by high temperature oxidation resistance; also known as Alloy 600) and other materials are known as weak, have relatively low worths and are generally referred to as grey absorbers. Knowledge of individual rod and rod cluster reactivity worths is of vital importance in controlling the core, as well as determining necessary concentrations of soluble neutron absorbers and additionally in providing fluid moderator, flow rate, density and composition requirements for the reactor. One common structure adapted for control rods is described in co-assigned U.S. Pat. No. 4,326,919, issued to HILL. This control rod is in the form of an elongated metallic cladding tube having a strong neutron absorbing material disposed within the tube and plugs at opposite ends thereof for sealing the absorber material within the tube. The neutron absorbing material is in the form of a stack of closely packed, high worth ceramic or metallic annular pellets which only partially fill the tube, leaving a void, space or axial gap between the top of the pellets and the upper end plug in defining a plenum chamber for receiving gases which are generated during the control operation. Pellets are used instead of a solid rod to increase the flexibility of the rods and minimize drag during withdrawal and insertion. Control rods affect reactivity by changing direct neutron absorption and are used for what is known as fast reactivity control. On the other hand, slower, longer term reactivity control is usually carried out by the soluble neutron absorbers and by grey rods which are of low worth relative to the control rods. Grey rods have structures almost identical to the control rods described above, except for the cladding filler. See, e.g., co-assigned U.S. Pat. No. 4,681,728, issued to VERONESI et al. Typically, grey rods have a relatively weak absorber material cladding, e.g. stainless steel, and a relatively weak absorber material cladding filler, e.g. zirconium pellets. More particularly, the soluble neutron absorbers, such as boric acid, are uniformly distributed in solution throughout the core coolant, leading to more uniform power distribution and fuel depletion than control rods. The concentration of soluble boron is normally decreased with core age to compensate for fuel depletion and fission product buildup. The buildup of fission products, such as Xenon-135 (hereinafter xenon), reduces reactivity by parasitically absorbing neutrons, thereby decreasing thermal utilization. The xenon is removed by neutron absorption or by decay. Upon a reduction in core power, such as during "load follow maneuvers," fewer thermal neutrons are available to remove the xenon and therefore the concentration of xenon in the core increases. Load follow maneuvers refers to any reactor power changes which are required because of changes in electrical demand. A typical maneuver is a daily load follow, in which the reactor is reduced to a low power value (normally 50 percent) for 6 or 8 hours during the night when electrical demand is at a minimum. The increase in xenon concentration is usually compensated for by either decreasing the concentration of soluble boron dissolved in the core coolant or by withdrawing the control rods from the core. However, both of these methods have drawbacks. Changing the boron concentration requires the processing of coolant which is difficult and expensive, and therefore not desired by the electrical utility, especially towards the end of core life. Removal of control rods means that the core's return to power capability is reduced. A potential solution to this problem is to use the low worth grey rods in the core at full power. These grey rods are available for removal at reduced power to compensate for the xenon buildup. As described in co-assigned U.S. Pat. No. 4,707,329, issued to FREEMAN, the drawback of this procedure is that moving these banks of grey rods changes the ever critical axial offset of the core and increases peaking factors. Also, because these low worth grey rod banks are in the core at power, shutdown margins can be affected. This patent suggests as a solution using, instead of grey rods, the full insertion into the core of a control rod whose worth can be changed uniformly in the axial direction during power operation to provide xenon compensation. The control rod is composed of an elongated inner cylindrical member and an elongated outer cylindrical member surrounding the inner member. Each of the elongated members is composed of alternating equal height high worth hafnium and low worth zirconium regions. The inner and outer members are axially movable relative to each other to adjust the degree to which the high and low worth regions of the respective members overlap and thereby change the overall worth of the rod. This patented control rod approach, however, is complicated due to requiring an elaborate mechanical, moving structure which is difficult to construct and operate, is relatively expensive, and may fail to fully compensate for the buildup of fission products. The above-cited '216 patent describes a type of grey rod for use with a 17.times.17 fuel assembly, wherein 12 of the 24 strong absorber rods are replaced by 12 stainless steel rods to improve core operations. The disadvantage with this grey rod design is that the combination of strong absorber rods and weak (low worth) rods in the same cluster do not provide for homogeneous absorptions and can result in power peaking penalties. Further, it is known that the use of low worth grey rods can reduce the coolant processing requirements for a reactor from many thousands of gallons per day to relatively insignificant amounts. A related, important goal is to operate in what is known as a zero boron change load follow (hereinafter ZBCLF) mode, which requires no soluble boron adjustments during load follow maneuvers. Unfortunately, conventional, low worth grey rods are incapable of allowing ZBCLF at all power conditions because their cumulative worth is deficient. One potential modification to the grey rods to increase their relative worths, at least when the diameter of the grey rods is rather large, e.g., 0.8 to 1.0" O.D., is to vary the size of the central hole in the annular pellets. That is, by decreasing the size of the hole, it is possible to increase the volume fraction of absorber material, thus increasing the reactivity worth. As a result, the number of grey rods in a typical design might actually be reduced from the normal compliment because of the increased reactivity worth. Reducing the number of grey rods is desired for two reasons: first, it simplifies the mechanical design of the upper internals and reactor vessel head/integrated heat package; and second, there is a significant reduction in capital cost due to elimination of some of the assembly, driveline mechanism, cabling, etc., costs associated with use of the larger number of rods. However, this alternative is not adaptable for all fuel assemblies. For example, it is not applicable to a standard 17.times.17 reactor, because the outer diameters of the rods used therein are too small (about 0.381 inch). In fact, even with approximately 100% volume fraction of stainless steel or INCONEL (i.e., 0.341 inch pellets inside a 0.381 inch O.D./0.344 inch I.D. cladding) the reactivity worth of the individual grey rods in a particular application would probably be insufficient to achieve ZBCLF: additional grey rods of the same (stainless or INCONEL) design would probably be required. However, the addition of more grey rods would increase the mechanical complexity of the reactor vessel internals/head area/integrated head package/etc. and would significantly increase the capital cost. Notwithstanding a theoretical desire to reach ZBCLF by increasing grey rod worth, a designer must be able to retain the desired stiffness criteria for grey rods, as well as prevent the weight of the grey rods from increasing, which would increase driveline mechanism requirements. Thus, merely increasing significantly the cladding thickness to increase worth would not only undesirably increase stiffness, but would also be difficult and expensive to manufacture. Moreover, using a solid grey rod of a relatively weak neutron absorber material would be less expensive than the thick walled tube suggested immediately above, but would further frustrate the stiffness criterion. A solid rod would also violate the weight criterion unless the O.D. of the rod were reduced. However, using a small rod might lead to vibration and wear problems in both the core thimbles and in the upper guide structures since these components were designed to accommodate rods of a certain outer diameter. In light of the above, a grey rod design which has the required worth to achieve ZBCLF, is adaptable to a "17.times.17" fuel assembly, is economically manufactured, and can be incorporated without complication of the remaining reactor structure or operation, is still desired. SUMMARY OF THE INVENTION Accordingly, it is a purpose of the present invention to provide a reactivity control means for a nuclear reactor which reduces construction, maintenance, fuel and operating costs. It is another purpose of the present invention to provide a grey rod design having a worth intermediate that of a relatively high worth conventional control rod and a relatively lower worth conventional grey rod. It is another purpose of the present invention to provide a grey rod design eliminating the need for a cyclical boron change during load follow operation. It is another purpose of the present invention to provide a grey rod design for controlling reactivity without impacting power distribution. It is another purpose of the present invention to provide a grey rod design which allows fewer grey rods to be used to absorb excess neutrons during operation of the nuclear reactor. It is another purpose of the present invention to provide a grey rod design which does not violate the stiffness and weight parameters currently observed for grey rods. Finally, it is a purpose of the present invention to provide a hybrid grey rod whose reactivity worth can be chosen to most efficiently absorb excess neutrons. To achieve the foregoing and other purposes of the present invention there is provided several hybrid grey rod designs, wherein geometric combinations of relatively strong and weak absorber materials are used to obtain various required reactivity worths. A first embodiment of the invention includes a grey rod having combinations of weak absorber material pellets, such as stainless steel or INCONEL, and strong absorber material pellets, such as hafnium, selected to obtain the required worth. The pellets can be of varying heights and are housed in a stainless steel cladding of a first thickness. A second embodiment includes a rod with relatively small diameter hafnium or other strong absorber material pellets received in a stainless steel or INCONEL cladding of a second, relatively greater thickness. A third embodiment includes annular stainless steel or INCONEL pellets, each with a smaller diameter hafnium or other strong absorber material pellet contained within the central hole of each stainless steel or INCONEL pellet, or a continuous hafnium or other strong absorber material wire received by the central holes of the stainless steel or INCONEL pellets. The cladding is again of stainless steel or INCONEL having the first thickness. A fourth embodiment includes pellets made of zirconium and hafnium as a homogeneous mixture, with the percentage of hafnium adjusted to obtain the desired reactivity worth. The cladding is again of stainless steel or INCONEL having the first thickness. Benefits of the present invention include a greater operating flexibility and reduction in the total number of grey rods required to achieve ZBCLF in certain applications. Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.
	abstract	A radiation phase change detection method includes: arranging a two-dimensional optical image pickup element, which includes a scintillator, so that, when a period of a self-image generated through a phase grating is defined as D1, and a pixel pitch of the two-dimensional optical image pickup element is defined as D2=kD1, k falls in a range of ½<k≤3/2, and so that interference fringes formed by D1 and D2 depending on a relationship in arrangement of the two-dimensional optical image pickup element with respect to the self-image have a period of 2 times D2 or more and 100 times D2 or less; acquiring images of the interference fringes before and after insertion of an object; and outputting an image on a phase change of the radiation caused by at least the object.
047486465	abstract	An X-ray lithography system, in which an X-ray beam is separated from synchrotron radiation beams and reflected by a scanning mirror which vertically scans the reflected X-ray beam. The X-ray is irradiated into an exposure chamber via a beryllium window, which is vertically oscillated in such a manner that the beryllium window is shifted up and down in synchronization with the scanning operation of the X-ray beam.
046719229	summary	BACKGROUND OF THE INVENTION The present invention relates to a nuclear reactor cooled by a liquid metal and more specifically relates to supporting the liquid metal-filled vessel and the contained reactor core. It is known that for the purpose of providing biological protection the vessel of a fast neutron nuclear reactor is placed in a concrete vessel shaft and its upper part is sealed by a metal slab, whose gaps and openings are filled with concrete. In solutions used on the Rhapsodie, Phenix and Super Phenix reactors, the slab rests on an annular bearing surface formed in the upper part of the vessel shaft and the vessel is directly suspended on said slab. The vessel is filled with a primary liquid metal such as sodium, which cools the reactor core by transferring the heat given off in the reactor core to exchangers in which a secondary fluid circulates, which is generally also sodium. The circulation of the liquid metal in the core and in the exchangers is brought about by pumps. The primary sodium temperature is close to 540.degree. C. at the outlet from the core, i.e. in the upper part of the vessel, whilst it drops to about 400.degree. C. at the outlet from the exchangers, i.e. in the lower part of the vessel. Hereinafter the term "hot" corresponds to the temperature of the liquid metal leaving the core, the term "tepid" to the temperaure of the liquid metal leaving the exchangers and reentering the core and the term "cold" to a temperature close to ambient temperature, but which may for example reach the fusion temperature of the liquid metal, i.e. approximately 100.degree. C. for sodium. In the best known constructions the reactor vessel is suspended from the upper slab and transmits to it a considerable load. To prevent excessive creep of the upper part of the vessel walls, it is necessary to cool the same by circulating tepid sodium along the said walls. This leads to a certain thermodynamic loss and this arrangement also requires the use of baffles which are difficult to construct. In addition, suspended vessel are to a certain extent sensitive to possible seismic movements. It has also been previously proposed to place the tepid vessel bottom on the bottom of the cold vessel shaft by means of distributed supports permitting radial differential expansion movements. These supports have, for example, been constituted by rollers or rods, or even Stellite or graphite blocks. This solution has not been adopted because it did not appear to offer sufficient reliability. Another solution which has in fact been used consists of supporting the tepid bottom vessel in its lower peripheral part by radially displaceable supports. The supports then receive high individual stresses, but can be more easily inspected. However, compared with suspended vessels there is a need to radially transfer internal loads. BRIEF SUMMARY OF THE INVENTION The present invention relates to the construction of a fast neutron nuclear reactor in which the support procedure adopted for the vessel makes its manufacture easier and less expensive than that of the aforementioned, known solutions. In addition, said vessel has safety and reliability characteristics which are at least as good as those of existing vessels. Therefore the present invention proposes a nuclear reactor cooled by a liquid metal comprising a liquid metal-filled vessel, which contains the reactor core, a sealing slab sealing off the upper part of the vessel and a vessel shaft in which the vessel is located, wherein the bottom of the vessel rests on the bottom of the vessel shaft, wherein means are provided for cooling the bottom of the vessel to a temperature close to ambient temperature and wherein the inner areas of the vessel traversed by a forced flow of liquid metal are entirely positioned above a horizontal limiting plane which, at the transition height between said plane and the bottom of the vessel, leads to a thermal stratification of the liquid metal and consequently to an appropriate limitation of the thermal stresses in the vessel walls and the internal structures. Preferably the transition height is equal to at least 1/10 of the vessel diameter. The use of a cold vessel bottom makes it possible to support the vessel and all the internal loads on the vessel shaft bottom by means of supports which are very simple because they are submitted to low thermal gradients and stresses. Preferably the space formed between the vessel shaft bottom and the vessel bottom and which is traversed by the supports is used for the circulation of a fluid for cooling the vessel bottom. This space can also be vertically divided into a lower space ensuring a centripetal circulation of the fluid and an upper space ensuring a centrifugal circulation in contact with the vessel bottom, the two spaces being separated by a fairing which can have detachable parts to facilitate inspection. The vessel supports traverse this fairing. The two spaces are able to communicate in the vicinity of the vessel axis by a baffle which can be filled with liquid metal in the case of a leak, stopping the circulation of the cooling fluid which is liable to react with the liquid metal. In order to limit shape defects and faults during the construction of the vessel shaft bottom and the vessel bottom and in order to permit the centering of the vessel resting by gravitation on its supports, a substantially conical, downwardly pointing shape is advantageously chosen for the two bottoms. The transition height corresponding to the temperature gradient at the vessel bottom leads to a heat loss, which is acceptable in a high power reactor. However, this loss can be reduced by placing within the said transition height thermal insulating inclusions having a thermal conductivity below that of the liquid metal, so as to limit the downward heat flux over the said height. Finally, in view of the fact that the vessel rests on the vessel shaft bottom, the connection between the upper part of the vessel and the slab merely serves to seal the primary confinement area, whilst permitting expansions of the vessel. To this end the vessel side wall can be connected to the slab via an expansion bellows with bending corrugations.
	abstract	A method of retrofitting a spent nuclear fuel system with a neutron absorbing apparatus. The method includes inserting a neutron absorbing apparatus into a first cell of an array of cells each configured to hold a spent nuclear fuel assembly. The neutron absorbing apparatus includes a first wall and a second wall supported by a corner spine to form a chevron shape and a first locking tab protruding outwardly from the first wall towards a first cell wall of the first cell. The method includes cutting a half-sheared second locking tab in the first cell wall of the first cell adjacent to and above the first locking tab of the neutron absorbing apparatus. Finally, the second locking tab is positioned to locking engage the first locking tab to retain the neutron absorbing apparatus in the first cell during removal of one of the fuel assemblies from the first cell.
