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047624027 | summary | BACKGROUND OF THE INVENTION The present invention relates to a system making it possible to obtain a selective reaction in photochemical processes on the basis of laser beams incorporating means for distributing said beams. The invention applies to photochemical processes requiring the combined action of several light emissions of different wavelengths in order to obtain a selective reaction, such as an isotopic separation or a photoisomerization. Isotopic separation can e.g. be used for eliminating an isotope which is incompatible with the industrial use of a product, such as in the case of purifying metals or for selecting a useful isotope, e.g. carbon or uranium. By the rearrangement of the atoms of a molecule previously excited by light emissions, the photoisomerization of molecules makes it possible to obtain a molecule having different spectroscopic and chemical properties. To obtain the sought selective reaction, it is possible to proceed in known manner in two stages. The first stage consists of selectively exciting an isotopic or chemical species on the basis of one or more laser radiations. The second stage consists of causing the transformation of the previously excited species by a final laser radiation having an adequate energy. The selective excitation of the species, i.e. the molecule or atom, takes place in known manner by successive passages of the molecule or atom in question to levels having an ever higher energy by absorption of photons, each photon coming from a pulse laser with a particular wavelength. In certain cases, selective excitation can be obtained by absorption of a single photon and therefore by the passage of the molecule or atom in question to a single energy level. The excited species is transformed by irradiating it with a laser beam of a wavelength such that it clears the level corresponding to said transformation. This leads either to the formation of a new molecule or to the ionization of a molecule or atom. In this way, it is possible to distinguish the species formed from other species and separate them. FIG. 1 shows an example of transitions at several levels in U.sup.235 making it possible to bring about its ionization. Thus, to separate the isotope U.sup.235 from uranium vapour, use is made of a selective excitation beam S.sub.1 constituted by two beams S'.sub.1 and S".sub.1 of respective wavelengths .lambda.'.sub.1 and .lambda.".sub.1, which bring the atoms of isotope U.sup.235 to two successive levels 1, 3. A final beam S.sub.2 of wavelength .lambda..sub.2 brings the excited atoms of U.sup.235 into an ionization state 5. The ionization energy of isotope U.sup.235 is equal to 6.12 eV, so that each of the wavelengths .lambda.'.sub.1, .lambda.".sub.1, .lambda..sub.2 is approximately 600 nm. In order to optimize the isotopic separation of U.sup.235, use can be made of a fourth wavelength .lambda..sub.1 " associated with a beam S.sub.1 "' in order to bring the atoms already at an intermediate energy level 7, occupied by a thermal process, to level 1, so as to be ionized following successive irradiations at wavelengths .lambda.".sub.1 and .lambda..sub.2. Throughout the remainder of the text, S.sub.1 will be used for the beam permitting the selective excitation of the species in question, whereby S.sub.1 can contain a single wavelength .lambda..sub.1 or can result from a superimposing of beams S'.sub.1, S".sub.1, . . . S.sub.1.sup.(n) of wavelengths .lambda.'.sub.1, .lambda.".sub.1, . . . .lambda..sub.1.sup.(n), with n being an integer equal to at least 1 and S.sub.2 is the beam of wavelength .lambda..sub.2 permitting the ionization or photodissociation of the previously excited species. The different wavelengths are obtained in known manner from dye lasers, (e.g. rhodamine lasers) excited by other lasers, which can be copper vapour lasers. This gives pulse-type light emissions of a few dozen ns and a repetition frequency of a few kHz. In known manner, beams S.sub.1 and S.sub.2 are transmitted in the same propagation direction into an enclosure containing the substance from which a chemical or isotopic species is to be extracted and which is in the form of a vapour flow. The effective absorption sections of the transitions corresponding to the selective excitation and transformation of the species in question can differ. The effective absorption sections of the transitions corresponding to the selective excitation can be 10 to 100 times greater than that corresponding to the transformation. Moreover, to retain a good selectivity, an excessive power of beam S.sub.1 must not be used, because this would lead to a loss of selectivity resulting e.g. from broadening through saturation, or to transitions with several photons. Following interaction of the beams S.sub.1 and S.sub.2 with the species in question, beam S.sub.1 is very attenuated compared with beam S.sub.2. Thus, the simultaneous presence of these two beams cannot be maintained throughout their passage in the enclosure. As a result of this interaction beam S.sub.2 is not very well used, its energy being wasted in the final part of the path where beam S.sub.1 is highly attenuated. Thus, the prior art means do not make it possible to optimize the use of these beams. SUMMARY OF THE INVENTION The object of the present invention is to obviate this disadvantage. This is achieved through the use of an apparatus making it possible to introduce the selective excitation beam S.sub.1 through the vapour to be treated at several points, whereby said beam can result from a superimposing of beams S'.sub.1, S".sub.1, . . . S.sub.1.sup.(n) of wavelength .lambda.'.sub.1, .lambda.".sub.1 . . . .lambda..sub.1.sup.(n) with n being an integer of at least 1, whereas beam S.sub.2 is only introduced once at the inlet of the apparatus. More specifically the present invention relates to a system making it possible to obtain a selective reaction in photochemical processes from laser beams comprising: in a sealed enclosure, the substance from which it is wished to extract an isotopic or chemical species, said substance being in the form of a vapour flow, laser sources emitting towards said enclosure a beam S.sub.1 permitting a selected excitation of the species to be extracted and a beam S.sub.2 permitting a transformation of said excited species, wherein said system also comprises means for distributing the beams having: means for superimposing the beams S'.sub.1, S".sub.1, . . . , S.sub.1.sup.(n), with n being an integer equal to at least 1, for constituting several beams S.sub.1 introduced at several points through the vapour to be treated, means for introducing into the enclosure the resulting beams S.sub.1 and the beam S.sub.2 so as to make them colinear, whilst still distinguishing them by one of their characteristics, such as a different polarization or an opposite proagation direction, said introduction means being periodically distributed on parallel arms defining propagation directions of said beams in the enclosure, so as to optimize the use of the light energies of the different beams. According to a constructional variant of the system according to the invention, the latter also comprises quarterwave plates making it possible to obtain a circular polarization of beams S.sub.1 and S.sub.2, when it is advantageous to have circularly polarized light beams to interact with the vapour, said means being located upstream and downstream of the introduction means. According to another embodiment of the system, the means for introducing beams S.sub.1 and S.sub.2 into the enclosure comprise Glan prisms, into which said beams are injected with two orthogonal polarizations and in directions such that after their passage in said prisms they are colinear. Each prism is located on an arm at the points where S.sub.1 is reintroduced into the enclosure. According to another embodiment of the system, the latter comprises for inverting beams S.sub.1 and S.sub.2 along parallel arms. According to an embodiment of the system corresponding to cavity operation, the means for introducing beams S.sub.1 and beam S.sub.2 into the enclosure comprise a Glan prism at each end of an arm corresponding to one propagation direction of beams S.sub.1 and S.sub.2 into the vapour and on each of the arms formed in the enclosure. Each of the beams S.sub.1 and S.sub.2 is introduced with the same polarization into one of the Glan prisms at each end of an arm and in directions which, following their passage in said prisms, enable them to have the same propagation direction, but the opposite sense. According to another embodiment of the system corresponding to cavity operation, the latter comprises means for reflecting beams S.sub.1 and S.sub.2 back on to themselves, said means incorporating plane mirrors associated with Pockels cells, each plane mirror - Pockels cell assembly being located at each end of the arms and means for inverting beam S.sub.2 towards other arms, said means incorporating a Pockels cell located on each arm. According to an embodiment of the system, the means for superimposing beams S'.sub.1, S".sub.1, . . . ,S.sub.1.sup.(n) so as to constitute beams S.sub.1 comprise a group of semitransparent plates having a reflection coefficient 0.5 which successively divide into two the different beams S'.sub.1, S".sub.1 . . . , S.sub.1.sup.(n), whilst superimposing the divided beams to obtain the different beams S.sub.1 used in the system. |
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abstract | In a nuclear fuel rod a cladding tube is provided having a closed inner space and manufactured from at least one of the materials in the group zirconium and a zirconium-based alloy, and a pile of nuclear fuel pellets arranged in the inner space in the cladding tube. The nuclear fuel pellets fill part of the inner space. A fill gas is arranged in the closed inner space to fill the rest of the inner space. The internal pressure of the fill gas in the nuclear fuel rod amounts to at least 2 bar (abs) or at least 10 bar (abs). The fill gas contains a proportion of inert gas a proportion of carbon monoxide that is greater than 3 volume percent of the fill gas or greater than 2 volume percent of the fill gas. |
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abstract | The exposure device is able to supply only EUV radiation to a mask, while eliminating radiation other than the EUV radiation. A multi layer made from a plurality of Mo/Si pair layers is provided upon the front surface of a mirror, and blazed grooves are formed in this multi layer. Radiation which is incident from a light source device is incident upon this mirror, and is reflected or diffracted. Since the reflected EUV radiation (including diffracted EUV radiation) and the radiation of other wavelengths are reflected or diffracted at different angles, accordingly their directions of progression are different. By eliminating the radiation of other wavelengths with an aperture and/or a dumper, it is possible to irradiate a mask only with EUV radiation of high purity. |
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051587416 | description | DETAILED DESCRIPTION OF THE INVENTION Modular pool-type liquid metal cooled nuclear reactors with relatively small pool capacity typically have sufficient surface area to accommodate dissipation of residual heat during periods of shutdown. However, such reactors have an overall relatively small power capacity. The problem remaining is to dissipate the residual heat without significantly damaging the containment housing structures. A completely passive cooling system eliminates reliance on energy driven pumps and fans and/or the need for intervention by operating personnel. Moreover, the containment vessel(s) itself must not be structurally modified due to size constraints on modular reactors, and the necessity of a smooth, unperforated tank structure to prevent any areas where stress might accumulate. Strict inspection requirements also require that the containment vessel be simple to inspect both during manufacture and erection of the structures. Referring to the drawings, a satellite embodiment of a pool-type liquid metal cooled nuclear fission reactor plant 10, with a power producing capability in the 1000 MWG range comprises a reactor primary vessel 12, typically consisting of a cylindrical tank positioned with its longitudinal axis extending vertically upward, and having an open upper end which is attached, covered and closed off by a deck 14. Reactor primary vessel 12 contains a pool of liquid metal coolant 16, such as sodium metal, with a heat producing core of fissionable fuel material 18 substantially submerged within the liquid metal pool 16 for transferring heat away from the fuel core 18. Fission action of the fuel material and the rate thereof is governed by neutron absorbing control rods (not shown) moving out from and into the fuel core 18. The reactor primary vessel 12 is enclosed within a concentrically surrounding containment vessel 20 in spaced apart relation. The space between the reactor primary vessel 12 and the containment vessel 20 is sealed and filled with a relatively inert gas such as nitrogen or argon. A baffle cylinder 22 concentrically encircles substantially the length of the concentrically superimposed containment and reactor vessels 20 and 12 in spaced apart relation to the outer containment vessel 20. A guard vessel 24 concentrically surrounds the baffle cylinder 22 with the superimposed containment and reactor vessel 20 and 12, in spaced apart relation to the outer baffle cylinder 22. A concrete silo 26 houses this composite of reactor components comprising the concentrically combined and spaced apart arrangement of a bottom supported guard vessel 24, baffle cylinder 22, containment vessel 20 and reactor primary vessel 12. The concrete silo 26 can be arranged concentrically with the assembly of vessels comprising the reactor vessel 12, or positioned off center thereto as shown in the drawings. Preferably the concrete silo 26 is substantially buried into the ground to the extent that its contained reactor vessel 12 and adjoining vessels are located at least below the ground surface. Placing the liquid metal containing reactor vessel 12 below ground surface precludes the possible escape of any leaking coolant liquid regardless of a loss of structural integrity of the plant. A containment dome 28 covers and encloses the upper portion of the concrete silo 26 and/or reactor plant components to preclude escape of radioactive material into the atmosphere. This arrangement of these combined enclosing vessel components in surrounding or encircling and spaced apart position, provides for their respective cylindrical side walls forming a series of partitions with intermediate spaces. Specifically, a space 30 between the partitions comprising the side walls of the reactor primary vessel, 12 and the containment vessel 20; a space 32 between the partitions comprising the side walls of the containment vessel 20 and baffle cylinder 22; a space 34 between the baffle cylinder 22 and the guard vessel 24; and a space 36 between the guard vessel 24 and the concrete silo 26. Such intermediate spaces provide for both retaining any coolant leakage and/or in channeling or directing cooling gases such as air. In a preferred embodiment of the invention wherein the above combined components are generally circular in cross-section and concentrically surround or encircle one another, the intermediate spaces 30, 32, and 34 are each substantially annular in cross-section. As noted above, the space 30 between the primary reactor and containment vessels 12 and 20, is sealed and contains an inert gas. The baffle cylinder 22 extends downward between the containment vessel 20 wall and the guard vessel 24 wall substantially to the bottom portion of the reactor primary vessel 12, and with the lower most end of the cylinder terminating a short distance above the bottom of the surrounding guard vessel. Thus, the baffle cylinder 22 provides for fluid communication below its lower end 38 between the space 34 intermediate the guard vessel 34 baffle cylinder 22 and the space 32 intermediate the baffle cylinder 22 and the containment vessel 20. The top entry loop joined, "satellite" assembly 40 of the nuclear reactor of this invention comprises a group of separated reactor units with each performing a specific role or function such as a unit 42 containing the fuel core 18 for producing heat energy, a unit(s) 44 containing a pump for inducing circulation of the heat transporting liquid metal coolant and a unit(s) 46 containing a heat exchanger for transferring the produced and transported heat from the circulating coolant to another medium for performing work. Thus, a typical top entry loop joined, satellite arranged reactor plant comprises a core of heat producing fissionable fuel 18 submerged in liquid metal coolant 16 as a distinct unit 42 which is housed and contained separately within a composite enclosure including the primary reactor and containment vessels 12 and 20 along with any other designed components such as a cylindrical baffle 22 and guard vessel 24 positioned and arranged as described hereinbefore. Additionally, this type of reactor plant includes one or more separate pump units 44 and/or heat exchanger units 46 each housed and contained separately within its respective composite enclosures corresponding generally with the main heat producing unit 42, namely a primary vessel 112, 212 and containment vessel 120, 220 along with any other designated components such as a baffle cylinder 122, 222 and guard vessel 124, 224. For example, each reactor unit 42 containing a heat producing fuel core 18 can be joined with one or more separate pump units 44 for circulating the heat carrying liquid metal coolant through the series of each separate unit of the satellite reactor assembly 40, and additionally with one or more separate heat exchanger units 46 for transferring the fuel core produced heat carried by the coolant to another medium or system for applying the heat energy to perform work, such as forming steam for generating electrically with a steam turbine driven generator. The several separate units of the plant satellite assembly 40, comprising the reactor fuel core unit 18, the coolant circulating pump unit(s) 44, and the heat exchanger unit(s) 46, are functionally connected for circulation of the heat transferring liquid metal coolant 16 through each unit in series by means of connecting conduits 48 which enter all unit by passing down through the top of each of the primary vessels. This measure preserves the integrity of the side walls and/or bottom of the primary or inner most vessels retaining the liquid metal coolant 16 and provides greater plant compactness. As such each conduit 48 connection between two separate units comprises a generally inverted U shaped pipe 50 with each downward extending leg 52 portion of the inverted U projecting down into an adjacent separate vessels through their top. This connection of a series comprising a fuel core unit 42 with a pump unit 44 and heat exchanger unit 46 and then back to the fuel core unit 42 with top entry conduits 48, provides a liquid metal coolant circuit or loop 54. The satellite arrangement for a liquid metal pool type reactor system can comprise several coolant circuits or loops 54. The downward extending legs 52 of each connecting conduit 48 preferably project a considerable distance down into each primary vessel whereby the circulating coolant circuit will not be likely to be interrupted by a low coolant level resulting from leakage. Typically the satellite system comprises a fuel containing reactor unit 18 combined with one or more pairs of circulating pump units 44 with heat exchanger units 46 in series, as illustrated. The several separate units of a liquid metal cooled, top entry loop, satellite type nuclear reactor plant 10 each carry the radioactive contaminated liquid metal coolant circulating therebetween. Each unit of the assembly is subject to the same potential for mishaps or failures as can occur in the single composite unit of an integrated reactor plant, including leakage and loss of coolant or damage due to breach of vessels or overheating, and the same hazards of leakage and exposure to the atmosphere of a liquid metal coolant such as sodium. Thus, each of the separate units, including specifically the fuel core, pump(s) and heat exchanger(s), of a satellite nuclear reactor plant is provided with the same protective structural measures and function, including, as shown in the drawing, a primary housing vessel, such as 12, 112 and 212, a containment vessel, such as 20, 120 and 220, a cylindrical baffle, such as 22, 122, and 222, and a guard vessel, such as 24, 124 and 224, as is employed for enhanced passive cooling and safety means in a single integrated reactor plant 10. Accordingly, as shown in the drawing, in keeping with this invention, each separate pump units(s) 44 heat exchanger unit(s) 46 is provided with a primary vessel 112 and 212, a containment vessel 120 and 220, a baffle cylinder 122 and 222, and a guard vessel 124 and 224, essentially like the composite arrangement provided for the fuel core unit 42. Further in accordance with this invention, the corresponding composite of enclosing components of each unit of the satellite assembly, comprising the fuel core, pump and heat exchanger primary vessels, containment vessels, baffle cylinder and guard vessels, are each spaced apart from their adjacent component thus providing spaces between each component comparable to the spaces 30, 32, and 34 between each of the composite of several components enclosing the fuel core. Additionally, the corresponding spaces between each of the composite components for all units consisting of the fuel core unit 42, pump unit(s) 44 and heat exchanger unit(s) 46, except for the space 30 between the primary vessels and their respective surrounding containment vessel which are sealed with an inert gas content, are interconnected for fluid communication therebetween. Thus the space 32 between the containment vessel 20 and baffle cylinder 22 of the fuel core unit 42 and each pump and heat exchanger units 44 and 46 is connected, and the space 34 between the baffle cylinder 22 and guard vessel 24 of each fuel core, pump and heat exchanger units 42, 44 and 46 is connected. Typically the space 30 between each of the units primary vessels and their respective surrounding containment vessel 20 are sealed off and filled with a suitable inert gas to isolate any leaking liquid metal coolant from contact with atmospheric air. This double vessel arrangement of the primary and containment vessels significantly reduces the possibility of a significant loss of liquid metal coolant resulting in an uncovering of the fuel core or disruption of the coolant circulation flowing through the loop circuit 54 and in turn its heat dissipating function. Preferably, the corresponding spaces for each unit of the satellite assembly 40 reactor plant, namely, the fuel core 42, pump 44 and heat exchanger 46 units, are each respectively interconnected through a manifold distributor duct or a duct system connecting each of the corresponding spaces of all units. For instance all spaces between the containment vessels 20, 120 and 220 and baffle cylinders 22, 122 and 222, such as space 32, are interconnected in fluid communication through one or more ducts 56 adjacent the upper end of said vessels and cylinders, and all spaces between the baffle cylinders 22, 122 and 222 and the guard vessels 24, 124 and 224, such as space 34, are interconnected in fluid communication through one or more ducts 58 adjacent to the upper end of said cylinders and vessels. The reactor plant 10 is provided with at least one, and preferably several, downcomer ducts 60 which projects substantially up above the ground level and is in fluid communication with spaces 34 between the baffle cylinders 22, 122 and 222 and the guard vessels 24, 124 and 224 of each unit 42, 44 and 46. A valve(s) 62 is provided to close off duct(s) 60 from opening to the ambient atmosphere. At least one, and preferably several, riser ducts 64 which also projects substantially up above the ground level and is in fluid communication with spaces 32 between the baffle cylinders 22, 122 and 222 and the containment vessels 20, 120 and 220 of each unit 42, 44 and 46. A valve(s) 66 is provided to close off duct(s) 64. As noted above, the spaces 34 and 32 of each unit are connected at their lower area below the bottom end 38 of the common partition or intermediate baffle cylinder 22, 122 and 222, whereby the spaces 34 and 32 are in fluid communication beneath the lower end 38 of the baffle cylinders. This arrangement of interconnecting the intermediate spaces 34 and 32 forms a circulating of heat carrying or transporting air coolant from the ambient atmosphere down duct 60, through spaces 34 and 32 and up duct 64 back out into the atmosphere. In operation, heat produced by the fuel is conveyed outward to the reactor primary vessel 12 by the natural convection of the liquid metal coolant 16, then transferred mainly by thermal radiation across the inert gas containing space 30 to the containment vessel 20. The heat is absorbed by air contained in the space 32 which is in contact with the outer surface of the containment vessel 20, and is carried along in the upward air flow resulting from the added heat inducing a natural draft within the space 32 and riser duct 64. The induced natural draft due to added heat circulates air through the fluid flow course 68 including drawing atmospheric air down in duct 60, through spaces 34 and 32 and up in duct 64 back out into the atmosphere. Heat is also transported and distributed by natural convection of primary sodium from unit 42 to units 44 and 46 via the U-tubes 48. Heat is removed by circulating air in a similar manner from these units as well. Collectively, heat transfer from all vessel units is sufficient to maintain safe structural temperatures during a mishap. However, in the unlikely event of a rupture of both of any one of the liquid metal coolant 16 containing primary vessels 12, 112 or 212, and any one of containment vessels 20, 120 or 220, the liquid metal could leak out into spaces 32 and/or 34. As such the hot liquid metal, typically comprising sodium, would be exposed to the circulating air coolant whereby a chemical fire is likely along with the potential for carrying hazardous radioactive material, sodium vapor and/or combustion products out into the atmosphere through the cooling fluid flow course 68. To cope with this postulated event, the valves 62 and 66 in downcomer ducts 60 and riser ducts 64, respectively, are closed which terminates circulation of cooling air through the fluid flow course 68. Further in accordance with this invention one or more openings 70 to the atmosphere are provided between the concrete silo 26 and the structural components comprising the units of the reactor satellite assembly 40. Openings 70 can be formed by an open perimeter area between the structural components of the reactor satellite assembly 40 and the concrete silo 26, such as the seismic gap 72 provided when the reactor assembly 40 rests on a reactor base 74 which is mounted on seismic isolating shock absorbers 76, as illustrated in the drawings. Opening(s) 70 provides for a backup or secondary passive heat removal system for top entry loop connected, satellite assembly liquid metal pool reactor 40 upon the closing of valves 62 and 66 and shutdown of the primary passive cooling system of fluid flow course 68, such as may be required by a vessel breach resulting in leakage of liquid metal coolant into space 32 and/or 34 or into spaces 122 and/or 124 and 222 and/or 224 of the satellite units 44 and 46. The added heat of the leaking hot liquid metal from the reactor fuel core 18 and vessel 12 induces a natural draft of air contacting the increased heat of structural components of the satellite assembly units such as results from air passing over the exterior of the guard vessels 24, 124 and 224. The heated air flows upward and out through opening 70 out into the atmosphere while cooler air from the ambient atmosphere is drawn down in through the opening 70 to replace the venting hot air. Thus, upon the occurrence of increased temperatures occurring on the surface of any one of the guard vessels 24, 124 and/or 224, due to liquid metal leakage and/or closure of valves 62 and 66, a passive natural circulation of atmospheric air in a secondary fluid flow course 72, through the seismic gap, removes heat from about the reactor components, providing an additional safety feature. This passive cooling due to natural circulation of air maintains a cooling effect over the overall outer surface of the guard vessels 24, 124 and 224 regardless of personnel action, automated means or availability of electrical or other sources of power. A significant aspect of this invention in that a support means 78 is provided for the cover deck 14 by the guard vessels 24, 124 and 224 resting on the reactor base 74. A preferred guard vessel support means 78 comprises a structural cylinder as illustrated which extends the cylindrical side wall of the guard vessels down therefrom to the reactor base 74 resting on seismic shock absorbers 76. Such a support means 78 can be formed by adding a cylindrical section extending down from the cylindrical guard vessels 24, 124 and 224, or by inserting and affixing a concave vessel bottom within a cylinder forming both the guard vessel side wall and support means 78. In any case, a cylindrical support means 78, or any other closed underlying support for the guard vessels should be provided with several openings such as orifices 80 to enable an ample flow of coolant air over the outer surface of the bottom of the guard vessels as well as over the side walls thereof through the phenomenon of passive natural circulation. The guard vessel support means 78, additionally includes upward projecting portions of the cylindrical side wall or columns or structural struts 82 extending up from the guard vessel top edges, continuing upward to the deck 14 bridging across the top of the reactor satellite units. These struts carry the loads on the deck via the guard vessels directly to the reactor base 74 support or reinforcement for the reactor deck 14, and the support means 78 are constructed so that vertical loads are transmitted between the support cylinders and the deck 14 by means such as columns or struts 80 so as not to impede the flow of cooling air circulating within the spaces 34 and 32 of each unit comprising the reactor fuel core unit 42, the pump unit(s) 44 and the heat exchanger unit(s) 46. The cylindrical support means 78 provide several significant functions. They transmit the weight carried by the reactor deck 14 to the reactor base 74, provide an outer flow annulus for the passive natural circulation of cooling air, and provide an extra vessel enclosure for retaining any leaking liquid metal coolant whereby a second or outer cooling air circuit can flow through the backup fluid flow course 72 separated from leaking metal coolant for cooling the system. The passive cooling due to natural circulation throughout the structural members of the top entry loop, satellite reactor assembly operates continuously due to generated or residual heat, and maintains the support cylinders 78 and related components including columns or struts 82 at near ambient temperatures. This eliminates or reduces any possibility for differential thermal expansion between the steel and concrete portions of the reactor plant under normal or faulted conditions. Thus a common problem associated with bottom supported vessels which must interface with the reactor deck is eliminated. |
042971683 | abstract | Rupture of boiling water reactor nuclear fuel cladding resulting from embrittlement by fission product cadmium is prevented by adding the stoichiometrically equivalent amount of V.sub.2 O.sub.4 or V.sub.2 O.sub.5 to the fuel. |
abstract | In a method for improving the energy generating output of a nuclear reactor containing one or more fuel rods in one or more fuel rod bundles while satisfying a maximum subcritical banked withdrawal position (MSBWP) reactivity limit, enrichments of individual fuel rods in an axial cross-section of a lattice being evaluated at the top of the fuel bundle are ranked, and the fuel pins of the highest ranked rod location in the lattice are replaced with pins containing natural uranium. A core simulation is then performed to determine whether there is any margin to a MSBWP reactivity limit. For each lower ranked candidate rod position, the pin replacing and core simulation functions are repeated until no rod location violates the MSBWP reactivity limit, so as to achieve a desired lattice design for the top of the fuel bundle. |
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claims | 1. A method, comprising:concurrently modulating an X-ray signal with a first radio frequency signal and with a second radio frequency signal to generate a modulated X-ray signal;transmitting the modulated X-ray signal into a field of view containing a sample;receiving backscatter of the modulated X-ray signal reflected from the sample; andprocessing the backscatter to identify the sample from a pattern of detected harmonics of the first radio frequency signal and the second radio frequency signal. 2. The method of claim 1, wherein the backscatter is generated by diffraction of the modulated X-ray signal by the sample. 3. The method of claim 1, wherein the detected harmonics include spurious harmonic products of the first radio frequency signal and the second radio frequency signal. 4. The method of claim 1, wherein processing the backscatter to identify the sample includes comparing a detected harmonic pattern against a plurality of a priori known harmonic pattern signatures. 5. An X-ray RADAR apparatus, comprising:means for concurrently modulating an X-ray signal with a first radio frequency signal and with a second radio frequency signal to generate a modulated X-ray signal;means for transmitting the modulated X-ray signal into a field of view containing a sample;means for receiving backscatter of the modulated X-ray signal reflected from the sample; andmeans for processing the backscatter to identify the sample from a pattern of detected harmonics of the first radio frequency signal and the second radio frequency signal. 6. The X-ray RADAR apparatus of claim 5, wherein the detected harmonics include spurious harmonic products of the first radio frequency signal and the second radio frequency signal. 7. The X-ray RADAR apparatus of claim 5, wherein processing the backscatter to identify the sample includes comparing a detected harmonic pattern against a plurality of a priori known harmonic pattern signatures. 8. The X-ray RADAR apparatus of claim 5, further comprising means for collimating the modulated X-ray signal before the transmitting. 9. A computer-implemented method, comprising:receiving data representative of backscatter of a radio frequency modulated X-ray signal reflected from a sample, the radio frequency modulated X-ray signal being concurrently radio frequency modulated with a first radio frequency signal and with a second radio frequency signal; andprocessing the data to identify the sample from a pattern of detected harmonics of the first radio frequency signal and the second radio frequency signal. 10. The computer-implemented method of claim 9, wherein the data is generated by diffraction of the radio frequency modulated X-ray signal by the sample. 11. The computer-implemented method of claim 9, wherein the detected harmonics include spurious harmonic products of the first radio frequency signal and the second radio frequency signal. 12. The computer-implemented method of claim 9, wherein processing the data to identify the sample includes comparing a detected harmonic pattern against a plurality of a priori known harmonic pattern signatures. 13. A program storage medium encoded with instructions that, when executed by a processor, perform a software implemented method, the software implemented method comprising:receiving data representative of backscatter of a radio frequency modulated X-ray signal reflected from a sample, the radio frequency modulated X-ray signal being radio frequency modulated concurrently with a first radio frequency signal and with a second radio frequency signal; andprocessing the data to identity the sample from a pattern of detected harmonics of the first radio frequency signal and the second radio frequency signal. 14. The program storage medium of claim 13, wherein the data is generated by diffraction of the radio frequency modulated X-ray signal by the sample. 15. The program storage medium of claim 13, wherein the detected harmonics include spurious harmonic products of the first radio frequency signal and the second radio frequency signal. 16. The program storage medium of claim 13, wherein processing the data to identify the sample includes comparing a detected harmonic pattern against a plurality of a priori known harmonic pattern signatures. 17. A computing apparatus, comprising:a processor;a bus system;a storage communicating with the processor over the bus system; andan application residing on the storage that, when invoked by the processor, performs a software implemented method, comprising:receiving data representative of backscatter of a radio frequency modulated X-ray signal reflected from a sample, the radio frequency modulated X-ray signal being radio frequency modulated concurrently with a first radio frequency signal and with a second radio frequency signal; andprocessing the data to identify the sample from a pattern of detected harmonics of the first radio frequency signal and the second radio frequency signal. 18. The computing apparatus of claim 17, wherein processing the data to identify a sample includes comparing the detected harmonic pattern against a plurality of a priori known harmonic pattern signatures. 19. An X-ray RADAR apparatus, comprising:a transmitter capable of:concurrently modulating an X-ray signal with a first radio frequency signal and with a second radio frequency signal to generate a modulated X-ray signal; andtransmitting the modulated X-ray signal into a field of view;a receiver capable of receiving backscatter of the modulated X-ray signal reflected from a sample within the field of view; anda processing unit capable of processing the backscatter to identify the sample from a pattern of detected harmonics of the first radio frequency signal and the second radio frequency signal. 20. The X-ray RADAR apparatus of claim 19, wherein the processing unit comprises:a processor;a bus system;a storage communicating with the processor over the bus system; andan application residing on the storage that, when invoked by the processor, performs a software implemented method, comprising:processing the backscatter to identify the sample from the pattern of the detected harmonics of the first radio frequency signal and the second radio frequency signal. |
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051714833 | claims | 1. A method of long term storage of hazardous material in a hollowed out chamber in a salt bed, comprising the steps of: (a) placing one or more sealed, hazardous material holding containers within a fluidized bed by completely surrounding the containers with a granular load distributing medium; and (b) closing the chamber. spreading a layer of the granular load distributing medium over a floor of the chamber; placing the containers in the chamber and on the layer; and filling the chamber with the medium to completely surround the containers. a chamber in a salt bed; one or more sealed containers holding the hazardous material; and a fluidized bed of a granular load distributing medium completely surrounding the containers and filling the chamber. 2. The method of claim 1 wherein step (a) comprises: 3. The method of claim 1 wherein the granular medium is selected from the class consisting of sand, bentonite and gypsum. 4. The method of claim 1 wherein the medium is granulated to have a particle size not to exceed about 2,000 microns. 5. The method of claim 1 further comprising the step of removing the granular load distributing medium from the chamber so that a sealed container may be inspected and/or removed from the chamber. 6. The method of claim 1 wherein in step (a) a plurality of sealed hazardous material holding containers is placed in the hollowed chamber in the form of a regularly spaced array and the fluidized bed completely surrounds the array of sealed containers. 7. A long term storage for hazardous material comprising: 8. The storage of claim 7 wherein the sealed containers are in a closely spaced array in the chamber. |
046413359 | summary | BACKGROUND OF THE INVENTION The invention relates to a primary-beam collimator for a stereo radiographic x-ray diagnostic installation with an x-ray tube having dual focal points spaced at a distance from each other. In such an arrangement the object under study is x-rayed alternately from each of the focal points. By simultaneously viewing the radiograph pair--obtained from two focal points--the observer perceives a spatial image. The use of such multifocal x-ray tubes presents the problem of ensuring adequate x-ray exposure of the relevant areas of the object examined, as sourced from each of the two focal points, while avoiding the exposure of more tissue than is required. SUMMARY OF THE INVENTION The principal object of the invention is to provide a primary-beam collimator of the type described above, by means of which each pyramid-shaped beam, originating from each focal point, can be optimally controlled. This object, as well as other objects which will become apparent from the discussion that follows, are achieved, according to the invention, by providing shutters which can be adjusted so that each beam pyramid may be individually controlled for each focal point. A further advantageous development of the invention consists in providing two external shutter leaves and two internal shutter leaves arranged between the external leaves so as to restrict the beams in planes perpendicular to the stereo base--i.e., the line connecting the two focal points--with each internal shutter leaf being adjustable in the direction of its corresponding adjacent external shutter leaf. The restriction of both beam pyramids in planes parallel to the stereo base can thus be achieved by means of a pair of shutter leaves common to both beam pyramids, while the restriction in planes perpendicular to the stereo base can be controlled by means of both external and internal shutter leaves for both beams. For this purpose the internal shutter leaves may be suitably shaped so that, when adjusted to their external positions, they permit the emission of a central beam pyramid from a central focal point and, in conjunction with the external shutter leaves, they close the external shutter openings. This configuration enables regular radiographs to be taken from a central focal point under the same optimal conditions of beam restriction as in the case of stereos. For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiment of the invention and to the accompanying drawings. |
051241129 | summary | FIELD OF THE INVENTION The present invention relates to a sealing joint which is especially suited for repairing leaks which are difficult to reach, for example, in a nuclear reactor. BACKGROUND OF THE INVENTION A nuclear reactor includes a plurality of pipes, pipe sockets and the like, in which cracks, especially in the vicinity of welds, may arise and in which, during repair, one end of the pipe may be released so as to form an open pipe end for fitting a suitable sealing sleeve thereon. In view of the radioactivity in a nuclear reactor, such a sealing sleeve must be capable of being operated at a large distance. The sealing joint according to the invention is especially designed to fulfil this requirement. SUMMARY OF THE INVENTION The sealing joint comprises at least two sealing bodies contacting each other in a contact surface and provided with through holes. The holes are delimited by an envelope surface in the sealing bodies and form a tubular channel through the sealing bodies and the contact surface therebetween. The invention is characterized in that the sealing bodies are displaceable in relation to each other along the contact surface and that sealing members are arranged around the channel between the sealing bodies. Each sealing body is divided into at least two discs in a plane intersecting the associated envelope surface along a closed curve, and between the discs a slot for a sealing ring is arranged in the envelope surface around the circumference of the hole. The volume of this slot is reduced when the discs, after the sealing joint has been applied around a pipe, are compressed to achieve sealing against the pipe. This causes the sealing ring to be partially pressed out of the slot and to be pressed with sealing force against the pipe. |
055815871 | abstract | A control rod driving apparatus adapted to drive a control rod assembly for a nuclear reactor is disposed in a housing mounted to a reactor pressure vessel of the nuclear reactor and includes a guide tube disposed in the housing, a connection pipe disposed inside the guide tube coaxially therewith and having one end to which a control rod assembly is connected, a ball spindle disposed inside the connection pipe and supported thereby so as to be rotatable by a ball nut assembly engaged with the ball spindle so as to be axially movable along the ball spindle, the ball nut assembly supporting another end of the connection pipe, a hydraulic drive operatively connected to the ball spindle to rotate the ball spindle, and a transmission mechanism operatively connected to the drive for transmitting a power of the drive to the ball spindle. When the hydraulic drive is driven, the ball spindle is rotated, the ball nut assembly engaged with the ball spindle is axially rotated, and the connection pipe supported by the ball nut assembly is then driven vertically to thereby drive the control rod assembly for inserting or withdrawing the control rod assembly into or from a reactor core. The reactor is a boiling water reactor. |
abstract | A medical imaging system for detecting ionizing radiation. The system includes one or more pixilated imagers positioned to acquire patient image data and one or more position sensors positioned to acquire patient position data. Once the patient image data and patient position data are acquired, one or more processors operably connected to each of the one or more pixilated imagers and one or more position sensors calculate a three-dimensional mass distribution based on patient image data and patient position data. |
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claims | 1. An apparatus for providing a variable X-ray aperture, the apparatus comprising:a first substrate;a second substrate located opposite the first substrate and spaced apart from the first substrate to form a gap between the first substrate and the second substrate;an X-ray attenuation fluid located in the gap between the first substrate and the second substrate;at least one charging electrode in electrical contact with the X-ray attenuation fluid; andat least one displacing electrode located on a surface of the first substrate facing the gap or on a surface of the second substrate facing the gap, wherein the displacing electrode is configured to displace the X-ray attenuation fluid to provide an aperture within the X-ray attenuation fluid. 2. The apparatus of claim 1, further comprising a controller operably coupled to the at least one displacing electrode. 3. The apparatus of claim 1, wherein the X-ray attenuation fluid forms a fluid layer in contact with the surface of the first substrate facing the gap and the surface of the second substrate facing the gap. 4. The apparatus of claim 1, further comprising a fluid reservoir in fluid communication with the X-ray attenuation fluid located in the gap between the first substrate and the second substrate. 5. The apparatus of claim 1, wherein the at least one displacing electrode comprises a thin-film electrode deposited on the surface of the first substrate facing the gap or on the surface of the second substrate facing the gap. 6. The apparatus of claim 1, wherein the at least one displacing electrode comprises at least two displacing electrodes, a first displacing electrode located on the surface of the first substrate facing the gap, and a second displacing electrode located on the surface of the second substrate facing the gap. 7. The apparatus of claim 1, wherein the at least one displacing electrode comprises a plurality of displacing electrodes comprising an annular shape and arranged concentrically on the surface of the first substrate facing the gap and/or on the surface of the second substrate facing the gap. 8. The apparatus of claim 1, wherein the at least one displacing electrode comprises a plurality of displacing electrodes arranged in an array on the surface of the first substrate facing the gap and/or on the surface of the second substrate facing the gap. 9. The apparatus of claim 1, wherein the X-ray attenuation fluid comprises a fluid metal or fluid alloy. 10. The apparatus of claim 1, wherein the first substrate and the second substrate independently comprise aluminum, glass, or silicon, or combinations of any thereof. 11. The apparatus of claim 2, wherein the controller is configured to provide an electrical charge to the displacing electrode to displace the X-ray attenuation fluid from at least a portion of the gap by electrostatic force between the displacing electrode and the X-ray attenuation fluid. 12. The apparatus of claim 4, wherein the fluid reservoir is configured to releasably hold X-ray attenuation fluid displaced from at least a portion of the gap by electrostatic force between the at least one displacing electrode and the X-ray attenuation fluid. 13. The apparatus of claim 4, wherein the fluid reservoir is located at a perimeter of the gap between the first substrate and the second substrate. 14. The apparatus of claim 9, wherein the X-ray attenuation fluid comprises mercury. 15. An apparatus for providing a variable X-ray aperture, the apparatus comprising:a first substrate;a second substrate located opposite the first substrate, and spaced apart from the first substrate to form a gap between the first substrate and the second substrate;a mercury layer located in the gap between the first substrate and the second substrate, the mercury layer in contact with a surface of the first substrate facing the gap and a surface of the second substrate facing the gap;at least one charging electrode in electrical contact with the mercury layer;at least one displacing electrode located on the surface of the first substrate facing the gap or on the surface of the second substrate facing the gap; anda controller operably coupled to the at least one displacing electrode;wherein the controller is configured to provide the displacing electrode with an electrical charge that displaces the mercury layer from at least a portion of the gap by electrostatic force between the displacing electrode and the mercury layer to provide an aperture within the attenuation fluid. 16. The apparatus of claim 15, further comprising a fluid reservoir in fluid communication with the mercury layer located in the gap between the first substrate and the second substrate, wherein the fluid reservoir is configured to releasably hold mercury displaced from at least a portion of the gap by electrostatic force between the at least one displacing electrode and the mercury. 17. The apparatus of claim 15, wherein the at least one displacing electrode comprises a plurality of thin-film electrodes deposited on the surface of the first substrate facing the gap and on the surface of the second substrate facing the gap, wherein the plurality of displacing electrodes comprise an annular shape and are arranged concentrically, or wherein the plurality of displacing electrodes are arranged in an array, on the surface of the first substrate facing the gap and/or on the surface of the second substrate facing the gap. 18. The apparatus of claim 15, wherein the first substrate and the second substrate independently comprise a material selected from the group consisting of aluminum, glass, silicon, and combinations of any thereof. 19. An apparatus for providing a variable aperture to control electromagnetic radiation, the apparatus comprising:a first substrate;a second substrate located opposite the first substrate and spaced apart from the first substrate to form a gap between the first substrate and the second substrate;an attenuation fluid located in the gap between the first substrate and the second substrate, the attenuation fluid configured to absorb electromagnetic radiation of a predetermined wavelength;at least one charging electrode in electrical contact with the attenuation fluid; andat least one displacing electrode located on a surface of the first substrate facing the gap or on a surface of the second substrate facing the gap, wherein the displacing electrode is configured to displace the attenuation fluid to provide an aperture within the attenuation fluid. 20. The apparatus of claim 19, wherein the attenuation fluid is configured to absorb electromagnetic radiation having a wavelength in the range of 0.01 to 10 nanometers. |
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063273209 | claims | 1. An apparatus for successively loading solid objects into a tube having a closed end and an open end, said apparatus comprising: a housing having a cylindrical bore extending at least partially therethrough, said bore having opposing first and second end portions, wherein said cylindrical bore is configured such that said first end portion is sized and configured with a first cross sectional width which extends a first axial length and defines a bore entry channel, and wherein said bore entry channel terminates into a chamber having a length and a second cross sectional width which is greater than that of said bore entry channel, said chamber being positioned such that it is proximate said second end portion of said cylindrical bore, said chamber having opposing forward and rearward portions; a cylindrical tube having an open end and a closed end, said tube positioned in said chamber such that a portion of said tube axially extends a distance therein so that said open end is held in the forward portion of said chamber such that it is spaced apart from said bore entry channel to define an axially extending gap space therebetween and held in said chamber such that said tube is at least partially air sealed with a rearward portion of said chamber, wherein said gap space is sized such that it has a distance which is less than the length of the solid objects being loaded into said tube therethrough; at least one fluid passage formed in said chamber such that it is disposed rearward of said tube open end and so that it outwardly extends through said housing; wherein, in operation, solid objects are successively directed axially along said bore entry channel into said chamber across said gap space into said open end of said tube, and wherein, in operation, said chamber and a region of said tube proximate said open end are configured to exhibit a reduced fluid pressure. feeding a plurality of solid objects successively into an open end of a bore entry channel; directing the plurality of solid objects through the bore entry channel into a chamber having a cross-sectional width which is larger than the cross-sectional width of the bore entry channel; causing the solid objects to jump axially across a gap space in the chamber to enter the open end of a tube; reducing the pressure in the chamber, and successively loading the tube with the plurality of solid objects. 2. An apparatus according to claim 1, wherein said at least one fluid passage are a plurality of radially extending circumferentially spaced apart passages. 3. An apparatus according to claim 1, wherein said cylindrical tube is a nuclear fuel tube which is sized and configured to receive substantially cylindrical fuel pellets, and wherein the objects which are successively loaded are cylindrical fuel pellets. 4. An apparatus according to claim 1, wherein said cylindrical bore is substantially axially aligned with said cylindrical tube. 5. An apparatus according to claim 1, wherein the reduced fluid pressure is a pressure which is lower than ambient pressure. 6. An apparatus according to claim 1, wherein said bore entry channel includes a tapered entrance section. 7. An apparatus according to claim 3, wherein said gap space has a length which is less than the length of the fuel pellets. 8. An apparatus according to claim 7, wherein said gap space has a length which is between about 1-5 mm. 9. An apparatus according to claim 7, wherein said gap space has a length which is about 3 mm. 10. An apparatus according to claim 2, wherein said fluid passages are configured to selectively direct air in and out of said chamber. 11. An apparatus according to claim 1, wherein said at least one fluid passage is configured to allow air to be withdrawn from said chamber. 12. An apparatus according to claim 2, wherein said fluid passages are formed in a rearward portion of said chamber such that they are rearward of said open end of said tube by a distance which is at least about 20 mm. 13. An apparatus according to claim 12, said apparatus further comprising a venturi device in fluid communication with said at least one fluid passage, and wherein, in operation, said venturi device and at least one fluid passage are configured to provide a reduced pressure in said chamber. 14. An apparatus according to claim 1, wherein said tube is held in said chamber such that it is axially offset from the axis of said bore entry channel. 15. An apparatus according to claim 3, wherein said tube extends across a major portion of the length of said chamber. 16. A method of successively loading solid objects into a tube having an open end and closed end, comprising: 17. A method according to claim 16, wherein the cylindrical tube is a nuclear fuel tube which is sized and configured to receive substantially cylindrical fuel pellets, and wherein the objects which are successively loaded are cylindrical fuel pellets. 18. A method according to claim 17, wherein the gap space has a distance which is less than the length of the fuel pellets. 19. A method according to claim 17, wherein the gap space has a length which is between about 1-5 mm. 20. A method according to claim 19, wherein the gap space has a length which is about 3 mm. 21. A method according to claim 16, wherein the fluid passages are formed in a rearward portion of the chamber such that they are rearward of the open end of the tube by a distance which is at least about 20 mm. 22. A method according to claim 16, wherein the bore entry channel has an axis and the tube has an axis, and wherein, in position in the chamber, the tube is arranged such that its axis is offset from that of the bore entry channel. 23. A method according to claim 16, wherein the tube is arranged in the chamber such that it extends across a major portion of the length of the chamber. |
055263860 | claims | 1. A method for improving the operational characteristics of a nuclear power electric generation plant that comprises the steps of: (a) inserting into a downstream portion of main steam piping from a steam generator in said nuclear power plant a micro-jet mixer; (b) supplying heat recovery boiler high pressure steam to said micro-jet mixer, (c) directing said high pressure inlet mixed steam into a high pressure stage of a main turbine of said nuclear power electric plant, wherein work is extracted by said high pressure stage of said main turbine; (d) directing a high pressure exhaust steam into a moisture separator reheater wherein said high pressure exhaust steam is mixed with a micro-jet exhaust steam wherein a moisture separator reheater discharge steam is formed that is further superheated; (e) directing said moisture separator reheater discharge steam into a low pressure stage of the main turbine of said nuclear power electric generation plant; whereby efficiency of said nuclear power electric generation plant is increased. (a) a micro-jet mixer receiving main steam from a steam generator in said nuclear power plant; (b) a heat recovery boiler providing high pressure steam to said micro-jet mixer wherein said high pressure steam is mixed with said main steam and forms a high pressure inlet mixed steam that is superheated; (c) a high pressure stage of a main turbine of said nuclear power electric plant, wherein work is extracted from the high pressure inlet mixed steam leaving a high pressure exhaust steam; (d) a moisture separator reheater wherein said high pressure exhaust steam is mixed with a micro-jet mixer exhaust steam forming a moisture separator discharge steam; (e) a low pressure mixer superheater for mixing said moisture separator discharge steam with a heat recovery boiler low pressure steam forming low pressure mixer superheater discharge steam; and (f) a low pressure stage of the main turbine of said nuclear power electric generation plant for receiving said low pressure mixer superheater discharge steam and extracting work therefrom. (a) a mixer shell having a cross section and having an inlet chamber for receiving main steam, an outlet chamber, and at least one HRB steam inlet for receiving heat recovery boiler outlet steam, (b) a perforated baffle located within said mixer shell having a plurality of micro-jets cuts therein, said micro-jets extending from an outer surface to an inner surface, wherein said heat recovery boiler outlet steam flowing along said outer surface, and said main steam flowing along said inner surface, wherein when said heat recovery boiler outlet steam exits said micro-jets and enters said main steam a combined flow is formed; (c) a slotted baffle located within said perforated baffle having a interior end and an attaching end, (d) an exit chamber located within said slotted baffle having a mixer end, a discharge end, and a chamber region, said mixed flow directed to said mixer end thereby forming a high pressure mixed steam, which is directed to a main steam piping; wherein said high pressure mixed steam is directed to the high pressure inlet of said main turbine. (a) inserting into a downstream portion of main steam piping from a steam generator in said nuclear power plant a high pressure mixer superheater; (b) supplying heat recovery boiler high pressure steam to said high pressure mixer superheater, (c) directing said superheated main steam into a high pressure stage of a main turbine of said nuclear power electric plant, wherein work is extracted by said high pressure stage of said main turbine; (d) directing a high pressure exhaust steam into a moisture separator reheater then entering a low pressure mixer where the separated high pressure exhaust steam is mixed with steam from a low pressure heat recovery boiler; and (e) directing said moisture separator reheater steam to a low pressure stage of the main turbine, wherein further work is extracted by said low pressure stage of said main turbine and efficiency of said nuclear power electric generation plant is increased. (a) inserting into a downstream portion of main steam piping from a steam generator in said nuclear power plant, a high pressure mixer superheater, (b) directing said high pressure exhaust steam and said high pressure mixture superheater outlet steam into a moisture separator reheater thereby forming a moisture separator discharge steam; (c) combining said moisture separator discharge steam with a low pressure heat recovery boiler discharge steam, in a low pressure mixer superheater forming a low pressure mixer superheater discharge steam; (d) said low pressure heat recovery boiler discharge steam being formed by, whereby efficiency of said nuclear power electric generation plant is increased. (a) inserting into a downstream portion of main steam piping from a steam generator, in said nuclear power plant, a micro-jet mixer; (b) supplying heat recovery boiler high pressure steam to said micro-jet mixer, (c) directing said high pressure inlet mixed steam into a high pressure stage of a main turbine of said nuclear power electric plant, wherein work is extracted by said a high pressure stage of said main turbine; (d) directing a high pressure exhaust steam into a moisture separator reheater where said high pressure exhaust steam is mixed with a micro-jet mixer exhaust steam wherein a moisture separator discharge steam is formed; (e) directing said moisture discharge steam to a low pressure mixer superheater where it is mixed with heat recovery boiler low pressure steam forming low pressure mixer superheater discharge steam; (f) directing said low pressure mixer superheater discharge steam into a low pressure stage of the main turbine of said nuclear power electric generation plant; whereby efficiency of said nuclear power electric generation plant is increased. 2. An apparatus for improving the operational characteristics of a nuclear power electric generation plant comprising: 3. The apparatus as recited in claim 2 wherein the micro-jet mixer comprises: 4. The apparatus in claim 3 wherein the cross-section is substantially circular in shape. 5. The apparatus in claim 3 wherein the cross-section is substantially in the shape of a regular polygon. 6. The apparatus in claim 3 having a plurality of slotted baffles. 7. The apparatus in claim 3 having a plurality of perforated baffles. 8. The apparatus in claim 3 wherein a plurality of exit chambers are used. 9. The apparatus in claim 3 wherein the mixer end of the exit chamber comprises a mixer assembly. 10. The apparatus in claim 8 wherein a mixer assembly is constructed of honeycomb mixing material. 11. The apparatus in claim 8 wherein the mixer assembly is a vortex mixer. 12. The apparatus in claim 3 wherein the micro-jets have a diameter from 10-20 mm. 13. The apparatus in claim 3 wherein the micro-jets are nozzle shaped with a nozzle inlet and a nozzle outlet. 14. The apparatus in claim 13 wherein the nozzle inlet is larger than the nozzle outlet. 15. The apparatus in claim 3 wherein the baffle-slots are rectangular slots of 5 cm in width and 10 cm in length. 16. The apparatus in claim 3 wherein the baffle-slots are ellipsoid in shape with the major axis being 12 cm and the minor axis being 6 cm in length. 17. A method for improving the operational characteristics of a nuclear power electric generation plant that comprises the steps of: 18. A method for improving the operational characteristics of a nuclear power electric generation plant that comprises the steps of: 19. A method for improving the operational characteristics of a nuclear power electric generation plant that comprises the steps of: 20. The method in claim 1 wherein said chemically fueled means is a turbine that drives a generator that supplies electricity. 21. The method in claim 20 wherein said turbine is a gas driven turbine. 22. The method in claim 20 wherein said turbine is a fossil fueled turbine. 23. The method in claim 1 wherein a high pressure stage exhaust steam is mixed with a second heat recovery boiler high pressure steam to form the low pressure mixer superheater discharge steam. 24. The method in claim 1 wherein a high pressure stage exhaust steam is mixed with heat recovery boiler low pressure steam to form the low pressure mixer superheater discharge steam. |
046413359 | claims | 1. An improvement to a stereo radiographic X-ray apparatus comprising first, second and third spaced-apart radiation focal points arranged such that the first and second focal points lie in a plane and the third focal point is located intermediate the first and second focal points in the plane, the improvement comprising: first and second pairs of X-ray opaque shutter leaves, each pair of shutter leaves being associated with a corresponding one of the first and second focal points and positioned to collimate radiation therefrom in planes which are perpendicular to said plane and comprising an internal shutter leaf and an external shutter leaf which are so positioned that the two internal shutter leaves are adjacent each other between the two external shutter leaves and radiation from the third focal point can be collimated by the two internal shutter leaves; and means for independently moving the shutter leaves, such that each of the said pairs of shutter leaves can individually collimate radiation from its corresponding focal point for stereo radiography and the two internal shutter leaves can alternatively collimate radiation from the third focal point and to close shutter apertures through which radiation from the first and second focal points is directed. |
description | This application claims the benefit of U.S. Provisional Application No. 60/546,840, entitled “AUTOMATED AND SEMI-AUTOMATED PROBING IN A CHARGED PARTICLE BEAM DEVICE,” filed Feb. 23, 2004, the disclosure of which is hereby incorporated herein by reference. This application is also related to commonly-assigned U.S. application Ser. No. 11/064,127, filed Feb. 23, 2005 entitled“CHARGED PARTICLE BEAM DEVICE PROBE OPERATION,” the disclosure of which is hereby incorporated herein by reference. This application is also related to commonly-assigned U.S. application Ser. No. 11/064,131, filed Feb. 23, 2005 entitled “PROBE TIP PROCESSING,” the disclosure of which is hereby incorporated herein by reference. The present application is also related to: (1) U.S. patent application Ser. No. 10/173,542, filed Jun. 17, 2002, entitled “MANIPULATION SYSTEM FOR MANIPULATING A SAMPLE UNDER STUDY WITH A MICROSCOPE”; (2) U.S. patent application Ser. No. 10/173,543, filed Jun. 17, 2002, entitled “MODULAR MANIPULATION SYSTEM FOR MANIPULATING A SAMPLE UNDER STUDY WITH A MICROSCOPE”; and (3) U.S. patent application Ser. No. 10/948,385, filed Sep. 23, 2004, entitled “METHOD, SYSTEM AND DEVICE FOR MICROSCOPIC EXAMINATION EMPLOYING FIB-PREPARED SAMPLE GRASPING ELEMENT”. A charged particle beam device (CPBD) is often required to examine and perform manipulation of micro- and nano-scale objects. In general, a CPBD employs a charged particle beam (CPB) to irradiate a sample under study, or a focused spot on the study, wherein the wavelength of the CPB is much smaller than the wavelength of light used in optical microscopes. Modern CPBD can view details at the atomic level with sub-nanometer resolution (e.g., down to about 0.1 nm resolution) at a magnification of up to about one million. CPB microscopes and others which may be similarly employed include scanning electron microscopes (SEM), focused ion beam (FIB) microscopes and transmission electron microscopes (TEM), among others. A scanning electron microscope (SEM) is another type of CPB microscope. In an exemplary SEM, a beam of electrons may be focused to a point (e.g., “spot” mode) and scanned over the surface of the specimen. Detectors collect the backscattered and secondary electrons reflected or otherwise originating from the surface of the specimen and convert them into a signal that is used to produce a realistic, multi-dimensional image of the specimen. SEMs can provide a magnification of up to about two hundred thousand, possibly higher. For some applications, a probe or plurality of probes may be used inside a CPBD to acquire additional data, properties and/or characteristics of samples. Such probes may also be used to performed tests on or with samples within the CPBD to collect such data, properties and/or characteristics of samples, among other purposes. However, it can be difficult to accurately position and/or orient a probe or sample within an SEM or other CPBD. In fact, it can be difficult to even distinguish between the plurality of probes that may be employed within the CPBD to manipulate the sample. It can also be difficult to verify adequate physical and/or electrical contact between a probe and a contact point on a sample. Disclosed herein are exemplary embodiments of manual, partially automated and substantially automated apparatus and methods for probing one or more samples in a charged particle beam device (CPBD). For example, such probing may comprise or support automated measurement or detection of one or more characteristics of the sample(s). Such characteristics may include mechanical, electrical, optical and/or chemical characteristics, and/or combinations thereof, without limitation. Exemplary samples within the scope of the present disclosure include, without limitation, an integrated circuit (IC), a partially finished IC, a de-processed IC, a transistor, other electronic and micro-electronic devices, micro-electromechanical systems (MEMS) devices, electro-optical devices and circuits, and combinations thereof, among others. Other samples may include nano-particles, nano-materials, coatings, biological samples, and combinations thereof. A CPBD within the scope of the present disclosure may be or include a charged particle beam microscope (CPBM), among others. For example, a CPBM may be or include a focused ion beam (FIB) microscope, a dual-beam FIB microscope, a scanning electron microscope (SEM), a scanning auger microscope (SAM), a transmission electron microscope (TEM), and an environmental scanning electron microscope (ESEM), among others. Of course, the scope of the present disclosure is not limited to the characteristics, samples or CPBDs described above. Embodiment of methods according to aspects of the present disclosure may include, at least in part, one or more steps or processes for performing the following operations: (1) preparing a sample for introduction into a CPBD; (2) introducing the sample into the CPBD; (3) preparing the sample for measurement using one or more probes; (4) preparing the probes for measurement of one or more characteristics of the sample; (5) locating the probes proximate corresponding target areas on the sample; (6) establishing contact between the probes and the target areas; (7) measuring the characteristic(s); (8) removal of probes and samples from the CPBD; and (9) processing data collected during one or more of the previous processes. Embodiment of methods according to aspects of the present disclosure may also or alternatively include transmitting data collected during one or more of such processes. Such data transmission may be by TCP/IP or other protocols, possibly depending on the transmission destination, wherein possible destinations may include components that are ancillary to, associated with, or merely configured to communicate with the CPBD, including components that are centrally or remotely located relative to the CPBD. One, several or each of such operations, or one or more of the steps or processes executed therefor, may be partially or substantially automated. Aspects of such automation may be provided by the automation of various devices employed to orient and otherwise operate one or more probes and one or more samples, as well as those devices employed to measure the characteristic(s), all of which may be communicatively coupled as an Automated Probing System (APS). Thus, communications may be sent between these devices to control initiation, adjustment or termination of the above-described operations, or for one or more of the steps or processes executed during such operations. Such communications may also be sent automatically between these devices, such as at the control of the APS and/or otherwise in the absence of user input. In one embodiment, the APS relies on or otherwise employs a Reference System (RS) by which the orientation of the moving components of the various devices comprising the APS can be referenced to each other and to fixed components or devices. The RS may thus support or provide monitoring of the spatial relationships within the APS, including spatial relationships between and among moving and fixed components or devices. For example, in one embodiment, the spatial relationships of moving components of the various devices is employed to automatically position probe tips relative to each other and/or to features of a sample being probed. Moreover, because the various devices of the APS can be communicatively coupled, information gathered by the RS can be communicated among the devices to initiate, monitor, adjust and/or terminate one or more processes performed by a component or device in the APS, as well as to collect data related to one or more such processes. The RS and/or other components of the APS, as well as the APS itself, may employ or rely on aspects of U.S. patent application Ser. No. 10/698,178, “SYSTEM AND METHOD OF PROCESSING DAG OCTREE,” filed Oct. 31, 2003, and/or U.S. patent application Ser. No. 10/749,256, “ISO-SURFACE EXTRACTION INTO SPLAT HIERARCHY,” filed Dec. 31, 2003, each of which are hereby incorporated by reference in their entirety herein. These applications relate to computer simulation and imaging aspects which may be employed to generate and display static and real-time images of probes, samples and CPBD chambers within the scope of the present disclosure. For example, such computer simulated imaging may be employed in support of collision avoidance procedures during the transport of samples and probes within a CPBD chamber according to aspects of the present disclosure. However, such collision avoidance may additionally or alternatively be implemented in a more physical form, such as by proximity and/or contact detection, including in a partially or substantially automated manner. The RS can comprise a variety of devices such as, without limitation, location sensors, pressure sensors, environmental sensors, material/element sensors, and/or timers, among others. The RS may also include one or more devices operable to execute location procedures, such as locating by imaging. The devices and/or components of the RS may be operable to gather information regarding the various devices and/or components of the APS and/or the steps, processes, actions or operations performed thereby. The RS may also include programming and/or software for converting the gathered information, such as into messages that may be communicated among the devices. For example, the messages from the RS may be in the form of an electronic signal, or may be in the form of a command generated by software associated with the RS. The RS may be implemented as a part of a Control Routine (CR) that may be programmed into one of the communicatively coupled devices of the APS. In one such embodiment, the RS is implemented in the CR as a set of procedures that are programmed into a position control device that provides operability to the probes. The CR may also comprise various sub-routines for enabling automated probing and other automated processes according to aspects of the present disclosure. Various aspects of the RS may vary depending on the type of process or processes to be performed by the RS, possibly including automated processes. For example, the information required by the RS during the automated preparation of a probe can vary from the information required by the RS during the automated measurement of a characteristic of a sample. In some embodiments, however, possibly regardless of the type of automated process or processes being performed, the RS relies on certain common factors, such as the position of a sample relative to a charged particle beam (CPB) produced by a CPBD, the position of probe tips relative to the sample, and a map of the sample. A map of the sample refers to data regarding the sample that can be used, for example, to determine the location of features on the sample. For example, the sample may be a semiconductor chip with certain features formed thereon. A map of the chip may provide location information regarding one or more of those features. A map of a sample can be obtained from a variety of sources including, for example, computer-aided design (CAD) data, manual training of the sample by a user, and/or a set of reference coordinates specified by a user and/or an external system. In embodiments in which the RS relies on the position of a sample relative to a CPB, the RS may use information obtained from a process implemented by the CR for determining the position of the sample positioned in a sample chamber of the CPBD relative to the CPB. Alternatively, or additionally, the CR may include one or more processes employable to determine the location of the sample relative to a positioning stage or probe tip, as well as one or more processes employable to determine the location of the stage or probe tip relative to the CPB. Alternatively, or additionally, the CR may include one or more processes employable to determine the location of the probe tip relative to the positioning stage, as well as one or more processes employable to determine the location of the stage relative to the CPB. In one embodiment, the CR implements a standard image-analysis procedure to determine the position of the sample relative to the CPB, the positioning stage and/or the probe tip. For example, the image can be derived from a representation created from the CPBD or other such device that can create a suitable representation for use by image-analysis software. Reference features on the sample, stage and/or probe tip can be used in the image-analysis to create a mathematical coordinate system to describe the location of the sample, stage and/or probe tip to the RS. In embodiments in which the RS relies on the position of the probe tips relative to the sample, the RS may use information obtained from a process implemented by the CR for determining the location of the probe tips relative to the position of the sample in the sample chamber. For example, the location of the probe tips relative to the CPB and/or stage may be determined using suitable image-analysis techniques. Alternatively, or additionally, the location of the probe tips relative to the probe positioner may be determined, and then the location of the probe tips relative to the CPB or stage may be determined. The location of the probe tips can be determined by image-analysis, or by moving the probe tips to a mechanical, electrical or laser sensor that provides suitable feedback for such a requirement, among other possible methods. In embodiments in which the RS relies on a map, the RS may communicate information to a device providing operability of the probes, such as a positioner control device, which may trigger such device to drive the position of the probe tips over specified features. For example, the coordinates of features relative to the map and the actual location of the sample under inspection, or the actual location of the probe tips, and/or the actual location of the positioners can be mathematically combined. Referring to FIG. 1, illustrated is at least a portion of one embodiment of an apparatus 100 according to aspects of the present disclosure. The apparatus 100 may include or be substantially similar to an APS according to one or more of the aspects described above. The apparatus 100 includes a positioner control device 102, a CPBD 104 and a measuring device 106. The positioner control device 102 may be configured to control a manipulation platform to which one or more probes are coupled. For example, the positioner control device 102 may be or include the S100 Nanomanipulator System commercially available from Zyvex Corporation, among other manipulators. The CPBD 104 may be or include an SEM or FIB available from FEI, Hitachi or JEOL, among others. The measuring device 106 may be or include the Keithley 4200, which is also commercially available, among other measuring devices. The positioner control device 102, the CPBD 104 and the measuring device 106 are coupled such that communications are sent between the devices to initiate, adjust, monitor, collect data relative to, and/or terminate processes. Such processes may include introducing a sample into a the CPBD 104, preparing a plurality of probes for taking a measurement of the sample, locating the probes proximate a target area on the sample, activating the probes to make contact with the target area, and/or taking the measurement, among others. The communications among the devices may be interpreted by the CR which, as described above, may be programmed into one or more of the devices of the apparatus 100. Consequently, the CR may instruct the devices of the apparatus 100 to initiate, monitor, collect data related to, adjust and/or terminate a particular process, such as preparing the probes or taking measurements, in response to communications received from the CPBD 104 and/or the measuring device 106. The CR may be programmed into a single computer or machine (e.g., a “master control computer”) that is responsible for directing the operation of one or more of the positioner control device 102, the CPBD 104 and the measuring device 106, at least in part, and may also be responsible for controlling one or more of the steps, processes, actions and/or operations described above. For example, a procedure for introducing a sample into the CPBD 104 may be controlled by the same computer that operates the positioner control device 102 and that drives probes to a desired location, and/or by the same computer that controls peripheral devices. In addition, Data Acquisition (DA) boards and other DA devices may be implemented in the computer or machine operating the positioner control device 102, for example, to enable the positioner control device 102 to take measurements that would otherwise be implemented by a computer, machine or operation system of the measuring device 106. In embodiments in which the CR and operation of one or all of the devices of the apparatus 100 or APS reside on a single machine, communication among the various devices may be enabled via software. In other embodiments, one or more of the positioner control device 102, the CPBD 104 and the measuring device 106 may comprise or be associated with a separate computer or machine to direct operation. In such embodiments, each device may be communicatively coupled by pathways such as wire, cable, network (e.g., TCP/IP network over Ethernet, 1394 connection, and/or USB, among others), or wireless protocol, among other means. Thus, communications between the devices of the apparatus 100 may be implemented as logical operations and/or subsystems that are accessed via a separate computer via a physical network, or may reside locally to a master control computer or other singular or plural computing device. Referring to FIG. 2, illustrated is a block diagram of at least a portion of one embodiment of an apparatus 200 according to aspects of the present disclosure. The apparatus 200 is one environment by which messages communicated between the devices of the apparatus 100 may be implemented. The apparatus 200 may be configured to fit within the chamber of the CPBD 104, including configurations in which components of the apparatus 200 are in communication with the positioner control device 102 and/or the measuring device 106, whether the positioner control device 102 and/or the measuring device 106 are also disposed within the CPBD 104 chamber or are external to the CPBD 104 chamber. The apparatus 200 may also include one or more of the CPBD 104, the positioner control device 102 and the measuring device 106. However, in the illustrated embodiment, the apparatus 200 is a discrete component or subassembly positioned within the chamber of the CPBD 104 and communicatively coupled to the CPBD 104, the positioner control device 102 and the measuring device 106. The apparatus 200 includes a manipulation platform 210 for manipulating one or more samples within the CPBD 104. Manipulation of a sample may include, without limitation, moving a sample in X, Y, Z, DX, DY and DZ directions. Manipulation of a sample may additionally or alternatively include the determination of physical and chemical characteristics of a sample, such as performing electrical, mechanical, optical, or chemical measurements, or combinations thereof. In one embodiment, the apparatus 200 includes a plurality of manipulation platforms 210, whether substantially similar or having varying configurations. The manipulation platform 210 may also be reconfigurable, such as may allow the custom alteration of the layout and/or functionality described below. The manipulation platform 210 includes at least one base 206 on which a plurality of manipulator module interfaces 212 are arranged. Each of the manipulator module interfaces 212 are configured to receive a manipulator module 260. In the illustrated embodiment, the manipulation platform 210 includes four manipulator module interfaces 212, and manipulator modules 260 are coupled to two of the manipulator module interfaces 212. However, other embodiments within the scope of the present disclosure may include a different number of manipulator module interfaces 212 and/or manipulator modules 260. Moreover, each manipulator module interface 212 need not be identical to the other manipulator module interfaces 212, and each manipulator module 260 need not be identical to the other manipulator modules 260. The manipulator platform 210 also includes a sample stage 215 configured to receive one or more samples to be manipulated within the CPBD 104. The sample stage 215 may alternatively be a discrete component coupled to the manipulator platform 210 by mechanical fasteners, adhesive, or other means. The manipulator platform 210 may also include a plurality of sample stages 215 each configured to receive one or more samples to be manipulated within the CPBD 104. The manipulator platform 210 also includes or is associated with an interface 207 that is configured to couple the base 206 to an SEM or other device employed as the CPBD 104 in FIG. 2. The interface 207 may be integral to the manipulator platform 210, or may be a discrete component coupled to the base 206 by mechanical fasteners, adhesive, or other means. The interface 207 may be or include a mechanical interface, an electrical interface, a combined mechanical/electrical interface, or separate mechanical and electrical interfaces, among others. Thus, for example, in an embodiment in which an SEM is employed as the CPBD 104 to which the base 206 is coupled via the interface 207, a sample may be arranged on sample stage 215 and the manipulation platform 210 may be positioned within the sample chamber of the SEM by way of an electrical and/or mechanical coupling to the SEM via the interface 207. Consequently, once the platform 210 is coupled to an SEM (or other CPBD 104), a sample arranged on the sample stage 215 may be imaged substantially simultaneously with the manipulation of the sample via the manipulator modules 260. As also depicted in the embodiment illustrated in FIG. 2, a positioner control device 102 may be coupled to the manipulation platform 210 via the interface 207. Consequently, the CPBD 104 and the positioner control device 102 may be communicatively coupled such that communications may be sent between the CPBD 104 and the positioner control device 102, as well as communications with sensors located within these devices and configured to derive information for use in the RS, for example. The positioner control device 102 may be programmed for automated control of the operation of manipulator modules 260 via the manipulator module interfaces 212. Thus, a CR as described above, which may include the RS as a set of methods, may also be programmed into the positioner control device 102 to instruct the devices making up the apparatus 200 (and/or the apparatus 100 of FIG. 1) to initiate, monitor, adjust or terminate one or more steps, process, actions or operations, and/or to collect data related thereto. For example, in response to communications received from the CPBD 104 and/or the measuring device 106, the CR and/or another function or feature of the positioner control device 102 may automate the initiation, monitoring adjustment, termination, and/or data collection related to preparing probes, preparing a sample, imaging a sample or taking a measurement. The embodiment shown in FIG. 2 also demonstrates that the measuring device 106 may be mechanically and/or electrically coupled to the manipulation platform 210. The measuring device 106 may be programmed for automated control of the measurement or detection of characteristics of a sample arranged on the stage 215. The coupling between the measuring device 106 and the manipulation platform 210 may enable communication between the measuring device 106 and the positioner control device 102. Thus, in one embodiment, the measuring device 106, the positioner control device 102 and the CPBD 104 are collectively coupled, each to the other two, thereby at least partially composing an APS as described above. As also described above, a CR comprising an RS configured to reference fixed and/or moving components of the measuring device 106, the positioner control device 102 and the CPBD 104, including relative movement of such components, can be programmed into one or more of the measuring device 106, the positioner control device 102 and the CPBD 104. Consequently, signals generated by the RS can be communicated by and through the communicative couplings between the measuring device 106, the positioner control device 102 and the CPBD 104. The positioner control device 102 may comprise any suitable processor-based system, such as a personal computer (PC), that may be configured to control the operation of one or more components of the apparatus 200. For example, the positioner control device 102 may communicate command signals (e.g., electrical signals) to the manipulator modules 260 via the manipulator module interfaces 212 to control the operation of the manipulator modules 260. Such communication may be via one or more conductive traces and/or other types of communication paths, such as those that may be extend along one or more surfaces of the manipulator platform 210 to the manipulator module interfaces 212. The positioner control device 102 may also include software executable to control components of the apparatus 200. For example, software executed by positioner control device 102 may generate and/or communicate command signals to one or more of the manipulator modules 260 via the manipulator module interfaces 212, possibly in an automated fashion and/or responsive to user input received by the positioner control device 102, the measuring device 106, and/or the CR. Such signals may also be generated and/or communicated in response to feedback or other communications received from the manipulator module interfaces 212 and/or the manipulator modules 260, and/or to communications received by the positioner control device 102 from the CPBD 104. In one embodiment, the manipulator modules 260 include logic for communicating their individual operative capabilities to the positioner control device 102. For example, a manipulator module 260 may comprise logic for transmitting information about its movement capabilities, such as whether it is configured to generate translational movement in one or more orthogonal dimensions, whether it can generate rotational movement about one or more orthogonal axes, its current orientation, and/or other information. The manipulator modules 260 may also include logic for communicating information about its end-effector and the type of probes assembled therein, where such information may again be communicated with the positioner control device 102, among other components of the apparatus 200. The manipulator modules 260 each couple to or otherwise interface with a corresponding manipulator module interface 212 on the platform 210. For example, each manipulator module 260 may include a communication interface (e.g., an electrical input and/or output interface) configured to couple with the communication path of one or each of the manipulator module interfaces 212. In one embodiment, such a communication interface or other portion of the manipulator modules 260 may include conductive traces for receiving input signals for controlling operation. Accordingly, coupling a manipulator module 260 to manipulator module interface 212 can include contacting or otherwise coupling the conductive traces on each of the manipulator module 260 and the manipulator module interface 212. The manipulator modules 260 may also include or be associated with motion and/or displacement sensors. Signals from such sensors can also be routed into the positioner control device 102. Consequently, the positioner control device 300 may be implemented with control software and/or hardware configured to monitor the position or orientation of a manipulator module 260 in real-time, as well as possibly calibrating or correcting the orientation. The positioner control device 102 may also include or be coupled to an imaging system, such as may be provided by or associated with the CPBD 104, and may thus perform or support real-time object recognition and positioning identification which may be employed to control the orientation of the manipulator modules 260 and/or end-effectors of the manipulator modules 260, possibly in an automated manner. At least with regard to some embodiments of automated processes that are described herein, the CR may be programmed or otherwise configured to recognize conditions that may require human intervention. In such embodiments, human intervention can be accommodated via a user interface suitable to such intervention. Additionally, or alternatively, the CR may be configured for initiation by a higher level control routine, as well as communication of system and/or process data with the higher level control routine. Referring to FIG. 3A, illustrated is a flow-chart diagram of at least a portion of one embodiment of a method 300a according to aspects of the present disclosure. The method 300a may be performed or executed by the apparatus 100 of FIG. 1 and/or the apparatus 200 of FIG. 2, among other apparatus according to aspects of the present disclosure. Moreover, one or more portions of the method 300a may be performed or executed in a substantially automated manner. In one embodiment, the method 300a is substantially automated. Additionally, aspects of the method 300a and other methods within the scope of the present disclosure are applicable to single probe and multiple probe applications. Thus, for the sake of simplicity and clarity, any reference herein to a plurality of probes or a multiple probe method, process or application is also applicable to a single probe or a single probe method, process or application. Also, each of the processes, procedures, actions and operations described below as composing one or more embodiments of the method 300a, as well as other methods within the scope of the present disclosure, may independently include multiple processes, procedures, actions and/or operations. The method 300a may include a probe selection step or process 305 by which one or more probes are selected based on a characteristic to be measured or detected. The probes may alternatively, or additionally, be selected based on the manner of measuring or detecting the characteristic. For example, probes suitable for measuring an electrical characteristic of a sample may include, without limitation, probes substantially comprising tungsten, platinum or gold wire, or probes having probe tips of such composition. The selection of one or more probes by or during the process 305 may be manual, partially automated or substantially automated. For example, manual embodiments of the process 305 may substantially rely on user input. Partially automated embodiments of the process 305 may automatically perform a subset of the actions and/or decisions of the process 305. Automated aspects of partially automated embodiments may include process initiation, process performance, process monitoring and/or adjustment (e.g., time, power, speed, force, etc.), process termination, and/or process errors, among others. Substantially automated embodiments of the process 305 may substantially rely on automated robotics and/or other machinery or apparatus, and/or substantially automated computing hardware and/or software, such that the selection of probes during process 305 may be performed in the substantial absence of user input. This convention, where the extent of automation may substantially be inversely proportional to the amount of user input required or employed during a particular method or method component, or a particular apparatus or function thereof, is also applicable to other aspects of the method 300a, as well as to aspects of other methods and apparatus within the scope of the present disclosure. The method 300a also includes a process 310 by which one or more selected probes are introduced into the chamber of a CPBD. In one embodiment, the process 310 may be at least partially automated, such that the probes may be introduced in the CPBD chamber with little or no user input regarding the particulars of, for example, the orientations or locations of the probes within the chamber. However, the process 310 may alternatively be substantially manual or substantially automated. Introducing the probes into the CPBD chamber may also include removing the probes from probe storage structure or locations, whether external or internal to the chamber of the CPBD or other portion of any device, system or other apparatus employed with or including the CPBD. A process 315 of the method 300a includes positioning the tips of the probes above contact points of a sample located in the CPBD chamber. Such positioning may be substantially manual, partially automated or substantially automated. In one embodiment, the positioning may substantially comprise horizontal positioning, such as in a plane that is substantially parallel to a surface of a sample or a platform supporting the sample within the CPBD, or in a plane that is substantially perpendicular to a charged particle beam (CPB) generated within the CPBD. Consequently, subsequent vertical positioning of the probe or probe tips may be in a plane that is substantially perpendicular to the plane of horizontal positioning. Additionally, although many aspects described herein regarding positioning probes or probe tips are described with respect to motion of the probes or tips relative to a stationary sample, such positioning may also include motion of the sample (or the stage or platform supporting the sample) relative to a stationary position of the probes or probe tips, as well as motion of both the sample and the probes or probe tips. The positioning of the probe tips according to aspects of the method 300a (whether positioning horizontally, vertically or otherwise) may employ the RS, which is configured to positionally reference moving and stationary components relative to one another and/or to a common coordinate system, as described above. Thus, information regarding the location and/or orientation of the probe and/or the probe tips (relative to the sample, manipulators installed within the CPBD chamber, and/or a map of the sample, for example) may be used by the RS to provide appropriate messages to the CR. Consequently, the CR may communicate appropriate messages to a positioner control device (e.g., the positioner controller device 102 of FIGS. 1 and 2) to accurately position the probes above the contact points of the sample. However, in some embodiments, the precision with which the probes or probe tips are positioned over the contact points of the sample may be decreased, such as when contact between the probe tips and the contact points may not be necessary, possibly due to the availability of positioning apparatus and/or methods other than those described with regard to the process 315. The CR may include one or more probe positioning sub-routines that monitor and/or detect the location and/or orientation of the probes relative to contact points on the sample, which may be registered by the RS. The probe positioning sub-routines may also include procedures for determining when a probe has reached a desired location above a contact point. Exemplary procedures for probe positioning and determining when the probe has reached the desired location include, without limitation, image processing associated with the CPBD, employing the CPB to locate alignment marks of the sample and/or underlying platform, referencing map data obtained by the RS, operating the CPBD in a teaching mode, referencing absolute coordinates on the sample (such as a list of coordinates previously determined), and executing an automated or semi-automated “point and click” process. A process 320 of the method 300a includes establishing physical and electrical contact between the probes and the contact points on the sample, such as by