	description	FIGS. 5a and 5b show a one cell spacer grid for nuclear fuel assemblies in accordance with the primary embodiment of this invention. As shown in the drawings, the one cell spacer grid 10a is designed to place and support one elongated fuel rod 25. This spacer grid 10a comprises a plurality of grid strips 15 and 16, which are integrated into a four-walled cell having a square cross-section and being used for placing and supporting one fuel rod 25. The configuration and construction of one of the grid strips 15 and 16 is shown in FIG. 6. As shown in FIG. 6, the dipper-shaped coolant mixing vane 22 (hereinbelow, referred to simply as xe2x80x9cdipper vanexe2x80x9d), formed at each of the upper and lower ends of the grid strip 15 or 16, is designed to be specifically curved in a way such that each vane 22 is convex and concave and the upper and lower dipper vanes 22 are opposed to each other in the convex and concave direction. Due to such dipper vanes 22, the coolant is effectively changed in its flowing direction within the one cell grid 10a, thus forming an active swirling motion at positions around the top corners of the grid 10a. In each of the dipper vanes 22, the concave portion performs a thermal hydraulic function capable of forming a swirling motion of the coolant, while the convex portion supports the fuel rod 25 within the cell of the grid 10. Since the upper and lower dipper vanes 22 are opposed to each other in the convex and concave direction as described above, the four upper support points, provided at the upper end of the grid 10a, and the four lower support points, provided at the lower end of the grid 10a, are alternately positioned along the boundary of the grid 10a. In the present invention, the upper and lower dipper vanes of each strip may have the same configuration as shown in FIGS. 5a and 5b or may have different configurations as shown in FIG. 7. FIG. 7 is a perspective view of one grid strip constituting the spacer grid in accordance with the first modification of the primary embodiment of this invention, with the dipper vanes being altered so as to reduce the pressure drop and to improve the mixing effect of coolant within a fuel assembly. A hole is formed on each of the dipper vanes 122 and 123 of FIG. 7 so as to allow the vane to be free from a pressure difference between the coolant flowing on the concave portion and the convex portion. FIG. 8 is a perspective view of a spacer grid 10, fabricated using the strips 15 and 16 of FIG. 6 and designed to be used in a nuclear fuel assembly having a 3xc3x973 array. FIG. 9 is a perspective view of a spacer grid 110 fabricated using the strips 115 and 116 of FIG. 7 to be used in a nuclear fuel assembly having a 3xc3x973 Array In the drawings, only one fuel rod 25, 125 is shown to be placed and supported within one cell of the grid 10, 110. Of course, it should be understood that the spacer grid 10, 110 of this invention may be designed to form a desired array, for example, a 14xc3x9714, 16xc3x9716, or 17xc3x9717 array. FIG. 10a is a front view of the grid strips constituting spacer grid according to the primary embodiment of this invention. FIG. 10b is a front view of grid strips, with the welded portions of the strips being altered from the structure of FIG. 10a in accordance with the second modification of the primary embodiment of this inventions. As shown in the drawings, the strips 15, 16, 315, 316, are generally classified into two types in accordance with the position of axial slots 226 and 326 extending from the ends of the strips to a depth. In order to fabricate a spacer grid using the strips 15, 16, 315, 316, the strips are assembled with each other by intersecting the strips at the slots 226, 326, thus forming a plurality of four-walled cells individually having four intersections. After the strips 15, 16, 315, 316 are assembled together as described above the strips are welded to each other. In the case of the strips 15, 16 of FIG. 10a, the assembled strips 15, 16 are welded together at the welding taps 227 formed at the ends of the slots 226. On the other hand, the assembled strips 315, 316 of FIG. 10b are welded together at the arcuate welding taps 327, 328 formed on the slots 326. When such arcuate welding taps 327, 328 are formed on the slots 326 as shown in FIG. 10b, it is possible to use the end portions of the intersections of the spacer grid as the dipper vanes, thus forming a stronger swirling motion of the coolant within the grid. In the present invention, the to process of welding the taps 227, 327, 328 is effectively performed through a TIG welding process or a laser beam welding process regardless of the positions of the taps 227, 327, 328 on the slots 226, 326. In the spacer grid 10 of this invention, each of the dipper vanes 22 supports a fuel rod 25 at its concave portion within the cell of the grid 10. Therefore, it is not necessary to cut away the grid strips 15, 16, 315, 316 at any portion for forming separate springs or dimples, and so the strips are free from a reduction in the effective sectional area. This finally increases the mechanical and structural strength of the strips. Since it is not necessary to cut away the grid strips 15, 16, 315, 316 at any portion for forming separate springs or dimples, the strips effectively prevent undesired lateral flow of coolant within the spacer grid. This allows the coolant to smoothly flow within the fuel assembly and allows the fuel rods 25 to be free from vibration. In one cell spacer grid 10a of this invention, the fuel rod 25 is supported by the dipper vanes 22 at four points at each of the upper and lower ends of the grid 10a. That is, the fuel rod supporting structure of the spacer grid 10a of this invention is improved, with the number of fuel rod supporting points within the grid 10a being increased in comparison with the conventional grids. The spacer grid 10a of this invention thus minimizes a fretting wear of the fuel rods 25 different from the conventional grid. Such a fuel rod supporting structure of this invention is more advantageous due the structure of spring-fuel rod-spring capable of absorbing external impact in double directions in comparison with the conventional structure of spring-fuel rod-dimple designed to absorb external impact in a single direction. In the spacer grid of this invention, the lower dipper vanes 22 control the amount and flowing direction of inflow coolant for one cell spacer grid 10a, while the upper dipper vanes 22 cooperate with the lower dipper vanes so as to form more active swirling motion of coolant within the fuel assembly. Such an active swirling motion of coolant within the fuel assembly is caused by the fact that the upper and lower dipper vanes 22 are opposed to each other in the convex and concave direction. Due to such shaped dipper vanes 22, it is possible to accomplish an axially twisted effect of one cell spacer grid 10a. This allows the coolant to maintain the desired active swirling motion within the total length of the fuel assembly. In the present invention, it should be understood that the upper and lower dipper vanes may be altered in shape and size as desired. The dipper vanes may be also formed with holes capable of accomplishing a uniform pressure distribution on the concave and convex portions while forming more active swirling motion of coolant within a fuel assembly. Such a swirling motion of the coolant within the fuel assembly improves the heat transferring efficiency from the elongated fuel rods 25 to the coolant and improves the thermal output power of a nuclear power plant. This is well known to those skilled in the art and further explanation is thus not deemed necessary. As described above the present invention provides a nuclear fuel spacer grid with dipper vanes. The spacer grid of this invention is designed to accomplish the effective operation of a nuclear fuel assembly and to minimize the fretting wear of the fuel rods, which is the important factor causing damage of the fuel assembly. The spacer grid of this invention improves the mechanical stability and safety of the fuel assembly, thus accomplishing the safety of a nuclear power plant even in case of the occurrence of an emergency. The spacer grid is also designed to allow coolant to smoothly flow within the fuel assembly and to result in a high coolant mixing effect. The spacer grid finally improves the thermal hydraulic performance of the nuclear power plant. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
	claims	1. A furnace isolation chamber for containing a component to be hot isostatically pressed in a hot isostatic press (HIP) system, comprising:longitudinally cylindrical sidewalls;a top end extending between and permanently connected to said side walls, thereby closing one end of the chamber; anda movable bottom end, which is opposite said top end and forms a base end of said chamber, said movable bottom end is adapted to receive said component, and comprises a mechanism for raising and lowering said component into a high temperature zone of the furnace in the HIP system,wherein said isolation chamber forms an integral part of the HIP system,wherein there is a temperature gradient from the top end of the furnace isolation chamber to the base end, with the base end of said chamber being located outside of the high temperature zone of the furnace. 2. The furnace isolation chamber of claim 1, wherein the portion of the chamber contained within the high temperature zone of the furnace in the HIP system contains no flanges or seal faces. 3. The furnace isolation chamber of claim 1, comprising at least one porous metal or ceramic filter. 4. The furnace isolation chamber of claim 3, wherein pressurizing gas is used in a HIP process, wherein said pressuring gas is able to act on the component to be hot isostatically pressed through the at least one porous metal or ceramic filter. 5. The furnace isolation chamber of claim 3, wherein the at least one porous metal or ceramic filter is located in the base of the chamber that is outside of the high temperature zone of the furnace. 6. The furnace isolation chamber of claim 3, wherein the at least one porous metal or ceramic filter is incorporated into at least one of the walls and a top portion of the isolation chamber or to combinations thereof. 7. The furnace isolation chamber of claim 6, wherein the at least one porous metal or ceramic filter is configured to transfer heat from the furnace via convective flow of gas there through. 8. The furnace isolation chamber of claim 1, wherein said chamber comprises at least one high temperature, high strength material comprising at least one of a metal, a ceramic, and a composite thereof. 9. The furnace isolation chamber of claim 8, wherein said metal, ceramic, and a composite thereof comprises molybdenum, tungsten, and carbon-carbon composites. 10. The furnace isolation chamber of claim 1, wherein said chamber is adapted to receive hazardous, toxic, or nuclear material. 11. The furnace isolation chamber of claim 1, wherein said component to be isostatically pressed comprises a nuclear material comprising a plutonium containing waste. 12. The furnace isolation chamber of claim 1, wherein said chamber is configured to remove particulates and provide physically clean filtered environment argon gas to materials being processed inside said chamber. 13. The furnace isolation chamber of claim 1, comprising a pressurizing gas for the HIP process comprising an inert gas chosen from Ar, and further comprising an impurity gas comprising oxygen, nitrogen, hydrocarbons, and combinations thereof. 14. The furnace isolation chamber of claim 1, wherein the temperature gradient from the top end of the furnace isolation chamber that is inside the furnace to the base end that is outside the furnace is at least 750° C., such that the base end of the furnace forms a cool zone. 15. The furnace isolation chamber of claim 14, wherein the base end of the chamber that is located outside the furnace further comprises at least device for measuring the presence of radioactivity from a radioactive containing gas that condenses on the walls of the cool zone of the chamber. 16. The furnace isolation chamber of claim 1, further comprising a pair of locking mechanisms configured to couple a filter end support to a filter sealing assembly and the filter sealing assembly to the chamber. 17. The furnace isolation chamber of claim 1, further comprising an O-ring and a pair of plates configured to compress and position the O-ring such that the O-ring makes contact with two outermost faces of the plates, respectively, and an interior face of the chamber. 18. The furnace isolation chamber of claim 1, further comprising a cooled heat sink comprising a high thermally conductive material, wherein said heat sink forms a thermal gradient within the furnace isolation chamber that causes unwanted gases to condense in or around the cooled heat sink. 19. The furnace isolation chamber of claim 18, wherein the high thermally conductive material comprises aluminum, copper or alloys of such materials. 20. The furnace isolation chamber of claim 18, wherein the cooled heat sink further comprises one or more cooling channels sufficient to recirculating coolant therethrough. 21. A method of consolidating a calcined material comprising radioactive material, said method comprising:mixing a radionuclide containing calcine with at least one additive to form a pre-HIP powder;loading the pre-HIP powder into a can;sealing the can;loading the sealed can into the furnace isolation chamber of claim 1, closing said HIP vessel; andhot-isostatic pressing the sealed can within the furnace isolation chamber of the HIP vessel. 22. The method of claim 21, wherein hot-isostatic pressing is performed at a temperature ranging from 300° C. to 1950° C. and a pressure ranging from 10 to 200 MPa for a time ranging from 10-14 hours. 23. The method of claim 18, wherein at least the loading step is performed remotely. 24. The furnace isolation chamber of claim 10, wherein said hazardous, toxic, or nuclear material is contained in a canister and said chamber is adapted to receive said canister.
	description	This application is a continuation of application Ser. No. 11/067,609, filed Feb. 25, 2005, which application claims the benefit of the following nine U.S. Provisional Applications: U.S. Provisional Patent Application No. 60/547,934 filed Feb. 25, 2004, entitled “Diamond Molding of Small and Microscale Capsules”; U.S. Provisional Patent Application No. 60/550,571 filed Mar. 3, 2005, entitled “Diamond Molding of Small and Microscale Capsules”; U.S. Provisional Patent Application No. 60/552,280 filed Mar. 10, 2005, entitled “Diamond Molding of Small and Microscale Capsules”; U.S. Provisional Patent Application No. 60/553,911 filed Mar. 16, 2005, entitled “Diamond Molding of Small and Microscale Capsules”; U.S. Provisional Patent Application No. 60/554,690 filed Mar. 19, 2004, entitled “Diamond and/or Silicon Carbide Molding of Small and Microscale or Nanoscale Capsules and Hohlraums”; U.S. Provisional Patent Application No. 60/557,786 filed Mar. 29, 2004, entitled “Diamond and/or Silicon Carbide Molding of Small and Microscale or Nanoscale Capsules and Hohlraums”; U.S. Provisional Patent Application No. 60/602,413 filed Aug. 17, 2004, entitled for “Diamond and/or Silicon Carbide Molding of Small and Microscale or Nanoscale Capsules and Hohlraums”; U.S. Provisional Patent Application No. 60/622,520 filed Oct. 26, 2004, entitled “Diamond and/or Silicon Carbide Molding of Small and Microscale or Nanoscale Capsules and Hohlraums”; and U.S. Provisional Patent Application No. 60/623,283 filed Oct. 28, 2004, entitled “Diamond and/or Silicon Carbide Molding of Small and Microscale or Nanoscale Capsules and Hohlraums.”The respective disclosures of these applications are incorporated herein by reference for all purposes. The following U.S. patents and patent applications, including any attachments thereto, are incorporated by reference: U.S. Pat. No. 6,144,028, issued Nov. 7, 2000, entitled “Scanning Probe Microscope Assembly and Corresponding Method for Making Confocal, Spectrophotometric, Near-Field, and Scanning Probe Measurements and Forming Associated Images from the Measurements”; U.S. Pat. No. 6,252,226, issued Jun. 26, 2001, entitled “Nanometer Scale Data Storage Device and Associated Positioning System”; U.S. Pat. No. 6,337,479, issued Jan. 8, 2002, entitled “Object Inspection and/or Modification System and Method”; U.S. Pat. No. 6,339,217, issued Jan. 15, 2002, entitled “Scanning Probe Microscope Assembly and Method for Making Spectrophotometric, Near-Field, and Scanning Probe Measurements”; U.S. Provisional Application No. 60/554,194, filed Mar. 16, 2004, entitled “Silicon Carbide Stabilizing of Solid Diamond and Stabilized Molded and Formed Diamond Structures”; U.S. patent application Ser. No. 11/046,526, filed Jan. 28, 2005, entitled “Angle Control of Multi-Cavity Molded Components for MEMS and NEMS Group Assembly”; and U.S. patent application Ser. No. 11/067,517, filed of even date herewith, entitled “Diamond Capsules and Methods of Manufacture.” The following documents provide background information related to the present application and are incorporated herein by reference: [KOMA] R. Komanduri et al., “Finishing of Silicon Nitride Balls,” Oklahoma State University, Web Page at asset (dot) okstate (dot) edu (slash) asset (slash) finish.htm (updated Aug. 21, 2003); [MEMS] Proceedings of the IEEE Micro Electro Mechanical Systems Workshop, February 1993, Florida, p.246; [PHYS] Physik Instrumente (PI) GmbH, “Datasheets: Options and Accessories,” Web page at www (dot) physikinstrumente (dot) de (slash) products (slash) prdetail.php?secid=1-39; [NOOL] Nonlinear Optics and Optoelectronics Lab, University Roma Tre (Italy), “Germanium on Silicon Near Infrared Photodetectors,” Web page at optow (dot) ele (dot) uniroma3 (dot) it (slash) optow—2002 (slash) labs (slash) SiGeNIR files (slash) SiGeNIR.htm; [SAIN] Saint-Gobain Ceramics, “ASTM F2094 Si3N4 Cerbec Ball Specifications,” Web page at www (dot) cerbec (dot) com (slash) TechInfo (slash) TechSpec.asp; [STOL] C. R. Stoldt et al., “Novel Low-Temperature CVD Process for Silicon Carbide MEMS” (preprint), C. R. Stoldt, C. Carraro, W. R. Ashurst, M. C. Fritz, D. Gao, and R. Maboudian, Department of Chemical Engineering, University of California, Berkeley; [SULL] J. P. Sullivan et al., “Amorphous Diamond MEMS and Sensors,” Sandia National Labs Report SAND2002-1755 (2002); and [UWST] University of Wisconsin—Stout—Statics and Strength of Material, (Physics 372-321), Topic 6.5:Pressure Vessels—Thin Wall Pressure Vessels, Web page at physics (dot) uwstout (dot) edu (slash) StatStr (slash) Statics (slash) index.htm.Copies of these documents have been made of record in the present application. The present invention relates in general to surface modification and measurement techniques and apparatus, and in particular to techniques and apparatus for modifying and measuring surfaces of diamond or other workpieces to nanoscale precision. Ball bearings are conventionally made of metal or ceramic materials that can be finished to a surface smoothness with deviations on the order of tens of nanometers. Standard methods for making ball bearings include using a stamping machine to cut a ball from a wire of metal or ceramic material, then rolling the ball between plates to smooth over the rough edges left from the stamping procedure. For other applications, hollow capsules are made from glass microballoons or from hollow cylindrical wires, in much the same fashion as ball bearings. Surface roughness or smoothness is imposed by laser ablation, and surface deviations of a few nanometers to tens of nanometers, depending on the hardness and integrity of the material, are typical. There is also interest in making ball bearings, hollow capsules and similar structures out of other materials that will allow surface finishes to a higher precision and that will also be suited for use at extreme temperatures (e.g. near absolute zero and/or above 100 K), or where extreme demands are placed on the strength and uniformity of the ball bearing or capsule. It is also sometimes desirable to provide surfaces having small-scale features (e.g., ridges, grooves or the like), and such features should be formed with micrometer or nanometer precision. It would therefore be desirable to provide apparatus and techniques for measuring surface quality and for shaping surfaces to micrometer (μm) or nanometer (nm) precision. The present invention provides apparatus and techniques for modifying and measuring surfaces of diamond workpieces and other workpieces to nanoscale precision. The apparatus and techniques exploit scanning probe microscopy (SPM) and atomic force microscopy (AFM) at a wide range of operating temperatures. Surfaces that can be modified and measured using the apparatus and techniques described herein include the inner and outer surfaces of shells of synthetic diamond capsules, which can be smoothed to a maximum surface deviation from a perfectly smooth surface of, e.g., 2 nm or less, as well as surfaces where it is desired to impart a more complex shape, e.g., gear-toothed surfaces, with atomic (0.1 nm) or near-atomic (on the order of 1-10 nm) precision; surfaces such as probe tips for atomic force microscopy (AFM) and scanning probe microscopy (SPM) instruments may also be measured and modified. Further, the apparatus and techniques described herein may be used to modify and measure diamond surfaces at temperatures from near absolute zero up to 900° C. or higher. A diamond shell or other diamond workpiece (e.g., a tip for an AFM probe) may be nanolapped at high temperatures to promote mechanical (diamond particle lap) or chemical lapping on suitable material laps, such as iron or chromium, manganese or titanium objects. Alternatively the AFM tip may incorporate a suitable chemical or mechanical lap material to provide lapping tips to interact with the workpiece. Additionally the object or lap structure may be differentially heated to provide, create, promote or enhance chemical, mechanical, acoustic, optical, or magnetic behavior, properties, crystal structure or other elements which are a function of the absolute or differential temperature of the object or a portion thereof. The object may be inspected and the tip motion informed by use of an interferometric microscope or interferometer equipped microscope (IM) whose principal optics are built into the temperature controlled region of the device. At high temperatures the IM will be preferentially operated at one optical wavelength in a region above the color temperature of the object and system, at low temperatures the IM will be operated at one wavelength in the infrared preferably in the region in which silicon and diamond are transparent, further in the all temperature regimes the IM may be used with suitable detector(s) covering a wide band of infrared and microwave frequencies to monitor the thermal distribution in real or near real time on the object and materials which may be associated with the object like solid hydrogen, a heated nanolap or other object or structure. Finally ultrasonic standing waves may be monitored by a scanning probe microscope (SPM) and/or IM to measure minute thermal or material gradients in the sample by observing the material displacement and local wavelength variations of the standing acoustic waves. The following detailed description together with the accompanying drawings will provide a better understanding of the nature and advantages of the present invention. To establish context for the apparatus and techniques described herein, examples of workpieces whose surfaces can be worked (measured and/or modified) in accordance with the present invention will first be described. It is to be understood, however, that the scope of the invention extends to workpieces of any material composition with arbitrarily-shaped surfaces. FIG. 1A is a cross-sectional view of a diamond capsule shell 102. Shell 102 has an outer surface 103 that can be measured or modified at nanoscale precision using apparatus and techniques described herein. In some embodiments, an access port 104 is provided through shell 102, and the inner surface 105 of shell 102 can also be modified. Where access port 104 is not provided, inner surface 105 is generally not subject to modification by nanomachining, but inner surface 105 can still be measured using interferometric techniques described below. FIG. 1B is a cross-sectional view of diamond shell sections 112 that can be joined together to make a complete capsule shell. Each section 112 has an inner surface 116 and an outer surface 118, either or both of which can be measured or modified to nanoscale precision using apparatus and techniques described herein. FIG. 1C is a perspective view of a cylindrical geared bearing 120. Geared bearing 120 has ridges 122 on its outer surface that, in operation, function as gear-like teeth. Using apparatus and techniques described herein, the surface of bearing 120 can be modified or measured to nanoscale precision. FIG. 1D is an illustration of a probe tip 130 suitable for scanning probe microscopy (SPM) or atomic force microscopy (AFM). Probe tip 130 can be manufactured from diamond as described in above-referenced application Ser. No. 11/046,526 and can then be measured and modified using techniques described herein. In some embodiments, the workpiece is made from diamond materials, including crystalline, polycrystalline (ordered or disordered), nanocrystalline and amorphous diamond. “Diamond” refers generally to any material having a diamond lattice structure on at least a local scale (e.g., a few nanometer), and the material may be based on carbon atoms, silicon atoms, silicon carbide or any other atoms capable of forming a diamond lattice. More specifically, in some embodiments, the workpiece is made of crystalline diamond. As is well known in the art, a crystal is a solid material consisting of atoms arranged in a lattice, i.e., a repeating three-dimensional pattern. In crystalline diamond, the lattice is a diamond lattice 200 as shown in FIG. 2A. Diamond lattice 200 is made up of atoms 202 connected by sp3 bonds 206 in a tetrahedral configuration. (Lines 208 are visual guides indicating edges of a cube and do not represent atomic bonds.) As used herein, the term “diamond” refers to any material having atoms predominantly arranged in a diamond lattice as shown in FIG. 2A and is not limited to carbon atoms or to any other particular atoms. Thus, a “diamond shell” may include predominantly carbon atoms, silicon atoms, and/or atoms of any other type(s) capable of forming a diamond lattice, and the term “diamond” as used herein is not limited to carbon-based diamond. In other embodiments, the workpiece can be an imperfect crystal. For example, the diamond lattice may include defects, such as extra atoms, missing atoms, or dopant or impurity atoms of a non-majority type at lattice sites; these dopant or impurity atoms may introduce non-sp3 bond sites in the lattice, as is known in the art. Dopants, impurities, or other defects may be naturally occurring or deliberately introduced during fabrication of shell 102. In still other embodiments, the workpiece is made of polycrystalline diamond. As is known in the art, polycrystalline diamond includes multiple crystal grains, where each grain has a relatively uniform diamond lattice, but the grains do not align with each other such that a continuous lattice is preserved across the boundary. The grains of a polycrystalline diamond workpiece might or might not have a generally