vertically translating the probes towards the sample via the positioner control device. The probe positioning of the process 320 may be substantially manual, partially automated or substantially automated. When more than one probe is being used, the probes may be lowered simultaneously, in groups, or one at a time, depending on the programming of the positioner control device, for example. In one embodiment, the CR includes a procedure to maintain contact between the probes and the sample until one or more measurement or detection processes are completed. For example, upon contact between a probe tip and a contact point on the sample, a signal may be automatically generated and transmitted to the positioner control device, which may activate a sub-routine of the CR. The activated sub-routine may include an automated process for determining the quality of the contact made with the sample, among other processes. One or more sample characteristics are measured or detected in a process 330 of the method 300a, wherein the process 330 may be substantially manual, partially automated or substantially automated. The above-described CR may activate a measuring device to perform the measurement or detection, possibly upon receiving communications that confirm physical and/or electrical contact between the probe tips and contact points. The measuring device may be substantially similar to the measuring device 500 shown in FIGS. 1 and 2. In some embodiments, the measuring device may be a commercially available device, and may include software and/or hardware for performing or supporting the measurement or detection of sample characteristics. The measuring device employed in the process 330 of the method 300a may also have substantially similar aspects to measuring devices described in U.S. Pat. No. 6,208,151, the entire disclosure of which is incorporated herein by reference. Although the embodiment shown in FIG. 3A depicts the method 300a in a flowchart format, such format should not be interpreted to require that the depicted components of the method 300a occur in series. For example, more than one of the depicted components of the method 300a can also be performed simultaneously. One such example entails preparing one or more probes while employing another one or more probes to measure or detect characteristics of a sample, wherein such probe preparation may be performed in-situ and/or ex-situ of the CPBD chamber in which the sample is being examined. The sequence of the components of the method 300a may also vary from the sequence depicted in FIG. 3A. Moreover, one or more components of the method 300a may be repeated or eliminated yet remain within the scope of the present disclosure. Referring to FIG. 3B, illustrated is at least a portion of another embodiment of the method 300a shown in FIG. 3A, herein designated by reference numeral 300b. Embodiments of the method 300b may include one or more of the components of the method 300a. For example, the illustrated embodiment of the method 300b includes each of the components of the method 300a shown in FIG. 3A, as well as one or more additional components. Thus, the following description of the method 300b is substantially directed towards those components which were not explicitly described with regard to the method 300a, although merely for the sake of simplicity and brevity, and without limiting the scope of either method 300a or method 300b within the scope of the present disclosure. Of course, embodiments of the method 300a within the scope of the present disclosure may also include one or more of the components of the method 300b shown in FIG. 3B. The method 300b may include a process 345 by which ex-situ preparation of one or more probes may optionally be performed. Consequently, the process 345 is depicted in FIG. 3B by dashed lines, in contrast to solid lines. This convention, in which optional processes, steps, actions and/or operations are depicted in dashed lines, as well as the directional indications (arrows) depicting the sequence of such components, is hereafter followed merely for the sake of clarity. Moreover, the depiction of any method, method component or sequence indicator by solid lines, in contrast to dashed lines, does not imply the necessity of such method, component or sequence in any particular embodiment, or otherwise limit the scope of the present disclosure to only those methods that include each aspect depicted by solid lines. To the contrary, any aspect depicted by solid lines or dashed lines in FIGS. 3A and 3B, or any other figure of the present disclosure, may be optional in one or more of the myriad apparatus and methods within the scope of the present disclosure. The probe preparation performed by the process 345 may include the preparation, conditioning and/or characterization of one or more probes, as described above. However, as also described above, such preparation, conditioning and/or characterization may be collectively referred to herein as “preparation.” Nonetheless, some methods within the scope of the present disclosure may not include preparation, conditioning and characterization of one or more probes, but may specifically include only: (1) preparation; (2) conditioning; (3) characterization; (4) preparation and conditioning; (5) preparation and characterization; or (6) conditioning and characterization; where preparation may include one or more processes exclusive of conditioning and characterization. Also, as described above, aspects described herein as applicable to a single probe may also be applicable to multiple probes, aspects described herein as applicable to multiple probes may also be applicable to a single probe, and the same hold true for single and multiple probe tips. The process 345 may be an ex-situ process in the sense that the probes being prepared by the process 345 undergo such preparation at a location outside of the chamber of the CPBD in which the probes are to be employed to measure or detect a characteristic of a sample oriented in the CPBD. Ex-situ preparation of the process 345 may include one or more processes for determining whether the characteristics of a selected probe are appropriate for the desired measurement or detection for which the probe is to be employed. Additionally, or alternatively, the ex-situ preparation of the process 345 may include one or more processes for effecting remedial measures (e.g., additional or optional probe preparation) if the characteristics of the probe are not appropriate for the intended measurement or detection. For example, oxide or other contamination that may hinder the utility of a probe as a measuring device may form on the probe tip prior to introducing the probe into the CPBD chamber. Consequently, the ex-situ preparation of the process 345 may include one or more chemical dip processes that may remove or reduce such contamination. Such processes may include one or more hydrofluoric acid or potassium hydroxide dip processes, among others. The ex-situ preparation of the process 345 may also or alternatively include one or more process to sharpen the tip of a probe, such as to improve utility when employing the probe to measure a characteristic of a sample. However, the method 300b may not include the process 345, such as when a selected probe is adequately prepared without requiring ex-situ preparation, possibly including embodiments in which the above-described probe preparation is performed in-situ once the probes have been introduced into the CPBD chamber. Nonetheless, in embodiments including the ex-situ probe preparation of the process 345, such preparation may be substantially manual, partially automated or substantially automated. The ex-situ preparation of the process 345 may also include sharpening, bending, shaping or other mechanical processing of one or more probes. Such mechanical processing may affect the entire probe or merely a portion of the probe, such as the probe tip, stem or body, for example. In one embodiment, the mechanical processing includes bending the probe to facilitate a dip process, such as one or more of those described above. For example, some probes may be manufactured from wire material stock and, thus, have a substantially cylindrical shape, wherein the mechanical bending process may place one or bends or turns in probe. In one embodiment, only one bend may be formed, such that the resulting probe has a substantially L-shaped profile, although the bend may not be substantially 90 degrees (e.g., the bend may be about 30 degrees in some embodiments, 45 degrees in other embodiments, and 60 degrees in other embodiments). In embodiments in which the probe is bent to include more than one turn, the bent probe may have a zigzag profile, a Z-shaped, or otherwise. Moreover, where probes are mechanically processed to include more than one bend, the bends may be in different planes. For example, a first bend may be in a first plane and a second bend may be in a second plane, where the first and second planes are not coincident, and possibly not parallel. In embodiments in which ex-situ probe preparation of the process 345 is performed, the CR may implement procedures for the probe preparation as a set of procedures by which the selected preparation process or processes may be monitored by sensors, or by duration of such processing, among other possibilities within the scope of the present disclosure. In one embodiment, the progress and/or completion of one or more probe preparation processes may be monitored or determined by imaging, such as via communication of an appropriate termination signal when the ex-situ preparation is complete. The method 300b may also include a process 350 by which one or more selected probes are stored in the chamber of the CPBD. The process 350 may be substantially manual or partially automated. However, in one embodiment, the process 350 is substantially automated, such that the probes may be stored in the CPBD chamber with little or no user input regarding the particulars of, for example, the storage orientations or locations of the probes within the chamber. The method 300b may also include an in-situ process 355 by which one or more probes may undergo probe preparation while located inside the chamber of the CPBD. The in-situ probe preparation of the process 355 may be substantially manual or partially automated. However, the in-situ probe preparation of the process 355 may also be substantially automated, possibly by employing an automated probe preparation system (APPS). The APPS may also be referred to herein or elsewhere as an automated probe conditioning system and/or an automated probe characterizing system. In one embodiment, the APPS may be implemented as a part of the CR described above, such that the APPS also described above may be operable to prepare one or more probes via an automated process. Embodiments of the above-described APPS may comprise one or more sensors, electrodes or counter electrodes, which may be operable to sense the presence of a probe (e.g., in the CPBD chamber) such that the sensor, electrode or other component of the APPS can subsequently be positioned proximate the probe. Alternatively, or additionally, the probe may be positioned proximate the sensor or other component of the APPS. The proximity of the probe and the APPS component may be about five cm or less, but may also include actual contact between the tip and the APPS component, depending on the type of probe preparation to be performed. When the desired proximity has been reached, the sensor or other APPS component may communicate a signal to the CR indicating such, which the RS may use to register the location of the probe tip (e.g., as located at an absolute location or a location relative to a coordinate system of the RS). When a probe tip location has been registered, the CR may automatically initiate a selected sub-routine, which may be or include a process for probe preparation. The process selected for initiation by the CR, whether automated or not, may depend upon CR programming. In embodiments in which the selected process includes probe characterization, the tip diameter, probe material and probe geometry may be measured and/or detected, among other possible physical and/or chemical properties of the probe and the probe tip. Such properties may be examined by one or more processes which may include, without limitation, field emission measurements, visual observation (e.g., with an SEM), energy dispersive x-ray spectroscopy (EDX), and scanning auger mapping. Implementation of these and other probe characterization processes may be controlled by instructions (such as sub-routines) that are provided as a part of the CR. Thus, the CR may be configured to initiate such processes, monitor their progress, and implement appropriate termination commands for the processes, among other actions. In embodiments in which the selected process includes probe conditioning, instructions (such as sub-routines) for implementing various conditioning procedures may be programmed as a part of the CR. Thus, the CR may also or alternatively be configured to initiate such processes, monitor their progress, and implement appropriate termination commands for the processes. Probe conditioning processes which may be selected can include decontaminating the probe or probe tip and/or sharpening the probe tip, among others. In one embodiment, the CR may be configured to implement a timer which may be employed in association with the initiation and/or termination of one or more probe conditioning procedures. A loop may also be provided within the CR such that one or more conditioning procedures may be repeated for one or more probes until an improved, desired or threshold level of conditioning is achieved. The selection of the one or more probe conditioning procedure(s) may depend on which property of the probe tip requires improvement, at least in part. In one embodiment, the APPS may be implemented in the CR as a sub-routine to provide commands for performing one or more of the following: (1) pulsing; (2) heating with, for example, e-beam, separate filament, laser, or electron bombardment; (3) field emission; (4) field ionization; (5) field evaporation; (6) field surface melting; (7) ion bombardment/ion milling/ion sputtering; (8); in-situ metal deposition; (9) metal dipping; (10) mechanical deformation of the tip; and (10) an electric charge forced dynamic hot metal flow tip formation (a process referred to hereafter as electric tip processing, or ETP). Pulsing employed during probe conditioning may comprise contacting the tips to drive current through the probe to remove contamination from the tip. Heating employed during probe conditioning may include heating by electron bombardment, wherein free electrons are generated by a heated filament and accelerated by an electric field to collide with the probe tip, thereby heating the tip by conversion of kinetic energy to thermal energy. This and/or other methods of heating a probe tip may be employed during probe preparation (e.g., probe conditioning) to desorb oxides and adsorbates, thereby cleaning the tip. Field emission processes which may be employed for probe preparation may include operating a field emission at a high current, which leads to changes of the tip geometry, thereby conditioning the probe tip. Field ionization processes which may be employed for probe preparation may include cleaning the probe tip by applying a high energy field to ionize atoms on the tip. In-situ metal deposition processes which may be employed for probe preparation may include sputtering a metal on the probe tip. Metal dipping processes which may be employed for probe preparation may include dipping at least the tip portion of the probe into a molten source of metal. Mechanical deformation processes which may be employed for probe preparation may include pulling or forging bulk metal and/or other materials to make a sharp probe tip. ETP may be employed to clean and/or sharpen a probe or probe tip in a non-oxidizing environment using electric current, electric field, and thermal mobilization of atoms, such as metal atoms where the probe or probe tip has a substantially metallic composition. One embodiment of ETP which may be employed to clean and sharpen a probe tip includes bringing a dull probe (to be sharpened) and a thin probe into close proximity. Thereafter, the probes are biased at different voltages such that any oxide or other dielectric or contaminant that is interposing the two probe tips breaks down. For example, the bias differential across the probe tips may be about equal to or greater than the breakdown voltage of the oxide, air or other material interposing the probe tips, such that current flow may be established between the two probes. Such oxide may have been previously formed or allowed to form, or may have undesirably formed, and its existence may have been previously confirmed or merely suspected. In one embodiment, the probes are biased to a relative differential of about 70 volts. The resulting current between the two probe tips can be sufficient to cause local melting of the thinner probe tip. As the thinner probe tip melts, or as the atoms of the metal become substantially mobile, the electric field driving the electric current between the two probes causes the melted metal of the thinner probe to be accelerated towards the larger probe. If this occurs rapidly enough, the majority of the melted metal may deposit onto the larger probe, while the material at the core of the thinner probe may substantially remain in a solid phase. The transfer of metal from the thinner probe to the larger probe can form a gap between the two probe tips, wherein growth of the gap during ongoing metal transfer from the thinner probe to the thicker probe can be allowed to continue until the gap creates sufficient separation between the probe tips to terminate the electric current established by the voltage differential. ETP can, in some embodiments, clean and/or sharpen the thinner probe. ETP may be performed either ex-situ or in-situ relative to the CPBD chamber employed to characterize a sample. The process environment in which ETP may be performed may also vary based on the compositions and/or geometries of the two probe tips, among other possible factors. For example, ETP may be performed in an ambient environment (e.g., room temperature air) or an inert gas environment, possibly at an elevated temperature (e.g., about 1000° C.). ETP may alternatively be performed in a substantial vacuum, such as at a nominal or maximum vacuum attainable within a chamber of a CPBD. Another probe preparation process that may be performed during the process 355 (and/or elsewhere in the method 300) is a cross-probe cleaning process. In one embodiment, a cross-probe cleaning process may include positioning the stem or body portions of two or more probes in close proximity, or in contact, in a mutually orthogonal orientation, such as forming a shape resembling a cross. However, in other embodiments the probes may not be mutually orthogonal, but may be oriented at a relative angle less than about 90 degrees (e.g., about 30 degrees). Thereafter, electrical current may be directed through the probes (possibly a single current if the probes are in physical contact), such that the probes are heated by resistive heating or otherwise to an elevated temperature. At high temperatures, oxides and/or other contaminants previously formed or deposited on the probe tips may dislodge. This process may be performed as an alternative to, or in addition to, one or more of the probe processing procedures described above. The above-described APPS may include one or more of the foregoing probe preparation procedures, one or more of which may be implemented as a substantially automated process as described herein, although one or more of the probe preparation procedures may also or alternatively be partially automated and/or substantially manual. Nonetheless, in embodiments in which one or more probe preparation procedures are employed, and the one or more probe preparation procedures collectively terminate, the CR may communicate to the positioner control device or the CPBD that such collective termination has occurred, and/or that the probes are properly prepared for the subsequent, intended sample characterization. Such communication may also be implemented as a substantially automated function. The method 300b may also include a process 380 by which probes and/or probe tips installed in a manipulator or other positioning device within a CPBD chamber can be exchanged with additional probes and/or probe tips stored within the CPBD chamber. For example, an end-effector rack located within the CPBD chamber and accessible by the manipulator may store replacement probes and/or probe tips which are substantially similar to those installed in a manipulator, such that one or more probes and/or probe tips that become excessively dull or contaminated can be replaced with sharper or cleaner probes and/or probe tips. However, the probes and/or probe tips stored in the end-effector rack may also be configured for a different type of measurement or detection of a sample characteristic relative to the type of measurement or detection for which the probes and/or probe tips installed in the manipulator are configured. Additionally, or alternatively, the probes and/or probe tips stored in the end-effector rack may be configured for measuring or detecting a different characteristic of the sample relative to the sample characteristic for which the probes and/or probe tips installed in the manipulator configured to measure or detect. The exchange of probes and/or probe tips between the manipulator and the end-effector rack may be substantially manual, partially automated or substantially automated. In addition to the exchange of probes, probe tips and/or end-effectors, the process 380 may include processes for positioning the manipulator proximate the rack or other storage structure where the additional end-effectors are stored, testing exchanged end-effectors, and repositioning the manipulator towards a probe preparation area or the sample being examined, among other possible processes. One or more of the procedures of the process 380 may be implemented by instructions or sub-routines in the APS described above, such as in the CR associated with the APS. The end-effector rack described may substantially resemble a rack structure, possibly similar to the apparatus 500 shown in FIG. 5 and described below. However, other end-effector storage structure configurations are also within the scope of the present disclosure. For example, the end-effector rack may be, include or resemble a revolving or static carousel, cartridge or other structure. The end-effector rack may also be or include electromechanical apparatus, such as may be employed to partially automate, substantially automated or otherwise assist dispensing end-effectors and/or replacing or rejuvenating end-effectors according to aspects of the present disclosure. However, for the sake of simplicity, reference herein to the end-effector rack The method 300b may also include a process 385 by which probes and/or probe tips can be rejuvenated by cleaning and/or shaping, for example. The rejuvenation of the process 385 may include one or more of the probe preparation processes described herein or otherwise within the scope of the present disclosure. The process 385 may be substantially manual, partially automated or substantially automated. For example, one or more of the procedures of the process 385 may be implemented by instructions or sub-routines in the APS described above, such as in the CR associated with the APS. The method 300b may also include a process 340 by which a sample may be removed from a sample examination area within a CPBD, including completely removing the sample from the CPBD. Such removal may be substantially manual, partially automated or substantially automated. In one embodiment, after all desired characteristics of a sample have been measured or detected, the CR may execute instructions or sub-routines to return the manipulator or other positioner to the end-effector rack to exchange end-effectors, while simultaneously removing the examined sample and preparing a new sample for introduction into the CPBD chamber, which may be implemented by employing grippers, tweezers, and/or other tools and/or methods, including those known to those of ordinary skill in the art. The method 300b may also include one or more procedures by which one or more samples internal or external to the CPBD chamber may be processed prior to and/or after examination. Such procedures may include ex-situ processing of two or more samples in parallel or in series, in-situ processing of two or more samples in parallel or in series, and/or ex-situ processing of one or more samples in parallel or in series with in-situ processing of one or more samples. Such processes may include a process 360 by which a device-under-test (DUT) may be de-processed, an ex-situ process 365 which may be employed to prepare a DUT for examination prior to introducing the DUT into the CPBD, and/or a process 370 by which a DUT may be transferred to or otherwise introduced into the CPBD, among other possible DUT processing procedures. Further examples include an in-situ process 375 by which a DUT which may be employed to prepare a DUT for examination once the DUT is introduced into the CPBD, a process 390 which may be employed to coarsely and/or precisely position or orient a DUT within the CPBD chamber, and a process 395 may be employed to remove a DUT from the CPBD, among other possible DUT processing procedures, as well as combinations of ones of these and other processes. Thus, one or more embodiments of the method 300b may generally include a plurality of such DUT preparation procedures, which may collectively be referred to herein as DUT preparation 397. In the embodiment illustrated in FIG. 3B, the method 300b includes DUT preparation 397 which includes each of processes 360, 365, 370, 375, 390 and 395. Of course, in other embodiments, the method 300b may include DUT preparation 397 which varies from the embodiment shown in FIG. 3B. A DUT may be substantially similar to one or more of the samples described above as capable of being examined within a CPBD to measure or detect characteristics thereof. Alternatively, a DUT may be or include at least a portion of a particular transistor or other device formed on or integral to such samples. Nonetheless, for the sake of simplicity, the terms “sample” and “DUT” may sometimes be interchangeable with regard to some aspects of the present disclosure. The process 360 of method 300b may be or include one or more optional procedures for de-processing a sample. In one embodiment, such sample de-processing includes removing one or more layers of the sample to expose a feature of interest on the sample. The process 365 of method 300b may be or include one or more optional procedures for preparing a sample for introduction into the CPBD, including procedures other than the de-processing procedures of the process 360. One or both of the processes 360 and 365 may be substantially manual, partially automated or substantially automated. For example, such de-processing and/or sample preparation may be implemented by the CR as automatic processes of the APS. In one such embodiment, procedures for de-processing and/or preparing a sample are initiated, adjusted, and terminated by sensors operable to monitor the status of the procedure. The sensors and the CR communicate to effect the procedure as an automated process. While myriad procedures may be employed for sample preparation, examples include chemical cleaning (e.g., by HF dip), chemical-mechanical-polishing or chemical-mechanical-planarizing (collectively referred to herein as CMP), self-assembled monolayer (SAM) deposition (such as after cleaning to prevent oxidation), selective deposition of one or more conductive and/or passivation layers (e.g., to prevent oxidation), and selective deposition of liquid metal and/or non-oxidizing metal, among others. The process 370 of method 300b may include transporting the sample into the CPBD chamber, possibly from a sample load station that may be substantially similar to or include a load lock, a wafer cassette, a wafer tape/ring, a GEL-PAK or other waffle pack, and/or a vacuum-release or other type of tray, among other means for securing a sample during transport. An automated sample transport system (ASTS) may be implemented as a part of the CR described above, for example, may be employed to load and unload samples relative to the CPBD chamber. For example, the ASTS may be implemented as a set of methods or sub-routines to monitor status and/or location of relevant devices, and/or to implement or provide commands. The ASTS may be enabled by appropriate software and hardware to communicate information used by the CR and/or the RS. In addition to hardware and software supporting such communications, the ASTS may include or be associated with a transport mechanism configured to provide the physical, mechanical aspect of transferring samples between a sample load station and the sample chamber. For example, the transport mechanism may include one or more electric motors, piezoelectric motors, MEMS motors, and/or pneumatic actuators, among other motion imparting apparatus, and may also include apparatus or features employed for friction reduction. The one or more in-situ procedures of the process 375 may include sample conditioning or other sample preparation that employs the CPBD, as well as focused-ion-beam (FIB) sputtering, non-liquid-metal-ion-source sputtering, ion gun sputtering, plasma cleaning, reactive gas cleaning and/or radical cleaning (e.g., to remove radicals), any of which can be implemented through instructions or sub-routines of the CR. In one embodiment, process 375 includes cleaning the sample in-situ with a method of plasma cleaning using an EVACTRON device commercially available from XEI Scientific, Redwood City, Calif. Generally, such devices can use a low-powered RF plasma to make oxygen radicals from air that then oxidize and chemically etch away hydrocarbons (e.g., from the interior surfaces of an SEM and/or samples, probes and other items therein). As described in operations manuals available with the EVACTRON device, the device is mounted on a specimen chamber port. The plasma itself is confined to the EVACTRON chamber, which prevents ion and electron bombardment damage to the instrument or sample. The radicals are carried out of the plasma into the whole of the specimen chamber by convection. These radicals oxidize hydrocarbons to make CO, H2O, and CO2 gases to be removed by a vacuum pump. The process 380 may include grounding the sample at the point or location where it will be probed, possibly relative to the CPBD chamber. In one embodiment, the sample is grounded to the stage, platform or other structure supporting the sample within the chamber. However, the sample may be suspended within the chamber, such as by bonding, grasping or otherwise coupling one or more probes with one or more surfaces or features of the sample, wherein one or more additional probes may be employed acquire the desired sample characteristic. In one embodiment of the method 300b, once a sample has been introduced into the CPBD chamber (e.g., by process 370) and optional in-situ sample preparation is performed (e.g., by process 375), the presence of the sample within the CPBD chamber may be communicated to the CR. Possibly upon also receiving information that probes are properly prepared and/or that the sample is adequately grounded within the CPBD chamber, the CR may access the RS and the positioner control device to locate the probe tips above contact point or other a feature of interest on the sample, among other actions. In this context, “above” the contact points refers to a position from which a final trajectory to the contact point can be determined and executed. For example, such a position from which the final trajectory originates may be normal to a plane in which the contact points collectively reside. Referring to FIG. 4, illustrated is a perspective view of at least a portion of one embodiment of a positioner 400 according to aspects of the present disclosure. The positioner 400 is one example of the above-described positioners or manipulators that may each be employed to position one or more probes 440 employed during the measurement or detection of a characteristic of a sample being examined in a CPBD, such as within the apparatus 100 of FIG. 1 or the apparatus 200 of FIG. 2, and/or according to aspects of the methods 300a or 300b shown in FIGS. 3A and 3B, respectively. The positioner 400 and other manipulators within the scope of the present disclosure may have a resolution that is about equal to the resolution of the CPBD in which the positioner is employed, and/or about equal to the dimensions of the features being examined on a sample within the CPBD. In other embodiments, the resolution of the positioners may be greater (i.e., smaller increments) than the resolution of the CPBD and/or sample feature dimensions. Nonetheless, aspects of the present disclosure are also applicable to embodiments in which the positioner resolution is less than the resolution of the CPBD and/or sample feature dimensions. For example, the probes 440 of the positioner 400 may be selected according to aspects of the selection process 305 of the method 300a shown in FIG. 3A. The probes 440 may also be exchanged according to aspects of the exchange process 380 of the method 300b, such as to replace dulled and/or contaminated probes with sharper and/or cleaner probes, or where probes of different utility are appropriate based on a particular characteristic being collected or a particular sample or sample feature being examined. The positioner 400 may include an end-effector 444 to which the probes 440 may be permanently or detachably assembled. The probes 440 may be or include tungsten polycrystalline wire probes, possibly having a “stem” diameter ranging between about 0.25 mm and about 0.50 mm and a tapered tip, where the radius of curvature of the tip apex may be less than about 10 nm. The end-effector 444 may be permanently or detachably coupled to a positioner body or handle 450. For example, a detachable coupling may be accomplished via one or more corresponding pairs of prongs 454 and sockets 448. Thus, in one embodiment, the end-effector 444 may include one or more examination probes (440) and one or more assembly probes (454, employable to assemble the end-effector 444 with the positioner 450). Each prong/socket pairing may correspond to one of the probes 440, as in the illustrated embodiment, or may correspond to more than one of the probes 440. Similarly, each socket 448 may be electrically connected to one or more leads extending from the body 450. However, other means for detachably coupling the end-effector 444 or probes 440 to the positioner 450 are also within the scope of the present disclosure. The end-effector 444 may also be configured to be stored in or otherwise interface an end-effector rack, such as described above. In one embodiment, as illustrated in FIG. 4, the end-effector 444 may have one or more flats 446, and/or one or more other interfaces corresponding to or configured to cooperate with the end-effector rack. The flats 446 or another portion of the end-effector 444, including a portion configured to interface with an end-effector rack, may have a predetermined orientation relative to the probes 440, such that the orientation of the probes 440 may be known once the end-effector 444 is coupled to the body 450. For example, the flats 446 may include two substantially parallel flats on opposing sides of the end-effector 444, and the orientations of each of the probes 440 may be known relative to one or more edges or surfaces of the flats 446. Referring to FIG. 5, illustrated is a perspective view of at least a portion of one embodiment of an apparatus 500 according to aspects of the present disclosure. The apparatus 500 includes an end-effector rack 555 which may be substantially similar to the end-effector rack(s) described above. The apparatus 500 also includes a plurality of end-effectors 440 which may be substantially similar to the end-effector 440 shown in FIG. 4. The apparatus 500 also includes a manipulator module 560 which may be substantially similar to the manipulator modules described above, such as the manipulator module 260 shown in FIG. 2. The manipulator module 560 may include a positioner or positioner body 450 which may be substantially similar to the positioner body 450 shown in FIG. 4. The manipulator module 560 is coupled to a manipulator module interface 511 of a manipulation platform 510. The manipulator module interface 511 and the manipulation platform 510 may be substantially similar to the manipulator module interfaces 212 and the manipulation platform 210, respectively, shown in FIG. 2. For example, the manipulator module 560 and the manipulation platform 510 may be configured to be installed within a CPBD chamber, such as the CPBD 104 shown in FIG. 1 or the CPBD 104 shown in FIG. 2. As shown in FIG. 5 and discussed above with regard to FIG. 4, a plurality of probes 440 may be assembled into respective end-effectors 444. However, in addition to probes 440, one or more tools, including those having different capabilities, may be assembled into one or more of the end-effectors 444. When an end-effector 444 so assembled is coupled with a positioner 450, the positioner 450 can have more than one measurement or detection capability, and possibly more than one manipulation capability. Such manipulation capability may used in conjunction with and/or in support of measurement and/or detection of one or more characteristics of one or more samples being examined within a CPBD. For example, multiple independent electrical probes 440 can be assembled in an end-effector 444, whereby a positioner 450 with such an end-effector 444 may be useful for measuring different kinds of samples. In addition, multiple positioners 450 equipped with end-effectors 444 having multiple probes 440 assembled therein can be used to take measurements according to the automated processes described herein. In addition, features of any given sample may require that the probes 440 be reconfigured or moved independently. Thus, in some embodiments, one or more independent fine-motion positioners may be associated with one or more coarse-motion positioners, where one or more of the fine-motion and coarse-motion positions may be substantially similar to other positions or manipulators described herein, with the possible exception of scale. The probes 440 assembled in an end-effector 444 coupled with a positioner 430 may be reconfigured to enable measurements of samples having different feature configurations. For example, some of the probes 440 may be flexible, such that they can be reconfigured with micro-scale and/or nano-scale embodiments of the positioners described herein or otherwise. In one embodiment, a first positioner may be oriented proximate a second positioner such that the first positioner may grasp or otherwise interface the second positioner or one or more probes assembled in the second positioner, such as to pull, bend or otherwise reposition the one or more probes after their initial orientation by the second positioner. These and other manipulations within the scope of the present disclosure may be performed before or after the probes are introduced into the sample chamber of a CPBD (i.e., either ex-situ or in-situ relative to the CPBD). In one embodiment, the probes 440 are assembled into the end-effectors 444, and the end-effectors 444 are arranged in the end-effector rack 555, such as in one or more of the illustrated end-effector stations 558 configured to receive and retain an end-effector 444 when not being used to measure or detect sample characteristics. The end-effectors 444 may be installed in the end-effector rack 555 by an ex-situ or in-situ process, which may be substantially manual, partially automated or substantially automated. Thereafter, the end-effector rack 555 may be coupled to a manipulator module interface 511 of the manipulation platform 510, either before or after the manipulation platform 510 has been positioned within a CPBD chamber. The end-effector rack 555 may be introduced into the CPBD chamber by one or more processes which may collectively be substantially manual, partially automated or substantially automated. For example, prior to introduction into the CPBD chamber, the end-effector rack 555 may be introduced into a load lock where sensors may determine pressure and/or other conditions of the load lock and/or CPBD chamber, and such conditions may be communicated to the above-described CR to determine when the proper conditions exist for transporting the end-effector rack 555 from the load lock into the CPBD chamber. One embodiment of a substantially automated process by which the end-effector rack 555 may be transported from the load lock to the CPBD chamber includes the use of a feeder, a conveyor, a parts loader, or similar transfer mechanisms, including those that may be equipped with location sensors or other location features. The transfer mechanism may also be configured to communicate to the CR information regarding when an end-effector 444 has been positioned within the CPBD chamber. Once the end-effector rack 555 has been positioned within the CPBD chamber, exchange of an end-effector 444 from the end-effector rack 555 to a positioner 450 may be accomplished, such as by presenting the rack 555 to the positioner 450. A positioning stage of the manipulator module 560 may position the rack 555 and the positioner 450 so that prongs 454 of an end-effector 444 and sockets 448 of a positioner 450 are coincident. The positioning stage may then translate or otherwise move away from the end-effector station 558, such as in a direction consistent with the function of the illustrated “U” shaped geometry of the end-effector station 558. Of course, one or more of the end-effector stations 558 may have other geometries. This process may also be reversed, substantially, such as may be employed to exchange an end-effector 444, or other processes in which an end-effector 444 may be returned or otherwise assembled to the end-effector rack 555 by using a positioner 450. Such processes may by substantially manual, partially automated or substantially automated, possibly in a similar manner as the removal of an end-effector 444 from the end-effector rack 555. For example, communications may be determined and sent by and through operations of a positioner control device or other feature configured to control operation of the positioner 450, and communications may also be determined and sent by and through operations of the CPBD and/or the CR. Referring to FIG. 6, illustrated is a flow-chart diagram of at least a portion of one embodiment of a method 600 according to aspects of the present disclosure. The method 600 may be employed in a partially or substantially automated point-and-click process, and/or in or with the above-described RS, such as for probe positioning. Thus, for example, the method 600 may be implemented in or performed by the apparatus 100 of FIG. 1 or the apparatus 200 of FIG. 2. Consequently, the method 600 may be performed in conjunction with the apparatus 400 shown in FIG. 4 and/or the apparatus 500 of FIG. 5. The method 600 may also be used or performed in conjunction with embodiments of the methods 300a or 300b shown in FIGS. 3A and 3B, whether in a substantially parallel, serial or interlaced manner. The method 600 may also be implemented in accord with the APS, CR and/or RS described above. The method 600 may be performed to achieve probe positioning that is guided by probe-current imaging. Aspects of probe-current imaging may be similar to aspects of specimen-current imaging, a process known by those skilled in the art. However, according to aspects of probe-current imaging, electrical current is conducted through the probe in contrast to (or in addition to) electrical current conducted through a sample under investigation. Probe-current imaging may include measuring current from or between one or more probes, a sample and/or ground, such as a functions of the raster location or coordinates of the CPB of a CPBD (as a “map,” for example). When a semi-automated point-and-click process is used, the probing process may at least temporarily depart from any then-functioning automation scheme. However, once probes have been properly located above contact points, such automation may resume, such as where a positioner control device may communicate signals to CR, which may loop the probing back into the automated scheme. The method 600 includes a process 605 by which a DUT (device-under-test) may be imaged, such as by an SEM or other CPBD. The process 605 may also include imaging one or more probes with the CPBD, possibly including all of the probes that may be assembled to a positioner or otherwise controlled by a manipulator module or positioned control device. The DUT and the imaged probes are then displayed on a computer screen or other display device associated with the CPBD in a process 610. User input may then be received by a process 615. For example, a user viewing the display of the process 610 may indicate which of the imaged probes is desired to be located from its imaged location. Such indication may be in the form of a mouse click, where the user manipulates a mouse to locate a pointer over the image of the desired probe or other imaged feature and then clicks a button on the mouse. Of course, user input means other than or in addition to computer mouse operations are also within the scope of the present disclosure. For the sake of simplicity, the initial, imaged location of the probe selected by the user will be referred to as Location 1. A subsequent process 620 also includes receiving user input. However, during this process, the user indicates a location to which the user desires the probe selected during the process 615 is to be translated. For the sake of simplicity, this target location indicated by the user may be referred to as Location 2. The user may indicate Location 2 in a manner substantially similar to the user's indication of Location 1 (e.g., by mouse-click). The target location may be substantially coincident with the contact point or other feature of interest on a sample being examined. However, the target location and feature of interest may not be substantially coincident in some embodiments within the scope of the present disclosure. For example, some devices being examined within the CPBD may be damaged by direct exposure to the CPB of the CPBD. In such scenarios, and possibly others, the target location may merely be in the vicinity of the feature of interest, but not coincident, such as when the target location may be slightly offset from the feature of interest, possibly in a direction conforming to a probe relocation path. The method 600 may also include a process 625 facilitating the receipt of user input indicating a desired or preferred relocation path. For example, a user may desire that the relocation path along which the selected probe should travel to the target location (i.e., the path connecting Location 1 and Location 2) may avoid an obstacle or area of the DUT or sample, or that this relocation path be the shortest path possible. In another example, the user may desire that the relocation path comprise a plurality of arcs connected end-to-end, possibly having substantially similar radii, or a plurality of similarly-shaped loops. The method 600 proceeds from one of process 620 and the process 625 to a process 630 during which the SEM or other CPBD device may be adjusted to limit exposure of its charged particle beam (CPB) to the probe selected by the user during the process 615. For example, the CPBD may be switched to a spot mode (in contrast to a raster mode, an unfocused mode, or a broader illumination mode, for example), and the subsequently narrowed CPB may be focused on the selected probe. In another embodiment, the non-selected probes may be hidden, sheltered or masked from the CPB, or other processes may be performed such that only the probe selected during the process 615 may be exposed to the CPB. The exposure of the selected probe to the CPB may continue during subsequent processes or steps of the method 600. Electrical current (e.g., to ground or an electrical reference point of the CPBD) is measured in each of the probes during a process 635. In one embodiment, current may only be measured in a limited number of the plurality of probes within the CPBD chamber, although this sub-set of probes includes the probe selected by the user during the process 615. The probe currents may be measured in a conventional manner. Those skilled in the art are familiar with the myriad, commercially available apparatus which may be employed for such probe current measurement, such as electrometers and various amplifiers, among others. Nonetheless, other apparatus are also within the scope of the present disclosure. The method 600 also includes a process 640 by which the probe that is exposed to the CPB by the process 630 is identified. For example, the current measured from the probe exposed to the CPBD may be greater in magnitude than the current measured from the other probes. Referring to FIG. 7, illustrated is a block diagram of at least a portion of one embodiment of an apparatus 700 according to aspects of the present disclosure. The apparatus 700 is one example of apparatus that may be employed to perform the method 600 shown in FIG. 6, or may otherwise may be employed during performance of the method 600. The apparatus 700 includes or is coupled to or otherwise associated with an SEM or other CPBD 705 having a chamber in which one or more probes may be utilized according to aspects of the present disclosure. The current in each probe is communicated via cables 710 to a current-to-voltage converter 715. Voltage signals corresponding to each of the probes may thus be communicated to an analog-to-digital converter (ADC) 720 or another device having such conversion capabilities, which may also be configured to communicate video signals with the CPBD 705 via cabling 725. The ADC 720 may be in communication with a computer (e.g., a personal computer) 730 and a digital-to-analog converter (DAC) 735. One or both of the ADC 720 and the DAC 735 may be integral components or functions of the computer 730, although they may also be discrete components coupled to the computer 730. The DAC 735 may also be in communication with the CPBD 705, such as through cabling 740. Such communication may regard the control of one or more aspects of the CPBD 705, such as the deflection or other aspects of the CPB. In one embodiment of operation of the apparatus 700, such as in accord with the method 600 of FIG. 6, an imaging unit the CPBD 705 may be employed to generate an image of a DUT and one or more probes oriented within the chamber of the CPBD 705, such that an image of the DUT and probes may be displayed on a screen of the computer 730. Thereafter, a user may select one of the probes displayed in such image, such as by using a mouse to position a pointer on the display screen over the image of the desired probe and pressing a button on the mouse. The user may also reposition the pointer to another site on the DUT displayed in the image on the screen of the computer 730 and again press a mouse button to indicate a target location to which the selected probe is to be positioned. Thereafter, the CPBD 705 may automatically switch to a “spot” mode, such as in response to receiving the user input regarding the target location, or the CPBD 705 may be manually switched to “spot” mode by the user. The narrowed CPB generated in the CPBD 705 may then be directed to the previously selected probe, or to the location corresponding to the location of the previously selected probe, as indicated by an increased current measured from the selected probe by the converter 715 and/or the ADC 720, among other possible components. Referring to FIG. 8, illustrated is another embodiment of the apparatus 700 shown in FIG. 7, herein designated by the reference numeral 800. The apparatus 800 may include or be associated with a CPBD 705 that may be substantially similar to the CPBD 705 shown in FIG. 7. However, the cabling 710 extending from probes located within the chamber of the CPBD 705 extend to a selector 850, whereby a reference signal may be communicated from a signal generator 855 to a selected one of the probes. The reference signal may also be communicated from the signal generator 855 to a console or other device 860 having display functionality and associated with the CPBD 705. A video signal from the CPBD 705 may also be communicated to the console 860. A comparison of the video signal from the CPBD 705 and the reference signal from the generator 855 may also be employed to determine which probe is exposed to the CPB generated by the CPBD 705 or which probe is being driven by the signal from the generator 855. For example, a manual, partially automated or substantially automated comparison may reveal a similarity between the video signal generated from the CPBD 705 and the reference signal being communicated to one of the probes. In one embodiment, the apparatus 800 may be used to perform the method 600 of FIG. 6, wherein the probe-current detection/imaging may be replaced by the comparison of the reference signal and the video signal. For example, a comparator unit 870 may be employed for such comparison. Referring to FIG. 9, illustrated is a flow-chart diagram of at least a portion of one embodiment of a method 900 according to aspects of the present disclosure. The method 900 may be employed in a partially or substantially automated process for probe positioning. Thus, for example, the method 900 may be implemented in or performed by one or more of the apparatus 100 of FIG. 1, the apparatus 200 of FIG. 2, the apparatus 700 of FIG. 7 and the apparatus 800 of FIG. 8. Consequently, the method 900 may be performed in conjunction with the apparatus 400 shown in FIG. 4 and/or the apparatus 500 of FIG. 5. The method 900 may also be implemented in accord with the APS, CR and/or RS described above. The method 900 may also be used or performed in conjunction with embodiments of the methods 300a or 300b shown in FIGS. 3A and 3B and/or the method 600 shown in FIG. 6, whether in a substantially parallel, serial or interlaced manner. For example, as in the illustrated embodiment, the method 900 may substantially include the method 600 of FIG. 6. Consequently, the method 900 may include one or more processes for determining and/or receiving current and target locations for a selected probe (possibly referred to herein as Location 1 and Location 2, respectively), as well as a user-desired relocation path connecting the current and target locations. The method 900 may be performed to achieve probe positioning that is guided by probe-current imaging. When a semi-automated process is used, such as a point-and-click process, the probing process may at least temporarily depart from any then-functioning automation scheme. However, once probes have been properly located above contact points, for example, such automation may resume, such as where a positioner control device may communicate signals to CR, which may loop the probing back into the automated scheme. The method 900 may also include a process 905 by which a scan or probe trajectory may be generated. The scan may be substantially similar or identical to a relocation path that may be received as user input, such as during the process 625 of the method 600. In other embodiments, the scan generated by the process 905 may merely approximate such user-input relocation path, possibly falling within the substantial vicinity of the user's relocation path. However, in one embodiment, the scan generated during the process 905 may have little similarity to the user's relocation path, other then its endpoints (e.g., initial and target locations, or Location 1 and Location 2 referred to above with regard to FIG. 6). During a process 910 of the method 900, the selected probe may be translated towards the target location, whether along the relocation path or otherwise. Such translation may be substantially limited to lateral movements, such as those being substantially parallel to the surface of the DUT or sample, or may also include a directional component that is substantially perpendicular to the surface of the DUT. The translation of the probe during the process 910 may also not be limited to translation, but may also include rotational movement about one or more axes of rotation. Thus, translation of one or more probes within the scope of the present disclosure may, at times, refer to both translation and rotation, which may collectively be referred to as positioning, repositioning, orientation and/or reorientation. The current in the translated probe, including current induced by the CPB generated by the CPBD, may be measured in a process 915 of the method 900. The current measurement of the process 915 may be a single measurement, or multiple periodic or randomly intermittent measurements, or even substantially continuous measurement. The process 915 may also include measuring current in probes other than or in addition to the probe being repositioned. Such current measurement may be performed by one or more functions or components of the apparatus 700 of FIG. 7 and/or the apparatus 800 of FIG. 8. In one embodiment, such aspects may be employed in or for collision avoidance processes and protocols, such as to prevent collisions between probes and other objects within the chamber of the CPBD. The method 900 may also include a process 920 during which positioning error may be determined for the probe being repositioned. For example, the probe-locating processes described herein may be employed to determine any difference between a desired location and the actual location of the probe. The process 920 may also include generating correctional drive signals which may be employed to correct any detected positioning error. The error and/or correction processes of the process 920 may be performed once, repeatedly at periodic or random intervals, or substantially continuously. The method 900 may also include a process 925 by which exposure of the CPB generated by the CPBD may be limited to the target location. The process 925 may be substantially similar to the process 630 shown in FIG. 6. A process 930 of the method 900 may include measuring current from a plurality of the probes in the CPBD, including the probe being repositioned, and identifying any probe having a greater current induced by the CPB. The process 930 may be substantially similar to the combination of the processes 635 and 640 of FIG. 6. The information gathered during the process 930, among other processes of the method 900, can be used to determine whether the probe being repositioned has arrived at its target location. For example, if the exposure of the CPB is limited to the target location by the process 925 described above, then the detection of an increased current induced in the probe being repositioned to the target location may provide an indication that the probe has successfully been repositioned in its target location. A decisional step 935 may be included in the method 900 to query whether the selected probe is arrived at its target location. The method 900 may thus proceed to processes for repositioning additional probes or otherwise end operations directed towards positioning the selected probe, collectively indicated in FIG. 9 by the “SUBSEQUENT PROCESSING” process 940, if it is determined during the decisional step 935 that the selected probe has successfully reached its target location. Alternatively, if the selected probe requires additional positioning, a portion of the method 900 may be repeated for the selected probe, possibly starting with the process 910, as shown in FIG. 9. Referring to FIG. 10, illustrated is a flow-chart diagram of at least a portion of one embodiment of a method 950 according to aspects of the present disclosure. The method 950 may be employed in a partially or substantially automated point-and-click process for probe positioning. Thus, for example, the method 950 may be implemented in or performed by one or more of the apparatus 100 of FIG. 1, the apparatus 200 of FIG. 2, the apparatus 700 of FIG. 7 and the apparatus 800 of FIG. 8. Consequently, the method 950 may be performed in conjunction with the apparatus 400 shown in FIG. 4 and/or the apparatus 500 of FIG. 5. The method 950 may also be implemented in accord with the APS, CR and/or RS described above. The method 950 may also be used or performed in conjunction with embodiments of the methods 300a or 300b shown in FIGS. 3A and 3B, the method 600 shown in FIG. 6, and/or the method 900 of FIG. 9, whether in a substantially parallel, serial or interlaced manner. Several aspects of the individual processes of the method 950 may be substantially similar to corresponding processes of the method 900 of FIG. 9, in which case the descriptions of the processes in the method 900 may also apply to one or more processes in the method 950. The method 950 may be performed to achieve probe positioning that is guided by probe-current imaging. When a semi-automated point-and-click process is used, the probing process may at least temporarily depart from any then-functioning automation scheme. However, in one embodiment, the method 950 may allow the probing process to substantially remain within any such automation scheme. For example, when the positioning procedure for a selected probe determines that the probe has reached the desired location (e.g., with respect to contact points on the DUT or sample being examined), the CR or other function or apparatus may signal the positioner control device or other device controlling probe positioning, which may initiate procedures for bringing the probe tips into physical and electrical contact with the desired contact points. This process may be referred to herein as “touch-down” of the probe tips, and may be substantially similar to the process 320 of FIGS. 3A and 3B. During touch-down, a positioner control device may translate the probes down and into physical and electrical contact with contact points on the sample. When more than one probe is being used, the probes may be lowered simultaneously, in groups, or one at a time, depending on the programming of the positioner control device. In one embodiment, the CR includes a procedure to cause the positioner control device to keep the probes in the proper position after successful touchdown and until the measurement is completed. As a tip makes contact, it may send a signal back to the positioner control device, which may activate a sub-routine of the CR. The activated sub-routine may provide an automated process for determining the quality of the contact made with the sample. The method 950 includes a process 953 during which a DUT and associated probes are imaged with a CPBD, and any current in the probes is acquired, including any current induced by the CPB generated by the CPBD. Aspects of the process 953 may be substantially similar to those described above. In a subsequent process 956 of the method 950, individual locations of each of the probes is determined, such as from an image of the beam-induced currents or of all probe currents. The method 950 may also include a process 959 during which target locations may be received, such as from user input, possibly in conjunction with corresponding relocation paths. However, the information may also be retrieved and/or input from a software interface, such as software that may be employed with a map of the DUT. The method 950 may proceed to a process 962 during which scans are generated along or in the vicinity of the relocation paths determined in the process 959, such that one or more probes may be translated along one or more corresponding relocation paths during a process 965. Current may then be measured in each translated probe and subsequently analyzed during a process 968, including any beam-induced currents. Such currents may be employed during a process 971 to determine any positional errors and/or generate correctional drive signals. One or more of the processes 965, 968 and 971 may be repeated until, as possibly determined by a decisional step 974, each of the probes being translated successfully arrives at its corresponding target location, at which time the method 950 ends or proceeds to additional processes. Referring to FIG. 11, illustrated is a flow-chart diagram of at least a portion of one embodiment of a method 980 according to aspects of the present disclosure. The method 980 may be employed in a substantially manual, a partially automated or a substantially automated point-and-click process for probe positioning. Thus, for example, the method 980 may be implemented in or performed by one or more of the apparatus 100 of FIG. 1, the apparatus 200 of FIG. 2, the apparatus 700 of FIG. 7 and the apparatus 800 of FIG. 8. Consequently, the method 980 may be performed in conjunction with the apparatus 400 shown in FIG. 4 and/or the apparatus 500 of FIG. 5. The method 950 may also be implemented in accord with the APS, CR and/or RS described above. The method 950 may also be used or performed in conjunction with embodiments of the methods 300a or 300b shown in FIGS. 3A and 3B, the method 600 shown in FIG. 6, the method 900 of FIG. 9, and/or the method 950 of FIG. 10, whether in a substantially parallel, serial or interlaced manner. The method 980 may be employed to determine physical and electrical contact with contact points on a DUT or sample within the chamber of a CPBD. For example, a process 983 may initially be performed to position one or more probe over a contact point, where such positioning may primarily be in a plane that is substantially parallel to a surface of the sample. Thereafter, a process 986 may vertically position the probes, such as in a direction that is substantially perpendicular to the sample surface. The method 980 includes a decisional step 989 by which the positioning processes 983 and 986 may be repeated if “touch-down” is not determined. However, if no additional positioning is determined necessary during the decisional step 989, an additional decisional step 992 of the method 980 may assess the adequacy of the electrical contact between the probes and their corresponding contact points on the sample. For example, if the electrical contact between a probe and a contact point is such that electrical resistance between the probe and contact point is excessive, the probe may be conditioned, characterized, cleaned or otherwise processed during a process 995, such as according to one or more of the probe preparation procedures described above. However, if the electrical contact between a probe and contact point is satisfactory (e.g., good ohmic contact), the intended measurement or detection of a characteristic of the sample may be performed, as indicated by the process 998 of the method 980. Thus, contacting a probe and a sample contact point may include laterally positioning of the probe over the sample contact point, vertically positioning the probe until physical contact is made between the probe and the contact point, verifying the physical contact via the touch-down processing described above, and verifying the electrical quality of the contact between the probe and contact point. Moreover, the method 980 may be substantially manual, partially automated or substantially automated according to aspects of the present disclosure. For example, the process 989 may include executing a sub-routine of the CR to determine whether physical contact between the probe and sample exists. The sub-routine may comprise programming to instruct a positioner control device or the CPBD to implement a procedure that obtains information indicative of physical contact between the probe tip and the sample. Such procedures may include: (1) detecting capacitance (AC and/or DC); (2) detecting force; (3) enabling visual observations of the probe tip and the sample; (4) scanning probe imaging methods; (5) observations of a mechanical pivot (vision); (6) determination of interaction with the CPB; and/or (7) using EDX for positioning information energy dispersive x-ray analysis. One embodiment of a capacitance-based procedure for determining probe-sample contact involves determining the capacity or change in capacity between the probe and the sample. An embodiment of a force-detection procedure for determining probe-sample contact may employ a force sensor that signals when localized forces meet or exceed a threshold value, which may indicate close proximity or mechanical contact of the tip with the contact point of the sample. Force-detection procedures can also be implemented with cantilevers or other springs combined with position detectors, whereby a spring constant may be used to calculate probe deflection as a function of force. Scanning probe imaging methods for determining probe-sample contact may provide data by which a signal indicating contact can be generated. With regard to mechanical pivot observation methods for determining probe-sample contact, mechanical contact of the probe can create a pivot point. Detection of any pivoting or rotation of the probe around a pivot point may be indicated by lateral deflections of the probe which may be analyzed with simultaneously acquired images of the CPB to reveal indications of mechanical contact of the probe. The existence of the pivot point, and optionally the location of the pivot point, may be communicated by the CPBD as a signal that touch-down has been made. With regard to EDX-based determination of probe-sample contact, x-rays induced by the CPB may interact with the sample and subsequently be analyzed to obtain information regarding the elemental composition of the sample, thereby supporting identification of the site to be contacted. These and other aspects of the method 980 may be implemented as an automated process within the APS, or as a semi-automated process performed outside of the APS subsequently reintroduced into the APS upon communications confirming that physical contact has been made. Consequently, the CR may initiate an additional sub-routine or set of procedures for determining that electrical contact has been made between the probe tip and the contact point. Alternatively, prior to determining electrical contact, sub-routines can be implemented by the CR to cause certain procedures to be performed to improve the probability that the probe tips have not only physically contacted the contact points, but have also electrically contacted the contact points, and remain in good electrical contact with the contact points. In one embodiment, such as according to certain procedures suitable for improving the probability of electrical contact, communications are sent between the CR and the positioner control device employed to position the probes. Suitable procedures may include: (1) scrubbing, which comprises moving the probe around, and “digging” into the contact; (2) using a separate “chisel probe,” which comprises employing another tip in to roughen up the contact surface; and (3) using a hammer probe, which comprises employing a probe to “hammer” another probe into the contact surface. Each such procedure can be implemented as a partially or substantially automated process by appropriate programming within the CR and communications between the CR and the positioner control device. Some processes for improving the probability of adequate electrical contact between a probe and sample contact point may be implemented in an ex-situ or in-situ probe preparation or sample preparation process. One such method includes dipping or coating the probe and/or sample with a metal that melts at a temperatures low enough to not damage the probe or sample. Consequently, the metal may “wet” the sample contact point, possibly increasing the likelihood of satisfactory ohmic contact because one or both of the probe and the sample contact point is allowed to contact softer metal. In one such embodiment, the metal may be one that will alloy with the probe. One embodiment of a sub-routine (e.g., of the CR) that may be activated during the process 992 to determine whether electrical contact between the probe and the contact point on the sample has been made includes programming to instruct the corresponding positioner control device and/or the CPBD to implement a procedure that obtains information indicative of any electrical contact between the probe tips and the sample. Such procedures may include, among others: (1) positioning two probes on a single contact point; (2) moving probes to share a contact to assure ohmic contact; (3) employing split probe contacts; (4) reversing probes and/or polarity; (5) current sensing; (6) conductance; and (7) changes in secondary electron emission (voltage contrast). For example, positioning two probes on a single contact point may comprise dropping two probes onto the same contact point and determining whether there is ohmic contact between the two probes. Ohmic contact between the two probes can be indicative of the existence of ohmic contact between either of the two probes and the contact point on the sample. A perspective view of an example of a split probe 1400 is illustrated in FIG. 14. The exemplary split probe 1400 employs a probe having a dielectric layer 1402 separating the probe 1400 into “halves” 1404 and 1406. Upon making physical contact between the split probe 1400 and the sample, the detection of ohmic contact between the two “halves” 1404 and 1406 can indicate ohmic contact between the split probe 1400 and the sample contact point. Reversing probes and or the polarity or probes to determine whether electrical contact has been made between the probe tips and the contact points can involve making physical contact between each of the two probes and the sample contact point, then: (1) switching the probes; or (2) switching the polarities of each of the probes. Changes in secondary electron emission (voltage contrast) generally involve putting the tip at a certain voltage and determining whether the signal will increase or decrease when the tip makes contact with the contact point. This procedure requires both physical and electrical contact, and thus, if employed, there is no need to execute the sub-routine for determining physical contact. Conductance and current sensing are similar procedures each requiring physical and electrical contact. Thus, if one of these is employed, there is no need to execute the sub-routine for determining physical contact. Each of the foregoing procedures for determining electrical probe-sample contact may be implemented as one or more partially or substantially automated processes, such as within the APS. Where implemented as one or more semi-automated processes, they may be performed outside of the APS and subsequently reintroduced into the APS upon communications confirming that electrical contact has been made. Depending on the sub-routine executed, the positioner control device or the CPBD may be responsible for sending the communication to the CR that electrical contact has been made. Referring to FIGS. 12A-12C, collectively, illustrated are schematic views of at least a portion of a probe 1210 during various stages of a probe preparation process according to aspects of the present disclosure. The composition of the probe 1210 may be substantially metallic. The process depicted in FIGS. 12A-12C may be employed to sharpen the probe 1210, such as to sharpen the tip 1215 of the probe 1210. Additionally, or alternatively, the process depicted in Firs. 12A-12C may be employed to clean the probe 1210 and/or probe tip 1215. However, for the sake of simplicity, the process depicted in FIGS. 12A-12C may be referred to herein as a probe sharpening process. The process depicted in FIGS. 12A-12C may also be substantially similar to the ETP described above, and may be employed to process solid probes (as in the embodiments of FIGS. 12A-12C) or split probes, among others. FIG. 12A depicts an initial or intermediate stage of the sharpening process. An additional probe 1220 is employed in the depicted process, where the probe 1210 to be sharpened may have a smaller diameter than the probe 1220, may be thinner than the probe 1220, or may otherwise have substantially smaller dimensions relative to the probe 1220, including cross-sectional dimensions and length dimensions. Also, although depicted in FIGS. 12A-12C as being substantially cylindrical, one or both of the probes 1210, 1220 may not be substantially cylindrical or otherwise have a substantially non-circular cross-sectional shape, such as a substantially square or rectangular shape, or an asymmetric shape, among others. In the illustrated embodiment, the probe 1210 initially has a diameter that is about 25% less than the diameter of the probe 1220. Of course, the relative diameters of the probes 1210, 1220 may vary from the illustrated embodiment within the scope of the present disclosure. As shown in FIG. 12A, the probes 1210, 1220 may be placed in contact to close an electrical loop with a voltage, current or thermal energy source 1230. In other embodiments, however, the probes 1210, 1220 may merely be in close relative proximity but may not be in physical contact with one another. FIG. 12B depicts a subsequent stage of the sharpening process relative to the stage depicted in FIG. 12A, and in which the tips 1215, 1225 of the probes 1210, 1220, respectively, have been heated to and maintained at an elevated temperature for a sufficient period of time that a portion of the metal forming the probe tip 1215 has dislodged, possibly re-depositing on the probe tip 1225. Thus, for example, the probe tip 1215 has narrowed, while the probe tip 1225 has increased in size. FIG. 12C depicts a subsequent stage of the sharpening process relative to the stage depicted in FIG. 12B, and in which the tips 1215, 1225 have been maintained at an elevated temperature for a sufficient period of time that an additional amount of metal has dislodged from the probe tip 1215 and possibly re-deposited on the probe tip 1225. Consequently, the probe tip 1215 may be substantially sharpened relative to its status depicted in FIGS. 12A and 12B. The probe tip 1225 may have also increased in size relative to its size depicted in FIGS. 12A and 12B. Although not limited within the scope of the present disclosure, the elevated temperature at which the probe tips 1215, 1225 are maintained during the probe tip sharpening process described above may range between about 600° C. and about 4000° C. In one embodiment, an elevated probe tip temperature within this range and others may result from resistive heating, such as that which may result from applying across the probe tips 1215, 1225 a voltage ranging between about 1 volt and about 500 volts and/or a current ranging between about 100 nanoamps and about 10 microamps. However, the scope of the present disclosure is not limited to such an embodiment. The elevated temperature at which the probe tips 1215, 1225 are maintained may also vary between the probe tips 1215, 1225. For example, the elevated temperature at which the probe tip 1215 is maintained may be more or less than the elevated temperature at which the probe tip 1225 is maintained. Additionally, the period of time during which either or both of the probe tips 1215, 1225 may be maintained may range between about 1 second and about 30 seconds. However, this period of time may be substantially less than 1 second, including embodiments effecting a substantially instantaneous metal transfer. Referring to FIGS. 13A-13C, collectively, illustrated are representations of images 1301-1303 that may each be created with a CPBD according to aspects of the present disclosure, such as those images which may be created when employing an SEM according to one or more partially or substantially automated processes described above. The images 1301-1303 each depict a plurality of probes 1310 that are each positioned over or contacting a corresponding contact point or other feature 1320 of a sample 1330 being investigated within the CPBD. When investigating a sample in a CPBD, such as employing one or more probes to perform electrical measurement or detection of a characteristic of a sample or sample feature, video rate images of the probes and/or sample can reveal useful information regarding the electrical signal(s) entering and exiting the probes and/or sample. In some situations, an image may shift vertically relative to the CPBD image display device, as depicted in FIG. 13A. In other situations, an image may shift horizontally relative to the CPBD image display device, as depicted in FIG. 13B. In still further situations, an image may oscillate and/or become blurry, as depicted in FIG. 13C. Moreover, these situations may overlap. For example, an image may shift vertically and horizontally, resulting in a diagonal shift having both vertical and horizontal components relative to the CPBD image display device, and an oscillating or blurred image may also shift vertically, horizontally or diagonally relative to the CPBD image display device. A vertical image shift may at least partially result from electrical bias inherent to the sample investigation, such as when a sample is being investigated in a “power-on” or operational mode relative to when the same sample is being investigated in a substantially identical manner but where the sample is passive, “powered-off” or otherwise unbiased (with the possible exception of any bias resulting from incidence of the CPB of the CPBD). One such example is shown in FIG. 13A, which depicts vertically shifted probes 1310′ and contact points 1320′ relative to the initially displayed probes 1310 and contact points 1320. A horizontal image shift may at least partially result from electrical current inherent to the sample investigation, such as when an electrical current is introduced onto a sample or one or more probes, in contrast to when the sample and probes are electrically static (with the possible exception of any bias resulting from incidence of the CPB of the CPBD). One such scenario may be during the above-described probe-current imaging, where the current introduced into the probes may cause the horizontal CPBD image shift in a similar manner to current passed through a semiconductor device, silicon chip or other device being tested. An example of such scenario is shown in FIG. 13B, which depicts horizontally shifted probes 1310″ and contact points 1320″ relative to the initially displayed probes 1310 and contact points 1320. An oscillation or blurring may at least partially result from electrical noise resident in the CPBD chamber or control lines, the sample, the probes, and/or other locations. One such example is shown in FIG. 13C, which depicts horizontally shifted probes 1310′″ relative to the initially displayed probes 1310. Images may also exhibit large jumps, possibly about equal to the width of the display screen, when switching electrical measurement scales, or when bias or current abruptly starts or stops. Combinations of motion may also be exhibited. For example, an image may move diagonally across the display screen. Such motion can indicate changing bias/current. Manual, partially automated and/or substantially automated detection and/or measurement (e.g., shift quantification or shift-distance) of such image shifting and/or motion may be employed alone or in combination with aspects of other methods and procedures described herein. For example, partially or substantially automated vision or detection of an image or image shift at video rates may be employed to gauge the quality of contact between a probe and a sample contact point. Such image shift and/or motion may also be employed to detect and/or measure electrical response, such as the response of a device or circuit in a sample being investigated in a CPBD. Of course, many other characteristics described above or otherwise within the scope of the present disclosure may also be measured and/or detected by processes employing or complimented by processes for detecting and/or measuring image shift and/or motion according to aspects of the present disclosure. In one embodiment, image shift and/or motion data may be collected and logged, possibly analyzed to determine relationships between image behavior, sample characteristics and/or characteristic measurement parameters. For example, the distance that an image may shift in response to current flowing through a probe may be correlated to the magnitude of the current. Consequently, this correlation may be employed to confirm connectivity, contact between the probe and another object, conductivity of the probe, etc. Thus, the present disclosure introduces an apparatus including a positioner controller configured to control manipulation of: (1) a device under test (DUT) within a charged particle beam device (CPBD); and (2) a probe employed to examine a characteristic of the DUT within the CPBD. The apparatus may also include a measurer. Control of the positioner controller and the measurer may be partially or substantially automated. One embodiment of such apparatus also includes a manipulation platform, which may also be partially or substantially automated. The manipulation platform may include a base and a stage coupled to the base and configured to receive a sample to be examined. The manipulation platform may also include a plurality of manipulator module interfaces each coupled to the base and configured to receive a corresponding one of a plurality of manipulator modules each configured to manipulate at least one of a probe and the sample received by the stage. The manipulation platform may also include an interface configured to transfer control and status information between the plurality of manipulator module interfaces and at least one of the measurer and the positioner controller. Other embodiments may include one more of: (1) a charged particle beam device (CPBD) in which a sample to be measured is positioned; (2) a positioner control device communicatively coupled to the CPBD and operable to individually manipulate each of a plurality of probes into contact with one of a plurality of contact points on the sample; (3) a measuring device communicatively coupled to the CPBD and the positioner control device and operable to perform one of a measurement and a detection of a characteristic associated with one of the plurality of contact points; and (4) a control routine operable to provide communications to at least one of the CPBD, the positioner control device and the measuring device. The present disclosure also introduces methods which can include exposing one of several probes to a CPB of a CPBD. Such method may also include examining a current in at least one of the probes, as the current may indicate which of the probes is exposed to the CPB. The present disclosure also introduces methods which can include introducing a generated signal current to one of a plurality of probes positioned in a CPBD, and exposing each of the probes to a CPB of the CPBD. In an image created by the CPBD, the probe to which the generated signal current is introduced is identified based on its unique representation relative to representations of other probes in the image. The present disclosure also introduces methods which can include imaging a DUT and a plurality of probes with a CPBD. Individual locations of each of the probes is determined based on beam induced probe current images. Target locations and/or probe relocation paths each corresponding to one of the probes may be retrieved from a software interface input or user input. Scans approximating the relocation paths may be generated, and each of the probes may be moved towards its target location based substantially on its relocation path. Beam induced currents corresponding to the probes may then be analyzed, and positioning errors and correctional drive signals may also be determined. The present disclosure also introduces methods which can include positioning a probe over a DUT located within a CPBD, translating the probe toward a contact point on the DUT, and iteratively repeating the positioning and the translating until touchdown of the probe on the contact point is determined. The quality of the electrical contact between the probe and the contact point is then assessed, and an electrical measurement is performed with the probe if the assessed quality of the electrical contact falls within a predetermined acceptance criteria. The present disclosure also introduces methods which can include including collecting data from a CPBD regarding a characteristic of a sample being examined within a chamber of the CPBD, storing the collected data, processing the stored data, and transferring electronically the processed data to an apparatus configured to electronically communicate with the CPBD. At least one of the collecting, storing, processing and transferring may be substantially automated. The apparatus configured to electronically communicate with the CPBD may be a master controller, such as those described above. A master controller may be or include one or more devices and/or units, whether hardware and/or software, which may be configured to control the overall sequencing of application logic. For example, a master controller may determine and execute a particular order of operations for a given process that is being engaged by a user or machine, or a set of such processes. The present disclosure also introduces methods which can include positioning a first probe tip proximate a second probe tip. At least one of the probe tips is heated such that a portion of probe material forming that probe tip dislodges to sharpen the probe tip. The present disclosure also introduces methods which can include examining a shift and/or motion of an image relative to a CPBD device on which the image is displayed. The status and/or change in status of an electrical characteristic of at least one of an environment of a CPBD chamber, a sample located with the CPBD chamber, and a probe located within the CPBD chamber may then be determined based on the image shift and/or motion. Although embodiments of the present disclosure have been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure. |
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abstract | In a nuclear power plant, a corrosion-resistant oxide film on a surface of the metal component of a reactor structure is exposed to a high-temperature water, the corrosion-resistant oxide film containing an oxide having a property of a P-type semiconductor, and a catalytic substance having a property of an N-type semiconductor is deposited on the oxide film. The oxide film maintains the property of the P-type semiconductor. |
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046844970 | claims | 1. A glaze forming composition for glazing nuclear fuel pellets with a burnable absorber, said composition comprising cadmium oxide (CdO) present in the range of about 50 to 95 percent by weight as a first burnable absorber and at least one glaze forming oxide. 2. The composition of claim 1 wherein said cadmium oxide is present in the range of about 80 to 90 percent by weight. 3. The composition of claim 1 wherein said cadmium oxide is present at about 89 percent by weight. 4. The composition of claim 1 wherein cadmium is present in the form of cadmium-113 isotope. 5. The composition of claim 1 wherein said glaze forming oxide is selected from the group consisting of silicon dioxide (SiO.sub.2), aluminum oxide (Al.sub.2 O.sub.3), boric oxide (B.sub.2 O.sub.3), sodium monoxide (Na.sub.2 O), potassium oxide (K.sub.2 O), lead monoxide (PbO), and mixtures thereof. 6. The composition of claim 1 wherein said glaze forming oxide comprises silicon dioxide. 7. The composition of claim 1 further including a second burnable absorber, said first and second burnable absorbers having different neutron capture cross sections. 8. The composition of claim 7 wherein said second burnable absorber comprises boron (B) in at least the form of boron-10 isotope. 9. The composition of claim 8 wherein said boron is present as sodium borate (Na.sub.2 B.sub.4 O.sub.7.10H.sub.2 O). 10. The composition of claim 8 wherein said boron is present as boric oxide (B.sub.2 O.sub.3). 11. The composition of cliam 8 wherein the ratio by weight of boron to cadmium is about 3.2 to 11. 12. The composition of claim 1 wherein said glaze forming oxide comprises a borosilicate glass. 13. The composition of claim 8 wherein said cadmium oxide is present in the amount of about 50 to 75 percent by weight, said second burnable absorber comprises boric oxide (B.sub.2 O.sub.3) present in the amount of about 2 to 3 percent by weight, and said glaze forming oxide comprises a mixture of potassium oxide (K.sub.2 O) and silicon dioxide (SiO.sub.2), wherein said potassium oxide is present in the amount of about 3 to 6 percent by weight, the balance being silicon dioxide. 14. A glazed nuclear fuel pellet comprising fissionable material formed into a body and a glaze provided over at least a portion of the surface of said body, said glaze comprising a mixture of at least 0.5 percent by weight cadmium oxide (CdO) as a first burnable absorber and at least one glaze forming oxide. 15. The pellet of claim 14 wherein said cadmium oxide is present in the range of about 50 to 95 percent by weight. 16. The pellet of claim 14 wherein said cadmium oxide is present in the range of about 80 to 90 percent by weight. 17. The pellet of claim 14 wherein said cadmium oxide is present at about 89 percent by weight. 18. The pellet of claim 14 wherein cadmium is present in the form of the cadmium-113 isotope. 19. The pellet of claim 14 wherein said glaze forming oxide is selected from the group consisting of silicon dioxide (SiO.sub.2), aluminum oxide (Al.sub.2 O.sub.3), boric oxide (B.sub.2 O.sub.3), sodium monoxide (Na.sub.2 O), potassium oxide (K.sub.2 O), lead monoxide (PbO), and mixtures thereof. 20. The pellet of claim 14 wherein said glaze forming oxide comprises silicon dioxide. 21. The pellet of claim 14 further including a second burnable absorber, said first and second burnable absorbers having different neutron capture cross sections. 22. The pellet of claim 21 wherein said second burnable absorber comprises boron (B) in at least the form of boron-10 isotope. 23. The pellet of claim 22 wherein said boron is present in the form as sodium borate (Na.sub.2 B.sub.4 O.sub.7.10H.sub.2 O). 24. The pellet of claim 22 wherein said boron is present as boric oxide (B.sub.2 O.sub.3). 25. The pellet of claim 22 wherein the ratio by weight of said boron to cadmium is about 3.2 to 11. 26. The pellet of claim 22 wherein said cadmium oxide is present in the amount of about 50 to 75 percent by weight, said second burnable absorber comprises boric oxide (B.sub.2 O.sub.3) present in the amount of about 2 to 3 percent by weight, and said glaze forming oxide comprises a mixture of potassium oxide (K.sub.2 O) and silicon dioxide (SiO.sub.2) wherein said potassium oxide is present in the amount of about 3 to 6 percent by weight, the balance being silicon dioxide. 27. The pellet of claim 14 wherein said glaze forming oxide comprises a borosilicate glass. |
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abstract | A near-field scanning optical microscope system exposes photoresist on a substrate. The system includes an NSOM probe, and translational stages capable of moving one of the probe and the substrate such that the probe traverses, in continuous motion, over the entire substrate. Another near-field scanning optical microscope system exposes photoresist on a substrate using an array of NSOM probes. Methods for exposing photoresist on a substrate include the steps of translating a surface of the substrate across an NSOM probe (or an array of NSOM probes) in continuous motion. |
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description | The United States Government has rights in this invention pursuant to Contract No. DE-AC02-06CH11357 between the United States Government and UChicago Argonne, LLC representing Argonne National Laboratory. The present invention relates generally to the temporal modulation of X-rays, and more particularly, relates to a method and apparatus for implementing Bragg-diffraction leveraged modulation of X-ray pulses using MicroElectroMechanical systems (MEMS) based diffractive optics. U.S. patent application Ser. No. 13/246,008 filed Sep. 27, 2011, entitled “METHOD FOR SPATIALLY MODULATING X-RAY PULSES USING MEMS-BASED X-RAY OPTICS” by Daniel Lopez et al., the present inventors, and assigned to the present assignee, discloses a method and apparatus for spatially modulating X-rays or X-ray pulses using MicroElectroMechanical or microelectromechanical systems (MEMS) based X-ray optics including oscillating MEMS micromirrors. A torsionally-oscillating MEMS micromirror and a method of leveraging the grazing-angle reflection property are provided to modulate X-ray pulses with a high-degree of controllability. Modern materials of technological importance are replete with cyclical and nonequilibrium processes that span multiple time-scales ranging from milliseconds to femtoseconds. They include, for example, next-generation denser and faster information storage devices, catalysts responsible for energy conversion, or optogenetic devices used for neurobiological control. A fundamental understanding of the ultrafast dynamics of charge-, spin- and atomic-organization in these materials is essential to understand the processes and to control them to attain the desired functions. The availability of synchrotron radiation X-ray sources during the past decade, especially the development of X-ray free-electron-lasers (XFELs), has allowed the probing of these processes with femtosecond to picosecond resolution following the excitation by an energy stimulus (pump) from an optical laser or a magnetic/electric pulse generator or a THz source. Recently, there has been an overwhelming interest in exploring time-domain science using X-ray pulses generated by synchrotron radiation sources. The unique properties of X-ray pulses (duration, pulse train, and the like) from these sources can be enhanced using ultrafast MEMS-based X-ray optics. A need exists to develop such ultrafast MEMS-based X-ray diffractive optics. A need exists for a method and apparatus for implementing Bragg-diffraction leveraged modulation of X-ray pulses using MicroElectroMechanical systems (MEMS) based X-ray diffractive optics. It is desirable to provide such MEMS based diffractive optics to control the delivery of hard X-ray pulses from a synchrotron radiation source. It is desirable to provide such method and apparatus for implementing Bragg-diffraction leveraged modulation of X-ray pulses that achieves a narrow width of the diffractive time-widow from high angular velocity of the MEMS based X-ray diffractive optics. Principal aspects of the present invention are to provide a method and apparatus for implementing Bragg-diffraction leveraged modulation of X-ray pulses using MicroElectroMechanical systems (MEMS) based diffractive optics. Other important aspects of the present invention are to provide such method and apparatus substantially without negative effect and that overcome some of the disadvantages of prior art arrangements. In brief, a method and apparatus are provided for implementing Bragg-diffraction leveraged modulation of X-ray pulses using MicroElectroMechanical systems (MEMS) based diffractive optics. An oscillating crystalline MEMS device generates a controllable time-window for diffraction of the incident X-ray radiation. A narrow width of the diffractive time-widow is achieved by a selected angular velocity of the MEMS device. In accordance with features of the invention, the oscillating crystalline MEMS device includes a single-crystal MEMS that can diffract or transmit X-ray radiation by changing its relative orientation to the incident X-ray beam. The oscillating MEMS device diffracts the X-ray pulses over a short period of time when the Bragg condition is satisfied. In accordance with features of the invention, the oscillating crystalline MEMS device with a high angular velocity, for example, of 1.262°/μs (microsecond) sorts consecutive X-ray pulses with a separation as close as 2.8±0.4 ns (nanosecond). The MEMS angular speed determines the width of the diffractive time window over which the Bragg condition is fulfilled. In accordance with features of the invention, the MEMS based X-ray diffractive optics includes a single-crystal-silicon (SCS) device layer formed on a Silicon-On-Insulator (SOI) wafer, using conventional semiconductor fabrication technique. The substrate beneath the crystal is removed to allow large out-of-plane oscillations and to allow transmission of X-rays. In accordance with features of the invention, the MEMS based X-ray diffractive optics includes in-plane comb-drive actuators, formed by, for example, inter-digitated capacitors (IDCs). In the following detailed description of embodiments of the invention, reference is made to the accompanying drawings, which illustrate example embodiments by which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. In accordance with features of the invention, a method and apparatus are provided for implementing Bragg-diffraction leveraged modulation of X-ray pulses using MicroElectroMechanical (MEMS) based X-ray diffractive optics. The novel MEMS X-ray diffractive apparatus of the invention provides a crucial capability in investigating dynamical processes in biological, chemical and energy materials, and provides a new method to manipulate pulse shape at the present and future X-ray sources, such as X-ray free-electron-lasers (XFELs). Having reference now to the drawings, in FIG. 1A, there is schematically shown example MEMS X-ray diffractive apparatus for implementing Bragg-diffraction leveraged modulation of X-ray pulses generally designated by the reference character 100 in accordance with preferred embodiments. MEMS X-ray diffractive apparatus 100 includes a MicroElectroMechanical (MEMS) based X-ray diffractive optics 102 used in the X-ray wavelength range as diffractive optics. MEMS X-ray diffractive apparatus 100 includes an X-ray source providing an X-ray radiation such as an X-ray beam, for example, a synchrotron storage-ring 104, such as the Advanced Photon Source (APS) at Argonne National Laboratory. The X-ray beam is monochromatized by a double-crystal monochromator 106, spatially filtered by an aperture 108, diffracted by the MEMS 102 and collected by a detector 110. Referring also to FIG. 1B, Bragg diffraction leveraged modulation operation generally designated by the reference character 112 is illustrated in accordance with preferred embodiments. Diffraction of x-ray pulses is realized by placing the MEMS Si-single-crystal in the Bragg condition depending on the energy of the X-rays and the diffraction plane. Incoming pulses applied to the MEMS based X-ray diffractive optics 102 are diffracted when the Bragg condition is satisfied during the dynamic rotation of the crystal, represented by diffracted pulses when θ=θB. When the Bragg condition is not satisfied during the dynamic rotation of the crystal, the X-ray pulses are either absorbed or transmitted. In accordance with features of the invention, the MEMS angular speed determines the width of the diffractive time window over which the Bragg condition is fulfilled. FIGS. 1C, and 1D and FIGS. 1E, and 1F respectively illustrate angular velocity of the MEMS and a varied diffractive timing window for higher and lower angular velocity in accordance with preferred embodiments. Referring to FIGS. 1C, and 1D, a higher angular velocity 114 is illustrated in FIG. 1C and diffraction of x-ray pulses is realized by placing the MEMS Si-single-crystal 102 in the Bragg condition. In FIG. 1D, an example diffractive time window generally designated by the reference character 116 is illustrated for the higher angular velocity 114 of the MEMS device 102. Referring to FIGS. 1E, and 1F, a lower angular velocity 118 is illustrated in FIG. 1E and diffraction of x-ray pulses is realized by placing the MEMS Si-single-crystal 102 in the Bragg condition. In FIG. 1F, an example diffractive time window generally designated by the reference character 120 is illustrated for the lower angular velocity 118 of the MEMS device 102. An illustrated width, Δtw, of the illustrated diffractive time window 120 is increased or stretched as compared to the illustrated width, Δtw, of the illustrated diffractive time window 116 resulting from the lower angular velocity. FIGS. 2A and 2B schematically illustrate respective example MEMS diffractive optics apparatus for implementing Bragg-diffraction leveraged modulation of X-ray pulses and an example static rocking curve shows a prominent Si(400) diffraction peak at 8 keV with nearly 50% reflectivity and broad peaks on the right which originate from the lattice strain in accordance with a preferred embodiment. Referring to FIG. 2A, an electron microscopy image is provided of an example MEMS based diffractive optics device generally designated by the reference character 200 used for implementing Bragg-diffraction leveraged modulation in accordance with preferred embodiments. MEMS based diffractive optics device 200 includes a single X-ray diffractive crystal 202, such as a Si(100) crystal with dimensions of 500 μm (long)×250 μm (wide)×25 μm (thick) suspended by a pair of torsional flexures 204, 206, which are anchored to a substrate 208. The flexures 204, 206 allow the crystal 202 to rotate in the torsional oscillation mode about an axis joining the anchors. The MEMS device 202 is fabricated using a SOI (silicon-on-insulator) wafer, which provides the single-crystal-silicon 202 necessary to diffract x-rays. The substrate 208 beneath the crystal is removed to allow large out-of-plane oscillations and to allow transmission of X-rays. The excitation is provided by in-plane comb-drive actuators 210, which are implemented, for example, by inter-digitated capacitors (IDCs) that provide torque with large force density. Referring to FIG. 2B, a typical rocking curve of the crystal is shown generally designated by the reference character 220 with a peak reflectivity close to 50%. It consists of a narrow and intense Si(400) peak and additional intensity in the broad peaks above θB. The static rocking curve shows a prominent Si(400) diffraction peak at 8 keV with nearly 50% reflectivity and broad peaks on the right which originate from the lattice strain. In FIG. 2B, these illustrated broad peaks originate from the lattice strain due to shallow diffusive phosphorous dopant layers introduced on the crystal surface during the MEMS fabrication. Since the X-ray diffractive properties of these dopant layers are not known, the intensity was fitted with two Gaussian peaks centered at 0.0038° and 0.0091° above the Si(400) peak. The large angular separation of these two shoulder peaks from the Si(400) peak and their lower intensities allowed an accurate analysis of the Si(400) peak. The line representing Si(400) peak shown in FIG. 2B, also modeled as a Gaussian, has a full-width-at-half-maximum (FWHM), Δθ(400) of 0.0034° (59 microradians). An analysis of the diffraction profile yields an extremely good fit to the measured data as shown in FIG. 2B. Parenthetically, it should be understood that dopant-induced strain can be eliminated in the future by appropriately modifying the MEMS fabrication process. FIGS. 3A, 3B, 3C, and 3D illustrate respective example dynamic performance of the MEMS diffractive optics in accordance with preferred embodiments. In FIG. 3A, normalized angular velocity generally designated by the reference character 300 over one oscillating cycle of MEMS, where ωmax=1.262°/μs. In FIG. 3B, experimental data generally designated by the reference character 320 is shown in the time domain where the position and intensity of the 8 keV diffracted X-ray peaks (locally expanded along the time axis by a factor of 20) over the oscillation cycle is plotted as a function of time over the oscillation period and the values of Δθ. The diffracted peak is narrowest when Δθ=0. The mirror image of diffraction profiles on the two branches of motion highlights the symmetric motion of the MEMS device 102. In FIG. 3C, illustrated data generally designated by the reference character 330 shows measured values dots and calculation with the measured time gap between the X-ray pulses fits perfectly with the following Eq. (2) set forth below when the maximum value of the MEMS deflection is ±2.69°. In FIG. 3D, illustrated data generally designated by the reference character 340 shows measured values dots and calculation with a width, Δtw, of Si(400) diffraction peak obtained from the time-domain diffraction profiles analyzed using the 3-Gaussian model shown as a function of Δθ. The measured values dots deviate from the following Eq. (3) set forth below represented by a solid line curve indicating increased dynamic distortion of the MEMS when deviating further from Δθ=0. Operation of the apparatus 100 and MEMS based diffractive optics device 200 of the invention may be understood as follows. When the crystal is strain and defect free, the value of Δθ(400) is determined by a convolution between the angular and energy widths of the incoming monochromatic beam and the Darwin width of the Si(400) crystal which was calculated to be 0.0028° (49 microradians). The measured Δθ(400) is about 20% broader, which can be accounted from the static deformation strain of the suspended 25-μm thick MEMS crystal. The static deformation of 0.0014° (24 microradians) was estimated from the measured concave curvature of the crystal from both optical and X-ray data. This broadens the rocking curve width to 0.0032° (55 microradians) in good agreement with the measured value. This detailed analysis of the static rocking curve ascertained that the MEMS is well suited as an X-ray diffractive optics. When the MEMS is so aligned that the X-ray incident angle is θ0 when crystal element is stationary, the time dependence of the incident angle θ during the oscillation can be described as θ(t)=θ0+αm cos(2πfmt). The angular velocity of MEMS, ω(t), is given by:ω(t)=ωmax sin(2πfmt) (1)where ωmax=2πfmαm is the maximum angular velocity of by the MEMS. The incident X-ray beam is diffracted at the Bragg condition, θ(t)=θB, and that occurs twice in an oscillation cycle. The value of |ω(t)/ωmax| is unity at T/4 and 3T/4 as shown in FIG. 3A, where T=1/fm is the oscillation period. For a crystal with a rocking curve width Δθ(hkd) (for diffraction plane hkl), the gap between two consecutive diffraction-windows (in an oscillation cycle), Δtg, and the width of the diffraction-time-window, Δtw, are dependent on the angular offset defined by Δθ=θB−θO and given by,Δtg=(1/fm)−(cos−1(Δθ/αm)/(π/fm)) (2)And, whereΔtw.=(Δθ(hkd))/(2πfmαm-((1−(Δθ/αm)2)1/2) (3) From these equations it can be noted that the smallest width of the diffraction-time-window, (Δθ(hkd))/(2πfmαm), is obtained when Δθ=0(θO=θB) corresponding to a gap between pulses of 1/(2fm). The dynamic performance of the MEMS is evaluated from X-ray intensity measurements in the time domain by subjecting it to the incident X-ray pulse-train during the APS standard operating mode in which the pulse-to-pulse separation is 153.4 ns. The MEMS is driven by a 70 Vpp actuation signal with frequency 2fm(fm=74.671 kHz), resulting in a harmonic oscillation with a nominal amplitude αm=±3° and period (T) of 13.392 μs. During each MEMS oscillation cycle, only the X-ray pulses that satisfy the Bragg condition over a defined Si(400) diffractive time window will be diffracted. In an experiment, the time dependence of the 8 keV diffracted X-ray intensities were collected for different values of Δθ by a fast-response avalanche photodiode detector (APD) operating in a charge-integrating mode, as further described below in an example method of operation. The profile of the diffractive time window is constructed by varying the arrival time of the X-ray pulses with respect to the MEMS driving signal. The measured diffractive window in the time domain is shown in FIG. 3B as a function of Δθ. Since Δtw is only several nanoseconds, the intensity traces in FIG. 3B are plotted in an expanded time scale by a factor of 20 to make their shapes clearly visible. The traces shown in FIG. 3B emphasize symmetrical performance of the MEMS in an oscillation cycle. Along the vertical axis, the intensity peaks are offset by the amount of Δθ, ranging from −2.4° to +2.0°, within the nominal oscillation amplitude of the MEMS. The intensity peaks are clearly in two branches, corresponding to the two instances in time when Bragg condition was met within an oscillatory cycle from two rotation directions. Their position on the plot is denoted by the solid dots in FIG. 3B. The two critical dynamic parameters, Δtg and Δtw, can be derived from the diffraction peaks, as is illustrated in FIG. 3B. The values of Δtg are plotted in FIG. 3C as a function of Δθ, along with a fit (solid line) using Eq. (2). The remarkable agreement between the data and the fit allowed accurate and independent determination of the MEMS oscillation amplitude, αm=±(2.692.±0.01)°, the only fitting parameter in the equation. As reflected in Eqs. (1)-(3), this is the most critical parameter necessary to describe all the dynamic properties of the MEMS. The diffraction profiles shown in FIG. 3B as a function Δθ (and the mirror images) retain the features measured in the static rocking curve FIG. 2B). However the width of the Si(400) peak (or Δtw) varies with Δθ and in fact, it is inversely proportional to the angular velocity of the MEMS, as expected from Eq. (3). Of all the peaks in the profiles, the narrowest and highest intensity peaks occurs when Δθ equals 0 (Δθ=0) at which the MEMS reaches the maximum angular velocity ωmax=1.262°/μs. It is important to notice that this angular velocity is nearly an order of magnitude higher than that of a flywheel, and is achieved with an order of magnitude lower linear velocity. The peak narrows when the angular velocity increases (FIGS. 3A, 3B and FIGS. 1C, 1D) and its intensity increases as |Δθ| decreases (FIG. 3B). Therefore, the time-domain diffraction profiles can be analyzed with confidence using the 3-Gaussian model (used to fit the static rocking curve in FIG. 2B) to extract the width Δtw of the most prominent Si(400) diffraction peak. The values of Δtw are shown as a function of Δθ in FIG. 3D, along with calculated values (solid line) using Eq. (3) with no adjustable parameters. Within experimental error, the data are adequately accounted for at Δθ=0 by Eq. (3), without introducing additional strain-related broadening of the rocking curve, demonstrating negligible dynamic distortion of the MEMS at this X-ray incident angle. Away from this condition, measured Δtw departs rapidly from that predicted by Eq. (3), suggesting that the broadening of Δθ(400) stems from growing amount of strain introduced by dynamic deformation. To highlight the narrowest diffractive window achieved with the MEMS optics, the measured dynamic diffraction profile at Δθ=0 is shown in detail in FIG. 4, along with a 3-Gaussian fit. The resulting Δtw corresponding to the prominent Si(400) peak is 2.8±0.4 ns. This is in excellent agreement with the value of 2.7 ns obtained from Eq. (3) using experimentally obtained value of Δθ(400)=0.0034°, αm=±2.69°, and fm=74.671 kHz. Referring also to FIG. 4, there is shown an example X-ray diffractive time window generally designated by the reference character 400 achieved with the MEMS based diffractive optics 102, 200. In FIG. 4, time in nanoseconds (ns) is shown relative the horizontal axis and intensity (arbitrary units) shown relative the vertical axis in accordance with preferred embodiments. The measured dynamic diffraction profile (dots) at Δθ=0 is fitted with a 3-Gaussians (lines). The dashed line curve reflects the peaks associated with a dopant layer identical to those observed in the static diffraction profile. The resulting Δtw for the prominent Si(400) peak is 2.8±0.4 ns in agreement with the that obtained from Eq. (3) using experimentally obtained values of Δθ(400)=0.0034°, αm=±2.69°, and fm=74.671 kHz. In accordance with features of the invention, it is hence concluded with full confidence that MEMS devices can be successfully used as an X-ray diffractive optics. This is the first demonstration of the potential of MEMS diffraction technology in the X-ray wavelength range to control the pulse train from a synchrotron radiation source. This opens many new avenues for the use of MEMS to manipulate and control X-ray radiation. For example, at any hard X-ray storage-ring or XFEL source 104, the present MEMS 102 can be used to select an X-ray pulse or a stream of pulses from a pulse-train with a pulse separation of over 2.8 ns. This accounts for most of the third-generation sources currently operational worldwide. The X-ray fluence from this optics 102 will be enhanced from the ultra-small beam dimensions obtainable from the new generation of storage-ring sources with sub-nm-rad emittance. There are four control parameters for MEMS operation, namely θB, Δθ(hld), αm, and fm, that add many new capabilities to control the X-ray energy, pulse selection, and the shape of the pulse. For example, MEMS optics can be used for time-domain science experiments requiring a broad range of X-ray energy from about 4 to 50 keV by choosing appropriate θB. This will commensurately broaden or narrow the diffractive time-window through the values of Δθ(hld). The values of angular amplitude αm can also be varied by orders of magnitude either by varying the voltage of MEMS excitation pulse or by varying the ambient pressure in which the device operates. This would allow selection of X-ray pulses from MHz-GHz sources. Furthermore, MEMS operation with large values of αm and fm will allow even narrower time windows than reported here, and one can even reach the ultimate potential to slice 100 ps duration X-ray pulses by one to two orders of magnitude (similar to laser slicing of electron bunches) at a storage-ring source, a unique capability for a broad research community. In summary, the reported performance of ultrafast MEMS with flexible control over the delivery and the shape of hard X-ray pulses will herald new opportunities in time-resolved X-ray studies at any synchrotron radiation source. In accordance with features of the invention, methods implemented with the MEMS based diffractive optics 102, 200 may be understood as follows: The torsional MEMS device 102, 200 includes a single-crystal-silicon mass 202 with a smooth surface suspended on opposite sides by a pair of torsional springs 204, 206. The crystal 202 can be rotated in an oscillatory motion about the torsional springs 204, 206 by applying an electrical field to the comb-drive actuators 210. Finite Element Analysis (FEA) was conducted to determine the modal response of the MEMS device 102, 200. Using CoventorWare® simulations show the first harmonic resonance occurring at 74.6 kHz which was verified from experimental measurements to be ≈74.7 kHz. The MEMS device 102, 200 were fabricated at the commercial foundry MEMSCAP using SOIMUMPS® fabrication process with a 25 μm thick device layer. The measured oscillation amplitude of about ±3° required an application of 70 Vpp. The x-ray experiments were performed at Sector 7-ID beamline, a dedicated beamline for ultrafast x-ray experiments of the Advanced Photon Source (APS) at Argonne National Laboratory. The X-ray beam, produced by an undulator source, was monochromatized by a flat diamond double-crystal monochromator tuned to photon energy of 8 keV with a bandwidth of 5×10−5. The X-ray beam was not focused and was defined by a pair of X-Y slits to a size of 100 μm (horizontal)×6 μm (vertical) before impinging on the MEMS device. The static rocking curves around the Si(400) Bragg angle was measured by using a high-resolution diffractometer with a minimum angular step size of 3.125°×10−5. The diffracted photons were detected by an avalanche photodiode (APD) operated in photon-counting mode. For dynamic measurement, the transient X-ray diffraction signal when Bragg condition was met was measured by another APD but operated in charge-integration mode. The integration mode is needed because every diffracted X-ray pulse contained multiple photons. The APD has a fast response with temporal resolution of approximately 5 ns. The APD signal output was digitized by a 500-MHz oscilloscope and recorded every 1 ns, which determines the temporal resolution in determining the delay time between the MEMS driver pulse and the X-ray pulse diffracted by the MEMS crystal element. The oscilloscope trace of 1 ms was measured 20 times to improve the signal-to-noise ratio. While the present invention has been described with reference to the details of the embodiments of the invention shown in the drawing, these details are not intended to limit the scope of the invention as claimed in the appended claims. |
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claims | 1. An x-ray chopper wheel assembly comprising:a disk chopper wheel configured to rotate about a rotation axis thereof, the rotation axis perpendicular to a rotation plane of the disk chopper wheel, the disk chopper wheel having a solid cross-sectional area in the rotation plane, the disk chopper wheel configured to absorb x-ray radiation received from an x-ray source at a source side of the disk chopper wheel, the disk chopper wheel defining one or more openings configured to pass x-ray radiation from the source side of the disk chopper wheel to an output side of the disk chopper wheel; andan output-side scatter plate arranged at the output side of the disk chopper wheel and configured to absorb x-rays scattered from the disk chopper wheel, the output-side scatter plate defining an open slot therein configured to pass x-ray radiation, the output-side scatter plate having a solid cross-sectional area in a plane substantially parallel to the rotation plane of the disk chopper wheel, wherein the solid cross-sectional area of the output-side scatter plate is substantially smaller than the solid cross-sectional area of the disk chopper wheel. 2. The assembly of claim 1, wherein the output-side scatter plate is secured relative to the disk chopper wheel with an output-side gap between the output-side scatter plate and the output side of the disk chopper wheel, the output-side gap in a range of approximately 0.5 mm to approximately 1.0 mm. 3. The assembly of claim 1, wherein the solid cross-sectional area of the output-side scatter plate is less than 50%, less than 25%, or less than 10% of the cross-sectional area of the disk chopper wheel. 4. The assembly of claim 1, wherein the output-side scatter plate comprises tungsten or another high-Z material and has a thickness on the order of 1.0 mm. 5. The assembly of claim 1, wherein the one or more openings are one or more radial slit openings having a slit length in a radial direction of the disk chopper wheel, and wherein the output-side scatter plate has a plate width in a direction parallel to the radial direction of the disk chopper wheel, the plate width being in a range of about 10% to about 70% greater than the slit length. 6. The assembly of claim 1, further comprising a source-side scatter plate having a solid cross-sectional area in a plane substantially parallel to the rotation plane of the disk chopper wheel, the source-side scatter plate configured to absorb x-ray radiation and defining an open slot therein configured to pass x-ray radiation, wherein the solid cross-sectional area of the source-side scatter plate is substantially smaller than the solid cross-sectional area of the disk chopper wheel. 7. The assembly of claim 6, wherein the disk chopper wheel and source-side scatter plate are arranged relative to each other to confine substantially x-ray radiation scattered from the disk chopper wheel. 8. The assembly of claim 7, wherein the solid cross-sectional area of the disk chopper wheel, the solid cross-sectional area of the source-side scatter plate, and a source-side gap between the disk chopper wheel and the source-side scatter plate limit leakage of scattered radiation to no more than 50% of scattered radiation or to a dose of no more than 5 milli-Rem per hour at a distance of 5 cm away from an outer surface of the assembly, whichever is greater. 9. The assembly of claim 8, wherein the solid cross-sectional area of the disk chopper wheel, the solid cross-sectional area of the source-side scatter plate, and a source-side gap between the disk chopper wheel and the source-side scatter plate limit leakage of scattered radiation to no more than 10% of scattered radiation or to a dose of no more than 0.5 milli-Rem per hour at a distance of 5 cm away from the outer surface of the assembly, whichever is greater. 10. The assembly of claim 8, wherein the solid cross-sectional area of the source-side scatter plate is less than 50%, less than 25%, or less than 10% of the cross-sectional area of the disk chopper wheel. 11. The assembly of claim 6, wherein a source-side gap between the source-side scatter plate and the source side of the disk chopper wheel is in a range of approximately 0.5 mm to approximately 1.0 mm. 12. The assembly of claim 6, wherein the source-side scatter plate comprises tungsten or another high-Z material and has a thickness on the order of 1.0 mm. 13. The assembly of claim 6, wherein the source-side scatter plate is configured to output a fan beam of x-rays through the open slot therein, which, in combination with the chopper wheel and output-side scatter plate, enables the assembly to output a pencil beam of x-rays. 14. The assembly of claim 1, wherein the x-ray chopper wheel assembly is configured to be mounted within a handheld x-ray scanner. 15. The assembly of claim 1, wherein the x-ray chopper wheel assembly is configured to be mounted within a fixed-mount or mobile x-ray scanning system. 16. An x-ray chopper wheel assembly comprising:a chopper wheel having a solid area configured to block x-ray radiation received at a source side of the chopper wheel from an x-ray source, the chopper wheel defining one or more openings configured to pass x-ray radiation from the source side of the chopper wheel to an output side of the chopper wheel; anda source-side scatter plate arranged relative to the chopper wheel with a source-side gap in a range of approximately 0.5 mm to approximately 1.0 mm between the source-side scatter plate and the source side of the chopper wheel, the source-side scatter plate being arranged to limit leakage, from the x-ray chopper wheel assembly, of x-rays scattered from the chopper wheel. 17. The assembly of claim 16, wherein the disk chopper wheel and source-side scatter plate are arranged relative to each other further to confine substantially the x-rays scattered from the disk chopper wheel. 18. The assembly of claim 16, further comprising an output-side scatter plate arranged at the output side of the chopper wheel and configured to absorb x-rays scattered from the chopper wheel, the output-side scatter plate defining an open slot therein configured to pass x-ray radiation, the output-side scatter plate having a solid area that is substantially smaller than the solid area of the chopper wheel. 19. An x-ray chopper wheel assembly comprising:a chopper wheel having a solid area configured to block x-ray radiation received at a source side of the disk chopper wheel from an x-ray source, the chopper wheel defining one or more openings configured to pass x-ray radiation from the source side of the chopper wheel to an output side of the chopper wheel; andan output-side scatter plate arranged relative to the chopper wheel with an output-side gap in a range of approximately 0.5 mm to approximately 1.0 mm between the output-side scatter plate and the output side of the chopper wheel. 20. The assembly of claim 19, further comprising a source-side scatter plate arranged at the source side of the chopper wheel and configured to absorb x-rays scattered from the chopper wheel, the source-side scatter plate defining an open slot therein configured to pass x-ray radiation, the source-side scatter plate having a solid area that is substantially smaller than the solid area of the chopper wheel. |
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062597566 | abstract | In a nuclear reactor core, control blades form discrete control blade groups forming a core pattern including first and second main groups, respectively, symmetrically and asymmetrically arranged about the core. Each main group has first and second sub-groups, each sub-group at each control blade location within the core being located alternately in orthogonally-related X and Y directions in plan view of the core. The first sub-group of the first main group includes an operational sub-group. The blades of the first and second main groups are used simultaneously. The blades of the second main group are used only as shallow blades. The blades of the first main group are movable into deep or shallow positions from withdrawn positions. Each fuel bundle operates without an adjacent control blade for a time period twice as long as any previous period of operation with an adjacent control blade inserted into the core. Any one control blade is fully withdrawn for two consecutive periods after insertion. The pattern repeats after three or more periods. |
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abstract | A lithographic apparatus, e.g. using an electron beam, to expose a radiation sensitive layer on a substrate to the pattern on a mask comprising pattern areas and opaque supports. The apparatus uses a variable shaped beam at the edges of the pattern areas to provide a uniform exposure, while avoiding illumination of the opaque supports. |
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description | This application is a divisional application of U.S. application Ser. No. 12/186,560, filed Aug. 6, 2008 now abandoned, the contents of which are incorporated herein by reference. The present application claims priority from Japanese Patent application serial no. 2007-208255, filed on Aug. 9, 2007, the content of which is hereby incorporated by reference into this application. The present invention relates to a reactor core, and more particularly, to a reactor core suitable for the use in a Boiling Water Reactor having an apparatus for adjusting cooling water flow rate. A fuel assembly used for a Boiling Water Reactor (BWR) includes a plurality of fuel rods and a channel box. Each of the fuel rods is filled with a plurality of fuel pellets including fissile material in the cladding tube, are bundled in a square lattice form. The square channel box encloses the bundled fuel rods. The square channel box has an outer width of about 14 cm and a square cross-section. A core, which is disposed in the reactor pressure vessel of a BWR, is loaded with a plurality of fuel assemblies internally. For nuclear fuel material that is used to a fuel pellet, enriched uranium or plutonium-enriched uranium is used in a chemical form of oxide. Because fuel rods are heated by the heat generated by the nuclear fission of the nuclear fuel material, they are cooled by cooling water (coolant) which is light water supplied to the core. The cooling water is circulated by pump. Thermal margin is expressed by a minimum critical power ratio (MCPR) and is defined by a value obtained by dividing fuel rod power at which cooling water transits to a film boiling state on the surface of the cladding tube of the fuel rod and heat removal efficiency starts to greatly decrease, by actual reactor power. The fuel rod power is critical power. It is necessary to maintain the thermal margin so that it is equal to or more than a designated value according to design criteria while the reactor is in operation and in a transient state. The thermal margin decreases as core power density increases. When a reactor is in rated operation, thermal power of fuel assemblies is the lowest in the outermost layer of the core where a large quantity of neutrons leaks. For this reason, in conventional technology, pore diameter of an orifice of the cooling water inlet disposed in the outermost layer region of the core is designed such that the pore diameter is smaller in the inner region than that in the outermost layer region, thereby increasing inflow resistance of the cooling water. In the region of the core other than the outermost layer region, that is, in the inner region where power of fuel assemblies relatively becomes high, the flow rate of the cooling water increases and thermal margin of the core during rated operation can be ensured. Japanese Patent Laid-open No. Hei 7(1995)-181280 describes the adjustment of the pore diameter of the orifice in the cooling water inlet. In the conventional technology, the core is divided into two regions, inner and outer regions, excluding the outermost layer region, and the pore diameter of the orifice in the coolant inlet located in the region on the outer side of 70% of the core radius in the radial direction is made smaller than the pore diameter of the orifice located in the region (central region) on the inner side of the outer region. To do so, flow rate of cooling water in the region on the inner side of 70% of the core radius where power is relatively high increases, thereby increasing thermal margin of the core. In an embodiment described in Japanese Patent Laid-open No. Hei 7(1995)-181280, fuel assemblies loaded in the core are divided into two groups according to in-core fuel dwelling time, and two types of orifices for the coolant inlets are used to efficiently improve thermal margin. However, in the conventional technology, from a perspective of maximization of thermal margin during rated operation, nothing is considered about the increase in power of the fuel assembly associated with the increase in the flow rate of the cooling water, which will be described later in this document. Further, the division of the core region and the setting of the pore diameter of the orifice in the cooling water inlet are not completely optimized. It is necessary to improve thermal margin by providing minimum change of the core system so as to improve power density of the core at low cost. Furthermore, extended cycle operation of the reactor is necessary to improve economical efficiency of fuel; inevitably, a large number of fuel assemblies loaded in the core must be exchanged after the operation cycle has been completed. Roughly, at least 25% of total number of fuel assemblies loaded in the core must be exchanged, and the batch number of fuel exchange is equal to or less than 4. This leads to the increase in the rate of new fuel assemblies that the in-core fuel dwelling time is a first cycle. Therefore, since the number of the fuel assemblies that power is high relatively increases in the core, thermal margin of the core reduces. Accordingly, it is necessary to ensure thermal margin by reducing the power of the fuel assemblies that the in-core fuel dwelling time is the first cycle and becoming flattened the peak of the power in the radial direction of the core. To reduce power generation cost, it is effective to improve thermal margin by minimizing the change of the core system and improve power density. On the other hand, extended cycle operation is effective for the improvement of the operating rate of the nuclear power plant. In both cases, the number of fuel assemblies to be exchanged is large. Roughly, equal to or more than 25% of fuel assemblies in the core (4 batches or less) must be exchanged under the condition in which enrichment is limited to 5 wt % or less. As stated above, this means that the percentage of high power fuel assemblies relatively increases in the core and the percentage of fuel assemblies which have low thermal margin increases. As stated above, it is necessary to ensure thermal margin by reducing the power of the fuel assemblies that the in-core fuel dwelling time is the first cycle and becoming flattened the peak of the power in the radial direction of the core. As a method for improving thermal margin, it is contemplated to use an apparatus for adjusting the flow rate of the cooling water (coolant) per the fuel assembly and provide a relative flow rate of the cooling water per the fuel assembly. Specifically, by reducing the resistance value of the orifice of the cooling water inlet located in the fuel support fitting into which the bottom of the fuel assembly, the thermal margin of which is to be improved, is inserted, it is possible to increase the flow rate of cooling water in the fuel assembly, the in-core fuel dwelling time of which is the first cycle, thereby improving the thermal margin. However, if the flow rate of the cooling water supplied to a fuel assembly increases, void fraction of the fuel assembly decreases and neutrons are easily moderated. When neutrons are easily moderated in a soiling Water Reactor, nuclear fission is accelerated, increasing the power of the fuel assembly. For this reason, when the flow rate of the cooling water supplied to the fuel assembly increases, relative power of the fuel assembly simultaneously increases. Therefore, sufficient effects on the improvement of thermal margin were not obtained. It is an object of the present invention to provide a reactor core which suppresses the increase in power of the fuel assembly resulting from the increase in the flow rate of the coolant in the fuel assembly, and improves the thermal margin. The present invention for achieving the above object is characterized in that A reactor core has an outermost region, a core region surrounded by the outermost region, a plurality of fuel support members, each of which is disposed at a lower end portion of the outermost region and the core region, and a plurality of fuel assemblies loaded in the outermost region and the core region and supported by each of the fuel support members, a plurality of the fuel assemblies disposed in the core region include a plurality of first fuel assemblies, each of which is inserted into a first coolant passage which is formed in the fuel support member and has a first resistor having an opening, and a plurality of second fuel assemblies, each of which is individually inserted into second coolant passages which is formed in the fuel support member and has a second resistor having an opening and a larger pressure loss than that of the first resistor; and, four fuel assemblies, each of which is adjacent to each of four lateral sides of each of a plurality of the first fuel assemblies, include either three or four second fuel assemblies. Four fuel assemblies adjacent to four lateral sides of the first fuel assembly 10 inserted into the first cooling water passage, wherein the first resistor having smaller pressure loss than that of the second resistor is provided, include either three or four second fuel assemblies, each of which is individually inserted into the second cooling water passages wherein the second resistor is provided. Therefore, either three or four second fuel assemblies, wherein flow rate of the coolant is small and power is low, are adjacent to the first fuel assembly wherein flow rate of the coolant increases. For this reason, the power increase rate of the first fuel assembly, wherein flow rate of the coolant increases, is suppressed due to the influence of either three or four second fuel assemblies, and the thermal margin of the reactor core is increased. When distance between a center of a core region and an axis of a fuel assembly located at the furthest position from the center of the core region within the core region is represented as L, the core region, which excludes an outermost region, includes an inner core region wherein fuel assemblies, each of which has the axis on an inner side of a L/√{square root over (2)} position in a radial direction of the core region from the center of the core region, are loaded, and the outer region surrounding the inner region, and when a number of first fuel assemblies among four fuel assemblies separately adjacent to four lateral sides of each of a plurality of first fuel assemblies is represented as α, an average number α of first fuel assemblies in the inner region is 1 or less, the above-mentioned object of the present invention can be achieved. By setting the average number α of the first fuel assemblies in the inner region at 1 or less, it is possible to further increase thermal margin of the core. According to the present invention, it is possible to suppress the increase in the power of a fuel assembly resulting from the increase in the flow rate of the coolant in the fuel assembly, and improves the thermal margin. Inventors studied a method for suppressing the increase in power of fuel assembly when the flow rate of the coolant in the fuel assembly increases. For this study, the inventors focused attention on the fact that the increase in power of one fuel assembly is affected by the power of fuel assemblies surrounding the one fuel assembly. In the outermost layer region of the core, power becomes lower than that of the central portion of the core due to the effect of neutron leakage, therefore, it is not necessary to improve the thermal margin. For this reason, the inventors attempted to apply measures to suppress the increase in power of the fuel assembly located in the region on the inner side of the outermost layer region of the core when the flow rate of the coolant increases. As shown in FIG. 4, excluding fuel assemblies loaded in an outermost layer region 9 of the core 5, the distance between a center of the core and an axis of the fuel assembly loaded in the furthest position from the center of the core is L. The core 5 shown in FIG. 4 shows one fourths of the core. The outermost layer region 9 is made of one layer of fuel assemblies loaded in the outermost position of the core 5. The core 5 includes an inner core region 7 in which fuel assemblies, each of which has the axis on the inner side of the L/√{square root over (2)} position from the center of the core, are loaded, and an outer core region 8 located between the inner core region 7 and the outermost layer region 9. The inventors also studied and discussed situations in which the fuel assemblies having low thermal margin at the beginning and at the end of operation cycle are located in both the inner core region 7 and the outer core region 8 of the core 5. Focusing attention on the fact that the power of one fuel assembly is affected by the power of the fuel assemblies surrounding the one fuel assembly, The inventors perform classification of a plurality of fuel assemblies loaded in the inner core region 7 and the outer core region 8 respectively into two groups, that is, a plurality of fuel assemblies 10 of the first group and a plurality of fuel assemblies 11 of the second group as shown in FIG. 6. Those fuel assemblies are held by fuel supports (fuel support members) installed at the lower end portion of the core 5. Normally, one fuel support holds the lower end portion of four fuel assemblies and forms four cooling water passages that supply cooling water separately to each fuel assembly. An orifice (resistor having an opening) is installed at each inlet of the four cooling water passages provided in the fuel support. The pore diameter of the first orifice provided at the inlet of the cooling water passage (referred to as first cooling water passage) into which a lower end portion of a fuel assembly 10 is inserted is larger than the pore diameter of the second orifice provided at the inlet of the cooling water passage (referred to as second cooling water passage) into which a lower end portion of a fuel assembly 11 is inserted. That is, an orifice coefficient of the first orifice is smaller than that of the second orifice. In the fuel support which holds fuel assemblies 12 disposed in the outermost layer region 9, the orifice coefficient of the third orifice provided at the inlet of the cooling water passage (referred to as third cooling water passage) into which lower end portion of a fuel assembly 12 is larger than an orifice coefficient of the second orifice. For example, the fuel assembly 10 is a fuel assembly that the in-core fuel dwelling time is a first cycle, the fuel assembly 11 is a fuel assembly that the in-core fuel dwelling time is a second cycle, and the fuel assembly 12 is a fuel assembly that the in-core fuel dwelling time is a third cycle. The fuel assemblies 11 are adjacent to the four lateral sides of the fuel assembly 10. Because the orifice coefficient of the first orifice is smaller than that of the second orifice, more cooling water is supplied to the fuel assembly 10 than the fuel assembly 11. Therefore, the power of the fuel assembly 10 will be increased. However, since the fuel assemblies 11 that the power is low are arranged adjacent fuel assembly 10 that the power is high, it is possible to prevent the power of the fuel assembly 10 from increasing. The inventors studied the change of the power increase rate of one fuel assembly 10 when the number of other fuel assemblies 10 adjacent to the former fuel assembly 10 is changed, and obtained new knowledge as shown in FIG. 5. The number of other fuel assemblies 10 adjacent to the one fuel assembly 10 is an average value of the core 5. FIG. 6 shows the arrangement of fuel assemblies 10 and 11 in the inner core region 7 and the outer core region 8 when the number of other adjacent fuel assemblies 10 is 0. That is, there are no other fuel assemblies 10 adjacent to four lateral sides of one fuel assembly 10. The arrangement of the first and second orifices is the same as that of the fuel assemblies 10 and 11. FIG. 7 shows the arrangement of fuel assemblies 10 and 11 when the number of other adjacent fuel assemblies 10 is 1, that is, when another fuel assembly 10 is adjacent to one lateral side of one fuel assembly 10. FIG. 8 shows the arrangement of fuel assemblies 10 and 11 when the number of other adjacent fuel assemblies 10 is 2. FIG. 9 shows the arrangement of fuel assemblies 10 and 11 when the number of other adjacent fuel assemblies 10 is 3. FIG. 10 shows the arrangement of fuel assemblies 10 and 11 when the number of other adjacent fuel assemblies 10 is 4. The core 5 is a BWRS type core loaded with 764 fuel assemblies, and the electric power of the BWR incorporating the core 5 is 1.1 million kW. With regard to the orifice coefficient of each orifice provided in each fuel support located at the lower end portion of the core 5, excluding the third orifice, when compared with the core having a uniform orifice coefficient, the orifice coefficient of the first orifice is −38%, and that of the second orifice is +32%. However, pressure loss of the entire core 5 is equivalent to that of the core having a uniform orifice coefficient. In the core described in Japanese Patent Laid-open No. Hei 7(1995)-181280, there is a mixture of fuel assemblies in the high flow rate region 22 and fuel assemblies in the low flow rate region 21. The orifice coefficient of the orifice which corresponds to the fuel assembly in the high flow rate region 22 is larger than the orifice coefficient of the orifice which corresponds to the fuel assembly in the low flow rate region 21. The average number of fuel assemblies (other fuel assemblies in the high flow rate area 22) adjacent to the lateral sides of one fuel assembly in the high flow rate region 22 is about two to four. In situations (see FIG. 5) in which the number of fuel assemblies 10 adjacent to the lateral sides of one fuel assembly 10 is different, the increase rate of the average flow rate of cooling water supplied to the fuel assembly 10 is about 7.5% when compared with the core having a uniform orifice coefficient. Herein, since the increase in power of the one fuel assembly is as shown in FIG. 5, for example, when the number of other adjacent fuel assemblies 10 shown in FIG. 10 is 4, the thermal margin increases by 0.5% when compared with the core having a uniform orifice coefficient. On the other hand, when the number of other adjacent fuel assemblies 10 shown in FIG. 6 is 0, the thermal margin increases by 2.1% when compared with the core having a uniform orifice coefficient. Based on the new knowledge shown in FIG. 5, the inventors found that if the number of other fuel assemblies 10 adjacent to one fuel assembly 10 is one or less, in other words, if the number of fuel assemblies 11, which has lower power than that of the fuel assembly 10, adjacent to the one fuel assembly 10 is three or four, it is possible to suppress the power increase rate in the fuel assembly 10 when compared with the conventional example. Setting the number of other fuel assemblies 10 adjacent to one fuel assembly 10 at 1 or less also means that four fuel assemblies adjacent to the four lateral sides of the one fuel assembly includes either three or four fuel assemblies 11. By disposing half of the fuel assemblies 10 among all of the fuel assemblies 10 located in either the inner core region, or the inner core region and the outer core region so that each of the above half of the fuel assemblies 10 is adjacent to one or zero other fuel assemblies 10, the inventors newly found that it is possible to suppress the increase in the power of the fuel assembly 10 in which flow rate of supplied cooling water increases. Embodiments which are based on this perspective will be described below. A reactor core applied to a Boiling Water Reactor (BWR) plant, which is a preferred embodiment of the present invention, will be explained with reference to FIGS. 1 to 3. First, structure of the BWR system to which the reactor core of the present embodiment is applied will be described. The BWR plant comprises a reactor 20 including a reactor pressure vessel (hereafter, referred to as RPV) 21, an inverter power supply apparatus 28 and a core flow rate control apparatus 29 and the like. The reactor 20 has the core 5A arranged in the RPV 21, and a neutron detector 26 and a flowmeter 27 are provided in the RPV 21. The core 5A is enclosed in the core shroud 30 provided in the RPV 21. A steam separator (not shown) and a dryer (not shown) are disposed at the upper part of the core 5A inside the RPV 21. A plurality of internal pumps 24 are installed in the RPV 21, an impeller 38 of each internal pump 24 is disposed in an annular down comer 31 formed between the RPV 21 and the core shroud 30. A plurality of fuel assemblies 22 are loaded in the core 5A, the lower end portion of each fuel assembly 22 is held by a fuel support 23 provided at the lower end portion of the core 5A. One fuel support 23 holds four fuel assemblies 22. When one fuel support 23 cannot hold four fuel assemblies 22 in the periphery portion of the core 5A, in some cases, one fuel support holds one fuel assembly 22. In the inside of the fuel support 23 which holds four fuel assemblies 22, there are provided four cooling water passages (not shown) which individually supply cooling water to each fuel assembly 22. An orifice (not shown) is installed at the inlet of each cooling water passage. A fuel support which holds one fuel assembly has one cooling water passage in which an orifice is provided at the inlet so as to supply cooling water to the fuel assembly. In most of the fuel supports 23 disposed in the inner core region 7 and the outer core region 8 of the core 5A, two first cooling water passages and two second cooling water passages are formed. A first orifice is provided at the inlet of the first cooling water passage, and a second orifice is provided at the inlet of the second cooling water passage. The lower end portion of fuel assembly 10 is inserted into the first cooling water passage, the lower end portion of fuel assembly 11 is inserted into the second cooling water passage, and each fuel assembly 10, 11 is held by a fuel support 23. FIG. 3 shows a partial cross-section of the core 5A. A plurality of control rods 32 are disposed in the core 5A. The cross-section of the control rod 32 is cruciform and the control rod 32 includes a plurality of neutron absorbing rods 33. The neutron absorption rod 33 is filled with B4C. Four fuel assemblies 22 are disposed so that they surround one control rod 32. Four fuel assemblies 22 that surround one control rod 32 forms a cell 34. The core 5A includes a plurality of cells 34. The fuel assembly 22 has 74 fuel rods 35 disposed in a square lattice form of 9 lines and 9 columns in a cylindrical channel box 36 having a square cross-section. Each fuel rod 35 is filled with a plurality of fuel pellets including nuclear fuel material. The lower end portion of four fuel assemblies 22 that surround one control rod 32 to form a cell 34 is held by one fuel support 23. The number of operation cycles of the fuel assembly 22, which indicates that the fuel assembly 22 dwelled in the core 5A while the reactor was in operation, is different as described later. In the state of new fuel assembly that burn-up is 0, average uranium enrichment of those fuel assemblies 22 is about 4%, and average discharged burn-up is about 45 GWd/t. By withdrawing a plurality of control rods 32 from the core 5A, reactor power increases. By driving an internal pump 24, the cooling water inside the down comer 31 is pressurized. The cooling water discharged from the impeller 38 is introduced into each fuel assembly 22 through the lower plenum 25 and each cooling water passage formed in the fuel supports 23. The cooling water is heated by heat generated by nuclear fission of nuclear fuel material in the fuel assembly 22, and a part of it changes to steam. Moisture included in the steam is removed by a separator and a dryer and then supplied to a turbine (not shown) from the RPV 21. The turbine is rotated by the steam, and a power generator (not shown) connected to the turbine is also rotated. The steam discharged from the turbine is condensed by the condenser (not shown) to become water. The condensed water is supplied to the RPV 21 as feed water. The core flow rate control apparatus 29 calculated the reactor power based on neutron fluxes measured by each neutron detector 26 and controls the inverter power supply apparatus 28 based on the obtained reactor power and the core flow rate measured by the flowmeter 27. By this control, the inverter power supply apparatus 28 regulates electric current supplied to the internal pump 24 and adjust revolutions of the internal pump 24. Thus, the core flow rate control apparatus 29 adjusts revolutions of the internal pump 24 and controls the core flow rate. The core flow rate is a flow rate of cooling water supplied to the core. The arrangement of fuel assemblies 22 in the core 5A which is a reactor core of the present embodiment will be described with reference to FIG. 1. The core 5A is loaded with 764 fuel assemblies 22 and has 191 control rods 32. Electric power of the BWR plant that uses a reactor 20 having the core 5A which is a BWR5 type core is 1.1 million kW. One operation cycle is 24 months, and the batch number for fuel exchange is 2.2 batches. Fuel exchange is conducted during the reactor shutdown period between an operation cycle and the next operation cycle. Excluding the outermost layer region 9 of the core 5A, 764 fuel assemblies 22 loaded in the core 5A are arranged such that a plurality of fuel assemblies 10 of the first group and a plurality of fuel assemblies 11 of the second group, as mentioned above, are arranged in the inner core region 7 and the outer core region 8 (see FIG. 4 for these regions) surrounded by the outermost layer region 9. The outermost layer region 9 is formed by a layer of fuel assemblies 22 loaded in the outermost position of the core 5A. The inner core region 7 of the present embodiment is a region in which fuel assemblies 22, each of which has the axis on the inner side of the L/√{square root over (2)}, position from the center of the core 5A, are loaded. The outer core region 8 is located between the inner core region 7 and the outermost layer region 9. The core 5A are loaded with fuel assemblies 22 which are experiencing the operation in the first operation cycle (referred to as fuel assemblies of a first in-core fuel dwelling time), fuel assemblies 22 which have been experienced the operation in the first operation cycle and are experiencing the operation in the second operation cycle (referred to as fuel assemblies of a second in-core fuel dwelling time), and fuel assemblies 22 which have been experienced the operation in the second operation cycle and are experiencing the operation in the third operation cycle (referred to as fuel assemblies of a third in-core fuel dwelling time). In FIG. 1, “1” represents the fuel assemblies 22 of a first in-core fuel dwelling time, “2” represents the fuel assemblies 22 of a second in-core fuel dwelling time, and “3” represents the fuel assemblies 22 of a third in-core fuel dwelling time. These expressions are the same in embodiments 2 through 5 described later. A plurality of fuel assemblies 22 loaded in the outermost layer region 9 of the core 5A, that is, a plurality of fuel assemblies 12 include the fuel assemblies 2 of the second in-core fuel dwelling time and the fuel assemblies 3 of the third in-core fuel dwelling time. All fuel assemblies 10 arranged in the inner core region 7 and the outer core region 8 of the present embodiment are fuel assemblies 1 of the first in-core fuel dwelling time. All fuel assemblies 11 arranged in the inner core region 7 and the outer core region 8 of the present embodiment are fuel assemblies 2 of the second in-core fuel dwelling time. The content of fissile material and the power of the fuel assembly become lower in sequential order of the fuel assemblies 1, the fuel assemblies 2, and the fuel assemblies 3. The pore diameter of the first orifice provided at the inlet of the first cooling water passage formed in the fuel support 23 is larger than the pore diameter of the second orifice provided at the inlet of the second cooling water passage formed in the fuel support 23. This means that the orifice coefficient of the first orifice is smaller than that of the second orifice. In the fuel support which holds fuel assemblies 12 including the fuel assemblies 2 and 3 arranged in the outermost layer region 9, the orifice coefficient of the third orifice provided at the inlet of the third cooling water passage inserting the lower end portion of the fuel assembly 12 is larger than the orifice coefficient of the second orifice. This is because the quantity of neutrons that leak from the fuel assemblies 12 arranged in the outermost layer region 9 to the outside of the core 5A is the greatest and the power of the fuel assemblies 12 decreases. With regard to the orifice coefficient of each orifice provided in each fuel support located at the lower end portion of the core 5A, excluding the third orifice, when compared with the core having a uniform orifice coefficient, the orifice coefficient of the first orifice is −38% and that of the second orifice is +32%. The orifice coefficient of the first orifice is smaller than that of the second orifice. However, pressure loss of the entire core 5 is equivalent to that of the core having a uniform orifice coefficient. The present embodiment is characterized in that other fuel assemblies 22, excluding the fuel assemblies 12 loaded in the outermost layer region 9 of the core 5A, include the fuel assemblies 10, each of which is inserted into the first cooling water passage having the first orifice, in which pressure loss is smaller than that of the core average, and the fuel assemblies 11, each of which is inserted into the second cooling water passage having a second orifice, in which pressure loss is larger than that of the core average, and other fuel assemblies 10 are not adjacent to the four lateral sides that form four sides of one fuel assembly 10. No fuel assemblies 10 are adjacent to the lateral sides of the one fuel assembly 10. The average number α of adjacent fuel assemblies in this case is 0. Herein, being adjacent to the lateral side of the fuel assembly means being adjacent to the fuel assembly in the direction of the arrangement of the fuel assemblies that are arranged on the lattice-like. A fuel assembly 11 having a lower infinite multiplication factor than that of the fuel assembly 10 is adjacent to (face-to-face with) each of the four lateral sides of the one fuel assembly 10. Moreover, in two diagonal directions of the fuel assembly 10, other four fuel assemblies 10 are arranged in four corner portions of the fuel assembly 10 so that the corner portions are adjacent to each other. The number 22 denotes the fuel assembly. In both the inner core region 7 and the outer core region 8, the number of other fuel assemblies 10 face-to-face-to-face with each the lateral sides of the one fuel assembly 10 is substantively 0, and the average number α of adjacent fuel assemblies is also 0. In the present embodiment, fuel assembly 22, the in-core fuel dwelling time of which is shorter than that of the core average, is fuel assembly 10. When compared to the core having a uniform orifice coefficient, excluding the outermost layer region, in the present embodiment, the average increase rate of the flow rate of cooling water in each fuel assembly 10 is about 7.5%, however, power increase rate of each fuel assembly 10 can be suppressed to 0.6%. When four fuel assemblies adjacent to the one fuel assembly 10 are all fuel assemblies 10, the power increase rate of the one fuel assembly 10 is 1.8, and in the present embodiment, it is suppressed to 0.6%. Therefore, the thermal margin of the core 5A increases by about 2%. In the present embodiment, four low power fuel assemblies 11, each of which is inserted into the second cooling water passage having a second orifice, are adjacent to four lateral sides of a fuel assembly 10 inserted into the first cooling water passage in which the first orifice, the orifice coefficient of which is smaller than that of the second orifice, is provided. The flow rate of the cooling water supplied to the fuel assembly 10 increases and the power of the fuel assembly 10 also increases. The flow rate of cooling water supplied to the fuel assemblies 11 is less than that of the fuel assembly 10, and the power of the fuel assemblies 11 is lower than that of the fuel assembly 10. As a result, although the flow rate of the cooling water in the fuel assembly 10 increases, four low power fuel assemblies 11 are individually adjacent to the lateral sides of the fuel assembly 10, therefore, the power increase rate of the fuel assembly 10 is suppressed as stated above. Consequently, the thermal margin of the core 5A increases by about 2%. Japanese Patent Laid-open No. Hei 7(1995)-181280 focuses attention on the improvement of the thermal margin by increasing the flow rate of the cooling water supplied to the fuel assembly. On the other hand, the present embodiment focuses on the suppression of the power increase rate, and by considering the suppression of the power increase rate, it is possible to further increase the thermal margin. A reactor core of embodiment 2 applied to a BWR, which is another embodiment of the present invention, will be described with reference to FIG. 11. The BWR plant using the core 5B has a reactor 20 shown in FIG. 2 and equipped with the core 5B. In the core 5B of the present embodiment, a plurality of fuel assemblies 10 and 11 are arranged in the inner core region 7 in which fuel assemblies 22, each of which has the axis on the inner side of the L/√{square root over (2)} position from the center of the core 5B, are loaded, and instead of providing fuel assemblies 10, a plurality of fuel assemblies 11 are arranged in the outer core region 8 located between the inner core region 7 and the outermost layer region 9. The structure of other portions of the BWR plant incorporating the core 5B is the same as that of embodiment 1. A plurality of fuel assemblies 11 arranged in the outer core region 8 include fuel assemblies 1 and fuel assemblies 2. In most fuel assemblies 1 loaded in the outer core region 8, a fuel assembly 2 is adjacent to each of four lateral sides of the fuel assembly 1. Lower end portion of Each of those fuel assemblies 1 and 2 is inserted into the second cooling water passage in which the second orifice is provided at the inlet. In the inner core region 7, in the same manner as the inner core region 7 of the embodiment 1, fuel assemblies 11 are adjacent to four lateral sides of a fuel assembly 10. This means that other fuel assemblies 10 are not adjacent to the four lateral sides of the one fuel assembly 10. Therefore, the average number α of adjacent fuel assemblies in the inner core region 7 is 0. Fuel assembly 10 arranged in the inner core region 7 is the fuel assembly 1 and the fuel assembly 11 is fuel assembly 2. The lower end portion of fuel assembly 1 in the inner core region 7 is inserted into the first cooling water passage. Furthermore, the lower end portion of the fuel assembly 2 in the inner core region 7 is inserted into the second cooling water passage. In the present embodiment, in the same manner as the embodiment 1, when compared with the core having a uniform orifice coefficient excluding the outermost layer region, average increase rate of the flow rate of the cooling water in each fuel assembly 10 is about 7.5%, but the power increase rate of each fuel assembly 10 is suppressed to 0.6%. Therefore, the thermal margin of the core 53 increases by about 2%. In the present embodiment, even when the flow rate of the cooling water in the fuel assembly 10 is increased, for the same reason as the embodiment 1, it is possible to increase the thermal margin when compared to the core in which pressure drop coefficient of the orifice is uniform. A reactor core of embodiment 3 applied to a BWR, which is another embodiment of the present invention, will be described with reference to FIG. 12. In the core 5C of the present embodiment, fuel assemblies 10 and 11 are arranged in the inner core region 7 and the outer core region 8, respectively, which are surrounded by the outermost layer region 9. The BWR plant which incorporates the core 5C is an ABWR plant that has an ABWR as a reactor 20. The ABWR plant also has the same structure as that of BWR plant of the embodiment 1 shown in FIG. 2 except for the core 5C and a recirculation system. The ABWR has internal pumps instead of jet pumps. The core 5C is an ABWR type core. Electric power of the ABWR plant is 1.35 million kW, and the core 5C is loaded with 872 fuel assemblies 22 that the average discharged burn-up is 45 GWd/t. There are provided 218 control rods 32, and hafnium type neutron absorption members are provided instead of neutron absorption rods 33. One operation cycle is 15 months, and batch number for fuel exchange is 3.8 batches. Therefore, in the core 5C, in addition to fuel assemblies 1, 2 and 3, fuel assemblies 22 which have been experienced the operation in the third operation cycle and are experiencing the operation in the fourth operation cycle (referred to as fuel assemblies of a fourth in-core fuel dwelling time) are loaded. The fuel assemblies 4 of a fourth in-core fuel dwelling time are loaded in the outermost layer region 9 of the core 5C. A plurality of the fuel assemblies 10 and a plurality of the fuel assemblies 11 are arranged in the inner core region 7 and the outer core region 8 surrounded by the outermost layer region 9. A plurality of the fuel assemblies 10 are the fuel assemblies 1. A plurality of the fuel assemblies 11 include the fuel assemblies 2, 3, and 4. Four fuel assemblies 11 are adjacent to four lateral sides of one fuel assembly 10. The lower end portion of the fuel assembly 1 which is the fuel assembly 10 is inserted into the first cooling water passage in which the first orifice is provided at the inlet. The lower end portion of each of the fuel assemblies 2, 3, and 4 which are fuel assemblies 11 is inserted into the second cooling water passage in which the second orifice is provided at the inlet. With regard to the orifice coefficient of each orifice provided in the fuel support 23, excluding the third orifice located in the outermost layer region 9, when compared with the core having a uniform orifice coefficient, the orifice coefficient of the first orifice is −41% and that of the second orifice is +19%. The orifice coefficient of the third orifice is larger than that of the second orifice. Pressure loss of the entire core 5C is equivalent to that of the core having a uniform orifice coefficient. Four fuel assemblies 11 are separately adjacent to four lateral sides of the one fuel assembly 10. Those fuel assemblies 11 adjacent to four lateral sides of the one fuel assembly 10 are at least two different types of fuel assemblies 22, the in-core fuel dwelling time of which is different from that of most fuel assemblies 10. Some of fuel assemblies 10 located in the periphery portion of the outer core region 8 are arranged such that one of four lateral sides is adjacent to a fuel assembly 10. The average number α of adjacent fuel assemblies located in the inner core region 7 and the outer core region 8 of the core 5C is almost 0. In the present embodiment, when compared with the core having a uniform orifice coefficient excluding the outermost layer region 9, average increase rate of the flow rate of the cooling water in each fuel assembly 10 is about 4.3%, however, power increase rate of each fuel assembly 10 is suppressed to 0%. As a result, the thermal margin of the core 5C increases by about 2%. Even in the core, the batch number of which is close to 4 batches, it is possible to improve the thermal margin of the core when the flow rate of the cooling water in the fuel assembly 10 is increased. In the present embodiment, even if the size of the core or batch number for fuel exchange are changed, the above advantages can be obtained. A reactor core of embodiment 4 applied to a BWR, which is another embodiment of the present invention, will be described with reference to FIG. 13. In the core 5D of the present embodiment, fuel assemblies 10 and 11 are arranged in the inner core region 7 and the outer core region 8, respectively, which are surrounded by the outermost layer region 9. In the same manner as embodiment 3, the BWR plant which incorporates the core 5D is an ABWR plant that has an ABWR as a reactor 20. The ABWR plant also has the same structure as that of the BWR plant of embodiment 1 shown in FIG. 2 except for the core 5D. The core 5D is an ABWR type core. With regard to the difference between core 5D and core 5C, the arrangement of fuel assemblies 22 and the orifice coefficient are different, and the fuel assemblies 10 of the core 5D include fuel assemblies 2. The core 5D also includes the inner core region 7 in which fuel assemblies 22, each of which has the axis on the inner side of the L/√{square root over (2)} position from the center of the core 5B, are loaded, and the outer core region 8 located between the inner core region 7 and the outermost layer region 9. In the inner core region 7 of the core 5D, excluding a part of the periphery portion of the inner core region 7, the fuel assemblies 10 and fuel assemblies 11 are arranged in the same manner as the inner core region 7 of the core 5C. In the part of the periphery portion of the inner core region 7 of the core 5D, the fuel assemblies 2 which are the fuel assemblies 10 are arranged. Therefore, in the part of the periphery portion of the inner core region 7, each of the fuel assemblies 2 which are the fuel assemblies 10 is adjacent to each of two lateral sides of one fuel assembly 1 which is the fuel assembly 10. In most of the inner core region 7 of the core 5D excluding the periphery portion, the fuel assemblies 11 are adjacent to four lateral sides of the one fuel assembly 1 which is the fuel assembly 10. Therefore, the average number α of adjacent fuel assemblies located in the inner core region 7 is almost 1. The outer core region 8 of the core 5D includes the first arrangement wherein the fuel assemblies 2 which are the fuel assemblies 10 are adjacent to two lateral sides of one fuel assembly 1 which is the fuel assembly 10, and the second arrangement wherein the fuel assemblies 11 are adjacent to four lateral sides of one fuel assembly 1 which is the fuel assembly 10. In this second arrangement, no other fuel assemblies 10 are arranged so that they are adjacent to four lateral sides of one fuel assembly 10. In the outer core region 8, the number of the second arrangements is larger than the number of the first arrangements. The first arrangement is located on the outermost layer region 9 side and the second arrangement is located on the inner core region 7 side. The average number α of adjacent fuel assemblies in the outer core region 8 is almost 1.5. The lower end portion of each of the fuel assemblies 1 and 2 which are the fuel assemblies 10 is inserted into the first cooling water passage, and the lower end portion of each of the fuel assemblies 2, 3, and 4 which are the fuel assemblies 11 is inserted into the second cooling water passage. With regard to the orifice coefficient of each orifice provided in the fuel support 23, excluding the third orifice located in the outermost layer region 9, when compared with the core having a uniform orifice coefficient, the orifice coefficient of the first orifice is −41% and that of the second orifice is +32%. The orifice coefficient of the third orifice is larger than the second orifice. Pressure loss of the entire core 5D is equivalent to that of the core having a uniform orifice coefficient. In the present embodiment, in the central portion of the inner core region 7, all of the four fuel assemblies adjacent to one fuel assembly 10 are the fuel assemblies 11. Furthermore, as described later, if the fuel assemblies 11 are used for two fuel assemblies adjacent to the fuel assembly 10 of the second in-core fuel dwelling time located in the outer periphery portion of the inner core region 7, when compared with the core having a uniform orifice coefficient excluding the outermost layer region, the average increase rate of the flow rate of the cooling water in each fuel assembly 10 is about 4.5%. However, the power increase rate of each fuel assembly 10 is suppressed to 0.6%. As a result, the thermal margin of the core 5D increases by about 2%. When the thermal margin of the fuel assembly of the second in-core fuel dwelling time located in the outer periphery portion of the inner core region 7 is low, in the present embodiment, the lower end portion of the fuel assembly 11 of the second in-core fuel dwelling time is inserted into the first cooling water passage in which the first orifice is provided. By doing so, with regard to the fuel assembly 10 of the second in-core fuel dwelling time located in the outer periphery portion of the inner core region 7, by using other fuel assemblies 10 for two fuel assemblies adjacent to one fuel assembly 10 of the second in-core fuel dwelling time, in other words, by using the fuel assemblies 11 for two other fuel assemblies adjacent to the one fuel assembly 10, as shown in FIG. 5, it is possible to suppress the power increase rate of the fuel assembly 10 of the second in-core fuel dwelling time. A reactor core of embodiment 4 applied to a BWR, which is another embodiment of the present invention, will be described with reference to FIG. 14. In the core 5E of the present embodiment, fuel assemblies 10 and 11 are arranged in the inner core region 7 and the outer core region 8, respectively, which are surrounded by the outermost layer region 9. The BWR plant which incorporates the core 5E has a reactor 20 equipped with the core 5E and shown in FIG. 1. In the same manner as embodiment 1, the boundary between the inner core region 7 and the outer core region 8 of the core 5E is the L/√{square root over (2)} point from the center of the core 5E. Fuel assemblies 2 and 3 are arranged in the outermost layer region 9 of the core 5E. Both fuel assemblies 10 and fuel assemblies 11 include the fuel assemblies 1 and fuel assemblies 2. In the inner core region 7 of the core 5E, all fuel assemblies 10 are arranged such that one lateral side of each fuel assembly 10 is adjacent to another fuel assembly 10. That is, one fuel assembly 2 which is fuel assembly 10 is adjacent to one lateral side of a certain fuel assembly 1 which is fuel assembly 10. Three fuel assemblies 2 which are fuel assemblies 11 are individually adjacent to other three lateral sides of one fuel assembly 1 which is fuel assembly 10. Three fuel assemblies 1 which are fuel assemblies 11 are individually adjacent to other three lateral sides of one fuel assembly 2 which is fuel assembly 10. The average number α of adjacent fuel assemblies located in the inner core region 7 is almost 1. In the same manner as the inner core region 7, in most of the outer core region 8, a fuel assembly 2 which is another fuel assembly 10 is adjacent to one lateral side of one fuel assembly 1 which is fuel assembly 10. The average number α of adjacent fuel assemblies located in the outer core region 8 is almost 1. The lower end portion of each of fuel assemblies 1 and 2 which are fuel assemblies 10 is inserted into the first cooling water passage, and the lower end portion of each of fuel assemblies 1 and 2 which are fuel assemblies 11 is inserted into the second cooling water passage. With regard to the orifice coefficient of each orifice provided in the fuel support 23, excluding the third orifice located in the outermost layer region 9, when compared with the core having a uniform orifice coefficient, the orifice coefficient of the first orifice is −38% and the second orifice is +33%. The orifice coefficient of the third orifice is larger than the second orifice. Pressure loss of the entire core is equivalent to that of the core having a uniform orifice coefficient. In the present embodiment, when compared with the core having a uniform orifice coefficient excluding the outermost layer region 9, average increase rate of the flow rate of cooling water in each fuel assembly 10 is about 6.5%, however, power increase rate of each fuel assembly 10 is suppressed to 0.7%. Thermal margin of the core 5E increases by about 2%. In the core 5E, it is possible to arrange a plurality of fuel assemblies 11 in the outer core region 8 instead of arranging fuel assemblies 10 and arrange a plurality of fuel assemblies 10 and 11 in the inner core region 7. In the inner core region 7, another fuel assembly 10 is adjacent to one lateral side of a fuel assembly 10, and fuel assemblies 11 are adjacent to other three lateral sides of the fuel assembly 10. |
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claims | 1. A method of diagnosing at least one system fault comprising the steps of:(a) identifying sensors available within a system, wherein identified sensors generate sensor data relating to system operating characteristics;(b) analyzing the sensor data to identify patterns indicative of at least one failure mode, wherein the sensor data is analyzed under a full-fault condition and under a no-fault condition;(c) determining a fault relationship based upon identified patterns;(d) comparing at least one system operating characteristic to the fault relationship to identify a system fault; and(e) generating at least one fault code indicative of the at least one failure mode when a system fault is identified in step (d). 2. The method of diagnosing at least one system fault as recited in claim 1, wherein step (b) further includes the steps of:(f) generating a full-fault data set under the full-fault condition and a no-fault data set under the no-fault condition from each of the identified sensors;(g) comparing the full-fault data set from each of the identified sensors with the no-fault data set from the same identified sensor,(h) identifying a maximum separation between the full-fault data set and the no-fault data set for each identified sensor;(i) selecting the identified sensor associatcd with a greatest maximum separation between the full-fault data set and the no-fault data set associated with the identified sensor; and(j) identifying the at least one system characteristic of step (d) based upon the selected identified sensor of step (i). 3. The method of diagnosing at least one system fault as recited in claim 1, wherein step (c) further includes the steps of:(k) determining a threshold value associated with the at least one system characteristic;(l) monitoring an actual value associated with the at least one system characteristic; andwherein step (e) further includes generating the at least one fault code based upon a comparison of the actual value and the threshold value. 4. The method of diagnosing at least one system fault as recited in claim 3, wherein step (k) further includes the steps of:(m) calculating a distance between the full-fault data set and the no-fault data set for the selected identified sensor associated with the maximum separation; and(n) maximizing the distance based upon filtering parameters and variable sub-selection. 5. The method of diagnosing at least one system fault as recited in claim 3, wherein step (e) further includes the step of:(o) identifying at least one other system characteristic not monitored by any of the identified sensors, wherein at least one other system characteristic is indicative of the at least one system failure mode associated with the at least one fault code. 6. The method of diagnosing at least one system fault as recited in claim 5, wherein step (e) further includes the steps of:(p) calculating an avenge value associated the at least one other system characteristic for a given sampling time; and(q) monitoring an actual value associated with the at least one other system characteristic. 7. The method of diagnosing at least one system fault as recited in claim 6, wherein step (e) further includes generating the at least one fault code when the actual value associated with the at least one system characteristic exceeds the threshold value and the actual value associated with the at least one other system characteristic exceeds the average value. 8. The method of diagnosing at least one system fault as recited in claim 7, wherein the at least one system characteristic is associated with a degree of actuation of at least one control valve within with the system. 9. The method of diagnosing at least one system fault as recited in claim 6, wherein step (e) further includes generating the at least one fault code when the actual value associated with the at least one system characteristic falls below the threshold value and the actual value associated with the at least one other system characteristic exceeds the avenge value. 10. The method of diagnosing at least one system fault as recited in claim 9, wherein the at least one system characteristic is a suction pressure associated with a compressor. 11. The method of diagnosing at least one system fault as recited in claim 1, wherein step (c) further includes the steps of:(r) analyzing the identified patterns; and(s) combining the idernified patterns with available physical system information to determine the fault relationship. 12. The method of diagnosing at least one system fault as recited in claim 1, further ineJuding the steps of:(t) determining a threshold value associated with the at least one system operation characteristic of step (d);(u) estimating a second system operating characteristic; and(v) measuring a third system operating characteristic, wherein the threshold value and the second system operating characteristic are calculated and estimated respectively based upon the third system operating characteristic. 13. The method of diagnosing at least one system fault as recited in claim 12, wherein the second system operating characteristic is indicative of the at least one system failure mode associated with the at least one fault code. 14. The method of diagnosing at least one system fault as recited in claim 13 wherein step (e) further includes the step of:(v) calculating an avenge value associated with the second system operating characteristic for a given sampling time; and(w) monitoring an actual value of the second system operating characteristic. 15. The method of diagnosing at least one system fault as recited in claim 14, wherein step (e) further includes generating the at least one fault code when the actual value associated with the at least one system operating characteristic exceeds the threshold value and the actual value of the second system operating characteristic exceeds the average value. 16. The method of diagnosing as least one system fault as recited in claim 1, wherein the system is a vapor compression system. 17. The method of diagnosing as least one system fault as recited in claim 16, wherein the identified sensors in the vapor compression system include at least one pressure sensor, at least one temperature sensor, and at least one valve sensor. 18. A vapor compression system comprising:at least one indoor unit including at least one indoor sensor and at least one indoor valve;at least one outdoor unit in communication with the at least one indoor unit and including at least one outdoor sensor and at least one outdoor valve;a control device for controlling the at least one indoor unit and the at least one outdoor unit, wherein the control device further includes:a controller that collects and interprets data from the at least one indoor sensor and the at least one outdoor sensor and generates at least one fault code based on the data, wherein the at least one fault code is generated based upon analysis of the data under a full-fault condition and under a no-fault condition. 19. The system of claim 18, wherein the controller combines the data with available system information from the at least one indoor unit and the at least one outdoor unit to generate the at least one fault code. 20. The system of claim 18, wherein the controller receives a plurality of data inputs associated with a plurality of system operating characteristics, calculates an indicator based upon the plurality of system operating charactedstics, and generates the at least one fault code based upon a comparison of the indicator to a threshold. |
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claims | 1. A method for producing a radionuclide, comprising the steps of:completely filling a target chamber with target fluid including a target material, the target chamber including an upper region and a lower region below the upper region;pressurizing the target chamber by flowing a gas toward a lower opening of the lower region;applying a particle beam to the target chamber at a beam power to irradiate the target material and produce a radionuclide in the target fluid; andwhile applying the particle beam, maintaining a space including a target fluid vapor in the upper region by preventing target fluid from flowing out from the target chamber from the upper region while permitting target fluid heated by the particle beam to flow through the lower opening against the gas pressure, and permitting a volume of the target fluid vapor space to vary in proportion to the beam power of the particle beam being applied to the target chamber. 2. The method of claim 1 further comprising, during application of the particle beam, condensing target fluid vapor in the upper region and flowing the condensed target fluid to the lower region. 3. The method of claim 1 further including, during application of the particle beam, cooling the target fluid that flowed out from the target chamber. 4. The method of claim 1 wherein the heated target fluid flowing out from the target chamber through the lower opening is flowed into a second chamber fluidly communicating with the lower opening. 5. The method of claim 4 wherein pressurizing includes flowing the gas into the second chamber. 6. A method for producing a radionuclide, comprising the steps of:completely filling a target chamber with target fluid including a target material, the target chamber including an upper region and a lower region below the upper region;pressurizing the target chamber;applying a particle beam to the target chamber to irradiate the target material and produce a radionuclide in the target fluid; andwhile applying the particle beam, preventing target fluid from flowing out from the target chamber from the upper region, maintaining a space including a target fluid vapor in the upper region, and maintaining an open target fluid flow path from a lower opening of the lower region to a second chamber to enable target fluid heated by the particle beam to flow out from the target chamber toward the second chamber during application of the particle beam. 7. The method of claim 6 wherein pressurizing the target chamber includes flowing a gas into the second chamber, and wherein the heated target fluid is flowed out from the target chamber through the lower opening against the gas pressure. 8. The method of claim 6 wherein the second chamber includes an expansion chamber. 9. The method of claim 6 wherein the second chamber includes an expansion chamber fluidly communicating with the lower opening via a lower liquid conduit. 10. The method of claim 6 wherein the second chamber includes a lower liquid conduit. 11. The method of claim 6 further comprising providing a target fluid return path from the second chamber to the lower opening during application of the particle beam. 12. The method of claim 6 further comprising, during application of the particle beam, condensing target fluid vapor in the upper region and flowing the condensed target fluid to the lower region. 13. The method of claim 6 wherein the particle beam is applied to the target chamber at a beam power, the target fluid vapor space has a volume, and the method includes permitting the volume of the target fluid vapor space to vary in proportion to the beam power of the particle beam being applied to the target chamber. |
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summary | ||
039986926 | summary | BACKGROUND OF THE INVENTION This invention relates to a nuclear reactor. In more detail, the invention relates to a reactor which is useful for breeding uranium-233 for use in a light-water breeder reactor. The design of light-water reactors capable of self-sustained breeding has been extensively studied at Bettis Atomic Power Laboratory. These designs all include a heterogeneous array of rods fueled with (U.sup.233, Th)O.sub.2 pellets with a moderator and coolant of light water. The designs also have as a common feature the use of a movable fuel region coupled with some form of axial fuel variation to attain reactivity control. One such design is described in detail in patent application Ser. No. 461,475, filed Apr. 16, 1974, now U.S. Pat. No. 3,957,575. Before any large-scale development of (U.sup.233, Th)O.sub.2 reactors can occur, it is necessary to develop an efficient means of obtaining large quantities of the fissile isotope U.sup.233. The only method by which U.sup.233 can be obtained in quantity is by the conversion of Th.sup.232 to U.sup.233. This requires the development of an efficient reactor which is fueled with available fuel and in which conversion of Th.sup.232 to U.sup.233 can be carried out. One such reactor which has been proposed is a reactor which uses only plutonium fissile fuel but operation of such a reactor is totally dependent on fissile fuel which must also be produced in a reactor. Another such reactor uses U.sup.235 as fuel with a low-cost diluent such as ZrO.sub.2 but such a reactor has a low thorium conversion ratio. Still another such reactor forms the subject matter of the present application. SUMMARY OF THE INVENTION According to the present invention, breeding of U.sup.233 for use in a light-water thermal reactor capable of self-sustained breeding is accomplished in a reactor fueled with U.sup.235 with U.sup.238 diluent and Pu.sup.239 fuel, if available, plus Th.sup.232 diluent. The fertile material Th.sup.232 is physically separated from the U.sup.235 and is preferably mixed with Pu.sup.239 to improve Th.sup.232 conversion to U.sup.233. A preferred design includes longitudinally movable seed regions containing the U.sup.235 and U.sup.238 which are surrounded by Pu.sup.239 -Th.sup.232 blanket regions. The seed material is capped with natural UO.sub.2 and the blanket fuel with Th.sup.232 O.sub.2 to reduce neutron leakage. |
summary | ||
description | This application claims the benefit of U.S. Provisional Application No. 61/185,887 filed Jun. 10, 2009. U.S. Provisional Application No. 61/185,887 filed Jun. 10, 2009 is incorporated herein by reference in its entirety. In a pressurized water reactor (PWR) or other type of nuclear reactor, movable control rods are used to control the nuclear reaction. The control rods include a neutron absorbing material, and are arranged to be inserted into the reactor core. In general, the further the control rods are inserted into the core, the more neutrons are absorbed and the more the nuclear reaction rate is slowed. Precise control of the amount of insertion, and accurate measurement of same, is useful in order to precisely control the reactivity. The control rods drive mechanism (CRDM) provides this control. In an emergency, the control rods can be fully inserted in order to quickly quench the nuclear reaction. In such a “scram”, it is useful to have an alternative fast mechanism for inserting the control rods. Additionally or alternatively, it is known to have dedicated control rods that are either fully inserted (thus turning the nuclear reaction “off”) or fully withdrawn (thus making the reactor operational). In such systems, the “on/off” rods are sometimes referred to as “shutdown rods” while the continuously adjustable control rods are sometimes referred to as “gray rods”. Given these considerations, it is known to construct a CRDM employing a lead screw that is engaged by a separable roller-nut assembly. During normal operation, the roller-nut assembly is clamped onto the lead screw by an affirmative magnetic force acting against biasing springs. By turning the roller nut the lead screw, and hence the attached control rods, are moved in precisely controllable fashion toward or away from the reactor core. In a scram, the electrical current is cut thus cutting the magnetic force, the biasing springs open the separable roller nut, and the gray rod including the lead screw scrams. An example of such a configuration is disclosed, for example, in Domingo Ricardo Giorsetti, “Analysis of the Technological Differences Between Stationary & Maritime Nuclear Power Plants”, M.S.N.E. Thesis, Massachusetts Institute of Technology (MIT) Department of Nuclear Engineering (1977) which is incorporated herein by reference in its entirety. For an integral pressurized water reactor (integral PWR), it is known to mount the CRDM externally and to couple with the control rods inside the pressure vessel by suitable feedthroughs. To reduce the extent of feedthroughs, it has also been proposed to integrate the CRDM within the pressure vessel. See, for example, Ishizaka et al., “Development of a Built-In Type Control Rod Drive Mechanism (CRDM) For Advanced Marine Reactor X (MRX)”, Proceedings of the International Conference on Design and Safety of Advanced Nuclear Power Reactors (ANP '92), Oct. 25-29, 1992 (Tokyo Japan) published by the Atomic Energy Society of Japan in October 1992, which is incorporated herein by reference in its entirety. Existing CRDM designs have certain disadvantages. These disadvantages are enhanced when an internal CRDM design is chosen in which the complex electro-mechanical CDRM is internal to the high pressure and high temperature environment within the pressure vessel. Placement of the CRDM internally within the pressure vessel also imposes difficult structural challenges. The separable roller-nut creates a complex linkage with the lead screw that can adversely impact gray rod insertion precision during normal operation. Reattachment of the roller-nut to the lead screw can be complex, and it may not be immediately apparent when contact is reestablished, thus introducing a positional offset after recovery from the scram event. Scramming the lead screw also has the potential to cause irrecoverable damage to the threading or structural integrity of the lead screw. Still further, wear over time can be a problem for the complex separable roller-nut. Another consideration is reliability. Because rod scramming is a safety-critical feature, it must operate reliably, even in a loss of coolant accident (LOCA) or other failure mode that may include interruption of electrical power, large pressure changes, or so forth. The control rod position detector is also typically a complex device. In some systems, an external position detector is employed, which requires feedthroughs across the pressure vessel wall. For the internal CRDM of the MRX reactor, a complex position detector was designed in which a transducer generates a torsional strain pulse that passes through a magnetoresistive waveguide, and magnetic field interactions are measured to adduce the rod position. In general, an internal position detector operating on an electrical resistance basis is prone to error due to temperature-induced changes in material resistivity. In one aspect of the disclosure, a control rod mechanism for use in a nuclear reactor, the control rod mechanism comprises: a control rod configured for insertion in a reactor core to absorb neutrons; a connecting rod connected with the control rod; a drive mechanism including a lead screw engaged with a motor-driven nut such that rotating the nut causes linear translation of the lead screw; and a latch operatively connecting the connecting rod to move together with the lead screw, the latch opening responsive to a loss or removal of electrical power to detach the connecting rod from the lead screw. In another aspect of the disclosure, a control rod control method comprises moving a control rod linearly using a lead screw and, responsive to a scram, detaching the control rod from the lead screw whereby the control rod scrams but the lead screw does not scram. In another aspect of the disclosure, a nuclear reactor comprises: a reactor core; a pressure vessel including a lower vessel section containing the reactor core, an upper vessel section disposed above the reactor core and above the lower vessel section, and a mid-flange located above a reactor core and disposed between the lower vessel section and the upper vessel section; and an internal control rod drive mechanism (CRDM) supported by the mid flange. In another aspect of the disclosure, a control rod drive mechanism (CRDM) for use in a nuclear reactor comprises: a connecting rod connected with at least one control rod; a lead screw; a drive mechanism configured to linearly translate the lead screw; an electromagnet coil assembly; and a latching assembly that latches the connecting rod to the lead screw responsive to energizing the electromagnet coil assembly and unlatches the connecting rod from the lead screw responsive to deenergizing the electromagnet coil assembly. 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 helical steam generators 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. One suitable configuration includes a stainless steel core former structure that contains the fuel assemblies and is replaceable in order to refuel the reactor, and which is supported by the lower vessel. The illustrative upper vessel 26 houses the steam generators 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. A cylindrical inner shell or upper flow shroud 30 separates a central riser region 32 from an annular down-corner region 34 in which the helical steam generators 14 are located. The illustrative steam generator 14 is a helical coil design, although other designs are contemplated. Primary reactor coolant flows across the outside of tubes of the steam generator 14 and secondary coolant flows inside the tubes of the steam generator 14. 