preferred orientation relative to each other, depending on the conditions under which the workpiece is fabricated. In some embodiments, the size of the crystal grains can be controlled so as to form nanoscale crystal grains; this form of diamond is referred to as “nanocrystalline diamond.” For example, the average value of a major axis of the crystal grains in nanocrystalline diamond can be made to be about 20 nm or less. In still other embodiments, the workpiece is made of amorphous diamond. Amorphous diamond, as described in above-referenced document [SULL], does not have a large-scale diamond lattice structure but does have local (e.g., on the order of 10 nm or less) diamond structure around individual atoms. In amorphous diamond, a majority of the atoms have sp3-like bonds to four neighboring atoms, and minority of the atoms are bonded to three other atoms in a sp2-like bonding geometry, similar to that of graphite; FIG. 2B depicts graphite-like sp2 bonds 214 between an atom 210 and three other atoms 212. The percentage of minority (sp2-bonded) atoms may vary; as that percentage approaches zero over some area, a crystal grain becomes identifiable. Thus, it is to be understood that the term “diamond material” as used herein includes single-crystal diamond, polycrystalline diamond (with ordered or disordered grains), nanocrystalline diamond, and amorphous diamond, and that any of these materials may include defects and/or dopants and/or impurities. Further, the distinctions between different forms of diamond material are somewhat arbitrary not always sharp; for example, polycrystalline diamond with average grain size below about 100 nm can be labeled nanocrystalline, and nanocrystalline diamond with grain size below about 10 nm can be labeled amorphous. A workpiece (e.g., a capsule shell or shell section) may include multiple layers of diamond material, and different layers may have different composition. For example, some but not all layers might include a dopant; different polycrystalline oriented layers might have a different preferred orientation for their crystal grains or a different average grain size; some layers might be polycrystalline oriented diamond while others are polycrystalline disoriented, and so on. In addition, coatings or implantations of atoms that do not form diamond lattices may be included in the workpiece. The workpiece may be fabricated as a unitary diamond structure, which may include crystalline, polycrystalline or amorphous diamond. Alternatively, the workpiece may be fabricated in sections (e.g., as shown in FIG. 1B), each of which is a unitary diamond structure, with the sections being joined together after fabrication. Examples of processes for fabricating diamond capsules are described in above-referenced application Ser. No. 11/067,517, and capsules or shells fabricated according to any of those processes may be used as workpieces in the context of the present invention. In still other embodiments, workpieces made of materials other than diamond materials may also be worked (measured and/or modified) using techniques and apparatus in accordance with the present invention. The workpiece may have any overall shape, including but not limited to spherical (e.g., FIG. 1A), ellipsoidal, or similar shapes. In some instances, a generally smooth workpiece (e.g., a spherical or ellipsoidal shape) may have local deviations. In other embodiments, the workpiece may have a polyhedral shape with rounded or sharp corners. Cross-sections of a workpiece in different planes may have different shapes. For example, a cylindrical capsule might have a circular cross section (similar to FIG. 1A) in a transverse plane and a rectangular cross section in a longitudinal plane. FIG. 3 shows a workpiece 300 under the cutting tool of an AFM guided nanomachining instrument 301 according to an embodiment of the present invention. In this embodiment, workpiece 300 is a section of a spherical shell as shown in FIG. 1B above and may be made of polycrystalline, nanocrystalline or amorphous diamond; another material may be applied to an inner or outer surface of the shell section. It is to be understood that a different workpiece of arbitrary shape and material composition may be substituted for workpiece 300. In this embodiment, AFM guided nanomachining is used to final machine or dress either the diamond material of workpiece 300 or its coating. The preferred embodiment of the instrument is constructed inside a thermally isolated container (not shown). The instrument includes either off the shelf piezoelectric actuators (tubes) with PTFE (Teflon) insulation or special piezoelectric actuators 305 combined with ceramic insulation 306. Special high/low temperature wire 307 is used to connect to a cantilever 304 that has a long tip 303. Tip 303 is advantageously made from single crystal diamond oriented for optimum hardness and wear resistance and is advantageously shaped so as to be usable as a cutting tool and/or probe tip. Workpiece 300 rests on a piezoelectric sample stage 302 and is held in place by sample support/holder 301 that can be attached to sample stage 302. In one embodiment, sample support/holder 301 may be a silicon or other substrate on which workpiece 300 has been fabricated, e.g., by diamond growth on a silicon substrate; other sample supports or holders may be substituted. The cantilever 304 is at right angles to the sample stage 302 (which itself is tiltable up to about 3° toward the cantilever base). Sample stage 302 can be used (without tilting) with a sample holder whose dimension in the direction parallel to cantilever 304 is not more than 80% of twice the cantilever length (i.e., 1.6 times the cantilever length). In one embodiment, an interferometric microscope (IM) is implemented using cantilever 304. As shown in FIG. 3, the sample stage and scanning assembly is at least partially surrounded by a large high numerical aperture reflecting objective 312 which is focused onto the sample (e.g., the surface of workpiece 300) by movements of the sample stage 302. In one embodiment, the rays 313 illuminating the sample and returning to the objective 312 are reflected from the back side of the cantilever 304 and out through an exit aperture 315 in objective 312 to the rest of the optics, which are advantageously placed outside the thermal container of the instrument and are not shown in FIG. 3. Alternatively, rays can be reflected from a secondary reflector carried with the cantilever substrate or from a separate reflector suspended just above the cantilever by suspensions from the exit aperture 315 of the reflecting objective 312. An AFM detection laser beam 314 is propagated to the back of the cantilever through the optically open exit 315 of objective 312. In one embodiment, the beam 314 passes through a bandpass filter (not shown in FIG. 3) that also serves as a secondary mirror. The bandpass filter is advantageously positioned on the substrate support of the cantilever 304 or suspended from the aperture 315 of objective 312. The bandpass filter has a sharp pass band around the laser wavelength and is otherwise reflective from long infrared/microwave to UV wavelengths. This arrangement permits operation of an IM (an actual interferometer formed in the microscope) and/or an imaging interferometric microscope (IIM) that can image and measure the heights of objects by sequential imaging using interferometric analysis techniques known in the art. In operation, interferometrically measured or SPM scanned irregularities or undesired elements of the sample can be removed by AFM guided nanomachining using tip 303. In another embodiment, the system of FIG. 3 operates in conjunction with acoustic waves generated by a surface acoustic wave electrode set 309 or by a modulated laser (not shown) operating at a wavelength that creates phonons by local electromagnetic interaction with the sample surface. A suitable wavelength can be chosen based on characteristic absorption of the object or sample. Either the IM or the SPM can be used to measure the acoustic standing waves generated by electrode set 309 or a laser; conventional acoustic-wave analysis techniques allow precise detection of deviations in the surface and characterization of any thermally induced irregularities. The same system can be used at temperatures of up to 140° C. with commercially available off the shelf piezoelectric components or at higher temperatures (e.g., up to 900° C.) with special all-ceramic insulated piezoelectric components to measure, finish, nanolap, nanomachine or make additions to the sample efficiently and quickly at the elevated temperature and then return to near absolute zero without breaking vacuum. For nanolapping, inducing local thermal differentials, or using acoustic waves for measurement, an alternative sample holder 308 with a built in acoustic wave generator 309 can be connected to an external current source by pads 311. In one embodiment, acoustic wave generator 309 includes interdigitated metal lines on a layer of silicon dioxide and a thermal heater 310 (such as a nickel and chromium patterned structure) In yet another embodiment the SPM uses a tip made of or coated with manganese, titanium, iron or other material having a carbon chemical or solubility affinity, in an appropriate shape. The SPM can be operated at a high-temperature to nanolap diamond into the an appropriate shape or correct perturbations in the diamond surface. Surfaces that can be worked include inner and outer surfaces of diamond shells. In one embodiment, the shell is formed in sections as described in above-referenced application Ser. No. 11/067,517, and the inner and/or outer surfaces of each section are worked to the desired surface quality before the sections are assembled. The peripheral edges of the diamond shell sections can also be worked to form latch or interference members therein. Examples of such members are described in above-referenced application Ser. No. 11/067,517. In another embodiment, the shell is formed with access ports therethrough, and the inner surface is worked using AFM-guided nanomachining with a tip having a long and narrow shape that can reach through the port to the interior. In other embodiments, the side walls of an access port can also be worked using suitable tips. In a further embodiment, surfaces made of materials other than diamond can also be worked. For example, to work a surface of a material that is solid only at low temperatures (e.g., around 4 K), a heated tip can be used to nanolap or thermally ablate the material into a gas while the thermal container holds the work surface at the low temperature. Suitable tips can be made of diamond, titanium, platinum or other material having an affinity for the work material and are advantageously appropriately shaped to reach the work surface. For example, as described above, the work surface may be inside a diamond shell and accessible via one or more access ports (openings) through the shell. The tip can be made long and narrow enough to reach through the access port to nanolap or ablate the work material inside. In still another embodiment, a suitably shaped tip can also be used to create an access port through a diamond shell. The access port can be created at an oblique angle through the shell or otherwise shaped such that a deformable flap of shell material can close the access port when pressure of a fluid inside the shell exceeds pressure of a fluid outside the shell, as described in above-referenced application Ser. No. 11/067,517. Access ports can also be made with dimensions and profiles suitable for removing a form substrate material from the interior of the shell (e.g. by etching the form substrate material). In some embodiments, it is desirable to measure the inner and outer surfaces of a hollow capsule made of diamond (or other material). For example, it may be useful to characterize the local surface roughness of either surface; the radius (in the case of a spherical capsule), major axis or other dimensions of the surface; and the relative alignment or concentricity of the inner and outer surfaces. It may further be desirable to maintain or obtain a particular concentricity (or alignment) limit or to intentionally create a precise concentricity (or alignment) offset between the surfaces. In the case of a spherical capsule, where the capsule wall is optically transparent (e.g., in the wavelength domain 20 microns to 10 nanometers for carbon-based diamond), this measurement may be made by using an interferometric microscope and/or a confocal microscope (these two functions may be combined) in conjunction with an index matching fluid that approximately matches the refractive index of diamond at the measurement wavelength. The outside surface may be measured first; the fluid is then placed between the first interferometric optical element, allowing the inner surface to be measured. Alternatively, two light wavelengths may be used, such that the index-matching fluid provides a closer match at one wavelength than the other, so that a stronger return of optical energy is obtained from the outer surface at one of the two wavelengths. By using two wavelengths of light to make the measurements, the outside and inside may be measured simultaneously or sequentially, relying on the change in effective index of refraction for a given matching fluid between two respective wavelengths of light. Such an operation can take place across a range of wavelengths (e.g., from about 10 nanometers to about 50 microns), depending on the material of which the capsule shell is formed. In addition, any coatings applied to the basic material of the capsule can be measured similarly. For instance, a diamond sphere with a SiC coating will exhibit wavelength related dependencies as reported in the above-referenced [MEMS]: Refractive index n=1.9-2.4 (wavelength not specified) for an alpha (SiC) PECVD film deposited with SiH4/CH4 flow ratio range=0.75-1.1, gas pressure=300 mTorr, RF power=150 W. With n=1.9-2.4 approximately matching the diamond (n approximately 2.418, with possible wavelength dependency), the SiC wavelength produces an index of around 2.4. In another embodiment, a partially matching fluid is used, and the interferometric system is arranged to have a very small depth of field of focus such that the outside surface can be distinguished by focus manipulation from the inside surface, allowing their relative concentricity to be measured. While the invention has been described with respect to specific embodiments, one skilled in the art will recognize that numerous modifications are possible. One skilled in the art will also recognize that the invention provides a number of advantageous techniques, tools and products, usable individually or in various combinations. These techniques, tools and products include but are not limited to: SPM measurement and modification at temperatures above about 70° C. or below about −40° C.; and/or AFM guided nanomachining at temperatures above about 70° C. or below about −40° C.; and/or AFM guided nanomachining of capsules or pellets; and/or SPM measurement and modification at temperatures above about 30° C. and below about 10° C.; and/or an SPM instrument with an integrated interferometric microscope; and/or an SPM instrument with an integrated microscope capable of interferometry; and/or an SPM instrument with reflecting imaging optics for wavelengths ranging from about 10 nm to about 2 mm; and/or an SPM instrument with reflecting imaging optics including a bandpass filter secondary reflector at its laser detection wavelength; and/or an SPM instrument having a piezoelectric stage with three axes of motion and a piezoelectric scanning head with three axes of motion; and/or an SPM instrument with a piezoelectric stage, where the sample platen is smaller in diameter then the cantilever length; and/or an SPM similar to any of the above in which the sample platen and the AFM cantilever are at right angles to each other; and/or a sample holder with a heater for an SPM or AFM instrument; and/or a sample holder with a surface acoustic wave generator for an SPM or AFM instrument; and/or an SPM instrument in which standing waves in the sample material due to surface acoustic waves are measured to determine local thermal or structural properties of a workpiece; and/or use of measurements of local thermal or structural properties measured by acoustic waves in making modifications including material addition or subtraction based on the acoustic standing waves; and/or a tip made of or coated with manganese, titanium, iron or other material having a carbon chemical or solubility affinity and usable at high temperatures to nanolap a diamond shape of any kind; and/or use of a heated tip made of or coated with diamond, titanium, platinum or other material having an affinity for hydrogen at very low temperatures to nanolap or thermally ablate solid material into a gas thus providing a properly shaped frozen surface; and/or any optical instrument for measuring hollow structures in which an index matching fluid is used and alternated with a substantially different index fluid or gas/vacuum to distinguish between the inner and outer surfaces and features of the structures; and/or any optical instrument for measuring hollow structures in which an index matching fluid is used and alternative wavelengths of light are employed with differing indexes in the index matching fluid to distinguish between the inner and outer surfaces and features of the structures; and/or any instrument which combines both of these operations; and/or any machining or polishing system in which a concentricity measurement is used to guide the removal of material on the outer surface of two surfaces (inner and outer) which are meant to have some given concentricity or alignment relationship. Thus, although the invention has been described with respect to specific embodiments, it will be appreciated that the invention is intended to cover all modifications and equivalents within the scope of the following claims.
039492281	abstract	A square-shaped electron beam is stepped from one predetermined position to another in a line-by-line scan to form a desired pattern on each chip of a semiconductor wafer to which the beam is applied. At each of the predetermined positions, the beam is on, off, or on for a portion of the time period at which the beam is disposed at the predetermined position. The beam also can be offset both along its direction of movement and perpendicular thereto at each of the predetermined positions. Control of this movement of the beam is obtained through utilizing a memory with no change being made in the memory if the predetermined position at the next line does not have any change from the predetermined position at the line along which the beam is moving.
040627233	summary	BACKGROUND OF THE INVENTION This invention relates generally to nuclear reactor systems and more particularly, to a liquid metal cooled nuclear reactor arrangement which facilitates both through the head instrumentation and refueling of assemblies from in the nuclear core. In any nuclear reactor which is intended to operate over an extended period of time, such as a reactor which is to be utilized in the generation of electrical power, a reactor facility should be constructed for removal and disposal of used or "spent" fuel element and for recharging or refueling of the reactor with new or unused fuel element. This of necessity involves providing access to the core of the nuclear reactor, this access usually being provided by an opening in the reactor vessel heads. With liquid metal cooled fast breader reactors, it is desirable that only a small opening in the vessel head be exposed at any one time to reduce the size of temporary shield and shielding required to prevent the release of fission gases, contact of a liquid metal coolant, such as sodium, with air, and exposure of personnel to radiation. In the past this has been accomplished with the use of rotating plugs or shields which serve to close off and seal the reactor vessel during normal reactor operation. The rotating plug systems of the prior art, of which U.S. Pat. No. 3,054,741 of J. Tatlock et al is one such example, generally included a first large plug which is approximately the size of the reactor vessel, and which may or may not also be substantially larger than the size of the nuclear core, and a second, smaller plug eccentrically supported thereon and having a lateral dimension approximately equal to 1/2 or greater than the lateral dimension of the core. The second plug has an eccentric opening and supports additional rotating plug so that access to every region of the core can be obtained by proper rotation of the plugs. In the design of fast spectrum reactors, provisions must also be made for control mechanisms and usually also for instrumentation for monitoring coolant conditions around and in each fuel assembly. Practically, for safety considerations and for ease in manufacturing, the control mechanism and instrumentation leads must pass through the vessel head. Also, as can be appreciated, it is desirable that the control mechanism be situated in a symmetrical arrangement about the center of the core so as to be better able to control the reactor during normal operation and/or to be able to rapidly shut down the nuclear chain reaction therein in the event of an emergency. In the prior art systems having relatively large rotating plug systems, it has been difficult to achieve the desirable arrangement of having control mechanism mounted on and passing through the reactor vessel head while having the control mechanisms situated in regular symmetrical pattern. This has been due to the fact that large eccentric tracks for large rotating plugs tend to, of necessity, yield nonsymmetrical arrangements of control mechanisms. Such schemes are further complicated by the desirability of providing instrumentation of the majority of fuel assemblies from in the nuclear core. In U.S. application Ser. No. 537,216 entitled "Core Access System for Nuclear Reactors" by Dupen filed Dec. 30, 1974, a nuclear reactor arrangement was disclosed which provided through the head refueling and also a regular symmetrical pattern of control and instrumentation mechanisms. In that arrangement, there is provided a large rotating cover having a lateral dimension at least as large as the core and a plurality of small rotating covers eccentrically disposed in openings in the large cover. The invention of that application closely revolved about the size of the circular openings for the small rotating covers. The nuclear core of the reactor arrangement was comprised of a plurality of hexagonally shaped assemblies and the lateral dimension of the openings thus related to the lateral dimension of groups of these assemblies. These groups of assemblies were designated potential control clusters each of which was defined as a regular pattern of one central assembly plus a multiple of six surrounding assemblies. The potential control clusters were defined in a central portion of the core so as to provide an interfitting arrangement thereof so that every assembly in that portion of the core formed a part of one and only one potential control cluster. Then the radial dimension of each of the circular openings in which the small rotating plugs were disposed was defined to be greater than the lateral distance between the central assemblies of two adjacent and contiguous potential control clusters but less than twice that distance. Also each of the smaller rotating covers contained access openings therethrough and were provided with removable closure plugs for closing off the openings. In this way, by properly locating and selecting the number of second smaller rotating covers, every assembly of the core can be reached through the access openings upon proper rotation of the first and second rotatable covers. Also a uniform symmetrical control pattern could be maintained with the control and instrumentation mechanisms located on the reactor vessel head and positioned over the central assembly of a potential control cluster. By doing this, the means for supporting the second rotatable covers could be located between respective control mechanisms of two adjacent potential control clusters. It is to an improved nuclear reactor arrangement which facilitates both through the head refueling and full instrumentation of the assemblies from in the nuclear core that the present invention is directed. SUMMARY OF THE INVENTION An improved nuclear reactor arrangement is provided to facilitate both through the head instrumentation and refueling of assemblies from in the nuclear core. The arrangement is of the type including a reactor vessel head comprising a large rotatable cover having a plurality of circular openings therethrough, a plurality of upwardly extending nozzles mounted on the upper surface of a large cover, and a plurality of upwardly extending skirts mounted on a large cover about the periphery or boundary of the circular openings; a plurality of small plugs for each of the openings in the large cover, the plugs also having nozzles mounted on the upper surface thereof, and drive mechanisms mounted on top of some of the nozzles and having means extending therethrough into the reactor vessel, the drive mechanisms and nozzles extending above the elevation of the upwardly extending skirts. The improvement in the above type of arrangement comprises a skirt extension and refueling plug for each of the holes of the large rotatable cover for providing access to the nuclear core over each of the assemblies therein. The extension skirt is mountable in sealing relationship to the upwardly extending skirts when the small plugs are removed from the holes in the large rotatable cover, the extension skirt extends upwardly above the elevation of the nozzles on a large rotatable cover when the drive mechanisms have been removed therefrom. The extension skirt includes a laterally extending lip which overlies and is above some of the nozzles in close proximity with the upwardly extending skirt and which supports bearing means for rotatably supporting the refueling plugs for rotation within a circular opening defined within the upwardly extending skirt. The refueling plug includes an opening therethrough through which the assemblies from in the nuclear core may pass. The opening in the refueling plug is such as to provide access over each of the assemblies of the nuclear core upon proper rotation of the refueling plug and the large rotatable cover. Such a nuclear reactor arrangement has particular application for a nuclear reactor system having a plurality of relatively small sized assemblies forming the nuclear core wherein it might be difficult to place rotational supporting bearings between adjacent nozzles as is done in the nuclear reactor arrangement of the type described in U.S. application Ser. No. 537,216. During reactor operation, control and instrumentation of the nuclear core takes place through the reactor vessel head, i.e. the large rotatable cover and a plurality of small stationary plugs supported within the holes of the large cover. In order to refuel or remove assemblies from within the core, a small plug within the large rotatable cover is removed and replaced with an extension skirt and refueling plug. The extension skirt provides a way of placing the rotational supporting bearings above the elevation of the nozzles extending upwardly on the reactor vessel head. After refueling has taken place, the refueling plug and extension skirt are removed and replaced with the instrumentation and control mechanism supporting plugs.