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 down-corner 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. It is also contemplated for the vessel head to be integral with the upper vessel 26, in which case the steam generator 14 and upper shroud 30 are optionally supported by lugs on the inside of the vessel head. The illustrative embodiment is an integral PWR in that it includes the internal steam generators 14, which in general may have various geometric configurations such as helical, vertical, slanted, or so forth. For the purpose of redundancy, it is generally advantageous to have more than one steam generator, whose pipes or tubes are typically interleaved within the downcomer region 34 to facilitate thermal uniformity; however, it is contemplated to include only a single steam generator. Although the illustrative steam generators 14 are shown disposed or wrapped proximate to the shroud 30, in general the steam generators may fill a substantial volume of the down-corner region 34, and in some embodiments the steam generators may substantially fill the annular volume between the outer surface of the shroud 30 and the inside surface of the pressure vessel 10. It is also contemplated for the internal steam generators or portions thereof to be disposed in whole or in part in the riser region 32, above the shroud 30, or elsewhere within the pressure vessel 10. On the other hand, in some 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, the upper internals section 24 in greater detail. In the illustrative design the upper internals section 24 provides support for control rod drives or drive mechanisms 40, 42 and control rod guide frames 44 and is also the structure through which control rod drive power and control instrumentation signals pass. This allows the upper vessel 26 and integral steam generator 14 to be removed independently of the control rod drives and associated structure. However, a more integrated design is also contemplated, such as using a common section for both the CRDM support and the integral steam generator support. With particular reference to the illustrative embodiment of FIG. 2, the upper internals structure 24 includes an upper internals basket 46, a CRDM support structure 48, control rod guide frames 44, and the control rod drive mechanisms 40, 42 themselves. The upper internals basket 46 is suitably a welded structure that includes the mid-flange 29 and the support structure for the control rod guide frames 44. In one suitable embodiment, the control rod guide frames 44 are separate 304L stainless steel welded structures that are bolted in place, the mid-flange 29 is a SA508 Gr 4N Cl 2 carbon steel forging, and the balance of the structure is 304L stainless steel. The CRDM support structure 48 includes support lattices for the control rod drives 40, 42 and guide structure for the in-core instruments. All of these are suitably 304L stainless steel. The CRDM support structure 48 is bolted to the upper internals basket 46. These are merely illustrative materials and construction, and other configurations and/or reactor-compatible materials are also contemplated. The illustrative example of FIG. 2 employs two types of control rod drives 40, 42: a hydraulic control rod drive type 42 that operates the shutdown rods which are either fully withdrawn or fully inserted into the core; and an electrical control rod drive type 40 that operates the gray rods which are inserted various amounts throughout the life of the core to control the nuclear reaction rate during normal reactor operation. The gray rods are also configured to scram, that is, to be rapidly inserted into the reactor core 12, during certain emergency conditions. In other embodiments, it is contemplated to omit the shutdown rods entirely in which case the gray rods also provide shutdown operation. With continuing reference to FIG. 2 and with further reference to FIGS. 3-5, aspects of the shutdown rods are illustrated. The shutdown rods are suitably arranged in clusters mounted on spiders or the like that are all operated in single bank and are all moved by a single shutdown rod drive 42. FIGS. 3-5 show only the single shutdown rod drive 42, but not the spiders and individual shutdown rods. This configuration is cognizant of the fact that the shutdown rods are used in a binary “on/off” manner, and are either all wholly inserted into the reactor core 12 in order to shut down the reaction, or are all wholly withdrawn from the reactor core 12 in order to allow normal reactor operation. With particular reference to FIG. 3, the shutdown rod drive 42 includes a cylinder housing 50, a cylinder cap 52, a cylinder base plate 54, and a connecting rod 56 providing connection to the shutdown rod lattice (not shown). The illustrative shutdown rod drive 42 of FIGS. 3-5 is a hydraulically actuated drive using reactor coolant inventory clean-up return fluid from high pressure injection pumps at approximately 500° F. (260° C.) and 1600 psi to hold the shutdown rod bank out of the reactor core 12. With particular reference to FIG. 4, a sectional view of the piston region with the rod in the withdrawn position is shown. In an enlarged portion of FIG. 4 a vent port 60 of the cylinder cap 52 is shown, together with a lift piston 62, piston rings 64 (which in some embodiments are metallic), a scram buffer 66, and a buffer cocking spring 68. The withdrawn position shown in FIG. 4 corresponds to the shutdown control drive cylinder 42 being pressurized. With particular reference to FIG. 5, a sectional view of the piston region with the rod in the inserted position is shown. An enlarged portion of FIG. 5 shows the lift piston 62, the piston rings 64, the scram buffer or scram buffer piston 66, a rod guide bushing 70, and rod sealing rings 72 (which in some embodiments are metallic). The cylinder base plate 54 is seen in the enlarged portion to include a pressure port or inlet port 74. The inserted position shown in FIG. 5 corresponds to the shutdown control drive cylinder 42 being unpressurized. In some embodiments, the coolant is allowed to bleed past the piston and shaft seals 64, 72 and becomes part of the inventory returned to the reactor vessel 10. The shutdown rod drive cylinder 42 is mounted above the reactor core 12. A hydraulic line (not shown) to actuate the cylinder 42 is routed through the flange 29 and instrument lines are routed through pressure tight conduit to common connectors that are also optionally used for the gray rod drives 40. The extension rods that connect the control rod spiders to the shutdown rod lattice are optionally designed so that they will slide through the lattice so that a single stuck cluster will not prevent the other sets of control rods from dropping. Additionally, the extension rods are designed to be disengaged from the control rod spider so that the shutdown rods remain in the core when the upper internals 24 are removed. Disengagement and reengagement is done using remote tooling at during refueling operations. During normal reactor operation, the shutdown rods are suspended completely out of the reactor core (that is, in the withdrawn position) by pressurization of the shutdown rod hydraulic cylinder 42. For example, in one suitable embodiment coolant inventory clean-up return fluid from the high pressure injection pumps is supplied at 500° F. (260° C.) and 1600 psi to the underside of the lift cylinder piston 62, via the inlet port 74 of the cylinder base 54. In this example, the fluid present in the cylinder 50 above the piston 62 is supplied from the reactor vessel 10 through the cylinder cap vent port 60, and is therefore at the reactor vessel conditions of 600° F. (315° C.) and 1500 psi, resulting in a net 100 psi pressure differential across the piston 62. Piston sizing is selected such that the developed pressure differential is sufficient to support the specified load of the shutdown rods and supporting spiders and other associated components and lift the shutdown rod bank through the cylinder stroke to the top stop of the piston 62. In the event of a vessel-pressurized scram, the shutdown rod bank is abruptly released by ceasing the supply of pressurized coolant to the bottom side of the lift piston 62 and venting the supply line to atmospheric pressure. In the aforementioned example the vessel pressure at the top surface of the lift piston 62 is expected to create an initial 1500 psig pressure differential across the lift piston, which acts along with the influence of gravity to propel the translating assembly (including the lift piston 62, scram buffer piston 66, cocking spring 68, connecting rod 56, and shutdown rod lattice (not shown) downward toward the full insertion position illustrated in FIG. 5. During the descent of the translating assembly, the force of the buffer cocking spring 68 holds the buffer piston 66 out of the bore of the lift piston 62, preserving a fluid-filled buffer cavity between the two pistons 62, 66. When the bottom surface of the buffer piston 66 impacts the fixed base plate 54 of the cylinder assembly, the continued travel of the lift piston 62 expels the trapped fluid through controlled flow restrictions, thereby dissipating the kinetic energy of the translating assembly. Additionally, kinetic energy is dissipated through elastic deformation of the translating assembly components, especially the long, relatively slender, connecting rod 56. Other kinetic energy dissipation mechanisms are also contemplated. When the fluid is expelled from the cavity, the lift piston 62 impacts the buffer piston 66, bringing the translating assembly to rest. With continuing reference to FIGS. 1 and 2 and with further reference to FIGS. 6-14, an illustrative embodiment of the gray rods and associated drive mechanisms 40 is described. As seen in FIG. 6, in the illustrative embodiment there are two different gray rod configurations (Type 1 and Type 2). The gray rods 80 are arranged as gray rod clusters, which in turn are yoked together in groups of two or four and supported by connecting rods 82 as shown in FIG. 6. The configuration Type 1 also includes a counterweight 84 in place of one connecting rod/cluster unit. More particularly, a yoke 86 connects two connecting rods 82 and the counterweight 84 to form a configuration of Type 1. A yoke 88 connects three connecting rods 84 to form a configuration of Type 2. The gray rod drives 40 are mounted above the reactor core 12. FIG. 7 shows a plan view of the locations of the gray rod drives 40 and of the shutdown rods lift cylinder 50, respective to the CRDM support structure 48. The shutdown rods lift cylinder 50 is centrally located. Four outboard gray rod drives 40, each moving two rod configurations of Type 1 including yokes 86, move simultaneously. Two inboard drives 40, each moving four rod configurations of Type 2 including yokes 88, move simultaneously. These different sets of drives 40 optionally move together or independently. Power and signal connections are suitably routed through a pressure tight conduit or in-core instrumentation guide 90 to connectors on the mid-flange 29 (not shown in FIG. 7). As with the shutdown rods, the extension rods that connect the control rod spiders to the rod lattice are optionally designed so that they will slide through the lattice so that a single stuck cluster will not prevent the other sets of control rods from dropping. Additionally, the extension rods are optionally designed to be disengaged from the control rod spider so that the gray rods can remain in the core when the upper internals are removed or be removed while the upper internals are on their support stand. Two suitable design styles for the gray rod control mechanism include the “magnetic jack” type and the “power screw” type. Of these, the power screw type is expected to provide more precise position control for the gray rod clusters, and With reference to FIG. 8, in one illustrated embodiment the gray rod control mechanism 40 employs a ball nut lifting rod configuration. FIG. 8 shows both the fully inserted state (left-side drawing) and fully withdrawn state (right-side drawing). The drawings of FIG. 8 show the yoke 88 of the Type 2 configuration; for the Type 1 arrangement the yoke 88 is replaced by the yoke 86. In the embodiment shown in FIG. 8, a bottom stop/buffer assembly 100 is mounted on a reactor support 101, optionally with additional lateral support provided for the electromagnet coil assembly. Lower and upper support tubes 102, 104, which mount to the top of the bottom stop 100, provide the guidance for the lead screw/torque taker assembly. A ball nut/motor assembly 106 mounts on top of the upper support tube 104 and an electromagnet coil assembly 108 mounts to the top of the motor. Within the electromagnet coil assembly 108 resides a lifting rod-to-lead screw latching assembly 110 that (when latched) supports a lifting/connection rod assembly 112 (seen extended in the inserted state, i.e. left-side drawing). A position indicator assembly is mounted to the support tubes 102, 104 between the ball nut/motor assembly 106 and the bottom stop assembly 100. In some embodiments, the position indicator is a string potentiometer suitably mounted below the latching assembly 110, although other mounting locations are contemplated. The illustrated string potentiometer includes a tensioned spool 120 mounted on the support tube 102 and a “string” or cable or the like 122 having an end attached to the lifting/connection rod assembly 112 such that the string or cable 122 is drawn off the spool 120 against the tension as the lifting/connection rod assembly 112 (and, hence the attached gray rod clusters) move toward the reactor core 12 (not shown in FIG. 8). When the motion is reversed, the tension in the tensioned spool 120 causes the string or cable 122 to roll back onto the spool 120. A rotational sensor 124 measures the rotation of the tensioned spool 120 using an encoder that counts passage of fiducial markers or another rotational metric. The mounting of the string potentiometer can be otherwise than that illustrated, so long as the tensioned spool 120 is mounted at a location that does not move with the gray rods and the string or cable 122 is secured to move with the gray rods. It is also contemplated to integrate the rotational sensor 124 with the tensioned spool 120. The string potentiometer provides an electrical output signal consistent with the location of the connecting rod or other component 112 that moves with the gray control rod, thus providing positional information for the gray control rods within the reactor core 12. The electrical position indication signal is conveyed out of the reactor vessel 10 through an electrical feedthrough (not shown), which can be made small and/or integrated with other electrical feedthroughs. The position indicator device is configured and calibrated for operation at reactor vessel temperature and radiation level. With continuing reference to FIG. 8 and with further reference to FIGS. 9-14, in the illustrated embodiment the translating assembly of the gray rod CRDM 40 includes three elements: a lead screw/torque taker assembly; a lifting rod/connecting rod assembly; and a latching system that operatively connects the lifting rod with the lead screw. FIG. 9 shows the lead screw/torque taker assembly in perspective (left side) and sectional (right side) views. A motor assembly includes a stator housing 130 housing a stator 132 and a rotor 134. An upper stator end plate 136 and a radial bearing 138 with adjustable spacer 140 complete an upper portion of the motor assembly, while a lower housing 142 and a thrust bearing 144 complete a lower portion of the motor assembly. A lower ball-nut assembly 150 disposed within the lower housing 142 is threaded to the rotor 134, and an upper ball nut assembly 152 is also threaded to the rotor 134. Both ball-nut assemblies 150, 152 are coupled in threaded fashion with a lead screw 160 (shown in part in FIG. 9). FIG. 9 further shows portions of the lifting rod 112 and the upper support tube 104. With reference to FIG. 10, the latching system is illustrated, including the lifting rod-to-lead screw latching assembly 110 and a portion of the electromagnet coil assembly 108. Also shown in FIG. 10 are an end 111 of the lifting rod 112 and a proximate end of the lead screw 160 terminating at or in the latching assembly 110. Latches 170 directly connect the top end 111 of the lifting rod 112 to the lead screw 160 for normal operation, and disconnect the lifting rod 112 during scram (see FIG. 11). The bottom of the lifting rod 112 is threaded to the top of the connecting rod 82 (optionally by the intermediary yoke 86 or intermediary yoke 88) thereby creating a continuous lifting rod/connecting rod assembly. The bottom of the connecting rod 82 couples directly to the control rod spiders thereby attaching the control rods to the mechanism. Optionally, a magnet 113 is disposed proximate to the top 111 of the lifting rod 112 to provide a magnetic signal for a magnetically-based position indicator (see FIG. 21). FIG. 10 also shows a portion of the motor including portions of the motor housing 130, stator 132, and rotor 134, which is shown in full in FIG. 9. The latches 170 are housed in a latch housing 172 that includes a spring guide for a latch spring 174. Additional components of the illustrated latching system embodiment include an electromagnet housing 176 housing electromagnets 177 forming an electromagnet coil stack, and permanent magnets 178 on the latches 170. The lead screw 160 is threaded into a latching system base 179 of the latch housing 172. The latches 170 are arranged to pivot about pivot locations 180 to provide a failsafe scram due to downward rod load. In this embodiment, the lead screw 160 is continuously supported by a ball nut motor assembly (best seen in FIG. 9) which allows for very fine control of lead screw position and consequently very fine control of the position of the control rod assembly. In the illustrated embodiment, the motor (e.g., stator 132, rotor 134) is a synchronous motor in which the rotor 134 is a permanent magnet. This design has advantages such as compactness and simplicity; however, other motor configurations are also contemplated. The lead screw 160 does not scram. Instead, during a scram the top end of the lifting rod 112 of the lifting rod/connection rod assembly is disconnected from the lead screw 160 by the magnetically activated latching system (see FIG. 11). When power is cut to the electromagnets 177 the failsafe latching system releases the lifting/connection rod assembly (and thus the control rod assembly) from the lead screw 160 thereby initiating a scram. A bottom stop and buffering system (not illustrated, but suitably similar to the bottom stop and buffering system of the illustrative shutdown rods described herein with reference to FIGS. 4 and 5) is incorporated into the base/buffer assembly to dissipate the kinetic energy at the end of the scram stroke and to set the rod bottom elevation. A torque taker (not shown) is attached to the lead screw 160 to react the motor torque thereby providing translation of the lead screw/control rod assembly. The normal state, that is, the state prior to scram, is shown in FIGS. 9 and 10. FIG. 9 illustrates the ball nut motor assembly and FIG. 10 shows the latching system engaged for normal operation. As seen in FIG. 10, the permanent magnets 178 on the latches 170 are magnetically attracted toward the powered electromagnets 177 thus pivoting the latches 170 about the pivot locations 180 and engaging the latches 170 with a mating region of the lifting rod 112. Thus, the latches 170 are secured with the lifting rod 112 in the normal state shown in FIG. 10. Further, the latching system base 179 is threaded to or otherwise secured with the lead screw 160. Accordingly, in the normal state of FIG. 10 the lifting rod 112 is secured with the lead screw 160 via the latching system, and so as the ball nut motor assembly shown in FIG. 9 translates the lead screw 160 the lifting rod 112 is translated with the lead screw 160. Scram is described with reference to FIG. 11, which shows the lifting rod 112, and consequently the control rod assembly, during a scram. To initiate scram the power to the electromagnets 177 is cut, that is, turned off. This removes the attractive force on the permanent magnets 178 on the latches 170, and the latch spring 174 extends to pivot the latches 170 about the pivot locations 180 and away from the mating region of the lifting rod 112. This disengages the latches 170 from the lifting rod 112, and the lifting/connection rod assembly (and thus the control rod assembly) falls toward the reactor 12. The lead screw 160 is seen in FIG. 11 still at the previous withdrawal height (that is, the lead screw 160 is not scrammed), but power to the electromagnet coils 177 has been cut so that the magnetic field from the coils is removed. As further shown in FIG. 11, the pivoting of the latches 170 about the pivot locations 180 is stopped by impingement at a location 181 with the spring guide of the latch housing 172. With continuing reference to FIG. 11 and further reference to FIGS. 12 and 13, to re-engage the mechanism after a scram, the lead screw 160 is driven to the fully inserted position via the ball nut motor (see again FIG. 9). A lead screw on-bottom sensor is used to confirm lead screw full insertion. With particular reference to FIG. 12, as the lead screw 160 nears the fully inserted position an angled camming surface 182 on the top 111 of the lifting rod 112, which is scrammed to the bottom, will cam the latches 170 to their near full out position. With particular reference to FIG. 13, when power is restored to the electromagnets 177, the latches 170 will fully re-engage with the mating region of the lifting rod 112 so that the lifting/connection rod assembly is once again connected to the lead screw 160. Normal operation can then resume as per FIG. 10. To reiterate, FIG. 12 shows the lead screw 160 being driven back down to the fully inserted position in preparation for re-engagement of the lifting rod 112. Power to the electromagnet coils 177 is still cut and the latches 160 are still disengaged. The angled camming surfaces 182 on the top 111 of the lifting rod 112 are camming the latches 170 back into partial engagement with the top 111 of the lifting rod 112. FIG. 13 shows the lead screw 160 still on bottom but with the power restored to the electromagnet coils 177. The restored magnet field has now re-engaged the latches 170 with the mating region of the lifting rod 112. FIG. 9 diagrammatically shows a suitable embodiment of the ball nut/motor assembly 106, including lower and upper ball nut assemblies 150, 152. In general, substantially any type of motor can be used, suitably configured for operation in the pressure vessel environment. With reference to FIGS. 14 and 15, an illustrative embodiment is shown which employs a brushless DC electronically controlled (BLDC) motor 184 with lower ball nut assembly 185. The assembly 184, 185 is an illustrative embodiment of the ball nut/motor assembly 106. With particular reference to FIG. 14, the illustrative BLDC motor 184 includes a wound stator core assembly 186 disposed between a stator outer shell 187 and a stator inner shell 188 and secured by a stator upper housing 189 and stator lower housing 190. A permanent magnet rotor 191 includes permanent magnets 192. The BLDC motor 184 produces torque from interaction of magnetic flux of the rotor magnets 192 and the current carrying stator conductors of the stator core assembly 186. The lower ball nut assembly 185 is analogous to the lower ball-nut assembly 150 of FIG. 9; however, in the illustrative assembly of FIG. 14 there is no upper ball-nut assembly corresponding to the upper ball nut assembly 152 of FIG. 9. The assembly of FIG. 14 also includes a radial bearing 193, a thrust bearing 194 secured by a thrust bearing lock nut 195, and a motor top cap 196. An insulated and environmentally robust electrical connection to the motor is provided by a lead wire gland 197. For example, some suitable insulated lead wire glands are available from Conax® Technologies (Buffalo, N.Y., USA). With particular reference to FIG. 15, the BLDC motor 184 and lower ball-nut assembly 185 are illustrated in the context of the control rod drive mechanism (CRDM) of FIGS. 10-13. The illustrative CRDM of FIG. 15 also includes the previously described electromagnet coil stack assembly 177, lifting rod-to-lead screw latching assembly 110, lead screw 160, and lifting rod 112. The ball-nut assembly 185 engages the lead screw 160 so that, as the motor 184 rotates the permanent magnet rotor 191 and the secured ball-nut assembly 185, the lead screw 160 is driven linearly. With returning reference to FIGS. 1 and 2, an advantage of the disclosed reactor design is that the middle section includes the internals support flange or “mid-flange” 29. This section can be made relatively thin, and provides support for the control rod drive mechanism and guides for the in-core instrumentation. This section provides electrical and hydraulic inputs for the control rod drive mechanisms (CRDMs). A reactor coolant drain penetration (not illustrated) is optionally also incorporated in this section. This drain line, if incorporated, is optionally isolated by an internal valve whenever the reactor is pressurized to limit or eliminate its potential as a loss of coolant accident (LOCA) site. The illustrated upper internals 24 including the CRDM do not include illustrated thermal insulation. However, it is contemplated to insulate these components using an insulation system capable of withstanding a design temperature of at least about 650° F. (343° C.). By using the insulation system, external cooling water will not be required although may optionally also be used. For example, cooling water can be supplied to the electrical devices to reduce the severity of the heat duty imposed by the operating environment. The insulation system facilitates locating the electrical CRDM within the pressure vessel, which reduces the overall height of the reactor vessel 10, significantly reduces the number of penetrations into the reactor vessel 10, and enables a complete reactor module to be shipped as a single unit. Another advantage is reduction of the overall height of the containment structure (not shown). Although the use of insulation is believed to be advantageous, other contemplated solutions include the use of water cooling and/or selecting materials capable of withstanding the high operating temperature without insulation. The illustrative reactor embodiment is an integral pressurized water reactor (PWR) configuration. However, one or more of the disclosed techniques, apparatuses, or so forth are also expected to be suitably used in other types of nuclear reactor vessels, such as boiling water reactors (BWRs) that can advantageously incorporate internal CRDM assemblies, efficient control rod position sensors, and so forth. The preferred embodiments have been illustrated and described. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. |
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041636899 | description | The device of this invention is adaptable for use in any solid fissile fuel element for a nuclear reactor; however, it is particularly adaptable for use in a Thermionic Nuclear Reactor as described in copending application Ser. No. 347,320 filed Feb. 25, 1964. In fuel elements operating at very high temperatures in the range of 1600.degree. C. to 2500.degree. C., i.e., at temperatures just below the melting point of the fuel, e.g., uranium oxide or the like, the gaseous and volatile fission products tend to migrate within the fuel mass toward areas of higher temperature. In nuclear fuel bodies which do not provide for central cooling, the temperature of the fuel increases as the center of the mass, generally corresponding to the center of gravity of the fuel, is approached because of the bulk heat source nature of the fuel. This migration occurs in uranium oxide and other uranium-plutonium bearing fuels having high volubility and characteristics. It has now been found that a void is formed in the center of such a solid fuel body into which the gaseous and volatile fission products migrate and collect. More specifically, at temperatures above about 1600.degree. C. in UO.sub.2 for example, nucleation of gases into bubbles or "pores" occurs, which "pores" or bubbles migrate along the thermal gradient to the region of highest temperature. Accordingly, the migratory bubbles accumulate at the hottest part of the fuel mass, i.e., the center in solid cylindrical, prismatic or other solid rod shape to form a void of significantly larger size than the individual bubbles. Thus, there is produced not only a temperature gradient radially decreasing from the center of the fuel mass but also a gaseous pressure gradient which pressure is higher in the center of the fuel mass than at the outer margins created by the migratory tendency of the gas and gas-like molecules. Thus, it can be seen that a port or vent in the fuel element cladding which communicates merely with the space between the cladding and fuel body will not be sufficient to remove all gaseous and volatile fission products due to the tendency of the gas molecules to flow away from the cooler cladding. In practice, such an arrangement would require the gases not only to filter through the fuel itself but also to overcome the effective back pressure due to migration of the gas molecules away from the cladding. It is this phenomena of migration that is utilized by the fuel vent of this invention to effectively remove all gaseous and volatile fission products as soon as possible after they are generated as set forth hereinafter. Referring to FIG. 1, there is disclosed a typical emitter of a nuclear fuel thermionic cell utilizing this invention comprising an outer cladding 10 of a material suitable for high temperature thermionic reactor use as an emitting surface for electrons having end caps 11 and 12 and containing fissile fuel mass or body 13. The fission product vent of this invention as utilized in the above fuel cell, comprises conduit 14 penetrating the center of end cap 11 and affixed and sealed thereto as by welding, brazing or the like and extending axially to the center of fissile fuel body 13. Proximate the lower end of conduit 14 distal the end affixed to end cap 11 is vent cap 15 affixed as by welding, brazing or the like and having vent hole 16 in the center thereof and of a diameter smaller than the inside diameter of conduit 14. Vent cap 15 may also be formed by swaging or the like, to reduce the end of conduit 14 to a smaller diameter equal to the diameter of vent hole 16. It will be appreciated that such fuel cells, when disposed in a thermionic nuclear reactor, may be coupled to an exterior gas disposal system (not shown) by means of appropriate conduits or other equivalent gas transport fixtures therein, which connect to conduits 14. Also when used in a thermionic nuclear fuel element comprising a plurality of such individual thermionic cells, such as those described in copending application Ser. No. 347,320, supra, upper pins 40 and lower pins 41 are provided on end caps 11 and 12 respectively of the emitter of the instant invention to maintain the emitter in a spaced apart relationship from adjacent collector surfaces (not shown). Such pins or other like connectors provide electrical contact between adjacent emitters (not shown) and collectors (not shown) all as described in the aforesaid copending application. Although a central void will form during reactor operation, due to phenomena discussed above, it is preferable during assembly of the fuel cell to leave or form a small void space 17 circumjacent end cap 15 and vent hole 16 to prevent plugging of said hole 16 by any loose granules of the fissile fuel. Typical fuel bodies 13 can be fabricated by compaction of granular UO.sub.2 or similar ceramic fissile materials by conventional means. In any event, after a sufficient period of operation in which fission product gases and volatiles have migrated toward the center of the fuel cell, a natural void 17 will be formed and act as a plenum for collection of said gases and volatiles in the event a central void is not initially provided. Referring to FIG. 2, during operation of a typical fuel cell containing UO.sub.2, a typical fissile fuel in a typical thermionic nuclear reactor, a temperature gradient increasing radially toward the center of the fuel mass 13 will develop due to the heat generation within the fuel coupled with the poor thermal conductivity of the fuel. Isothermal lines 18 are illustrative of the typical temperatures found within the fuel mass. A gas bubble 20 generated near the periphery of the fuel mass will migrate to the higher temperature regions in the direction of the arrows until it reaches central void 17. Due to greater pressure of gases within the fuel cell, they will then pass through hole 16 (FIGS. 1 and 3) in conduit end cap 15, through conduit 14 and out to the space between the collector and emitter or to other conduit systems (not shown) for disposal outside the reactor. Although molten fuel is sometimes considered desirable from the standpoint of fission gas release in connection with various prior art nuclear fuel elements, it must be noted that the migration phenomenon utilized in the present invention operates only when the fuel is below its melting point; otherwise the molten fuel will reacto to forces of gravity or acceleration and may penetrate into the vent tube 14. The maximum gas bubble migration tendency is produced with the establishment of the greatest differential temperature gradients and as the maximum central temperature approaches the melting point of the fuel material. To reduce the possibility of inadvertently operating at temperatures above the melting point of the fuel, FIG. 3 illustrates an embodiment wherein the fissile fuel is fabricated in the form of wafers 33 having a central hole 34 stacked with metal disks 35 having central hole 36 sandwiched between each of said wafers. In operation, metal disks 35 act as thermal conductors carrying the heat away from the center portion of the fuel cell thus reducing the temperature difference between central void 17 and cladding 10. It should be noted that the diameter of central hole 36 in metal disk 35 must be slightly larger than the outside diameter of conduit 14 in order to allow for fission product gases to pass by the barrier formed by disks 35 to reach central void 17. To facilitate migration of gas particles across metal disk 35, said disk may possess a plurality of perforations. In addition, because of the high temperatures encountered disks 35 must be fabricated out of a high temperature refractory metal such as tungsten, rhenium, molybdenum or the like or an alloy of same. The metal conductors or fins may be embedded in the fuel in any geometry which does not block bubble migration to the center. The use of the above thermally conductive devices will permit a higher emitter cladding surface temperature and thus greater thermionic conversion ability since the central portion can be operated at near melting temperature with a smaller temperature difference between the center of the fuel mass and the cladding. In both embodiments of this invention it is only necessary that fuel in the molten state not be near the vent hole 16 for long periods of time, i.e., one or more hours, to avoid plugging of the vent hole. Although the foregoing embodiments have been described in detail, there are obviously many other embodiments and variations in configuration which can be made by a person skilled in the art without departing from the spirit, scope or principle of this invention. Therefore, this invention is not to be limited except in accordance with the scope of the appended claims. |
056299630 | description | In said FIGS. 1 and 2: 11 shows the storage tank, PA1 12 shows the radioactive fissile material solution stored in the intermediate spaces, PA1 13 shows the tubes containing the neutron absorbing material, PA1 13' shows the vertical metal walls of said tubes, PA1 14 shows said neutron absorbing material PA1 30 shows said schematized homogenizing means PA1 31 shows said cooling means. The tubes 13 are located in compartments distributed throughout the radioactive solution 12. Said compartments are delimited by metal walls 12'. 15 indicates the level of the liquid inside the tank 11. In the preferred variant illustrated, the tubes of neutron absorbing material 13 are located in compartments, thereby defining volumes 20 for circulation by the convection of ambient air. Said circulation is represented diagrammatically by means of arrows in FIG. 1. Said tubes are located on studs 21. The air enters through the orifices 22 created at the base of the tank, said tank being raised. Finally, 23 shows a perforated cover. Said cover serves in particular to stabilize the tubes 13 of neutron absorbing material 14. The value of the tanks of the invention is demonstrated by the data given in the Table below. An annular tank according to the prior art and a tank with an array of tubes according to the present invention have been dimensioned for given volumes of radioactive solution to be stored, and the reductions in required floor space have been calculated. ______________________________________ Diameter of required floor space (reduction) Volume of radio- Array of tubes active solution INVENTION to be stored Annular tank Reduction (m.sup.3) (m) (m) in space ______________________________________ 0.5 2.7 1.9 32% 1 3.3 2.33 50% 2 4.9 2.7 69% 4 6 3 75% ______________________________________ |
summary | ||
046831169 | summary | BACKGROUND OF THE INVENTION This invention relates to the nuclear art and it has particular relationship to nuclear reactors for supplying electrical power. In the interest of safety and reliability, the cost of constructing and installing a nuclear power plant has increased to a high level. In view of the high investment demanded, it is desirable that the economics of the power reactor be such as to moderate the rate structure to the extent practicable. It is accordingly an object of this invention to provide a nuclear reactor for electrical power purpose in whose use and operation material reduction in rates as compared to current reactors shall be obtainable. SUMMARY OF THE INVENTION In reactors in accordance with the teachings of the prior art, the nuclear core of a reactor includes a plurality of fuel assemblies. Each fuel assembly includes a plurality of elongated fuel rods and in addition a plurality of so-called "thimbles" which are essentially tubes. Control rods are moveable into and out of the thimbles of some, but not all, of the fuel assemblies. The thimbles also serve the purpose of securing each fuel assembly into an integrated unit. For this purpose the thimbles are secured to the top and bottom nozzle of each fuel assembly. In prior art reactors, all fuel assemblies, those which receive or guide control rods and those which do not, are alike. They all have thimbles which serve to secure the assembly into an integrated unit. The assemblies which receive control rods are herein referred to as controlled assemblies. The assemblies which do not have control rods are referred to herein as non-controlled assemblies. The controlled assemblies are described as having control-rod or thimble locations or positions and the non-controlled assemblies are described as having non-control-rod locations or positions. This invention arises from the realization that substantial advantages can be achieved by structuring the noncontrolled assemblies differently from the controlled assemblies. The expression control rods as used in this application and in the art in its general sense refers to three kinds of rods: control rods, grey rods and water displacement rods. The rods of the three types are mounted in clusters on a spider. Each control-rod and grey-rod cluster is associated with a separate fuel assembly into whose thimbles the control rods are moveable. The water displacement rods are moveable into thimbles in a plurality of neighboring fuel assemblies. The different rods and their mounting are described in application Ser. No. 715,125 filed Mar. 26, 1985, to Franklin D. Obermeyer and Luciano Veronesi for Nuclear Reactor assigned to Westinghouse Electric Corporation and incorporated herein by reference. This invention concerns itself predominantly with fuel assemblies which receive control rods or grey rods; i.e., with rods each of whose clusters are associated, and penetrate into, a particular fuel assembly. However, fuel assemblies in accordance with this invention may be structured so that they also receive water displacement rods. The fuel-assembly guide-thimble geometry in controlled assemblies is fixed and constricted by the control rod array of the associated clusters. The thimbles in each such assembly must be precisely positioned so that the control rods do not blind as they are moved inwardly and outwardly of the thimbles. Non-controlled assemblies, particularly those which do not receive any rods, are not so constricted thus affording flexibility as to their construction and design. In arriving at this invention it has been realized that while there must be similarities between controlled and non-controlled assemblies, there may be marked differences. Advantage may be taken of these differences to provide an improved reactor. The non-controlled fuel assemblies must be compatible with the controlled assemblies in the following respects. Both types of assemblies: 1. Must have the same pressure gradient along the assemblies (vertically from bottom to top) to minimize cross-flow between assemblies. 2. Must have the same cross-sectional envelope dimensions. 3. Must interface with the upper and lower core plates in the same way. 4. Must interface with the refueling machine gripper in the same way. 5. Must have grids as disclosed, for example, in Andrews U.S. Pat. No. Re. 28,079 and the grids must be located substantially in the same positions along the assemblies. 6. Must meet the same seismic requirements and respond to a loss-of-coolant accident (LOCA) in the same way. The non-controlled assemblies need not be similar to, or compatible with, the controlled assemblies in at least the following respects: 1. The number and spacing of the fuel rods need not be the same. 2. The overall or aggregate length of the fuel rods need not be the same. 3. The guide thimbles are not required in the non-controlled assemblies. 4. The structural members or tie rods in non-control-rod locations, which bind an assembly into an integrated unit, need not include provisions for insertion of control rods so that, for example, their cross-section thickness may be greater than that of thimbles. 5. In non-controlled assemblies, the structural members can be located anywhere in the fuel assembly cross-section and not necessarily in the thimble locations of the controlled assemblies. 6. The number of structural members and the number of fuel rods in non-controlled assemblies need not be the same as the number of thimbles and fuel rods in controlled assemblies. 7. It is not necessary that the top nozzle of a non-controlled assembly accommodate the spider of a control-rod cluster during a scram when rods are fully inserted. Therefore, the vertical length of the top nozzle may be reduced so that longer fuel rods can be accommodated. 8. The top nozzle adapter plate of a non-controlled assembly need not include provisions for attaching hollow guide thimbles. This invention results from evaluation of the above-stated limitations and freedoms. This evaluation has led to the creation of a nuclear reactor whose controlled and non-controlled fuel assemblies are different. Advantage is taken of the above freedoms to provide non-controlled assemblies which endow the nuclear reactor according to this invention with marked advantages over prior-art reactors in which all assemblies are alike. In accordance with this invention, there is provided a nuclear reactor whose non-controlled assemblies have structural members which are hollow tubes or cladding at least certain of which contain burnable neutron absorbers or neutron poison. Typically, the neutron absorbers may be pellets of gadolinium compounds or of borosilicate glass, which may contain a high percentage of boron 10 or boron carbide in a matrix of aluminum oxide (see, for example, application Ser. No. 352,731 filed Feb. 26, 1982 to William G. Carlson et al. for Burnable Neutron Absorbers and assigned to Westinghouse Electric Corporation). The structural member is sealed throughout and protects the neutron absorbers from the coolant and the coolant cannot distribute the poison throughout the reactor. A burnable neutron absorber includes neutron absorber material; e.g. boron or gadolinium, in such low concentration that it burns out in a given time during the fuel cycle. For example, a burnable neutron absorber may burn out during the first year of a three-year cycle. After that, it no longer absorbs neutrons substantially. The burnable neutron absorber is thus effective only during the early part of the cycle when the reactivity of the fuel is high. The neutron-absorber material in control rods on the other hand is in such high concentration that the quantity of material which is converted during the life of the reactor does not materially reduce the effectiveness of the control rods. In the construction of a non-controlled fuel assembly, a skeleton including the bottom nozzle, and the structural members, held together by grids is provided. The structural members have end plugs at the bottom by which they are secured to the bottom nozzle. They are open at the top. The structural members are bulged above and below each grid. Then the neutron absorber pellets and a spring for holding the pellets is inserted in each structural member. After evacuation, heating and back-filling with an inert gas, an end plug is secured to each structural member. The fuel rods are then inserted in the skeleton and the top nozzle is mounted and the structural members secured to it. The thickness of the structural members in the non-controlled fuel assemblies is greater than the thickness of the thimbles which serve as structural members in the controlled assemblies. Typically, a thimble in a controlled assembly, which is a hollow circular cylinder, has an OD of 0.484 inch and an ID of 0.448 inch or a thickness of 0.018 inch, while a structural member of a non-controlled assembly has an OD of 0.484 inch and an ID of 0.423 inch or a thickness of 0.031 inch. There are substantially fewer structural members in the non-controlled assembly than in the controlled assembly. Typically, there are 24 thimbles, 1 instrumentation tube and 264 fuel rods in a controlled assembly having 17.times.17 or 289 total locations. In a non-controlled assembly according to this invention having the same number of locations, there are only 8 structural members and one instrumentation tube. Fuel rods are inserted in the other locations so that there are 304 fuel rods. As far as fuel content is concerned, the effect of increasing the number of fuel rods in the non-controlled assembly is to increase the effective fuel length for the overall assembly by 8.7 inches. The fuel cycle cost is reduced by 1.2%. The KW/ft is reduced by approximately 6% and the pellet-clad interaction (PCI) margin is increased, resulting in improved reliability. The reduction in the KW/ft also increases the margin between the operational flow of coolant and the design limit at which there is overheating. It has been prior-art practice in reactor fuel bundles, which do not include thimbles for control rods, to provide tie rods which are cylinders filled with nuclear fuel. Tie rods of this type have the disadvantage that they grow non-uniformly during operation of the reactor and become disengaged from the nozzles. The structural members, according to this invention, grow more uniformly so that the structural integrity of the non-controlled fuel assemblies remains sound. |
claims | 1. An apparatus for producing a thick flowing liquid metal layer or first wall for a fusion reactor comprising: a toroid having a top, a bottom, an inner toroidal chamber, an inner toroidal wall, and a central toroidal axis about which said toroid is axisymmetric; a series of toroidal magnets each of which surrounds said toroid and creates a confining magnetic field inside said toroid where said field serves to confine a plasma; an entrance means for inputting the liquid metal at said top portion of said toroidal chamber; a plurality of electrodes separated by at least one insulator where said electrodes are positioned so that said liquid metal is electrically coupled to said electrodes and where said electrodes are electrically coupled to a power source which when activated results in the formation of a poloidal current in said liquid metal layer and where said poloidal current flows in the same direction as a current in said toroidal magnets so that said poloidal current interacts with a magnetic field formed by said toroidal magnets to force the liquid metal against said inner wall of said toroid; an exit means located at said bottom of said toroidal chamber where said liquid metal exits said toroidal chamber; a pump coupled to said exit means; a heat extraction and power conversion device where said conversion device is fluidly coupled to said pump and said entrance means. 2. The apparatus of claim 1 wherein said liquid metal is lithium. claim 1 3. The apparatus of claim 1 where said entrance means is two continuous, concentric fluid entry apertures separated by a conductorxe2x80x94insulatorxe2x80x94conductor matrix. claim 1 4. The apparatus of claim 3 where said apertures are axisymmetric about said central toroidal axis. claim 3 5. The apparatus of claim 1 where electrically conductive structures protrude from the inner wall of said toroid and into said liquid metal layer. claim 1 6. The apparatus of claim 5 where said structures are nonsymmetric. claim 5 7. The apparatus of claim 1 wherein said electrodes are approximately perpendicular to said inner wall of said toroid. claim 1 8. The apparatus of claim 1 wherein said electrodes are not approximately perpendicular to said inner wall of said toroid to reduce neutron streaming. claim 1 9. The apparatus of claim 3 where a pair of continuous electrodes of said plurality of electrodes and separated by a continuous insulator are positioned at an upper edge of said entrance means so that the liquid metal streams establish and maintain electrical contact with the electrode as said liquid metal stream enters said toroidal chamber and flows down said inner wall to exit at said bottom of said toroidal cavity, thus, forming a liquid metal conductive link from one electrode to its opposition as separated by said insulator, and where said pair of continuous electrodes and said continuous insulator is axisymmetric about said toroidal axis. claim 3 10. The apparatus of claim 4 wherein a first pair of electrodes, separated by a first insulator, is positioned at an upper edge of said entrance means so that said first electrode pair contacts said liquid metal streams as they flow through said entry apertures on entry to said toroidal chamber and a second pair of electrodes, separated by a second insulator, is positioned at a bottom edge of said exit means so that said second electrode contacts said liquid metal stream as it exits said toroidal cavity and where said first pair and said second pair of electrodes is continuous and axisymmetric about said toroidal axis. claim 4 11. The apparatus of claim 1 in which said exit means is a continuous exit aperture, axisymmetric about said toroidal axis. claim 1 12. The apparatus of claim 10 where said exit means is a pair of concentric apertures positioned near the bottom of the toroidal chamber and where said apertures are axisymmetric about said toroid axis. claim 10 13. An apparatus for producing a thick flowing liquid metal layer or first wall for a fusion reactor comprising: a toroid having a top, a bottom, an inner toroidal chamber, an inner toroidal wall, and a toroidal axis about which said toroid is axisymmetric; a series of toroidal magnets each of which surrounds said toroid and creates a confining magnetic field inside said toroid which serves to confine a plasma; a plurality of entrance means for inputting the liquid metal into said top portion of said toroidal chamber; a plurality of electrodes separated by at least one insulator where said electrodes are positioned so that said liquid metal is electrically coupled to said electrode and where said electrodes are electrically coupled to a power source which when activated results in the formation of a poloidal current in said liquid metal layer and where said poloidal current flows in the same direction as a current in said toroidal magnets so that said poloidal current interacts with a magnetic field formed by said toroidal magnets to force the liquid metal against said inner wall of said toroid; a plurality of exit means located at said bottom of said toroidal chamber where said liquid metal exits said toroidal chamber; a plurality of pumps linking said exit means to said entrance means or to a heat extraction and power conversion device where said conversion device is fluidly coupled to one of said entrance means. 14. The apparatus of claim 13 where said plurality of entrance means are formed by a first pair of entrance apertures where said apertures are continuous and axisymmetric about said toroidal axis and a second pair of entrance apertures where said second pair of entrance apertures are continuous, concentric and are axisymmetric about said toroidal axis and encircle said first pair of entrance apertures so that said second entrance pair are further from said top of said toroid than said first entrance pair. claim 13 15. The apparatus of claim 14 where said plurality of exit means is formed by a first pair of exit apertures where said first pair are continuous and axisymmetric about said toroidal axis and a second pair of exit apertures where said first pair of exit apertures are continuous, concentric and axisymmetric about said toroidal axis and encircle said first pair of exit apertures so that said second pair of exit apertures are further from the bottom of said toroid than said first pair of exit apertures. claim 14 16. The apparatus of claim 15 where a first pair of continuous electrodes of said plurality of electrodes, separated by a continuous insulator, are positioned at an upper edge of said first pair of entrance apertures and a second pair of continuous electrodes, separated by a continuous insulator, are positioned at a bottom edge of said first pair of exit apertures so that a cool liquid metal first layer flows through said first pair of entrance apertures and is in electrical contact with the first electrode pair and a second warm liquid metal streams enters said toroidal chamber through said second pair of entrance apertures and where both streams flow down each side of said toroidal chamber inner wall and where said first layer flows over said second layer with both streams exiting at said bottom of said toroidal chamber at a first pair of exit apertures and a second pair of exit apertures respectively and where said first layer makes electrical contact with said second pair of electrodes, thus, forming a liquid metal conductive link from one electrode to its opposition as linked by said liquid metal and where both pairs of continuous electrodes and both continuous insulators are axisymmetric about said toroidal axis. claim 15 17. The apparatus of claim 15 where said heat extraction and power conversion device links said first pair of entrance apertures to a first pump coupled to said second exit pair aperture and where a second pump links said first pair of exit apertures to said second pair of entrance apertures. claim 15 |
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description | A nuclear reactor includes nuclear reaction control mechanisms, such as control rods and/or control drums, which control the reactivity of the nuclear fuel of the nuclear reactor. For example, in a conventional design, a nuclear reactor may include a plurality of solid cylindrical control drums installed in a reflector region surrounding the core of the nuclear reactor, with a section of the cross-section of each of the control drums containing a neutron absorbing material (e.g., a nuclear reaction poison, etc.), and the rest of the cross-section containing a neutron scattering material (e.g., a nuclear reflecting material, a nuclear shielding material, etc.). A conventional control drum may be constructed of solid materials, such as graphite or beryllium, formed to shape; or packed with neutron absorbing materials in a first radial section of the control drum, and with neutron scattering materials in the rest of the control drum. When the plurality of control drums are in the control position (e.g., with the neutron absorbing section of the control drum facing the reactor core and/or the nuclear fuel rods in the nuclear reactor core), the neutron absorbing material absorbs neutrons emitted from the nuclear reactor core, thereby decreasing the reactivity of the reactor and/or preventing the reactor from reaching a critical state. The control drums in the control position are therefore used to shut down an operating nuclear reactor, or to maintain the nuclear reactor in a shutdown state. When the plurality of control drums are rotated to the operating position (e.g., with the neutron absorbing section facing away from the reactor core and/or the nuclear fuel rods), the neutrons emitted from the nuclear reactor core are not absorbed, and the nuclear reactor is allowed to reach criticality. Therefore, the control drums are in the operating position when the nuclear reactor is in a start-up state, or while the nuclear reactor is operating. However, there are several issues facing the design of conventional control drums. First, conventional control drums are designed to be fabricated from solid neutron absorbing/scattering materials that are formed to specific shapes. It may be difficult to form these materials to the specific desired shapes, and/or the materials, such as beryllium, etc., may be hazardous to work with. This can make the control drum very expensive to produce. Another issue facing conventional control drum designs relates to the physical expansion of the control drum during operating conditions of the nuclear reactor. For example, conventional control drums are typically constructed with stainless steel containment surrounding the neutron absorbing/scattering materials, and these materials, particularly the neutron absorbing/scattering materials within the control drums. may experience thermal expansion due to the heat generated from the nuclear reaction of the nuclear reactor core and/or the radiation absorbed by the materials. This thermal expansion may lead to cracking of the stainless steel containment of the control drum, and the loss/leakage of the neutron absorbing/scattering materials within the control drum. Various example embodiments relate to an improved control drum, as well as systems, apparatuses, and/or methods for operating a nuclear reactor with a plurality of improved control drums. In at least one example embodiment, a control drum for a nuclear reactor may include an outer shell, an inner shell, a plurality of tubes, the plurality of tubes including at least one neutron absorbing tube and at least one neutron scattering tube, and at least one baffle plate arranged between the outer shell and the inner shell, the at least one baffle plate including a plurality of perforations, and at least one perforation of the plurality of perforations configured to support a tube of the plurality of tubes. Some example embodiments of the control drum provide that the plurality of perforations are arranged along at least one ring of the at least one baffle plate, the at least one ring including at least a first sector and a second sector, the first sector including a plurality of neutron absorbing tubes and the second sector including a plurality of neutron scattering tubes. Some example embodiments of the control drum provide that the at least one baffle plate is a plurality of baffle plates, and the plurality of baffle plates are each arranged between the outer shell and the inner shell along a longitudinal direction of the control drum. Some example embodiments of the control drum provide that the at least one perforation of the plurality of perforations includes at least one spring configured to allow for expansion of the corresponding supported tube. Some example embodiments of the control drum provide that the inner shell is configured to mate with a drive shaft via a magnetic coupling, the drive shaft is configured to mate with a drive mechanism, and the drive mechanism is configured to rotate the control drum such that the at least one neutron absorbing tube faces at least one nuclear fuel rod during a first state and the at least one neutron scattering tube faces the at least one nuclear fuel rod during a second state. According to at least one example embodiment, the control drum may further include at least one torsional spring attached to the inner shell, the at least one torsional spring configured to rotate the control drum such that the at least one neutron absorbing tube faces the at least one nuclear fuel rod during a third state. Some example embodiments of the control drum provide that the third state is a fail-safe state where at least one of the magnetic coupling or the drive mechanism has failed. Some example embodiments of the control drum provide that the at least one neutron absorbing tube is configured to store neutron absorbing materials, the neutron absorbing materials having a form of a powder, pellets, or a solid, and the at least one neutron scattering tube is configured to store neutron scattering materials, the neutron scattering materials having a form of a powder, pellets, or a solid. Some example embodiments of the control drum provide that the control drum is horizontally mounted in a reflector region surrounding a nuclear fuel assembly. Some example embodiments of the control drum provide that the control drum is installed in a mobile nuclear reactor. In at least one example embodiment, a nuclear reactor may include a plurality of nuclear fuel rods, a plurality of control drums, each control drum of the plurality of control drums attached to a drive shaft of a plurality of drive shafts, and at least one control drum of the plurality of control drums includes, a plurality of tubes, the plurality of tubes including at least one neutron absorbing tube and at least one neutron scattering tube and at least one baffle plate arranged between an outer shell and an inner shell, the at least one baffle plate including a plurality of perforations, and at least one perforation of the plurality of perforations configured to support a tube of the plurality of tubes, and a plurality of motors attached to the plurality of drive shafts, at least one motor of the plurality of motors configured to rotate the at least one control drum such that the at least one neutron absorbing tube of the at least one control drum faces the plurality of nuclear fuel rods during a first state, and the at least one neutron scattering tube of the at least one control drum faces the plurality of nuclear fuel rods during a second state. Some example embodiments of the nuclear reactor provide that the plurality of perforations are arranged along at least one ring of the at least one baffle plate, the at least one ring including at least a first sector and a second sector, the first sector including a plurality of neutron absorbing tube and the second sector including a plurality of neutron scattering tube. Some example embodiments of the nuclear reactor provide that the at least one baffle plate is a plurality of baffle plates, and the plurality of baffle plates are each arranged between the outer shell and the inner shell along a longitudinal direction of the control drum. Some example embodiments of the nuclear reactor provide that the at least one perforation of the plurality of perforations includes at least one spring configured to allow for expansion of the corresponding supported tube. Some example embodiments of the nuclear reactor provide that the inner shell is configured to mate with the drive shaft, the drive shaft is configured to mate with a drive mechanism, and the drive mechanism is configured to rotate the at least one control drum such that the at least one neutron absorbing tube faces the plurality of nuclear fuel rods during a first state and the at least one neutron scattering tube faces the plurality of nuclear fuel rods during a second state. According to at least one example embodiment, the nuclear reactor may further include at least one torsional spring attached to the inner shell, the at least one torsional spring configured to rotate the control drum such that the at least one neutron absorbing tube faces the plurality of nuclear fuel rods during a third state. Some example embodiments of the nuclear reactor provide that the third state is a fail-safe state where at least one of the magnetic coupling or the drive mechanism has failed. Some example embodiments of the nuclear reactor provide that the at least one neutron absorbing tube is configured to store neutron absorbing materials, the neutron absorbing materials having a form of a powder, pellets, or a solid, and the at least one neutron scattering tube is configured to store neutron scattering materials, the neutron scattering materials having a form of a powder, pellets, or a solid. Some example embodiments of the nuclear reactor provide that the plurality of control drums are horizontally mounted in a nuclear reactor core. Some example embodiments of the nuclear reactor provide that the neutron absorbing materials includes at least one of boron carbide, hafnium, gadolinium, and the neutron scattering materials includes at least one of beryllium, graphite, europium. It should be noted that these figures are intended to illustrate the general characteristics of methods and/or structure utilized in certain example embodiments and to supplement the written description provided below. These drawings are not, however, to scale and may not precisely reflect the precise structural or performance characteristics of any given example embodiment, and should not be interpreted as defining or limiting the range of values or properties encompassed by example embodiments. Some detailed example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the example embodiments set forth herein. Accordingly, while example embodiments are capable of various modifications and alternative forms, example embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the figures. It should be understood that when an element or layer is referred to as being “on,” “connected to,” “coupled to,” or “covering” another element or layer, it may be directly on, connected to, coupled to, or covering the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout the specification. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It should be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of example embodiments. Spatially relative terms (e.g., “beneath,” “below,” “lower,” “above,” “upper,” and the like) may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It should be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” may encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. The terminology used herein is for the purpose of describing various example embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, including those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Also, it is noted that example embodiments may be described as a process depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations may be performed in parallel, concurrently or simultaneously. In addition, the order of the operations may be re-arranged. A process may be terminated when its operations are completed, but may also have additional steps not included in the figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination may correspond to a return of the function to the calling function or the main function. Various example embodiments are directed towards an improved control drum, as well as systems, apparatuses, and/or methods for operating a nuclear reactor with a plurality of improved control drums. The control drum of one or more of the example embodiments may be particularly beneficial for small-scale (e.g., <300 MWe reactors) and/or mobile nuclear reactors because the control drums may be mounted in the nuclear reactor in a horizontal orientation, thereby decreasing the size requirements for the reactor control systems of the nuclear reactor in comparison to conventional control drums which must be mounted in a vertical orientation. The example embodiments may be particularly useful for small, mobile nuclear reactors, such as nuclear power plants for naval vessels, spacecraft, etc., as well as for portable nuclear reactors for transportation to geographic areas that lack access to electricity, such as geographic areas that have been devastated by a natural disaster. Additionally, the control drum of the example embodiments may also provide the additional benefit of accommodating the expansion of the neutron absorbing material and the neutron scattering material from the heat generated by the nuclear reactor and/or from the absorption of radiation generated by the nuclear reactor. Further, the control drum of the example embodiments may also allow a nuclear reactor designer to further fine-tune and/or optimize the distribution of the neutron absorbing materials, thereby improving the performance of the nuclear reactor and the control of the nuclear reactor. FIG. 1 illustrates a side view of a nuclear reactor core including a plurality of control drums according to at least one example embodiment. According to at least one example embodiment, a nuclear reactor core 100 may include a nuclear fuel assembly 110, a plurality of control drums 200, a reflector region 120, and/or a vessel 130, but the example embodiments are not limited thereto. The nuclear reactor core 100 may be used in a gas-cooled nuclear reactor, but the example embodiments are not limited thereto, and the nuclear reactor may be another type of nuclear reactor, such as a boiling water reactor (BWR), pressurized water reactor (PWR), heavy water reactor, breeder reactor, etc. Further, according to some example embodiments, the nuclear reactor may be a mobile nuclear reactor (e.g., a portable nuclear reactor that may be installed on a vehicle, naval vessel, submersible vehicle, spacecraft, etc., and/or may be transported to different locations). In other example embodiments, the nuclear reactor may be used in an immobile and/or large-scale nuclear reactor (e.g., a commercial nuclear power plant, etc.). According to at least one example embodiment, the vessel 130 is a body (e.g., container) which is configured to hold the nuclear fuel assembly 110, the plurality of control drums 200, the reflector region 120, and other structures, such as the coolant pipes (not shown), etc., of the nuclear reactor core, and may be formed from a metal or metal-alloy, such as stainless steel, etc., which does not interact with fission-inducing neutrons and is capable of withstanding the high operating temperatures of the nuclear reactor core. A reflector region 120 may surround the nuclear fuel assembly 110 and may be constructed from a neutron reflecting material (e.g., beryllium, graphite, europium, etc.). The reflector region 120 may reflect (and/or shield) neutrons emitted by the nuclear chain reaction from the nuclear fuel rods 111 back towards the nuclear fuel assembly 110. Additionally, the reflector region 120 may include a plurality of control drums 200. Each of the control drums 200 may include at least one neutron absorbing section (e.g., poison section, etc.) 236 and at least one neutron scattering section (e.g., reflecting section, shielding section, etc.) 237. The control drums 200 may be mounted in a horizontal orientation (e.g., longitudinally, etc.) in relation to the nuclear fuel assembly 110, or in other words the end plates of the control drums 200 are in a horizontal orientation. In other example embodiments, the control drums 200 may be mounted in a vertical orientation (e.g., radially, etc.) in relation to the nuclear fuel assembly 110, or in other words, the end plates of the control drums 200 are in a vertical orientation. The neutron absorbing section 236 of the control drums 200 may include at least one absorbing tube 231 that is longitudinally arranged within the at least one neutron absorbing section 236. The neutron scattering section 237 may include at least one scattering tube 232 that is longitudinally arranged within the at least one neutron scattering section 237. The control drums 200 may each be rotated into various positions, such as a startup position, an operation position, a shutdown position, etc., by a respective control drum drive mechanism, such as a drive shaft 260 and drive mechanism 280. The control drum drive mechanism will be discussed in further detail in connection with FIG. 2A. The neutron absorbing section 236 and the neutron scattering section 237 will be discussed in further detail in connection with FIG. 2C. When the control drums 200 are in the shutdown position, the control drums 200 are rotated such that the neutron absorbing sections 236 of the control drums 200 face towards the nuclear fuel assembly 110, and the neutron scattering sections 237 of the control drums 200 face away from the nuclear fuel assembly 110. While in the shutdown position, the neutron absorbing sections 236 of the control drums 200 absorb the neutrons emitted by the nuclear fuel rods 111, thereby decreasing and/or preventing the nuclear fuel rods 111 from reaching criticality (e.g., a self-sustaining nuclear fission chain reaction). When the control drums 200 are in the startup position, the control drums 200 are rotated such that the neutron absorbing sections 236 face away from the nuclear fuel assembly 110, and the neutron scattering sections 237 face towards the nuclear fuel assembly 110. While in the startup position, the neutron scattering sections 237 of the control drums 200 reflect back any neutrons emitted by the nuclear fuel rods 111, thereby allowing the nuclear fuel rods 111 to reach criticality. However, the example embodiments are not limited thereto, and there may be other positions to which the control drums 200 may be set, such as one or more operational positions, etc. The nuclear fuel rods 111 may contain fissile materials, such as enriched uranium (U-235), plutonium (PU-239), etc. As discussed above, when the neutron absorbing section 236 of the control drums 200 face away from the nuclear fuel assembly 110, the fissile material within the nuclear fuel rods 111 undergo a nuclear fission process. This nuclear fission process generates heat which may be transferred to a gas (e.g., helium, etc.) that is pumping within the heat pipes 112. The heated gas may be used to drive electric turbines (not shown) that generate electricity. According to some example embodiments, the nuclear fuel assembly 110 may further include coolant pipes (not shown) that are used to pump coolant (e.g., water, borated water, a liquid metal, such as NaK, etc., liquid sodium, molten sodium, gases, etc.) into the nuclear fuel assembly 110 to lower the operating temperature of the nuclear reactor core to a desired (safe) temperature. Additionally, according to at least one example embodiment, the nuclear reactor core 100 may further include a secondary control system (not shown) that includes a plurality of control rods (not shown) which may be inserted into the nuclear fuel assembly 110 to further control the nuclear chain reaction (e.g., the reactivity level) of the nuclear fuel rods 111 inside the nuclear fuel assembly 110. While FIG. 1 illustrates an example nuclear reactor core, the example embodiments are not limited thereto. For example, the shape of the nuclear reactor core and/or the elements of the nuclear reactor core (e.g., the control drums, nuclear fuel assembly, vessel, reflector region, fuel rods, heat pipes, etc., may be different from the shapes shown in FIG. 1, and/or the number of each individual element may differ from the amount shown in FIG. 1. For example, the shape of the vessel, nuclear fuel assembly, control drums, etc., may be a square shape, a pentagonal shape, a hexagonal shape, an octagonal shape, etc., and/or the number of control drums, fuel rods, heat pipes, etc., may be greater than or less than the numbers illustrated in FIG. 1. Referring now to FIGS. 2A to 2C, FIG. 2A illustrates an exterior view of a control drum according to at least one example embodiment, FIG. 2B illustrates an interior view of a control drum according to at least one example embodiment, and FIG. 2C illustrates a close-up view of a baffle plate, absorbing tubes, and scattering tubes according to at least one example embodiment. Referring now to FIG. 2A, according to at least one example embodiment, a control drum 200 may include an outer shell 210, an inner shell 220, a plurality of baffle plates 230, and/or a plurality of end plates 240, but the example embodiments are not limited thereto and may include a greater or lesser number of constituent elements. For example, the number of baffle plates may be greater or lesser than the number shown in FIG. 2A. The outer shell 210, the inner shell 220, the plurality of baffle plates 230, and the plurality of end plates 240 may be constructed using a material that does not interact with fission-inducing neutrons, and is capable of withstanding the high operating temperatures of a nuclear reactor core, such as stainless steel, etc., but the example embodiments are not limited thereto. The plurality of baffle plates 230 may be arranged longitudinally between the outer shell 210 and the inner shell 220, and may support at least one neutron absorbing tubes (e.g., neutron poison rods, control rods, etc.) (not shown), and/or at least one neutron scattering tubes (e.g., neutron reflecting rods, shielding rods, etc.) (not shown), but are not limited thereto. The baffle plates 230, neutron absorbing tubes, and neutron scattering tubes will be discussed in further detail in connection with FIGS. 2B and 2C. The control drum 200 may further include two end plates 240 located at each end of the control drum 200. At least one of the end plates 240 may include an interior opening 235 and a torsional spring 250, etc., but the example embodiments are not limited thereto. According to at least one example embodiment, the torsional spring 250 may be located (e.g., installed, attached and/or engaged, etc.) within the interior opening 235 and/or the inner shell 220, but is not limited thereto. The torsional spring 250 may be configured to return (e.g., rotate) the control drum to an control position and/or shutdown position (e.g., where the neutron absorbing section and/or neutron absorbing tubes of the control drum face the nuclear fuel assembly 110 and/or the nuclear fuel rods in the nuclear reactor core) from an operating position (e.g., where the neutron absorbing section and/or neutron absorbing tubes of the control drum face away from the nuclear fuel assembly 110 and/or the nuclear fuel rods). Further, the control drum 200 may be mated to a drive shaft 260 via a magnetic coupling 270 at the interior opening 235, and the drive shaft 260 may be mated to a drive mechanism 280. However, the example embodiments are not limited thereto, and other coupling mechanism may be used to mate the control drum to the drive shaft and the drive shaft to the drive mechanism, such as gears, etc. The drive mechanism 280 may include a motor, a braking system, etc., and may be configured to rotate the control drum 200 based on instructions (e.g., command signals, messages, etc.) received from at least one control processor (not shown) of the nuclear reactor via a network (not shown) and/or communication bus (not shown). The instructions may include a desired position (e.g., an angular position to which the drive mechanism 280 is to turn the control drum 200) information and/or a desired rotation rate information (e.g., the rotation speed at which the drive mechanism 280 is to turn the control drum 200), etc., but the example embodiments are not limited thereto and may include other indications. For example, the control drums may be in the shutdown position (e.g., 0°) during a shutdown state, fail-safe state, and/or SCRAM state of the nuclear reactor. The control processor may then transmit a start-up instruction to the drive mechanism 280, which then rotates the control drum 200 to the operating position (e.g., 180°) at a desired speed using the drive shaft 260. The control processor may also transmit a shut-down instruction to the drive mechanism 280 which causes the drive mechanism 280 to rotate the control drum 200 to the shutdown position at a desired speed using the drive shaft 260. Additionally, the example embodiments are not limited thereto, and the control processor may transmit instructions to the drive mechanism 280 to rotate the control drum 200 into intermediate positions between the shutdown position and the operating position (e.g., a position between 0° and 180°), wherein a portion of the neutron absorbing tubes may still be facing the nuclear fuel assembly 110 and/or otherwise have a material effect on the reactivity of the nuclear fuel assembly 110. Further, according to some example embodiments, the torsional spring 250 may act as a fail-safe device, and may be configured to automatically rotate the control drum 200 to the shutdown position (e.g., 0°) in the event that there is a failure in the drive mechanism 280 (e.g., a power failure to the drive mechanism 280, a disruption in the communications from the control processor to the drive mechanism 280, a failure in the drive mechanism 280 (e.g., motor) itself, etc.), and/or the magnetic coupling 270, etc., in order to automatically decrease the reactivity of the nuclear fuel assembly 110 and/or shutdown the nuclear fuel assembly 110 in the event of any abnormal event in the controlling of the control drum 200. While FIG. 2A illustrates the control drum 200 as having a cylindrical shape, the example embodiments are not limited thereto, and the control drum 200 may take the form any desired shape (e.g., prisms, etc.). Additionally, while various angles are discussed in relation to the positions (e.g., shutdown and operating positions) of the control drum, the example embodiments are not limited thereto and these angles are provided for example purposes only. One of ordinary skill in the art will understand that any desired angles and/or positions may be used in accordance with the design parameters of the nuclear reactor. Referring now to FIGS. 2B and 2C, according to at least one example embodiment, the interior of a control drum 200 may include a plurality of baffle plates 230, a plurality of absorbing tubes 231, and a plurality of scattering tubes 232, etc., but the example embodiments are not limited thereto. As illustrated in FIG. 2B, the interior of the control drum 200 may include a plurality of baffle plates 230 arranged longitudinally within the control drum 200 at desired distances. The plurality of baffle plates 230 may support a plurality of absorbing tubes 231 and a plurality of scattering tubes 232 using a plurality of perforations 233 within the baffle plates 230. As illustrated in FIG. 2C, each of the baffle plates may be drilled with a plurality of perforations 233 to support the absorbing tubes 231 (e.g., neutron absorbing tubes/rods, neutron poison tubes/rods, etc.) and/or scattering tubes 232 (e.g., neutron scattering tubes/rods, neutron reflecting tubes/rods, neutron shielding tubes/rods, etc.). According to some example embodiments, the perforations 233 may be arranged in one or more concentric rings around a central opening of the baffle plate 230, but the example embodiments are not limited thereto and the perforations 233 may be arranged in any desired arrangement and/or location on the baffle plate 230. Additionally, while FIGS. 2B and 2C illustrate a number of perforations that do not hold an absorbing tube 231 or a scattering tube 232 for the sake of clearly illustrating the various elements of the baffle plates 230, the example embodiments are not limited thereto. For example, according to at least one example embodiment, each of the perforations may hold either an absorbing tube 231 or a scattering tube 232. Additionally, the number of perforations are not limited to the number of perforations illustrated in FIGS. 2B and 2C, and instead there may be a greater or lesser number of perforations in the baffle plates 230. Each of the perforations 233 may further include a spring holder 234, which may include at least one spring 234A. The spring holder 234 may receive, engage and/or support a tube or rod, such as an absorbing tube 231 or a scattering tube 232, using the attached spring 234A. The diameter of the perforation 233 may be larger than the diameter of the tube, such that when the tube inserted into the perforation 233 experiences physical expansion due to thermal conditions and/or absorbed radiation, the tube is not materially constricted by the diameter of the perforation 233, and the tube does not crack and/or rupture due to the physical expansion of the tube. Further, the spring(s) 234A of the spring holder 234 are configured to support the inserted tube so that some or all of the vibrations and/or shocks experienced by the control drum 200 and/or nuclear reactor are absorbed by the spring(s) 234A of the spring holder 234. According to at least one example embodiment, each of the absorbing tubes 231 (e.g., neutron absorbing tubes, neutron poison rods, etc.) may include a container (e.g., rod, canister, etc.), which stores (e.g., contain, hold, etc.) neutron absorbing material, such as boron, carbide, hafnium, gadolinium, etc. While FIGS. 2B and 2C illustrate the absorbing tubes 231 as having a cylindrical shape, the example embodiments are not limited thereto and the absorbing tubes 231 may take the form any desired shape (e.g., prisms, etc.). The container of the absorbing tube 231 may be constructed using a material that does not interact with fission-inducing neutrons and is capable of withstanding the high operating temperatures of a nuclear reactor core, such as stainless steel, etc., and is configured to store the neutron absorbing material(s) internally. The neutron absorbing material may be formed as a solid mass, formed as a plurality of pellets, formed as a powder, gas, etc., but the example embodiments are not limited thereto. Additionally, the absorbing tube may be a solid mass formed from one or more of the neutron absorbing materials without the use of the container, and/or the container may be externally plated with the neutron absorbing material(s). Further, according to other example embodiments, the container may store a mixture of neutron absorbing materials, or in other words the container may store two or more neutron absorbing materials. Additionally, according to some example embodiments, the container may include several segments (and/or chambers) where each segment may be formed using (and/or stores) a separate neutron absorbing material, based on the design requirements for the reactivity control characteristics of the nuclear reactor design. According to at least one example embodiment, each of the scattering tubes 232 scattering tubes 232 (e.g., neutron scattering tubes/rods, neutron reflecting tubes/rods, neutron shielding tubes/rods, etc.) may include a container (e.g., rod, canister, etc.), which stores (e.g., contain, hold, etc.) neutron scattering material, such as beryllium, graphite, europium, etc. While FIGS. 2B and 2C illustrate the scattering tubes 232 as having a cylindrical shape, the example embodiments are not limited thereto and the scattering tubes 232 may take the form any desired shape (e.g., prisms, etc.). The container of the scattering tubes 232 may be constructed using a material that does not interact with fission-inducing neutrons and is capable of withstanding the high operating temperatures of a nuclear reactor core, such as stainless steel, etc., and is configured to store the neutron scattering material(s) internally. The neutron scattering material may be formed as a solid mass, formed as a plurality of pellets, formed as a powder, gas, etc., but the example embodiments are not limited thereto. Additionally, the scattering tube 232 may be a solid mass formed from one or more of the neutron scattering materials without the use of the container, and/or the container may be externally plated with the neutron scattering material(s). Further, according to other example embodiments, the container may store a mixture of neutron scattering materials, or in other words the container may store two or more neutron scattering materials. Additionally, according to some example embodiments, the container may include several segments (and/or chambers) where each segment may be formed using (and/or stores) a separate neutron scattering material, based on the design requirements for the reactivity control characteristics of the nuclear reactor design. According to some example embodiments, each baffle plate 230 may include at least one neutron absorbing sector (e.g., poison sector, etc.) 236A and at least one neutron scattering sector (e.g., reflecting sector, shielding sector, etc.) 237A. The neutron absorbing sector 236A may be a first radial sector of the baffle plate 230 wherein some or all of the absorbing tubes 231 are arranged, and the neutron scattering sector 237A may be a second radial sector of the baffle plate 230 wherein some or all of the scattering tubes 232 are arranged, etc. The neutron absorbing sectors 236A of the plurality of baffle plates 230 may compose the neutron absorbing section 236 of a control drum 200, and the neutron scattering sectors 237A of the plurality of baffle plates 230 may compose the neutron scattering section 237 of the control drum 200. According to some example embodiments, one or more scattering tubes 232 may be located in the neutron absorbing section 236, e.g., at the edges of the neutron absorbing section 236, and/or one or more absorbing tubes 231 may be located in the neutron scattering section 237 based on the neutron absorption/scattering design requirements of the control drums for a nuclear reactor. Additionally, according to other example embodiments, each ring (and/or row, etc.) of the neutron absorbing section 236 or neutron scattering section 237, may include absorbing rods 231 and/or scattering rods 232 of a different absorbing and/or scattering material from the other rings (and/or rows) of the control drum, based on the design requirements for the reactivity control characteristics of the nuclear reactor design. In other words, the absorbing tubes and the scattering tubes may be arranged in various desired patterns or arrangements, and there may be radial, azimuthal, and/or axial variation of the absorbing/scattering tubes. While FIG. 2C illustrates one neutron absorbing section, and one neutron scattering section, the example embodiments are not limited thereto. For example, the example embodiments may include two or more neutron absorbing sections and/or neutron scattering sections, etc. Referring now to FIG. 3, FIG. 3 illustrates a flowchart depicting a method of operating at least one control drum in a nuclear reactor according to at least one example embodiment. According to at least one example embodiment, in operation S300, at least one control processor may transmit a startup command to at least one drive mechanism connected to at least one control drum. The control drum may be assumed to start in a shutdown position. Additionally, the startup command may include a desired startup angular position and/or desired startup rotation rate (e.g., a desired position for the control drum and/or rotation rate during the startup state of the nuclear reactor core). In operation S310, the drive mechanism rotates the control drum from its current position, e.g., the shutdown state (and/or position), to the desired startup angular position at the desired startup rotation rate included in the startup command. In operation S320, the control processor may transmit an operational command to the drive mechanism. The operational command may include a desired operational angular position and/or desired operational rotation rate (e.g., a desired position for the control drum and/or rotation rate during the operational state of the nuclear reactor core based on the reactivity conditions of the nuclear reactor core). In operation S330, the drive mechanism rotates the control drum from its current position, e.g., the startup state (and/or position), to the desired operational angular position at the desired operational rotation rate included in the operational command. However, according to some example embodiments, the operational state may be the same as the startup state, and operations S320 and S330 may be omitted. In operation S340, the control processor may transmit a shutdown command to the drive mechanism. The shutdown command may include a desired shutdown angular position and/or desired shutdown rotation rate (e.g., a desired position for the control drum and/or rotation rate during the shutdown state of the nuclear reactor core based on the reactivity conditions of the nuclear reactor core). In operation S350, the drive mechanism rotates the control drum from its current position, e.g., the operational state (and/or position), to the desired shutdown angular position at the desired shutdown rotation rate included in the shutdown command. As will be appreciated, the methods, systems, and/or apparatuses according to the example embodiments have several advantages. The control drum of the example embodiments may be mounted in a nuclear reactor in a horizontal orientation, thereby decreasing the size requirements for the reactor control systems of the nuclear reactor in comparison to conventional control drums which must be mounted in a vertical orientation. Additionally, the control drum of the example embodiments may also provide the additional benefit of accommodating the expansion of the neutron absorbing material and the neutron scattering material from the heat generated by the nuclear reactor and/or from the absorption of radiation generated by the nuclear reactor. Further, the control drum of the example embodiments may also allow a nuclear reactor designer to further fine-tune and/or optimize the distribution of the neutron absorbing materials, thereby improving the performance of the nuclear reactor and the control of the nuclear reactor. This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims. |
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040381331 | description | DETAILED DESCRIPTION OF THE INVENTION In the first example of the invention shown by FIGS. 1 through 6, a small section of the concrete pressure vessel 1 of a gas-cooled fast breeder reactor is shown, this supporting the upper end of one of the fuel assemblies vertically elongated casings or cans 2 containing a bundle of fuel rods 3 positioned in the usual manner, and having an upper end 2a and extending downwardly therefrom and having an open lower end 2b extending below the bottom ends of the fuel rods 3. This lower end of the casing is normally termed the nozzle, because the gas coolant flows downwardly therethrough at relatively high velocity. Although not shown in the case of this first example, a plurality of the fuel assemblies are grouped together adjacent to each other, the casings being of hexagonal shape so that they can nest close together in groups, as indicated by FIG. 7 showing a second example of the invention. The casing 2 has a vertical tubular suspension rod 3 with a supported connection above the casing via the pressure vessel top 1 and a lower end with a releasable screw-threaded connected 3a to the casing's upper end 2a, so that the casing is suspended thereby. The suspension rod customarily is tensioned not only by the weight of the fuel assembly, but also because it is required to hold the assembly with its upper end 2a tightly within one of the openings in the usual grid plate 4 and down through which the gas coolant flows into the upper end of the assembly's casing, the details of the construction involved not being shown because it can be conventional. The casing 2 can, of course, be lowered from the grid plate opening upon release of the upward force applied through the suspension tube 3. The instrumentation tube 5 is shown with its lower end 5a terminating within the bottom end or nozzle 2b of the casing, this instrumentation tube 5 having an upper end 5b which independently of the connection of the suspension tube 3 with the pressure vessel, is fixed above the casing 2 by projecting upwardly through the pressure vessel top into the tubular pressure containment 6 where the instrumentation tube's top end has an enlargement or collar supporting that upper end by resting on the top wall 6a of the pressure containment tube 6. Although not shown, normally a thermocouple would be inthe bottom end 5a of the instrumentation tube with its necessary electrical lines extending upwardly to the top end of the instrumentation tube above the wall 6a, from which the lines would extend to external instrumentation. When servicing is required, the instrumentation tube 5, being slidable throughout its length relative to the other parts, can be slid upwardly and removed from the pressure vessel 1, without disturbing the fuel assembly or its casing's suspension rod 3. On the other hand, during core servicing, by release of the casing's upper end from the suspension rod, the fuel element can be lowered while, if desired, with the instrumentation tube remaining unmoved. The present invention provides a secondary or emergency suspension system for the casing 2 in which the fuel rods and all the other necessary parts of the fuel assembly are carried, by taking advantage of the above facts concerning the typical construction of the components of a gas-cooled reactor core. As previously noted, the bottom end of the casing 2 is formed by the nozzle 2b. The lower part of the hexagonal portion or can proper merges into these nozzles, this being done in the usual fashion in the present case but, and this is noteworthy, the nozzle connection is formed by abutting parts 7. In other words, the nozzle can direct an upward force into the casing extending above it. The top end of the nozzle has a cross bar 8 extending across it and including a central collar 9 which is internally threaded and into which an externally threaded vertically bored mounting 10 is screwed, the mounting 10 depending from the cross bar 8. The mounting 10 has a bottom shank 10a which is counterbored and internally threaded. To hold the instrumentation tube 5 concentrically with respect to the casing's bottom end or nozzle 2b down through which the gas coolant flows, a tube guide 11 has an externally threaded shank which is screwed into the internally threaded counterbore of the mounting 10. The instrumentation tube 5 is vertically slidable in this tube guide 11 but is normally held by the tube guide concentrically within the nozzle. According to the present invention, this tube guide is made with an annular recess 11a which mounts four symmetrically arranged latches 12 which swing inwardly to engage an annular recess 5c formed in the bottom end of the instrumentation tube 5, this annular recess serving as a common latch catch for all four of the latches. To effect this mounting, the upper ends of the latches, in each instance, form inwardly extending hooks 12a which form pivot points by rocking in the recess 11a, the latches depending from these upper ends and forming inwardly extending latch surfaces 12b which, upon downward movement of the fuel assembly if accidentally released, engage the annular shoulder formed by the bottom end of the annular recess 5c, the latches' upper ends 12a then abutting an external flange formed by the bottom surface of the tube guide 11 defined by the recess 11a. Under these conditions, the latches function as four vertical struts or columns transmitting the weight of the fuel assembly from the shoulder of the tube guide 11, formed by its annular recess 11a, downwardly through the latches and to the latch surfaces 12b to the shoulder formed by the recess 5c in the instrumentation tube's bottom end, the instrumentation tube 5 then carrying the weight of the assembly, in tension. Radially outward movement of the four latches is prevented by a vertically slidable locking ring 13 from which two wings 13a diametrically extend in radial directions with their outer ends spaced inwardly from the inside of the casing's nozzle, this locking ring 13 normally resting on radially outwardly extending shoulder elements 12c which extend from the latches in each instance, the latches having wedge surfaces 12d above these shoulders 12c and which are engaged by the locking ring 13 under normal conditions. In this way the four latch members are pressed radially inwardly so long as the locking ring 13 rests on the shoulder 12c and wedge inwardly the wedging surfaces 12d of the latches. The midportions of the latches form inwardly extending shoulders 12e which form abutments, while the bottom end of the tube guide 11 forms an opposing abutment, and a ring 14 is positioned slidably on the instrumentation tube 5 between these two mutually opposing abutment surfaces. In the event of an accidental release of the casing and theoretically possible buckling of the upstanding portions of the latches, the locking ring 13 holds the latches firmly inwardly while the ring 14 is engaged between the opposing abutment surfaces so as to carry the weight of the fuel assembly, even in the event of such partial failure of the latches. Although the latch arrangement described may be formed by relatively loose parts, in the event the suspension of the fuel assembly should fail, the possible falling distance of the fuel assembly is extremely short and its downward motion is restrained before the assembly can gain an unmanageable downward velocity. To effect unlatching when either the instrumentation tube is to be lifted or the fuel assembly is to be lowered, the tools shown by FIG. 5 and 6 may be used, FIG. 6 showing only the upper end of the tool but it being understood that the tube is long enough to be used through the vessel bottom when the reactor is shut down. This tool comprises an outer tube 15 having vertical slots 15a positioned to provide clearance for the four latches, these latches being flat parts as indicated by FIG. 5. Using this tool, as shown by FIG. 3, the outer tube 15 can be inserted through the open bottom end of the casing's nozzle, to engage and lift the vertically slidable locking ring 13 so that the four latches are unlocked and can be swung radially outwardly. The tool comprises also a relatively slidable inner tube 16 having a top end chamfered inwardly, the latches having outwardly flared lower ends 12f for engagement by the inwardly chamfered end of the inner tube 16 as it is slid upwardly while the outer tube 15 holds the locking ring 13 upwardly, the latches being then swung to their unlocking positions as shown by FIG. 4. When the latches are thus unlocked, intentional lowering of the fuel element can be effected, the tool being correspondingly lowered while holding the latches unlocked. Also, of course, the instrumentation tube 5 can be lifted free of the fuel assembly. In the event no tool is available, and other forms of tools are possible, the wings 13a of the ring 13 permit almost any kind of tool to be used to push the locking ring upwardly, and with the latches thus unlocked, the use of other tools can be used to move these latches to their unlatched position. When the fuel assembly is returned to its position shown by FIG. 1, the tool can be used to hold the latches unlatched during reinsertion of the instrumentation tube 5, this ordinarily being drawn upwardly during intentional removal of the fuel assembly. In the second example of the invention, the casings of the adjacent or adjoining fuel assemblies of the group of fuel assemblies shown by FIG. 7, are used as a secondary suspension means. A reactor core may comprise a substantially larger number of assemblies, only seven being shown in FIG. 7. Having reference to FIGS. 8 and 9, it can be seen that the latches substantially correspond to those shown in the case of the first example. The difference is that in this second example the portions 12a' of the latches, rock in openings 12e' formed in each of the flat sides of the hexagonal shape, while the locking ring 13' rests on the inside surfaces of all of the latches by way of their inwardly extending shoulders 12c', while the latching surfaces 12b' engage in recesses formed in the rings 17 which encircle the nozzles and, in part, provide the abutting surfaces 7 previously referred to. With this somewhat reversed arrangement, there are two latches adjacent to each other as to each of the opposing flat sides of the fuel assembly group forming the core, as can be seen from FIG. 7. Therefore, as to any one of the assemblies, the latches of all of the assemblies surrounding that assembly, must be released when the one assembly is to be removed, and this is shown by FIG. 9 in the case of three of the assemblies. In this case the tool has the inner sliding tube 16' slotted for clearance of the latches, and it is the outer sliding tool 15' which has the chamfered ends, the chamfer being inwardly in this case to engage the depending latch lever portions which function as latch release means. FIG. 9 shows the action with the latches released. The latch catches formed by the recesses in the ring 17 may be subject to wear, but these rings can be made of suitable hard material. In this second example, the instrumentation tube is not used as the secondary suspension, but it could, or course be used for its normal purpose to determine the temperature of the gas coolant flowing downwardly through the nozzle of the assembly, as to each assembly. |