	claims	1. A laser irradiation apparatus comprising:a laser oscillator configured to emit a laser light;an optical element configured to converge the laser light in one direction; andmeans for shielding an end region in a major-axis direction of the laser light, which is disposed between the optical element and an irradiation surface and is configured to make energy intensity in the irradiation surface higher in an end region in the major-axis direction of the laser light than a central region in the major-axis direction of the laser light,wherein the means for shielding comprises a slit plate, andwherein a surface of the slit plate facing the irradiation surface is tapered. 2. The laser irradiation apparatus according to claim 1, wherein the laser oscillator is configured to emit a continuous-wave laser or a pulsed laser with a repetition rate of 10 MHz or more. 3. The laser irradiation apparatus according to claim 1, wherein the optical element is a cylindrical lens or a diffractive optical element. 4. A laser irradiation apparatus comprising:a laser oscillator configured to emit a laser light;an optical element configured to converge the laser light in one direction; andmeans for shielding an end region in a major-axis direction of the laser light, which is disposed between the optical element and an irradiation surface,wherein the means for shielding is disposed at a position which satisfies 0.5 <Lλ<100 or 1 <L <200, where a distance between the means for shielding and the irradiation surface is L μm and a wavelength of the laser light is λμm,wherein energy intensity in the irradiation surface is higher in an end region in the major-axis direction of the laser light than a central region in the major-axis direction of the laser light. 5. The laser irradiation apparatus according to claim 4, wherein the laser oscillator is configured to emit a continuous-wave laser or a pulsed laser with a repetition rate of 10 MHz or more. 6. The laser irradiation apparatus according to claim 4, wherein the optical element is a cylindrical lens or a diffractive optical element. 7. The laser irradiation apparatus according to claim 4, wherein the means for shielding is a reflecting mirror. 8. A laser irradiation apparatus comprising:a laser oscillator configured to emit a laser light;a diffractive optical element configured to converge the laser light in one direction; anda reflecting mirror for shielding an end region in a major-axis direction of the laser light, which is disposed between the diffractive optical element and an irradiation surface and is configured to make energy intensity in the irradiation surface higher in an end region in the major-axis direction of the laser light than a central region in the major-axis direction of the laser light,wherein the reflecting mirror is disposed by inclining a reflective surface to the irradiation surface. 9. The laser irradiation apparatus according to claim 8, wherein the laser oscillator is configured to emit a continuous-wave laser or a pulsed laser with a repetition rate of 10 MHz or more. 10. A laser irradiation method comprising steps of:passing a laser light emitted from a laser oscillator through an optical element;shielding an end region in a major-axis direction of the laser light passed through the optical element by means for shielding comprising a slit plate, thereby obtaining a laser light in which energy intensity of an end region in the major-axis direction is higher than a central region; andirradiating an irradiation surface with the laser light in which energy intensity of the end region in the major-axis direction is higher than the central region; andwherein a surface of the slit plate facing the irradiation surface is tapered. 11. The laser irradiation method according to claim 10, wherein the laser oscillator is configured to emit a continuous-wave laser or a pulsed laser with a repetition rate of 10 MHz or more. 12. The laser irradiation method according to claim 10, wherein the optical element is a cylindrical lens or a diffractive optical element. 13. A laser irradiation method comprising steps of:passing a laser light emitted from a laser oscillator through an optical element;shielding an end region in a major-axis direction of the laser light passed through the optical element by means for shielding disposed at a position which satisfies 0.5 <Lλ<100 or 1 <L <200, where a distance between the means for shielding and an irradiation surface is L μm and a wavelength of the laser light is λμm; andirradiating the irradiation surface with the laser light in which energy intensity of an end region in the major-axis direction is higher than a central region, after shielding the end region in the major-axis direction of the laser light. 14. The laser irradiation method according to claim 13, wherein the laser oscillator is configured to emit a continuous-wave laser or a pulsed laser with a repetition rate of 10 MHz or more. 15. The laser irradiation method according to claim 13, wherein the optical element is a cylindrical lens or a diffractive optical element. 16. The laser irradiation method according to claim 13, wherein the means for shielding is a reflecting mirror. 17. A laser irradiation method comprising steps of:passing a laser light emitted from a laser oscillator through a diffractive optical element;shielding an end region in a major-axis direction of the laser light passed through the diffractive optical element by a reflecting mirror, thereby obtaining a laser light in which energy intensity of an end region in the major-axis direction is higher than a central region; andirradiating an irradiation surface with the laser light in which energy intensity of the end region in the major-axis direction is higher than the central region,wherein the reflecting mirror is disposed by inclining a reflective surface to the irradiation surface. 18. The laser irradiation method according to claim 17, wherein the laser oscillator is configured to emit a continuous-wave laser or a pulsed laser with a repetition rate of 10 MHz or more. 19. The laser irradiation apparatus according to claim 7, wherein the reflecting mirror is disposed by inclining a reflective surface to the irradiation surface. 20. The laser irradiation method according to claim 16, wherein the reflecting mirror is disposed by inclining a reflective surface to the irradiation surface. 21. The laser irradiation apparatus according to claim 8, further comprising a damper, wherein a laser light reflected by the reflecting mirror is configured to be absorbed by the damper. 22. The laser irradiation method according to claim 17, further comprising a step of absorbing a laser light reflected by the reflecting mirror by a damper.
	summary
047132116	claims	1. A process for the shutdown of a high temperature pebble-bed nuclear reactor having a core of spherical fuel elements, a reflector surrounding the core comprising a top reflector, a side reflector and a bottom reflector, means for the removal of decay heat, means for shutdown of the reactor over an extended period of time comprising at least one first absorber rod removably displaceable into the core of the reactor, and means for the rapid shutdown of the reactor comprising a plurality of second absorber rods removably displaceable into the side reflector of the reactor, the shutdown reactivity of said second absorber rods being such that the reactor may be reduced to a subcritical state under any condition by insertion of same into said side reflector, the process for shutdown of the reactor for all non-reactivity accidents comprising displacing only that portion of said second absorber rods into said side reflector which is sufficient to reduce the reactor to a subcritical state, the shutdown reactivity of said second absorber rods being such that only a portion of the total plurality of said absorber rods is required to achieve a subcritical state, removing decay heat to reduce the temperature of the reactor to a predetermined lower level and subsequently causing said reactor to become critical at said predetermined lower level. 2. The process of claim 1 wherein said predetermined temperature level is approximately 500.degree. C. 3. The process of claim 1 wherein said reactor possesses a power capacity of from 300 to 500 MW.sub.el. 4. The process of claim 1 wherein all of the reflector rods are inserted into the reflector in the event of a reactivity accident. 5. The process of claim 1 wherein about one third to one half of the reflector rods are inserted into the reflector for an operational shut-down or nonreactivity accident.
053923243	claims	1. In a fast-neutron nuclear reactor comprising a vessel containing a reactor fuel core and a system for cooling said core in which a liquid metal circulates and on which is placed at least one steam generator including a substantially cylindrical casing having a vertical axis, in which the liquid metal circulates, water-feed means and means for heat exchange between the liquid metal and the feed water, a device for removing residual power from said reactor at shutdown and/or under accident conditions, including, around said casing of said at least one steam generator, a tubular unit for recovering heat and for guiding a cooling gas including a metal shell covered on the outside by a layer of thermally insulating material and carrying, on its internal surface, a plurality of fins placed longitudinally of the shell and means for causing the cooling gas to flow in an annular space between said tubular unit and said casing of said at least one steam generator constituted by a vertical chimney connected to an upper part of said annular space via a pipe and at least one air inlet port in said annular space, at a lower part of said tubular unit, wherein said tubular unit is connected to a support structure of the steam generator by means of a bellows. 2. Device according to claim 1, wherein an expansion bellows is interposed on the pipe linking said tubular unit to said chimney.
	summary
	summary
	claims	1. A position measurement system for measuring a position of an object, the position measurement system comprising:a first incremental measurement unit configured to measure 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 configured to measure 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. 2. A position measurement system according to claim 1, wherein during initialization of the second incremental measurement unit, the second integer value is determined on the basis of a predetermined relationship between the first integer value, the first fraction, the second integer value and the second fraction. 3. A position measurement system according to claim 1, wherein the position measurement system is constructed and arranged to calibrate the second incremental measurement unit on the basis of a position measurement by the first incremental measurement unit. 4. A position measurement system according to claim 2, wherein an output signal of the first incremental measurement unit Xout1 substantially equalsXout1=IC1+(N1+φ1+ε1)·p1wherein:p1=a size of the first distance stepIC1=an initialization constantN1=the first integer valueφ1=the first fraction,ε1=a measurement error,and wherein an output signal of the second incremental measurement unit Xout2 substantially equalsXout2=IC2+(N2+φ2+ε2)·p2wherein:p2=a size of the second distance stepIC2=an initialization constantN2=the second integer valueφ2=the second fraction,ε2=a measurement error. 5. A position measurement system according to claim 4 wherein the predetermined relationship or the calibration is obtained by equating the output signal Xout1 of the first incremental measurement unit at a measurement position to the output signal Xout2 of the second incremental measurement unit at the measurement position. 6. A position measurement system according to claim 4 wherein the predetermined relationship is obtained bycalibrating the first incremental measurement unit at a first measurement position thereby initializing IC1 and N1,initializing the second incremental measurement unit at a second measurement position such that the output signal Xout2 of the second incremental measurement unit at the second measurement position corresponds to the output signal Xout1 of the first incremental measurement unit at the first measurement position, thereby initializing IC2. 7. A position measurement system according to claim 4, wherein the initialization of the second incremental measurement unit comprises equating the second integer value N2 by a round off operation. 8. A position measurement system according to claim 1, wherein the first incremental measurement unit comprises a grating and a first encoder head constructed and arranged to co-operate with the grating, wherein the second incremental measurement unit comprises a second encoder head constructed and arranged to co-operate with the grating and wherein the first distance step is a function of a pitch of the grating. 9. A position measurement system according to claim 8, wherein the grating is mounted to the reference frame and the first and second encoder heads are mounted to the object. 10. A position measurement system according to claim 8, wherein the grating is mounted to the object and the first and second encoder heads are mounted to the reference frame. 11. A position measurement system according to claim 8, wherein the second incremental measurement unit comprises a further grating constructed and arranged to co-operate with the first encoder head or with the second encoder head. 12. A position measurement system according to claim 1, wherein the first incremental measurement unit comprises a reflective surface constructed and arranged to reflect a radiation beam of an interferometer of the position measurement system to a first optical sensor of the first incremental measurement unit or to a second optical sensor of the second incremental measurement unit and wherein the first distance step is a function of a wavelength of the radiation beam. 13. A position measurement system according to claim 12, wherein the reflective surface is mounted to the object and the optical sensors are mounted to the reference frame. 14. A position measurement system according to claim 12, wherein the reflective surface is mounted to the reference frame and the optical sensors are mounted to the object. 15. A position measurement system according to claim 12, wherein the second incremental measurement unit comprises a further reflective surface constructed and arranged to reflect a radiation beam of the interferometer of the position measurement system to the first optical sensor or the second optical sensor. 16. A position measurement system according to claim 1, wherein the position measurement system is constructed and arranged to initialize the first incremental measurement unit on the basis of the second number and the first fraction. 17. 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;a projection system configured to project the patterned radiation beam onto a target portion of the substrate; anda position measurement system for measuring a position of the support or the substrate table, the position measurement system comprising:a first incremental measurement unit configured to measure a first number of first distance steps in a distance between a reference frame and the support or the substrate table, wherein the first number equals a first integer value plus a first fraction,a second incremental measurement unit configured to measure a second number of second distance steps in a distance between the reference frame and the support or the substrate table, 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. 18. A lithographic apparatus according to claim 17, wherein during initialization of the second incremental measurement unit, the second integer value is determined on the basis of a predetermined relationship between the first integer value, the first fraction, the second integer value and the second fraction. 19. A lithographic apparatus according to claim 17, wherein the position measurement system is constructed and arranged to calibrate the second incremental measurement unit on the basis of a position measurement by the first incremental measurement unit. 20. A lithographic apparatus according to claim 17, wherein the first incremental measurement unit comprises a grating and a first encoder head constructed and arranged to co-operate with the grating, wherein the second incremental measurement unit comprises a second encoder head constructed and arranged to co-operate with the grating and wherein the first distance step is a function of a pitch of the grating. 21. A lithographic apparatus according to claim 17, wherein the first incremental measurment unit comprises a reflective surface constructed and arranged to reflect a radiation beam of an interferometer of the position measurement system to a first optical sensor of the first incremental measurement unit or to a second optical sensor of the second incremental measurement unit and wherein the first distance step is a function of a wavelength of the radiation beam. 22. A lithographic apparatus according to claim 17, wherein the position measurement system is constructed and arranged to initialize the first incremental measurement unit on the basis of the second number and the first fraction.
039309401	description	The fuel assembly which is illustrated in transverse cross-section in FIG. 1 is of a type which is in very wide use at the present time. The assembly consists of a cluster of canned nuclear fuel pins 10 of elongated shape which are located at the nodes of a uniform hexagonal lattice. The fuel pins are carried by a support grid (not shown in FIG. 1), said grid being attached to a sleeve 14 which limits a duct for the circulation of coolant. The relative spacing of the fuel pins is determined by means of a spacing device which comprises in the case of each fuel pin 10 a metal wire 12 which is wound in a helix on the can and is applied against the cans of adjacent fuel pins or against the wall of the sleeve. The coolant flows in a general direction at right angles to the plane of FIG. 1 through a series of subchannels which communicate with each other and are delimited either solely by fuel pins or by fuel pins and the sleeve. In the case which is illustrated in which the fuel-pin lattice is triangular and in which the sleeve has a hexagonal transverse cross-sectional shape, the sub-channels can be divided into three groups: A first group is constituted by the sub-channels 16 of generally triangular shape each formed by the space which is provided for the coolant by three adjacent fuel pins which are located at the apices of a triangle Heating surfaces extend over one-half of the periphery of said subchannels 16 which are provided in the gratest number; they will be referred-to hereinafter as "inner sub-channels" and the fuel pins which are surrounded only by said sub-channels will be referred-to as "inner fuel pins." The rate of flow through each inner sub-channel will be designated as Di. A second group is constituted by the subchannels 18 which will be referred-to as "edge sub-channels" and are each constituted by the space which is provided for the coolant by two fuel pins located at the periphery of the cluster (so-called "edge pins") and by the corresponding portion of one face of the sleeve 14. The sub-channels are limited by heating surfaces which represent in the same manner as the preceding sub-channels approximately one-half of the surface of one fuel pin. The rate of flow through each edge sub-channel will be designated as Db. A third group is constituted by the sub-channels 20 or so-called "corner sub-channels," the number of which is equal to the number of corners of the transverse cross-section of the sleeve 14. Each sub-channel 20 is constituted by the space which is provided for the coolant between a "corner pin" located within a dihedron of the sleeve 14 and the two wall portions of the sleeve which constitute said dihedron. The coolant which flows through a corner subchannel is surrounded by a heat-transfer surface which represents one-sixth of the surface area of a fuel pin. The rate of flow through a corner sub-channel will be designated as Dc. Finally, the fuel pins and sub-channels which form part of the second group and the third group will be generally designated by the terms "lateral sub-channels" and "lateral fuel pins" in contrast to the "inner sub-channels" and "inner fuel pins." If not consideration is given to the unitary pressure drops within the sub-channels which arise essentially from the spacer wires, the heating to which the coolant is subjected is identical within all the sub-channels which are assumed to be isolated from each other only on condition that the following relation is satisfied: EQU Di = Db = 3 Dc If this condition is fulfilled, the outlet temperature of the coolant will be substantially equal in all the sub-channels provided that the inlet temperatures are the same. If no account is taken of unitary pressure drops which are essentially due to the presence of the spacer wires, it can be considered that the flow rate D within a given sub-channel is provided by the formula: EQU D = K .sup.. S .sup.. y.sup.0.66 (1) In this formula, S is the transverse cross-sectional area of the sub-channel, y is the hydraulic diameter of the channel and K is a coefficient which is identical in the case of all sub-channels but is a function of the pressure difference between the upstream and downstream ends of the sub-channels. In the case of an assembly in accordance with the prior art of the type illustrated in FIG. 1, it is observed that the equality relation given above is not satisfied and that we have: EQU Di < 3 Dc < Db Referring now to FIGS. 2 to 10, there will now be described a number of different arrangements according to the invention which make it possible to achieve or at least come close to the conditions of equilibrium of the channels. In order to satisfy or at least approximate to the condition Di = 3 Dc, it is necessary to reduce the spacing between each corner pin and the sleeve. In the form of construction which is illustrated in FIG. 2 (in which the components corresponding to those illustrated in FIG. 1 bear the same reference numerals to which is assigned the index a), this result is achieved by providing each lateral fuel pin 10a with a spacer wire 22a having a smaller diameter than that of the spacer wires 12a which are fitted on the inner fuel pins. The ratio to be adopted between the diameters of the wires 22a and 12a in order to satisfy the relation Di = 3 Dc will evidently be a function of the diameter of the fuel pins and of the diameter of the wires 12a. The ratio can be determined by making use of the above formula (1) which gives D as a function of the cross-sectional area of the channel and of the hydraulic diameter. In the case of a fuel pin diameter of the order of 7 mm and a spacing of 1 mm between inner pins, that is to say in the case of conditions commonly met with, the ratio between the diameters of the wires 22a and 12a is found to be of the order of 0.6. The difference in heat build-up between the central sub-channels and corner sub-channels is also minimized if the arrangement illustrated in FIG. 3 is adopted. This figure illustrates on a large scale a portion of the transverse cross-section of a fuel assembly and again shows a sleeve 14' in which are placed canned-fuel pins 10'. Each fuel pin is again fitted with a helically wound spacer wire 12' which has a constant diameter in the case of the central fuel pins. However, in contrast to the wire 12 of FIG. 1, the wire 12' extends from the can to a radial distance which is not constant in the case of the lateral fuel pins. This radial distance is smaller in the zones of the wire which are intended to be applied against the sleeve 14' than in the zones which are intended to be applied against the can of an adjacent fuel pin, the radical distance of projection in the zones last mentioned being the same as the constant distance of projection from the pins of the central portion. The sleeve 14' evidently has slightly smaller dimensions than in the case of FIG. 1. The difference between the maximum distance of projection of the wires 12' and the minimum distance of projection will evidently be chosen so that the coolant temperature at the outlets of all the sub-channels 16, 18 and 20 should be substantially the same. In order that the sleeve 14' should be intimately applied against the spacer wires 12' and thus leave no clearance which would constitute a short-circuit, use can advantageously be made of a sleeve of the type which was illustrated and described in French Pat. No. 1,519,592 as filed on Dec. 5, 1966 by Commissariat a l'Energie Atomique. In the embodiment which is illustrated in FIGS. 3 and 4, the periodic modifications of the radial projection of the wires 12' which are intended to be placed on the lateral fuel pins are made by flattening the wire at intervals by pinching, for example. If p designates the pitch of the wire (that is to say the length of wire between two points which will be located on a same generator-line of the can), it will be possible to pinch the wire 12' along sections having a length of approximately p/3 at intervals p. The distance of pinching will evidently be greater in the case of corner-pin wires. Particular care must obviously be taken at the time of positioning of the wire on the can to ensure that the flattened portions are placed at levels which are different in the case of lateral fuel pins which cooperate with different faces of the sleeve 14: the need for this arrangement is apparent from FIG. 3 in which the wires 12' are all shown in cross-section at the same level. It is readily apparent that the helical spacer members can be constituted by components other than wires. For example, as illustrated in FIG. 5, each fuel pin 10" can be provided with a fin 12". The fin of each lateral pin is then truncated as shown at 21 in FIG. 5. The arrangements illustrated in FIGS. 2 to 5 make it possible to bring the cross-sectional area and the hydraulic diameter of the corner sub-channels to values which balance the flow rates within the corner sub-channels and the inner sub-channels. But the correlative reduction in cross-sectional area and hydraulic diameter of the edge channels is not sufficient to ensure that the condition Di = Db is also satisfied. In the embodiment which is illustrated in FIG. 6, this second condition is satisfied by providing the walls of the sleeve 14b with longitudinal ribs 24 which project between all the adjacent lateral fuel pins 10b and fill a suitable proportion of the primitive edge sub-channels. The ribs 24 which are illustrated in FIG. 6 are constituted by strips of semi-circular cross-sectional shape which are placed against the flat internal face of the sleeve 14b. Said strips are attached by welding or brazing. The embodiment which is illustrated in FIG. 6 can permit a number of different alternatives insofar as concerns on the one hand the shape of the ribs and on the other hand the structural arrangement of these latter. In the alternative form which is illustrated in FIG. 7, the wall of the sleeve 14c is deformed in order to constitute longitudinal ribs 24c. In the variant shown in FIG. 8, six plates 26 are provided with ribs 24b and are engaged by sliding between the suitably dimensioned sleeve 14d and the lateral fuel pins 10d. It is apparent that the ribs 24d of FIG. 8 have a shape which is no longer semi-circular but triangular. Again in all these cases, the transverse cross-sectional shape of the ribs is determined by means of the above formula (1) and by taking into account the fact that the radial distance of projection of the wires 22 is smaller than that of the wires 12. While the arrangements shown in FIGS. 2, 6, 7 and 8 do in fact serve to balance the inner sub-channels with the corner sub-channels as well as to reduce the unbalance between the edge sub-channels and the inner sub-channels (shown in FIG. 2) or even virtually to remove said unbalance (as shown in FIGS. 6, 7 and 8), these arrangements are nevertheless atteneded by one disadvantage: as can be seen by making a comparison between on the one hand FIG. 1 and on the other hand FIGS. 2 and 6, a number of bearing points at which the fuel pins are applied against each other by means of spacer wires has been dispensed with. In particular, it is apparent that the lateral fuel pins are no longer applied against each other. In order to eliminate this disadvantage, wires which project to a variable radial distance can be mounted on the lateral fuel pins (this arrangement being shown in FIGS. 3 and 4) or, alternatively, the solution illustrated in FIGS. 9 and 10 can be adopted. In these figures, the components which correspond to those already shown bear the same reference numerals to which is assigned the index e. The lateral fuel pins of the cluster carry a spacer wire 22e having a smaller diameter than the wires 12e which are provided on the inner fuel pins. The cross-sectional area of the lateral sub-channels is thus reduced. Tube sections 28 are engaged over the wires 22e and have an external diameter which is equal to that of the wires 12e. The length and position of said tube sections are such that each lateral fuel pin is applied against the adjacent pins by means of said sections whereas that portion of the wire which is located opposite to the sleeve 14e remains uncovered. In practice, each tube section which is carried by an edge pin will represent between one-half and two-thirds of one turn of the helically wound wire 22e. The tube sections carried by the corner pins will have a slightly smaller length. In the embodiment which is illustrated in FIG. 9, the sleeve is further provided with internal ribs 24e which are intended to balance the flow within the edge sub-channels and the inner sub-channels. Said internal ribs are constituted by longitudinal splines of triangular cross-sectional shape and are formed in one piece with the sleeve 14e. It will be readily apparent that the invention is not limited solely to the embodiments which have been described by way of example with reference to the accompanying drawings and that the scope of this patent extends to any alternative form which remains within the definition of equivalent means.
	description	The present invention relates to separating amorphous iron oxides; more particularly, relates to acquiring characteristics of radioactive iron oxides during various periods on operating a nuclear power plant to solve radiation buildup problem; providing parameters for improving water quality and chemistry performance indicator of the power plant; and separating crystalline deposits while the dissolving rate of radioactive iron oxides reaches more than 90%. No patents concerning separating amorphous radioactive iron oxides for nuclear power plant are found. In related documents, methods for characteristic analysis and quantitative analysis over radioactive iron oxides in a nuclear power plant are done through infrared spectrophotometer, Mössibour apparatus and X-ray diffractometer (XRD). But, most methods analyze crystalline radioactive iron oxides only and methods for amorphous ones are not available. Toshiba Co. and Hitachi Co., Japan, use external standard methods for analysis with XRD. GE Co., USA, uses Rietveld method for analysis with Mössibour apparatus, where simulation is processed by computer for quantitative analysis. However, on judging mixing ratios of radioactive iron oxides in metal rust, accuracy is a problem. Hence, the prior arts do not fulfill all users' requests on actual use. The main purpose of the present invention is to acquire characteristics of radioactive iron oxides during various periods on operating a nuclear power plant to solve radiation buildup problem; to provide parameters for improving water quality and chemistry performance indicator of the power plant; and to separate crystalline deposits while the dissolving rate of radioactive iron oxides reaches more than 90%. To achieve the above purpose, the present invention is a method of separating amorphous iron oxides, comprising steps of: (a) obtaining a water sample of corrosion product (crud); (b) filtering the water sample of corrosion product (crud) to obtain granules containing radioactive iron oxides; (c) dispersing the granules containing radioactive iron oxides through ultrasonic vibration to be added with an acid liquor to obtain a solution containing amorphous radioactive iron oxides with granules containing crystalline radioactive iron oxides and separating the solution containing amorphous radioactive iron oxides and the granules containing crystalline radioactive iron oxides through filtering; (d) processing inductively coupled plasma (ICP) quantitative analysis to the solution containing amorphous radioactive iron oxides to obtain a density of amorphous iron; and (e) processing XRD analysis to the granules containing crystalline radioactive iron oxides to obtain a weight percentage of crystalline radioactive iron oxides in each granule; dissolving the granules containing crystalline radioactive iron oxides with aqua regia (chlorazotic acid) to obtain a solution containing crystalline radioactive iron oxides; and processing ICP quantitative analysis to the solution containing crystalline radioactive iron oxides to obtain a density of crystalline iron. Accordingly, a novel method of separating amorphous iron oxides is obtained. The following description of the preferred embodiment is provided to understand the features and the structures of the present invention. Please refer to FIG. 1 to FIG. 5, which are a block view showing the preferred embodiment according to the present invention and views showing step (b) to step (e). As shown in the figures, the present invention is a method of separating amorphous iron oxides, comprising the following steps: (a) Sampling 1: A water sample of corrosion product (crud) 11 is taken from at a condensate demineralizer (CD) inlet, a CD outlet or a feed water (FW) port of a nuclear power plant. (b) Filtering 2: In FIG. 2, the water sample of corrosion product (crud) 11 is filtered by using a circle filtering paper and a stainless frame to obtain granules which contain radioactive iron oxides and have granular size bigger than 0.45 micrometers (μm). Therein, the circle filtering paper has pores having a size of 0.45 micrometers (μm) and has a diameter of 47 millimeters (mm). (c) Dissolving and separating 3: In FIG. 3, the aggregating granules 21 containing radioactive iron oxides are dispersed through ultrasonic vibration 31 to be added with an acid liquor 32 at a temperature of 40 Celsius degrees (° C.) to 100° C. for 5 to 60 minutes. Amorphous radioactive iron oxides in the granules 21 containing radioactive iron oxides is dissolved to form a solution 211 containing amorphous radioactive iron oxides. Then the granules 212 containing crystalline radioactive iron oxides are left and separated from the solution 211 containing amorphous radioactive iron oxides through filtering 33. Therein, the acid liquor 32 is formed by mixing a first acid liquor 321 and a second acid liquor 322; the first acid liquor 321 is hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, acetic acid, carbonic acid or hydrofluoric acid and has a density between 0.01 M and 5M, preferred 0.05M˜2M; the second acid liquor 322 is hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, acetic acid, carbonic acid or hydrofluoric acid and has a density between 0.05M and 3M, preferred 0.1 M˜1.5M; the first acid liquor 321 and the second acid liquor 322 have a mixing rate of 20%˜99%: 1%˜80%; and, the acid liquor has a pH value of pH0.01˜pH2.0, preferred pH0.1˜pH0.5. (d) Analyzing solution 4: In FIG. 4 inductively coupled plasma (ICP) quantitative analysis is processed to the solution 21 containing amorphous radioactive iron oxides to obtain a density of amorphous iron. (e) Analyzing granules 5: In FIG. 5, X-ray diffraction (XRD) analysis is processed to the granules 212 containing crystalline radioactive iron oxides to obtain a weight percentage of crystalline radioactive iron oxides in each granule. The granules 212 containing crystalline radioactive iron oxides are dissolved with aqua regia 51 (chlorazotic acid) to obtain a solution 212a containing crystalline radioactive iron oxides. Then, ICP quantitative analysis is processed to the solution 212a containing crystalline radioactive iron oxides to obtain a density of crystalline iron. Through the above steps, the present invention analyzes corrosion product (crud) of a nuclear or thermal power plant and does so for related studies on various radioactive iron oxides. For example, the studies on crystalline radioactive iron oxides, like α-FeOOH, β-FeOOH, γ-FeOOH, δ-FeOOH, α-Fe2O3, γ-Fe2O3, Fe3O4, etc.; and on amorphous radioactive iron oxides, like Fe(OH)3, Fe(OH)2, etc. To sum up, the present invention is a method of separating amorphous iron oxides, where characteristics of radioactive iron oxides during various periods on operating a nuclear power plant are acquired to solve radiation buildup problem; parameters for improving water quality and chemical indicator performance of the power plant are thus provided; crystalline deposits are separated while the dissolving rate of radioactive iron oxides reaches more than 90%; and the present invention does not use complex utilities, is easy to use and has a low operation cost for fast analysis.
	claims	1. A method of fragmentation of elements of a nuclear reactor, comprising:placing a plurality of elements inside a cask;cutting the plurality of elements inside the cask after the step of placing the plurality of elements inside the cask, wherein the cask comprises at least one perforation configured to drain water;wherein for each of the elements, the steps of placing and cutting the plurality of elements comprises:lowering the element into the cask so that a length of the element in the cask is equivalent to a full internal height of the cask, wherein the lowering occurs using a gripper having clamping jaws;after the lowering step, intercepting the element at an upper edge of the cask, lifting the element, and positioning the element using video surveillance and artificial lighting so that a hydraulic cutter is directly under the clamping jaws;cutting the element at a position corresponding to a level of the upper edge of the cask when the element has been lowered into the cask in accordance with the lowering step, thereby separating a fragment of the element and a remaining portion of the element that is an upper part of the element, the fragment having a length equal to the full internal height of the cask; andlowering the remaining portion of the element inside the cask so that a length of the remaining portion of the element in the cask is equivalent to the full internal height of the cask; andcutting the element repeatedly to provide fragments until the element is completely cut to fragments that are no longer than the full internal height of the cask, andwherein the cutting of each of the plurality of elements is carried out with remote control in a process vessel under water. 2. The method according to claim 1, wherein the cutting the plurality of elements is carried out until the cask is completely filled. 3. The method according to claim 1, wherein the cask is moved to a storage location after tilling the cask with fragments of the elements. 4. The method according to claim 2, wherein the cask is moved to a storage location after filling the cask with fragments of the elements.
	description	1. Field of the Invention The present invention relates to a flow rate verification failure diagnosis apparatus, a flow rate verification failure diagnosis system, a flow rate verification failure diagnosis method, and a control program product for flow rate verification failure diagnosis. 2. Description of Related Art In a film deposition device or a dry etching device in a semiconductor manufacturing process, special gas such as silane or phosphine, corrosive gas such as chlorinated gas, combustible gas such as hydrogen gas, or the like are used. Flow rates of these gases should strictly be controlled. The reason of this is because the gas flow rate directly affects a quality of the process. Specifically, the gas flow rate greatly affects a film quality in a film deposition process or a quality of a circuit processing in an etching process, whereby a yield of a semiconductor product is determined according to precision of the gas flow rate. Another reason is that most of these gases are harmful to a human body and environment or have explosiveness. These gases are not allowed to be directly disposed in the atmosphere after they are used, so that a device used in a semiconductor manufacturing process should be provided with detoxifying device in accordance with a type of gas. However, the detoxifying device described above has limited processing capacity in general. Therefore, when the flow rate more than the allowable value flows, it cannot perfectly process the gas, so that the deleterious gas might be flown out in the atmosphere or the detoxifying device might be broken. Moreover, since these gases, especially high-purity dust-free gas that can be used in a semiconductor manufacturing process, are expensive, and limitation is imposed on some gases for their use due to natural deterioration, they cannot be preserved in a large quantity. In view of this, a known mass flow controller serving as a flow rate control device has conventionally been mounted in a semiconductor manufacturing process circuit so that a gas flows in an optimum flow rate for every type of gas. The mass flow controller described above changes the set flow rate by changing the applied voltage thus responding to changes in a process recipe. However, these gases used in the semiconductor manufacturing process, especially the material gas for the film deposition among the so-called process gases, might cause precipitation of solid substances in a gas line due to its characteristics, so that the flow volume might be changed. The mass flow controller is formed with a capillary tube inside in order to supply a fixed flow rate with high precision. Even a small amount of precipitation of the solid substance on this portion could deteriorate the flow precision of the gas to be supplied. Further, since a gas with high corrosivity for an etching processor the like is flown, the corrosion of the mass flow controller cannot be avoided even if a material having a high corrosion resistance such as a stainless material or the like is used. As a result, a secular deterioration could occur, deteriorating the flow precision. As described above, in the mass flow controller, the relationship between the applied voltage and the actual flow rate changes, so that the actual flow rate might possibly change. Therefore, the mass flow controller needs to be periodically subject to flow rate verification and calibration. The flow rate verification of the mass flow controller is basically performed by using a film flowmeter. However, this measurement is performed with a part of a pipe removed. After the measurement, the pipe should be assembled in the original state, and a leakage check should be executed. Therefore, the work is very time-consuming. Accordingly, it is ideal that the flow rate verification can be executed without removing the pipe. One of methods of performing a flow rate verification in a state where pipes are assembled is disclosed in Japanese Unexamined Patent Application Publication No. 2006-337346. FIG. 11 is a schematic configuration diagram of a conventional flow rate verification system 100. In the conventional flow rate verification system 100, a gas passage 103 is provided between a first shutoff valve 101 and a second shutoff valve 102, and process gas whose flow rate is adjusted by a mass flow controller 110 is supplied to a process chamber 111. The gas passage 103 is communicated with an inlet of a vacuum pump 104 via a discharge passage 105. In the discharge passage 105, a third shutoff valve 106, a temperature sensor 108, a pressure sensor 107, and a fourth shutoff valve 109 are disposed. The flow rate verification system 100 has a verification controller connected to the devices 106, 107, 108, and 109 for storing compression factor data peculiar to gaseous species and a value of volume of a predetermined space defined by an outlet of the mass flow controller 110 and the second and fourth shutoff valves 102 and 109. At first measurement time, the flow rate verification system 100 obtains a mass G1 from a pressure P1 measured by the pressure sensor 107, a temperature T1 measured by the temperature sensor 108, a first compression factor Z1 corresponding to the pressure P1 and the temperature T1, and a volume V indicated with a broken line in the diagram. At second measurement time, the flow rate verification system 100 obtains a mass G2 from a pressure P2 measured by the pressure sensor 107, a temperature T2 measured by the temperature sensor 108, a second compression factor Z2 corresponding to the pressure P2 and the temperature T2, and the volume V. The flow rate verification system 100 obtains difference between the mass G1 at the first measurement time and the mass G2 at the second measurement time and verifies the flow rate of the mass flow controller 110 on the basis of the difference. The above mentioned flow rate verification system 100 performs a flow rate verification using gas actually used for processing and corrects measurement values with factors peculiar to the gaseous species. Thus, the flow rate verification precision is high. However, the conventional flow rate verification system 100 performs the flow rate verification on the basis of measurement results of the pressure sensor 107 and the temperature sensor 108 disposed in a gas box. Even in a case where it is determined that there is abnormality in the flow rate verification result, cause of the abnormality is not limited to the mass flow controller 110 while the flow rate verification is underway. There are cases that the cause of the abnormality is a failure in the pressure sensor 107 or disturbance (such as a temperature change in the gas box). The conventional flow rate verification system 100 does not have measures for verifying probability of occurrence of abnormality in the flow rate of the mass flow controller while the flow rate verification is underway. Consequently, in the conventional flow rate verification system 100, the pipes and the like have to be taken from the mass flow controller 110, and the mass flow controller 110 has to be taken from the gas box in order to diagnose failure in each of the devices. The failure test cannot be performed under the same conditions as those when the flow rate verification system 100 detects the flow rate abnormality. It cannot therefore discriminate between the case where the flow rate abnormality is caused only by a failure in the mass flow controller 110 while the flow rate verification is underway and the case where the flow rate abnormality is caused by a failure in another device configuring the flow rate verification system 100. Therefore, in the conventional flow rate verification system 100, when the flow rate abnormality is detected, the cause of the flow rate abnormality is not limited to abnormality in the mass flow controller 110 while the flow rate verification is underway. Thus, the reliability of the flow rate verification is low. The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a flow rate verification failure diagnosis apparatus, a flow rate verification failure diagnosis system, a flow rate verification failure diagnosis method, and a control program product for flow rate verification diagnosis that can improve the reliability of the flow rate verification. To achieve the purpose of the invention, there is provided a flow rate verification failure diagnosis apparatus comprising a gas supply pipe system including flow rate control devices and a flow rate verification unit having a pressure measurement device, the flow rate verification unit detecting flow rate abnormality by measuring a flow rate of fluid in each of the flow rate control device on the basis of pressure of the fluid measured by the pressure measurement device. The flow rate verification failure diagnosis apparatus further comprises a failure diagnosis device having a mode to diagnose a failure in the pressure measurement device in a case of the flow rate verification unit detecting the flow rate abnormality. According to another aspect of the invention, preferably, a flow rate verification failure diagnosis system comprises a gas supply pipe system including flow rate control devices and a flow rate verification unit having a pressure measurement device, the flow rate verification unit detecting flow rate abnormality by measuring a flow rate of fluid in the flow rate control devices on the basis of pressure of the fluid measured by the pressure measurement device. The flow rate verification failure diagnosis system further comprises a flow rate control device failure diagnosis device for determining a failure causing the flow rate abnormality in other devices besides the flow rate control devices when the flow rate verification unit determines a flow rate abnormality in all of the flow rate control devices and a failure causing the flow rate abnormality in a specific one of the flow rate control devices when the flow rate verification unit determines the flow rate abnormality only in the specific flow rate control device. According to another aspect of the invention, preferably, a flow rate verification failure diagnosis method is adapted to diagnose a failure causing flow rate abnormality when a flow rate verification unit detects the flow rate abnormality, the flow rate verification unit measuring a flow rate of fluid on the basis of pressure measured by a first pressure measurement device. The flow rate verification failure diagnosis method determines a failure causing the flow rate abnormality in a specific one of the flow rate control devices when the flow rate verification unit detects the flow rate abnormality in the specific flow rate control device among the flow rate control devices and a failure causing the flow rate abnormality in other devices besides the flow rate control devices when the flow rate verification unit detects the flow rate abnormality in all of the flow rate control devices. According to another aspect of the invention, preferably, a flow rate verification failure diagnosis program recorded on a computer readable medium product to be executed in a computer controlling a gas supply pipe system includes flow rate control devices and a flow rate verification unit having a pressure measurement device, the flow rate verification unit measuring flow rate of the flow rate control devices on the basis of pressure measured by the pressure measurement device and performing flow rate verification. The program comprises the step of diagnosing a failure causing the flow rate abnormality when the flow rate abnormality is detected in the gas supply pipe system. A detailed description of preferred embodiments of a flow rate verification failure diagnosis apparatus, a flow rate verification failure diagnosis system, a flow rate verification failure diagnosis method, and a control program product for flow rate verification failure diagnosis embodying the present invention will now be given referring to the accompanying drawings. <General Configuration of Flow Rate Verification Failure Diagnosis Apparatus and Flow Rate Verification Failure Diagnosis System> FIG. 1 is a schematic configuration diagram of a flow rate verification failure diagnosis apparatus 8, a gas supply pipe system 25, and a flow rate verification failure diagnosis system 26. The flow rate verification failure diagnosis apparatus 8 and the flow rate verification failure diagnosis system 26 are applied to, for example, a gas box 20 shown in FIG. 1. The gas supply pipe system 25 is obtained by installing a plurality of gas units 6A, 6B, 6C, . . . in the gas box 20. Each of the gas units 6A, 6B, 6C, . . . has the same configuration. The subscripts “A”, “B”, “C”, . . . of reference numerals are attached for convenience so that a plurality of gas units, flow devices, flow rate control devices, and the like constructing the gas units are distinguished from each other. In the following, when it is unnecessary to distinguish the components from each other, the subscripts are omitted as appropriate. The gas units 6A, 6B, 6C, . . . are connected in parallel to a gas supply valve 15 to supply various process gases to a treatment chamber (not shown). A flow rate verification unit 10 is disposed in parallel with the gas supply valve 15. The gas units 6A, 6B, 6C, . . . are connected to a vacuum pump (not shown) via the flow rate verification unit 10 to discharge the process gases. In the gas box 20, a controller 21 and a gas box temperature sensor 22 are provided. The controller 21 is a controller of the flow rate verification unit 10 and is connected to a higher-level apparatus 23 provided on a semiconductor manufacturing apparatus side. A flow rate verification failure diagnosis program 30 which will be described later is stored in storage media such as a CD-ROM. In the higher-apparatus 23, the flow rate verification failure diagnosis program 30 is installed. The gas box temperature sensor 22 measures temperature in the gas box 20. <Configuration of Gas Unit> The gas unit 6 is formed with a regulator 1, a pressure sensor 2, an input open/close valve 3, a mass flow controller 4, and an output open/close valve 5 connected in series. In the gas unit 6, process gas is adjusted to a set pressure by the regulator 1, the flow rate of the process gas is adjusted by the mass flow controller 4, and the process gas is outputted from the output open/close valve 5. The process gas outputted from the output open/close valve 5 is supplied to a not-shown treatment chamber via the gas supply valve 15 or discharged via the flow rate verification unit 10. To each of the gas units 6, process gases of various kinds are supplied. <Flow Rate Verification Unit> In the flow rate verification unit 10, a pressure sensor 12 and a temperature sensor 13 are disposed between a first shutoff valve 11 and a second shutoff valve 14. <Electric Block Configuration of Controller> FIG. 2 is an electric block diagram of the controller 21. The controller 21 is a known computer. The controller 21 has a CPU 31 for processing and