description | 1. Field of the Invention The present invention relates to a method of fabricating an X-ray mask and a method of fabricating a semiconductor device with an X-ray mask fabricated by this method. 2. Description of the Background Art In proximity X-ray exposure, an X-ray mask and a wafer formed with a resist film are arranged in proximity to each other, for executing X-ray irradiation. In this case, the X-ray mask is prepared from a membrane mask having an X-ray absorber pattern formed on an X-ray transmitter. The wafer is irradiated with X-rays through this membrane mask. Thus, an optical image is formed on the resist film with the X-rays transmitted through the X-ray transmitter portion of the membrane mask. At this time, atoms forming the resist film absorb the X-rays. Thus, the resist film generates secondary electrons, thereby causing chemical change on molecules forming the resist film. A latent image of a pattern corresponding to the pattern of the X-ray transmitter portion of the membrane mask is formed on the resist film due to the chemical change. Thereafter the resist film is developed by removing either the latent image portion or a portion other than the latent image portion. Thus, the pattern of the X-ray absorber portion of the membrane mask is transferred to the resist film. The resolution R of the pattern formed on the resist film decided by the optical image is expressed as follows:R=k√{square root over ( )}(λ×G)where k represents a constant depending on the resist process or the like, λ represents the exposure wavelength, and G represents the distance between the surface of the X-ray mask and the surface of the resist film formed on the wafer. The distance G is hereinafter referred to as a mask-to-resist interval. When a membrane mask having a mask-to-resist interval G of 10 μm is employed, exposure is currently performed with light having an exposure wavelength λ in the range of 0.7 nm to 1.2 nm. If the pattern formed on the membrane mask to be transferred to the resist film is about 60 nm, the resolution R of the transferred pattern satisfies a prescribed criterion. In order to further improve the resolution R, the exposure wavelength λ or the mask-to-resist interval G may be reduced. If the mask-to-resist interval G is reduced, however, the X-ray mask and the resist film disadvantageously come into contact with each other, to increase the danger of breakage of the X-ray mask. Further, the mask-to-resist interval G cannot be extremely reduced due to a setting error included therein. If the exposure wavelength λ is reduced, the energy of secondary electrons generated in the resist film due to X-ray irradiation is increased to disadvantageously reduce the resolution R. A method of improving the resolution R of a pattern with a conventional X-ray mask under prescribed conditions of an exposure wavelength λ and a mask-to-resist interval G is now described. A principle of forming an optical image with an X-ray phase-shift mask improving resolution R without changing an exposure wavelength λ and a mask-to-resist interval G is described with reference to FIG. 1. This principle is described in Jpn. J. Appl. Phys., Vol. 38 (1999) pp. 7076–7079 by K. Fujii, K. Suzuki and Y. Matsui, December, 1999. FIG. 1 is a diagram for illustrating the effect of an X-ray phase-shift mask 1 having a line-and-space pattern (hereinafter referred to as “L & S pattern”) formed by alternately arranging openings provided with no X-ray absorbers and shielding portions provided with X-ray absorbers. In the X-ray phase-shift mask 1, X-ray absorbers 2 are provided beneath an X-ray transmitter 3, as shown in FIG. 1. In general, X-rays are substantially absorbed by the X-ray absorbers 2 and substantially transmitted through the X-ray transmitter 3. Therefore, consider X-ray intensity levels on a point P of a resist film located immediately under an opening between a pair of adjacent X-ray absorbers 2 and a point Q of the resist film located immediately under a shielding portion consisting of one of the X-ray absorbers 2. FIG. 1 illustrates optical images formed by X-rays transmitted through the openings with solid lines and those formed by X-rays transmitted through the shielding portions with dotted lines. As understood from FIG. 1, the X-rays transmitted through the openings form optical images not only immediately under the openings but also immediately under the shielding portions. Therefore, the resolution R of the X-ray phase-shift mask 1 is reduced. In practice, however, the X-rays transmitted through the openings and those transmitted through the shielding portions are superposed with each other to form the optical images. In order to improve the optical image contrast, therefore, the X-ray phase shift-mask 1 must be so formed that the X-rays transmitted through the openings and the shielding portions respectively strengthen the optical images at the point P and weaken the optical images at the point Q. Conditions for improving the optical image contrast are now described. It is assumed that tabs denotes the phase shift quantity of X-rays transmitted through the X-ray absorbers 2 and φgeo denotes geometric phase difference of X-rays resulting from difference between optical paths D→P and C→P. In this case, X-rays (B→D→P) transmitted through the openings and X-rays (A→C→P) transmitted through the shielding portions strengthen each other under the following condition:φgeo+φabs=0 (1) At the point Q, X-rays (B→D→Q) transmitted through the openings and X-rays (A→C→Q) transmitted through the shielding portions weaken each other under the following condition:φgeo−φabs=π (2) Therefore, the optimum phase condition corresponding to both conditions of the expressions (1) and (2) is expressed as follows:λgeo=−φabs=0.5π The optical image contrast is defined as (Ip−Iq)/(Ip+Iq), where Ip represents the intensity of X-rays on portions of the resist film located immediately under the openings, and Iq represents intensity of X-rays on portions of the resist film located immediately under the shielding portions. It is assumed that X-ray intensity at the point P resulting from X-rays transmitted through the openings is 1, and X-ray intensity at the point Q resulting from X-rays transmitted through the openings is expressed as a. The X-ray intensity at the point P resulting from X-rays transmitted through the shielding portions is 1/MC times the X-ray intensity at the point P resulting from X-rays transmitted through the openings. Therefore, X-ray intensity at the point Q resulting from the X-rays transmitted through the shielding portions is expressed as a/MC, where MC represents the mask contrast corresponding to the inverse number of the transmittance of the X-ray absorbers 2. Under the aforementioned conditions, the optical image contrast in the optimum phase condition is expressed as follows:((1+2a/MC)−|1/MC−2a|)/((1+2a/MC)+|1/MC−2a|)) Further, the optical image contrast reaches the maximum value 1 when 2a=1/MC, which is the condition for obtaining an ideal optical image. The aforementioned prior art Jpn. J. Appl. Phys., Vol. 38 (1999) by K. Fujii, K. Suzuki and Y. Matsui describes the following: Consider a case of an exposure wavelength λ of 0.78 nm, a mask-to-resist interval G of 12 μm and mask contrast MC of 2.5, for example. In this case, the phase shift quantity φabs reaches 0.54π in an X-ray mask employing tantalum (Ta) films of 290 nm in thickness as X-ray absorbers 2 in an L & S pattern having a pitch of 70 nm. Consider a case of an exposure wavelength λ of 0.78 nm, a mask-to-resist interval G of 7 μm and mask contrast MC of 2. In this case, the phase shift quantity φabs reaches 0.57π in an X-ray mask employing molybdenum (Mo) films of 370 nm in thickness as X-ray absorbers 2 in an L & S pattern having a pitch of 50 nm. Problems related to an X-ray mask implementing the aforementioned optimum phase condition are described. The prior art describes an X-ray phase-shift mask 1 employing X-ray absorbers 2 having mask contrast MC of either 2 or 2.5 satisfying the optimum phase condition. This prior art further describes that the resolution R can be improved with respect to different mask-to-resist intervals G without changing the exposure wavelength λ. In order to improve the resolution R, it is also effective to reduce the exposure wavelength λ, as hereinabove described. However, the aforementioned prior art describes no method of improving the resolution R by reducing the exposure wavelength λ without changing the mask-to-resist interval G in order to avoid a risk such as breakage of the mask. In-practice, tungsten and tantalum generally employed as the materials for the X-ray absorbers 2 have absorption edges, i.e., boundaries of wavelengths capable of absorbing X-rays, of 0.69 nm and 0.73 nm respectively. In order to satisfy the condition φabs =−0.5π, therefore, the mask contrast MC must be increased also as to a wavelength slightly shorter than that of an X-ray absorption edge. Consequently, no X-rays are transmitted through the X-ray absorbers 2. Thus, the degree of contribution of the phase shift effect is reduced, to reduce the optical image contrast. When the mask contrast MC is about 2 to 3 similarly to a general one, it follows that the phase shift quantity φabs of the X-ray absorbers 2 approaches zero from −0.5π. In this case, the optimum phase condition cannot be implemented. When a pattern is transferred with a wider mask-to-resist interval G which the geometric phase difference φgeo does not satisfy the optimum phase condition, the resolution R of the pattern is deteriorated. In the conventional X-ray mask, the optical image contrast reaches the maximum value 1 when 2a=1/MC. However, the value a is decided by the size of the pattern formed on the X-ray mask, the exposure wavelength λ of X-rays and the mask-to-resist interval G. In practice, the ideal state of the optical image contrast 1 cannot be implemented unless the mask contrast MC satisfies 2a=1/MC after the size of the pattern formed on the X-ray mask, the exposure wavelength λ of X-rays and the mask-to-resist interval G are decided. When X-ray absorbers 2 constituted of a single substance are employed as in the prior art, the phase shift quantity φabs and the mask contrast MC are unequivocally decided. Therefore, the mask contrast MC does not necessarily satisfy the condition 2a=1/MC. While various X-ray masks have been developed in order to solve the aforementioned problems, there has been developed no X-ray mask capable of further improving the resolution of a pattern of a semiconductor device formed with the X-ray mask. An object of the present invention is to provide a method of fabricating an X-ray mask capable of improving the resolution of a pattern of a semiconductor device and a method of fabricating a semiconductor device with an X-ray mask fabricated by the method. A method of fabricating an X-ray mask according to a first aspect of the present invention comprises steps of forming an X-ray transmitter and forming a laminated (stacked) X-ray absorber on the X-ray transmitter. According to this method, at least two types of layers having different compositions are employed for the laminated X-ray absorber. According to the aforementioned method of fabricating an X-ray mask, it is possible to fabricate an X-ray mask having a prescribed function, which has not been implementable with an X-ray absorber consisting of a layer of a single composition, by adjusting at least either the transmittances or the phase shift quantities of at least two types of layers having different compositions. A method of fabricating an X-ray mask according to a second aspect of the present invention comprises steps of forming a dug portion and a portion other than the dug portion on an X-ray transmitter and forming an X-ray absorber on the portion other than the dug portion. According to the aforementioned method of fabricating an X-ray mask, it is possible to fabricate an X-ray mask having a prescribed function, which has not been implementable by simply forming a single X-ray absorber, by adjusting at least either the transmittances or the phase shift quantities of the portion other than the dug portion and the X-ray absorber. A method of fabricating a semiconductor device of the present invention carries out an exposure step with an X-ray mask on condition that geometric X-ray phase difference between the phase of X-rays transmitted through an X-ray transmission part of the X-ray mask and the phase of X-rays transmitted through an X-ray absorber of the X-ray mask is in the range including 0.57π and in proximity to 0.57π between a resist film located on a position for forming an optical image with the X-rays and the X-ray mask. The X-ray mask comprises an X-ray transmitter and the X-ray absorber consisting of a laminated structure having at least two layers formed on the X-ray transmitter. The laminated structure includes at least two layers having different compositions. At least either a condition that the phase shift quantity of the X-rays transmitted through the X-ray absorber is in the range of 0.37π to 0.6π or a condition that the transmittance of the X-rays transmitted through the X-ray absorber is in the range of 30% to 60% holds. According to the aforementioned structure, a pattern can be transferred from the X-ray mask to the resist film with high optical image contrast, whereby the accuracy of the pattern formed on the semiconductor device can be improved. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. First Embodiment An X-ray mask obtained by a method of fabricating an X-ray mask according to a first embodiment of the present invention and an exemplary method of fabricating a semiconductor device with the X-ray mask are now described. In an exemplary X-ray mask fabricated according to the first embodiment, each of X-ray absorbers formed on an X-ray transmitter includes at least two layers having different element structural ratios, as shown in FIG. 11. The phase shift quantity of X-rays transmitted through the X-ray absorbers is in the range of 0.3π to 0.6π, and the transmittance of the X-rays transmitted through the X-ray absorbers is in the range of 30% to 60%. An exemplary method of fabricating a semiconductor device with the X-ray mask carries out two steps, i.e., a first step of calculating geometric X-ray phase difference between the phase of X-rays transmitted through X-tray transmission parts and the phase of X-rays transmitted through the X-ray absorbers of the X-ray mask between a resist film located on a position for forming an optical image with the X-rays and the X-ray mask and a second step of calculating the phase shift quantity of the X-rays transmitted through the X-ray absorbers. When the average exposure wavelength of X-rays absorbed by the resist film is larger than 0.3 nm and smaller than 0.7 nm, the X-ray mask according to this embodiment is preferably employed on condition that the geometric phase difference of X-rays is in the range including 0.5π and in proximity to 0.5π. When the average exposure wavelength of X-rays absorbed by the resist film is larger than 0.3 nm and smaller than 0.7 nm, further, the X-ray mask according to this embodiment may be employed on condition that the absolute value of difference between the geometric phase difference and the phase shift quantity of the X-rays transmitted through the X-ray absorbers is in the range including c and in proximity to n. In the aforementioned method of fabricating an X-ray mask according to this embodiment, each of the X-ray absorbers is formed in a laminated structure of at least two layers having different element structural ratios, whereby both of the transmittance and the phase shift quantity of the X-rays transmitted through the X-ray absorbers can be properly adjusted. Thus, it is possible to fabricate an X-ray mask, which has not been implementable with a conventional method of fabricating an X-ray mask employing an X-ray absorber having a single composition, by the method of fabricating an X-ray mask according to this embodiment. In other words, it is possible to fabricate an X-ray mask attaining high optical image contrast regardless of the values of a mask-to-resist interval G and an exposure wavelength λ. A physical principle utilized for thinking out the method of fabricating an X-ray mask according to this embodiment is now described. The complex refractive index n of a substance 1 is defined as 1−δ1+iβi, where 1−δ1 and β1 represent the real part and the imaginary part of the complex number respectively. The substance 1 consists of a single composition. The transmittance T1 and the phase shift quantity φabs1 of an X-ray absorber consisting of a single substance employed in a conventional X-ray mask are expressed as follows:T1=exp(−4πβ1t/λ)φabs1=−2πδ1t/λ From the relation 1n(T1)=2β1/(δ1×φabs1), a prescribed relational expression holds between the transmittance T1 and the phase shift quantity φabs1 of the substance 1. Therefore, it is impossible to control the transmittance T1 and the phase shift quantity φabs1 independently of each other when employing the substance I consisting of a single composition. In the above expressions, t represents the film thickness of the substance 1 and λ represents the exposure wavelength. In other words, the transmittance T1 is reduced if the phase shift quantity φabs1 is increased, and the former is increased if the latter is reduced. Now consider the X-ray mask having the X-ray absorbers each formed by two layers, consisting of a material identical to that for the aforementioned X-ray absorbers and a material different from this material respectively, employed in this embodiment. With reference to the two layers, it is assumed that T1a and φabs1a represent the transmittance and the phase shift quantity of a substance 1a respectively, and 1−δ2+β2, T2 and φabs2 represent the complex refractive index, the transmittance and the phase shift quantity of a substance 2 respectively. The total transmittance φtotal and the total phase shift quantity φtotal of the two layers are expressed as follows:Ttotal=T1a×T2 φtotal=φabs1a×φabs2 The transmittance T1 of the X-ray absorber consisting of a single layer and the total transmittance Ttotal of the two layers are set to the same value, so that the following relation holds:T1=Ttotal When only the phase shift quantities are changed, the following relations (3) and (4) hold: ln ( T total ) = ln ( T 1 a ) + ln ( T 2 ) = 2 β 1 / δ 1 × ϕ abs 1 a + 2 β 2 / δ 2 × ϕ abs 2 = 2 β 1 / δ 1 × ( ϕ total - ϕ abs 2 ) + 2 β 2 / δ 2 × ϕ abs 2 ( 3 ) It is assumed here that the following relation holds:φabs1=φtotal−φabs2 1n(Ttotal)=1n(T1) (4)2β1/δ1×(φtotal−φabs2)+2β2/δ2×φabs2=2β1/δ1×φabs1 This expression is arranged as follows:β1/δ1×(φtotal−φabs2)=(β1/δ1−β2/δ2)×φabs2 From β1/δ1>0 and φabs2<0, therefore, the substance 2 may be selected on necessary condition of β1/δ1>β2/δ2 in order to shift the phase shift quantity toward the minus side, i.e., in order to attain φtotal<φabs2. In order to shift the phase shift quantity toward the plus side, i.e., in order to attain φtotal>φabs2, on the other hand, the substance 2 may be selected on necessary condition of β1/δ1<β2/δ2. Thus, according to the inventive method of fabricating an X-ray mask, X-ray absorbers each having a laminated structure formed by a plurality of types of substances consisting of different compositions are so employed that it is possible to attain such an effect that the phase shift quantity can be adjusted without changing the transmittance of the X-ray absorbers, which has not been attainable in a conventional X-ray mask employing only a single type of X-ray absorber. Consider a case of changing only the transmittance while setting the phase shift quantity φabs1 of the X-ray mask having the X-ray absorber consisting of a single layer and the phase shift quantity φtotal of the X-ray mask having the X-ray absorbers each consisting of two-layers. The total transmittance In(Ttotal) is expressed as follows: In ( T total ) = In ( T 1 a ) + In ( T 2 ) = 2 β 1 / δ 1 × ( ϕ total - ϕ abs 2 ) + 2 β 2 / δ 2 × ϕ abs 2 = 2 β 1 / δ 1 × ( ϕ abs 1 - ϕ abs 2 ) + 2 β 2 / δ 2 × ϕ abs 2 = In ( T 1 ) - 2 ( β 1 / δ 1 - β 2 / δ 2 ) × ϕ abs 2 From the relation φabs2<0, therefore, the substance 2 may be selected for forming X-ray absorbers on necessary condition of β1/δ1>β2/δ2 in order to increase the transmittance so that In(Ttotal)>In(T1). The transmittance is naturally in the range of 0% to 100%, and hence In(T1a)<0. In order to satisfy this condition, the phase shift quantity of the substance 2 employed for the X-ray absorbers must satisfy the relation φabs1<φabs2. In order to reduce the transmittance, on the other hand, the X-ray absorbers may be made of a material satisfying the condition β1/δ1<β2/δ2 as the substance 2. Thus, it is possible to implement a combination of a transmittance and a phase shift quantity, which is not implementable in a conventional X-ray absorber consisting of a substance having a single composition, by employing X-ray absorbers each having a laminated or mixed structure consisting of different elements or different composition ratios. Thus, it is possible to attain such an unparalleled remarkable effect that X-ray absorbers having a more proper phase condition or a more proper transmittance with respect to an exposure wavelength are formable. When the aforementioned principle is applied to the relation between first, second and third substances, it is possible to form X-ray absorbers each having an effect similar to the above with a laminated or mixed structure consisting of substances of three types of substances including the first, second and third substances. Further, X-ray absorbers each having a laminated or mixed structure consisting of substances having at least four types of compositions can also attain an effect similar to the above when the X-ray absorbers are fabricated through a principle similar to the above. When X-ray absorbers each having a mixed structure including a plurality of types of compositions are employed, an X-ray mask exhibits a sectional structure similar to that shown in FIG. 1. Another phase shift effect not mentioned in the prior art is now described. The prior art shows results obtained on condition that the X-rays mutually strengthen the intensity levels thereof on the surface portions of the resist film located immediately under the openings while weakening the intensity levels thereof on the surface portions of the resist film located immediately under the shielding portions. When 2a=1/MC, however, optical image intensity reaches zero after the X-rays are superposed with each other on the portions located immediately under the shielding portions, and ideal optical image contrast of 1 is obtained if the optical image intensity is plus on the portions located immediately under the openings. In other words, conditions 2a=1/MC and φgeo−φabs=π may be satisfied, and an ideal state is obtained also under a phase condition different from the condition φgeo−φabs=0.5π described with reference to the prior art. In other words, the ideal state of the optical image contrast of 1 is obtained also at a mask-to-resist interval G different from that satisfying the condition φgeo−φabs=0.5π by satisfying the conditions 2a=1/MC and φgeo−φabs=π with reference to the phase shift quantity and the mask contrast MC of X-ray absorbers. This is also one of principles employed in the present invention. Thus, it is possible to implement a combination of a transmittance and a phase shift quantity, which is not implementable in an X-ray absorber consisting of a substance having a single composition with respect to each wavelength, by employing X-ray absorbers each having a laminated or mixed structure consisting of different elements. Consequently, higher optical image contrast than the conventional one can be obtained also when at least either the interval between the X-ray mask and a wafer or the range of the exposure wavelength λ is different from the conventional value. As a result, a semiconductor device having a finer pattern than the conventional one can be formed. FIG. 2 shows the relation between the contrast of an optical image formed by X-rays on a resist film and the transmittance of X-ray absorbers 2 formed on an X-ray mask in a case of irradiating the resist film with X-rays through the X-ray mask formed with a 35 nm L & S mask pattern. The transmittance corresponds to the inverse number of mask contrast MC. In this case, the exposure wavelength λ is set to 0.8 nm, and the thickness of and the materials (compositions) for the X-ray absorbers 2 are so selected that the phase shift quantity of the X-ray absorbers 2 reaches −0.5π with respect to this exposure wavelength λ. Further, the mask-to-resist interval G is set to 3.06 μm so that geometric phase difference reaches 0.5π. As understood from FIG. 2, the optical image contrast depends on the transmittance of the X-ray absorbers 2. The optical image contrast is at the maximum value of 0.82 when the transmittance is substantially 50%, the former is at least 0.7 when the latter is in the range of 30% to 60%, and the former is substantially at least 0.5 when the latter is in the range of 25% to 95%. In other words, FIG. 2 shows that relatively high optical image contrast of at least 0.7 is obtained in relation to the 35 nm L & S pattern when the mask-to-resist interval G is so set that the geometric phase difference is 0.57π, the phase shift quantity of the X-ray absorbers 2 is −0.5π and the transmittance of the X-ray absorbers 2 is in the range of 30% to 60%. Thus, the optical image contrast, depending on the transmittance of the X-ray absorbers 2 of the X-ray mask, varies with the transmittance of the X-ray absorbers 2 also when the geometric phase difference and the phase shift quantity of the X-ray absorbers 2 are at optimum values. It is therefore understood that the resolution of the pattern can be improved by properly selecting the transmittance of the X-ray absorbers 2. FIG. 3 shows the relation between the phase shift quantity of the X-ray absorbers 2 and optical image contrast with reference a pattern shape and a pattern size, a mask-to-resist interval G and an exposure wavelength λ selected similarly to those of the L & S pattern described with reference to FIG. 2 and the transmittance of the X-ray absorbers 2 of 50%. As understood from FIG. 3, the optical image contrast depends on the phase shift quantity of the X-ray absorbers 2. Therefore, the optical image contrast is at least 0.7 when the phase shift quantity is in the range of 0.3π to 0.6π, and the former is at least 0.55 when the latter is in the range of 0.2π to 0.65π. In other words, relatively high optical image contrast of at least 0.7 is obtained in a 35 nm L & S pattern when the mask-to-resist interval G is so set that the geometric phase difference is 0.57π, the transmittance of the X-ray absorbers 2 is 50% and the phase shift quantity of the X-ray absorbers 2 is in the range of 0.3π to 0.6π. FIG. 4 is a graph plotting the transmittance of a comparative X-ray absorber 2 of tungsten (W) having a phase shift quantity of −0.5π with respect to each wavelength. The transmittance is substantially in the range of 30% to 45% in the comparative X-ray exposure wave range of 0.7 nm to 1.2 nm. The transmittance is 45% particularly in the wave range proximate to 0.8 nm, and hence it is understood that there is a condition for obtaining high optical image contrast substantially identical to that resulting from the transmittance of 50%. In order to set the geometric phase difference to 0.5π with respect to a 35 nm L & S pattern, the mask-to-resist interval G must be set to a value proximate to 3 μm. It is difficult to stably implement such a small mask-to-resist interval G, and no 35 nm L & S pattern can be formed. Consider a method of forming a 35 nm L & S pattern at a mask-to-resist interval G larger than 3 μm by reducing the exposure wavelength λ below 0.7 nm. Tungsten has an absorption edge, corresponding to an end of a wavelength capable of absorbing X-rays, of 0.69 nm. Therefore, the transmittance of tungsten is remarkably reduced at a wavelength slightly shorter than the absorption edge. At a film thickness for setting a phase shift quantity to −0.5π, therefore, tungsten exhibits a transmittance of not more than 10%. When the exposure wavelength λ is further reduced, the transmittance is gradually increased. Therefore, the transmittance is not more than 30% when the exposure wavelength λ is in the range of 0.4 nm to 0.68 nm. The transmittance first reaches the optimum value of 50% when the exposure wavelength λ is reduced to 0.3 nm. Therefore, the comparative X-ray absorber 2 exhibits a relatively low transmittance when the exposure wavelength λ is in the range of 0.4 to 0.68 nm, even if the optimum phase condition is satisfied. It is therefore disadvantageously difficult to improve the resolution also when reducing the exposure wavelength π of the X-ray absorber 2. In a comparative X-ray mask, the transmittance is less than 50% when the exposure wavelength λ is in the range of 0.3 nm and 1.2 nm and the phase shift quantity is −0.5π. Therefore, the comparative X-ray mask does not necessarily satisfy the optimum phase and transmittance conditions. The X-ray mask according to this embodiment solves these problems. When each of the X-ray absorbers 2 is in a two-layer structure consisting of different elements or compositions, the transmittance can be increased while keeping the phase shift quantity intact, as already described with reference to the principle of the present invention. The necessary condition therefor is β1/δ1>β2/δ2. It is naturally necessary to satisfy the condition that the transmittance of each layer is not more than 100%. When the exposure wavelength λ is 0.4 nm, a tungsten layer having a thickness of about 40 nm and density of 16.2 g/cm3 exhibits a phase shift quantity of −0.5π and a transmittance of about 31%. Table 1 shows thicknesses and transmittances of layers of tungsten and other materials on condition that the first layers of X-ray absorbers 2 having two-layer structures are prepared from tungsten and second layers thereof are prepared from elements, other than tungsten, having values β/δ smaller than that of tungsten, the total phase shift quantities of the X-ray absorbers 2 are −0.5π and the transmittances thereof are 50%. TABLE 1First LayerSecond LayerThicknessTrans-ThicknessTrans-Element(nm)mittance (%)Element(nm)mittance (%)W23450.1Li408199.9W23350.2Be115099.6W23250.4B86699.1W22950.8C54798.4W19855.7Na240089.7W18358.2Mg139685.9W16960.7Al98982.4W14664.9Si123177.0W10972.5P190568.9W6383.1S195060.2W21752.6K278395.1W21652.8Ca146894.6W21153.5Sc81893.4W20953.9Ti55292.7W20454.6V41991.5W20255.1Cr34990.7W19656.0Mn35189.2W19057.0Fe33287.7W18458.1Co30586.1W17659.5Ni30384.0W16661.2Cu32881.7W15563.3Zn42979.0W14365.5Ga56076.3W12668.9Ge66872.5W10773.0As66668.5W8378.3Se88463.8W17359.9Pd34683.5W17559.7Ag35483.8W17759.2Cd41784.4W16761.1In50181.8W16162.1Sn51580.5W15962.5Sb55679.9W15463.4Te62878.8W13666.9Cs166074.7W9775.1Ba129766.6 Lithuim (Li), beryllium (Be), boron (B), carbon (C), sodium (Na), magnesuium (Mg), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), potassium (K), calcium (Ca), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn); iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), arsenic (As), selenium (Se), palladium (Pd), silver (Ag), cadmium (Cd), indium (In), tin (Sn), antimony (Sb), tellurium (Te), cesium (Cs) and barium (Ba) can be listed as the materials for the second layers. Materials including mixtures of the aforementioned elements, carbides such as silicon carbide and tungsten carbide, nitrides such as silicon nitride, aluminum nitride and chromium nitride, oxides such as silicon oxide and chromium oxide, a fluoride and an iodide are preferably employed as the materials for the second layers. In practice, a material having excellent workability is selected from these materials, to be applied to X-ray absorbers. When any of the aforementioned materials is employed, the thickness of the tungsten layer included in the two-layer structure is reduced as compared with an X-ray absorber consisting of a single layer and hence the tungsten layer, which is hard to work, can be advantageously readily worked. When any of carbon (C), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), arsenic (As), selenium (Se), palladium (Pd), silver (Ag), cadmium (Cd), indium (In), tin (Sn), antimony (Sb) and tellurium (Te) is employed as the material for the second layer, the thickness of the two-layer structure can be reduced below 1000 nm. Thus, the thickness of the X-ray absorbers each having a two-layer structure can be relatively reduced, whereby the aspect ratio of the X-ray absorbers can also be relatively reduced. However, workability depends on the working process in addition to the materials, and hence a material having a small film thickness is not necessarily easy to work. The two layers forming each of the X-ray absorbers having a two-layer structure according to this embodiment are formed independently of each other mainly in consideration of workability of the X-ray absorbers. If the first and second layers are simultaneously workable, however, an effect similar to the aforementioned improvement of the optical image contrast can be attained also when single-layer X-ray absorbers, each consisting of a total element structural ratio of the elements forming the first and second layers, such as those shown in FIG. 1 are employed. Results of calculation of optical image contrast values in 35 nm L & S patterns with reference to various thicknesses of single-layer X-ray absorbers consisting of tungsten and two-layer X-ray absorbers containing tungsten are described with reference to FIGS. 5 to 10. Light applied to X-ray exposure employed in this embodiment is described. Radiation emitted from a radiation generator having deflection magnetic field strength of 3.5 T and acceleration energy of 0.585 GeV is employed for the X-ray exposure. This radiation is condensed on a beam line employing two platinum mirrors having an oblique angle of incidence of 1°. The condensed light passes through a beryllium window of 18 μm in thickness serving as a vacuum barrier. The light passing through the beryllium window is applied to a resist film as X-rays. In an X-ray mask 1, an X-ray transmitter 3 is prepared from diamond, while each of X-ray absorbers 2 has a two-layer structure consisting of a tungsten layer and a diamond layer. Portions provided with the X-ray absorbers 2 and those provided with no X-ray absorber 2 form an L & S pattern having a period of a pitch of 70 nm. This X-ray mask 1 is employed for transferring the pattern to a resist film with a mask-to-resist interval G of 6 μm. The resist film is prepared from photosensitive resin based on polyhydroxystyrene bromide having a bromine content of 45 percent by weight. Optical image contrast is calculated from an absorbed energy image on the resist film. In order to investigate an effect attained when reducing the exposure wavelength λ below 0.7 nm, optical image contrast is calculated with reference to various thicknesses, ranging from 2 μm to 100 μm, of a diamond film forming the X-ray transmitter 3. The average exposure wavelength of X-rays absorbed by the resist film is 0.74 nm when the thickness of the diamond film is 2 μm, the former is 0.37 nm when the latter is 100 μm, and the former is about 0.4 nm when the latter is in the range of 60 μm to 80 μm. The thickness of the diamond film forming the X-ray transmitter 3 is varied for reducing the exposure wavelength λ of X-rays absorbed by the resist film. If the exposure wavelength λ is reducible, another method may alternatively be employed in place of that of varying the thickness of the diamond film. FIG. 5 is a graph showing results of calculation obtained when varying the thickness of a tungsten layer forming an X-ray absorber with reference to the relation between optical image contrast in a case of employing the X-ray absorber consisting of a single tungsten layer and the thickness of a diamond film forming an X-ray transmitter. FIG. 6 shows results obtained when varying the thicknesses of tungsten layers with reference to the relation between optical image contrast in a case of employing the X-ray mask 1 according to this embodiment and the thickness of the diamond film. The X-ray mask 1 consists of the X-ray absorbers 2 each having a two-layer structure including a first layer of tungsten having a thickness of 230 nm and a second layer of diamond. FIG. 6 shows optical image contrast in a case of varying the thicknesses of the diamond layers forming the X-ray absorbers 2 in the range of 0 to 1150 nm. In the comparative X-ray absorber shown in FIG. 5, the optical image contrast varies with the thickness of the tungsten layer and the thickness of the diamond film forming the X-ray transmitter. However, it is understood that the highest optical image contrast is obtained when the thickness of the tungsten layer is 300 nm if the exposure wavelength λ is relatively short and the thickness of the diamond film forming the X-ray transmitter is at least 60 μm. It is also understood that the X-ray mask 1 according to this embodiment having the X-ray absorbers 2 of the two-layer structure shown in FIG. 6 obtains higher optical image contrast than the X-ray mask having the comparative X-ray absorber shown in FIG. 5 when the thickness of the first layers of tungsten is 230 nm and the thickness of the second layers of diamond is in the range of 250 nm to 550 nm. In other words, the X-ray mask 1 according to this embodiment obtains higher optical image contrast than the X-ray mask employing the comparative X-ray absorber when the thickness of the diamond film forming the X-ray transmitter is 60 μm to 100 μm and the average exposure wavelength of X-rays absorbed by the resist film is proximate to 0.4 nm. Table 1 shows a combination of a tungsten layer having a thickness of 229 nm and a carbon layer having a thickness of 547 nm as a two-layer structure exhibiting a phase shift quantity of −0.5π and a transmittance of 50% when the exposure wavelength λ is 0.4 nm. As compared with a case of performing exposure with a broad exposure spectrum as in the X-ray mask 1 according to this embodiment, however, optical image contrast is rather increased when the thickness of the second layers of diamond is slightly reduced if the average exposure wavelength of X-rays absorbed by the resist film is 0.4 nm. Employment of such a broad exposure spectrum may result in deviation from an optimum condition assumed in response to the average exposure wavelength of X-rays absorbed by the resist film. Also in this case, higher optical image contrast is obtained also with respect to the broad exposure spectrum when employing two-layer X-ray absorbers as in the X-ray mask 1 according to this embodiment. Difference between effects of optical image contrast resulting from the sizes of mask patterns is now described. More specifically, optical image contrast values are compared by varying the widths of X-ray absorbers 2 in the range of 15 nm to 55 nm in L & S patterns having pitches of 70 nm. FIG. 7 is a graph plotting optical image contrast values in a case of employing a tungsten layer of 300 nm in thickness as a comparative X-ray absorber while varying the thickness of a diamond film forming an X-ray transmitter. FIG. 8 is a graph plotting optical image contrast values in a case of employing layers of tungsten and diamond having thicknesses of 230 nm and 250 nm respectively as the X-ray absorbers 2 each having a two-layer structure according to this embodiment while varying the thickness of the diamond film forming the X-ray transmitter. It is understood from FIG. 7 that the comparative X-ray absorber can improve the optical image contrast by increasing the line width of a mask pattern by about 10 nm to 20 nm. A similar effect is observed also in the X-ray absorbers each having a two-layer structure, as shown in FIG. 8. In other words, optical image contrast can be further improved by increasing the line width of the mask pattern by about 10 nm to 20 nm. Comparing FIGS. 7 and 8 with each other, it is understood effective to increase the width of an absorber pattern by about 10 nm for improving optical image contrast particularly when the thickness of the diamond layers forming the X-ray absorbers 2 is at least 40 μm. FIG. 9 shows optical image contrast values in a case of further increasing the mask-to-resist interval G to 8 μm. This is a graph plotting the optical image contrast values while varying the thicknesses of the X-ray absorbers 2 and the thickness of the diamond film forming the X-ray transmitter when the line width of the X-ray absorbers 2 of an L & S pattern having a pitch of 70 nm is 55 nm. FIG. 10 is a graph showing optical image contrast values obtained in an X-ray mask having the same mask-to-resist interval G as that of the X-ray mask shown in FIG. 9 while varying the thickness of second layers of diamond with two-layer X-ray absorbers 2 including first layers of tungsten having a thickness of 230 nm and the second layers of diamond. The line width of the X-ray absorbers 2 is 55 nm identically to the aforementioned case. In a 35 nm L & S pattern, geometric phase difference is 0.38π rad if the mask-to-resist interval G is 8 μm and the exposure wavelength λ is 0.4 nm. In other words, the geometric phase difference is smaller than the optimum value of 0.5 πrad. FIG. 9 shows that the optical image contrast is higher in a case of employing tungsten layers of 500 nm in thickness as X-ray absorbers as compared with a case of employing tungsten layers having the optimum thickness of 300 nm for a mask-to-resist interval G of 6 μm when the geometric phase difference deviates from the optimum value. Thus, it is understood that the optimum condition for X-ray absorbers varies with the mask-to-resist interval G. When the exposure wavelength k is 0.4 nm, the tungsten layers having the thickness of 500 nm exhibit a transmittance of 23% and a phase shift quantity of −0.63π. In other words, it is understood that the transmittance and the optimum phase shift quantity of the X-ray absorbers vary with the mask-to-resist interval G. It is understood that the difference between the geometric phase difference and the phase shift quantity of the mask satisfies 0.38π−(−0.63π)=1.01π, i.e., the phase condition described with reference to the principle employed in the present invention. FIG. 10 is a graph showing optical image contrast values obtained by varying the phase shift quantities of X-ray absorbers each having a two-layer structure of tungsten and diamond with a transmittance in the range of 49% to 51% with respect to a mask-to-resist interval G of 8 μm. When X-ray absorbers of a two-layer structure are employed, the phase shift quantity thereof can be changed without substantially changing the transmittance of the X-ray mask. The line width of the X-ray absorbers is 55 nm, similarly to the aforementioned case. It is understood from Table 1 that the phase shift quantity of the X-ray absorbers is −0.5 πwhen the thickness of diamond layers is 550 nm. It is also understood from Table 1 that the phase shift quantity of the X-ray absorbers is increased toward the minus side when the thickness of the diamond layers is at least 550 nm. As understood from FIG. 10, optical image contrast values are substantially identical to each other when the thickness of diamond layers forming two-layer X-ray absorbers is 700 nm and the thickness of a tungsten layer forming a single-layer X-ray absorber is 500 nm. It is also understood that the optical image contrast is increased when the thickness of the diamond layers is further increased and the phase shift quantity of the X-ray absorbers is increased toward the minus side as compared with the case that the thickness of the first tungsten layers of the X-ray absorbers is 500 nm. In other words, it is understood that an optical image having higher contrast than the prior art is obtained also when the geometric phase difference remarkably deviates from 0.5π, if X-ray absorbers having a two-layer structure are employed and the phase shift quantity as well as the transmittance of the X-ray absorbers are adjusted. The X-ray mask 1 according to this embodiment is described with reference to an L & S pattern attaining a particularly remarkable effect. Also when employing X-ray absorbers having a hole pattern or a more complex two-dimensional mask pattern, however, a desired resist pattern is formed if at least either the mask-to-resist interval G or the exposure wavelength λ is properly selected. According to this embodiment, adjustment of conditions such as the phase shift quantity and the transmittance, performed in the comparative single-layer X-ray absorber, is performed with the X-ray absorbers having a two-layer structure. Thus, a semiconductor device having a finer pattern can be formed with an exposure wavelength λ shorter than the conventional one and a mask-to-resist interval G wider than the conventional one. Therefore, it is not impossible to form a hole pattern or a more complex two-dimensional mask pattern. In other words, a hole pattern or a more complex two-dimensional mask pattern can be formed similarly to that transferable in the comparative X-ray absorber. Further, it is possible to form a semiconductor device having a fine pattern by selecting at least either a proper phase shift quantity or a proper transmittance. An element such as bromine employed in this embodiment as a resist film having an absorption edge in an exposure waveband, there is such an exposure wave range that the maximum energy of secondary electrons generated in the resist film remains unchanged also when the exposure wavelength λ is reduced. Therefore, such a remarkable effect is attained that influence by the secondary electrons deteriorating the resolution is suppressed. When the X-ray absorbers 2 according to this embodiment are combined with a resist film having an absorption edge in an exposure wave range, therefore, influence by secondary electrons is suppressed also when the exposure wavelength λ is reduced. Consequently, an optical image having high contrast can be provided. Therefore, it is possible to form a resist film having a more accurate pattern than the comparative example. Second Embodiment An X-ray mask according to a second embodiment of the present invention is now described with reference to FIGS. 11 and 12. FIG. 11 shows the structure of an X-ray mask formed by X-ray absorbers having a two-layer structure. In the X-ray mask according to this embodiment, a diamond film 11 having a thickness of 5 μm is employed as an X-ray transmitter, and an amorphous chromium oxide film 12 is employed as an etching stopper. Diamond layers 13 serving as first layers are formed on the chromium oxide film 12. Tungsten layers 14 serving as second layers are formed on the diamond layers 13. The diamond layers 13 and the tungsten layers 14 form the X-ray absorbers of the two-layer structure. The X-ray absorbers of the two-layer structure have a high ratio of a pattern to a line width, i.e., a high aspect ratio. Therefore, it is difficult to accurately work the X-ray absorbers. According to this embodiment, therefore, the etching stopper is inserted between the diamond film 11 and the diamond layers 13. Thus, the pattern of the X-ray absorbers can be accurately worked. If the transmittances and the phase shift quantities are not remarkably different from each other between the first and second layers of the X-ray absorbers, etching stoppers or hard mask material layers 15 for the second or first layers of the X-ray absorbers may be inserted between tungsten layers 14 and diamond layers 13 serving as the first and second layers respectively, as shown in FIG. 16. Each of the X-ray absorbers is so separated into two layers that optimum etching gas and optimum conditions can be set for the respective layers. For example, tungsten, etched with etching gas mainly composed of fluorine, is hardly etched with etching gas mainly composed of oxygen, On the other hand, diamond, readily etched with oxygen plasma, is not etched with fluorine-based plasma dissimilarly to tungsten. Therefore, accurate pattern working can be implemented by selecting the optimum etching gas for attaining a high etching selection ratio with respect to underlayer films when etching the respective layers. In the X-ray absorbers according to this embodiment, the diamond layers 13 serving as the first layers are provided under the tungsten layers 14. When the diamond layers 13 serving as the first layers are etched, therefore, the tungsten layers 14 serve as hard masks for the diamond layers 13. Consequently, an accurate pattern for the X-ray absorbers is formed while controlling the shapes of side walls of the diamond layers 13. The diamond layers 13 serving as the first layers are etched with etching gas mainly composed of oxygen. Therefore, etching stoppers are preferably formed by oxide films containing an oxide such as silicon oxide, tungsten oxide or tantalum oxide, which is hardly etched with oxygen plasma. Alternatively, the etching stoppers may be formed by nitride films containing a nitride such as silicon nitride, chromium nitride or tungsten nitride, so far as a selection ratio with respect to underlayer films is in excess of a prescribed value. In the X-ray mask according to this embodiment, the tungsten layers 14 are formed on the diamond layers 13, in consideration of easiness of etching. However, diamond layers 13 may alternatively be provided on tungsten layers 14 as shown in FIG. 12, for attaining an effect of improving optical image contrast similarly to the X-ray absorbers having the tungsten layers 14 provided on the diamond layers 13 as shown in FIG. 11. Third Embodiment An X-ray mask according to a third embodiment of the present invention is now described with reference to FIG. 13. FIG. 13 is a diagram for illustrating an X-ray mask formed with X-ray absorbers on portions other than trenches dug in a diamond film 11 serving as an X-ray transmitter. In the X-ray mask shown in FIG. 13, the portions other than the dug portions, partially forming the X-ray transmitter, i.e., projections are employed as the X-ray absorbers. Therefore, no layers may be formed as the first layers of the X-ray absorbers. Consequently, steps of film formation and working can be simplified. In this case, prescribed adjustment is so performed that low membrane stress is caused only in the dug regions of the diamond film 11 serving as the X-ray transmitter. Thus, stress fluctuation is reduced in pattern working of the diamond film 11 serving as the X-ray transmitter. Consequently, the possibility of positional distortion of the X-ray mask is reduced. Ions are implanted before working the dug regions of the X-ray transmitter. Thus, membrane stress of the X-ray transmitter is so adjusted as to obtain X-ray absorbers of a two-layer structure having a small degree of positional distortion. Difference between etching rates of portions of the diamond film 11 subjected to ion implantation and portions not subjected to ion implantation is utilized thereby enabling working of an accurate pattern without employing etching stoppers. While boron ions are implanted in this embodiment, phosphorus ions or the like may alternatively be employed. Fourth Embodiment An X-ray mask according to a fourth embodiment of the present invention is now described with reference to FIG. 14. FIG. 14 is a block diagram of an X-ray mask provided with X-ray absorbers each having a two-layer structure consisting of layers having different pattern sizes. In the X-ray mask according to this embodiment, an etching stopper 110 is formed on an X-ray transmitter 100, as shown in FIG. 14. In this X-ray mask, further, first X-ray absorbers 120 are formed on the etching stopper 110, and second X-ray absorbers 130 are formed on the first X-ray absorbers 120. Referring to FIG. 14, the pattern size of the second X-ray absorbers 130 is smaller than that of the first X-ray absorbers 120. Optical image contrast can be improved by adjusting the mask pattern size with respect to a periodic pattern having the same pattern pitch, as described with reference to the first embodiment. When the X-ray mask according to this embodiment is employed, it is possible to adjust the mask pattern size of a layer having a larger absolute value of a phase shift quantity and a lower transmittance among respective layers, for example. Consequently, it is possible to form a pattern having higher optical image contrast than the prior art. The X-ray mask shown in FIG. 15 attains an effect of improving optical image contrast also when the second X-ray absorbers 130 have a larger mask pattern size than the first X-ray absorbers 120. In this case, however, it is difficult to measure the mask pattern size of the first X-ray absorbers 120. Therefore, it is preferable to increase the mask pattern size of the first X-ray absorbers 120 beyond that of the second X-ray absorbers 130, as shown in FIG. 14. Fifth Embodiment A method of fabricating a semiconductor device with the inventive X-ray mask according to a fifth embodiment of the present invention is now described. According to this embodiment, a semiconductor device is fabricated with an exposure method similar to that according to the first embodiment. A diamond film having a thickness of 5 μm is employed as the material for an X-ray transmitter. Tungsten layers having a thickness of 230 nm and density of 16.2 g/cm3 are employed as first X-ray absorbers. Further, diamond layers having a thickness of 250 nm and density of 3.5 g/cm3 are employed as second X-ray absorbers. The tungsten and diamond layers serving as the first and second X-ray absorbers respectively form X-ray absorbers having a two-layer structure. In other words, an X-ray mask similar in structure to that shown in FIG. 11 is employed. In the method of fabricating a semiconductor device according to this embodiment, a mask pattern having a period of a pitch of 70 nm formed on the X-ray mask is transferred onto a resist film as a 35 nm L & S pattern. Radiation emitted from a radiation generator having deflection magnetic field strength of 3.5 T and acceleration energy of 0.585 GeV is employed as exposure light. This radiation is condensed on a beam line through two platinum mirrors having an oblique angle of incidence of 1°. The condensed light passes through a beryllium window having a thickness of 18 μm serving as a vacuum barrier and a diamond filter having a thickness of 55 μm. A mask-to-resist interval G is 6 μm. The photosensitized resist film has a bromine content of 45 percent by weight, contains novolac bromide as base resin and has a thickness of 0.2 μm. Thus, the pattern of the 35 nm L & S pattern is formed on the resist film. The pattern on this resist film is etched. Thereafter an underlayer film is worked. Then, the underlayer film is cleaned and formed. The resist film is exposed again with another X-ray mask. The aforementioned steps are so repeated as to fabricate a semiconductor device. X-ray absorbers having a two-layer structure are employed for transferring the pattern of the X-ray mask to the resist film. Thus, a semiconductor device having higher performance than a conventional one can be fabricated with a pattern finer than a conventional one. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims. |
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046648828 | abstract | A segmented fuel and moderator rod and fuel assembly for a BWR. The segmented rod has a lower fuel region and an upper moderator region for passing coolant having a void fraction of between about 0-20% through the upper portion of the BWR core which is normally undermoderated. The segmented rod displaces one or more conventional fuel rods in the fuel bundle. A method of moderating a BWR core is also disclosed. |
052710521 | claims | 1. A nuclear reactor control system comprising a nuclear reactor vessel having a coolant solution circulating through said reactor vessel, said coolant solution being comprised of an isotopically enriched boron-10 boric acid solution, said boric acid solution containing a boron-10 to boron-11 atomic isotope ratio of at least 30%. 2. The nuclear reactor control system of claim 1, wherein the control system further comprises: (a) a reactor coolant system which contains said coolant solution, said coolant system connected to said reactor vessel; (b) a refueling water storage tank, said refueling water storage tank containing a natural boric acid solution; (c) conduit means for connecting said refueling water storage tank to said reactor vessel. a refueling inlet line connecting at least one of the group consisting of the concentration system, the boron-10 storage system, and the make-up system to said residual heat removal system; a refueling outlet line connected to said residual heat removal system upstream from said refueling outlet line and an isolation valve located between the refueling outlet line and the refueling inlet line. 3. The control system of claim 2, wherein said isotopically enriched boron-10 boric acid solution has a boron-10 to boron-11 isotope ratio of up to 95:5, at the start of the reactor cycle. 4. The control system of claim 2, wherein said isotopically enriched boron-10 boric acid solution has a boron-10 to boron-11 isotope ratio which is about 75:25 at the start of the reactor cycle. 5. The control system of claim 3, wherein said nuclear reactor is a pressurized water nuclear reactor. 6. The control system of claim 5 which includes a make-up system containing an enriched boric acid solution, flow coupled to said reactor coolant system. 7. The control system of claim 6, which includes a boron-10 storage system flow coupled to said reactor coolant system and a concentration system flow coupled to said boron-10 storage system. 8. The control system of claim 7, wherein said boron-10 storage system is an ion exchange system and said concentration system is an evaporation system. 9. The control system of claim 7 which includes a residual heat removal system flow coupled to said coolant system; 10. The control system of claim 9 which includes an analyzer to monitor the temperature of the solution in said refueling outlet line. 11. The control system of claim 9 which includes an analyzer to monitor the boron-10 enrichment of the solution in said refueling outlet line. |
description | This application is a continuation of copending International Application No. PCT/DE99/00447, filed Feb. 18, 1999, which designated the United States. The present invention relates to a containment vessel of a nuclear power plant, having a condensing chamber, a pressure chamber and a condenser disposed in a top region of the pressure chamber. The invention also relates to a method of operating a condenser in a nuclear power plant. Modern safety concepts of nuclear power plants are conceived with the aim that, in the event of accidents, the effects on the nuclear power plant will be limited and the environment will not be contaminated. An important point in that respect is that sufficient cooling of important components of the nuclear power plant be ensured in every operating situation. In order to increase safety, emergency cooling devices provided for cooling are generally constructed as passive components which are operable independently of external power sources and solely-on the basis of laws of physics. An article entitled “SWR 1000—Der Siedewasserreaktor der Zukunft” [SWR 1000—The Boiling Water Reactor of the Future], Siemens Power Journal, pages 18 to 22, February 1996, Siemens AG, Germany, Order No. A96001-U90-A314, discloses an innovative construction and safety concept for a boiling water reactor. In the boiling water reactor described therein, the reactor pressure vessel is disposed centrally in a containment vessel, known as the containment. In order to provide for the emergency cooling of the boiling water reactor, a closed-off condensing chamber and a flood basin disposed above it are provided in an interior space of the containment vessel. The flood basin is open toward a central region in which the reactor pressure vessel is disposed. The flood basin forms a pressure chamber with the central region. A so-called building condenser is disposed above the flood basin, i.e. in the top region of the pressure chamber or of the containment vessel. The building condenser is connected to a cooling liquid of a cooling basin disposed above the containment vessel and serves to dissipate heat from the pressure chamber. The efficiency of the building condenser reacts in a sensitive manner to the presence of noncondensible gases, such as nitrogen or hydrogen, in which case the latter in particular may be produced in the event of serious accidents. That is because the noncondensible gases reduce the capacity of the building condenser to dissipate heat from any steam present in the pressure chamber into the cooling basin. Hydrogen accumulates in the top region of the pressure chamber due to its low specific weight, so that a high concentration of noncondensible gases may be present precisely in the surroundings of the building condenser. The high concentration leads to a pressure increase in the containment vessel in that case, due to the deficient heat dissipation through the building condenser. In order to dissipate heat from the pressure chamber in the event of an accident, concepts are known in which the pressure chamber is connected through a flow path to a condenser that is disposed in a cooling basin which is located, for example, on the containment vessel. Superheated steam located in the pressure chamber in the event of an accident passes through that flow path together with the noncondensible gases into the condenser. The steam is cooled down and condensed there by heat emission to the cooling basin. A mixture of liquid and noncondensible gases therefore forms in the condenser. The mixture is passed back into the containment vessel again in order to ensure that no radioactivity can pass into the environment. A gas/liquid separation device is generally provided in order to separate off the noncondensible gases. The latter are directed into the condensing chamber and trapped there so that they cannot escape again into the pressure chamber. The liquid is optionally used for cooling the reactor pressure vessel or is likewise directed into the condensing chamber. To that end, control valves in appropriate pipelines are often used. That concept or comparable concepts for heat dissipation in the event of an accident are described, for example, in U.S. Pat. No. 5,102,617, U.S. Pat. No. 5,149,492, U.S. Pat. No. 5,570,401 and European Patent Applications 0 681 300 A1 and 0 620 560 A1. A common feature of all of the known concepts is that the steam to be cooled down is directed together with the noncondensible gases into the condenser. It is known from European Patent Application 0 492 899 A1 to provide a flow path between the condensing chamber and the pressure chamber. The flow path is automatically opened from a certain pressure difference between those two chambers in order to direct superheated steam into the condensing chamber for dissipating the heat and reducing the pressure in the event of an accident. The flow path is constructed as a U-shaped pipe, which may be referred to as a condensing pipe. Two legs of the U-shaped pipe are disposed with their respective openings inside the pressure chamber or inside the condensing chamber. Liquid is located in a U-shaped or siphon-like bend, so that the flow path formed by the U-shaped pipe is closed as long as the pressure in the pressure chamber is not substantially higher than that in the condensing chamber. It is accordingly an object of the invention to provide a containment vessel of a nuclear power plant having a condenser, and a method of operating a condenser in a nuclear power plant, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and in which an efficiency of the condenser is largely unaffected by noncondensible gases. With the foregoing and other objects in view there is provided, in accordance with the invention, a containment vessel of a nuclear power plant, comprising an interior space; a condensing chamber disposed in the interior space; a pressure chamber disposed in the interior space, the pressure chamber having a top region; a condenser communicating with the pressure chamber through a flow path; and a drain pipe for noncondensible gases, the drain pipe disposed in the interior space and fluidically connecting the top region of the pressure chamber to the condensing chamber. With the objects of the invention in view, there is also provided a containment vessel of a nuclear power plant, comprising an interior space; a condensing chamber disposed in the interior space; a pressure chamber disposed in the interior space; a condenser disposed in the pressure chamber and defining a region around the condenser; and a drain pipe for noncondensible gases, the drain pipe fluidically connecting the region around the condenser to the condensing chamber, and the drain pipe having a top end disposed above the condenser. The two embodiments are based on the common inventive concept of ensuring a high efficiency of the condenser by preventing noncondensible gases from coming into contact with the condenser in too high a concentration. In principle, the condenser may be disposed both inside and outside the pressure chamber. If it is disposed outside the pressure chamber, superheated steam is directed to it through a flow path from the top region of the pressure chamber. In the first embodiment, the noncondensible gases are drawn off beforehand from the top region of the pressure chamber through the drain pipe into the condensing chamber. In the case of a condenser disposed inside the pressure chamber, provision is made in the second embodiment for the noncondensible gases to be drawn off directly from the surroundings of the condenser through the use of the drain pipe. In this case, the condenser is disposed in particular in the top region of the pressure chamber. A common feature of both embodiments is the fact that the drain pipe is constructed as a simple pipe and is disposed completely inside the containment vessel. An immediate and direct connection is made between the pressure chamber and the condensing chamber by the drain pipe. In particular, no further components are connected in the flow path formed by the drain pipe. Therefore, the noncondensible gases are drawn off into the condensing chamber in an expedient and direct manner in both embodiments due to the configuration of the drain pipe. The condensing chamber is filled up to a filling level with a cooling liquid, which forms a so-called water receiver. The noncondensible gases are, for example, hydrogen or inert gases, such as air or nitrogen. Air or nitrogen mixes comparatively easily with the steam in the region of the condenser. As a result, the capacity of the condenser to dissipate heat may be substantially impaired. Due to the fact that less heat is then dissipated, the pressure in the pressure chamber increases, specifically until the steam/inert-gas mixture flows over automatically into the condensing chamber through the drain pipe. The steam condenses there in the water receiver and the noncondensible gases remain behind in the gas space of the condensing chamber. The steam/inert-gas mixture flows into the condensing chamber until the concentration of the noncondensible gases has been reduced to such an extent that the condenser can again dissipate all of the heat being supplied. If hydrogen is present, it collects in the top region of the pressure chamber due to its low specific weight. If a large quantity of hydrogen is present, the condenser is surrounded by hydrogen. The efficiency of the condenser is then substantially impaired and the condenser dissipates little heat. As a result, inert gases appear to a comparable degree to increase the pressure in the pressure chamber and virtually pure hydrogen flows over into the condensing chamber. In this way, a large part of the hydrogen is directed into the condensing chamber. After hydrogen has flown off, the condenser is again mainly surrounded by steam and can readily dissipate the heat of the steam. The noncondensible gases remain in the condensing chamber, which is largely closed off from the pressure chamber, and cannot escape into the pressure chamber. The concentration of noncondensible gases in the region of the condenser therefore remains small. It is thus ensured that the mode of operation of the condenser is largely unaffected by the noncondensible gases. An essential advantage of the configuration of the drain pipe is the fact that the condenser may have a simple structure. In particular, it is sufficient to construct its heat-exchange capacity for virtually pure saturated steam. The heat-exchanging surface of the condenser may thus be constructed to be simpler and smaller than would be the case if there were no drain pipe. As a rule, the heat-exchanging areas are tubes, which are packed to form compact heat-exchanger bundles. A further advantage is that the entire gas space of the condensing chamber is available for storing the hydrogen being released, for example in the event of an accident. In the event of an accident, the pressure increase in the containment vessel is therefore smaller than if there were no possibility of the hydrogen flowing over through the drain pipe. The top end of the drain pipe is preferably disposed above the condenser, so that hydrogen, which collects in the topmost region of the pressure chamber above the condenser due to its low specific weight, can be drawn off in an expedient manner. In accordance with another feature of the invention, in order to permit an especially simple construction of the drain pipe and a maintenance-free and reliable operation of the drain pipe, the drain pipe preferably forms a permanently open flow path. Thus no valves, slides or similar shut-off mechanisms are provided in the drain pipe. In accordance with a further feature of the invention, the bottom end of the drain pipe is immersed in the cooling liquid of the condensing chamber. As a result, steam which is directed with the noncondensible gases through the drain pipe into the condensing chamber condenses directly upon being introduced into the condensing chamber. In accordance with an added feature of the invention, the bottom end of the drain pipe discharges into the cooling liquid above a lower end of a condensing pipe which is run, for example, from the pressure chamber into the condensing chamber. Such condensing pipes are provided in order to direct large steam quantities from the pressure chamber into the condensing chamber and to condense them there, so that the pressure in the pressure chamber and thus in the containment vessel is reduced. The condensing pipe is accordingly immersed deeper in the cooling liquid of the condensing chamber than the drain pipe, and there is a smaller water column in the drain pipe than in the condensing pipe. The effect of the smaller immersion depth of the drain pipe is that, in the event of minor accidents with little escape of steam, steam is transferred into the condensing chamber merely through the drain pipe, while the substantially larger condensing pipes remain closed by water plugs. In accordance with an additional feature of the invention, the condenser is fluidically connected to an external cooling basin. Such a condenser is also referred to as a building condenser. It can dissipate the heat from the containment vessel into the surroundings of the containment vessel. In this case, the cooling basin is disposed on the containment vessel, in particular outside the same. With the objects of the invention in view, there is additionally provided a method of operating a condenser in a nuclear power plant, which comprises automatically drawing off noncondensible gases from a region above the condenser, so that the efficiency of the condenser is largely unaffected by noncondensible gases. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a containment vessel and a method of operating a condenser in a nuclear power plant, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. Referring now in detail to the single FIGURE of the drawing, there is seen a reactor pressure vessel 2 which is disposed centrally in a closed containment vessel 1, that is also merely referred to as a containment. A condensing chamber 4 and a flood basin 8 disposed above it are provided laterally next to the reactor pressure vessel 2, as further built-in components in the containment vessel 1. The flood basin 8 is open at the top toward an interior space of the containment vessel 1. The interior space is also designated as a pressure chamber 6. The latter forms a common pressure space with the flood basin 8. The condensing chamber 4 and the flood basin 8 are each partly filled with a cooling liquid f, in particular water, up to a filling level n. The maximum filling level n in the flood basin 8 is determined by a top end of an overflow pipe 10. The overflow pipe 10 connects the flood basin 8 to the condensing chamber 4 and discharges into the cooling liquid f of the condensing chamber 4. If the maximum filling level n is exceeded, the cooling liquid f flows off from the flood basin 8 into the condensing chamber 4. Furthermore, the flood basin 8 is connected through a flood line 12 to the reactor pressure vessel 2 and can supply the latter with sufficient cooling liquid f in an emergency. The condensing chamber 4 is largely closed off from the pressure chamber 6. It is merely connected to the pressure chamber 6 through a condensing pipe 14. The condensing pipe 14 is immersed in the cooling liquid f of the condensing chamber 4, so that no gas exchange takes place between the condensing chamber 4 and the pressure chamber 6. The condensing pipe 14 is closed by a water plug 15, which is formed by a water column in the condensing pipe 14. Steam only flows into the condensing chamber 4 through the condensing pipe 14 for condensing in the event of an accident, if the pressure in the pressure chamber 6 increases. A condenser 16, which is designated as a building condenser, is disposed in a top region of the containment vessel 1 and thus in a top region of the pressure chamber 6, in the left-hand half of the FIGURE. The condenser 16 is constructed as a heat exchanger with heat-exchanger tubes and is fluidically connected to a cooling basin 18. In principle, the condenser 16 may also be disposed outside the containment vessel 1 in this cooling basin 18 and may be connected through pipelines to the interior space of the containment vessel, in particular to the pressure chamber 6. The cooling basin 18 is disposed outside the containment vessel 1 on a cover 20 thereof. The condenser 16 absorbs heat from its surroundings inside the containment vessel 1 and transfers it to the cooling basin 18. As a result, heat can be dissipated from the containment vessel 1 to the external surroundings. A drain pipe 22 is preferably disposed in the region of the condenser 16. It is important that its top end 24 is disposed in the top region of the pressure chamber 6 and in particular at a level above the condenser 16. Its bottom end 26 discharges into the cooling liquid f of the condensing chamber 4. The drain pipe 22 is constructed as a simple pipe which is free of built-in components and forms an open flow path from the pressure chamber 6 into the cooling liquid f of the condensing chamber 4. In this case, “free of built-in components” means that no valves or other fittings or components are connected in the flow path. In this case, the immersion depth of the drain pipe 22 in the cooling liquid f is smaller than that of the overflow pipe 10 and that of the condensing pipe 14, which has a substantially larger cross-sectional area than the drain pipe 22. The bottom end 26 of the drain pipe 22 is therefore disposed above respective outlet orifices 28 of the condensing pipe 14 and the overflow pipe 10. In the event of an accident, for example in the event of a fracture in a steam line in the containment vessel 1 and an escape of steam associated therewith, the temperature and the pressure in the containment vessel 1 increase. Various emergency cooling devices, of which only the condenser 16 and the flood basin 8 with the associated flood line 12 are shown in the FIGURE, ensure that the final pressure in the event of an accident in the containment vessel 1 does not exceed an admissible limit value. This is primarily achieved by cooling and condensing of the steam. An important factor in this case is the condenser 16, with which heat can be dissipated to the outside from the containment vessel 1. In the course of an accident, noncondensible gases, in particular hydrogen, will possibly be released, and these noncondensible gases accumulate in the top region of the containment vessel 1, i.e. in the top region of the pressure chamber 6. The noncondensible gases which collect in the top region of the pressure chamber 6 lead to an increase in the pressure in the containment vessel 1. Due to the configuration of the drain pipe 22 and the increased pressure in the region of the top end 24, the mixture of steam and noncondensible gases there flows off through the drain pipe 22 from the top region of the pressure chamber 6 into the condensing chamber 4. The entrained steam is condensed in the condensing chamber 4. Therefore, by virtue of the drain pipe 22, an accumulation of noncondensible gases, for which the entire gas space in the condensing chamber 4 is available, is avoided in the region around the condenser 16. In principle, the noncondensible gases impair the efficiency of the condenser 16 by virtue of the fact that they substantially reduce the heat exchange capacity of the condenser 16. When noncondensible gases are present, substantially less heat per unit of time and per unit of area can be dissipated from the steam to the cooling basin 18 by the heat exchanger 16 than when noncondensible gases are absent. Since the latter are drawn off from the surroundings of the condenser 16, the condenser 16 can be constructed for saturated steam. The condenser 16 therefore does not need to have any large and specially constructed heat-exchange areas, which would be absolutely necessary if noncondensible gases were present in order to be able to dissipate sufficient heat. The condenser 16 may therefore have a simple, compact and thus cost-effective construction. Due to the smaller immersion depth of the drain pipe 22 as compared with that of the condensing pipe 14, steam will flow out of the pressure chamber 6 into the condensing chamber 4 solely through the drain pipe 22 as long as there is only a low positive pressure in the pressure chamber 6 relative to the pressure in the condensing chamber 4. Steam can only flow through the condensing pipe 14 into the condensing chamber 4 at greater pressure differences between the pressure chamber 6 and the condensing chamber 4, which only occur briefly in exceptional cases. The condensing pipe 14 has a large cross section of flow and therefore enables very large steam quantities to be directed for condensing into the condensing chamber 4 in the shortest possible time. According to the present novel concept, in a containment vessel 1 with a condenser 16, noncondensible gases are automatically drawn off from the active region of the condenser 16 into the condensing chamber 4 through a flow path. In this case, the flow path is formed by a simple drain pipe 22. The mode of operation of the drain pipe 22 is purely passive, thus no external control actions are necessary. The drain pipe 22 also requires no movable components and is therefore maintenance-free. The reliability of performance of the condenser 16 is ensured by the configuration of the drain pipe 22, so that the condenser 16 may have a simple structure. |
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abstract | A multilayer mirror 1 that has elliptical reflection faces and provides a divergent angle xcex4 of X-rays, is included. The elliptical reflection faces of the multilayer mirror 1 have two focal points. When an X-ray source 2 is arranged at one focal point A, and X-rays that are diverged from the X-ray source 2 are reflected at the multilayer mirror 1, the reflected X-rays converge on another focal point B. The X-ray source 2 is arranged at one focal point A of the multilayer mirror 1. Additionally, a distance L2 from the center of the reflection faces of the multilayer mirror 1 to another focal point B (in other words, convergent point of reflected X-rays) is set to make a convergent angle xcex8c of X-rays at the focal point B nearly twice as great as the divergent angle xcex4. With the above-noted configuration, both small angle resolution and intensity of incident X-rays to a sample may be optimized, and small angle scattering may be performed with high precision. |
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summary | ||
description | 1. Field of the Invention The present invention relates generally to a nuclear core component hold-down assembly and more particularly to such a hold-down assembly that is compatible with a top mounted instrumentation system that can provide a defined channel at a central location in the fuel assembly for the insertion and removal of in-core instrumentation. 2. Description of the Prior Art The primary side of nuclear reactor power generating systems which are cooled with water under pressure comprises a closed circuit which is isolated and in heat exchange relationship with a secondary side for the production of useful energy. The primary side comprises the reactor vessel enclosing a core internal structure that supports a plurality of fuel assemblies containing fissile material, the primary circuit within heat exchange steam generators, the inner volume of a pressurizer, pumps and pipes for circulating pressurized water; the pipes connecting each of the steam generators and pumps to the reactor vessel independently. Each of the parts of the primary side comprising a steam generator, a pump and a system of pipes which are connected to the vessel form a loop of the primary side. For the purpose of illustration, FIG. 1 shows a simplified nuclear reactor primary system, including a generally cylindrical reactor pressure vessel 10 having a closure head 12 enclosing a nuclear core 14. A liquid reactor coolant, such as water is pumped into the vessel 10 by pump 16 through the core 14 where heat energy is absorbed and is discharged to a heat exchanger 18, typically referred to as a steam generator, in which heat is transferred to a utilization circuit (not shown), such as a steam driven turbine generator. The reactor coolant is then returned to the pump 16, completing the primary loop. Typically, a plurality of the above described loops are connected to a single reactor vessel 10 by reactor coolant piping 20. An exemplary reactor design is shown in more detail in FIG. 2. In addition to the core 14 comprised of a plurality of parallel, vertical, co-extending fuel assemblies 22, for purposes of this description, the other vessel internal structures can be divided into the lower internals 24 and the upper internals 26. In conventional designs, the lower internals function is to support and align core components and guide instrumentation as well as direct flow within the vessel. The upper internals restrain or provide a secondary restraint for the fuel assemblies 22 (only two of which are shown for simplicity in this figure), and support and guide instrumentation and components, such as control rods 28. In the exemplary reactor shown in FIG. 2, coolant enters the reactor vessel 10 through one or more inlet nozzles 30, flows down through an annulus between the vessel and the core barrel 32, is turned 180° in a lower plenum 34, passes upwardly through a lower support plate 37 and a lower core plate 36 upon which the fuel assemblies 22 are seated and through the assemblies. In some designs, the lower support plate 37 and the lower core plate 36 are replaced by a single structure, the lower core support plate, at the same elevation as 37. The coolant flow through the core and surrounding area 38 is typically large on the order of 400,000 gallons per minute at a velocity of approximately 20 feet per second. The resulting pressure drop and frictional forces tend to cause the fuel assemblies to rise, which movement is restrained by the upper internals, including a circular upper core plate 40. Coolant exiting the core 14 flows along the underside of the upper core plate and upwardly through a plurality of perforations 42. The coolant then flows upwardly and radially to one or more outlet nozzles 44. The upper internals 26 can be supported from the vessel or the vessel head and include an upper support assembly 46. Loads are transmitted between the upper support assembly 46 and the upper core plate 40, primarily by a plurality of support columns 48. A support column is aligned above a selected fuel assembly 22 and perforations 42 in the upper core plate 40. The rectilinearly moveable control rods 28 typically include a drive shaft 50 and a spider assembly 52 of neutron poison rods that are guided through the upper internals 26 and into aligned fuel assemblies 22 by control rod guide tubes 54. The guide tubes are fixedly joined to the upper support assembly 46 and connected by a split pin 56 force fit into the top of the upper core plate 40. The pin configuration provides for ease of guide tube assembly and a replacement if ever necessary and assures that the core loads, particularly under seismic or other high loading accident conditions are taken primarily by the support columns 48 and not the guide tubes 54. This support column arrangement assists in retarding guide tube deformation under accident conditions which could detrimentally affect control rod insertion capability. FIG. 3 is an elevational view, represented in vertically shortened form, of a fuel assembly being generally designated by reference character 22. The fuel assembly 22 is the type used in a pressurized water reactor and has a structural skeleton which, at its lower end includes a bottom nozzle 58. The bottom nozzle 58 supports the fuel assembly 22 on a lower core support plate 36 in the core region of the nuclear reactor. In addition to the bottom nozzle 58, the structural skeleton of the fuel assembly 22 also includes a top nozzle 62 at its upper end and a number of guide tubes or thimbles 54, which extend longitudinally between the bottom and top nozzles 58 and 62 and at opposite ends are rigidly attached thereto. The fuel assembly 22 further includes a plurality of transverse grids 64 axially spaced along and mounted to the guide thimbles 54 (also referred to as guide tubes) and an organized array of elongated fuel rods 66 transversely spaced and supported by the grids 64. Also, the assembly 22 has an instrumentation tube 68 located in the center thereof and extending between and mounted to the bottom and top nozzles 58 and 62. With such an arrangement of parts, fuel assembly 22 forms an integral unit capable of being conveniently handled without damaging the assembly of parts. As mentioned above, the fuel rods 66 in the array thereof in the assembly 22 are held in spaced relationship with one another by the grids 64 spaced along with fuel assembly length. Each fuel rod 66 includes nuclear fuel pellets 70 and is closed at its opposite ends by upper and lower end plugs 72 and 74. The pellets 70 are maintained in a stack by a plenum spring 76 disposed between the upper end plug 72 and the top of the pellet stack. The fuel pellets 70, composed of fissile material, are responsible for creating the reactive power of the reactor. It is important to manage the axial and radial power profile of the core because the power output of the reactor is limited by the hottest temperature experienced along a fuel rod 66. There is a need to keep the operating conditions below that which will result in a departure from nucleate boiling along the cladding of the fuel rod 66. Under that type of condition the heat transfer from the fuel rod 66 to the adjacent coolant deteriorates raising the temperature of the fuel rod which can result in cladding failure. A liquid moderator/coolant such as water or water containing boron, is pumped upwardly through a plurality of flow openings in the lower core support plate 36 to the fuel assembly 22. The bottom nozzle 58 of the fuel assembly passes the coolant upwardly along the fuel rods of the assembly in order to extract the heat generated therein for the production of useful work. To control the fission process, a number of control rods 78 are reciprocally moveable in the guide thimbles 54 located at predetermined positions in the fuel assembly 22. Specifically, a rod cluster control mechanism (spider pack) 80 positioned above the top nozzle 62 supports the control rods 78. The control mechanism has an internally threaded cylindrical hub member 82 with a plurality of radially extending flukes or arms 52. Each arm 52 is interconnected to the control rods 78 such that the control rod mechanism 80 is operable to move the control rods vertically in the guide thimbles 54 to thereby control the fission process in the fuel assembly 22, under the motive power of control rod drive shafts 50 which are coupled to the control rod hubs 82, all in a well-known manner. As previously mentioned, the fuel assemblies are subject to hydraulic forces that may exceed the weight of the fuel assemblies and therefore cause the fuel assemblies to “float” in the reactor if they are not properly secured. If a fuel assembly were to float upward just enough to cause it to be disengaged from the seating surface of the lower core plate on which it sits, it would vibrate laterally, and this condition could subject the fuel assembly to severe fretting. Because of this possibility, fuel assembly designs have included elements whose purpose is to prevent floating. One method of preventing floating is to mount springs (86 shown in FIG. 3) on the tops of the fuel assemblies. The springs are compressed between the upper core plate and the remainder of the fuel assembly, thereby providing sufficient hold-down force to prevent the fuel assembly from being disengaged from seating surfaces on the lower core support plate. Another example of such a spring arrangement is described in U.S. Pat. No. 4,728,487. The foregoing patent describes a hold-down arrangement comprising a vertical column centrally supported on the upper surface of the top nozzle adapter plate. A spring is concentrically wound around the column and a hold-down bar (yoke) is slidably mounted on the column over the spring. The hold-down bar rests against the upper core plate when installed in the reactor and compresses the spring to hold down the fuel assembly and core component. In conventional reactor designs, such as the one described in the patent, thermal couples are positioned at the lower end of the support columns 48 and the thermal couple signal cabling are fed through the support columns and exit the reactor through penetrations in the reactor head 12, which are not shown in FIG. 2. The in-core flux detectors and other in-core instrumentation that are located in the fuel assembly instrumentation thimbles are fed through penetrations in the lower head of the reactor, the lower support plate 37 and lower core plate 36 into the instrument thimbles (also referred to as instrumentation tubes) 68 through the bottom of the fuel assemblies 22. In the conventional designs no instruments are fed into the instrument thimbles through the top of the fuel assemblies. Access to the top of the instrumentation thimbles are blocked by the hold-down arrangement described in U.S. Pat. No. 4,728,487. The Westinghouse AP1000 reactor is a third generation-plus pressurized water reactor design. The moveable bottom-mounted in-core instrumentation has been replaced by a fixed top-mounted instrumentation system that accesses the core through penetrations in the reactor head 12. Thus, no vessel penetrations exist beneath the bottom of the core. The in-core instrumentation is important for providing an in-core flux map and signals necessary for monitoring core exit temperatures of the reactor core, which are used to calibrate neutron detectors and to optimize core performance. Accordingly, a new design is required to access the instrument thimbles 68 from the top of the fuel assembly 22 and provide a centering alignment and shielding the instrumentation components from cross flow. Such a design is desired that will provide effective shielding with minimal changes to the conventional hold-down devices. The hold-down assembly of this invention accommodates the foregoing need by providing a base plate that fits within the fuel assembly top nozzle and is secured to the adapter plate via a cylindrical tube spring guide. The cylindrical tube spring guide extends through and above the base plate and has a spring or spring coils that circumscribe the spring guide's outer surface. A hold-down bar is slidably mounted in an upper portion of the spring guide above the springs and the springs are compressed between the hold-down bar and the base plate with the hold-down bar bearing upon the reactor internals upper core plate lower surface when the fuel assembly is installed in the reactor core. The springs hold the base plate down against the fuel assembly top nozzle adapter plate and prevent the core component assembly, e.g., wet annular burnable absorber assembly, from lifting off the top nozzle adapter plate. The hold-down bar is mounted on the spring guide with at least two radially inwardly extending pins welded to the yoke. The pins travel within slots in the spring guide. Openings in the hold-down base plate are aligned with the guide thimbles in the fuel assemblies and accommodate and support core component rod assemblies such as wet annular burnable absorber assemblies, primary source and secondary source assemblies, water displacer rod assemblies, thimble plug devices, and peripheral power suppression assemblies. The spring guide is a hollow cylindrical tube with two different interior diameters. The upper section has a larger inner diameter to receive the instrumentation shroud with sufficient cavity length to accommodate the differential thermal and irradiation growth between the reactor vessel and the fuel assembly. The lower portion of the interior of the spring guide has a smaller inner diameter to guide the top mounted instrumentation shroud passing through the top nozzle adapter plate into the instrumentation tube of the fuel assembly. The top of the spring guide has a protrusion above the hold-down yoke bar that extends through and above the upper core plate when the fuel assembly is installed in the reactor core to fully shield the instrumentation shroud from exposure to the upper core outlet flow jet disturbances as well as the induced cross flow that would otherwise impinge on the suspended instrumentation shroud. FIG. 4 is an elevational view, partially in section of the fuel assembly shown in FIG. 3 with the hold-down device 88 of this invention installed in the fuel assembly top nozzle 62. The hold-down device can better be appreciated by reference to FIG. 5 which shows a perspective view of the hold-down device 88 with an in-core instrumentation thimble assembly 110 extending therethrough. The hold-down assembly 88 generally comprises a base plate 90, a cylindrical tube spring guide 94, an inner and outer coil springs, or alternately a single spring 98, and a hold-down bar or yoke 96. The springs 98 are compressed between the yoke 96 and the base plate 90 with the yoke bearing upon the under side of the reactor internals upper core plate which is shown as reference character 40 in FIG. 2. The springs 98 hold the base plate 90 down against the fuel assembly top nozzle adapter plate 84 as can be observed from FIG. 4. The yoke 96 is slidably mounted on the spring guide 94 with two radially, inwardly extending, diametrically spaced pins 100 welded to the yoke 96. The pins 100 travel within slots 102 in the spring guide 94. The spring guide 94 extends above the upper limit of travel of the hold-down bar 96, as defined by the slots 102, a selected distance of approximately 5 in. (12.7 cm.), so that a portion of that extension protrudes above the upper core plate 40. The portion 104 of the spring guide 94 that extends through and above an aperture in the upper core plate 40 shields the instrumentation shroud 108 from the upper core outlet flow jet disturbances as well as the induced cross flow impinging on the suspended instrumentation shroud 108. Thus, the plate mounted core component hold-down assembly 88 of this invention is specifically designed to be compatible with a top mount instrumentation system and provides a defined channel at a central location in the fuel assembly. The invention is compatible with the insertion and removal of the fixed in-core detector instrumentation 110 to provide a guided path for the fixed in-core detector during insertion and to provide a shield in the area 104 against cross flow during reactor operation. The core component assemblies with the top mounted instrumentation interface that the hold-down system of this invention has to accommodate include the wet annular burnable absorber assembly, primary source and secondary source assemblies, water adapter rod assembly, thimble plugging device and peripheral power suppression assembly. The holes 120 shown in FIG. 5 are for attaching the rodlets of the core component assemblies. The openings 122 are coolant flow through passages. FIG. 6 shows a cross-section of the hold-down device 88 of this invention illustrated in FIG. 5. From FIG. 6 it can be appreciated that the spring guide 94 is a hollow cylindrical tube with two different inner diameters 112 and 114. The upper section 112 has a larger inner diameter to receive the instrumentation shroud 108 with sufficient cavity length in the region 112 to accommodate the differential thermal and irradiation growth between the reactor vessel and the fuel assembly so that the in-core instrumentation assembly 110 is not exposed to the coolant forces. The lower portion 114 of the spring guide 94 has a smaller inner diameter to guide the top mounted instrumentation 110 passing through the top nozzle adapter plate 84 into the instrumentation tube 68 of the fuel assembly 22. FIG. 7 shows a cross-sectional view of the upper section of the fuel assembly skeleton with the hold-down assembly 88 of this invention attached to the adapter plate 84 of the top nozzle 62. From this view it can be readily seen that the cylindrical spring guide 94 extends through and below a central opening 92 in the base plate 90 and rests upon the adapter plate 84 thus creating a space 128 between the adapter plate 84 and the base plate 90. The space 128 is provided so that the holddown force is carried by the spring guide 94 and not the base plate 90. The view of FIG. 7 clearly shows the enlarged diameter upper section 112 that narrows at approximately mid-height of the cylindrical spring guide 94, to the smaller diameter lower section 114. The lower section 114 of the spring guide 94 mates at 118 with the upper opening of the instrument tube 68 within the instrument tube counter bore 116. The arrangement shown in FIG. 7 is illustrated with the core component rodlet assemblies 126, such as a wet annular burnable absorber assembly, supported and extending axially down from the base plate 90. FIG. 7 shows that the spring guide 94 is attached to the base plate 90 by a welded or brazed joint. The hold-down assembly 88 is constructed from a material such as stainless steel or Inconel. Thus, this invention provides a plate mounted core component hold-down assembly that is specifically designed to be compatible with a top mount instrumentation system and supplies a defined channel at a central location in the fuel assembly. The defined channel through the spring guide 94 is compatible with the insertion and removal of fixed in-core detector instrumentation to provide a guided path for the fixed in-core detector during insertion and to provide a shield against cross flow during reactor operation. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
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claims | 1. A cooling structure for a control rod drive mechanism that is placed at an upper portion of a reactor vessel and by which a control rod is inserted into and withdrawn from a reactor core, the cooling structure for the control rod drive mechanism comprising:a housing that is fixed to the upper portion of the reactor vessel;an air intake unit that takes cooling air into the housing;a first exhaust duct that is arranged side by side with the air intake unit in a circumferential direction of the housing, into which cooling air in the housing is suctioned through a first inlet at a lower portion thereof, and that guides the cooling air upward;a second exhaust duct that is disposed below the air intake unit, into which cooling air in the housing is suctioned through a second inlet, and that guides the cooling air to the first exhaust duct; anda discharging unit that is attached to an upper portion of the housing and discharges cooling air in the first exhaust duct to exterior. 2. The cooling structure for the control rod drive mechanism according to claim 1, whereinthe housing includes a plurality of vertically disposed structures arranged side by side at predetermined intervals in a circumferential direction, andthe second exhaust duct is communicatively connected to the first exhaust duct by penetrating through the structures. 3. The cooling structure for the control rod drive mechanism according to claim 2, wherein each of the structures is formed in a hollow shape, has a third inlet through which cooling air in the housing is suctioned, and is communicatively connected to the second exhaust duct through a thorough hole. 4. The cooling structure for the control rod drive mechanism according to claim 1, wherein the second exhaust duct includes a projecting unit projecting inside the housing and the second inlet is formed on the projecting unit. 5. The cooling structure for the control rod drive mechanism according to claim 1, wherein the first inlet is provided with a flow rate adjusting member for adjusting an amount of cooling air flow. 6. The cooling structure for the control rod drive mechanism according to claim 1, wherein the second exhaust duct includes a flow rate adjusting member for adjusting an amount of cooling air flow. 7. The cooling structure for the control rod drive mechanism according to claim 1, wherein the housing has an openable and closable operation opening formed below the air intake unit, and the second inlet is formed below the operation opening. 8. The cooling structure for the control rod drive mechanism according to claim 1, wherein the discharging unit includes an exhaust fan. 9. A cooling method for a control rod drive mechanism that is placed at an upper portion of a reactor vessel and by which a control rod is inserted into and withdrawn from a reactor core by using a magnetic jack, the cooling method comprising:taking cooling air into inside of a housing in which the magnetic jack is housed along an upper side wall of the housing;extracting cooling air in the housing to an exhaust duct along an entire periphery of a lower side wall of the housing after cooling the magnetic jack while directing the cooling air downward; anddischarging the cooling air to exterior by an exhaust fan after directing the cooling air upward through the exhaust duct. 10. The cooling method for the control rod drive mechanism according to claim 9, wherein the exhaust duct is arranged side by side with an air intake unit in a circumferential direction of the housing, and cooling air that has cooled the magnetic jack is suctioned in through a first inlet at a lower portion of the exhaust duct, is suctioned in through a second inlet formed below the air intake unit, and is discharged by directing the cooling air upward through the exhaust duct. 11. A nuclear reactor comprising:a reactor vessel;a core barrel disposed in the reactor vessel;a reactor core disposed in the core barrel;a plurality of control rods that controls the reactor core;a control rod drive mechanism placed at an upper portion of the reactor vessel and by which the control rods are inserted into and withdrawn from the reactor core; anda control rod drive mechanism cooling device that cools the control rod drive mechanism with cooling air, whereinthe nuclear reactor produces electricity by generating steam by heat exchange between nuclear fuel and coolant, and driving a power generating turbine with generated steam, andthe control rod drive mechanism cooling device includesa housing that is fixed to the upper portion of the reactor vessel,an air intake unit that takes cooling air into the housing,a first exhaust duct that is arranged side by side with the air intake unit in a circumferential direction of the housing, into which cooling air in the housing is suctioned through a first inlet at a lower portion thereof, and that guides the cooling air upward,a second exhaust duct that is disposed below the air intake unit, into which cooling air in the housing is suctioned through a second inlet, and that guides the cooling air to the first exhaust duct, anda discharging unit that is provided to an upper portion of the housing and discharges cooling air in the first exhaust duct to exterior. |
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summary | ||
claims | 1. A hollow-beam aperture for a charged-particle-beam (CPB) microlithography apparatus, comprising: a first member, multiple second members, and a circular center member made of a CPB-absorbing material, the circular member having a radius; the center member being supported relative to the first member by support bars extending radially from the first member to the center member; the second members being situated between the support bars and the first member, and the second members being displaceable relative to the first member radially toward the center member; the second members each having a distal edge, the distal edges being configured to engage the support bars whenever the second members are displaced maximally toward the center member; and the distal edges each defining a cutout having a respective edge configured as an arc having a radius greater than the radius of the center member such that, whenever the second members are displaced maximally toward the center member, a substantially annular aperture is defined between the center member and the cutouts. 2. The hollow-beam aperture of claim 1 , further comprising a respective spring situated relative to the first member and each of the second members, the springs being configured to urge the respective second members toward the center member, and the springs being contiguous with the first and second members and connecting the respective second members to the first member. claim 1 3. The hollow-beam aperture of claim 1 , wherein: claim 1 the first member defines angled edges in a region between the second members; and each second member defines angled edges that conform to and contact corresponding angled edges of the first member in a manner, whenever the second members are displaced maximally toward the center member, serving to maintain concentricity of the cutouts relative to the center portion. 4. A CPB microlithography apparatus, comprising the hollow-beam aperture of claim 1 . claim 1 5. A hollow-beam aperture for a charged-particle-beam microlithography apparatus, comprising: a first member defining a cutout having a radial dimension; a cylindrical beam-absorbing member having an axis and a radius relative to the axis, the radius of the beam-absorbing member being smaller than the radial dimension of the cutout; multiple support bars supporting the beam-absorbing member relative to the first member and concentrically with the cutout such that the axis of the beam-absorbing member is perpendicular to the plane of the first member, and the beam-absorbing member extends through the cutout, thereby forming a substantially annular aperture between the beam-absorbing member and the first member; and a second member defining a circular cutout having a radius no larger than the radial dimension of the cutout in the first member and larger than the radius of the beam-absorbing member, the second member being configured to be attached superposedly to the first member such that the cutout of the second member is coaxial with the beam-absorbing member, and the beam-absorbing member also extends through the second cutout. 6. A CPB microlithography apparatus, comprising the hollow-beam aperture of claim 5 . claim 5 7. A hollow-beam aperture, comprising: a main body defining a circular opening having an axis and a radius; a beam-absorbing body situated concentrically relative to the circular opening and connected to the main body by at least one support bar contiguous with the main body and the beam-absorbing body, the beam-absorbing body having a radius that is smaller than the radius of the circular opening; and the main body defining at least one void situated relative to the circular opening and the beam-absorbing body, the void being configured so as to cause the circular opening and beam-absorbing body to define a substantially annular beam-transmitting aperture, when the hollow-beam aperture is viewed along the axis, extending through the main body and concentric with the beam-absorbing body. 8. The hollow-beam aperture of claim 7 , wherein the circular opening has outer sides and tapered inner sides. claim 7 9. The hollow-beam aperture of claim 8 , wherein the beam-absorbing body is conical relative to the axis. claim 8 10. The hollow-beam aperture of claim 7 , wherein the beam-absorbing body is defined by a portion of the main body that is relatively thick in a beam-transmission direction, and the substantially annular beam-transmitting aperture is defined by a portion of the main body that is relatively thin in the beam-transmission direction. claim 7 11. The hollow-beam aperture of claim 10 , wherein the circular opening is machined by EDM using the beam-absorbing body as an EDM electrode. claim 10 12. The hollow-beam aperture of claim 7 , wherein the circular opening has a truncated conical profile as viewed along a direction perpendicular to the axis of the beam-absorbing body, the circular opening extending into the main body from a first surface of the main body. claim 7 13. The hollow-beam aperture of claim 12 , wherein: claim 12 the main body defines at least two voids each having a respective axis that is parallel to the axis of the beam-absorbing body, the voids extending into the main body from a second surface of the main body opposite the first surface; the voids are arranged such that their respective axes are spaced equally from one another about the axis of the beam-absorbing body in a rotationally symmetric manner; and each of the voids intersects, within the main body, a respective portion of the circular opening. 14. The hollow-beam aperture of claim 13 , wherein each of the voids has a truncated conical profile as viewed along a direction perpendicular to the axis of the beam-absorbing body. claim 13 15. A CPB microlithography apparatus, comprising the hollow-beam aperture of claim 7 . claim 7 16. A method for manufacturing a hollow-beam aperture for use in a charged-particle-beam (CPB) microlithography apparatus, comprising: (a) providing a main body made of a CPB-absorbing material; (b) on a first surface of the main body, machining a circular opening having an axis and a radius; (c) on a second surface of the main body opposite the first surface, machining the main body to define a beam-absorbing body concentrically relative to the circular opening, the beam-absorbing body having a radius smaller than the radius of the circular opening, the circular opening and the beam-absorbing body each having a relatively thick dimension in a beam-transmission direction and being separated from each other by a portion of the main body that is relatively thin in the beam-transmission direction; and (d) machining the main body to define at least one void situated relative to the circular opening and the beam-absorbing body, the void being configured so as to cause the circular opening and the beam-absorbing body to define a beam-transmitting aperture that is concentric with the beam-absorbing body and substantially annular in profile when viewed along the axis, the beam-transmitting aperture extending through the portion of the main body, between the beam-absorbing body and the circular opening, that is relatively thin in the beam-transmission direction. 17. The method of claim 16 , wherein step (b) comprises machining the circular opening to have a truncated conical profile as viewed along a direction perpendicular to the axis, and to extend into the main body from the first surface. claim 16 18. The method of claim 16 , wherein step (b) comprises machining an annular groove in the first surface. claim 16 19. A microelectronic-device fabrication process, comprising the steps: (a) preparing a wafer; (b) processing the wafer; and (c) assembling devices formed on the wafer during steps (a) and (b), wherein step (b) comprises the steps of (i) applying a resist to the wafer; (ii) exposing the resist; and (iii) developing the resist; and step (ii) comprises providing a CPB microlithography apparatus as recited in claim 4 ; and using the CPB microlithography apparatus to expose the resist with the pattern defined on the reticle. claim 4 20. A microelectronic-device fabrication process, comprising the steps: (a) preparing a wafer; (b) processing the wafer; and (c) assembling devices formed on the wafer during steps (a) and (b), wherein step (b) comprises the steps of (i) applying a resist to the wafer; (ii) exposing the resist; and (iii) developing the resist; and step (ii) comprises providing a CPB microlithography apparatus as recited in claim 6 ; and using the CPB microlithography apparatus to expose the resist with the pattern defined on the reticle. claim 6 21. A microelectronic-device fabrication process, comprising the steps: (a) preparing a wafer; (b) processing the wafer; and (c) assembling devices formed on the wafer during steps (a) and (b), wherein step (b) comprises the steps of (i) applying a resist to the wafer; (ii) exposing the resist; and (iii) developing the resist; and step (ii) comprises providing a CPB microlithography apparatus as recited in claim 15 ; and using the CPB microlithography apparatus to expose the resist with the pattern defined on the reticle. claim 15 22. A method for manufacturing a hollow-beam aperture for use in a charged-particle-beam (CPB) microlithography apparatus, comprising: (a) providing a main body made of a CPB-absorbing material; (b) on a first surface of the main body, machining an annular opening having an axis and a radius, and defining a beam-absorbing body having a radius smaller than the radius of the annular opening, the annular opening and the beam-absorbing body each having a relatively thick dimension in a beam-transmission direction and being separated from each other by a portion of the main body that is relatively thin in the beam-transmission direction; and (c) machining the main body to define at least one void situated relative to the annular opening and the beam-absorbing body, the void being configured so as to cause the annular opening and the beam-absorbing body to define a beam-transmitting aperture that is concentric with the beam-absorbing body and substantially annular in profile when viewed along the axis, the beam-transmitting aperture extending through the portion of the main body, between the beam-absorbing body and the annular opening, that is relatively thin in the beam-transmission direction. 23. A hollow-beam aperture for a charged-particle-beam (CPB) microlithography apparatus, comprising: a charged-particle-stopping member defining a cutout extending along an axis through a thickness dimension of the charged-particle-stopping member; and a support member defining multiple openings, the support member being situated relative to the cutout in the charged-particle-stopping member so as to collectively define a substantially annular aperture coaxial with the axis. 24. The hollow-beam aperture of claim 23 , further comprising a reinforcing member defining an opening coaxial with the axis. claim 23 25. The hollow-beam aperture of claim 24 , wherein the charged-particle-stopping member, the support member, and the reinforcing member are integrated as a unitary construct. claim 24 26. A method for manufacturing a hollow-beam aperture for use in a charged-particle-beam (CPB) microlithography apparatus, comprising: (a) providing a main body having first and second main surfaces and a thickness dimension extending along an axis between the first and second main surfaces; (b) defining multiple second openings extending from the first main surface into the thickness dimension, the second openings being situated radially symmetrically relative to the axis; (c) defining a third opening extending from the second main surface into the thickness dimension, the third opening being situated coaxially with the axis and intersecting the second openings in the thickness dimension so as to define a substantially annular aperture as viewed along the axis. 27. The method of claim 26 , further comprising the steps: claim 26 before, step (b), defining a first opening extending along the axis from the second main surface into the thickness dimension, the first opening having a bottom surface; and step (b) comprises defining the multiple second openings extending from the bottom surface further into the thickness dimension from the bottom surface. |