calculating data, a ROM (Read Only Memory) 32 for storing a program, a RAM 33 as a readable/writable volatile memory for storing data and a program, an NVRAM 34 as a readable/writable nonvolatile memory for storing data and a program, an input/output interface (hereinbelow, called “input/output I/F”) 35 for controlling input/output of signals to/from devices in the gas box 20, and a communication interface (hereinbelow, called “communication I/F”) 36 connected to the higher-level apparatus 23 to control transmission/reception of data. In the NVRAM 34, a pressure sensor output fluctuation abnormality detection program 37 and a zero-point shift detection program 38 are stored. The programs 37 and 38 will be described later. The NVRAM 34 is also provided with an output fluctuation band initial value storing member 39 for storing an “output fluctuation band initial value” indicative of the difference between the maximum and minimum values of pressures outputted from the normal pressure sensor 12 at the time of a flow rate verification, and a pressure average initial value storing member 40 for storing a “pressure average initial value” indicative of an average value of pressures measured at the time of the flow rate verification by the normal pressure sensor 12. The “output fluctuation band initial value” and the “pressure average initial value” may be theoretical values in designing or actual measurement values obtained by executing a pressure sensor output fluctuation abnormality detecting process (see FIG. 4) and a pressure sensor zero-point shift detecting process (FIG. 5) after attachment of the flow rate verification failure diagnosis apparatus 8 to the semiconductor manufacturing apparatus or completion of assembly of the flow rate verification failure diagnosis apparatus 8. To the input/output I/F 35, the gas box temperature sensor 22 and the first shutoff valve 11, the pressure sensor 12, the temperature sensor 13, and the second shutoff valve 14 of the flow rate verification unit 10 are connected. On the other hand, to the higher-level apparatus 23, the pressure sensor 2, the input open/close valve 3, the mass flow controller 4, and the output open/close valve 5 of each of the gas units 6 and the gas supply valve 15 are connected. <Flow Rate Verification Method> Next, a flow rate verification method applying the gas supply pipe system 25 and the flow rate verification unit 10 of the first embodiment will be described. For example, in a case of performing flow rate verification on the gas unit 6J, output open/close valves 5A to 5I of the gas units 6A to 6I and the gas supply valve 15 are closed. On the other hand, an input open/close valve 3J and an output open/close valve 5J of the gas unit 6J, and the first shutoff valve 11 and the second shutoff valve 14 in the flow rate verification unit 10 are opened. In this state, a process gas is supplied from a process gas supply source 7J to a mass flow controller 4J. In order to make the controlled flow rate of the mass flow controller 4J stable, after the process gas is supplied to the gas unit 6J for 30 seconds, the second shutoff valve 14 of the flow rate verification unit 10 is closed. As a result, the pressure in the flow rate verification unit 10 increases. The pressure sensor 12 measures elapsed time since a pressure P1 (for example, 5 kPa) is detected until a pressure P2 (for example, 13 kPa) is detected. The reason why the time is measured is because the pressure rise time varies according to the flow rate. When the pressure sensor 12 detects 13 kPa, the second shutoff valve 14 is opened to proceed to the next flow rate verification. The controller 21 receives measurement results from the pressure sensor 12 and the temperature sensor 13 to calculate the flow rate as follows. A pressure increase amount ΔP between the first shutoff valve 11 and the second shutoff valve 14 is obtained by subtracting the pressure P1 from the pressure P2. Since the pressure sensor 12 detects pressure at predetermined intervals (for example, 0.1 second intervals), by counting the number of pressure detecting times since the pressure sensor 12 detects the pressure P1 until the pressure sensor 12 detects the pressure P2, measurement time Δt in which the pressure between the first shutoff valve 11 and the second shutoff valve 14 rises from P1 to P2 is obtained. By dividing the pressure increase amount ΔP by the measurement time Δt, an increase pressure value ΔP/Δt per unit time is obtained. A gas constant R is obtained by using the gas constant as it is of the process gas used. Temperature T is a temperature detected by the temperature sensor 13. Further, a tank volume V is measured in advance before the flow rate verification and stored in the NVRAM 34. By assigning the known numerical values (the increase pressure value ΔP/Δt per unit time, gas constant R, temperature T, and tank volume V) to the following equation 1, a flow rate Q is calculated. Flow ⁢ ⁢ rate ⁢ ⁢ Q = Δ ⁢ ⁢ P Δ ⁢ ⁢ t × V RT Equation ⁢ ⁢ 1 The flow rate verification unit 10 compares the calculated flow rate Q with a set flow rate of the mass flow controller 4J. When the calculated flow rate Q and the set flow rate coincide with each other, the flow rate verification unit 10 determines that the mass flow controller 4J properly controls the flow rate (normal). When they do not coincide with each other, the flow rate verification unit 10 determines that the mass flow controller 4J does not properly control the flow rate (abnormal). <Flow Rate Verification Failure Diagnosis Method> The flow rate verification failure diagnosis method will be described with reference to FIG. 3. FIG. 3 is a flowchart showing operations of the flow rate verification failure diagnosis program 30 executed by the higher-level apparatus 23 shown in FIG. 2. The higher-level apparatus 23 completes the flow rate verification on all of the mass flow controllers 4 in the gas box 20, and detection of the flow rate abnormality triggers the execution of the flow rate verification failure diagnosis program 30 shown in FIG. 3. Concretely, the higher-level apparatus 23 determines whether the flow rate abnormality occurs in all of the mass flow controllers 4 (flow rate control devices) in step 1 (hereinbelow, written as “S1”) in FIG. 3. In the case where it is determined that no flow rate abnormality occurs in all of the mass flow controllers 4 (S1:No), the higher-level apparatus 23 determines that the mass flow controller 4 that detects flow rate abnormality fails. On the other hand, in the case where the higher-level apparatus 23 determines that there is flow rate abnormality in all of the mass flow controllers 4 (S1:Yes), whether or not all of the flow rates Q of the mass flow controllers 4 in which flow rate abnormality occurs are deviated in the same direction from the set flow rate is determined in S2. In the case where all of the flow rates Q of the mass flow controllers 4 in which flow rate abnormality occurs are not deviated in the same direction from the set flow rate (S2:No), in S3, whether pressure fluctuation in the pressure sensor 12 is normal or not is determined. The determining method will be described later. In the case where the pressure fluctuation in the pressure sensor 12 is not normal (S3:No), it is determined that abnormality occurs in the output fluctuation in the pressure sensor 12 of the flow rate verification unit 10. On the other hand, in the case where the pressure fluctuation in the pressure sensor 12 is normal (S3:Yes), it is determined that the flow rate verification unit 10 fails. In the case where all of the flow rates Q of the mass flow controllers 4 in which flow rate abnormality occurs are deviated in the same direction from the set flow rate (S2:Yes), in S4, the temperature measured by the gas box temperature sensor 22 is inputted via the controller 21, and whether fluctuation occurs in the temperature in the gas box 20 or not is determined. In the case where it is determined that temperature fluctuates in the gas box 20 (S4:No), it is determined that flow rate abnormality is detected on the basis of the temperature change in the gas box 20 (the apparatus disturbance influence). A failure caused by the temperature change (disturbance) in the gas box 20 may be directly determined by the controller 21 in the flow rate verification failure diagnosis apparatus 8. In the case where it is determined that there is no temperature fluctuation in the gas box 20 (S4:Yes), in S5, whether the zero point of the pressure sensor 12 shifts or not is detected. The process of detecting the zero-point shift in the pressure sensor 12 will be described later. In the case where it is determined that the zero point of the pressure sensor 12 does not shift (S5:No), it is determined that the flow rate abnormality is detected due to occurrence of a span error in the pressure sensor 12 of the flow rate verification unit 10. When it is determined that the zero point of the pressure sensor 12 shifts (S5:Yes), the cause of the flow rate abnormality detected is determined as the shift of the zero point of the pressure sensor 12. <Pressure Sensor Output Fluctuation Detecting Method> FIG. 4 is a flowchart of the pressure sensor output fluctuation abnormality detection program 37 shown in FIG. 2. In the case of detecting whether the output fluctuation of the pressure sensor 12 is normal or not (S3 in FIG. 3), the higher-level apparatus 23 transmits an output fluctuation detection instruction to the controller 21 of the flow rate verification failure diagnosis apparatus 8. When the controller 21 receives the output fluctuation detection instruction, the CPU 31 reads the pressure sensor output fluctuation abnormality detection program 37 from the NVRAM 34, copies it to the RAM 33, and executes it. Thereby, the controller 21 determines whether the output fluctuation of the pressure sensor 12 is normal or not. Concretely, in the case of performing the failure diagnosis of the gas supply pipe system 25, the higher-level apparatus 23 closes the input open/close valve 3 and the output open/close valve 5 in each of the gas units 6 and the gas supply valve 15 to cut off the supply of the process gas to a not-shown treatment chamber. The controller 21 closes the first and second shutoff valves 11 and 14 to cut off a discharge line. When an output fluctuation detection instruction is received from the higher-level apparatus 23 to the controller 21, the controller 21 opens the second shutoff valve 14 while the first shutoff valve 11 of the flow rate verification unit 10 is closed in S11 in FIG. 4, thereby forming a vacuum in a tank (in the flow rate verification unit 10) constructed by pipe lines connecting the first and second shutoff valves 11 and 14. The controller 21 determines whether the pressure in the flow rate verification unit 10 becomes equal to or less than a predetermined pressure on the basis of a pressure detection result of the pressure sensor 12 in S12. The predetermined pressure is determined from the capability of a vacuum pump, the precision of the pressure sensor, and the precision of the flow rate verification. In the present embodiment, the predetermined pressure is set as 80 Pa. In the case where the pressure in the flow rate verification unit 10 is decreased to 80 Pa or less to form a vacuum (S12:Yes), the program advances to S14. On the other hand, in the case where the pressure in the flow rate verification unit 10 is not decreased to 80 Pa or less to form a vacuum (S12:No), in S13, whether vacuuming time has elapsed one minute or not is determined. When the vacuuming time has not elapsed one minute (S13:No), the program returns to S12. In contrast, even when the pressure in the flow rate verification unit 10 has not been decreased to 80 Pa or less and a vacuum is not formed yet (S12:No), if the vacuuming time has elapsed one minute (S13:Yes), the program advances to S14 for the following reason. For example, in the case where the pressure sensor 12 does not accurately measure the pressure in the flow rate verification unit 10 due to a failure or the like, the flow rate verification unit 10 is prevented from being broken down due to excessive vacuuming. The second shutoff valve 14 is closed in S14, and the pressure between the first shutoff valve 11 and the second shutoff valve 15 is started to be monitored by the pressure sensor 12 in S15. In S16, whether or not 0.5 second has elapsed since the pressure monitor has started is determined. Until 0.5 second elapses (S16:No), the pressure sensor 12 waits. On the other hand, when 0.5 second elapses after the pressure monitor started (S16:Yes), in S17, the pressure measured by the pressure sensor 12 is stored in the RAM 33. Accordingly, in S18, whether 60 seconds have elapsed since the pressure monitor started or not is determined. In the case where 60 seconds have not elapsed since the pressure monitor started (S18:No), the program returns to S16 and determines whether or not 0.5 second has elapsed since the pressure was received from the pressure sensor 12 and stored in the RAM 33. After a lapse of 0.5 second, the controller 21 stores the pressure measured by the pressure sensor 12 again to the RAM 33. As mentioned above, the pressure is sampled every 0.5 second during 60 seconds since the pressure monitor was started (S18:Yes), in S19, the maximum and minimum values of 120 pieces of pressure sampling data stored in the RAM 33 are obtained, so that the pressure fluctuation band is calculated from the difference between the maximum and minimum values. In S20, the “pressure fluctuation band initial value” is read out from the pressure fluctuation band initial value storing member 39 and compared with the pressure fluctuation band obtained in S19. In S21, whether the difference between the pressure fluctuation band obtained in S19 and the initial value is within an allowable fluctuation pressure band or not is determined, thus recognizing how much the output value of the pressure sensor 12 is deviated from the initial value. The allowable fluctuation pressure band is set according to the precision of the flow rate verification. Preferably, the severer the flow rate verification precision is, the more the allowable fluctuation pressure band is decreased. In the present embodiment, the allowable fluctuation pressure band is set to 26 Pa. In the case where the difference between the pressure fluctuation band obtained in S19 and the “pressure fluctuation band initial value” is 26 Pa or less (S21:Yes), in S22, it is determined that the output fluctuation of the pressure sensor 12 is normal. Accordingly, an output fluctuation normal signal is transmitted to the higher-level apparatus 23, and the process is finished. On the other hand, when the difference between the pressure fluctuation band obtained in S19 and the “pressure fluctuation band initial value” is not 26 Pa or less (S21:No), in S23, it is determined that the output fluctuation of the pressure sensor 12 is abnormal. Accordingly, an output fluctuation abnormal signal is transmitted to the higher-level apparatus 23 and, the process is finished. In S3 in FIG. 3, when the output fluctuation normal signal is received from the controller 21, the higher-level apparatus 23 determines that flow rate abnormality occurs due to output fluctuation abnormality in the flow rate verification unit 10. On the other hand, in S3 in FIG. 3, when the output fluctuation abnormal signal is received from the controller 21, the higher-level apparatus 23 determines that flow rate abnormality occurs due to an output fluctuation abnormality in the pressure sensor 12 of the flow rate verification unit 10. <Pressure Sensor Zero-Point Shift Detecting Method> A method of detecting a zero-point shift of the pressure sensor 12 will be described. FIG. 5 is a flowchart showing the operation of a pressure sensor zero-point shift detecting program illustrated in FIG. 3. In the case of determining whether the zero point of the pressure sensor 12 has shifted or not in S5 in FIG. 3, the higher-level apparatus 23 transmits a zero-point shift detection instruction to the controller 21 of the flow rate verification failure diagnosis apparatus 8. When the controller 21 receives the zero-point shift detection instruction, the CPU 31 reads out the zero-point shift detection program 38 from the NVRAM 34, copies it into the RAM 33, and executes it. As a result, the controller 21 determines whether the zero point of the pressure sensor 12 is normal or not. The pressure sensor zero-point shift detecting process is basically similar to the pressure sensor output fluctuation detecting process shown in FIG. 4 except for handling of the pressure measured by the pressure sensor 12. Therefore, the points different from the pressure sensor output fluctuation abnormality detecting process shown in FIG. 4 will be mainly described. The same reference numerals are assigned to process similar to the pressure sensor output fluctuation abnormality detecting process shown in FIG. 4 in the diagram, and description thereof is accordingly omitted. When a vacuum of 80 Pa or less is formed in the flow rate verification unit 10, or after one minute elapsed since the flow rate verification unit 10 started to be evacuated, the CPU 31 closes the second shutoff valve 14 and subsequently starts monitoring the pressure in the flow rate verification unit 10 on the basis of the measurement result of the pressure sensor 12 (see S11, S12:Yes, S13:Yes, S14, and S15). The CPU 31 obtains the pressure detection result from the pressure sensor 12 every 0.5 second for a period of time since the pressure monitor was started until 60 seconds elapse. In the CPU 31, a pressure addition value is obtained by adding a newly measured pressure to the pressures measured until just before the newly obtained pressure is measured, and the CPU 31 overwrites the pressure addition value with the calculated value to store in the RAM 33 (S14, S16:Yes, S31, and S18:No). When 60 seconds have elapsed since the pressure monitor started (S18:Yes), in S32, a pressure addition value stored in the RAM 33 is divided by the number of sampling times (120), thereby calculating an average of the pressure values (pressure average value) in 60 seconds. The “pressure average initial value” is read out from the pressure average initial value storing member 40 in S33 and compared with the pressure average value calculated in S32. In S34, whether or not the difference between the pressure average value calculated in S32 and the “pressure average initial value” is equal to or less than an allowable pressure value is determined. The allowable pressure value is set according to the precision of the flow rate verification. Preferably, the severer the flow rate verification precision is, the more the allowable pressure value is decreased. In the present embodiment, the allowable pressure value is set to 80 Pa. In the case where the difference between the pressure average value calculated in S32 and the pressure average initial value is 80 Pa or less (S34:Yes), in S35, it is determined that the zero point of the pressure sensor 12 is normal. A zero-point normal signal is transmitted to the higher-level apparatus 23, and then, the process is finished. On the other hand, when the difference between the pressure average value calculated in S32 and the pressure average initial value is not 80 Pa or less (S34:No), in S36, it is determined that the zero point of the pressure sensor 12 is abnormal. A zero-point abnormal signal is transmitted to the higher-level apparatus 23, and, the process is finished. In S5 in FIG. 3, when the zero-point normal signal is received from the controller 21, the higher-level apparatus 23 determines that flow rate abnormality occurs due to a span error in the pressure sensor 12. On the other hand, in S5 in FIG. 3, when the zero-point abnormal signal is received from the controller 21, the higher-level apparatus 23 determines that the flow rate abnormality occurs due to the zero-point shift of the pressure sensor 12 of the flow rate verification unit 10. <Operations and Advantages> In the case where the flow rate verification unit 10 detects flow rate abnormality in any of the mass flow controllers 4, the flow rate verification failure diagnosis apparatus 8 of the first embodiment diagnoses a failure in the pressure sensor 12 of the flow rate verification unit 10 thereby separating the flow rate abnormality caused by a failure in the pressure sensor 12 from the flow rate abnormality caused by a failure in the mass flow controller 4. Therefore, by the flow rate verification failure diagnosis apparatus 8 of the first embodiment, the flow rate abnormality is not erroneously determined as abnormality caused by a failure in the mass flow controller 4 until it is determined that the flow rate abnormality is caused by a failure in the pressure sensor 12. Thus, the reliability of the flow rate verification can be improved. In particular, the flow rate verification failure diagnosis apparatus 8 of the first embodiment diagnoses a failure in the pressure sensor 12 under the same conditions as those when the flow rate abnormality is detected without detaching the mass flow controller 4 from the gas unit 6. Therefore, the flow rate verification failure diagnosis apparatus 8 can clearly distinguish between the case where the flow rate abnormality is caused by a failure in the pressure sensor 12 and the case where the flow rate abnormality is caused by a failure in the mass flow controller 4. In the flow rate verification failure diagnosis apparatus 8, the flow rate verification failure diagnosis system 26, and the flow rate verification failure diagnosis method of the first embodiment, the flow rate verification unit 10 is evacuated, and the first and second shutoff valves 11 and 14 are closed to hermetically close the flow rate verification unit 10. After that, the pressure in the flow rate verification unit 10 is measured by the pressure sensor 12 and monitored (see S11, S12:Yes, S13:Yes, S14, S15, S16:Yes, S31, and S18:Yes in FIG. 5). The flow rate verification failure diagnosis apparatus 8 compares the pressure average value obtained by averaging the pressures measured by the pressure sensor 12 and the pressure average initial value with each other. When the difference exceeds the permissible range (80 Pa in the embodiment), the flow rate verification failure diagnosis apparatus 8 determines occurrence of a failure such that the zero point shifts in the pressure sensor 12 (see S32, S33, S34:No, and S36 in FIG. 5). Therefore, the flow rate verification failure diagnosis apparatus 8 of the first embodiment can detect the cause of the flow rate abnormality, which is the zero-point shift of the pressure sensor 12 separately from the other failures. Thus, the failure can be handled more easily. In the flow rate verification failure diagnosis apparatus 8, the flow rate verification failure diagnosis system 26, and the flow rate verification failure diagnosis method of the first embodiment, the flow rate verification unit 10 is evacuated, and then the first and second shutoff valves 11 and 14 are closed to hermetically close the flow rate verification unit 10. After that, the pressure in the flow rate verification unit 10 is measured by the pressure sensor 12 and monitored (see S11, S12:Yes, S13:Yes, S14, S15, S16:Yes, S17, and S18:Yes in FIG. 4). Subsequently, the flow rate verification failure diagnosis apparatus 8 compares the output fluctuation band of the pressure measured by the pressure sensor 12 and the output fluctuation band initial value of the pressure sensor 12. When the difference exceeds the allowable range, the flow rate verification failure diagnosis apparatus 8 determines occurrence of a failure such that output fluctuation abnormality occurs in the pressure sensor 12 (see S19, S20, S21:No, and S23 in FIG. 4). Therefore, the flow rate verification failure diagnosis apparatus 8 of the first embodiment can detect the cause of the flow rate abnormality, which is the output fluctuation abnormality in the pressure sensor 12 separately from the other failures. Thus, the failure can be handled more easily. In the case where the flow rate verification unit 10 detects flow rate abnormality in any of the mass flow controllers 4, when the temperature in the gas box 20 changes, the flow rate verification failure diagnosis apparatus 8 (higher-level apparatus 23) and the flow rate verification failure diagnosis system 26 of the first embodiment determine that the flow rate abnormality occurs due to a change in the temperature in the gas box 20. Therefore, the flow rate abnormality that is caused by the temperature change in the gas box 20 (disturbance) can be detected separately from the other failures. The failure can be handled more easily. In the flow rate verification failure diagnosis system 26 and the flow rate verification failure diagnosis method of the first embodiment, when the flow rate verification unit 10 determines that flow rate abnormality occurs in all of the mass flow controllers 4, it is determined that there is a failure as the cause of the flow rate abnormality other than the mass flow controllers 4. When the flow rate verification unit 10 determines that there is flow rate abnormality only in a specific mass flow controller 4, it is determined that there is a failure as the cause of the flow rate abnormality in the specific mass flow controller 4. In this way, the flow rate verification unit 10 discriminates between the case where the cause of flow rate abnormality exists in a mass flow controller and the case where the cause of flow rate abnormality does not exist in a mass flow controller (see S1 in FIG. 3). Therefore, the flow rate verification failure diagnosis system 26 and the flow rate verification failure diagnosis method of the first embodiment can distinguish between the case where the cause of flow rate abnormality is in the mass flow controller 4 and the case where the cause is somewhere else under the same conditions as those when the flow rate is verified before the mass flow controller 4 is detached and tested. Thus, the reliability of the flow rate verification can be improved. The flow rate verification failure diagnosis program 30 of the first embodiment measures the flow rates of the plurality of mass flow controllers 4 on the basis of the pressure measured by the pressure sensor 12. In the case where the flow rate verification unit 10 detects flow rate abnormality, the higher-level apparatus 23 controlling the flow rate verification unit 10 performing a flow rate verification is allowed to diagnose a failure as the cause of the flow rate abnormality (see FIG. 3). Thus, the causes of the flow rate abnormalities can be distinguished from each other, so that the reliability of the flow rate verification can be enhanced. A second embodiment of a flow rate verification failure diagnosis apparatus of the present invention will now be described with reference to the drawings. <General Configuration of Flow Rate Verification Failure Diagnosis Apparatus> FIG. 6 is a diagram showing a schematic configuration of a flow rate verification failure diagnosis apparatus 8A and a flow rate verification failure diagnosis system 26A. The flow rate verification failure diagnosis apparatus 8A and the flow rate verification failure diagnosis system 26A of the second embodiment are different from the flow rate verification failure diagnosis apparatus of the first embodiment with respect to the point that they are applied to a gas supply pipe system 25A having a flow rate verification unit 10A. The points different from the first embodiment will be mainly described here. The same reference numerals are designated to the same components as those in the first embodiment in the drawings, and their description will not be repeated. The subscripts “A”, “B”, “C”, . . . of the reference numerals are attached for convenience so that gas units and the like are distinguished from each other. In the following, when it is unnecessary to distinguish the components from each other, the subscripts are not shown. The flow rate verification failure diagnosis apparatus 8A has, in a gas box 20A, a circuit configuration for supplying purge gas from a purge gas unit 50 to a plurality of gas units 60A, 60B, 60C, . . . . In the flow rate verification failure diagnosis apparatus 8A, the purge gas unit 50 is obtained by connecting a regulator 52, a second pressure sensor 55 as an example of “second pressure measuring member”, a measurement open/close valve 56, a check valve 57, a purge gas supply valve 58, and a mass flow controller 59 in series, thereby constructing a part of a purge gas line 71. The flow rate verification unit 10A (which will be described later) is disposed between the regulator 52 and the second pressure sensor 55. In such the purge gas unit 50, the regulator 52 is connected to a purge gas supply source 51, and the mass flow controller 59 is connected to a not-shown treatment chamber. A discharge line 72 is connected on the downstream side of the regulator 52. In the discharge line 72, a first discharge valve 53 and a second discharge valve 54 are disposed from the upstream side. The discharge line 72 is connected to a not-shown vacuum pump. In the gas unit 60, an input valve 62, a regulator 63, a third pressure sensor 64, an output valve 65, and a mass flow controller 66 are connected in series. The gas unit 60 serves as a part of a gas line 73. In the gas unit 60, a purge gas supply line 74 branched from the purge gas line 71 is connected on the upstream side of the mass flow controller 66. In the purge gas supply line 74, a check valve 67 and a purge gas input valve 68 are disposed in order from the upstream side. In such the gas unit 60, the input valve 62 is connected to a process gas supply source 61, and the mass flow controller 66 is connected to a not-shown treatment chamber. To each of the gas lines 60, process gases A, B, C, . . . of different kinds are supplied. <Flow Rate Verification Unit> The flow rate verification unit 10A is obtained by connecting a shutoff valve 41, a tank 42, a temperature sensor 43, a first pressure sensor 44 serving as an example of “first pressure measuring member”, and a regulator 45 in order from the upstream side. Since the volume between the regulator 52 and the measurement open/close valve 56 is small, the flow rate verification unit 10A assures volume necessary for measuring pressure drop time by providing the tank 42. The regulator 45 is provided to make the primary-side pressure of the mass flow controllers 59, 66A, 66B, 66C, . . . constant at the time of flow rate verification. <Electric Block Configuration of Controller> FIG. 7 is an electric block diagram of a controller 21A shown in FIG. 6. The controller 21A is a microcomputer similar to that in the first embodiment. However, the flow rate verification is performed by the pressure drop method, so that the processes in a pressure sensor output fluctuation abnormality detection program 37A and a pressure sensor zero-point shift detection program 38A are different from those of the first embodiment. To the input/output I/F 35, the gas box temperature sensor 22 and the shutoff valve 41, the temperature sensor 43, and the first pressure sensor 44 in the flow rate verification unit 10A are connected. To the input/output I/F 35, the second discharge valve 54 and the measurement open/close valve 56 are also connected. To the higher-level apparatus 23, the first and second discharge valves 53 and 54, the second pressure sensor 55, the measurement open/close valve 56, the purge gas supply valve 58, and the mass flow controller 59 in the purge gas unit 50, the input valve 62, the third pressure sensor 64, the output valve 65, the mass flow controller 66, and the purge gas input valve 68 of each of the gas units 60 are connected. <Flow Rate Verification Method> For example, in the case of performing a flow rate verification of a mass flow controller 66A, the higher-level apparatus 23 closes input valves 62A, 62B, and 62C and output valves 65A, 65B, and 65C of process gas lines 73A, 73B, and 73C to interrupt supply of the process gases A, B, and C. Further, the higher-level apparatus 23 closes the first and second discharge valves 53 and 54 to interrupt discharge. The higher-level apparatus 23 also closes the purge gas supply valve 58 and purge gas input valves 68B and 68C and opens the shutoff valve 41, the measurement open/close valve 56, and a purge gas input valve 68A, thereby replacing the process gas residing in the process gas line 73A with purge gas. During replacement with purge gas, the regulator 52 adjusts the pressure of the purge gas to the set pressure. After the purge gas line 71 is stabilized in the set pressure, the higher-level apparatus 23 closes the shutoff valve 41 to interrupt the supply of the purge gas. Even after that, the purge gas is outputted from the mass flow controller 66A, and the measurement value of the first pressure sensor 44 gradually decreases. At this time, the regulator 45 adjusts the pressure on its downstream side to the set pressure, thereby preventing a volume change in the check valves 57, 67A, 67B, 67C, . . . , so that the flow rate measurement of the mass flow controller 66A can be performed in a stable manner. The higher-level apparatus 23 measures pressure drop time until the first pressure sensor 44 measures a target pressure. On the basis of the pressure drop time, the higher-level apparatus 23 measures flow rate of the mass flow controller 66A. The higher-level apparatus 23 then compares between the pressure drop time in the initial state of the mass flow controller 66A and the pressure drop time which is measured this time, thereby calculating a flow rate change rate, and the flow rate verification of the mass flow controller 66A is performed. When flow rate abnormality is detected by the above mentioned flow rate verification, the higher-level apparatus 23 executes the failure diagnosis program shown in FIG. 3. At this time, the pressure sensor output fluctuation abnormality detecting process and the pressure sensor zero-point shift detecting process are performed as follows. <Pressure Sensor Output Fluctuation Abnormality Detection> FIG. 8 is a flowchart of the pressure sensor output fluctuation abnormality detection program 37A shown in FIG. 7. When the controller 21A receives a pressure fluctuation detection instruction from the higher-level apparatus 23, the CPU 31 reads out the pressure sensor output fluctuation abnormality detection program 37A from the NVRAM 34, copies it to the RAM 33, and executes it. By this operation, the controller 21A detects output fluctuation abnormality of the first pressure sensor 44. The pressure sensor output fluctuation abnormality detecting process shown in FIG. 8 is applied to the gas supply pipe system 25A having the flow rate verification unit 10A, so that the processes until the pressure in the system 8A is started to be monitored by the first pressure sensor 44 are different from the first embodiment. At the time of determining whether an output fluctuation of the first pressure sensor 44 is normal or not, the higher-level apparatus 23 closes the first and second discharge valves 53 and 54 and the purge gas input valves 68A, 68B, 68C . . . to interrupt the supply and discharge of the purge gas. The higher-level apparatus 23 also closes the input valves 62A, 62B, 62C, . . . and the output valves 65A, 65B, 65C, . . . to interrupt supply of the process gas. In this state, the controller 21A closes the shutoff valve 41 and opens the second discharge valve 54 and the measurement open/close valve 56, thereby forming a vacuum in the flow rate verification unit 10A (see S41). In the case where the pressure measured by the first pressure sensor 44 becomes equal to or less than 80 Pa, or in the case where one minute elapsed since vacuuming was started, the controller 21A closes the measurement open/close valve 56 (see S12:Yes, S13:Yes, and S42). After that, the controller 21A measures pressure by the first pressure sensor 44 every 0.5 second, stores the pressure in the RAM 33, and monitors the pressure in the unit 10A. When 60 seconds elapsed after the pressure monitor started, the controller 21A obtains pressure fluctuation band on the basis of the maximum pressure value and the minimum pressure value stored in the RAM 33, determines whether there is abnormality in the output fluctuation of the first pressure sensor 44 on the basis of the difference between the pressure fluctuation band and the pressure fluctuation band initial value, transmits the determination result to the higher-level apparatus 23, and finishes the process (see S15 to S23). <Pressure Sensor Zero-point Shift Detecting Process> Next, the pressure sensor zero-point shift detecting process will be described. FIG. 9 is a flowchart of the pressure sensor zero-point shift detecting program 38A illustrated in FIG. 7. Since the pressure sensor zero-point shift detecting process shown in FIG. 9 is applied to the gas supply pipe system 25A including the flow rate verification unit 10A, processes performed before the first pressure sensor 44 starts monitoring the pressure in the system 8A and a pressure value as a criterion are different from those of the first embodiment. At the time of determining whether the zero point of the first pressure sensor 44 has shifted or not, the higher-level apparatus 23 closes the first and second discharge valves 53 and 54 and the purge gas input valves 68A, 68B, 68C, . . . to interrupt the supply and discharge of the purge gas. The higher-level apparatus 23 also closes the input valves 62A, 62B, 62C, . . . and the output valves 65A, 65B, 65C, . . . to interrupt the supply of the process gas. In S51, the controller 21A closes the shutoff valve 41 and opens the second discharge valve 54 and the measurement open/close valve 56 in a state where the first discharge valve 53, the purge gas supply valve 58 of the purge gas unit 50, and the purge gas input valve 68 of each of the gas units 60 are closed. In this state, the not-shown vacuum pump is driven by the higher-level apparatus 23 to form a vacuum in the flow rate verification unit 10A. In S52, on the basis of the pressure measured by the first pressure sensor 44, the pressure in the unit 10A becomes equal to or less than the predetermined value is determined. The predetermined value is set in a manner similar to that at the time where the pressure rises (for example, see S12 in FIG. 5). In the present embodiment, the predetermined value is −97 kPaG. When the pressure in the unit 10A becomes equal to or less than −97 kPaG (S52:Yes), the program advances to S53. On the other hand, when the pressure in the unit 10A is not −97 kPaG or less (S52:No), whether vacuuming time exceeds one minute or not is determined in S13. When the vacuuming time has not elapsed one minute (S13:No), the program returns to S52. In contrast, when the vacuuming time elapsed one minute (S13:Yes) even if the pressure in the unit 10A is not equal to or less than −97 kPaG, the program advances to S53. In S53, the measurement open/close valve 56 is closed, and hermetic space is formed between the shutoff valve 41 and the measurement open/close valve 56. In S15, the first pressure sensor 44 starts monitoring the pressure in the unit 10A. The controller 21A obtains the pressure detection result from the first pressure sensor 44 every 0.5 second until 60 seconds elapse since the pressure monitor started. Each time the pressure measurement result is obtained, the controller 21A obtains a pressure addition value obtained by adding a newly measured pressure to pressures measured until just before the pressure measurement, and overwrites the pressure addition value stored in the RAM 33 with the calculated value (see S16:Yes, S31, and S18:No). When 60 seconds elapse after the pressure monitor started, the pressure addition value stored in the RAM 33 is divided by the number of sampling times (120) of the pressure, thereby calculating a pressure average value. The obtained pressure average value is compared with the “pressure average initial value” (see S32 and S54). In S54, the difference between the pressure average value and the “pressure average initial value” is obtained, and whether the value of deviation of the pressure average value from the “pressure average initial value” is equal to or less than an allowable pressure value or not is determined. Preferably, the allowable pressure value is determined in a manner similar to that at the time of pressure rise (for example, see S34 in FIG. 5). In the present embodiment, the allowable pressure value is set to 3 kPa. In the case where the value of deviation of the pressure average value from the “pressure average initial value” is equal to or less than the allowable pressure value (S54:Yes), a zero-point normal signal indicating that the pressure sensor zero point is normal is transmitted to the higher-level apparatus 23 in S35, and the process is finished. On the other hand, when the value of deviation of the pressure average value from the “pressure average initial value” is not equal to or less than the allowable pressure value (S54:No), a zero-point abnormal signal indicating that the pressure sensor zero point is abnormal is transmitted to the higher-level apparatus 23, and the process is finished. <Operations and Advantages> In the case where the flow rate verification unit 10A detects flow rate abnormality in any of the mass flow controllers 59, 66A, 66B, 66C, . . . , the flow rate verification failure diagnosis apparatus 8A of the second embodiment diagnoses a failure in the first pressure sensor 44 of the flow rate verification unit 10A and separates the flow rate abnormality caused by a failure in the first pressure sensor 44 from the flow rate abnormality caused by a failure in the mass flow controllers 59, 66A, 66B, 66C, . . . . Therefore, the flow rate verification failure diagnosis apparatus 8A of the second embodiment does not erroneously determine that flow rate abnormality is caused by a failure in the mass flow controllers 59, 66A, 66B, 66C, . . . until it is determined that the flow rate abnormality is caused by a failure in the first pressure sensor 44. Thus, the reliability of the flow rate verification can be improved. In particular, the flow rate verification failure diagnosis apparatus 8A of the second embodiment diagnoses a failure in the first pressure sensor 44 under the same conditions as those when the flow rate abnormality is detected without detaching the mass flow controllers 59, 66A, 66B, 66C, . . . from the gas units 50 and 60. Therefore, the flow rate verification failure diagnosis apparatus 8A can clearly distinguish between the case where the flow rate abnormality is caused by a failure in the first pressure sensor 44 and the case where the flow rate abnormality is caused by a failure in the mass flow controllers 59, 66A, 66B, 66C, . . . . In the flow rate verification failure diagnosis apparatus 8A, the flow rate verification failure diagnosis system 26A, and the flow rate verification failure diagnosis method of the second embodiment, in a state where the shutoff valve 41 is closed and the second discharge valve 54 and the measurement open/close valve 56 are opened, a vacuum is formed in the flow rate verification unit 10A, and the measurement open/close valve 56 is closed to hermetically close the flow rate verification unit 10A. After that, the pressure in the flow rate verification unit 10A is measured by the first pressure sensor 44 and monitored (see S51, S52:Yes, S13:Yes, S53, S15, S16:Yes, S31, and S18:Yes in FIG. 9). In the flow rate verification failure diagnosis apparatus 8A, the flow rate verification failure diagnosis system 26A, and the flow rate verification failure diagnosis method, the pressure average value obtained by averaging the pressures measured by the first pressure sensor 44 is compared with the pressure average initial value. When the difference exceeds the allowable value (3 kPa in the present embodiment), a failure is determined such that the zero point in the first pressure sensor 44 shifts (see S32, S54, S55:No, and S36 in FIG. 9). Therefore, the flow rate verification failure diagnosis apparatus 8A, the flow rate verification failure diagnosis system 26A, and the flow rate verification failure diagnosis method of the second embodiment can detect the cause of the flow rate abnormality, which is the zero-point shift of the first pressure sensor 44, separately from the other failures. The failure can be handled more easily. In the flow rate verification failure diagnosis apparatus 8A, the flow rate verification failure diagnosis system 26A, and the flow rate verification and failure diagnosis method of the second embodiment, in a state where the shutoff valve 41 is closed and the second discharge valve 54 and the measurement open/close valve 56 are opened, a vacuum is formed in the flow rate verification unit 10A. Subsequently, the measurement open/close valve 56 is closed to hermetically close the flow rate verification unit 10A. After that, the pressure in the flow rate verification unit 10A is measured by the first pressure sensor 44 and monitored (see S41, S12:Yes, S13:Yes, S42, S15, S16:Yes, S17, and S18:Yes in FIG. 8). In the flow rate verification failure diagnosis apparatus 8A, the flow rate verification failure diagnosis system 26A, and the flow rate verification failure diagnosis method, the output fluctuation band of the pressure measured by the first pressure sensor 44 and the output fluctuation band initial value of the first pressure sensor 44 are compared. When the difference exceeds the allowable value, occurrence of a failure such that output fluctuation abnormality occurs in the first pressure sensor 44 is determined (see S19, S20, S21:No, and S23 in FIG. 8). Therefore, the flow rate verification failure diagnosis apparatus 8A, the flow rate verification failure diagnosis system 26A, and the flow rate verification failure diagnosis method of the second embodiment can detect the cause of the flow rate abnormality, which is the output fluctuation abnormality in the first pressure sensor 44, separately from the other failures. The failure can be handled more easily. A flow rate verification failure diagnosis apparatus of a third embodiment of the present invention will now be described. The flow rate verification failure diagnosis apparatus of the third embodiment is applied to the gas supply pipe system 25A shown in FIG. 6 in a manner similar to the second embodiment. In the pressure sensor zero-point shift detecting process of the second embodiment, on the basis of a pressure measurement result of the first pressure sensor 44, a vacuum is formed in the flow rate verification unit 10A, and the abnormality of zero-point shift is detected. However, in the case where abnormality occurs in the first pressure sensor 44, a vacuum may not be formed in the unit 10A. In this case, an error occurs in the pressure measured by the first pressure sensor 44, and accurate zero-point detection cannot be performed. Consequently, in the flow rate verification failure diagnosis apparatus of the third embodiment, the external I/F 35 of the controller 21A is provided with the second discharge valve 54, the measurement open/close valve 56, the shutoff valve 41, the temperature sensor 43, and the first pressure sensor 44 and, in addition, the second pressure sensor 55 installed downstream of the flow rate verification unit 10A. The controller 21A determines whether there is abnormality in the span of the first pressure sensor 44 installed in the flow rate verification unit 10A using, as a reference, a pressure measured by the second pressure sensor 55 installed on the outside of the flow rate verification unit 10A. In the case where no abnormality in the span is determined, it is determined that the zero point of the first pressure sensor 44 shifts (see S68:Yes, and S69 in FIG. 10, and S5 in FIG. 3). The points different from the second embodiment will be mainly described here. The same reference numerals are designated to the same components as those in the second embodiment, and their description will not be repeated. FIG. 10 is a flowchart of a pressure sensor span abnormality detection program executed by the flow rate verification failure diagnosis apparatus of the third embodiment of the present invention. At the time of determining whether the zero point of the first pressure sensor 44 shifts, the higher-level apparatus 23 closes the first and second discharge valves 53 and 54 and the