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abstract | When a power source is lost after an operation stop of a nuclear power plant, a first open/close valve is opened via a first battery at an early stage and steam in a reactor pressure vessel (RPV) is condensed in a suppression pool. The heat of the water in the suppression pool is transmitted to a cooling water pool located below inner space between first and second reactor containment vessels surrounding the RPV. A second open/close valve is opened via a second battery at the early stage and cooling water in a tank is injected into the RPV. After the early stage, a third open/close valve is opened via a third battery, and a cooling medium becomes steam by an evaporator in the RPV, the steam being condensed by a condenser disposed in the inner space to become a liquid of the cooling medium and is returned to the evaporator. |
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062721976 | claims | 1. A fuel assembly for a nuclear reactor including: a plurality of fuel pins having respective axes extending substantially parallel to each other; at least two structural grids spaced apart from each other, the structural grids being in contact with said fuel pins and maintaining said fuel pins substantially mutually parallel and preventing contact therebetween, wherein the fuel assembly further comprises at least one mixing grid situated intermediate said at least two structural grids, said mixing grid having turbulence inducing means to promote turbulence in a coolant flowing through said fuel assembly in use, wherein said mixing grid is positioned and fixedly located out of contact with said fuel pins and wherein the mixing grid is formed from a single sheet of metal wherein the plane of the metal sheet from which the mixing grid is formed lies in a plane which is transverse to the axes of the fuel pins. 2. A fuel assembly according to claim 1, wherein the thickness of the sheet material is lies in the range from 0.5 mm to about 1 mm. 3. A fuel assembly according to claim 1 wherein the mixing grid is in the form of a framework having an array of apertures of predetermined size and shape. 4. A fuel assembly according claim 1 wherein the turbulence inducing means include vanes attached to the mixing grid. 5. A fuel assembly according to claim 1 wherein the vanes are integrally formed with the mixing grid. 6. A fuel assembly according to claim 3 wherein the framework includes framework members surrounding each aperture and wherein at least some of the framework members surrounding each aperture are twisted out of the plane of the sheet so as to form turbulence inducing features. 7. A fuel assembly according to claim 1 wherein the mixing grid does not extend to and encompass an outer peripheral ring of fuel pins. 8. A fuel assembly according to claim 1 wherein the mixing grid is located and held in position within the fuel pin assembly by thimble tubes in which moderator control rods run. 9. A fuel assembly according to claim 8 wherein the mixing grid is located by swaging to the thimble tubes. 10. A fuel assembly according to claim 8 wherein the mixing grid is first joined to short tubes which are fitted over the thimble tubes and are fixed to the thimble tubes. 11. A fuel assembly according to claim 1 wherein the mixing grid is located at a position between two adjacent structural grids where, during operation of the reactor in use, the hottest region of the fuel pins is located. 12. A mixing grid for use in a fuel pin assembly including a plurality of fuel pins having respective axes extending substantially parallel to each other, at least two structural grids spaced apart from each other, the structural grids being in contact with the fuel pins and maintaining the fuel pins substantially mutually parallel and preventing contact therebetween, said mixing grid including turbulence inducing means to promote turbulence in a coolant flowing through the fuel assembly in use and wherein: said mixing grid is formed from a single sheet of metal; said mixing grid is sized and configured to be situated intermediate said at least two structural grids, positioned and fixedly located out of contact with said fuel pins, and such that, when said mixing grid is so positioned, the plane of the metal sheet from which the mixing grid is formed lies in a plane which is transverse to the axes of the fuel pins. 13. A fuel assembly according to claim 8 wherein the mixing grid is located by welding to the thimble tube. |
06198793& | description | DESCRIPTION OF THE INVENTION It shall be shown theoretically on the basis of FIGS. 1-20, how, with the help of the design process according to the invention and the illumination device according to the invention, a system can be provided for any desired illumination distributions A in a plane, which satisfies the requirements with reference to uniformity and telecentry. In FIG. 1, a principle diagram of the beam path of a system with two honeycomb plates is illustrated. The light of source 1 is collected by means of a collector lens 3 and converted into a parallel or convergent pencil beam. The field honeycombs 5 of the first honeycomb plate 7 decompose the light pencil and produce secondary light sources at the site of the pupil honeycombs 9. The field lens 12 forms these secondary sources in the exit pupil of the illumination system or the entrance pupil of the subsequent objective. Such an arrangement is characterized by an interlinked beam path of field and pupil planes from the source up to the entrance pupil of the objective. For this, the designation "Kohler illumination" is also often selected. The illumination system according to FIG. 1 is considered segmentally below. Since the intersection of the light and aperture distribution is in the plane of the field honeycombs, the system can be described independent of source type and collector mirror. The field and pupil imaging is illustrated for the central pair of honeycombs 20, 22 in FIGS. 2A and 2B. The field honeycomb 20 is imaged on the reticle 14 or the mask to be imaged by means of the pupil honeycomb 22 and the field lens 12. The geometric extension of the field honeycomb 20 determines the shape of the illuminated field in the reticle plane 14. The image scale is approximately given by the ratio of the distances from pupil honeycomb 22 to reticle 14 and field honeycomb 20 to pupil honeycomb 22. The optical effect of the field honeycomb 20 is designed such that an image of light source 1, a secondary light source, is formed at the site, i.e., the position, of pupil honeycomb 22. If the extension of the light source is small, for example, approximately punctiform, then all of the light beams run through the optical axis of the pupil honeycomb 22. In such a case, an illumination device can be produced, in which the pupil honeycomb is dispensed with. As is shown in FIG. 2B, the task of field lens 12 consists of imaging the secondary light sources in the entrance pupil 26 of objective 24. If a field lens is introduced into the beam path, then the field imaging is influenced in such a way that it forms the annular field by control of the distortion. The imaging scale of the field honeycomb image is thus not changed. A special geometric form of a field honeycomb and a pupil honeycomb of the course of the light beams is shown in FIG. 3. In the form of embodiment represented in FIG. 3, the shape of field honeycomb 20 is selected as a rectangle. Thus, the aspect ratio of the field honeycomb 20 corresponds to the ratio of the arc length to the annular width of the required annular field in the reticle plane. The annular field is formed by the field lens, as shown in FIG. 4. Without the field lens, as shown in FIG. 3, a rectangular field is formed in the reticle plane. As shown in FIG. 4, a grazing-incidence field mirror 32 is used for the shaping of annular field 30. Under the secondary condition that the beam reflected by the reticle must no longer run back into the illumination system, one or two field mirrors 32 are required, each time depending on the position of the entrance pupil of the objective. If the principal rays run divergently into the objective that is not shown, then a field mirror 32 is sufficient, as shown in FIG. 4. In the case of the convergent principal beam path, two field mirrors are required. The second field mirror must rotate the orientation of the ring. Such a configuration is shown in FIG. 5. In the case of an illumination system in the EUV wavelength region, all components must be formed reflectively. Due to the high reflection losses at .lambda.=10 nm-14 nm, it is advantageous that the number of reflections be kept as small as possible. In the construction of the reflective system, the mutual vignetting of the beams must be taken into consideration. This can occur due to construction of the system in a zigzag beam path or by operating with obscurations. The process according to the invention will be described below for the preparation of a design for an EUV illumination system with any desired illumination in a plane A, as an example. The definitions necessary for the process of the invention are shown in FIG. 6. First, the beam path is calculated for the central pair of honeycombs. In a first step, the size of field honeycombs 5 of the field honeycomb plate 7 will be determined. As indicated previously, the aspect ratio (x/y) results for rectangular honeycombs from the shape of the annular field in the reticle plane. The size of the field honeycomb is determined by expansion or extension A of the intensity distribution of the arbitrary light source in the plane of the field honeycombs and the number N of the field honeycombs on the honeycomb plate, which in turn is given by the number of secondary light sources. The number of secondary light sources results in turn from the uniformity of the pupil illumination as well as the intermixing. The honeycomb surface A.sub.honeycomb of a field honeycomb can be expressed as follows with x.sub.honeycomb, y.sub.honeycomb : EQU A.sub.honeycomb =x.sub.honeycomb.multidot.y.sub.honeycomb =(x.sub.field /y.sub.field).multidot.y.sub.honeycomb whereby x.sub.field, y.sub.field describe the magnitude of the rectangle, which establishes the annular field. Further, the following is valid for the number N of field honeycombs: EQU N=A/A.sub.honeycomb =A/[y.sup.2.sub.honeycomb.multidot.(x.sub.field /y.sub.field)]. From this, there results for the size of the individual field honeycomb: y.sub.honeycomb =A/[N.multidot.(x.sub.field +L /y.sub.field +L )] PA1 d.sub.1 =L/(1+.beta..sub.honeycomb) PA1 d.sub.2 =d.sub.1.multidot..beta..sub.honeycomb PA1 An homogeneous illumination, for example, of an annular field PA1 An homogeneous and field-independent pupil illumination PA1 The combining of the exit pupil of the illumination system and the entrance pupil of the objective PA1 The adjustment of a pregiven structural length PA1 The uptake of the maximum possible optical conductance or optical flux value. PA1 Annular field: R=100 mm, segment -60.degree., field height .+-.3.0 mm, which corresponds to a rectangular field of 105 mm.times.6 mm PA1 y=6 mm PA1 x=17.5 mm PA1 y=1 mm. PA1 Annular field: R=100 mm, segment=60.degree., field height.+-.3.0 mm. PA1 Position of the entrance pupil: S.sub.EP =1927.4 mm. This corresponds to a principal beam angle of i.sub.PB =2.97.degree. for y=100 mm. PA1 Aperture at the reticle: NA=0.025. PA1 Aperture at the source: NA=0.999. PA1 Distance between the source and the collector mirror: d.sub.1 =100.0 mm. PA1 Honeycomb size on the first tele-mirror, 1 mm.times.17.5 mm. PA1 d.sub.3 =100 mm. PA1 Compression factor .phi..sub.honeycomb /.phi..sub.second honeycomb =4:1. PA1 Tilt angle a of the grazing-incidence mirror, .alpha.=80.degree.. PA1 Collector mirror is shaped as an ellipsoid with R.sub.collector and Ex.sub.collector. PA1 Carrier surfaces R.sub.2 and R.sub.3 : spherical. PA1 Honeycomb radius R.sub.honeycomb spherical. PA1 Field mirror toric without concentric component: R.sub.4x, R.sub.4y, R.sub.5x, R.sub.5y. PA1 Annular field: R=100 mm, segment 60.degree., field height .+-.3.0 mm, which corresponds to a rectangular field of 105 mm.times.6 mm. PA1 Aperture at the reticle: NA.sub.ret =0.025. PA1 Aperture at the source: NA.sub.source =0.999. PA1 d.sub.1 =100.0 mm PA1 Structural length L=d.sub.3 +d.sub.4 =1400 mm. PA1 Number of honeycombs within an x-row of the diaphragm diameter=4. and EQU x.sub.honeycomb =(x.sub.field /y.sub.field).multidot.y.sub.honeycomb The honeycomb size and the size of the rectangular field establish the imaging scale .beta..sub.honeycomb of the honeycomb imaging and thus the ratio of the distances d.sub.1 and d.sub.2. EQU .beta..sub.honeycomb =x.sub.field /y.sub.field =d.sub.2 /d.sub.1 The pregiven structural length L for the illumination system and the honeycomb imaging scale .beta..sub.honeycomb determine the absolute size of d.sub.1 and d.sub.2 and thus the position of the pupil honeycomb plate. The following is valid: Then, d.sub.1 and d.sub.2 determine in turn the radius of the pupil honeycombs. The following is valid: ##EQU1## In order to image the pupil honeycombs in the entrance pupil of the objective and to remodel the rectangular field into an annular field, one or more field lenses, preferably of toroidal form, are introduced between the pupil honeycomb and the reticle. By introducing the field mirror, the previously given structural length is increased, since among other things, the mirror must maintain minimum distances in order to avoid vignettings. The positioning of the field honeycombs depends on the intensity distribution in the plane of the field honeycombs. The number N of the field honeycombs is pregiven by the number of secondary light sources. The field honeycombs will preferably be arranged on the field honeycomb plate in such a way that they cover the illuminated surfaces without mutually vignetting. In order to position the pupil honeycombs, the raster pattern of the secondary light sources in the entrance pupil of the objective will be given in advance. The secondary light sources are imaged by the field lens counter to the direction of light. The diaphragm plane of this imaging is found in the reticle plane. The images of the secondary light sources give the (x, y, z) positions of the pupil honeycombs. The tilt and rotational angles remain as degrees of freedom for producing the light path between the field and pupil honeycombs. If a pupil honeycomb is assigned to each field honeycomb in one configuration of the invention, then the light path will be produced by tilting and rotating from field and pupil honeycombs. Thereby beam pencils are deviated in such a way that the center beams all intersect the optical axis in the reticle plane. The assignment of field and pupil honeycombs is freely made. One possibility for arrangement would be to assign spatially adjacent honeycombs to each other each time. Thereby, the deflecting angles become minimal. Another possibility consists of equilibrating the intensity distribution in the pupil plane. This is made, for example, if the intensity distribution has a distribution in the plane of the field honeycombs. If the field and pupil honeycombs have similar positions, the distribution is transferred to the pupil illumination. The intensity can be equalized by intermixing of the assignment. Advantageously, the individual components of field honeycomb plate, pupil honeycomb plate and field mirror of the illumination system are arranged in the beam path such that a beam path free of vignetting is possible. If such an arrangement has effects on the imaging, then the individual light channels and the field lenses must be post-optimized. With the design process described above, illumination systems for EUV lithography are obtained for any desired illumination A with two normal-incidence and one to two grazing-incidence reflections, and these systems have the following properties: Arrangements of field honeycombs and pupil honeycombs will be described below for one form of embodiment of the invention with field and pupil honeycomb plates. First, different arrangements of the field honeycombs on the field honeycomb plate will be considered. The intensity distribution can be selected as desired. The introduced examples are limited to simple geometric forms, such as circle, rectangle, or the coupling of several circles or rectangles. The intensity distribution will be homogeneous within the illuminated region or have a slowly varying course. The aperture distribution will be independent of the field. In the case of circular illumination A of field honeycomb plate 100, field honeycombs 102 may be arranged, for example, in columns and rows, as shown in FIG. 7. As an alternative to this, the space points of the honeycombs can be distributed uniformly by shifting the rows over the surface, as shown in FIG. 8. The latter arrangement is better adapted to a uniform distribution of the secondary light sources. A rectangular illumination A is shown in FIG. 9. A shift of the rows, as shown in FIG. 10, leads to a more uniform distribution of the secondary light sources. However, these are arranged within a rectangle corresponding to the expansion of the field honeycomb plate. In the case of rectangular illumination, it is necessary, in order to produce the light path between the field and pupil honeycombs, to tilt the field honeycombs, so that the beam pencils impinge on the pupil honeycombs, which are arranged, for example, inside a circle, and, which also must be tilted. If illumination A of field honeycomb plate 100 comprises several circles, A1, A2, A3, A4, for example by coupling several sources, then in the case of uniform honeycomb size, intermixing is insufficient with an arrangement of the honeycombs in rows and columns according to FIG. 11. A more uniform illumination is obtained by shifting the honeycomb rows, as shown in FIG. 12. FIGS. 13 and 14 show the distribution of field honeycombs 102 in the case of combined illumination from the individual rectangles A1, A2, A3, A4. Now, for example, arrangements of the pupil honeycombs on the pupil honeycomb plate will be described. In the arrangement of pupil honeycombs, two points of view are to be considered: 1. For minimizing the tilt angle of field and pupil honeycombs for producing the light path, it is advantageous to maintain the arrangement of field honeycombs. This is particularly advantageous with an approximately circular illumination of the field honeycomb plate. 2. For homogeneous filling of the pupil, the secondary light sources will be distributed uniformly in the entrance pupil of the objective. This can be achieved by providing a uniform raster pattern of secondary light sources in the entrance pupil of the objective. These are imaged counter to the direction of light with the field lens in the plane of the pupil honeycombs and determine in this way the ideal site of the pupil honeycombs. If the field lens is free of distortion, then the distribution of the pupil honeycombs corresponds to the distribution of the secondary light sources. However, since the field lens forms the annular field, distortion is purposely introduced. This does not involve rotation-symmetric hour-glass or barrel-shaped distortion, but involves the bending of horizontal lines into arcs. In the ideal case, the y distance of the arcs remains constant. Real grazing-incidence field mirrors, however, also show an additional distortion in the y-direction. A raster 110 of secondary light sources 112 in the entrance pupil of the objective, which is also the exit pupil of the illumination system, is shown in FIG. 15, as it had been produced for distortion-free imaging. The arrangement of the secondary light sources 112 corresponds precisely to the pregiven arrangement of pupil honeycombs. If the field lenses are utilized for shaping the annular field, as in FIG. 16, then the secondary light sources 112 lie on arcs 114. If the pupil honeycombs of individual rows are placed on the arcs which hold up the distortion, then one can place the secondary light sources again on a regular raster. If the field lens also introduces distortion in the y-direction, then the pupil is distorted in the y-direction, as shown in FIG. 17. The expansion of the illuminated surface onto the field honeycomb plate is given in advance with the definition of the input illumination. The illumination of the pupil honeycomb plate is determined by the structural length and the aperture in the reticle plane. As described extensively above, the two surfaces must be fine-tuned to one another by rotating and tilting the field and pupil honeycombs. For illustration, the problems with refractory superstructures will be explained. The examples, however, can be transferred directly to reflective systems. Various cases can be distinguished for a circular illumination of field honeycomb plates, as presented below. If a collecting effect is introduced by tilting the field honeycombs, and a diverging effect is introduced by tilting the pupil honeycombs, then the pencil cross section can be reduced. The tilt angles of the individual honeycombs are determined by means of the mid rays for each pair of honeycombs. The system acts like a tele-system for the mid rays, as shown in FIG. 18. How far the field honeycombs must be tilted, depends on the convergence of the impinging beam pencil. If the convergence is adapted to the reduction of the pencil cross section, the field honeycombs can be introduced onto a planar substrate without a tilt angle. A special case results, if the convergence between the field and the pupil honeycomb plate corresponds to the aperture at the reticle, as shown in FIG. 19. No divergng effect must be introduced by the pupil honeycombs, so they can be utilized without surface tilt. If the light source also has a very small light conductance, the pupil honeycomb can be completely dispensed with. A magnification of the pencil cross section is possible, if diverging action is introduced by tilting of the field honeycombs, and collecting effect is introduced by tilting the pupil honeycombs. The system operates like a retro-focus system for the mid rays, as shown in FIG. 20. If the divergence of the impinging radiation corresponds to the pencil enlargement between field and pupil honeycombs, then the field honeycombs can be used without surface tilt. Instead of the round form that has been described, rectangular or other forms of illumination A of the field honeycomb plate are possible. The following drawings describe one form of embodiment of the invention, in which a pinch-plasma source is used as the light source of the EUV illumination system. The principal construction without field lens of such a form of embodiment is shown in FIG. 21; FIG. 22 shows the abbreviations necessary for the system derivation, whereby for better representation, the system was plotted linearly and mirrors were indicated as lenses. An illumination system with pinch-plasma source 200, as shown in FIG. 21, comprises a light source 200, a collector mirror 202, which collects the light and reflects it in the field honeycomb plate 204. By reflection at the field honeycombs, the light is introduced into the respective pupil honeycombs of pupil honeycomb plate 206 and from there to reticle 208. The pinch-plasma source is an expanded light source (approximately 1 mm) with a directional radiation in a relatively small steradian region of approximately .OMEGA.=0.3 sr. Based on the expansion, a pupil honeycomb condenser 206 is recommended for illumination with a pinch-plasma source. The following dimensional specifications are used, for example, for an illumination system for EUV lithography: Aperture at the reticle: NA.sub.ret =0.025 Aperture at the source: NA.sub.source =0.3053 Structural length L=1400.0 mm Number of honeycombs, which find place in an x-row: 4 d.sub.1 =330.0 mm If the following coupling of the individual quantities is now considered: ##EQU2## the system can be completely derived from the pregiven quantities. If one utilizes the allowances for annular field, aperture at the reticle, etc. in the above formulas, then the following system parameters result: ##EQU3## The total system with the previously indicated dimensions is shown in FIG. 23 up to the reticle plane in the yz section. The mid and the two edge beams are depicted for the central field honeycomb (0, 0) and the two outermost field honeycombs each time. A secondary light source is produced in the pupil plane by each honeycomb. The total system is shown in FIG. 24 with an x-z fan of beams, which impinge on the central honeycomb. FIGS. 25 and 26 show the illumination of the reticle with the rectangular field (-52.5 mm<x<+52.5 mm; -3.0 mm<x<+3.0 mm) according to FIGS. 25 or 26 in contour lines and 3D representation. The individual partial images are optimally superimposed in the reticle plane also in the case of the expanded secondary light sources, which are produced by the pinch-plasma source, since a pupil honeycomb plate is used. In comparison to this, the illumination of the reticle without pupil honeycomb plate is shown in contour lines and 3D representation in FIGS. 27 and 28. The partial images of the field honeycombs are not sharply imaged due to the finite aperture at the field honeycomb plate. FIG. 29 shows an intensity segment parallel to the y-axis for x=0.0 with and without pupil honeycomb plate. Whereas an ideal rectangular profile is formed with pupil facets, the profile decomposes without the pupil facets. FIG. 30 shows the integral scan energy decisive for the lithography process, i.e., the integration of intensity along the scan path. The absolutely homogeneous integral scan energy can be clearly recognized. In FIG. 31, the pupil illumination of the exit pupil is shown in the center of the field. Corresponding to the honeycomb distribution, circular intensity peaks are produced in the pupil illumination. The maximum aperture amounts to NA.sub.ret =0.025. In FIG. 32, the total energy of the partial pupils is shown along the y-axis. The intensity distribution in the pupil has a y-tilt due to the bent beam path. The total energy of the partial pupils, which lie on the y-axis is plotted. The total energy of the individual partial pupils can be adjusted via the reflectivity of the individual facets or honeycombs, so that the energy of the partial pupils can at least be controlled in a rotational symmetric manner. Another possibility for achieving this consists in designing the reflectivity of the collector mirror independent of site. The forms of embodiment of the invention, which use different light sources, for example, are described below. In FIGS. 33-39, another form of embodiment of the invention is explained in detail relative to a laser-plasma source as the light source. If the field honeycomb plate is shaped as a plane, then the aperture in the reticle plane (NA.sub.theoretical =0.025) is given in advance by the ellipsoid or collector mirror. Since the distance from the light source to the ellipsoid or collector mirror should amount to at least 100 mm in order to avoid contaminations, a rigid relationship between structural length and collection efficiency results, as recorded in the following table: TABLE 1 Collection efficiency Structural length L Collection angle .theta. .pi. (0.degree.-90.degree.) 1000 mm 14.3.degree. 2%-12% 2000 mm 28.1.degree. 6%-24% 3000 mm 41.1.degree. 12%-35% 4000 mm 53.1.degree. 20%-45% 5000 mm 90.0.degree. 50%-71% As can be seen from this, the collection efficiency for justifiable structural lengths of 3000 mm is only 35%. In order to achieve high collection efficiencies for justifiable structural lengths, in the particularly advantageous form of embodiment of the invention according to FIGS. 33-39, the illumination device is formed as a tele-system. In the represented form of embodiment, a laser-plasma source is used as the light source, whereby the field honeycomb plate is found in the convergent beam path of a collector mirror, which images the light source on the reticle. In the case of the example of embodiment considered below, the shape of the honeycombs of the field honeycomb plate corresponds to the shape of the field, whereby, in order to determine the honeycomb size, the field arc of the annular field is drawn up into a rectangle. In the listed examples, the following results for the rectangular field x=2.pi.r 60.degree./360.degree.=104.7 mm.apprxeq.105 mm The following is selected as the honeycomb size: In principle, the honeycomb size can be selected freely. The following is valid: the more the honeycombs, the better, and also of course: the more the honeycombs, the smaller the individual honeycomb. The smaller the honeycombs are in comparison to the field, the larger the imaging scale must be between the first honeycomb and the field. If the field honeycombs have a very high aspect ratio, it is advantageous if the field honeycomb rows are arranged offset from one another. Due to the off-set honeycomb rows, there is a uniform arrangement of the secondary light sources on the pupil honeycomb plate. In the case of an aspect ratio of, e.g.: 1:16, it is favorable to offset the honeycomb rows each time by 1/4 of the honeycomb length. Secondary light sources, which are arranged on the field honeycomb plate corresponding to the distribution of the field honeycombs are produced on the pupil honeycomb plate. The pupil honeycomb plate is illuminated with small intensity peaks for a point light source. In order to reduce the structural length of the illumination system, the illumination system is formed as a telescopic system (tele-system). One form of embodiment for forming such a telescopic system consists of arranging the honeycombs of the field honeycomb plate on a collecting surface, and of arranging the honeycombs of the pupil honeycomb plate on a diverging surface. In this way, the surface normal lines of the honeycomb centers are adapted to the surface normal lines of the carrier surface. As an alternative to this, one can superimpose prismatic components for the honeycombs on a planar plate. This would correspond to a Fresnel lens as a carrier surface. The above-described tele-honeycomb condenser thus represents a superimposition of the classical tele-system and the honeycomb condenser. The compression of the field honeycomb plate to the pupil honeycomb plates is possible until the secondary light sources overlap. For a laser plasma source with a small Etendu and source diameter of 0.05 mm, the surface field honeycombs plate and pupil honeycombs plate can be compressed in a large region. In FIGS. 33 to 36, different arrangements are shown schematically, form which the drastic reduction in structural length, which can be achieved with a tele-system, becomes apparent. FIG. 33 shows an arrangement exclusively with collector mirror 300 and laser-plasma light source 302. With a planar arrangement of collector mirror, field honeycomb plate 304 and pupil honeycomb plate 306, as shown in FIG. 34, the structural length can be shortened only by the zigzag light path. Since the optical conductance of a point source is approximately zero, the field honeycomb plate 304, is, in fact, fully illuminated, but the pupil honeycomb plate 306 is illuminated only with individual peaks. However, now if the honeycombs are introduced onto curved carrier surfaces, i.e., the system is configured as a tele-system with a collecting mirror and a diverging mirror, as shown in FIG. 35, then the structural length can be shortened and the illumination can be compressed on the pupil honeycomb plate. In the case of the design according to FIG. 36, the individual honeycombs are arranged tilted on a planar carrier surface. The honeycombs of the pupil honeycomb plate have the task of correctly superimposing the fields on the reticle in the case of expanded secondary light sources. However, if a sufficiently good point light source is present, then the second honeycomb plate is not necessary. The field honeycombs can then be introduced either onto the collecting or onto the diverging tele-mirror. If the field honeycombs are found on the collecting tele-mirror, they can be designed as either concave or planar. The field honeycombs on the diverging tele-mirror can be designed as convex, concave or planar. Collecting honeycombs lead to a real pupil plane; diverging honeycombs lead to a virtual pupil plane. Collector lens 300 and tele-honeycomb condenser or tele-system 310 produce the pregiven rectangular field illumination of 6 mm.times.105 mm with correct aperture NA=0.025 in the image plane of the illumination system. As in the previous examples, with the help of one or more field lenses 314 arranged between tele-honeycomb condenser 310 and reticle 312, the annular field is formed, which strikes the entrance pupil of the objective and assures the homogeniety of the field illumination necessary for the exposure process. An intersection for the design of the field lens 314 is the plane of the secondary light sources. This must be imaged by the field lens 314 in the entrance pupil of the objective. In the pupil plane of this image, which corresponds to the reticle plane, the annular field must be produced. In FIG. 37, a form of embodiment of the invention with only one field mirror 314 is shown. In the form of embodiment with one field mirror, the annular field can be produced and the entrance pupil can be impinged on. Since reticle 316, however, is impinged on only under 2.97.degree., there is the danger that the light pencil will run back into the illumination system. It is provided in a particularly advantageous form of embodiment to use as field mirrors two grazing-incidence mirrors. This way, the annular field is again rotated and the illumination system will be left "behind" the field lens 314. By using two field mirrors, one also has more degrees of freedom in order to adjust telecentry and field illumination. The design of tele-systems will now be described on the basis of examples of embodiment, whereby the numerical data not will represent a limitation of the system according to the invention. In the first example of embodiment of a tele-system, this comprises a collector unit, a diverging mirror and a collecting mirror as well as field lenses, whereby the honeycombs are introduced only onto the first tele-mirror. All honeycombs are identical and lie on a curved carrier surface. The parameters used are represented in FIG. 39 and are selected as follows below: FIG. 40 shows an arrangement of a tele-system with collector mirrors, whereby the mirrors are unstructured, i.e., they do not comprise honeycombs. The two mirrors show a compression factor of 4:1. The shortening of the structural length due to the tele-system is obvious. With the tele-system, the structural length amounts to 852.3 mm, but without the tele-system, it would amount to 8000.0 mm. In FIG. 41, a fan of beams is shown in the x-z plane for the system according to FIG. 40. FIG. 42 in turn represents a fan of beams in the x-z plane, whereby the mirrors of the system according to FIG. 40 are now structured and have field honeycombs. Secondary light sources are formed on the second mirror of the tele-system due to the field honeycombs on the first mirror of the tele-system. In the field, the pencils are correctly overlaid, and a strip with -52.5 mm<x<+52.5 mm is homogeneously illuminated. In FIG. 43, the total system up to the entrance pupil of the objective is shown. The total system comprises: light source 302, collector mirror 300, tele-honeycomb condenser 310, field mirror 314, reticle 316 and entrance pupil of the projection objective 318. The drawn-in edge beams 320, 322 impinge on the reticle and are drawn up to the entrance pupil of the objective. FIG. 44 shows an x-z fan of beams of a configuration according to FIG. 43, which passes through the central field honeycomb 323. This pencil is in fact physically not meaningful, since it would be vignetted by the second tele-mirror, but shows well the path of the light. One sees on field mirrors 314 how the orientation of the annular field is rotated through the second field mirror. The beams cannot run undisturbed into the objective (not shown) after reflection at reticle 316. FIG. 45 shows a beam pencil, which passes through the central field honeycomb 323 as in FIG. 44, runs along the optical axis and is focused in the center of the entrance pupil. FIG. 46 describes the illumination of the reticle field with the annular field produced by the configuration according to FIGS. 40 to 45 (R=100 mm, segment=60.degree., field height.+-.3.0 mm). In FIG. 47, the integral scan energy decisive for the lithography process (integration of the intensity along the scan path) represents an arrangement according to FIGS. 40 to 46. The integral scan energy varies between 95% and 100%. The uniformity thus amounts to .+-.2.5%. In FIG. 48, the pupil illumination in the field center is shown. The beam angles are referred to the centroid beam. Corresponding to the honeycomb distribution, circular intensity peaks IP result in the pupil illumination. The obscuration in the center M is caused by the second tele-mirror. The illumination system described in FIGS. 31 to 48 has the advantage that the collecting angle can be increased to above 90.degree. without anything further, since the ellipsoid can also enclose the source. Further, the structural length can be adjusted by the tele-system. A reduction of structural length is limited due to the angular acceptance of the layers and the imaging error of the surfaces with a strong optical effect. If an arrangement can be produced with only one field honeycomb plate for point light sources or sources with very small expansion, for example, in the case of laser-plasma sources with diameters .ltoreq.50 .mu.m, then the honeycombs can be introduced onto collecting mirror 380 of the tele-system or onto the diverging second tele-mirror 352. This is shown in FIGS. 48A-48C. The introduction onto the second tele-mirror 352 has several advantages: In the case of collecting honeycombs, a real pupil plane is formed in "air", which is freely accessible, as shown in FIG. 48A. In the case of diverging honeycombs, in fact a virtual pupil plane is formed, which is not accessible, as shown in FIG. 48B. The negative focal length of the honeycombs, however, can be increased. In order to avoid an obscuration, as shown in FIG. 48C, the mirrors of the tele-system 350, 352, can be tilted toward one another, so that the beam pencil does not disturb each other, e.g. by crossing. A second example of embodiment for a tele-system will be described below, which comprises a planar facet honeycomb condenser. The system described below is particularly characterized by the fact that the collector unit forms a tele-unit with a mirror. The collecting effect of the tele-system is then completely transferred onto the collector mirror. Such a configuration will spare a mirror. Further, in the case of the planar facet honeycomb condenser, the honeycombs are planar shaped. Such a system has a high system efficiency of 27% with two normal-incidence mirrors (65%) and two grazing-incidence mirrors (80%). Further, a large collecting efficiency can be realized, whereby the collecting steradian amounts to 2 .pi., but which can still be broadened. Based on the zigzag beam path, there are no obscurations in the pupil illumination. In addition, in the described form of embodiment, the structural length can be easily adjusted. The collector or ellipsoid mirror collects the light radiated from the laser-plasma source and forms the source on a secondary light source. A multiple number of individual planar field honeycombs are arranged in a tilted manner on a carrier plate. The field honeycombs decompose the collimated light pencil into partial bundles and superimpose these in the reticle plane. The form of the field honeycombs corresponds to the rectangular field of the field to be illuminated. Further, the illumination system has two grazing-incidence toroid mirrors, which form the annular field, correctly illuminate the entrance pupil of the objective, and assure the homogeneity of the field illumination corresponding to the exposure process. In contrast to the first example of embodiment of a tele-system with collector unit as well as two other mirrors, in the presently described form of embodiment, the laser-plasma source alone is imaged by the ellipsoid mirror in the secondary light source. This saves one normal-incidence mirror and permits the use of planar field honeycombs. Such a savings presupposes that no pupil honeycombs are necessary, i.e., the light source is essentially punctiform. The mode of action will be described in more detail on the basis of FIGS. 49-51. FIG. 49 shows the image of the laser-plasma source 400 through ellipsoid mirror 402. A secondary light source 410 is formed. In the imaging of FIG. 50, a tilted planar mirror 404 defects the light pencil and guides it to the ellipsoid mirror in front of the reticle plane 406. In the imaging of FIG. 51, tilted field honeycombs 408 are dividing the light pencil and superimpose the partial bundles in the reticle plane. In this way, a multiple number of secondary light sources 410 are produced, which are distributed uniformly over the pupils. The tilt angles of the individual field honeycombs 408 correspond, at the space-point of the field honeycombs, to the curvatures of a hyperboloid, which images the laser-plasma source in the reticle plane, together with the ellipsoid mirror. The diverging effect of the tele-unit is thus introduced by the tilt angle of the field honeycombs or facets. In FIG. 52, the abbreviations are drawn in, as they are used in the following system derivation. For better presentation, the system was drawn linearly. The following values are used as a basis for the example of embodiment described below, without the numerical data being seen as a limitation: The dimensions are coupled together as follows: ##EQU4## The system can be completely determined with the process of the invention for the design of an illumination system with the use of planar field honeycombs and the pre-given values. If one inserts the design tolerances in the above formulas, then the following system parameters result: ##EQU5## The field lenses are constructed similar to the case of the first example of embodiment of a tele-system, i.e., two toroid mirrors are again used as field lenses. In FIGS. 53-58, the beam courses of a system are shown with the previously given parameters as an example. In FIG. 53) the beam course is shown for an ellipsoid mirror, which assumes aperture NA=0.999 and images on a secondary light source 410. In the form of embodiment according to FIG. 54, a planar mirror 404 is arranged at the position of the field honeycomb plate, which mirrors back the pencil. The beams are extended up to the reticle plane 406. One of the secondary light sources 410 lies within the beam pencil. Finally, in FIG. 55, the construction according to the invention is shown, in which deflecting mirror 404 is replaced by the field honeycomb plate 412. A fan of beams is depicted, which each time goes through the center of the individual field honeycombs. These beams intersect on the optical axis in the reticle plane 406. FIG. 56 finally shows the total system up to entrance pupil 414 of the objective with field lenses 416. The depicted edge beams 418, 420 strike on reticle 406 and are further calculated up to the entrance pupil of the objective. In FIG. 57, an x-z fan of beams is depicted for the system of FIG. 56, and this fan strikes the central field honeycomb 422. The beams illuminate the ring on reticle 406 with the correct orientation. In FIG. 58, in addition, the entrance pupil 424 of the projection objective is represented. The depicted beam pencil runs along the optical axis (central pencil) and is thus focused in the center of the entrance pupil. In FIG. 59, the illumination of the reticle is shown with an annular field (R=100 mm, segment=600, field height .+-.3.0 mm), which is based on an illumination arrangement according to FIGS. 52-58. The integral scan energy which is decisive for the lithographic process, i.e., the integration of the intensity along the scan path, is shown in FIG. 60. The integral scan energy varies between 100% and 105%. The uniformity or homogeneity thus amounts to .+-.2.5%. FIG. 61 represents the pupil illumination of the above-described system in the field center. The beam angles are referred to the centroid beam. Corresponding to the field honeycomb distribution, circular intensity peaks are produced in the pupil illumination. The pupil is completely filled. There are no center obscurations, since in the case of the described second form of embodiment, the mirrors are arranged in zigzag fashion. In FIG. 62, the intensity course is shown in the scan direction with the use of two different laser-plasma sources. Whereas with only one field honeycomb plate for the 50-.mu.m source, the desired rectangular course is obtained, the 200.mu.m source shows at the edges a clear blurring. This source can no longer be considered punctiform. The use of a second faceted mirror comprising pupil honeycombs, such as, for example, in the case of the pinch-plasma source, is necessary for the correct pencil superimposition in the entrance pupil of the objective. In FIGS. 63A+63B two possibilities are shown for the formation of the field honeycomb plate. In FIG. 63A, the honeycombs 500 are arranged on a curved carrier surface 502. Thus the inclination of the honeycombs corresponds to the tangential inclination of the carrier surface. Such plates are described, for example, in the case of the first form of embodiment of a tele-system according to the invention with two mirrors and a separate collector mirror. If the field honeycombs 500 are shaped in planar manner, such as, for example, in the case of the second form of embodiment that is described, in which collector unit and field honeycomb plate are combined into one tele-system, then the individual field honeycombs are arranged under a pregiven tilt angle on the honeycomb plate 504. Depending on the distribution of the tilt angle on the plate, one obtains either collecting or diverging effects. A plate with a diverging effect is illustrated. Of course, honeycomb plates with planar honeycombs can be used also in systems according to the first example of embodiment with a collector unit and two tele-mirrors. In the case of such a system, the honeycombs are then tilted onto one of the mirrors such that a diverging effect is produced and onto the other in such a way that a collecting action is adjusted. FIG. 64 shows a form of embodiment of the invention, which is defined as a refractive system with lenses for wavelengths, for example, of 193 nm or 157 nm. The system comprises a light source 600, a collector lens 602, as well as a field honeycomb plate 604 and a pupil honeycomb plate 606. Prisms 608 arranged in front of the field honeycombs serve for adjusting the light path between the field honeycomb plate 604 and the pupil honeycomb plate 606. With the device according to the invention or the design process according to the invention, for the first time, an arrangement or a design process for illumination systems is given, which finds use particularly in EUV lithography, in which a uniform illumination of a reticle field is produced with uniform imaging and filling of the entrance pupil for light sources with any desired illumination A in a predetermined surface. |
abstract | A nuclear reactor includes a pressure vessel, and a control rod assembly including at least one movable control rod comprising a neutron absorbing material, a control rod drive mechanism (CRDM) for controlling movement of the at least one control rod, and a coupling operatively connecting the at least one control rod and the CRDM. The coupling includes a first portion comprising a first material having a first density at room temperature, and a second portion comprising a second material having a second density at room temperature that is greater than the first density. In some embodiments the coupling includes a connecting rod including a hollow or partially hollow connecting rod tube comprising a first material having a first density and a filler disposed in the hollow or partially hollow connecting rod tube, the filler comprising a second material having a second density greater than the first density. |
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summary | ||
043572090 | description | FIG. 1 FIG. 1 shows in detail one form of the invention. In the system designated as S we will treat that portion of the system on the right designated as operating unit A and that part of the system on the left designated as operating unit B. The nuclear reactor is generally designated as N and includes radiating fins 10 and nuclear rods 12 with a motor drive mechanism 14 for moving the rods in and out of the reactor N. A coolant circulating system 16 maintains the nuclear reactor at a safe temperature level. A heat exchanger 18 may be provided adjacent the reactor for assisting and maintaining the coolant circulating system. Surrounding the system S and incorporating the operating units A and B is a partitioned jacket 20 having a partition 22. The right hand chamber 24 may be used in the manner set out in U.S. Pat. No. 4,102,752. The left hand chamber 26 may have an operating unit similar to operating unit A for right hand chamber 24 or it may have an entirely different operating system for receiving a different type of circulating material such as sulfur, mercury, sodium, alcohol, or other various types of organic or inorganic liquids or gases as the case may be for taking advantage of temperature transfer capabilities within the system as differing from the operating unit A. Intakes 28 and 30 deliver fluids to chambers 24 and 26 respectively and discharges 32 and 34 discharge heated fluid from the right and left hand chambers 24 and 26 respectively to the operating units A and B respectively. It will be obvious that the coolant circulating system 16 should include some type of pump 36. It should be noted that the bottom of the nuclear reactor core N is not encased by the left and right hand chambers 24 and 26. Operating unit A for example would take in sea water or the like through intake 28. Preferably the incoming sea water is preheated in a heat exchanger 38 to a temperature of at least 125.degree. F. and preferably greater than 150.degree. F. The preheated sea water passes through the conduit 28 into the boiler chamber 24. The reactor N may be either fission or fusion type as is known the art. The liquid level 40 in the boiler chamber 24 should be maintained at a level so as to completely surround the core of the reactor N. As the liquid in the chamber 24 is heated by the reactor N, steam is generated and heated to a temperature of at least about 250.degree. F. and may be considerably higher depending upon the liquid used for generation. A superatmospheric pressure would be required for assuming much higher temperatures such as 1,000 degrees or more. The high temperature high pressure steam passes out of the boiler 24 through the conduit or discharge 32 to an expansion turbine 42 of known construction. In driving the turbine 42, the steam is cooled to about the boiling point of water and the prevailing atmospheric pressure and the steam is exhausted from the turbine 42 through the line 44 whereby it is conveyed into a heat exchanger 38. Of course heat exchanger 38 is illustrated schematically but in the heat exchanger 38, the steam exhausting from the turbine 42 is maintained in heat exchange contact with the incoming sea water supplied through the intake pipe 28. The steam in the heat exchanger 38 is cooled and condensed to the extent that the exit line 46 carries potable water, i.e. water at a temperature of about 70.degree.-80.degree. F. This water is delivered by the exit line 46 to a pump 48 capable of delivering a high volume of water under pressure through line 50 to a municipal or agricultural water distribution network. The pump 48 is operatively connected to and driven by the turbine 42 by means of a shaft 52 or other similar such connection. Of course reduction gearing may be utilized between the turbine 42 and pump 48 but such an arrangement is known in the art. Steam leaving the boiler 24 through the line 32 is of course substantially pure water having been distilled from the sea water. As the pure water is removed, the concentration of salts in the boiler 24 increases. Periodically, the concentrated salt solution is drawn off through the line 52 upon opening of the valve 54. The solution which would be drawn off in this manner is highly concentrated in various salts contained in the sea water and it has been found desirable that this highly concentrated solution may be evaporated to dryness or otherwise dried to produce salt for use on roads or the like. In order to provide a control over the temperature of the system, thermal sensors 56 and 58 are utilized. Sensors may be provided in other portions of the system. These sensors are connected to a thermal responsive valve 60 and may be of an electrical or thermal coupled type such as bimetallic elements or the like. Valve 60 is normally closed so that all incoming sea water passes through the heat exchanger 38 to be preheated as mentioned previously. Sensors 56 and 58 indicate a rise in temperature beyond thermal capabilities of the system permitting valve 60 to open allowing cold sea water to flow through the by-pass line 62 directly into the feed line 28 without being preheated in the heat exchanger 38. Sea water is typically in a temperature of 40.degree. to 50.degree. and a rapid cooling of the system will occur. Other safe guards can be included which are known in the art. It will now be obvious that instead of utilizing sea water, another type of fluid can be utilized which can be pumped in on the other side of the reactor and in the area of the operating unit B. The system may vary as far as the operation is concerned and as far as the driving capability or the means for taking heat off or the like. FIG. 2 FIG. 2 shows the reactor N partitioned in four separate chambers 64, 66, 68 and 70. Intake lines 72, 74, 76 and 78 are provided for each of the chambers and discharge lines 80, 82, 84 and 86 are provided for purposes as will be obvious from the aforementioned description of operation. It will be noted in FIG. 2, that the chambers allow for various fluids to be pumped in of different consistencies temperature values and the like. FIG. 3 In FIG. 3, it will be noted that instead of the chambers being set out in a quadrant form as shown in FIG. 2, the chambers might be constructed in a stacked arrangement so that the reactor end may be provided with one or more chambers such as 88 and 90. The chambers could be divided as in FIG. 2 or they could be further horizontally divided making an additional stacked series. It will be obvious that various combinations could be worked out in this regard. It will be noted that chamber 88 includes an intake 92 and a discharge 94. Further chamber 90 includes an intake 96 and a discharge 98 similar and for the same purposes of those previously described. It is of special interest that each of the producable energy units will have a separate variable energy output control so as to make available a plurality of individual sources of useable energy each of varying degrees yet all from a single reactor. While this invention has been described as having a preferred design, it will be understood that it is capable of further modification. This application, is therefore, intended to cover any variations, uses, or adaptations of the invention following the general principles thereof and including such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains, and as may be applied to the essential features hereinbefore set forth and fall within the scope of this invention or the limits of the claims. |
041742567 | abstract | Nuclear reactor with a MHD driven gas-core vortex, that may be preceded by an enrichment section and followed by a reprocessing section, both sections based on gas-cores that are MHD driven gas-vortexes, in which the nuclear reactor functions with a mixture of e.g. UF.sub.6 and one or more light gases such as H.sub.2, DT, He. |
042882893 | claims | 1. A fushion machine comprising a hollow toroidal chamber, a gas of ionized isotopes of hydrogen in said chamber, means for establishing an inducing magnetic field whose amplitude is controllably variable and which has a component perpendicular to the plane of said hollow toroidal chamber and said component being coaxial with the axis of revolution of said hollow toroidal chamber so that an increasing circular plasma electric current is induced in said hollow toroidal chamber as said inducing magnetic field increases, and generating means for generating a strong focusing magnetic field whose amplitude is controllably variable to be proportional to the plasma current and which is toroidally disposed about said axis of revolution and enters on one side of said hollow toroidal cylinder, passes through said hollow toroidal chamber and exits on the other side of said hollow toroidal cylinder in a direction parallel to said axis of revolution. 2. The fusion machine of claim 1 wherein the strong focusing magnetic field varies along a path traced azimuthally about its cylindrical periphery. 3. The fusion machine of claim 2 wherein the strong focusing magnetic field periodically varies along said azimuthal path. 4. The fusion machine of claim 3 wherein the flux lines of the strong focusing magnetic field periodically varies between convex and concave bowing along said azimuthal path. 5. The fusion machine of claim 4 wherein the amplitude of the strong focusing magnetic field varies in synchronism with the amplitude of the inducing magnetic field. 6. The fusion machine of claim 4 wherein said strong focusing generating means comprises a plurality of pairs of magnet sections in operative proximity with said toroidal chamber. 7. The fusion machine of claim 4 wherein the number of pairs of magnetic sections range between 3 and 8. 8. The fusion machine of claim 4 wherein adjacent magnetic sections are on opposite sides of said toroidal chamber. 9. The fusion machine of claim 8 wherein adjacent magnetic sections are separated by an air gap. 10. The fusion machine of claim 9 wherein the length of the air gap is between 50% and 80% of the length of a magnet section. 11. The fusion machine of claim 4 wherein alternate magnet sections are focusing sections and the intervening magnet sections are defocusing sections. 12. The fusion machine of claim 11 wherein each defocusing section has a field index n.sub.D in the range of 4.5 to 8. 13. The fusion machine of claim 12 wherein the field index n.sub.D equals 7. 14. The fusion machine of claim 12 wherein each focusing section has a field index n.sub.F =1-n.sub.D. 15. The fusion machine of claim 6 wherein said magnet sections are arrays of current conductors aligned parallel to the azimuthal of the toroidal chamber. |
045253242 | summary | Irradiated nuclear reactor fuel elements are kept in a basin filled with water where the radioactivity of the fuel elements falls off or decays with time. After a predetermined period of storage during which the heat generated by the radioactive decay falls off exponentially, the fuel elements are packed in transport containers and are brought to an interim storage facility. At this location, the fuel elements are stored before they are subjected to reprocessing. DE-OS No. 29 29 467 discloses such an intermediate storage facility which is configured as a dry storage facility whereat the fuel elements are placed into gas-tight storage containers after being removed from the transport containers. They are then placed in several storage rooms of a longitudinally extending storage building wherein they are stacked horizontally. The storage containers are cooled by natural convection. The cooling air gradually warms and moves upwardly and transfers the heat to the ambient by means of a heat exchanger. In a proposed embodiment of a storage room wherein the containers are horizontally stacked, horizontally arranged stationary storage tubes are provided within the room. The storage containers are packed into the storage tubes whereupon the tube is closed at its loading opening by means of a suitable plug. In this proposed embodiment, an indirect cooling of the storage containers is achieved by the rising cooling air. SUMMARY OF THE INVENTION It is an object of the invention to provide a dry storage facility of the kind referred to above wherein an improved transfer of heat between the rising cooling air and the storage containers or the storage tubes containing the storage containers is achieved. It is still another object of the invention to provide an arrangement of the storage tubes in a storage module which permits a substantial amount of space to be saved within the dry storage facility without reducing its storage capacity. A dry storage facility stores radioactive materials such as irradiated nuclear reactor fuel elements that release heat produced by radioactive decay, the radioactive materials being held in gas-tight elongated storage containers. The dry storage facility of the invention includes an enclosure having a storage module disposed therein for accommodating the elongated storage containers, the latter being grouped into a plurality of sets of containers. According to a feature of the invention, the storage module includes means for holding the sets of containers in respective horizontal planes arranged one atop the other. The holding means includes ancillary holding means for holding each two mutually adjacent ones of the sets so as to cause the containers in one plane to be disposed in a direction transverse to the containers in the next adjacent plane. Convection cooling means is provided for cooling the storage containers. The enclosure of the dry storage facility can be, for example, an underground storage facility or a specially reinforced concrete building with very thick walls. This crosswise arrangement of the elongated storage containers causes a swirling of the rising cooling air which always flows into the intermediate spaces defined by the storage containers or storage tubes and which spaces are covered from above by the next layer of storage containers or storage tubes. The formation of an upward verically rising laminar flow is almost completely prevented so that the heat transferred to the available air is improved. In a further advantageous embodiment of the invention, the storage room or module includes a plurality of storage tubes for holding corresponding ones of the storage containers, the storage tubes being grouped into a plurality of sets of storage tubes. The sets are mounted in the storage module in respective horizontal planes one atop the other with the tubes of each set extending in a direction transverse to the tubes of the next adjacent set. The tubes of each set also extend longitudinally at an angle to the longitudinal direction of the transport passageway. This arrangement of the storage tubes permits a saving to be realized in the floor space of the storage facility. The width of the transport passageway between the storage modules on both sides of the storage facility and the width of the track of the crane-like transport vehicle can be configured so as to be narrower than heretofore because the loading of the storage modules is conducted at an angle with respect to both the transport passageway and the track of the bridge crane of the transport vehicle. The sets of storage tubes in the storage module are stacked as described above. According to another feature of the invention, every other one of the sets of storage tubes of a storage module is arranged therein so that the longitudinal axes of the tubes extend in a first direction; whereas, the tubes of the remaining sets of storage tubes of the module extend in a second direction transverse to the first direction. The tubes of every other one of the sets extending in the first direction are laterally displaced from the tubes of the next adjacent set of tubes extending in the first direction; and, the tubes of every other one of the sets extending in the second direction are laterally displaced from the tubes of the next adjacent set of tubes extending in the second direction. Because of this advantageous arrangement of the storage tubes and the storage containers placed therein, the rising cooling air is caused to continuously change its direction as it rises in the module through the stack of storage tubes and is thereby swirled. This swirling action increases the contact of the rising cooling air with the surfaces of the storage tubes thereby increasing the quantity of heat transferred to and conducted away by the cooling air. According to a further feature of the invention, each of the storage modules can be configured as a separate block-like unit having a square base and being bounded on its four sides by vertical walls with two diagonally opposite corners of the unit defining a vertical diagonal plane bisecting the unit into two triangular halves. The storage modules are arranged along the side of the transport passageway so as cause the diagonal plane to extend parallel to the longitudinal direction of the passageway. Because of this arrangement of the storage modules with respect to the transport passageway, two of the vertical walls face the passageway and the storage module can be loaded in crosswise fashion with elongated storage containers through both of the last-mentioned vertical walls. More specifically, the storage module can be loaded with respective sets of storage containers which lie crosswise to each other. In this way, a very effective use of space is made possible in the storage area of the enclosure wherein the storage modules are arranged. With the arrangement above, one of the triangular halves of each of the storage modules faces the passageway whereas the other one of the triangular halves of each of the storage modules faces away from the passageway. The transport facility in the enclosure includes a bridge crane and overhead guide means such as guide rails for guiding the bridge crane above and along the transport passageway. According to a further feature of the invention, the triangular half of each of the storage modules facing the passageway can be configured so as to permit the overhead guide means to be disposed thereover. Also, and according to another feature, the other triangular half of the storage module is adapted to accommodate an exhaust conduit thereabove for conducting away the cooling medium from the storage module. With the above arrangement of the storage modules, both the transport passageway and the area taken up by the passageway and the storage modules as a group can be dimensioned so as to be narrower. The transport vehicle travels above half of the storage modules along the transport passageway. Half of the surface region of each storage module facing the passageway can be used for loading operations. The space requirements for the loading operation of the storage modules is therefore held to a minimum. The other triangular half of each storage module serves as an exhaust conduit which can be connected to a main exhaust conduit. |
059828390 | claims | 1. An automated inspection assembly for inspecting a pipe of a nuclear reactor, the pipe having a circumference, said assembly comprising: a mounting subassembly comprising a support element, a coupling element movably coupled to said support element, and a clamp configured to mount said assembly to the pipe, said clamp coupled to an end of said support element, said coupling element movable along said support element; and a scanning subassembly coupled to said mounting subassembly, said scanning subassembly comprising a scanning arm and a scanning head configured to scan at least a portion of the pipe circumference, said scanning arm movably coupled to said coupling element, said scanning head movably coupled to an end of said scanning arm. a mounting subassembly comprising a support element, a coupling element movably coupled to said support element, and a clamp configured to mount said assembly to the pipe, said clamp coupled to an end of said support element, said coupling element movable along said support element; a scanning subassembly coupled to said mounting subassembly and comprising a scanning arm and a scanning head configured to scan at least a portion of the pipe circumference, said scanning arm movably coupled to said coupling element, said scanning head movably coupled to an end of said scanning arm; and a remotely operated vehicle coupled to said mounting subassembly. 2. An assembly in accordance with claim 1 wherein said scanning head comprises a substantially "U" shaped transducer support assembly sized to receive the pipe. 3. An assembly in accordance with claim 2 wherein said transducer support assembly is configured to rotate about the pipe. 4. An assembly in accordance with claim 1 wherein said scanning head comprises a substantially "C" shaped element sized to receive the pipe. 5. An assembly in accordance with claim 4 wherein said scanning subassembly further comprises a transducer support assembly coupled to an inner circumference of said "C" shaped element. 6. An assembly in accordance with claim 5 wherein said transducer support assembly is substantially "U" shaped and comprises two leg portions extending from a back portion, a first transducer element coupled to an end of one of said leg portions and a second transducer element coupled to an end of the other of said leg portions. 7. An assembly in accordance with claim 5 wherein said scanning subassembly further comprises a motor configured to move said transducer support assembly with respect to said "C" shaped element. 8. An assembly in accordance with claim 1 wherein said mounting subassembly is configured to couple said assembly to a remotely operated vehicle. 9. An assembly in accordance with claim 1 further comprising a remote motion control system coupled to at least said scanning head and configured to control movement of said scanning head during a scan. 10. An automated inspection assembly for inspecting a pipe of a nuclear reactor, the pipe having a circumference, said assembly comprising: 11. An assembly in accordance with claim 10 wherein said scanning head comprises a substantially "U" shaped transducer support assembly sized to receive the pipe. 12. An assembly in accordance with claim 11 wherein said transducer support assembly is configured to rotate about the pipe. 13. An assembly in accordance with claim 10 wherein said scanning head comprises a substantially "C" shaped element sized to receive the pipe. 14. An assembly in accordance with claim 13 wherein said scanning subassembly further comprises a transducer support assembly coupled to an inner circumference of said "C" shaped element. 15. An assembly in accordance with claim 14 wherein said transducer support assembly is substantially "U" shaped and comprises two leg portions extending from a back portion, a first transducer element coupled to an end of one of said leg portions and a second transducer element coupled to an end of the other of said leg portions. 16. An assembly in accordance with claim 14 wherein said scanning subassembly further comprises a motor configured to move said transducer support assembly with respect to said "C" shaped element. |
abstract | A weight compensation apparatus for compensating for a weight of a stage that is movable along a vertical reference plane including a pulley having a pulley shaft, a belt which is wound around and supported by the pulley, and has the stage at one end and a counter mass corresponding to the stage at the other end, and a hydrostatic bearing which has an arcuated bearing portion, and supports the pulley shaft by causing a fluid to flow into a bearing gap between the bearing portion and the pulley shaft. |
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045340528 | claims | 1. A block for partially limiting a radiation beam emitted by a radiation source in a given reference direction, for limiting a first part of the beam corresponding to a maximum half angle of opening, said block being formed by a limiting block having moving means for allowing said limiting block to move in a parallel direction to a first axis transverse to said reference direction, said limiting block comprising a cylindrical active surface which defines limits for the beam, said limits being a function of the position which said cylindrical active surface occupies along said first axis, said moving means allowing movement of said limiting block such that the orientation of the active surface is not modified and said limits are tangential to the cylindrical active surface for all positions of said limiting block. 2. The limiting block as claimed in claim 1, wherein said cylindrical active surface comprises an edge in the form of an arc of a circle forming a directrix, whose projection on a straight reference line corresponding to said reference direction represents a height of said active surface. 3. The limiting block according to claim 2, wherein said arc of a circle comprises a radius determined by the following relationship: EQU R=H/sin .alpha. R being the radius of the arc of a circle, H being the height of the cylindrical active surface, .alpha. being the angle representing the maximum half angle of opening of the beam. R being the radius of the arc of a circle, H being the height of the cylindrical active surface, .alpha. being the angle representing the maximum half angle of opening of the beam. 4. The limiting block as claimed in claim 2, wherein said arc of a circle comprises a center O situated on an axis perpendicular to said reference direction and passing through the end of said arc of a circle the closest to said source. 5. The limiting block according to claim 4, wherein said arc of a circle comprises a radius determined by the following relationship: EQU R=H/sin .alpha. 6. In a collimator for delimiting a useful beam from a radiation beam, comprising a first limiting assembly having a first longitudinal axis transversal to the reference direction of the radiation beam, a second limiting assembly having a second longitudinal axis perpendicular to the first one and also transveral to the reference direction, these two assemblies being superimposed and centered on said direction, the first and the second limiting assemblies each comprise a first and a second limiting block such as claimed in one of the preceding claims, cooperating with paths of rectilinear movement, for allowing said limiting blocks to move along the longitudinal axis of the assembly to which they belong. 7. The collimator as claimed in claim 6, wherein said paths of movement cooperate with rolling means formed by rollers which said limiting blocks comprise so as to allow rectilinear movement of these blocks. 8. The collimator as claimed in claim 7, further comprising drive means cooperating with studs for securing said limiting blocks so as to ensure the motorized movements of said limiting blocks. 9. The collimator as claimed in claim 6, further comprising drive means cooperating with studs for securing said limiting blocks so as to ensure the motorized movements of said limiting blocks. |
summary | ||
description | Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is seen a measurement device 2, or measuring cell, arranged around a component, a line segment or medium tube 1. The measurement device forms a part of a nuclear power station. The medium tube 1 forms a part of a coolant loop, for example of a primary circuit system. The measurement device 2 comprises a first concave casing part 4 and a second concave casing part 6. The respective inner wall 8 and the respective outer wall 10 of the first casing part 4 and the second casing part 6 preferably consist of austenitic steel. A cadmium screen 12 in the form of cadmium sheeting is fitted on the respective inner sides of the outer walls 10 in order to stop thermal neutrons. A source chamber 14 is provided in the first casing part 4 to accommodate a neutron source 16 which serves as the emitter. A counter-tube chamber 17 is arranged in the second casing part 6 to accommodate two parallel counter tubes 18 which serve as the receiver. The wall 19 of the counter-tube chamber 17 lying toward the outer wall 10 also has a cadmium screen 12. Embodiments having a plurality of emitters and/or receivers are also possible, and may for example be used to pick up concentration drops or signal differences. In order to protect the neutron source 16 and the counter tubes 18 against high temperatures of the medium tube 1, a cooling duct 20 is arranged between the source chamber 14 and the inner wall 8, or between the counter-tube chamber 17 and the inner wall 8. The length of the cooling duct 20 in the vertical direction corresponds to at least the length of the measurement device 2. Depending on the embodiment of the medium tube 1, the cooling duct 20 may, for example, be annular or elongate in design. Coolant 22 flows through the cooling duct 20 in the direction of the arrows 23. The coolant 22, for example air, is propelled through the cooling duct 20 by means of a fan 24. The fan 24 is, for example, arranged at the lower end of the first casing part 4. A temperature sensor 26 for determining the temperature of the coolant 22 is arranged at the opposite end of the first casing part 4. A signal representing the measured value determined by the temperature sensor 26 is fed to a non-illustrated temperature control system. The temperature control system guarantees that the temperature of the coolant 22 does not exceed an upper threshold or fall below a lower threshold. To this end, the power of the fan 24 and the resulting flow of cooling air are controlled. If appropriate, the first casing part 4 and the second casing part 6 also comprise, between the inner wall 8 and the cooling duct 20, an insulation layer 28 in addition to the cooling duct 20. Air is used as the insulator. Similar to the cooling duct 20, the insulation layer 28 may, for example, be of annular or elongate design. The gap formed between the inner wall 8 and the outer wall 10 of the first casing part 4 is filled with an absorbing moderator 30. Polyethylene is thereby used as the absorbing moderator 30. Similarly, the gap in the second casing part 6 is also filled with absorbing moderator 30. The absorbing moderator 30, the cadmium screen 12 consisting of neutron-absorbing material, and the outer wall 10 consisting of austenitic material form a layered shield 31 against the radiation produced by the neutron source 16. Spacers 32 that are resistant to temperature and that do not expand, are incorporated in the radial direction in the insulation layer 28 and in the cooling duct 20. The spacers 32, for example support devices, serve to prevent a thermally induced change in the measurement geometry, in particular the length of the measurement path. For example, ceramic or mica glass is used as the material resistant to temperature and expansion. FIG. 2 shows the measurement device 2 in cross section. The first casing part 4 and the second casing part 6 are connected to one another by means of a number of externally fitted fastening elements 34. In this regard, the measurement device as a whole encloses or clamps the medium tube 1. The fastening elements 34 are, for example, designed as clips, screws or clamping devices. From this view it can be seen that two counter tubes 18 are again provided; it is also possible for more than two counter tubes to be provided. The neutron source 16 and the two counter tubes 18 are arranged in the source chamber 14 and in the counter-tube chamber 17, respectively. In order to cool the neutron source 16 and the two counter tubes 18, the insulation layer 28 and the cooling duct 20 run concentrically around the medium tube 1. Further, the spacers 32 are fitted at regular intervals in the insulation layer 28 and the cooling duct 20. Similarly to FIG. 1, the outer walls 10 and the wall 19 of the counter-tube chamber 17 respectively have a cadmium screen 12. Using the neutron source 16, a neutron flux 36 is sent through the coolant 38 flowing in the medium tube 1. The neutron flux 36 passes through the boron-enriched coolant 38. The neutron flux 36 is attenuated in dependence on the boron concentration in the coolant 38. The altered neutron flux 36 is determined by means of the neutron detectors, i.e. the counter tubes 18. Signals representing the measured values formed by the counter tubes 18 are transmitted to an evaluation unit 40. From the count rate and the temperature of the coolant 38 (the measuring sensor is not illustrated for reasons of clarity), the evaluation unit 40 determines the concentration of boron or boric acid. Since the neutron source 16 is arranged diagonally opposite the two counter tubes 18, the neutron flux 36 passes through the coolant 38 over the entire width of the diameter d of the medium tube 1. Accordingly, a substantially straight-line measurement path is formed between the neutron source 16 and the counter tubes 18 in the medium tube 1. Because of its highly effective, active thermal insulation using the controllable cooling air flow in the cooling duct 6, the described measurement device 2 exhibits good behavior in terms of thermal influences when determining the boron concentration. The measurement device 2 is therefore suitable, in particular, for direct use on the primary loop of a reactor plant, where temperatures of up to 380xc2x0 C. may occur. The measurement device 2 is mechanically constructed in such a way that even strong temperature fluctuations do not cause any geometrical changes, and therefore do not have any effects on the measuring method. Any possible remaining dependency of the method involving the measurement of neutron absorption on the thermodynamic state of the coolant 38 and the hydraulic system procedure in the primary cooling circuit can be eliminated by computer-assisted evaluation methods in the evaluation unit 40. In order to improve accuracy and obtain a fast display, further process information relevant to the measurement of the boron concentration is thereby also used in addition to the measurement signal from the measurement device 2. This information is processed in the evaluation unit 40 by using model-based plausibility and balancing algorithms. In addition, the radiation-screening construction of the measurement device 2 precludes significant exposure of the operating personnel to radiation. It will be understood that in the context of large-surface components 2 it is possible to use a similar measurement device 2 but with the neutron source 16 and the counter tubes 18 arranged in a one-piece casing. In the case of such a device, it is favorable to use a reflection measurement signal. In this case, the signal put out by the neutron source 16 is reflected inside the component 1 and then picked up by the counter tubes 18. |
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description | First of all, the expression of crystal lattice plane indices (Miller indices) will be briefly explained. A germanium crystal and a silicon crystal, which are used in embodiments of the invention, each has a crystal structure of cubic lattice, so that there are six lattice planes equivalent to (100) plane. These equivalent planes are represented by {100} in general. Similarly, there are six directions equivalent to [100] direction, these equivalent directions being represented by less than 100 greater than . This specification uses such general expressions. FIG. 1 is a plan view of the first embodiment of the invention and FIG. 2 is its perspective view. Referring to FIG. 2, a channel-cut monochromator 10 is made of a germanium single crystal block. The block is a parallelepiped of 35 mm long, 20 mm wide and 25 mm high and has five kinds of reflecting surface pairs formed by processing grooves on the block. Each groove is 20 mm deep and therefore each reflecting surface is 20 mm high. The channel-cut monochromator has a bottom surface which can be a reference plane. The block has been cut so as to be a parallelepiped having a crystallographic axis shown in FIG. 2. That is, a longitudinal edge 52 is parallel to less than 100 greater than direction, a lateral edge 54 is parallel to less than 110 greater than direction and a vertical edge 56 is parallel to less than 110 greater than direction. The grooves can be machined by a diamond wheel machine, a diamond-tool NC milling machine or a supersonic processing machine. Referring to FIG. 1, the first reflecting surface pair 11 is composed of two reflecting surfaces 12 and 14 parallel to each other for diffracting X-rays by Ge{220} or Ge{440} plane. That is, the reflecting surfaces 12 and 14 are so processed as to be parallel to {220} and {440} planes of germanium single crystal. The {220} and {440} planes are parallel to each other and are different in interplaner spacing (d-value) only. The reflecting surfaces 12 and 14 are parallel to a longitudinal side 90 of the single crystal block. The second reflecting surface pair 16 is composed of two reflecting surfaces 18 and 20 parallel to each other for diffracting X-rays by Ge {400} plane. That is, the reflecting surfaces 18 and 20 are so processed as to be parallel to {400} plane of germanium single crystal. The reflecting surfaces 18 and 20 are perpendicular to the longitudinal side 90. The third reflecting surface pair 22 is composed of two reflecting surfaces 24 and 26 parallel to each other for diffracting X-rays by Ge {422} plane. That is, the reflecting surfaces 24 and 26 are so processed as to be parallel to {422} plane of germanium single crystal. The reflecting surfaces 24 and 26 are inclined by 54.7 degrees to the longitudinal side 90. The fourth reflecting surface pair 28 is composed of two reflecting surfaces 30 and 32 parallel to each other for diffracting X-rays by Ge {511} plane. That is, the reflecting surfaces 30 and 32 are so processed as to be parallel to {511} plane of germanium single crystal. The reflecting surfaces 30 and 32 are inclined by 74.4 degrees to the longitudinal side 90. The fifth reflecting surface pair 34 is composed of two reflecting surfaces 36 and 38 parallel to each other for diffracting X-rays by Ge {111} plane. Although the reflecting surface 36 is parallel to {111} plane of germanium single crystal, the other reflecting surface 38 is not parallel to {111} plane of germanium single crystal. That is, the reflecting surface 38 is an asymmetrical reflecting surface for condensing a beam width. The reflecting surface 36 is inclined by 35.3 degrees to the longitudinal side 90. There is a direct path between the two reflecting surfaces 12 and 14 of the first reflecting surface pair 11. An X-ray beam 42 can pass through the direct path in no contact with any reflecting surfaces. Surfaces other than the reflecting surfaces mentioned above, for example, side surfaces 86 and 88 shown in FIG. 3, have been suitably cut off so as not to intercept various incident X-ray beams and output X-ray beams. In FIG. 1, the channel-cut monochromator 10 can be rotated around an axis of rotation 40 which extends perpendicularly to the drawing sheet. The five kinds of reflecting surface pairs are designed based on an imaginary circle 46 whose center coincides with the axis of rotation 40. That is, each reflecting surface pair is so designed that an X-ray beam incident on the reflecting surface pair or its extension line is tangent to the imaginary circle 46 whose radius is 2.5 mm. In this embodiment, an X-ray beam is reflected two times (i.e., one time at each reflecting surface of the pair) at all of the five kinds of reflecting surface pairs and then goes out from the monochromator. Each reflection surface of the five kinds of reflection surface pairs is perpendicular to the reference plane. The axis of rotation 40 of the monochromator is also perpendicular to the reference plane. FIG. 3 is a plan view showing a manner in which X-rays coming from in seven kinds of directions are reflected by or pass through the channel-cut monochromator shown in FIG. 1. The X-ray beam indicated by xe2x80x9cdirectxe2x80x9d is to pass through the monochromator 10 in no contact with any reflecting surface. The X-ray beam indicated by xe2x80x9c220xe2x80x9d is to be reflected by {220} plane of germanium crystal. Similarly, the X-ray beams indicated by 440, 400, 422, 511 and 111 are to be reflected by {440}, {400}, {422}, {511} and {111} planes of germanium crystal. It is noted that a direction perpendicular to the drawing sheet coincides with less than 110 greater than direction of the germanium crystal. Although FIG. 3 shows various directions of incident X-ray beams with the channel-cut monochromator 10 being stationary, the incident X-ray beam is generally always in the same direction in the actual high-resolution X-ray diffractometer, so that the channel-cut monochromator 10 is rotated to alter the direction of the incident X-ray beam to the monochromator. There will be described hereinafter, with referring to drawings, the seven states of monochromator rotation for seven directions of the incident X-ray beams. FIG. 4 shows a state in which an X-ray beam 42 passes through the direct path. The channel-cut monochromator 10 is so rotated and adjusted around the axis of rotation 40 that the reflecting surfaces 12 and 14 become parallel to the X-ray beam 42. The X-ray beam 42 passes through the channel-cut monochromator 10 so as to be tangent to the imaginary circle 46, so that the X-ray beam 42 is in no contact with any reflecting surface. The distance between the reflecting surface 12 and the X-ray beam 42 is 1 mm. This direct beam is usable for X-ray diffraction measurement of a polycrystalline thin film. FIG. 5 shows a state in which an X-ray beam is diffracted by {220} plane of germanium crystal. The channel-cut monochromator 10 is so rotated around the axis of rotation 40 that the first reflecting surface 12 of the first reflecting surface pair is inclined by 22.65 degrees to the X-ray beam 42. Stating in detail, the channel-cut monochromator 10 is rotated clockwise by 22.65 degrees from the state shown in FIG. 4. The X-ray incident angle value to the first reflecting surface 12 is determined by the wavelength of the used characteristic X-ray (CuKxcex11 in the embodiment), the d-value of {220} plane of germanium crystal and the Bragg""s law. The X-ray beam 42 is incident so as to be tangent to the imaginary circle 46. The X-ray beam 42 is incident on the first reflecting surface 12 and diffracted by {220} plane of germanium crystal and then is incident on the second reflecting surface 14 and similarly diffracted by {220} plane to go out as an output X-ray beam 48. The X-ray beam 48 becomes parallel to the incident X-ray beam 42 but is shifted translationally by a distance L. Therefore, if an X-ray beam was incident on the desired region of a sample in the state shown in FIG. 4, it is necessary to shift the sample translationally by the distance L for irradiating the same desired region when the optical system is altered to the state shown in FIG. 5. Of course, the X-ray source requires no movement. An X-ray beam from this {220} reflection has comparatively a high intensity and is suitable for reflection coefficient measurement (near the total reflection region with glancing incident angles). The {220} reflection is also suitable for the four-crystal monochromator, as shown in FIG. 11 explained below, for obtaining the rocking curve. FIG. 6 shows a state in which an X-ray beam is diffracted by {440} plane of germanium crystal. A reflecting surface pair to be used is the first reflecting surface pair (reflecting surfaces 12 and 14) which is the same pair as for {220} reflection shown in FIG. 5. Since {440} plane and {220} plane are parallel to each other, the same reflection surface pair can be used, noting that the d-values are different so that the incident angle of the X-ray beam 42 to the reflecting surface 12 should be altered. That is, the channel-cut monochromator 10 is so rotated around the axis of rotation 40 that the first reflecting surface 12 is inclined by 50.38 degrees to the X-ray beam 42. Stating in detail, the channel-cut monochromator 10 is rotated clockwise by 50.38 degrees from the state shown in FIG. 4. The X-ray beam 42 is incident so as to be tangent to the imaginary circle 46. The X-ray beam 42 is incident on the first reflecting surface 12 and diffracted by {440} plane of germanium crystal and then is incident on the second reflecting surface 14 and similarly diffracted by {440} plane to go out as an output X-ray beam 48. The X-ray beam 48 becomes parallel to the incident X-ray beam 42 but is shifted translationally by a distance which is different from that in FIG. 5. An X-ray beam from this {440} reflection has a lower intensity than that from {220} reflection but a high resolution and is suitable for the four-crystal monochromator, as shown in FIG. 11 explained below, for obtaining rocking curves. FIG. 7 shows a state in which an X-ray beam is diffracted by {400} plane of germanium crystal. The channel-cut monochromator 10 is so rotated around the axis of rotation 40 that the first reflecting surface 18 of the second reflecting surface pair is inclined by 33.0 degrees to the X-ray beam 42. Stating in detail, the channel-cut monochromator 10 is rotated counterclockwise by 57.0 degrees from the state shown in FIG. 4. The X-ray beam 42 is incident so that its extension line 50 is tangent to the imaginary circle 46. The X-ray beam 42 is incident on the first reflecting surface 18 and diffracted by {400} plane of germanium crystal and then is incident on the second reflecting surface 20 and similarly diffracted by {400} plane to go out as an output X-ray beam 48. An X-ray beam from this {400} reflection is suitable for obtaining rocking curves with the quasi parallel arrangement. That is, when the rocking curve of GaAs {400} plane (or an epitaxial layer growing thereon) is measured, an X-ray beam diffracted by {400} plane of germanium crystal can be used to make the quasi parallel arrangement of the double crystal method. The d-value of {400} plane of germanium crystal is close to the d-value of GaAs {400} plane to be measured. FIG. 8 shows a state in which an X-ray beam is diffracted by {422} plane of germanium crystal. The channel-cut monochromator 10 is so rotated around the axis of rotation 40 that the first reflecting surface 24 of the third reflecting surface pair is inclined by 41.84 degrees to the X-ray beam 42. Stating in detail, the channel-cut monochromator 10 is rotated counterclockwise by 83.46 degrees from the state shown in FIG. 4. The X-ray beam 42 is incident so that its extension line is tangent to the imaginary circle 46. The X-ray beam 42 is incident on the first reflecting surface 24 and diffracted by {422} plane of germanium crystal and then is incident on the second reflecting surface 26 and similarly diffracted by {422} plane to go out as an output X-ray beam 48. An X-ray beam from this {422} reflection is suitable for obtaining rocking curves with the quasi parallel arrangement. That is, when the rocking curve of an asymmetrical {422} plane of GaAs (or an epitaxial layer growing thereon) is measured, an X-ray beam diffracted by {422} plane of germanium crystal can be used to make the quasi parallel arrangement of the double crystal method. FIG. 9 shows a state in which an X-ray beam is diffracted by {511} plane of germanium crystal. The channel-cut monochromator 10 is so rotated around the axis of rotation 40 that the first reflecting surface 30 of the fourth reflecting surface pair is inclined by 45.03 degrees to the X-ray beam 42. Stating in detail, the channel-cut monochromator 10 is rotated counterclockwise by 29.37 degrees from the state shown in FIG. 4. The X-ray beam 42 is incident so that its extension line 50 is tangent to the imaginary circle 46. The X-ray beam 42 is incident on the first reflecting surface 30 and diffracted by {511} plane of germanium crystal and then is incident on the second reflecting surface 32 and similarly diffracted by {511} plane to go out as an output X-ray beam 48. An X-ray beam from this {511} reflection is suitable for obtaining rocking curves with the quasi parallel arrangement. That is, when the rocking curve of an asymmetrical {511} plane of GaAs (or an epitaxial layer growing thereon) is measured, an X-ray beam diffracted by {511} plane of germanium crystal can be used to make the quasi parallel arrangement of the double crystal method. FIG. 10a shows a state in which an X-ray beam is diffracted by {111} plane of germanium crystal. The channel-cut monochromator 10 is so rotated around the axis of rotation 40 that the first reflecting surface 36 of the fifth reflecting surface pair is inclined by 13.64 degrees to the X-ray beam 42. Stating in detail, the channel-cut monochromator 10 is rotated clockwise by 158.34 degrees from the state shown in FIG. 4. The X-ray beam 42 is incident so that its extension line is tangent to the imaginary circle 46. The X-ray beam 42 is incident on the first reflecting surface 36 and diffracted by {111} plane of germanium crystal and then is incident on the second reflecting surface 38 which is not parallel to the first reflecting surface 36 as described in detail below. FIG. 10b is an enlarged plan view of the vicinity of the fifth reflecting surface pair. Although the first reflecting surface 36 is parallel to {111} plane 58 of the germanium crystal, the second reflecting surface 38 is inclined counterclockwise by xcex1=10.7 degrees to {111} plane 58. When an X-ray beam is diffracted by {111} plane 58 of the germanium crystal at the second reflecting surface 38, the X-ray beam width is condensed to one eighth. That is, the beam width W2 of the output X-ray beam 48 becomes one eighth of the beam width W1 of the incident X-ray beam 42. For example, when the beam width of the incident X-ray beam 42 is 0.8 mm, the beam width of the output X-ray beam 48 becomes 0.1 mm. The condensed X-ray beam 48 from this asymmetrical {111} reflection has comparatively a high intensity and is suitable for reflection coefficient measurement. The fifth reflecting surface pair may have two asymmetrical reflecting surfaces. FIG. 18 is an enlarged plan view showing such a modification. The first reflecting surface 60 is inclined clockwise by 7.2 degrees to {111} plane 58 of the germanium crystal while the second reflecting surface 62 is inclined counterclockwise by 7.2 degrees to {111} plane 58 of the germanium crystal. An incident X-ray beam 42 is diffracted by {111} plane 58 at the first reflecting surface 60 to have a beam width condensed to {fraction (1/3.16)} (a square root of one tenth). It is further diffracted by {111} plane 58 also at the second reflecting surface 62 to have a beam width further condensed to {fraction (1/3.16)} (a square root of one tenth). As a result, the beam width W2 of the output X-ray beam 48 becomes one tenth of the beam width W1 of the incident X-ray beam 42. The channel-cut monochromator according to the invention may include two or more kinds of reflecting surface pairs each having one or two asymmetrical reflecting surface. Besides, not only the condensing-type asymmetrical reflecting surface but also the expanding-type asymmetrical reflecting surface may be used. The channel-cut monochromator shown in FIG. 1 may be combined with itself to form the four-crystal monochromator. FIG. 11 is a plan view showing such an application. Two channel-cut monochromators 10a and 10b are arranged so as to be mirror symmetrical. Each channel-cut monochromator is so adjusted in posture that X-rays are diffracted by {220} plane of germanium crystal. An incident X-ray beam 42 is reflected by the first reflecting surface pair of the first channel-cut monochromator 10a and further reflected by the first reflecting surface pair of the second channel-cut monochromator 10b to go out as an output X-ray beam 48. The output X-ray beam 48 is on the same straight line as the incident X-ray beam 42. It is noted that the right-side channel-cut monochromator 10b may be an ordinary channel-cut monochromator having only one reflecting surface pair for {220} reflection. In stead of {220} reflection, {440} reflection of the germanium crystal may be combined with itself similarly to form the four-crystal monochromator. Although the channel-cut monochromator 10 is made of germanium single crystal in the embodiment described above, it may be made of silicon single crystal. X-ray beams reflected by {400}, {422} and {511} planes of the silicon crystal are usable, as in the case of germanium, for measurement of GaAs samples with the quasi parallel arrangement of the double crystal method. Next, the second embodiment of the invention will be explained by referring to FIG. 12 showing a plan view of the second embodiment and FIG. 13 showing its perspective illustration. In FIG. 12, A hybrid-type channel-cut monochromator 67 is composed of a channel-cut monochromator 64 made of silicon single crystal and a channel-cut monochromator 66 made of germanium single crystal united (bonded) to each other to form an integral unit. The two channel-cut monochromators 64 and 66 have the same shape and are united so as to be centrosymmetrical around the axis of rotation 40. The hybrid-type channel-cut monochromator 67 is expected to measure silicon or GaAs, which is typical semiconductor crystal, and to obtain rocking curves with the parallel arrangement or the quasi parallel arrangement of the double crystal method. The rocking curve of silicon single crystal (or an epitaxial layer growing thereon) can be measured with the silicon channel-cut monochromator 64 in the parallel arrangement of the double crystal method, while the rocking curve of GaAs single crystal (or an epitaxial layer growing thereon) can be measured with the germanium channel-cut monochromator 66 in the quasi parallel arrangement of the double crystal method. There will be explained first a shape of the silicon channel-cut monochromator 64. The first reflecting surface pair 68 is composed of two reflecting surfaces 70 and 72 parallel to each other for diffracting X-rays by {400} plane of silicon crystal. The second reflecting surface pair 74 is composed of two reflecting surfaces 76 and 78 parallel to each other for diffracting X-rays by {422} plane of silicon crystal. The third reflecting surface pair 80 is composed of two reflecting surfaces 82 and 84 parallel to each other for diffracting X-rays by {511} plane of silicon crystal. The three kinds of reflecting surface pairs are designed based on an imaginary circle 46. That is, each reflecting surface pair is so designed that an X-ray beam incident on the reflecting surface pair or its extension line is tangent to the imaginary circle 46, this structure being the same as the first embodiment shown in FIG. 1. The germanium channel-cut monochromator 66 also includes the three kinds of reflecting surface pairs. It is noted that the hybrid-type channel-cut monochromator 67 has no direct path. FIG. 14 is a plan view showing a manner in which X-rays coming from in six kinds of directions are reflected by the hybrid-type channel-cut monochromator 67 shown in FIG. 1. The X-ray beam indicated by xe2x80x9cSi 400xe2x80x9d is to be reflected by {400} plane of silicon crystal. Similarly, the X-ray beams indicated by Si 422 and Si 511 are to be reflected by {422} and {511} planes of silicon crystal. Besides, the X-ray beams indicated by Ge 400, Ge 422 and Ge 511 are to be reflected by {400}, {422} and {511} planes of germanium crystal. It is noted that a direction perpendicular to the drawing sheet coincides with less than 110 greater than direction of silicon crystal and germanium crystal. Although FIG. 14 shows various directions of incident X-ray beams with the channel-cut monochromator 67 being stationary, the incident X-ray beams are generally always in the same direction in the actual high-resolution X-ray diffractometer, so that the channel-cut monochromator 67 is rotated to alter the direction of the incident X-ray beam to the monochromator 67. There will be described hereinafter the six states of monochromator rotation for six directions of the incident X-ray beams. FIG. 15 shows a state in which an X-ray beam is diffracted by {511} plane of silicon crystal. FIG. 16 shows a state in which an X-ray beam is diffracted by {400} plane of silicon crystal. FIG. 17 shows a state in which an X-ray beam is diffracted by {422} plane of silicon crystal. In each state, the channel-cut monochromator 67 is so rotated by the predetermined angle around the axis of rotation 40 that each reflecting surface is inclined by the predetermined angle (an incident angle satisfying the Bragg""s law) to the incident X-ray beam. Similarly, using germanium crystal, the channel-cut monochromator 67 is rotated to diffract X-rays by Ge {511} Ge {400} and Ge {422} planes. |