purge gas input valves 68A, 68B, 68C, . . . to interrupt the supply and discharge of the purge gas. The higher-level apparatus 23 closes the input valves 62A, 62B, 62C, . . . and the output valves 65A, 65B, 65C, . . . to interrupt supply of the process gas. In this state, in S61, the flow rate verification failure diagnosis apparatus of the third embodiment opens the shutoff valve 41 and closes the measurement open/close valve 56 to introduce the purge gas into the flow rate verification unit 10A. The flow rate verification unit 10A adjusts the pressure by the regulator 52 of the purge gas unit 50 so that the pressure in the unit 10A becomes 500 kPa. In S62, when it is detected that the pressure in the flow rate verification unit 10A becomes 500 kPa on the basis of a pressure PT2 measured by the second pressure sensor 55, the controller 21A closes the shutoff valve 41 to fill the flow rate verification unit 10A with purge gas. In S63, pressure monitoring by the first pressure sensor 44 of the flow rate verification unit 10A and the second pressure sensor 55 of the purge gas unit 50 starts. In S64, whether 0.5 second has elapsed since the pressure monitor started or not is determined. In the case where 0.5 second has not elapsed yet since the pressure monitor started (S64:No), the controller 21A waits. In the case where 0.5 second has elapsed since the pressure monitor started (S64:Yes), in S65, a pressure PT1 measured by the first pressure sensor 44 and a pressure PT2 measured by the second pressure sensor 55 of the purge gas unit 50 are inputted and stored in the RAM 33. In S18, whether 60 seconds have elapsed since the pressure monitor started or not is determined. In the case where 60 seconds have not elapsed yet since the pressure monitor started (S18:No), the program returns to S64. By repeating the processes in S64 to S18, the pressures PT1 and PT2 measured every 0.5 second by the first and second pressure sensors 44 and 55 are accumulated and stored in the RAM 33. After a lapse of 60 seconds since the pressure monitor started (S18:Yes), the program advances to S66 where an average value of the pressures PT1 measured by the first pressure sensor 44 for the period of 60 seconds since the pressure monitor started is calculated. In S67, the average of the pressure values calculated in S66 is compared with an average value (reference value) of the pressures PT2 measured by the second pressure sensor 55 for the period of 60 seconds since the pressure monitor started. In S68, whether the difference between the average of the pressure values calculated in S66 and the reference value is equal to or less than an allowable pressure value or not is determined. The allowable pressure value is determined in a manner similar to that at the time of pressure rise. In the present embodiment, the allowable pressure value is set to 3 kPa. When the difference between the average of the pressure values calculated in S66 and the reference value is equal to or less than the allowable pressure value (S68:Yes), in S69, a span point normal signal indicating that the span point of the first pressure sensor 44 is normal is transmitted to the higher-level apparatus 23. After that, the process is finished. On the other hand, in the case where the difference between the average of the pressure values calculated in S66 and the reference value is not equal to or less than the allowable pressure value (S68:No), in S70, a span point abnormal signal indicating that the span point of the first pressure sensor 44 is abnormal is transmitted to the higher-level apparatus 23. After that, the process is finished. In S5 in FIG. 3, when the span point normal signal is received from the controller 21A, the higher-level apparatus 23 determines that the zero point of the first pressure sensor 44 in the flow rate verification unit 10A has shifted, and that the flow rate abnormality is caused by the zero-point shift of the first pressure sensor 44. On the other hand, in S5 in FIG. 3, when the span point abnormal signal is received from the controller 21A, the higher-level apparatus 23 determines that the zero point of the first pressure sensor 44 in the flow rate verification unit 10A has not shifted, and that the flow rate abnormality is caused by a span error in the first pressure sensor 44 in the flow rate verification unit 10A. <Operations and Advantages> In the case where the flow rate verification unit 10A detects flow rate abnormality in any of the mass flow controllers 59, 66A, 66B, 66C, . . . , using the second pressure sensor 55 provided on the outside of the flow rate verification unit 10A as a reference, the flow rate verification failure diagnosis apparatus of the third embodiment diagnoses a failure in the first pressure sensor 44 of the flow rate verification unit 10A and separates the flow rate abnormality caused by a failure in the first pressure sensor 44 from the flow rate abnormality caused by a failure in the mass flow controllers 59, 66A, 66B, 66C, . . . . Therefore, in the flow rate verification failure diagnosis apparatus of the third embodiment, it is not erroneously determined that flow rate abnormality is caused by a failure in the mass flow controllers 59, 66A, 66B, 66C, . . . until it is determined that the flow rate abnormality is caused by a failure in the first pressure sensor 44. Thus, the reliability of the flow rate verification can be improved. In particular, the flow rate verification failure diagnosis apparatus of the third embodiment diagnoses a failure in the first pressure sensor 44 under the same conditions as those when the flow rate abnormality is detected without detaching the mass flow controllers 59, 66A, 66B, 66C, . . . from the gas units 50 and 60. Therefore, the flow rate verification failure diagnosis apparatus can clearly distinguish between the case where the flow rate abnormality is caused by a failure in the first pressure sensor 44 and the case where the flow rate abnormality is caused by a failure in the mass flow controllers 59, 66A, 66B, 66C, . . . . In the flow rate verification failure diagnosis apparatus, the flow rate verification failure diagnosis system, and the flow rate verification failure diagnosis method of the third embodiment, in a state where the shutoff valve 41 is opened and the measurement open/close valve 56 is closed, purge gas (gas for measurement) is introduced into the flow rate verification unit 10A. When the second pressure sensor 55 detects that the pressure in the unit 10A reaches a target pressure, the shutoff valve 41 is closed, and purge gas is introduced to a portion between the shutoff valve 41 and the measurement open/close valve 56 (see S61 and S62 in FIG. 10). Subsequently, in the flow rate verification failure diagnosis apparatus, the flow rate verification failure diagnosis system, and the flow rate verification failure diagnosis method, the pressure in portion between the shutoff valve 41 and the measurement open/close valve 56 is measured by the first and second pressure sensors 44 and 55 and monitored (see S63, S64, S65, and S18:Yes in FIG. 10). In the flow rate verification failure diagnosis apparatus, the flow rate verification failure diagnosis system, and the flow rate verification failure diagnosis method, the pressure average value obtained by averaging the pressures PT1 measured by the first pressure sensor 44 in the flow rate verification unit 10A is compared with the pressure average value (reference value) obtained by averaging the pressures PT2 measured by the second pressure sensor 55 provided on the downstream side of the flow rate verification unit 10A. When the difference exceeds the allowable value (3 kPa in the present embodiment), it is determined that the span point in the first pressure sensor 44 shifts (see S66, S67, S68:No, and S70 in FIG. 5). Therefore, the flow rate verification failure diagnosis apparatus, the flow rate verification failure diagnosis system, and the flow rate verification failure diagnosis method of the third embodiment can detect the cause of the flow rate abnormality, which is the span error in the first pressure sensor 44, separately from the other failures. The failure can be handled more easily. In the flow rate verification failure diagnosis method of the third embodiment, for example, in the case where the flow rate verification unit 10A performs the flow rate verification by the pressure drop method, even when a vacuum cannot be formed in the portion between the shutoff valve 41 and the measurement open/close valve 56, it can be properly detected that the flow rate abnormality is caused by a failure in the first pressure sensor 44. The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. For example, in the above mentioned embodiments, cause of the flow rate abnormality is determined in the order as shown in FIG. 3. However, the order is not limited to the order shown in FIG. 3. For example, in the above mentioned embodiments, the mass flow controllers 4, 59, and 66 are applied as one example of a flow rate control device. However, devices such as a mass flow manometer may be applied as a flow rate control device. While the presently preferred embodiments of the present invention have been shown and described, it is to be understood that this disclosure is for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.
052375994	summary	BACKGROUND OF THE INVENTION The present invention relates to an X-ray apparatus having an X-ray beam limiting device assembled with an X-ray tube for stereoradiography. In medical examinations such as angiography, stereoradiography has the advantage of being able to obtain stereo images. An X ray apparatus for the stereoradiography has used an X-ray tube having a pair of X-ray focal points positioned a certain distance apart. X-rays are alternately irradiated from the one focal point to the other of the X-ray tube to a living body (a subject) through an X-ray beam limiting device, and the X-ray transmitted through the living body are detected by a film or an image intensifier (referred to as "I.I." hereinafter). An observer can obtain a stereo penetrating image, when his right eye sees an image formed according to the transmitted X-rays from the X-ray focal point and his left eye sees an image formed according to the transmitted X-rays from the X-ray focal point. Japanese Laid-Open No. 60-127698 discloses a example of X-ray beam limiting devices. The above-mentioned X-ray beam limiting device is placed at irradiation-opening side of an X-ray tube having a pair X-ray focal points for one target. The X-ray beam limiting device comprises: a rectangular limiting means for rectangularly shaping the X-rays; compensating filters for compensating a difference in the X-ray absorptions by heart muscles and lungs and which are situated at the X-ray-focal-point side of the rectangular limiting means; a circular limiting blade having two circular holes for shaping the X-rays from the X-ray focal points into circles according to a circular effective detection area (i.e. an input window) of an I.I.; and inside limiting blades for shaping the rectangular irradiation field defined by the rectangular limiting means into individual squares for the X-ray focal points. In normal stereoradiography, a subject contacts the effective detection area. In such contact stereoradiography, the X-ray penetrating image of the subject is detected at an enlargement ratio of 1 to 1, and thus the distance between the X-ray focal points and is 63 mm, which is approximately equal to the distance between the eyes. The blades of the rectangular limiting means and the inside limiting blades are controlled and moved by a stepping motor so that even when the SID (Source-Image Distance) is changed, a square X-ray irradiation field is circumscribed on the circular effective detection area of the I.I. Each of the circular holes has a maximum diameter according to the minimum SID. Then, when the SID is at minimum, the X-rays are shaped by the circular holes into a cone, resulting in a circular X-ray irradiation field which coincides with the circular effective detection area, not in a square X-ray irradiation field. However, when the SID is at maximum or relatively long, a circular X-ray irradiation field on the detection surface resulting from the circular holes would be a circle larger than the exterior of the I.I. As a result, the X-ray is shaped into a pyramid, thus resulting in the square X-ray irradiation field. Four corners of the square X-ray irradiation field may go out of the boundary of the exterior of the I.I. This results in condition in which some of the X-rays are out of the boundary of the exterior of the I.I. and directly leak behind the I.I. Thus, a patient may receive more X-rays than necessary, or other people like an operator may be exposed to the leaked X-rays. To the contrary, when the SID setting range is limited to avoid the leakage behind the I.I., the device fails to provide sufficient information for diagnoses due to a short SID. Presently, there is a demand for a magnifying stereoradiographic device which can both perform high-speed serial stereoradiography (:several frames per second in the case of film photography; several tens of frames per second in the case of I.I. photography) and provide magnified images. For example, for a magnifying stereoradiography with magnification of two in which a subject is placed at the middle between the X-ray focal points and the X-ray detection surface, it is required to use an X-ray tube having an interval between the focal points reduced to approximately 35 mm. As stated above, where the X-ray tube having shorter distances between the focal points is used, the triangular space, in which the X-ray irradiation is not affected, becomes too small to accomodate the conventional horizontally-moving beam limiting means for preventing the above-mentioned x-ray leakage. SUMMARY OF THE INVENTION Thus, it is an object of the present invention to provide an X-ray apparatus having an X-ray beam limiting device which prevents the X-ray beams from directly leaking over the detection surface without restricting the SID or the effective detection area. It is a further object of the present invention to provide an X-ray beam limiting device which prevents the exterior of the detector from increasing its size. These and other objects can be achieved according to the present invention, in one aspect by providing, an X-ray apparatus comprising: an X-ray tube having a pair of X-ray focal points placed a predetermined distance apart from each other; an X-ray detector having a detection surface in which an circular input window is placed; and a X-ray beam limiting device for limiting an X-ray beam irradiated from each of the X-ray focal points of the X-ray tube onto the circular input window of the X-ray detector, wherein the beam limiting device includes an element for limiting the X-ray beams so that an irradiation field of each one of the X-ray beams onto the detection surface can be formed into shape which is circumscribed on the circular input window. Preferably, the limiting element comprises a blade unit consisting of a plurality of blades and being capable of limiting each of the X-ray beams to the polygonal shape which enables the X-ray irradiation field onto the detection surface of the X-ray detector to be circumscribed on the input window and to remain within the detection surface, and a control unit for adjusting each position of the plural blades. The X-ray detector is preferably an image intensifier and the polygonal shape is preferably approximately octagonal. It is preferred that the blade unit comprises a first set of blades projecting a V-shaped aperture having a base to the detection surface, a second set of blades projecting a V-shaped aperture to the detection surface, and a third set of blades projecting a rectangular aperture to the detection surface. Further, the first set of blades and the second set of blades are placed so that the V-shaped aperture having the base projected by one of the first set of blades and the V-shaped aperture projected by one of the second set of blades are faced each other in a longitudinal direction of the rectangular aperture projected by the third set of blades. The three sets of blades are placed, from one side near to the X-ray tube toward another side near to the X-ray detector, in an order of positioning from the first to the third set of blades. It is preferred that the first set of blades are individually rotatable round an axis right to a longitudinal direction of the rectangular aperture. Also, it is preferred that the second set of blades are slidable in a transverse direction right to a longitudinal direction of the rectangular aperture, and the third set of blades are slidable in transverse and longitudinal directions of the rectangular aperture. Further, it is preferred that the control unit is able to adjust each position of the blades in accordance with at least either one of a distance between the X-ray tube and the X-ray detector, and a size of the input window of the X-ray detector. As a result, the irradiation field of the X-ray beams onto the detection surface of the detector can be formed by the first to third set of blades into an almost octagonal shape, which is circumscribed on the input window. And more, when the distance between the X-ray tube and the X-ray detector is changed, it can be kept that the irradiation field is circumscribed on the input window. Thus, the irradiation field can be rounded along the boundary of the input window as possible as it could be, and remains within the detection surface. This prevents x-ray beams from leaking over the X-ray detector.
	summary
	abstract	Disclosed is a system for extracting energy from inertial confinement fusion reactions, which includes a central target chamber for receiving fusion target material. A plurality of energy drivers are arranged around the target chamber so as to supply energy to fusion target material in the chamber to initiate an inertial confinement fusion reaction of the material, releasing energy in the forms of fusion plasma and heat. A plurality of structures for extracting energy from the fusion reaction are provided, and comprise devices to extract high voltage DC energy from the fusion plasma, and means to extract thermal energy from the central target chamber. Power to the energy drivers may be supplied from high voltage DC energy extracted from the fusion reactions. The energy drivers may use an apodizing filter to impart a desired shape to the wavefront of the driving energy for causing the fusion reactions, to avoid hydrodynamic instabilities.
	summary
040597695	claims	1. A radiation source for Mossbauer investigations of tellurium compounds consisting of 5MgO.Te.sup. 125m O.sub.3. 2. A starting material for a radiation source for Mossbauer investigations of tellurium compounds consisting of 5Mg O.Te.sup.124 O.sub.3. 3. The starting material as claimed in claim 2 wherein the starting material is formed according to the following equation Te.sup.124 + 3H.sub.2 O.sub.2 +5MgSO.sub.4 +10KOH.fwdarw.5MgO.Te.sup.124 O.sub.3 +5K.sub.2 SO.sub.4 +8H.sub.20, then the 5MgO.Te.sup.124 O.sub.3 is dried and calcined.
052456455	claims	1. A structural part for a nuclear reactor fuel assembly, comprising: a) a zirconium alloy material having at least one alloy ingredient selected from the group consisting of oxygen and silicon, a tin alloy ingredient, at least one alloy ingredient selected from the group consisting of iron, chromium and nickel, and a remainder of zirconium and unavoidable contaminants; b) the zirconium alloy material having a content of the oxygen in a range of substantially from 700 to 2000 ppm, a content of the silicon of substantially up to 150 ppm, a content of the iron in a range of substantially from 0.07 to 0.5% by weight, a content of the chromium in a range of substantially from 0.05 to 0.35% by weight, a content of the nickel of substantially up to 0.1% by weight, and a content of the tin in a range of substantially from 0.8 to 1.7% by weight; c) the alloy ingredients selected from the group consisting of iron, chromium and nickel being precipitated out of a matrix of the zirconium alloy as secondary phases, having a diameter with a geometric mean value in a range of substantially from 0.1 to 0.3 .mu.m; and d) a degree of recristallization of the zirconium alloy being less than or equal to 10% and a sample of the zirconium alloy, after a recristallization annealing with a degree of recrystallization of the sample of zirconium alloy of 97.+-.2%, having a grain size with a geometric mean value less than or substantially equal to 3 .mu.m. a) a zirconium alloy material having at least one alloy ingredient selected from the group consisting of oxygen and silicon, a tin alloy ingredient, at least one alloy ingredient selected from the group consisting of iron, chromium and nickel, and a remainder of zirconium and unavoidable contaminants; b) the zirconium alloy material having a content of the oxygen in a range of substantially from 700 to 2000 ppm, a content of the silicon of substantially up to 150 ppm, a content of the iron in a range of substantially from 0.07 to 0.5% by weight, a content of the chromium in a range of substantially from 0.05 to 0.35% by weight, a content of the nickel of substantially up to 0.1% by weight, and a content of the tin in a range of substantially from 0.8 to 1.7% by weight; c) the alloy ingredients selected from the group consisting of iron, chromium and nickel being precipitated out of a matrix of the zirconium alloy as secondary phases, having a diameter with a geometric mean value in a range of substantially from 0.1 to 3 .mu.m; and d) a degree of recrystallization of the zirconium alloy being less than or equal to 10 % and a sample of the zirconium alloy, after a recrystallization annealing with a degree of recrystallization of 97.+-.2%, having a grain size with a geometric mean value less than or substantially equal to 3 .mu.m. 2. The structural part according to claim 1, wherein the content of iron is in a range of substantially from 0.07 to 0.3% by weight, and the content of chromium is in a range of substantially from 0.05 to 0.15% by weight, in said zirconium alloy. 3. The structural part according to claim 1, wherein said zirconium alloy has a texture with a Kearns parameter f.sub.r wherein 0.6.ltoreq.f.sub.r .ltoreq.1. 4. The structural part according to claim 1, wherein said zirconium alloy has a texture with a Kearns parameter f.sub.r wherein 0.6.ltoreq.f.sub.r .ltoreq.0.8. 5. The structural part according to claim 1, wherein the content of tin in said zirconium alloy is in a range of substantially from 0.9 to 1.1% by weight. 6. The structural part according to claim 1, wherein the contents of said alloy ingredients iron and chromium in said zirconium alloy are in a ratio of substantially 2:1. 7. The structural part according to claim 1, wherein the contents of said alloy ingredients iron and chromium in said zirconium alloy are in a ratio of substantially 2:1, and the contents of said alloy ingredients iron and chromium have a sum of substantially 0.4 to 0.6 % by weight. 8. The structural part according to claim 1, wherein contents of said alloy ingredients iron and chromium have a sum of substantially 0.4 to 0.6% by weight. 9. The structural part according to claim 6, wherein the contents of said alloy ingredients iron and chromium have a sum of substantially 0.4% by weight. 10. The structural part according to claim 1, wherein the content of oxygen is in a range of substantially from 1000 to 1800 ppm, the content of silicon is in a range of substantially from 80 to 120 ppm, the content of iron is in a range of substantially from 0.35 to 0.45% by weight, the content of chromium is in a range of substantially from 0.2 to 0.3 % by weight, and the content of tin is in a range of substantially from 1 to 1.2% by weight. 11. The structural part according to claim 2, wherein said zirconium alloy is Zircaloy-2. 12. The structural part according to claim 2, wherein said zirconium alloy is Zircaloy-4. 13. A structural part formed of a casing tube of a nuclear fuel-filled fuel rod or a spacer for a fuel rod of a nuclear reactor fuel assembly, comprising:

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