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description | 1. Field of the Invention The invention relates to manufacture of neutron detectors, and specifically relates to coating boron lined neutron detectors. 2. Discussion of Prior Art Recently, high sensitivity neutron detectors for homeland security have become increasingly important and increasingly in demand. Many known neutron detectors utilize He-3, a neutron sensitive material known to provide a detector of high sensitivity. The He-3 is provided within a volume that includes a cathode within a detection arrangement. Recently, the availability of He-3 has been has become insufficient to satisfy the demand associated with high sensitivity neutron detectors. Other than He-3 there are only a few neutron sensitive materials that are useful for constructing a neutron detector, including certain isotopes of uranium, lithium and boron. Focusing upon boron, the majority (e.g., approximately 80%) of naturally occurring boron is B-11, which has 5 protons and 6 neutrons, and the remainder (e.g., approximately 20%) is boron 10 (B-10), which has 5 protons and 5 neutrons. The B-10 isotope is useful for neutron detection. Thus, for use in a neutron detector, it is typically desirable to enrich the concentration of B-10. The detection of neutrons is based on the generation of secondary radiations at a converter material. With B-10 (10B) as the converter material, the reaction is described as follows when a neutron is captured: 10B+n→7Li+4α(2.792 MeV, ground state) and 7Li+4α+0.48 MeV γ (2.310 MeV, excited state) The energy released by the reaction is approximately 2.310 million electron volts (MeV) in 94% of all reactions (2.792 MeV in the remaining 6%), and equals the energy imparted to the two reaction products (the energy of the captured neutron is negligible by comparison). The reaction products, namely an alpha particle (a) and a lithium nucleus (7Li) are emitted isotropically from the point of neutron capture by B-10 in exactly opposite directions and, in the case of the dominant excited state, with kinetic energies of 1.47 MeV and 0.84 MeV, respectively. As such, the use of boron as a neutron sensitive material is known and useful. Herein after boron may be discussed generically with the understanding that the content of B-10 is suitably sufficient. Focusing for the moment upon the physical construction of neutron detectors, a detector includes an anode and a cathode. One example detector includes a wire extending on an axis for the anode and a cylindrical cathode circumscribing the anode. The cathode is lined with neutron sensitive material such as boron. Known techniques for providing a boron lining within a neutron detector include the use of borane gas, which is decomposed to provide the boron lining as a precipitate, and the use of mineral oil, which carries boron in a suspension. However, with the increased demand for boron-based neutron detectors, such known techniques may not adequately/effectively/economically satisfy the demand. A new generation of neutron detector production would be most beneficial. The following summary presents a simplified summary in order to provide a basic understanding of some aspects of the systems and/or methods discussed herein. This summary is not an extensive overview of the systems and/or methods discussed herein. It is not intended to identify key/critical elements or to delineate the scope of such systems and/or methods. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later. One aspect of the invention provides a method for providing a boron-lined neutron detector. The method includes providing a boron-containing material and providing water. The method includes mixing the boron-containing material into the water to create a water-based liquid mixture and providing a substrate of a cathode of the neutron detector. The method includes applying the water-based liquid mixture to the substrate of the cathode and removing water from the water-based liquid applied to the substrate to leave a boron-containing layer upon the substrate that is sensitive to neutron impingement. Another aspect of the invention provides a method for providing a boron-lined neutron detector. The method includes providing a B-10 containing material, and providing water. The method includes mixing the B-10 containing material into the water to create a water-based liquid mixture and providing a substrate of a cathode of the neutron detector. The method includes applying the water-based liquid mixture to the substrate of the cathode and removing water from the water-based liquid applied to the substrate to leave a B-10 containing layer upon the substrate that is sensitive to neutron impingement. Example embodiments that incorporate one or more aspects of the invention are described and illustrated in the drawings. These illustrated examples are not intended to be a limitation on the invention. For example, one or more aspects of the invention can be utilized in other embodiments and even other types of methods or devices. Moreover, certain terminology is used herein for convenience only and is not to be taken as a limitation on the invention. Still further, in the drawings, the same reference numerals are employed for designating the same elements. An example embodiment of a neutron detector 10 made via a method in accordance with one aspect of the invention is shown in FIG. 1. Basically, the neutron detector 10 includes a pair of electrodes, which are an anode 12 and a cathode 14. The anode 12 and cathode 14 are separated from each other within a volume 16. In the shown example the cathode 14 provides part of the outer boundary of the volume 16. The volume 16 is sealed and contains a gas, such as argon with an additive of carbon-dioxide. The anode 12 is electrically conductive and electrically connected to detection electronics as will be appreciated by the person of skill in the art. In the shown example, the anode 12 is elongate and extends along an axis 18 of the neutron detector 10 and the cathode 14 is cylindrical and extends around the anode 12 and the axis 18. In one example, the anode 12 is a wire that is in the range of 0.0254-0.0508 mm (0.001-0.002 inches) in diameter. As mentioned, such a size range is merely an example. Accordingly, such an example should not be considered to be a limitation upon the invention. The cathode 14 includes a supporting substrate 20 and a layer 22 (FIG. 2) of a neutron sensitive boron material on the substrate. In one specific example, the boron material is enriched to have a high content of B-10. One example of a high content of B-10 is a content of B-10 greater than 90%. In a more specific example, the boron material is ˜98% pure boron with an enrichment of 99% content of B-10. Although there is improved sensitivity via use of increased enrichment, in general, a 96% enrichment content of B-10 may be a useful cost/benefit selection. The layer 22 of the cathode 14 faces (i.e., is exposed to) the anode 12. As such, the layer 22 is an interior face of the cathode 14 which contains boron. Another way of presenting this is that the cathode 14 has an interior face that includes the boron. It is to be appreciated that the layer 22 includes B-10, but may also include other boron isotopes or other materials. Since the B-10 is providing the desired function for neutron detection, the boron-containing layer is referred to as the B-10 or the B-10 layer. Sensing a neutron is accomplished by a current pulse that occurs between the anode 12 and cathode 14, through the gas, when a neutron impinges upon the B-10 boron of the cathode. When a neutron is absorbed by a B-10 atom in the layer 22 on the cathode 14, an alpha particle (i.e., a helium-4 nucleus) and lithium-7 nucleus—both positively charged—are generated and are ejected in opposite directions along a straight line, the orientation of which is random. One of these particles will not emerge from the B-10 layer because its direction of motion is towards the cathode. The other particle moves towards the gas/coating interface from which it will emerge if it has enough energy. When one of these nuclear particles passes into the gas within the volume 16, it ionizes the gas. The negative ion particles, electrons, drift towards the anode 12 and as the negatively charged particles approach sufficiently near the anode (e.g., within 1-3 anode diameters) the negatively charged particles accelerate to the point of generating even more charge. This is called “gas gain” and it generates enough charge so that the resulting current has a perceptible effect within an associated electronics arrangement 24 (shown schematically within FIG. 1) operatively connected to the neutron detector 10. Thus, the current at the anode 12 is detectable and quantifiable. It is to be appreciated that in one example, the associated electronics arrangement 24 includes an electronic amplifier in order to aid in processing the current generated at the anode. It is to be appreciated that general operation/structure of neutron detectors and associated electronics arrangements will be appreciated by the person of skill in the art. In accordance with one aspect of the present invention, the B-10 layer 22 is provided via the use of applying the B-10 within an aqueous-based liquid (e.g., a water-based dispersion of B-10). Hereinafter the phrase “water-based” is used with the understanding that the phase is to be broadly interpreted to include various mixtures, solutions, suspensions, dispersions and the like that includes water as a primary liquid, but that other liquids may be present. Also, hereinafter the term “mixture” is used with the understanding that the term means various mixtures, solutions, suspensions, dispersions and the like. FIG. 3 shows an example of a top-level flow chart for an example of a method 100 in accordance with an aspect of the present invention. At an initial step 102, boron-containing material is provided. The material includes that desired B-10. Water is provided at step 104. The boron-containing material is mixed with the water at step 106. A water-based mixture is thus provided. In turn, the water-based mixture is applied to the substrate of the cathode at step 108. Finally, at step 110, water is removed from the water-based liquid that was applied to the substrate which leaves a boron, and specifically B-10, containing layer upon the substrate. The layer 22, which includes the B-10, is sensitive to neutron impingement. It is to be appreciated that the water-based mixture may be varied. One example water-based mixture ingredient listing is provided as follows, but should not be taken as a limitation upon the present invention. The ingredients are Boron-10 metal powder (e.g., from EaglePicher or Boron Products, which is a division of Ceradyne), enriched and with particle size distribution of minimum 75% less than 1 micron, minimum 95% less than 3 microns and balance less than 15 microns, DI Water >2.0 MOhm, Dow N3000 polyethelyene oxide, Ciba Dispex A40, Boric acid, and Elmers washable school glue #E 304 or equivalent. It is to be appreciated that various parameters may be used and varied within the method for providing a boron-lined neutron detector via water-based liquid mixture and still be within the scope of the present invention. Table 1 provides ingredient lists for some examples. It is to be appreciated that these examples and the ingredients provided therein are not specific limitations upon the present invention. TABLE 1IngredientsExample 1Example 2Example 3Example 4Water (cc)300100200100F108 (g)10W360 (g)10Boron Powder (g)30102010N3000 polyox (5%) (g)51102010CO530 (10%) (g)5Dispex A40 (g)0.60.20.40.2Defoamer (drops)XMilled (ball Zr)XX-preX-preX-preElmers glue (g)2.95.8HCl (g) (37%)1boric acid 3.1% (g)2.5HS-2111.66Total mass406.6113.1226.2120.2Wherein:Water is provided as the basic volume for the associated values of other ingredients.F108 is a surfactant made by BASF and chemically is a block copolymer (tri-block) with polypropylene oxide as the center block and polyethylene oxide as the end blocks, and with a Molecular Weight (MW) of 18,000.W630 is a water dispersion of aluminium oxide particales, with the aluminium oxide content of 30% (weight) and a small amount of acetic acid utilized to adjust pH (added by the manufacturer). The particle size of the aluminium oxide is 50-100 nanometers (median) an manufactured by Evonik/Degussa Corporation.Boron powder is Boron with B-10 (90+%).N3000 polyox is a polyethylene oxide made by Dow, with a MW of 300,000 (weight average) and which functions as a thickener.CO530 (Igepal) is a surfactant one of a family of surfactants in the akylphenylethoxylate category, specifically, nonylphenylethoxylate, with the ethoxylate of 6 repeat units (average). HLB = 7, and produced by Rhodia.Dispex A40 is a hydrophilic, narrow-fraction ammonium salt dispersant, which is polyacrylic acid (MW~5000) neutralized with ammonia.Defoamer is BYK-033 made by BYK-Chemie (German), and is an emulsion of alkylamines + mineral oil, and is a mild silicone-free defoamer.Milled “X” means that all ingredients were mixed together and then milled, X-pre means that the boron powder, the Dispex and ¼ to ⅓ of the total water were milled using milling media, and then the remaining water and other ingredients were added and mixing was continued without milling media.Elmers glue acts as a binder and possibly as a surfactant.HCl = hydrogen chloride, added to try to provide better adhesion to the aluminium by theoretically etching some of the oxide layer. It was also used to see the effects of pH change.HS-211 = polyvinylacetate/polyvinyl alcohol mixture which acts as a binder and surfactantbinders can also have roles as thickeners and surfactantsWherein: Water is provided as the basic volume for the associated values of other ingredients. F108 is a surfactant made by BASF and chemically is a block copolymer (tri-block) with polypropylene oxide as the center block and polyethylene oxide as the end blocks, and with a Molecular Weight (MW) of 18,000. W630 is a water dispersion of aluminum oxide particles, with the aluminum oxide content of 30% (weight) and a small amount of acetic acid utilized to adjust pH (added by the manufacturer). The particle size of the aluminum oxide is 50-100 nanometers (median) an manufactured by Evonik/Degussa Corporation. Boron powder is Boron with B-10 (90+%). N3000 polyox is a polyethylene oxide made by Dow, with a MW of 300,000 (weight average) and which functions as a thickener. CO530 (Igepal) is a surfactant one of a family of surfactants in the alkylphenylethoxylate category, specifically, nonylphenylethoxylate, with the ethoxylate of 6 repeat units (average). HLB=7, and produced by Rhodia. Dispex A40 is a hydrophilic, narrow-fraction ammonium salt dispersant, which is polyacrylic acid (MW˜5000) neutralized with ammonia. Defoamer is BYK-033 made by BYK-Chemie (German), and is an emulsion of alkylamines+mineral oil, and is a mild silicone-free defoamer. Milled: “X” means that all ingredients were mixed together and then milled, X-pre means that the boron powder, the Dispex and ¼ to ⅓ of the total water were milled using milling media, and then the remaining water and other ingredients were added and mixing was continued without milling media. Elmers glue acts as a binder and possibly as a surfactant. HCl=hydrogen chloride, added to try to provide better adhesion to the aluminum by theoretically etching some of the oxide layer. It was also used to see the effects of pH change. HS-211=polyvinylacetate/polyvinyl alcohol mixture which acts as a binder and surfactant *binders can also have roles as thickeners and surfactants It is to be noted that the examples of Table 1 provide for useful results. For example, the water based mixture of Example 4 when used to provide the layer within a 48 inch long and one inch diameter tubular aluminum material substrate 20 yielded a fairly uniform layer 22. Specifically, upon testing, variance in sensitivity through the length was only approximately 6%. It is to be appreciated that the amount of material providing the layer 22 can be varied. As a corollary, the thickness of the layer 22 can be varied. In one example, a loading provided by the layer 22 onto the substrate 20 of between about 0.1 mg/cm2 and about 1.0 mg/cm2 in boron is provided. A more specific loading range would be about 0.2-0.6 mg/cm2 in boron. An even more specific loading range would be about 0.35-0.4 mg/cm2 in boron. It is contemplated that different, and specifically higher, loading is possible. In part it, the amount of boron loading may dependant upon how many detectors are ultimately provided within an array. For example, more detectors within an array might suggest that a thinner coating would be beneficial. There is a trade-off in coating thickness between catching as many neutrons as possible in an individual detector and allowing for greater neutron transparency to allow for capture in other detectors in the array for greater overall neutron sensitivity. It is to be noted that other ingredients may be added and/or substituted. Also, some of the ingredients listed within the presented examples may be omitted and/or substituted within yet other examples. For example, fumed silica may be part of the ingredients. E160, which is a polyethylene oxide made by Meisai Chemical (Japan) and a MW of 1,600,000, may be part of the ingredients. Also, the ingredients may include PMV#304, which is a polyvinylmethylether/maleicanhydride alternating copolymer, a MW of approximately 1,000,000, made by GAF/Rhodia and functioning as a binder. Also, the ingredients may include EM15+c38, which is a random copolymer of ethylacrylate and methacrylic acid, a MW of about 1,000,000, made by Ciba and functioning as a binder. Possible alternative surfactants are Pluronic PPO_PEO block copolymer surfactants such as F108, L92, P104 (from BASF), Surfynol/Dynol acetylenic diol surfactants (from Air Products), and Ethox 1437—nonionic PPO-PEO variations (from Ethox Chemicals). Possible alternative dispersants are Daxad polymethacrylic acid, both sodium and ammonium salts (from WR Grace) or Sodium hexametaphosphate. Possible alternative thickeners are other MW Polyox grades, up to MW of approximately 7,000,000, Dow Polyglycols, Hydroxy Ethyl cellulose, Polyacrylimides, Polyvinyl alcohol. Possible alternative binders include Colloidal alumina (Degussa/Evonic, Cabot), Colloidal silica (Degussa/Evonic, Cabot), and Colloidal graphite (Acheson colloids). It is to be appreciated that mixing of the water-based mixture may be varied. One example procedure is provided as follows, but should not be taken as a limitation upon the present invention. The following procedure is intended for suspending 30 grams of enriched boron, in a mixture that is approximately 300 milliliters. Larger or smaller batches may be made with this procedure with the appropriate attention to the change in scale. In a plastic weighing dish weigh 30.0 grams of the B10 powder. Transfer this powder to a 500 milliliter nalgene bottle. 85.0 grams of de-ionized (DI) water is added to the nalgene bottle. 0.6 grams of Dispex A40 is added to the nalgene bottle using a disposable transfer pipette. The bottle is capped and the mixture is gently swirled for approximately 15 seconds. The bottle is opened and clean milling media is added such that it fills to within about ½ inch of the liquid surface. The bottle is capped and placed on a roller for 45 minutes to 1 hour. The person operating of the roller device should be trained to set the roller speed properly and listen for the action of the milling media to ensure that proper milling action is taking place. Subsequently, the mixture and milling media are poured into a transfer bottle. Using the plastic filter strainer, the mixture is poured back into the mixing bottle, separating out the milling media in the strainer. An additional 215.0 g of DI water is used to rinse the transfer bottle and the milling media into the mixing bottle. This should bring the mixture to 300 grams of total of DI water. Thoroughly rinse the transfer bottle and milling media. Store the cleaned milling media in DI water. Next, 30.0 grams of 5% N3000 is added to the mixture. 7.5 grams of 3.1% boric acid in DI water mixture is added to the mixture. 8.7 grams of Elmers glue or equivalent is added. The mixture is capped and placed on the rollers for a minimum of 30 minutes prior to use. The mixture should be kept on rollers when not in use. The maximum time that the mixture should be permitted to set before use without some form of agitation is 30 minutes. It is to be appreciated that the method of applying the water-based mixture may have many variations within the scope of the invention. For example, FIG. 4 shows a block diagram for a portion of a method 200 that produces neutron detectors that are tubular in general shape. Moreover, the block diagram is associated with depositing the B-10 layer 22 onto cathode substrate material (i.e., providing a substrate 20) that has a bulk length that is later cut to a shorter length for individual neutron detectors. At block 202 of the method 200, a supply of water-based liquid mixture that contains B-10 is premade (i.e., water and material are provided and mixed together) provided within a tank. The liquid mixture is supplied into the elongate, tubular substrate material 20 to thus apply the mixture to the substrate. FIG. 5 is an illustration showing plural tubular substrates 20 supported by and connected to a structure 300 that circulates the liquid mixture into the substrates via supply and exhaust valves. Supplying of the water-based liquid mixture may be accomplished is several ways. For example, the liquid mixture may flow into the tubular substrate via a down flow (e.g., gravity fed). Alternately, the liquid mixture may be pumped-up or even vacuumed up into the tubular substrate. The liquid mixture thus is on contact with the cathode substrate. With the liquid mixture in contact with the substrate, the material, and in particular the B-10, can engage and adhere to the surface(s) of the substrate. In due course, the excess liquid mixture is removed (e.g., drained) from the tubular substrate at function block 204 (FIG. 4). An amount of the liquid mixture, and in particular the material within the mixture, remains in contact with the substrate as a coating. It is to be appreciated that water is present within the liquid mixture coating that remains in contact with the tubular substrate. In other words, the liquid mixture coating is moist. A next step is to remove the remaining water to leave just a layer. As such, drying is performed at function block 206. Such, drying may be done via application of heat, air flow or other drying actions. Subsequently, to aid in creation of a layer that has a desired level of durability, the substrate with a layer is baked at function block 208. Subsequently, the B-10 coated tubular substrate can be cut to length and further construction of the neutron detector(s) can occur. Turning to some examples of details concerning the later process steps, drying is done to remove the water vehicle from the coating and thus converts the liquid suspension into a dried layer 22 on the substrate 20. In one example, air heated to 200° F. is blown down the center of the coated cylindrical substrate at a velocity of 1000 ft/min. This drying technique provides several advantages over simply air drying at room temperature or drying in an oven. The heated convective flow, with flow direction from top to bottom, and cylindrical substrates held in a vertical orientation provides for the creation of a uniform layer 22 that is rapidly dried. Tubes 4 feet in length can typically be dried to a solid coating after approximately 3 minutes. The rapid drying helps to prevent separation of the suspended particles from the water vehicle prior to drying, helping to prevent a condition that could cause “rivers” to form in the coating. Proper control of the drying parameters can strongly affect the top-to-bottom uniformity. Other alternative methods that could be used for providing a uniform coating would include a controlled withdrawal rate of the mixture from the tube, or a drier that rotated the tube to maintain uniformity. With regard to baking one possible function is to remove excess organics that would not be removed during the relatively lower temperature drying process. Temperature, and potentially the atmosphere (air, or purged, or vacuum) would be selected to yield out-gassing of the undesired organic components. Some of the organics might be left behind intentionally to act as binders. It may be beneficial that the organics not outgas over time once in the hermetic volume. It appears that a 225° C. under high vacuum (5*10−5 torr or less) for a period of at least 4 hours may be sufficient for baking. The invention has been described with reference to the example embodiments described above. Modifications and alterations will occur to others upon a reading and understanding of this specification. Example embodiments incorporating one or more aspects of the invention are intended to include all such modifications and alterations insofar as they come within the scope of the appended claims. |
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claims | 1. A method for adjusting an optical axis in an inspection apparatus that uses a charged particle beam, the method comprising:providing the inspection apparatus with a charged-particle-beam (CPB) optical system for guiding an observation charged particle beam along the optical axis from an object to a detector, the CPB optical system including a cathode lens and an X-Y stage for holding the object;providing self-emitting beam source on a surface of the X-Y stage;generating an observation charged particle beam from the self-emitting beam source for obtaining an image of the object at the detector; anddetermining a position of the X-Y stage using the observation charged particle beam to adjust the optical axis. 2. The method of claim 1, further comprising:wobbling a voltage of electrical power applied to the cathode lens; andwhile moving the X-Y stage and thus the object relative to and across the optical axis, determining the position of the X-Y stage at which the obtained image of the object does not move as the voltage is wobbled. 3. The method of claim 1, wherein the CPB optical system further comprises an imaging-optical system and an objective-optical system, wherein the imaging-optical system is situated downstream of the objective-optical system and includes a front imaging lens group. 4. The method of claim 3, wherein adjusting the optical axis comprises performing an optical-axis alignment between the cathode lens and the front imaging lens group. 5. The method of claim 3, wherein:the imaging-optical system further comprises a rear imaging lens group; andadjusting the optical axis further comprises performing an optical-axis alignment between the front imaging lens group and the rear imaging lens group. 6. The method of claim 1, further comprising measuring and correcting an aberration of the CPB optical system using an aberration-measurement pattern. 7. In an inspection apparatus that includes a charged-particle-beam (CPB) optical system having a cathode lens and including an X-Y stage for holding an object, a method for adjusting an optical axis of the CPB optical system, the method comprising:guiding a charged particle beam from the object through the optical system along the optical axis to a detector;from an adjustment CPB source located on a surface of the X-Y stage, generating an adjustment charged particle beam that propagates from the adjustment CPB source to the detector and produces an image of the object at the detector; anddetermining a position of the X-Y stage using the adjustment charged particle beam to adjust the optical axis. 8. A method for aligning an inspection apparatus, comprising:using a first optical system, guiding a first energy beam from a specimen to a first detector along a first optical axis;using a second optical system, guiding a second energy beam from the specimen to a second detector along a second optical axis;obtaining an image of a pattern to measure a location of the specimen relative to the second optical axis and a distance of the specimen to the second optical axis:determining a baseline from the distance between the first and second optical axes; andusing the baseline, aligning an evaluated area of the specimen to the first optical axis to align the specimen with respect to the first optical axis. 9. The method of claim 8, wherein the primary optical system comprises an optical system for imaging electrons from the specimen at a detector by using a mapping projection-optical system. 10. The method of claim 8, further comprising:arranging a fiducial plate defining thereon a first mark and a second mark; andobtaining an image of the first mark by the first detector through the first optical system and obtaining an image of the second mark by the second detector through the second optical system to thereby define a distance between the first and second optical axes with reference to a relative positional relationship between the first mark and the second mark. 11. The method of claim 10, wherein the second energy beam is a light beam. 12. The method of claim 8, wherein the second optical system comprises a scanning electron microscope. 13. The method of claim 12, wherein the second energy beam is an electron beam. 14. The method of claim 8, further comprising a stage on which the specimen is mounted, the stage comprising at least one of:a resolution chart having a line pattern array of lines elongated along a first direction and gradually changing pitch distances along a second direction perpendicular to the first direction; anda beam-position-measuring pattern having a cross pattern or a pattern of L-shaped features. 15. The method of claim 8, wherein the specimen has a surface comprising an evaluated region and a fiducial mark provided at the same height as the evaluated region. 16. The method of claim 8, wherein the first optical system includes an optical source comprising a laser diode. 17. A charged-particle-beam (CPB) apparatus, comprising:an irradiation-optical system having a respective optical axis and being situated and configured for guiding a primary charged particle beam from a beam source to a surface of a specimen on a stage;a detection-optical system situated and configured for detecting a secondary beam of charged beam of charged from the surface and for producing an image of the surface, the detection-optical system and irradiation-optical system being situated in a vacuum environment;a beam deflector provided in at least one of the irradiation-optical system and detection-optical system; andan off-axis optical system having an optical axis situated at a predetermined distance from the axis of the irradiation-optical system, the off-axis optical system being configured to illuminate the specimen with an optical aligment beam passing from outside the vacuum environment through a window and through an objective lens situated in the vacuum environment so as to align the specimen with the axis of the irradiation-optical system. 18. The CPB apparatus of claim 17, wherein the detection-optical system comprises a detector and a projection-optical system, the projection-optical system being situated and configured for projecting the charged particle beam from the specimen to a detection surface of the detector. 19. The CPB apparatus of claim 17, wherein the off-axis optical system comprises an optical microscope situated and configured for viewing the surface of the specimen. 20. The CPB apparatus of claim 17, wherein the off-axis optical system comprises a light source provided within an atmosphere. 21. The CPB apparatus of claim 20, wherein the off-axis optical system comprises an objective lens including an aperture stop at which an image of the light source is formed for obtaining a Koehier illumination of the surface of the specimen. 22. The CPB apparatus of claim 17, wherein the off-axis optical system further comprises a condenser lens and either a half mirror or a beam splitter. 23. The CPB apparatus of claim 17, wherein the off-axis optical system forms an image of the specimen surface on a charged-coupled device (CCD). 24. The CPB apparatus of claim 23, wherein a signal from the CCD is video-processed to form an image used for performing the alignment. 25. The CPB apparatus of claim 17, wherein the beam deflector comprises an E×B configured for transmitting a primary beam and deflecting a trajectory of a secondary beam. 26. The CPB apparatus of claim 17, further comprising a first column, a second column, and a specimen chamber. 27. The apparatus of claim 17, wherein the optical alignment beam is supplied through an optical fiber and converged by a lens. 28. In an apparatus including a specimen stage, a charged-particle-beam (CPB) optical system having a main optical axis, and an off-axis optical system having a respective optical axis, a method for measuring an off-axis distance in the apparatus, the method comprising:providing a first pattern on the specimen stage;obtaining a first image of the first pattern using the off-axis optical system;providing a second pattern at a known distance from the first pattern;obtaining a second image of the second pattern using the CPB optical system; anddetermining a distance between the main optical axis and the optical axis of the off-axis optical system based on the first and second images. 29. In an apparatus including a specimen stage, a charged-particle-beam (CPB) optical system having a main optical axis, and an off-axis optical system having a respective optical axis, a method for measuring an off-axis distance in the apparatus, the method comprising:providing a first pattern on the specimen stage;obtaining a first image of the first pattern using the off-axis optical system;using a stage-position-measuring device, measuring a first stage position when obtaining the first image;using the CPB optical system, obtaining a second image of a pattern on the specimen stage, the pattern being either the first pattern or a second pattern situated a known distance from the first pattern;using the stage-position-measuring device, measuring a second stage position when obtaining the second image; anddetermining a distance between the main optical axis and the optical axis of the off-axis optical system based on the first and second images and the respective first and second stage positions. 30. The method of claim 29, wherein the CPB optical system projects an image of a charged particle beam from the specimen to a detection surface. 31. The method of claim 29, wherein at least one of the first and second patterns is a fiducial mark provided on the specimen stage. 32. The method of claim 29, wherein at least one of the first and second patterns constitutes a portion of a pattern to be evaluated. 33. The method of claim 29, wherein the first pattern is a light-visible pattern and the second pattern is a CPB-visible pattern. 34. A method for evaluating a specimen with an image obtained using a charged particle beam, the method comprising:using an off-axis optical system, obtaining an image of a pattern provided on the specimen;while obtaining the image, measuring a position of a stage holding the specimen;reading or measuring a stage-position baseline; andcalculating a target stage position from the obtained image, measured stage position, and baseline, and moving the stage toward the target stage position. 35. The method of claim 34, wherein:the image of the pattern is produced using a CPB optical system including a projection-optical system; andthe projection-optical system converges an image, carried by a charged particle beam propagating from the specimen, at a detection surface of a detector. 36. The method of claim 34, wherein the off-axis optical system is used as a viewing microscope that produces a magnified image of the pattern. 37. In an inspection apparatus including a stage for mounting a specimen for inspection, a charged-particle-beam (CPB) source for generating a charged particle beam from a surface of the specimen, a CPB detector for detecting the charged particle beam, and a deflector situated between the stage and the CPB detector, a method for adjusting an optical axis of the inspection apparatus, the method comprising:generating a charged particle beam from the CPB source so as to cause the charged particle beam to be generated from the surface of the specimen;obtaining a first image of the specimen by detecting the charged particle beam while not applying a voltage to the deflector;obtaining a second image of the specimen by detecting the charged particle beam while applying a voltage to the deflector; andsetting the voltage applied to the deflector based on the first and second images, so as to adjust the optical axis. 38. The method of claim 37, wherein the step of generating the charged particle beam from the surface of the specimen comprises using a self-emitting beam source as the specimen. |
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abstract | Disclosed is a liquid-phase oxidative decomposition method for radioactively contaminated carbonaceous material, providing a method of oxidizing carbon into a gas in liquid phase to treat radioactively contaminated carbonaceous material. The method comprises the following steps: ball milling a mixture of a molybdenum-containing substance and a carbonaceous material, thermally treating the ball milled mixture, and performing liquid-phase oxidation of the thermally treated mixture. The thermal treatment causes carbon to enter space between molybdenum atoms so as to reduce the particle size of carbon and improve the chemical reactivity of carbon, and an oxidant is then used to oxidize the carbon in the space between molybdenum atoms into a gas in liquid phase, while the molybdenum-containing moiety is converted into a water-soluble substance. The method of has technical effects of mild reaction conditions, low energy consumption, high operation safety, and facilitates the recovery of elements attached to carbonaceous material. |
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050842315 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS A fission reactor complex 100 includes a concrete containment structure 102 enclosing a reactor vessel 104 containing a reactor core 106, as shown in FIG. 1. Reactor core 106 includes a frame for holding a multitude of fuel elements 108 in position to promote a controlled chain reaction. Additional fuel elements 110 are stored in a storage area 112. Fuel elements are transferred between storage area 112 and core 106 by a transfer mechanism 114 which includes a conventional refueling bridge 116, a conventional grapple 118, and an interconnecting refueling mast 120. Bridge 116 is moved on tracks on a refueling floor 122 which extends over water 124 which submerses storage area 112 and core 106. A gate 126 can be opened to permit a fuel element to be transferred between storage area 112 and core 106 without lifting the fuel element out of water 124. Mast 120 is shown in an extended condition over core 106 so that it can deposit a fuel element 128 therein. Mast 120 includes four tubes: an outermost tube 130, a first intermediate tube 132, a second intermediate tube 134 and an innermost tube 136 are visible when mast 120 is extended. Intermediate tubes 132 and 134 are referred to herein as "inner tubes" in relation to outermost tube 130 and as "outer tubes" in relation to innermost tube 136. Shown in dashed lines are transfer mechanism 114 and fuel element 128 in a prior position in transit from storage area 112 to core 106 with mast 120 in a retracted condition. Bridge 116 includes a hoist mechanism 138 which provides for extension and retraction of the inner tubes 132, 134 and 136, as well as control of grapple 118. Hoist mechanism 138 is linked to innermost tube 136 through hoist cables 202, shown in FIG. 2. A respective flange 210, 212, 214, 216 is welded on the lowermost end of each tube 130, 132, 134, 136. As hoist mechanism 138 forces innermost tube 136 to retract from a fully extended condition, innermost tube 136 slides within and relative to intermediate tube 132 until flange 214 is contacted by grapple mounting bolts on flange 216. Further retraction causes tubes 134 and 136 to retract together and slide within and relative to tube 132 until flange 214 contacts flange 212. Inner tubes 132, 134 and 136 retract together into outermost tube 130 until flange 212 contacts flange 210 which serves as the stop for retraction. Four roller assemblies 220 are bolted to and circumferentially spaced around each outer flange 210, 212 and 214. Each roller assembly 220 comprises a roller housing 222, a guide roller 224 and an axle 226 used for rotatably attaching the roller 224 to the roller housing 222, as indicated in FIGS. 2 and 3. Guide rollers 224 help centralize inner tubes 130, 132 and 134. Further guidance is provided by bushings 230 on the top ends of inner tubes 132, 134 and 136 and sleeves 232 attached to the inner surfaces of outer tubes 130, 132 and 134. Sleeves 232 are held in place by portions of roller housings 222 which protrude through respective flanges 210-214. Sleeves 232 serve as downward stops for inner tubes 132-136 as they define the lower limit of travel for bushing 230. As shown in FIG. 3, springs 334 space sleeves 232 from roller housings 222. As indicated with respect to innermost tube 136 in FIG. 4, each inner tube 132, 134, 136, has multiple grooved longitudinal (vertical) tracks 402 formed thereon. More specifically, each outer flange 210, 212, 214 supports four guide rollers 224 for engaging four tracks 402 of the next inner tube 132, 134, 136. As indicated in FIG. 5, rollers 224 have grooves 506 for mating with grooves 504 of tracks 402. Grooved tracks 402 are cold-formed using a groove forming tool 600, shown in FIG. 6. Tool 600 includes an annular die holding fixture 602 and four die assemblies 604 evenly spaced about the circumference of fixture 602. Each die assembly 604 includes a roller die 606, mounting 608 for holding roller die 606 and permitting it to rotate, and a bolt 610 which is welded to mounting 608. Roller dies 606 can be of a hardened tool steel. Threads of each bolt 610 are engaged with mating threads of fixture 602 so that turning a bolt 610 forces the respective roller die 606 in or out as desired. To form grooved tracks 402, tool 600 is mounted on a tube, e.g., tube 136, at a longitudinal position at which tract 402 is to be formed. Bolts 610 are adjusted so that roller dies 606 contact the outer surface of tube 136. Tool 600 is then moved repeatedly over the length of tube 136 over which track 402 is to be defined. Bolts 610 are gradually tightened between traversals, increasing the pressure with which roller dies 606 apply to tube 136. Grooved tracks 402 are formed progressively in this manner. As depicted in FIG. 5, this process results a flattening of tubes 132, 134 and 136 on which tracks 402 are formed and along the regions in which tracks 402 are formed. In addition, the cold forming hardens the steel of the tube being worked. This hardening and flattening contribute to the torsional rigidity of the tube. Tubes 130, 132, 134 and 136 have respective diameters of about 3", 4", 5" and 6" respectively, with wall thicknesses of 1/2". These dimensions provide for "nestability" of tubes 130-136. The tubes are fabricated using stainless steel 304. Individual tube lengths are about 20' each, providing a retracted mast length of about 21' and an extended length of about 69 ft. The dimensions and materials listed above can be varied according to the context. Tracks 402 can be cold formed or machined. Other variations upon and modifications to the disclosed embodiments are provided by the present invention, the scope of which is limited only by the following claims. |
description | The present invention relates to a charged particle beam exposure apparatus such as an electron beam exposure apparatus or ion beam exposure apparatus mainly used to expose a semiconductor integrated circuit, and a charged particle beam exposure method and, more particularly, to an electron beam exposure apparatus which directly exposes a pattern on a substrate such as a wafer using an electron beam, an electron beam exposure apparatus which illuminates a master such as a mask with an electron beam and performs projection exposure for the substrate through a reduction electron optical system using the electron beam from the master, and a charged particle beam exposure method of exposing a substrate by scanning with a charged particle beam. Electron beam exposure apparatuses include a point-beam type apparatus which uses a beam spot and a variable rectangular beam type apparatus which uses a beam having a variable-size rectangular cross section. A point-beam type electron beam exposure apparatus uses a single electron beam and can perform drawing at high resolution. However, the electron beam exposure apparatus has a low throughput and thus is only used in limited applications such as research and development, exposure mask manufacturing, and the like. A variable rectangular beam type electron beam exposure apparatus has a throughput which is one or two orders of magnitude higher than that of a point-beam type apparatus. Since the electron beam exposure apparatus basically uses a single electron beam for drawing, it often has a problem with the throughput in exposing a pattern comprising highly-integrated fine patterns of about 0.1 μm. To solve this problem, there is available a stencil mask type electron beam exposure apparatus. The apparatus forms a pattern to be drawn in a stencil mask as pattern-transmitting holes and transfers the pattern to be drawn onto a sample surface through a reduction electron optical system by illuminating the stencil mask with an electron beam. Japanese Patent Laid-Open No. 9-245708 discloses a multi electron beam exposure apparatus. The apparatus illuminates a substrate having a plurality of apertures with electron beams, irradiates a sample surface with a plurality of electron beams having passed through the plurality of apertures through a reduction electron optical system, and deflects the plurality of electron beams to scan the sample surface. At the same time, the apparatus draws a desired pattern by individually applying/not applying the plurality of electron beams in accordance with a pattern to be drawn. In both apparatuses, an area to be exposed at one time, i.e., exposure area is larger than a conventional apparatus. Accordingly, the throughput can be increased. However, since the area to be exposed at one time, i.e., exposure area is larger than the conventional apparatus, use of an astigmatism correcting unit arranged in a reduction electron optical system for correcting astigmatism of the reduction electron optical system causes an aberration other than astigmatism (particularly, distortion). It is thus difficult to form a desired pattern on a wafer. Japanese Patent Laid-Open No. 9-245708 also discloses an electron beam exposure method of performing drawing while scanning a wafer with electron beams. FIG. 8A shows a conventional scanning electron beam exposure apparatus. In FIG. 8A, reference symbol S denotes an electron source which emits an electron beam, and B, a blanker. An electron beam from the electron source S forms an image of the electron source S at the same position as the blanker B through an electron lens L1. The image of the electron source is reduced and projected onto a wafer W through a reduction electron optical system comprising electron lenses L2 and L3. The blanker B is an electrostatic deflector which is located at the same position as the image of the electron source S formed through the electron lens L1. The blanker B controls whether to irradiate the wafer with an electron beam. More specifically, when the wafer is not to be exposed to an electron beam, the blanker B deflects the electron beam, and a blanking aperture BA located on the pupil of the reduction electron optical system cuts off the deflected electron beam, i.e., an electron beam EBoff. On the other hand, when the wafer is to be exposed to an electron beam, an electron beam EBon having passed through the blanking aperture BA is controlled by an electrostatic deflector DEF to scan the wafer W. A method of performing drawing on the wafer by scanning will be described with reference to FIG. 8B. For example, to draw a pattern of a character “A”, a drawing region is divided into a plurality of pixels. While the deflector DEF moves an electron beam to perform scanning in the X direction, the blanker B performs control such that each pixel constituting part of the pattern (gray portion) is irradiated with the electron beam and each of the remaining pixels shields the electron beam. When the scanning in the X direction ends, the electron beam is stepped in the Y direction, and the scanning in the X direction restarts. Electron beam irradiation is controlled during the scanning, thereby drawing the pattern. However, when pixels are exposed by scanning with an electron beam, the position of the electron beam in the scanning direction (X direction) changes over time while the position of the electron beam in a direction perpendicular to the scanning direction (Y direction) remains constant, as shown in FIG. 9A. The pixel exposure distribution in the scanning direction (X direction) has the average value or integrated value obtained when the electron beam moves between the pixels (to be referred to as a moving average hereinafter), as shown in FIG. 9B. FIG. 9C shows the resulting pixel intensity distribution (moving average). In this case, even if an electron beam has an axisymmetric Gaussian intensity distribution, drawing by scanning causes the intensity distribution to spread in the scanning direction (X direction). The intensity distribution looks as if there were astigmatism. Thus, it is difficult to form a desired fine pattern on a wafer. The present invention has been made in consideration of the conventional drawback, and has as its object to provide a charged particle beam exposure apparatus capable of, when correcting astigmatism of a reduction electron optical system, reducing generation of an aberration other than astigmatism and performing exposure to a desired pattern. To attain the above-mentioned object, according to the present invention, there is provided a charged particle beam exposure apparatus which exposes a substrate using a charged particle beam, characterized by comprising first formation means for forming an image of a charged particle source which emits a charged particle beam, second formation means for forming a plurality of images of the charged particle source from the image of the charged particle source, a reduction electron optical system which reduces and projects the plurality of images of the charged particle source onto the substrate, and first astigmatism generation means for generating astigmatism when the first formation means forms the image of the charged particle source in order to correct astigmatism generated in the reduction electron optical system. According to the present invention, preferably, the apparatus further comprises second astigmatism generation means for generating astigmatism in the reduction electron optical system, wherein out of astigmatisms generated in the reduction electron optical system, astigmatism which does not vary during exposure is corrected by the first astigmatism generation means while varying astigmatism is corrected by the second astigmatism generation means. The charged particle beam exposure apparatus according to the present invention can preferably be used to, particularly, manufacture a device with a fine pattern such as a semiconductor chip including an IC or LSI, liquid crystal panel, CCD, thin-film magnetic head, micromachine, or the like. According to the present invention, the first astigmatism generation means generates astigmatism when the first formation means forms an image of the charged particle source, thereby correcting astigmatism on the substrate. This makes it possible to suppress generation of an aberration other than astigmatism and perform exposure to a desired pattern in correcting astigmatism of the reduction electron optical system. According to the present invention, there is provided a charged particle beam exposure method of exposing a substrate by scanning with a charged particle beam, characterized by comprising an adjustment step of making a size in a scanning direction of a charged particle beam on a substrate smaller than a size in a direction perpendicular to the scanning direction. The method preferably further comprises a first measurement step of measuring the size in the scanning direction of the charged particle beam on the substrate, and a second measurement step of measuring the size in the direction perpendicular to the scanning direction of the charged particle beam on the substrate, wherein a result of moving-averaging a result of the first measurement step and a result of the second measurement step are evaluated, and the adjustment step is executed based on a result of the evaluation. A device manufacturing method according to the present invention is characterized in that the above-mentioned charged particle beam exposure method is used to manufacture devices. The present invention has been made in consideration of the above-mentioned conventional drawback, and has as its object to provide a charged particle beam exposure apparatus capable of performing exposure to a desired fine pattern. 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. As an example of a charged particle beam exposure apparatus, this embodiment will illustrate an electron beam exposure apparatus. Note that this embodiment can be applied to not only exposure apparatuses using electron beams but also exposure apparatuses using ion beams. <Explanation of Components of Electron Beam Exposure Apparatus> FIG. 1 is a view schematically showing the main part of an electron beam exposure apparatus according to an embodiment of the present invention. In FIG. 1, an electron beam generated by an electron gun (not shown) forms a crossover image 1 (to be referred to as an electron source 1 hereinafter). An electron beam emitted from the electron source 1 passes through a beam shaping optical system 2 and forms an image SI of the electron source 1. At this time, a first stigmator 3 serving as a magnetic octupole stigmator can cause astigmatism in the image SI. This astigmatism can correct any astigmatism in an electron beam image projected onto a wafer 9 (to be described later). The electron beam from the image SI becomes almost parallel through a collimator lens 4. The almost parallel electron beam comes incident on an aperture array 5 having a plurality of apertures. The aperture array 5 has the plurality of apertures, and the almost parallel electron beam passes through the apertures to be divided into a plurality of electron beams. The plurality of electron beams derived from the aperture array 5 form intermediate images of the image SI through an electrostatic lens array 6 having a plurality of electrostatic lenses. A blanker array 7 which has a plurality of blankers is arranged on the plane of the intermediate images. A reduction electron optical system 8 comprising two symmetric magnetic doublet lenses 81 and 82 is provided downstream of the intermediate image plane. The plurality of intermediate images are projected onto the wafer 9. At this time, electron beams deflected by the blanker array 7 are shielded by a blanking aperture BA and thus do not come incident on the wafer 9. On the other hand, electron beams not deflected by the blanker array 7 are not shielded by the blanking aperture BA and thus come incident on the wafer 9. That is, the blanker array 7 individually controls to apply/not to apply (performs on-off control for) the plurality of electron beams derived from the aperture array 5 to the wafer 9. A deflector 10 which simultaneously displaces a plurality of electron beams in the X and Y directions to desired positions, a second stigmator 11 serving as an electrostatic octupole stigmator which simultaneously adjusts any astigmatism of the plurality of electron beams, and a focus coil 12 which simultaneously adjusts the focuses of the plurality of electron beams are arranged in the lower doublet lens 82. Reference numeral 13 denotes an X-Y stage 13 on which the wafer 9 is mounted and which can move in the X and Y directions perpendicular to the optical axis. An electrostatic chuck 15 for chucking the wafer 9 and a semiconductor detector 14 for measuring the shape of electron beams which has a single knife edge extending in the X and Y directions on the electron beam incident side are arranged on the X-Y stage 13. The X-direction shape of electron beams can be measured using a change in output of the semiconductor detector 14 when the electron beams are moved to perform scanning in the Y direction with respect to the single knife edge extending in the X direction. The Y-direction shape of the electron beams can be measured using a change in output of the semiconductor detector 14 when the electron beams are moved to perform scanning in the X direction with respect to the single knife edge extending in the Y direction. Note that the first stigmator 3 may be arranged at any position between the light source 1 and the aperture array 5 but it is preferably arranged between the light source 1 and a position where the image SI is to be formed. In this case, when the beam shaping optical system 2 forms the charged particle source image SI, the first stigmator 3 will cause astigmatism. For example, the first stigmator 3 is used to correct any astigmatism which does not change upon deflecting the electron beams such as one caused by lens decentering in apparatus assembly. The second stigmator 11 is used to correct any astigmatism which changes upon deflecting electron beams. <Explanation of System Configuration and Exposure Method> FIG. 2 is a diagram of the configuration of a system according to this embodiment. A first stigmator control circuit 21 is a control circuit which controls astigmatism of the electron source image SI by adjusting a difference in focal length in a direction perpendicular to the first stigmator 3. A blanker array control circuit 22 is a control circuit which individually controls the plurality of blankers of the blanker array 7. A deflector control circuit 23 is a control circuit which controls the deflector 10. A second stigmator control circuit 24 is a control circuit which controls astigmatism of the reduction electron optical system 8 by adjusting a difference in focal length in a direction perpendicular to the second stigmator 11. An electron beam shape detection circuit 25 is a detection circuit which processes signals from the semiconductor detector 14. A focus control circuit 26 is a control circuit which controls the focal position of the reduction electron optical system 8 by adjusting the focal length of the focus coil 12. A stage drive control circuit 27 is a control circuit which controls to drive the X-Y stage 13 in cooperation with a laser interferometer (not shown) which detects the position of the X-Y stage 13. A main control system 28 controls the above-mentioned plurality of control circuits and manages the entire electron beam exposure apparatus. FIG. 3 is a view for explaining an expose method according to this embodiment. The main control system 28 instructs the deflector control circuit 23 on the basis of exposure control data to make the deflector 10 deflect a plurality of electron beams. The main control system 28 also instructs the blanker array control circuit 22 to perform on-off control for the blankers of the blanker array 7 in accordance with a pattern to which the wafer 9 is to be exposed (to be drawn on the wafer 9). Each electron beam performs scanning exposure for a corresponding element exposure region (EF) on the wafer 9, as shown in FIG. 3. Electron beam element exposure regions (EF) are two-dimensionally juxtaposed to each other, and a subfield (SF) comprising a plurality of element exposure regions (EF) to be simultaneously exposed is exposed. In one example, the number of electron beams is 32×32=1,024. Each electron beam draws an element exposure region (EF) of about 2 μm square. The diameter of one electron beam on the wafer 9 is about 60 nm. 1,024 (=32×32) element exposure regions constitute one subfield (SF). The size of one subfield (SF) is about 64 μm square. After the main control system 28 exposes one subfield (SF1), it instructs the deflector control circuit 23 to make the deflector 10 deflect a plurality of electron beams in order to exposure the next subfield (SF2). At this time, a change in subfield due to the deflection causes a change in aberration generated when each electron beam is reduced and projected through the reduction electron optical system 8. The second stigmator control circuit 24 performs correction in accordance with instructions from the main control system 28 such that the astigmatism becomes constant. The astigmatism can be measured as the shape of the electron beams using the semiconductor detector 14 and the knife edge extending in the X and Y directions. The relationship between the deflected position and the beam shape is calculated in advance. Astigmatism which changes due to deflection caused by subfield switching during exposure is corrected under the control of the second stigmator control circuit 24 using the second stigmator 11. In the above-mentioned embodiment, after a group of about-2-mm-square subfields each comprising a group of 1,024 (=32×32) about-64-μm-square subfields are exposed, the X-Y stage is moved by about 2 mm to exposure the next subfield group (1,024 subfields). Although not shown, the deflector 10 comprises a main deflector used when the deflection width is large, and a sub-deflector used when the deflection width is small. The main deflector is an electromagnetic deflector while the sub-deflector is an electrostatic. deflector. The electrostatic sub-deflector performs scanning during exposure while the electromagnetic main deflector switches between subfields. <First Operation Explanation> Operation of an electron beam exposure apparatus according to the first embodiment of the present invention will be described with reference to FIG. 4. As the wafer process of the exposure apparatus, a main control system 28 executes the following steps. (Step 4-1) The main control system 28 makes a deflector control circuit 23 deflect a plurality of electron beams to a subfield SF1 and makes an electron beam shape detection circuit 25 scan the knife edge of a semiconductor detector 14 using only central beams located at the almost center of the subfield, thereby measuring the diameters in the X and Y directions of the beams. The main control system 28 makes a focus control circuit 26 change the focus and measures the beam diameters in the X and Y directions. Let Fx be a focus position where the beam diameter in the X direction is the smallest; Fy, a focus position where the beam diameter in the Y direction is the smallest; and Fx−Fy, the astigmatism amount of the subfield. Sequential switching is performed between subfields, and the astigmatism amount of central beams for each subfield is detected.(Step 4-2) In step 4-1, the astigmatism amount of central beams for each subfield, as shown in FIG. 5, is obtained. With this astigmatism amount, the maximum astigmatism amount (H_AS) and minimum astigmatism amount (L_AS) are calculated, thereby calculating the average astigmatism amount (M_AS=(H_AS+L_AS)/2).(Step 4-3) An astigmatism amount obtained by subtracting the average astigmatism amount from the astigmatism amount for each subfield is used as the varying astigmatism amount for each subfield. The average astigmatism amount can be considered as an astigmatism amount which does not vary during exposure when subfield switching is performed. The varying astigmatism amount can be considered as an astigmatism amount which varies.(Step 4-4) The average astigmatism amount is corrected by a first stigmator 3. The function of the first stigmator 3 will be described with reference to FIG. 6. When the first stigmator 3 is not driven, an electron source image SI is almost circular, and a plurality of electron source images on a blanker array 7 are also almost circular. Astigmatism of a reduction electron optical system 8 makes elliptical a plurality of electron source images on a wafer 9. On the other hand, when the first stigmator 3 is driven, the electron source image SI becomes elliptical so as to cancel any astigmatism of the reduction electron optical system 8. At the same time, the plurality of electron source images on the blanker array 7 become elliptical. As a result, the plurality of electron source images on the wafer 9 becomes almost circular. To correct astigmatism, astigmatism is made to occur in the original electron source image SI, and no aberration other than astigmatism of the reduction electron optical system 8 occurs. The first stigmator 3 adjusts the amount of astigmatism before the electron source image SI is reduced. To correct astigmatism of the reduction electron optical system 8, an astigmatism amount larger than that for a second stigmator 11 must be added because of longitudinal magnification. For this reason, an electromagnetic one is used as the first stigmator 3 to increase the driving amount for correcting astigmatism. On the other hand, an electrostatic one is used as the second stigmator. An electromagnetic stigmator has poorer responsiveness than an electrostatic stigmator. Under the circumstances, in this embodiment, the average astigmatism amount is corrected by the magnetic first stigmator 3 while the varying astigmatism amount is corrected by the electrostatic second stigmator 11. (Step 4-5) The wafer 9 is loaded onto a stage 13. (Step 4-6) The main control system 28 makes the deflector control circuit 23 deflect a plurality of electron beams to a subfield to be exposed. (Step 4-7) The main control system 28 instructs the second stigmator to correct a varying astigmatism amount corresponding to the subfield to be exposed, concurrently with step 4-5. (Step 4-8) Exposure is performed for the subfield to be exposed. (Step 4-9) When exposure for all subfields completes, the flow advances to step 4-10; otherwise, the flow returns to step 4-6. (Step 4-10) The wafer 9 is unloaded from the stage 13. According to this embodiment, astigmatism of a reduction electron optical system can be corrected while suppressing generation of an aberration other than astigmatism. This makes it possible to expose a wafer to a desired fine pattern. If this apparatus is used in the manufacturing of devices, devices can be manufactured at higher yield than a conventional case. <Second Operation Explanation> Operation of an electron beam exposure apparatus according to the second embodiment of the present invention will be described with reference to FIG. 7. As the wafer process of the exposure apparatus, a main control system 28 executes the following steps. (Step 7-1) The main control system 28 makes an electron beam shape detection circuit 25 scan the knife edge of a semiconductor detector 14 using only central beams located at the almost center of a subfield, thereby measuring the diameters in the X and Y directions of the beams.(Step 7-2) In step 7-1, the beam shape in the X direction (scanning direction) is moving-averaged by the width of each pixel and is stored.(Step 7-3) An astigmatism amount in which the X-direction moving average beam shape almost coincides with the Y-direction moving average beam shape is calculated.(Step 7-4) The calculated astigmatism amount is corrected by a first stigmator 3. Astigmatism is adjusted such that the size of electron beams on the substrate in the scanning direction (X direction) is smaller than that in a direction perpendicular to the direction (Y direction). In addition, the function of the first stigmator 3 will be described with reference to FIG. 6. When the first stigmator 3 is not driven, an electron source image SI is almost circular, and a plurality of electron source images on a blanker array 7 are also almost circular. However, electron beams distort in the scanning direction (X direction), as described above, and a plurality of electron source images on a wafer 9 have the shape of an ellipse extending in the X direction. On the other hand, when the first stigmator 3 is driven, astigmatism is adjusted such that the size in the scanning direction (e.g., the width in the X direction) of the electron beams on the substrate is smaller than that in a direction perpendicular to the direction (e.g., the width in the Y direction). The electron source image SI has the shape of an ellipse extending in the Y direction. At the same time, the plurality of electron source images on the blanker array 7 have the shape of an ellipse extending in the Y direction. As a result, any X-direction distortion in the plurality of electron source images on the wafer 9 is corrected, and the electron source images become almost circular. To correct distortion of electron beams, astigmatism is made to occur in the original electron source image SI, and no aberration other than astigmatism of a reduction electron optical system 8 occurs. (Step 7-5) The wafer 9 is loaded onto a stage 13. (Step 7-6) The main control system 28 makes the deflector control circuit 23 deflect a plurality of electron beams to a subfield to be exposed. (Step 7-7) Exposure is performed for the subfield to be exposed. (Step 7-8) When exposure for all subfields completes, the flow advances to step 7-9; otherwise, the flow returns to step 7-6. (Step 7-9) The wafer 9 is unloaded from the stage 13. As described above, a scanning charged particle beam exposure apparatus according to this embodiment can correct any distortion of electron beams due to scanning and can expose a wafer to a desired pattern. If this apparatus is used in the manufacturing of devices, devices can be manufactured at higher yield than a conventional case. (Device Production Method) An example of a device production method using the above-mentioned electron beam exposure apparatus will be explained. FIG. 10 shows the manufacturing flow of a microdevice (e.g., a semiconductor chip such as an IC or LSI, liquid crystal panel, CCD, thin-film magnetic head, micromachine, or the like). In step 1 (circuit design), a semiconductor device circuit is designed. In step 2 (exposure control data creation), exposure control data for an exposure apparatus is created based on the designed circuit pattern. In step 3 (wafer manufacture), a wafer is manufactured by using a material such as silicon. In step 4 (wafer process) called a preprocess, an actual circuit is formed on the wafer by lithography using the prepared wafer and the exposure apparatus, into which the exposure control data is input. Step 5 (assembly) called a postprocess is the step of forming a semiconductor chip by using the wafer formed in step 4, and includes an assembly process (dicing and bonding) and packaging process (chip encapsulation). In step 6 (inspection), the semiconductor device manufactured in step 5 undergoes inspections such as an operation confirmation test and durability test of the semiconductor device manufactured in step 5. After these steps, the semiconductor device is completed and shipped (step 7). FIG. 11 shows the detailed flow of the above-mentioned wafer process. In step 11 (oxidation), the wafer surface is oxidized. In step 12 (CVD), an insulating film is formed on the wafer surface. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition. In step 14 (ion implantation), ions are implanted in the wafer. In step 15 (resist processing), a photosensitive agent is applied to the wafer. In step 16 (exposure), the circuit pattern is printed onto the wafer using the above-mentioned exposure apparatus. In step 17 (development), the exposed wafer is developed. In step 18 (etching), the resist is etched except for the developed resist image. In step 19 (resist removal), an unnecessary resist after etching is removed. These steps are repeated to form multiple circuit patterns on the wafer. With the manufacturing method according to this embodiment, highly integrated semiconductor devices which have been difficult to manufacture by a conventional method can be manufactured at low cost. As has been described above, a charged particle beam exposure apparatus according to the present invention can reduce, when correcting astigmatism of a reduction electron optical system, generation of an aberration other than astigmatism and can perform exposure to a desired pattern. Also, if this apparatus is used in the manufacturing of devices, devices can be manufactured at higher yield than a conventional case. According to the present invention, when performing exposure by scanning with charged particle beams, any distortion of electron beams due to the scanning can be reduced, and,exposure to a desired fine pattern can be performed. If a scanning charged particle beam exposure apparatus to which the present invention is applied is used in the manufacturing of devices, devices can be manufactured at higher yield than a conventional case. As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the claims. |
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041727614 | claims | 1. A cellular grid structure for a nuclear fuel element, comprising a plurality of tubular ferrules for defining openings for nuclear fuel rods, an encircling band within which the ferrules are grouped, at least some of the tubular ferrules being constituted by twin ferrule units, each said twin ferrule unit being constituted by a single bent metal strip, a bridge piece dividing means separating the interior of the twin ferrule unit into two similar openings for two adjacent fuel rods, and locating means for locating the nuclear fuel rods in the respective openings. 2. A grid structure according to claim 1, wherein said locating means includes a resilient member associated with each bridge piece dividing means and having a part projecting into each adjacent opening. 3. A grid structure according to claim 1 wherein each bridge piece dividing means is a partition integral with the metal strip which frames the adjacent openings. 4. A grid structure according to claim 1, wherein each bridge piece dividing means comprises a non-integral metal strip extending across the respective ferrule unit. 5. A grid structure according to claim 1, wherein each bridge piece dividing means has extremities which project beyond the plane of the grid and each extremity is shaped to retain a resilient member forming part of said locating means. |
description | This application claims priority to and the benefit of Korean Patent Application No. 10-2008-0125378 filed in the Korean Intellectual Property Office on Dec. 10, 2008, the entire disclosure of which is incorporated herein by reference. The present invention relates to an electromagnetic wave interference (EMI)/radio frequency interference (RFI) shielding resin composite material, and a molded product made using the same. Electromagnetic wave generation is increased through highly efficient, high power consuming, and highly integrated electro-electronic devices. Electromagnetic waves cause malfunctions to other devices and systems or damage to the human body, so effective electromagnetic wave shield techniques are required in order to shield the electromagnetic waves. EMI shielding effectiveness is represented by the following Equation 1.S.B.(shielding effectiveness)=R+A+B [Equation 1] In the above Equation 1, R represents surface reflection of an electromagnetic wave, A represents internal absorption of an electromagnetic wave, and B represents loss by multi-reflection. The conventional method of shielding electromagnetic waves includes an applied painting and plating method using a metallic material. Since the metallic material has high conductivity (R value, impedance is low) and a high electromagnetic wave shield rate through the surface reflection of electromagnetic waves, it is possible for even a thin metal to effectively shield electromagnetic waves. However, the painting and plating techniques, particularly the plating process, include complicated steps such as removing oils, etching, neutralizing, activating, accelerating, metal depositing, activating, first plating, second plating, third plating, and so on. Accordingly these techniques have drawbacks such as high production costs and low productivity, particularly in view of recent demands for increased productivity. In contrast, an electromagnetic wave shielding material using a polymer composite resin can be obtained by simply injecting a composite resin, so it is a very economical process with regard to production cost and productivity. However, in the case of a composite material using the polymer composite resin, since the electrical conductivity is lower than that of a metallic material, it is important to improve the surface reflection and internal absorption among the factors shown in Equation 1. Accordingly, the resin composite material has the drawback of deteriorated or reduced electromagnetic wave shielding efficiency when it is too thin. In order to increase the electromagnetic wave shielding efficiency of a resin composite material, the surface impedance thereof is decreased (electrical conductivity is increased), the R value is increased, and internal electromagnetic wave scattering/absorption is further induced, so that the A value is increased to provide a highly effective electromagnetic wave shielding composite resin. The following publications relate to shielding electromagnetic waves coming from all electronic devices such as radio frequency interference (RFI): an electromagnetic wave shielding device including a polymer substrate coated with metal on its surface (U.S. Patent Application Publication No. 2007-0199738); an electromagnetic wave shielding material including a non-conductive polymer, a conductive polymer, and an electrically conductive metal powder (U.S. Patent Application Publication No. 2007-0056769); a method of manufacturing an electrically conductive immersed fiber by coating a conductive fiber with a compatibilizer such as an organic wetting agent, and compositing the same in a resin (U.S. Patent Application Publication No. 2002-0108699); an electrically conductive thermoplastic elastomer including a conductive filler of nickel plated with silver in a styrene-ethylene-butadiene-styrene copolymer (SEBS) based matrix material which is a non-conductive resin (U.S. Pat. No. 6,638,448); an electrically conductive composition in which a carbonaceous conductive filler is immersed in a blend of two polymer resins having different polarities and the carbonaceous conductive filler is disposed on one having the higher polarity (U.S. Pat. No. 6,409,942); and a thermoplastic electromagnetic wave shielding sheet including a sheet material or polymer carrier that is capable of becoming porous during a thermoforming process and including a low-melting point metal conductive filler (U.S. Pat. No. 5,869,412). However, these techniques provide resins with only electrical conductivity and thus do not satisfy the required electromagnetic wave shielding effects. An exemplary aspect of the present invention provides an electromagnetic wave interference (EMI)/radio frequency interference (RFI) shielding resin composite material having high performance due to excellent electromagnetic wave shield effects. Another aspect of the present invention provides a molded product made using the EMI/RFI shielding resin composite material. According to one aspect of the present invention, an EMI/RFI shielding resin composite material is provided that includes (A) a thermoplastic polymer resin; (B) an electrically conductive filler having a polyhedral shape or being capable of forming a polyhedral shape; and (C) a low-melting point metal. The EMI/RFI shielding resin composite material includes about 30 to about 85 volume % of the thermoplastic polymer resin (A); about 5 to about 69 volume % of the electrically conductive filler having a polyhedral shape or being capable of forming a polyhedral shape (B); and about 1 to about 10 volume % of the low-melting point metal (C). The EMI/RFI shielding resin composite material may optionally further include a glass fiber filler (D) in an amount of about 50 parts by weight or less, based on about 100 parts by weight of the EMI/RFI shielding resin composite material. The thermoplastic polymer resin (A) may include a polyamide, polyalkylene terephthalate, a polyacetal, a polycarbonate, a polyimide, a polyphenylene oxide, a polysulfone, a polyphenylene sulfide, a polyamide imide, a polyether sulfone, a liquid crystal polymer, a polyetherketone, a polyetherimide, a polyolefin, acrylonitrile-butadiene-styrene, a polystyrene, a syndiotactic polystyrene, or a combination thereof. The electrically conductive filler (B) having a polyhedral shape or being capable of forming a polyhedral shape may be a needle-shaped electrically conductive filler having a polyhedral interior, a sheet-shaped electrically conductive filler having a polyhedral interior, a globular electrically conductive filler having a polyhedral interior, or a combination thereof. The needle-shaped electrically conductive filler having a polyhedral interior may be a metal filler fabricated in a needle shape by pressing and cutting a dendrite metal filler fabricated through an electrolysis process or a porous metal filler fabricated through a thermal process, or a needle-shaped metal filler fabricated by polishing a metal lump; the sheet-shaped electrically conductive filler having a polyhedral interior may be a metal filler fabricated in a sheet shape by pressing a dendrite metal filler fabricated through an electrolysis process or a porous metal filler fabricated through a thermal process, or a sheet-shaped metal filler fabricated through a pulverization process; and the globular electrically conductive filler having a polyhedral interior may be a globular metal filler fabricated through a melt injection process. The electrically conductive filler (B) may be a metal conductive filler that can be broken down or pulverized by a shear stress applied during the process of producing the EMI/RFI shielding resin composite material to thereby form a polyhedral shape. Also, the electrically conductive filler (B) may have a shear strength of under about 300 MPa, and it may include aluminum, copper, magnesium, iron, nickel, molybdenum, zinc, silver, alloys thereof, or combinations thereof. The low-melting point metal (C) may be solid solution including two or more kinds of metal elements. Also, the low-melting point metal (C) may include a primary component including tin, bismuth, lead, or a combination thereof, and a secondary component including aluminum, nickel, silver, germanium, indium, zinc, or a combination thereof. The low-melting point metal (C) may have a solidus temperature which is lower than the temperature used in the process of making the EMI/RFI shielding resin composite material. According to another aspect of the present invention, a molded product made using the EMI/RFI shielding resin composite material is provided. Hereinafter, further embodiments will be described in detail. The present invention now will be described more fully hereinafter in the following detailed description of the invention, in which some, but not all embodiments of the invention are described. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used herein, when specific definition is not provided, the term “electromagnetic wave interference (EMI)/radio frequency interference (RFI)” refers to “electromagnetic wave interference (EMI) or radio frequency interference (RFI)”. According to one embodiment, the electromagnetic wave shielding effectiveness (S.B) represented by the following Equation 1 may be improved by improving inner absorption of electromagnetic waves.S.B.=R+A+B [Equation 1] In the above Equation, R represents surface reflection of an electromagnetic wave, A represents internal absorption of an electromagnetic wave, and B represents loss by multi-reflection. The inventors of the present invention found that when a conductive filler is formed to have many surfaces, scattered reflection of electromagnetic waves whose characteristics are similar to light is induced and thus the amounts of scattering and absorption are increased, which leads to an increase in the A value, in the course of researching a method for increasing the A value at the same electric conductivity level. The EMI/RFI shielding resin composite material according to one embodiment includes (A) a thermoplastic polymer resin; (B) an electrically conductive filler having a polyhedral shape or being capable of forming a polyhedral shape; and (C) a low-melting point metal. The electromagnetic wave interference (EMI)/radio frequency interference (RFI) shielding resin composite material includes about 30 to about 85 volume % of the thermoplastic polymer resin (A); about 5 to about 69 volume % of an electrically conductive filler having a polyhedral shape or being capable of forming a polyhedral shape (B); and about 1 to about 10 volume % of the low-melting point metal (C) based on the total weight of the EMI/RFI shielding resin composite material. The EMI/RFI shielding resin composite material according to one embodiment can be prepared by mixing the components. The EMI/RFI shielding resin composition can have a structure including a matrix of the thermoplastic polymer resin, and the electrically conductive filler having a polyhedral shape or being capable of forming a polyhedral shape and low-melting point metal dispersed in the matrix to provide a network. Exemplary components included in the EMI/RFI shielding resin composite material according to embodiments will hereinafter be described in detail. (A) Thermoplastic Polymer Resin Exemplary thermoplastic polymer resins include without limitation polyamides; polyalkylene terephthalates such as polyethylene terephthalate, polybutylene terephthalate, and the like; polyacetals; polycarbonates; polyimides; polyphenylene oxides; polysulfones; polyphenylene sulfides; polyamide imides; polyether sulfones; liquid crystal polymers; polyetherketones; polyetherimides; polyolefins such as polypropylene, polyethylene, and the like; acrylonitrile-butadiene-styrene; polystyrene; syndiotactic polystyrene; and the like, and combinations and blends thereof. The EMI/RFI shielding resin composite material may include the thermoplastic polymer resin in an amount of about 30 to about 85 volume %, and in another embodiment, about 50 to about 80 volume % based on the total amount of EMI/RFI shielding resin composite material. When the EMI/RFI shielding resin composite material includes the thermoplastic polymer resin in an amount within these ranges, the process and the EMI shielding efficiency and processibility can be improved. (B) Electrically Conductive Filler The electrically conductive filler according to an embodiment can minimize impedance for a network formed by a thermoplastic polymer resin dispersed in a matrix, and effectively scatter electromagnetic waves, or radio waves, by existing in a polyhedral shape before or after the fabrication process of an EMI/RFI shielding resin composite material. The electrically conductive filler may have a polyhedral shape or may be capable of forming a polyhedral shape, and it may have a needle shape, a sheet shape, or a globular shape. In other words, the needle-shaped electrically conductive filler may have a polyhedral needle-shaped interior, the sheet-shaped electrically conductive filler may have a polyhedral sheet-shaped interior, and the globular electrically conductive filler may have a polyhedral globular interior. The needle-shaped electrically conductive filler having a polyhedral interior may be a metal filler fabricated in a needle shape by pressing and cutting a dendrite metal filler fabricated through an electrolysis process or a porous metal filler fabricated through a thermal process, or a needle-shaped metal filler fabricated by polishing a metal lump. The sheet-shaped electrically conductive filler having a polyhedral interior may be a metal filler fabricated in a sheet shape by pressing a dendrite metal filler fabricated through an electrolysis process or a porous metal filler fabricated through a thermal process, or a sheet-shaped metal filler fabricated through a pulverization process. The globular electrically conductive filler having a polyhedral interior may be a globular metal filler fabricated through a melt injection process. Also, in exemplary embodiments, the electrically conductive filler may be broken down and pulverized by shear stress applied during the fabrication process of the EMI/RFI shielding resin composite material, i.e., during the process of mixing the components of the resin composite material, to thereby form a polyhedral shape. The electrically conductive filler may have a shear strength of under about 300 MPa, for example from about 10 MPa to about 300 MPa, and as another example about 10 MPa to about 100 MPa. When the electrically conductive filler has a shear strength within the above ranges, it may be broken down and pulverized during the process used to make the composite material. When the electrically conductive filler has a shear strength of at least more than about 10 MPa, it is possible to prevent the metal filler from collapsing during the process. When the electrically conductive filler includes two or more kinds of metals, the shear strength of each metal should fall within the above ranges. As described above, the electrically conductive filler which is formed in a polyhedral shape or is capable of forming a polyhedral shape during the process of making the EMI/RFI shielding resin composite material may include a metal such as aluminum, copper, magnesium, iron, nickel, molybdenum, zinc, silver, alloys thereof, and the like, and combinations thereof. The EMI/RFI shielding resin composite material may include the electrically conductive filler in an amount of about 5 to about 69 volume %, for example about 20 to about 40 volume %, based on the total amount of the EMI/RFI shielding resin composite material. When the EMI/RFI shielding resin composite material includes the electrically conductive filler in an amount within these ranges, the electromagnetic wave shielding efficiency can be excellent, and an EMI/RFI shielding resin composite material may be easily fabricated using a conventional injection molding process. (C) Low-Melting Point Metal The low-melting point metal according to an embodiment can maximize the network formed by the thermoplastic polymer resin and the electrically conductive filler to thereby further decrease impedance. In other words, the low-melting point metal can serve as a supplementary agent for the electrically conductive filler. When the low-melting point metal is used alone without using an electrically conductive filler, it can agglomerate in the thermoplastic polymer resin, which can minimize or eliminate the shielding effect and deteriorate electrical conductivity. The low-melting point metal is a solid solution including at least two kinds of metal elements, and includes a main component (i.e., a majority component comprising greater than 50%, for example at least about 75%, or at least about 85%, or at least about 90%, or higher, of the total weight percent of the low-melting point metal) and a minor component (i.e., a minority component comprising less than 50% of the total weight of the low-melting point metal). Exemplary main components can include without limitation tin, bismuth, lead, and the like, and combinations thereof, and exemplary minor components can include without limitation copper, aluminum, nickel, silver, germanium, indium, zinc, and the like, and combinations thereof. According to one embodiment, the main component can include tin for an environmentally-friendly material. The low-melting point metal may have a solidus temperature (temperature at which solidification is complete) that is lower than the melt processing temperature (melting point) of the thermoplastic polymer resin of the composite material. When the low-melting point metal has a solidus temperature that is lower by more than 20° C. than the melt processing temperature of the thermoplastic polymer resin of the composite material, it can be beneficial for the process of manufacturing a composite material. In another embodiment, the low-melting point metal may have a solidus temperature that is higher by more than about 100° C. than the environment in which the composite material is used. A more detailed description follows. In order for the low-melting point metal to form a network in the thermoplastic polymer resin during manufacturing of the EMI/RFI shielding resin composite material, the solidus temperature and the liquidus temperature of the low-melting point metal that affect the dispersion have the following order: liquidus temperature>melting point of thermoplastic polymer resin>solidus temperature. Such solidus temperature may be controlled by the amount ratio of the main component and the minor component of the low-melting point metal. Thereby, it is possible to control the physical properties such as liquidus temperature (temperature at the beginning of solidification) and mechanical strength. In one embodiment, when aluminum is used as the electrically conductive filler, the solid solution can include aluminum; similarly, when the electrically conductive filler is copper, the solid solution can include copper. One method of controlling the solidus temperature of the low-melting point metal by adjusting the amount of the main component and the minor component includes providing a solid solution with another metal. A non-limiting example of the method includes controlling the solidus temperature of tin/copper (97/3 weight ratio) to 227° C., or the solidus temperature of tin/copper/silver (92/6/2 weight ratio) to 217° C. The EMI/RFI shielding resin composite material may include the low-melting point metal in an amount of about 1 to about 10 volume %, and in another embodiment about 2 to about 5 volume %, based on the total amount of EMI/RFI shielding resin composite material. When the EMI/RFI shielding resin composite material includes the low-melting point metal in an amount within these ranges, it is possible to form electrically conductive filler networks. (D) Glass Fiber Filler In exemplary embodiments, the EMI/RFI shielding resin composite material may further optionally include a glass fiber filler to improve the strength. The glass fiber filler may have a diameter of about 8 to about 13 μm and a length of about 2 to about 5 mm, but is not limited thereto. Use of a glass fiber filler with a diameter and length within these ranges can reinforce the composite material and improve the process of making the composite material. The EMI/RFI shielding resin composite material may include the glass fiber filler in an amount of about 50 parts by weight or lower, and in another embodiment, about 2 to about 50 parts by weight, based on about 100 parts by weight of the EMI/RFI shielding resin composite material. When the EMI/RFI shielding resin composite material includes the glass fiber filler in an amount within these ranges, it is possible to improve the strength of the EMI/RFI shielding resin composite material. (E) Other Additives The EMI/RFI shielding resin composite material according to one embodiment may further optionally include a variety of known additives, as required, such as an antioxidant, an ultraviolet (UV) absorber, a flame retardant, a lubricant, a dye and/or pigment, and so on, as long as they do not damage the effects of the invention. The skilled artisan will understand the types and amounts of additives and how to use additives in the present invention without undue experimentation. The EMI/RFI shielding resin composite material may include the additives in an amount of about 0 to about 60 parts by weight, and in another embodiment, about 1 to about 30 parts by weight, based on about 100 parts by weight of the EMI/RFI shielding resin composite material. Another embodiment of the present invention provides a molded product made using the EMI/RFI shielding resin composite material. The molded product is applicable in fields requiring an EMI/RFI shield, and is particularly applicable for a display device such as a TV and a PDP, and an electro-electronic device such as a computer, a mobile phone, and an office automation device. The following examples illustrate the present invention in more detail. However, they are exemplary embodiments of the present invention and are not limiting. A person having ordinary skill in this art can sufficiently understand parts of the present invention that are not specifically described. (A) Thermoplastic Polymer Resin The thermoplastic polymer resin is polyphenylene sulfide (PPS). Ryton PR-35 manufactured by Chevron Phillips Chemical Co. is used for the PPS resin, and it has a zero shear viscosity of 1000[P] measured at 315.5° C. under a nitrogen atmosphere. (B) Electrically Conductive Filler Having a Polyhedral Shape or Being Capable of Forming a Polyhedral Shape Needle-shaped copper formed through a polishing process to have a diameter of 40 μm and a length of 2.5 to 3 mm, sheet-shaped aluminum having an average thickness of 350 nm along with needle-shaped aluminum, and sheet-shaped copper having an average thickness of 500 nm are used as electrically conductive filler having a polyhedral shape or being capable of forming a polyhedral shape. The shear strength of the aluminum is 30 MPa, and the shear strength of the copper is 42 MPa. (C) Low-Melting Point Metal A tin/aluminum low-melting point metal and a tin/copper low-melting point metal containing tin as a primary component are used as the low-melting point metal. In the case of the tin/aluminum low-melting point metal, a tin/aluminum solid solution with a mixing ratio of tin and aluminum of 99.7 wt % and 0.3 wt %, respectively, and a solidus temperature of 228° C., is used. In the case of the tin/copper low-melting point metal, a tin/copper solid solution with a mixing ratio of tin and copper of 96 wt % and 4 wt %, respectively, and a solidus temperature of 227° C., is used. (D) Glass Fiber Filler The glass fiber filler is ECS 03 T-717PL (manufactured by Nippon Electric Glass) having a diameter of 13 μm and a length of 3 mm and coated with silanes on its surface to improve the interface adherence with the thermoplastic polymer resin of PPS. An EMI/RFI shielding resin composite material is made using the above components in the compositions of Examples 1 to 5 and Comparative Example 1 shown in the following Table 1 and Comparative Examples 2 and 3 shown in the following Table 2 and each composition is extruded using a conventional twin screw extruder and an injector to provide pellets. As shown in the following Table 1, if the amount of glass fiber filler is recalculated into parts by weight, it would be 6.4 parts by weight based on the total of 100 parts by weight of the EMI/RFI shielding resin composite material. Also, as shown in the following Table 2, samples of Comparative Example 3 are fabricated by injection-molding PPS in a sheet shape, and performing a typical plating process, which includes removal of grease, etching, neutralization, activation, deposition, activation, and plating process, and plating both sides of a sheet-shaped sample with Cu and Ni. The state of the electrically conductive filler in the EMI/RFI shielding resin composite material fabricated according to Example 5 is presented in FIGS. 1 to 3. FIG. 1 is an optical microscopic photograph showing the state of an aluminum electrically conductive filler and a low-melting point metal existing in an EMI/RFI shielding resin composite material fabricated according to Example 5. It can be seen from FIG. 1 that polyhedral-shaped aluminum connects the low-melting point metal. FIG. 2 is an optical microscopic photograph showing the state of a needle-shaped aluminum electrically conductive filler existing in the EMI/RFI shielding resin composite material fabricated according to Example 5. FIG. 2 shows the state of the needle-shaped aluminum forming a polyhedral shape. FIG. 3 is an optical microscopic photograph showing the state of a sheet-shaped aluminum electrically conductive filler existing in the EMI/RFI shielding resin composite material fabricated according to Example 5. FIG. 3 shows the state of the sheet-shaped aluminum forming a polyhedral shape. Also, samples having a thickness of 2.1T are fabricated by injection-molding the fabricated pellets with a conventional injection molder, and the electromagnetic wave shielding efficiencies of the samples are measured based on the ASTM D4935 method. The measurement results are shown in the following Tables 1 and 2. TABLE 1Com-parativeExampleExample(volume %)123451PPS606060606060Needle-shaped38—29—26—aluminumNeedle-shaped —38—29—40copperSheet-shaped—— 9— 7—aluminumSheet-shaped ——— 9——copperSn/Al 2— 2— 2—low-meltingpoint metalSn/Cu — 2— 2——low-meltingpoint metalglass fiber filler———— 5—Shielding effect 49.6-54.7-48.8-51.5-42.3-55.5-[dB] at 2.1 T92.292.1108.3106.1110.291.8Average 70.6 68.3 83.0 80.3 85.7 62.8shielding effect [dB] at 2.1 T TABLE 2Comparative ExampleVolume %23PPS6060Carbon fiber2)40—Needle-shaped stainless steel1)—40Shielding effect[dB] at 2.1 T11.0-24.733.0-85.0Average shielding effect19.555.0[dB] at 2.1 T1)Needle-shaped stainless steel fabricated to have a diameter of 10 μm and a length of 200 μm by a cutting process2)Pitch-based carbon fiber having a diameter of 11 μm and a length of 6 mm In Tables 1 and 2, the shielding effect is considered excellent when the average shielding effect result is high. As shown in Tables 1 and 2, when the samples have the same thickness, the EMI/RFI shielding resin composite material of Examples 1 to 5 exhibits superior electromagnetic wave shielding effects as compared to Comparative Examples 1 to 3. Particularly, the EMI/RFI shielding resin composite material of Comparative Example 1, which did not include a low-melting point metal, exhibits inferior shielding effects as compared to Examples 1 to 5. Also, the EMI/RFI shielding resin composite material of Comparative Example 3, which includes needle-shaped stainless steel having a smooth surface and does not significantly form a polyhedral shape during the process, exhibits deteriorated shielding effects as compared to Examples 1 to 5. It can be seen from the results that the electromagnetic wave shielding effect is improved when an electrically conductive filler having a polyhedral shape and a low-melting point metal are used together. Particularly, it can be seen from the results of Example 5 that although a glass fiber filler is added to reinforce the physical properties, the addition of the glass fiber increased the viscosity of the basic resin. The increased viscosity promotes the melting tension/dispersion of a low-melting point metal to thereby activate the networking of the filler, and at the same time the increased viscosity raises the shear stress applied to a metal filler and thereby induces increased polishing/pulverization action, which leads to an increase in the electromagnetic wave shielding effect. Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing description. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined in the claims. |
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abstract | A digital apparatus is provided for monitoring environment. The apparatus has a high-pressure chamber easy in maintenance. By using a supporting unit, the chamber is stably set in a container. In addition, the supporting unit reduces problem of saturated-humidity absorption so that wastage of utilities and rate of fake signals are both decreased. Thus, the chamber is prevented from mist and vapor for keeping good function. |
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summary | ||
044302584 | claims | 1. A method of producing solid gamma ray calibration standards, comprising the steps of: (a) preparing a calibrated aqueous solution of radioactive material; (b) adding a first volume of said calibrated aqueous solution of radioactive material to a second volume of a first solvent comprising an alcohol having less than 5 carbon atoms to form a first solution, and wherein said first volume is less than said second volume; (c) dissolving an unsaturated polyester resin in styrene; (d) mixing said resin dissolved in styrene with said first solution to form a mixture; (e) adding a hardening catalyst to said mixture; (f) stirring said mixture until a clear second solution is produced; and (g) curing said second solution for a selected period of time. 2. A method as claimed in claim 1 wherein said calibrated aqueous solution is acidic, ranging in strength from 0.1 N HCl to 4 N HCl. 3. A method as claimed in claim 2 wherein said first solvent further includes a stabilizing agent to complex metal and hydrogen ions in said calibrated aqueous solution so as to prevent plate-out and allow said calibrated aqueous solution to be solidified. 4. A method as claimed in claim 3 wherein said stabilizing agent is triisooctylamine. 5. A method as claimed in claim 2 wherein the maximum ratio of said first volume to said second volume is 1:10 when said calibrated aqueous solution has a strength of 4 N. 6. A method as claimed in claim 4 wherein the concentration of said triisooctylamine ranges from 0.01% to 10% by volume. 7. A method as claimed in claim 1 wherein the first solvent is n-butanol. 8. A method as claimed in claim 1 wherein said calibrated aqueous solution of radioactive material contains a selected amount of stable element corresponding to each radioactive element in said solution. 9. A method as claimed in claim 2 wherein said radioactive material comprises mixed radionuclides selected from the group consisting of Cd-109, Co-57, Ce-139, Hg-203, Sn-113, Cs-137, Y-88 and Co-60; Ce-139, Sn-113, Cs-137 and Co-60; Ba-133, Cs-137 and Co-60; Ba-133, Cs-137, Mn-54 and Co-60; Cd-109, Eu-152 and Co-60; and Eu-154, Eu-155 and Sb-125. 10. A method as claimed in claim 2 wherein said radioactive material comprises a single isotope selected from the group consisting of Sn-113, Eu-152, Eu-154, Eu-155, Cd-109, Co-57, Co-58, Co-60, Ce-144, Ce-139, Y-88, Cs-134, Cs-137, Cr-51, Fe-59, Zn-65, Mn-54, Ba-133, Sb-125, Hg-203, Na-22 and Sr-85. 11. A method as claimed in claim 1 wherein said calibrated aqueous solution is basic with an hydroxide concentration ranging from 0.01 N to 0.2 N and wherein said calibrated aqueous solution further includes a sulfite reducing agent in a concentration ranging from 1 to 100 parts per million. 12. A method as claimed in claim 11 wherein said radioactive material comprises a single isotope selected from the group consisting of I-125, I-129, I-131 and Cr-51. 13. A method as claimed in claim 1 wherein said hardening catalyst is methyl ethyl ketone peroxide. 14. A solid gamma ray calibration standard produced in accordance with the method of claim 1. |
054854911 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a conventional reactor coolant pump (RCP) motor 2 to which the invention is applied. It being understood that the invention is applicable to any type of rotating electrical apparatus (e.g., a generator) operating in any environment including a hazardous environment, such as a nuclear containment vessel. The exemplary RCP motor 2 includes a central rotatable shaft 4 having a drive shaft coupling 6 at one end of the shaft 4 for connection to a RCP (not shown), a rotor 8 having rotor windings 9 and a rotor core 10, and a flywheel 12. The exemplary flywheel 12 is located at the opposite end of the shaft 4 with respect to the drive shaft coupling 6. The RCP motor 2 further includes an upper bearing assembly 14, an air cooler 16, a stator 18 having a stator core 20 and stator windings 22, and a lower radial bearing assembly 26, all contained in a housing 30 having a motor mounting flange 28. Alternatively, the RCP motor 2 may not have the air cooler 16. Referring now to FIG. 2A, the RCP motor 2 further includes an upper bearing oil heat exchanger 34 and an oil lift system 36. The RCP motor 2 is interconnected with a diagnostic system 32 which includes a plurality of sensors 38a-38c, cables 40a-40c and analog to digital (A/D) converters 42a-42c. The system 32 also includes a processor 44. As will be described in detail below, the plural sensors 38 for the RCP motor 2 are positioned thereon and therein, in order to sense a plurality of operating conditions of the RCP motor 2. The sensors 38 are interconnected with the converters 42 by cables 40, such as the exemplary conventional twisted pair cables. Alternatively, coaxial cables, fiber optic cables or any other suitable interconnection may be provided. Each of the converters 42 converts an electrical signal (e.g., a voltage, a current, a resistance, etc. or an equivalent light beam) provided by a sensor 38 into a corresponding digital value for use by the processor 44. The exemplary processor 44 includes a microprocessor 46, a port 47 having an attached printer 49, an input/output (I/O) bus 48, a random access memory (RAM) 50 and a real time clock 51. It being understood that the invention is applicable to any type of processor (e.g., a personal computer (PC), a mini-computer, a mainframe computer, or any other type of processing device), output device (e.g., a cathode ray tube (CRT), etc.), port or I/O bus (e.g., serial, RS-232, RS-422, parallel, VME, AT-bus, etc.), or memory (e.g., EEPROM, disk, etc.). As will be described in detail below, the microprocessor 46 uses the I/O bus 48 to read digital values, representative of the electrical signals from the corresponding sensors 38, from the A/D converters 42. The microprocessor 46 then stores the digital values in the memory 50 for later use in diagnosing the operability of the RCP motor 2. Those skilled in the art will recognize that the location of the exemplary processor 44 is generally within several hundred feet of the exemplary RCP motor 2, in order to accommodate the capabilities of the exemplary cables 40. Referring now to FIG. 2B, the RCP motor 2 is interconnected by a local processor 45 with a remote diagnostic system 33. The remote diagnostic system 33 is interconnected with the local processor 45 by a local data highway controller 52 and a remote data highway controller 54. The operation of the exemplary processor 45 is generally the same as described above for the processor 44 (see FIG. 2A). As will be described below, the processor 45 provides intermediate data storage for the remote diagnostic system 33. The controllers 52,54 are interconnected by a cable 56. It being understood that the invention is applicable to any type of data highway (e.g., a data acquisition network, a process control network, a wide area network, etc.) and any type of cable interconnection (e.g., a coaxial cable, a fiber optic cable, telephone lines, etc.). In the exemplary embodiment, the cable 56 passes through a bulkhead 58 (e.g., a bulkhead connector, a penetrator, etc.) at a barrier 60 (e.g., a biological barrier, a containment vessel, etc.). The controllers 52,54 provide a preselected periodic mapping of data specified by the remote diagnostic system 33 to and from the processor 45. The exemplary remote diagnostic system 33 has a processor 62 which is similar to the processor 44 (see FIG. 2A) and includes a microprocessor 64, a port 65 having an attached printer 67, an I/O bus 66, a RAM memory 68 and a real time clock 69. In a manner similar to the operation of the processor 44, the microprocessor 64 uses the I/O bus 66 to read digital values, representative of the electrical signals from the corresponding sensors 38, and stores the values in the memory 68. The principal difference between the system 33 and the system 32 (see FIG. 2A), being the intermediate data storage in the processor 45 and the intermediate data communication by the controllers 52,54. Oil Lift System Condition Monitor Referring now to FIG. 3, the oil lift system 36 generally surrounds the shaft 4 and includes an upper oil reservoir 70 (shown in shadow), a plurality of upper guide bearing shoes 72, a plurality of guide bearing oil spray nozzles 74, a plurality of upper thrust bearing shoes 76 and a plurality of lower thrust bearing shoes 78. Each of the shoes 76,78 has an input check valve 80. A high pressure manifold 82 has a plurality of flow controllers 84 which are each interconnected by an oil line 86 with a corresponding check valve 80. Each of the exemplary controllers 84 controls a flow of oil in the corresponding oil line 86 to the corresponding check valve 80 and limits the exemplary oil flow to approximately one quart of oil per minute. A separate oil line 88 connects the manifold 82 to the spray nozzles 74. An oil line 89 provides a return path for recirculating oil from the oil reservoir 70 of the oil lift system 36. The oil line 89 connects the oil reservoir 70 with an oil strainer 90. The strained oil is recirculated by an oil pump 92 having a drive shaft 93 which is driven by a motor 94. The pump 92, in turn, pumps the oil through a check valve 96. Next, the recirculating oil passes through a flowmeter 98 and an oil filter 100. Finally, an oil line 101 provides an entrance path for the recirculating, filtered oil to reenter the manifold 82. A temperature, flow and pressure of the recirculating oil are monitored, respectively, by exemplary diagnostic sensors which include a temperature detector 102 which is connected at an input 103 of the flowmeter 98, the flowmeter 98, and a pressure transducer 104 which is connected at an output 105 of the flowmeter 98. Alternatively, the diagnostic sensors may include the flowmeter 98 and the pressure transducer 104, but not the temperature detector 102. Each of the sensors 98,102,104 have outputs 106,108,110, respectively, which are connected by cables 40 to A/D converters 42 (see FIG. 2A). The outputs 106,108,110 provide electrical signals (e.g., 0 to +10 VDC, +4 to +20 mA, a variable resistance, etc. or an equivalent light beam) which correspond to a rate of oil flow between the input 103 and the output 105 of the flowmeter 98, an oil temperature at the input 103 of the flowmeter 98, and an oil pressure at the output 105 of the flowmeter 98, respectively. A pressure switch 107 ensures that there is adequate pressure in the oil line 101 during start-up of the RCP motor 2 (see FIG. 1). Upper Thrust Bearing Condition Monitor FIG. 4 is a cross-sectional view of the upper bearing assembly 14. The assembly 14 includes a thrust runner 112 which is interconnected with the shaft 4, a guide bearing 114 for a vertical surface of the thrust runner 112, a guide bearing chamber seal 116, two thrust bearings 118,120 for two horizontal surfaces of the thrust runner 112, a runner seal 122, a guide bearing seal 124, a flywheel seal 126, a ratchet plate 128, a viscosity pump 130, a flow chamber 132 for connection to the upper bearing oil heat exchanger 34 (see FIG. 2A), and an oil bath 134. The assembly 14 has a plurality of sensors which include a radial position proximity probe 136 for determining a radial position of the flywheel 12, an axial position proximity probe 138 for determining a vertical position of the flywheel 12, a thrust load cell 140 for determining a load on the upper thrust bearing 118, three RTD's 142,144,146 for determining a temperature of the guide bearing 114 and the thrust bearings 118,120, respectively. The exemplary assembly 14 further has two proximity probes 148,150 for respectively determining an orientation of the thrust bearing shoes 76,78 (see FIG. 3) of the thrust bearings 118,120, and a temperature sensor 152 for determining an oil temperature in the flow chamber 132 at an inlet of the oil heat exchanger 34 (see FIG. 2A). It being understood that alternative embodiments of the assembly 14 may eliminate the proximity probes 148,150 and the temperature sensor 152. The assembly 14 also has a temperature sensor 154 for determining an oil temperature in the oil bath 134, a level sensor 156 for determining an oil level in the oil bath 134, and two temperature sensors 158,160 (see FIG. 2A) for determining a water inlet temperature and a water outlet temperature, respectively, of the heat exchanger 34 (see FIG. 2A). Those skilled in the art will recognize that, in a manner similar to the operation of the sensors 98,102,104 (see FIG. 3), the sensors 136-160 also have outputs (not shown) which are cabled to the plural A/D converters 42 (see FIG. 2A). The converters 42, in turn, provide digital values to the processor 44 (see FIG. 2A) which correspond to the electrical signals provided by the sensors 136-160. Alternatively, the processor 44 further includes software routines which calculate, for example, for the upper bearing assembly 14, values representative of an efficiency of the upper bearing oil heat exchanger 34 (see FIG. 2A), a load on the thrust bearings 118,120, a film thickness of oil on the thrust bearings 118,120, a maximum temperature of the bearings 114, 118,120, and various other parameters associated with oil lubrication. Lower Guide Bearing Condition Monitor FIG. 5 is a cross-sectional view of the lower radial bearing assembly 26. The assembly 26 includes a lower bearing seal 162, a lower guide bearing 164, a lower bearing insulator 166, and an oil bath 168 having a standpipe 170, an oil pan 172 and a plurality of cooling coils 174. The assembly 26 has a plurality of sensors which include a radial position proximity probe 176 for determining a radial position of the shaft 4, plural RTD's 178 which are located close to a bearing surface of the guide bearing 164 for determining a temperature of the guide bearing, a temperature sensor 180 for determining an oil temperature in the oil bath 168, and a level sensor 182 for determining an oil level in the oil bath 168. Those skilled in the art will recognize that, in a manner similar to the operation of the sensors 98,102,104 (see FIG. 3), the sensors 176-182 also have outputs (not shown) which are cabled to the A/D converters 42 (see FIG. 2A). The converters 42, in turn, provide digital values to the processor 44 (see FIG. 2A) which correspond to the electrical signals provided by the sensors 176-182. Alternatively, the processor 44 further includes software routines which calculate, for example, for the lower bearing assembly 26, various conditions of the guide bearing 164 including clearance and alignment, an overall alignment of the RCP motor 2 (see FIG. 1) with the RCP (not shown), and various other parameters representative of oil lubrication. Alternatively, the processor 44 may also include software routines which calculate values representative of a maximum temperature of the guide bearing 164. Bearing Insulation Resistance Monitor Referring now to FIGS. 2A and 6, a current transformer (CT) 184 surrounds the rotating shaft 4 above the rotor 8. The CT 184 has an output 185 which is connected by the cable 40 to the corresponding A/D converter 42 and, in turn, to the I/O bus 48 of the processor 44 (see FIG. 2A). The CT 184 senses an alternating current Is which flows in the shaft 4. As discussed below, the processor 44 monitors the current sensed by CT 184, in order to diagnose the joint operability of three insulators 190,192,194. Continuing to refer to FIG. 6, the thrust runner 112 of the shaft 4, as discussed above, rotates about the upper guide bearing 114 and the two thrust bearings 118,120. The shaft 4 also rotates about the lower guide bearing 164. The upper bearings 114,118,120 are electrically connected at node 186 to the upper oil reservoir 70 (see FIG. 3). The exemplary lower bearing 164 is electrically insulated from a node 188 by the lower bearing insulator 166. Alternatively, the insulator 166 is not provided and the lower bearing 164 is electrically connected to the node 188. Regardless, under normal operation of the RCP motor 2 (see FIG. 1), a housing of the RCP (not shown) electrically connects the lower bearing 164 to the node 188. Accordingly, this shunts any direct current flow and, thus, protects the upper bearings 114,118,120 from any damage caused by direct current flow in the shaft 4. The node 188 is electrically connected to the stator 18 (see FIG. 1) and is grounded to the housing 30 of the RCP motor 2 (see FIG. 1). The exemplary bearings 114,118,120,164 are separated from the shaft 4 by a corresponding oil film of approximately 0.005 inch thickness. Accordingly, those skilled in the art will recognize that the bearings 114,118,120,164 are electrically connected, in both a resistive and a capacitive manner, to the shaft 4 by the corresponding oil film. An upper bearing electrical insulator 190 includes two layers of insulation 190a,190b which are internally connected at an internal node 191. The insulator 190 insulates the node 186 and the upper oil reservoir 70 (see FIG. 3) from the ground at node 188. Similarly, a plurality of insulators, such as the exemplary two insulators 192,194, also insulate the node 186 and the upper oil reservoir 70 from the ground at node 188. Under normal operation of the RCP motor 2 (see FIG. 1) the insulators 190,192,194 substantially electrically insulate the rotating shaft 4 and the bearings 114,118,120 from the RCP motor housing 30 (see FIG. 1) and the stator 18 (see FIG. 1). In this manner, the insulators 190,192,194 substantially eliminate any current flowing in the motor shaft 4 and, therefore, any current flowing through the bearings 114,118,120. Accordingly, an increase in the alternating current is above a predetermined baseline value indicates a degradation of the insulators 190,192,194 (i.e., a corresponding increase in alternating current flowing through the insulators) of the upper bearing assembly 14. Those skilled in the art will appreciate that a degradation of the insulator 166 of the lower radial bearing assembly 26 (see FIG. 5) cannot normally be monitored because the housing of the RCP (not shown) effectively shorts the lower guide bearing 164 to the node 188. Labyrinth Seal Condition Monitor Referring again to FIGS. 4 and 5, the upper bearing assembly 14 includes the flywheel seal 126 which, under normal operation prevents oil residue and oil vapor from entering a labyrinth section 203. Similarly, the lower radial bearing assembly 26 includes the lower bearing seal 162, which, under normal operation prevents oil residue and oil vapor from entering a labyrinth section 204. Two hydrocarbon vapor sensors 206,208 are positioned in the labyrinth sections 203,204, respectively. The sensors 206,208 effectively monitor the condition of the labyrinth seals 126,162 during normal motor operation. Oil residue or oil vapor may enter the labyrinth sections 203,204, for example, if there is a deformation of the fins of the seals 126,162, or if a seal clearance (e.g., 0.009 to 0.012 inch in the exemplary embodiment) increases. Those skilled in the art will recognize that, in a manner similar to the operation of the sensors 98,102,104 (see FIG. 3), the sensors 206,208 also have outputs (not shown) which are cabled to the A/D converters 42 (see FIG. 2A). The converters 42, in turn, provide digital values to the processor 44 (see FIG. 2A) which correspond to the electrical signals provided by the sensors 206,208. Software Routines FIGS. 7A-7B are flowcharts of software routines executed by the exemplary processor 44 (see FIG. 2A), in order to perform data collection, data trending and diagnosis of an individual sensed value, or a derivative thereof. Referring to FIGS. 2A-2B and 7A, the routine begins in response to a periodic timer interrupt of the clock 51. A test at step 250 examines a configuration flag (REMOTE) stored in memory 50 in order to determine whether a sensed value (S) is read from the local A/D converters 42 or from the data highway controller 54. If a remote value is used, then such value is read from the data highway controller 54 at step 252. On the other hand, if a local value is used, then such value is read from the A/D converter 42 at step 254. In either case, at step 256, a time value (T) is read from the real time clock 51. At step 258 the time value (T) and the sensed value (S), obtained at either step 252 or 254, are stored in a data array in the memory 50. Then, at step 260, a comparison value (C) is determined as a function of three variables: S, a predetermined baseline value (B), and a predetermined deadband value (D). The exemplary predetermined values B,D are stored in the memory 50 and are determined from baseline or calibration values for a particular parameter of RCP motor 2. Alternatively, the predetermined values B,D may be determined from other sensed parameters of the RCP motor 2. The value of the predetermined deadband value (D) may be zero. An Equation for C is provided by: EQU C= (S-B) D Eq. (1) At step 262, if C is less than or equal to zero, which indicates that the sensed value (S) is within an acceptable predetermined range for a new or newly refurbished motor, the routine exits. Otherwise, if C is positive, the processor 44, at step 264, uses C to index a lookup table in memory 50 and determine a predicted time (M) of operability of the RCP motor 2 before motor maintenance or inspection is required. Alternatively, the lookup table may indicate that motor maintenance or inspection is required during the next scheduled outage. Finally, at step 266, the exemplary processor 44 uses port 47 and outputs a report to printer 49. The report includes an identification of the sensed parameter (S) and the predicted time (M). Alternatively, the report indicates that motor maintenance or inspection is required during the next scheduled outage. Referring now to FIGS. 2A-2B and 7B, FIG. 7B is a flowchart of a software routine which calculates a derivative of the sensed values (S) from the data array of FIG. 7A, in order to diagnose a period of operability of the RCP motor 2. The routine begins in response to a periodic timer interrupt of the clock 51. At step 270, the processor 44 determines a least squares linear approximation using the last N sets of variables (S ,T) in the data array which is updated by the routine of FIG. 7A. An Equation for the linear approximation is: EQU S'=a(T'-T.sub.1)+b Eq. (2) where: a: is a slope which represents a derivative, dS/dt; PA1 b: is a value of S' at a time T.sub.1 of a first sample in the array; and PA1 T.sub.1 : is a time corresponding to the first sample in the array. PA1 Ti: ranges from T.sub.1 to T.sub.N ; and PA1 Si: ranges from S.sub.1 to S.sub.N. PA1 S.sub.N : is a current sensed value; PA1 S.sub.M : is a minimum acceptable sensed value; and PA1 S.sub.O : is a typical sensed value, after manufacture or refurbishment, of the RCP motor 2. Equations for "a" and "b" are: ##EQU1## where: N: is 100 in the exemplary embodiment; Then, at step 272, a comparison value (C1) is determined as a function of three variables: "a", a predetermined baseline value (B1), and a predetermined deadband value (D1). The predetermined values B1,D1 are stored in the memory 50 and are determined from baseline or calibration values for a particular parameter of RCP motor 2. Alternatively, the predetermined values B1,D1 may be determined from other sensed parameters of the RCP motor 2. The value of the predetermined deadband value (D1) may be zero. An Equation for C1 is provided by: EQU C1= (a-B1) -D1 Eq. (4) At step 274, if C1 is less than or equal to zero, which indicates that the derivative "a" of the sensed value (S) is within an acceptable predetermined range for a new or newly refurbished motor, the routine exits. Otherwise, if C1 is positive, the processor 44, at step 276, uses C1 to index a lookup table in memory 50 and determine a predicted time (M) of operability of the RCP motor 2 before motor maintenance or inspection is required. Alternatively, the lookup table may indicate that motor maintenance or inspection is required during the next scheduled outage. Finally, at step 278, the processor 44 uses port 47 and outputs a report to printer 49. The report includes an identification of the sensed parameter (S), the derivative (a) and the predicted time (M). Alternatively, the report indicates that motor maintenance or inspection is required during the next scheduled outage. Alternatively, in selected RCP motor 2 subsystems, the predicted time (M) of operability of the RCP motor 2 may be calculated from one or both of the following Equations: ##EQU2## where: T.sub.M : is a typical maintenance interval, after manufacture or refurbishment, for the RCP motor 2; The above described software routines compare a single sensed value, or a derivative of the sensed value, with a predetermined value. It being understood that the invention is applicable to multiple sensed values having multiple predetermined values. Referring now to FIGS. 2A and 3, an example of a subsystem utilizing multiple values is the oil lift system 36. In the exemplary oil lift system 36, as discussed above with FIG. 3, the rate of oil flow provided by the flowmeter 98 is corrected based on the oil temperature provided by the temperature detector 102. The rate of oil flow is well-known as a direct function of oil temperature. The exemplary processor 44 uses the sensed temperature to index a lookup table in memory 50 and determine a correction factor for the sensed oil flow. The processor 44 then multiplies the sensed oil flow by the correction factor, in order to obtain a corrected oil flow value at a standard temperature. Alternatively, as discussed above, no temperature correction of the oil flow is provided. Regardless of whether temperature correction of the oil flow is provided, an indication of an oil line problem is provided by a step change in the oil flow sensed by the flowmeter 98, a step change in the oil pressure sensed by the pressure transducer 104, or by step changes in both the oil flow and the oil pressure. An indication of an oil leak (e.g., a cracked or broken oil line) is provided by a step increase in the oil flow and a step decrease in the oil pressure. Similarly, an indication of an oil line blockage is provided by a step decrease in the oil flow. In either case of a breakage or a blockage, the sensed pressure and sensed flow must be outside of the corresponding acceptable predetermined range for a new or newly refurbished motor. The predicted time (M) for motor maintenance, in either case, is determined from a minimum of the individual times determined by pressure and flow. Furthermore, the above described report also includes an identification of whether there was a breakage or a blockage. Continuing to refer to FIG. 3, an overall condition of the oil lift system 36, such as an oil line blockage or breakage, may also be determined. Expected changes in oil flow and oil pressure are empirically predetermined for various conditions of the oil lift system 36. These predetermined changes include an expected flow change (F.sub.T) for a blocked oil line (e.g., line 86), an expected flow change (F.sub.S) for two or more blocked spray nozzles (e.g., nozzles 74), an expected flow change (F.sub.O) for an open oil line (e.g., line 86), and an expected pressure change (P.sub.O) for an open oil line (e.g., line 86). Baseline values (B.sub.F,B.sub.P,B.sub.T) and deadband values (D.sub.F,D.sub.P,D.sub.T) are also empirically determined for sensed oil flow, oil pressure and oil temperature (S.sub.F,S.sub.P,S.sub.T) from the corresponding sensors 98,104,102, respectively. A breakage condition, such as a completely open or broken oil line (e.g., line 86 or line 88) is generally indicated whenever sensed oil flow (S.sub.F) exceeds the sum of the flow baseline and deadband values (i.e., B.sub.F +D.sub.F) and whenever sensed pressure (S.sub.P) is less than the difference of the pressure baseline and deadband values (i.e., B.sub.P -D.sub.P). Alternatively, whenever sensed pressure (S.sub.P) is within the pressure deadband range of the pressure baseline (i.e., (B.sub.P -D.sub.P).ltoreq.S.sub.P .ltoreq.(B.sub.P +D.sub.P)), then the possibility of a blocked condition is examined. In this case, whenever the sensed oil flow (S.sub.F) is less than the difference of the flow baseline and the expected flow change (F.sub.T) for a blocked oil line (i.e., S.sub.F <(B.sub.F -F.sub.T)), a blockage of a shoe oil line (e.g., line 86) is indicated. Similarly, whenever the sensed oil flow (S.sub.F is less than the difference of the flow baseline and the expected flow change (F.sub.S) for multiple blocked spray nozzle lines (i.e., S.sub.F <(B.sub.F -F.sub.S)), a blockage of two or more spray nozzles (e.g., nozzles 74) is indicated. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
claims | 1. A method of forming a low-dose (LDR) brachytherapy device, the method comprising:forming a plurality of substrates having a water-insoluble form of a radioactive material thereon; andpositioning the plurality of substrates on a carrier core; andforming a medical device from the carrier core and the plurality of substrates, wherein forming the plurality of substrates having the water-insoluble form of the radioactive material thereon comprises:depositing a solution comprising a soluble form of a radioactive material on a substrate; andconverting the soluble form of the radioactive material to a water-insoluble form of the radioactive material on the substrate, andwherein converting the soluble form of the radioactive material to a water insoluble form of the radioactive material comprises exposing the substrate and the water-soluble form of the radioactive material to plasma thereby decomposing the soluble form of the radioactive material to a water-insoluble form of the radioactive material. 2. The method of claim 1, wherein the plasma comprises hydrogen plasma and/or an oxygen plasma. 3. The method of claim 2, wherein the hydrogen or oxygen plasma is at atmospheric pressure or in a partial vacuum. 4. The method of claim 2, wherein the soluble form the radioactive material comprises a salt of Pd-103. 5. The method of claim 4, wherein the salt of Pd-103 comprises tetraaminopalladium chloride. 6. The method of claim 1, wherein the substrate comprises a polymer substrate. 7. The method of claim 1, wherein forming a medical device comprises enclosing the substrates, the carrier core and the water-insoluble form of the radioactive material with a biocompatible material. 8. The method of claim 1, wherein depositing a solution comprising a soluble form of a radioactive material on a substrate comprises depositing an array of spaced-apart globules of the soluble form of the radioactive material on the substrate. 9. The method of claim 8, wherein the substrate comprises micro-wells, and the array of spaced-apart globules are deposited in at least some of the micro-wells on the substrate. 10. The method of claim 8, wherein the substrate is substantially planar. 11. The method of claim 8, wherein forming a medical device from the carrier core and the plurality of substrates comprises:adhering a polymer sheet on the substrate and the water-insoluble form of the radioactive material; andsizing elongated portions of the carrier core to thereby form a brachytherapy strand. 12. The method of claim 11, wherein forming a medical device from the substrate and the water-insoluble form of the radioactive material comprises:positioning the brachytherapy strand in a biocompatible tube;filling the tube with a curable thermoplastic resin; andcuring the thermoplastic resin such that the radioactive material is sealed. 13. The method of claim 1, wherein the solution comprises a soluble form of Pd-103 comprising [Pd(NH3)4]Cl2 and/or PdCl2. 14. The method of claim 13, wherein the solution comprises [Pd(NH3)4]Cl2 dissolved in ammonium hydroxide (NH4OH) and/or PdCl2 dissolved in HCl. 15. The method of claim 1, wherein the radioactive material comprises I-125. 16. The method of claim 1, further comprising coating the plurality of substrates with a biocompatible coating. 17. The method of claim 16, wherein the biocompatible coating comprises a polyurethane sleeve. 18. The method of claim 17, wherein the polyurethane sleeve has a thickness greater than 150 micrometers. 19. The method of claim 1, wherein depositing the solution comprises depositing discrete, spaced-apart globules of the solution using a solenoid dispensing system having a controlled pressurized fluid source, a micro-syringe pump and/or micropipette. 20. The method of claim 19, wherein a volume for each of the globules is between 5 and 500 nanoliters. 21. The method of claim 19, further comprising depositing the respective volumes of the globules to an accuracy of 10% of an intended volume. 22. The method of claim 19, wherein the globules are spaced apart by about 500-1000 μm. 23. The method of claim 1, wherein each of the substrates is an elongated body. 24. The method of claim 1, wherein depositing a solution comprising a soluble form of a radioactive material on a substrate comprises depositing spaced-apart globules of the soluble form of the radioactive material, wherein the globules have a volume of about 30-200 nanoliters. |
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abstract | An ion implantation system having a dose cup located near a final energy bend of a scanned or ribbon-like ion beam of a serial ion implanter for providing an accurate ion current measurement associated with the dose of a workpiece or wafer. The system comprises an ion implanter having an ion beam source for producing a ribbon-like ion beam. The system further comprises an AEF system configured to filter an energy of the ribbon-like ion beam by bending the beam at a final energy bend. The AEF system further comprises an AEF dose cup associated with the AEF system and configured to measure ion beam current, the cup located substantially immediately following the final energy bend. An end station downstream of the AEF system is defined by a chamber wherein a workpiece is secured in place for movement relative to the ribbon-like ion beam for implantation of ions therein. The AEF dose cup is beneficially located up stream of the end station near the final energy bend mitigating pressure variations due to outgassing from implantation operations at the workpiece. Thus, the system provides accurate ion current measurement before such gases can produce substantial quantities of neutral particles in the ion beam, generally without the need for pressure compensation. Such dosimetry measurements may also be used to affect scan velocity to ensure uniform closed loop dose control in the presence of beam current changes from the ion source and outgassing from the workpiece. |
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048030414 | summary | BACKGROUND OF THE INVENTION The invention relates to a process for the recycling of nuclear fuels contained in a first metal can, within which said pellets have previously been irradiated in a fast neutron nuclear reactor. In fast neutron nuclear reactors, the fissile material is in the form of pellets, normally constituted by a mixed uranium and plutonium oxide (UO.sub.2, PuO.sub.2). These pellets are stacked within metal cans to form the nuclear fuel rods. These rods are arranged in bundles in sleeves with a hexagonal cross-section, so as to form nuclear fuel assemblies. When a new assembly is placed in a fast neutron nuclear reactor core, there is a certain radial clearance between the nuclear fuel pellets and the cans containing said pellets. This initial clearance is provided to take account of the swelling of the pellets occurring under irradiation and to ensure a satisfactory introduction of the oxide pellets into the can during production. Moreover, the irradiation time of the assemblies in the core of a fast neutron nuclear reactor is limited by the deformation undergone by the fuel rod and the hexagonal tube, said deformations being essentially caused by the swelling of the steel. In the present state of the art, the nuclear fuel assemblies are then dismantled, the rods cut up and the fuel removed. These operations obviously take a long time and are very expensive, the latter particularly penalizing the costs of the fuel cycle of fast neutron nuclear reactors. The present invention is based on the observation that when the irradiated assemblies are removed as a result of the swelling of the cans, the combustion level of the fuel pellets is low compared with the combustion possibilities intrinsically offered by said fuel. In the particular case of a fast neutron clear reactor comprising a zero reactivity drop core, such as is proposed in French patent applications Nos. 84 12123 and 85 01203, reprocessing would be considerably spaced if the irradiation time of the assemblies was not limited by the swelling of the cans. It would therefore appear that the limitation of the irradiation time of the assemblies imposed by the swelling of the cans leads to a mediocre exploitation of the possibilities offered by the actual fuel. In particular, the reprocessing of the fuel after a single irradiation period of limited duration is not justified and considerably increases operating costs. SUMMARY OF THE INVENTION The present invention relates to a process making it possible to recycle nuclear fuel pellets after they have undergone one or more irradiations. Thus, the reprocessing of the fuel can be eliminated or limited to the fuel which has reached very high combustion levels and namely roughly three times those presently achieved following a single irradiation. This leads to a considerable drop in operating costs. The present invention therefore proposes a process for the recycling of nuclear fuel pellets contained in a first metal can in which these pellets have previously been irradiated in a fast neutron nuclear reactor, wherein the process comprises extracting the pellets from the first can and introducing them into a new metal can having a slightly larger internal diameter than that of the first can. According to a preferred embodiment of the invention, the pellets are extracted from the first can by progressively melting the latter from one of its ends, the thus exposed pellets then being introduced immediately into the new can. Preferably, the first can is then melted by means of a coil supplied by a high frequency electric current producing a thermal skin effect by induction. In order to ensure that the melted can does not stick again to the remainder of the can, the melted part of the can is removed either by means of a refractory material deflector to which the first can only adheres after melting, or by blowing a neutral gas onto the melted part of the can. According to another feature of the invention, the introduction of the pellets into the new can is facilitated by preheating the latter. Moreover, to limit contamination of the new can, it is preferable to place the latter within a sleeve. |
description | This patent application is a continuation-in-part application claiming priority under 35 U.S.C. § 120 from prior co-pending U.S. patent application Ser. No. 15/898,308, filed on Feb. 16, 2018, which claims the benefit of U.S. provisional patent application Ser. No. 62/472,659, filed on Mar. 17, 2017. The content of U.S. application Ser. No. 15/898,308 and 62/472,659 are incorporated-by-reference herein in their entireties. This invention was made with government support under Contract No. DE-NE0008222 awarded by the Department of Energy. The U.S. Government has certain rights in this invention. The invention relates to fuels for nuclear reactors, and more particularly to methods of improving water resistance of nuclear fuels. Uranium dioxide (UO2) is currently the primary uranium compound used in nuclear fuel worldwide. Efforts to enhance the safety and performance of light water reactors is behind research into alternative accident tolerant fuels. Several high density uranium fuels have been considered for use in existing light water reactors. One promising fuel is uranium silicide (U3Si2) due to its high uranium density (17% higher than UO2), high thermal conductivity, and high melting temperature (1665° C.). See K. E. Metzger et al., Model of U3Si2 Fuel System Using Bison Fuel Code, Proceedings of ICAPP, Apr. 6-9, 2014, Paper No. 14343, pp. 1-5. However, recent testing has shown that U3Si2 may suffer from some situational problems and therefore may require additional features to remedy these potential problems. A method of protecting fissile material from oxidation due to exposure to water or steam is described herein. It has been found while that many nuclear fuels have good water resistance at 300° C. similar to widely used fissile materials such as UO2, as water temperature increases, the grain boundaries of many nuclear fuels are preferentially attacked by water and steam. Recent testing indicates that such vulnerable fuel compositions, such as U3Si2, suffer excess oxidation at temperatures higher than 360° C. and will be completely oxidized in steam below 600° C. in a short period of time as shown in FIG. 1, a graph showing the results of thermogravitational analysis of U3Si2 in the water vapor atmosphere. Thermogravitational (TG) analysis is commonly used to determine selected characteristics of materials that exhibit either mass loss or gain due to, for example, decomposition or oxidation as a function of temperature. Commercially available TG analyzers continuously weigh a sample as it is heated to a target temperature, up to about 2000° C. As the temperature increases, various components of the sample are decomposed or oxidized and the weight percentage of each resulting mass change can be measured. Results are plotted with temperature on the X-axis and total mass change on the Y-axis. Significant changes in mass during heating indicates that the material is no longer thermally stable. With mass change of 16.87%, as shown in FIG. 1, U3Si2 completely oxidizes into uranium oxides (UO2 and U3O8). The oxidation of the fission material could lead to significant safety concerns in design basis accidents such as a loss of coolant accident and hypothetical reactivity insertion accidents. A method to protect fissile material from oxidation, in various aspects, comprises coating the fissile material. Coating U3Si2 pellets or protecting the U3Si2 grain boundaries, for example, will prevent pellet fragmentation and excess oxidation of the pellets by the coolant following leakage through the cladding barrier onto the fuel during reactor operation and by high temperature steam in design basis accident conditions if a cladding break occurs. To improve the water and steam oxidation resistance of U3Si2 or other suitable fissile materials at temperatures higher than 360° C., a water resistant coating is applied to the surface of the material using any suitable coating method. Exemplary coating methods include atomic layer deposition, thermal spray techniques such as plasma arc spray and physical vapor depositions, chemical vapor deposition, electroless plating, and electroplating. The coating materials may be any material that will coat, i.e., adhere to, the surface of the fissile material of choice, not react with the fissile material, have a solubility at least as low as and preferably less than that of UO2, and be flexible enough to remain substantially in place, not spall from the U3Si2, as the fissile material swells in use. To enhance commercial viability, the coating material is preferably easy to apply. In various aspects, a suitable coating material may be selected from the group consisting of ZrSiO4, FeCrAl, Cr, Zr, Al—Cr, CrAl, ZrO2, CeO2, TiO2, SiO2, UO2, ZrB2, Na2O—B2O3—SiO2—Al2O3 glass, Al2O3, Cr2O3, carbon, SiC, Ni, Cr, and combinations thereof. A nuclear fuel material is also described. The material comprises a fissile material, such as U3Si2, coated with a water resistant layer. The coating layer, in various aspects, may be selected from the group consisting of ZrSiO4, FeCrAl, Cr, Zr, Al—Cr, CrAl, ZrO2, CeO2, TiO2, SiO2, UO2, ZrB2, Na2O—B2O3—SiO2—Al2O3 glass, Al2O3, Cr2O3, carbon, SiC, Ni, Cr, and combinations thereof. The water resistant coating may lie beneath an integral fuel burnable absorber (IFBA) layer for controlling the core reactivity in nuclear reactor operation. The IFBA layer may be a thin layer of a zirconium compound, such as zirconium diboride (ZrB2), a boron compound, such as B2O3—SiO2 glass, and combinations of a zirconium compound and a boron compound. See for example, U.S. Pat. No. 4,751,041, incorporated herein by reference. As used herein, the singular form of “a”, “an”, and “the” include the plural references unless the context clearly dictates otherwise. Thus, the articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element. Directional phrases used herein, such as, for example and without limitation, top, bottom, left, right, lower, upper, front, back, and variations thereof, shall relate to the orientation of the elements shown in the accompanying drawing and are not limiting upon the claims unless otherwise expressly stated. In the present application, including the claims, other than where otherwise indicated, all numbers expressing quantities, values or characteristics are to be understood as being modified in all instances by the term “about.” Thus, numbers may be read as if preceded by the word “about” even though the term “about” may not expressly appear with the number. Accordingly, unless indicated to the contrary, any numerical parameters set forth in the following description may vary depending on the desired properties one seeks to obtain in the compositions and methods according to the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter described in the present description should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Further, any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include any and all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. A method of forming a water resistant boundary on fissile material for use in a water cooled nuclear reactor comprises coating the fissile material to a desired thickness with a suitable coating material. The fissile material may be any suitable fissile material. U3Si2 is an exemplary fissile material for this process, and for the reasons expressed above, is a preferred material in many aspects. Although the coating method described herein may be used with other fissile materials, such as UO2 and others listed below, for convenience, the fissile material may be referred to as U3Si2. Suitable fissile materials can comprise a uranium-containing ceramic fissile material. The uranium-containing ceramic fissile material can comprise, for example, uranium silicides (e.g., UU3Si2, U3Si5, U3Si); uranium nitrides (e.g., UN, U15N); uranium carbides (e.g., UC); uranium borides (e.g., UBx, UB2, UB4), where X is an integer (metal borides (e.g., uranium borides) may have a wide variety of metal:boron ratios); uranium phosphides (e.g., UP); uranium sulfides (e.g., US2); uranium oxides (e.g., UO2, UCO); or mixtures of any of these. As a promising candidate for next generation fuel, U3Si2 offers: 1. a higher thermal conductivity than UO2; 2. a higher uranium loading than UO2; and 3. a melting temperature that allows the fuel to stay solid under light water reactor normal operating and transient conditions. To counter the poor water resistance of U3Si2 at higher temperatures (e.g., 360° C. and above), in various aspects, a water resistant coating may be applied to one or both of U3Si2 pellets and the U3Si2 grain boundaries, which will prevent, or at least substantially slow, the contact of U3Si2 with water and therefore improves the water resistance of the fuel pellets if a leak in the fuel cladding occurs. The coating material in various aspects, should form a robust coating over at least the exposed portions of the fissile material, such as on the pellets and grain boundaries. The term “robust coating”, as used herein, is a coating that has low solubility in coolant, is easy to apply, does not react with the fissile material of choice, and has some flexibility as the pellet swells during irradiation. A “low solubility” as used herein is a relative term and means for purposes of this application that the solubility of the coating material is at least as low as, and in various aspects, less than, the solubility of UO2 when UO2 is used as a fissile material. The coating materials may be any material that will coat, i.e., adhere to, the surface of the fissile material of choice and not react with the fissile material. As stated, the coating material in various aspects, has a solubility at least as good as, and preferably less than, that of UO2. Solubility values for UO2 are available in the literature. In various aspects, the coating material is flexible enough to remain substantially in place as the fissile material swells in use. Those skilled in the art understand that fissile material swells in use because as fission occurs, the original atom forms two atoms of less dense material than the original atom. In addition, gas may be trapped at the grain boundaries which will cause more swelling. Those skilled in the art can calculate roughly the degree of swelling, but because of the trapped gas, swelling calculations in advance of use in a reactor may not be precise. The coating should be sufficiently flexible to avoid delamination as the fissile material swells. Some deviation, however, may be tolerated allowing a crack or delaminated portion in the coating upon swelling of the fissile material. In such instances, the coating still functions to reduce the exposure of the fissile material to the water or steam, thereby slowing oxidation and contributing to the useful life of the fissile material. Reducing the rate of oxidation of the fissile material in the event of exposure to water or steam will allow time for corrective action in the event of a beyond design basis accident. In various aspects, a suitable coating material may be selected from the group consisting of ZrSiO4, FeCrAl, Cr, Zr, Al—Cr, CrAl, ZrO2, CeO2, TiO2, SiO2, UO2, ZrB2, Na2O—B2O3—SiO2—Al2O3 glass, Al2O3, Cr2O3, carbon, SiC, Cr, Ni, and combinations thereof. Coating of the U3Si2 grains can be accomplished by adding FeCrAl, CrAl, or Na2O—B2O3—SiO2—Al2O3 glass solids to the U3Si2 powder that melt at temperatures less than U3Si2 (1662° C.) but at the sintering temperature of the U3Si2 pellets (1200 to 1600° C.). In various aspects, the coating may be formed by deposition of particles selected from the group consisting of ZrSiO4, FeCrAl, Cr, Zr, Al—Cr, CrAl, ZrO2, CeO2, TiO2, SiO2, UO2, ZrB2, Na2O—B2O3—SiO2—Al2O3 glass, Al2O3, Cr2O3, carbon, SiC, Ni, Cr, and combinations thereof. Each of these materials has better water resistance than U3Si2. A coating can be applied to each U3Si2 pellet's circumferential, or side, surface and optionally applied to its top and bottom surfaces. Fuel pellets may be any shape and reference to circumferences or other surface contours are for convenience and are not limiting. In use, fuel pellets are typically in the form of generally cylindrical pellets stacked on end to form a generally cylindrical column which is held against the end plug of a fuel rod by means of a spring at the top end of the stack of pellets in the rod positioned between the top pellet and the top end plug of the fuel rod. In this configuration, the tops and bottoms of the pellets are not exposed to any water that might leak into the fuel rod. Any exposure to oxidizing fluids, if at all, will be minimal. To enhance commercial viability, the coating material is preferably easy to apply. The coating step used in the method may be any suitable coating process. For example, coating may be done by a physical vapor deposition process or by atomic layer deposition (ALD). The coating process may, for example, be a thermal spray process, such as a hot or cold spray process or a plasma arc spray process. Atomic Layer Deposition (ALD) is a thin film deposition method in which a film is grown on a substrate by exposing its surface to alternate gaseous species. ALD is based on the sequential use of a gas phase chemical process. The majority of ALD reactions use two chemicals, called precursors. These precursors react with the surface of a material one at a time in a sequential, self-limiting, manner, so that the reaction terminates once all the reactive sites on the surface are consumed. Consequently, the maximum amount of material deposited on the surface after a single exposure to all of the precursors (a so-called ALD cycle) is determined by the nature of the precursor-surface interaction. Through the repeated exposure to separate precursors, a thin film is slowly deposited. By varying the number of cycles it is possible to grow materials uniformly and with high precision on arbitrarily complex and large substrates. In contrast to chemical vapor deposition, the precursors are never present simultaneously in the deposition chamber, but they are inserted as a series of sequential, non-overlapping pulses. In ALD, the water resistant coating would be grown on the U3Si2 pellet surface by exposing the U3Si2 pellet to gaseous precursors of the desired coating material. The precursors chosen for the deposition also contain a carrier gas. The temperature used in the deposition may range from 25° C. to 600° C., preferably from 200° C. to 450° C., and more preferably from 265° C. to 350° C., or other temperatures with any of the foregoing ranges. Temperatures greater than 600° C. should be avoided. Alternatively, deposition of the coating may be by sputtering or chemical vapor deposition. In a typical chemical vapor deposition process, the substrate is exposed to one or more reactive precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, by-products are also produced, which are removed by gas flow through a reaction chamber. A suitable thermal deposition method, in various aspects, includes either a hot spray or cold spray methods. In a hot thermal spray process, the coating feedstock material is melted by a heat source or by plasma created by a high frequency arc between an anode and a tungsten cathode (i.e. plasma arc spray). This softened liquid or molten material is then carried by process gas and would be sprayed onto the surface U3Si2 pellets. On the U3Si2 pellet surface, this material solidifies and forms a solid layer. A cold spray method may proceed by delivering a carrier gas to a heater where the carrier gas is heated to a temperature sufficient to maintain the gas at a desired temperature, for example, from 100° C. to 1200° C., after expansion of the gas as it passes through the nozzle. In various aspects, the carrier gas may be pre-heated to a temperature between 200° C. and 1200° C., with a pressure, for example, of 5.0 MPa. In certain aspects, the carrier gas may be pre-heated to a temperature between 200° C. and 1000° C., or in certain aspects, 300° C. and 900° C. and in other aspects, between 500° C. and 800° C. The temperature will depend on the Joule-Thomson cooling coefficient of the particular gas used as the carrier. Whether or not a gas cools upon expansion or compression when subjected to pressure changes depends on the value of its Joule-Thomson coefficient. For positive Joule-Thomson coefficients, the carrier gas cools and must be preheated to prevent excessive cooling which can affect the performance of the cold spray process. Those skilled in the art can determine the degree of heating using well known calculations to prevent excessive cooling. See, for example, for N2 as a carrier gas, if the inlet temperature is 130° C., the Joule-Thomson coefficient is 0.1° C./bar. For the gas to impact the tube at 130° C. if its initial pressure is 10 bar (˜146.9 psia) and the final pressure is 1 bar (˜14.69 psia), then the gas needs to be preheated to about 9 bar*0.1° C./bar or about 0.9 C to about 130.9° C. For example, the temperature for helium gas as the carrier is preferably 450° C. at a pressure of 3.0 to 4.0 MPa, and the temperature for nitrogen as the carrier may be 1100° C. at a pressure of 5.0 MPa, but may also be 600° C.-800° C. at a pressure of 3.0 to 4.0 MPa. Those skilled in the art will recognize that the temperature and pressure variables may change depending on the type of the equipment used and that equipment can be modified to adjust the temperature, pressure and volume parameters. Suitable carrier gases are those that are inert or are not reactive, and those that particularly will not react with the particles or the substrate. Exemplary carrier gases include nitrogen (N2), hydrogen (H2), argon (Ar), carbon dioxide (CO2), and helium (He). There is considerable flexibility in regard to the selected carrier gases. Mixtures of gases may be used. Selection is driven by both physics and economics. For example, lower molecular weight gases provide higher velocities, but the highest velocities should be avoided as they could lead to a rebound of particles and therefore diminish the number of deposited particles. The cold spray process relies on the controlled expansion of the heated carrier gas to propel the particles onto the substrate. The particles impact the substrate or a previous deposited layer and undergo plastic deformation through adiabatic shear. Subsequent particle impacts build up to form the coating. The particles may also be warmed to temperatures one-third to one-half the melting point of powder expressed in degrees Kelvin before entering the flowing carrier gas in order to promote deformation. The nozzle is rastered (i.e., sprayed in a pattern in which an area is sprayed from side to side in lines from top to bottom) across the area to be coated or where material buildup is needed. Referring to FIG. 3, a thermal spray assembly 10 is shown. Assembly 10 includes a heater 12, a powder or particle hopper 14, a gun 16, nozzle 18 and delivery conduits 34, 26, 32 and 28. High pressure gas enters conduit 34 for delivery to heater 12, where heating occurs quickly; substantially instantaneously. When heated to the desired temperature, the gas is directed through conduit 26 to gun 16. Particles held in hopper 14 are released and directed to gun 16 through conduit 28 where they are forced through nozzle 18 towards the substrate 22 by the pressurized gas jet 20. The sprayed particles 36 are deposited onto substrate 22 to form a coating comprised of particles 24. This process generally describes both cold spray and hot spray assemblies. The hot spray process occurs at a temperature hot enough to soften or melt the particles being deposited. An alternative coating method, in various aspects, includes a plasma arc spray process, such as that shown in FIG. 4. A plasma torch 40 generates a hot gas jet 50. A typical plasma torch 40 includes a gas port 56, a cathode 44, an anode 46, and a water cooled nozzle 42, all surrounded by an insulator 48 in a housing 68. A high frequency arc is ignited between the electrodes, i.e., between the anode 46 and a tungsten cathode 44. A carrier gas flowing through the port 56 between the electrodes 44/46 is ionized to form a plasma plume. The carrier gas may be helium (He) hydrogen (H2), nitrogen (N2), or any combination thereof. The jet 50 is produced by an electric arc that heats the gas as the pressurized gas expands through nozzle 42. The heated gas forms an arc plasma core which operates, for example, at 12,000° C. to 16,000° C. The gases expand as a jet 50 through the water cooled nozzle 42. Powders, or particles, are injected through ports 52 into the hot jet 50 where they are softened or melted, and forced onto the substrate 60 to form a coating 54. The rate of spray may be, for example, from 2 to 10 kg/hour at a particle velocity of about 450 m/s or less. The coating thickness achieved with thermal sprays, such as plasma arc sprays, varies depending on the material sprayed, but can range, for example, from 0.005 to 5 mm. A typical thickness for the coatings described herein may be from 5 to 1000 microns, and in various aspects, the thickness of the coating may be from 10 to 100 microns. The thickness of the water-resistant coating varies from 10 microns to 200 microns for plasma arc spray applied coatings, and 1 micron to 20 microns for physical vapor deposited coatings and from 0.5 microns to 2 microns for ALD. The coating materials include ZrSiO4, FeCrAl, Cr, Zr, Al—Cr, CrAl, ZrO2, CeO2, TiO2, SiO2, UO2, ZrB2, Na2O—B2O3—SiO2—Al2O3 glass, Al2O3, Cr2O3, carbon, and SiC, and combinations thereof. U3Si2 has less cracking compared to UO2 in operation due to a much higher thermal conductivity. Even if cracking is developed, the coating can still cover substantial surface area of U3Si2 pellet to prevent it from excess oxidation. The water-resistant coating may also be applied via an electroless plating coating technique. The electroless plating coating technique can comprise submerging the object to be coated (e.g., the substrate, a fissile material) in a chemical bath comprising metal cations. The metal cations can be chemically reduced to form a metallic coating on the substrate. The reduction may be accomplished via an autocatalytic reaction between the metal cations and a reducing agent such as hypophosphite and/or borohydride. The chemical bath may also comprise one or more of the following: a complexing agent (to increase phosphate solubility and/or to slow the reaction), a stabilizer, (to slow the reduction by co-depositing with the reduced metal), a buffer, (to maintain the acidity of the bath), a brightener (to improve the surface finish), a surfactant, (to keep the deposited layer hydrophilic in order to reduce pitting and staining), and an accelerator (to counteract the reduction of plating rate caused by complexing agents). The surface of the substrate may be activated prior to the electroless plating process in order to ensure that the autocatalytic reduction process can proceed. When the electroless plating coating technique is employed, the water-resistant coating can comprise metallic nickel (Ni) and/or metallic chromium (Cr). Thus, the metal cations in the chemical bath may comprise one or both of Ni cations or Cr cations. The electroless plating coating technique can be used to apply a water-resistant coating onto any fissile material of the present disclosure. A water-resistant coating applied to a fissile material of the present disclosure via an electroless plating coating technique can comprise a thickness of 5 microns to 20 microns such as, for example, 5 microns to 15 microns, 5 microns to 10 microns, 10 microns to 20 microns, 10 microns to 15 microns, or 15 micron to 20 microns. Referring to FIG. 2, described below, the water-resistant coating 74 may also comprise Ni and/or Cr as described above. The water-resistant coating may also be applied via an electroplating coating technique. The electroplating coating technique can comprise creating a water-resistant metal coating on the object to be coated (e.g., the substrate, a fissile material) via the reduction of metal cations by a direct electric current. The metal cations can be reduced to form a metallic coating on the substrate. The substrate can act as the cathode of an electrolytic cell, and the anode can comprise the metal to be applied as a coating and/or an inert conductive material. An electrolyte solution can be in contact with the substrate and can comprise a salt solution comprising metal cations to be reduced and coated onto the substrate. The substrate can be electrically conductive. When the electroplating coating technique is employed, the water-resistant coating can comprise metallic nickel (Ni) and/or metallic chromium (Cr). Thus, the metal cations in the electrolyte solution may comprise one or both of Ni cations or Cr cations. The electroplating coating technique can be used to apply a water-resistant coating onto any fissile material of the present disclosure. The fissile material can comprise an electrically conductive fissile material. A water-resistant coating applied to a fissile material of the present disclosure via an electroless plating coating technique can comprise a thickness of 1 micron to 20 microns such as, for example, 1 micron to 5 microns, 2 microns to 20 microns, 3 microns to 20 microns, 4 microns to 20 microns, 5 microns to 20 microns, 5 microns to 15 microns, 5 microns to 10 microns, 10 microns to 20 microns, 10 microns to 15 microns, or 15 micron to 20 microns. Referring to FIG. 2, described below, the water-resistant coating 74 may also comprise Ni and/or Cr as described above. In addition, burnable absorbers can also be coated by using either an ALD process or a thermal spray process on the circumferential surface of the coated U3Si2 pellets. The integral fuel burnable absorber may be a thin layer of a zirconium compound, such as zirconium diboride (ZrB2), a boron compound, such as B2O3—SiO2 glass, and combinations of a zirconium compound and a boron compound coated on the fuel pellets following application of the water resistant coating layer. See for example, U.S. Pat. No. 4,751,041, incorporated herein by reference. Burnable absorbers are a type of burnable poison used to control the core reactivity in nuclear reactor operation. These burnable absorbers provide temporary reactivity control primarily effective during the beginning of a reactor cycle and compensates for the excess reactivity present early in cycle due to the loading of fresh fuel. The layer of burnable absorber material is applied after the water resistant layer is applied, so that it overlays the water resistant coating layer. Oxidation of U3Si2 is a potential safety concern and one of the key issues for implementation of U3Si2 fuel in light water reactors. Coating on U3Si2 will slow down oxidation especially at higher steam temperatures, and is one of the economic methods to solve the potential safety concerns. The method as described herein produces coated fissile material, such as a coated fuel pellet shown in FIG. 2. A plurality of pellets are typically stacked in a fuel rod 70. The fissile material 72 in various aspects comprises U3Si2 coated with a water resistant layer 74 selected from the group consisting of ZrSiO4, FeCrAl, Cr, Zr, Al—Cr, CrAl, ZrO2, CeO2, TiO2, SiO2, UO2, ZrB2, Na2O—B2O3—SiO2—Al2O3 glass, Al2O3, Cr2O3, carbon, SiC, Ni, Cr, and combinations thereof. The fuel pellet may also comprise an overlayer 76 of a burnable absorber material, such as zirconium diboride (ZrB2), a boron compound, such as B2O3—SiO2 glass, and combinations of a zirconium compound and a boron compound. There may be a gap 78 filled with a gas, such as helium, between the overlayer 76 and the fuel cladding 80. The exterior of the cladding 80 is surrounded by a coolant 82, typically water in a water cooled reactor. Various aspects of the subject matter described herein are set out in the following examples. Example 1—A method comprising: coating a fissile, uranium-containing ceramic material with a water-resistant layer, the layer being non-reactive with the fissile, uranium-containing ceramic material, wherein the coating is applied to a surface of the fissile, uranium-containing ceramic material. Example 2—The method recited in Example 1, wherein the fissile, uranium-containing ceramic material comprises a uranium silicide, a uranium nitride, a uranium carbide, a uranium boride, a uranium phosphide, a uranium sulfides, a uranium oxide, or combinations thereof. Example 3—The method recited in Example 1 or 2, wherein the fissile, uranium-containing ceramic material comprises U3Si2, U3Si5, U3Si, UN, U15N, UC, UB2, UB4, UP, US2, UO2, UCO, or combinations thereof. Example 4—The method recited in any of Examples 1-3, wherein the fissile, uranium-containing ceramic material is in the form of a pellet. Example 5—The method recited in any of Examples 1-4, wherein the water resistant layer is selected from the group consisting of ZrSiO4, FeCrAl, Cr, Zr, Al—Cr, CrAl, ZrO2, CeO2, TiO2, SiO2, UO2, ZrB2, Na2O—B2O3—SiO2—Al2O3 glass, Al2O3, Cr2O3, carbon, SiC, Ni, Cr, and combinations thereof. Example 6—The method recited in any of Examples 1-5, wherein the coating is applied by atomic layer deposition. Example 7—The method recited in any of Examples 1-5, wherein the coating is applied by an electroless plating coating technique. Example 8—The method recited in any of Examples 1-5, wherein the coating is applied by a thermal spray process. Example 9—The method recited in Example 8, wherein the thermal spray process is physical vapor deposition. Example 10—The method recited in any of Examples 1-5, wherein the coating is applied by an electroplating coating technique, and wherein the fissile, uranium-containing ceramic material is electrically conductive. Example 11—The method recited in Example 8, wherein the thermal spray process is a plasma arc spray. Example 12—The method recited in Example 11, wherein the thickness of the coating is from 1 micron to 200 microns. Example 13—The method recited in Example 8, wherein the thermal spray process is a cold spray process. Example 14—The method recited in Example 8, wherein the thermal spray process is a hot spray process. Example 15—The method recited in any of Examples 1-14, further comprising applying a layer of burnable absorbers over the water resistant layer. Example 16—The method recited in Example 15, wherein the burnable absorbers are selected from the group consisting of ZrB2, B2O3—SiO2 glass, and combinations thereof. Example 17—A fuel for use in a nuclear reactor comprising: a fissile, uranium-containing ceramic material coated with a water-resistant layer, wherein the coating is applied to a surface of the fissile, uranium-containing ceramic material. Example 18—The fuel recited in Example 17, wherein the water-resistant layer is selected from the group consisting ZrSiO4, FeCrAl, Cr, Zr, Al—Cr, CrAl, ZrO2, CeO2, TiO2, SiO2, UO2, ZrB2, Na2O—B2O3—SiO2—Al2O3 glass, Al2O3, Cr2O3, carbon, SiC, Ni, Cr and combinations thereof. Example 19—The fuel recited in any of Examples 17-18, wherein the fissile, uranium-containing ceramic material comprises a uranium silicide, a uranium nitride, a uranium carbide, a uranium boride, a uranium phosphide, a uranium sulfides, a uranium oxide, or combinations thereof. Example 20—The fuel recited in any of Examples 17-19, wherein the fissile, uranium-containing ceramic material comprises U3Si2, U3Si5, U3Si, UN, U15N, UC, UB2, UB4, UP, US2, UO2, UCO, or combinations thereof. Example 21—The fuel recited in any of Examples 17-20, further comprising an integral fuel burnable absorber layer over the water resistant layer for controlling the core reactivity in nuclear reactor operation. Example 22—The fuel recited in Example 21, wherein the absorber layer is selected from the group consisting of ZrB2, B2O3—SiO2 glass, and combinations thereof. The present invention has been described in accordance with several examples, which are intended to be illustrative in all aspects rather than restrictive. Thus, the present invention is capable of many variations in detailed implementation, which may be derived from the description contained herein by a person of ordinary skill in the art. All patents, patent applications, publications, or other disclosure material mentioned herein, are hereby incorporated by reference in their entirety as if each individual reference was expressly incorporated by reference respectively. All references, and any material, or portion thereof, that are said to be incorporated by reference herein are incorporated herein only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. As such, and to the extent necessary, the disclosure as set forth herein supersedes any conflicting material incorporated herein by reference and the disclosure expressly set forth in the present application controls. The present invention has been described with reference to various exemplary and illustrative embodiments. The embodiments described herein are understood as providing illustrative features of varying detail of various embodiments of the disclosed invention; and therefore, unless otherwise specified, it is to be understood that, to the extent possible, one or more features, elements, components, constituents, ingredients, structures, modules, and/or aspects of the disclosed embodiments may be combined, separated, interchanged, and/or rearranged with or relative to one or more other features, elements, components, constituents, ingredients, structures, modules, and/or aspects of the disclosed embodiments without departing from the scope of the disclosed invention. Accordingly, it will be recognized by persons having ordinary skill in the art that various substitutions, modifications or combinations of any of the exemplary embodiments may be made without departing from the scope of the invention. In addition, persons skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the various embodiments of the invention described herein upon review of this specification. Thus, the invention is not limited by the description of the various embodiments, but rather by the claims. |
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051851245 | description | Corresponding reference numerals refer to like parts throughout the several views of the drawings. DETAILED DESCRIPTION The gauging apparatus of the present invention is applied in its embodiment to check the critical dimensional characteristics of cells 10 utilized in a nuclear fuel bundle spacer, generally indicated at 12 in FIG. 1, to establish the spacings between fuel rods 14 making up the bundle. Each cell may be of the type disclosed in commonly assigned, copending application entitled "Composite Spacer With Inconel grid and Zircaloy Band", U.S. Pat. No. 5,089,221, issued Feb. 18, 1991. As such, each cell is constructed having octagonally shaped end bands 15 interconnected by a pair of resilient legs which serve as springs 18. Two flat panels of each of the end bands are formed ends with inwardly projecting stops 16 in diametrically opposed relation to springs 18. When a fuel rod 14 is inserted through the cell, the springs act to bias the fuel rod against stops 16 to center it in the cell. When the cells are conjoined in matrix or egg crate array to create spacer 12, the stops of the multiplicity of cells also establish the spacings between fuel rods 14. Since rod to rod spacing Y in a fuel bundle is a critical dimension, the dimensional characteristics of the individual cells that contribute to the establishment of this spacing must be held to strict tolerances. The gauging apparatus of the present invention provides a convenient quality assurance check of these critical cell dimensional characteristics. Turning to FIG. 2, the gauging apparatus of the invention includes a fixture, generally indicated 20, having a planar base 22 and a pair of upstanding, parallel sidewalls 24 and 26 in perpendicular relation to the base. As seen in FIGS. 3 and 5, the separation W between the sidewalls is equal to the nominal cell width measured between diametrically opposed flat panels of the cell end bands 15, and the sidewall height is also equal to dimension W. To gauge the dimensional characteristics of a cell, it is placed in fixture 20. The corrected gauging position of the cell in the fixture is with the flat panels of the cell end bands between the two stop- containing panels resting squarely on fixture base 22. If it fits between sidewalls 24 and 26 with minimal play, its width dimension W in the horizontal direction is accepted. To check cell width W in the vertical direction, a plate 36 is placed across the tops of the fixture sidewalls 24, 26. If the cell fits between this plate and fixture base 22 with minimal play, this width dimension is accepted. As best seen in FIGURE 4, a pair of steps 28, upstanding from the fixture base, are separated by a distance L that is slightly greater than the nominal length of a cell. If a cell can assume a gauging position between steps 28 with minimal gaps between the cell ends and these steps, its length is considered acceptable. Referring to FIGS. 3 and 4, a pin 30 is then inserted though the cell bore defined by end bands 15. This pin is semicylinderical, such that its cylindrical surface portion 30a rests on stops 16 with its flat surface portion 30b well clear of springs 18 which are seen to be in their relaxed states. Thus, the springs do not press pin 30 against the stops, which would tend to distort the essentially free standing cell. The diameter of the cylindrical portion of pin 30 is equal to the nominal diameter of a fuel rod. It will be appreciated that such distortion can not occur when the cells are conjoined in spacer array. As seen in FIG. 1, the orientations of the cells in the spacer are such that only the flat band panels of adjacent cells are joined in abutting relation. Thus, it is the gap X between a fuel rod 14 and the exterior flat panel surface that establishes critical fuel rod spacing Y and in fact equals Y/2. Therefore, gap X established by stops 16 is a critical cell dimensional characteristic. To check this critical dimension, a pair of "go, no go" feeler gauges 32 and 34, seen in FIG. 4, are utilized. Feeler gauge 32 has a thickness equal to the minimum allowable gap X dimension, while feeler gauge 34 has a thickness slightly larger than the maximum allowable gap X dimension. Thus, if feeler gauge 32 can not be inserted through the gaps X between pin 30 and the fixture base and sidewalls, the minimum allowable gap dimensional requirement is not met, and the cell is disqualified. On the other hand, if feeler gauge 34 can be inserted through any one of the gaps, the cell fails the maximum allowable gap dimension requirement and is rejected. These gap dimensions are checked by the feeler gauges just beyond both ends of the cell, and fixture sidewall 26 is relieved, as indicated at 26a in FIG. 4, to facilitate introduction of the gauges. In practice, it is only necessary to gauge the gaps between the pin and the fixture base and between the pin and one fixture sidewall. If these gaps are in-tolerance, then the gaps between a fuel rod and the exterior surfaces of respectively diametrically opposed flat panels of the end bands 15 will also be in-tolerance. A fuel rod will thus be essentially centered in the cell, as is required to achieve requisite rod spacing throughout the spacer. Referring to FIG. 5, if the quality assurance checks of the flat panel gaps X indicate their dimensions to be in-tolerance, it remains to check the relaxed positions of the springs 18 as a gauge of whether they will exert adequate spring force to bias a fuel rod into a centered position in the cell against stops 16. To this end, plate 36 is placed across the top of fixture 20 to fully confine and thus maintain the shape of the cell, and a cylindrical pin 38 is then inserted through the cell to rest on stops 16. The diameter of this pin is selected to be sufficiently less than the fuel rod nominal diameter, such that springs 18 should lightly contact pin 38. If they do, it is determined that the springs, as formed, are in requisite relaxed positions to exert adequate centering forces on a fuel rod when inserted through the cell. However, if the springs do not contact pin 38, the cell is rejected for defective springs. FIG. 6 illustrates a gauging fixture 44 dimensioned such that separation W between its sidewalls 46 is equal to the nominal width, i.e., diameter, of a tubular spacer cell 48, such as disclosed in commonly assigned Matzner et al. U.S. Pat. No. 4,508,679. The height W of the sidewalls, measured from base 50, is also equal to the nominal cell diameter. Thus, when a cell 48 is placed in fixture 44, the sidewalls serve as a gauge of the cell diameter, as does a plate 50 resting on the top edges of the sidewalls. A pin 52 of a diameter equal to the nominal diameter of a fuel rod is inserted through the cell bore to rest on stops 54. "GO, no go" feeler gauges are then utilized to check the gaps between pin 52 and the base and between the pin and at least one sidewall of the fixture. Steps 28 on fixture base 50 gauge the cell length. The present invention thus provides gauging apparatus for facilitating the quality assurance inspection of individual spacer cells to determine that their dimensional characteristics are such that requisite fuel rod spacing will be achieved when the cells are assembled in a spacer array. With frequent utilization of the gauging apparatus, excursions in the cell manufacturing process trending toward out-of-tolerance fuel rod spacings can be detected early and corrected. The gauging apparatus can also play a role in refining the tooling to emphasize accuracy in imparting those dimensional characteristics to the cell that are critical to achieving acceptable fuel rod spacing. It is seen from the foregoing that the objectives set forth, including those made apparent from the preceding Detailed Description, are efficiently attained, and, since certain changes may be made in the construction set forth without departing from the scope of the invention, it is intended that all matters of detail be taken as illustrative and not in a limiting sense. |
abstract | A method for producing uniform activity targets according to an embodiment of the invention may include arranging a plurality of targets in a holding device having an array of compartments, each target being assigned to a compartment based on a known flux of a reactor core so as to facilitate an appropriate exposure of the targets to the flux based on target placement within the array of compartments. The holding device may be positioned within the reactor core to irradiate the targets. The method may be used to produce brachytherapy and/or radiography targets (e.g., seeds, wafers) in a reactor core such that the targets have relatively uniform activity. |
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041464311 | claims | 1. In an elongated slender nuclear fuel element for use in a nuclear reactor, the element being of cylindrical form and having a locally flexible metallic sheath, a plurality of close-fitting nuclear fuel pellets of non-enriched UO.sub.2 in end-to-end stacked array therein, said sheath being deformable under normal operating pressure within a reactor into both axial and peripheral pellet gripping relation, the majority of said pellets each having at least one end thereof recessed to provide axial expansion relief, to accommodate individual axial pellet expansion in operation and to substantially preclude longitudinal ratcheting of the sheath due to differential axial expansion between pellet and sheath, the improvement comprising a non-bonding lining layer interposed between the pellets and the sheath on the peripheral adjoining surfaces thereof to facilitate peripheral distribution of stresses in the sheath to substantially preclude longitudinally extending rupture failure of the sheath due to peripheral stresses operating over a minimal peripheral gauge length. 2. A fuel element according to claim 1 wherein said non-bonding layer is selected from the group consisting of graphite, siloxane and silicon. |
abstract | A method of early sensing of water leakage, through chemical concentration monitoring, in a nuclear reactor system using a liquid metal and molten salt, the method including: measuring an electrical conductivity and a mass spectrum of a first channel and a second channel of a heat-related device included in the nuclear reactor system using the liquid metal and the molten salt; calculating a first identification value associated with the water leakage in the heat-related device using the measured electrical conductivity; calculating a second identification value associated with the water leakage in the heat-related device using the measured mass spectrum; and sensing the water leakage by comparing a predetermined reference value and a summed identification value, the summed identification value being the sum of the first identification value and the second identification value. |
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056339011 | claims | 1. A permanent pool cavity seal for a containment arrangement including a wall defining a refueling pool floor and a refueling pool cavity extending about a nuclear reactor vessel having an annular flange thereabout, said permanent pool cavity seal comprising: an annular inner seal ring mounted on, and extending about, said nuclear reactor flange; an annular outer seal ring mounted on, and extending about, said refueling pool floor; an annular support ring upstanding from said outer seal ring, an annular seal plate having its outer periphery sealingly connected to said support ring and its inner periphery disposed above and closely adjacent said inner seal ring; a plurality of support arms disposed beneath said seal plate and extending radially from said refueling pool cavity wall to engage said seal plate at an intermediate transverse location of a bottom side thereof; and an annular flexible seal operative to accommodate thermally induced axial and radial expansion and contraction of said nuclear reactor vessel with respect to said refueling pool cavity wall, said flexible seal having a cross-section of substantial J-shape and being disposed substantially completely beneath said seal plate, said flexible seal being sealingly weldedly attached about one peripheral edge to said bottom side of said seal plate and about its other peripheral edge to said inner seal ring. 2. The permanent pool cavity seal according to claim 1 in which each of said seal plate, said support ring and said J-shaped flexible seal are formed from a plurality of circumferentially arranged arcuate members. 3. The permanent pool cavity seal according to claim 1 including a plurality of access holes extending through said seal plate at circumferentially spaced locations thereabout, and an access hole cover removably attached to each said access hole. 4. The nuclear containment arrangement of claim 1 wherein each support arm has at least a leveling screw to adjust the level of said seal plate. |
summary | ||
abstract | A device for submersibly cleaning surfaces inside a nuclear reactor includes a pump and a nozzle connected to said pump. The nozzle is arranged to face surfaces to be cleaned. The device includes cleaning means capable of removing debris on surfaces to be cleaned. The device includes adjustable flotation means, capable of adjusting the flotation capability of the device depending on a type of cleaning application. |
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043615058 | claims | 1. A process for treating a radioactive waste, which comprises mixing a radioactive liquid waste produced from radioactive material handling facilities with at least 2% by weight of a binder based on solid matter in the radioactive waste, said binder comprising an organosilicon monomer containing at least two different reactive groups in one molecule and being soluble or dispersible in the radioactive liquid waste, then drying the radioactive liquid waste containing said binder into powder, and shaping the powder containing the binder into pellets. 2. A process according to claim 1, wherein the radioactive liquid waste is mixed with an organosilicon monomer having a reactive group that is converted to a hydroxyl group by hydrolysis when dissolved in water and an organic functional group. 3. A process according to claim 2, wherein the radioactive liquid waste containing the binder is supplied into a vessel provided with a rotating shaft with blades therein, and the rotating shaft is revolved while heating the radioactive liquid waste, thereby making the radioactive liquid waste into powder. 4. A process according to claim 3, wherein the radioactive liquid waste is a radioactive liquid waste containing a sodium salt as a main component, and the radioactive liquid waste containing the sodium salt as a main component is mixed with the binder. 5. A process according to claim 2 or 4, wherein organosilicon monomer has an amine group. 6. A process according to claim 1, wherein the binder comprises said organosilicon monomer and colloidal silica in a mixing ratio of colloidal silica to the monomer of 0.1 to 1. 7. A process according to claim 6, wherein the the liquid organosilicon monomer has a reactive group that is converted to a hydroxyl group by hydrolysis when dissolved in water and an organic functional group. 8. A process according to claim 6, wherein the radioactive liquid waste containing the binder is supplied into a vessel provided with a rotating shaft with blades therein, and the rotating shaft is revolved while heating the radioactive liquid waste, thereby making the radioactive liquid waste into powder. 9. A process according to claim 8, wherein the radioactive liquid waste is a radioactive liquid waste containing a sodium salt as a main component, and the radioactive liquid waste containing the sodium salt as a main component is mixed with the silane coupling agent. 10. A process according to claim 6, 7 or 8, wherein the binder comprises an organosilicon monomer having an amine group. 11. A process according to claim 6, wherein the the binder comprises the organosilicon monomer, colloidal silica and an alkyl silanol at a mixing ratio of the alkyl silanol to the mixture of the organosilicon monomer and the colloidal silica of 0.1-1. 12. A process according to claim 11, wherein the organosilicon monomer has an amine group. |
claims | 1. A method for employing patterning process statistics for ground rules waivers and optimization, comprising:applying Optical Proximity Correction (OPC) to alter a ground rules layout using plan of record process methods to improve mask pattern images;simulating images produced by a mask;mapping patterning process variation distributions into a distribution for an intersect area by creating a histogram based upon a plurality of processes for the intersect area; andanalyzing the intersect area with a processor using the histogram to provide ground rule waivers and optimization. 2. The method as recited in claim 1, wherein simulating images produced by a mask includes simulating images on computer through process lithography models. 3. The method as recited in claim 1, wherein applying OPC to alter a mask pattern using plan of record process methods includes applying lithographic exposure focus and dose distributions. 4. The method as recited in claim 1, wherein mapping patterning process variation distributions into an intersect area distribution includes analyzing the histogram to grant acceptable ground rules waivers and acceptable geometrical changes for a given a set of ground rules. 5. The method as recited in claim 1, further comprising: modifying a ground rules layout based upon the analyzing step. 6. The method as recited in claim 5, further comprising: fabricating a semiconductor chip in accordance with modified ground rules. 7. A computer program product employing patterning process statistics for ground rules waivers and optimization, comprising a non-transitory computer useable storage medium including a computer readable program, wherein the computer readable program when executed on a computer causes the computer to:applying Optical Proximity Correction (OPC) to alter a ground rules layout using plan of record process methods to improve mask pattern images;simulating images produced by a mask;mapping patterning process variation distributions into a distribution for an intersect area by creating a histogram based upon a plurality of processes for the intersect area; andanalyzing the intersect area using the histogram to provide ground rule waivers and optimization. 8. The computer program product as recited in claim 7, wherein simulating images produced by a mask includes simulating images on computer through process lithography models. 9. The computer program product as recited in claim 7, wherein applying OPC includes applying lithographic exposure focus and dose distributions. 10. The computer program product as recited in claim 7, wherein mapping the patterning process variation distributions into an intersect area distribution by creating a histogram includes analyzing the histogram to grant acceptable ground rules waivers and acceptable geometrical changes for a given a set of ground rules. 11. The computer program product as recited in claim 7, wherein the program further causes the computer to modify a ground rules layout based upon the analyzing step. 12. The computer program product as recited in claim 11, wherein the program further causes the computer to fabricate a semiconductor chip in accordance with modified ground rules. 13. A system employing patterning process statistics for ground rules waivers and optimization, comprising:a processing device configured to apply Optical Proximity Correction (OPC) to alter a ground rules layout to create a mask pattern to which patterning process variation distributions are applied to create, waive and optimize ground rules for semiconductor chip layouts; andan analysis module configured to map the patterning process variation distributions into a distribution for an intersect area by creating a histogram based upon a plurality of processes for the intersect area and to analyze the intersect area using the histogram to provide ground rule waivers and layout optimization. 14. The system as recited in claim 13, wherein the analysis module includes a software program run on the processing device. 15. The system as recited in claim 13, wherein processing device includes through process lithography models to simulate images produced by a mask. 16. The system as recited in claim 13, wherein the patterning process variation distributions include lithographic exposure focus and dose distributions. 17. The system as recited in claim 13, wherein the analysis module determines ground rules waivers and acceptable geometrical changes for a given a set of ground rules based upon the histogram. 18. The system as recited in claim 13, wherein the analysis module outputs a modified layout according to waived and optimized ground rules. 19. The system as recited in claim 18, wherein the modified layout is employed to fabricate a semiconductor chip. 20. The system as recited in claim 18, wherein an intersect area includes an area of overlap between a pair of layers in a layout. |
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052157059 | description | DETAILED DESCRIPTION The spring force gauge of the present invention, generally indicated at 10 in FIG. 1, is illustrated in position to measure the fuel rod-centering force of a spring 12 assembled with a pair of ferrules 14 and 16 of a nuclear fuel bundle spacer, generally indicated at 18. For details of the spacer construction, reference may be had to the above-cited Matzner et al. Patent, the disclosure of which is specifically incorporated herein by reference. As mentioned above in connection with this patent, spring 12 is a double-acting loop spring of generally elliptical shape having one resilient side 12a acting in ferrule 14 and a second resilient side 12b acting in ferrule 16. Thus, spring side 12a exerts a force on a fuel rod (not shown) inserted through ferrule 14 to bias it against inwardly formed stops 20, best seen in FIG. 2, thereby maintaining the fuel rod centered within the ferrule bore. Spring side 12b performs the same function with respect to a fuel rod inserted through ferrule 16. Gauge 10 is uniquely structured to accurately measure the fuel rod-centering force exerted by the individual spring sides 12a, 12b to determine if the spring force meets quality assurance standards. Thus, as seen in FIGS. 1 and 2, gauge 10 includes a probe, generally indicated at 22, having an elongated cylindrical body 24 for insertion into a ferrule, ferrule 16 in the drawing. The upper end of the probe body is joined with a handle 25 to accommodate manual manipulation of the gauge into spring force gauging position. A flange 26, extending laterally from the probe body, serves to mount a cylindrical alignment rod 28 via a shouldered bolt 30 extending through a clearance hole 32 in the flange and threaded into a counter-sunk and tapped axial bore 34 in the alignment rod. Thus, as probe 22 is inserted into ferrule 16, alignment rod 28 is inserted into ferrule 14. The diameters of the alignment rod and the probe body are each equal to the nominal diameter of a fuel rod, and thus their insertions into the ferrule bores simulate the presence of fuel rods. The shoulder of bolt 30 bottoms out on the shoulder of bore 34 before the bolt head can clamp down on flange 26 to provide for limited floating motion of the alignment rod relative to the probe body. This feature accommodates acceptably minor nonparallelism between the axes of the alignment rod and the probe body as spring 12 forces them against stops 20 and into centered portions in their respective ferrule bores. A plunger 36 is received in a transverse bore 38 formed in the probe body and is loosely captured therein by a roll pin 40 passing through a transversely elongated hole 42 in the plunger. Thus the plunger is free for limited reciprocation in its bore. The axial location of the plunger is such that its face 43, of a curvature corresponding to that of a fuel rod peripheral surface, confronts and is acted upon by side 12b of the spring, while spring side 12a is being loaded by the presence of the alignment rod in ferrule 14. The plunger is then subjected to the fuel rod-centering force exerted by spring side 12b in ferrule 16. To measure this force, the probe body is formed with an axially elongated slot 44 opening at its lower end into transverse 38 for accommodating an elongated arm 46 pivotally mounted to the probe body at a mid-length point by a roll pin 48. The lower end of the arm extends into a slot 50 formed in the plunger to present a contact surface in engagement with plunger at the bottom surface of the slot. The upper end of the arm is positioned to engage the tip 51 of a miniature load cell 52 threadedly received in a transverse tapped bore 54 formed in the probe body. The load cell may be of a conventional button strain gauge type, such as an Omega model LCK-25 available from Omega Engineering of Stamford, Connecticut. It is thus seen that the fuel rod centering force exerted by side 12b of the spring on plunger 36 is precisely communicated to the load cell 52 by pivoting arm 46. The resulting deflection of the load cell tip 51 is translated into an electrical signal proportional to the spring force, which is fed via wires 56 routed through handle 25 to a force-reading meter 58. Alternately, the load cell signals may be fed to a data acquisition system where they are computer processed and recorded for subsequent printout of the spring forces and spring locations for each spacer. The threaded mounting of the load cell permits adjustment of the transverse position of the load cell tip for calibration purposes and to adjustably position the plunger for fuel rods of differing nominal diameters. Completing the description of the gauge construction, an L-shaped spacer cover includes a vertical portion 60 affixed to probe body 24 by screws 61 and a lateral portion 62 having holes 63 through which alignment rod 28 and the cylindrical portion of the probe body extend. The lateral portion serves a spacing function by engaging the upper edges of the ferrules to control the depth of alignment rod-probe insertion and thus ensure that the plunger face is properly aligned with the spring side whose fuel rod-centering force is to be measured. The present invention thus provides a compact handheld gauge which is conveniently inserted into the multiple ferrules of a nuclear fuel bundle spacer in succession to accurately measure the fuel rod-centering spring forces acting in each ferrule. This quality assurance test can be performed expeditiously to qualify spacers at their manufacturing site for use in nuclear fuel bundles. It is seen from the foregoing Detailed Description that the objectives of the present invention are efficiently attained, and, since certain changes may be made in the construction set forth, it is intended that matters of detail be taken as illustrative and not in a limiting sense. |
summary |
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